Conservapedia - User contributions [en]

Genetic code

2016-10-30T21:23:32Z

H22:

'''Genetic code''' is the instructions in a [[gene]] that tell the [[cell]] how to make a specific protein. A, T, G, and C are the "letters" of the [[DNA]] code; they stand for the chemicals [[adenine]], [[thymine]], [[guanine]], and [[cytosine]], respectively, that make up the nucleotide bases of DNA. Each gene's code combines the four chemicals in various ways to spell out 3-letter "words" that specify which amino acid is needed at every step in making a protein.
All living things use the same genetic code system, however, there exist some viruses that contain only RNA, which has the nucleotide base of [[uracil]] ("U") instead of thymine ("T"). While there are 64 possible three nucleotide combinations (codons), only 20 amino acids are normally used. Most of amino acids are encoded by multiple codons.

Three codons do not encode any amino acid but instead serve to mark the end of the protein. However in some very specific proteins two of these codons encode the two very rare amino acids (selenocysteine and pyrrolysine). They are not present in majority of the proteins and require additional regulatory sequences to be included.

Genetic code is the same for human, animals, plants and all other organisms. It may be differences and exceptions in some small and very specific genomes, but these are minor and rather rare. Scientists currently do not have explanation why the genetic code is universal when it would be 1.5 × 1084 possible genetic codes to choose from.<ref name="isbn0-674-05075-4">{{cite book | vauthors = Yarus M | title = Life from an RNA World: The Ancestor Within | publisher = Harvard University Press | location = Cambridge | date = 2010 | pages = 163 | isbn = 0-674-05075-4 }}</ref>. It is also not clear why exactly these 20 amino acids have been selected as the protein building blocks. Much more different amino acids occur in the living world.

The "word" combinations in more complex genetic strings if written out could literally fill a space as large as an encyclopedia.

== Sources ==
http://www.genome.gov/glossary.cfm?key=genetic%20code%20%28ATGC%29

== References ==
<references/>

[[Category:Genetics]]

Genetic code

2016-10-30T21:21:53Z

H22:

'''Genetic code''' is the instructions in a [[gene]] that tell the [[cell]] how to make a specific protein. A, T, G, and C are the "letters" of the [[DNA]] code; they stand for the chemicals [[adenine]], [[thymine]], [[guanine]], and [[cytosine]], respectively, that make up the nucleotide bases of DNA. Each gene's code combines the four chemicals in various ways to spell out 3-letter "words" that specify which amino acid is needed at every step in making a protein.
All living things use the same genetic code system, however, there exist some viruses that contain only RNA, which has the nucleotide base of [[uracil]] ("U") instead of thymine ("T").

While there are 64 possible three nucleotide combinations (codons), only 20 amino acids are normally used. Most of amino acids are encoded by multiple codons. Three codons do not encode any amino acid but instead serve to mark the end of the protein. However in some very specific proteins two of these codons encode the two very rare amino acids (selenocysteine and pyrrolysine). They are not present in majority of the proteins and require additional regulatory sequences to be included.

Genetic code is the same for human, animals, plants and all other organisms. It may be differences exceptions in some small and very specific genomes, but these are minor and rather rare. Scientists currently do not have explanation why the genetic code is universal when it would be 1.5 × 1084 possible genetic codes to choose from.<ref name="isbn0-674-05075-4">{{cite book | vauthors = Yarus M | title = Life from an RNA World: The Ancestor Within | publisher = Harvard University Press | location = Cambridge | date = 2010 | pages = 163 | isbn = 0-674-05075-4 }}</ref>. It is also not clear why exactly these 20 amino acids have been selected as the protein building blocks. Much more different amino acids occur in the living world.

The "word" combinations in more complex genetic strings if written out could literally fill a space as large as an encyclopedia.

== Sources ==
http://www.genome.gov/glossary.cfm?key=genetic%20code%20%28ATGC%29

== References ==
<references/>

[[Category:Genetics]]

Deoxyribonucleic acid

2016-10-30T20:46:08Z

H22:

[[Image:799.gif|right|thumb|300px]]
'''Deoxyribonucleic acid''' (DNA) is a chemical inside [[cell]]s which carries the hereditary information. It is a molecular [[polymer]] formed of [[nucleotide|deoxyribonucleotides]]. Most organisms use DNA as their hereditary material. [[Offspring]] of [[Human reproduction|sexual reproduction]] [[organism]]s contain DNA from both parents.

==Structure==

Most commonly as a double-stranded [[helix]] comprising two complimentary molecules held together by hydrogen bonds, this is commonly called "dsDNA" (double-stranded DNA).<ref>Single-stranded DNAs (ssDNA) do exist in certain [[bacteriophage]]s, however they cannot be replicated without first creating the complimentary strand to use as a template.</ref> The [[nucleotide]]s which are the "building blocks" of DNA have three main parts: A nitrogenous base (the "letters" in the sequence), a [[sugar]], and a [[phosphate]] group. When nucleotides are joined into DNA strands, they form a chain with the phosphate group of one nucleotide binding to the ribose of the next.

DNA strands "compliment" each other by having compatible sequences, allowing the bases on one strand to form bonds with the bases on the other strand. There are four nitrogenous bases, Adenonine (A), Cytosine (C), Guanine (G), and Thymine (T). Under the base pairing rules, A pairs with T and G pairs with C. This allow cell to repair the DNA correctly if only one strand is damaged.

DNA contains [[gene]]s that encode for [[protein]]s. These are produced by the DNA first being turned into m[[RNA]] and then into polypeptides (this process is called the [[Central dogma of molecular biology|central dogma]] of molecular biology). All organisms use DNA as their hereditary material.

==Organisation==
Most of the cells in multi-cellular organisms (human including) retain a complete copy of all DNA of the first cell from which the organism started to grow. It is often possible to clone the organism, or part of it, from a single cell, while doing so with a human cell has severe ethical implications.

All DNA required for a cell to grow into organism is called genome. A cell containing only one genome is called a haploid cell. Humans are diploid (one genome from each parent). Other organisms may have cells with more genomes, for instance, a cell of bread [[wheat]] contains six (hexaploid).

==History==
In the late 19th century [[Friedrich Miescher]], a Swiss [[biochemist]], discovered an unusual [[acid]] in the [[nuclei]] of cells. The acid was named deoxyribonucleic acid, or DNA. In 1944 the American [[biologist]]s, [[Alfred Hershey]], [[Thomas Gilmore]] and [[Martha Chase]] used experiments with [[bacteria]] and [[bacteriophage]]s to show that DNA passed [[gene]]s from one generation to the next.

In countries like Soviet Union discoveries related to DNA and its functions were initially seen as unacceptable due providing hints that the life has been created. Many researchers have lost they jobs in these atheistic societies for being interested in genes and DNA ([[Lysenkoism]]).

At that time, it was unclear how this simple molecule could hold all the complex information controlling the development of humans, animals and plants. Scientists knew it was made of four chemical bases called [[adenine]] (A), [[thymine]] (T), [[guanine]] (G) and [[cytosine]] (C), plus [[phosphoric acid]] and a [[sugar]]. They also knew that the ratios of A and T as well as G and C were always the same, but they did not know the rules that controlled the arrangement.

British scientists [[Rosalind Franklin]] and [[Maurice Wilkins]] passed [[X-ray]]s through DNA to study the patterns made when the crystals diffracted them. From studying photographs of patterns, Rosalind Franklin concluded that DNA must be a [[helix]]. [[James Watson]] and [[Francis Crick]], working in [[Cambridge]], used this information to help them solve the puzzle of DNA structure. They built a model showing that if A always paired with T and G paired with C, DNA must be like a ladder made of two strands twisted together in a double helix. The sugar and phosphoric acid were the sides of the ladder, and the rungs were the paired bases that were held together through hydrogen bonding.

Watson and Crick suggested that DNA could unzip itself into two separate strands, and each strand could act as a pattern to grow a new strand. Crick showed later that areas of the DNA known as genes worked in groups of three to code for amino acids, the building blocks of proteins. These groups are called [[codon]]s. They make about fifty thousand different types of [[protein]], which make all the different types of cell in the body. Indian biochemist [[Har Gobind Khorana]] made all the possible codons and worked out which codons controlled which [[amino acid]]. Most codons are redundant and code for the same amino acids, these mostly are different in only the third base pair. This means that differences in genotype can build up in the third position (thereby changing the genotype) without changing the protein (keeps the same phenotype).

If the DNA in one cell was stretched out, it would be about three feet long. Although DNA has a very simple structure, it can carry an enormous amount of [[information]]. Scientists do not yet understand the function of all DNA, but in 1991 a project called the [[Human Genome Project]] began to use computers to map the three billion base pairs which make up the 46 human [[chromosome]]s.

==Modern understanding==
[[Image:818.gif|right|thumb|Structure of DNA.]]
Small lengths of DNA called [[gene]]s serve as the instructions for the body to carry out its functions and give rise to the physical traits of the organism.<ref>"Eye-color genes, through the proteins they encode, direct the amount and placement of melanin in the iris." [http://www.hhmi.org/cgi-bin/askascientist/highlight.pl?kw=&file=answers%2Fgenetics%2Fans_044.html Ask A Scientist - Genes and eye color]</ref> DNA is packaged into [[chromosomes]]. Each individual human being has 23 pairs of [[chromosome]]s, where one set is inherited from his/her mother and the other set is inherited from his/her father. 22 of these chromosomes are referred to as [[autosome]]s, while the remaining chromosomes are the sex chromosomes. Males possess a single X chromosome and a single Y chromosome; whereas females possess a pair of X chromosomes. In total, it is estimated that there are roughly 20300 protein-coding genes in the human genome. Due to mRNA splicing, it is estimated that these genes encode for over 1 million different protein products.

DNA also contains sequences that regulate how and when genes are used by the cell and sequences for important RNA that is not translated into protein (parts of [[ribosome]], etc.).

The "language" in that protein structure is described in DNA is called the [[genetic code]]. Genetic code is the same for all organisms, from human to plants and yeasts (few known exceptions are rare and just tiny deviations). The universality of the genetic code is difficult to explain from the evolutionary point of view. This universality makes possible to move the genes from one organism into another, where after the possible modifications (as a rule, regulatory sequences must be adjusted and introns removed) they often still work. For instance, human insulin is currently produced by modified yeasts or bacteria. Wider usage of the genetically modified organisms brings the known risks and ethical problems.

[[Prokaryotic DNA]] is circular (a closed loop). Whereas, [[eukaryotic DNA|eukaryotic chromosomes]] are linear (with ends), with the notable exception of [[Mitochondrial DNA]] and plastid (chloroplast) DNA, which is separate from the DNA in the nucleus.<ref>Mitochondria and chloroplasts are thought to have originated as prokaryotic cells living symbiotically inside of primitive eukaryotic cells, this is called the [[endosymbiotic hypothesis]]</ref> The ends of eukaryotic chromosomes are protected by [[telomere]]s, which are always tightly condensed except during S phase of [[mitosis]].<ref>Campbell, Neil A, et. al. ''Biology''. 6th ed. San Francisco: Benjamin Cummings, 2002. 299, 530-31.</ref> Telomeres are partially lost during cell division, and must be regrown later. Most of the cells in animal body are not capable of restoring they telomeres so can divide only limited number of times (Hayflick limit <ref>{{cite journal |author=Watson JD |title=Origin of concatemeric T7 DNA |journal=Nature New Biol. |volume=239 |pages=197–201 |year=1972 |pmid=4507727 |issue=94 |doi=10.1038/newbio239197a0}}</ref>).

== Mutations ==
[[Mutation]]s are simply variations in DNA sequence between individuals. The vast majority of spontaneous mutations in DNA are called "neutral" because they do not affect the [[phenotype|observable traits]] of the individual organism. Others can have beneficial effects and some can disrupt important functions Differential distribution of various types of neutral mutations within the population is the basis for modern [[DNA fingerprinting]]. It is mutations in DNA, giving rise to novel alleles ("versions" of a gene), which cause phenotypic variations between individuals of a particular species. For instance, in humans, single-gene mutations are responsible for differences in [[ABO blood type]], eye color, hair color, and even the ability to taste certain molecules. Sadly, there are also thousands of mutations known to cause human disease; notably sickle-cell anemia, a few rare forms of autism, and (when the mutations spontaneously occur in a somatic cell) various types of cancer. That said, it is important to note that most phenotypic traits (e.g. height) and hereditary diseases arise as the net effect of several different genetic variations.

Usually a mutation is harmless if present in only one of the two or more genomes in same cell (it is said most of mutations are recessive), or even may be beneficial. Offspring of the parents who are already genetically related often inherits the same mutation in both genomes, so diseases are more frequent. If the mutation is diagnosed early in the life, sometimes diet and other similar measures may be applied, resulting a normal life later.<ref name=Al2015>{{cite journal|last1=Al Hafid|first1=N|last2=Christodoulou|first2=J|title=Phenylketonuria: a review of current and future treatments.|journal=Translational pediatrics|date=October 2015|volume=4|issue=4|pages=304–17|pmid=26835392}}</ref>

[http://www.ncbi.nlm.nih.gov/omim OMIM] (Online Mendelian Inheritance in Man), is an online database of genes known to be mutated in disease states. [[Mendelian inheritance]] refers to the inheritance pattern observed in traits that are determined by a single gene. This pattern was first discovered by [[Gregor Mendel]], an Austrian monk, during his work with pea plants from 1856-1863. Although Mendel published his work in 1866, it's significance was largely ignored until it was rediscovered in the early 20th century; more than two decades after his death.

==See also==
*[[DNA library]]
*[[Transcription]]

==External links==
*[http://www.learner.org/interactives/dna/index.html Interactive DNA] Learn about genetics, genetic engineering, the Human Genome Project and the ethical implications of these new technologies.
*[http://www.blackwellpublishing.com/trun/artwork/Animations/cloningexp/cloningexp.html Animated guide to DNA cloning]

== References ==
<references/>

[[Category:Genetics]]
[[Category:Police State]]

Panspermia

2016-10-22T20:22:42Z

H22:

[[Image:Mars_meteorite.jpg|thumb|250px|[[Meteorite]] believed to have once been a part of [[Mars]] and to contain [[fossil]] evidence that primitive [[life]] may have existed on Mars.[http://spaceflight.nasa.gov/gallery/images/mars/meteorites/html/s94_032549.html] ]]

'''Panspermia''' is a theory that originated in the 19th century in opposition to the theory of [[spontaneous generation]]. Panspermia propounded that reproductive bodies of living organisms exist throughout the universe and develop wherever the environment is favorable. The basic tenet of panspermia is that primitive [[life]], which originated someplace else, was deposited on Earth’s surface by means of a collision with some other object that already harbored life.

This theory has been repopularized upon the realization of the improbability that life formed through [[abiogenesis]] on earth, and is now more commonly called [[exogenesis]].

== Objections to Panspermia ==
The full theory of panspermia requires two events to explain the presence of life on earth:

# The generation of life outside the earth, and then
# The transfer of this life to earth.

Many scientists have objected that the generation of life cannot occur, or have occurred, outside of a planetary environment, where heavier elements are plentiful. Almost the only elements present in interstellar space are [[hydrogen]] and [[helium]]—and the latter, being an inert or [[noble gas]], is not a component of life in any form known to man.

The generation objection by itself would not destroy panspermia. But the transference event requires a transit through space, followed by a passage through the earth's [[atmosphere]] and then an impact on the ground or at sea. Either of these events is fraught with danger. The unprotected space outside of an atmosphere is subject to unfiltered [[radiation]] in various forms. These include the products of [[radioactive decay]], [[cosmic rays]] (the highest-energy form of [[electromagnetic radiation]] known to man), and the [[stellar wind]], a stream of particles that fly out from any star as it continuously burns. Even if any life forms could survive the spatial passage, it must then somehow penetrate the atmosphere and risk incineration from sheer friction, and then must survive the impact.

A test done by attaching a piece of bacteria-smeared rock to a returning [[Russia]]n spacecraft in September 2008 showed the difficulty of life surviving a fall through Earth's atmosphere, with [[temperature]]s on the rock reaching 1700 degrees [[Celsius]], despite an entry speed little more than half that which a meteorite would experience.<ref>Sarfati, Jonathan, [http://creationontheweb.com/content/view/6077 Panspermia theory burned to a crisp: bacteria couldn’t survive on meteorite], 10th October 2008 (Creation Ministries International).</ref> However this source talks about the temperatures no deeper than 2 cm below the surface of the meteorite. Deeper layers may provide more protection.

== Directed panspermia ==
In 1973, [[Francis Crick]], co-discoverer of [[DNA]], and [[Leslie Orgel]] proposed<ref>Crick, F. H. C., and Orgel, L. E. "Directed Panspermia," ''Icarus'', 19, 341 (1973).</ref> a new mechanism, which they called ''[[directed panspermia]],'' to mitigate the hazards of transport and entry detailed above. They assume that an advanced [[civilization]] fired a brace of [[rocket]] [[missiles]], each laden with a [[payload]] of [[bacteria]] and/or [[blue-green algae]], in all directions. Crick and Orgel estimated that a payload of one [[metric ton]] could contain 1017 micro-organisms organized in ten or a hundred separate samples.

The theory has gained some attractiveness primarily by proposing to explain why so many life-forms on earth depend on the element [[molybdenum]], which is rare on earth but might not have been so rare on the planet of origin of these micro-organisms.

However, this theory is subject to a number of logical objections:

# Where and how did life form or come to this other world, for an intelligent race to build a civilization capable of launching guided missiles into interstellar, or even inter-galactic, space? Did life ''originate'' on that world, or was it ''deposited'' on that world in the very fashion in which that other world allegedly deposited life on earth? Directed panspermia thus appears to be an example of [[infinite regression]], and violative of [[Occam's razor]].
# Crick and Orgel totally ignore the question of the ''motive'' for firing this hypothetical brace of missiles. The attitude of such a civilization toward humanity would have to be one of four things:
## Irrelevant—that civilization was dying when it fired the missiles, and is now dead.
## Indifferent—having fired the missiles, they really don't care whether any of them landed intact or not, or whether any of them spawned a new civilization or not. But if so, then why bother with such a project? One can only imagine the sort of political debate that might have begun before the first launch-pad gantry crane was erected, and plagued the project for its duration. Such debates on alleged wastefulness ultimately curtailed [[Project Apollo]], constantly threaten the abandonment of the [[International Space Station]], and place the current plans for re-exploration of the moon by [[National Aeronautics and Space Administration|NASA]] in serious doubt. (They also invite disaster to themselves. Suppose, for instance, one of their "child" civilizations should decide to look for them and go to war with them to poach their technology, resources, and so on?)
## Friendly—that civilization plans a follow-up visit with a view to establishing trade and travel. Such a theory would no doubt have its appeal to non-believers hoping for a [[God-substitute]] to solve all the world's problems—which is a common theme in the [[science fiction]] of the twenty-first century. (Indeed, the intellectual heirs of [[Gene Roddenberry]] explicitly proposed a race of "Progenitors" who were ultimately responsible for the spawning of humanity, "Vulcankind," and all the other hundreds of races that Mr. Roddenberry and his successors conceived for the fictional [[Star Trek]] "universe".)
## Hostile—that civilization intended to create new planets for its own people to settle, in which case we are in the way, and "they" will follow up their life-seeding project with an expeditionary force consisting of warships. This theme pervaded the popular [[science fiction]] of the middle part of the twentieth century, especially in the early years of the [[Cold War]] between the [[United States of America]] and the [[Union of Soviet Socialist Republics]].

For all the attention that Drs. Crick and Orgel paid to the design of one of those missiles, and the stresses and radiation bombardment it must have had to withstand while in transit, they said ''absolutely nothing'' in consideration of motive. Without such predictions, one cannot even make a decent public-policy recommendation.

== References ==
<references/>

[[Category:Biology]]

Intron

2016-10-22T20:00:07Z

H22:

An '''Intron''' is a non-protein-coding sequence of [[DNA]] that is initially copied into [[RNA]] but is cut out of the final RNA transcript (mature mRNA). They are found in most multicellular eukaryotes, but are rare in housekeeping genes and RNA-coding genes. They are also rare or absent in most unicellular eukaryotes and prokaryotes, but present in the DNA or RNA of viruses that infect eukaryotic cells. In contrast to introns, the protein-coding segments of DNA are called [[exon]]s. The presence of introns in many genes can cause problems with protein purification when bacteria are used to propagate a protein, as they lack the machinery to excise introns from genes. The presence of these foreign structures causes the bacteria to recognize and degrade the protein, in a specific reaction that may be part of the bacterial defense against bacteriophage infection. The gene containing the protein to be purified must therefore have its introns excised before being subcloned into a suitable plasmid. This is often done using a [[cDNA library]].

Some introns may be included or excluded from the final RNA transcript, producing alternative versions of the protein. These variations (alternative splicing) may depend on the organ, development stage, environment and other similar factors. In humans, most of the genes (95%) that have introns also have the alternative splicing.<ref>Pan, Q; Shai O; Lee LJ; Frey BJ; Blencowe BJ (Dec 2008). Deep surveying of alternative splicing complexity in the human transcriptome by high-throughput sequencing. Nature Genetics. 40 (12): 1413–1415. Free abstract available at http://www.nature.com/ng/journal/v40/n12/full/ng.259.html</ref>

== Sources ==
* http://www.genome.gov/glossary.cfm?key=intron
* Molecular Cell Biology, 5th ed. Lodish et al. New York: W. H. Freeman and Co, 2004. pp 111–112.
== References ==
<references/>

[[Category:Genetics]]

Intron

2016-10-22T19:57:05Z

H22:

An '''Intron''' is a non-protein-coding sequence of [[DNA]] that is initially copied into [[RNA]] but is cut out of the final RNA transcript (mature mRNA). They are found in most multicellular eukaryotes, but are rare in housekeeping genes and RNA-coding genes. They are also rare or absent in most unicellular eukaryotes and prokaryotes, but present in the DNA or RNA of viruses that infect eukaryotic cells. In contrast to introns, the protein-coding segments of DNA are called [[exon]]s. The presence of introns in many genes can cause problems with protein purification when bacteria are used to propagate a protein, as they lack the machinery to excise introns from genes. The presence of these foreign structures causes the bacteria to recognize and degrade the protein, in a specific reaction that may be part of the bacterial defense against bacteriophage infection. The gene containing the protein to be purified must therefore have its introns excised before being subcloned into a suitable plasmid. This is often done using a [[cDNA library]].

Some introns may be included or excluded from the final RNA transcript, producing alternative versions of the protein. These variations (alternative splicing) may depend on the organ, development stage, environment and other similar factors. In humans, most of the genes (95%) that have introns also have the alternative splicing.<ref>Pan, Q; Shai O; Lee LJ; Frey BJ; Blencowe BJ (Dec 2008). "Deep surveying of alternative splicing complexity in the human transcriptome by high-throughput sequencing". Nature Genetics. 40 (12): 1413–1415. Free abstract available at http://www.nature.com/ng/journal/v40/n12/full/ng.259.html</ref>

== Sources ==
* http://www.genome.gov/glossary.cfm?key=intron
* Molecular Cell Biology, 5th ed. Lodish et al. New York: W. H. Freeman and Co, 2004. pp 111–112.
== References ===
<references/>

[[Category:Genetics]]

DNA library

2016-10-22T19:29:58Z

H22:

A '''DNA library''' a collection of the multiple DNA fragments that is a population of the genetically transformed micro-organisms (usually bacteria or yeast). Each such micro-organism has a fragment of the library DNA, storing and propagating it.

A cell would not retain and replicate a random piece of foreign DNA inside it. To make this possible, the DNA fragments are flanked by additional sequences, making cell to treat them as part of the own genome.

== Types of the libraries ==
A cDNA library is obtained by extracting mRNA (from a particular tissue or an entire organism) and converting these RNA fragments back into DNA (with the help of the enzyme reverse transcriptase). It represents the genes that have been active (expressed) in the living sample at the time when the mRNA was purified.

A genomic library is obtained by fragmenting genomic DNA into pieces small enough to be carried by the transformed micro-organism. Such fragments from the library then can be sequenced separately, and the DNA sequence of the whole genome can be later re-constructed from the overlapping regions.

== Using of the library ==
A library is a mixture of the transformed micro-organism carrying different fragments. To obtain individual "books", a highly diluted mixture of the library is seeded on the surface of the gel. Yeasts or bacteria will then form multiple colonies on that surface. If it has been diluted enough, each such colony starts from a single transformed cell and contains only one fragment of the library DNA (the same fragment that the initial cell originally contained). Such colony can be later further grown, obtaining large amount of the single fragment of the library DNA. The fragment can be later purified out of the cell and used in various experiments.

== Sources ==
http://www.genome.gov/glossary.cfm?key=library

[[Category:Genetics]]
[[Category:Libraries]]

Amino acid

2016-10-22T18:46:17Z

H22:

'''Amino acids''' are a group of 21 different [[molecule]]s which, when [[chemical bond|bonded]] in sequence, make up [[protein]]s. They consist of an [[organic]] side chain bonded to an ''[[amine]]'' and a ''[[carboxylic acid]]'' (-COOH) group (hence the name ''amino acid''). These two different [[functional group]]s make amino acids [[bifunctional]].

==Table of Properties==

A table of amino acid name, abbreviation and properties is as follows:

{| class="wikitable"
! Amino Acid
! 3-Letter
! 1-Letter
! Side chain polarity
! Side chain acidity or basicity
|- align="center"
| Alanine
| Ala
| A
| nonpolar
| neutral
|- align="center"
| Arginine
| Arg
| R
| polar
| strongly basic
|- align="center"
| Asparagine
| Asn
| N
| polar
| neutral
|- align="center"
| Aspartic acid
| Asp
| D
| polar
| acidic
|- align="center"
| Cysteine
| Cys
| C
| polar
| neutral
|- align="center"
| Glutamic acid
| Glu
| E
| polar
| acidic
|- align="center"
| Glutamine
| Gln
| Q
| polar
| neutral
|- align="center"
| Glycine
| Gly
| G
| nonpolar
| neutral
|- align="center"
| Histidine
| His
| H
| polar
| weakly basic
|- align="center"
| Isoleucine
| Ile
| I
| nonpolar
| neutral
|- align="center"
| Leucine
| Leu
| L
| nonpolar
| neutral
|- align="center"
| Lysine
| Lys
| K
| polar
| basic
|- align="center"
| Methionine
| Met
| M
| nonpolar
| neutral
|- align="center"
| Phenylalanine
| Phe
| F
| nonpolar
| neutral
|- align="center"
| Proline
| Pro
| P
| nonpolar
| neutral
|- align="center"
| Serine
| Ser
| S
| polar
| neutral
|- align="center"
| Threonine
| Thr
| T
| polar
| neutral
|- align="center"
| Tryptophan
| Trp
| W
| nonpolar
| neutral
|- align="center"
| Tyrosine
| Tyr
| Y
| polar
| neutral
|- align="center"
| Valine
| Val
| V
| nonpolar
| neutral
|}

== α-amino acids ==
'''α-amino acids''' (α is the Greek letter ''[[alpha]]'') have the general formula '''RCH(NH2)COOH'''. There are around 20 naturally occurring α-amino acids which [[polymer]]ise by [[condensation polymerisation]] to form all known [[polypeptides]] (which form the primary structure of [[protein]]s) in biological organisms during [[gene translation]]. Some organisms contain atypical amino acids in their proteins, such as the D-amino acids, selenocystine or pyrolysine. These atypical amino acids are particularly common in organelles such as mitochondria and are encoded in variants of the standard [[genetic code]], such as [[amber codons]].

== Zwitterions ==
Due to the acidic carboxylic acid group and the alkaline amine group on amino acids they can form ions with themselves called '''zwitterions'''. The word zwitterion is derived from the German for [[hermaphrodite]], and in this case refers to the fact that amino acid zwitterions have both positive and negative [[charge]]s.

=== Formation of zwitterions ===
[[Zwitterion]]s form from amino acids when the hydrogen from the carboxylic acid group (-COO'''H''') dissociates from the molecule and forms a [[dative covalent bond]] with the nitrogen in the amine group (-'''N'''H2). This forms an ion with two charges: RCH(NH3+)COO-.

=== Physical properties of α-amino acids due to zwitterions ===
The formation of zwitterions dramatically affects the physical properties of amino acids. The zwitterion is the predominant form in the [[solid phase]] and aqueous [[solution]]. Due to the two charges on zwitterions, there is a much stronger intermolecular attraction between the ions, raising the melting point of an amino acid far above the melting point of organic compounds with similar [[molecular mass]] and numbers of [[electron]]s. For example, the amino acid [[glycine]] decomposes at 262 °C (without melting) where propanoic acid melts at -21 °C.<ref>Chemistry 2, Ratcliff B. & Eccles H., 2001, Cambridge University Press, ISBN 0-521-79882-5</ref>

== Optical isomerism of amino acids ==
All α-amino acids except glycine CH2(NH2)COOH and proline are complex enough to have the two [[optical isomerism|optical isomers]] that are mirror images of each other (L and R). This is because they have four different groups around the alpha carbon, forming a [[chiral centre]].

All living organisms use exclusively L optical isomers of amino acids for they proteins. The reasons of this are unknown and difficult to explain from the evolutionary point of view, as a naturally occurring chemical reaction normally produces L and R isomers in equal proportions, and most of the physical properties of the L and R forms are identical.

== See also ==
*[[Alkaptonuria]]

== References ==
<references/>

[[Category:Biochemistry]]
[[Category:Acids]]

Amino acid

2016-10-22T18:45:07Z

H22:

'''Amino acids''' are a group of 21 different [[molecule]]s which, when [[chemical bond|bonded]] in sequence, make up [[protein]]s. They consist of an [[organic]] side chain bonded to an ''[[amine]]'' and a ''[[carboxylic acid]]'' (-COOH) group (hence the name ''amino acid''). These two different [[functional group]]s make amino acids [[bifunctional]].

==Table of Properties==

A table of amino acid name, abbreviation and properties is as follows:

{| class="wikitable"
! Amino Acid
! 3-Letter
! 1-Letter
! Side chain polarity
! Side chain acidity or basicity
|- align="center"
| Alanine
| Ala
| A
| nonpolar
| neutral
|- align="center"
| Arginine
| Arg
| R
| polar
| strongly basic
|- align="center"
| Asparagine
| Asn
| N
| polar
| neutral
|- align="center"
| Aspartic acid
| Asp
| D
| polar
| acidic
|- align="center"
| Cysteine
| Cys
| C
| polar
| neutral
|- align="center"
| Glutamic acid
| Glu
| E
| polar
| acidic
|- align="center"
| Glutamine
| Gln
| Q
| polar
| neutral
|- align="center"
| Glycine
| Gly
| G
| nonpolar
| neutral
|- align="center"
| Histidine
| His
| H
| polar
| weakly basic
|- align="center"
| Isoleucine
| Ile
| I
| nonpolar
| neutral
|- align="center"
| Leucine
| Leu
| L
| nonpolar
| neutral
|- align="center"
| Lysine
| Lys
| K
| polar
| basic
|- align="center"
| Methionine
| Met
| M
| nonpolar
| neutral
|- align="center"
| Phenylalanine
| Phe
| F
| nonpolar
| neutral
|- align="center"
| Proline
| Pro
| P
| nonpolar
| neutral
|- align="center"
| Serine
| Ser
| S
| polar
| neutral
|- align="center"
| Threonine
| Thr
| T
| polar
| neutral
|- align="center"
| Tryptophan
| Trp
| W
| nonpolar
| neutral
|- align="center"
| Tyrosine
| Tyr
| Y
| polar
| neutral
|- align="center"
| Valine
| Val
| V
| nonpolar
| neutral
|}

== α-amino acids ==
'''α-amino acids''' (α is the Greek letter ''[[alpha]]'') have the general formula '''RCH(NH2)COOH'''. There are around 20 naturally occurring α-amino acids which [[polymer]]ise by [[condensation polymerisation]] to form all known [[polypeptides]] (which form the primary structure of [[protein]]s) in biological organisms during [[gene translation]]. Some organisms contain atypical amino acids in their proteins, such as the D-amino acids, selenocystine or pyrolysine. These atypical amino acids are particularly common in organelles such as mitochondria and are encoded in variants of the standard [[genetic code]], such as [[amber codons]].

== Zwitterions ==
Due to the acidic carboxylic acid group and the alkaline amine group on amino acids they can form ions with themselves called '''zwitterions'''. The word zwitterion is derived from the German for [[hermaphrodite]], and in this case refers to the fact that amino acid zwitterions have both positive and negative [[charge]]s.

=== Formation of zwitterions ===
[[Zwitterion]]s form from amino acids when the hydrogen from the carboxylic acid group (-COO'''H''') dissociates from the molecule and forms a [[dative covalent bond]] with the nitrogen in the amine group (-'''N'''H2). This forms an ion with two charges: RCH(NH3+)COO-.

=== Physical properties of α-amino acids due to zwitterions ===
The formation of zwitterions dramatically affects the physical properties of amino acids. The zwitterion is the predominant form in the [[solid phase]] and aqueous [[solution]]. Due to the two charges on zwitterions, there is a much stronger intermolecular attraction between the ions, raising the melting point of an amino acid far above the melting point of organic compounds with similar [[molecular mass]] and numbers of [[electron]]s. For example, the amino acid [[glycine]] decomposes at 262 °C (without melting) where propanoic acid melts at -21 °C.<ref>Chemistry 2, Ratcliff B. & Eccles H., 2001, Cambridge University Press, ISBN 0-521-79882-5</ref>

== Optical isomerism of amino acids ==
All α-amino acids except glycine CH2(NH2)COOH and proline are complex enough to have the two [[optical isomerism|optical isomers]] that are mirror images of each other (L and R). This is because they have four different groups around the alpha carbon, forming a [[chiral centre]] and allowing to occur.

All living organisms use exclusively L optical isomers of amino acids for they proteins. The reasons of this are unknown and difficult to explain from the evolutionary point of view, as a naturally occurring chemical reaction normally produces L and R isomers in equal proportions, and most of the physical properties of the L and R forms are identical.

== See also ==
*[[Alkaptonuria]]

== References ==
<references/>

[[Category:Biochemistry]]
[[Category:Acids]]

Genome

2016-10-22T18:26:49Z

H22:

A '''genome''' is all the [[hereditary]] information held by an [[organism]]. This includes both expressed and non-expressed genetic [[information]]. In most organisms, it is stored in [[DNA]]; however, [[retrovirus]]es store it in [[RNA]], another type of [[nucleic acid]]. The information is encoded in the form of triplets of organic molecules called [[nucleotides]].

[[Eukaryotic cell|Eukaryote]]s (including humans) have the following types of genomic material:
# the [[Nucleus|nuclear]] genome: Information found inside the nucleus of a cell.
# the [[mitochondria]]l genome: Information found in the [[mitochondria]]<ref>http://www.medterms.com/script/main/art.asp?articlekey=3580</ref>
# plants also have the [[chloroplast]] genome (human and animals obviously do not).

Chloroplast and mitochondrial genomes are somewhat remotely similar to the genomes of the independent organisms (while significantly smaller by size and number of genes). These separate genomes are used as evidence for the [[endosymbiotic hypothesis]], although they can also be explained by creationist models. Most of the genetic information is stored in the nuclear genome, where also many mitochondrial and chloroplast proteins are encoded.

In addition, organisms often inherit other material from their parents, such as proteins, RNA molecules, and other chromosomal factors like methyl groups attached to certain base pairs. These are regarded as the purview of [[epigenetics]].

The [[Human Genome Project]] mapped the genome of humans (''Homo sapiens'') in a 13-year study, and is considered one of the marvels of modern human [[medicine]] and [[biology]]. All of the information is stored in a database.<ref>http://www.ornl.gov/sci/techresources/Human_Genome/home.shtml</ref> It is expected that the results of the project will allow scientists to predict how genetics influences drug interaction with the body, and lead to target specific drugs.<ref>Collins, Francis S. and McKusick, Victor A. [http://jama.ama-assn.org/cgi/content/full/285/5/540 Implications of the Human Genome Project for Medical Science] ''JAMA'', 2001;285:540-544, 7th February 2001.</ref>

Genomes of other species have been recorded as well, such as mice,<ref>http://www.ncbi.nlm.nih.gov/genome/guide/mouse/</ref> chimpanzees<ref>http://www.nature.com/nature/focus/chimpgenome/index.html</ref> and yeast.<ref>http://www.yeastgenome.org/</ref> The mouse genome sequence from the C57BL/6J strain has about 30,000 genes, and 99% of them have direct counterparts in humans.<ref>http://www.nature.com/nature/journal/v420/n6915/full/420509a.html</ref>

The chimpanzee represented the first non-human primate sequenced. The differences in the chimpanzee and human genomes are small, with 99% of the DNA sequence preserved.<ref>http://www.nih.gov/news/pr/aug2005/nhgri-31.htm</ref> The differences can be classified in terms of differences in local single nucleotide substitutions, insertions, deletions and repetitions of sequences. A relatively large number of difference between the chimpanzee and human genomes are not due to substitutions.<ref>http://207.210.67.162/~striz/docs/chimpc.pdf</ref> When this is taken into account, humans and chimpanzees still share 96% of their sequence, and are genetically closer than rats and mice.<ref>http://www.nih.gov/news/pr/aug2005/nhgri-31.htm</ref>

== Creationist View ==
Instead of seeing DNA as evidence for [[evolution]], creation scientists see DNA as confirming evidence of [[God]]'s divine plan. He has encoded into DNA His blueprints for making life. It is thus no surprise that the DNA of similar animals shares many sequences. DNA can be seen as a successful prediction of creation science.<ref>Matthews, Michael, [http://www.answersingenesis.org/docs2003/0425dna.asp DNA—what does it prove?] Answers in Genesis, 25th April, 2003.</ref>
== References ==
<references/>

[[Category:Molecular Biology]]
[[Category:Medicine]]

Etiolated

2016-10-22T18:12:25Z

H22:

An '''etiolated''' [[plant]] is one that it is characterized, due to lack of light, by symptoms of yellowing, failure of leaf expansion, thin [[stem]]s and elongation.

Obtaining these symptoms (as well discarding them in the presence of light) is the active, complex reaction of the plant, governed by light receptors and controlled by many genes and plant hormones. <ref>James B. Reid, Natasha A. Botwright, Jennifer J. Smith, Damian P. O'Neill, and L. Huub J. Kerckhoffs. (2002). Control of Gibberellin Levels and Gene Expression during De-Etiolation in Pea. Plant Physiology, 128(2): 734–741. Available online (https://www.ncbi.nlm.nih.gov/pmc/articles/PMC148934).</ref>, not just a result of the bad growth conditions.

Green color is primarily caused by [[chlorophyll]] that is needed for [[photosynthesis]]. There are two pathways so synthesize the chlorophyll, and one of them is light dependent. Algae, ferns and coniferous have both pathways and synthesize chlorophyll also in the darkness. Hence they grow in green in the darkness as well. Flowering plants that only have the light-dependent pathway can only become green in the presence of light. <ref>J Y Suzuki and C E Bauer (1992). Light-independent chlorophyll biosynthesis: involvement of the chloroplast gene chlL (frxC). Plant Cell. 1992 Aug; 4(8): 929–940. Available online (https://www.ncbi.nlm.nih.gov/pmc/articles/PMC160185/).</ref>

== References ==
<references/>

[[Category:Biology]]

Intelligence testing

2016-10-18T21:24:10Z

H22:

'''Intelligence testing''' began in an organized way in the early 20th Century with the [[Stanford-Binet]] test. The purpose was to form an estimate of a person's aptitude before investing time and money in their education, in the belief that aptitude or intelligence was a fixed quantity.

At the time these tests were developed, medical science and psychology were
in their infancy. Ideas such as [[eugenics]] still had currency, and intelligence tests were used to weed out so-called "defectives".

Testers classified people as idiots, imbeciles, morons, normal, above average, and geniuses on a numerical scale based on [[mental age]]. For children, dividing the mental age by chronological age produces the [[intelligence quotient]] (IQ) used for placement in slow or rapid classes.

The study based on survey data from 702 Nordic research works concludes that a typical neuropsychologist used 9 tests in a standard assessment, and 25 tests overall in their practice. The selection of tests to use has been influenced by nationality, competence level, practice profile, and by attitude toward test selection. Testing patients with psychiatric disorders was associated with more tests.<ref>Egeland J, Løvstad M, Norup A, Nybo T, Persson BA6, Rivera DF, Schanke AK, Sigurdardottir S, Arango-Lasprilla J. (2016). Following international trends while subject to past traditions: neuropsychological test use in the Nordic countries. Clin Neuropsychol. Sep 27:1-22. [https://www.ncbi.nlm.nih.gov/pubmed/27670676]</ref> The average IQ scores for many populations have been rising at an average rate of three points per decade since the early 20th century ([[Flynn effect]]). It is not clear if whether "people are getting more and more clever" or just there are differences between past and current testing. <ref name="DickensFlynn2001">
William T. Dickens and James R. Flynn, [http://www.apa.org/journals/features/rev1082346.pdf Heritability Estimates Versus Large Environmental Effects:The IQ Paradox Resolved], ''Psychological Review'' 2001. Vol. 108, No. 2. 346-369.
</ref><ref>
William T. Dickens and James R. Flynn, "[http://www.brookings.edu/views/papers/dickens/20020205.pdf The IQ Paradox: Still Resolved]," ''Psychological Review'' 109, no. 4 (2002).
</ref>

In the United States, intelligence tests were to classify recruits and draftees for service in World War II. The more technical jobs were assigned to men with higher scores. Sociologists also noted racial differences in IQ scores, and some supposed that these differences were inherent. A controversy over this matter has raged ever since.

Open questions for psychologists and sociologists focus on what produces differences in [[intelligence]], whether intelligence can be developed or stunted by upbringing and education, and why different [[race]]s or cultural groups have significantly different scores.

The two main reasons given are:
#that there may be inherent differences between the races
#that upbringing, education and social factors can skew the results

== Influention of environment ==
After nearly a century of IQ testing and [[educational reform]]s, some researchers have begun to assert that IQ can be influenced by the child's environment by as much as 30 points.<ref>3 weeks of intensive play of WFF 'N PROOF: The Game of Modern Logic increased average IQ scores by more than 20 points. [http://wffnproof.com/]</ref> See [[Educational games]].

A 1976 year study that covered 258 children (IQ between 80 and 119) finally concluded that the major correlating factor is "a favorable parental social and educational background" <ref>Fisch RO, Bilek MK, Horrobin JM, Chang PN (1976) Children with superior intelligence at 7 years of age: a prospective study of the influence of perinatal, medical, and socioeconomic factors. Am J Dis Child. 1976 May;130(5):481-7. Abstract available at
https://www.ncbi.nlm.nih.gov/pubmed/1274898</ref>. The more recent 2016 year study also showed that the measured IQ potential is significantly lower in developing countries. <ref name='kodila'>Kodila-Tedika O1, Asongu SA2, Azia-Dimbu F3. (2016) J Biosoc Sci. 2016 May 26:1-13, available at [https://papers.ssrn.com/sol3/papers.cfm?abstract_id=2661437]
Statistics and intelligence in developing countries</ref> and increases after the national statistics improves (<ref name='kodila'/> references [[Nigeria]] and [[Kenya]]).

Test results can also be influenced by other factors. Steele and Joshua Aronson found that when they gave a group of Stanford undergraduates a standardized test and told them that it was a measure of their intellectual ability, the white students did much better than their black counterparts. But when the same test was presented simply as an abstract laboratory tool, with no relevance to ability, the scores of blacks and whites were virtually identical.<ref>[http://www.gladwell.com/2000/2000_08_21_a_choking.htm]</ref> See [[Pressure and failure]].

==Liberal bias==

The field of intelligence testing has been acrimonious and contentious. Researchers such as [[Arthur Jensen]] and [[Charles Murray]] have been pilloried in the mass media, accused of maintaining views which different or even opposite of their actual views.<ref>Evolution advocate Gould portrays Murray as saying intelligence can be measured with a single number; Murray, of course, makes it clear in his book (as well as in a follow-up retort to Gould) that intelligence is too complex to be measured with a single number.</ref>

One professor had to come to Jensen's defense, after [[Stephen Jay Gould]] attacked him in print:

:I object to Gould's tendency to visit the alleged sins of early investigators on present day investigators. If Goddard, Brigham, and others once tended to view various human races as relatively superior or inferior in intelligence and therefore relatively worthy or unworthy, this does not mean that present-day investigators, like Jensen (1980) or Rushton (1995), are necessarily guilty of such views. In fact, from my personal acquaintance with Jensen and his publications, I can attest that he does not view the African race (if one accepts that it is a race) as in any way less worthy than other so-called races. [http://www.psych.utoronto.ca/~reingold/courses/intelligence/cache/carroll-gould.html]

[[Charles Murray]] said:

*As soon as anyone argues that racial differences in intelligence are authentic, not an artifact of biased tests, everyone decodes that as saying the differences are grounded in genes. It is a non-sequitur, but an invariable one in my experience. America's intellectual elites are hysterical about the possibility of black - white genetic differences in IQ.
*As you know, The Bell Curve actually took a mild, agnostic stand on the subject. Dick Herrnstein and I said that nobody yet knows what the mix between environmental and genetic causes might be, and it makes no practical difference anyway. The only policy implication of the black - white difference, whatever its sources, is that the U.S. should return forthwith to its old ideal of treating people as individuals.
*But how many people know this? No one who hasn't read the book. Everyone went nuts about genes, so much so that most people now believe that race and genes is the main topic of our book. [http://www.eugenics.net/papers/mssel.html]

The Bell Curve book is not the only controversial study on IQ among different races or groups of people. Danish professor [[Helmuth Nyborg]] has conducted studies of IQ which indicate [[Politically correct language|politically incorrect]] results such as: on average, white people have higher IQs than black people, and men have higher IQs than women. His latest research finds that on average, [[atheists]] have IQs about 5.8 points higher than people of [[faith]], prompting similar outrage among his critics, who claim that such results might be due to cultural biases.[http://danish.newsvine.com/_news/2007/02/05/554043-professor-atheists-are-more-intelligent-than-believers]

== See also ==

*[[Theory of multiple intelligences]]
*[[Moral intelligence]]
*[[Bodily-kinesthetic intelligence]]
*[[Emotional intelligence]]
*[[Atheism and intelligence]]

==External links==
*[http://www.eugenics.net/papers/mssel.html As the Bell Curves] - [[Charles Murray]] and [[Daniel Seligman]] - (Originally published in The National Review, December 8, 1997)

==Notes==
<references/>

[[Category:Psychology]]

Deoxyribonucleic acid

2016-10-18T20:59:38Z

H22:

[[Image:799.gif|right|thumb|300px]]
'''Deoxyribonucleic acid''' (DNA) is a chemical inside [[cell]]s which carries the hereditary information. It is a molecular [[polymer]] formed of [[nucleotide|deoxyribonucleotides]]. Most organisms use DNA as their hereditary material. [[Offspring]] of [[Human reproduction|sexual reproduction]] [[Organism|organisms]] contain DNA from both parents.

==Structure==

Most commonly as a double-stranded [[helix]] comprising two complimentary molecules held together by hydrogen bonds, this is commonly called "dsDNA" (double-stranded DNA).<ref>Single-stranded DNAs (ssDNA) do exist in certain [[bacteriophage]]s, however they cannot be replicated without first creating the complimentary strand to use as a template.</ref> The [[nucleotide]]s which are the "building blocks" of DNA have three main parts: A nitrogenous base (the "letters" in the sequence), a [[sugar]], and a [[phosphate]] group. When nucleotides are joined into DNA strands, they form a chain with the phosphate group of one nucleotide binding to the ribose of the next.

DNA strands "compliment" each other by having compatible sequences, allowing the bases on one strand to form bonds with the bases on the other strand. There are four nitrogenous bases, Adenonine (A), Cytosine (C), Guanine (G), and Thymine (T). Under the base pairing rules, A pairs with T and G pairs with C. This allow cell to repair the DNA correctly if only one strand is damaged.

DNA contains [[gene]]s that encode for [[protein]]s. These are produced by the DNA first being turned into m[[RNA]] and then into polypeptides (this process is called the [[Central dogma of molecular biology|central dogma]] of molecular biology). All organisms use DNA as their hereditary material.

==Organisation==
Most of the cells in multi-cellular organisms (human including) retain a complete copy of all DNA of the first cell from which the organism started to grow. It is often possible to clone the organism, or part of it, from a single cell, while doing so with a human cell has severe ethical implications.

All DNA required for a cell to grow into organism is called genome. A cell containing only one genome is called a haploid cell. Humans are diploid (one genome from each parent). Other organisms may have cells with more genomes, for instance, a cell of bread [[wheat]] contains six (hexaploid).

==History==
In the late 19th century [[Friedrich Miescher]], a Swiss [[biochemist]], discovered an unusual [[acid]] in the [[nuclei]] of cells. The acid was named deoxyribonucleic acid, or DNA. In 1944 the American [[biologist]]s, [[Alfred Hershey]], [[Thomas Gilmore]] and [[Martha Chase]] used experiments with [[bacteria]] and [[bacteriophage]]s to show that DNA passed [[gene]]s from one generation to the next.

At that time, it was unclear how this simple molecule could hold all the complex information controlling the development of humans, animals and plants. Scientists knew it was made of four chemical bases called [[adenine]] (A), [[thymine]] (T), [[guanine]] (G) and [[cytosine]] (C), plus [[phosphoric acid]] and a [[sugar]]. They also knew that the ratios of A and T as well as G and C were always the same, but they did not know the rules that controlled the arrangement.

British scientists [[Rosalind Franklin]] and [[Maurice Wilkins]] passed [[X-ray]]s through DNA to study the patterns made when the crystals diffracted them. From studying photographs of patterns, Rosalind Franklin concluded that DNA must be a [[helix]]. [[James Watson]] and [[Francis Crick]], working in [[Cambridge]], used this information to help them solve the puzzle of DNA structure. They built a model showing that if A always paired with T and G paired with C, DNA must be like a ladder made of two strands twisted together in a double helix. The sugar and phosphoric acid were the sides of the ladder, and the rungs were the paired bases that were held together through hydrogen bonding.

Watson and Crick suggested that DNA could unzip itself into two separate strands, and each strand could act as a pattern to grow a new strand. Crick showed later that areas of the DNA known as genes worked in groups of three to code for amino acids, the building blocks of proteins. These groups are called [[codon]]s. They make about fifty thousand different types of [[protein]], which make all the different types of cell in the body. Indian biochemist [[Har Gobind Khorana]] made all the possible codons and worked out which codons controlled which [[amino acid]]. Most codons are redundant and code for the same amino acids, these mostly are different in only the third base pair. This means that differences in genotype can build up in the third position (thereby changing the genotype) without changing the protein (keeps the same phenotype).

If the DNA in one cell was stretched out, it would be about three feet long. Although DNA has a very simple structure, it can carry an enormous amount of [[information]]. Scientists do not yet understand the function of all DNA, but in 1991 a project called the [[Human Genome Project]] began to use computers to map the three billion base pairs which make up the 46 human [[chromosome]]s.

==Modern understanding==
[[Image:818.gif|right|thumb|Structure of DNA.]]
Small lengths of DNA called [[gene]]s serve as the instructions for the body to carry out its functions and give rise to the physical traits of the organism.<ref>"Eye-color genes, through the proteins they encode, direct the amount and placement of melanin in the iris." [http://www.hhmi.org/cgi-bin/askascientist/highlight.pl?kw=&file=answers%2Fgenetics%2Fans_044.html Ask A Scientist - Genes and eye color]</ref> DNA is packaged into [[chromosomes]]. Each individual human being has 23 pairs of [[chromosome]]s, where one set is inherited from his/her mother and the other set is inherited from his/her father. 22 of these chromosomes are referred to as [[autosome]]s, while the remaining chromosomes are the sex chromosomes. Males possess a single X chromosome and a single Y chromosome; whereas females possess a pair of X chromosomes. In total, it is estimated that there are roughly 20300 protein-coding genes in the human genome. Due to mRNA splicing, it is estimated that these genes encode for over 1 million different protein products.

DNA also contains sequences that regulate how and when genes are used by the cell and sequences for important RNA that is not translated into protein (parts of [[ribosome]], etc).

The "language" in that protein structure is described in DNA is called the [[genetic code]]. Genetic code is the same for all organisms, from human to plants and yeasts (few known exceptions are rare and just tiny deviations). The universality of the genetic code is difficult to explain from the evolutionary point of view. This universality makes possible to move the genes from one organism into another, where after the possible modifications (as a rule, regulatory sequences must be adjusted and introns removed) they often still work. For instance, human insulin is currently produced by modified yeasts or bacteria. Wider usage of the genetically modified organisms brings the known risks and ethical problems.

[[Prokaryotic DNA]] is circular (a closed loop). Whereas, [[eukaryotic DNA|eukaryotic chromosomes]] are linear (with ends), with the notable exception of [[Mitochondrial DNA]] and plastid (chloroplast) DNA, which is separate from the DNA in the nucleus.<ref>Mitochondria and chloroplasts are thought to have originated as prokaryotic cells living symbiotically inside of primitive eukaryotic cells, this is called the [[endosymbiotic hypothesis]]</ref> The ends of eukaryotic chromosomes are protected by [[telomere]]s, which are always tightly condensed except during S phase of [[mitosis]].<ref>Campbell, Neil A, et. al. ''Biology''. 6th ed. San Francisco: Benjamin Cummings, 2002. 299, 530-31.</ref> Telomeres are partially lost during cell division, and must be regrown later. Most of the cells in animal body are not capable of restoring they telomeres so can divide only limited number of times (Hayflick limit <ref>{{cite journal |author=Watson JD |title=Origin of concatemeric T7 DNA |journal=Nature New Biol. |volume=239 |pages=197–201 |year=1972 |pmid=4507727 |issue=94 |doi=10.1038/newbio239197a0}}</ref>).

== Mutations ==
[[Mutation]]s are simply variations in DNA sequence between individuals. The vast majority of spontaneous mutations in DNA are called "neutral" because they do not affect the [[phenotype|observable traits]] of the individual organism. Others can have beneficial effects and some can disrupt important functions Differential distribution of various types of neutral mutations within the population is the basis for modern [[DNA fingerprinting]]. It is mutations in DNA, giving rise to novel alleles ("versions" of a gene), which cause phenotypic variations between individuals of a particular species. For instance, in humans, single-gene mutations are responsible for differences in [[ABO blood type]], eye color, hair color, and even the ability to taste certain molecules. Sadly, there are also thousands of mutations known to cause human disease; notably sickle-cell anemia, a few rare forms of autism, and (when the mutations spontaneously occur in a somatic cell) various types of cancer. That said, it is important to note that most phenotypic traits (e.g. height) and hereditary diseases arise as the net effect of several different genetic variations.

Usually a mutation is harmless if present in only one of the two or more genomes in same cell (it is said most of mutations are recessive), or even may be beneficial. Offspring of the parents who are already genetically related often inherits the same mutation in both genomes, so diseases are more frequent. If the mutation is diagnosed early in the life, sometimes diet and other similar measures may be applied, resulting a normal life later.<ref name=Al2015>{{cite journal|last1=Al Hafid|first1=N|last2=Christodoulou|first2=J|title=Phenylketonuria: a review of current and future treatments.|journal=Translational pediatrics|date=October 2015|volume=4|issue=4|pages=304–17|pmid=26835392}}</ref>

[http://www.ncbi.nlm.nih.gov/omim OMIM] (Online Mendelian Inheritance in Man), is an online database of genes known to be mutated in disease states. [[Mendelian inheritance]] refers to the inheritance pattern observed in traits that are determined by a single gene. This pattern was first discovered by [[Gregor Mendel]], an Austrian monk, during his work with pea plants from 1856-1863. Although Mendel published his work in 1866, it's significance was largely ignored until it was rediscovered in the early 20th century; more than two decades after his death.

==See also==
*[[DNA library]]
*[[Transcription]]

==External links==
*[http://www.learner.org/interactives/dna/index.html Interactive DNA] Learn about genetics, genetic engineering, the Human Genome Project and the ethical implications of these new technologies.
*[http://www.blackwellpublishing.com/trun/artwork/Animations/cloningexp/cloningexp.html Animated guide to DNA cloning]

== References ==
<references/>

[[Category:Genetics]]
[[Category:Police State]]

Deoxyribonucleic acid

2016-10-18T20:58:04Z

H22:

[[Image:799.gif|right|thumb|300px]]
'''Deoxyribonucleic acid''' (DNA) is a chemical inside [[cell]]s which carries the hereditary information. It is a molecular [[polymer]] formed of [[nucleotide|deoxyribonucleotides]]. Most organisms use DNA as their hereditary material. [[Offspring]] of [[Human reproduction|sexual reproduction]] [[Organism|organisms]] contain DNA from both parents.

==Structure==

Most commonly as a double-stranded [[helix]] comprising two complimentary molecules held together by hydrogen bonds, this is commonly called "dsDNA" (double-stranded DNA).<ref>Single-stranded DNAs (ssDNA) do exist in certain [[bacteriophage]]s, however they cannot be replicated without first creating the complimentary strand to use as a template.</ref> The [[nucleotide]]s which are the "building blocks" of DNA have three main parts: A nitrogenous base (the "letters" in the sequence), a [[sugar]], and a [[phosphate]] group. When nucleotides are joined into DNA strands, they form a chain with the phosphate group of one nucleotide binding to the ribose of the next.

DNA strands "compliment" each other by having compatible sequences, allowing the bases on one strand to form bonds with the bases on the other strand. There are four nitrogenous bases, Adenonine (A), Cytosine (C), Guanine (G), and Thymine (T). Under the base pairing rules, A pairs with T and G pairs with C. This allow cell to repair the DNA correctly if only one strand is damaged.

DNA contains [[gene]]s that encode for [[protein]]s. These are produced by the DNA first being turned into m[[RNA]] and then into polypeptides (this process is called the [[Central dogma of molecular biology|central dogma]] of molecular biology). All organisms use DNA as their hereditary material.

==Organisation==
Most of the cells in multi-cellular organisms (human including) retain a complete copy of all DNA of the first cell from which the organism started to grow. It is often possible to clone the organism, or part of it, from a single cell, while doing so with a human cell has severe ethical implications.

All DNA required for a cell to grow into organism is called genome. A cell containing only one genome is called a haploid cell. Humans are diploid (one genome from each parent). Other organisms may have cells with more genomes, for instance, a cell of bread [[wheat]] contains six (hexaploid).

==History==
In the late 19th century [[Friedrich Miescher]], a Swiss [[biochemist]], discovered an unusual [[acid]] in the [[nuclei]] of cells. The acid was named deoxyribonucleic acid, or DNA. In 1944 the American [[biologist]]s, [[Alfred Hershey]], [[Thomas Gilmore]] and [[Martha Chase]] used experiments with [[bacteria]] and [[bacteriophage]]s to show that DNA passed [[gene]]s from one generation to the next.

At that time, it was unclear how this simple molecule could hold all the complex information controlling the development of humans, animals and plants. Scientists knew it was made of four chemical bases called [[adenine]] (A), [[thymine]] (T), [[guanine]] (G) and [[cytosine]] (C), plus [[phosphoric acid]] and a [[sugar]]. They also knew that the ratios of A and T as well as G and C were always the same, but they did not know the rules that controlled the arrangement.

British scientists [[Rosalind Franklin]] and [[Maurice Wilkins]] passed [[X-ray]]s through DNA to study the patterns made when the crystals diffracted them. From studying photographs of patterns, Rosalind Franklin concluded that DNA must be a [[helix]]. [[James Watson]] and [[Francis Crick]], working in [[Cambridge]], used this information to help them solve the puzzle of DNA structure. They built a model showing that if A always paired with T and G paired with C, DNA must be like a ladder made of two strands twisted together in a double helix. The sugar and phosphoric acid were the sides of the ladder, and the rungs were the paired bases that were held together through hydrogen bonding.

Watson and Crick suggested that DNA could unzip itself into two separate strands, and each strand could act as a pattern to grow a new strand. Crick showed later that areas of the DNA known as genes worked in groups of three to code for amino acids, the building blocks of proteins. These groups are called [[codon]]s. They make about fifty thousand different types of [[protein]], which make all the different types of cell in the body. Indian biochemist [[Har Gobind Khorana]] made all the possible codons and worked out which codons controlled which [[amino acid]]. Most codons are redundant and code for the same amino acids, these mostly are different in only the third base pair. This means that differences in genotype can build up in the third position (thereby changing the genotype) without changing the protein (keeps the same phenotype).

If the DNA in one cell was stretched out, it would be about three feet long. Although DNA has a very simple structure, it can carry an enormous amount of [[information]]. Scientists do not yet understand the function of all DNA, but in 1991 a project called the [[Human Genome Project]] began to use computers to map the three billion base pairs which make up the 46 human [[chromosome]]s.

==Modern understanding==
[[Image:818.gif|right|thumb|Structure of DNA.]]
Small lengths of DNA called [[gene]]s serve as the instructions for the body to carry out its functions and give rise to the physical traits of the organism.<ref>"Eye-color genes, through the proteins they encode, direct the amount and placement of melanin in the iris." [http://www.hhmi.org/cgi-bin/askascientist/highlight.pl?kw=&file=answers%2Fgenetics%2Fans_044.html Ask A Scientist - Genes and eye color]</ref> DNA is packaged into [[chromosomes]]. Each individual human being has 23 pairs of [[chromosome]]s, where one set is inherited from his/her mother and the other set is inherited from his/her father. 22 of these chromosomes are referred to as [[autosome]]s, while the remaining chromosomes are the sex chromosomes. Males possess a single X chromosome and a single Y chromosome; whereas females possess a pair of X chromosomes. In total, it is estimated that there are roughly 20300 protein-coding genes in the human genome. Due to mRNA splicing, it is estimated that these genes encode for over 1 million different protein products.

DNA also contains sequences that regulate how and when genes are used by the cell and sequences for important RNA that is not translated into protein (parts of [[ribosome]], etc).

The "language" in that protein structure is described in DNA is called the [[genetic code]]. Genetic code is the same for all organisms, from human to plants and yeasts (few known exceptions are rare and just tiny deviations). The universality of the genetic code is difficult to explain from the evolutionary point of view. This universality makes possible to move the genes from one organism into another, where after the possible modifications (as a rule, regulatory sequences must be adjusted and introns removed) they often still work. For instance, human insulin is currently produced by modified yeasts or bacteria. Wider usage of the genetically modified organisms brings the known risks and ethical problems.

[[Prokaryotic DNA]] is circular (a closed loop). Whereas, [[eukaryotic DNA|eukaryotic chromosomes]] are linear (with ends), with the notable exception of [[Mitochondrial DNA]] and plastid (chloroplast) DNA, which is separate from the DNA in the nucleus.<ref>Mitochondria and chloroplasts are thought to have originated as prokaryotic cells living symbiotically inside of primitive eukaryotic cells, this is called the [[endosymbiotic hypothesis]]</ref> The ends of eukaryotic chromosomes are protected by [[telomere]]s, which are always tightly condensed except during S phase of [[mitosis]].<ref>Campbell, Neil A, et. al. ''Biology''. 6th ed. San Francisco: Benjamin Cummings, 2002. 299, 530-31.</ref> Telomeres are partially lost during cell division, and must be regrown later. Most of the cells in animal body are not capable of restoring they telomeres so can divide only limited number of times (Hayflick limit <ref>{{cite journal |author=Watson JD |title=Origin of concatemeric T7 DNA |journal=Nature New Biol. |volume=239 |pages=197–201 |year=1972 |pmid=4507727 |issue=94 |doi=10.1038/newbio239197a0}}</ref>).

== Mutations ==
[[Mutation]]s are simply variations in DNA sequence between individuals. The vast majority of spontaneous mutations in DNA are called "neutral" because they do not affect the [[phenotype|observable traits]] of the individual organism. Others can have beneficial effects and some can disrupt important functions Differential distribution of various types of neutral mutations within the population is the basis for modern [[DNA fingerprinting]]. It is mutations in DNA, giving rise to novel alleles ("versions" of a gene), which cause phenotypic variations between individuals of a particular species. For instance, in humans, single-gene mutations are responsible for differences in [[ABO blood type]], eye color, hair color, and even the ability to taste certain molecules. Sadly, there are also thousands of mutations known to cause human disease; notably sickle-cell anemia, a few rare forms of autism, and (when the mutations spontaneously occur in a somatic cell) various types of cancer. That said, it is important to note that most phenotypic traits (e.g. height) and hereditary diseases arise as the net effect of several different genetic variations.

Usually a mutation is harmless if present in only one of the two or more genomes in same cell (it is said most of mutations are recessive), or even may be beneficial. Offspring of the parents who are already genetically related often inherits the same mutation in both genomes, so diseases are more frequent. If the mutation is diagnosed early in the life, diet and other similar measures may be applied, resulting a normal life later.<ref name=Al2015>{{cite journal|last1=Al Hafid|first1=N|last2=Christodoulou|first2=J|title=Phenylketonuria: a review of current and future treatments.|journal=Translational pediatrics|date=October 2015|volume=4|issue=4|pages=304–17|pmid=26835392}}</ref>

[http://www.ncbi.nlm.nih.gov/omim OMIM] (Online Mendelian Inheritance in Man), is an online database of genes known to be mutated in disease states. [[Mendelian inheritance]] refers to the inheritance pattern observed in traits that are determined by a single gene. This pattern was first discovered by [[Gregor Mendel]], an Austrian monk, during his work with pea plants from 1856-1863. Although Mendel published his work in 1866, it's significance was largely ignored until it was rediscovered in the early 20th century; more than two decades after his death.

==See also==
*[[DNA library]]
*[[Transcription]]

==External links==
*[http://www.learner.org/interactives/dna/index.html Interactive DNA] Learn about genetics, genetic engineering, the Human Genome Project and the ethical implications of these new technologies.
*[http://www.blackwellpublishing.com/trun/artwork/Animations/cloningexp/cloningexp.html Animated guide to DNA cloning]

== References ==
<references/>

[[Category:Genetics]]
[[Category:Police State]]

Deoxyribonucleic acid

2016-10-18T20:41:46Z

H22:

[[Image:799.gif|right|thumb|300px]]
'''Deoxyribonucleic acid''' (DNA) is a chemical inside [[cell]]s which carries the hereditary information. It is a molecular [[polymer]] formed of [[nucleotide|deoxyribonucleotides]]. Most organisms use DNA as their hereditary material. [[Offspring]] of [[Human reproduction|sexual reproduction]] [[Organism|organisms]] contain DNA from both parents.

==Structure==

Most commonly as a double-stranded [[helix]] comprising two complimentary molecules held together by hydrogen bonds, this is commonly called "dsDNA" (double-stranded DNA).<ref>Single-stranded DNAs (ssDNA) do exist in certain [[bacteriophage]]s, however they cannot be replicated without first creating the complimentary strand to use as a template.</ref> The [[nucleotide]]s which are the "building blocks" of DNA have three main parts: A nitrogenous base (the "letters" in the sequence), a [[sugar]], and a [[phosphate]] group. When nucleotides are joined into DNA strands, they form a chain with the phosphate group of one nucleotide binding to the ribose of the next.

DNA strands "compliment" each other by having compatible sequences, allowing the bases on one strand to form bonds with the bases on the other strand. There are four nitrogenous bases, Adenonine (A), Cytosine (C), Guanine (G), and Thymine (T). Under the base pairing rules, A pairs with T and G pairs with C. This allow cell to repair the DNA correctly if only one strand is damaged.

DNA contains [[gene]]s that encode for [[protein]]s. These are produced by the DNA first being turned into m[[RNA]] and then into polypeptides (this process is called the [[Central dogma of molecular biology|central dogma]] of molecular biology). All organisms use DNA as their hereditary material.

==Organisation==
Most of the cells in multi-cellular organisms (human including) retain a complete copy of all DNA of the first cell from which the organism started to grow. It is often possible to clone the organism, or part of it, from a single cell, while doing so with a human cell has severe ethical implications.

All DNA required for a cell to grow into organism is called genome. A cell containing only one genome is called a haploid cell. Humans are diploid (one genome from each parent). Other organisms may have cells with more genomes, for instance, a cell of bread [[wheat]] contains six (hexaploid).

==History==
In the late 19th century [[Friedrich Miescher]], a Swiss [[biochemist]], discovered an unusual [[acid]] in the [[nuclei]] of cells. The acid was named deoxyribonucleic acid, or DNA. In 1944 the American [[biologist]]s, [[Alfred Hershey]], [[Thomas Gilmore]] and [[Martha Chase]] used experiments with [[bacteria]] and [[bacteriophage]]s to show that DNA passed [[gene]]s from one generation to the next.

At that time, it was unclear how this simple molecule could hold all the complex information controlling the development of humans, animals and plants. Scientists knew it was made of four chemical bases called [[adenine]] (A), [[thymine]] (T), [[guanine]] (G) and [[cytosine]] (C), plus [[phosphoric acid]] and a [[sugar]]. They also knew that the ratios of A and T as well as G and C were always the same, but they did not know the rules that controlled the arrangement.

British scientists [[Rosalind Franklin]] and [[Maurice Wilkins]] passed [[X-ray]]s through DNA to study the patterns made when the crystals diffracted them. From studying photographs of patterns, Rosalind Franklin concluded that DNA must be a [[helix]]. [[James Watson]] and [[Francis Crick]], working in [[Cambridge]], used this information to help them solve the puzzle of DNA structure. They built a model showing that if A always paired with T and G paired with C, DNA must be like a ladder made of two strands twisted together in a double helix. The sugar and phosphoric acid were the sides of the ladder, and the rungs were the paired bases that were held together through hydrogen bonding.

Watson and Crick suggested that DNA could unzip itself into two separate strands, and each strand could act as a pattern to grow a new strand. Crick showed later that areas of the DNA known as genes worked in groups of three to code for amino acids, the building blocks of proteins. These groups are called [[codon]]s. They make about fifty thousand different types of [[protein]], which make all the different types of cell in the body. Indian biochemist [[Har Gobind Khorana]] made all the possible codons and worked out which codons controlled which [[amino acid]]. Most codons are redundant and code for the same amino acids, these mostly are different in only the third base pair. This means that differences in genotype can build up in the third position (thereby changing the genotype) without changing the protein (keeps the same phenotype).

If the DNA in one cell was stretched out, it would be about three feet long. Although DNA has a very simple structure, it can carry an enormous amount of [[information]]. Scientists do not yet understand the function of all DNA, but in 1991 a project called the [[Human Genome Project]] began to use computers to map the three billion base pairs which make up the 46 human [[chromosome]]s.

==Modern understanding==
[[Image:818.gif|right|thumb|Structure of DNA.]]
Small lengths of DNA called [[gene]]s serve as the instructions for the body to carry out its functions and give rise to the physical traits of the organism.<ref>"Eye-color genes, through the proteins they encode, direct the amount and placement of melanin in the iris." [http://www.hhmi.org/cgi-bin/askascientist/highlight.pl?kw=&file=answers%2Fgenetics%2Fans_044.html Ask A Scientist - Genes and eye color]</ref> DNA is packaged into [[chromosomes]]. Each individual human being has 23 pairs of [[chromosome]]s, where one set is inherited from his/her mother and the other set is inherited from his/her father. 22 of these chromosomes are referred to as [[autosome]]s, while the remaining chromosomes are the sex chromosomes. Males possess a single X chromosome and a single Y chromosome; whereas females possess a pair of X chromosomes. In total, it is estimated that there are roughly 20300 protein-coding genes in the human genome; however, due to mRNA splicing, it is estimated that these genes encode for over 1 million different protein products.

The "language" in that protein structure is described in DNA is called the [[genetic code]]. Genetic code is the same for all organisms, from human to plants and yeasts (few known exceptions are rare and just tiny deviations). The universality of the genetic code is difficult to explain from the evolutionary point of view. This universality makes possible to move the genes from one organism into another, where after the possible modifications (as a rule, regulatory sequences must be adjusted and introns removed) they often still work. For instance, human insulin is currently produced by modified yeasts or bacteria. Wider usage of the genetically modified organisms brings the known risks and ethical problems.

[[Prokaryotic DNA]] is circular (a closed loop). Whereas, [[eukaryotic DNA|eukaryotic chromosomes]] are linear (with ends), with the notable exception of [[Mitochondrial DNA]] and plastid (chloroplast) DNA, which is separate from the DNA in the nucleus.<ref>Mitochondria and chloroplasts are thought to have originated as prokaryotic cells living symbiotically inside of primitive eukaryotic cells, this is called the [[endosymbiotic hypothesis]]</ref> The ends of eukaryotic chromosomes are protected by [[telomere]]s, which are always tightly condensed except during S phase of [[mitosis]].<ref>Campbell, Neil A, et. al. ''Biology''. 6th ed. San Francisco: Benjamin Cummings, 2002. 299, 530-31.</ref> Telomeres are partially lost during cell division, and must be regrown later. Most of the cells in animal body are not capable of restoring they telomeres so can divide only limited number of times (Hayflick limit <ref>{{cite journal |author=Watson JD |title=Origin of concatemeric T7 DNA |journal=Nature New Biol. |volume=239 |pages=197–201 |year=1972 |pmid=4507727 |issue=94 |doi=10.1038/newbio239197a0}}</ref>).

== Mutations ==
[[Mutation]]s are simply variations in DNA sequence between individuals. The vast majority of spontaneous mutations in DNA are called "neutral" because they do not affect the [[phenotype|observable traits]] of the individual organism. Others can have beneficial effects and some can disrupt important functions Differential distribution of various types of neutral mutations within the population is the basis for modern [[DNA fingerprinting]]. It is mutations in DNA, giving rise to novel alleles ("versions" of a gene), which cause phenotypic variations between individuals of a particular species. For instance, in humans, single-gene mutations are responsible for differences in [[ABO blood type]], eye color, hair color, and even the ability to taste certain molecules. Sadly, there are also thousands of mutations known to cause human disease; notably sickle-cell anemia, a few rare forms of autism, and (when the mutations spontaneously occur in a somatic cell) various types of cancer. That said, it is important to note that most phenotypic traits (e.g. height) and hereditary diseases arise as the net effect of several different genetic variations.

Usually a mutation is harmless if present in only one of the two or more genomes in same cell (it is said most of mutations are recessive), or even may be beneficial. Offspring of the parents who are already genetically related often inherits the same mutation in both genomes, so diseases are more frequent. If the mutation is diagnosed early in the life, diet and other similar measures may be applied, resulting a normal life later.<ref name=Al2015>{{cite journal|last1=Al Hafid|first1=N|last2=Christodoulou|first2=J|title=Phenylketonuria: a review of current and future treatments.|journal=Translational pediatrics|date=October 2015|volume=4|issue=4|pages=304–17|pmid=26835392}}</ref>

[http://www.ncbi.nlm.nih.gov/omim OMIM] (Online Mendelian Inheritance in Man), is an online database of genes known to be mutated in disease states. [[Mendelian inheritance]] refers to the inheritance pattern observed in traits that are determined by a single gene. This pattern was first discovered by [[Gregor Mendel]], an Austrian monk, during his work with pea plants from 1856-1863. Although Mendel published his work in 1866, it's significance was largely ignored until it was rediscovered in the early 20th century; more than two decades after his death.

==See also==
*[[DNA library]]
*[[Transcription]]

==External links==
*[http://www.learner.org/interactives/dna/index.html Interactive DNA] Learn about genetics, genetic engineering, the Human Genome Project and the ethical implications of these new technologies.
*[http://www.blackwellpublishing.com/trun/artwork/Animations/cloningexp/cloningexp.html Animated guide to DNA cloning]

== References ==
<references/>

[[Category:Genetics]]
[[Category:Police State]]

Switzerland

2016-10-18T20:05:48Z

H22:

{{Country
|name =''Schweizerische Eidgenossenschaft (German) Confédération suisse (French) Confederazione Svizzera (Italian) Confederaziun svizra (Romansch)''
|map =Switzerland rel 2000.jpg
|map2 =Switzerland location.png
|flag =Flag of Switzerland.png
|arms =Arms of Switzerland.png
|capital =Bern
|capital-raw =
|government-raw =[[Federal|Federal State]], [[direct democracy]]
|language =[[German language|German]], [[French language|French]], [[Italian language|Italian]], [[Romansch]]
|king =
|queen =
|monarch-raw =
|president =Johann Schneider-Ammann (2016)
|president-raw =
|chancellor =
|chancellor-raw =
|pm =
|pm-raw =
|area =41,285 sq mi
|pop =8,121,830 (July 2015 est.)<ref name="CIA">[https://www.cia.gov/library/publications/the-world-factbook/geos/sz.html Switzerland - The World Factbook]. ''CIA''. Retrieved August 16, 2016.</ref>
|pop-basis =
|gdp =$482.3 billion (2015 est.)<ref name="CIA"/>
|gdp-year =
|gdp-pc =$58,600 (2015 est.)<ref name="CIA"/>
|currency =Swiss franc
|idd =
|tld =
}}

'''Switzerland''' is a country located in [[Central Europe]] between [[Germany]], [[Italy]], [[France]], and [[Austria]]. Its capital is [[Bern]], and its largest city is [[Zurich]]. Four languages have been designated as official: [[German language|German]], [[French language|French]], [[Italian language|Italian]], and [[Romansch language|Romansch]] (a dialect spoken by a small minority, closely related to [[Latin]]). Switzerland has been an independent country since 1291 and is a confederation of 26 cantons with elements of direct democracy in that all laws passed by parliament can be overturned by arranging a [[referendum]]. Switzerland is also well known for having strict [[Political neutrality|neutrality]].

==People==
Switzerland sits at the crossroads of several major European cultures, which have heavily influenced the country's languages and cultural practices. Switzerland has four official languages—German, French, Italian, and Romansch (based on Latin and spoken by a small minority in the Canton Graubunden). The [[German]] spoken is predominantly a Swiss dialect, but newspapers and some broadcasts use [[High German]]. Many Swiss speak more than one language. [[English]] is widely known, especially among professionals.
[[File:Alphorn players in Vals Switzerland.JPG|thumb|250px|left|Alphorn players in Vals.]]
More than 75% of the population lives in the central plain, which stretches between the [[Alps]] and the [[Jura]] Mountains and from [[Geneva]] in the southwest to the [[Rhine]] River and [[Lake Constance]] in the northeast. Resident foreigners and temporary foreign workers make up about 20% of the population.

According to the Swiss Federal Office of Statistics, the population in Switzerland increased to an estimated 7,523,934 by July 2006. Three-quarters of this growth was attributed to migration. Switzerland naturalized 22% more people in 2006 compared to 2005, totaling 46,700 persons. By the end of 2006, there were 850,000 foreigners working legally in Switzerland. The rise of German immigrants, as confirmed in earlier reports, increased by 10.6% (+10,000). Portuguese workers also increased by 7.4% (+7000). On the other hand, the number of the Italians continued to drop by –3.2% (-5000). The major ethnic groups are: German 65%, French 10%, and Italians 6%.

Almost all Swiss are literate. Switzerland's 13 university institutes enrolled 111,100 students in the academic year of 2004-05. About 25% of the adult population holds a diploma of higher learning.

The Constitution guarantees freedom of worship, and the different religious communities co-exist peacefully. While the majority of the Swiss population is still nominally Christian, like much of Europe, the country is quickly becoming secular. Despite this trend, [[Evangelical Christianity]] has seen rapid growth in Switzerland recently.<ref>Kumar, Anugrah (December 5, 2011). [http://www.christianpost.com/news/evangelical-churches-growing-fast-in-switzerland-63962/ Evangelical Churches Growing Fast in Switzerland]. ''The Christian Post''. Retrieved October 6, 2016.</ref>

Switzerland consistently ranks high on quality of life indices, including highest per capita income, one of the highest concentrations of computer and Internet usage per capita, highest insurance coverage per individual, and high health care rates. For these and many other reasons, it serves as an excellent [[test market]] for businesses hoping to introduce new products into Europe.

==Government==
[[File:Swiss Federal Palace (Bundeshaus) in Berne.jpg|thumb|The Swiss Federal Palace (''Bundeshaus'') in Bern.]]
Switzerland is a federal state composed of 26 [[canton]]s (20 are "full" cantons and six "half" cantons for purposes of representation in the federal legislature) that retain many attributes of [[sovereignty]], such as fiscal autonomy and the right to manage internal cantonal affairs. The 1874 Constitution began, "Together, the peoples of the 23 sovereign Cantons of Switzerland united by the present alliance..." Similarly, under the current 2000 Constitution, cantons hold all powers not specifically delegated to the federation. Switzerland's federal institutions are:
*A bicameral legislature—the Federal Assembly;
*A collegial executive of seven members—the Federal Council; and
*A judiciary consisting of a regular court in [[Lausanne]]—the Federal Tribunal—and special military and administrative courts.
**The Federal Insurance Tribunal is an independent division of the Federal Tribunal that handles social security questions; its seat is in [[Lucerne]].
**The Federal Criminal Court, located in [[Bellinzona]], is the [[court of first instance]] for all criminal cases under federal jurisdiction.
*The Constitution provides for separation of the three branches of government.

===Federal Assembly===
The Federal Assembly is the primary seat of power, although in practice the executive branch has been increasing its power at the expense of the legislative branch. The Federal Assembly has two houses—the Council of States and the National Council. These two houses have equal powers in all respects, including the right to introduce legislation. Legislation cannot be vetoed by the executive nor reviewed for constitutionality by the judiciary, but all laws (except the budget) can be reviewed by popular referendum before taking effect. The 46 members of the Council of States (two from each canton and one from each half canton) are directly elected in each canton by majority voting. The 200 members of the National Council are directly elected in each canton under a system of proportional representation. Members of both houses serve for 4 years.

The Federal Assembly meets quarterly for 3-week plenary sessions. The parliamentary committees of the two houses, which are often key in shaping legislation, meet behind closed doors, but both majority and minority positions are presented during the plenary sessions. The Federal Assembly is a militia parliament, and members commonly retain their traditional professions. Individual members of parliament have no personal staff.

The Assembly can be legally dissolved only after the adoption of a popular initiative calling for a complete revision of the Constitution. All citizens 18 or older have the right to vote and run for office in national, cantonal, and communal elections unless individually disqualified by the relevant legislature.

===Federal Council===
The top executive body is the seven-member cabinet called the Federal Council. The Federal Assembly individually elects the seven Federal Councilors in a joint session of both houses at the opening of a new legislature. Federal Councilors are elected for 4-year terms; there are no term limits and no provision to recall the cabinet or individual members during the legislature. Each year, the Federal Assembly elects from among the seven Federal Councilors a president and vice president, following the principle of seniority. The member who is vice president one year traditionally is elected president the next. Although the Constitution provides that the Federal Assembly chooses and supervises the cabinet, the latter has gradually assumed a preeminent role in directing the legislative process as well as executing federal laws.

Under an arrangement between the four major parties called the "magic formula" which was introduced in 1959 but ended in December 2003, two Federal Councilors (ministers) were elected each from the Christian Democrats (CVP), the Social Democrats (SP), and the Free Democrats (FDP) and one from the Swiss People's Party (SVP). Under the new magic formula starting January 1, 2004, the new party composition of the cabinet changed to the following composition: 1 Christian Democrat, 2 Social Democrats, 2 Free Democrats, and 2 representatives of the Swiss People's Party. This arrangement was shaken up in the aftermath of the 2008 federal elections: a leftist coalition of Social Democrats, Greens and Christian Democrats formed a parliamentary majority to oust Councilor [[Christoph Blocher]], the iconic leader of the [[Swiss People's Party]], from office even though his party had just achieved a decisive electoral victory. He was replaced by party colleague Evelin Widmer-Schlumpf, who was subsequently banned from the party for conspiring against Blocher, along with fellow Councilor Samuel Schmid. Both Widmer-Schlumpf and Schmid were much more moderate on the political spectrum, as opposed to the conservative Blocher. The two went on to form a new breakaway party, the Conservative Democratic Party (BDP). The Swiss People's Party has since returned as a participant in the national government following the demission of Schmid in 2008, who was replaced by Ueli Maurer, and following the resignation of Widmer-Schlumpf in 2015 after a record election for the SVP and a poor election for the BDP, being replaced by Guy Parmelin of the SVP.<ref>Mombelli, Armando (December 10, 2015). [http://www.swissinfo.ch/eng/politics/cabinet-elections_how-will-new-ingredients-change--magic-formula--/41825058 People’s Party gains second seat in cabinet]. ''Swissinfo''. Retrieved August 10, 2016.</ref>

The Constitution requires that Federal Councilors act collectively in all matters, not as individual ministers or as representatives of their parties. Each Councilor heads one of seven federal departments and is responsible for preparing legislation pertaining to matters under its jurisdiction. The president, who remains responsible for the department he heads, has limited prerogatives and is first among equals (there is no formal prime minister).

====Federal Council Membership====
The Swiss Federal Council, as of 2016:

*Environment, Transport, Energy and Communications — Doris Leuthard (CVP) — Vice-President for 2016
*Finance — Ueli Maurer (SVP)
*Foreign affairs — Didier Burkhalter (FDP)
*Justice and Police — Simonetta Sommaruga (SP)
*Economic Affairs, Education and Research — Johann Schneider-Ammann (FDP) — President for 2016
*Home Affairs — Alain Berset (SP)
*Defence, Civil Protection and Sports — Guy Parmelin (SVP)

*Federal Chancellor — Walter Thurnherr (Ex Officio, CVP)

===Judiciary===
[[File:Lausanne, Switzerland.jpg|thumb|The Federal Tribunal of Switzerland is based in Lausanne (pictured), in the Canton of Vaud.]]
The administration of justice is primarily a cantonal function. The Federal Tribunal is limited in its jurisdiction. Its principal function is to hear appeals of civil and criminal cases. It also hears complaints of violations of the constitutional rights of citizens and has authority to review cantonal court decisions involving federal law as well as certain administrative rulings of federal departments. However, it has no power to review federal legislation for constitutionality. The Tribunal's 30 full-time and 30 part-time judges are elected by the Federal Assembly for 6-year terms. The Federal Criminal Court is the court of first instance for criminal cases involving organized and white-collar crime, money laundering, and corruption, which are under federal jurisdiction. The Court’s 11 judges are elected by the Federal Assembly for 6-year terms.

===Local Government===
[[File:Landsgemeinde Glarus 2006.jpg|thumb|The Landsgemeinde, an old form of direct democracy where the citizens publically vote in the town square once a year. As of 2016, only two cantons, Glarus and Appenzell Innerrhoden, still use this system.]]
The cantons regulate local government. The basic unit of local government, which administers a village, town, or city, is the commune or municipality. Citizenship is derived from membership in a commune and can be conferred on non-Swiss by a commune. Cantons are subordinate to federal authority but keep autonomy in implementing federal law.

===[[Referendum|Referenda]]===
A strong emphasis on ballot votes arises out of the traditional Swiss belief that the will of the people is the final national authority. Every constitutional amendment adopted by parliament is automatically brought to the ballot and has to carry a double majority of votes and cantons in order to become effective. The voters themselves may actively seek changes to the Constitution by means of the popular [[initiative]]: 100,000 voters may with their signatures request a national vote on a proposed [[constitutional amendment]]. New federal legislation also is subject to popular review, under the so-called referendum: 50,000 signatures suffice to call a ballot vote on any federal law adopted by parliament. The Assembly can declare an act to be too urgent to allow time for popular consideration, but this is rare. At any rate, an act passed urgently must have a time limit and is later subject to the same constitutional provisions on popular review as other legislation. This device provides a useful channel for linking laws closely to the will of the people and reducing the influence of elites. A stunning example of this process occurred in November 2009, when Swiss voters turned out at the polls in huge numbers to approve of an amendment to the constitution banning the construction of [[minaret]]s.<ref>http://www.admin.ch/ch/d//pore/va/20091129/det547.html Official voting results (in German)</ref> This decision of a vast majority of voters to take a stand against political Islam came after a campaign in which the establishment elites had presented a unified front against the measure: all political parties except the [[Swiss People's Party]] had strongly opposed the suggested amendment, and most of the media openly mocked its supporters as racist and foolish.

Swiss citizens are capable of not taking proposals personally: for instance, proposals for longer vacations, or for basic (government funded) income for every citizen have been rejected by public referenda.

===Political Conditions===
Although it has a diverse society, Switzerland has a stable government. Most voters support the government in the armed neutrality underlying its foreign and defense policies. Domestic policy poses no major problems, but the changing international environment has generated a significant reexamination of Swiss policy in key areas such as defense, neutrality, and immigration. Quadrennial national elections typically produce only marginal changes in party representation.

In recent years, Switzerland has seen a gradual shift in the party landscape. The rightist Swiss People's Party (SVP), traditionally the junior partner in the four-party coalition government, more than doubled its voting share from 11% in 1987 to 22.5% in 1999, and finally to 26.6% in 2003, thus overtaking its three coalition partners. This shift in voting shares ended the 44-year old "magic formula," the power-broking agreement of the four coalition parties, and gave a second seat in the 7-person Swiss cabinet to the Swiss People's Party at the expense of the Christian Democrats, now the weakest of the four major parties. For the first time in Swiss history, the SVP has two seats in the government, reflecting its new status as Switzerland's most popular party. As of the 2015 federal elections, the SVP received 29.4% of the popular vote and has 65 seats in the national council, records for the party.<ref>{{cite news|title=Anti-immigration party wins Swiss election in 'slide to the Right'|url=http://www.telegraph.co.uk/news/worldnews/europe/switzerland/11939953/Anti-immigration-party-wins-Swiss-election-in-slide-to-the-Right.html|accessdate=19 October 2015|work=The Daily Telegraph|agency=Reuters|date=19 October 2015}}</ref>

On December 10, 2003, [[Christoph Blocher]]—a self-made industrialist and main figure of the right-populist Swiss People's Party known for his strong opinions on asylum and migration and law and order issues—was elected to the cabinet by parliament, replacing the incumbent Christian Democrat Justice and Police Minister Ruth Metzler. The parliament also elected the Free Democrat Hans-Rudolf Merz to replace retiring Finance Minister Kaspar Villiger. Both Blocher and Merz were strong advocates of drastic public spending cuts in order to reduce the country's mounting $102 billion francs state deficit and staunch opponents to Switzerland's entering the European Union. On June 14, 2006, the Federal Council elected Doris Leuthard of the Christian Democratic Party. Leuthard replaced the retiring Joseph Deiss and has assumed the Economics and Trade portfolio that Deiss managed. Leuthard’s election and Deiss’ resignation did not change the dynamics of the Federal Council. Blocher was not re-elected in 2007.

The Constitution limits federal influence in the formulation of domestic policy and emphasizes the roles of private enterprise and cantonal government. However, the Confederation has been compelled to enlarge its policymaking powers in recent years to cope with national problems such as education, agriculture, energy, environment, organized crime, and narcotics.

====EU relations and politics====
Because every country surrounding Switzerland, with the exception of [[Lichtenstein]], is a member of the [[European Union]], matters related to the EU are prominent in Swiss politics. In 1992, the Swiss government applied for membership in the European Economic Area (EEA), but on a referendum on December 6, 1992, at a "historically high" turnout of 78.7%, the Swiss population narrowly rejected membership in the organization, even though the liberal elites strongly supported membership.<ref name="Arm's length">Miserez, Marc-Andre (December 2, 2012). [http://www.swissinfo.ch/eng/20-years-on_switzerland-poised-to-keep-eu-at-arm-s-length/34083578 Switzerland poised to keep EU at arm's length]. ''Swissinfo''. Retrieved August 16, 2016.</ref><ref name="CH&EU">[https://www.eda.admin.ch/dam/eda/en/documents/publications/EuropaeischeAngelegenheiten/Schweiz-und-EU_en.pdf Switzerland and the European Union] (PDF) (2nd ed.). ''Federal Department of Foreign Affairs''. 2016. Retrieved August 16, 2016.</ref> After that, starting in 1993, several bilateral agreements were adopted between the Swiss Government and the EU, which allowed Switzerland to integrate with the EU without joining the EU or EEA.<ref name="Arm's length"/> In 2001, immediate membership negotiations with the EU were overwhelmingly rejected by the Swiss people, with 76.8% voting against, in a referendum held on March 4.<ref name="CH&EU"/><ref>[http://news.bbc.co.uk/2/hi/europe/1201133.stm Swiss say 'no' to EU]. ''BBC News''. March 4, 2001. Retrieved August 16, 2016.</ref> Despite these victories for EU-sceptics, Swiss voters approved other referendums advocating for increased integration with the EU, including accepting several bilateral agreements and joining the Schengen Area, which removed all border controls, and Swiss voters also rejected several referendums advocating for reversing integration.<ref name="CH&EU"/> Despite this, on February 9, 2014, Swiss voters narrowly approved a referendum proposed by the right-wing and anti-EU [[Swiss People's Party]] that intends to limit immigration through quotas (which violates the EU principle of the free movement of people), requires businesses to give Swiss citizens priority when hiring, and restricts immigrants accessibility to benefits.<ref>Dacey, Jessica & Geiser, Urs (February 9, 2014). [http://www.swissinfo.ch/eng/quotas-and-questions_swiss-agree-to-curb-immigration-and-rethink-eu-deal/37877780 Swiss agree to curb immigration and rethink EU deal]. ''Swissinfo''. Retrieved August 16, 2016.</ref> Additionally, in 2016, Switzerland withdrew its frozen application for EU membership, which had been dormant since 1992, accepting a motion introduced by SVP parliamentarian Lukas Reimann.<ref>Goulard, Hortense (June 15, 2016). [http://www.politico.eu/article/switzerland-withdraws-application-to-join-the-eu/ Switzerland withdraws application to join the EU]. ''POLITICO''. Retrieved August 16, 2016.</ref><ref>[http://www.swissinfo.ch/eng/european-policy_swiss-to-withdraw-dormant-eu-bid/42229112 Swiss to withdraw dormant EU bid]. ''Swissinfo''. June 15, 2016. Retrieved August 16, 2016.</ref><ref>[http://www.dailymail.co.uk/news/article-3644697/Switzerland-WITHDRAWS-application-European-Union-member-state-one-week-Brexit-vote.html 'Only a few lunatics want to join the EU now': Switzerland WITHDRAWS application to become a European Union member state one week before the Brexit vote]. ''The Daily Mail''. June 16, 2016. Retrieved August 16, 2016.</ref>

==Foreign Relations==
Traditionally, Switzerland has avoided [[alliance]]s that might entail military, political, or direct economic action. Since its forces suffered a major military defeat in the [[Battle of Marignano]] in 1515, it has stayed strictly [[Political neutrality|neutral]]. Switzerland maintains diplomatic relations with almost all countries and has no major dispute in its bilateral relations. Historically, it has served as a neutral intermediary between hostile powers and host to major international treaty conferences. After [[World War I]], it hosted the [[League of Nations]] headquarters; during [[World War II]] it represented German interests in America and American and British interests in Germany. Since 1980, Switzerland has represented American interests in [[Iran]]. It also played a key role in brokering a truce agreement between the Sudanese Government and Sudan's Peoples Liberation Army (SPLA) for the Nuba Mountain region, signed after a week's negotiations taking place near [[Lucerne]] in January 2002.

The Swiss Constitution declares the preservation of Switzerland's independence and welfare as the supreme objective of Swiss [[foreign policy]]. Below this overarching goal, the Constitution sets five specific foreign policy objectives: to further the peaceful coexistence of nations; promote respect for [[human rights]], [[democracy]], and the [[rule of law]]; promote Swiss economic interests abroad, alleviate need and poverty in the world; and preserve natural resources.

The Swiss feel a moral obligation to undertake social, economic, and humanitarian activities that contribute to world peace and prosperity. This is manifested by Swiss bilateral and multilateral diplomatic activity, assistance to developing countries, and support for the extension of international law, particularly humanitarian law. Switzerland (mainly Geneva) is home to many international governmental and nongovernmental organizations, including the [[International Committee of the Red Cross]] (whose flag is essentially the Swiss flag with colors reversed—the Red Cross historically being a Swiss organization). One of the first international organizations, the [[Universal Postal Union]], is located in Bern.

===International Organizations===
In recent years, the Swiss have broadened the scope of activities in which they feel able to participate without compromising their neutrality. Swiss voters first rejected [[United Nations]] membership by a 3-to-1 margin in 1986 but in March 2002 adopted it, albeit in a very close election, making Switzerland the first country to join the UN based on a popular referendum decision. In similar fashion, the electorate rejected a government proposition to deploy Swiss troops as UN peacekeepers (Blue Helmets) in 1994, but Switzerland joined NATO's Partnership for Peace and the Euro-Atlantic Partnership Council in 1996 and 1997, respectively, and deployed Yellow Berets to support the OSCE in Bosnia. In June 2001, Swiss voters approved new legislation providing for the deployment of armed Swiss troops for international peacekeeping missions under UN or OSCE auspices as well as closer international cooperation in military training.

On September 10, 2002, Switzerland became a full member of the United Nations. Switzerland had previously been involved as party to the Statute of the International Court of Justice and member of most UN specialized agencies, as well as the International Atomic Energy Agency. Switzerland has long participated in many UN activities, including the Economic Commission for Europe, UN Environment Program, the UN High Commissioner for Refugees, UN Educational, Scientific and Cultural Organization, UN Conference for Trade and Development, UN Industrial Development Organization, and the Universal Postal Union (UPU). Prior to its formal accession, Switzerland had maintained a permanent observer mission at UN Headquarters since 1948.

Switzerland also is a member of the following international organizations: World Trade Organization, Organization for Economic Cooperation and Development, European Free Trade Association, Bank for International Settlements, Council of Europe, and Organization for Security and Cooperation in Europe (OSCE). In 1992, Swiss voters approved membership in the Bretton Woods organizations but later that year rejected the European Economic Area agreement, which the government viewed as a first step toward EU membership.

Switzerland has furnished military observers and medical teams to several UN operations. Switzerland is an active participant in the OSCE, its foreign minister serving as Chairman-in-Office for 1996. Switzerland also is an active participant in the major nonproliferation and export control regimes.

===[[War on Terror]]===
The Swiss Government on June 25, 2003, eased most of the sanctions against the Republic of [[Iraq]] in accord with UN Security Council Resolution (UNSCR) 1483. The government lifted the trade embargo, flight restrictions, and financial sanctions in place since August 1990. The weapons embargo and the asset freeze, the scope of which was extended, remain in force, and restrictions on the trade in Iraqi cultural goods were newly imposed. Though not a member at the time, Switzerland had joined UN sanctions against Iraq after the invasion of Kuwait. Switzerland in recent years joined UN and EU economic sanctions imposed on Sierra Leone, UNITA (Angola), Liberia, Serbia and Montenegro, Burma, Zimbabwe, Sudan, Democratic Republic of the Congo, and Côte d'Ivoire. On October 15, 2003, the Federal Council ended the import restrictions on raw diamonds from Sierra Leone and lifted sanctions against Libya.

Switzerland in October 2000 implemented an ordinance to enforce UN sanctions against the Taliban (UNSCR 1267), which it subsequently amended in April 2001 in accord with tighter UN regulations (UNSCR 1333). On May 2, 2002, the Swiss Government eased the sanctions regime in accord with UNSCR 1388 and 1390, lifting the ban on the sale of acetic acid (used in drug production), Afghani Airlines, and Afghani diplomatic representations. The weapons embargo, travel restrictions, and financial sanctions remain in force. The Swiss Government in November 2001 issued an ordinance declaring illegal the terrorist organization [[al Qaeda]] as well as possible successor or supporting organizations. More than 200 individuals or companies linked to international terrorism have been blacklisted to have their assets frozen. Thus far, Swiss authorities have blocked about 72 accounts totaling 34 million francs.

==Defense==
[[File:Swiss Army. Leopard 2-2A4 tank-Steel Parade 2006.jpg|thumb|200px|left|A Swiss Leopard 2-2A4 tank in a 2006 parade in the city of Thun.]]
On May 18, 2003, Swiss voters approved the military reform project "Army XXI" that will drastically reduce the size of the Swiss Army. In January 2004, the 524,000-strong militia started paring down to 220,000 conscripts, including 80,000 reservists. The defense budget of currently SF 4.3 billion ($3.1 billion) will be trimmed by SF 300 million, and some 2,000 jobs are expected to be shed between 2004 and 2011. The mandatory time of service will be curtailed from 300 to 260 days. All able-bodied Swiss males aged 20 to 30 must serve. Thereafter, most personnel are assigned to civil protection duties until the age of 37. Each Swiss militaman is required to keep his Sig 550 service rifle at home, properly maintained and in working order. Up until 2007, soldiers also received a sealed box of 50 bullets: they were meant to be used in the journey from home to the reporting station in case of invasion. This requirement has since been abolished and ammunition returned.

[[File:Switzerland - Air Force McDonnell Douglas FA-18C Hornet - cropped.jpg|thumb|200px|A Swiss McDonnell Douglas FA-18C Hornet in 2011.]]
A new category of soldiers called "single-term conscripts" will discharge the total time of service of about 300 days of active duty in one go. Recruiting is on a voluntary basis and should not exceed 20% of a year's draft. The armed forces have a small nucleus of about 3,600 professional staff, half of whom are either instructors or staff officers, with the remainder mostly being fortification guards. The army has virtually no full-time active combat units but is capable of full mobilization within 72 hours. Women may volunteer to serve in the armed forces and may now join all units, including combat troops. About 2,000 women already serve in the army but, so far, have not been allowed to use weapons for purposes other than self-defense.
The armed forces are organized in four army corps and an air force and are equipped with modern, sophisticated, and well-maintained gear. In 1993, the Swiss Government procured 34 [[F/A-18 Hornet|F/A-18 fighters]] from the United States.

Switzerland has a rich history of providing mercenaries to the battlefield of Europe, ever since the Middle Ages up until the Napoleonic period. Nowadays Swiss citizens are forbidden to join foreign armies, with the notable exception of the Pontifcial Swiss Guard (''Guardia Svizzera Pontificia'') which constitutes the tiny armed forces of [[Vatican City|the State of the Vatican City]]. In order to join, Swiss male citizens must have a proven Catholic faith and a certificate of good conduct from the Army, besides meeting physical criteria.

During the [[Cold War]], Switzerland had plans to build [[Nuclear weapon|nuclear weapons]]. Detailed plans were produced, and Switzerland had a storage of [[uranium]] and unsuccessfully tried to purchase [[plutonium]]. However, the [[Treaty on the Non-Proliferation of Nuclear Weapons]], signed in 1969 and ratified in 1977, seemed to be a better alternative, and the program wound down until it was dissolved in 1988.<ref>Edwards, Rob (May 25, 1996). [https://www.newscientist.com/article/mg15020310-500-swiss-planned-a-nuclear-bomb/ Swiss planned a nuclear bomb]. ''New Scientist''. Retrieved September 9, 2016.</ref><ref>[http://nuclearweaponarchive.org/Nwfaq/Nfaq7-4.html 7.4 States Formerly Possessing or Pursuing Nuclear Weapons]. ''nuclearweaponarchive.org''. Retrieved September 9, 2016.</ref><ref>[http://nuclearweaponarchive.org/Library/Swissdoc.html Swiss Nuclear Program]. ''nuclearweaponarchive.org''. Retrieved September 9, 2016.</ref>

==Economy==
Despite a dearth of [[natural resources]], the Swiss economy is among the world's most advanced and prosperous. Per capita income is virtually the highest in the world, as are wages. Trade has been the key to prosperity in Switzerland. The country is dependent upon [[export]] markets to generate income while dependent upon imports for raw materials and to expand the range of goods and services available in the country. Switzerland has liberal investment and trade policies, notwithstanding agriculture, and a conservative fiscal policy. The Swiss legal system is highly developed, commercial law is well defined, and solid laws and policies protect investments. The Swiss franc is one of the world's soundest currencies, and the country is known for its high standard of banking and financial services. Switzerland is a member of a number of international economic organizations, including the [[World Trade Organization]] (WTO), the [[International Monetary Fund]], the [[World Bank]], and the [[Organization for Economic Cooperation and Development]] (OECD).
[[File:Cathedral Lausanne Bessieres.JPG|thumb|left|300px|Lausanne, Cathedral, Bessieres Bridge and St-Martin Bridge.]]
Switzerland's machinery, metals, electronics, and chemicals sectors are world-renowned for precision and quality. Together they account for well over half of Swiss export revenues. In agriculture, Switzerland is about 60% self-sufficient. Only 7.5% of the remaining imports originated from the U.S. Swiss farmers are one of the most highly protected and subsidized producer group in the world. OECD estimates show that Switzerland is subsidizing more than 70% of its agriculture, compared to 35% in the EU. According to the newly adopted "2008-2011 Agricultural Program", Switzerland intends to reduce its subsidies from SF 14.1 billion (U.S. $11.6 billion) to SF 13.6 billion (U.S. $10.5 billion) over the next four years. In March 2007, the parliament increased the initial government bill by SF 150 million (U.S. $123 million) on the grounds that Swiss farm reforms were going too fast. The parliament also accepted international parallel imports for fertilizers and tractors. Swiss farmers will be allowed to import tractors produced in China or India and sold in the EU, and save up to $41 million (SF 50 million) annual in expenses. German [[fertilizer]] could save another $20 million (SF 25 million). A more general bill on parallel imports will be presented by the Justice Ministry to parliament by the end of 2007.

[[Tourism]], [[banking]], [[engineering]], and [[insurance]] are significant sectors of the economy and heavily influence the country's economic policies. Swiss trading companies have unique marketing expertise in many parts of the world, including Eastern Europe, the Far East, Africa, and the Middle East. Not only does Switzerland have a highly developed [[tourism]] infrastructure (making it a good market for tourism-related equipment and services), the Swiss also are intrepid travelers. Per capita, more Swiss visit the United States every year than from any other country. Tourism is the most important U.S. export to Switzerland (earning almost $1.5 billion). In 2004, more than 285,000 Swiss came to the United States as tourists.

In 2005, the dollar/Swiss franc exchange rate continued to be shaped by geopolitical tensions. The dollar depreciated further against the Swiss franc from SF 1.49 in October 2002 to SF 1.31 in 2003, to 1.28 in 2005 to 1.23 in July 2006, and 1.22 in January 2007. The strengthening of the Euro, however, helped Switzerland to minimize the pressure from a weakening dollar. The Swiss National Bank raised interest rates on June 15, 2006 to 1.5%, the third increase since January 2006. The Swiss National Bank also said it expected economic growth to be a robust 2.5% in 2006 and 2007.

While the number of bankruptcies in Switzerland had been on the rise for four years, reaching alarming levels in 2005 (10,800), the rate dropped by 4.7% in 2006. Compared to other European countries, Switzerland's bankruptcy rates ranks fourth (1.35%) among the hardest hit countries, after Luxemburg (2.39%), Austria (1.9%) and France (1.49%).

The Swiss economy expanded by 2.7% in 2006, the fastest rate in six years, thus confirming sustained growth over the last four years. GDP growth was primarily due to the positive evolution of private consumption and expansion of investment in fixed assets and software. For once, all export industries benefited from increased demand from foreign markets. With a surplus of $9.6 billion (SF 11.7 billion), the Swiss trade balance reached unprecedented levels. On the inflation side, import prices increased more rapidly than exports.

Switzerland was ranked as the most competitive economy in the World Economic Forum’s 2006 Global Competitiveness Report for the first time, reflecting the country’s sound institutional environment, excellent infrastructure, efficient markets, competent macroeconomic management, world-class educational attainment, and high levels of technological innovation, which boost Switzerland's competitiveness in the global economy. The country has a well-developed infrastructure for scientific research, companies spend generously on research and development, and intellectual property protection is strong. Business activity benefits from a well-developed institutional framework, characterized by the rule of law, an efficient judicial system, and high levels of transparency and accountability within public institutions. Higher education and training are rapidly growing in importance as engines of productivity growth.

===Global Economic Crisis===
[[File:Aerial view of Zurich.JPG|thumb|200px|A view of Zürich from the air.]]
Being a nation that depends upon exports for economic growth, and due to the fact that it is so closely linked to the economies of Western Europe and the United States, Switzerland was not able to escape recent slowdowns experienced in these countries. During most of the 1990s, the Swiss economy was Western Europe's weakest, with annual GDP growth averaging 0% between 1991 and 1997. Beginning in late 1997, the economy steadily gained momentum until peaking in 2000 with 3% growth in real terms. The economy returned to lackluster growth during 2001-2003, but has been growing at or above potential since 2004–2.5% per annum. The Swiss Economic Ministry reports that strong global demand, particularly in the U.S. and Asia, and better Euro zone growth has helped Switzerland’s economic recovery. Long-run economic growth, however, is predicated on structural reforms. In order to maximize its economic potential, Switzerland will need to push through difficult agrarian and competition policy reforms. These are essential if the government is to reduce its budget deficits and meet its 3% growth target.

The recent economic upswing had some positive impact on the labor market. Unemployment decreased from 4.1% in December 2003 to 3.1% in March 2007. Swiss in the 15-25 age bracket continue to fight unemployment numbers with a rate of 5.4%, and hotel and restaurant industry workers with 10.4%. One-fourth of the country's full-time workers are unionized. In general, labor/management relations are good, mostly characterized by a willingness on both sides to settle disputes by negotiations rather than by labor action. About 600 collective bargaining agreements exist today in Switzerland and are regularly renewed without major problems. However, the mood is changing. The massive layoffs that resulted from both the global economic slowdown and major management scandals have strained the traditional Swiss "labor peace." Swiss trade unions encouraged strikes against several companies, including the national airline SWISS, Coca-Cola, and Orange (the French telecom operator), but total days lost to strikes remain among the lowest in the OECD. Uncertainties concerning the proper management of pension funds, and the prospect of a potential hike in the retirement age from 65 to 67 have stirred heated political debate.

===Trade with the EU===
[[File:Gotthard-basistunnel02-hannes-ortlieb.jpg|thumb|left|A view inside the [[Gotthard Base Tunnel]], which opened in 2016 and is the longest tunnel in the world.]]
The Swiss economy earns roughly half of its corporate earnings from the export industry, and 62% of Swiss exports are destined for the [[EU]] market. The EU is Switzerland's largest trading partner, and economic and trade barriers between them are minimal. In the wake of the Swiss voters' rejection of the European Economic Area Agreement in 1992, the Swiss Government set its sights on negotiating bilateral sectoral agreements with the EU. After more than 4 years of negotiations, an agreement covering seven sectors (research, public procurement, technical barriers to trade, agriculture, civil aviation, land transport, and the free movement of persons) was achieved at the end of 1998. Parliament officially endorsed the so-called "Bilaterals I" in 1999, and the Swiss people approved them in a referendum in May 2000. The agreements, which had to be ratified by the European Parliament as well as legislatures in all 15 EU member states, entered into force on June 1, 2002. Switzerland has so far attempted to mitigate possible adverse effects of non-membership by conforming many of its regulations, standards, and practices to EU directives and norms. Full access to the Swiss market for the original 15 EU member states entered into force in June 2004, ending as a result the “national preference”. The Swiss agreed to extend these preferences to the 10 new EU members on September 25, 2005.

The Swiss Government embarked in July 2001 on a second round of bilateral negotiations with the EU known as “Bilaterals II”. Talks focused on customs fraud, environment, statistics, trade in processed agricultural goods, media, the taxation of savings, and police/judicial cooperation (dubbed the Schengen-Dublin accords). Amid a fierce political debate over the essence of Swiss-EU relations and populist warnings against EU workers and criminals entering Switzerland, the Schengen-Dublin package was approved on June 5, 2005 by a referendum of 54.6%. Fears of cheap labor coming from new EU member states have prompted the government to provide for tripartite surveillance committees to ensure that decent wages are enforced. The EU has still to ratify the extension of Schengen to Switzerland, and implement the bilateral agreements on research and development and media cooperation.

As part of the bilateral agreement on the taxation of savings signed in June 2003, Swiss banks will levy a withholding tax on EU citizens' savings income. The tax, which started on July 1, 2005, will increase gradually to 35% by 2011, with 75% of the funds being transferred to the EU.

On November 26, 2006, the Swiss electorate approved a government bill to contribute 1 billion Swiss francs (about $800 million) to the 10 new EU member states. In a nationwide referendum, 53.4% of voters accepted the “Eastern Europe Cooperation Act,” which entitles the government to spend 1 billion Swiss francs on projects in primarily [[Central Europe]]an states over the next 10 years. Switzerland had pledged this contribution to share the burden of the EU’s eastern expansion in order to facilitate the conclusion of the second set of bilateral negotiations with the EU. The right-populist Swiss People’s Party (SVP), which prompted the referendum, was disappointed, but pleased that it mobilized a 47% opposition. The Eastern Europe Cooperation Act gives a new legal basis for Swiss aid to countries in Eastern Europe. The act has a 10-year term and replaces the former federal Law on Aid to Eastern Europe, which came into force in 1995. Since the fall of the Berlin Wall, Switzerland has spent SF 3.5 billion on about 1,000 aid projects in East-[[Central Europe]] to help countries in the region transform into market economies. Sixty percent of the SF 1 billion is to come from the budget of the departments of foreign and economic affairs, mainly from cuts in aid programs to other parts of the world. The remaining 40% will be taken from the regular budget of the federal administration. The funds are to be used on projects chosen by Switzerland and focused on education, trade promotion, environment, and internal security. The money is paid directly to the projects and does not go the EU cohesion fund in Brussels. Switzerland has no formal agreement with the European Union concerning these contributions. Instead, there is a Memorandum of Understanding (MOU) that sets out the general conditions of the Swiss commitment to the ten new EU member states. Under the MOU, almost half of the funding will go to Poland. Hungary's benefit will be SF 131 million, while the Czech Republic will receive SF 110 million.

The Swiss federal government remains deeply divided over whether to eventually join the EU, and in a March 2001 referendum more than 70% of Swiss voters rejected rapid steps toward EU membership. The issue of EU membership is likely to be shelved for several years, if not a decade. In May 2005, the government said it could sign a framework agreement with the European Union, as an alternative to joining the organization, to encourage dialogue and create a platform for closer cooperation.

Switzerland nevertheless expressed interest in reaching a third layer of bilateral agreements that would involve energy, the Galileo satellite navigation system, health, and agriculture. But recent harsh criticism by the European Commission against preferential cantonal tax treatment for foreign holdings cooled the political climate surrounding the EU. Unilateral trade retaliation—as threatened by the EU if the Swiss cantons do not change their cantonal tax regimes—has not occurred, but the political damage is done, including greater anti-EU feelings among the population. The pressure to negotiate with the EU could turn sour as the EU has already asked Switzerland to pay another SF 300-350 million ($240–280 million, on top of the SF 1 billion cohesion fund) to provide further financial aid to Romania and Bulgaria, which joined the EU on January 1, 2007. Unlike the November 2006 referendum, the newly enacted Eastern Europe Cooperation Act does not provide for an automatic referendum on further payments. The parliament will decide on the additional aid request.

The government also decided in November 2006 to once more consider adoption of the EU “Cassis-de-Dijon” principle for trade after a first setback in 2004. If adopted, EU products could be imported in Switzerland without having to go through the burdensome Swiss certification and Swiss language requirement process. Currently, Swiss retail prices are on average 20-40% higher than in the EU. If parallel imports are allowed under adoption of the Cassis-de-Dijion principle, prices could drop by 10%. Possible exceptions have been reduced from 129 products to 40, but hurdles remain on the labeling of alcohol contained in Alcopops, the Swiss ban of phosphates in washing machine powders, the real origin of “EU meat”, and on the stringent Swiss generic food production requirements. The “Cassis de Dijon principle” will not apply to the many farming and industrial products already covered by mutual recognition agreements (MRAs) under the EU-Swiss Bilaterals I and II; nor will it apply to other products such as pesticides, motor engines, and weapons that require an authorization. The impact, as a result, may not be as large as expected. Another issue is that Swiss and EU MRAs concluded with third countries may also benefit from adoption of the Cassis-de-Dijon principle (these goods would also have to receive WTO most favored nation status).

The government has reaffirmed its wish to strengthen ties with other non-EU trading partners in Asia and America. Exploratory talks on a Free Trade Agreement between the U.S. and Switzerland failed to result in negotiations, due to Swiss problems with free trade in agriculture, but the two sides did agree to a new framework for economic, trade, and investment discussions. This new agreement is the Swiss-U.S. Trade and Investment Cooperation Forum (the “Forum”) and is currently assessing areas where the two governments could facilitate greater trade and investment flows.

Switzerland ranks 17th among the main trading partners of the U.S. worldwide. The United States is the second-largest importer (11.5%) of Swiss goods after Germany (20%). The U.S. exports more to Switzerland each year than to all the countries of the former Soviet Union and Eastern Europe combined, and Switzerland imports more U.S. products and services than does Spain. In addition, the United States is the largest foreign investor in Switzerland, and conversely, the primary destination of Swiss foreign investment. It is estimated that 200,000 American jobs depend on Swiss foreign investments. Total U.S.-Swiss bilateral trade increased from $15.33 billion during 2003 to $16 billion in 2004.

In 2016, the [[Gotthard Base Tunnel]], the longest tunnel in the world at 35 miles (57 km) was opened.<ref>[http://www.bbc.com/news/world-europe-36423250 Gotthard tunnel: World's longest and deepest rail tunnel opens in Switzerland]. ''BBC''. June 1, 2016. Retrieved September 9, 2016.</ref> The Gotthard Base Tunnel was a part of the [[AlpTransit]] program, which sought to improve rail travel speeds from the north to south and advance European integration.<ref>[https://www.alptransit-portal.ch/en/overview/ AlpTransit: Overview]. ''alptransit-portal.ch''. Retrieved September 9, 2016.</ref><ref>Barrow, Keith (June 15, 2016). [http://www.railjournal.com/index.php/europe/gotthard-base-tunnel-the-final-straight.html Gotthard Base Tunnel: the final straight]. ''railjournal.com''. Retrieved September 9, 2016.</ref>

==History==
[[File:Roman column - Nyon, Vaud, Switzerland.jpg|thumb|left|200px|Roman ruins in Nyon, Switzerland, along the shores of Lake Geneva.]]
Originally inhabited by the Helvetians, or Helvetic [[Celt|Celts]], the territory comprising modern Switzerland came under Roman rule during the Gallic wars in the 1st century BC and remained a Roman province until the 4th century AD. Under Roman influence, the population reached a high level of civilization and enjoyed a flourishing commerce. Important cities, such as [[Geneva]], [[Basel]], and [[Zurich]], were linked by military roads that also served as trade arteries between Rome and the northern tribes.

After the decline of the [[Roman Empire]], Switzerland was invaded by [[Germanic tribe|Germanic tribes]] from the north and west. Some tribes, such as the Alemanni in central and northeastern Switzerland, and the [[Burgundian|Burgundians]], who ruled western Switzerland, settled there. In 800, the country became part of [[Charlemagne]]'s empire. It later passed under the dominion of the [[Holy Roman Emperor|Holy Roman emperors]] in the form of small ecclesiastic and temporal holdings subject to imperial sovereignty.

With the opening of a new important north-south trade route across the [[Alps]] in the early 13th century, the Empire's rulers began to attach more importance to the remote Swiss mountain valleys, which were granted some degree of autonomy under direct imperial rule. Fearful of the popular disturbances flaring up following the death of the Holy Roman Emperor in 1291, the ruling families from Uri, Schwyz, and Unterwalden signed a charter to keep public peace and pledging mutual support in upholding autonomous administrative and judicial rule. The anniversary of the charter's signature (August 1, 1291) today is celebrated as Switzerland's National Day.

[[File:D aigle Castle Switzerland.jpg|thumb|300px|D'aigle Castle.]]
Between 1315 and 1388 the Swiss Confederates inflicted three crushing defeats on the [[Habsburgs]], whose aspiration to regional dominion clashed with Swiss self-determination. During that period, five other localities (cantons in modern-day parlance) joined the original three in the Swiss Confederation. Buoyed by their feats, the Swiss Confederates continuously expanded their borders by military means and gained formal independence from the [[Holy Roman Empire]] in 1499. Routed by the [[France|French]] and [[Venice|Venetians]] near [[Milan]] in 1515, they renounced expansionist policies. By then the Swiss Confederation had become a union of 13 localities with a regularly convening diet administering the subject territories. Swiss mercenaries continued for centuries to serve in other armies; the Swiss Guard of the Pope is a vestige of this tradition.

The [[Protestant Reformation|Reformation]] led to a division between the [[Protestant]] followers of [[Ulrich Zwingli|Zwingli]] and [[John Calvin|Calvin]] in the German and French parts of the country respectively, and the [[Roman Catholic Church|Catholics]]. Despite two centuries of civil strife, the common interest in the joint subject territories kept the Swiss Confederation from falling apart. The traffic in mercenaries as well as the alienation between the predominantly Protestant Swiss and their Catholic neighbors kept the Swiss Confederation out of the wars of the European powers, which formally recognized Swiss neutrality in the [[Treaty of Westphalia]] in 1648. The Swiss remained neutral during the War of the First Coalition against revolutionary France, but [[Napoleon Bonaparte|Napoleon]], nonetheless, invaded and took control of the country in 1797-98, replacing the loose confederation with a centrally governed unitary [[Satellite nation|satellite state]] under French influence. The Swiss people highly disliked the massive changes that were occurring under Napoleon, and there were at least four coups d'état that occurred between 1800 and 1802.<ref name="Geschichte">[http://history-switzerland.geschichte-schweiz.ch/swiss-revolution-helvetic-republic-1798.html Swiss Revolution and the Helvetic Republic (1798)]. ''geschichte-schweiz.ch''. 2004. Retrieved September 9, 2016.</ref> Napoleon was forced to withdraw his troops in 1802, and after a civil war broke out, the Act of Mediation was signed on February 18, 1803, which restored much of the independence and autonomy of the Swiss Cantons.<ref name="Geschichte"/><ref>[http://www.swissinfo.ch/eng/swiss-celebrate-napoleon-s-historic-act/3174096 Swiss celebrate Napoleon's historic act]. ''Swissinfo''. February 20, 2003. Retrieved September 9, 2016.</ref>

The [[Congress of Vienna]] in 1815 removed all remaining French control and re-established the old confederation of sovereign states and enshrined Switzerland's status of permanent armed neutrality in international law. In 1848, after a brief civil war between Protestant liberals seeking a centralized national state and Catholic conservatives clinging on to the old order, the majority of Swiss Cantons opted for a Federal State, modeled in part on the [[U.S. Constitution]]. The Swiss Constitution established a range of civic liberties and made far-reaching provisions to maintain cantonal autonomy to placate the vanquished Catholic minority. The Swiss amended their Constitution extensively in 1874, establishing federal responsibility for defense, trade, and legal matters, as well as introducing direct democracy by popular referendum. To this day, cantonal autonomy and referendum democracy remain trademarks of the Swiss polity.

Switzerland [[Industrial revolution|industrialized]] rapidly during the 19th century and by 1850 had become the second most industrialized country in Europe after [[Great Britain]]. During [[World War I]] serious tension developed between the German, French, and Italian-speaking parts of the country, and Switzerland came close to violating its neutrality but managed to stay out of hostilities. Labor unrest culminating in a general strike in 1918 marked the interwar period, but in 1937 employers and the largest trade union concluded a formal agreement to settle disputes peacefully, which governs workplace relations to the present day. During [[World War II]], Switzerland came under heavy pressure from the [[Fascism|fascist]] powers, which after the fall of France in 1940 completely surrounded the country. Some political and economic leaders displayed a mood of appeasement, but a combination of tactical accommodation and demonstrative readiness to defend the country helped Switzerland survive unscathed.

The [[Cold War]] enhanced the role of neutral Switzerland and offered the country a way out of its diplomatic isolation after World War II. Economically, Switzerland integrated itself into the [[United States|American]]-led Western postwar order, but it remained reluctant to enter supranational bodies. Switzerland did not join the [[United Nations]], even though [[Geneva]] became host to the UN's European headquarters, and the country played an active role in many of the UN's specialized agencies. Switzerland also remained aloof in the face of European integration efforts, waiting until 1963 to join the [[Council of Europe]]. It still remains outside the [[European Union]]. Instead, Switzerland in 1960 helped form the European Free Trade Area, which did not strive for political union. Following the Cold War, Switzerland joined the Bretton Woods institutions in 1992 and became a member of the United Nations in 2002.

{{Copyright Details (US Government)}}

Source = [http://www.state.gov/r/pa/ei/bgn/3431.htm]

==See also==

*[[Aar]] (river)
*[[Campaign for an Independent and Neutral Switzerland]]

==References==
<References/>

[[Category:European Countries]]
[[Category:Landlocked Countries]]
[[Category:Christian-Majority Countries]]
[[Category:Switzerland]]

Deoxyribonucleic acid

2016-10-18T19:24:13Z

H22: Extended

[[Image:799.gif|right|thumb|300px]]
'''Deoxyribonucleic acid''' (DNA) is a chemical inside [[cell]]s which carries the hereditary information. It is a molecular [[polymer]] formed of [[nucleotide|deoxyribonucleotides]]. Most organisms use DNA as their hereditary material. [[Offspring]] of [[Human reproduction|sexual reproduction]] [[Organism|organisms]] contain DNA from both parents.

==Structure==

Most commonly as a double-stranded [[helix]] comprising two complimentary molecules held together by hydrogen bonds, this is commonly called "dsDNA" (double-stranded DNA).<ref>Single-stranded DNAs (ssDNA) do exist in certain [[bacteriophage]]s, however they cannot be replicated without first creating the complimentary strand to use as a template.</ref> The [[nucleotide]]s which are the "building blocks" of DNA have three main parts: A nitrogenous base (the "letters" in the sequence), a [[sugar]], and a [[phosphate]] group. When nucleotides are joined into DNA strands, they form a chain with the phosphate group of one nucleotide binding to the ribose of the next.

DNA strands "compliment" each other by having compatible sequences, allowing the bases on one strand to form bonds with the bases on the other strand. There are four nitrogenous bases, Adenonine (A), Cytosine (C), Guanine (G), and Thymine (T). Under the base pairing rules, A pairs with T and G pairs with C. This allow cell to repair the DNA correctly if only one strand is damaged.

DNA contains [[gene]]s that encode for [[protein]]s. These are produced by the DNA first being turned into m[[RNA]] and then into polypeptides (this process is called the [[Central dogma of molecular biology|central dogma]] of molecular biology). All organisms use DNA as their hereditary material.

==Organisation==
Most of the cells in multi-cellular organisms (human including) retain a complete copy of all DNA of the first cell from which the organism started to grow. It is often possible to clone the organism, or part of it, from a single cell, while doing so with a human cell has severe ethical implications.

All DNA required for a cell to grow into organism is called genome. A cell containing only one genome is called a haploid cell. Humans are diploid (one genome from each parent). Other organisms may have cells with more genomes, for instance, a cell of bread [[wheat]] contains six (hexaploid).

==History==
In the late 19th century [[Friedrich Miescher]], a Swiss [[biochemist]], discovered an unusual [[acid]] in the [[nuclei]] of cells. The acid was named deoxyribonucleic acid, or DNA. In 1944 the American [[biologist]]s, [[Alfred Hershey]], [[Thomas Gilmore]] and [[Martha Chase]] used experiments with [[bacteria]] and [[bacteriophage]]s to show that DNA passed [[gene]]s from one generation to the next.

At that time, it was unclear how this simple molecule could hold all the complex information controlling the development of humans, animals and plants. Scientists knew it was made of four chemical bases called [[adenine]] (A), [[thymine]] (T), [[guanine]] (G) and [[cytosine]] (C), plus [[phosphoric acid]] and a [[sugar]]. They also knew that the ratios of A and T as well as G and C were always the same, but they did not know the rules that controlled the arrangement.

British scientists [[Rosalind Franklin]] and [[Maurice Wilkins]] passed [[X-ray]]s through DNA to study the patterns made when the crystals diffracted them. From studying photographs of patterns, Rosalind Franklin concluded that DNA must be a [[helix]]. [[James Watson]] and [[Francis Crick]], working in [[Cambridge]], used this information to help them solve the puzzle of DNA structure. They built a model showing that if A always paired with T and G paired with C, DNA must be like a ladder made of two strands twisted together in a double helix. The sugar and phosphoric acid were the sides of the ladder, and the rungs were the paired bases that were held together through hydrogen bonding.

Watson and Crick suggested that DNA could unzip itself into two separate strands, and each strand could act as a pattern to grow a new strand. Crick showed later that areas of the DNA known as genes worked in groups of three to code for amino acids, the building blocks of proteins. These groups are called [[codon]]s. They make about fifty thousand different types of [[protein]], which make all the different types of cell in the body. Indian biochemist [[Har Gobind Khorana]] made all the possible codons and worked out which codons controlled which [[amino acid]]. Most codons are redundant and code for the same amino acids, these mostly are different in only the third base pair. This means that differences in genotype can build up in the third position (thereby changing the genotype) without changing the protein (keeps the same phenotype).

If the DNA in one cell was stretched out, it would be about three feet long. Although DNA has a very simple structure, it can carry an enormous amount of [[information]]. Scientists do not yet understand the function of all DNA, but in 1991 a project called the [[Human Genome Project]] began to use computers to map the three billion base pairs which make up the 46 human [[chromosome]]s.

==Modern understanding==
[[Image:818.gif|right|thumb|Structure of DNA.]]
Small lengths of DNA called [[gene]]s serve as the instructions for the body to carry out its functions and give rise to the physical traits of the organism.<ref>"Eye-color genes, through the proteins they encode, direct the amount and placement of melanin in the iris." [http://www.hhmi.org/cgi-bin/askascientist/highlight.pl?kw=&file=answers%2Fgenetics%2Fans_044.html Ask A Scientist - Genes and eye color]</ref> DNA is packaged into [[chromosomes]]. Each individual human being has 23 pairs of [[chromosome]]s, where one set is inherited from his/her mother and the other set is inherited from his/her father. 22 of these chromosomes are referred to as [[autosome]]s, while the remaining chromosomes are the sex chromosomes. Males possess a single X chromosome and a single Y chromosome; whereas females possess a pair of X chromosomes. In total, it is estimated that there are roughly 20300 protein-coding genes in the human genome; however, due to mRNA splicing, it is estimated that these genes encode for over 1 million different protein products.

The "language" in that protein structure is described in DNA is called the [[genetic code]]. Genetic code is the same for all organisms, from human to plants and yeasts (few known exceptions are rare and just tiny deviations). The universality of the genetic code is difficult to explain from the evolutionary point of view. This universality makes possible to move the genes from one organism into another, where they sometimes still work. For instance, human insulin is currently produced by modified yeasts or bacteria. Wider usage of the genetically modified organisms brings the known risks and ethical problems.

[[Prokaryotic DNA]] is circular (a closed loop). Whereas, [[eukaryotic DNA|eukaryotic chromosomes]] are linear (with ends), with the notable exception of [[Mitochondrial DNA]] and plastid (chloroplast) DNA, which is separate from the DNA in the nucleus.<ref>Mitochondria and chloroplasts are thought to have originated as prokaryotic cells living symbiotically inside of primitive eukaryotic cells, this is called the [[endosymbiotic hypothesis]]</ref> The ends of eukaryotic chromosomes are protected by [[telomere]]s, which are always tightly condensed except during S phase of [[mitosis]].<ref>Campbell, Neil A, et. al. ''Biology''. 6th ed. San Francisco: Benjamin Cummings, 2002. 299, 530-31.</ref> Telomeres are partially lost during cell division, and must be regrown later. Most of the cells in animal body are not capable of restoring they telomeres so can divide only limited number of times (Hayflick limit <ref>{{cite journal |author=Watson JD |title=Origin of concatemeric T7 DNA |journal=Nature New Biol. |volume=239 |pages=197–201 |year=1972 |pmid=4507727 |issue=94 |doi=10.1038/newbio239197a0}}</ref>).

== Mutations ==
[[Mutation]]s are simply variations in DNA sequence between individuals. The vast majority of spontaneous mutations in DNA are called "neutral" because they do not affect the [[phenotype|observable traits]] of the individual organism. Others can have beneficial effects and some can disrupt important functions Differential distribution of various types of neutral mutations within the population is the basis for modern [[DNA fingerprinting]]. It is mutations in DNA, giving rise to novel alleles ("versions" of a gene), which cause phenotypic variations between individuals of a particular species. For instance, in humans, single-gene mutations are responsible for differences in [[ABO blood type]], eye color, hair color, and even the ability to taste certain molecules. Sadly, there are also thousands of mutations known to cause human disease; notably sickle-cell anemia, a few rare forms of autism, and (when the mutations spontaneously occur in a somatic cell) various types of cancer. That said, it is important to note that most phenotypic traits (e.g. height) and hereditary diseases arise as the net effect of several different genetic variations.

Usually a mutation is harmless if present in only one of the two or more genomes in same cell (it is said most of mutations are recessive), or even may be beneficial. Offspring of the parents who are already genetically related often inherits the same mutation in both genomes, so diseases are more frequent. If the mutation is diagnosed early in the life, diet and other similar measures may be applied, resulting a normal life later.<ref name=Al2015>{{cite journal|last1=Al Hafid|first1=N|last2=Christodoulou|first2=J|title=Phenylketonuria: a review of current and future treatments.|journal=Translational pediatrics|date=October 2015|volume=4|issue=4|pages=304–17|pmid=26835392}}</ref>

[http://www.ncbi.nlm.nih.gov/omim OMIM] (Online Mendelian Inheritance in Man), is an online database of genes known to be mutated in disease states. [[Mendelian inheritance]] refers to the inheritance pattern observed in traits that are determined by a single gene. This pattern was first discovered by [[Gregor Mendel]], an Austrian monk, during his work with pea plants from 1856-1863. Although Mendel published his work in 1866, it's significance was largely ignored until it was rediscovered in the early 20th century; more than two decades after his death.

==See also==
*[[DNA library]]
*[[Transcription]]

==External links==
*[http://www.learner.org/interactives/dna/index.html Interactive DNA] Learn about genetics, genetic engineering, the Human Genome Project and the ethical implications of these new technologies.
*[http://www.blackwellpublishing.com/trun/artwork/Animations/cloningexp/cloningexp.html Animated guide to DNA cloning]

== References ==
<references/>

[[Category:Genetics]]
[[Category:Police State]]

Deoxyribonucleic acid

2016-10-17T05:35:17Z

H22:

[[Image:799.gif|right|thumb|300px]]
'''Deoxyribonucleic acid''' (DNA) is a chemical inside [[cell]]s which carries the hereditary information. It is a molecular [[polymer]] formed of [[nucleotide|deoxyribonucleotides]]. Most organisms use DNA as their hereditary material. [[Offspring]] of [[Human reproduction|sexual reproduction]] [[Organism|organisms]] contain DNA from both parents.

==Structure==

Most commonly as a double-stranded [[helix]] comprising two complimentary molecules held together by hydrogen bonds, this is commonly called "dsDNA" (double-stranded DNA).<ref>Single-stranded DNAs (ssDNA) do exist in certain [[bacteriophage]]s, however they cannot be replicated without first creating the complimentary strand to use as a template.</ref> The [[nucleotide]]s which are the "building blocks" of DNA have three main parts: A nitrogenous base (the "letters" in the sequence), a [[sugar]], and a [[phosphate]] group. When nucleotides are joined into DNA strands, they form a chain with the phosphate group of one nucleotide binding to the ribose of the next.

DNA strands "compliment" each other by having compatible sequences, allowing the bases on one strand to form bonds with the bases on the other strand. There are four nitrogenous bases, Adenonine (A), Cytosine (C), Guanine (G), and Thymine (T). Under the base pairing rules, A pairs with T and G pairs with C. This allow cell to repair the DNA correctly if only one strand is damaged.

DNA contains [[gene]]s that encode for [[protein]]s. These are produced by the DNA first being turned into m[[RNA]] and then into polypeptides (this process is called the [[Central dogma of molecular biology|central dogma]] of molecular biology). All organisms use DNA as their hereditary material.

==Organisation==
Most of the cells in multi-cellular organisms (human including) retain a complete copy of all DNA of the first cell from which the organism started to grow. It is often possible to clone the organism, or part of it, from a single cell, while doing so with a human cell has severe ethical implications.

All DNA required for a cell to grow into organism is called genome. A cell containing only one genome is called a haploid cell. Humans are diploid (one genome from each parent). Other organisms may have cells with more genomes, for instance, a cell of bread [[wheat]] contains six (hexaploid).

==History==
In the late 19th century [[Friedrich Miescher]], a Swiss [[biochemist]], discovered an unusual [[acid]] in the [[nuclei]] of cells. The acid was named deoxyribonucleic acid, or DNA. In 1944 the American [[biologist]]s, [[Alfred Hershey]], [[Thomas Gilmore]] and [[Martha Chase]] used experiments with [[bacteria]] and [[bacteriophage]]s to show that DNA passed [[gene]]s from one generation to the next.

At that time, it was unclear how this simple molecule could hold all the complex information controlling the development of humans, animals and plants. Scientists knew it was made of four chemical bases called [[adenine]] (A), [[thymine]] (T), [[guanine]] (G) and [[cytosine]] (C), plus [[phosphoric acid]] and a [[sugar]]. They also knew that the ratios of A and T as well as G and C were always the same, but they did not know the rules that controlled the arrangement.

British scientists [[Rosalind Franklin]] and [[Maurice Wilkins]] passed [[X-ray]]s through DNA to study the patterns made when the crystals diffracted them. From studying photographs of patterns, Rosalind Franklin concluded that DNA must be a [[helix]]. [[James Watson]] and [[Francis Crick]], working in [[Cambridge]], used this information to help them solve the puzzle of DNA structure. They built a model showing that if A always paired with T and G paired with C, DNA must be like a ladder made of two strands twisted together in a double helix. The sugar and phosphoric acid were the sides of the ladder, and the rungs were the paired bases that were held together through hydrogen bonding.

Watson and Crick suggested that DNA could unzip itself into two separate strands, and each strand could act as a pattern to grow a new strand. Crick showed later that areas of the DNA known as genes worked in groups of three to code for amino acids, the building blocks of proteins. These groups are called [[codon]]s. They make about fifty thousand different types of [[protein]], which make all the different types of cell in the body. Indian biochemist [[Har Gobind Khorana]] made all the possible codons and worked out which codons controlled which [[amino acid]]. Most codons are redundant and code for the same amino acids, these mostly are different in only the third base pair. This means that differences in genotype can build up in the third position (thereby changing the genotype) without changing the protein (keeps the same phenotype).

If the DNA in one cell was stretched out, it would be about three feet long. Although DNA has a very simple structure, it can carry an enormous amount of [[information]]. Scientists do not yet understand the function of all DNA, but in 1991 a project called the [[Human Genome Project]] began to use computers to map the three billion base pairs which make up the 46 human [[chromosome]]s.

==Modern understanding==
[[Image:818.gif|right|thumb|Structure of DNA.]]
Small lengths of DNA called [[gene]]s serve as the instructions for the body to carry out its functions and give rise to the physical traits of the organism.<ref>"Eye-color genes, through the proteins they encode, direct the amount and placement of melanin in the iris." [http://www.hhmi.org/cgi-bin/askascientist/highlight.pl?kw=&file=answers%2Fgenetics%2Fans_044.html Ask A Scientist - Genes and eye color]</ref> DNA is packaged into [[chromosomes]]. Each individual human being has 23 pairs of [[chromosome]]s, where one set is inherited from his/her mother and the other set is inherited from his/her father. 22 of these chromosomes are referred to as [[autosome]]s, while the remaining chromosomes are the sex chromosomes. Males possess a single X chromosome and a single Y chromosome; whereas females possess a pair of X chromosomes. In total, it is estimated that there are roughly 20300 protein-coding genes in the human genome; however, due to mRNA splicing, it is estimated that these genes encode for over 1 million different protein products.

[[Prokaryotic DNA]] is circular (a closed loop). Whereas, [[eukaryotic DNA|eukaryotic chromosomes]] are linear (with ends), with the notable exception of [[Mitochondrial DNA]] and plastid (chloroplast) DNA, which is separate from the DNA in the nucleus.<ref>Mitochondria and chloroplasts are thought to have originated as prokaryotic cells living symbiotically inside of primitive eukaryotic cells, this is called the [[endosymbiotic hypothesis]]</ref> The ends of eukaryotic chromosomes are protected by [[telomere]]s, which are always tightly condensed except during S phase of [[mitosis]].<ref>Campbell, Neil A, et. al. ''Biology''. 6th ed. San Francisco: Benjamin Cummings, 2002. 299, 530-31.</ref> Telomeres are partially lost during cell division, and must be regrown later. Most of the cells in animal body are not capable of restoring they telomeres so can divide only limited number of times (Hayflick limit <ref>{{cite journal |author=Watson JD |title=Origin of concatemeric T7 DNA |journal=Nature New Biol. |volume=239 |pages=197–201 |year=1972 |pmid=4507727 |issue=94 |doi=10.1038/newbio239197a0}}</ref>).

== Mutations ==
[[Mutation]]s are simply variations in DNA sequence between individuals. The vast majority of spontaneous mutations in DNA are called "neutral" because they do not affect the [[phenotype|observable traits]] of the individual organism. Others can have beneficial effects and some can disrupt important functions Differential distribution of various types of neutral mutations within the population is the basis for modern [[DNA fingerprinting]]. It is mutations in DNA, giving rise to novel alleles ("versions" of a gene), which cause phenotypic variations between individuals of a particular species. For instance, in humans, single-gene mutations are responsible for differences in [[ABO blood type]], eye color, hair color, and even the ability to taste certain molecules. Sadly, there are also thousands of mutations known to cause human disease; notably sickle-cell anemia, a few rare forms of autism, and (when the mutations spontaneously occur in a somatic cell) various types of cancer. That said, it is important to note that most phenotypic traits (e.g. height) and hereditary diseases arise as the net effect of several different genetic variations.

Usually a mutation is harmless if present in only one of the two or more genomes in same cell (it is said most of mutations are recessive), or even may be beneficial. Offspring of the parents who are already genetically related often inherits the same mutation in both genomes, so diseases are more frequent. If the mutation is diagnosed early in the life, diet and other similar measures may be applied, resulting a normal life later.<ref name=Al2015>{{cite journal|last1=Al Hafid|first1=N|last2=Christodoulou|first2=J|title=Phenylketonuria: a review of current and future treatments.|journal=Translational pediatrics|date=October 2015|volume=4|issue=4|pages=304–17|pmid=26835392}}</ref>

[http://www.ncbi.nlm.nih.gov/omim OMIM] (Online Mendelian Inheritance in Man), is an online database of genes known to be mutated in disease states. [[Mendelian inheritance]] refers to the inheritance pattern observed in traits that are determined by a single gene. This pattern was first discovered by [[Gregor Mendel]], an Austrian monk, during his work with pea plants from 1856-1863. Although Mendel published his work in 1866, it's significance was largely ignored until it was rediscovered in the early 20th century; more than two decades after his death.

==See also==
*[[DNA library]]
*[[Transcription]]

==External links==
*[http://www.learner.org/interactives/dna/index.html Interactive DNA] Learn about genetics, genetic engineering, the Human Genome Project and the ethical implications of these new technologies.
*[http://www.blackwellpublishing.com/trun/artwork/Animations/cloningexp/cloningexp.html Animated guide to DNA cloning]

== References ==
<references/>

[[Category:Genetics]]
[[Category:Police State]]

Deoxyribonucleic acid

2016-10-17T05:28:49Z

H22:

[[Image:799.gif|right|thumb|300px]]
'''Deoxyribonucleic acid''' (DNA) is a chemical inside [[cell]]s which carries the hereditary information. It is a molecular [[polymer]] formed of [[nucleotide|deoxyribonucleotides]]. Most organisms use DNA as their hereditary material. [[Offspring]] of [[Human reproduction|sexual reproduction]] [[Organism|organisms]] contain DNA from both parents.

==Structure==

Most commonly as a double-stranded [[helix]] comprising two complimentary molecules held together by hydrogen bonds, this is commonly called "dsDNA" (double-stranded DNA).<ref>Single-stranded DNAs (ssDNA) do exist in certain [[bacteriophage]]s, however they cannot be replicated without first creating the complimentary strand to use as a template.</ref> The [[nucleotide]]s which are the "building blocks" of DNA have three main parts: A nitrogenous base (the "letters" in the sequence), a [[sugar]], and a [[phosphate]] group. When nucleotides are joined into DNA strands, they form a chain with the phosphate group of one nucleotide binding to the ribose of the next.

DNA strands "compliment" each other by having compatible sequences, allowing the bases on one strand to form bonds with the bases on the other strand. There are four nitrogenous bases, Adenonine (A), Cytosine (C), Guanine (G), and Thymine (T). Under the base pairing rules, A pairs with T and G pairs with C. This allow cell to repair the DNA correctly if only one strand is damaged.

DNA contains [[gene]]s that encode for [[protein]]s. These are produced by the DNA first being turned into m[[RNA]] and then into polypeptides (this process is called the [[Central dogma of molecular biology|central dogma]] of molecular biology). All organisms use DNA as their hereditary material.

==Organisation==
Most of the cells in multi-cellular organisms (human including) retain a complete copy of all DNA of the first cell from which the organism started to grow. It is often possible to clone the organism, or part of it, from a single cell, while doing so with a human cell has severe ethical implications.

All DNA required for a cell to grow into organism is called genome. A cell containing only one genome is called a haploid cell. Humans are diploid (one genome from each parent). Other organisms may have cells with more genomes, for instance, a cell of bread [[wheat]] contains six (hexaploid).

==History==
In the late 19th century [[Friedrich Miescher]], a Swiss [[biochemist]], discovered an unusual [[acid]] in the [[nuclei]] of cells. The acid was named deoxyribonucleic acid, or DNA. In 1944 the American [[biologist]]s, [[Alfred Hershey]], [[Thomas Gilmore]] and [[Martha Chase]] used experiments with [[bacteria]] and [[bacteriophage]]s to show that DNA passed [[gene]]s from one generation to the next.

At that time, it was unclear how this simple molecule could hold all the complex information controlling the development of humans, animals and plants. Scientists knew it was made of four chemical bases called [[adenine]] (A), [[thymine]] (T), [[guanine]] (G) and [[cytosine]] (C), plus [[phosphoric acid]] and a [[sugar]]. They also knew that the ratios of A and T as well as G and C were always the same, but they did not know the rules that controlled the arrangement.

British scientists [[Rosalind Franklin]] and [[Maurice Wilkins]] passed [[X-ray]]s through DNA to study the patterns made when the crystals diffracted them. From studying photographs of patterns, Rosalind Franklin concluded that DNA must be a [[helix]]. [[James Watson]] and [[Francis Crick]], working in [[Cambridge]], used this information to help them solve the puzzle of DNA structure. They built a model showing that if A always paired with T and G paired with C, DNA must be like a ladder made of two strands twisted together in a double helix. The sugar and phosphoric acid were the sides of the ladder, and the rungs were the paired bases that were held together through hydrogen bonding.

Watson and Crick suggested that DNA could unzip itself into two separate strands, and each strand could act as a pattern to grow a new strand. Crick showed later that areas of the DNA known as genes worked in groups of three to code for amino acids, the building blocks of proteins. These groups are called [[codon]]s. They make about fifty thousand different types of [[protein]], which make all the different types of cell in the body. Indian biochemist [[Har Gobind Khorana]] made all the possible codons and worked out which codons controlled which [[amino acid]]. Most codons are redundant and code for the same amino acids, these mostly are different in only the third base pair. This means that differences in genotype can build up in the third position (thereby changing the genotype) without changing the protein (keeps the same phenotype).

If the DNA in one cell was stretched out, it would be about three feet long. Although DNA has a very simple structure, it can carry an enormous amount of [[information]]. Scientists do not yet understand the function of all DNA, but in 1991 a project called the [[Human Genome Project]] began to use computers to map the three billion base pairs which make up the 46 human [[chromosome]]s.

==Modern understanding==
[[Image:818.gif|right|thumb|Structure of DNA.]]
Small lengths of DNA called [[gene]]s serve as the instructions for the body to carry out its functions and give rise to the physical traits of the organism.<ref>"Eye-color genes, through the proteins they encode, direct the amount and placement of melanin in the iris." [http://www.hhmi.org/cgi-bin/askascientist/highlight.pl?kw=&file=answers%2Fgenetics%2Fans_044.html Ask A Scientist - Genes and eye color]</ref> DNA is packaged into [[chromosomes]]. Each individual human being has 23 pairs of [[chromosome]]s, where one set is inherited from his/her mother and the other set is inherited from his/her father. 22 of these chromosomes are referred to as [[autosome]]s, while the remaining chromosomes are the sex chromosomes. Males possess a single X chromosome and a single Y chromosome; whereas females possess a pair of X chromosomes. In total, it is estimated that there are roughly 20300 protein-coding genes in the human genome; however, due to mRNA splicing, it is estimated that these genes encode for over 1 million different protein products.

[[Prokaryotic DNA]] is circular (a closed loop). Whereas, [[eukaryotic DNA|eukaryotic chromosomes]] are linear (with ends), with the notable exception of [[Mitochondrial DNA]] and plastid (chloroplast) DNA, which is separate from the DNA in the nucleus.<ref>Mitochondria and chloroplasts are thought to have originated as prokaryotic cells living symbiotically inside of primitive eukaryotic cells, this is called the [[endosymbiotic hypothesis]]</ref> The ends of eukaryotic chromosomes are protected by [[telomere]]s, which are always tightly condensed except during S phase of [[mitosis]].<ref>Campbell, Neil A, et. al. ''Biology''. 6th ed. San Francisco: Benjamin Cummings, 2002. 299, 530-31.</ref>

== Mutations ==
[[Mutation]]s are simply variations in DNA sequence between individuals. The vast majority of spontaneous mutations in DNA are called "neutral" because they do not affect the [[phenotype|observable traits]] of the individual organism. Others can have beneficial effects and some can disrupt important functions Differential distribution of various types of neutral mutations within the population is the basis for modern [[DNA fingerprinting]]. It is mutations in DNA, giving rise to novel alleles ("versions" of a gene), which cause phenotypic variations between individuals of a particular species. For instance, in humans, single-gene mutations are responsible for differences in [[ABO blood type]], eye color, hair color, and even the ability to taste certain molecules. Sadly, there are also thousands of mutations known to cause human disease; notably sickle-cell anemia, a few rare forms of autism, and (when the mutations spontaneously occur in a somatic cell) various types of cancer. That said, it is important to note that most phenotypic traits (e.g. height) and hereditary diseases arise as the net effect of several different genetic variations.

Usually a mutation is harmless if present in only one of the two or more genomes in same cell (it is said most of mutations are recessive), or even may be beneficial. Offspring of the parents who are already genetically related often inherits the same mutation in both genomes, so diseases are more frequent. If the mutation is diagnosed early in the life, diet and other similar measures may be applied, resulting an normal life.<ref name=Al2015>{{cite journal|last1=Al Hafid|first1=N|last2=Christodoulou|first2=J|title=Phenylketonuria: a review of current and future treatments.|journal=Translational pediatrics|date=October 2015|volume=4|issue=4|pages=304–17|pmid=26835392}}</ref>

[http://www.ncbi.nlm.nih.gov/omim OMIM] (Online Mendelian Inheritance in Man), is an online database of genes known to be mutated in disease states. [[Mendelian inheritance]] refers to the inheritance pattern observed in traits that are determined by a single gene. This pattern was first discovered by [[Gregor Mendel]], an Austrian monk, during his work with pea plants from 1856-1863. Although Mendel published his work in 1866, it's significance was largely ignored until it was rediscovered in the early 20th century; more than two decades after his death.

==See also==
*[[DNA library]]
*[[Transcription]]

==External links==
*[http://www.learner.org/interactives/dna/index.html Interactive DNA] Learn about genetics, genetic engineering, the Human Genome Project and the ethical implications of these new technologies.
*[http://www.blackwellpublishing.com/trun/artwork/Animations/cloningexp/cloningexp.html Animated guide to DNA cloning]

== References ==
<references/>

[[Category:Genetics]]
[[Category:Police State]]

Intelligence testing

2016-10-16T22:07:52Z

H22:

'''Intelligence testing''' began in an organized way in the early 20th Century with the [[Stanford-Binet]] test. The purpose was to form an estimate of a person's aptitude before investing time and money in their education, in the belief that aptitude or intelligence was a fixed quantity.

At the time these tests were developed, medical science and psychology were
in their infancy. Ideas such as [[eugenics]] still had currency, and intelligence tests were used to weed out so-called "defectives".

Testers classified people as idiots, imbeciles, morons, normal, above average, and geniuses on a numerical scale based on [[mental age]]. For children, dividing the mental age by chronological age produces the [[intelligence quotient]] (IQ) used for placement in slow or rapid classes.

The study based on survey data from 702 Nordic research works concludes that a typical neuropsychologist used 9 tests in a standard assessment, and 25 tests overall in their practice. The selection of tests to use has been influenced by nationality, competence level, practice profile, and by attitude toward test selection. Testing patients with psychiatric disorders was associated with more tests.<ref>Egeland J, Løvstad M, Norup A, Nybo T, Persson BA6, Rivera DF, Schanke AK, Sigurdardottir S, Arango-Lasprilla J. (2016). Following international trends while subject to past traditions: neuropsychological test use in the Nordic countries. Clin Neuropsychol. Sep 27:1-22. [https://www.ncbi.nlm.nih.gov/pubmed/27670676]</ref>

In the United States, intelligence tests were to classify recruits and draftees for service in World War II. The more technical jobs were assigned to men with higher scores. Sociologists also noted racial differences in IQ scores, and some supposed that these differences were inherent. A controversy over this matter has raged ever since.

Open questions for psychologists and sociologists focus on what produces differences in [[intelligence]], whether intelligence can be developed or stunted by upbringing and education, and why different [[race]]s or cultural groups have significantly different scores.

The two main reasons given are:
#that there may be inherent differences between the races
#that upbringing, education and social factors can skew the results

== Influention of environment ==
After nearly a century of IQ testing and [[educational reform]]s, some researchers have begun to assert that IQ can be influenced by the child's environment by as much as 30 points.<ref>3 weeks of intensive play of WFF 'N PROOF: The Game of Modern Logic increased average IQ scores by more than 20 points. [http://wffnproof.com/]</ref> See [[Educational games]].

A 1976 year study that covered 258 children (IQ between 80 and 119) finally concluded that the major correlating factor is "a favorable parental social and educational background" <ref>Fisch RO, Bilek MK, Horrobin JM, Chang PN (1976) Children with superior intelligence at 7 years of age: a prospective study of the influence of perinatal, medical, and socioeconomic factors. Am J Dis Child. 1976 May;130(5):481-7. Abstract available at
https://www.ncbi.nlm.nih.gov/pubmed/1274898</ref>. The more recent 2016 year study also showed that the measured IQ potential is significantly lower in developing countries. <ref name='kodila'>Kodila-Tedika O1, Asongu SA2, Azia-Dimbu F3. (2016) J Biosoc Sci. 2016 May 26:1-13, available at [https://papers.ssrn.com/sol3/papers.cfm?abstract_id=2661437]
Statistics and intelligence in developing countries</ref> and increases after the national statistics improves (<ref name='kodila'/> references [[Nigeria]] and [[Kenya]]).

Test results can also be influenced by other factors:
*Steele and Joshua Aronson found that when they gave a group of Stanford undergraduates a standardized test and told them that it was a measure of their intellectual ability, the white students did much better than their black counterparts. But when the same test was presented simply as an abstract laboratory tool, with no relevance to ability, the scores of blacks and whites were virtually identical.<ref>[http://www.gladwell.com/2000/2000_08_21_a_choking.htm]</ref> See [[Pressure and failure]].

==Liberal bias==

The field of intelligence testing has been acrimonious and contentious. Researchers such as [[Arthur Jensen]] and [[Charles Murray]] have been pilloried in the mass media, accused of maintaining views which different or even opposite of their actual views.<ref>Evolution advocate Gould portrays Murray as saying intelligence can be measured with a single number; Murray, of course, makes it clear in his book (as well as in a follow-up retort to Gould) that intelligence is too complex to be measured with a single number.</ref>

One professor had to come to Jensen's defense, after [[Stephen Jay Gould]] attacked him in print:

:I object to Gould's tendency to visit the alleged sins of early investigators on present day investigators. If Goddard, Brigham, and others once tended to view various human races as relatively superior or inferior in intelligence and therefore relatively worthy or unworthy, this does not mean that present-day investigators, like Jensen (1980) or Rushton (1995), are necessarily guilty of such views. In fact, from my personal acquaintance with Jensen and his publications, I can attest that he does not view the African race (if one accepts that it is a race) as in any way less worthy than other so-called races. [http://www.psych.utoronto.ca/~reingold/courses/intelligence/cache/carroll-gould.html]

[[Charles Murray]] said:

*As soon as anyone argues that racial differences in intelligence are authentic, not an artifact of biased tests, everyone decodes that as saying the differences are grounded in genes. It is a non-sequitur, but an invariable one in my experience. America's intellectual elites are hysterical about the possibility of black - white genetic differences in IQ.
*As you know, The Bell Curve actually took a mild, agnostic stand on the subject. Dick Herrnstein and I said that nobody yet knows what the mix between environmental and genetic causes might be, and it makes no practical difference anyway. The only policy implication of the black - white difference, whatever its sources, is that the U.S. should return forthwith to its old ideal of treating people as individuals.
*But how many people know this? No one who hasn't read the book. Everyone went nuts about genes, so much so that most people now believe that race and genes is the main topic of our book. [http://www.eugenics.net/papers/mssel.html]

The Bell Curve book is not the only controversial study on IQ among different races or groups of people. Danish professor [[Helmuth Nyborg]] has conducted studies of IQ which indicate [[Politically correct language|politically incorrect]] results such as: on average, white people have higher IQs than black people, and men have higher IQs than women. His latest research finds that on average, [[atheists]] have IQs about 5.8 points higher than people of [[faith]], prompting similar outrage among his critics, who claim that such results might be due to cultural biases.[http://danish.newsvine.com/_news/2007/02/05/554043-professor-atheists-are-more-intelligent-than-believers]

== See also ==

*[[Theory of multiple intelligences]]
*[[Moral intelligence]]
*[[Bodily-kinesthetic intelligence]]
*[[Emotional intelligence]]
*[[Atheism and intelligence]]

==External links==
*[http://www.eugenics.net/papers/mssel.html As the Bell Curves] - [[Charles Murray]] and [[Daniel Seligman]] - (Originally published in The National Review, December 8, 1997)

==Notes==
<references/>

[[Category:Psychology]]

Deoxyribonucleic acid

2016-10-16T22:03:24Z

H22: Extended

[[Image:799.gif|right|thumb|300px]]
'''Deoxyribonucleic acid''' (DNA) is a chemical inside [[cell]]s which carries the hereditary information. It is a molecular [[polymer]] formed of [[nucleotide|deoxyribonucleotides]]. Most organisms use DNA as their hereditary material. [[Offspring]] of [[Human reproduction|sexual reproduction]] [[Organism|organisms]] contain DNA from both parents.

==Structure==

Most commonly as a double-stranded [[helix]] comprising two complimentary molecules held together by hydrogen bonds, this is commonly called "dsDNA" (double-stranded DNA).<ref>Single-stranded DNAs (ssDNA) do exist in certain [[bacteriophage]]s, however they cannot be replicated without first creating the complimentary strand to use as a template.</ref> The [[nucleotide]]s which are the "building blocks" of DNA have three main parts: A nitrogenous base (the "letters" in the sequence), a [[sugar]], and a [[phosphate]] group. When nucleotides are joined into DNA strands, they form a chain with the phosphate group of one nucleotide binding to the ribose of the next.

DNA strands "compliment" each other by having compatible sequences, allowing the bases on one strand to form bonds with the bases on the other strand. There are four nitrogenous bases, Adenonine (A), Cytosine (C), Guanine (G), and Thymine (T). Under the base pairing rules, A pairs with T and G pairs with C. This allow cell to repair the DNA correctly if only one strand is damaged.

DNA contains [[gene]]s that encode for [[protein]]s. These are produced by the DNA first being turned into m[[RNA]] and then into polypeptides (this process is called the [[Central dogma of molecular biology|central dogma]] of molecular biology). All organisms use DNA as their hereditary material.

==Organisation==
Most of the cells in multi-cellular organisms (human including) retain a complete copy of all DNA of the first cell from which the organism started to grow. It is often possible to clone the organism, or part of it, from a single cell, while doing so with a human cell has severe ethical implications.

All DNA required for a cell to grow into organism is called genome. A cell containing only one genome is called a haploid cell. Humans are diploid (one genome from each parent). Other organisms may have cells with more genomes, for instance, a cell of bread [[wheat]] contains six (hexaploid).

==History==
In the late 19th century [[Friedrich Miescher]], a Swiss [[biochemist]], discovered an unusual [[acid]] in the [[nuclei]] of cells. The acid was named deoxyribonucleic acid, or DNA. In 1944 the American [[biologist]]s, [[Alfred Hershey]], [[Thomas Gilmore]] and [[Martha Chase]] used experiments with [[bacteria]] and [[bacteriophage]]s to show that DNA passed [[gene]]s from one generation to the next.

At that time, it was unclear how this simple molecule could hold all the complex information controlling the development of humans, animals and plants. Scientists knew it was made of four chemical bases called [[adenine]] (A), [[thymine]] (T), [[guanine]] (G) and [[cytosine]] (C), plus [[phosphoric acid]] and a [[sugar]]. They also knew that the ratios of A and T as well as G and C were always the same, but they did not know the rules that controlled the arrangement.

British scientists [[Rosalind Franklin]] and [[Maurice Wilkins]] passed [[X-ray]]s through DNA to study the patterns made when the crystals diffracted them. From studying photographs of patterns, Rosalind Franklin concluded that DNA must be a [[helix]]. [[James Watson]] and [[Francis Crick]], working in [[Cambridge]], used this information to help them solve the puzzle of DNA structure. They built a model showing that if A always paired with T and G paired with C, DNA must be like a ladder made of two strands twisted together in a double helix. The sugar and phosphoric acid were the sides of the ladder, and the rungs were the paired bases that were held together through hydrogen bonding.

Watson and Crick suggested that DNA could unzip itself into two separate strands, and each strand could act as a pattern to grow a new strand. Crick showed later that areas of the DNA known as genes worked in groups of three to code for amino acids, the building blocks of proteins. These groups are called [[codon]]s. They make about fifty thousand different types of [[protein]], which make all the different types of cell in the body. Indian biochemist [[Har Gobind Khorana]] made all the possible codons and worked out which codons controlled which [[amino acid]]. Most codons are redundant and code for the same amino acids, these mostly are different in only the third base pair. This means that differences in genotype can build up in the third position (thereby changing the genotype) without changing the protein (keeps the same phenotype).

If the DNA in one cell was stretched out, it would be about three feet long. Although DNA has a very simple structure, it can carry an enormous amount of [[information]]. Scientists do not yet understand the function of all DNA, but in 1991 a project called the [[Human Genome Project]] began to use computers to map the three billion base pairs which make up the 46 human [[chromosome]]s.

==Modern understanding==
[[Image:818.gif|right|thumb|Structure of DNA.]]
Small lengths of DNA called [[gene]]s serve as the instructions for the body to carry out its functions and give rise to the physical traits of the organism.<ref>"Eye-color genes, through the proteins they encode, direct the amount and placement of melanin in the iris." [http://www.hhmi.org/cgi-bin/askascientist/highlight.pl?kw=&file=answers%2Fgenetics%2Fans_044.html Ask A Scientist - Genes and eye color]</ref> DNA is packaged into [[chromosomes]]. Each individual human being has 23 pairs of [[chromosome]]s, where one set is inherited from his/her mother and the other set is inherited from his/her father. 22 of these chromosomes are referred to as [[autosome]]s, while the remaining chromosomes are the sex chromosomes. Males possess a single X chromosome and a single Y chromosome; whereas females possess a pair of X chromosomes. In total, it is estimated that there are roughly 20300 protein-coding genes in the human genome; however, due to mRNA splicing, it is estimated that these genes encode for over 1 million different protein products.

[[Prokaryotic DNA]] is circular (a closed loop). Whereas, [[eukaryotic DNA|eukaryotic chromosomes]] are linear (with ends), with the notable exception of [[Mitochondrial DNA]] and plastid (chloroplast) DNA, which is separate from the DNA in the nucleus.<ref>Mitochondria and chloroplasts are thought to have originated as prokaryotic cells living symbiotically inside of primitive eukaryotic cells, this is called the [[endosymbiotic hypothesis]]</ref> The ends of eukaryotic chromosomes are protected by [[telomere]]s, which are always tightly condensed except during S phase of [[mitosis]].<ref>Campbell, Neil A, et. al. ''Biology''. 6th ed. San Francisco: Benjamin Cummings, 2002. 299, 530-31.</ref>

[[Mutation]]s are simply variations in DNA sequence between individuals. The vast majority of spontaneous mutations in DNA are called "neutral" because they do not affect the [[phenotype|observable traits]] of the individual organism. Others can have beneficial effects and some can disrupt important functions Differential distribution of various types of neutral mutations within the population is the basis for modern [[DNA fingerprinting]]. It is mutations in DNA, giving rise to novel alleles ("versions" of a gene), which cause phenotypic variations between individuals of a particular species. For instance, in humans, single-gene mutations are responsible for differences in [[ABO blood type]], eye color, hair color, and even the ability to taste certain molecules. Sadly, there are also thousands of mutations known to cause human disease; notably sickle-cell anemia, a few rare forms of autism, and (when the mutations spontaneously occur in a somatic cell) various types of cancer. That said, it is important to note that most phenotypic traits (e.g. height) and hereditary diseases arise as the net effect of several different genetic variations.

[http://www.ncbi.nlm.nih.gov/omim OMIM] (Online Mendelian Inheritance in Man), is an online database of genes known to be mutated in disease states. [[Mendelian inheritance]] refers to the inheritance pattern observed in traits that are determined by a single gene. This pattern was first discovered by [[Gregor Mendel]], an Austrian monk, during his work with pea plants from 1856-1863. Although Mendel published his work in 1866, it's significance was largely ignored until it was rediscovered in the early 20th century; more than two decades after his death.

==See also==
*[[DNA library]]
*[[Transcription]]

==External links==
*[http://www.learner.org/interactives/dna/index.html Interactive DNA] Learn about genetics, genetic engineering, the Human Genome Project and the ethical implications of these new technologies.
*[http://www.blackwellpublishing.com/trun/artwork/Animations/cloningexp/cloningexp.html Animated guide to DNA cloning]

== References ==
<references/>

[[Category:Genetics]]
[[Category:Police State]]

Deoxyribonucleic acid

2016-10-16T21:16:06Z

H22: Here probably link and name are swapped.

[[Image:799.gif|right|thumb|300px]]
'''Deoxyribonucleic acid''' (DNA) is a chemical inside [[cell]]s which carries the hereditary information. It is a molecular [[polymer]] formed of [[nucleotide|deoxyribonucleotides]]. Most organisms use DNA as their hereditary material. [[Offspring]] of [[Human reproduction|sexual reproduction]] [[Organism|organisms]] contain DNA from both parents.

==Structure==

Most commonly as a double-stranded [[helix]] comprising two complimentary molecules held together by hydrogen bonds, this is commonly called "dsDNA" (double-stranded DNA).<ref>Single-stranded DNAs (ssDNA) do exist in certain [[bacteriophage]]s, however they cannot be replicated without first creating the complimentary strand to use as a template.</ref> The [[nucleotide]]s which are the "building blocks" of DNA have three main parts: A nitrogenous base (the "letters" in the sequence), a [[sugar]], and a [[phosphate]] group. When nucleotides are joined into DNA strands, they form a chain with the phosphate group of one nucleotide binding to the ribose of the next.

DNA strands "compliment" each other by having compatible sequences, allowing the bases on one strand to form bonds with the bases on the other strand. There are four nitrogenous bases, Adenonine (A), Cytosine (C), Guanine (G), and Thymine (T). Under the base pairing rules, A pairs with T and G pairs with C.

DNA contains [[gene]]s that encode for [[protein]]s. These are produced by the DNA first being turned into m[[RNA]] and then into polypeptides (this process is called the [[Central dogma of molecular biology|central dogma]] of molecular biology). All organisms use DNA as their hereditary material. Offspring of sexually reproducing organisms contain DNA from both parents.

==History==
In the late 19th century [[Friedrich Miescher]], a Swiss [[biochemist]], discovered an unusual [[acid]] in the [[nuclei]] of cells. The acid was named deoxyribonucleic acid, or DNA. In 1944 the American [[biologist]]s, [[Alfred Hershey]], [[Thomas Gilmore]] and [[Martha Chase]] used experiments with [[bacteria]] and [[bacteriophage]]s to show that DNA passed [[gene]]s from one generation to the next.

At that time, it was unclear how this simple molecule could hold all the complex information controlling the development of humans, animals and plants. Scientists knew it was made of four chemical bases called [[adenine]] (A), [[thymine]] (T), [[guanine]] (G) and [[cytosine]] (C), plus [[phosphoric acid]] and a [[sugar]]. They also knew that the ratios of A and T as well as G and C were always the same, but they did not know the rules that controlled the arrangement.

British scientists [[Rosalind Franklin]] and [[Maurice Wilkins]] passed [[X-ray]]s through DNA to study the patterns made when the crystals diffracted them. From studying photographs of patterns, Rosalind Franklin concluded that DNA must be a [[helix]]. [[James Watson]] and [[Francis Crick]], working in [[Cambridge]], used this information to help them solve the puzzle of DNA structure. They built a model showing that if A always paired with T and G paired with C, DNA must be like a ladder made of two strands twisted together in a double helix. The sugar and phosphoric acid were the sides of the ladder, and the rungs were the paired bases that were held together through hydrogen bonding.

Watson and Crick suggested that DNA could unzip itself into two separate strands, and each strand could act as a pattern to grow a new strand. Crick showed later that areas of the DNA known as genes worked in groups of three to code for amino acids, the building blocks of proteins. These groups are called [[codon]]s. They make about fifty thousand different types of [[protein]], which make all the different types of cell in the body. Indian biochemist [[Har Gobind Khorana]] made all the possible codons and worked out which codons controlled which [[amino acid]]. Most codons are redundant and code for the same amino acids, these mostly are different in only the third base pair. This means that differences in genotype can build up in the third position (thereby changing the genotype) without changing the protein (keeps the same phenotype).

If the DNA in one cell was stretched out, it would be about three feet long. Although DNA has a very simple structure, it can carry an enormous amount of [[information]]. Scientists do not yet understand the function of all DNA, but in 1991 a project called the [[Human Genome Project]] began to use computers to map the three billion base pairs which make up the 46 human [[chromosome]]s.

==Modern understanding==
[[Image:818.gif|right|thumb|Structure of DNA.]]
Small lengths of DNA called [[gene]]s serve as the instructions for the body to carry out its functions and give rise to the physical traits of the organism.<ref>"Eye-color genes, through the proteins they encode, direct the amount and placement of melanin in the iris." [http://www.hhmi.org/cgi-bin/askascientist/highlight.pl?kw=&file=answers%2Fgenetics%2Fans_044.html Ask A Scientist - Genes and eye color]</ref> DNA is packaged into [[chromosomes]]. Each individual human being has 23 pairs of [[chromosome]]s, where one set is inherited from his/her mother and the other set is inherited from his/her father. 22 of these chromosomes are referred to as [[autosome]]s, while the remaining chromosomes are the sex chromosomes. Males possess a single X chromosome and a single Y chromosome; whereas females possess a pair of X chromosomes. In total, it is estimated that there are roughly 20300 protein-coding genes in the human genome; however, due to mRNA splicing, it is estimated that these genes encode for over 1 million different protein products.

[[Prokaryotic DNA]] is circular (a closed loop). Whereas, [[eukaryotic DNA|eukaryotic chromosomes]] are linear (with ends), with the notable exception of [[Mitochondrial DNA]] and plastid (chloroplast) DNA, which is separate from the DNA in the nucleus.<ref>Mitochondria and chloroplasts are thought to have originated as prokaryotic cells living symbiotically inside of primitive eukaryotic cells, this is called the [[endosymbiotic hypothesis]]</ref> The ends of eukaryotic chromosomes are protected by [[telomere]]s, which are always tightly condensed except during S phase of [[mitosis]].<ref>Campbell, Neil A, et. al. ''Biology''. 6th ed. San Francisco: Benjamin Cummings, 2002. 299, 530-31.</ref>

[[Mutation]]s are simply variations in DNA sequence between individuals. The vast majority of spontaneous mutations in DNA are called "neutral" because they do not affect the [[phenotype|observable traits]] of the individual organism. Others can have beneficial effects and some can disrupt important functions Differential distribution of various types of neutral mutations within the population is the basis for modern [[DNA fingerprinting]]. It is mutations in DNA, giving rise to novel alleles ("versions" of a gene), which cause phenotypic variations between individuals of a particular species. For instance, in humans, single-gene mutations are responsible for differences in [[ABO blood type]], eye color, hair color, and even the ability to taste certain molecules. Sadly, there are also thousands of mutations known to cause human disease; notably sickle-cell anemia, a few rare forms of autism, and (when the mutations spontaneously occur in a somatic cell) various types of cancer. That said, it is important to note that most phenotypic traits (e.g. height) and hereditary diseases arise as the net effect of several different genetic variations.

[http://www.ncbi.nlm.nih.gov/omim OMIM] (Online Mendelian Inheritance in Man), is an online database of genes known to be mutated in disease states. [[Mendelian inheritance]] refers to the inheritance pattern observed in traits that are determined by a single gene. This pattern was first discovered by [[Gregor Mendel]], an Austrian monk, during his work with pea plants from 1856-1863. Although Mendel published his work in 1866, it's significance was largely ignored until it was rediscovered in the early 20th century; more than two decades after his death.

==See also==
*[[DNA library]]
*[[Transcription]]

==External links==
*[http://www.learner.org/interactives/dna/index.html Interactive DNA] Learn about genetics, genetic engineering, the Human Genome Project and the ethical implications of these new technologies.
*[http://www.blackwellpublishing.com/trun/artwork/Animations/cloningexp/cloningexp.html Animated guide to DNA cloning]

== References ==
<references/>

[[Category:Genetics]]
[[Category:Police State]]

Talk:Atheistic science

2016-10-16T21:09:25Z

H22:

First, what are "non-materialistic phenomena"? Second, black holes most certainly exist. Cygnus X-1 and Sagittarius A* are examples. [[User:QuantumDude|QuantumDude]] ([[User talk:QuantumDude|talk]]) 00:16, 8 February 2016 (EST)

:Black holes are an implausible fiction of atheistic science. They help sell atheistic pseudo-scientific magazines to the public. They are contrary to [[quantum mechanics]] and are one of the [[Counterexamples to Relativity]].--[[User:Aschlafly|Andy Schlafly]] ([[User talk:Aschlafly|talk]]) 10:00, 8 February 2016 (EST)

::Black holes are demonstrated to exist though, Cygnus X-1 is a known black hole, along with many others, and relativity is known to be more accurate for celestial bodies than Newtonian physics. I don't understand where "atheism" comes into the picture for any of this? [[User:QuantumDude|QuantumDude]] ([[User talk:QuantumDude|talk]]) 10:06, 8 February 2016 (EST)
:::QuantumDude, "Last week, famed physicist Stephen Hawking made headlines with this bold statement: 'there are no black holes.'". - PBS, 2014[http://www.pbs.org/newshour/updates/hawking-meant-black-holes/]

:::Second, you wrote: "First, what are 'non-materialistic phenomena'?" I believe you know what was meant by this phrase and you are just being difficult.

:::Lastly, I am not going to comment on other matters related to this article or talk page and merely wanted to make these two points. [[User:Conservative|Conservative]] ([[User talk:Conservative|talk]]) 11:09, 8 February 2016 (EST)
:::::Saying that he is not going to say any more on a specific subject (or anything at all), and coming back very shortly thereafter, is something Cons does quite frequently. [[User:SamHB|SamHB]] ([[User talk:SamHB|talk]]) 12:42, 8 February 2016 (EST)

::::I genuinely do NOT know what "non-materialistic phenomena" are, as I've never actually heard the term before, jeez. [[User:QuantumDude|QuantumDude]] ([[User talk:QuantumDude|talk]]) 11:31, 8 February 2016 (EST)
::::Also, if you read the article which you just linked it specifically says black holes have been observed for decades and that Hawking is NOT saying black holes do not exist. [[User:QuantumDude|QuantumDude]] ([[User talk:QuantumDude|talk]]) 11:34, 8 February 2016 (EST)
QuantumDude, you continue to be purposefully difficult. Non-materialistic phenomena are phenomena which are not materialistic/natural. Not exactly rocket science. Are you going to tell me next that you never heard the words miracle/supernatural?
:::::Actually, it is quite possible, though unlikely, that QuantumDude really has never heard the words "miracle" or "supernatural". Very unlikely, since they are part of the English language in general. But one could conceivably discuss science without ever having heard those words. [[User:SamHB|SamHB]] ([[User talk:SamHB|talk]]) 12:42, 8 February 2016 (EST)

The point in citing the quote/article was to point out that how you define a black hole is an issue. [[User:Conservative|Conservative]] ([[User talk:Conservative|talk]]) 12:18, 8 February 2016 (EST)

See points 1 and 6 in [[Counterexamples to Relativity]]. Also, "non-materialistic phenomena" are the very real things that cannot be explained by material science, such as [[migration]].--[[User:Aschlafly|Andy Schlafly]] ([[User talk:Aschlafly|talk]]) 12:16, 8 February 2016 (EST)
::By the way, QunatumDude, if you are an atheist, I have a question for you: "Why don't you join a barter exchange and ask members of the barter exchange if they want to barter with you and you will give them "dark matter" in exchange for various goods/services. :) [[User:Conservative|Conservative]] ([[User talk:Conservative|talk]]) 12:25, 8 February 2016 (EST)
:::Challenging people on whether they are atheists is something that Cons does quite frequently. You can ignore him when discussing topics, such as science, that are not related to religion.
:::Also, saying that dark matter probably exists is not the same as saying that you have some available for sale or barter. Or are you saying that you have some red top quarks for sale? [[User:SamHB|SamHB]] ([[User talk:SamHB|talk]]) 12:42, 8 February 2016 (EST)

Well, QD, you've really stepped into a hornet's nest, haven't you? Congratulations. [[User:SamHB|SamHB]] ([[User talk:SamHB|talk]]) 12:42, 8 February 2016 (EST)

:Well I had hoped them to be SOMEWHAT reasonable :/ [[User:QuantumDude|QuantumDude]] ([[User talk:QuantumDude|talk]]) 12:45, 8 February 2016 (EST)
::"whole generations of cosmologists have invested such time, energy, and vast sums of money into identifying this elusive matter that dreams of its existence are likely to die hard." - ''New Doubt About Dark Matter'', Forbes 2014.

::Of course, young earth creation scientists didn't spend a dime on this foolish boondoggle. Young earth creationist scientists base their science on evidence/experiments and not desperate and foolhardy dreams. [[User:Conservative|Conservative]] ([[User talk:Conservative|talk]]) 13:22, 8 February 2016 (EST)

:::I didn't even mention dark matter lol. [[User:QuantumDude|QuantumDude]] ([[User talk:QuantumDude|talk]]) 13:27, 8 February 2016 (EST)
I don't blame you for not mentioning dark matter given the embarrassing state of affairs for atheists.

Millions of missing link fossils with round after round of handfuls of controversial "missing links" being debunked is another great embarrassment to atheists/evolutionists.[http://creation.com/that-quote-about-the-missing-transitional-fossils][http://creation.com/missing-links-parade]

Another favorite of mine is the supposed cow like creatures evolving into whales. How many cows or cow like creatures have you ever seen on the beach? :) [[User:Conservative|Conservative]] ([[User talk:Conservative|talk]]) 13:44, 8 February 2016 (EST)

:Conservative you are going off on a complete tangent totally unrelated to anything I was talking about. Can we stay on topic please? Or is thinking about that too hard for you? [[User:QuantumDude|QuantumDude]] ([[User talk:QuantumDude|talk]]) 14:02, 8 February 2016 (EST)

:The article would highly benefit from more citations, including the reference to the current official position of the Church. Some research works brought intermediate, still questionable conclusions with potentially so nasty social consequences, that asking to interpret with care may be reasonable. But this probably more applies to various forms of scientific racism, abortion and things the like. It is really an explanation required why black holes, wormholes, aliens, dark matter and magnetic butterflies are selected as examples instead or why and how do these theories promote atheism in any way. Most of them belong to pseudoscience; serious scientists do not accept them as proven because of the lack of experimental evidence. Hence while the article may address a real thing, it seems currently completely out of focus. [[User:H22|H22]] ([[User talk:H22|talk]]) 17:04, 16 October 2016 (EDT)

Talk:Atheistic science

2016-10-16T21:04:37Z

H22:

First, what are "non-materialistic phenomena"? Second, black holes most certainly exist. Cygnus X-1 and Sagittarius A* are examples. [[User:QuantumDude|QuantumDude]] ([[User talk:QuantumDude|talk]]) 00:16, 8 February 2016 (EST)

:Black holes are an implausible fiction of atheistic science. They help sell atheistic pseudo-scientific magazines to the public. They are contrary to [[quantum mechanics]] and are one of the [[Counterexamples to Relativity]].--[[User:Aschlafly|Andy Schlafly]] ([[User talk:Aschlafly|talk]]) 10:00, 8 February 2016 (EST)

::Black holes are demonstrated to exist though, Cygnus X-1 is a known black hole, along with many others, and relativity is known to be more accurate for celestial bodies than Newtonian physics. I don't understand where "atheism" comes into the picture for any of this? [[User:QuantumDude|QuantumDude]] ([[User talk:QuantumDude|talk]]) 10:06, 8 February 2016 (EST)
:::QuantumDude, "Last week, famed physicist Stephen Hawking made headlines with this bold statement: 'there are no black holes.'". - PBS, 2014[http://www.pbs.org/newshour/updates/hawking-meant-black-holes/]

:::Second, you wrote: "First, what are 'non-materialistic phenomena'?" I believe you know what was meant by this phrase and you are just being difficult.

:::Lastly, I am not going to comment on other matters related to this article or talk page and merely wanted to make these two points. [[User:Conservative|Conservative]] ([[User talk:Conservative|talk]]) 11:09, 8 February 2016 (EST)
:::::Saying that he is not going to say any more on a specific subject (or anything at all), and coming back very shortly thereafter, is something Cons does quite frequently. [[User:SamHB|SamHB]] ([[User talk:SamHB|talk]]) 12:42, 8 February 2016 (EST)

::::I genuinely do NOT know what "non-materialistic phenomena" are, as I've never actually heard the term before, jeez. [[User:QuantumDude|QuantumDude]] ([[User talk:QuantumDude|talk]]) 11:31, 8 February 2016 (EST)
::::Also, if you read the article which you just linked it specifically says black holes have been observed for decades and that Hawking is NOT saying black holes do not exist. [[User:QuantumDude|QuantumDude]] ([[User talk:QuantumDude|talk]]) 11:34, 8 February 2016 (EST)
QuantumDude, you continue to be purposefully difficult. Non-materialistic phenomena are phenomena which are not materialistic/natural. Not exactly rocket science. Are you going to tell me next that you never heard the words miracle/supernatural?
:::::Actually, it is quite possible, though unlikely, that QuantumDude really has never heard the words "miracle" or "supernatural". Very unlikely, since they are part of the English language in general. But one could conceivably discuss science without ever having heard those words. [[User:SamHB|SamHB]] ([[User talk:SamHB|talk]]) 12:42, 8 February 2016 (EST)

The point in citing the quote/article was to point out that how you define a black hole is an issue. [[User:Conservative|Conservative]] ([[User talk:Conservative|talk]]) 12:18, 8 February 2016 (EST)

See points 1 and 6 in [[Counterexamples to Relativity]]. Also, "non-materialistic phenomena" are the very real things that cannot be explained by material science, such as [[migration]].--[[User:Aschlafly|Andy Schlafly]] ([[User talk:Aschlafly|talk]]) 12:16, 8 February 2016 (EST)
::By the way, QunatumDude, if you are an atheist, I have a question for you: "Why don't you join a barter exchange and ask members of the barter exchange if they want to barter with you and you will give them "dark matter" in exchange for various goods/services. :) [[User:Conservative|Conservative]] ([[User talk:Conservative|talk]]) 12:25, 8 February 2016 (EST)
:::Challenging people on whether they are atheists is something that Cons does quite frequently. You can ignore him when discussing topics, such as science, that are not related to religion.
:::Also, saying that dark matter probably exists is not the same as saying that you have some available for sale or barter. Or are you saying that you have some red top quarks for sale? [[User:SamHB|SamHB]] ([[User talk:SamHB|talk]]) 12:42, 8 February 2016 (EST)

Well, QD, you've really stepped into a hornet's nest, haven't you? Congratulations. [[User:SamHB|SamHB]] ([[User talk:SamHB|talk]]) 12:42, 8 February 2016 (EST)

:Well I had hoped them to be SOMEWHAT reasonable :/ [[User:QuantumDude|QuantumDude]] ([[User talk:QuantumDude|talk]]) 12:45, 8 February 2016 (EST)
::"whole generations of cosmologists have invested such time, energy, and vast sums of money into identifying this elusive matter that dreams of its existence are likely to die hard." - ''New Doubt About Dark Matter'', Forbes 2014.

::Of course, young earth creation scientists didn't spend a dime on this foolish boondoggle. Young earth creationist scientists base their science on evidence/experiments and not desperate and foolhardy dreams. [[User:Conservative|Conservative]] ([[User talk:Conservative|talk]]) 13:22, 8 February 2016 (EST)

:::I didn't even mention dark matter lol. [[User:QuantumDude|QuantumDude]] ([[User talk:QuantumDude|talk]]) 13:27, 8 February 2016 (EST)
I don't blame you for not mentioning dark matter given the embarrassing state of affairs for atheists.

Millions of missing link fossils with round after round of handfuls of controversial "missing links" being debunked is another great embarrassment to atheists/evolutionists.[http://creation.com/that-quote-about-the-missing-transitional-fossils][http://creation.com/missing-links-parade]

Another favorite of mine is the supposed cow like creatures evolving into whales. How many cows or cow like creatures have you ever seen on the beach? :) [[User:Conservative|Conservative]] ([[User talk:Conservative|talk]]) 13:44, 8 February 2016 (EST)

:Conservative you are going off on a complete tangent totally unrelated to anything I was talking about. Can we stay on topic please? Or is thinking about that too hard for you? [[User:QuantumDude|QuantumDude]] ([[User talk:QuantumDude|talk]]) 14:02, 8 February 2016 (EST)

:The article would highly benefit from more citations, including the reference to the current official position of the Church. Some research works brought intermediate, still questionable conclusions with potentially so nasty social consequences, that asking to interpret with care may be reasonable. But this probably more applies to various forms of scientific racism, abortion and things the like. It is really an explanation required why black holes, wormholes, aliens, dark matter and magnetic butterflies as selected as examples or why and how do they promote atheism in any way. Hence why the article may address a real thing, it seems completely out of focus. [[User:H22|H22]] ([[User talk:H22|talk]]) 17:04, 16 October 2016 (EDT)

Intelligence testing

2016-10-16T20:32:34Z

H22: Extended

'''Intelligence testing''' began in an organized way in the early 20th Century with the [[Stanford-Binet]] test. The purpose was to form an estimate of a person's aptitude before investing time and money in their education, in the belief that aptitude or intelligence was a fixed quantity.

At the time these tests were developed, medical science and psychology were
in their infancy. Ideas such as [[eugenics]] still had currency, and intelligence tests were used to weed out so-called "defectives".

Testers classified people as idiots, imbeciles, morons, normal, above average, and geniuses on a numerical scale based on [[mental age]]. For children, dividing the mental age by chronological age produces the [[intelligence quotient]] (IQ) used for placement in slow or rapid classes.

The study based on survey data from 702 Nordic research works concludes that a typical neuropsychologist used 9 tests in a standard assessment, and 25 tests overall in their practice. The selection of tests to use has been influenced by nationality, competence level, practice profile, and by attitude toward test selection. Testing patients with psychiatric disorders was associated with more tests.<ref>Egeland J, Løvstad M, Norup A, Nybo T, Persson BA6, Rivera DF, Schanke AK, Sigurdardottir S, Arango-Lasprilla J. (2016). Following international trends while subject to past traditions: neuropsychological test use in the Nordic countries. Clin Neuropsychol. Sep 27:1-22. [https://www.ncbi.nlm.nih.gov/pubmed/27670676]</ref>

In the United States, intelligence tests were to classify recruits and draftees for service in World War II. The more technical jobs were assigned to men with higher scores. Sociologists also noted racial differences in IQ scores, and some supposed that these differences were inherent. A controversy over this matter has raged ever since.

Open questions for psychologists and sociologists focus on what produces differences in [[intelligence]], whether intelligence can be developed or stunted by upbringing and education, and why different [[race]]s or cultural groups have significantly different scores.

The two main reasons given are:
#that there may be inherent differences between the races
#that upbringing, education and social factors can skew the results

== Influention of environment ==
After nearly a century of IQ testing and [[educational reform]]s, some researchers have begun to assert that IQ can be influenced by the child's environment by as much as 30 points.<ref>3 weeks of intensive play of WFF 'N PROOF: The Game of Modern Logic increased average IQ scores by more than 20 points. [http://wffnproof.com/]</ref> See [[Educational games]].

A 1976 year study that covered 258 children (IQ between 80 and 119) finally concluded that the major correlating factor is "a favorable parental social and educational background" <ref>Fisch RO, Bilek MK, Horrobin JM, Chang PN (1976) Children with superior intelligence at 7 years of age: a prospective study of the influence of perinatal, medical, and socioeconomic factors. Am J Dis Child. 1976 May;130(5):481-7. Abstract available at
https://www.ncbi.nlm.nih.gov/pubmed/1274898</ref>. The more recent 2016 year study also showed that the measured IQ potential is significantly lower in developing countries. <ref name='kodila'>Kodila-Tedika O1, Asongu SA2, Azia-Dimbu F3. (2016) J Biosoc Sci. 2016 May 26:1-13, available at [https://papers.ssrn.com/sol3/papers.cfm?abstract_id=2661437]
Statistics and intelligence in developing countries</ref> and increases after the national statistics to improves (<ref name='kodila'/> references [[Nigeria]] and [[Kenya]]).

Test results can also be influenced by other factors:
*Steele and Joshua Aronson found that when they gave a group of Stanford undergraduates a standardized test and told them that it was a measure of their intellectual ability, the white students did much better than their black counterparts. But when the same test was presented simply as an abstract laboratory tool, with no relevance to ability, the scores of blacks and whites were virtually identical.<ref>[http://www.gladwell.com/2000/2000_08_21_a_choking.htm]</ref> See [[Pressure and failure]].

==Liberal bias==

The field of intelligence testing has been acrimonious and contentious. Researchers such as [[Arthur Jensen]] and [[Charles Murray]] have been pilloried in the mass media, accused of maintaining views which different or even opposite of their actual views.<ref>Evolution advocate Gould portrays Murray as saying intelligence can be measured with a single number; Murray, of course, makes it clear in his book (as well as in a follow-up retort to Gould) that intelligence is too complex to be measured with a single number.</ref>

One professor had to come to Jensen's defense, after [[Stephen Jay Gould]] attacked him in print:

:I object to Gould's tendency to visit the alleged sins of early investigators on present day investigators. If Goddard, Brigham, and others once tended to view various human races as relatively superior or inferior in intelligence and therefore relatively worthy or unworthy, this does not mean that present-day investigators, like Jensen (1980) or Rushton (1995), are necessarily guilty of such views. In fact, from my personal acquaintance with Jensen and his publications, I can attest that he does not view the African race (if one accepts that it is a race) as in any way less worthy than other so-called races. [http://www.psych.utoronto.ca/~reingold/courses/intelligence/cache/carroll-gould.html]

[[Charles Murray]] said:

*As soon as anyone argues that racial differences in intelligence are authentic, not an artifact of biased tests, everyone decodes that as saying the differences are grounded in genes. It is a non-sequitur, but an invariable one in my experience. America's intellectual elites are hysterical about the possibility of black - white genetic differences in IQ.
*As you know, The Bell Curve actually took a mild, agnostic stand on the subject. Dick Herrnstein and I said that nobody yet knows what the mix between environmental and genetic causes might be, and it makes no practical difference anyway. The only policy implication of the black - white difference, whatever its sources, is that the U.S. should return forthwith to its old ideal of treating people as individuals.
*But how many people know this? No one who hasn't read the book. Everyone went nuts about genes, so much so that most people now believe that race and genes is the main topic of our book. [http://www.eugenics.net/papers/mssel.html]

The Bell Curve book is not the only controversial study on IQ among different races or groups of people. Danish professor [[Helmuth Nyborg]] has conducted studies of IQ which indicate [[Politically correct language|politically incorrect]] results such as: on average, white people have higher IQs than black people, and men have higher IQs than women. His latest research finds that on average, [[atheists]] have IQs about 5.8 points higher than people of [[faith]], prompting similar outrage among his critics, who claim that such results might be due to cultural biases.[http://danish.newsvine.com/_news/2007/02/05/554043-professor-atheists-are-more-intelligent-than-believers]

== See also ==

*[[Theory of multiple intelligences]]
*[[Moral intelligence]]
*[[Bodily-kinesthetic intelligence]]
*[[Emotional intelligence]]
*[[Atheism and intelligence]]

==External links==
*[http://www.eugenics.net/papers/mssel.html As the Bell Curves] - [[Charles Murray]] and [[Daniel Seligman]] - (Originally published in The National Review, December 8, 1997)

==Notes==
<references/>

[[Category:Psychology]]

Talk:Intelligence testing

2016-10-16T20:04:11Z

H22:

Cut from end of article:

"why different races or cultural groups have significantly different scores" This is attempting to be an encyclopedia, and when discussing science the word 'significantly' should not be used lightly. [[user:stevendavy]]

:Many have ascribed such differences to the cultural bias of the tests [http://wilderdom.com/personality/intelligenceCulturalBias.html].

I take it cultural bias in intelligence test is a myth [http://eric.ed.gov/ERICWebPortal/Home.portal?_nfpb=true&_pageLabel=RecordDetails&ERICExtSearch_SearchValue_0=ED174627&ERICExtSearch_SearchType_0=eric_accno&objectId=0900000b8011cfd9]. Sorry for being misinformed. [[User:BillyBoy|BillyBoy]] 08:42, 31 March 2007 (EDT)

:You are not misinformed (the claims are well-known). I would just rather we provided a balanced and well-organized treatment. I have spent a lot of time helping to develop Wikipedia's race and intelligence article series, with a stress on objectivity, impartiality, and balance.

:I would attribute this claim to [[Adrian Dove]] and also explain a bit more about why anyone would want to ascribe the difference in scores to vocabulary or to knowledge of inner-city life. --[[User:Ed Poor|Ed Poor]] 08:46, 31 March 2007 (EDT)

:*In the fall of 1994, the publication of Hermstein and Murray's book ''[[The Bell Curve]]'' sparked a new round of debate about the meaning of intelligence test scores and the nature of intelligence. The debate was characterized by strong assertions as well as by strong feelings. Unfortunately, those assertions often revealed serious misunderstandings of what has (and has not) been demonstrated by scientific research in this field. Although a great deal is now known, the issues remain complex and in many cases still unresolved. Another unfortunate aspect of the debate was that many participants made little effort to distinguish scientific issues from. political ones, Research findings were often assessed not so much on their merits or their scientific standing as on their supposed political implications. [http://www.lrainc.com/swtaboo/taboos/apa_01.html (Stalking the Wild Taboo)]

:::Thanks for the answer. You mentioned Wikipedia's race and intelligence article series, with a stress on objectivity, impartiality, and balance. Isn't the object of Conservapedia to avoid that kind of [[Differences_with_Wikipedia|wikipedian]] liberal bias?
:::[[User:BillyBoy|BillyBoy]] 08:58, 31 March 2007 (EDT)

The irony of you tarring everyone with one brush ...

That particular article series is well-done. I had a lot to do with it. "Impartiality" is not [[liberal bias]]. Pretending to be impartial while cherry-picking sources that support your own POV is the problem. --[[User:Ed Poor|Ed Poor]] 09:07, 31 March 2007 (EDT)

==Wikipedia's bias==

I've tidied up the Wikipedia articles several times, but I saw today that the old liberal bias has crept back again. Jensen and also ''The Bell Curve'' are vilified, and Gould's POV is exalted. Gould puts words into others' mouths, and Wikipedia lets him get away with it. (I guess evolutionists like Gould can do no wrong, and conservatives can do no right, eh?) --[[User:Ed Poor|Ed Poor]] [[User talk:Ed Poor|Talk]] 13:33, 20 July 2007 (EDT)
::At some time I tried to fix Wikipedia article providing references to the relevant works of the real scientific research but all got removed so that cannot even find in edit history. If there is any single article in Wikipedia that provides clearly false, misleading and biased information, backed up only by the supporting team watching the edits, then this one article it is. [[User:H22|H22]] ([[User talk:H22|talk]]) 16:04, 16 October 2016 (EDT)

Intelligence testing

2016-10-16T19:09:11Z

H22: Provided two research references

'''Intelligence testing''' began in an organized way in the early 20th Century with the [[Stanford-Binet]] test. The purpose was to form an estimate of a person's aptitude before investing time and money in their education, in the belief that aptitude or intelligence was a fixed quantity.

At the time these tests were developed, medical science and psychology were
in their infancy. Ideas such as [[eugenics]] still had currency, and intelligence tests were used to weed out so-called "defectives".

Testers classified people as idiots, imbeciles, morons, normal, above average, and geniuses on a numerical scale based on [[mental age]]. For children, dividing the mental age by chronological age produces the [[intelligence quotient]] (IQ) used for placement in slow or rapid classes.

In the United States, intelligence tests were to classify recruits and draftees for service in World War II. The more technical jobs were assigned to men with higher scores. Sociologists also noted racial differences in IQ scores, and some supposed that these differences were inherent. A controversy over this matter has raged ever since.

Open questions for psychologists and sociologists focus on what produces differences in [[intelligence]], whether intelligence can be developed or stunted by upbringing and education, and why different [[race]]s or cultural groups have significantly different scores.

The two main reasons given are:
#that there may be inherent differences between the races
#that upbringing, education and social factors can skew the results

== Influention of environment ==
After nearly a century of IQ testing and [[educational reform]]s, some researchers have begun to assert that IQ can be influenced by the child's environment by as much as 30 points.<ref>3 weeks of intensive play of WFF 'N PROOF: The Game of Modern Logic increased average IQ scores by more than 20 points. [http://wffnproof.com/]</ref> See [[Educational games]].

A 1976 year study that covered 258 children (IQ between 80 and 119) finally concluded that the major correlating factor is "a favorable parental social and educational background" <ref>Fisch RO, Bilek MK, Horrobin JM, Chang PN (1976) Children with superior intelligence at 7 years of age: a prospective study of the influence of perinatal, medical, and socioeconomic factors. Am J Dis Child. 1976 May;130(5):481-7. Abstract available at
https://www.ncbi.nlm.nih.gov/pubmed/1274898</ref>. The more recent 2016 year study also showed that the measured IQ potential is significantly lower in developing countries. <ref name='kodila'>Kodila-Tedika O1, Asongu SA2, Azia-Dimbu F3. (2016) J Biosoc Sci. 2016 May 26:1-13, available at [https://papers.ssrn.com/sol3/papers.cfm?abstract_id=2661437]
Statistics and intelligence in developing countries</ref> and increases after the national statistics to improves (<ref name='kodila'/> references [[Nigeria]] and [[Kenya]]).

Test results can also be influenced by other factors:
*Steele and Joshua Aronson found that when they gave a group of Stanford undergraduates a standardized test and told them that it was a measure of their intellectual ability, the white students did much better than their black counterparts. But when the same test was presented simply as an abstract laboratory tool, with no relevance to ability, the scores of blacks and whites were virtually identical.<ref>[http://www.gladwell.com/2000/2000_08_21_a_choking.htm]</ref> See [[Pressure and failure]].

==Liberal bias==

The field of intelligence testing has been acrimonious and contentious. Researchers such as [[Arthur Jensen]] and [[Charles Murray]] have been pilloried in the mass media, accused of maintaining views which different or even opposite of their actual views.<ref>Evolution advocate Gould portrays Murray as saying intelligence can be measured with a single number; Murray, of course, makes it clear in his book (as well as in a follow-up retort to Gould) that intelligence is too complex to be measured with a single number.</ref>

One professor had to come to Jensen's defense, after [[Stephen Jay Gould]] attacked him in print:

:I object to Gould's tendency to visit the alleged sins of early investigators on present day investigators. If Goddard, Brigham, and others once tended to view various human races as relatively superior or inferior in intelligence and therefore relatively worthy or unworthy, this does not mean that present-day investigators, like Jensen (1980) or Rushton (1995), are necessarily guilty of such views. In fact, from my personal acquaintance with Jensen and his publications, I can attest that he does not view the African race (if one accepts that it is a race) as in any way less worthy than other so-called races. [http://www.psych.utoronto.ca/~reingold/courses/intelligence/cache/carroll-gould.html]

[[Charles Murray]] said:

*As soon as anyone argues that racial differences in intelligence are authentic, not an artifact of biased tests, everyone decodes that as saying the differences are grounded in genes. It is a non-sequitur, but an invariable one in my experience. America's intellectual elites are hysterical about the possibility of black - white genetic differences in IQ.
*As you know, The Bell Curve actually took a mild, agnostic stand on the subject. Dick Herrnstein and I said that nobody yet knows what the mix between environmental and genetic causes might be, and it makes no practical difference anyway. The only policy implication of the black - white difference, whatever its sources, is that the U.S. should return forthwith to its old ideal of treating people as individuals.
*But how many people know this? No one who hasn't read the book. Everyone went nuts about genes, so much so that most people now believe that race and genes is the main topic of our book. [http://www.eugenics.net/papers/mssel.html]

The Bell Curve book is not the only controversial study on IQ among different races or groups of people. Danish professor [[Helmuth Nyborg]] has conducted studies of IQ which indicate [[Politically correct language|politically incorrect]] results such as: on average, white people have higher IQs than black people, and men have higher IQs than women. His latest research finds that on average, [[atheists]] have IQs about 5.8 points higher than people of [[faith]], prompting similar outrage among his critics, who claim that such results might be due to cultural biases.[http://danish.newsvine.com/_news/2007/02/05/554043-professor-atheists-are-more-intelligent-than-believers]

== See also ==

*[[Theory of multiple intelligences]]
*[[Moral intelligence]]
*[[Bodily-kinesthetic intelligence]]
*[[Emotional intelligence]]
*[[Atheism and intelligence]]

==External links==
*[http://www.eugenics.net/papers/mssel.html As the Bell Curves] - [[Charles Murray]] and [[Daniel Seligman]] - (Originally published in The National Review, December 8, 1997)

==Notes==
<references/>

[[Category:Psychology]]

Black hole

2016-10-16T18:27:13Z

H22:

[[Image:Iu8969hu.jpg|right|thumb|300px|Artist's conception of a binary system consisting of a black hole (upper left) and a main sequence star (lower right). The black hole is drawing matter from the star via an ''accretion disk'' (blue) around it, and some of this matter forms a gas jet (also blue).]]
A '''black hole''' is any object that lies entirely inside its own Schwarzschild radius, given by
:<math>r=\frac{2G}{c^2}\ m</math>
where
*G is Newton's gravitational constant;
*c is the speed of light;
*m is the mass of the object.

Numerically,
:<math>r=1.5 \times 10^{-27}\ m</math>
in meters and kilograms.

This is a concept of gravity, under [[General Relativity]]. For any normal object, from things one would see on Earth up to stars that are not extremely massive or dense (much more massive or dense than the Sun), the Schwarzschild radius is very tiny relative to the object. This means that the object does not lie inside that radius, and cannot be a black hole. For example, the Schwarzschild radius of the Earth is about one centimeter, and that of the Sun is about three kilometers. The Earth could only become a black hole if it were compressed into a radius of one centimeter.

What makes the Schwarzschild radius significant is that the behavior of gravity, under General Relativity, is determined by the Schwarzschild metric, and is (not surprisingly) nearly identical to the behavior given by Newton's law of gravity. The difference only shows up at distances at or near the Schwarzschild radius. If the Earth were compressed to a radius of one centimeter or less, the behavior of gravity would become radically different as one approached that distance. Normal world-lines would cease to be "time-like", and such world-lines would be unable to make progress from inside the Schwarzschild radius to outside of it. This is a rather paradoxical situation when viewed in the way we normally view the way the universe works. In short, no object, and no light, can actually pass from inside the radius to outside. The surface at this radius is called the '''event horizon'''.

The concept of the Schwarzschild radius was worked out by Karl Schwarzschild in 1916, as part of his solution (the first solution ever worked out) of Einstein's field equation for General Relativity. At first, neither Einstein nor Schwarzschild believed that something could be so dense that these objects could exist.

==Pre-history==
The notion of something that has gravity so strong that light can't escape actually dates back to the 18th century, when scientists became aware of the finite speed of light and the concept of escape velocity. The [[corpuscular theory of light]] held that light was made up of invisibly small particles, and that these particles moved along ballistic trajectories, like tiny bullets. In this framework, it was believed possible that a distant star could be so massive that light emitted from its surface would be dragged back down again. This theory was first advanced by John Michell, who wrote in 1783, "If the semi-diameter of a sphere of the same density as the Sun in the proportion of five hundred to one, and by supposing light to be attracted by the same force in proportion to its [[Mass (science)|mass]] with other bodies, all light emitted from such a body would be made to return towards it, by its own proper gravity."<ref name="r1">http://www.aps.org/publications/apsnews/200911/physicshistory.cfm</ref>

Suggesting the same possibility independently, Pierre-Simon Laplace wrote in 1796, "It is therefore possible that the greatest luminous bodies in the universe are on this account invisible."<ref name="r1" />

This appeared to depend on the corpuscular theory of light, which gave way to the [[wave theory of light]] in the early 19th century, so the idea of "dark" or "invisible" stars fell from favor. It was believed that light, being a wave and having no mass, might be unaffected by gravity. Research into [[quantum mechanics]], however, reignited interest in the light-as-particles view, ultimately resulting in the modern notion of [[wave-particle duality]]. Under this theory, light could be affected by gravity, so the question of whether light could be emitted from extraordinarily massive bodies was once again open.

But the wave-versus-particle nature of light turned out to be a [[red herring]]. Under the "equivalence principle", it is known that anything, wave, particle, or whatever, that can be construed to have a trajectory, will have that trajectory bent by a gravitational field.

But none of this mattered at the time. A star (or other body) large enough to show this effect was utterly inconceivable. A sphere of Uranium at its normal density would have to weigh 10 million times the mass of the Sun, and be as large as the Earth's orbit, to lie inside its Schwarzschild radius. (Though such a large block of Uranium would not have its normal density.)

And the term "black hole" was unheard-of.

==20th century history==
By the mid-20th century, the physics of stellar dynamics and quantum mechanics had advanced to the point that it was possible to conceive of incredibly dense objects. Stars such as the Sun are actually "inflated" to their current size by the radiation pressure from the fusion reactions going on within them. When stars have consumed all their fuel, that pressure stops, and the material collapses to a much smaller size. The normal interatomic spacing, with electrons orbiting the nuclei, no longer applies. A variety of things can occur, including the electrons combining with the protons to make a "neutron star". Various phenomena were formulated, such as neutron stars, supernovas, pulsars, and magnetars. Before long these objects were actually observed. (Pulsars were observed before the theory had been worked out, and supernovas had been observed since antiquity.)

Stellar evolution and dynamics are quite complicated. Once a star has burned up all its Hydrogen, it may, depending on its size, burn Helium, and then heavier elements, all the way up to Iron. (Iron is the most stable nucleus; fission or fusion of Iron nuclei is not energetically favored.) As the material becomes more compressed, it is held up by the "electron degeneracy pressure" instead of the normal radiation pressure. The normal atomic structure, with orbiting electrons, is replaced by a collection of nuclei and unbound electrons, obeying the rules of quantum mechanics, particularly the Pauli exclusion principle. This pressure generally stops further collapse, leading to a [[white dwarf]]. White dwarfs may continue accreting matter from nearby objects. If the mass is over the "Chandrasekhar limit" of 1.4 solar masses, the gravitational force is too strong even for the degeneracy pressure, and the star becomes a supernova, neutron star, or black hole. The theory of this gravitational collapse was worked out in the 1930's.

If the mass is greater than the Tolman-Oppenheimer-Volkoff limit of about 1.5 solar masses, the neutron star becomes a black hole.

The properties of these objects (the "event horizon", and matter and information may only pass through the event horizon in one direction) were worked out in the 1950's. The exact solutions to Einstein's equation were worked out in the 1960's for rotating black holes (the Kerr solution), electrically charged black holes (the Reissner-Nordström solution), or both (the Kerr-Newman solution). Various theorems relating to thermodynamics were worked out by Stephen Hawking in the 1970's.

The term "black hole" was coined by John Wheeler in 1967. The term caught on very quickly in both the scientific community and the public at large, helped by the catchy nature of the phrase. Because of the remarkable nature of black holes, the concept quickly became a staple of science fiction stories, "popular" science magazines, television shows, and movies such as ''Event Horizon'' (1997), ''The Black Hole'' (TV, 2006), and ''Interstellar'' (2014). The latter movie put a lot of effort into making the visual depiction of the black hole scientifically accurate.

This was all theoretical at the time. There was no evidence that a black hole actually existed until the early 1970's, when scientists began to suspect that the radio source "Cygnus X1" was an actual black hole, and the 1990's, when scientists began to suspect that there was a black hole near the radio source "Sagittarius A*" at the center of our galaxy. (The name is pronounced with the word "star".) Since then evidence has accumulated that enormous black holes lie at the center of many galaxies.

==Methods of Observation==
Black holes are literally invisible by traditional means of observation (that is, emission or reflection of some sort of radiation) and so cannot be directly observed, their nature is determined by other means. The evidence that a black hole provides is its extraordinarily strong gravity, which can be deduced from its effect on the motions of nearby stars.
<ref name="Gillessen">{{cite journal
|last1=Gillessen |first1=S.
|last2=Eisenhauer |first2=F.
|last3=Trippe |first3=S.
|last4=Alexander |first4=T.
|last5=Genzel |first5=R.
|last6=Martins |first6=F.
|last7=Ott |first7=T.
|display-authors=3
|title=Monitoring Stellar Orbits around the Massive Black Hole in the Galactic Center
|journal=The Astrophysical Journal
|volume=692
|issue=2|page=1075|date=2009
|doi=10.1088/0004-637X/692/2/1075
|arxiv=0810.4674
|bibcode=2009ApJ...692.1075G
|ref=harv
}}</ref> Since 1995, astronomers have tracked the motions of 90 stars orbiting an invisible object coincident with the radio source in the center of our galaxy, Milky way. The astronomers were able to infer that a 2.6 million sollar mass object must be contained within the radius of 0.02 [[light-year]]s to cause the motions of those stars.<ref name="Ghez1998">{{cite journal
|last1=Ghez |first1=A. M.
|last2=Klein |first2=B. L.
|last3=Morris |first3=M.
|last4=Becklin |first4=E. E.
|display-authors=3
|title=High Proper‐Motion Stars in the Vicinity of Sagittarius A*: Evidence for a Supermassive Black Hole at the Center of Our Galaxy
|journal=The Astrophysical Journal
|volume=509
|issue=2|page=678|date=1998
|doi=10.1086/306528
|arxiv=astro-ph/9807210 |bibcode=1998ApJ...509..678G
|ref=harv
}}</ref>

Colliding black holes should produce gravitational waves, possible to detect experimentally. On 24 September 2015 the [[LIGO]] observatory made the first-ever successful observation of such event. <ref name="PRL-20160211">{{cite journal |author=Abbott, B.P. |title=Observation of Gravitational Waves from a Binary Black Hole Merger |url=http://journals.aps.org/prl/abstract/10.1103/PhysRevLett.116.061102 |journal=[[Phys. Rev. Lett.]] |volume=116 |pages=061102 |year=2016 |doi=10.1103/PhysRevLett.116.061102 |display-authors=etal|arxiv = 1602.03837 |bibcode = 2016PhRvL.116f1102A }}</ref><ref name="NYT-20160211-db">{{cite news |last=Overbye |first=Dennis |authorlink=Dennis Overbye |title=Physicists Detect Gravitational Waves, Proving Einstein Right |url=http://www.nytimes.com/2016/02/12/science/ligo-gravitational-waves-black-holes-einstein.html |date=11 February 2016 |work=[[New York Times]] |accessdate=11 February 2016 }}</ref> The signal was consistent with theoretical predictions. The gravitational wave signal suggests that the separation of the two holes prior to merger was just 350 km, hence they must be small in size, leaving black holes as the most plausible interpretation.

While matter and energy, even light, may not escape a black hole, Stephen Hawking has shown that when described by quantum mechanics, they should emit [[Hawking radiation]], which absent of an influx of mass-energy would lead to the evaporation of the black hole in a burst of gamma rays. This radiation may be possible to observe. However all results obtained to date remain unverified and debatable.<ref name="Milanoguys">{{cite journal|title=Hawking radiation from ultrashort laser pulse filaments |first1=F. |last1=Belgiorno |first2=S. L. |last2=Cacciatori |first3=M. |last3=Clerici |first4=V. |last4=Gorini |first5=G. |last5=Ortenzi |first6=L. |last6=Rizzi |first7=E. |last7=Rubino |first8=V. G. |last8=Sala |first9=D. |last9=Faccio |arxiv=1009.4634 |doi=10.1103/PhysRevLett.105.203901 |date=2010 |journal=Phys. Rev. Lett. |volume=105 |page=203901}}</ref><ref>{{cite news|title=Ultrafast Laser Pulse Makes Desktop Black Hole Glow|newspaper=[[Wired (magazine)|Wired]]|date=September 29, 2010|first=Lisa|last=Grossman|url=http://www.wired.com/wiredscience/2010/09/hawking-radiation-in-the-lab/|accessdate=April 30, 2012}}</ref>

==History of the idea==

===General Relativity===
As it happened, the question became unavoidable shortly after the publication in 1915 of Einstein's [[general theory of relativity]]. [[Karl Schwarzschild]] solved the Einstein field equations in a way that describes the geometry of spacetime outside a spherically symmetric, uncharged, non-rotating distribution of mass. Well away from the center of this distribution of mass, the Schwarzschild solution closely matches the Newtonian model of a gravitational field; only close to the mass, where the curvature of spacetime is large, do significant differences between the two models appear. But if the diameter of the mass distribution is taken to be arbitrarily small, then the region of spacetime immediately surrounding the mass appears to take on extremely curious properties, properties so curious that many questioned whether they had any physical interpretation at all. Therefore, Schwarzschild showed that black holes were possible under the theory of [[general relativity]].

[[File:Cygnusx1.jpg|right|200px|thumb|Jet-powered nebula formed from the accretion disk of the binary star Cygnus-X1]]
However, neither Schwarzschild himself nor [[Albert Einstein]], who developed the theory of relativity, believed that black holes actually existed.<ref name="amazing-space.stsci.edu">http://amazing-space.stsci.edu/resources/explorations/blackholes/lesson/whatisit/history.html</ref> Einstein even tried to re-work general relativity to render these [[Singularity|singularities]] impossible. However, Roger Penrose and Stephen Hawking proved the first of many Singularity Theorems, which states that singularities must form if certain conditions are present. This demonstrated that, rather than mathematical oddities, singularities are a fairly generic consequence of realistic solutions to relativity: any mass with radius less than its Schwarzschild radius is a black hole. Since then, support for black holes among the scientific community has grown.

==Nature of a Black Hole==
===Mathematics===

There are several solutions of the Einstein field equations that are used to model black holes. The simplest of these is the Schwarzchild metric. From this metric, one can calculate the Schwarzschild radius, which defines the boundary (event horizon) of the black hole, to be
:<math>r_s=\frac{2GM}{c^2}</math>,
where
* rs is the Schwarzschild radius;
* G is the gravitational constant;
* M is the mass of the gravitating object;
* c is the speed of light in vacuum.

If the black hole has a nonzero electric charge, it is modeled by the Reissner-Nordström metric. Astronomical objects are generally electrically neutral, since otherwise they would attracted charged particles of opposite sign and quickly become neutral. Therefore, the Reissner-Nordström metric is largely of theoretical interest.

A far more realistic situation occurs when the black hole is spinning (i.e. has nonzero angular momentum). Then the Schwarzschild solution is insufficient (as it was for the charged case), and instead one turns to the Kerr metric. Since astrophysical black holes are generically believed to have angular momentum, this is the solution that best describes them. Among the more interesting consequences of the Kerr metric is the phenomenon of frame dragging, in which the rotating black hole literally pulls nearby spacetime along with it.

If one wishes to consider a black hole that is both charged and spinning, one employs the Kerr-Newman metric, which combines the Reissner-Nordström and Kerr metrics. Since the no-hair theorem states that (non-quantum) black holes are unique up to mass, charge, and angular momentum, the Kerr-Newman metric is sufficient to describe any classical black hole.

===Time and Distance===
Within a certain distance from an arbitrarily small distribution of mass — a distance now known as the [[Schwarzschild radius]] — the curvature of spacetime becomes so great that no paths leading away from the mass exist. That is to say, a test particle released inside the Schwarzschild radius will inevitably move in toward the mass, not because the force of gravity is great as in the Newtonian approximation, but because spacetime is curved to such an extent that ''no other directions exist.'' A particle within the Schwarzschild radius can no more move further from the central mass than it can go backwards in time. In fact, from the frame of reference of an infalling observer beyond the Schwarzschild radius, all directions that once pointed away from the central mass now point backwards in time. Once inside the Schwarzschild radius, further motion toward the central mass is as inevitable as further motion through time is for any other observer.

For some time after the publication of the Schwarzschild solution, the validity of these results was hotly debated. In the solution's original coordinate frame, some terms in the equations ''diverged,'' or became infinite, at the Schwarzschild radius, leading physicists to wonder whether the results of the equations in that region had any valid physical interpretation. One proposed interpretation was that at the Schwarzschild radius, all time for the infalling observer would stop. This led to the use of the term "frozen stars;" it wasn't believed frozen stars were cold, but rather that they were literally frozen in time.

Later refinement of the Schwarzschild solution demonstrated that the apparent infinities were merely an artifact of the coordinate frame chosen, and that an infalling observer in fact can pass beyond the Schwarzchild radius. In fact, the equations predicted he would notice no effects when doing so. But any attempt on the part of that infalling observer to communicate with the outside universe, say by sending a radio message, would be doomed to failure, as the radio waves would traverse geodesics through the severely curved spacetime and end up bent toward the central mass. From this, we can say that nothing that occurs within the Schwarzschild radius can ever affect events outside the Schwarzschild radius. This gives the Schwarzschild radius of a non-rotating black hole its other name: the [[event horizon]].

===Inside the Event Horizon===
What actually exists inside the event horizon of a black hole is a question physics is unable to answer. Some postulate that within the event horizon exists a point of zero (or nearly zero) volume but infinite energy density, a point sometimes referred to as a ''gravitational singularity,'' after the notion of a mathematical singularity (a term referring to a point in an equation at which one would have to solve by dividing by zero, a feat presently impossible in mathematics) in a field equation. Others suspect that infinite energy density is a physical impossibility, and that a black hole contains actual finitely-dense matter compressed into a [[degenerate matter|degenerate]] form, such as quark-degenerate matter. Since all black holes are surrounded by an event horizon which prevents any information or messages from leaving, all these theories are non-[[falsifiable]]; we can never be sure what the interior structure of a black hole is like.

===Properties of Black Holes===

Black holes described with classical mechanics only have three intrinsic properties by which one differs from another: mass, electric charge, and angular momentum. Mass describes the amount of matter inside the event horizon. Angular momentum refers to whether the black hole is stationary or rotating around an axis. While the singularity of a non-rotating black hole may be an infinitely small point, the singularity of a rotating black hole would be in the shape of an infinitely thin ring. Quantum mechanics, which postulates that information loss cannot occur in a black hole, suggests properties beyond the three suggested by classical physics. Using this description, information must also be emitted by black holes. This radiation, referred to as Hawking Radiation, is thermal radiation that has currently only been described mathematically.

Although radiation from inside the event horizon has not yet been observed, there is much phenomenon that occurs outside the horizon due to the black hole. Matter entering a spinning black hole is first swirled around by the black hole’s gravity, causing it to heat up and emit x-rays, which can be used to detect the black hole. In the supermassive black holes at the centers of galaxies, some of the matter does not fall into the black hole. Instead it is blasted into space in twin jets of hot gas perpendicular to the accretion disc, in a phenomenon known as an Active Galactic Nucleus.

==Origins of Black Holes==
[[Image:Hs-2005-02-e-web.jpg|right|thumb|300px|The [[red supergiant]] star V838 Monocerotis, an example of one type of star which may become a black hole.]]
Stellar-mass black holes are said to form when stars more than ten times the mass of the Sun run out of fuel and die. The process of death occurs when stars that have fused the products of their own fusion into larger and larger elements, up to iron. The star then tries to fuse the iron core that forms as a result, but this does not produce enough energy to hold the outer layers of the star apart against the pull of gravity. When this happens, the iron core at the center of the star implodes in a supernova, and the outer layers of the star are blasted into space in one of the most energetic events in the universe—one star going out in a supernova can give off as much light as an entire galaxy. Not all supernovae result in black holes, but if the mass of the core is large enough, about 1.5-3.0 times the mass of the Sun (this value is termed the Tolman-Oppenheimer-Volkoff limit, and its value is not yet known to great precision), the leftover gravity of the shrinking core stalls the outward rush of the initial blast, and crushes the core into a point of infinite density: a black hole.

Extremely small black holes, with masses of around 1015 grams, have been theorized to have formed in the early universe. Any sufficiently small primordial black hole would be expected to evaporate within the lifetime of the universe, but the rate of evaporation is not currently known with any certainty.

At the opposite end of the spectrum, objects with the characteristics of supermassive black holes, millions or billions of times more massive than the sun, have been detected at the centers of many [[galaxies]], including our own [[Milky Way]]. In our galaxy, the hypothesized supermassive black hole is in the constellation Sagittarius, and is known as Sagittarius A* (pronounced "A star"). Based on the extraordinary angular velocity of stars near the galactic center, Sagittarius A* is believed to be on the order of two to three million solar masses. It is unknown how supermassive black holes form, though several models have been proposed. One hypothesis simply begins with a black hole of stellar mass which grows over the lifetime of the galaxy that surrounds it. Another proposal describes supermassive black holes as a natural, in fact nearly unavoidable, consequence of galactic formation. To date, no one theory of supermassive black hole formation is favored over all others.

Physicists trying to understand the theory of black hole formation have once again hit a dead end.<ref>http://www.fromquarkstoquasars.com/new-research-mathematically-proves-quantum-effects-stop-formation-black-holes/</ref>

==Speculative Future Exploration==

Scientists have speculated that if a rotating black hole is large enough, a person could pass through the center of the ring-shaped singularity and possibly enter a wormhole. However, it would have to be a very large hole, for if it were not, the hypothetical astronaut would never survive to reach the event horizon due to tidal forces.

Matter coming close to the event horizon of a small black hole undergoes a process called spaghettification, a term coined by Stephen Hawking in his book ''A Brief History of Time'' to describe extraordinarily strong tidal forces. Because the mass at the center of the black hole is so dense, the gravitational pull on the near end of an object is much greater than the pull on the object’s far end. This causes the object to be stretched out in a way resembling a piece of spaghetti, and generally torn in two.

==White Holes==
Because the [[Quantitative Introduction to General Relativity|general relativity equations]] are symmetric with respect to time, one can reverse the time parameter to yield an equation describing a hypothetical object which expels, rather than attracts, matter and energy.<ref>http://cosmology.berkeley.edu/Education/BHfaq.html#q10</ref> As this is the exact opposite of a black hole, it is called a '''white hole'''.

However, there is no evidence white holes actually exist. If they generate new matter and energy, this would violate the [[Law of the conservation of mass]]. Therefore, some scientists have proposed that matter falling into black holes goes through a [[wormhole]] to emerge at a white hole. While such wormholes are allowed by general relativity, they would be extremely unstable,<ref>http://casa.colorado.edu/~ajsh/schww.html</ref> and there is no evidence that they exist.

Scientists, who have been extremely eager to promote the idea of black hole existence, have shown a strong aversion to the white hole theory, even though, like a white hole, a black hole has never been observed directly. This may reflect an anti-creation bias on the part of scientists who are uncomfortable with the idea that matter and energy can be created outside of what scientific theories dictate should happen.

Fundamentalists and creationists have used white holes to attempt to solve the cosmic time problem. Dr. [[Russell Humphreys]] used a white hole in his model of the universe during [[Creation week]] to allow millions of years to pass in outer space while only three days passed on Earth.

==In Popular Culture==
Black holes are increasingly promoted by [[liberal]] publications, such as the science page of the ''[[New York Times]]'', glossy magazines, and the movies the ''Event Horizon'' (1997), ''The Black Hole'' (TV, 2006), and ''Interstellar'' (2014). They are sometimes seen as a [[sacred cow]]s of [[atheistic science]], and used to be commonly mentioned in atheistic propaganda. However both proving or disproving of the actual existence of black holes does not very obviously support any religion-related view.

Black holes have been a device in science fiction ever since their prediction. Many sci-fi books, movies, and television shows use black holes as a method of travel (see the Potential Future Exploration section above) or as a threat to a space-going vessel. In at least one season of the show ''Star Trek: the Next Generation'' by Gene Roddenberry, artificially created miniature black holes are used as power sources for spaceships and natural ones as incubators for the young of an alien race. Neither of these uses has much of a basis in reality, of course.

Contrary to popular myth, a black hole is not a cosmic vacuum cleaner. In other words, a one-solar-mass black hole is no better than any other one-solar-mass object (such as, for example, the Sun) at "sucking in" distant objects. However, a one-solar-mass black hole has the same amount of matter as any other one-solar-mass object but compressed into a much smaller space, making it impossible to move fast enough to leave a black hole once there. If a spaceship could land on a black hole, it would never be able to take off again.

The term "black hole" is also used as a metaphor for a place that it is hard to get out of, generally containing a high concentration of something unpleasant. Ex: "The inner city is a black hole of crime and drug use." The "Black Hole of Calcutta" long predates the celestial use of the term; it was a horrible underground prison in [[Calcutta]], India.

==See also==
*[[Black hole firewall]]
==References==
{{reflist}}
==External links==
*[http://imagine.gsfc.nasa.gov/docs/science/know_l2/black_holes.html Black Holes]
*[http://cosmology.berkeley.edu/Education/BHfaq.html Black Holes (Frequently Asked Questions)]

{{Relativity}}
[[Category:Physics]]
[[Category:Relativity]]

Black hole

2016-10-16T17:53:11Z

H22:

[[Image:Iu8969hu.jpg|right|thumb|300px|Artist's conception of a binary system consisting of a black hole (upper left) and a main sequence star (lower right). The black hole is drawing matter from the star via an ''accretion disk'' (blue) around it, and some of this matter forms a gas jet (also blue).]]
A '''black hole''' is any object that lies entirely inside its own Schwarzschild radius, given by
:<math>r=\frac{2G}{c^2}\ m</math>
where
*G is Newton's gravitational constant;
*c is the speed of light;
*m is the mass of the object.

Numerically,
:<math>r=1.5 \times 10^{-27}\ m</math>
in meters and kilograms.

This is a concept of gravity, under [[General Relativity]]. For any normal object, from things one would see on Earth up to stars that are not extremely massive or dense (much more massive or dense than the Sun), the Schwarzschild radius is very tiny relative to the object. This means that the object does not lie inside that radius, and cannot be a black hole. For example, the Schwarzschild radius of the Earth is about one centimeter, and that of the Sun is about three kilometers. The Earth could only become a black hole if it were compressed into a radius of one centimeter.

What makes the Schwarzschild radius significant is that the behavior of gravity, under General Relativity, is determined by the Schwarzschild metric, and is (not surprisingly) nearly identical to the behavior given by Newton's law of gravity. The difference only shows up at distances at or near the Schwarzschild radius. If the Earth were compressed to a radius of one centimeter or less, the behavior of gravity would become radically different as one approached that distance. Normal world-lines would cease to be "time-like", and such world-lines would be unable to make progress from inside the Schwarzschild radius to outside of it. This is a rather paradoxical situation when viewed in the way we normally view the way the universe works. In short, no object, and no light, can actually pass from inside the radius to outside. The surface at this radius is called the '''event horizon'''.

The concept of the Schwarzschild radius was worked out by Karl Schwarzschild in 1916, as part of his solution (the first solution ever worked out) of Einstein's field equation for General Relativity. At first, neither Einstein nor Schwarzschild believed that something could be so dense that these objects could exist.

==Pre-history==
The notion of something that has gravity so strong that light can't escape actually dates back to the 18th century, when scientists became aware of the finite speed of light and the concept of escape velocity. The [[corpuscular theory of light]] held that light was made up of invisibly small particles, and that these particles moved along ballistic trajectories, like tiny bullets. In this framework, it was believed possible that a distant star could be so massive that light emitted from its surface would be dragged back down again. This theory was first advanced by John Michell, who wrote in 1783, "If the semi-diameter of a sphere of the same density as the Sun in the proportion of five hundred to one, and by supposing light to be attracted by the same force in proportion to its [[Mass (science)|mass]] with other bodies, all light emitted from such a body would be made to return towards it, by its own proper gravity."<ref name="r1">http://www.aps.org/publications/apsnews/200911/physicshistory.cfm</ref>

Suggesting the same possibility independently, Pierre-Simon Laplace wrote in 1796, "It is therefore possible that the greatest luminous bodies in the universe are on this account invisible."<ref name="r1" />

This appeared to depend on the corpuscular theory of light, which gave way to the [[wave theory of light]] in the early 19th century, so the idea of "dark" or "invisible" stars fell from favor. It was believed that light, being a wave and having no mass, might be unaffected by gravity. Research into [[quantum mechanics]], however, reignited interest in the light-as-particles view, ultimately resulting in the modern notion of [[wave-particle duality]]. Under this theory, light could be affected by gravity, so the question of whether light could be emitted from extraordinarily massive bodies was once again open.

But the wave-versus-particle nature of light turned out to be a [[red herring]]. Under the "equivalence principle", it is known that anything, wave, particle, or whatever, that can be construed to have a trajectory, will have that trajectory bent by a gravitational field.

But none of this mattered at the time. A star (or other body) large enough to show this effect was utterly inconceivable. A sphere of Uranium at its normal density would have to weigh 10 million times the mass of the Sun, and be as large as the Earth's orbit, to lie inside its Schwarzschild radius. (Though such a large block of Uranium would not have its normal density.)

And the term "black hole" was unheard-of.

==20th century history==
By the mid-20th century, the physics of stellar dynamics and quantum mechanics had advanced to the point that it was possible to conceive of incredibly dense objects. Stars such as the Sun are actually "inflated" to their current size by the radiation pressure from the fusion reactions going on within them. When stars have consumed all their fuel, that pressure stops, and the material collapses to a much smaller size. The normal interatomic spacing, with electrons orbiting the nuclei, no longer applies. A variety of things can occur, including the electrons combining with the protons to make a "neutron star". Various phenomena were formulated, such as neutron stars, supernovas, pulsars, and magnetars. Before long these objects were actually observed. (Pulsars were observed before the theory had been worked out, and supernovas had been observed since antiquity.)

Stellar evolution and dynamics are quite complicated. Once a star has burned up all its Hydrogen, it may, depending on its size, burn Helium, and then heavier elements, all the way up to Iron. (Iron is the most stable nucleus; fission or fusion of Iron nuclei is not energetically favored.) As the material becomes more compressed, it is held up by the "electron degeneracy pressure" instead of the normal radiation pressure. The normal atomic structure, with orbiting electrons, is replaced by a collection of nuclei and unbound electrons, obeying the rules of quantum mechanics, particularly the Pauli exclusion principle. This pressure generally stops further collapse, leading to a [[white dwarf]]. White dwarfs may continue accreting matter from nearby objects. If the mass is over the "Chandrasekhar limit" of 1.4 solar masses, the gravitational force is too strong even for the degeneracy pressure, and the star becomes a supernova, neutron star, or black hole. The theory of this gravitational collapse was worked out in the 1930's.

If the mass is greater than the Tolman-Oppenheimer-Volkoff limit of about 1.5 solar masses, the neutron star becomes a black hole.

The properties of these objects (the "event horizon", and matter and information may only pass through the event horizon in one direction) were worked out in the 1950's. The exact solutions to Einstein's equation were worked out in the 1960's for rotating black holes (the Kerr solution), electrically charged black holes (the Reissner-Nordström solution), or both (the Kerr-Newman solution). Various theorems relating to thermodynamics were worked out by Stephen Hawking in the 1970's.

The term "black hole" was coined by John Wheeler in 1967. The term caught on very quickly in both the scientific community and the public at large, helped by the catchy nature of the phrase. Because of the remarkable nature of black holes, the concept quickly became a staple of science fiction stories, "popular" science magazines, television shows, and movies such as ''Event Horizon'' (1997), ''The Black Hole'' (TV, 2006), and ''Interstellar'' (2014). The latter movie put a lot of effort into making the visual depiction of the black hole scientifically accurate.

This was all theoretical at the time. There was no evidence that a black hole actually existed until the early 1970's, when scientists began to suspect that the radio source "Cygnus X1" was an actual black hole, and the 1990's, when scientists began to suspect that there was a black hole near the radio source "Sagittarius A*" at the center of our galaxy. (The name is pronounced with the word "star".) Since then evidence has accumulated that enormous black holes lie at the center of many galaxies.

==Methods of Observation==
Black holes are literally invisible by traditional means of observation (that is, emission or reflection of some sort of radiation) and so cannot be directly observed, their nature is determined by other means. The evidence that a black hole provides is its extraordinarily strong gravity, which can be deduced from its effect on the motions of nearby stars.
<ref name="Gillessen">{{cite journal
|last1=Gillessen |first1=S.
|last2=Eisenhauer |first2=F.
|last3=Trippe |first3=S.
|last4=Alexander |first4=T.
|last5=Genzel |first5=R.
|last6=Martins |first6=F.
|last7=Ott |first7=T.
|display-authors=3
|title=Monitoring Stellar Orbits around the Massive Black Hole in the Galactic Center
|journal=The Astrophysical Journal
|volume=692
|issue=2|page=1075|date=2009
|doi=10.1088/0004-637X/692/2/1075
|arxiv=0810.4674
|bibcode=2009ApJ...692.1075G
|ref=harv
}}</ref> Since 1995, astronomers have tracked the motions of 90 stars orbiting an invisible object coincident with the radio source in the center of our galaxy, Milky way. The astronomers were able to infer that a 2.6 million sollar mass object must be contained within the radius of 0.02 [[light-year]]s to cause the motions of those stars.<ref name="Ghez1998">{{cite journal
|last1=Ghez |first1=A. M.
|last2=Klein |first2=B. L.
|last3=Morris |first3=M.
|last4=Becklin |first4=E. E.
|display-authors=3
|title=High Proper‐Motion Stars in the Vicinity of Sagittarius A*: Evidence for a Supermassive Black Hole at the Center of Our Galaxy
|journal=The Astrophysical Journal
|volume=509
|issue=2|page=678|date=1998
|doi=10.1086/306528
|arxiv=astro-ph/9807210 |bibcode=1998ApJ...509..678G
|ref=harv
}}</ref>

Colliding black holes should produce gravitational waves, possible to detect experimentally. On 24 September 2015 the [[LIGO]] observatory made the first-ever successful observation of such event. <ref name="PRL-20160211">{{cite journal |author=Abbott, B.P. |title=Observation of Gravitational Waves from a Binary Black Hole Merger |url=http://journals.aps.org/prl/abstract/10.1103/PhysRevLett.116.061102 |journal=[[Phys. Rev. Lett.]] |volume=116 |pages=061102 |year=2016 |doi=10.1103/PhysRevLett.116.061102 |display-authors=etal|arxiv = 1602.03837 |bibcode = 2016PhRvL.116f1102A }}</ref><ref name="NYT-20160211-db">{{cite news |last=Overbye |first=Dennis |authorlink=Dennis Overbye |title=Physicists Detect Gravitational Waves, Proving Einstein Right |url=http://www.nytimes.com/2016/02/12/science/ligo-gravitational-waves-black-holes-einstein.html |date=11 February 2016 |work=[[New York Times]] |accessdate=11 February 2016 }}</ref> The signal was consistent with theoretical predictions. The gravitational wave signal suggests that the separation of the two holes prior to merger was just 350 km, hence they must be small in size, leaving black holes as the most plausible interpretation.

While matter and energy, even light, may not escape a black hole, Stephen Hawking has shown that when described by quantum mechanics, they should emit [[Hawking radiation]], which absent of an influx of mass-energy would lead to the evaporation of the black hole in a burst of gamma rays. This radiation may be possible to observe. However all results obtained to date remain unverified and debatable.<ref name="Milanoguys">{{cite journal|title=Hawking radiation from ultrashort laser pulse filaments |first1=F. |last1=Belgiorno |first2=S. L. |last2=Cacciatori |first3=M. |last3=Clerici |first4=V. |last4=Gorini |first5=G. |last5=Ortenzi |first6=L. |last6=Rizzi |first7=E. |last7=Rubino |first8=V. G. |last8=Sala |first9=D. |last9=Faccio |arxiv=1009.4634 |doi=10.1103/PhysRevLett.105.203901 |date=2010 |journal=Phys. Rev. Lett. |volume=105 |page=203901}}</ref><ref>{{cite news|title=Ultrafast Laser Pulse Makes Desktop Black Hole Glow|newspaper=[[Wired (magazine)|Wired]]|date=September 29, 2010|first=Lisa|last=Grossman|url=http://www.wired.com/wiredscience/2010/09/hawking-radiation-in-the-lab/|accessdate=April 30, 2012}}</ref>

==History of the idea==

===General Relativity===
As it happened, the question became unavoidable shortly after the publication in 1915 of Einstein's [[general theory of relativity]]. [[Karl Schwarzschild]] solved the Einstein field equations in a way that describes the geometry of spacetime outside a spherically symmetric, uncharged, non-rotating distribution of mass. Well away from the center of this distribution of mass, the Schwarzschild solution closely matches the Newtonian model of a gravitational field; only close to the mass, where the curvature of spacetime is large, do significant differences between the two models appear. But if the diameter of the mass distribution is taken to be arbitrarily small, then the region of spacetime immediately surrounding the mass appears to take on extremely curious properties, properties so curious that many questioned whether they had any physical interpretation at all. Therefore, Schwarzschild showed that black holes were possible under the theory of [[general relativity]].

[[File:Cygnusx1.jpg|right|200px|thumb|Jet-powered nebula formed from the accretion disk of the binary star Cygnus-X1]]
However, neither Schwarzschild himself nor [[Albert Einstein]], who developed the theory of relativity, believed that black holes actually existed.<ref name="amazing-space.stsci.edu">http://amazing-space.stsci.edu/resources/explorations/blackholes/lesson/whatisit/history.html</ref> Einstein even tried to re-work general relativity to render these [[Singularity|singularities]] impossible. However, Roger Penrose and Stephen Hawking proved the first of many Singularity Theorems, which states that singularities must form if certain conditions are present. This demonstrated that, rather than mathematical oddities, singularities are a fairly generic consequence of realistic solutions to relativity: any mass with radius less than its Schwarzschild radius is a black hole. Since then, support for black holes among the scientific community has grown.

==Nature of a Black Hole==
===Mathematics===

There are several solutions of the Einstein field equations that are used to model black holes. The simplest of these is the Schwarzchild metric. From this metric, one can calculate the Schwarzschild radius, which defines the boundary (event horizon) of the black hole, to be
:<math>r_s=\frac{2GM}{c^2}</math>,
where
* rs is the Schwarzschild radius;
* G is the gravitational constant;
* M is the mass of the gravitating object;
* c is the speed of light in vacuum.

If the black hole has a nonzero electric charge, it is modeled by the Reissner-Nordström metric. Astronomical objects are generally electrically neutral, since otherwise they would attracted charged particles of opposite sign and quickly become neutral. Therefore, the Reissner-Nordström metric is largely of theoretical interest.

A far more realistic situation occurs when the black hole is spinning (i.e. has nonzero angular momentum). Then the Schwarzschild solution is insufficient (as it was for the charged case), and instead one turns to the Kerr metric. Since astrophysical black holes are generically believed to have angular momentum, this is the solution that best describes them. Among the more interesting consequences of the Kerr metric is the phenomenon of frame dragging, in which the rotating black hole literally pulls nearby spacetime along with it.

If one wishes to consider a black hole that is both charged and spinning, one employs the Kerr-Newman metric, which combines the Reissner-Nordström and Kerr metrics. Since the no-hair theorem states that (non-quantum) black holes are unique up to mass, charge, and angular momentum, the Kerr-Newman metric is sufficient to describe any classical black hole.

===Time and Distance===
Within a certain distance from an arbitrarily small distribution of mass — a distance now known as the [[Schwarzschild radius]] — the curvature of spacetime becomes so great that no paths leading away from the mass exist. That is to say, a test particle released inside the Schwarzschild radius will inevitably move in toward the mass, not because the force of gravity is great as in the Newtonian approximation, but because spacetime is curved to such an extent that ''no other directions exist.'' A particle within the Schwarzschild radius can no more move further from the central mass than it can go backwards in time. In fact, from the frame of reference of an infalling observer beyond the Schwarzschild radius, all directions that once pointed away from the central mass now point backwards in time. Once inside the Schwarzschild radius, further motion toward the central mass is as inevitable as further motion through time is for any other observer.

For some time after the publication of the Schwarzschild solution, the validity of these results was hotly debated. In the solution's original coordinate frame, some terms in the equations ''diverged,'' or became infinite, at the Schwarzschild radius, leading physicists to wonder whether the results of the equations in that region had any valid physical interpretation. One proposed interpretation was that at the Schwarzschild radius, all time for the infalling observer would stop. This led to the use of the term "frozen stars;" it wasn't believed frozen stars were cold, but rather that they were literally frozen in time.

Later refinement of the Schwarzschild solution demonstrated that the apparent infinities were merely an artifact of the coordinate frame chosen, and that an infalling observer in fact can pass beyond the Schwarzchild radius. In fact, the equations predicted he would notice no effects when doing so. But any attempt on the part of that infalling observer to communicate with the outside universe, say by sending a radio message, would be doomed to failure, as the radio waves would traverse geodesics through the severely curved spacetime and end up bent toward the central mass. From this, we can say that nothing that occurs within the Schwarzschild radius can ever affect events outside the Schwarzschild radius. This gives the Schwarzschild radius of a non-rotating black hole its other name: the [[event horizon]].

===Inside the Event Horizon===
What actually exists inside the event horizon of a black hole is a question physics is unable to answer. Some postulate that within the event horizon exists a point of zero (or nearly zero) volume but infinite energy density, a point sometimes referred to as a ''gravitational singularity,'' after the notion of a mathematical singularity (a term referring to a point in an equation at which one would have to solve by dividing by zero, a feat presently impossible in mathematics) in a field equation. Others suspect that infinite energy density is a physical impossibility, and that a black hole contains actual finitely-dense matter compressed into a [[degenerate matter|degenerate]] form, such as quark-degenerate matter. Since all black holes are surrounded by an event horizon which prevents any information or messages from leaving, all these theories are non-[[falsifiable]]; we can never be sure what the interior structure of a black hole is like.

===Properties of Black Holes===

Black holes described with classical mechanics only have three intrinsic properties by which one differs from another: mass, electric charge, and angular momentum. Mass describes the amount of matter inside the event horizon. Angular momentum refers to whether the black hole is stationary or rotating around an axis. While the singularity of a non-rotating black hole may be an infinitely small point, the singularity of a rotating black hole would be in the shape of an infinitely thin ring. Quantum mechanics, which postulates that information loss cannot occur in a black hole, suggests properties beyond the three suggested by classical physics. Using this description, information must also be emitted by black holes. This radiation, referred to as Hawking Radiation, is thermal radiation that has currently only been described mathematically.

Although radiation from inside the event horizon has not yet been observed, there is much phenomenon that occurs outside the horizon due to the black hole. Matter entering a spinning black hole is first swirled around by the black hole’s gravity, causing it to heat up and emit x-rays, which can be used to detect the black hole. In the supermassive black holes at the centers of galaxies, some of the matter does not fall into the black hole. Instead it is blasted into space in twin jets of hot gas perpendicular to the accretion disc, in a phenomenon known as an Active Galactic Nucleus.

==Origins of Black Holes==
[[Image:Hs-2005-02-e-web.jpg|right|thumb|300px|The [[red supergiant]] star V838 Monocerotis, an example of one type of star which may become a black hole.]]
Stellar-mass black holes are said to form when stars more than ten times the mass of the Sun run out of fuel and die. The process of death occurs when stars that have fused the products of their own fusion into larger and larger elements, up to iron. The star then tries to fuse the iron core that forms as a result, but this does not produce enough energy to hold the outer layers of the star apart against the pull of gravity. When this happens, the iron core at the center of the star implodes in a supernova, and the outer layers of the star are blasted into space in one of the most energetic events in the universe—one star going out in a supernova can give off as much light as an entire galaxy. Not all supernovae result in black holes, but if the mass of the core is large enough, about 1.5-3.0 times the mass of the Sun (this value is termed the Tolman-Oppenheimer-Volkoff limit, and its value is not yet known to great precision), the leftover gravity of the shrinking core stalls the outward rush of the initial blast, and crushes the core into a point of infinite density: a black hole.

Extremely small black holes, with masses of around 1015 grams, have been theorized to have formed in the early universe. Any sufficiently small primordial black hole would be expected to evaporate within the lifetime of the universe, but the rate of evaporation is not currently known with any certainty.

At the opposite end of the spectrum, objects with the characteristics of supermassive black holes, millions or billions of times more massive than the sun, have been detected at the centers of many [[galaxies]], including our own [[Milky Way]]. In our galaxy, the hypothesized supermassive black hole is in the constellation Sagittarius, and is known as Sagittarius A* (pronounced "A star"). Based on the extraordinary angular velocity of stars near the galactic center, Sagittarius A* is believed to be on the order of two to three million solar masses. It is unknown how supermassive black holes form, though several models have been proposed. One hypothesis simply begins with a black hole of stellar mass which grows over the lifetime of the galaxy that surrounds it. Another proposal describes supermassive black holes as a natural, in fact nearly unavoidable, consequence of galactic formation. To date, no one theory of supermassive black hole formation is favored over all others.

Physicists trying to understand the theory of black hole formation have once again hit a dead end.<ref>http://www.fromquarkstoquasars.com/new-research-mathematically-proves-quantum-effects-stop-formation-black-holes/</ref>

==Speculative Future Exploration==

Scientists have speculated that if a rotating black hole is large enough, a person could pass through the center of the ring-shaped singularity and possibly enter a wormhole. However, it would have to be a very large hole, for if it were not, the hypothetical astronaut would never survive to reach the event horizon due to tidal forces.

Matter coming close to the event horizon of a small black hole undergoes a process called spaghettification, a term coined by Stephen Hawking in his book ''A Brief History of Time'' to describe extraordinarily strong tidal forces. Because the mass at the center of the black hole is so dense, the gravitational pull on the near end of an object is much greater than the pull on the object’s far end. This causes the object to be stretched out in a way resembling a piece of spaghetti, and generally torn in two.

==White Holes==
Because the [[Quantitative Introduction to General Relativity|general relativity equations]] are symmetric with respect to time, one can reverse the time parameter to yield an equation describing a hypothetical object which expels, rather than attracts, matter and energy.<ref>http://cosmology.berkeley.edu/Education/BHfaq.html#q10</ref> As this is the exact opposite of a black hole, it is called a '''white hole'''.

However, there is no evidence white holes actually exist. If they generate new matter and energy, this would violate the [[Law of the conservation of mass]]. Therefore, some scientists have proposed that matter falling into black holes goes through a [[wormhole]] to emerge at a white hole. While such wormholes are allowed by general relativity, they would be extremely unstable,<ref>http://casa.colorado.edu/~ajsh/schww.html</ref> and there is no evidence that they exist.

Scientists, who have been extremely eager to promote the idea of black hole existence, have shown a strong aversion to the white hole theory, even though, like a white hole, a black hole has never been observed directly. This may reflect an anti-creation bias on the part of scientists who are uncomfortable with the idea that matter and energy can be created outside of what scientific theories dictate should happen.

Fundamentalists and creationists have used white holes to attempt to solve the cosmic time problem. Dr. [[Russell Humphreys]] used a white hole in his model of the universe during [[Creation week]] to allow millions of years to pass in outer space while only three days passed on Earth.

==In Popular Culture==
Black holes are increasingly promoted by [[liberal]] publications, such as the science page of the ''[[New York Times]]'', glossy magazines, and the movies the ''Event Horizon'' (1997), ''The Black Hole'' (TV, 2006), and ''Interstellar'' (2014). They are sometimes seen as a [[sacred cow]]s of [[atheistic science]], while proving of they actual existence would not provide any obvious proof for atheism assumptions.

Black holes have been a device in science fiction ever since their prediction. Many sci-fi books, movies, and television shows use black holes as a method of travel (see the Potential Future Exploration section above) or as a threat to a space-going vessel. In at least one season of the show ''Star Trek: the Next Generation'' by Gene Roddenberry, artificially created miniature black holes are used as power sources for spaceships and natural ones as incubators for the young of an alien race. Neither of these uses has much of a basis in reality, of course.

Contrary to popular myth, a black hole is not a cosmic vacuum cleaner. In other words, a one-solar-mass black hole is no better than any other one-solar-mass object (such as, for example, the Sun) at "sucking in" distant objects. However, a one-solar-mass black hole has the same amount of matter as any other one-solar-mass object but compressed into a much smaller space, making it impossible to move fast enough to leave a black hole once there. If a spaceship could land on a black hole, it would never be able to take off again.

The term "black hole" is also used as a metaphor for a place that it is hard to get out of, generally containing a high concentration of something unpleasant. Ex: "The inner city is a black hole of crime and drug use." The "Black Hole of Calcutta" long predates the celestial use of the term; it was a horrible underground prison in [[Calcutta]], India.

==See also==
*[[Black hole firewall]]
==References==
{{reflist}}
==External links==
*[http://imagine.gsfc.nasa.gov/docs/science/know_l2/black_holes.html Black Holes]
*[http://cosmology.berkeley.edu/Education/BHfaq.html Black Holes (Frequently Asked Questions)]

{{Relativity}}
[[Category:Physics]]
[[Category:Relativity]]

Black hole

2016-10-16T17:52:23Z

H22: Restored the reference that appears to be used elsewhere.

[[Image:Iu8969hu.jpg|right|thumb|300px|Artist's conception of a binary system consisting of a black hole (upper left) and a main sequence star (lower right). The black hole is drawing matter from the star via an ''accretion disk'' (blue) around it, and some of this matter forms a gas jet (also blue).]]
A '''black hole''' is any object that lies entirely inside its own Schwarzschild radius, given by
:<math>r=\frac{2G}{c^2}\ m</math>
where
*G is Newton's gravitational constant;
*c is the speed of light;
*m is the mass of the object.

Numerically,
:<math>r=1.5 \times 10^{-27}\ m</math>
in meters and kilograms.

This is a concept of gravity, under [[General Relativity]]. For any normal object, from things one would see on Earth up to stars that are not extremely massive or dense (much more massive or dense than the Sun), the Schwarzschild radius is very tiny relative to the object. This means that the object does not lie inside that radius, and cannot be a black hole. For example, the Schwarzschild radius of the Earth is about one centimeter, and that of the Sun is about three kilometers. The Earth could only become a black hole if it were compressed into a radius of one centimeter.

What makes the Schwarzschild radius significant is that the behavior of gravity, under General Relativity, is determined by the Schwarzschild metric, and is (not surprisingly) nearly identical to the behavior given by Newton's law of gravity. The difference only shows up at distances at or near the Schwarzschild radius. If the Earth were compressed to a radius of one centimeter or less, the behavior of gravity would become radically different as one approached that distance. Normal world-lines would cease to be "time-like", and such world-lines would be unable to make progress from inside the Schwarzschild radius to outside of it. This is a rather paradoxical situation when viewed in the way we normally view the way the universe works. In short, no object, and no light, can actually pass from inside the radius to outside. The surface at this radius is called the '''event horizon'''.

The concept of the Schwarzschild radius was worked out by Karl Schwarzschild in 1916, as part of his solution (the first solution ever worked out) of Einstein's field equation for General Relativity. At first, neither Einstein nor Schwarzschild believed that something could be so dense that these objects could exist.

==Pre-history==
The notion of something that has gravity so strong that light can't escape actually dates back to the 18th century, when scientists became aware of the finite speed of light and the concept of escape velocity. The [[corpuscular theory of light]] held that light was made up of invisibly small particles, and that these particles moved along ballistic trajectories, like tiny bullets. In this framework, it was believed possible that a distant star could be so massive that light emitted from its surface would be dragged back down again. This theory was first advanced by John Michell, who wrote in 1783, "If the semi-diameter of a sphere of the same density as the Sun in the proportion of five hundred to one, and by supposing light to be attracted by the same force in proportion to its [[Mass (science)|mass]] with other bodies, all light emitted from such a body would be made to return towards it, by its own proper gravity."<ref name="r1">http://www.aps.org/publications/apsnews/200911/physicshistory.cfm</ref>

Suggesting the same possibility independently, Pierre-Simon Laplace wrote in 1796, "It is therefore possible that the greatest luminous bodies in the universe are on this account invisible."<ref name="r1" />

This appeared to depend on the corpuscular theory of light, which gave way to the [[wave theory of light]] in the early 19th century, so the idea of "dark" or "invisible" stars fell from favor. It was believed that light, being a wave and having no mass, might be unaffected by gravity. Research into [[quantum mechanics]], however, reignited interest in the light-as-particles view, ultimately resulting in the modern notion of [[wave-particle duality]]. Under this theory, light could be affected by gravity, so the question of whether light could be emitted from extraordinarily massive bodies was once again open.

But the wave-versus-particle nature of light turned out to be a [[red herring]]. Under the "equivalence principle", it is known that anything, wave, particle, or whatever, that can be construed to have a trajectory, will have that trajectory bent by a gravitational field.

But none of this mattered at the time. A star (or other body) large enough to show this effect was utterly inconceivable. A sphere of Uranium at its normal density would have to weigh 10 million times the mass of the Sun, and be as large as the Earth's orbit, to lie inside its Schwarzschild radius. (Though such a large block of Uranium would not have its normal density.)

And the term "black hole" was unheard-of.

==20th century history==
By the mid-20th century, the physics of stellar dynamics and quantum mechanics had advanced to the point that it was possible to conceive of incredibly dense objects. Stars such as the Sun are actually "inflated" to their current size by the radiation pressure from the fusion reactions going on within them. When stars have consumed all their fuel, that pressure stops, and the material collapses to a much smaller size. The normal interatomic spacing, with electrons orbiting the nuclei, no longer applies. A variety of things can occur, including the electrons combining with the protons to make a "neutron star". Various phenomena were formulated, such as neutron stars, supernovas, pulsars, and magnetars. Before long these objects were actually observed. (Pulsars were observed before the theory had been worked out, and supernovas had been observed since antiquity.)

Stellar evolution and dynamics are quite complicated. Once a star has burned up all its Hydrogen, it may, depending on its size, burn Helium, and then heavier elements, all the way up to Iron. (Iron is the most stable nucleus; fission or fusion of Iron nuclei is not energetically favored.) As the material becomes more compressed, it is held up by the "electron degeneracy pressure" instead of the normal radiation pressure. The normal atomic structure, with orbiting electrons, is replaced by a collection of nuclei and unbound electrons, obeying the rules of quantum mechanics, particularly the Pauli exclusion principle. This pressure generally stops further collapse, leading to a [[white dwarf]]. White dwarfs may continue accreting matter from nearby objects. If the mass is over the "Chandrasekhar limit" of 1.4 solar masses, the gravitational force is too strong even for the degeneracy pressure, and the star becomes a supernova, neutron star, or black hole. The theory of this gravitational collapse was worked out in the 1930's.

If the mass is greater than the Tolman-Oppenheimer-Volkoff limit of about 1.5 solar masses, the neutron star becomes a black hole.

The properties of these objects (the "event horizon", and matter and information may only pass through the event horizon in one direction) were worked out in the 1950's. The exact solutions to Einstein's equation were worked out in the 1960's for rotating black holes (the Kerr solution), electrically charged black holes (the Reissner-Nordström solution), or both (the Kerr-Newman solution). Various theorems relating to thermodynamics were worked out by Stephen Hawking in the 1970's.

The term "black hole" was coined by John Wheeler in 1967. The term caught on very quickly in both the scientific community and the public at large, helped by the catchy nature of the phrase. Because of the remarkable nature of black holes, the concept quickly became a staple of science fiction stories, "popular" science magazines, television shows, and movies such as ''Event Horizon'' (1997), ''The Black Hole'' (TV, 2006), and ''Interstellar'' (2014). The latter movie put a lot of effort into making the visual depiction of the black hole scientifically accurate.

This was all theoretical at the time. There was no evidence that a black hole actually existed until the early 1970's, when scientists began to suspect that the radio source "Cygnus X1" was an actual black hole, and the 1990's, when scientists began to suspect that there was a black hole near the radio source "Sagittarius A*" at the center of our galaxy. (The name is pronounced with the word "star".) Since then evidence has accumulated that enormous black holes lie at the center of many galaxies.

==Methods of Observation==
Black holes are literally invisible by traditional means of observation (that is, emission or reflection of some sort of radiation) and so cannot be directly observed, their nature is determined by other means. The evidence that a black hole provides is its extraordinarily strong gravity, which can be deduced from its effect on the motions of nearby stars.
<ref name="Gillessen">{{cite journal
|last1=Gillessen |first1=S.
|last2=Eisenhauer |first2=F.
|last3=Trippe |first3=S.
|last4=Alexander |first4=T.
|last5=Genzel |first5=R.
|last6=Martins |first6=F.
|last7=Ott |first7=T.
|display-authors=3
|title=Monitoring Stellar Orbits around the Massive Black Hole in the Galactic Center
|journal=The Astrophysical Journal
|volume=692
|issue=2|page=1075|date=2009
|doi=10.1088/0004-637X/692/2/1075
|arxiv=0810.4674
|bibcode=2009ApJ...692.1075G
|ref=harv
}}</ref> Since 1995, astronomers have tracked the motions of 90 stars orbiting an invisible object coincident with the radio source in the center of our galaxy, Milky way. The astronomers were able to infer that a 2.6 million sollar mass object must be contained within the radius of 0.02 [[light-year]]s to cause the motions of those stars.<ref name="Ghez1998">{{cite journal
|last1=Ghez |first1=A. M.
|last2=Klein |first2=B. L.
|last3=Morris |first3=M.
|last4=Becklin |first4=E. E.
|display-authors=3
|title=High Proper‐Motion Stars in the Vicinity of Sagittarius A*: Evidence for a Supermassive Black Hole at the Center of Our Galaxy
|journal=The Astrophysical Journal
|volume=509
|issue=2|page=678|date=1998
|doi=10.1086/306528
|arxiv=astro-ph/9807210 |bibcode=1998ApJ...509..678G
|ref=harv
}}</ref>

Colliding black holes should produce gravitational waves, possible to detect experimentally. On 24 September 2015 the [[LIGO]] observatory made the first-ever successful observation of such event. <ref name="PRL-20160211">{{cite journal |author=Abbott, B.P. |title=Observation of Gravitational Waves from a Binary Black Hole Merger |url=http://journals.aps.org/prl/abstract/10.1103/PhysRevLett.116.061102 |journal=[[Phys. Rev. Lett.]] |volume=116 |pages=061102 |year=2016 |doi=10.1103/PhysRevLett.116.061102 |display-authors=etal|arxiv = 1602.03837 |bibcode = 2016PhRvL.116f1102A }}</ref><ref name="NYT-20160211-db">{{cite news |last=Overbye |first=Dennis |authorlink=Dennis Overbye |title=Physicists Detect Gravitational Waves, Proving Einstein Right |url=http://www.nytimes.com/2016/02/12/science/ligo-gravitational-waves-black-holes-einstein.html |date=11 February 2016 |work=[[New York Times]] |accessdate=11 February 2016 }}</ref> The signal was consistent with theoretical predictions. The gravitational wave signal suggests that the separation of the two holes prior to merger was just 350 km, hence they must be small in size, leaving black holes as the most plausible interpretation.

While matter and energy, even light, may not escape a black hole, Stephen Hawking has shown that when described by quantum mechanics, they should emit [[Hawking radiation]], which absent of an influx of mass-energy would lead to the evaporation of the black hole in a burst of gamma rays. This radiation may be possible to observe. However all results obtained to date remain unverified and debatable.<ref name="Milanoguys">{{cite journal|title=Hawking radiation from ultrashort laser pulse filaments |first1=F. |last1=Belgiorno |first2=S. L. |last2=Cacciatori |first3=M. |last3=Clerici |first4=V. |last4=Gorini |first5=G. |last5=Ortenzi |first6=L. |last6=Rizzi |first7=E. |last7=Rubino |first8=V. G. |last8=Sala |first9=D. |last9=Faccio |arxiv=1009.4634 |doi=10.1103/PhysRevLett.105.203901 |date=2010 |journal=Phys. Rev. Lett. |volume=105 |page=203901}}</ref><ref>{{cite news|title=Ultrafast Laser Pulse Makes Desktop Black Hole Glow|newspaper=[[Wired (magazine)|Wired]]|date=September 29, 2010|first=Lisa|last=Grossman|url=http://www.wired.com/wiredscience/2010/09/hawking-radiation-in-the-lab/|accessdate=April 30, 2012}}</ref>

==History of the idea==

===General Relativity===
As it happened, the question became unavoidable shortly after the publication in 1915 of Einstein's [[general theory of relativity]]. [[Karl Schwarzschild]] solved the Einstein field equations in a way that describes the geometry of spacetime outside a spherically symmetric, uncharged, non-rotating distribution of mass. Well away from the center of this distribution of mass, the Schwarzschild solution closely matches the Newtonian model of a gravitational field; only close to the mass, where the curvature of spacetime is large, do significant differences between the two models appear. But if the diameter of the mass distribution is taken to be arbitrarily small, then the region of spacetime immediately surrounding the mass appears to take on extremely curious properties, properties so curious that many questioned whether they had any physical interpretation at all. Therefore, Schwarzschild showed that black holes were possible under the theory of [[general relativity]].

[[File:Cygnusx1.jpg|right|200px|thumb|Jet-powered nebula formed from the accretion disk of the binary star Cygnus-X1]]
However, neither Schwarzschild himself nor [[Albert Einstein]], who developed the theory of relativity, believed that black holes actually existed.<ref name="amazing-space.stsci.edu">http://amazing-space.stsci.edu/resources/explorations/blackholes/lesson/whatisit/history.html</ref> Einstein even tried to re-work general relativity to render these [[Singularity|singularities]] impossible. However, Roger Penrose and Stephen Hawking proved the first of many Singularity Theorems, which states that singularities must form if certain conditions are present. This demonstrated that, rather than mathematical oddities, singularities are a fairly generic consequence of realistic solutions to relativity: any mass with radius less than its Schwarzschild radius is a black hole. Since then, support for black holes among the scientific community has grown.

==Nature of a Black Hole==
===Mathematics===

There are several solutions of the Einstein field equations that are used to model black holes. The simplest of these is the Schwarzchild metric. From this metric, one can calculate the Schwarzschild radius, which defines the boundary (event horizon) of the black hole, to be
:<math>r_s=\frac{2GM}{c^2}</math>,
where
* rs is the Schwarzschild radius;
* G is the gravitational constant;
* M is the mass of the gravitating object;
* c is the speed of light in vacuum.

If the black hole has a nonzero electric charge, it is modeled by the Reissner-Nordström metric. Astronomical objects are generally electrically neutral, since otherwise they would attracted charged particles of opposite sign and quickly become neutral. Therefore, the Reissner-Nordström metric is largely of theoretical interest.

A far more realistic situation occurs when the black hole is spinning (i.e. has nonzero angular momentum). Then the Schwarzschild solution is insufficient (as it was for the charged case), and instead one turns to the Kerr metric. Since astrophysical black holes are generically believed to have angular momentum, this is the solution that best describes them. Among the more interesting consequences of the Kerr metric is the phenomenon of frame dragging, in which the rotating black hole literally pulls nearby spacetime along with it.

If one wishes to consider a black hole that is both charged and spinning, one employs the Kerr-Newman metric, which combines the Reissner-Nordström and Kerr metrics. Since the no-hair theorem states that (non-quantum) black holes are unique up to mass, charge, and angular momentum, the Kerr-Newman metric is sufficient to describe any classical black hole.

===Time and Distance===
Within a certain distance from an arbitrarily small distribution of mass — a distance now known as the [[Schwarzschild radius]] — the curvature of spacetime becomes so great that no paths leading away from the mass exist. That is to say, a test particle released inside the Schwarzschild radius will inevitably move in toward the mass, not because the force of gravity is great as in the Newtonian approximation, but because spacetime is curved to such an extent that ''no other directions exist.'' A particle within the Schwarzschild radius can no more move further from the central mass than it can go backwards in time. In fact, from the frame of reference of an infalling observer beyond the Schwarzschild radius, all directions that once pointed away from the central mass now point backwards in time. Once inside the Schwarzschild radius, further motion toward the central mass is as inevitable as further motion through time is for any other observer.

For some time after the publication of the Schwarzschild solution, the validity of these results was hotly debated. In the solution's original coordinate frame, some terms in the equations ''diverged,'' or became infinite, at the Schwarzschild radius, leading physicists to wonder whether the results of the equations in that region had any valid physical interpretation. One proposed interpretation was that at the Schwarzschild radius, all time for the infalling observer would stop. This led to the use of the term "frozen stars;" it wasn't believed frozen stars were cold, but rather that they were literally frozen in time.

Later refinement of the Schwarzschild solution demonstrated that the apparent infinities were merely an artifact of the coordinate frame chosen, and that an infalling observer in fact can pass beyond the Schwarzchild radius. In fact, the equations predicted he would notice no effects when doing so. But any attempt on the part of that infalling observer to communicate with the outside universe, say by sending a radio message, would be doomed to failure, as the radio waves would traverse geodesics through the severely curved spacetime and end up bent toward the central mass. From this, we can say that nothing that occurs within the Schwarzschild radius can ever affect events outside the Schwarzschild radius. This gives the Schwarzschild radius of a non-rotating black hole its other name: the [[event horizon]].

===Inside the Event Horizon===
What actually exists inside the event horizon of a black hole is a question physics is unable to answer. Some postulate that within the event horizon exists a point of zero (or nearly zero) volume but infinite energy density, a point sometimes referred to as a ''gravitational singularity,'' after the notion of a mathematical singularity (a term referring to a point in an equation at which one would have to solve by dividing by zero, a feat presently impossible in mathematics) in a field equation. Others suspect that infinite energy density is a physical impossibility, and that a black hole contains actual finitely-dense matter compressed into a [[degenerate matter|degenerate]] form, such as quark-degenerate matter. Since all black holes are surrounded by an event horizon which prevents any information or messages from leaving, all these theories are non-[[falsifiable]]; we can never be sure what the interior structure of a black hole is like.

===Properties of Black Holes===

Black holes described with classical mechanics only have three intrinsic properties by which one differs from another: mass, electric charge, and angular momentum. Mass describes the amount of matter inside the event horizon. Angular momentum refers to whether the black hole is stationary or rotating around an axis. While the singularity of a non-rotating black hole may be an infinitely small point, the singularity of a rotating black hole would be in the shape of an infinitely thin ring. Quantum mechanics, which postulates that information loss cannot occur in a black hole, suggests properties beyond the three suggested by classical physics. Using this description, information must also be emitted by black holes. This radiation, referred to as Hawking Radiation, is thermal radiation that has currently only been described mathematically.

Although radiation from inside the event horizon has not yet been observed, there is much phenomenon that occurs outside the horizon due to the black hole. Matter entering a spinning black hole is first swirled around by the black hole’s gravity, causing it to heat up and emit x-rays, which can be used to detect the black hole. In the supermassive black holes at the centers of galaxies, some of the matter does not fall into the black hole. Instead it is blasted into space in twin jets of hot gas perpendicular to the accretion disc, in a phenomenon known as an Active Galactic Nucleus.

==Origins of Black Holes==
[[Image:Hs-2005-02-e-web.jpg|right|thumb|300px|The [[red supergiant]] star V838 Monocerotis, an example of one type of star which may become a black hole.]]
Stellar-mass black holes are said to form when stars more than ten times the mass of the Sun run out of fuel and die. The process of death occurs when stars that have fused the products of their own fusion into larger and larger elements, up to iron. The star then tries to fuse the iron core that forms as a result, but this does not produce enough energy to hold the outer layers of the star apart against the pull of gravity. When this happens, the iron core at the center of the star implodes in a supernova, and the outer layers of the star are blasted into space in one of the most energetic events in the universe—one star going out in a supernova can give off as much light as an entire galaxy. Not all supernovae result in black holes, but if the mass of the core is large enough, about 1.5-3.0 times the mass of the Sun (this value is termed the Tolman-Oppenheimer-Volkoff limit, and its value is not yet known to great precision), the leftover gravity of the shrinking core stalls the outward rush of the initial blast, and crushes the core into a point of infinite density: a black hole.

Extremely small black holes, with masses of around 1015 grams, have been theorized to have formed in the early universe. Any sufficiently small primordial black hole would be expected to evaporate within the lifetime of the universe, but the rate of evaporation is not currently known with any certainty.

At the opposite end of the spectrum, objects with the characteristics of supermassive black holes, millions or billions of times more massive than the sun, have been detected at the centers of many [[galaxies]], including our own [[Milky Way]]. In our galaxy, the hypothesized supermassive black hole is in the constellation Sagittarius, and is known as Sagittarius A* (pronounced "A star"). Based on the extraordinary angular velocity of stars near the galactic center, Sagittarius A* is believed to be on the order of two to three million solar masses. It is unknown how supermassive black holes form, though several models have been proposed. One hypothesis simply begins with a black hole of stellar mass which grows over the lifetime of the galaxy that surrounds it. Another proposal describes supermassive black holes as a natural, in fact nearly unavoidable, consequence of galactic formation. To date, no one theory of supermassive black hole formation is favored over all others.

Physicists trying to understand the theory of black hole formation have once again hit a dead end.<ref>http://www.fromquarkstoquasars.com/new-research-mathematically-proves-quantum-effects-stop-formation-black-holes/</ref>

==Speculative Future Exploration==

Scientists have speculated that if a rotating black hole is large enough, a person could pass through the center of the ring-shaped singularity and possibly enter a wormhole. However, it would have to be a very large hole, for if it were not, the hypothetical astronaut would never survive to reach the event horizon due to tidal forces.

Matter coming close to the event horizon of a small black hole undergoes a process called spaghettification, a term coined by Stephen Hawking in his book ''A Brief History of Time'' to describe extraordinarily strong tidal forces. Because the mass at the center of the black hole is so dense, the gravitational pull on the near end of an object is much greater than the pull on the object’s far end. This causes the object to be stretched out in a way resembling a piece of spaghetti, and generally torn in two.

==White Holes==
Because the [[Quantitative Introduction to General Relativity|general relativity equations]] are symmetric with respect to time, one can reverse the time parameter to yield an equation describing a hypothetical object which expels, rather than attracts, matter and energy.<ref>http://cosmology.berkeley.edu/Education/BHfaq.html#q10</ref> As this is the exact opposite of a black hole, it is called a '''white hole'''.

However, there is no evidence white holes actually exist. If they generate new matter and energy, this would violate the [[Law of the conservation of mass]]. Therefore, some scientists have proposed that matter falling into black holes goes through a [[wormhole]] to emerge at a white hole. While such wormholes are allowed by general relativity, they would be extremely unstable,<ref>http://casa.colorado.edu/~ajsh/schww.html</ref> and there is no evidence that they exist.

Scientists, who have been extremely eager to promote the idea of black hole existence, have shown a strong aversion to the white hole theory, even though, like a white hole, a black hole has never been observed directly. This may reflect an anti-creation bias on the part of scientists who are uncomfortable with the idea that matter and energy can be created outside of what scientific theories dictate should happen.

Fundamentalists and creationists have used white holes to attempt to solve the cosmic time problem. Dr. [[Russell Humphreys]] used a white hole in his model of the universe during [[Creation week]] to allow millions of years to pass in outer space while only three days passed on Earth.

==In Popular Culture==
'''''Black holes are a [[sacred cow]] of [[atheistic science]]'''''.

Black holes are increasingly promoted by [[liberal]] publications, such as the science page of the ''[[New York Times]]'', glossy magazines, and the movies the ''Event Horizon'' (1997), ''The Black Hole'' (TV, 2006), and ''Interstellar'' (2014). They are sometimes seen as a [[sacred cow]]s of [[atheistic science]], while proving of they actual existence would not provide any obvious proof for atheism assumptions.

Black holes have been a device in science fiction ever since their prediction. Many sci-fi books, movies, and television shows use black holes as a method of travel (see the Potential Future Exploration section above) or as a threat to a space-going vessel. In at least one season of the show ''Star Trek: the Next Generation'' by Gene Roddenberry, artificially created miniature black holes are used as power sources for spaceships and natural ones as incubators for the young of an alien race. Neither of these uses has much of a basis in reality, of course.

Contrary to popular myth, a black hole is not a cosmic vacuum cleaner. In other words, a one-solar-mass black hole is no better than any other one-solar-mass object (such as, for example, the Sun) at "sucking in" distant objects. However, a one-solar-mass black hole has the same amount of matter as any other one-solar-mass object but compressed into a much smaller space, making it impossible to move fast enough to leave a black hole once there. If a spaceship could land on a black hole, it would never be able to take off again.

The term "black hole" is also used as a metaphor for a place that it is hard to get out of, generally containing a high concentration of something unpleasant. Ex: "The inner city is a black hole of crime and drug use." The "Black Hole of Calcutta" long predates the celestial use of the term; it was a horrible underground prison in [[Calcutta]], India.

==See also==
*[[Black hole firewall]]
==References==
{{reflist}}
==External links==
*[http://imagine.gsfc.nasa.gov/docs/science/know_l2/black_holes.html Black Holes]
*[http://cosmology.berkeley.edu/Education/BHfaq.html Black Holes (Frequently Asked Questions)]

{{Relativity}}
[[Category:Physics]]
[[Category:Relativity]]

Black hole

2016-10-16T17:48:52Z

H22: Moved popular culture part from observations to popular culture

[[Image:Iu8969hu.jpg|right|thumb|300px|Artist's conception of a binary system consisting of a black hole (upper left) and a main sequence star (lower right). The black hole is drawing matter from the star via an ''accretion disk'' (blue) around it, and some of this matter forms a gas jet (also blue).]]
A '''black hole''' is any object that lies entirely inside its own Schwarzschild radius, given by
:<math>r=\frac{2G}{c^2}\ m</math>
where
*G is Newton's gravitational constant;
*c is the speed of light;
*m is the mass of the object.

Numerically,
:<math>r=1.5 \times 10^{-27}\ m</math>
in meters and kilograms.

This is a concept of gravity, under [[General Relativity]]. For any normal object, from things one would see on Earth up to stars that are not extremely massive or dense (much more massive or dense than the Sun), the Schwarzschild radius is very tiny relative to the object. This means that the object does not lie inside that radius, and cannot be a black hole. For example, the Schwarzschild radius of the Earth is about one centimeter, and that of the Sun is about three kilometers. The Earth could only become a black hole if it were compressed into a radius of one centimeter.

What makes the Schwarzschild radius significant is that the behavior of gravity, under General Relativity, is determined by the Schwarzschild metric, and is (not surprisingly) nearly identical to the behavior given by Newton's law of gravity. The difference only shows up at distances at or near the Schwarzschild radius. If the Earth were compressed to a radius of one centimeter or less, the behavior of gravity would become radically different as one approached that distance. Normal world-lines would cease to be "time-like", and such world-lines would be unable to make progress from inside the Schwarzschild radius to outside of it. This is a rather paradoxical situation when viewed in the way we normally view the way the universe works. In short, no object, and no light, can actually pass from inside the radius to outside. The surface at this radius is called the '''event horizon'''.

The concept of the Schwarzschild radius was worked out by Karl Schwarzschild in 1916, as part of his solution (the first solution ever worked out) of Einstein's field equation for General Relativity. At first, neither Einstein nor Schwarzschild believed that something could be so dense that these objects could exist.

==Pre-history==
The notion of something that has gravity so strong that light can't escape actually dates back to the 18th century, when scientists became aware of the finite speed of light and the concept of escape velocity. The [[corpuscular theory of light]] held that light was made up of invisibly small particles, and that these particles moved along ballistic trajectories, like tiny bullets. In this framework, it was believed possible that a distant star could be so massive that light emitted from its surface would be dragged back down again. This theory was first advanced by John Michell, who wrote in 1783, "If the semi-diameter of a sphere of the same density as the Sun in the proportion of five hundred to one, and by supposing light to be attracted by the same force in proportion to its [[Mass (science)|mass]] with other bodies, all light emitted from such a body would be made to return towards it, by its own proper gravity."<ref name="r1">http://www.aps.org/publications/apsnews/200911/physicshistory.cfm</ref>

Suggesting the same possibility independently, Pierre-Simon Laplace wrote in 1796, "It is therefore possible that the greatest luminous bodies in the universe are on this account invisible."<ref name="r1" />

This appeared to depend on the corpuscular theory of light, which gave way to the [[wave theory of light]] in the early 19th century, so the idea of "dark" or "invisible" stars fell from favor. It was believed that light, being a wave and having no mass, might be unaffected by gravity. Research into [[quantum mechanics]], however, reignited interest in the light-as-particles view, ultimately resulting in the modern notion of [[wave-particle duality]]. Under this theory, light could be affected by gravity, so the question of whether light could be emitted from extraordinarily massive bodies was once again open.

But the wave-versus-particle nature of light turned out to be a [[red herring]]. Under the "equivalence principle", it is known that anything, wave, particle, or whatever, that can be construed to have a trajectory, will have that trajectory bent by a gravitational field.

But none of this mattered at the time. A star (or other body) large enough to show this effect was utterly inconceivable. A sphere of Uranium at its normal density would have to weigh 10 million times the mass of the Sun, and be as large as the Earth's orbit, to lie inside its Schwarzschild radius. (Though such a large block of Uranium would not have its normal density.)

And the term "black hole" was unheard-of.

==20th century history==
By the mid-20th century, the physics of stellar dynamics and quantum mechanics had advanced to the point that it was possible to conceive of incredibly dense objects. Stars such as the Sun are actually "inflated" to their current size by the radiation pressure from the fusion reactions going on within them. When stars have consumed all their fuel, that pressure stops, and the material collapses to a much smaller size. The normal interatomic spacing, with electrons orbiting the nuclei, no longer applies. A variety of things can occur, including the electrons combining with the protons to make a "neutron star". Various phenomena were formulated, such as neutron stars, supernovas, pulsars, and magnetars. Before long these objects were actually observed. (Pulsars were observed before the theory had been worked out, and supernovas had been observed since antiquity.)

Stellar evolution and dynamics are quite complicated. Once a star has burned up all its Hydrogen, it may, depending on its size, burn Helium, and then heavier elements, all the way up to Iron. (Iron is the most stable nucleus; fission or fusion of Iron nuclei is not energetically favored.) As the material becomes more compressed, it is held up by the "electron degeneracy pressure" instead of the normal radiation pressure. The normal atomic structure, with orbiting electrons, is replaced by a collection of nuclei and unbound electrons, obeying the rules of quantum mechanics, particularly the Pauli exclusion principle. This pressure generally stops further collapse, leading to a [[white dwarf]]. White dwarfs may continue accreting matter from nearby objects. If the mass is over the "Chandrasekhar limit" of 1.4 solar masses, the gravitational force is too strong even for the degeneracy pressure, and the star becomes a supernova, neutron star, or black hole. The theory of this gravitational collapse was worked out in the 1930's.

If the mass is greater than the Tolman-Oppenheimer-Volkoff limit of about 1.5 solar masses, the neutron star becomes a black hole.

The properties of these objects (the "event horizon", and matter and information may only pass through the event horizon in one direction) were worked out in the 1950's. The exact solutions to Einstein's equation were worked out in the 1960's for rotating black holes (the Kerr solution), electrically charged black holes (the Reissner-Nordström solution), or both (the Kerr-Newman solution). Various theorems relating to thermodynamics were worked out by Stephen Hawking in the 1970's.

The term "black hole" was coined by John Wheeler in 1967. The term caught on very quickly in both the scientific community and the public at large, helped by the catchy nature of the phrase. Because of the remarkable nature of black holes, the concept quickly became a staple of science fiction stories, "popular" science magazines, television shows, and movies such as ''Event Horizon'' (1997), ''The Black Hole'' (TV, 2006), and ''Interstellar'' (2014). The latter movie put a lot of effort into making the visual depiction of the black hole scientifically accurate.

This was all theoretical at the time. There was no evidence that a black hole actually existed until the early 1970's, when scientists began to suspect that the radio source "Cygnus X1" was an actual black hole, and the 1990's, when scientists began to suspect that there was a black hole near the radio source "Sagittarius A*" at the center of our galaxy. (The name is pronounced with the word "star".) Since then evidence has accumulated that enormous black holes lie at the center of many galaxies.

==Methods of Observation==
Black holes are literally invisible by traditional means of observation (that is, emission or reflection of some sort of radiation) and so cannot be directly observed, their nature is determined by other means. The evidence that a black hole provides is its extraordinarily strong gravity, which can be deduced from its effect on the motions of nearby stars.
<ref name="Gillessen">{{cite journal
|last1=Gillessen |first1=S.
|last2=Eisenhauer |first2=F.
|last3=Trippe |first3=S.
|last4=Alexander |first4=T.
|last5=Genzel |first5=R.
|last6=Martins |first6=F.
|last7=Ott |first7=T.
|display-authors=3
|title=Monitoring Stellar Orbits around the Massive Black Hole in the Galactic Center
|journal=The Astrophysical Journal
|volume=692
|issue=2|page=1075|date=2009
|doi=10.1088/0004-637X/692/2/1075
|arxiv=0810.4674
|bibcode=2009ApJ...692.1075G
|ref=harv
}}</ref> Since 1995, astronomers have tracked the motions of 90 stars orbiting an invisible object coincident with the radio source in the center of our galaxy, Milky way. The astronomers were able to infer that a 2.6 million sollar mass object must be contained within the radius of 0.02 [[light-year]]s to cause the motions of those stars.<ref name="Ghez1998">{{cite journal
|last1=Ghez |first1=A. M.
|last2=Klein |first2=B. L.
|last3=Morris |first3=M.
|last4=Becklin |first4=E. E.
|display-authors=3
|title=High Proper‐Motion Stars in the Vicinity of Sagittarius A*: Evidence for a Supermassive Black Hole at the Center of Our Galaxy
|journal=The Astrophysical Journal
|volume=509
|issue=2|page=678|date=1998
|doi=10.1086/306528
|arxiv=astro-ph/9807210 |bibcode=1998ApJ...509..678G
|ref=harv
}}</ref>

Colliding black holes should produce gravitational waves, possible to detect experimentally. On 24 September 2015 the [[LIGO]] observatory made the first-ever successful observation of such event. <ref name="PRL-20160211">{{cite journal |author=Abbott, B.P. |title=Observation of Gravitational Waves from a Binary Black Hole Merger |url=http://journals.aps.org/prl/abstract/10.1103/PhysRevLett.116.061102 |journal=[[Phys. Rev. Lett.]] |volume=116 |pages=061102 |year=2016 |doi=10.1103/PhysRevLett.116.061102 |display-authors=etal|arxiv = 1602.03837 |bibcode = 2016PhRvL.116f1102A }}</ref><ref name="NYT-20160211-db">{{cite news |last=Overbye |first=Dennis |authorlink=Dennis Overbye |title=Physicists Detect Gravitational Waves, Proving Einstein Right |url=http://www.nytimes.com/2016/02/12/science/ligo-gravitational-waves-black-holes-einstein.html |date=11 February 2016 |work=[[New York Times]] |accessdate=11 February 2016 }}</ref> The signal was consistent with theoretical predictions. The gravitational wave signal suggests that the separation of the two holes prior to merger was just 350 km, hence they must be small in size, leaving black holes as the most plausible interpretation.

While matter and energy, even light, may not escape a black hole, Stephen Hawking has shown that when described by quantum mechanics, they should emit [[Hawking radiation]], which absent of an influx of mass-energy would lead to the evaporation of the black hole in a burst of gamma rays. This radiation may be possible to observe. However all results obtained to date remain unverified and debatable.<ref name="Milanoguys">{{cite journal|title=Hawking radiation from ultrashort laser pulse filaments |first1=F. |last1=Belgiorno |first2=S. L. |last2=Cacciatori |first3=M. |last3=Clerici |first4=V. |last4=Gorini |first5=G. |last5=Ortenzi |first6=L. |last6=Rizzi |first7=E. |last7=Rubino |first8=V. G. |last8=Sala |first9=D. |last9=Faccio |arxiv=1009.4634 |doi=10.1103/PhysRevLett.105.203901 |date=2010 |journal=Phys. Rev. Lett. |volume=105 |page=203901}}</ref><ref>{{cite news|title=Ultrafast Laser Pulse Makes Desktop Black Hole Glow|newspaper=[[Wired (magazine)|Wired]]|date=September 29, 2010|first=Lisa|last=Grossman|url=http://www.wired.com/wiredscience/2010/09/hawking-radiation-in-the-lab/|accessdate=April 30, 2012}}</ref>

==History of the idea==

===General Relativity===
As it happened, the question became unavoidable shortly after the publication in 1915 of Einstein's [[general theory of relativity]]. [[Karl Schwarzschild]] solved the Einstein field equations in a way that describes the geometry of spacetime outside a spherically symmetric, uncharged, non-rotating distribution of mass. Well away from the center of this distribution of mass, the Schwarzschild solution closely matches the Newtonian model of a gravitational field; only close to the mass, where the curvature of spacetime is large, do significant differences between the two models appear. But if the diameter of the mass distribution is taken to be arbitrarily small, then the region of spacetime immediately surrounding the mass appears to take on extremely curious properties, properties so curious that many questioned whether they had any physical interpretation at all. Therefore, Schwarzschild showed that black holes were possible under the theory of [[general relativity]].

[[File:Cygnusx1.jpg|right|200px|thumb|Jet-powered nebula formed from the accretion disk of the binary star Cygnus-X1]]
However, neither Schwarzschild himself nor [[Albert Einstein]], who developed the theory of relativity, believed that black holes actually existed.<ref name="amazing-space.stsci.edu"/> Einstein even tried to re-work general relativity to render these [[Singularity|singularities]] impossible. However, Roger Penrose and Stephen Hawking proved the first of many Singularity Theorems, which states that singularities must form if certain conditions are present. This demonstrated that, rather than mathematical oddities, singularities are a fairly generic consequence of realistic solutions to relativity: any mass with radius less than its Schwarzschild radius is a black hole. Since then, support for black holes among the scientific community has grown.

==Nature of a Black Hole==
===Mathematics===

There are several solutions of the Einstein field equations that are used to model black holes. The simplest of these is the Schwarzchild metric. From this metric, one can calculate the Schwarzschild radius, which defines the boundary (event horizon) of the black hole, to be
:<math>r_s=\frac{2GM}{c^2}</math>,
where
* rs is the Schwarzschild radius;
* G is the gravitational constant;
* M is the mass of the gravitating object;
* c is the speed of light in vacuum.

If the black hole has a nonzero electric charge, it is modeled by the Reissner-Nordström metric. Astronomical objects are generally electrically neutral, since otherwise they would attracted charged particles of opposite sign and quickly become neutral. Therefore, the Reissner-Nordström metric is largely of theoretical interest.

A far more realistic situation occurs when the black hole is spinning (i.e. has nonzero angular momentum). Then the Schwarzschild solution is insufficient (as it was for the charged case), and instead one turns to the Kerr metric. Since astrophysical black holes are generically believed to have angular momentum, this is the solution that best describes them. Among the more interesting consequences of the Kerr metric is the phenomenon of frame dragging, in which the rotating black hole literally pulls nearby spacetime along with it.

If one wishes to consider a black hole that is both charged and spinning, one employs the Kerr-Newman metric, which combines the Reissner-Nordström and Kerr metrics. Since the no-hair theorem states that (non-quantum) black holes are unique up to mass, charge, and angular momentum, the Kerr-Newman metric is sufficient to describe any classical black hole.

===Time and Distance===
Within a certain distance from an arbitrarily small distribution of mass — a distance now known as the [[Schwarzschild radius]] — the curvature of spacetime becomes so great that no paths leading away from the mass exist. That is to say, a test particle released inside the Schwarzschild radius will inevitably move in toward the mass, not because the force of gravity is great as in the Newtonian approximation, but because spacetime is curved to such an extent that ''no other directions exist.'' A particle within the Schwarzschild radius can no more move further from the central mass than it can go backwards in time. In fact, from the frame of reference of an infalling observer beyond the Schwarzschild radius, all directions that once pointed away from the central mass now point backwards in time. Once inside the Schwarzschild radius, further motion toward the central mass is as inevitable as further motion through time is for any other observer.

For some time after the publication of the Schwarzschild solution, the validity of these results was hotly debated. In the solution's original coordinate frame, some terms in the equations ''diverged,'' or became infinite, at the Schwarzschild radius, leading physicists to wonder whether the results of the equations in that region had any valid physical interpretation. One proposed interpretation was that at the Schwarzschild radius, all time for the infalling observer would stop. This led to the use of the term "frozen stars;" it wasn't believed frozen stars were cold, but rather that they were literally frozen in time.

Later refinement of the Schwarzschild solution demonstrated that the apparent infinities were merely an artifact of the coordinate frame chosen, and that an infalling observer in fact can pass beyond the Schwarzchild radius. In fact, the equations predicted he would notice no effects when doing so. But any attempt on the part of that infalling observer to communicate with the outside universe, say by sending a radio message, would be doomed to failure, as the radio waves would traverse geodesics through the severely curved spacetime and end up bent toward the central mass. From this, we can say that nothing that occurs within the Schwarzschild radius can ever affect events outside the Schwarzschild radius. This gives the Schwarzschild radius of a non-rotating black hole its other name: the [[event horizon]].

===Inside the Event Horizon===
What actually exists inside the event horizon of a black hole is a question physics is unable to answer. Some postulate that within the event horizon exists a point of zero (or nearly zero) volume but infinite energy density, a point sometimes referred to as a ''gravitational singularity,'' after the notion of a mathematical singularity (a term referring to a point in an equation at which one would have to solve by dividing by zero, a feat presently impossible in mathematics) in a field equation. Others suspect that infinite energy density is a physical impossibility, and that a black hole contains actual finitely-dense matter compressed into a [[degenerate matter|degenerate]] form, such as quark-degenerate matter. Since all black holes are surrounded by an event horizon which prevents any information or messages from leaving, all these theories are non-[[falsifiable]]; we can never be sure what the interior structure of a black hole is like.

===Properties of Black Holes===

Black holes described with classical mechanics only have three intrinsic properties by which one differs from another: mass, electric charge, and angular momentum. Mass describes the amount of matter inside the event horizon. Angular momentum refers to whether the black hole is stationary or rotating around an axis. While the singularity of a non-rotating black hole may be an infinitely small point, the singularity of a rotating black hole would be in the shape of an infinitely thin ring. Quantum mechanics, which postulates that information loss cannot occur in a black hole, suggests properties beyond the three suggested by classical physics. Using this description, information must also be emitted by black holes. This radiation, referred to as Hawking Radiation, is thermal radiation that has currently only been described mathematically.

Although radiation from inside the event horizon has not yet been observed, there is much phenomenon that occurs outside the horizon due to the black hole. Matter entering a spinning black hole is first swirled around by the black hole’s gravity, causing it to heat up and emit x-rays, which can be used to detect the black hole. In the supermassive black holes at the centers of galaxies, some of the matter does not fall into the black hole. Instead it is blasted into space in twin jets of hot gas perpendicular to the accretion disc, in a phenomenon known as an Active Galactic Nucleus.

==Origins of Black Holes==
[[Image:Hs-2005-02-e-web.jpg|right|thumb|300px|The [[red supergiant]] star V838 Monocerotis, an example of one type of star which may become a black hole.]]
Stellar-mass black holes are said to form when stars more than ten times the mass of the Sun run out of fuel and die. The process of death occurs when stars that have fused the products of their own fusion into larger and larger elements, up to iron. The star then tries to fuse the iron core that forms as a result, but this does not produce enough energy to hold the outer layers of the star apart against the pull of gravity. When this happens, the iron core at the center of the star implodes in a supernova, and the outer layers of the star are blasted into space in one of the most energetic events in the universe—one star going out in a supernova can give off as much light as an entire galaxy. Not all supernovae result in black holes, but if the mass of the core is large enough, about 1.5-3.0 times the mass of the Sun (this value is termed the Tolman-Oppenheimer-Volkoff limit, and its value is not yet known to great precision), the leftover gravity of the shrinking core stalls the outward rush of the initial blast, and crushes the core into a point of infinite density: a black hole.

Extremely small black holes, with masses of around 1015 grams, have been theorized to have formed in the early universe. Any sufficiently small primordial black hole would be expected to evaporate within the lifetime of the universe, but the rate of evaporation is not currently known with any certainty.

At the opposite end of the spectrum, objects with the characteristics of supermassive black holes, millions or billions of times more massive than the sun, have been detected at the centers of many [[galaxies]], including our own [[Milky Way]]. In our galaxy, the hypothesized supermassive black hole is in the constellation Sagittarius, and is known as Sagittarius A* (pronounced "A star"). Based on the extraordinary angular velocity of stars near the galactic center, Sagittarius A* is believed to be on the order of two to three million solar masses. It is unknown how supermassive black holes form, though several models have been proposed. One hypothesis simply begins with a black hole of stellar mass which grows over the lifetime of the galaxy that surrounds it. Another proposal describes supermassive black holes as a natural, in fact nearly unavoidable, consequence of galactic formation. To date, no one theory of supermassive black hole formation is favored over all others.

Physicists trying to understand the theory of black hole formation have once again hit a dead end.<ref>http://www.fromquarkstoquasars.com/new-research-mathematically-proves-quantum-effects-stop-formation-black-holes/</ref>

==Speculative Future Exploration==

Scientists have speculated that if a rotating black hole is large enough, a person could pass through the center of the ring-shaped singularity and possibly enter a wormhole. However, it would have to be a very large hole, for if it were not, the hypothetical astronaut would never survive to reach the event horizon due to tidal forces.

Matter coming close to the event horizon of a small black hole undergoes a process called spaghettification, a term coined by Stephen Hawking in his book ''A Brief History of Time'' to describe extraordinarily strong tidal forces. Because the mass at the center of the black hole is so dense, the gravitational pull on the near end of an object is much greater than the pull on the object’s far end. This causes the object to be stretched out in a way resembling a piece of spaghetti, and generally torn in two.

==White Holes==
Because the [[Quantitative Introduction to General Relativity|general relativity equations]] are symmetric with respect to time, one can reverse the time parameter to yield an equation describing a hypothetical object which expels, rather than attracts, matter and energy.<ref>http://cosmology.berkeley.edu/Education/BHfaq.html#q10</ref> As this is the exact opposite of a black hole, it is called a '''white hole'''.

However, there is no evidence white holes actually exist. If they generate new matter and energy, this would violate the [[Law of the conservation of mass]]. Therefore, some scientists have proposed that matter falling into black holes goes through a [[wormhole]] to emerge at a white hole. While such wormholes are allowed by general relativity, they would be extremely unstable,<ref>http://casa.colorado.edu/~ajsh/schww.html</ref> and there is no evidence that they exist.

Scientists, who have been extremely eager to promote the idea of black hole existence, have shown a strong aversion to the white hole theory, even though, like a white hole, a black hole has never been observed directly. This may reflect an anti-creation bias on the part of scientists who are uncomfortable with the idea that matter and energy can be created outside of what scientific theories dictate should happen.

Fundamentalists and creationists have used white holes to attempt to solve the cosmic time problem. Dr. [[Russell Humphreys]] used a white hole in his model of the universe during [[Creation week]] to allow millions of years to pass in outer space while only three days passed on Earth.

==In Popular Culture==
'''''Black holes are a [[sacred cow]] of [[atheistic science]]'''''.

Black holes are increasingly promoted by [[liberal]] publications, such as the science page of the ''[[New York Times]]'', glossy magazines, and the movies the ''Event Horizon'' (1997), ''The Black Hole'' (TV, 2006), and ''Interstellar'' (2014). They are sometimes seen as a [[sacred cow]]s of [[atheistic science]], while proving of they actual existence would not provide any obvious proof for atheism assumptions.

Black holes have been a device in science fiction ever since their prediction. Many sci-fi books, movies, and television shows use black holes as a method of travel (see the Potential Future Exploration section above) or as a threat to a space-going vessel. In at least one season of the show ''Star Trek: the Next Generation'' by Gene Roddenberry, artificially created miniature black holes are used as power sources for spaceships and natural ones as incubators for the young of an alien race. Neither of these uses has much of a basis in reality, of course.

Contrary to popular myth, a black hole is not a cosmic vacuum cleaner. In other words, a one-solar-mass black hole is no better than any other one-solar-mass object (such as, for example, the Sun) at "sucking in" distant objects. However, a one-solar-mass black hole has the same amount of matter as any other one-solar-mass object but compressed into a much smaller space, making it impossible to move fast enough to leave a black hole once there. If a spaceship could land on a black hole, it would never be able to take off again.

The term "black hole" is also used as a metaphor for a place that it is hard to get out of, generally containing a high concentration of something unpleasant. Ex: "The inner city is a black hole of crime and drug use." The "Black Hole of Calcutta" long predates the celestial use of the term; it was a horrible underground prison in [[Calcutta]], India.

==See also==
*[[Black hole firewall]]
==References==
{{reflist}}
==External links==
*[http://imagine.gsfc.nasa.gov/docs/science/know_l2/black_holes.html Black Holes]
*[http://cosmology.berkeley.edu/Education/BHfaq.html Black Holes (Frequently Asked Questions)]

{{Relativity}}
[[Category:Physics]]
[[Category:Relativity]]

Black hole

2016-10-16T17:42:13Z

H22: Fixed broken template reference

[[Image:Iu8969hu.jpg|right|thumb|300px|Artist's conception of a binary system consisting of a black hole (upper left) and a main sequence star (lower right). The black hole is drawing matter from the star via an ''accretion disk'' (blue) around it, and some of this matter forms a gas jet (also blue).]]
A '''black hole''' is any object that lies entirely inside its own Schwarzschild radius, given by
:<math>r=\frac{2G}{c^2}\ m</math>
where
*G is Newton's gravitational constant;
*c is the speed of light;
*m is the mass of the object.

Numerically,
:<math>r=1.5 \times 10^{-27}\ m</math>
in meters and kilograms.

This is a concept of gravity, under [[General Relativity]]. For any normal object, from things one would see on Earth up to stars that are not extremely massive or dense (much more massive or dense than the Sun), the Schwarzschild radius is very tiny relative to the object. This means that the object does not lie inside that radius, and cannot be a black hole. For example, the Schwarzschild radius of the Earth is about one centimeter, and that of the Sun is about three kilometers. The Earth could only become a black hole if it were compressed into a radius of one centimeter.

What makes the Schwarzschild radius significant is that the behavior of gravity, under General Relativity, is determined by the Schwarzschild metric, and is (not surprisingly) nearly identical to the behavior given by Newton's law of gravity. The difference only shows up at distances at or near the Schwarzschild radius. If the Earth were compressed to a radius of one centimeter or less, the behavior of gravity would become radically different as one approached that distance. Normal world-lines would cease to be "time-like", and such world-lines would be unable to make progress from inside the Schwarzschild radius to outside of it. This is a rather paradoxical situation when viewed in the way we normally view the way the universe works. In short, no object, and no light, can actually pass from inside the radius to outside. The surface at this radius is called the '''event horizon'''.

The concept of the Schwarzschild radius was worked out by Karl Schwarzschild in 1916, as part of his solution (the first solution ever worked out) of Einstein's field equation for General Relativity. At first, neither Einstein nor Schwarzschild believed that something could be so dense that these objects could exist.

==Pre-history==
The notion of something that has gravity so strong that light can't escape actually dates back to the 18th century, when scientists became aware of the finite speed of light and the concept of escape velocity. The [[corpuscular theory of light]] held that light was made up of invisibly small particles, and that these particles moved along ballistic trajectories, like tiny bullets. In this framework, it was believed possible that a distant star could be so massive that light emitted from its surface would be dragged back down again. This theory was first advanced by John Michell, who wrote in 1783, "If the semi-diameter of a sphere of the same density as the Sun in the proportion of five hundred to one, and by supposing light to be attracted by the same force in proportion to its [[Mass (science)|mass]] with other bodies, all light emitted from such a body would be made to return towards it, by its own proper gravity."<ref name="r1">http://www.aps.org/publications/apsnews/200911/physicshistory.cfm</ref>

Suggesting the same possibility independently, Pierre-Simon Laplace wrote in 1796, "It is therefore possible that the greatest luminous bodies in the universe are on this account invisible."<ref name="r1" />

This appeared to depend on the corpuscular theory of light, which gave way to the [[wave theory of light]] in the early 19th century, so the idea of "dark" or "invisible" stars fell from favor. It was believed that light, being a wave and having no mass, might be unaffected by gravity. Research into [[quantum mechanics]], however, reignited interest in the light-as-particles view, ultimately resulting in the modern notion of [[wave-particle duality]]. Under this theory, light could be affected by gravity, so the question of whether light could be emitted from extraordinarily massive bodies was once again open.

But the wave-versus-particle nature of light turned out to be a [[red herring]]. Under the "equivalence principle", it is known that anything, wave, particle, or whatever, that can be construed to have a trajectory, will have that trajectory bent by a gravitational field.

But none of this mattered at the time. A star (or other body) large enough to show this effect was utterly inconceivable. A sphere of Uranium at its normal density would have to weigh 10 million times the mass of the Sun, and be as large as the Earth's orbit, to lie inside its Schwarzschild radius. (Though such a large block of Uranium would not have its normal density.)

And the term "black hole" was unheard-of.

==20th century history==
By the mid-20th century, the physics of stellar dynamics and quantum mechanics had advanced to the point that it was possible to conceive of incredibly dense objects. Stars such as the Sun are actually "inflated" to their current size by the radiation pressure from the fusion reactions going on within them. When stars have consumed all their fuel, that pressure stops, and the material collapses to a much smaller size. The normal interatomic spacing, with electrons orbiting the nuclei, no longer applies. A variety of things can occur, including the electrons combining with the protons to make a "neutron star". Various phenomena were formulated, such as neutron stars, supernovas, pulsars, and magnetars. Before long these objects were actually observed. (Pulsars were observed before the theory had been worked out, and supernovas had been observed since antiquity.)

Stellar evolution and dynamics are quite complicated. Once a star has burned up all its Hydrogen, it may, depending on its size, burn Helium, and then heavier elements, all the way up to Iron. (Iron is the most stable nucleus; fission or fusion of Iron nuclei is not energetically favored.) As the material becomes more compressed, it is held up by the "electron degeneracy pressure" instead of the normal radiation pressure. The normal atomic structure, with orbiting electrons, is replaced by a collection of nuclei and unbound electrons, obeying the rules of quantum mechanics, particularly the Pauli exclusion principle. This pressure generally stops further collapse, leading to a [[white dwarf]]. White dwarfs may continue accreting matter from nearby objects. If the mass is over the "Chandrasekhar limit" of 1.4 solar masses, the gravitational force is too strong even for the degeneracy pressure, and the star becomes a supernova, neutron star, or black hole. The theory of this gravitational collapse was worked out in the 1930's.

If the mass is greater than the Tolman-Oppenheimer-Volkoff limit of about 1.5 solar masses, the neutron star becomes a black hole.

The properties of these objects (the "event horizon", and matter and information may only pass through the event horizon in one direction) were worked out in the 1950's. The exact solutions to Einstein's equation were worked out in the 1960's for rotating black holes (the Kerr solution), electrically charged black holes (the Reissner-Nordström solution), or both (the Kerr-Newman solution). Various theorems relating to thermodynamics were worked out by Stephen Hawking in the 1970's.

The term "black hole" was coined by John Wheeler in 1967. The term caught on very quickly in both the scientific community and the public at large, helped by the catchy nature of the phrase. Because of the remarkable nature of black holes, the concept quickly became a staple of science fiction stories, "popular" science magazines, television shows, and movies such as ''Event Horizon'' (1997), ''The Black Hole'' (TV, 2006), and ''Interstellar'' (2014). The latter movie put a lot of effort into making the visual depiction of the black hole scientifically accurate.

This was all theoretical at the time. There was no evidence that a black hole actually existed until the early 1970's, when scientists began to suspect that the radio source "Cygnus X1" was an actual black hole, and the 1990's, when scientists began to suspect that there was a black hole near the radio source "Sagittarius A*" at the center of our galaxy. (The name is pronounced with the word "star".) Since then evidence has accumulated that enormous black holes lie at the center of many galaxies.

==Methods of Observation==
Black holes are literally invisible by traditional means of observation (that is, emission or reflection of some sort of radiation) and so cannot be directly observed, their nature is determined by other means. The evidence that a black hole provides is its extraordinarily strong gravity, which can be deduced from its effect on the motions of nearby stars.
<ref name="Gillessen">{{cite journal
|last1=Gillessen |first1=S.
|last2=Eisenhauer |first2=F.
|last3=Trippe |first3=S.
|last4=Alexander |first4=T.
|last5=Genzel |first5=R.
|last6=Martins |first6=F.
|last7=Ott |first7=T.
|display-authors=3
|title=Monitoring Stellar Orbits around the Massive Black Hole in the Galactic Center
|journal=The Astrophysical Journal
|volume=692
|issue=2|page=1075|date=2009
|doi=10.1088/0004-637X/692/2/1075
|arxiv=0810.4674
|bibcode=2009ApJ...692.1075G
|ref=harv
}}</ref> Since 1995, astronomers have tracked the motions of 90 stars orbiting an invisible object coincident with the radio source in the center of our galaxy, Milky way. The astronomers were able to infer that a 2.6 million sollar mass object must be contained within the radius of 0.02 [[light-year]]s to cause the motions of those stars.<ref name="Ghez1998">{{cite journal
|last1=Ghez |first1=A. M.
|last2=Klein |first2=B. L.
|last3=Morris |first3=M.
|last4=Becklin |first4=E. E.
|display-authors=3
|title=High Proper‐Motion Stars in the Vicinity of Sagittarius A*: Evidence for a Supermassive Black Hole at the Center of Our Galaxy
|journal=The Astrophysical Journal
|volume=509
|issue=2|page=678|date=1998
|doi=10.1086/306528
|arxiv=astro-ph/9807210 |bibcode=1998ApJ...509..678G
|ref=harv
}}</ref>

Colliding black holes should produce gravitational waves, possible to detect experimentally. On 24 September 2015 the [[LIGO]] observatory made the first-ever successful observation of such event. <ref name="PRL-20160211">{{cite journal |author=Abbott, B.P. |title=Observation of Gravitational Waves from a Binary Black Hole Merger |url=http://journals.aps.org/prl/abstract/10.1103/PhysRevLett.116.061102 |journal=[[Phys. Rev. Lett.]] |volume=116 |pages=061102 |year=2016 |doi=10.1103/PhysRevLett.116.061102 |display-authors=etal|arxiv = 1602.03837 |bibcode = 2016PhRvL.116f1102A }}</ref><ref name="NYT-20160211-db">{{cite news |last=Overbye |first=Dennis |authorlink=Dennis Overbye |title=Physicists Detect Gravitational Waves, Proving Einstein Right |url=http://www.nytimes.com/2016/02/12/science/ligo-gravitational-waves-black-holes-einstein.html |date=11 February 2016 |work=[[New York Times]] |accessdate=11 February 2016 }}</ref> The signal was consistent with theoretical predictions. The gravitational wave signal suggests that the separation of the two holes prior to merger was just 350 km, hence they must be small in size, leaving black holes as the most plausible interpretation.

While matter and energy, even light, may not escape a black hole, Stephen Hawking has shown that when described by quantum mechanics, they should emit [[Hawking radiation]], which absent of an influx of mass-energy would lead to the evaporation of the black hole in a burst of gamma rays. This radiation may be possible to observe. However all results obtained to date remain unverified and debatable.<ref name="Milanoguys">{{cite journal|title=Hawking radiation from ultrashort laser pulse filaments |first1=F. |last1=Belgiorno |first2=S. L. |last2=Cacciatori |first3=M. |last3=Clerici |first4=V. |last4=Gorini |first5=G. |last5=Ortenzi |first6=L. |last6=Rizzi |first7=E. |last7=Rubino |first8=V. G. |last8=Sala |first9=D. |last9=Faccio |arxiv=1009.4634 |doi=10.1103/PhysRevLett.105.203901 |date=2010 |journal=Phys. Rev. Lett. |volume=105 |page=203901}}</ref><ref>{{cite news|title=Ultrafast Laser Pulse Makes Desktop Black Hole Glow|newspaper=[[Wired (magazine)|Wired]]|date=September 29, 2010|first=Lisa|last=Grossman|url=http://www.wired.com/wiredscience/2010/09/hawking-radiation-in-the-lab/|accessdate=April 30, 2012}}</ref>

==History of the idea==

===General Relativity===
As it happened, the question became unavoidable shortly after the publication in 1915 of Einstein's [[general theory of relativity]]. [[Karl Schwarzschild]] solved the Einstein field equations in a way that describes the geometry of spacetime outside a spherically symmetric, uncharged, non-rotating distribution of mass. Well away from the center of this distribution of mass, the Schwarzschild solution closely matches the Newtonian model of a gravitational field; only close to the mass, where the curvature of spacetime is large, do significant differences between the two models appear. But if the diameter of the mass distribution is taken to be arbitrarily small, then the region of spacetime immediately surrounding the mass appears to take on extremely curious properties, properties so curious that many questioned whether they had any physical interpretation at all. Therefore, Schwarzschild showed that black holes were possible under the theory of [[general relativity]].

[[File:Cygnusx1.jpg|right|200px|thumb|Jet-powered nebula formed from the accretion disk of the binary star Cygnus-X1]]
However, neither Schwarzschild himself nor [[Albert Einstein]], who developed the theory of relativity, believed that black holes actually existed.<ref name="amazing-space.stsci.edu"/> Einstein even tried to re-work general relativity to render these [[Singularity|singularities]] impossible. However, Roger Penrose and Stephen Hawking proved the first of many Singularity Theorems, which states that singularities must form if certain conditions are present. This demonstrated that, rather than mathematical oddities, singularities are a fairly generic consequence of realistic solutions to relativity: any mass with radius less than its Schwarzschild radius is a black hole. Since then, support for black holes among the scientific community has grown.

==Nature of a Black Hole==
===Mathematics===

There are several solutions of the Einstein field equations that are used to model black holes. The simplest of these is the Schwarzchild metric. From this metric, one can calculate the Schwarzschild radius, which defines the boundary (event horizon) of the black hole, to be
:<math>r_s=\frac{2GM}{c^2}</math>,
where
* rs is the Schwarzschild radius;
* G is the gravitational constant;
* M is the mass of the gravitating object;
* c is the speed of light in vacuum.

If the black hole has a nonzero electric charge, it is modeled by the Reissner-Nordström metric. Astronomical objects are generally electrically neutral, since otherwise they would attracted charged particles of opposite sign and quickly become neutral. Therefore, the Reissner-Nordström metric is largely of theoretical interest.

A far more realistic situation occurs when the black hole is spinning (i.e. has nonzero angular momentum). Then the Schwarzschild solution is insufficient (as it was for the charged case), and instead one turns to the Kerr metric. Since astrophysical black holes are generically believed to have angular momentum, this is the solution that best describes them. Among the more interesting consequences of the Kerr metric is the phenomenon of frame dragging, in which the rotating black hole literally pulls nearby spacetime along with it.

If one wishes to consider a black hole that is both charged and spinning, one employs the Kerr-Newman metric, which combines the Reissner-Nordström and Kerr metrics. Since the no-hair theorem states that (non-quantum) black holes are unique up to mass, charge, and angular momentum, the Kerr-Newman metric is sufficient to describe any classical black hole.

===Time and Distance===
Within a certain distance from an arbitrarily small distribution of mass — a distance now known as the [[Schwarzschild radius]] — the curvature of spacetime becomes so great that no paths leading away from the mass exist. That is to say, a test particle released inside the Schwarzschild radius will inevitably move in toward the mass, not because the force of gravity is great as in the Newtonian approximation, but because spacetime is curved to such an extent that ''no other directions exist.'' A particle within the Schwarzschild radius can no more move further from the central mass than it can go backwards in time. In fact, from the frame of reference of an infalling observer beyond the Schwarzschild radius, all directions that once pointed away from the central mass now point backwards in time. Once inside the Schwarzschild radius, further motion toward the central mass is as inevitable as further motion through time is for any other observer.

For some time after the publication of the Schwarzschild solution, the validity of these results was hotly debated. In the solution's original coordinate frame, some terms in the equations ''diverged,'' or became infinite, at the Schwarzschild radius, leading physicists to wonder whether the results of the equations in that region had any valid physical interpretation. One proposed interpretation was that at the Schwarzschild radius, all time for the infalling observer would stop. This led to the use of the term "frozen stars;" it wasn't believed frozen stars were cold, but rather that they were literally frozen in time.

Later refinement of the Schwarzschild solution demonstrated that the apparent infinities were merely an artifact of the coordinate frame chosen, and that an infalling observer in fact can pass beyond the Schwarzchild radius. In fact, the equations predicted he would notice no effects when doing so. But any attempt on the part of that infalling observer to communicate with the outside universe, say by sending a radio message, would be doomed to failure, as the radio waves would traverse geodesics through the severely curved spacetime and end up bent toward the central mass. From this, we can say that nothing that occurs within the Schwarzschild radius can ever affect events outside the Schwarzschild radius. This gives the Schwarzschild radius of a non-rotating black hole its other name: the [[event horizon]].

===Inside the Event Horizon===
What actually exists inside the event horizon of a black hole is a question physics is unable to answer. Some postulate that within the event horizon exists a point of zero (or nearly zero) volume but infinite energy density, a point sometimes referred to as a ''gravitational singularity,'' after the notion of a mathematical singularity (a term referring to a point in an equation at which one would have to solve by dividing by zero, a feat presently impossible in mathematics) in a field equation. Others suspect that infinite energy density is a physical impossibility, and that a black hole contains actual finitely-dense matter compressed into a [[degenerate matter|degenerate]] form, such as quark-degenerate matter. Since all black holes are surrounded by an event horizon which prevents any information or messages from leaving, all these theories are non-[[falsifiable]]; we can never be sure what the interior structure of a black hole is like.

===Properties of Black Holes===

Black holes described with classical mechanics only have three intrinsic properties by which one differs from another: mass, electric charge, and angular momentum. Mass describes the amount of matter inside the event horizon. Angular momentum refers to whether the black hole is stationary or rotating around an axis. While the singularity of a non-rotating black hole may be an infinitely small point, the singularity of a rotating black hole would be in the shape of an infinitely thin ring. Quantum mechanics, which postulates that information loss cannot occur in a black hole, suggests properties beyond the three suggested by classical physics. Using this description, information must also be emitted by black holes. This radiation, referred to as Hawking Radiation, is thermal radiation that has currently only been described mathematically.

Although radiation from inside the event horizon has not yet been observed, there is much phenomenon that occurs outside the horizon due to the black hole. Matter entering a spinning black hole is first swirled around by the black hole’s gravity, causing it to heat up and emit x-rays, which can be used to detect the black hole. In the supermassive black holes at the centers of galaxies, some of the matter does not fall into the black hole. Instead it is blasted into space in twin jets of hot gas perpendicular to the accretion disc, in a phenomenon known as an Active Galactic Nucleus.

==Origins of Black Holes==
[[Image:Hs-2005-02-e-web.jpg|right|thumb|300px|The [[red supergiant]] star V838 Monocerotis, an example of one type of star which may become a black hole.]]
Stellar-mass black holes are said to form when stars more than ten times the mass of the Sun run out of fuel and die. The process of death occurs when stars that have fused the products of their own fusion into larger and larger elements, up to iron. The star then tries to fuse the iron core that forms as a result, but this does not produce enough energy to hold the outer layers of the star apart against the pull of gravity. When this happens, the iron core at the center of the star implodes in a supernova, and the outer layers of the star are blasted into space in one of the most energetic events in the universe—one star going out in a supernova can give off as much light as an entire galaxy. Not all supernovae result in black holes, but if the mass of the core is large enough, about 1.5-3.0 times the mass of the Sun (this value is termed the Tolman-Oppenheimer-Volkoff limit, and its value is not yet known to great precision), the leftover gravity of the shrinking core stalls the outward rush of the initial blast, and crushes the core into a point of infinite density: a black hole.

Extremely small black holes, with masses of around 1015 grams, have been theorized to have formed in the early universe. Any sufficiently small primordial black hole would be expected to evaporate within the lifetime of the universe, but the rate of evaporation is not currently known with any certainty.

At the opposite end of the spectrum, objects with the characteristics of supermassive black holes, millions or billions of times more massive than the sun, have been detected at the centers of many [[galaxies]], including our own [[Milky Way]]. In our galaxy, the hypothesized supermassive black hole is in the constellation Sagittarius, and is known as Sagittarius A* (pronounced "A star"). Based on the extraordinary angular velocity of stars near the galactic center, Sagittarius A* is believed to be on the order of two to three million solar masses. It is unknown how supermassive black holes form, though several models have been proposed. One hypothesis simply begins with a black hole of stellar mass which grows over the lifetime of the galaxy that surrounds it. Another proposal describes supermassive black holes as a natural, in fact nearly unavoidable, consequence of galactic formation. To date, no one theory of supermassive black hole formation is favored over all others.

Physicists trying to understand the theory of black hole formation have once again hit a dead end.<ref>http://www.fromquarkstoquasars.com/new-research-mathematically-proves-quantum-effects-stop-formation-black-holes/</ref>

==Speculative Future Exploration==

Scientists have speculated that if a rotating black hole is large enough, a person could pass through the center of the ring-shaped singularity and possibly enter a wormhole. However, it would have to be a very large hole, for if it were not, the hypothetical astronaut would never survive to reach the event horizon due to tidal forces.

Matter coming close to the event horizon of a small black hole undergoes a process called spaghettification, a term coined by Stephen Hawking in his book ''A Brief History of Time'' to describe extraordinarily strong tidal forces. Because the mass at the center of the black hole is so dense, the gravitational pull on the near end of an object is much greater than the pull on the object’s far end. This causes the object to be stretched out in a way resembling a piece of spaghetti, and generally torn in two.

==White Holes==
Because the [[Quantitative Introduction to General Relativity|general relativity equations]] are symmetric with respect to time, one can reverse the time parameter to yield an equation describing a hypothetical object which expels, rather than attracts, matter and energy.<ref>http://cosmology.berkeley.edu/Education/BHfaq.html#q10</ref> As this is the exact opposite of a black hole, it is called a '''white hole'''.

However, there is no evidence white holes actually exist. If they generate new matter and energy, this would violate the [[Law of the conservation of mass]]. Therefore, some scientists have proposed that matter falling into black holes goes through a [[wormhole]] to emerge at a white hole. While such wormholes are allowed by general relativity, they would be extremely unstable,<ref>http://casa.colorado.edu/~ajsh/schww.html</ref> and there is no evidence that they exist.

Scientists, who have been extremely eager to promote the idea of black hole existence, have shown a strong aversion to the white hole theory, even though, like a white hole, a black hole has never been observed directly. This may reflect an anti-creation bias on the part of scientists who are uncomfortable with the idea that matter and energy can be created outside of what scientific theories dictate should happen.

Fundamentalists and creationists have used white holes to attempt to solve the cosmic time problem. Dr. [[Russell Humphreys]] used a white hole in his model of the universe during [[Creation week]] to allow millions of years to pass in outer space while only three days passed on Earth.

==In Popular Culture==

Black holes have been a device in science fiction ever since their prediction. Many sci-fi books, movies, and television shows use black holes as a method of travel (see the Potential Future Exploration section above) or as a threat to a space-going vessel. In at least one season of the show ''Star Trek: the Next Generation'' by Gene Roddenberry, artificially created miniature black holes are used as power sources for spaceships and natural ones as incubators for the young of an alien race. Neither of these uses has much of a basis in reality, of course.

Contrary to popular myth, a black hole is not a cosmic vacuum cleaner. In other words, a one-solar-mass black hole is no better than any other one-solar-mass object (such as, for example, the Sun) at "sucking in" distant objects. However, a one-solar-mass black hole has the same amount of matter as any other one-solar-mass object but compressed into a much smaller space, making it impossible to move fast enough to leave a black hole once there. If a spaceship could land on a black hole, it would never be able to take off again.

The term "black hole" is also used as a metaphor for a place that it is hard to get out of, generally containing a high concentration of something unpleasant. Ex: "The inner city is a black hole of crime and drug use." The "Black Hole of Calcutta" long predates the celestial use of the term; it was a horrible underground prison in [[Calcutta]], India.

==See also==
*[[Black hole firewall]]
==References==
{{reflist}}
==External links==
*[http://imagine.gsfc.nasa.gov/docs/science/know_l2/black_holes.html Black Holes]
*[http://cosmology.berkeley.edu/Education/BHfaq.html Black Holes (Frequently Asked Questions)]

{{Relativity}}
[[Category:Physics]]
[[Category:Relativity]]

Black hole

2016-10-16T17:40:50Z

H22: Extended, and holly cows with glossy journals should be moved to the public press section

[[Image:Iu8969hu.jpg|right|thumb|300px|Artist's conception of a binary system consisting of a black hole (upper left) and a main sequence star (lower right). The black hole is drawing matter from the star via an ''accretion disk'' (blue) around it, and some of this matter forms a gas jet (also blue).]]
A '''black hole''' is any object that lies entirely inside its own Schwarzschild radius, given by
:<math>r=\frac{2G}{c^2}\ m</math>
where
*G is Newton's gravitational constant;
*c is the speed of light;
*m is the mass of the object.

Numerically,
:<math>r=1.5 \times 10^{-27}\ m</math>
in meters and kilograms.

This is a concept of gravity, under [[General Relativity]]. For any normal object, from things one would see on Earth up to stars that are not extremely massive or dense (much more massive or dense than the Sun), the Schwarzschild radius is very tiny relative to the object. This means that the object does not lie inside that radius, and cannot be a black hole. For example, the Schwarzschild radius of the Earth is about one centimeter, and that of the Sun is about three kilometers. The Earth could only become a black hole if it were compressed into a radius of one centimeter.

What makes the Schwarzschild radius significant is that the behavior of gravity, under General Relativity, is determined by the Schwarzschild metric, and is (not surprisingly) nearly identical to the behavior given by Newton's law of gravity. The difference only shows up at distances at or near the Schwarzschild radius. If the Earth were compressed to a radius of one centimeter or less, the behavior of gravity would become radically different as one approached that distance. Normal world-lines would cease to be "time-like", and such world-lines would be unable to make progress from inside the Schwarzschild radius to outside of it. This is a rather paradoxical situation when viewed in the way we normally view the way the universe works. In short, no object, and no light, can actually pass from inside the radius to outside. The surface at this radius is called the '''event horizon'''.

The concept of the Schwarzschild radius was worked out by Karl Schwarzschild in 1916, as part of his solution (the first solution ever worked out) of Einstein's field equation for General Relativity. At first, neither Einstein nor Schwarzschild believed that something could be so dense that these objects could exist.

==Pre-history==
The notion of something that has gravity so strong that light can't escape actually dates back to the 18th century, when scientists became aware of the finite speed of light and the concept of escape velocity. The [[corpuscular theory of light]] held that light was made up of invisibly small particles, and that these particles moved along ballistic trajectories, like tiny bullets. In this framework, it was believed possible that a distant star could be so massive that light emitted from its surface would be dragged back down again. This theory was first advanced by John Michell, who wrote in 1783, "If the semi-diameter of a sphere of the same density as the Sun in the proportion of five hundred to one, and by supposing light to be attracted by the same force in proportion to its [[Mass (science)|mass]] with other bodies, all light emitted from such a body would be made to return towards it, by its own proper gravity."<ref name="r1">http://www.aps.org/publications/apsnews/200911/physicshistory.cfm</ref>

Suggesting the same possibility independently, Pierre-Simon Laplace wrote in 1796, "It is therefore possible that the greatest luminous bodies in the universe are on this account invisible."<ref name="r1" />

This appeared to depend on the corpuscular theory of light, which gave way to the [[wave theory of light]] in the early 19th century, so the idea of "dark" or "invisible" stars fell from favor. It was believed that light, being a wave and having no mass, might be unaffected by gravity. Research into [[quantum mechanics]], however, reignited interest in the light-as-particles view, ultimately resulting in the modern notion of [[wave-particle duality]]. Under this theory, light could be affected by gravity, so the question of whether light could be emitted from extraordinarily massive bodies was once again open.

But the wave-versus-particle nature of light turned out to be a [[red herring]]. Under the "equivalence principle", it is known that anything, wave, particle, or whatever, that can be construed to have a trajectory, will have that trajectory bent by a gravitational field.

But none of this mattered at the time. A star (or other body) large enough to show this effect was utterly inconceivable. A sphere of Uranium at its normal density would have to weigh 10 million times the mass of the Sun, and be as large as the Earth's orbit, to lie inside its Schwarzschild radius. (Though such a large block of Uranium would not have its normal density.)

And the term "black hole" was unheard-of.

==20th century history==
By the mid-20th century, the physics of stellar dynamics and quantum mechanics had advanced to the point that it was possible to conceive of incredibly dense objects. Stars such as the Sun are actually "inflated" to their current size by the radiation pressure from the fusion reactions going on within them. When stars have consumed all their fuel, that pressure stops, and the material collapses to a much smaller size. The normal interatomic spacing, with electrons orbiting the nuclei, no longer applies. A variety of things can occur, including the electrons combining with the protons to make a "neutron star". Various phenomena were formulated, such as neutron stars, supernovas, pulsars, and magnetars. Before long these objects were actually observed. (Pulsars were observed before the theory had been worked out, and supernovas had been observed since antiquity.)

Stellar evolution and dynamics are quite complicated. Once a star has burned up all its Hydrogen, it may, depending on its size, burn Helium, and then heavier elements, all the way up to Iron. (Iron is the most stable nucleus; fission or fusion of Iron nuclei is not energetically favored.) As the material becomes more compressed, it is held up by the "electron degeneracy pressure" instead of the normal radiation pressure. The normal atomic structure, with orbiting electrons, is replaced by a collection of nuclei and unbound electrons, obeying the rules of quantum mechanics, particularly the Pauli exclusion principle. This pressure generally stops further collapse, leading to a [[white dwarf]]. White dwarfs may continue accreting matter from nearby objects. If the mass is over the "Chandrasekhar limit" of 1.4 solar masses, the gravitational force is too strong even for the degeneracy pressure, and the star becomes a supernova, neutron star, or black hole. The theory of this gravitational collapse was worked out in the 1930's.

If the mass is greater than the Tolman-Oppenheimer-Volkoff limit of about 1.5 solar masses, the neutron star becomes a black hole.

The properties of these objects (the "event horizon", and matter and information may only pass through the event horizon in one direction) were worked out in the 1950's. The exact solutions to Einstein's equation were worked out in the 1960's for rotating black holes (the Kerr solution), electrically charged black holes (the Reissner-Nordström solution), or both (the Kerr-Newman solution). Various theorems relating to thermodynamics were worked out by Stephen Hawking in the 1970's.

The term "black hole" was coined by John Wheeler in 1967. The term caught on very quickly in both the scientific community and the public at large, helped by the catchy nature of the phrase. Because of the remarkable nature of black holes, the concept quickly became a staple of science fiction stories, "popular" science magazines, television shows, and movies such as ''Event Horizon'' (1997), ''The Black Hole'' (TV, 2006), and ''Interstellar'' (2014). The latter movie put a lot of effort into making the visual depiction of the black hole scientifically accurate.

This was all theoretical at the time. There was no evidence that a black hole actually existed until the early 1970's, when scientists began to suspect that the radio source "Cygnus X1" was an actual black hole, and the 1990's, when scientists began to suspect that there was a black hole near the radio source "Sagittarius A*" at the center of our galaxy. (The name is pronounced with the word "star".) Since then evidence has accumulated that enormous black holes lie at the center of many galaxies.

==Methods of Observation==
Black holes are literally invisible by traditional means of observation (that is, emission or reflection of some sort of radiation) and so cannot be directly observed, their nature is determined by other means. The evidence that a black hole provides is its extraordinarily strong gravity, which can be deduced from its effect on the motions of nearby stars.
<ref name="Gillessen">{{cite journal
|last1=Gillessen |first1=S.
|last2=Eisenhauer |first2=F.
|last3=Trippe |first3=S.
|last4=Alexander |first4=T.
|last5=Genzel |first5=R.
|last6=Martins |first6=F.
|last7=Ott |first7=T.
|display-authors=3
|title=Monitoring Stellar Orbits around the Massive Black Hole in the Galactic Center
|journal=The Astrophysical Journal
|volume=692
|issue=2|page=1075|date=2009
|doi=10.1088/0004-637X/692/2/1075
|arxiv=0810.4674
|bibcode=2009ApJ...692.1075G
|ref=harv
}}</ref> Since 1995, astronomers have tracked the motions of 90 stars orbiting an invisible object coincident with the radio source in the center of our galaxy, Milky way. The astronomers were able to infer that a 2.6 million {{Solar mass|link=y}} object must be contained in a volume with a radius of 0.02 [[light-year]]s to cause the motions of those stars.<ref name="Ghez1998">{{cite journal
|last1=Ghez |first1=A. M.
|last2=Klein |first2=B. L.
|last3=Morris |first3=M.
|last4=Becklin |first4=E. E.
|display-authors=3
|title=High Proper‐Motion Stars in the Vicinity of Sagittarius A*: Evidence for a Supermassive Black Hole at the Center of Our Galaxy
|journal=The Astrophysical Journal
|volume=509
|issue=2|page=678|date=1998
|doi=10.1086/306528
|arxiv=astro-ph/9807210 |bibcode=1998ApJ...509..678G
|ref=harv
}}</ref>

Colliding black holes should produce gravitational waves, possible to detect experimentally. On 24 September 2015 the [[LIGO]] observatory made the first-ever successful observation of such event. <ref name="PRL-20160211">{{cite journal |author=Abbott, B.P. |title=Observation of Gravitational Waves from a Binary Black Hole Merger |url=http://journals.aps.org/prl/abstract/10.1103/PhysRevLett.116.061102 |journal=[[Phys. Rev. Lett.]] |volume=116 |pages=061102 |year=2016 |doi=10.1103/PhysRevLett.116.061102 |display-authors=etal|arxiv = 1602.03837 |bibcode = 2016PhRvL.116f1102A }}</ref><ref name="NYT-20160211-db">{{cite news |last=Overbye |first=Dennis |authorlink=Dennis Overbye |title=Physicists Detect Gravitational Waves, Proving Einstein Right |url=http://www.nytimes.com/2016/02/12/science/ligo-gravitational-waves-black-holes-einstein.html |date=11 February 2016 |work=[[New York Times]] |accessdate=11 February 2016 }}</ref> The signal was consistent with theoretical predictions. The gravitational wave signal suggests that the separation of the two holes prior to merger was just 350 km, hence they must be small in size, leaving black holes as the most plausible interpretation.

While matter and energy, even light, may not escape a black hole, Stephen Hawking has shown that when described by quantum mechanics, they should emit [[Hawking radiation]], which absent of an influx of mass-energy would lead to the evaporation of the black hole in a burst of gamma rays. This radiation may be possible to observe. However all results obtained to date remain unverified and debatable.<ref name="Milanoguys">{{cite journal|title=Hawking radiation from ultrashort laser pulse filaments |first1=F. |last1=Belgiorno |first2=S. L. |last2=Cacciatori |first3=M. |last3=Clerici |first4=V. |last4=Gorini |first5=G. |last5=Ortenzi |first6=L. |last6=Rizzi |first7=E. |last7=Rubino |first8=V. G. |last8=Sala |first9=D. |last9=Faccio |arxiv=1009.4634 |doi=10.1103/PhysRevLett.105.203901 |date=2010 |journal=Phys. Rev. Lett. |volume=105 |page=203901}}</ref><ref>{{cite news|title=Ultrafast Laser Pulse Makes Desktop Black Hole Glow|newspaper=[[Wired (magazine)|Wired]]|date=September 29, 2010|first=Lisa|last=Grossman|url=http://www.wired.com/wiredscience/2010/09/hawking-radiation-in-the-lab/|accessdate=April 30, 2012}}</ref>

==History of the idea==

===General Relativity===
As it happened, the question became unavoidable shortly after the publication in 1915 of Einstein's [[general theory of relativity]]. [[Karl Schwarzschild]] solved the Einstein field equations in a way that describes the geometry of spacetime outside a spherically symmetric, uncharged, non-rotating distribution of mass. Well away from the center of this distribution of mass, the Schwarzschild solution closely matches the Newtonian model of a gravitational field; only close to the mass, where the curvature of spacetime is large, do significant differences between the two models appear. But if the diameter of the mass distribution is taken to be arbitrarily small, then the region of spacetime immediately surrounding the mass appears to take on extremely curious properties, properties so curious that many questioned whether they had any physical interpretation at all. Therefore, Schwarzschild showed that black holes were possible under the theory of [[general relativity]].

[[File:Cygnusx1.jpg|right|200px|thumb|Jet-powered nebula formed from the accretion disk of the binary star Cygnus-X1]]
However, neither Schwarzschild himself nor [[Albert Einstein]], who developed the theory of relativity, believed that black holes actually existed.<ref name="amazing-space.stsci.edu"/> Einstein even tried to re-work general relativity to render these [[Singularity|singularities]] impossible. However, Roger Penrose and Stephen Hawking proved the first of many Singularity Theorems, which states that singularities must form if certain conditions are present. This demonstrated that, rather than mathematical oddities, singularities are a fairly generic consequence of realistic solutions to relativity: any mass with radius less than its Schwarzschild radius is a black hole. Since then, support for black holes among the scientific community has grown.

==Nature of a Black Hole==
===Mathematics===

There are several solutions of the Einstein field equations that are used to model black holes. The simplest of these is the Schwarzchild metric. From this metric, one can calculate the Schwarzschild radius, which defines the boundary (event horizon) of the black hole, to be
:<math>r_s=\frac{2GM}{c^2}</math>,
where
* rs is the Schwarzschild radius;
* G is the gravitational constant;
* M is the mass of the gravitating object;
* c is the speed of light in vacuum.

If the black hole has a nonzero electric charge, it is modeled by the Reissner-Nordström metric. Astronomical objects are generally electrically neutral, since otherwise they would attracted charged particles of opposite sign and quickly become neutral. Therefore, the Reissner-Nordström metric is largely of theoretical interest.

A far more realistic situation occurs when the black hole is spinning (i.e. has nonzero angular momentum). Then the Schwarzschild solution is insufficient (as it was for the charged case), and instead one turns to the Kerr metric. Since astrophysical black holes are generically believed to have angular momentum, this is the solution that best describes them. Among the more interesting consequences of the Kerr metric is the phenomenon of frame dragging, in which the rotating black hole literally pulls nearby spacetime along with it.

If one wishes to consider a black hole that is both charged and spinning, one employs the Kerr-Newman metric, which combines the Reissner-Nordström and Kerr metrics. Since the no-hair theorem states that (non-quantum) black holes are unique up to mass, charge, and angular momentum, the Kerr-Newman metric is sufficient to describe any classical black hole.

===Time and Distance===
Within a certain distance from an arbitrarily small distribution of mass — a distance now known as the [[Schwarzschild radius]] — the curvature of spacetime becomes so great that no paths leading away from the mass exist. That is to say, a test particle released inside the Schwarzschild radius will inevitably move in toward the mass, not because the force of gravity is great as in the Newtonian approximation, but because spacetime is curved to such an extent that ''no other directions exist.'' A particle within the Schwarzschild radius can no more move further from the central mass than it can go backwards in time. In fact, from the frame of reference of an infalling observer beyond the Schwarzschild radius, all directions that once pointed away from the central mass now point backwards in time. Once inside the Schwarzschild radius, further motion toward the central mass is as inevitable as further motion through time is for any other observer.

For some time after the publication of the Schwarzschild solution, the validity of these results was hotly debated. In the solution's original coordinate frame, some terms in the equations ''diverged,'' or became infinite, at the Schwarzschild radius, leading physicists to wonder whether the results of the equations in that region had any valid physical interpretation. One proposed interpretation was that at the Schwarzschild radius, all time for the infalling observer would stop. This led to the use of the term "frozen stars;" it wasn't believed frozen stars were cold, but rather that they were literally frozen in time.

Later refinement of the Schwarzschild solution demonstrated that the apparent infinities were merely an artifact of the coordinate frame chosen, and that an infalling observer in fact can pass beyond the Schwarzchild radius. In fact, the equations predicted he would notice no effects when doing so. But any attempt on the part of that infalling observer to communicate with the outside universe, say by sending a radio message, would be doomed to failure, as the radio waves would traverse geodesics through the severely curved spacetime and end up bent toward the central mass. From this, we can say that nothing that occurs within the Schwarzschild radius can ever affect events outside the Schwarzschild radius. This gives the Schwarzschild radius of a non-rotating black hole its other name: the [[event horizon]].

===Inside the Event Horizon===
What actually exists inside the event horizon of a black hole is a question physics is unable to answer. Some postulate that within the event horizon exists a point of zero (or nearly zero) volume but infinite energy density, a point sometimes referred to as a ''gravitational singularity,'' after the notion of a mathematical singularity (a term referring to a point in an equation at which one would have to solve by dividing by zero, a feat presently impossible in mathematics) in a field equation. Others suspect that infinite energy density is a physical impossibility, and that a black hole contains actual finitely-dense matter compressed into a [[degenerate matter|degenerate]] form, such as quark-degenerate matter. Since all black holes are surrounded by an event horizon which prevents any information or messages from leaving, all these theories are non-[[falsifiable]]; we can never be sure what the interior structure of a black hole is like.

===Properties of Black Holes===

Black holes described with classical mechanics only have three intrinsic properties by which one differs from another: mass, electric charge, and angular momentum. Mass describes the amount of matter inside the event horizon. Angular momentum refers to whether the black hole is stationary or rotating around an axis. While the singularity of a non-rotating black hole may be an infinitely small point, the singularity of a rotating black hole would be in the shape of an infinitely thin ring. Quantum mechanics, which postulates that information loss cannot occur in a black hole, suggests properties beyond the three suggested by classical physics. Using this description, information must also be emitted by black holes. This radiation, referred to as Hawking Radiation, is thermal radiation that has currently only been described mathematically.

Although radiation from inside the event horizon has not yet been observed, there is much phenomenon that occurs outside the horizon due to the black hole. Matter entering a spinning black hole is first swirled around by the black hole’s gravity, causing it to heat up and emit x-rays, which can be used to detect the black hole. In the supermassive black holes at the centers of galaxies, some of the matter does not fall into the black hole. Instead it is blasted into space in twin jets of hot gas perpendicular to the accretion disc, in a phenomenon known as an Active Galactic Nucleus.

==Origins of Black Holes==
[[Image:Hs-2005-02-e-web.jpg|right|thumb|300px|The [[red supergiant]] star V838 Monocerotis, an example of one type of star which may become a black hole.]]
Stellar-mass black holes are said to form when stars more than ten times the mass of the Sun run out of fuel and die. The process of death occurs when stars that have fused the products of their own fusion into larger and larger elements, up to iron. The star then tries to fuse the iron core that forms as a result, but this does not produce enough energy to hold the outer layers of the star apart against the pull of gravity. When this happens, the iron core at the center of the star implodes in a supernova, and the outer layers of the star are blasted into space in one of the most energetic events in the universe—one star going out in a supernova can give off as much light as an entire galaxy. Not all supernovae result in black holes, but if the mass of the core is large enough, about 1.5-3.0 times the mass of the Sun (this value is termed the Tolman-Oppenheimer-Volkoff limit, and its value is not yet known to great precision), the leftover gravity of the shrinking core stalls the outward rush of the initial blast, and crushes the core into a point of infinite density: a black hole.

Extremely small black holes, with masses of around 1015 grams, have been theorized to have formed in the early universe. Any sufficiently small primordial black hole would be expected to evaporate within the lifetime of the universe, but the rate of evaporation is not currently known with any certainty.

At the opposite end of the spectrum, objects with the characteristics of supermassive black holes, millions or billions of times more massive than the sun, have been detected at the centers of many [[galaxies]], including our own [[Milky Way]]. In our galaxy, the hypothesized supermassive black hole is in the constellation Sagittarius, and is known as Sagittarius A* (pronounced "A star"). Based on the extraordinary angular velocity of stars near the galactic center, Sagittarius A* is believed to be on the order of two to three million solar masses. It is unknown how supermassive black holes form, though several models have been proposed. One hypothesis simply begins with a black hole of stellar mass which grows over the lifetime of the galaxy that surrounds it. Another proposal describes supermassive black holes as a natural, in fact nearly unavoidable, consequence of galactic formation. To date, no one theory of supermassive black hole formation is favored over all others.

Physicists trying to understand the theory of black hole formation have once again hit a dead end.<ref>http://www.fromquarkstoquasars.com/new-research-mathematically-proves-quantum-effects-stop-formation-black-holes/</ref>

==Speculative Future Exploration==

Scientists have speculated that if a rotating black hole is large enough, a person could pass through the center of the ring-shaped singularity and possibly enter a wormhole. However, it would have to be a very large hole, for if it were not, the hypothetical astronaut would never survive to reach the event horizon due to tidal forces.

Matter coming close to the event horizon of a small black hole undergoes a process called spaghettification, a term coined by Stephen Hawking in his book ''A Brief History of Time'' to describe extraordinarily strong tidal forces. Because the mass at the center of the black hole is so dense, the gravitational pull on the near end of an object is much greater than the pull on the object’s far end. This causes the object to be stretched out in a way resembling a piece of spaghetti, and generally torn in two.

==White Holes==
Because the [[Quantitative Introduction to General Relativity|general relativity equations]] are symmetric with respect to time, one can reverse the time parameter to yield an equation describing a hypothetical object which expels, rather than attracts, matter and energy.<ref>http://cosmology.berkeley.edu/Education/BHfaq.html#q10</ref> As this is the exact opposite of a black hole, it is called a '''white hole'''.

However, there is no evidence white holes actually exist. If they generate new matter and energy, this would violate the [[Law of the conservation of mass]]. Therefore, some scientists have proposed that matter falling into black holes goes through a [[wormhole]] to emerge at a white hole. While such wormholes are allowed by general relativity, they would be extremely unstable,<ref>http://casa.colorado.edu/~ajsh/schww.html</ref> and there is no evidence that they exist.

Scientists, who have been extremely eager to promote the idea of black hole existence, have shown a strong aversion to the white hole theory, even though, like a white hole, a black hole has never been observed directly. This may reflect an anti-creation bias on the part of scientists who are uncomfortable with the idea that matter and energy can be created outside of what scientific theories dictate should happen.

Fundamentalists and creationists have used white holes to attempt to solve the cosmic time problem. Dr. [[Russell Humphreys]] used a white hole in his model of the universe during [[Creation week]] to allow millions of years to pass in outer space while only three days passed on Earth.

==In Popular Culture==

Black holes have been a device in science fiction ever since their prediction. Many sci-fi books, movies, and television shows use black holes as a method of travel (see the Potential Future Exploration section above) or as a threat to a space-going vessel. In at least one season of the show ''Star Trek: the Next Generation'' by Gene Roddenberry, artificially created miniature black holes are used as power sources for spaceships and natural ones as incubators for the young of an alien race. Neither of these uses has much of a basis in reality, of course.

Contrary to popular myth, a black hole is not a cosmic vacuum cleaner. In other words, a one-solar-mass black hole is no better than any other one-solar-mass object (such as, for example, the Sun) at "sucking in" distant objects. However, a one-solar-mass black hole has the same amount of matter as any other one-solar-mass object but compressed into a much smaller space, making it impossible to move fast enough to leave a black hole once there. If a spaceship could land on a black hole, it would never be able to take off again.

The term "black hole" is also used as a metaphor for a place that it is hard to get out of, generally containing a high concentration of something unpleasant. Ex: "The inner city is a black hole of crime and drug use." The "Black Hole of Calcutta" long predates the celestial use of the term; it was a horrible underground prison in [[Calcutta]], India.

==See also==
*[[Black hole firewall]]
==References==
{{reflist}}
==External links==
*[http://imagine.gsfc.nasa.gov/docs/science/know_l2/black_holes.html Black Holes]
*[http://cosmology.berkeley.edu/Education/BHfaq.html Black Holes (Frequently Asked Questions)]

{{Relativity}}
[[Category:Physics]]
[[Category:Relativity]]