Difference between revisions of "Talk:Field theory"

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(Newton, action at a distance, and propagation speed in the 1600s)
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:::"Field theory" used to mean what you say, but I think today it connotes a "field" that takes time to travel ... as in "quantum field theory."  I don't think a distinction is made between particles or waves; the key distinction is between instantaneous action versus action at the speed of light.--[[User:Aschlafly|Andy Schlafly]] 21:43, 15 November 2009 (EST)
 
:::"Field theory" used to mean what you say, but I think today it connotes a "field" that takes time to travel ... as in "quantum field theory."  I don't think a distinction is made between particles or waves; the key distinction is between instantaneous action versus action at the speed of light.--[[User:Aschlafly|Andy Schlafly]] 21:43, 15 November 2009 (EST)
 
::::We'll have to agree to disagree. [[User:JacobB|JacobB]] 21:44, 15 November 2009 (EST)
 
::::We'll have to agree to disagree. [[User:JacobB|JacobB]] 21:44, 15 November 2009 (EST)
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:::Could I ask you two to lower the temperature of this a bit?  The question of "action at a distance" is one that I was going to work on before all my time got sucked up into the black hole that is the general relativity article.  I put out requests to [[User:KSorenson]] and [[User:SaraT]] requesting their input, because they both have expertise in historical matters like this.  They both were kind enough to reply.  See their talk pages.  It seems that "action at a distance" probably didn't refer to transmission of force faster than the speed of light back in the 1600's, because such issues weren't considered important then.  And Newton's theory couldn't have been a "field theory" back then, because "vector fields" hadn't been invented.  The "gravitational field" got invented later, and Newton's theory became a "field theory" retroactively.  Whether Newton's gravitational field propagated faster than the speed of light isn't important; it's a classical (pre-1900) theory.  Some people were concerned with this issue, but it's been replaced by GR.  And Sara seems to say that Newton's concern over action at a distance was about other issues, namely, force between things not in physical contact.  We can say now that it refers to speed, but that doesn't seem to be what the issue was in the 1600s.  [[User:PatrickD|PatrickD]] 21:54, 15 November 2009 (EST)

Revision as of 02:54, November 16, 2009

Andy, I'm not going to undo something you've written, but a force field and action at a distance are the same thing. Action at a distance means precisely that - one object, affecting another, without touching it. A force field is precisely that - an object generates a field of force around it, which allows it to affect objects without touching them. JacobB 21:22, 15 November 2009 (EST)

Action at a distance certainly is not the same as electromagnetic waves, which do not act instantaneously on a distance object as Newtonian gravity does. Perhaps the meaning of "force field" is ambiguous (it's not defined in my dictionary).--Andy Schlafly 21:24, 15 November 2009 (EST)
You're absolutely right. Newtonian gravity is a theory which implies instant transmission of gravity, and Maxwell's equations set a speed limit. However, both theories constitute "action at a distance," and both constitute "field theories." The term "field theory" is used for theories like Newtonian gravity, Maxwell's electromagnetism, or quantum field theory BECAUSE they describe action at a distance - in opposition to theories like quantum chromodynamics, or general relativity as it is currently incorporated into the standard model, which describe forces as being carried by particles - photons, gravitons, etc. JacobB 21:29, 15 November 2009 (EST)
No, I don't think that's right, Jacob. "Action at a distance" means instantaneous action. Electromagnetic waves don't fit.
"Field theory" used to mean what you say, but I think today it connotes a "field" that takes time to travel ... as in "quantum field theory." I don't think a distinction is made between particles or waves; the key distinction is between instantaneous action versus action at the speed of light.--Andy Schlafly 21:43, 15 November 2009 (EST)
We'll have to agree to disagree. JacobB 21:44, 15 November 2009 (EST)
Could I ask you two to lower the temperature of this a bit? The question of "action at a distance" is one that I was going to work on before all my time got sucked up into the black hole that is the general relativity article. I put out requests to User:KSorenson and User:SaraT requesting their input, because they both have expertise in historical matters like this. They both were kind enough to reply. See their talk pages. It seems that "action at a distance" probably didn't refer to transmission of force faster than the speed of light back in the 1600's, because such issues weren't considered important then. And Newton's theory couldn't have been a "field theory" back then, because "vector fields" hadn't been invented. The "gravitational field" got invented later, and Newton's theory became a "field theory" retroactively. Whether Newton's gravitational field propagated faster than the speed of light isn't important; it's a classical (pre-1900) theory. Some people were concerned with this issue, but it's been replaced by GR. And Sara seems to say that Newton's concern over action at a distance was about other issues, namely, force between things not in physical contact. We can say now that it refers to speed, but that doesn't seem to be what the issue was in the 1600s. PatrickD 21:54, 15 November 2009 (EST)