The Laser Interferometer Gravitational Wave Observatory (LIGO) is a large scientific project with the goal of detecting gravitational waves.
LIGO "consists of two detectors situated 1,865 miles (3,002 kilometers) apart in isolated regions in the states of Washington and Louisiana. Each L-shaped facility has two arms positioned at right angles to each other and running 2.5 miles (4 kilometers) from a central building. Lasers are beamed down each arm and bounced back by mirrors, essentially acting as a ruler for the arm. Sensitive detectors can tell if the length of the arms of a LIGO detector varies by as little as 1/10,000 the width of a proton, representing the incredibly small scale of the effects imparted by passing gravitational waves [which would supposedly distort the space and thereby affect the distance the laser beams travel]. LIGO has two observatories to act as a check on the other to rule out that a potential gravitational-wave signal detection is not due to a local, terrestrial disturbance; both facilities will detect a true gravitational wave moving at the speed of light nearly simultaneously. Although the twin LIGO facilities act as a single observatory, they are not designed for "observing" in the conventional sense. Instead of eyes, the facilities can be thought more of as "ears" listening for gravitational waves, or even as a skin trying to "feel" the slightest of movements."[1]
The evolution of gravitational wave detection mechanisms has always been a quest for greater sensitivity and greater rejection of seismic noise, since the waves from even enormous cosmic events are so tiny when they reach Earth. The more sensitive the device is, the farther away it will be able to detect events, and hence the more events it will detect. A major upgrade (tenfold increase in sensitivity) was begun in 2010, ending with the "advanced LIGO" (aLIGO) in 2015.
In 2010 it was reported that a successful observation had been made, and this might even have been submitted to a scientific journal. This was soon deemed a hoax, and it was later revealed that it had been a test injection of false data, authorized by management, to test the integrity of the reporting system.[2]
As it is based on the hugely successful and nearly universally accepted Theory of relativity, and the sorts of things that it might detect (neutron star mergers, black hole mergers, etc.) are well characterized, its chances of success were always considered good if the sensitivity and noise rejection could be sufficiently improved. The upgrade of 2010 was expected to be sufficient to make actual detections. That upgrade was completed in 2015 and, on September 14, 2015, an event (merger of two black holes) was detected. A second detection occurred on December 26, 2015. See Gravitational waves.
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