| Gravitational waves are ripples in space-time, created by accelerating masses, even a car produces them. However, only extremely large masses doing extremely large accelerations can create measureable amplitudes, such events can be found in the catastrophic events in the universe, such as merging black holes or exploding supernova cores. Gravitational waves were predicted by Albert Einstein in his Theory of General Relativity, but only recently have scientists had the technology to begin steps to detecting these waves. Scientists have no direct evidence for gravitational waves; however, they do have indirect evidence in the form of measurements taken on a binary nuetron star system. The measurements closely match predictions, so scientists are confident that gravitational waves really do exist.
Ligo is a joint Caltech/MIT project involving two gravitational wave detectors. These detectors work by using two precisely perpendicular laser beams of exact wavelength. The setup for the detectors is 4 kilometers long, to provide for the extremely small size of the gravitational waves. The interference pattern of the lasers will stay the same, unless the beams are moved, either by vibration or by gravitational waves. Two are necessary to account for the fact that even something such as a truck driving a few hundred yards from the detector could cause the movement of the beams, as they are extremely sensitive. They are so sensitive, in fact, that thermal fluctuations in the wires used to hold the detectors are unacceptable, so glass wires are being utilized. Since gravitational waves are theorized to travel at the speed of light, and experimental data seemingly confirms this, if both detectors do not have the same change, then the data is thrown out. The two sites are in Livingstone, Louisiana, and Hanford, Washington. Seperated by 2000 miles, the exact same vibrations at the exact same time are extremely unlikely. A third will most likely be added internationally, to aid in triangulation of the source of the gravitational waves.
Ligo is scheduled to go online in 2003.
Sources:
- http://www.ligo.caltech.edu/LIGO_web/about/factsheet.html
- http://www.newscientist.com/news/news.jsp?id=ns99991256
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