Though gravitational waves are invisible, they do have a measurable effect on the space they travel through by causing distances to shrink and stretch. To detect these changes a laser light is used as a very precise stopwatch to measure this effect. By shooting lasers down a cavity that is almost 4 km in length, and measuring the time each of the light returns, scientists can detect if a gravitational wave interferred with the laser's path.
"Since the speed of light is constant, if the race down the interferometer arms and back is a “tie” it means that the light traveled the exact same distance and the arms are exactly the same length...However, if one of these arms is stretched or shrunk, say by a gravitational wave, the race will not be a tie; the beam traveling down the shorter arm will win the race and interfere with the beam traveling down the longer arm, creating a signal."
Some History behind the Project:
In 1916, the year after correctly formulating the theory of general relativity, Albert Einstein predicted that accelerating masses create ripples that propagate through the fabric of spacetime known as gravitational waves. However, these ripples are so unbelievably minuscule that Einstein himself thought they would never be detected. A century after this prediction, the Laser Interferometer Gravitational-wave Observatory (LIGO) has made the first direct detection of this elusive phenomenon.
For more information about the LIGO project Click Here
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