The largest gravitational detector in the world is the Laser Interferometry Gravitational wave Observatory (LIGO) in the United States, with a length of 4km long. LIGO consists of 2 almost identical L-shaped structures based in Louisiana and Washington (USA), almost 3,200km (2,000 miles) apart. The arms of these facilities stretch to 4km (2.4 miles) long, providing LIGO with the extreme sensitivity required for the detection of gravitational waves. This massive project underwent its first science run (i.e. space observations as opposed to instrumental tests) on 29 June 2002 for 2 weeks, which will enable the development of tools for data analysis. However, the direct detection of gravitational waves is not expected until 2006, when the current detector sensitivities are due to be greatly increased.Although there is indirect proof of the existence of gravitational waves, no direct measurements have been made to date, due to the extreme sensitivity necessary for detection. The length of the detectors allows LIGO’s acute sensitivity, which is vital for observing the tiny fluctuations caused by a gravitational ripple. Separate sites are required as a control system;there are a whole host of common, natural occurrences that could produce the same response as a gravitational wave, however, it is unlikely that these local phenomena would be identically reproduced in a site almost 2000 miles away. LIGO is the result of a collaboration between California Institute of Technology (Caltech) and Massachusetts Institute of Technology (MIT).