LIGO, which stands for the Laser Interferometer Gravitational-Wave Observatory, is a large-scale physics experiment aiming to directly detect gravitational waves. Cofounded in 1992 by Kip Thorne and Ronald Drever of Caltech and Rainer Weiss of MIT, LIGO is a joint project between scientists at MIT, Caltech, and many other colleges and universities. It is sponsored by the National Science Foundation (NSF). At the cost of $620 million, it is the largest and most ambitious project ever funded by the NSF.Observations at LIGO began in 2002, ended in 2010, and no gravitational waves have been reported. The original detectors were disassembled and were replaced by improved versions known as ""Advanced LIGO"". As of February 2015, two such advanced detectors (one in Livingston, Louisiana and the other in Hanford, Washington) have been brought into engineering mode. On September 18, 2015, Advanced LIGO became fully operational and began formal science operations at twice the sensitivity of the initial LIGO interferometers.