The LIGO experiment first detected gravitational waves in 2015. On September 14, 2015, LIGO’s twin detectors in Livingston, Louisiana, and Hanford, Washington, recorded the signal later named GW150914.
The waves came from the merger of two black holes roughly 1.3 billion light-years away. As the black holes spiraled together, they produced ripples in spacetime predicted by Albert Einstein’s general theory of relativity. LIGO detected those ripples by measuring extraordinarily small changes in the lengths of its perpendicular arms with laser interferometry.
LIGO stands for Laser Interferometer Gravitational-Wave Observatory. Virgo is another gravitational-wave detector, but it joined the worldwide detection network later and was not responsible for the first observation. LISA is a planned space-based observatory, while CERN is a particle-physics research organization rather than a gravitational-wave experiment.
The discovery was announced in February 2016 and earned the 2017 Nobel Prize in Physics for Rainer Weiss, Barry Barish, and Kip Thorne.