When were gravitational waves first detected?

Albert Einstein predicted gravitational waves — ripples in spacetime — in 1916 as part of his general theory of relativity. The waves are so faint that detecting them required measuring changes in distance smaller than a thousandth of the width of a proton. LIGO's two detectors in Hanford, Washington, and Livingston, Louisiana, recorded a signal from two black holes, about 36 and 29 times the mass of the Sun, merging roughly 1.3 billion light-years away. The event was named GW150914 after its date. Rainer Weiss, Barry Barish and Kip Thorne won the 2017 Nobel Prize in Physics for the discovery.