Direct detection of gravitational waves

On 14 September 2015 at 5:51am EDT, ripples in the fabric of spacetime were detected by gravitational-wave observatories in Louisiana and Washington state. Five months later, after going through peer review and checking for every possible source of error, physicists with the Laser Interferometer Gravitational-Wave Observatory (LIGO) confirmed that gravitational waves had been directly detected for the first time . The gravitational waves were emitted by two black holes about 1.3 billion years ago, in the final fractions of a second before they combined into one. After a long journey the waves reached the LIGO detectors 7 milliseconds apart, gently disturbing the laser beams that measure distortions in spacetime. At the time the LIGO detectors weren’t officially in science mode—engineers were still doing final checks to make sure the instruments were working as designed. But the signal was so strong that there was no other interpretation: Scientists had finally heard the ringing of spacetime in the form of gravitational waves, a hundred years after Einstein proposed their existence. (Image credit: Caltech/MIT/LIGO Lab)

Date in History: 14 September 2015