General relativity has passed every test that multiple generations of researchers have thrown at it. Those tests include the three that Albert Einstein proposed when he introduced the theory in 1915 as well as repeated precision experiments performed in the lab and through astronomical observations.
The 2015 direct detection of gravitational waves from the merger of two black holes1 marked the opening of a new avenue for testing general relativity. The discovery occurred four decades after Russell Hulse and Joseph Taylor Jr confirmed the existence of gravitational waves indirectly by observing their effect on the orbit of a binary pulsar,2 and it offered the promise of unprecedented access to the strong-field regime of gravity. The now hundreds of mergers that have been spotted by the Laser Interferometer Gravitational-Wave Observatory (LIGO) in the US, Virgo in Italy, and KAGRA in Japan involve black holes and neutron stars that are...
