Precision experimental tests of general relativity

Partly settled. Some of it is understood, some is still argued about.

In 1999 GR had been confirmed only in weak fields (light bending, Mercury's perihelion, Shapiro delay) and indirectly in strong fields via the binary pulsar PSR 1913+16 (Nobel 1993). Since then, direct gravitational-wave detections (from 2015) matched GR's predicted waveforms precisely, and the Event Horizon Telescope imaged the shadows of the supermassive black holes M87* (2019) and Sagittarius A* (2022), both consistent with GR. No confirmed deviation from GR has been found in any regime tested so far, though the search for departures (especially near the Planck scale) continues.

A theory written down with pencil and paper in 1915 has now been checked against light bending around the sun, orbiting neutron stars, colliding black holes, and a literal photograph of a black hole's shadow — and it has never once been caught wrong.

References

• What problems of physics and astrophysics seem now to be especially important and interesting (thirty years later, already on the verge of the XXI century)?, V L Ginzburg, Physics-Uspekhi 42 (4) 353-373, 1999
• First M87 Event Horizon Telescope Results. I. The Shadow of the Supermassive Black Hole, Event Horizon Telescope Collaboration, The Astrophysical Journal Letters 875, L1, 2019
• First Sagittarius A* Event Horizon Telescope Results. I. The Shadow of the Supermassive Black Hole in the Center of the Milky Way, Event Horizon Telescope Collaboration, The Astrophysical Journal Letters 930, L12, 2022