General Relativity
Einstein's 1915 theory of gravity, describing it as the curvature of spacetime caused by mass and energy. Predicts black holes, gravitational waves, and time dilation.
General relativity is Albert Einstein's 1915 theory of gravity, which replaced Newton's framework with the idea that mass and energy curve spacetime, and that what we experience as gravitational force is actually objects moving along the straightest possible paths through this curved geometry.
Among its many confirmed predictions: the bending of light by gravity (gravitational lensing), the precession of Mercury's orbit, time dilation in gravitational fields (essential for GPS to work), gravitational waves (first directly detected in 2015), and the existence of black holes.
General relativity remains the best-tested theory of gravity but is incompatible with quantum mechanics at very small scales. Reconciling the two — finding a theory of quantum gravity — is among the great open problems in physics.