A theory which states that space and time are actually a four-dimensional continuum known as "spacetime", and that gravity is a manifestation of the
curvature of the geometry of this four-dimensional spacetime. General
Relativity explains the gravitational bending of
starlight, how gravity slows down the flow of time, predicts the existence of blackholes, and even predicts the expansion of the universe. The theory was formulated by Albert Einstein in order to incorporate gravity into his theory of
relativity.
The famous eclipse experiment of
1919 confirmed
Einstein's prediction that light rays would bend in a gravitational field, according to his theory of
general relativity.