Einstein proposed the equivalence principle as the foundation of the general theory of relativity. By considering the consequences of the equivalence principle, Einstein concluded that we live in a curved spacetime.

Light must change its path near a massive object not because light is bent by gravity, but because spacetime is The distribution of matter determines the curvature of spacetime; other objects (and even light) entering a region of spacetime must follow its curvature.

black hole — a region in spacetime where gravity is so strong that nothing—not even light—can escape. spacetime — system of one time and three space coordinates, with respect to which the time and place of an event can be specified. equivalence principle — concept that a gravitational force and a suitable acceleration are indistinguishable within a sufficiently local environment. massive object not because light — bent by gravity, but because spacetime is.