system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: If light doesn't have mass, why can't it escape the gravitational pull of a black hole?
gpt
According to general relativity, gravity is not a force, but the curvature of spacetime itself.

Photons follow straight lines through space, but in a curved spacetime those straight lines might look as though a force is acting on the photon to an outside observer.