system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How does gravity bend light if light is massless?
gpt
Because gravity bends space-time itself. 

The light is still going straight,  by its own point of view, but the space-time is curved by the gravity,  so something traveling straight through curved space-time alters its direction relative to an observer outside the curved region. 

Black holes basically curve space-time inward to the point that there's no getting back out of that gravity well.