What do black holes do to time?

Answer 1

Black holes could be said to do the same thing to time as do other sources of gravity, only to a more extreme degree. In General Relativity, which was Einstein's theory of gravity, he proposed that space and time were equivalent and merged into a single entity - spacetime - and the effect of gravitation's influence was a local curvature in spacetime. His predictions were verified with accurate chronometers at sea level experiencing the higher pull from gravity, than those at higher a;titudes. The effect was referred to as gravitational time dilation; a clock in greater gravity would seem to run more slowly than one at lower gravity (higher altitude).

A distant observer watching somebody falling into a black hole would notice they seemed to get slower and more redshifted as they approached the event horizon, but never quite crossed it. They would also become more difficult to observe as they were redshifted by gravity into invisibility.

From a subjective standpoint however, somebody falling into a black hole (hopefully a large one, so they could survive being turned into spaghetti by tidal force) would not notice any time dilation, and might in fact not know when they had crossed the event horizon.

The question of what happens in the singularity at the center of a black hole is not described well by our current models in physics; most agree that time stops (or that spacetime stops being a manifold).