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According to the theory of general relativity, time dilation occurs in regions of strong gravitational fields such as black holes.
This means that time appears to slow down for an observer near a black hole compared to an observer in a weaker gravitational field.
However, this time dilation effect does not allow for travel through time.
In fact, the extreme gravitational forces of a black hole would likely lead to the destruction of any object that attempted to travel through it.
As for what may be on the other "end" of a black hole, our current understanding suggests that all matter and energy that enters a black hole is crushed into a singularity, a point of infinite density where the known laws of physics break down.