system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: The theory that black holes can be used for time travel.
gpt
First it's important to realize that Black Holes aren't really holes, they're just an astronomical amount of stuff all compressed down to a relatively small size. But with all that stuff in such a small area of space comes a lot of gravity. Gravity does not just affect 3-dimensional space such as an object or a person, but also the 4th dimension of time. The more gravity that affects an object, the slower time moves for it (and the faster time moves around it from it's point of view). So black holes can be used for time travel in a sense that you're pressing the fast-forward button on the rest of the universe around you and when you get to the part of the movie you want to watch you can just move away from the black hole and continue.

The drawback here is that it only works as a fast-forward and cannot (to our current knowledge) be used to go backwards. It's not exactly time travel, it's more like stasis.