8. Black Holes
This is another one of the more well-known theories out there, but there is also a lot of controversy surrounding them. This is because nobody is quite sure what would happen if someone were to travel through a black hole. However, because of their enormous gravitational pull, some scientists believe that they are able to slow down time as you get closer to them. This has led scientists to further speculate that black holes are natural time machines that would also make time travel possible.
