Cosmic Strings

Cosmic strings are tiny (smaller than sub-atomic particles!) 1-dimensional objects created in the early times of our universe. These strings may lie everywhere across our universe, and are under immense pressure.

What they do do, however, is posses hugely strong gravitational fields. These, like black holes, distort spacetime and can allow time travel to the future.

By getting two cosmic strings close together, or getting a cosmic string next to a black hole, you could warp spacetime enough to cause closed time-like curves, which is like a timeline that loops back on itself!

The sad thing is, there is still much speculation (even more than the other theories!) on whether cosmic strings do actually exist; and even if they do, no one knows what form a cosmic string may take, or where we could find some.