Many theories of time deal with it was another dimension. While it is more strictly linked to causality and entropy than regular spacial dimensions, it may be only our perspective in it that makes us see any difference. Going back in time may be as simple as taking a step backward for other types of consciousnesses.

Eigenstate theory says in a nutshell for even the smallest of actions/movements/events occurring in the present, an infinite (or seemingly so) top-level universes are created. If that is true and there were a way to move between eigenstates, it may be possible to move to a given point in the past. This does not work to go to the future as eigenstates are the product of events, and as such don't exist until events happen.