Traveling backwards in time is functionally equivalent to exceeding the speed of light; in fact, an object is traveling faster than the speed of light in one in

Traveling backwards in time is functionally equivalent to exceeding the speed of light; in fact, an object is traveling faster than the speed of light in one inertial frame of reference if and only if there is a second inertial frame of reference, with relative velocity to the first less than the speed of light, in which it is traveling backwards in time. Technical matters of relativity aside, consider that you can't actually change how fast you move through time. You can't make time move faster or slower, at least within your own frame of reference. Time doesn't just move in a fixed direction, it moves at a fixed rate. Note that this is pretty close to how special relativity actually works, modulo semantics of "rate" when dealing with time. There are also thermodynamic considerations. One direction of time does seem to be privileged in terms of entropy. This doesn't necessarily mean that time travel is impossible, as far as I'm aware, but it does mean that "forward" in time isn't completely arbitrary, and reversing that may be thermodynamically unfavored.