I believe time is "movement". If there's space where nothing moves, time doesn't seem to advance (or it just doesn't manifest in any way). So to the matter of going backwards in time we would need to reverse the ongoing movement. This would need understanding of what made universe move at all. What was the moment when time started? What was before time is wrong kind of thinking since it assumes the time being started already. If we go to the beginning of time you could think of it like going towards north, so long that there's no direction to move more north and that is where it all started.
Also not sure to what scale the reverse should be done. I mean is it supposed to be done inside our solar system or entire space. What the heck would even be the means to do such
Maybe human has advanced to the level of such understanding and have experimented on timetravel, only to each time rewind us to stoneage. Each time they fail to "protect" themselves from it and shit starts over.
This assumes there's only one universe. There are theories of parallel etc universies.
Either way while we don't have definition for time (outside the clock) we are not in position to understand any of this. There is also possibility that whole timetravel concept will always be only inside human mind and never part of material reality. Originating from feelings of regret.
This post was edited by Crud1ty on May 29 2018 01:46pm