yes, this is an interesting question for me.. how do we know that someone sa future already travelled sa past and this is now the result?
Is it possible that if one can travel back to the past will require all the energy of the universe (level 3 civilization as they call it) to break the speed of light - which will destroy the universe if we use it and in effect we can only travel once. And because this technology destroys everything else, so we didnt want to use this but what if someone did use it depite the fact.. he travels to past to become god...(imaginative mode. hehe)
Just sharing my ideas (crazy, but who knows, this might become a best seller and a movie someday)...





..anyway, i still find predestination paradoxes more interesting..try watching Donnie Darko..