As I see it one of two thing can happen with time travel. 1- Time travel is not possible at all. 2- We time travel and destroy the universe. Here's why, - The universe has a set mass, and therefore a set gravitational pull. If you go back in time you have just increased the mass of the universe and eventhough it's a small mass it will still change everything. -And also the atoms that you are made of are were making up somthing else in the past. So the question is then can you have a duplicate copy of matter in the same universe? Or would it destory the duplicate copys of matter then decreasing the mass of the universe.