If realy someone goes back into the past and change something. You wouldn't remember, because you would see your "new" reality as the right one. So who cares if anyone changes your past
Ähm timetravel is a thing a lot of people went crazy, because they thought too long about pradoxes.
I saw a documentary, they said, that if you spin around a galactic string you can go in to the future but not into the past. (I thought: show me galactic string)