But if you could loop back to visit the universe at an earlier point in time a famous paradox arises What if you killed your grandfather when he was a child Then your father or mother wouldn't have been born so you wouldn't have been born so you wouldn't have been able to go back in time to kill your grandfather in the first place The simplest resolution to the grandfather paradox is that when you go back in time you're actually not going back into your own history but to a copy and everything you do there influences the new alternate future of that universe not your own past If what you do when you go back in time actually influences your own past and the effects of your time travel do loop back to the present future past no problem You go back in time kill your grandfather thus you aren't born so you can't go back in time thus your grandfather isn't killed thus you are born so you go back in time and kill your grandfather and so on I'm showing this as a looping linear series of events but really it's two entangled histories happening in
