Quantum physics says that there is an infinite number of possibilities and parallels to the one that we know, and every event is also played out in a parallel world. It's kind of a crazy idea, but someone called Saibal Mitra at the University of Amsterdam says that if you could back up your memory in case of a catastrophic event, you could actually revert to that back-up and find an alternative world in which the Earth didn't explode or collide with Mars.