" if there are indeed many copies of "you", with identical past lives and memories, this kills the traditional notion of determinism: you can't predict your own future-even if you have complete knowledge of the entire past and future history of the cosmos! The reason you can't is that there's no way for you to determine which of these copies is "you"(they all feel that they are). Yet their lives will typically begin to differ eventually, so the best you can do is predict probabilities for what you'll experience from now on. "

― Max Tegmark , Our Mathematical Universe: My Quest for the Ultimate Nature of Reality