Quantum physics has given the idea of the multiverse nonfiction cred. If you want to know exactly how the multiverse seems reasonable, I suggest you do a lot of reading. Quantum physics is hard, counter-intuitive, and can only be put in layman’s terms with thought experiments that are more approximations than accuracies. As I understand it, the most fundamental particles that make up atoms behave probabilistically. We can only assign odds as to where they are and where they are going. In fact, as we become more accurate in locating them we become less accurate in their movement and vice versa. It’s called the Uncertainty Principle. One way of explaining how, say, a single particle can interact with itself to form a wave function, is by saying that the particle takes every possible path to it’s destination. The particle may end up in this spot or that, but given the multiverse, it ends up in every spot. Get it? Neither do I.
A you isn’t as good as the you, but only because you’ve grown attached to yourself. This is more a comfort of legacy than a continuation of soul. A multiverse makes us both more insignificant in our redundancy and more significant in our abundance. It’s quite a thing to think about.
If this multiverse stuff interests you, check out The Hidden Reality: Parallel Universes and the Deep Laws of the Cosmos by my favorite science writer, Brian Greene.