Background: There are two competing schools in quantum physics regarding the probabilistic nature of the universe. Given an experiment like Schrodinger’s Cat, one school says that the cat is both alive and dead until the box is open, the other posits multiple universes, some where the cat is dead, some where it is not.
Claim: If the latter school is correct, then everyone experiences themselves living forever(or until the probability of living longer is zero). I do not mean that their consciousness lives on past their body, but that they survive bodily for the longest chain of posibilities that exists.
Assumptions: I assume the scientific frame of mind. I assume that there is no immortal soul, that our consciousness is an emergent property of our our anatomy. And I will assume that the latter school is correct, and that at every instant, there are diverging universes representing the possible outcomes of a probabilistic system.
The proof, given the assumptions, is simple. If we cease to experience anything when we die, then our experience will always take the path that keeps us alive: if there is a possible universe in which we continue to live, then we will continue to live. Our experience will always follow the outcome in which we continue to experience. It sounds like a truism.
There is an issue of having already diverged from the universe in which you live forever, and are now in a universe that will end in a zero probability of survival situation.
Further claim: All possible universes always have an outcome in which we experience living for ever.
This claim is vindicated by the fact of quantum physics that there is never a zero probability situation. The maths that predict the probability involve equations that only ever approximate zero, never actually reaching it. But no matter how small the probability is that our experience continues to exist, it is the only outcome that we can experience.
The longest chain of possible existence, then, is infinite. So all people can expect to live forever.
I do not propose this as a fact, only as an inevitable outcome of the second of the two schools of quantum understanding. For some, this may be a reason to reject that school (though the remaining possibilities are equally unsatisfying). I don’t really like the conclusion, but I think it is valid.