I’ve read many discussions debating “quantum immortality” over the years. They never seem to get anywhere.
Is QI true? Should you expect to be immortal? This seems like one of those “wrong questions” that Eliezer talks about. That is, there’s really no way even in principle to figure out if it’s true. Suppose the MWI is correct and you play Russian roulette and repeatedly find yourself surviving, seemingly way too often for it to be chance. Well, by the MWI you’d predict that somewhere in the multiverse there would exist a successor of yourself who would have exactly that experience. So the fact that you find yourself being that successor does not prove that playing Russian roulette is harmless. Your amplitude (probability) is greatly reduced, and whether you view that as harmful or not may depend on other considerations. Normally you do care very much about probabilities, although perhaps you can make an argument why you should not care in this case. Either way, the fact that you are alive doesn’t by itself answer the question.
How about this, though. Suppose you were uncertain about the MWI versus other interpretations. Would finding yourself alive after many trials of Russian roulette be evidence in favor of the MWI? I don’t think so, although I’m not 100% sure of my reasoning. Try the standard Bayesian approach. The probability of finding myself alive in a conventional collapse interpretation is very low. Now we are tempted to say that the probability of finding myself alive in the MWI is high, in fact it is certain that I will survive in some branches. And if this is correct, then survival does strongly argue in favor of the MWI, by Bayes’ theorem.
But is it right to say that the probability of finding myself alive is certain, in the MWI? We know that in those branches where I survive, my quantum amplitude (probability) is greatly reduced. Normally in the MWI if we are going to use Bayesian reasoning, we have to discount branches by their probability weighting, or else we are going to get the wrong answer. We can’t just treat all branches as equally probable. But if we apply that discounting in this case, the Bayesian argument in favor of the MWI goes away. The probability we need to use for finding ourselves alive in the MWI is just as low as it is in a conventional collapse interpretation. Hence even very low probability survival is not evidence for the MWI. (BTW I think I am reconstructing an argument from Wei Dai many years ago on his everything-exists mailing list.)
I’ve read many discussions debating “quantum immortality” over the years. They never seem to get anywhere.
Is QI true? Should you expect to be immortal? This seems like one of those “wrong questions” that Eliezer talks about. That is, there’s really no way even in principle to figure out if it’s true. Suppose the MWI is correct and you play Russian roulette and repeatedly find yourself surviving, seemingly way too often for it to be chance. Well, by the MWI you’d predict that somewhere in the multiverse there would exist a successor of yourself who would have exactly that experience. So the fact that you find yourself being that successor does not prove that playing Russian roulette is harmless. Your amplitude (probability) is greatly reduced, and whether you view that as harmful or not may depend on other considerations. Normally you do care very much about probabilities, although perhaps you can make an argument why you should not care in this case. Either way, the fact that you are alive doesn’t by itself answer the question.
How about this, though. Suppose you were uncertain about the MWI versus other interpretations. Would finding yourself alive after many trials of Russian roulette be evidence in favor of the MWI? I don’t think so, although I’m not 100% sure of my reasoning. Try the standard Bayesian approach. The probability of finding myself alive in a conventional collapse interpretation is very low. Now we are tempted to say that the probability of finding myself alive in the MWI is high, in fact it is certain that I will survive in some branches. And if this is correct, then survival does strongly argue in favor of the MWI, by Bayes’ theorem.
But is it right to say that the probability of finding myself alive is certain, in the MWI? We know that in those branches where I survive, my quantum amplitude (probability) is greatly reduced. Normally in the MWI if we are going to use Bayesian reasoning, we have to discount branches by their probability weighting, or else we are going to get the wrong answer. We can’t just treat all branches as equally probable. But if we apply that discounting in this case, the Bayesian argument in favor of the MWI goes away. The probability we need to use for finding ourselves alive in the MWI is just as low as it is in a conventional collapse interpretation. Hence even very low probability survival is not evidence for the MWI. (BTW I think I am reconstructing an argument from Wei Dai many years ago on his everything-exists mailing list.)