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JoshuaZ comments on [Draft] Holy Bayesian Multiverse, Batman! - Less Wrong
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I think you mean risk non-averse. Since if many worlds is wrong, you fail.
This is an unconvincing argument. First, you don't know the prior probability of humanity surviving. Second, we don't know how many observers to expect in the universe. The relevant class isn't humans but "life intelligent enough to discuss anthropic considerations and MWI" - that class might be much larger.
I'm not sure that class includes humans, actually.
It certainly doesn't include all humans. I think I wrote somewhere on LW that the anthropic Doomsday problem can be solved if the future is ruled by central powers which enforce a prohibition on anthropic talk.
If many-worlds is right you still fail - at least if you define "self" with any sort of continuity, when you die in many-worlds you die in real life.
Mostly agreed. Besides, the same mathematical structure exists in the Copenhagen interpretation too, though it's labeled differently; quantum mechanics is quantum mechanics. It is however evidence for the claim that conscious people can be represented by a wavefunction that contains other possibilities, even if those other possibilities are overwhelmingly probable..
But if you only die in some of the branches, then you'll experience yourself living.
If QI is true, then it's when you die in ALL of the many worlds that you no longer experience anything.
You're presupposing that there's a fact of the matter about what "you" [the person you are now] will experience at a future moment. But the person you are now does not exist at any future moment. In fact, future moments merely contain people who are very similar to you - they remember everything you remember and a little bit more.
Therefore, all we can say is that in a branch where you die, there is no-one who remembers being you, but in a branch where you survive, there is a person who remembers being you. There is no such thing as a 'you' which is identical at different moments, no 'thread of identity' that connects you with your future and past selves, and which magically 'chooses' a branch where 'you' survive. In other words, there is no 'transtemporal identity'.
Fundamentally, what you're trying to achieve in a 'quantum immortality' experiment is to experience a fantastically unlikely event. But when you rephrase this in terms that don't presuppose transtemporal identity, all you're saying is that you want there to be a person somewhere, in some Everett branch, who experiences something fantastically unlikely. Therefore, it makes no difference whether those who fail to experience something fantastically unlikely are killed or left alone.
The real question here is simply "If you experienced something fantastically unlikely, would you take this to be evidence that MWI is true and Copenhagen is false?"
(It's an awkward question because the Copenhagen interpretation is incoherent. We ought to ask the question above about a single-universe interpretation that actually makes sense, like Bohm's interpretation or the GRW theory. But for now let's just pretend that Copenhagen does make sense.)
And if so, does experiencing something humdrum constitute evidence that MWI is false? Surely not.
It seems to me that either (a) experiencing anything at all, regardless of how likely or unlikely it is, gives an equal amount of "anthropic evidence" in favour of MWI, whatever that means; or else (b) There is no sense whatsoever in which observations as opposed to a priori reasoning can favour MWI over Copenhagen (pretending the latter is coherent).
I don't think (a) makes sense, because surely any theory whatsoever comes equipped with an anthropic "dimmer switch" that can be "brightened" or "dimmed" arbitrarily. For instance, to 'brighten' Copenhagen we could just stipulate that there are N parallel non-interacting Copenhagen universes rather than 1. We could even let N be infinite.
So that just leaves (b).
Could constitute observational evidence for something strange, something to follow in thinking about the future, but not in thinking about counterfactuals where quantum mechanics works.
No. If you die in some of the branches, in those branches you'll experience dying, and then you won't experience anything any more.
You're right about the first part. I'll fix it when I get to a real computer.
Since we observed humanity surviving, I think it's alright to use a more specific reference class. If the anthropic principle holds for life in general, then it also holds for just JoshuaZ, right?
No matter what p(S) is, p(S|MW) is larger.
Yes, but I don't know how much larger. So claiming that one should update "radically upwards" is questionable without a lot more of an idea how much and what sorts of life we should expect.
If you make the case that p(S) should include any life, then I can concede the adverb perhaps shouldn't be so dramatic. Are we in agreement that it would be dramatic if we only included humanity exactly like us? If so, I'd like a second opinion from others if a specific anthropic principle is allowed, because it seems reasonable to me.
Yes, because there are times in the history of humanity where we got close to being wiped out (the Toba event being possibly the best documented).
I'd be very curious if anyone else agrees with you there. I don't understand the basis for such a specific reference class, since every intelligent species that thinks about MWI will be in the same position.