[Draft] Holy Bayesian Multiverse, Batman!

Let C be the event that the Copenhagen interpretation is correct

The complement of "Many Worlds is true" is not "the Copenhagen interpretation is correct". I'm not at all confident "the Copenhagen interpretation is correct" is even a logical possibility.

[-]JoshuaZ15y30

Surviving a quantum death trap is a convincing argument in favor of the many-worlds hypothesis, but you'd have to be pretty risk-averse to seek it out.

I think you mean risk non-averse. Since if many worlds is wrong, you fail.

Cosmology is an analagous quantum death trap, and the entire human race witnessed it from the inside.

If you haven't thought about this argument before, you should update your belief in the many-worlds interpretation radically upwards.

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.

[-]FAWS15y40

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.

[-]Jack15y30

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.

[-]Manfred15y10

Surviving a quantum death trap is a convincing argument in favor of the many-worlds hypothesis, but you'd have to be pretty risk-averse to seek it out.

I think you mean risk non-averse. Since if many worlds is wrong, you fail.

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.

Cosmology is an analagous quantum death trap, and the entire human race witnessed it from the inside.

If you haven't thought about this argument before, you should update your belief in the many-worlds interpretation radically upwards.

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.

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..

[-]b1shop15y00

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.

[-]AlephNeil15y100

But if you only die in some of the branches, then you'll experience yourself living.

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.)

[-]AlephNeil15y20

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?"

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).

[-]Vladimir_Nesov15y00

And if so, does experiencing something humdrum constitute evidence that MWI is false?

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.

[-]ArisKatsaris15y10

But if you only die in some of the branches, then you'll experience yourself living.

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.

[-]b1shop15y00

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.

[-]JoshuaZ15y10

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.

[-]b1shop15y00

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.

[-]JoshuaZ15y10

. Are we in agreement that it would be dramatic if we only included humanity exactly like us? I

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 like a second opinion from others if a specific anthropic principle is allowed, because it seems reasonable to me.

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.

[-]knb15y20

Here is something I find confusing. If you believe you will have "continuity of consciousness" after being cryopreserved and revived, and you also believe in many-worlds, should you accept the Quantum Immortality hypothesis?

I never really thought of that before.

[-]Pavitra15y10

Don't update too drastically. There's a nontrivial probability that there exists some other theory you haven't thought of, that would also assign high conditional credence to you observing yourself to exist.

[-]humpolec15y10

Is there an analogous experiment for Tegmark's multiverse?

You set up an experiment so that you survive only if some outcome, anticipated by your highly improbable theory of physics, is true.

Then you wake up in a world which is with high probability governed by your theory.

[-]DanielVarga15y20

The analogous experiment for Tegmark's multiverse is called Permutation City.

[-]MinibearRex15y10

It's not at all clear to me how it is that, if the many worlds theory is correct, I will experience myself not dying. Assuming the many worlds theory is accurate, in some worlds the versions of "me" that are present there will cease to exist and not feel anything anymore, and in others the versions of "me" will survive. The many worlds interpretation doesn't tell me anything about which set of universe I (singular) am in.

[-]DanielLC15y00

The probability of Batman finding that he survives after the first coinflip is not 50% or 100% in either interpretation. It's more like one in several trillion. If you add "Given that you're batman, and just did the experiment", it's clearly 100% in any interpretation.

There's another, bigger problem. Compare quantum immortality to if he had actual immortality, and just never died. You make it sound like the probabilities will come out the same. They will not. The probability of being batman after flipping the coin is lower in the many worlds version is lower, since the probability amplitude is lower. For example, if he lived 20 years before the coin flip, and, if he survives, 20 years after, in the many worlds interpretation, he'd be twice as likely to be in the "before" section, whereas if it's just guaranteed not to kill him, they'd be equal.

In addition, if you add a huge number of bystanders, one is less likely to be batman in the many worlds version, so it works out that one is about as likely to be batman before in either version, but more likely to be him after in the actual immortality version.

[-]mwengler15y00

Since you participate in hypothetical MWIs where Batman lives or dies, to test this hypothesis you pretty much need to kill yourself. If you find yourself surviving all your attempts to kill yourself, you have great evidence for your particular version of MWI immortality.

of course if you are wrong, you are dead and gone. Bummer.

[-]humpolec15y00

If I understand correctly, under MW you anticipate the experience of surviving with probability 1, and under C with probability 0.5. I don't think that's justified.

In both cases the probability should be either conditional on "being there to experience anything" (and equal 1), OR unconditional (equal the "external" probability of survival, 0.5). This is something in between. You take the external probability in C, but condition on the surviving branches in MW.

[+]b1shop15y-120

LESSWRONG
LW

LESSWRONG
LW

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[Draft] Holy Bayesian Multiverse, Batman!

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The Fiendish Setup:

From Batman's Point of View

From Joker's Point of View

Proving Many-Worlds