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Science seems to be self-defeating re: Boltzmann Brains: our best theories imply we're probably BB's, but that's "cognitively unstable" (aka "I really don't want to believe that"), so we're probably not BB's and we can't trust our best theories.

Just ditch this idea that minds can come from mindless stuff. It just creates problems. You're not a Boltzmann Brain, you're not a brain at all. There. Now we have cognitive stability.

I get that, but if we are BBs then our scientific theories are incorrect; this is straightforward paradox, it has something in common with the "Liar' sentence.

If our scientific theories are correct, we are most likely to be Boltzmann brains.
If we are Boltzmann brains our scientific theories are incorrect.

Do you not see the problem? — Janus

If we are Boltzmann brains then our scientific theories are almost certainly incorrect.

Yes, I see the problem. But still, as I said:

If our scientific models entail that we are most likely Boltzmann brains, and if our scientific models are correct, then we are most likely Boltzmann brains.

If our scientific models entail that we are most likely Boltzmann brains, and if we are not most likely Boltzmann brains, then our scientific models are incorrect.

Science seems to be self-defeating re: Boltzmann Brains: our best theories imply we're probably BB's, but that's "cognitively unstable" (aka "I really don't want to believe that"), so we're probably not BB's and we can't trust our best theories.

Just ditch this idea that minds can come from mindless stuff. It just creates problems. You're not a Boltzmann Brain — RogueAI

So, regarding the argument here, your claim is that we can dismiss (4) a priori?

The probability of our being a normal observer is 100%. Here we are.

... The Big Freeze has not happened. — creativesoul

You're begging the question.

The Boltzmann brain problem is that given that our scientific theories entail the eventual formation of an exceptionally large number of Boltzmann brains with experiences like ours, it is exceptionally probable that the Big Freeze has happened and that we are Boltzmann brains having the illusory experience of being normal observers before the Big Freeze.

Is there something that you disagree with in Carroll's conclusion? — wonderer1

I'm not denying that there are scientific models that avoid the Boltzmann brain problem. I'm simply explaining that, as per the words of cosmologists like Carroll, the current leading scientific model entails that we are most likely Boltzmann brains.

I'm then questioning his suggestion that we can dismiss the conclusion that we are most likely Boltzmann brains a priori, as that then entails that we can dismiss some empirically well-supported scientific model a priori. For example, as per @RogueAI's comment above, one supposed solution is to dismiss (4) a priori. Is that really rational?

But moving on from Boltzmann brains, although slightly related, there is perhaps something else to consider.

If there is an infinite multiverse and if every metaphysical possibility is realized in some universe then it would seem to follow that there are an infinite number of universes in which solipsism¹ is correct, an infinite number of universes in which idealism¹ is correct, an infinite number of universes in which common sense external world realism¹ is correct, an infinite number of universes in which monotheism¹ is correct, an infinite number of universes in which polytheism¹ is correct, an infinite number of universes in which atheism¹ is correct, and so on.

¹ _{When considered as making a limited claim only about the nature of the universe in which they are an inhabitant.}

And given the cardinality of infinite sets, the probability that we are in one type of universe rather than some other empirically indistinguishable (to us) universe is equal.

So if it is rational to believe in an infinite multiverse in which every metaphysical possibility is realized, and if your metaphysics is a metaphysical possibility, then it is no less rational to believe in it than in any other.

Which would make all of these arguments rather pointless. You'd be as equally likely to be right as wrong, and either way entirely by accident.

As for whether or not it is rational to believe in such a multiverse:

Is it more rational to believe that this is necessarily the only universe? Is it more rational to believe that there are necessarily a finite number of universes? Is it more rational to believe that even an infinite multiverse necessarily only realizes some subset of all metaphysical possibilities? Is it more rational to believe that an infinite multiverse in which every metaphysical possibility is realized is less probable?

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There are four ifs there, so, giving equal likelihood to each, we end up with a 6,25% chance of being in an infinite multiverse in which every possibility is realized. — Lionino

That's not how it works.

We are likely not in one, but if we are, then the same thing that applies to Boltzmann brains applies here: we have no reason to believe in any reasoning we do — which bears no weight on whether it is true or not, but still. — Lionino

With Boltzmann brains there are a finite number of brains, with more of them having incorrect scientific theories than correct scientific theories, and so if we are Boltzmann brains then we are more likely to have incorrect scientific theories than correct scientific theories.

In an infinite multiverse there are not more universes in which we have incorrect scientific theories than correct scientific theories. Given the nature of infinity, there are an equal number of each universe, and so we are equally likely to have incorrect scientific theories as correct scientific theories.

Besides, this line of reasoning does not depend on scientific evidence at all. It is a priori reasoning: is it more rational to believe that an infinite multiverse in which every metaphysical possibility is realized is less probable?

My belief that it is a worthwhile issue. It is pretty common sense: if several smart(er than me) people work on something, is it not rational to conclude that there is something to it? — Lionino

Certainly, in relation to science or mathematics or any subject where much information has to be incorporated into a coherent understanding of the field. Not so much in relation to philosophy, which is potentially a pursuit for everyone, and the questions are naturally accessible to any intelligent and thoughtful person.

Is a question without a decidable or even satisfying answer worth pursuing? Perhaps is would be better, once one has become aware of and thought about such questions and their possible answers enough to realize they cannot be definitively answered, to move past them.

And do we not come to understand the world through reason? — Lionino

I'd say we come to understand the world via the background presuppositions that underpin human life and reason itself and that understanding may be elaborated and augmented by reason. In any case is not the world presupposed in any attempt to come to understand it?

Is it more rational to believe that an infinite multiverse in which every metaphysical possibility is realized is less probable? — Michael

What determines what is metaphysically possible? Is it merely what is logically possible? Are they the same? is any possible universe governed by logic?

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Boltzmann brains don't involve disembodied cognition. Cognition embodied much differently than ours for the most part, but not disembodied. — wonderer1

Thanks for that. I'll take your word for that. I shouldn't get involved in some of this, I've neither the time nor the knowledge to be said to "know enough" to join in such discourse.

There's much of this stuff I outright reject due to some other commitments I have.

The probability of our being a normal observer is 100%. Here we are.

... The Big Freeze has not happened.
— creativesoul

You're begging the question. — Michael

Proudly.

I'm stating the case. If you reject the brute fact that we are normal observers, then all bets are off.

The Boltzmann brain problem is that given that our scientific theories entail the eventual formation of an exceptionally large number of Boltzmann brains with experiences like ours, it is exceptionally probable that the Big Freeze has happened and that we are Boltzmann brains having the illusory experience of being normal observers before the Big Freeze. — Michael

How do you get from

"given that our scientific theories entail the eventual formation of an exceptionally large number of Boltzmann brains with experiences like ours"

to

"it is exceptionally probable that the Big Freeze has happened"

The Boltzmann brain problem is that given that our scientific theories entail the eventual formation of an exceptionally large number of Boltzmann brains with experiences like ours... — Michael

That's not the only possibility entailed by our scientific theories.




How long does instantaneous existence last? I've been chatting with Banno for over a decade. Jeep/Wayfarer too. Sam 26 even longer.

I did suspect that you may have dissipated in a quantum puff for a while, but here you are, making it less likely that heat death has already happened.

Seems to me the difference between and others here is that he is pretty convinced by the Boltzmann discussion, while the others are more comfortable acknowledging that it is interesting but very far form conclusive.

How long does instantaneous existence last? I've been chatting with Banno for over a decade. Jeep/Wayfarer too. Sam 26 even longer. — creativesoul

I believe the idea is that, if you are a BB, no, you have not been chatting with anyone for any amount of time. Rather, you, a BB, have existed for only a moment. The gigantic number of particles needed just happened to drift into the exact arrangement needed to give you all the "memories" you have, which only seem to have taken place over long periods of time.

All nonsense. But a very fun idea.

Seems to me the difference between ↪Michael and others here is that he is pretty convinced by the Boltzmann discussion, while the others are more comfortable acknowledging that it is interesting but very far form conclusive. — Banno

You seem to misunderstand what I am saying. I don't believe that I am a Boltzmann brain or that I am most likely a Boltzmann brain.

I am simply explaining that, as per the words of the cosmologists who know better than me, our best scientific models entail that we are most likely Boltzmann brains.

Therefore, either we are most likely Boltzmann brains or our best scientific models are mistaken.

How do you get from

"given that our scientific theories entail the eventual formation of an exceptionally large number of Boltzmann brains with experiences like ours"

to

"it is exceptionally probable that the Big Freeze has happened" — creativesoul

Because we ought reason as if we are randomly selected from the set of all possible observers with experiences like ours, and the set of all possible observers with experiences like ours contains exceptionally more post-Big Freeze Boltzmann brains than pre-Big Freeze normal observers.

That's not the only possibility entailed by our scientific theories. — creativesoul

It's what cosmologists say is the most likely consequence of our best scientific theories. This is precisely why the Boltzmann brain problem is seen as a problem. It's not just some crazy hypothesis by some crazy philosopher.

ok, good. And the next step is to agree that there is something fishy here. Which is what I am saying. It’s incomplete.

And the next step is to agree that there is something fishy here. Which is what I am saying. It’s incomplete. — Banno

See the argument here.

If we can dismiss the claim that we are most likely Boltzmann brains a priori then we can dismiss the possibility of heat death a priori, or we can dismiss the possibility of quantum fluctuations a priori, even though we have a posteriori evidence in favour of them.

So sure, something is fishy here, but there appear to be no good solutions.

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The only choice is then to reject 2. — Lionino

Which is why I keep saying: either we are most likely Boltzmann brains or our scientific theories are incorrect.

There is an infinite amount of Boltzmann brains though. — Lionino

Well, this ties into my rejection of an infinite past. Even though we can say that if the universe will last forever then the number of Boltzmann brains will increase to infinity, it must be the case that the time from the Big Bang to now is finite, and so that as of now there have been a finite number of brains (whether normal or Boltzmann).

And if your argument for the multiverse follows, the same can be applied for the Boltzmann brains. So Carroll is wrong and we are as likely to be Boltzmann brains with accurate as with inaccurate scientific knowledge. Thoughts? — Lionino

Yes, that would seem to follow if we allow for infinite "parallel" universes (as my reasoning against an infinite past wouldn't hold).

Or perhaps we don't need to reject either heat death or quantum fluctuations, but just the possibility of quantum fluctuations generating a macroscopic object — which is against our scientific theories but not as harshly so. And even if we don't want to do so, by your footnote here, it can be that the time after the heat death is neither infinite or sufficiently large to make it so that there are more Boltzmann brains than ordinary brains. — Lionino

This would be one solution. However, this still entails that we can dismiss some possible empirical fact a priori:

1. If quantum fluctuations can form macroscopic objects then we are almost certainly quantum fluctuations
2. This conclusion is silly/cognitively unstable
3. Therefore quantum fluctuations cannot form macroscopic objects

Of course, it may be true that quantum fluctuations cannot form macroscopic objects, but there's something less-than-rational about the suggestion that we can dismiss such a possibility a priori, especially given that "we are quantum fluctuations" isn't a contradiction.

An a priori but non-necessary truth is peculiar.

Perhaps the simplest solution is to reject scientific realism in favour of instrumentalism. The mathematics of quantum fluctuations are just a useful tool, not something to be taken so literally.

Therefore, either we are most likely Boltzmann brains or our best scientific models are mistaken. — Michael

Unfortunately it is not nonsense but follows from our scientific theories. — Lionino

What are these models/theories? What predictions do they make? How are they tested?

I am aware of the idea that, in an infinite amount of time, an infinite amount of matter will eventually be arranged in every possible configuration. I don't see that as a model/theory. It's just an idea. Something to contemplate. We can't test it. It's speculation. RougeAI has twice (that I've seen) asked:

How would you calculate density for a infinite number of things (e.g., Boltzmann brains) in an infinitely large space? — RogueAI

The answer is, you couldn't. A crazy large number of particles need to come together in exactly the right way at same time to make a BB. But, since there is infinite space for these infinite particles to be spread throughout, we can't know that that number of particles will ever touch even a single other particle.

What are these models/theories? What predictions do they make? How are they tested? — Patterner

There's the Lambda-CDM model which entails eternal expansion (and eventual heat death), and the energy-time uncertainty principle which entails quantum fluctuations.

Given enough time (which there will be with eternal expansion), quantum fluctuations can generate macroscopic objects, including human-like brains. And given enough time (which there will be with eternal expansion), the number of human-like brains generated from quantum fluctuations will outnumber the number of ordinary human brains that ever existed.

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I believe the idea is that, if you are a BB, no, you have not been chatting with anyone for any amount of time. Rather, you, a BB, have existed for only a moment. The gigantic number of particles needed just happened to drift into the exact arrangement needed to give you all the "memories" you have, which only seem to have taken place over long periods of time.

All nonsense. But a very fun idea. — Patterner

Regarding the idea...

What would it take to even be able to physically reconfigure a normal human observer? All the necessary parts. What do all normal observers have in common such that that's exactly what makes them normal human observers? That's a matter of necessary elemental constituency and existential dependency. There's a bit of work involved there.

Or...

I don't know for sure, but my impression of Witt leads me to think that ideas such as Boltzmann Brains would count as bewitchment.

Given that the sheer number/quantity of particles necessary for reconfiguring me involves reconfiguring everything that I am existentially dependent upon(everything that effected/affected me either directly or indirectly), and I am a normal human observer.

Normal human observers have been affected/effected and/or otherwise influenced, whether directly or indirectly, by all sorts of things. Some of those things are external to us, some of those things are parts of us, some of those things are a combination thereof.

You'd need to recreate the entire universe according to a strict determinist(causal) account. Boltzmann Brains are supposed to come from that... aren't they? Do they presuppose that all it takes to recreate an observer is to recreate and rearrange just the biological components?

Do they presuppose that all it takes to recreate an observer is to recreate the biological components? — creativesoul

That is my understanding. If the memories of all the stimulus we take in and actions we perform are stored physically in our brains, then there's no need to actually take in the stimulus and perform the actions. We can just arrange the physical brain in the way that it would come ro be arranged at the end of all that.

There's the Lambda-CDM model which entails eternal expansion (and eventual heat death), and the energy-time uncertainty principle which entails quantum fluctuations.

Given enough time (which there will be with eternal expansion), quantum fluctuations can generate macroscopic objects, including human-like brains. And given enough time (which there will be with eternal expansion), the number of human-like brains generated from quantum fluctuations will outnumber the number of ordinary human brains that ever existed. — Michael

Pretty sure that the size of space does not factor in it. If you take one m³ of space it will have the same density of particles popping in and out of existence as one cm³ — assuming same conditions. So having more space increases the likelihood of a Boltzmann brain forming if anything. — Lionino

It looks like you two are talking about the same thing. How many virtual particles have been observed in the same place at the same time? Because quantum fluctuations need to account for something like 1.4 x 10^26 atoms (I don't know how many particles that is) coming into existence all at the same time in the space that takes up a brain in order to make a Boltzman Brain. Not just that number, of course, but also the variety.

Talking as if memories are distinct entities, things that can be stored, seems mistaken to me. Without a tree there is no memory of one. Our memories of trees are existentially dependent upon trees, regardless of their meaningful content, regardless of their veracity. Our memories of trees cannot be reconstructed in any other manner other than series of physical and mental events from whence they emerged.

It looks like you two are talking about the same thing. How many virtual particles have been observed in the same place at the same time? Because quantum fluctuations need to account for something like 1.4 x 10^26 atoms (I don't know how many particles that is) coming into existence all at the same time in the space that takes up a brain in order to make a Boltzman Brain. Not just that number, of course, but also the variety. — Patterner

:up:

And not just the number and variety but also the complexity of the arrangement.