I'm not assuming it. It's what physicists like Boltzmann, Eddington, Feynman, Sean Carroll, Brian Greene, and others say. I'm deferring to their expertise. — Michael

So, an argument from authority then? Even worse, it seems that they are not really saying what you seem to want them to be saying.

It seems you use "perceive" were you might better use "interact".

That might be all that is problematic with this thread. — Banno

Interact? Why do you want to talk, share and communicate with your cup?
We are interested in perception and belief, not interaction.

So, an argument from authority then? — Janus

Yes. I defer to what physicists say about what the scientific evidence entails, as is proper.

Even worse, it seems that they are not really saying what you seem to want them to be saying. — Janus

I don’t want them to be saying anything. I’m simply reporting on what they're saying.

See, for example, Big Brain Theory: Have Cosmologists Lost Theirs?

It could be the weirdest and most embarrassing prediction in the history of cosmology, if not science.

If true, it would mean that you yourself reading this article are more likely to be some momentary fluctuation in a field of matter and energy out in space than a person with a real past born through billions of years of evolution in an orderly star-spangled cosmos. Your memories and the world you think you see around you are illusions.

This bizarre picture is the outcome of a recent series of calculations that take some of the bedrock theories and discoveries of modern cosmology to the limit. Nobody in the field believes that this is the way things really work, however. And so in the last couple of years there has been a growing stream of debate and dueling papers, replete with references to such esoteric subjects as reincarnation, multiple universes and even the death of spacetime, as cosmologists try to square the predictions of their cherished theories with their convictions that we and the universe are real.

...

Alan Guth, a cosmologist at the Massachusetts Institute of Technology who agrees this overabundance is absurd, pointed out that some calculations result in an infinite number of free-floating brains for every normal brain, making it “infinitely unlikely for us to be normal brains.” Welcome to what physicists call the Boltzmann brain problem, named after the 19th-century Austrian physicist Ludwig Boltzmann, who suggested the mechanism by which such fluctuations could happen in a gas or in the universe. Cosmologists also refer to them as “freaky observers,” in contrast to regular or “ordered” observers of the cosmos like ourselves. Cosmologists are desperate to eliminate these freaks from their theories, but so far they can’t even agree on how or even on whether they are making any progress.

A straightforward reading of this is that cosmologists accept that our best scientific models, best supported by the scientific evidence, entail that we are most likely Boltzmann brains.

Of course, like you and others they cannot accept the conclusion, and so believe that the scientific models must be wrong. Which is why, as I said earlier, either we are most likely Boltzmann brains or our science is incorrect.

But as explained by the simple argument here, avoiding this "absurd" conclusion is no easy task, as rejecting one of the premises – contrary to the evidence that favours them – simply to avoid the conclusion doesn't seem rational.

Which is why, as I said earlier, either we are most likely Boltzmann brains or our science is incorrect. — Michael

Are you familiar with The Relativity of Wrong?

Yes. How is that relevant?

It's hasn't been clear to me that when you say, "or our science is incorrect", that you recognize the relativity of incorrectness.

It's hasn't been clear to me that when you say, "or our science is incorrect", that you recognize the relativity of incorrectness. — wonderer1

Then I'll make it clear: I'm not saying that therefore all science is completely wrong and that all the facts may be utterly different than what we believe them to be.

The argument here provides a more precise account: either (7) is true or at least one of (1)-(4) is false.

The argument here provides a more precise account: either (7) is true or at least one of (1)-(4) is false. — Michael

Whether (1) is true is unknown. As far as I know, the universe as we know it might end with a false vacuum decay tomorrow.

Whether (1) is true is unknown. As far as I know, the universe as we know it might end with a false vacuum decay tomorrow. — wonderer1

Yes, there are 4 major predictions: Big Freeze, Big Rip, Big Crunch, and vacuum instability.

With Big Freeze being considered to have the most evidential support.

Is the "absurdity" of (7) sufficient justification to reject the evidence that suggests that the Big Freeze is most likely?

My view is along the lines of Sean Carroll's. (Again, from The Big Picture.)

It makes sense, as Wittgenstein would say, to apportion the overwhelming majority of our credence to the possibility that the world we see is real, and functions pretty much as we see it. Naturally, we are always willing to update our beliefs in the face of new evidence. If there comes a clear night, when the stars in the sky rearrange themselves to say, “I AM YOUR PROGRAMMER. HOW DO YOU LIKE YOUR SIMULATION SO FAR?” we can shift our credences appropriately.

And yet there's the argument here.

You're claiming that the "absurdity" of (7) is sufficient justification to reject the evidence that suggests that (1), (2), (3), and/or (4) is true. Is that really rational?

It must be that the universe won't succumb to the Big Freeze, because if it will then we are most likely Boltzmann brains!

It must be that the time between the Big Bang and the Big Freeze is infinite, because if it isn't then we are most likely Boltzmann brains!

It must be that the time after the Big Freeze is finite (and sufficiently small), because if it isn't then we are most likely Boltzmann brains!

It must be that the probability of a Boltzmann brain with experiences like ours forming via quantum fluctuation or nucleation within a finite time is zero, because if it isn't then we are most likely Boltzmann brains!

You're welcome to do it. But then you leave room for sceptics, anti-realists, idealists, and solipsists to dogmatically reject whatever scientific evidence supports common-sense non-sceptical external world realism. You've set the precedent.

You're claiming that the "absurdity" of (7) is sufficient justification to reject the evidence that suggests that (1), (2), (3), and/or (4) is true. — Michael

No. I am claiming 1-4 are insufficiently justified given the present state of scientific knowledge and my ability to distinguish well evidenced science from highly speculative science.

No. I am claiming 1-4 are insufficiently justified given the present state of scientific knowledge and my ability to distinguish well evidenced science from highly speculative science. — wonderer1

You're not just saying that.

If (1)-(4) are true then (7) is true. You're saying that (7) is false. Therefore you're saying that (1), (2), (3), and/or (4) is false.

You're dismissing some outcome on purely theoretical grounds irrespective of the strength of its evidence. I’m asking if that's rational.

You're dismissing some outcome on purely theoretical grounds irrespective of the strength of its evidence. — Michael

Nah, it's a matter of my understanding of the strength of the evidence.

Nah, it's a matter of my understanding of the strength of the evidence. — wonderer1

So you're a cosmologist who understands the sigma level of each of (1), (2), (3), and (4)? I wasn't aware.

As you follow Sean Carroll, see here:

In brief, the BB problem arises if our universe (1) lasts forever (or at least an extraordinarily long time, much longer than 10¹⁰⁶⁶ years), and (2) undergoes random fluctuations that could potentially create conscious observers. If the rate of fluctuations times the lifetime of the universe is sufficiently large, we would expect a “typical” observer to be such a fluctuation, rather than one of the ordinary observers (OOs) that arise through traditional thermodynamic evolution in the wake of a low-entropy Big Bang. We humans here on Earth have a strong belief that we are OOs, not BBs, so there is apparently something fishy about a cosmological model that predicts that almost all observers are BBs.

This mildly diverting observation becomes more pressing if we notice that the current best-fit model for cosmology – denoted ΛCDM, where Λ stands for the cosmological constant (vacuum energy) and CDM for “cold dark matter” – is arguably a theory that satisfies both conditions (1) and (2).

...

It is therefore reasonable to worry that BBs will be produced in the eventual future, and dominate the number of intelligent observers in the universe. Note that this conclusion doesn’t involve speculative ideas such as eternal inflation, the cosmological multiverse, or the string theory landscape – it refers to ordinary ΛCDM, the best-fit model constructed by cosmologists to describe the universe we live in today.

...

I will argue that cosmologies dominated by BBs should be rejected, not because I have empirical evidence that I am not one and I should be, but because such models are cognitively unstable.

...

The best we can do is to decline to entertain the possibility that the universe is described by a cognitively unstable theory, by setting our prior for such a possibility to zero (or at least very close to it). That is what priors are all about: setting credences for models on the basis of how simple and reasonable they seem to be before we have collected any relevant data. It seems unreasonable to grant substantial credence to the prospect that we have no right to be granting substantial credence to anything. If we discover that a certain otherwise innocuous cosmological model doesn’t allow us to have a reasonable degree of confidence in science and the empirical method, it makes sense to reject that model, if only on pragmatic grounds. This includes theories in which the universe is dominated by Boltzmann Brains and other random fluctuations. It’s not that we’ve gathered evidence against such theories by noticing that we are not BBs; it’s that we should discard such theories from consideration even before we’ve looked.

So, it seems to be exactly what I said above. The best evidence supports (1)-(4), and (7) follows. And his argument is that because (7) is just silly, we must reject (1), (2), (3), and/or (4) despite the evidence in their favour. It's a conceded dogma.

I'm asking if that's rational.

If it's rational to reject (7) a priori then it's rational to reject (1), (2), (3), and/or (4) a priori. If it's not rational to reject (1), (2), (3), and/or (4) a priori then it's not rational to reject (7) a priori.

We have a choice to make.

Then I'll make it clear: I'm not saying that therefore all science is completely wrong and that all the facts may be utterly different than what we believe them to be. — Michael

If we are Boltzmann brains—random quantum fluctuations will false memories—then it stands to reason that all our science is completely wrong because based on false memory. But since it is our science that (purportedly) tells us that we are Boltzman brains and that hence all our science is wrong, why would it be rational to believe such a self-eliminating conclusion? It is precisely this problem that you have so far completely failed to address.

Also, Caroll in your post above seems to be saying that it is only in the unimaginably far future that BBs will arise in any case, so, given that, why is it likely that we are BBs now?

But since it is our science that (purportedly) tells us that we are Boltzman brains and that hence all our science is wrong, why would it be rational to believe such a self-eliminating conclusion? It is precisely this problem that you have so far completely failed to address. — Janus

I'm not saying that it is rational to believe that we are Boltzmann brains. I am simply explaining that our best scientific models seem to entail that we are most likely Boltzmann brains. Therefore, either our scientific models are correct and we are most likely Boltzmann brains or we are not most likely Boltzmann brains and our scientific models are incorrect.

I'm then questioning the extent to which it is rational to reject some scientific model a priori when it is supported a posteriori.

Therefore, either our scientific models are correct and we are most likely Boltzmann brains or we are not most likely Boltzmann brains and our scientific models are incorrect. — Michael

No, you have it backwards, if we are BBs our scientific models are necessarily incorrect (assuming that it would even be possible for BBs to have scientific models, which is extremely questionable), as I already explained.

No, you have it backwards, if we are BBs our scientific models are necessarily incorrect (assuming that it would even be possible for BBs to have scientific models, which is extremely questionable), as I already explained. — Janus

1. Our scientific models tell us that we are most likely Boltzmann brains.
2. If what our scientific models tell us is true then we are most likely Boltzmann brains.
3. If we are not most likely Boltzmann brains then what our scientific models tell us is false.

(2) and (3) seem quite straightforward.

Compare with:

1. John tells us that it is raining.
2. If what John says is true then it is raining.
3. If it is not raining then what John says is false.

You're just doubling down and are still ignoring the fact that if we are BBs our scientific models are incorrect; illusory because based on illusory memories.

You're just doubling down and are still ignoring the fact that if we are BBs our scientific models are incorrect. — Janus

I'm not ignoring it because I've never disputed it. If we are Boltzmann brains then our scientific models are almost certainly incorrect.

This doesn't refute what I said above:

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. This is a straightforward modus ponens.

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. This is a straightforward modus tollens.

1. The universe will succumb to the Big Freeze
2. The time between the Big Bang and the Big Freeze is finite
3. The time after the Big Freeze is infinite1
4. The probability of a Boltzmann brain with experiences like ours forming via quantum fluctuation or nucleation within a finite time is non-zero

5. Given (1) and (2) the number of normal observers is finite
6. Given (3) and (4) the number of Boltzmann brains with experiences like ours is infinite1
7. Given (5) and (6) we are infinitely more likely to be a Boltzmann brain than a normal observer1

The current scientific evidence supports (1)-(4), and (5)-(7) are rational deductions. — Michael

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

I'm not sure how (6) follows from (3) and (4). The Big Freeze has not happened. If (6) is rejected, then so too is (7).

This also seems to rely on disembodied cognition as a logical possibility. Logical possibility alone does not warrant belief/assent.

What about all of the scientific evidence in favor of embodied cognition and/or against disembodied cognition?

For me, that is an argument from authority, which I don't accept, so we are going to disagree on this. — Janus

It wasn't quite an argument. You asked me why I think something is worthwhile, I gave one of my reasons why — rather, I agreed that what you said is indeed one of my reasons.

Actually, I think the argument from language(s) makes solipsism most highly implausible. Did you invent the English language and write all the poetry and literature that exists without even being aware of doing it, using many words you don't even know the meaning of.

Did you invent all of mathematics and science, which use countless concepts and theorems you don't even understand, without being aware of having done so? What about all the other languages? — Janus

That is a possible argument against solipsism, that all the body of knowledge produced so far is generated/contained by/in my mind, and yet we struggled with Abstract Algebra 2.
But that is not what the person said, I didn't even understand what he said as it is not clearly written, so that is why I said it is unsuccessful; but there is nothing extraordinary about coming up with symbols for concepts, people make up conlangs all the time.

Questioning the background of our experiences is incoherent, since it presupposes the background of our experiences in the very act of questioning. — Janus

Questioning is a process that involves reason. Does it presuppose the outside world when we use reason? I don't think so.

Published by the Journal of High Energy Physics - what's the problem? — Banno

4.9 impact factor is not horribly high. But that aside, single researcher, 2006... If I had more mastery over the subject I would feel more comfortable judging the content myself, but as far as layman in Statistical Physics goes, I would wager that I am getting outdated information.

Nah, it's a matter of my understanding of the strength of the evidence.
— wonderer1

So you're a cosmologist who understands the sigma level of each of (1), (2), (3), and (4)? I wasn't aware. — Michael

No, but just think about it. To have strong empirical evidence of BBs fluctuating into existence would require gathering evidence from the future, and lots of it. I'm fairly confident that physicists aren't doing so. This is a matter of modeling based on theories which have important matters unresolved, not a matter of observations of the proposed processes (BBs) occuring.

Do you think you might have a naive faith in the reliability of modelling based on incomplete scientific understanding?

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. This is a straightforward modus ponens. — Michael

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?

It wasn't quite an argument. You asked me why I think something is worthwhile, I gave one of my reasons why — rather, I agreed that what you said is indeed one of my reasons. — Lionino

You gave it as a justification for your belief.

That is a possible argument against solipsism, that all the body of knowledge produced so far is generated/contained by/in my mind, and yet we struggled with Abstract Algebra 2.
But that is not what the person said, I didn't even understand what he said as it is not clearly written, so that is why I said it is unsuccessful; but there is nothing extraordinary about coming up with symbols for concepts, people make up conlangs all the time. — Lionino

I don't know who you are referring to nor do I understand what you are trying to say in your second sentence.

Questioning is a process that involves reason. Does it presuppose the outside world when we use reason? I don't think so. — Lionino

Reason is nothing without its basic presuppositions, which are not themselves arrived at, or justified by, reason.

So, it seems to be exactly what I said above. The best evidence supports (1)-(4), and (7) follows. And his argument is that because (7) is just silly, we must reject (1), (2), (3), and/or (4) despite the evidence in their favour. It's a conceded dogma. — Michael

Did you read the full paper? If so, do you think that you followed Carroll's reasoning well?

I'm asking if that's rational. — Michael

It would be a straw man to claim that your argument and psychologizing stand in for Carroll's perspective.

Conclusion
We therefore conclude that the right strategy is to reject cosmological models that would be
dominated by Boltzmann Brains (or at least Boltzmann Observers among those who have
data just like ours), not because we have empirical evidence against them, but because they
are cognitively unstable and therefore self-undermining and unworthy of serious consideration. If we construct a model such as ΛCDM or a particular instantiation of the inflationary multiverse that seems to lead us into such a situation, our job as cosmologists is to modify it until this problem is solved, or search for a better theory. This is very useful guidance when it comes to the difficult task of building theories that describe the universe as a whole.
Fortunately, the criterion that random fluctuations dominate the fraction of observers in
a given cosmological model might not be as difficult to evade as might be naively expected, if Hilbert space is infinite-dimensional and local de Sitter phases settle into a truly stationary
vacuum state, free of dynamical Boltzmann fluctuations. That conclusion depends sensitively on how one interprets what happens inside the quantum state, an issue that is unfortunately murky in the current state of the art. If any were needed, this gives further impetus to the difficult task of reconciling the foundations of quantum mechanics and cosmology. [Emphasis added.]

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

This also seems to rely on disembodied cognition as a logical possibility. Logical possibility alone does not warrant belief/assent. — creativesoul

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