Solipsism is a philosophical idea. It is a language construct.
— creativesoul

The idea that all ideas boil down to language... — Lionino

Who said that?

Never a good sign when one neglects to address what was written in lieu of something that was not.

On ChatGPT, here is an example of it contradicting itself three times in a row.
https://chat.openai.com/share/96378835-0a94-43ce-a25b-f05e5646ec40
And don't ever ask it to do any engineering https://chat.openai.com/share/b5241b53-e4d8-4cab-9a81-87fa73d740ad — Lionino

Yeah, ChatGPT doesn't reason. It basically just repeats what it's read elsewhere. Sometimes it makes stuff up. I tried using it for programming once and it fabricated a function that doesn't exist.

ChatGPT doesn't reason. It basically just repeats what it's read elsewhere. — Michael

Chomsky called it glorified plagiarism, or words to that effect/affect.

Several are mentioned in the Wikipedia article, e.g. Boltzmann, Eddington, Feynman, Sean Carroll, and Brian Greene. — Michael

Those are people who have considered the possibility that we are Boltzmann brains. Not people who claim what you attribute to them. I already quoted Sean Carroll on the topic and it seemed pretty clear to me that Carroll doesn't make the claim that you are attributing to him. Do you agree?

Such a scenario is cognitively unstable...

An excellent phrase.

Those are people who have considered the possibility that we are Boltzmann brains. Not people who claim what you attribute to them. I already quoted Sean Carroll on the topic and it seemed pretty clear to me that Carroll doesn't make the claim that you are attributing to him. — wonderer1

"The consensus amongst cosmologists is that some yet to be revealed error is hinted at by the surprising calculation that Boltzmann brains should vastly outnumber normal human brains."

They accept that the science entails that we are most likely Boltzmann brains. They consider this proof that something is wrong with the science.

This is consistent with what I've been saying.

Either we are most likely Boltzmann brains or our science is inaccurate.

And I want to know what justifies the assertion that we are not Boltzmann brains given that the science suggests otherwise.

As for Carroll specifically, see Why Boltzmann Brains Are Bad:

Some modern cosmological models predict the appearance of Boltzmann Brains: observers who randomly fluctuate out of a thermal bath rather than naturally evolving from a low-entropy Big Bang.

...

The issue is not that the existence of such observers is ruled out by data, but that the theories that predict them are cognitively unstable: they cannot simultaneously be true and justifiably believed.

The science says one thing; he then suggests that it's irrational to believe it, i.e. that it's rational to reject the science.

"The consensus amongst cosmologists is that some yet to be revealed error is hinted at by the surprising calculation that Boltzmann brains should vastly outnumber normal human brains."

They accept that the science entails that we are most likely Boltzmann brains. They consider this proof that something is wrong with the science. — Michael

What you put in quotes there was something that someone wrote on Wikipedia. Can you quote a physicist making such a claim?

What you put in quotes there was something that someone wrote on Wikipedia. Can you quote a physicist making such a claim? — wonderer1

Brian Greene

I am confident that I am not a Boltzmann brain. However, we want our theories to similarly concur that we are not Boltzmann brains, but so far it has proved surprisingly difficult for them to do so. So, I see Boltzmann brains as a mathematical problem that we need to solve, as opposed to an existential affront. I believe it is a problem that we will one day overcome.

Sean Carroll

Some modern cosmological models predict the appearance of Boltzmann Brains: observers who randomly fluctuate out of a thermal bath rather than naturally evolving from a low-entropy Big Bang.

...

The issue is not that the existence of such observers is ruled out by data, but that the theories that predict them are cognitively unstable: they cannot simultaneously be true and justifiably believed.

Sean Carroll (again)

We're not arguing that Boltzmann Brains exist — we're trying to avoid them.

An argument that regular observers are more common than Boltzmann observers:
http://www.arxiv.org/abs/hep-th/0611271

What is clear is that the physics is incomplete. Hence there remains good reason for Boltzmann scepticism.

What is clear is that the physics is incomplete. Hence there remains good reason for Boltzmann scepticism. — Banno

:up:

An argument that regular observers are more common than Boltzmann observers:
http://www.arxiv.org/abs/hep-th/0611271 — Banno

Not sure if I would trust that.

Adding to the above, there's also Is the Universe a Vacuum Fluctuation?:

The author proposes a big bang model in which our Universe is a fluctuation of the vacuum, in the sense of quantum field theory. The model predicts a Universe which is homogeneous, isotropic and closed, and consists equally of matter and anti-matter. All these predictions are supported by, or consistent with, present observations.

Although it doesn't specifically refer to Boltzmann brains, the above is analogous to a Boltzmann universe, and as quantum fluctuations giving rise to a 14 billion year old universe is exponentially less likely than a quantum fluctuation giving rise to a several decades old brain, it stands to reason that evidence of the former is also evidence of the latter.

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

Somewhat of a coincidence, but that scientist wrote a paper that continues the work of the article I posted above.

Cool. There's also the argument that Boltzmann brains count as a marker for absurdity: Any method for calculating probabilities ought come to the conclusion that the most likely observer is the one we know exists - us. So if the calculation shows a Boltzmann brain to be more likely than a regular observer, the calculation probably has a methodological error. Also from Vilenkin.

Adding to the above, there's also Is the Universe a Vacuum Fluctuation?: — Michael

That is not nearly as self defeating as a scientific hypothesis.

Any method for calculating probabilities ought come to the conclusion that the most likely observer is the one we know exists - us. — Banno

If we are Boltzmann brains then a calculation that shows a Boltzmann brain to be more likely than a regular observer has satisfied the above.

Your reasoning (or Vilenkin's) seems to beg the question.

Perhaps a different line of reasoning:

Borrowing from Tryon and Vilenkin, assume that any universe is itself a quantum fluctuation. Which is more likely; that we are a decades old Boltzmann brain or that we are an ordinary brain in a 14 billion year old Boltzmann universe?

I suppose the answer to that depends on what "surrounds" this universe. If it's an infinite and eternal vacuum then presumably there are an infinite number of Boltzmann universes and an infinite number of Boltzmann brains and so it is meaningless to say that one is more likely than the other.

We're just either a Boltzmann brain or an ordinary brain in a Boltzmann universe, with no evidence or reasoning to prefer either.

That is not nearly as self defeating as a scientific hypothesis. — wonderer1

You think a quantum fluctuation universe is more likely than quantum fluctuation brains with false, consistent memories?

You think a quantum fluctuation universe is more likely than quantum fluctuation brains with false memories? — Michael

As an explanation for our observations, yes.

Your reasoning (or Vilenkin's) seems to beg the question. — Michael

Hmm. The point is that the reasoning here is unstable - it remains equivocal, even for you, and downright dubious for others.

And what is the rational response in such circumstances? I don't think it is to conclude that you are a Boltzmann brain.

Also, I am pleased that you did not disappear in a puff of probability, as i had feared - both because it makes my view more likely, and because this discourse has some amusement value.

And also, potentially, in terms of simple probability. A large volume at a high temperature may well be more likely than a small volume with a high level of order. Regular physics explains the rise of regular observes vers in the large hot volume.

And again, again, it remains that there are no tight grounds for accepting the calculations involved. It is "cognitively unstable" - or if folk prefer simple language, there are no observations that settle the issue, and hence it remains mere speculation.

And again, again, it remains that there are no tight grounds for accepting the calculations involved. It is "cognitively unstable" - or if folk prefer simple language, there are no observations that settle the issue, and hence it remains mere speculation. — Banno

Exactly.

or if folk prefer simple language, there are no observations that settle the issue, and hence it remains mere speculation — Banno

The same with us not being Boltzmann brains.

As an explanation for our observations, yes. — wonderer1

How so? There will be Boltzmann brains that have the same observations as ordinary observers; and in fact, there will be significantly (infinitely?) more Boltzmann brains that have those same observations as ordinary observers.

...and the longer you spend on this topic, the less likely it is that you are one of them.

And around and around. Language on idle.

...and the longer you spend on this topic, the less likely it is that you are one of them. — Banno

But still more likely than not being one.

How so? There will be Boltzmann brains that have the same observations as ordinary observers; and in fact, there will be significantly (infinitely?) more Boltzmann brains that have those same observations as ordinary observers. — Michael

Okay, show your math.

The problem of induction is that there is no reason to be sure that the future will be like the past, or simply that we can't derive a "will be" from a "has been". We agree on that? — Lionino

Yes, as I said, inductive inferences, unlike valid deductive inferences, are not logically necessary.

If we do, according to your proposal that "something should be thought to be less likely if it is less plausible in light of our experience", the problem of induction dissolves. — Lionino

I don't think so. All we have to go on in order to decide what is more or less likely to happen is prior experience, Is the Sun more or less likely to rise tomorrow? It's really not a question of deductive certainty at all.

I understand what you say about consistency with our past experiences, but in this one case I don't think it applies, since we are questioning the background of our experiences. — Lionino

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

For the most part, yes, people who are just as smart as or smarter than me are still arguing about it. And for them it is profession, not hobby. So it leads me to conclude it is not something that we can brush aside easily. — Lionino

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

Another, the argument from language is bad, — Lionino

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?

In a single de Sitter universe with a cosmological constant, and starting from any finite spatial slice, the number of "normal" observers is finite and bounded by the heat death of the universe. If the universe lasts forever, the number of nucleated Boltzmann brains is, in most models, infinite; cosmologists such as Alan Guth worry that this would make it seem "infinitely unlikely for us to be normal brains". — https://en.wikipedia.org/wiki/Boltzmann_brain#In_single-universe_scenarios

The general principle is that the time between the Big Bang and the Big Freeze is finite. Therefore the number of normal observers is finite.

The time after the Big Freeze is infinite. The time required for a Boltzmann brain to form via nucleation is very large – $10^{10^{69}}$ years in fact – but still finite. Given infinite time anything that can happen within a finite time – however large – will happen an infinite number of times.

Therefore there are infinitely more Boltzmann brains – of every variety that has a non-zero probability of forming; including those that appear to themselves to be normal observers – than normal observers. Therefore any randomly selected observer is infinitely more likely to be a Boltzmann brain – even one that appears to itself to be a normal observer – than to be a normal observer.

This is the model that is best supported by the current evidence.

Less supported models are those that predict a Big Crunch or a Big Rip, each of which avoid the problem of Boltzmann brains.

Personally, I think it would be strange to argue that either the Big Crunch or the Big Rip must be correct, or that the time after the Big Freeze must be finite, or that the probability of a Boltzmann brain forming must be zero, simply because it must be that we are not most likely to be a Boltzmann brain.

In fact I'll set out the above in a more structured format:

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.

If (7) is false then at least one of (1)-(4) is false. But which of (1)-(4) is it rational to reject for no other reason than that "(7) must be false!"?

¹ _{If the time after the Big Freeze is finite but sufficiently large, i.e. many orders of magnitude greater than the time required for a Boltzmann brain to form, then although we are not infinitely more likely to be Boltzmann brains, we are still more likely to be Boltzmann brains.}