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.

As in, "wouldn't it be nice if we could avoid that circularity?" — Count Timothy von Icarus

Consider the degree to which people interact with the the world, including each other, avoiding circularity seems rather unrealistic. Just try to comprehend the feedback loops involved in the interactions of two good friends over a period of years, and perhaps the naivete of avoiding circularity will be obvious.

For me, as an electrical engineer, dealing with loopy causality is routine. So I can understand this not being so obvious to others. However to me the OP issues seem more a matter of trying to fit the complexity of the situation into an overly simplistic box.

Perhaps that's why I don't see the problems that you see. The problems you point out are where supervenience fails to explain something, or fails to rule out things that would be *bad* explanations. I don't see that as a problem, because I have much smaller ambitions for what supervenience is supposed to be. — flannel jesus

:up:

It’s tantamount to sorcery. — NOS4A2

I personally think, that in your specific case, it may be best to leave you thinking so.

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.

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?

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?

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.

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.

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.

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.

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

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?

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.

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.

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

As an explanation for our observations, yes.

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.

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

:up:

"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?

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?

Which is why I asked the question: given that we have scientific evidence that entails that we are most likely Boltzmann brains, what justifies our claim that we are not most likely Boltzmann brains? — Michael

What scientist makes the claim that we have scientific evidence that we are most likely Boltzmann brains?

So it's back to what I said here. Either we are most likely Boltzmann brains or we cannot trust our scientific knowledge. — Michael

That's a false dichotomy, and things aren't nearly that black or white.

There are areas in which I can and do trust my scientific knowledge with my life (and the lives of other people) depending on it. There are other areas of scientific knowledge in which I can't trust my knowledge to nearly the same extent.

Perhaps the most relevant question in this discussion is the extent to which you can trust your scientific knowledge?

FWIW:

ChatGPT 3.5

User
are there any physicists who believe we are boltzmann brains

ChatGPT
The concept of Boltzmann brains is a speculative idea in physics proposed by Ludwig Boltzmann and later expanded upon by physicists like Sean Carroll and others. It suggests that it's statistically more likely for a conscious observer, like a human brain, to spontaneously fluctuate into existence in a high-entropy state rather than to arise through the natural process of evolution. While some physicists entertain this idea as a thought experiment to explore the implications of cosmology and the second law of thermodynamics, it's not widely accepted as a serious hypothesis. Instead, it raises questions about the nature of reality and our understanding of the universe.

User
do any physists claim to be a boltzmann brain

ChatGPT
It's unlikely that any physicist would claim to be a Boltzmann brain in a literal sense. The concept of Boltzmann brains is primarily a thought experiment rather than a literal assertion about the nature of consciousness or existence. Physicists who discuss the idea typically use it to explore the implications of certain cosmological theories and the second law of thermodynamics, rather than as a statement about their own existence.

Why? They're entailed by our best scientific theories. — Michael

They are entailed by extrapolation of some scientific theories to a future universe we don't find ourselves in a position to observe. There are lots of theories outside of physics that have a lot of evidentiary support as well.

To quote Sean Carroll from The Big Picture:

Is it possible that you and your surrounding environment, including all of your purported knowledge of the past and the outside world, randomly fluctuated into existence out of a chaotic soup of particles? Sure, it’s possible. But you should never attach very high credence to the possibility. Such a scenario is cognitively unstable, in the words of David Albert. You use your hard-won scientific knowledge to put together a picture of the world, and you realize that in that picture, it is overwhelmingly likely that you have just randomly fluctuated into existence. But in that case, your hard-won scientific knowledge just randomly fluctuated into existence as well; you have no reason to actually think that it represents an accurate view of reality. It is impossible for a scenario like this to be true and at the same time for us to have good reasons to believe in it. The best response is to assign it a very low credence and move on with our lives.

The general gist seems to be:

1. our scientific theories suggest that we are most likely Boltzmann brains
2. we are not most likely Boltzmann brains
3. therefore, our scientific theories are mistaken

The point I am making is that, by this very argument, (2) is not supported by the scientific evidence. Rather it's something like "common sense" or "intuition" or "faith". — Michael

I've been pointing out that there is science outside of physics, and on the basis of sufficient knowledge of the diversity of scientific findings we have reasons to reject 1.

I'm then asking if it's reasonable to favour common sense, intuition, or faith over scientific evidence. — Michael

I'd say it is human nature for us to favor intuition regardless of whether it is reasonable to do so. Regardless, I've pointed out that there are multiple lines of scientific evidence to consider, and one speculative extrapolation in physics doesn't provide a basis for dismissing the larger scientific picture that allows for the existence of this forum.

Of course, if you admit that we can sometimes be justified in believing that the scientific evidence is mistaken then you open yourself up to arguments for idealism or theism, as it would certainly be hypocritical, or special pleading, to argue that we must believe in an external material world because there is scientific evidence for it but that we must not believe that we are Boltzmann brains even though there is scientific evidence for it. — Michael

I'm a fallibilist and I haven't argued that "we must believe" anything.

:up:

This isn't just an assumption. Rather:
— Michael

The preponderance of evidence to date, based on measurements of the rate of expansion and the mass density, favors a universe that will continue to expand indefinitely, resulting in the "Big Freeze" scenario below...

BB speculations are scientifically self defeating.

We only take such evidence seriously on the assumption that humans actually make empirical observations rather than experience phantasms occuring in a BB. Given the bigger picture, resulting from empirical observations considered more broadly, the evidence points towards us being the result of biological evolution. Do you think the majority of physicists would disagree?

You're right that it's not a matter of observation (and perhaps that my binary distinction is unfair), but it's wrong to suggest that it's as simple as speculation. Rather it's a consequence of our best understandings of quantum mechanics and thermodynamics. — Michael

I'm not suggesting it is simple speculation, but it does depend on assumptions such as that the universe is eternal. Furthermore, science is hardly exhaustively covered by quantum mechanics and thermodynamics, and the best scientific case is for us being the result of biological evolution.

There are, broadly speaking, four possibilities:

1. We are Boltzmann brains and our scientific theories are mostly correct
2. We are Boltzmann brains and our scientific theories are mostly incorrect
3. We are not Boltzmann brains and our scientific theories are mostly correct
4. We are not Boltzmann brains and our scientific theories are mostly incorrect

If our scientific theories are mostly correct then either (1) or (3) is the case, with (1) being most likely (as per those very scientific theories).

So one of these is true:

a. We are most likely Boltzmann brains (1 or 3)
b. Our scientific theories are mostly incorrect (2 or 4) — Michael

This ignores the fact that some aspects of science are far more speculative than others, and that a binary distinction between mostly correct and mostly incorrect doesn't address the fact that Boltzmann brains are a matter of speculation and not observation.

It doesn't follow that I am most likely not a Boltzmann brain. It only follows that the probability that I am a Boltzmann brain gets smaller as the time increases. But due to the sheer number of Boltzmann brains, it is always the case that the probability that I am a Boltzmann brain is greater than the probability that I am not a Boltzmann brain. — Michael

It seems to me there is a problem with you being a Boltzmann brain and yet so predictable. Should we expect that if you are a BB? Where's the batty?

:100: :up:

In the context of Neuroscience this seems very poor curriculum. A historical perspective maybe? — Mark Nyquist

It's a philosophy course. Why think it is "in the context of neuroscience"?

How far along is your daughter in her study of neuroscience?

When we believe any thing of external existence, or suppose an object to exist a moment after it is no longer perceived, this belief is nothing but a sentiment
— David Hume

That quotation is from the “Abstract”, which is a summary of the Treatise. The argument itself is around 1.4.2 (that’s Book.Part.Section).

But there must be secondary sources that could make it more manageable. — Jamal

Bringing up the Hume quote is good, but can your daughter then make a case for it not being nothing but sentiment, but rather a matter of pattern recognition occurring in neural networks?

Perhaps the latter is the result of unreasonable expectations about the former. As if by asking a question there must then be an answer. The natural sense of awe and wonder is lost. Replaced by artifactual realms beyond and a desire for escape and transcendence. — Fooloso4

So it seems to me.

My experience off this forum has me tending toward thinking the poison is quite well contained here — AmadeusD

And yet here you argue that you don't know anything about the world around you. So I don't know why we should take you seriously when you talk about experience off the forum.

What is the light reflected/refracted by?
— wonderer1

No idea. My part in the process(and as such, the point at whcih I could say anything about it) comes after that, as best I can tell. I could say "the objects" but then im stuck with literally nothing else to say about it. — AmadeusD

Hopefully your philosophy poisoning isn't so deep that you can't recover.

Virtual particles pop out of a vacuum attached to a QM universe. Moreover, they have physical causes.
— ucarr

Have any of these mathematical conveniences ever been detected? — jgill

Casimir effect:

The typical example is of two uncharged conductive plates in a vacuum, placed a few nanometers apart. In a classical description, the lack of an external field means that there is no field between the plates, and no force would be measured between them.[13] When this field is instead studied using the quantum electrodynamic vacuum, it is seen that the plates do affect the virtual photons which constitute the field, and generate a net force[14] – either an attraction or a repulsion depending on the specific arrangement of the two plates. Although the Casimir effect can be expressed in terms of virtual particles interacting with the objects, it is best described and more easily calculated in terms of the zero-point energy of a quantized field in the intervening space between the objects. This force has been measured and is a striking example of an effect captured formally by second quantization.[15][16]

Every explanation attempting to do so just ignores entirely that we literally do not see objects, but reflected/refracted light which in turn causes us to 'see' a visual construct. — AmadeusD

What is the light reflected/refracted by?

I thought that too, except "Sherlock Holmes" refers to something that seems to go beyond something that's just "instantiated in a brain". — RogueAI

Well, there are lots of ideas of ideas of Sherlock Holmes instantiated in lots of people's brains. But what seems to go beyond something instantiated in a brain?

I mean, when you're reading Arthur Conan Doyle or Mary Shelly or Stephen King, are you thinking of brains? — RogueAI

No. Things can be represented with other things, such as ideas with written words. Typically we are thinking of things represented in our brains. Representations in our brains no more need to to resemble what is represented, than a string of letters on a page needs to resemble the landscape it describes.

You're talking about fictional things: ghosts, Dracula, Sherlock Holmes, God, etc. Fictional things exist as ideas, otherwise, we wouldn't be able to intelligently talk about them. — RogueAI

From ny physicalist perspective you are equivocating between an idea as instantiated in a brain, and what the idea refers to.

I can always count on you to go for the ad hominem. A lot of materialists here do. It's like they're emotionally invested in it or something. — RogueAI

And it is like you don't recognize that your ignorance makes your opinion on the matter uninteresting, and tedious to respond to.

I'm a scientific ignoramus. — RogueAI

At least we can agree on that.