Boltzmann brains and limitless energy....

[JuneSpring25]

TL;DR Summary

A question about quantum fluctuations and the limits on energy from the vacuum

Hello!

Amateur question alert! Please excuse any misuse of terms. Answers gratefully received.

I have a question about the energy that can be drawn from the vacuum through quantum fluctuations.

My understanding is there are very strict limits on how much energy can be borrowed for how long from the vacuum so it never violates conservation of energy in the end:

https://www.sciencedaily.com/releases/2019/10/191002102750.htm

I'm confused about this in relation to the concept of Boltzmann brains. As I understand it, Boltzmann brains refers to the idea that if the universe continues indefinitely all possible objects will form from random quantum fluctuations, no matter how unlikely, including brains. (I know the reality of this is doubted by many physicists and philosophers for various reasons but on a hypothetical level...)

I had always assumed if they could exist these structures would only exist for split seconds at a time but in this article by Sean Carroll (where he ultimately argues against Botlzmann brains on philosophical grounds but not in terms of physical laws) he talks about the potential for quantum fluctuations to create 'civilizations which last for millions of years.'

https://arxiv.org/abs/1702.00850

Would it really be possible to draw so much energy from the vacuum? Could it then be possible, no matter how unlikely, given enough time, for an object to stay together and draw energy from the vacuum forever just by the way the quantum fluctuations kept turning out? For a Boltzmann brain or other random object to last forever? This would seem to be contradicted by the other article that says there are strict limits on the time and amount of energy that can be borrowed but if whole ongoing civilisations could be made from random quantum fluctuations, it doesn't sound like there is a limit.

I understand that in most cases a Boltzmann brain is going to be hugely statistically likely to decay almost instantly but given infinite time, could quantum fluctuation coincide to keep providing it with energy to keep together indefinitely?

I'm not hoping for this is true by the way, the idea of infinite life brings the possibility of infinite suffering so I don't like it, just trying to understand if the laws of energy conservation do break down in this case.

Thanks in advance for any replies!

 

[Nugatory]

I have a question about the energy that can be drawn from the vacuum through quantum fluctuations.
My understanding is there are very strict limits on how much energy can be borrowed for how long from the vacuum so it never violates conservation of energy in the end

This is a common misunderstanding of the confusing term “vacuum fluctuations”, reinforced by many misleading pop-sci explanations such as that sciencedaily.com article (which is not an acceptable source under the forum rules). To get a better sense of what is really going on with the vacuum states you could try https://www.physicsforums.com/threads/misconceptions-about-virtual-particles-comments.865706/ and some of the Insights articles linked from it.

I'm confused about this in relation to the concept of Boltzmann brains. As I understand it, Boltzmann brains refers to the idea that if the universe continues indefinitely all possible objects will form from random quantum fluctuations…..Would it really be possible to draw so much energy from the vacuum?……This would seem to be contradicted by the other article that says there are strict limits on the time and amount of energy that can be borrowed but if whole ongoing civilisations could be made from random quantum fluctuations, it doesn't sound like there is a limit.

That Sean Carroll paper, on the other hand, is a valid source and a good discussion of an interesting problem. The contradiction you see between it and the sciencedaily piece is partly because the latter is mostly junk and partly because Carroll is using the word “fluctuation” in an accurate sense unrelated to the energy-borrowing idea that you’re thinking of - pay particular attention to the first few pages of section 4 and also the bulleted list on page 13.

The Carroll paper is interesting enough that we will leave this thread open for a while, but all posters are asked to be mindful of the forum rules about acceptable sources backed by the peer-reviewed literature.

 

[DaveC426913]

I had always assumed if they could exist these structures would only exist for split seconds at a time

Well, because it would die in the vacuum of space.

"Like any brain in such circumstances (the hostile vacuum of space with no blood supply or body), it would almost immediately stop functioning and begin to deteriorate."
https://en.wikipedia.org/wiki/Boltzmann_brain

There's no reason to assume the brain is not made of well-formed molecules with chemical bonds that will last as long as a vanilla Earth brain.


But consider: the length of time for a brain to form that is replete with body, blood, heart and spacesuit - is only a fraction longer (cosmically-speaking) than the time to form a naked, doomed brain.

 

[Melbourne Guy]

Well, because it would die in the vacuum of space.

I feel the 'brain' aspect is a red herring in BB discussions and should not be taken literally.

As Carroll notes in the paper cited above, "A Boltzmann Brain is a configuration of matter that is (along with its local environment) as close as possible to thermal equilibrium, while still qualifying as an intelligent observer."

(I know the reality of this is doubted by many physicists and philosophers for various reasons but on a hypothetical level...)

I acknowledge it is only one perspective, but Carroll concludes that we can't definitely decide on the actually of BBs because it requires reconciliation of quantum mechanics and general relativity. So, as with so many other elements of the cosmos, a full working of the problem is on hold until the theory of everything arrives!

 

[DaveC426913]

I feel the 'brain' aspect is a red herring in BB discussions and should not be taken literally.

I thought so too, until I looked it up. The OP appears to assume that a BB, by its ephemeral nature, must evaporate as soon as it forms, but that's not really true.

I think that is germane to the argument about borrowing energy temporarily. A brain that forms and stays coherent may well put the idea of "borrowing" energy in a different light for the OP.

Anyway, carry on.

 

[Nugatory]

I think that is germane to the argument about borrowing energy temporarily. A brain that forms and stays coherent may well put the idea of "borrowing" energy in a different light for the OP.

The entire "borrowing energy" concept is irrelevant here, as Carroll makes clear. The fluctuations that we're dealing with are stochastic entropy decreases, not the something-from-nothing vacuum fluctuations that we encounter in so many pop-sci articles.

 

[jbriggs444]

But consider: the length of time for a brain to form that is replete with body, blood, heart and spacesuit - is only a fraction longer (cosmically-speaking) than the time to form a naked, doomed brain.

That sounds like nonsense. The likelihood that any given BB will have an attached body is essentially zero.

It's like the probability that a randomly materialized copy of the Mona Lisa will just happen to have "DaveC426913" in the lower right corner where Leonardo's signature should be.

 

[Melbourne Guy]

That sounds like nonsense. The likelihood that any given BB will have an attached body is essentially zero.

What is the discriminating factor, @jbriggs444? Shouldn't the same 'essentially zero' likelihood apply to any macro object spontaneously emerging, whether brain or whole human or Mona Lisa?

And if the time period in which these events can occur is so long, isn't 'essentially zero' not actually zero, which means it will occur?

 

[DaveC426913]

The likelihood that any given BB will have an attached body is essentially zero.

It's like the probability that a randomly materialized copy of the Mona Lisa will just happen to have "DaveC426913" in the lower right corner where Leonardo's signature should be.

Yes. And yes.

If I didn't know better, I'd ask if you are not familiar with the premise of Boltzmann Brains.

A body and spacesuit and spoofed Mona Lisa are nothing more than a rounding error on the scale required for Boltzmann Brains.

That's the whole point of it being a brain: the most complex single object in creation. Way, way more complex - and therefore unlikely to form spontaneously - than a spacesuit or painting

 

[jbriggs444]

What is the discriminating factor, @jbriggs444? Shouldn't the same 'essentially zero' likelihood apply to any macro object spontaneously emerging, whether brain or whole human or Mona Lisa?

Yes, over the long run, all possible events will occur. But the relative frequency of two low probability events (e.g. BB vs BB + body) can vary dramatically even though both probabilities are "essentially zero".

 

[jbriggs444]

That's the whole point of it being a brain: the most complex single object in creation.

Nope. That is not the whole point of it. It is not even a correct point.

In any case, a brain plus an attached body capable of supporting that brain is more "complex" than a brain alone. More "complex" in the sense that assembling one by chance has a lower probability of occurring per attempt.

 

[JuneSpring25]

Thank you for all the responses. Sorry for messing up on the first source there!

I understand we're talking about *extremely* unlikely events but as another poster said, the premise of the Boltzmann brain idea is based on extremely unlikely events being inevitable given infinite time. I accept the brain is a bit of a red-herring, it could be any structure, but does the theory allow for the possibility that some macro object could continue existing eternally? Carroll talks about whole galaxies appearing through infinite random fluctuations - given infinite time, wouldn't a new object which could be used as a source of energy keep appearing for infinity in one of these galaxies? Insanely unlikely but is it made probable by infinite time?

 

[JuneSpring25]

As a follow up, doesn't many worlds create this scenario? If all possible outcomes are realized in some world, one of them must contain a kind of perpetual motion machine as the random fluctuations would always keep adding to it?

If these are different random fluctuations to that ones in many world theory, why don't they also lead to many worlds? I thought one of the ideas behind many worlds was to get rid of randomness and explain why we only get one result in a seemingly random process.

 

[Melbourne Guy]

Insanely unlikely but is it made probable by infinite time?

Yes, and @Chalnoth provided a neat assessment some years ago:

https://www.physicsforums.com/threads/boltzmann-brains.894790/post-5644119​

Apart from this, it seems that the statistical likelihood of any macro-sized object fluctuating its way into being can be determined...but the outcome is so sensitive to your assumptions that all answers are equivalently pointless estimates.

 

[Nugatory]

As a follow up, doesn't many worlds create this scenario?

”Create” is too strong of a word, but if by “this scenario” you mean the appearance of Boltzmann fluctuations the answer has to be yes, because analyzing a problem using many worlds must give the exact same results as analyzing it using any other interpretation of QM. Thus introducing MW here can only complicate and distract, without suggesting any new result we don’t already have.
You will note that Carroll was able to write this piece without considering any particular interpretation, whether MW or any other. We should all try to be like Carroll.

If all possible outcomes are realized in some world, one of them must contain a kind of perpetual motion machine as the random fluctuations would always keep adding to it?

No, that is a complete non sequitur. Boltzmann fluctuations may in principle lead to very improbable rearrangements of matter if we're just willing to wait long enough (how long do we have wait for something that has one chance in $10^{10^{100}}$ of happening in any given galactic lifetime?) but there is no rearrangement of matter that can be a perpetual motion machine. This "anything can happen" thinking is another popular misunderstanding of many-worlds.

If these are different random fluctuations to that ones in many world theory, why don't they also lead to many worlds? I thought one of the ideas behind many worlds was to get rid of randomness and explain why we only get one result in a seemingly random process.

Many worlds is not what you're thinking it is. I think that you may be missing the underlying premise of Carroll's paper because he is writing for an audience that is already familiar with both modern cosmology and modern quantum mechanics, and that familiarity comes from a decade or more of graduate-level work at the leading edge of those fields.

The closest to a layman-friendly summary of the premise (and I cannot stress enough that this is a huge corner-cutting oversimplification) that I can come up with is:

"Remember the old joke about how if we allowed an infinite number of monkeys with typewriters to type away for an infinite time, eventually one of them would produce the complete works of Shakespeare? Well, if we give an an infinite number of atoms infinite time to combine in various ways, eventually some of them would luck into forming a brain. OK, given that premise... let's run with it"​

 

[Nugatory]

This thread shows some of the difficulties of discussing an advanced paper at any other level so is closed.

As with all thread closures, if you have something to add to the thread you can PM any mentor to as that it be reopened.