B How do we resolve the Boltzmann Brain problem

I think this refutes the standard picture since if ylour universe would just keep expanding we should be a boltzmann brain.



I would bet on the "big rip" (dark energy getting stronger) since that would also resolve the hubble tension.
 

kimbyd

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I think this refutes the standard picture since if ylour universe would just keep expanding we should be a boltzmann brain.



I would bet on the "big rip" (dark energy getting stronger) since that would also resolve the hubble tension.
A complete vacuum doesn't actually fluctuate, so there are no sources which could cause Boltzmann brains to come into existence:
 
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Otherwise an infinite amount of boltzmann brains would emerge every second if space is infinite.
Again, what do you think refutes what standard picture?
 
Again, what do you think refutes what standard picture?
If our universe would just continue to expand we would run into the boltzmann brain problem and there would not be a complete vacuum since there would always be particles.
 
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If our universe would just continue to expand we would run into the boltzmann brain problem and there would not be a complete vacuum since there would always be particles.
Why do you think that this is the "standard picture"? The whole point of @kimbyd's post is that the "standard picture" does not have this problem because there are no "vacuum fluctuations" to produce Boltzmann brains.
 
Why do you think that this is the "standard picture"? The whole point of @kimbyd's post is that the "standard picture" does not have this problem because there are no "vacuum fluctuations" to produce Boltzmann brains.
That only offered a solution for absolute vacuum but our universe will never become empty in the standard picture, just accelerated expansion forever.
 
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That only offered a solution for absolute vacuum
All of the arguments for why Boltzmann brains should be produced also assume an absolute vacuum. So if an absolute vacuum does not produce Boltzmann brains, all of those arguments are wrong.
 

kimbyd

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That only offered a solution for absolute vacuum but our universe will never become empty in the standard picture, just accelerated expansion forever.
Yes, it will. Or to be more precise, eventually every Hubble volume will contain either one or zero particles, with the Hubble volumes containing zero particles growing exponentially in number while the number containing a single particle remains static. Both types of Hubble volume will necessarily be in a ground state, and thus not fluctuate.
 
Yes, it will. Or to be more precise, eventually every Hubble volume will contain either one or zero particles, with the Hubble volumes containing zero particles growing exponentially in number while the number containing a single particle remains static. Both types of Hubble volume will necessarily be in a ground state, and thus not fluctuate.
Why would a volume containging a single particle always be in the ground state?
 
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Why would a volume containging a single particle always be in the ground state?
Because if there is only a single particle, it must already have given up all possible energy--if it hadn't, it would be able to emit particles like photons, which would mean more than one particle would be in that Hubble volume. "Given up all possible energy" means the particle is in its ground state.
 
Case0
Boltzmann brains can emerge in complete vacuum, thus both space* and time must me limited but you cannot reach the end of our universe since it's expanding at the speed of light.

*at least space where vacuum fluctuations can occur.

Case1
A boltzmann brain can emerge from a single particle, this require our universe to only exist for a finite amount of time.

Time being limited in this context means that eventually our current universe/aeon will come to an end eventually, it's hard to tell what if anything would follow after that.

case2
A boltzmann brain can only emerge when 2 particles are sufficiently close (such as the same Hubble volume). this is compatible with the standard picture of our universe just continuing expanding forever.
 
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A complete vacuum doesn't actually fluctuate, so there are no sources which could cause Boltzmann brains to come into existence:
Are you really sure about this paper? Carroll's own commentary on it says it relies heavily on the Everttian many worlds interpretation of Qm. And since we dont know that this is the correct interpretation of QM are you really sure this paper is so solid? http://www.preposterousuniverse.com/blog/2014/05/05/squelching-boltzmann-brains-and-maybe-eternal-inflation/
 
Are you really sure about this paper? Carroll's own commentary on it says it relies heavily on the Everttian many worlds interpretation of Qm. And since we dont know that this is the correct interpretation of QM are you really sure this paper is so solid? http://www.preposterousuniverse.com/blog/2014/05/05/squelching-boltzmann-brains-and-maybe-eternal-inflation/
I took a look and it obviously doesn't prove anything, i am pretty sure it's wrong, it does however offer a way out (case2, earlier post).
 
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kimbyd

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Are you really sure about this paper? Carroll's own commentary on it says it relies heavily on the Everttian many worlds interpretation of Qm. And since we dont know that this is the correct interpretation of QM are you really sure this paper is so solid? http://www.preposterousuniverse.com/blog/2014/05/05/squelching-boltzmann-brains-and-maybe-eternal-inflation/
The interpretation is irrelevant because there's no system that can perform measurements of any kind in an empty universe. All interpretations reduce to the many worlds interpretation in that limit.
 
The interpretation is irrelevant because there's no system that can perform measurements of any kind in an empty universe. All interpretations reduce to the many worlds interpretation in that limit.
That's incorrect
1. the universe never becomes empty and there may also be vacuum fluctuations allowing for interactions.
2. why do you bring up "measurements" if interpretation is irrelevant?

So you are already assuming "no vacuum fluctuations" and that a measurement of some kind is required to collapse the wavefunction, this isn't the case for the penrose interpretation where the wavefunction can self-collapse.
 
Case0
Boltzmann brains can emerge in complete vacuum, thus both space* and time must me limited but you cannot reach the end of our universe since it's expanding at the speed of light.

*at least space where vacuum fluctuations can occur.

Case1
A boltzmann brain can emerge from a single particle, this require our universe to only exist for a finite amount of time.

Time being limited in this context means that eventually our current universe/aeon will come to an end eventually, it's hard to tell what if anything would follow after that.

case2
A boltzmann brain can only emerge when 2 particles are sufficiently close (such as the same Hubble volume). this is compatible with the standard picture of our universe just continuing expanding forever.
This is if you count hadrons as single particles or if all hadrons are unstable.
 
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the universe never becomes empty
@kimbyd already responded to this; see post #10.

why do you bring up "measurements" if interpretation is irrelevant?
She's making the point that if there is no way to make any measurements, then all interpretations reduce to the MWI. Another way to put it would be that without measurements, all interpretations say we just have unitary evolution, and "we just have unitary evolution" is equivalent to the MWI.
 
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The interpretation is irrelevant because there's no system that can perform measurements of any kind in an empty universe. All interpretations reduce to the many worlds interpretation in that limit.
One of the paper's own authors appears to disagree .From the link I posted above. " As far as quantum fluctuations are concerned, we readily admit that our analysis relies heavily on the Everett/Many-Worlds formulation of quantum theory. In that view, there is nothing truly random and unpredictable about quantum dynamics."
Do you have a reference for the claim that interpretation is irrelevant ?
 
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One of the paper's own authors appears to disagree .
But note carefully that Carroll says "Everett formulation", not "Everett interpretation". At the end of the article, he explains the difference:

Finally, it’s interesting to note the role of “interpretations of quantum mechanics” in this story. (I don’t like that term, since we’re not discussing “interpretations,” we’re comparing manifestly different physical theories.) In the Everett formulation, the wave function is a direct reflection of reality; when it is stationary, so is the quantum system. Other approaches take a very different tack. There are formulations of quantum mechanics where collapse of the wave function is truly random and unpredictable; there are others with hidden variables, in which the true state of the universe isn’t defined by the wave function. In any of those cases, our analysis is completely beside the point. It’s interesting to think — but perhaps unsurprising in retrospect — that the correct formulation of quantum mechanics might have crucial implications for the evolution of the universe.

These "other formulations" are not the other standard interpretations of standard QM--Copenhagen etc. They are, as Carroll says in the quote, "manifestly different physical theories". For example, random and unpredictable collapse is a formulation like the GRW model, which makes different predictions from standard QM. If something like the GRW model were actually correct, then it would be impossible for an empty de Sitter universe to stay that way forever; at any time, a random "collapse" could happen that would kick the universe into a different quantum state. All Carroll is saying is that he is not considering such models; he is only considering standard QM, where as long as no measurement is made you just have unitary evolution. And if the entire universe is in its ground state, unitary evolution just says it stays that way forever, never changing at all.
 

kimbyd

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He's making the point that if there is no way to make any measurements, then all interpretations reduce to the MWI.
She

One of the paper's own authors appears to disagree .From the link I posted above. " As far as quantum fluctuations are concerned, we readily admit that our analysis relies heavily on the Everett/Many-Worlds formulation of quantum theory. In that view, there is nothing truly random and unpredictable about quantum dynamics."
Do you have a reference for the claim that interpretation is irrelevant ?
Basically because I'm disregarding hidden variable interpretations. All interpretations that involve unitary evolution of the wavefunction as some component of the system should act like the many worlds interpretation here. It's technically possible for something else to be going on, that the unitary wavefunction evolution is an illusion and something fundamentally different is going on under the hood.
 

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