Out of curiosity, do you [Yudkowsky/other readers of this comment] have a metaphysics you think is likely correct and which dissolves the Boltzmann Brain problem?
The Solomonoff Induction universal prior solves it because it takes a lot more bits to “locate” a Boltzmann brain than a human in a well ordered Earth environment.
The “locate” issue in SI solves both Boltzmann and the dust theory issues alluded to in OP—anything can implement any computation but you still need a computer program that outputs something and weird mappings will make that program longer.
You still have a puzzle about which language you use for the computer programs, and what exactly input and output mean, it doesn’t solve everything but does dissolve much of the mystery.
This has always seemed very likely to me. It seems way easier to create a world governed by a few rules of physics that would incentivize perceptrons than randomly stumble into complicated perceptron architecture via random physics.
My theory: something happens to prevent the infinitely protracted heat death of the universe From taking up much probability space. For example, the simulation is turned off because it has become boring. Or, someone figures out how to abundantly create new universes in states of low entropy, meaning that states before such creation are far more likely than states after such creation. Or, we’re wrong about how probability measure works over conscious observers, and Boltzmann brains are actually exponentially unlikely.
It’s not like we know this is a real problem; it’s merely a case where our theoretical physics gives a crazy result when pushed too far. We know there are places where our understanding breaks down, and this is one of them.
There used to exist the Steady-state model. If it was true, then the problem would immediately dissolve because classical minds would emerge with a far, far bigger density than the paradox-inducing Boltzmann ones. This could imply that the real physics (not even metaphysics!) also somehow dissolves the issue, but we have yet to understand the mechanism (a false vacuum decay which stops the universe from expanding and creates matter in sufficient quantities to make classical brains likely to emerge instead of the Boltzmann one?)
What is weird about this, is that in an eternal steady state universe the number of living observers in a given time period is much larger than the number of observers (including Boltzman brains) in a simialr slice of a universe approaching thermal equilibrium. So, depedning on how your Anthropic reasoning work, you could argue from the fact of your own existance that the universe must be steady state, regardless of any evidence otherwise.
(This is kind of a tension inherent in all Anthropic arguments, I am more likely to ‘be me’ (as opposed to someone else, like a Boltzman brain) in a universe with fewer people, but most possible observers are in the crowded universes, so I am more likely to be in a crowded one. Similar logic, threading oppsosite conclusions.)
This paper (2015) argues that the idea of quantum fluctuations without an observer/measuring apparatus to decohere the wavefunction is confused, and therefore (I didn’t fully understand this part), depending on unknown details of physics/cosmology, even thermal fluctuations (what the OP discusses) in an old universe that give rise to Boltzmann brains might not be a thing. (ETA: this sounds like it overlaps with Mitchell Porter’s top-level comment that “[maybe] De Sitter space simply doesn’t last long enough before decaying into flat space.”)
(That doesn’t help with the problems with the mathematical multiverse, or which computations a physical system implements.)
Though I think the Boddy-Carroll-Pollack argument is separate from the swampland argument that Mitchell Porter is referencing. The swampland argument is saying that long-lived de Sitter space might not be possible at all in quantum gravity, whereas the Boddy-Carroll-Pollack argument is saying that long-lived de Sitter space might not give rise to Boltzmann Brains at all.
Logical positivism. Boltzmann brains occur after the heat death of the universe, which makes them causally isolated from our observations (anything that happens after all observers in the universe are killed is an arbitrary part of the model because we can’t pass any information to it and gain any information from it), therefore they can’t influence our probability measure.
By “the BB problem”, you might mean the problem of how to know whether you are a BB, but the OP explains how, and I can’t imagine what else you might mean by “the BB problem”.
The wiki page had Yudkowsky describe the problem as follows:
Yudkowsky’s paradox
Suppose your model of physics says that the universe will eventually dissolve into a sea of particles in thermal equilibrium, and these particles will then exist indefinitely.
Then an exponentially vast supermajority of all observer-moments in this universe take place inside brains that momentarily assemble themselves from the sea of entropy by random fluctuations, and probably dissolve a moment later. These are “Boltzmann brains”.
The vast supermajority of Boltzmann brains have relatively disordered experiences; they momentarily see chaos before dissolving again.
So your own, far more ordered and orderly experience in this very moment weighs heavily against the hypothesis “I am a Boltzmann brain”. Inder most systems of anthropic reasoning this weighs heavily against the possibility “a supervast majority of all moments of consciousness are vastly less orderly than my own”.
To be clear, it’s not “Yudkowsky’s paradox” as Yudkowsky is explaining a standard and known problem in cosmology here.
Admittedly, many cosmologists are not super careful when reasoning about Boltzmann Brains and they also disagree about what exactly is the problem they pose (e.g., see this dialectic between Carroll (2017)and Elga (2025)about whether belief in Boltzmann Brains leads to “cognitive instability”). But the core phenomenon of Boltzmann Brains and that they seem like bad news for many cosmological models is well-understood.
After a brief chat with one of the AI’s I had the impression that the main value of the BB was more about model/theory evaluation. Basically a theory that predicts a lot of the phenomenon should be questioned and probably “back to the drawing board” case.
A lot I don’t follow here but seems like the post might be challenging that, or perhaps some more simplified applications of that view.
But after the chats I actually wonder if that is the critical aspect rather than juts how we deal with infinities/really long time frames or how we think/define of equilibriums as the more critical areas of exploration.
Out of curiosity, do you [Yudkowsky/other readers of this comment] have a metaphysics you think is likely correct and which dissolves the Boltzmann Brain problem?
The Solomonoff Induction universal prior solves it because it takes a lot more bits to “locate” a Boltzmann brain than a human in a well ordered Earth environment.
I was previously skeptical that SI actually produces different results than SIA and wrote about that in https://www.lesswrong.com/posts/Jqwb7vEqEFyC6sLLG/solomonoff-induction-and-sleeping-beauty but I’ve changed my mind. The argument there doesn’t generalize to large numbers of observers. (I still believe my other arguments posted that year that “reality” is a meaningless concept, see https://www.lesswrong.com/posts/zm3Wgqfyf6E4tTkcG/the-short-case-for-verificationism and https://www.lesswrong.com/posts/PSichw8wqmbood6fj/this-territory-does-not-exist.)
The “locate” issue in SI solves both Boltzmann and the dust theory issues alluded to in OP—anything can implement any computation but you still need a computer program that outputs something and weird mappings will make that program longer.
You still have a puzzle about which language you use for the computer programs, and what exactly input and output mean, it doesn’t solve everything but does dissolve much of the mystery.
This has always seemed very likely to me. It seems way easier to create a world governed by a few rules of physics that would incentivize perceptrons than randomly stumble into complicated perceptron architecture via random physics.
My theory: something happens to prevent the infinitely protracted heat death of the universe From taking up much probability space. For example, the simulation is turned off because it has become boring. Or, someone figures out how to abundantly create new universes in states of low entropy, meaning that states before such creation are far more likely than states after such creation. Or, we’re wrong about how probability measure works over conscious observers, and Boltzmann brains are actually exponentially unlikely.
It’s not like we know this is a real problem; it’s merely a case where our theoretical physics gives a crazy result when pushed too far. We know there are places where our understanding breaks down, and this is one of them.
There used to exist the Steady-state model. If it was true, then the problem would immediately dissolve because classical minds would emerge with a far, far bigger density than the paradox-inducing Boltzmann ones. This could imply that the real physics (not even metaphysics!) also somehow dissolves the issue, but we have yet to understand the mechanism (a false vacuum decay which stops the universe from expanding and creates matter in sufficient quantities to make classical brains likely to emerge instead of the Boltzmann one?)
What is weird about this, is that in an eternal steady state universe the number of living observers in a given time period is much larger than the number of observers (including Boltzman brains) in a simialr slice of a universe approaching thermal equilibrium. So, depedning on how your Anthropic reasoning work, you could argue from the fact of your own existance that the universe must be steady state, regardless of any evidence otherwise.
(This is kind of a tension inherent in all Anthropic arguments, I am more likely to ‘be me’ (as opposed to someone else, like a Boltzman brain) in a universe with fewer people, but most possible observers are in the crowded universes, so I am more likely to be in a crowded one. Similar logic, threading oppsosite conclusions.)
This paper (2015) argues that the idea of quantum fluctuations without an observer/measuring apparatus to decohere the wavefunction is confused, and therefore (I didn’t fully understand this part), depending on unknown details of physics/cosmology, even thermal fluctuations (what the OP discusses) in an old universe that give rise to Boltzmann brains might not be a thing. (ETA: this sounds like it overlaps with Mitchell Porter’s top-level comment that “[maybe] De Sitter space simply doesn’t last long enough before decaying into flat space.”)
(That doesn’t help with the problems with the mathematical multiverse, or which computations a physical system implements.)
Ah I just left basically the same pointer haha.
Though I think the Boddy-Carroll-Pollack argument is separate from the swampland argument that Mitchell Porter is referencing. The swampland argument is saying that long-lived de Sitter space might not be possible at all in quantum gravity, whereas the Boddy-Carroll-Pollack argument is saying that long-lived de Sitter space might not give rise to Boltzmann Brains at all.
Logical positivism. Boltzmann brains occur after the heat death of the universe, which makes them causally isolated from our observations (anything that happens after all observers in the universe are killed is an arbitrary part of the model because we can’t pass any information to it and gain any information from it), therefore they can’t influence our probability measure.
By “the BB problem”, you might mean the problem of how to know whether you are a BB, but the OP explains how, and I can’t imagine what else you might mean by “the BB problem”.
The wiki page had Yudkowsky describe the problem as follows:
Yudkowsky’s paradox
Suppose your model of physics says that the universe will eventually dissolve into a sea of particles in thermal equilibrium, and these particles will then exist indefinitely.
Then an exponentially vast supermajority of all observer-moments in this universe take place inside brains that momentarily assemble themselves from the sea of entropy by random fluctuations, and probably dissolve a moment later. These are “Boltzmann brains”.
The vast supermajority of Boltzmann brains have relatively disordered experiences; they momentarily see chaos before dissolving again.
So your own, far more ordered and orderly experience in this very moment weighs heavily against the hypothesis “I am a Boltzmann brain”. Inder most systems of anthropic reasoning this weighs heavily against the possibility “a supervast majority of all moments of consciousness are vastly less orderly than my own”.
To be clear, it’s not “Yudkowsky’s paradox” as Yudkowsky is explaining a standard and known problem in cosmology here.
Admittedly, many cosmologists are not super careful when reasoning about Boltzmann Brains and they also disagree about what exactly is the problem they pose (e.g., see this dialectic between Carroll (2017) and Elga (2025) about whether belief in Boltzmann Brains leads to “cognitive instability”). But the core phenomenon of Boltzmann Brains and that they seem like bad news for many cosmological models is well-understood.
After a brief chat with one of the AI’s I had the impression that the main value of the BB was more about model/theory evaluation. Basically a theory that predicts a lot of the phenomenon should be questioned and probably “back to the drawing board” case.
A lot I don’t follow here but seems like the post might be challenging that, or perhaps some more simplified applications of that view.
But after the chats I actually wonder if that is the critical aspect rather than juts how we deal with infinities/really long time frames or how we think/define of equilibriums as the more critical areas of exploration.