How can they be conscious if there is no function/computation going on? And who argues that they are not conscious (I haven't found anyone except David Wallace just stating that this is his view on a panel).

If they are not conscious, in cosmology it seems that when Boltzmann brains are discussed (which is quite commonly) they are always assumed as conscious. That is with functionalism being the most popular view on consciousness according to PhilPapers 2020 Survey.

So the Boltzmann brain thought experiment - random configurations of matter can pop in and out of existence, and if that happens enough times, practically anything could randomly pop in and out of existence, including a brain. And it does seem to happen enough times in cosmology, so much so that some theories predict more Boltzmann brains than actual observers. An issue arises - we should expect ourselves to be the most typical observer, and under those theories, the most typical observer is a Boltzmann brain.

The argument is - certain versions of functionalism state that consciousness is a computation, in others it is some kind of function. Brain processes information and certain ways of information processing feel like subjective experience under functionalism. When a structure identical to a brain randomly pops into existence, there is no computation, function or information processing going on there. Therefore my question is - what does functionalism say about Boltzmann brains?

  • Please make this question useful for StackExchange by adding two things: an explanation of what a Boltzmann brain is, and an argument for why there would be no function/computation going on. You seem to be just arbitrarily rejecting one of the premises of the though experiment. Commented Feb 23, 2022 at 12:52
  • @DavidGudeman done Commented Feb 23, 2022 at 14:49
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    "When a structure identical to a brain randomly pops into existence, there is no computation, function or information processing going on there." - false. A Boltzmann brain acts like any brain, calculating and processing during the brief seconds that it is alive.
    – causative
    Commented Feb 23, 2022 at 17:39
  • @causative does it exist for a "brief second" or a single moment? In other words does it change it's state like a behaving brain would do at least once? Commented Feb 23, 2022 at 17:51
  • @nikishev.yes, once formed, it works just like a normal brain, because it's made of the same atoms as a normal brain, arranged in the same way, governed by the same laws of physics. Until it dies because it's surrounded by vacuum.
    – causative
    Commented Feb 23, 2022 at 17:53

2 Answers 2


The argument isn't really about brains floating in a vacuum any more than Schrödinger's cat argument is about cats. You can add bodies and an environment for the brains if you like.

E.g., you could state it this way: we see what looks like biological evolution in the fossil record. Hypothesis 1: biological evolution actually happened. Hypothesis 2: the entire planet, including all the scientists, popped randomly into existence last Thursday and the appearance of the "fossils" is pure coincidence. The problem is that some inflationary models suggest that you should have an extremely strong "everything is random and meaningless" prior, so strong that hypothesis 2 looks more likely than hypothesis 1, and more generally all science is impossible because nothing can shake your prior.

  • As far as I understand the entire planet won't just pop into existence, it will exist for a moment and immediately pop out of existence, or there could even be a random succession of states that would look like a succession of real states of our planet but they will be random "under the hood". My point is that since they are random, there is no computation going on, so brains that pop into existence like that won't have any consciousness under functionalism, they will merely have structure identical to our brain structure. Commented Feb 23, 2022 at 11:10
  • to clarify, if the entire planet popped into existence, it could contain structure that is identical to scientists and so on, but those scientists will not have any subjective experience, so they could exist but they are outside of our reference frame because they are not observers. In other words we should expect ourselves to be typical observers, and boltzman brains are not observers, nor are brains on "boltzman planets", so their existence doesn't matter to what we should expect ourselves to be assuming we are typical. Commented Feb 23, 2022 at 11:18
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    @nikishev. What I'm saying is that (as far as I know) none of your assumptions about the random states are integral to the argument. Whatever you think is necessary for consciousness, including genuine causal evolution for an arbitrary time after the last-Thursday starting point, is more common than actual evolution if the volume of inflating space is large enough. It can be large enough because the scale factor increases by a factor of 10^10000000000000000000000000000000 per second in inflationary regions, and sublinearly in noninflationary regions.
    – benrg
    Commented Feb 23, 2022 at 18:17
  • can the evolution be causal in fluctuations? E.g. can a ball pop into existence on a planet and fall down and bounce not in virtue of a succession of random states of matter that happen to be identical structurally to a ball bouncing, but in virtue of actual gravity and bounciness? Commented Feb 24, 2022 at 7:48
  • Poppycock. Stuff like that always happens on a Tuesday. It's the Jeremy Bearimy principle. Commented Jun 16, 2023 at 23:49

The Bolzmann brain. It's supposed to be a temporary existence of particles making up a brain. In an infinite space filled with particles in thermodynamic equilibrium (or real particles coming from a virtual Planck pre-big-bang state) there is a chance that a constellation of particles comes into existence by chance. In fact, any combination has a chance to come into existence, given infinite time and infinite space.

This view is held by some modern cosmologists, who see the universe as coming from quantum fluctuations, which continued their travel after the creation.

Even a whole universe can come into existence in an infinite space filled with particles in thermodynamical equilibrium. There is a chance the particles have the right fluctuations of position and momenta to condense into galaxies, stars, planets, and life on them. Literary everything can pop up in this infinity of particles. At one moment a river can show up, or a barking dog, while somewhere near infinity, an apple appears.

Are these structures persistent? If they form a neuron, will it, together with 80 billions others with the right connection strengths between them, continue to operate? Or are they just that temporary fluctuation of particles with the right conditions?

We gotta ask: what particles is the gas made of? We need the two basic fields of nature be in thermal equilibrium. But suppose they have condensed into quarks and leptons. The quarks have condensed in protons and neutrons and the neutrons, protons, and electrons into atomic nuclei with surrounding electric shells. Suppose these atoms are present in the gas. How will a brain pop up? Is it even possible that a brain pops up like this?

No, it isn't. Only an evolutionary process inevitably leads to lively structures. The fluctuations have to overcome one crucial thing, which fluctuations alone can't supply. Interactions and history. The atoms can only fluctuate in density. There couldn't form right spatial relations between atomic nuclei with the right electronic structùres between them.

Then what about a gas of nuclei and electrons? Could the nuclei arrange in a grain of salt cubic pattern with the right electrons between them? No. A grain of salt needs a process to form. Like all stuff in our universe. And even if it could form, the grain of salt wouldn't last in the surrounding gas.

But what if the surrounding would be a right fluctuation? It would last, not? Then we can relocate our attention to be bigger border. How can the fluctuation last in such a hostile gas? Well, but what if the surrounding is the right fluctuation?

Well, we could make the whole of infinite space a fluctuation in which there are no fluctuations left. This should happen once in a while, given enough time.

And there it all goes astray.

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