[throwup238]

> Over a sufficiently long time, random fluctuations could cause particles to spontaneously form literally any structure of any degree of complexity, including a functioning human brain

Can anyone explain this bit to me? The formation of biological brains was a multi-billion year climb against entropy. How would a brain form spontaneously without those random fluctuations tearing the constituent components apart?

I’m having trouble understanding the logic here. Random fluctuations don’t imply that any order from those fluctuations can be preserved. The higher order features like brains are path dependent on something resisting those random fluctuations to allow something stable to form, whether that’s an atomic particle, cell, organ, or organism.

IANAP and I don’t know what I’m talking about

[kelnos]

The point isn't that they can be preserved; you're right that they probably wouldn't be. But all it takes is a single instant where "you" are randomly "conjured" into being: your Boltzmann brain has all your memories and everything. Even if that brain dissipates a small fraction of a second later, for that tiny amount of time, you would believe in the world as we all know it.

And the bizarre thing about this is you can't say "oh look, I've been in existence long enough to type this sentence, so I and my memories and reality must be real, and not just a random spontaneous formation of a brain", because at every single instant, you could be that brand-new Boltzmann brain, never before formed, and the bits where you thought "oh look, I've been in existence long enough..." are just the memories spontaneously implanted into that brain.

It's kinda wild. I'm not sure I buy it as a realistic possibility, but it can be fun (or terrifying) to think about.

[jancsika]

This seems like a physicist with no philosophical background spontaneously (heh) discovering our epistemic hard-dependency on sensory perception.

In terms of philosophy, what's here that can't be found in, say, Descartes or Hume?

[axlee]

The difference between this concept and, let's say, Descarte's evil demon, is not the philosophical skepticism but its explicit grounding in physics and thermodynamics. It basically attempts to answer the question "Where would that evil demon come from?". It materializes Descarte's thought experiment and shows that it could actually happen within the confines of our scientific knowledge, unlike malicious demons.

[jancsika]

I think it's the other way around.

Descartes/Hume are saying that to even bootstrap our understanding of reality, we have a hard dependency on sensory perception. (I mention Hume because he points out that even Descartes' singular ground-truth can't lead anywhere else without linking sensory perception back into the mix.) And when I say "nearly anything" it includes our notions about the laws of physics. (Which, btw, cannot be derived from Descartes' singular ground-truth.)

At best, BB is a restatement of what I wrote with the philosophically irrelevant detail that the BB hypothesis relies on all the same laws of physics we have in common with our universe. But I imagine it's really meant commonly as a weaker claim-- one which takes the laws of physics as epistemological ground-truth to derive an ambiguity about the nature of our reality within that universe.

My speculation is that science-minded people think BB is the most potent thought experiment for the same reason non-musicians might think Pachelbel's Canon in D is the best ever-- they've heard it a lot at places filled with people they admire.

[soulofmischief]

As someone familiar with both Descartes and Boltzmann, I will chime in and say that you're approaching this from an angle of contempt and defensiveness, imagining the Boltzmann brain as an inferior subset of or analogy to long-studied philosophical and metaphysical issues such as ground truth or the evil demon. Instead, I implore you to give benefit of the doubt and attempt to understand the differences.

The Boltzmann brain is not making some grand statement on ground truth or perception. It's not about intrinsics or perception at all. Boltzmann discussed how the universe, even in a state of 100% thermodynamic equilibrium, may spontaneously end up in a state of non-equilibrium, reducing entropy. The Boltzmann brain was a concept developed by others in response to this theory.

In fact, many theories are such that a Boltzmann brain actually has a higher chance of occurring than all of the billions of years of coincidences which led up to me typing this message out to you.

It's purely an argument of entropy and spontaneous symmetry breaking. The sensory and perceptive states described by the Boltzmann brain only serve to illustrate the point, and are not the main subject of the problem.

Don't forget that philosophy was the first science, and viewing people as "science-minded" (and therefore not philosophy-minded) hurts the scientific legitimacy of philosophy, and also only serves to exclude. Many scientists also have deep philosophical grounding. Many also have deep musical grounding. You yourself are exhibiting a lack of domain knowledge regarding the Boltzmann brain, filtering it through your "philosophy-minded" perspective, so maybe we can dispense with these kinds of judgements and focus on the core argument.

The world is not so black and white, and there is no false dichotomy between people who are "science-minded" and "philosophy-minded". Both follow the same exact scientific method of inquiry.

Additionally, "the same reason non-musicians might think Pachelbel's Canon in D is the best ever" comes across as a strawman. Some people might prefer that piece overall, but it's not a crime for someone to enjoy it. But relatively few probably consider it "the best ever".

But also, who cares? Why judge? I have a lot of favorite modern pieces which are technically inferior to most classical pieces. But as a musician, not just an engineer, I consider sensory evocation to be equally as important as technicality.

[sdwr]

Sounds about right, except Pachelbel's Canon actually is the best song ever for non-musicians.

It showcases harmony and contrasting lines in the simplest, punchiest, most pleasing way. It's fundamentally "the good stuff", and untrained ears slurp it up like babies w pats of butter.

[raattgift]

Probably no physicist thinks that Boltzman brains are a potent thought experiment. BBs are short-hand for a problem in combining cosmology and statistical mechanics in a way in which there is a hierarchy of vastly improbable configurations fluctuating into existence out of thermal equilibrium.

Discounting Brain-in-a-Vat (because it's cognitively useless), the problem in a nutshell is that we inhabit a universe which appears (a) to have had a hot dense phase in approximate thermal equilibrium, (b) a future sparse phase in approximate thermal equilibrium, and (c) a whole bunch of structure in between those. Is the structure a fluctuation in (a)? Could (a) be a fluctuation in (b)? These are reasonable questions about which one can ask: is there astrophysical or laboratory evidence available to determine the answers?

One problem is that if (a) (early conditions) is a fluctuation in (b) (late conditions), wherein (a) simply evolves into (c) (complex structure with galaxies and so on) and then (b), what mechanisms could suppress simpler configurations than (a)?

A huge huge huge number of low-entropy Boltzmann brains fluctuating into existence is vastly more likley (on Boltzmann entropy grounds) than an early very-very-very-very-very-low-entropy universe compatible with the standard model of particle physics and the cosmic microwave background and galaxies all over the sky, in which there is a nonzero chance of human brains arising via evolutionary processes.

A tiny change in a Boltzmann brain as it fluctuates into existence could lead to a significant loss of false memory; a tiny change in a maximally-hot maximally-dense phase in the early universe could lead to completely different chemical elements (or none at all).

So Boltzmann brains highlight some metaphysical ratholes one can fall into with respect to the fine-tuning of the (a) state, and have provoked work on how (a) could be so generic an outcome that the evolution of (a)->(c) is "unsurprising". The hard part is coming up with observables which usefully compare a given hypothetical solution and our own sky.

[anon34223879]

I would question the idea of bootstrapping; rather sensory perception is a QC/QA function that confirms the brain's construct of reality.

The only reason we can generally agree on the nature of any object is our common evolution and generally the same sensory ability. (but that isn't universal and differs widely across species)

[griffzhowl]

Yes, and the idea of Boltzmann brains depends for its credence on those physical principles used to derive it. And those principles in turn depend on the reality (or at least reasonable reliability) of our memories and the whole history of experimental and theoretical development leading to them. So trying to use it as an arugment for philosophical scepticism, or that it's a probable scenario, would be self-defeating, denying its own evidence.

It does give a technically detailed construction for how such a scenrio might come about though, as you say, so it can be interesting to think about.

[jancsika]

Sure. But as I said to another respondent, it's a much weaker claim than those which already exist in the philosophical literature.

That doesn't matter if BB is just a bridge for physicists to a deeper understand of philosophy. But I have a sneaking suspicion that BB is part of a basket of ideas in a kind of bubble category of "Philosophy for the Scientist." Similar to those "101 Jokes for Golfers" books-- I mean, fine, but if those are the only jokes you know you're probably insufferable at parties.

[lazide]

Well, the BB isn’t necessarily a serious proposal.

Rather, when you do the math on all the billion/trillion to one shots that are definitely happening, every second of every day, in physics - and look around at the universe as it appears to exist now and how many of those shots had to play out in a specific way - and then do the math on the probability of a BB spontaneously existing, then it’s really absurd that we aren’t somehow BB’s.

[moi2388]

But this presupposes that consciousness is a mere instant. If I am conscious ‘now’ and maintain this State for Lets say 2 seconds, the chances of me being a boltzmann brain pretty quickly drop to near 0

[lazide]

And how could you actually determine if we’re actually in second 2, or actually in second 0 with knowledge/memories/sensory input which makes you think we’re in second 2?

At some point it does boil down to faith that we aren’t in that scenario/it isn’t what is occurring. Philosophically, it’s hard/impossible to fully logic our way out of this kind of problem.

[moi2388]

You can’t, for a single point. My argument is that you don’t have consciousness for a single point. Thoughts take time, we have streams of consciousness.

If I can determine a current point (I argue I can), with memories, then remain conscious for let’s say 2 seconds, the chance of me being a Boltzmann brain already dropped to almost 0.

At any point you could say false memories were planted, but this assumes that I am only conscious in an instant, and merely remember previous states. Both research and my own experience seem to indicate it’s not this coherent, and we have a much longer instant of consciousness or ‘moment’.

A Boltzmann brain only makes sense for particular instants thermodynamically, coherency is as good as impossible

[lazide]

You might want to re-read my prior comment.

[medo-bear]

Taking scientific knowledge to their weird limits might also signal something perhaps more likely: a missing puzzle in our knowledge

[Symmetry]

A mere trillion years is a tiny fraction of the time it would take for a brain to form like this spontaneously. This concept arose when people generally thought the universe was in a generally steady state and had existed forever. Even though generally say that entropy always increases if you wait long enough you might see reversals if you wait periods of time proportional to something like e^N where N is the number of particles in the system. So it's weird that we're in this low entropy solar system, but you'd expect something like that to happen every once in a while across infinite time. But since a brain has many less particles than a solar system [citation needed] you should expect brains to form from spontanious entropy reversals much more often than galaxies do. There's a principle called the "incompressability of phase space" that means that a low entropy solar system with a low entropy brain is necessarily much less likely than just the low entropy brain, because entropy reversal across an entire solar system is just so mind boggling unlikely.

Of course nowadays the cosmic redshift, etc, make us think that the universe is not eternal but began a short few billion years ago and will end in a big crunch or big rip long before we expect a single Boltzman brain to arise through the random walk of particles.

[raattgift]

You have the analysis right (incompressibility of phase space), but maybe not the application.

Bbs are arguments against the early low-entropy state of the universe being a fluctuation out of thermal equilibrium, and of a future universe fluctuating out of the approximately de Sitter state of the far future.

Expanding steady state was an effort to capture the increasing evidence (including redshift relations) in favour of a Lemaître-style dense early universe, and to avoid several problems with ~static universes.

Since a steady-state cosmology has neither an early low-entropy configuration nor a late homogeneous equilibrium state (steady-state means homogeneity & isotropy in time as well as space: the "perfect cosmological principle"), I'm not sure how a BB argument arises in such a model. In an expanding steady-state model, is there some mechanism for making BBs other than to have them appear with the other components of new gas which under self-gravitation fragments into systems with negative heat capacity?

[sdwr]

"Because the earth existing is more unlikely than winning the lottery, we should expect to see winning lottery tickets floating in space"

[bee_rider]

We should expect that there will be at some point winning lottery ticket floating in space.

I don’t think we should expect to see them, though, because they are probably very far away in time and/or space.

Also the concept of a winning lottery ticket would seem to require the existence of a lottery game, which would seem to require some sort of society to play it. We are probably not the minimal working example of a society that is able to invent a lottery, but I bet that society is closer to us in complexity than it is to a scrap of paper.

[qingcharles]

This reads like a paragraph from H2G2.

[immibis]

Yes - if the observable universe is just a low entropy random fluctuation.

[sdwr]

The point of the Boltzmann brain is that it's spontaneous (which is also what makes it impossible). If a billion years of slowly ratcheting up complexity counts as a "random fluctuation", then every brain is a Boltzmann brain.

[praptak]

If time is infinite then the argument from exponential complexity doesn't really work as a counterargument to Boltzmann brains. It might take Rayo's number of years plus five for a good measure but it is still bound to happen with absolute certainty.

[FabHK]

The point is not that it's likely (or practically possible) that such a brain would come into being spontaneously. The point is that it is (mathematically) still more likely than some other theories about the formation of the universe (namely those that give it the order we see, low entropy, by "miraculous" happy accident), thus showing that those theories are most likely nonsense, by reductio ad absurdum. (Those other theories can't be true, otherwise we might as well find brains in space.)

[quantadev]

It's about quantum mechanics and the fact that "empty space" is not really empty. Particles do pop into existence (from nothing), according to QM, so there's a non-zero probability for any "pattern" to pop into existence. Sort of like if you have an infinite number of coin flips then at some place and time you'll land on heads a million times in a row, no matter how unlikely. And for any million-bit sequence you're guaranteed to hit it too. So a human "brain" is just a pattern that's likewise guaranteed to be "encountered".

A similar concept is how the first replicator RNA/DNA got created as the beginning of life. If RNA can exist in large numbers of random sequences, then a sequence that can replicate itself only has to "happen" once and then life is started and will never slow down but will grow in complexity, as long as the environment can support it.

[throwup238]

I get the part about popping into existence but how would even so much as a bilipid layer around a single cell form, let alone a whole brain? Where are all the antiparticles in this, except shooting around? Even if all the particles pop into existence perfectly placed for a single quanta of Plank time, aren’t the antiparticles destructively interfering with all the other particles even before they begin to annihilate? I imagine they would prevent any chemical reaction happening at all at that density. What about all the force carriers? Can they even pop into existence in the quantum foam coupled?

It wouldn’t really resemble a brain in biological sense of the world because the only stimuli it can and will react to is its own disintegration. It’s hard to justify it even “existing” at all. A “virtual” brain in the sense of virtual particles perhaps, except it seems quantitatively useless.

[quantadev]

The probability of even a Hydrogen atom popping into existence is astronomically low, but the point is that one could. And if one can, then many can, and on and on. The point is that it's not impossible, just improbable. But by definition of one did pop into existence, it's a stable state and would therefore not just simply vanish after forming.

[throwup238]

How is that possible without producing an antiparticle pair?

[post-it]

The antiparticle could be a few metres away.

[throwup238]

I think the time-energy uncertainty relation limits their distance and it is very small, closer to a Planck length than any precision we can measure. They have to be close enough to annihilate within a specific time limit related to the energy of the particles (ΔE·Δt ≥ ℏ/2) and the higher energy the particles like a full proton, the less time they have.

[stoperaticless]

> Sort of like if you have an infinite number of coin flips then at some place and time you'll land on heads a million times in a row, no matter how unlikely.

If random event result is any real (i.e. not limited integers and fractions) number from interval 0-1, then no number will appear twice even after infinite number of throws.

Open question surely follows: Time and space, are they integer or real?

[quantadev]

That's kind of like asking if spacetime is quantized or not. We have bits of evidence in both directions. For example, the entropy of a 2D (conventional) Event Horizon, is identical to the number of planc-length (square) units of area on the EH sphere, and so that's a definitely quantity/number, for any given Black Hole mass. You could interpret that as saying the EH is broken up into "pixels" sort of, which a kind of quantized view of spacetime if our universe is indeed a big Event Horizon.

[GoblinSlayer]

Due to Bekenstein bound for any given energy there's maximum entropy or maximum number of microstates, so the same microstate can repeat.

[nox101]

I'm with you. There are forces that would prevent random particles from being in any configuration "at random".

Example: At random, 2x2x2cm ice cube in center of sun sized star. You can't get from here to their because an ice cube will never form next to heat.

In some alternate reality where atoms materialize in random configurations out of nothing maybe, but that's not our reality where atoms interact with other atoms and that interaction prevents the vast majority of combinations. It doesn't matter if time is infinite.

[wanderingstan]

> In some alternate reality where atoms materialize in random configurations out of nothing maybe

Quantum mechanics says that this reality. Look into virtual particles.

[blueprint]

> How would a brain form spontaneously without those random fluctuations tearing the constituent components apart?

>> Over a sufficiently long time

[throwup238]

I just don’t understand how it would be possible over any time period, doesn’t matter if it’s a billion years or even 10^10^10^10… years. There are conservation laws governing how particles can pop into existence and them all popping into existence in just the right place is only even remotely plausible if you ignore the antiparticles that are formed in the same space.

[evoke4908]

Forget about the particles for a second. This is about fundamental quantum fields. The fields can randomly fluctuate from the vacuum state into a more ordered state where virtual particles are created.

The conjecture here is that a given volume of space must, at some point, randomly evolve into the quantum state you're interested. When the quantum fields align into the same state that a bunch of particles would represent, those particles appear out of the vacuum.

The trick that makes this work is that conservation laws don't apply on very small time scales. That's how virtual particles work after all. The energy can only be temporarily borrowed from the vacuum, unless you pay the energy cost to make that particle 'real' by destroying its virtual pair (see Hawking radiation).

You might imagine TV static, just random visual noise. There's no real reason the randomness can't line up to produce one single coherent frame before decohering. Just imagine that in 3 (or 11) dimensions.

I don't think an antiparticle pair is a strict requirement for virtual particles either. As long as energy is conserved on macro timescales, the universe doesn't really care what state the quantum fields are in.

[blueprint]

Conservation of energy is only considered true "locally", but not globally. There are many examples of this in nature, believe it or not. If you wanted to have a system that perfectly conserved energy, how would you expect to measure its existence, or changes in state, anyway?

Besides, even if you assume conservation of particle number, it only has to be eventual conservation. Suppose I borrow some energy from "over here" temporarily and accidentally assemble them into a perfect brain for a second, then they can disperse again, if they like.

A bigger question is, if energy were conserved globally, where exactly did those handy particles come from in the first place anyway?

[raattgift]

Among the de Sitter invariant states for massive fields is the Euclidean or Bunch-Davies vacuum, which allows for pair production with separations greater than the horizon distance. Since our universe seems to be marching towards a state highly similar to the Euclidean vacuum, such pairs seem (a) physically plausible (b) and with some low probability could arise in groups which (c) because they are interacting particles, might nucleate.

Nucleated objects could be long-lasting, which blunts the Boltzmann brain (Bb) picture, as under fluctuation theory the Bb is ephemeral and time-reversible. On the other hand, it's historically been attractive to think of the nucleation of a inflating patch of spacetime (with low enough entropy that structure like galaxies might form as it expands and fragments gravitationally).

[goatlover]

The big bang may have began as a highly improbable low entropy fluctuation in the vacuum state.

[jmyeet]

Think of it this way: you've probably heard about the million monkeys on a million typewriters will eventually produce Shakespeare? Ultimately something deeply meaningful like that is just a sequence of symbols and you generate enough randomo sequences of symbols, one or more of them will be literature.

A Boltzman Brain is basically that but for a quantum system. In the far future, it's suspected the Universe will undergo heat death and eventaully reach thermodynamic equilibrium but that doesn't mean nothing happens on a quantum level. A chaotic system as otherwise thermodynamic equilibrium is still capable of having temporary, localized order without violating entropy.

So over any sufficiently long period of time (we're talking 10^100000+ years here), you'll get all sorts of interesting arranagements of matter. One of these is a localized reality where it or being in it are capable of sentience.. They won't have any conception of the Universe outside of this but, for a time, they will be able to contemplate their reality.

Think of it another way: take a bucket filled with random elements, mix it and tip it on the floor. Do this enough times and one of those bucket pours will be sentient life.

[eclecticfrank]

Adding to the million monkeys on a million typewriters: There is Project Babel, an algorithm that strives to produce every combination of letters (and then also words) possible.

It's "books" are filled mostly with gibberish but theoretically, if running long enough, it will generate books that have not been written yet.

https://en.wikipedia.org/wiki/The_Library_of_Babel_(website)