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

• quantadev 2y ago
  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 2y ago
    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 2y ago
      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 2y ago
        How is that possible without producing an antiparticle pair?
        • post-it 2y ago
          The antiparticle could be a few metres away.
          • throwup238 2y ago
            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.
            • quantadev 2y ago
              I think maybe the original Boltzmann brain may have been about pre-existing matter particles having the ability to just "jump" to a new location (similar to how they can tunnel thru a barrier), and so you can have them all just "jump" into the shape of a perfect square, perfect crystal, or even perfectly formed cat. So it's not necessarily about the "from pure empty space" version of it. This is all just a thought experiment and not intended to be taken literally.
            • raattgift 2y ago
              Honestly, you have a series of good questions and unfortunately I don't think your other interlocutor is helping. I'll give it a try. This is very much a hand-wave. tl;dr: Boltzman brains (Bb) from energy gradients: a "formless" high-energy fluctuation in a cold gas returns to thermal equilibrium through a Bb state. The classical cartoon for a Standard Model of Particle Physics human Boltzmann brain (SMBb) is a cold (too cold for metabolism) Maxwell-Boltzmann gas or soup of atoms which in principle could condense into biological molecules via chains of endothermic and exothermic reactions. The gas is on average too cold for the endothermic parts, though, which essentially means no products comparable to those from anabolism. From fluctuation theory randomly there will be high-temperature regions which allow for endothermy. In a hot bubble, which quickly cools by dissipation, complex molecules are (briefly) energetically favourable as their formation also lowers, locally, the temperature of the hot spot in which it's embedded. The Boltzmann brain formed in this way is liable to be cooked apart by the heat of the hot spot outside the small region that cooled as the Bb condensed in it. You've been wondering about how an SMBb might form. The starting point is a cold gas of photons. In that gas regions with vast amounts of gammas can fluctuate out of equilibrium: this is the hot spot. Particle pair productions and complicated decay chains serve to cool the hot spot (inelastically scattering gammas, among other processes), and consequently forming complex bound states embedded within the super-hot-but-rapidly-cooling spot is energetically favourable. Yes one has to have some luck (or some extra constraint or mechanism) in matter/antimatter asymmetry, which should be encoded in the grand canonical ensemble for interacting particles. The SMBb will be torn apart by gammas and other radiation in the hot spot in which it is momentarily a cold spot. One might compare this with a different extremely hot "hot spot" in which complicated states can form briefly. High-entropy pulsional pair-instability supernovae (PPISN) <https://online.kitp.ucsb.edu/online/stars-c17/woosley/pdf/Woosley_Stars17Conf_KITP.pdf https://online.kitp.ucsb.edu/online/stars-c17/woosley/pdf/Wo...> (see especially the graph on slide 5) are massive stars whose core rises to pair production temperatures. The pair-production cools the core of the very hot (~ 0.3 GK), very massive star; the cooling means less radiation supporting the star's bulk above the core. Gravitation from the sheer mass of the star itself drives a thermal runaway. However, during the runaway, there will be further cooling via nuclear processes that tend to generate a large neutrino flux. Soon however the star and all the heavy daughter products which condense during the pair-producing phase tend to be violently explosively disassembled. The "hot spot" for a Standard Model Boltzmann brain might be several terakelvins hotter than a PPISN's core (the SMBb bubble ought to be gamma gas reaching QCD or even GUT temperatures), but won't be massive enough to self-gravitate. Animatter is the least of the SMBb's worries, given all the hotter radiation surrounding the cold spot formed by condensing into the brain itself.
  • stoperaticless 2y ago
    > 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?
    • GoblinSlayer 2y ago
      Due to Bekenstein bound for any given energy there's maximum entropy or maximum number of microstates, so the same microstate can repeat.
    • quantadev 2y ago
      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.
• kelnos 2y ago
  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 2y ago
    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 2y ago
      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.
      • griffzhowl 2y ago
        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.
• blueprint 2y ago
  > How would a brain form spontaneously without those random fluctuations tearing the constituent components apart? >> Over a sufficiently long time
  • throwup238 2y ago
    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 2y ago
      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.
    • goatlover 2y ago
      The big bang may have began as a highly improbable low entropy fluctuation in the vacuum state.
    • blueprint 2y ago
• jmyeet 2y ago
  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 2y ago
    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) https://en.wikipedia.org/wiki/The_Library_of_Babel_(website)
• FabHK 2y ago
  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.)
• praptak 2y ago
  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.
• nox101 2y ago
  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 2y ago
    > In some alternate reality where atoms materialize in random configurations out of nothing maybe Quantum mechanics says that this reality. Look into virtual particles.
• Symmetry 2y ago
  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 2y ago
    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 2y ago
    "Because the earth existing is more unlikely than winning the lottery, we should expect to see winning lottery tickets floating in space"