Materialism Raises Fears You're a Soon-to-Die Boltzmann Brain

Let us imagine a disorderly universe consisting only of atoms randomly bouncing about. Materialists believe that minds and beliefs arise from certain combinations of matter in brains. If a disorderly universe existed for enough time and had enough mass, it might happen (under the assumptions of materialism) that some random combination of atoms might produce a self-conscious brain.

In the simplest case we can imagine, this might result in a mere flicker of self-consciousness that lasted only a few seconds. But in a more complicated case, the transient brain formed from random atom combinations might actually include beliefs and sensations that briefly persisted. Even though it might be surrounded by pure disorder, like a chunk of chicken in a big pot of soup, this short-lived brain could conceivably involve some random arrangements of atoms that might briefly convince the brain that it was viewing an orderly external world. The term philosophers and physicists use for such a hypothetical brain is a Boltzmann brain.

A Boltzmann brain is a hypothetical brain that arises from a random combination of atoms somewhere in space. A Boltzmann brain has internal states which make it seem like there is an orderly external world that doesn't exist. Just as a television playing a DVD can show a stream of images even when it is not receiving external television signals, a brain could conceivably have a set of internal states that might convince it that observations of an orderly external world were occurring, even though the brain was not actually getting light signals from such an orderly external world, and was actually surrounded by disorderly atoms bouncing around like the particles in a soup.

Let us imagine the brief appearance of a Boltzmann brain. First let us imagine a disorderly universe consisting not of planets and stars, but just random particles bouncing around. Because of some very improbable combination of atoms, some neurons come into existence, which create a consciousness that includes what seems like memories and perceptions of an external world. But the memories are false, and do not correspond to anything that happened. And the perceptions are also false, and do not correspond to anything in the external world.

Now, you may say that we can rule out such a possibility immediately, because it would just be too improbable that there could be so unlikely a random combination of atoms. One argument against the possibility is that there hasn't been enough time for there to be a significant chance of a Boltzmann brain, because the universe has only existed for about 13 billion years. But this does nothing to argue against the possibility that you may be a Boltzmann brain, because if you are a Boltzmann brain, the universe could really be far older than 13 billion years old (perhaps infinitely old); and your belief that the universe is 13 billion years old could simply be a belief that very recently appeared when random atoms combined to make your brain.

You may say think to yourself something like this:

I know in my mind so many things – all those things I learned in school. And I have so many memories – all the memories of a lifetime. It is way too unlikely that any random combination of atoms could ever produce a brain with all this knowledge and all these memories.

But there is a reason why such an argument is not convincing under materialist assumptions. Let us consider a possibility that we may consider a minimal Boltzmann brain. The minimal Boltzmann brain merely consists of the following:

1. A brain with a sense of self-hood.
   
2. A brain with the belief that it has lots of knowledge learned during years of life, and the belief that it has a lifetime in memories.
   
3. A brain that merely has the thoughts, recollections and sensations that you had during the past 30 seconds.
   

Now, under the assumptions of materialism, this minimal Boltzmann brain would be sufficient to account for your mental experience during the past 30 seconds. And under the assumptions of materialism, it could be that your mind is really only 30 seconds old, having arisen 30 seconds ago from a random combination of atoms in a disorderly universe, one that produced a minimal Boltzmann brain.

Assuming that memories can be stored in brains, it would require a most improbable combination of atoms to give you a Boltzmann brain with thousands of detailed memories. But it might require a vastly less improbable combination of atoms to give you a Boltzmann brain that did not really have all those memories, but merely had the belief it had thousands of detailed memories, and that merely had whatever memories you had recalled in the past 30 seconds. Under materialist assumptions, you could be such a Boltzmann brain, perhaps one that could have arisen only 30 seconds ago, from a random combination of atoms in a disorderly universe.

Now you may say that in regard to the possibility of a Boltzmann brain that had arisen only a few seconds or minutes ago, and one that didn't really have a lifetime of memories and knowledge but only the belief that it had a lifetime of memory and knowledge, it would still be too improbable that such a rare combination of atoms would occur by chance. So, you may reason, you can still believe in materialism and still think it is most improbable that you a recently formed Boltzmann brain. But such an argument is not a very convincing one. For while it is clear that while your recent appearance as a Boltzmann brain would be very improbable, it is not clear that it would be less improbable than your existence (under materialist assumptions) if you are not a Boltzmann brain, and everything you see around you is real.

The type of situation that we supposedly live in is one that is also fantastically improbable to occur by chance. Having an external universe like ours that is habitable with life (and with just the right fundamental constants allowing life to exist) requires a long series of coincidences, and some have estimated that the likelihood of all of these coincidences happening is less than 1 in ten to the hundredth power (much less than 1 in 1,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000). Then there is the origin of life, which seems to have required luck with a likelihood of less than 1 chance in 10 to the two hundredth power. Then there are all kinds of improbabilities in getting large multicellular organisms such as humans.

So under materialist assumptions the total unlikelihood of any intelligent organism such as you existing in a physical universe like the one we see around us may be less than 1 in 10 to the 300th power. And while it would be very unlikely that atoms combining in space would combine to briefly give you an illusion of perceiving an external world that does not exist, it is not at all clear that this would be less likely than 1 in 10 to the 300th power. It therefore seems that if you regard your consciousness as being caused by a brain, then you should have no great confidence about whether the external world exists, and should think there is a significant chance that you are merely a Boltzmann brain who originated a short time ago from a random combination of atoms in a disorderly universe, your sensations being merely illusions created by random states in your random brain.

It has often been said that from a thermodynamic standpoint, a Boltzmann brain in a disorderly universe is far more likely than a universe as orderly as ours. The most likely thing from a thermodynamic standpoint is a universe consisting of a gas of fairly uniform temperature. Deviations from such a thing are called statistically unlikely, and it said that the higher the deviation, the higher the unlikelihood. A Boltzmann brain would seem to involve a thermodynamic deviation relatively small, and might be potentially much more likely than a universe such as ours, which is a gigantic thermodynamic deviation.

On page 316 of his book Fashion Faith and Fantasy in the New Physics of the Universe, cosmologist Roger Penrose says, “One can make a very rough estimate of the probability that life, as it now exists on Earth, with all its detailed molecular and atomic locations and motions, came about simply by chance encounters from particles coming in from space in, let us say, six days!” Penrose then estimates that such a thing would have a probability of about 1 in 10 to the ten to the sixtieth power. That is a probability not anything like the microscopic probability of 1 in 10⁶⁰ but instead an almost infinitely smaller probability. It's the probability you would have if you started out with one tenth and then kept multiplying by one tenth a total number of times equal to a trillion trillion trillion trillion trillion times. But then Penrose tells us that this fantastically unlikely event (a life-filled Earth like ours suddenly forming from random collisions of particles) would be far more probable than the existence of a universe as orderly as ours, saying it “would be a far 'cheaper' way of producing intelligent beings than the way in which it was actually done!” He's indicating that the incredibly improbable sudden formation of a life-stocked planet like ours would actually be much more likely than the chance of you getting a universe such as ours accidentally.

In light of such a calculation, under materialist assumptions an individual should perhaps suspect that he is merely a Boltzmann brain recently formed from random atomic collisions, as that might be far more likely than for him to be a regular brain in a universe such as ours.

Physicist Sean Carroll has written about Boltzmann brains, and seems to have the idea that the concept is mainly an issue in physics or cosmology. He seems to think we can get rid of the specter of Boltzmann brains by picking the right cosmology model, such as one that doesn't generate too many Boltzmann brains. Such ideas are not correct. Properly considered, Boltzmann brains are mainly an issue in the philosophy of mind rather than physics or cosmology. The real issue is whether random combinations of matter can briefly produce someone who had the same thoughts, beliefs and sensations you had in the past 30 seconds. If that is so, it is very troubling, and you cannot remove your worry about this by assuring yourself that the universe is too young to have produced Boltzmann brains. The very belief that the universe is only 13 billion years old is one that merely could have popped up a few seconds or minutes ago in your Boltzmann brain formed by a random combination of atoms. So under materialist assumptions it could still be true that the universe might have existed forever, and there would have been time for countless trillions of Boltzmann brains to have arisen, no matter how improbable they are.

Now, in response to this a materialist may say something like, “I don't care too much about such a possibility because it makes no practical difference, and my life will be the same regardless of whether I am or am not a Boltzmann brain.” But this isn't true at all. If you are a Boltzmann brain, it has the greatest immediate consequences, because if you a Boltzmann brain it is extremely likely that you will die today.

The longer a Boltzmann brain persists while seeming to have sensations of an orderly external world, the greater an unlikelihood is required. After all, brains presumably need blood, but a Boltzmann brain is presumably just a brain floating about that doesn't have a surrounding body to keep pumping it blood (although it may have a sphere of blood around it for a while). So it is overwhelmingly likely that any Boltzmann brain will have existed less than a day, and will continue to live for less than a day. Under materialist assumptions, your memory of experiencing things a long ago time does not rule out the idea that you are a Boltzmann brain that arose from chance combinations of atoms a few minutes ago or hours ago in a chaotic universe, for when that Boltzmann brain arose it could have simply included such memories.

So if you are a materialist, you should fear that you a Boltzmann brain that is going to die today, living only the very, very short typical lifespan of a Boltzmann brain. Another thing you should be terrified about if you are a materialist is that today you will either go blind and deaf, and experience no more sensations for the rest of your life, or that you will experience nothing but unintelligible visual noise and auditory noise for the rest of your life. After all, each second of sensations experienced by a Boltzmann brain (in which it seems merely by chance atom combinations to experience an orderly external world) requires a great coincidence in which random particle movements conspire to resemble a meaningful, orderly reality. Every minute that something so improbable continues is like an additional minute at the roulette table in which you are betting all your winnings on Red 14, and continuing to win (and actually far more improbable). Such luck is very unlikely to continue for very long.

So it seems that if you are a materialist, you should be quite terrified that you a Boltzmann brain, and that you will either die today or that today you will stop having any more meaningful sensations, experiencing either blindness for the rest of your life, or meaningless noise sensations perhaps resembling what you see when you look through a kaleidoscope.

You can never prove that you are not a Boltzmann brain by having some long stream of sensations or recall experiences that you think are “too long and complicated for a Boltzmann brain to have.” Because once you start thinking along the lines of Boltzmann brains, you lose confidence that you actually had such a long stream of experiences and recall experiences. It could be that a few seconds ago you appeared when some random atoms combined in space, and that your belief that you recently had this “long stream of sensations and recall experiences” is merely a belief that arose a few seconds ago when your Boltzmann brain originated.

You may think: we can rule out the idea of Boltzmann brains, because it's too improbable that an organ as complicated as a brain would appear by a random combination of atoms. But because of the Boltzmann brain scenario, as a materialist you could not be confident that you actually have some very complicated brain. If you believe that consciousness and something like human mentality can arise from mere combinations of atoms, then you cannot rule out a scenario like the following:

1. Your mind arose after a relatively simple combination of a small number of atoms, forming only a very simple, tiny brain.
   
2. It could be that the mental state that arose after this relatively simple combination of a small number of atoms includes the untrue belief that mental experience like your present experience requires a very complicated brain.
   

If you are one of those persons who believes in a multiverse (an incredibly vast collection of universes), then if you are a materialist you should be particularly worried that you are a recently formed Boltzmann brain, because under materialist assumptions the more universes that exist, the more Boltzmann brains should be created.

Although the concept of a Boltzmann brain may sound silly, it is a serious philosophical problem for anyone who believes that consciousness can arise from combinations of matter. It seems that anyone who has such a belief can have no great confidence that everyone he observes at this instant really exists. And when you are lying with your eyes closed on your bed, waiting to fall asleep, experiencing no complex sensations, that is when (under materialist assumptions) you should be most afraid that you are merely a very recently formed Boltzmann brain who will not live another hour. For in that state you cannot say, “It is too unlikely that I would have such detailed sensations of the world if it did not exist, and I were just a Boltzmann brain that very recently appeared from random atom combinations.” For lying awake with your eyes closed, you are not having any complex sensations at all.

Is there some way to rule out the Boltzmann brain scenario, some way to slay this nasty specter? There is. The answer is to switch from the philosophical position of neuralism to the philosophical position of nonneuralism. Once we do that, the whole Boltzmann brain issue disappears.

We may use the term neuralism for the doctrine that minds come from brains. Although sometimes sold as science, neuralism is a philosophical position, not science. Scientists have no proof that minds are produced by brains, and the type of evidence they sometimes present to try to back up such a claim does not hold up well to critical scrutiny. The claim that brains make minds is a speech custom of neuroscientists rather than anything they have good evidence for believing.

An alternate position is that minds do not come from brains, and cannot come from brains or any other combinations of matter. We may use the term nonneuralism for this position. Nonneuralism is a non-sectarian position in the philosophy of mind that may be held without contradiction by Christians, Muslims, Buddhists, philosophical theists, agnostics or atheists, regardless of whether they do or not believe in Darwinism. Nonneuralism itself does not involve any specific belief about the source of human minds, although some nonneuralists may suspect such a source is cosmic or metaphysical or spiritual or transcendent rather than some local biological source.

Once you adopt the position of nonneuralism, Boltzmann brains are no longer a possibility that troubles you. If you believe minds cannot arise from brains, and cannot arise from any combination of matter, then you will believe that Boltzmann brains cannot possibly exist.

There are many reasons for adopting the position of nonneuralism. Explained in detail at this site, they include the following:

1. The fact that no one has ever advanced a credible explanation for how any type of matter (whether it be neurons or anything else) could produce self-hood, consciousness, thoughts, ideas or beliefs.
2. The fact that there is no credible theory of how a brain could be converting human mental experiences and sensations so that they can be stored for years as neural states.
3. The fact that there is no credible neural theory of how brains could achieve the instantaneous memory recall that humans have (which would be an "instantly finding a needle in a mountain-sized haystack" trick for a brain to perform).
4. The fact that there is no credible theory of how humans could be neurally storing memories that can last for 50 years, given the extremely short lifetimes of the protein molecules that make up synapses.
5. The fact that brains sometimes undergo enormous damage (such as loss of between 50% and 80% of their neurons through hydroencephaly or hemispherectomy) while showing only small changes in memory or cognition.
6. The fact that many people have vivid near-death experiences while their brains have electrically shut down during cardiac arrest, as the brain does within 30 seconds after the heart stops, such experiences suggesting our minds are not generated by our brains.

An additional reason for adopting the position of nonneuralism is that if you adopt such a position, you will not think there is any possibility that you are a Boltzmann brain, and that you will not suspect that maybe the people you see in front of you are mere illusions who will disappear (as you will disappear) a few minutes or hours in the future when your Boltzmann brain (floating about in a disorderly universe) dies. The nonneuralist can consistently say to himself: Boltzmann brains can never exist because brains by themselves do not and cannot produce minds.