This is, far and away, the most unsettling paradox I have covered here. If you are easily upset by thinking about philosophical, existential creepiness, you probably shouldn’t read this. You have been warned.


So. The universe. You know the one. Big place, lots of room, with black holes and stars and planets and stuff. It’s a pretty complicated place. Earth, especially, is very complicated. The water cycle, the biosphere, photosynthesis and cellular respiration, all very complicated. And humans are the most complicated things of all!

Sometimes we don’t realize how complicated humans are, because we’re used to them. But here’s one way to think about it: humans have been studying human behavior, in one way or another, for at least thousands of years. It’s been called philosophy, psychology, neurology, whatever. On the other hand, we’ve only really been studying stars since 1608, when telescopes were invented. And not only have we had more time to study humans, we’ve dedicated more brain power to it. Right now, there are about 109,000 psychologists in the USA alone, whereas there are probably about 70,000 astrophysicists worldwide. (Sources: and

However, if you give an astrophysicist a few pieces of information on a star, like its mass, composition, and location, they can tell you without a shadow of a doubt what that star will be doing in a million, billion, or even trillion years. If you give a psychologist a few pieces of information on a person, like their age, gender, and general personality, they might be able to make some guesses, but chances are low that they’ll be able to predict what that person will do within the next hour, let alone for the rest of their life.

That wasn’t the paradox, that was just a tangent. Back to the creepiness.

As we have established, humans, and the world we live in, are complicated. We are highly ordered, we have low entropy, however you want to describe it. And yet, the universe, and existence in general, seems to trend towards disorder. That’s the jist of the second law of thermodynamics, right? Things generally get less complicated, not more. (I’m not a physicist, but I’m pretty sure that’s mostly right.) So, Earth’s highly ordered life is something of a fluke. A highly unlikely fluctuation. Somehow, despite fundamental laws of physics, incredibly complicated systems, billions of tons of biomaterial, not to mention computers and machines, have arisen. And among those things, there are human brains. These brains are capable of imagining things, of creating whole new worlds within them. They are even capable of tricking themselves into thinking those worlds are real, though dreams and hallucinations.

Do you see where I’m going with this? If complexity is a fluctuation, then what is more likely: a HUGE fluctuation the size of a planet, or… a three-pound fluctuation, a single human brain?

A brain, with no sensory input, nothing else in existence. In such a state, wouldn’t the brain get bored? Might it not dream or hallucinate a whole world, its fantasy of a place as complicated as it is? Might it not simulate other brains, other people with whom to communicate? When I’m on the bus, my mind starts to wander and fantasize. Imagine what my mind could do if I didn’t have the window to look out, nor eyes to look with. No body, no stimuli, nothing else out there in the void.

As I have mentioned, I am not a physicist, but from what I’ve read, the science is still out on which scenario is more likely: reality is real, or reality is your hallucination. But even if the probability slides one way or another, you can never be certain. Because if you read that the question is settled, and scientists are sure this is the real world, well, couldn’t you have imagined reading that?

Of course, this has been a question for far longer than quantum mechanics has been around. Plato wondered if he was trapped in a cave, and Rene Descartes wondered if he was being tricked by a demon. Now, we wonder if we are statistical fluctuations. This idea has been troubling us for a long, long time, with no resolution in sight.

This article is over, but the question is not.

Sweet dreams…

2 thoughts on “Boltzmann brains

  1. >> Things generally get less complicated, not more.

    No, that’s not quite right, and the difference is important. =Overall= things tend to get more disordered; putting things in order requires energy, and the production of energy makes other things disordered; the disorder from the production of energy is greater than the order created by putting that energy to use.

    The earth is not a closed system; it gets a seaish amount of free energy from the sun. So, the thin layer on the surface of the earth can become ordered by using this energy to build life. And if we just look at that thin layer, radioactive decay deep in the earth also supplies “free” energy that life can use. Meanwhile, the sun, the earth’s core, and outer space become more chaotic. Compared to the thin layer of life on earth, that’s a lot of chaos creation that allows life to happen.

    As to fluctuations, the hard part isn’t the fluctuation itself, but the boundary conditions. For this to be a workable simulation, boundary conditions (the edge of the simulation has to match or mimic the edge of the universe being simulated). If we are a simulation, it’s most likely to be simulations all the way down. But perfect ones? A computer program without bugs? I doubt it. And if there are bugs, they will limit “how far down” the simulation of a simulation is viable. If we look in the right place, we might notice.

    So, is quantum mechanics a bug in the universe? I’ll leave that for you to ponder. 🙂



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