A Brief Introduction to The Boltzmann Brain Theory

27 May 2024

The second law of thermodynamics states that the disorder (entropy) of an isolated system will increase over time. This principle is so fundamental in our lives that many people might not even be aware of it, but it is the reason, for example, that an egg can become scrambled eggs, but we never see scrambled eggs suddenly reassemble into an egg. Ludwig Boltzmann explained the continuous increase in entropy by stating that randomly moving particles always have many more disordered arrangements available to them than ordered ones, which is why the entire system is much more likely to end up in a disordered state than an ordered one. Since the Universe is also an isolated system, it follows that its entropy is constantly increasing as well. This implies that at the beginning of the world, the Universe was in a "super-ordered" state. But how did the Universe come into existence?

Current scientific models can describe the history of the Universe back to the moment of the Big Bang. The most crucial question is: what happened at the moment of the Big Bang? According to the most widely accepted theory, the Universe simply arises from nothing, as quantum mechanics allows for such an occurrence, albeit with very low probability. Thus, the Universe emerged from nothing in this super-ordered state. Since then, it has been expanding, and its entropy has been increasing. But if the Universe can emerge from nothing, why couldn't a human brain emerge from nothing in the same way?

This is the essence of theBoltzmann Brain Theory. What if you, dear reader, are a brain that emerged from nothing? This brain was created at this very moment and contains all the memories you have experienced. You believe that you have lived for many years, but in reality, you were born at this moment, and all your memories are false. Moreover, there is a good chance that in the next moment, you will be swallowed up by the nothingness from which you emerged. Can you prove in any way that you are not such a Boltzmann brain? It's a crazy and terrifying theory, isn't it? The theory of a Universe emerging from nothing is much more believable than a brain emerging from nothing. But there is a little problem. Our current universe is full of brains.

There are billions of people on Earth, each with their own brain and consciousness. Since the universe has existed for billions of years, it is currently in a much more disordered (higher entropy) state than at the beginning of time. We also know that the more complex something is, the less likely it is to emerge from nothing. Based on this, it is much more probable for a brain to emerge from nothing than for a universe with galaxies, solar systems, and billions of brains to do so. Therefore, purely on a statistical basis, it is much more likely that we are Boltzmann brains and that the universe is merely an illusion to us rather than the entire universe had arisen from nothing.

Of course, one could argue that these billions of brains didn't just emerge from nothing. The Universe started from a single point and has been continuously expanding. During this process, stars and galaxies formed, as well as solar systems with planets where life could develop. The development of the brain is the result of millions of years of evolution. The evolution of our brains is due to simple physical laws and countless random events, which is not comparable to simply emerging from nothing. However, there is a response to this argument, which I call the "Soft Boltzmann Brain Theory."

Imagine that the world, similar to our current universe, begins with a Big Bang. However, as a result of continuous expansion, instead of stars and galaxies, a structure capable of computation forms. We can call it a brain, but if that's confusing, we can consider it some sort of primitive life form. Over time, this entity evolves and develops self-awareness. We can view this as a kind of “abstract evolution.” It is abstract because, instead of living beings, it is thoughts that compete with each other. Essentially, the entity exists in a state of continuous dreaming. It couldn't do much else but dream since nothing else exists outside of it, as it is the entire Universe itself. At a certain stage of development, this unified consciousness splits into many parallel consciousnesses, somewhat like cell division. Such a form of Soft Boltzmann Brain is not much different from our Universe.

The Universe as we know it emerged from nothing. Its functioning is governed by fundamental physical laws, and life developed over a long time thanks to evolution. Strangely, our Universe is fine-tuned for life. If any physical constant were even slightly different from what it is now, the intelligent life we know could not have developed. The most accepted explanation for this fine-tuning is that there are countless universes, each with different physical constants. We perceive our universe as fine-tuned because it is the only one we know. This is the anthropic principle.

A Soft Boltzmann Brain also emerges from nothing. Initially, it is not intelligent and its functioning is governed by simple physical laws, similar to our Universe. Since this Boltzmann Brain is incapable of perceiving the outside world (because there is no outside world), it exists in a continuous dream state. When it becomes self-aware and then splits into many consciousnesses, it begins to examine itself and finds that the Universe (which it hallucinates) is fine-tuned for life, which is obvious since it created it for itself. The distant stars and galaxies are all parts of the hallucination, making this a much smaller and simpler structure than our currently known Universe. Therefore, theoretically, it is more likely for such a structure to emerge from nothing than our currently known (wasteful) Universe.

Is it possible that we are actually parts of such a Soft Boltzmann Brain? If we think about it, there is really no way to refute this. Any experiment we conduct in the world we hallucinate for ourselves will appear to be a reality since we cannot outsmart our own minds. (A few years ago, I wrote an entire article on why it is impossible to prove that the world we know is a hallucination.)

The Boltzmann Brain Theory is a type of Simulation Hypothesis. According to the Simulation Hypothesis, the reality we know is just a simulation created by a civilization with more advanced technology, much like in the movie "The Matrix." The Simulation Hypothesis can provide answers to things like the fine-tuning of the Universe, but as a creation theory, it is not as strong since it simply pushes the problem to a higher level. We get an answer to where our Universe comes from, but a new question arises: where do those who created the simulation come from?

The Boltzmann Brain Theory offers a simple answer to this question: the computer simulating our Universe simply emerged from nothing. (Here, the words "computer" and "brain" are freely interchangeable.)

There has been only one argument successfully raised against the Boltzmann Brain Theory, which Sean Carroll calls “cognitive instability.” In a nutshell, the argument is that if the Universe as we know it is actually just a hallucination of a Boltzmann Brain, then we cannot use the laws observed here to explain the “external” world, as we cannot know anything about it. For example, it is possible that the second law of thermodynamics does not hold in the “external” world, so we cannot use it to explain the Boltzmann Brain universe. This, of course, does not rule out the possibility that we are indeed parts of a Boltzmann Brain; it merely states that we cannot use the second law of thermodynamics to argue in favor of it.

Finally, I would like to address whether there is any point in considering whether the Universe we live in is actually a Boltzmann Brain.

As I mentioned before, there is no way to prove or disprove this. It’s the same situation as with the simulation hypothesis. Only one question makes sense: Can we hack the simulation? If not, and we can have no influence on the “external” reality, then for us, the simulation is the ultimate reality. In a Soft Boltzmann Brain universe, reality is essentially the interface between individual consciousnesses; it is actually a part of these consciousnesses and does not exist without them. This could potentially allow consciousness to have an impact on the reality that surrounds us. During the early days of quantum mechanics, many scientists, such as Eugene Wigner, were seriously interested in investigating this. However, there is no evidence to support this, so it is very likely that we cannot influence reality with our consciousness, or at least not in a way that violates physical laws.

Another interesting consequence is that if we live in such a Soft Boltzmann Brain universe, then essentially every person is the same individual, somewhat like in Andy Weir's story "The Egg."

It's hard not to notice that the Soft Boltzmann Brain Theory resembles a concept of God, as the Soft Boltzmann Brain, like God, has existed since the beginning of time and is omnipotent. However, in this case, God is not separate from us. We are one with it.

Of course, I would rather leave theological speculations to the theologians. What might be even more interesting is what a society would look like where the moral foundations stem from the belief that the world is a Soft Boltzmann Brain and we are all one. With such an attitude and much less ego, the world might be a much happier and more sustainable place.

Many experts believe that sooner or later, we will reach the state of technological singularity. According to Ray Kurzweil, for example, we will be able to simulate the human brain on a computer. Once technology reaches this point, we will no longer need a physical body, just a computer running our consciousness. Over time, we might transform the entire solar system into a single gigantic computer, a Matrioshka brain. Many scientists take this theory so seriously that they believe it explains why we don't find evidence of intelligent extraterrestrial life forms. The reason we don't find aliens is because we're looking for them in the wrong way. Instead of searching for habitable planets, we should be looking for these Matrioshka brains. If an alien species visits us in the distant future, they will find a single giant brain with many more or less separate consciousnesses living in it, exactly like a Soft Boltzmann Brain.

It is conceivable that in the distant future, humanity will exist as a single giant mind, but it is also possible that we already exist this way. Although we have not learned more about the world around us, after understanding the Boltzmann Brain Theory, we may look at it a little differently. Either way, such contemplation is always exciting and fun. I hope you feel the same way by the end of this article. Happy pondering...