Absurdism and Neuroscience: What is a Boltzmann Brain?

In my neuroscience research throughout the years, I’ve found many crossovers between the sciences. Naturally, the study of an organ will be categorized under biology. The transmission of neurotransmitters and the interactions between the axons and dendrites, communicating with each other via different signals in reaction to whatever stimuli you encounter in your everyday life, are a prime example of chemistry. (and, naturally, the strong ties between psychology and neuroscience and how the brain influences the mind through these chemical interactions.).

What you don’t see often in neuroscience is space:, the void that we find ourselves amongst. But, there exists one theory which is still trying to be understood by both neuroscientists and theoretical astrophysicists alike. As of May 2025, there exists approximately 8 billion people on this Earth — meaning 8 billion chances to be a working brain based and grounded in reality. In comparison, however, these 8 billion people are nothing compared to the idea of an infinite — the infinite which we know as the Universe, both observable and non-observable. Enter the Boltzmann Brain.

The idea of a Boltzmann Brain is named after Ludwig Boltzmann, a physicist who theorized a thought experiment that, in summary, suggests the odds of your neurochemistry being a swirl of various chemicals circulating through space should be higher than that of being one of the 8 billion people with existence grounded in reality.

But how possible is it to be a Boltzmann Brain? Well, certain specific conditions for this outcome to be plausible. According to the second law of thermodynamics, for this theory to work, the universe , known in this theory as a Boltzmann universe , would have to be in a low-entropy state and experience spontaneous, periodic bursts of movement to recreate the movements of brainwaves.

Boltzmann’s explanation for the oblivion of humans to a Boltzmann Universe could be explained by the devoid of intelligent life within humans and their knowledge only being known of the observable Boltzmann Universe rather than the heat death of the universe, which would be in accordance per thermodynamics.

In other words, newer research finds that the vacuum upholding the universe is a Minkowski Space (a flat space-time vacuum). This implies that, theoretically, with Hawking Radiation emitted from the de Sitter cosmological horizon, a Boltzmann brain could exist in a positive cosmological constant.

So, whether you’re a Boltzmann or not, you exist — you’re here ( grounded in reality or not). So seize the day and be in charge of your part in your (possibly Boltzmann) universe!

References:

• Carroll, Sean (29 December 2008). “Richard Feynman on Boltzmann Brains”
• Boltzmann, Ludwig (1896). “Lectures on Gas Theory”
• Dyson, Lisa; Kleban, Matthew; Susskind, Leonard (2002). “Disturbing Implications of a Cosmological Constant”. Journal of High Energy Physics. 2002 (10)

(This was also published under OpenScope, but I am the original author.)