Boltzmann brain

A Boltzmann brain is a hypothesized self-aware entity that arises due to random fluctuations out of a state of chaos. The idea is named for the physicist Ludwig Boltzmann (1844–1906), who advanced an idea that the Universe is observed to be in a highly improbable non-equilibrium state because only when such states randomly occur can brains exist to be aware of the Universe. The term for this idea was then coined in 2004 by Andreas Albrecht and Lorenzo Sorbo.

The Boltzmann brains concept is often stated as a physical paradox. It has also been called the "Boltzmann babies paradox". The paradox states that if one considers the probability of our current situation as self-aware entities embedded in an organized environment versus the probability of stand-alone self-aware entities existing in a featureless thermodynamic "soup", then the latter should be vastly more probable than the former.

The Boltzmann brains concept has been proposed as an explanation for why we observe such a large degree of organization in the Universe (a question more conventionally addressed in discussions of entropy in cosmology).

Boltzmann proposed that we and our observed low-entropy world are a random fluctuation in a higher-entropy universe. Even in a near-equilibrium state, there will be fluctuations in the level of entropy. The most common fluctuations will be relatively small, resulting in only small amounts of organization, while larger fluctuations and their resulting greater levels of organization will be comparatively more rare. Large fluctuations would be almost inconceivably rare, but are made possible by the enormous size of the Universe and by the idea that if we are the results of a fluctuation, there is a "selection bias": we observe this very unlikely Universe because the unlikely conditions are necessary for us to be here, an expression of the anthropic principle.

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