Boltzmann Brain hypothesis
Overview
A Boltzmann Brain is a thought experiment derived from thermodynamics and statistical mechanics, particularly from the work of Ludwig Boltzmann. It suggests that, in a universe governed by entropy and randomness, it may be more probable for a single conscious entity (a "brain" with false memories and perceptions) to randomly fluctuate into existence than for the entire low-entropy universe to arise as we observe it.
If the universe is eternal and random fluctuations are allowed, it could be statistically more likely for a disembodied brain to momentarily arise with the illusion of experience than for a coherent, long-lasting universe to exist. This leads to a paradox: if this were true, we should expect to be Boltzmann Brains ourselves, which undermines trust in our perceptions.
- Boltzmann, L. (1895), on entropy and statistical mechanics.
I treat this as I treat the Brain in a vat and the Simulation hypothesis: a reminder that certainty about the external world is unavailable, not a live alternative to realism. A Boltzmann brain's model of the world would be contradicted by its very next moment of experience, and mine keeps not being, which is as much as any model can ask for (Knowledge).