Suppose your model of physics says that the universe will eventually dissolve into a sea of particles in thermal equilibrium, and these particles will then exist indefinitely.

Then an exponentially vast supermajority of all observer-moments in this universe take place inside brains that momentarily assemble themselves from the sea of entropy by random fluctuations, and probably dissolve a moment later. These are “Boltzmann brains”.

The vast supermajority of Boltzmann brains have relatively disordered experiences; they momentarily see chaos before dissolving again.

So your own, far more ordered and orderly experience in this very moment weighs heavily against the hypothesis “I am a Boltzmann brain”. Under most systems of anthropic reasoning this weighs heavily against the possibility “a supervast majority of all moments of consciousness are vastly less orderly than my own”.

Full article:

• A relatively brief explanation of Boltzmann Brains.