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".

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A relatively brief explanation of Boltzmann Brains.