  Most versions of classical physics imply that if the 4-volume of the entire
space-time is infinite or at least extremely large, then random fluctuations in
the matter will by coincidence create copies of us in remote places, so called
"Boltzmann brains." That is a problem because it leads to the wrong prediction
that _we_ should be Boltzmann brains. The question arises, how can any theory
avoid making this wrong prediction? In quantum physics, it turns out that the
discussion requires a formulation of quantum theory that is more precise than
the orthodox interpretation. Using Bohmian mechanics for this purpose, we point
out a possible solution to the problem based on the phenomenon of "freezing" of
configurations.
