Reality, we have learned to our shock, is not a collection of separate magisteria, but a single unified process governed by mathematically simple low-level rules. Different buildings on a university campus do not belong to different universes, though it may sometimes seem that way. The universe is not divided into mind and matter, or life and nonlife; the atoms in our heads interact seamlessly with the atoms of the surrounding air. Nor is Bayes’s Theorem different from one place to another.