One World Is (Probably) Just as Good as Many

One of our most sophisticated accounts of objective chance in quantum mechanics involves the Deutsch-Wallace theorem, which uses state-space symmetries to justify agents’ use of the Born rule when the quantum state is known. But Wallace (2003, 2012) argues that this theorem requires an Everettian approach to measurement. I find that this argument is unsound, and I demonstrate a counter-example by applying the Deutsch-Wallace theorem to a Bohm-style pilot-wave theory.