Making Sense of Probability in Everettian Quantum Mechanics

Harvey R. Brown (Oxford University)

Abstract: For some commentators on Everettian (“many worlds”) quantum mechanics, the role of probability is the Achilles’ heel of the interpretation. For other commentators, the Deutsch-Wallace theorem therein (which provides a decision-theoretic derivation of quantum probabilities) is a philosophical sensation, which is akin to deriving an ought from an is, or alternatively, which provides the first significant justification of Lewis’ Principal Principle. To further complicate matters, the two authors of the derivation appear to disagree about what it means. I am hoping to shed a little light on the debate by asking what probability means in physics in the first place. (The talk will be based in part on joint work with Gal Ben-Porath.)