Everettian Probabilities, The Deutsch-Wallace Theorem and the Principal Principle

摘要: This paper is concerned with the nature of probability in physics, and quantum mechanics particular. It starts a brief discussion evolution Itamar Pitowsky's thinking about theory from 1994 to 2008, role Gleason's 1957 theorem his derivation Born Rule. defence therein as logic partial belief leads us into broader which existence objective "chances'' questioned, status David Lewis’ influential Principal Principle critically examined. followed by sketch work Deutsch Wallace resulted Deutsch-Wallace (DW) Everettian mechanics. noteworthy that authors this important decision-theoretic Rule have different views concerning meaning probability. The theorem, was subject 2007 critique Meir Hemmo Pitowsky, examined, along recent related John Earman. Here our main argument DW does not provide justification Principle, contrary claims Simon Saunders. A final section analyses effect redundant, conclusion seems be reinforced consideration probabilities ``deviant'' branches multiverse.