Against the empirical viability of the Deutsch–Wallace–Everett approach to quantum mechanics

• We deny that subjective Everettian quantum mechanics can be called empirically viable.
• A decision theoretical implementation of the Born rule gives no scientific predictions.
• We examine the more empirical, subjective approach by Greaves and Myrvold.
• We criticize this approach based on its limited scientific value.

The subjective Everettian approach to quantum mechanics presented by Deutsch and Wallace fails to constitute an empirically viable theory of quantum phenomena. The decision theoretic implementation of the Born rule realized in this approach provides no basis for rejecting Everettian quantum mechanics in the face of empirical data that contradicts the Born rule. The approach of Greaves and Myrvold, which provides a subjective implementation of the Born rule as well but derives it from empirical data rather than decision theoretic arguments, avoids the problem faced by Deutsch and Wallace and is empirically viable. However, there is good reason to cast doubts on its scientific value.