Everettian theory as pure wave mechanics plus a no-collapse probability postulate

Nadia Blackshaw, Alexander Franklin

Jonathan Baxter

Everettian quantum mechanics is often said to lack coherent probability because every possible measurement result occurs. If all of them exist globally, what is probability supposed to be a probability of? This paper defends an axiomatic answer: normalized Born measure is postulated as objective probability over the records borne by an observer's future continuations. Collapse interpretations likewise postulate the Born probabilities, but instead assign them to possible global outcomes. Neither theory derives the probabilities from its ontology. The contribution is an explicit record-level probability model that separates probabilities for future local records from certainty about their global existence. I use this model to answer objections to the axiomatic approach and argue that neither global selection nor a further theory of personal persistence is required. At the level of recorded results, the Everettian law supports the same predictions and empirical inferences as the collapse law, despite the theories' different ontologies.

Jeffrey Alan Barrett

Hugh Everett III's pure wave mechanics is a deterministic physical theory with no probabilities. He nevertheless sought to show how his theory might be understood as making the same statistical predictions as the standard collapse formulation of quantum mechanics. We will consider Everett's argument for pure wave mechanics, how it depends on the notion of branch typicality, and the relationship between the predictions of pure wave mechanics and the standard quantum probabilities.

David John Baker

Sumio Wada

We argue that quantum mechanics makes sense without such controversial postulates as the wave function collapse, the quantum probability rule and the observable postulate. We only need the existence of a wave function as a representation of a state, its dynamical evolution rule and another rather trivial postulate proposed here (Read-Off Postulate). The wave function collapse and the probability rule are replaced with intrinsic properties of the theory, i.e. decoherence and relative frequency, respectively. Interpretation of the wave function as a faithful representation of the reality naturally emerges, although quantum reality has a peculiar feature which distinguishes it from classical reality.

Lina Jansson