Typical worlds

- Pure wave mechanics is an deterministic physical theory with no probabilities.
- It can be understood as providing a weak explanation of the standard quantum statistics.
- But the standard probabilistic predictions require the addition of strong auxiliary assumptions.
- These assumptions are part of any physical theory that successfully explains the probabilities.

Hugh Everett III presented pure wave mechanics, sometimes referred to as the many-worlds interpretation, as a solution to the quantum measurement problem. While pure wave mechanics is an objectively deterministic physical theory with no probabilities, Everett sought to show how the theory might be understood as making the standard quantum statistical predictions as appearances to observers who were themselves described by the theory. We will consider his argument and how it depends on a particular notion of branch typicality. We will also consider responses to Everett and the relationship between typicality and probability. The suggestion will be that pure wave mechanics requires a number of significant auxiliary assumptions in order to make anything like the standard quantum predictions.