Everett’s pure wave mechanics and the notion of worlds

Abstract

Everett (1957aEverett ( , b, 1973 relative-state formulation of quantum mechanics has often been taken to involve a metaphysical commitment to the existence of many splitting worlds each containing physical copies of observers and the objects they observe. While there was earlier talk of splitting worlds in connection with Everett, this is largely due to DeWitt's (Phys Today 23:30-35, 1970) popular presentation of the theory. While the thought of splitting worlds or parallel universes has captured the popular imagination, Everett himself favored the language of elements, branches, or relative states in describing his theory. The result is that there is no mention of splitting worlds or parallel universes in any of Everett's published work. Everett, however, did write of splitting observers and was willing to adopt the language of many worlds in conversation with people who were themselves using such language. While there is evidence that Everett was not entirely comfortable with talk of many worlds, it does not seem to have mattered much to him what language one used to describe pure wave mechanics. This was in part a result of Everett's empirical understanding of the cognitive status of his theory.

Understanding quantum mechanics: a review and synthesis in precise language

“…In each single run of measurement, the A state branches into several different states. Each branch represents a different measurement event outcome, and the corresponding relative state for S. All branches exist simultaneously; Everett's original paper does not directly link branches to independent reality, partly due to the challenge of finding appropriate non-mathematical language [443].…”

Multiplicity in Everett׳s interpretation of quantum mechanics

“…Unless specified otherwise, emphasis is always in the original. 4 See for instanceOsnaghi et al (2009), Byrne (2010,Barrett (2011),Barrett and Byrne (2012) andBarrett (2014).5 Inevitably, there is some overlap between this paper andBarrett (1999). But Barrett's excellent review of Everett's approach is now more than 15 years old.…”

“…The relation between this more recent approach and Everett's own views is analyzed inBarrett (2011Barrett ( , 2014. Briefly, Everett's understanding of empirical faithfulness only requires that the observer and relative record be found in some decomposition of the state.…”

Typical worlds

“…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.1 Everett himself did not refer to branches as worlds in his written work. See Barrett (2011bBarrett ( , 2016a for discussions of his metaphysical commitments and the role of metaphysics in interpreting pure wave mechanics more generally. 2 See Barrett (2016b) for a preliminary discussion of typicality in pure wave mechanics.…”