Original Paper in Philosophy of Physics

European Journal for Philosophy of Science

, Volume 1, Issue 2, pp 277-302

First online:

Open Access This content is freely available online to anyone, anywhere at any time.

Everett’s pure wave mechanics and the notion of worlds

  • Jeffrey A. BarrettAffiliated withDepartment of Logic and Philosophy of Science, University of California, Irvine Email author 


Everett (1957a, 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.


Hugh Everett III Quantum measurement problem Pure wave mechanics Relative-states Many worlds Parallel universes Emergent worlds Bryce DeWitt