The many-worlds interpretation (MWI) is a philosophical position about how the mathematics used in quantum mechanics relates to physical reality. It asserts that the universal wavefunction is objectively real, and that there is no wave function collapse.[1] This implies that all possible outcomes of quantum measurements are physically realized in some "world" or universe.[2] In contrast to some other interpretations of quantum mechanics, the evolution of reality as a whole in MWI is rigidly deterministic[1]: 9 and local.[3] Many-worlds is also called the relative state formulation or the Everett interpretation, after physicist Hugh Everett, who first proposed it in 1957.[4][5]Bryce DeWitt popularized the formulation and named it many-worlds in the 1970s.[6][1][7][8]
The many-worlds interpretation implies that there are most likely an uncountable number of universes.[13] It is one of a number of multiverse hypotheses in physics and philosophy. MWI views time as a many-branched tree, wherein every possible quantum outcome is realized. This is intended to resolve the measurement problem and thus some paradoxes of quantum theory, such as Wigner's friend,[4]: 4–6 the EPR paradox[5]: 462 [1]: 118 and Schrödinger's cat,[6] since every possible outcome of a quantum event exists in its own universe.
^Harvey R. Brown; Christopher G. Timpson (2016). "Bell on Bell's Theorem: The Changing Face of Nonlocality". In Mary Bell; Shan Gao (eds.). Quantum Nonlocality and Reality: 50 years of Bell's theorem. Cambridge University Press. pp. 91–123. arXiv:1501.03521. doi:10.1017/CBO9781316219393.008. ISBN9781316219393. S2CID118686956. On locality:"Amongst those who have taken Everett's approach to quantum theory at all seriously as an option, it is a commonplace that—given an Everettian interpretation—quantum theory is (dynamically) local-there is no action-at-a-distance" on determinism:"But zooming-out (in a God's-eye view) from a particular branch will be seen all the other branches, each with a different result of measurement being recorded and observed, all coexisting equally; and all underpinned by (supervenient on) the deterministically, unitarily, evolving universal wavefunction"
^Cecile M. DeWitt, John A. Wheeler (eds,) The Everett–Wheeler Interpretation of Quantum Mechanics, Battelle Rencontres: 1967 Lectures in Mathematics and Physics (1968)
^Bryce Seligman DeWitt, The Many-Universes Interpretation of Quantum Mechanics, Proceedings of the International School of Physics "Enrico Fermi" Course IL: Foundations of Quantum Mechanics, Academic Press (1972)
^H. Dieter Zeh, On the Interpretation of Measurement in Quantum Theory, Foundations of Physics, vol. 1, pp. 69–76, (1970).
^Wojciech Hubert Zurek, Decoherence and the transition from quantum to classical, Physics Today, vol. 44, issue 10, pp. 36–44, (1991).
^Wojciech Hubert Zurek, Decoherence, einselection, and the quantum origins of the classical, Reviews of Modern Physics, 75, pp. 715–775, (2003)