D5 S1 Tomasz Bigaj - Consistent histories and many worlds

The Many-Worlds Interpretation of Quantum Mechanics: Current Status and Relation to Other Interpretations.
Research workshop of the Israeli Science Foundation, Tel-Aviv University, October 2022

Tomasz Bigaj

Consistent histories and many worlds
Two fundamental features of the many worlds interpretation are: the privileged status of the universal wave function as the only fundamental beable, and the deterministic evolution thereof (Vaidman 2021). In contrast to that, the consistent histories approach treats wave functions purely instrumentally as pre-probabilities, and stresses the stochastic character of quantum processes (Griffiths 2002, 2013). The unitary evolution of the wave function constitutes only one possible history out of many alternative histories. A unitary family of histories is special in that it assigns only probabilities 0 or 1 to individual histories, whereas histories based on incompatible projectors are assigned non-trivial probabilities, and thus are not deterministic. It is stressed that no history, whether deterministic or probabilistic, has the privileged status of being the “real” one. Hence on the face of it the consistent histories approach is clearly non-Everettian. And yet many authors insist that the consistent histories formalism “does Everett nicely”, to use Simon Saunders’ expression (Saunders 2010, see also Hartle 2010, Halliwell 2010, Wallace 2012). Characteristically, an appeal to the consistent histories approach is made in the context of the problem of quasi-classicality (the emergence of the classical features of the world) and the role of decoherence in selecting an approximately classical evolution of the world. But doesn’t this analysis contradict the Principle of Equality, which states that all individual frameworks (histories) are equally acceptable? In this talk I will analyze the apparent conflict between the Everettian conception and the consistent histories approach. I will pose the question which of the fundamental assumptions of these conceptions have to be abandoned or relaxed in order to combine them together into one coherent theory.

Griffiths, R. (2002), Consistent Quantum Theory, Cambridge University Press, Cambridge.
Griffiths, R. (2013), “A consistent quantum ontology”, Stud. Hist. Phil. Mod. Phys. 44, 93-114.
Halliwell, J. (2010), “Macroscopic superpositions, decoherent histories and the emergence of hydrodynamic behaviour”, in: S. Saunders, J. Barrett, A. Kent, D. Wallace (eds.), Many Worlds? Everett, Quantum Theory and Reality, OUP, Oxford.
Hartle, J. (2010), “Quasiclassical realms”, in: S. Saunders, J. Barrett, A. Kent, D. Wallace (eds.), Many Worlds? Everett, Quantum Theory and Reality, OUP, Oxford.
Saunders, S. (2010), “Many worlds? Introduction”, in: S. Saunders, J. Barrett, A. Kent, D. Wallace (eds.), Many Worlds? Everett, Quantum Theory and Reality, OUP, Oxford.
Vaidman, L. (2021), "Many-Worlds Interpretation of Quantum Mechanics", The Stanford Encyclopedia of Philosophy (Fall 2021 Edition), Edward N. Zalta (ed)
Wallace, D. (2012), “Chaos, decoherence and branching”, in: The Emergent Multiverse: Quantum Theory according to the Everett Interpretation, OUP, Oxford

[luckyluckydog]

nice talk on what is IMO the best approach to quantum mechanics