Abstract
Most interpretations of Quantum Mechanics alternative to Copenhagen interpretation try to avoid the dualistic flavor of the latter. One of the basic goals of the former is to avoid the ad hoc introduction of observers and observations as an inevitable presupposition of physics. Non-Copenhagen interpretations usually trust in decoherence as a necessary mechanism to obtain a well-defined, observer-free transition from a unitary quantum description of the universe to classicality. Even though decoherence does not solve the problem of the definite outcomes, it helps to explain why we do not observe superpositions and, according to Zurek’s existential interpretation, why a specific preferred basis emerges through system–environment interactions. The aim of this paper is to show why such interpretation ends up begging the question and provides little progress in understanding the quantum-to-classical transition; the ultimate reason being that preferred bases always correlate to human observation. Benefitting from the technical discussion, some remarks will be offered in the last section regarding the role of classical observations as a necessary condition to make workable the formalism of Quantum Mechanics and scientific activity itself.
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Notes
For an affordable description of the most important interpretations see, e.g., the different entries under the heading “Quantum Mechanics” in the Stanford Encyclopedia of Philosophy.
When referring to Copenhagen interpretation I will mainly understand Bohr’s stance on Copenhagen interpretation regarding classicality, see, e.g. Faye (2014) and Bacciagaluppi (2016). This does not remove generality to the main thesis of this paper because, in this respect, Bohr and Heisenberg agree (Heisenberg 1958, Chapter 3).
In that precise sense, my analysis may also help to enlarge the top-down view of the classical limit of QM presented in a recent book (Fortin and Lombardi 2017).
There is no need for the “environment” to be in some sense external to the system. Overall, the macroscopic degrees of freedom of a system can be decohered by the residual degrees of freedom of that same system (Wallace 2008). But this makes the problem of the preferred basis even more pressing: the “residual” degrees of freedom have to be determined in each situation in a practical, non-fundamental, manner.
For historical and contemporary discussion on Bohr’s understanding of the correspondence principle and its different interpretations, see Bokulich (2014).
As far as I know, Dennett (1991) was the first to establish the functionalist link between “classically perceived reality” and predictability.
Given an abstract Hilbert space and Hamiltonian, we could envisage a system-environment partition where the preferred basis is de-localized, i.e. formed by superpositions of localized vector states. In Schrödinger-cat terms, had we not observations, we would be a priori equally entitled to use as basis the superpositions of dead cat and live cat.
[T]he Copenhagen development of quantum theory exemplifies a clear rejection of the [Appearance from Reality] Criterion. The famous Measurement Problem in the philosophy of quantum mechanics is not a problem from an empiricist point of view (…).The rejection may not be unique in the history of science, but is brought home to us inescapably by the advent of the new quantum theory. Even if that theory is superseded (or if fundamental physics develops in accordance with a new interpretation under which the Criterion can be satisfied) our view of science must be forever modified in the light of this historical episode. (van Fraassen 2008, p. 292).
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Sánchez-Cañizares, J. Classicality First: Why Zurek’s Existential Interpretation of Quantum Mechanics Implies Copenhagen. Found Sci 24, 275–285 (2019). https://doi.org/10.1007/s10699-018-9574-y
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DOI: https://doi.org/10.1007/s10699-018-9574-y