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arXiv:1906.10524

The limits of quantum superposition: Should "Schrödinger's cat" and "Wigner's friend" be considered "miracle" narratives?

Antoine Suárez

Published Jun 23, 2019• 2 citations
arXivHTMLPDF

Abstract

Physicians define death as the "irreversible" breakdown of all brain-functions including brain-stem. By "irreversible" they mean a damage that is beyond the human capacity to restore the patient's healthy state. In the same line I propose to complete the definition of quantum physics in [1] by Principle D (Detection): "Detection outcomes (like death) are ordinarily irreversible and observer-independent". It is then argued that this principle excludes generalization of quantum superposition to visible objects bearing observer-dependent outcomes. However this exclusion is not absolute: It rather means that "Schrödinger's cat" and "Wigner's friend" should be considered "miracle" narratives beyond the domain of science.

DOI
10.48550/arxiv.1906.10524

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Physicians define death as the "irreversible" breakdown of all brain-functions including brain-stem. By "irreversible" they mean a damage that is beyond the human capacity to restore the patient's healthy state. In the same line I propose to complete the definition of quantum physics in [1] by Principle D (Detection): "Detection outcomes (like death) are ordinarily irreversible and observer-independent". It is then argued that this principle excludes generalization of quantum superposition to visible objects bearing observer-dependent outcomes. However this exclusion is not absolute: It rather means that "Schrödinger's cat" and "Wigner's friend" should be considered "miracle" narratives beyond the domain of science.
In his famous thought experiment, Schrodinger(1935) imagined a cat that measures the value of a quantum mechanical observable with its life. Since Schrodinger’s time,no any interpretations or modifications of quantum mechanics have been proposed which gives clear unambiguous answers to the questions posed by Schrodinger’s cat of how long superpositions last and when (or whether) they collapse?In this book appropriate modification of quantum mechanics is proposed.We claim that canonical interpretation of the wave function ψ=с1ψ1+с2ψ2 is correct only when the wave function supports ψ1 and ψ2 essentially overlap. When these ones have separated supports we claim that canonical interpretation of the wave function ψ is no longer valid for a such cat state.Possible solution of the Schrodinger’s cat paradox is considered. We pointed out that the collapsed state of the cat always shows definite and predictable outcomes even if the cat also consists of a superposition:|cat>=с1|alive cat>+с2|death cat>.Using new quantum mechanical formalism the EPRB-paradox is considered.We find that the EPRB-paradox can be resolved by nonprincipal and convenient relaxing of the Einstein’s locality principle.
By assuming (i) a universal, observer-independent quantum state, by considering (ii) measurement processes with wave function collapse as part of quantum mechanical time evolution (also within isolated systems), and by (iii) clearly distinguishing the state of a quantum system from the knowledge of conscious observers about this state, we suggest a modified Copenhagen interpretation of quantum mechanics that resolves Wigner's Friend and extended Wigner's Friend paradoxes. The suggested interpretation leads to differences in some outcome probabilities compared to previous analyses which, in principle, make it possible to falsify the suggested modifications or the previous analyses (or both). The fundamental problem of the incompleteness of quantum mechanics in the Copenhagen interpretation regarding the lack of a precise definition and a mechanistic description of the measurement process (including the collapse of the wave function) is not addressed in this study. However, the argumentation regarding the resolution of Wigner's Friend paradoxes also applies to attempts for such a mechanistic description using collapse models with stochastic extensions to the Schrödinger equation or trying to model wave function collapse with unitary time evolution and irreversibility of the measurement process resulting from quantum statistical mechanics.
This paper offers a comprehensive analysis of Wigner’s Friend paradox (1961), a foundational thought experiment in quantum mechanics that highlights the tension between the internal perspective of a measuring observer (who experiences a definite outcome) and the external perspective of a super-observer who treats the entire laboratory as a quantum system in superposition. It traces the historical lineage from Schrödinger’s cat and von Neumann’s measurement theory, provides a formal mathematical description of the state evolution and logical structure of the paradox, examines implications for major interpretations of quantum mechanics (Copenhagen, Everettian many-worlds, QBism, relational quantum mechanics, and objective collapse theories), and discusses modern extensions such as the Frauchiger–Renner paradox. The work explores profound philosophical and epistemological consequences for the nature of observation, objectivity, intersubjectivity, and the role of consciousness in quantum theory (2026).
There has been a surge of recent interest in the Wigner's Friend paradox, sparking several novel thought experiments and no-go theorems. The main narrative has been that Wigner's Friend highlights a counterintuitive feature that is unique to quantum theory, and which is closely related to the quantum measurement problem. Here, we challenge this view. We argue that the gist of the Wigner's Friend paradox can be reproduced without assuming quantum physics, and that it underlies a much broader class of enigmas in the foundations of physics and philosophy. To show this, we first consider several recently proposed Extended Wigner's Friend scenarios, and demonstrate that some of their implications for the absoluteness of observations can be reproduced by classical thought experiments that involve the duplication of agents. Crucially, some of these classical scenarios are technologically much easier to implement than their quantum counterparts. Then, we argue that the essential structural ingredient of all these scenarios is a feature that we call "Restriction A": that a physical theory cannot give us a probabilistic description of the observations of all agents. Finally, we argue that this difficulty is at the core of other puzzles in the foundations of physics and philosophy, and demonstrate this explicitly for cosmology's Boltzmann brain problem. Our analysis suggests that Wigner's Friend should be studied in a larger context, addressing a frontier of human knowledge beyond quantum foundations: to obtain reliable predictions for experiments in which these predictions can be privately but not intersubjectively verified.
In a recent paper, Żukowski and Markiewicz showed that Wigner's Friend (and, by extension, Schrödinger's Cat) can be eliminated as physical possibilities on purely logical grounds. I validate this result and demonstrate the source of the contradiction in a simple experiment in which a scientist S attempts to measure the position of object ∣O⟩=∣A⟩S+∣B⟩S|O\rangle = |A\rangle_S + |B\rangle_S∣O⟩=∣A⟩S​+∣B⟩S​ by using measuring device M chosen so that ∣A⟩M≈∣A⟩S|A\rangle_M \approx |A\rangle_S∣A⟩M​≈∣A⟩S​ and ∣B⟩M≈∣B⟩S|B\rangle_M \approx |B\rangle_S∣B⟩M​≈∣B⟩S​. I assume that the measurement occurs by quantum amplification without collapse, in which M can entangle with O in a way that remains reversible by S for some nonzero time period. This assumption implies that during this "reversible" time period, ∣A⟩M≠∣A⟩S|A\rangle_M \neq |A\rangle_S∣A⟩M​=∣A⟩S​ and ∣B⟩M≠∣B⟩S|B\rangle_M \neq |B\rangle_S∣B⟩M​=∣B⟩S​ -- i.e., the macroscopic pointer state to which M evolves is uncorrelated to the position of O relative to S. When the scientist finally observes the measuring device, its macroscopic pointer state is uncorrelated to the object in position ∣A⟩S|A\rangle_S∣A⟩S​ or ∣B⟩S|B\rangle_S∣B⟩S​, rendering the notion of "reversible measurement" a logical contradiction.