Foundations of Physics 51 (2):1-31 (2021)

Eric Cavalcanti
Griffith University
In a recent no-go theorem [Bong et al., Nature Physics ], we proved that the predictions of unitary quantum mechanics for an extended Wigner’s friend scenario are incompatible with any theory satisfying three metaphysical assumptions, the conjunction of which we call “Local Friendliness”: Absoluteness of Observed Events, Locality and No-Superdeterminism. In this paper I discuss the implications of this theorem for QBism, as seen from the point of view of experimental metaphysics. I argue that the key distinction between QBism and realist interpretations of quantum mechanics is best understood in terms of their adherence to different theories of truth: the pragmatist versus the correspondence theories. I argue that a productive pathway to resolve the measurement problem within a pragmatist view involves taking seriously the perspective of quantum betting agents, even those in what I call a “Wigner bubble”. The notion of reality afforded by QBism, I propose, will correspond to the invariant elements of any theory that has pragmatic value to all rational agents—that is, the elements that are invariant upon changes of agent perspectives. The classical notion of ‘event’ is not among those invariants, even when those events are observed by some agent. Neither are quantum states. Nevertheless, I argue that far from solipsism, a personalist view of quantum states is an expression of its precise opposite: Copernicanism.
Keywords Foundations of Quantum Mechanics, Experimental Metaphysics, Wigner's friend paradox, QBism, Pragmatism
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DOI 10.1007/s10701-021-00417-0
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References found in this work BETA

Quantum Theory: A Pragmatist Approach.Richard Healey - 2012 - British Journal for the Philosophy of Science 63 (4):729-771.
Remarks on the Mind-Body Question.E. Wigner - 2003 - In John Heil (ed.), Philosophy of Mind: A Guide and Anthology. Oxford University Press.

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QBism and Relational Quantum Mechanics compared.Jacques Pienaar - 2021 - Foundations of Physics 51 (5):1-18.

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