The Completeness of Quantum Mechanics and the Determinateness and Consistency of Intersubjective Experience: Wigner's Friend and Delayed Choice

Determinate and intersubjectively consistent experience of experimental outcomes is compatible with quantum mechanics without sacrificing free will, locality, or the completeness of the theory. A realist psi-epistemic account—treating the quantum state as knowledge rather than reality—yields a single world where all observers agree on definite outcomes. This approach eliminates the measurement problem and, combined with neutral monism, also resolves the hard problem of consciousness. The account requires no relative states, subjective collapse, or hybrid models.

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Abstract

Recent experiments (gedanken or otherwise) and theorems in quantum mechanics (QM), such as new iterations on Wigner's friend and delayed choice, have led many people to claim that QM is not compatible with determinate and intersubjectively consistent experience (what some call absoluteness of observed events), such as experiences of experimental outcomes. In the case of delayed choice the tension is between our experience of free will and a possible "superdeterminism" at work in QM. At the very least, some have suggested that the only way to save absoluteness of observed events, is to give up one or more of the following assumptions: free will, locality, or the completeness of QM. Our goal in this paper is to provide a take on QM that explains why there is and must always be determinate and intersubjectively consistent experience about all experimental outcomes (absoluteness of observed events). Our take accepts the completeness of the theory and requires no invocation of relative states (e.g., outcomes being relative to branches, conscious observers, etc.). And finally, this take requires no allegedly hybrid models such as claims about "subjective collapse." We provide a take on QM that yields a single world wherein all the observers (conscious or otherwise) agree about determinate and definite outcomes, because those outcomes are in fact determinate and definite. We provide a realist psi-epistemic take on QM that saves the absoluteness of observed events and the completeness of QM, without giving up free will or locality. We also show how our realist psi-epistemic account eliminates the measurement problem and, coupled with our take on neutral monism, also eliminates the hard problem of consciousness.