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arXiv:1901.10825

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

Michael Silberstein, W. M. Stuckey

Published Jan 28, 2019• 3 citations
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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.

DOI
10.48550/arxiv.1901.10825

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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.
Abstract Recent experiments (gedanken or otherwise) and theorems in quantum mechanics (QM) have led many people to claim that QM is not compatible with determinate and intersubjectively consistent experience, what some call the “absoluteness” of observed events; examples include new iterations on Wigner’s friend and delayed choice. Herein 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. On our view there is no need for conscious experience to explain measurement collapse nor any need for measurement collapse to resolve the hard problem. The key here is to reject the unquestioned assumptions that inexorably lead to the measurement problem and the hard problem. This will require a reconception of QM and, a reconception of matter, conscious experience and their relationship to one another.
We discuss the implications for the determinateness and intersubjective consistency of conscious experience in two gedanken experiments from quantum mechanics (QM). In particular, we discuss Wigner's friend and the delayed choice quantum eraser experiment with a twist. These are both cases (experiments) where quantum phenomena, or at least allegedly possible quantum phenomena/experiments, and the content/efficacy of conscious experience seem to bear on one another. We discuss why these two cases raise concerns for the determinateness and intersubjective consistency of conscious experience. We outline a 4D-global constraint-based approach to explanation in general and for QM in particular that resolves any such concerns without having to invoke metaphysical quietism (as with pragmatic accounts of QM), objective collapse mechanisms or subjective collapse. In short, we provide an account of QM free from any concerns associated with either the standard formalism or relative-state formalism, an account that yields a single 4D block universe with determinate and intersubjectively consistent conscious experience for all conscious agents. Essentially, the mystery in both experiments is caused by a dynamical/causal view of QM, e.g., time-evolved states in Hilbert space, and as we show this mystery can be avoided by a spatiotemporal, constraint-based view of QM, e.g., path integral calculation of probability amplitudes using future boundary conditions. What will become clear is that rather than furiously seeking some way to make dubious deep connections between quantum physics and conscious experience, the kinds of 4D adynamical global constraints that are fundamental to both classical and quantum physics and the relationship between them, also constrain conscious experience. That is, physics properly understood, already is psychology.
The notion of measurements is central to many debates in quantum mechanics. One critical point is whether a measurement can be regarded as an absolute event, giving the same result for any observer in an irreversible manner. Using ideas from the gedanken experiment of Wigner's friend, it has been argued that, when combined with the assumptions of locality and no superdeterminism, regarding a measurement as an absolute event is incompatible with the universal validity of quantum mechanics. We consider a weaker assumption: Is the measurement event realized relatively to the observer when he only partially observed the outcome? We proposed a protocol to show that this assumption in conjunction with the natural assumptions of no superdeterminism and locality is also not compatible with the universal validity of quantum mechanics.
This paper offers a conceptual and formal analysis of non-absoluteness in perspectival interpretations of quantum mechanics. Extended Wigner-type experiments reveal a fundamental tension between the universality of quantum mechanics, the absoluteness of observed events, and the possibility of intersubjective agreement. I argue that denying observer-independent events cannot remain a mere interpretive slogan: it requires a precise account of how perspectival statements, tracking assumptions, meta-level descriptions, and intersubjective communication are to be formulated. Many existing approaches either implicitly reintroduce observer-independent structure or leave key notions underdetermined. Within this framework, Convivial Solipsism provides a coherent account of non-absolute events, preserving the universality of quantum mechanics while rejecting the need for a global viewpoint. To make this claim precise, the paper introduces the basic elements of a formal perspectival logic designed to distinguish well-formed perspectival statements from illegitimate unindexed or absolutizing statements. The paper concludes that scientific objectivity need not rest on observer-independent facts, but can instead be grounded in the internal coherence of perspectival structures.
How can we address the idea of observers in quantum mechanics? The long-standing Wigner’s friend thought experiment provides a conceptual framework for thinking about this question. It considers the the difficulty of reconciling unitary, evolution of systems and non-unitary state update after a making observations. Following from a recent suggested protocol with two friends that share and entangled state, we prove and investigate, in a photonic experiment, a strong no-go theorem for this Wigner’s friend scenario. Specifically, if quantum mechanics applies at the scale of observers, then there are constraints on the set of assumptions: locality; no-superdeterminism; and absoluteness of observed events. We note that this new theorem places strictly stronger constraints on physical reality than Bell’s theorem.
I take a pragmatist perspective on quantum theory. This is not a view of the world described by quantum theory. In this view quantum theory itself does not describe the physical world, nor our observatons, experiences or opinions of it. Instead, the theory offers reliable advice on when to expect an event of one kind or another, and on how strongly to expect each possible outcome of that event. The actual outcome is a perspectival fact: a fact relative to a physical context of assessment. Measurement outcomes and quantum states are both perspectival. By noticing that each must be relativized to an appropriate physical context one can resolve the measurement problem and the problem of nonlocal action. But if the outcome of a quantum measurement is not an absolute fact, then why shoud the statistics of such outcomes give us any objective reason to accept quantum theory? One can describe extensions of the scenario of Wigner's friend in which a statement expressing the outcome of a quantum measurement would be true relative to one such context but not relative to another. However, physical conditions in our world prevent us from realizing such scenarios. Since the outcome of every actual quantum measurement is certified at what is essentially a single context of assessment, the outcome relative to that context is an objective fact in the only sense that matters for science. We should accept quantum theory because the statistics these outcomes display are just those it leads us to expect.