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arXiv:2401.15790

The Combination Problem for Relational Quantum Mechanics

Emily Adlam

Published Jan 28, 2024• 15 citations
arXivHTMLPDF

Abstract

This article uses the existing literature on the panpsychist combination problem as a starting point to think about how to address a structurally similar combination problem in relational quantum mechanics. I note some similarities and differences between the two problems, and I consider various proposed solutions to the panpsychist problem, assessing the prospects for a similar solution in the context of RQM. I argue that overall the prospects for solving RQM's combination problem look better for RQM with cross-perspective links than for orthodox versions of RQM.

DOI
10.48550/arxiv.2401.15790

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This article uses the existing literature on the panpsychist combination problem as a starting point to think about how to address a structurally similar combination problem in relational quantum mechanics. I note some similarities and differences between the two problems, and I consider various proposed solutions to the panpsychist problem, assessing the prospects for a similar solution in the context of RQM. I argue that overall the prospects for solving RQM's combination problem look better for RQM with cross-perspective links than for orthodox versions of RQM.
Relational quantum mechanics (RQM) is an interesting alternative to the standard responses to the measurement problem in quantum mechanics. But it suffers from a distinctive kind of epistemic solipsism: an observer can’t in principle know anything beyond their immediate present experience. This makes RQM self-undermining: it takes away the evidence we have for believing in quantum mechanics in the first place. Recently, Adlam and Rovelli have proposed a solution to this problem in the form of a new postulate they call cross-perspective links. Here I argue that this postulate does indeed solve the skeptical problem, but it also removes those aspects of RQM that make it distinctively relational. Nevertheless, the result of equipping RQM with cross-perspective links is an interesting interpretation in its own right.
Relational quantum mechanics (RQM) purportedly resolves the measurement problem by the postulate that physical variables can take determinate values that are relational in the sense that they are indexed to particular systems. Physical variables take on relational definite values if and only if two systems interact. The discrete nature of interactions required creates an ambiguity as to whether quantum events take place in the context of weak and continuous measurements and interactions. We provide a careful analysis of this problem, explain what a full solution to this problem would require, and then analyse certain proposed resolutions - finding all of them to be insufficient in their present form. Since ‘interactions’ (and the quantum events they underpin) are central to all versions of RQM, no version of RQM presented in the literature so far resolves the measurement problem.
Relational Quantum Mechanics (RQM) is an interpretation of quantum theory based on the idea of abolishing the notion of absolute states of systems, in favor of states of systems relative to other systems. Such a move is claimed to solve the conceptual problems of standard quantum mechanics. Moreover, RQM has been argued to account for all quantum correlations without invoking non-local effects and, in spite of embracing a fully relational stance, to successfully explain how different observers exchange information. In this work, we carry out a thorough assessment of RQM and its purported achievements. We find that it fails to address the conceptual problems of standard quantum mechanics--related to the lack of clarity in its ontology and the rules that govern its behavior--and that it leads to serious conceptual problems of its own. We also uncover as unwarranted the claims that RQM can correctly explain information exchange among observers, and that it accommodates all quantum correlations without invoking non-local influences. We conclude that RQM is unsuccessful in its attempt to provide a satisfactory understanding of the quantum world.
Abstract Relational Quantum Mechanics posits that facts about the properties of physical systems are relative to other systems. As recently pointed out by Adlam, this gives rise to the question of the relationship between the facts that obtain relative to complex systems and the facts that obtain relative to their constituents. In this paper, I respond to Adlam’s discussion of what she calls the Combination Problem. My starting point is a maximally permissive default view according to which any collection of systems counts as a new system and composites inherit all facts that obtain relative to their constituents. Subsequently, I advance three main claims: First, that Adlam’s arguments in favour of a more restrictive approach are not compelling. Second, that even if they were, she is wrong to claim that a ‘tamed’ version of RQM with postulated links between perspectives is in a better position to support such a restrictive approach. And third, that the possibly most difficult aspect of the Combination Problem in fact pertains to the combination of quantum states and probabilities. While significant challenges for the permissive solution arise here, I argue that they are likely to arise for any plausible response to the Combination Problem. More tentatively, I propose a strategy to mitigate the difficulty based on the observer-dependence of relative quantum state assignments. Along the way, I address crucial foundational issues in Relational Quantum Mechanics, from cross-perspective communication to the link between relative facts and experiences to empirical adequacy.