Abstract This essay compares and contrasts relational quantum mechanics (RQM) with a pragmatist view of quantum theory (DP). It first explains important points of agreement. Then it points to two problems faced by RQM and sketch DP’s solutions to analogous problems. As both RQM and DP have taken the Born Rule to require relative facts, the essay next says what these might be. The main objection to RQM as originally conceived is that its ontology of relative facts is incompatible with scientific objectivity and undercuts the evidential base of quantum theory. In contrast, DP’s relative facts have all the objectivity one needs to accept quantum theory as scientific knowledge. But a very recent modification to RQM has successfully addressed the main objection, bringing the two views into even closer alignment.
Abstract This essay compares and contrasts relational quantum mechanics (RQM) with a pragmatist view of quantum theory (DP). It first explains important points of agreement. Then it points to two problems faced by RQM and sketch DP’s solutions to analogous problems. As both RQM and DP have taken the Born Rule to require relative facts, the essay next says what these might be. The main objection to RQM as originally conceived is that its ontology of relative facts is incompatible with scientific objectivity and undercuts the evidential base of quantum theory. In contrast, DP’s relative facts have all the objectivity one needs to accept quantum theory as scientific knowledge. But a very recent modification to RQM has successfully addressed the main objection, bringing the two views into even closer alignment.
Relational Quantum Mechanics (RQM) claims to be an interpretation of quantum theory \cite{Rovelli.21}. However, there are significant departures from quantum theory: (i) in RQM measurement outcomes arise from interactions which entangle a system S and an observer A without decoherence, and (ii) such an outcome is a "fact" relative to the observer A , but it is not a fact relative to another observer B who has not interacted with S or A during the foregoing measurement process. For B the system S⊗A remains entangled. We derive a GHZ-like contradiction showing that relative facts described by these statements are incompatible with quantum theory. Hence Relational Quantum Mechanics should not be considered an interpretation of quantum theory, according to a criterion for interpretations that we have introduced. The criterion states that whenever an interpretation introduces a notion of outcomes, these outcomes, whatever they are, must follow the probability distribution specified by the Born rule.
This paper examines the metaphysical foundations of Relational Quantum Mechanics (RQM), with special attention to its compatibility with scientific realism. We argue that RQM faces a dilemma. In its original formulation, RQM secures a sparse ontology of relative quantum events, but lacks the world-building structure needed to explain how these events jointly constitute a single, coherent reality of the kind presupposed by scientific realism. Recent discussions have already emphasized the difficulties that RQM faces concerning intersubjective agreement, communication, and the emergence of stable facts. Our contribution is to diagnose these difficulties as symptoms of a deeper metaphysical problem: RQM provides relative facts, but no clear account of what makes them facts of one world. We then assess the revised formulation proposed by Adlam and Rovelli, centered on the Cross-Perspective Links (CPL) principle. While CPL aims to restore intersubjective agreement by guaranteeing consistency across perspectives, we argue that it does so at a significant cost. It introduces observer-independent facts, persistent information-bearing structures, and global consistency constraints that sit uneasily with the relational spirit of the original interpretation. Thus, RQM either remains thoroughly relational but metaphysically too weak to support robust scientific realism, or it repairs this weakness by compromising its own relational foundations.
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 The introduction explains the origin and development of the views expressed in these essays. Fruitful interaction with physicists applying quantum theory provided the kernel for the author’s growing interest in contemporary pragmatism, initially as a source of ideas that could solve conceptual problems blocking an understanding of quantum theory. These pragmatist ideas were later applied to more general issues in the philosophy of science and metaphysics. After briefly sketching the pragmatist view of quantum theory defended in the essays, the introduction explains the implications—for the place of quantum theory in science, for metaphysics, and for the philosophy of science and specifically for the issue of scientific realism. New results in the foundations of physics prompted revision of the original view of the objectivity of quantum event outcomes. Some later essays show how elaborating a pragmatist view of the function of truth helped to acknowledge that the outcome of a quantum measurement is a relative fact that remains objective in the sense that matters for science: others take a neo-pragmatist view of causation, explanation, and laws in science. All these later essays illustrate the neo-pragmatist moral that by focusing on the intellectual function of a concept, one can satisfy a demand for understanding that might otherwise provoke a fruitless metaphysical quest.
Abstract The following paper explores the metaphysical significance of Relational Quantum Mechanics (RQM). For this, I will first outline Rovelli’s philosophical framework, and then offer a reconstruction of Rovelli’s seminal argument in favour of RQM. I will then explore some healthy lines of philosophical work that may be undertaken to strengthen RQM. First, I will frame RQM in the debate between realist and antirealist readings of QM and defend the general claim that RQM is compatible with realism. Then, I discuss the main ontological interpretations of RQM, which I classify as “dispositional”, “transcendental” and “structural”, and argue that all of them remain committed to substantialist assumptions that limit the radicality of Rovelli’s proposal. Finally, I analyse recent developments on RQM’s ontology and suggest that preserving its ontological originality requires an assessment on the concept of “pattern”.
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.