Macroscopic Facts, Quantum Mechanics, and Metaphysical Realism

Juha T. Saatsi

A. J. Leggett

A. J. Leggett

Nora Berenstain

Privileged-perspective realism (PPR) is a version of metaphysical realism that takes certain irreducibly perspectival facts to be partly constitutive of reality. PPR asserts that there is a single metaphysically privileged standpoint from which these perspectival facts obtain. This chapter discusses several views that fall under the category of privileged-perspective realism. These include presentism, which is PPR about tensed facts, and non-multiverse interpretations of quantum mechanics, which the chapter argues, constitute PPR about world-indexed facts. Using the framework of the bird perspective and the frog perspective, it argues that PPR views are motivated by the assumption that the frog perspective is metaphysically primary. The chapter considers case studies of metaphysical interpretations of special relativity and quantum mechanics in order to demonstrate that such motivations for PPR are non-naturalistic. It considers psychological factors that motivate the appeal of PPR views and offers naturalistic explanations of why we should not expect them to lead to good metaphysics of science.

Raoni Wohnrath Arroyo, Jonas R. Becker Arenhart

It is a widespread consensus among metaphysicians that the bundle and substratum theories are substantially different metaphysical theories of individuality. In a realist stance towards metaphysics, they cannot both track the truth when describing fundamental reality, thus they’re rival metaphysical theories. Against that consensus, Jiri Benovsky has advanced a metametaphysical thesis that they are in fact metaphysically equivalent. This paper challenges Benovsky’s equivalence thesis with two counter-arguments based on the metaphysics of quantum mechanics: quantum metaphysical indeterminacy and wavefunction realism. As we shall argue, while both substratum and bundle theories arguably fail in standard quantum mechanics, they fail in different ways. Hence, given Benovsky’s own notion of metaphysical equivalence, they are not equivalent.

Andréa Oldofredi, Antonio Vassallo

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.