Clarify acceptance of key metaphysical distinctions by quantum relativists

Ascertain whether proponents of perspectivist Relational Quantum Mechanics endorse the metaphysical distinctions employed by fragmentalism and external relativism—such as between a single comprehensive über‑reality and multiple particular realities, between how things are and how they are in reality, and between facts that obtain versus facts that constitute reality—needed to secure coherence within their perspectivist framework.

Background

Fine’s trilemma indicates that perspectivists must abandon at least one of Neutrality, Coherence, or Absolutism, and various forms of perspectivism rely on metaphysical distinctions to remain coherent. The paper highlights that it is unsettled whether quantum relativists will accept these distinctions, which would shape the viability of fragmentalism or external relativism as foundations for RQM.

Resolving this issue is important for evaluating the conceptual commitments and costs of adopting a perspectivist version of RQM.

References

Fragmentalists have relied on distinctions between how things are and how they are in reality (Fine 2005, 262), between facts that obtain and those that constitute reality (Iaquinto 2019, 696), or between facts that exist and those that obtain (Iaquinto 2020, 577). Merlo (2022) can be taken to argue that some such differentiation is indispensable for fragmentalism to be tenable. But it is not clear whether the quantum relativists would be happy to make these notions their own.

— Relational Quantum Mechanics, Quantum Relativism, and the Iteration of Relativity  (2403.04069 - Riedel, 2024) in Section 3.3 (Towards Perspectival Quantum Mechanics)