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Observer-Relative Interpretations

Emily Adlam

Published Jun 12, 2025• 0 citations
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Abstract

Abstract This chapter explores a serious epistemic problem for the class of ‘orthodox interpretations’ (including QBism, neo-Copenhagen interpretations, pragmatic interpretations and some versions of relational quantum mechanics) and discusses various possible attempts at a solution. I contend that the difficulty of making sense of intersubjectivity in orthodox interpretations makes these approaches self-undermining. I argue that these approaches forbid observers from sharing information with one another or even past versions of themselves, and explain why information-sharing is an essential feature of scientific practice and scientific epistemology. I also discuss some ‘Extended Wigner’s Friend’ theorems which have recently attracted interest in quantum foundations, arguing that we must interpret these theorems in light of the social dimensions of scientific knowledge.

DOI
10.1093/9780197808887.003.0009

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Abstract This chapter explores a serious epistemic problem for the class of ‘orthodox interpretations’ (including QBism, neo-Copenhagen interpretations, pragmatic interpretations and some versions of relational quantum mechanics) and discusses various possible attempts at a solution. I contend that the difficulty of making sense of intersubjectivity in orthodox interpretations makes these approaches self-undermining. I argue that these approaches forbid observers from sharing information with one another or even past versions of themselves, and explain why information-sharing is an essential feature of scientific practice and scientific epistemology. I also discuss some ‘Extended Wigner’s Friend’ theorems which have recently attracted interest in quantum foundations, arguing that we must interpret these theorems in light of the social dimensions of scientific knowledge.
We define a class of Copenhagenish interpretations encompassing modern interpretations that follow the Copenhagen spirit. These interpretations are characterized by four postulates: Observers Observe, Universality, Anti-ψψψ-ontology, and Completeness. We explain why such interpretations are not equivalent to the textbook (or orthodox) interpretation, nor to the view that one should shut up and calculate, nor to strict operationalism. We then discuss what lessons are implied for Copenhagenish interpretations by the measurement problem, the Wigner's friend thought experiment, and the simple variants of the Wigner's friend thought experiment that we term Wigner's enemy, stalkee, and penpal. In particular, we discuss how Copenhagenish interpretations give multiple distinct descriptions of each experiment, where these descriptions are each individually true, yet cannot be combined into any single description. To make such interpretations consistent, then, one requires epistemological constraints forbidding certain perspectives from being combined. We discuss these constraints, their motivations, and some of the challenges they introduce.
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This work presents a historical-epistemological analysis of the foundations of quantum mechanics. From a philosophical point of view, the relationships between quantum mechanics and scientific realism are highlighted, as well as the influence of the neo-positivist philosophy of the first decades of the 20th century. The great significance of measurement in the context of quantum mechanics is underlined, as an essential element in providing a coherent description of reality moving from the microcosm to the macrocosm, as well as the role that the measurement apparatus and the consciousness of the observer assume during the act of measurement, the ontological problem, the problem of the objectification of the wave function and the problem of the definition of discernibility. This is followed by an overview of the most important alternative proposals to the standard interpretation (Copenhagen interpretation), with particular reference to hidden variable theories, and other alternatives to standard quantum mechanics that profoundly modify the vision of reality, such as the Everett’s many-worlds theory, the QBism, the unified holistic approach.
This paper offers a comprehensive analysis of Wigner’s Friend paradox (1961), a foundational thought experiment in quantum mechanics that highlights the tension between the internal perspective of a measuring observer (who experiences a definite outcome) and the external perspective of a super-observer who treats the entire laboratory as a quantum system in superposition. It traces the historical lineage from Schrödinger’s cat and von Neumann’s measurement theory, provides a formal mathematical description of the state evolution and logical structure of the paradox, examines implications for major interpretations of quantum mechanics (Copenhagen, Everettian many-worlds, QBism, relational quantum mechanics, and objective collapse theories), and discusses modern extensions such as the Frauchiger–Renner paradox. The work explores profound philosophical and epistemological consequences for the nature of observation, objectivity, intersubjectivity, and the role of consciousness in quantum theory (2026).