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European Journal for Philosophy of Science

Quantum indeterminacy: a matter of degree?

Maria Nørgaard

Published Mar 1, 2025• 4 citations
Publisher

Abstract

Abstract The degreed view is an influential account in the debate on quantum value indefiniteness, linking the gradedness of quantum properties to quantum indeterminacy. This paper challenges the connection between degrees and indeterminacy by presenting an example of a graded quantum property that does not entail metaphysical indeterminacy. Through an investigation of two graded approaches to location in quantum mechanics, the paper argues that while the first account, degreed instantiation of exact location , is indeterminate, the second account, degreed quantum location , is not. This indicates that indeterminacy and degrees are not inherently linked, offering a novel perspective on quantum ontology. The paper advocates adopting a graded view of quantum properties without indeterminacy, potentially leading to a paradigm shift in understanding quantum phenomena.

DOI
10.1007/s13194-025-00637-5

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Abstract The degreed view is an influential account in the debate on quantum value indefiniteness, linking the gradedness of quantum properties to quantum indeterminacy. This paper challenges the connection between degrees and indeterminacy by presenting an example of a graded quantum property that does not entail metaphysical indeterminacy. Through an investigation of two graded approaches to location in quantum mechanics, the paper argues that while the first account, degreed instantiation of exact location , is indeterminate, the second account, degreed quantum location , is not. This indicates that indeterminacy and degrees are not inherently linked, offering a novel perspective on quantum ontology. The paper advocates adopting a graded view of quantum properties without indeterminacy, potentially leading to a paradigm shift in understanding quantum phenomena.
Abstract Many features of quantum mechanics (QM) suggest that, at the microscopic level, objects sometimes fail to determinately instantiate their properties. In recent years, many have argued that this phenomenon indicates the existence of an ontological kind of indeterminacy, often called metaphysical indeterminacy , which is supposed to affect the ontology of QM. As insisted by Glick ('Against Quantum Indeterminacy, 2017, Thought), however, once we look at the major realist approaches to QM we learn that the indeterminacy disappears from the description of the world at its most fundamental level. This absence might be taken as a good reason for adopting some form of eliminativism towards quantum mechanical indeterminacy. The aim of this paper is to distinguish three ways of defending eliminativism, and to argue that none of them eventually succeeds. The upshot is that QM does in fact suggest the existence of metaphysical indeterminacy, although only as an emergent phenomenon.
There has been recent interest in formulating theories of non-representational indeterminacy. The aim of this paper is to clarify the relevance of quantum mechanics to this project. Quantum-mechanical examples of vague objects have been offered by various authors, displaying indeterminate identity, in the face of the famous Evans argument that such an idea is incoherent. It has also been suggested that the quantum-mechanical treatment of state-dependent properties exhibits metaphysical indeterminacy. In both cases it is important to consider the details of the metaphysical account and the way in which the quantum phenomenon is captured within it. Indeed if we adopt a familiar way of thinking about indeterminacy and apply it in a natural way to quantum mechanics, we run into illuminating difficulties and see that the case is far less straightforward than might be hoped.
The paper investigates the existence and the nature of quantum indeterminacy in a particular realist interpretation of quantum mechanics, that is, the Modal Hamiltonian Interpretation (MHI)-together with an ontology of properties for quantum systems. In doing so, it serves a twofold purpose. First, it advances the debate on quantum ontology by showing precisely how and why indeterminacy arises in a quantum world-as described by the MHI. Second, it offers a naturalistic example of genuine metaphysical indeterminacy, an example coming from our best physics.
The question of whether Everettian quantum mechanics (EQM) justifies the existence of metaphysical indeterminacy has recently come to the fore. Metaphysical indeterminacy has been argued to emerge from three sources: coherent superpositions, the indefinite number of branches in the quantum multiverse and the nature of these branches. This paper reviews the evidence and concludes that those arguments don't rely on EQM alone and rest on metaphysical auxiliary assumptions that transcend the physics of EQM. We show how EQM can be ontologically interpreted without positing metaphysical indeterminacy by adopting a deflationary attitude towards branches. Two ways of developing the deflationary view are then proposed: one where branches are eliminated, and another where they are reduced to the universal quantum state.
It has frequently been suggested that quantum mechanics may provide a genuine case of ontic vagueness or metaphysical indeterminacy. However, discussions of quantum theory in the vagueness literature are often cur- sory and, as I shall argue, have in some respects been mis- guided. Hitherto much of the debate over ontic vagueness and quantum theory has centered on the indeterminate construal of ontic vagueness, and whether the quantum phenomenon of entanglement produces particles whose identity is indeterminate. I argue that this way of framing the debate is mistaken. A more thorough ex- amination of quantum theory and the phenomenon of entanglement reveals that quantum mechanics is best in- terpreted as supporting what I call the property construal of ontic vagueness, where vague properties are understood in terms of determinable properties without the corresponding determinates.
Abstract In Everettian quantum mechanics, the universal quantum state is fundamental, non-contingent, and wholly determinate. By contrast, the parallel worlds of diverging EQM, and the contingency constituted by self-location amongst those worlds, are emergent and partly indeterminate. In particular, it is indeterminate both how many worlds there are, and what microscopic qualitative features those worlds have. This chapter discusses various ways to understand indeterminacy in the Everettian multiverse, and argues that the indeterminacies of EQM present no obstacle to the analytic ambitions of quantum modal realism. Everettians can understand quantum indeterminacy using models of indeterminacy that are familiar from the philosophical literature on vagueness.