The paper argues that quantum mechanics provide examples of genuine metaphysical indeterminacy that cannot be accounted for in purely modal terms. The best account of quantum indeterminacy has it that quantum systems have determinable properties without thereby having a unique determinate of that determinable.
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.
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.
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.
We use the framework of determinable and determinate properties to provide a novel account of the constraints imposed by the Kochen-Specker theorem. Specifically, we show that the result may be understood as a prohibition on the possibility of providing an account of quantum properties, as they are usually represented using Hilbert space operators, according to which quantum systems are fully determinate. That is, the Kochen-Specker theorem entails that any account of quantum properties compatible with the predictions of quantum mechanics must exhibit determinable-based metaphysical indeterminacy.