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Facing the Ontological Challenges of Quantum Mechanics

Olímpia Lombardi

Published Feb 19, 2026• 0 citations
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Abstract

Abstract In the previous chapter, the structure of the ontology proposed by the MHI was introduced. In this ontology, properties are the fundamental items and quantum systems are non-objectual bundles of properties. However, as is well known, metaphysics is underdetermined by physics; in particular, quantum mechanics is compatible with different ontological pictures. Thus, arguing in favor of a certain quantum ontology over others requires showing how fruitful it is in the task of offering reasonable solutions to interpretative problems. This chapter is devoted to show the advantages of the proposed picture for dealing with the ontological challenges of quantum mechanics: contextuality, non-separability, and indistinguishability. Finally, the top-down approach presented in Chapter 8 is revisited, showing how it acquires an ontological significance from the perspective of the ontology of properties proposed by the MHI.

DOI
10.1093/9780198951407.003.0011

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Abstract In the previous chapter, the structure of the ontology proposed by the MHI was introduced. In this ontology, properties are the fundamental items and quantum systems are non-objectual bundles of properties. However, as is well known, metaphysics is underdetermined by physics; in particular, quantum mechanics is compatible with different ontological pictures. Thus, arguing in favor of a certain quantum ontology over others requires showing how fruitful it is in the task of offering reasonable solutions to interpretative problems. This chapter is devoted to show the advantages of the proposed picture for dealing with the ontological challenges of quantum mechanics: contextuality, non-separability, and indistinguishability. Finally, the top-down approach presented in Chapter 8 is revisited, showing how it acquires an ontological significance from the perspective of the ontology of properties proposed by the MHI.
Abstract In Chapter 4, the MHI was introduced in terms of interpretative postulates that define the ontological reference of each physical term of quantum mechanics in its standard formulation. On the basis of that presentation, an ontology of properties, framed in the algebraic formalism of quantum mechanics, was proposed. The aim of this chapter is to set out in detail the structure of the ontology proposed by the MHI, now with the technical metaphysical resources developed in the previous chapter. In particular, the nature of the properties that constitute the fundamental ontological items is discussed, and it is argued that quantum systems are not objects at all, but mere collections of properties that do not retain their identity either synchronically or diachronically. More precisely, quantum systems turn out to be non-objectual bundles of properties.
Standard quantum mechanics poses serious challenges to some principles deeply entrenched in traditional metaphysics. In particular, the theory defies the ontological category of individual object through three of its features: contextuality, non-separability, and indistinguishability. The difficulties have prompted the development of non-traditional ontological frameworks intended to account for the quantum domain. Some approaches advocate replacing the classical conception of a realm of objects endowed with properties by an ontology that either dispenses with the category of object altogether or treats it as a derivative notion. The Modal-Hamiltonian Interpretation (MHI) of quantum mechanics and Ontic Structural Realism (OSR) exemplify this position. MHI proposes an ontology in which quantum systems are non-objectual bundles of properties linked by definite physical relations. The OSR defends the ontological primacy of structures, within which objects are construed as nodes of relations. The aim of this article is to compare these two ontological approaches, highlighting both their points of convergence and their divergences, particularly in light of the ontological challenges posed by quantum mechanics. With this aim, the article is structured as follows. Section 2 outlines the ontology of MHI, introducing the distinction between type-properties and case-properties, characterizing quantum systems as non-objectual bundles, and analyzing the role of symmetry groups in providing physical content to the theory and governing actualization. Section 3 turns to OSR, examining its motivations, its distinction between physical and mathematical structures, and the modal character of structures. Section 4 offers a systematic comparison of the two approaches, considering their respective motivations and scope, their shared commitment to an object-free ontology, the role played by symmetry groups within each framework, and their contrasting interpretations of modality. Finally, Section 5 presents some concluding remarks.
Abstract Since Galileo, physics has traditionally adopted a closed-system view, framed in the more generic strategy of describing highly idealized and generally non-existent situations. However, in the field of quantum mechanics—and also in other fields of physics—an open-system view has been gaining strength in recent decades, maybe under the influence of the practical success of the environment-induced decoherence (EID) developments. This trend is at odds with the perspective of the MHI, which openly adopts a closed-system view. The aim of this chapter is to discuss several aspects of quantum mechanics that reveal the difficulties faced by an open-systems approach. On this basis, a case is made for a closed-system approach that leads to a top-down view of quantum mechanics. This top-down view is in agreement with the ontology of properties introduced in Chapter 4, which will be developed in detail in the following Chapters 9, 10, and 11.
The purpose of this talk is to briefly recall the main principles of quantum mechanics in order to understand the ontological challenges introduced by the theory. In particular, I will argue that quantum mechanics defies the category of individual for three different reasons: contextuality, non-separability, and indistinguishability. Each one of these three features of the theory violates a traditional ontological principle: the Principle of Omnimode Determination, the Principle of Separability, and the Principle of Identity of Indiscernibles, respectively. Therefore, any interpretation of quantum mechanics should formulate a “global” solution, according to which the three ontological challenges could be adequately tackled in terms of a single ontology.
Abstract The issue about the nature of quantum systems usually hinges on the category of individual: the question is whether this category can be applied to understand the peculiarities of quantum behavior. However, some metaphysical subtleties are commonly overlooked in this discussion. What is the difference between the notions of object and of individual? What metaphysical principles are quantum systems supposed to fulfill? What ontological kinds of properties are involved in the quantum domain? These questions should be taken into account when the issue at stake is the ontological nature of quantum systems and, more generally, the structure of the quantum realm. In order to address these and other metaphysical questions, different ontological distinctions that are scarcely taken into account in the debate are brought to the fore in this chapter. In light of these distinctions, the ontological challenges that quantum mechanics poses to the ontological picture presupposed by traditional metaphysics will be discussed in the following chapter.
The existence of ontologically different but empirically indistinguishable versions of non-relativistic quantum mechanics is one of the most serious and widely discussed cases of metaphysical underdetermination. I argue that this problem is unlikely to disappear when we turn to the next more fundamental theory, namely relativistic quantum field theory. The problem is merely overshadowed by yet another interpretational controversy, but it persists regardless of the outcome of this latter debate. I further argue that one should not be too optimistic about transferring ontological lessons learned in the context of one physical theory to the context of a more fundamental theory.