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arXiv:2509.10680

A Realist Approach to Quantum Individuality: Against the "Received" and "Alternative" Views

Christian DE RONDE, Ivan Klarreich

Published Sep 12, 2025• 0 citations
arXivHTMLPDF

Abstract

In this work we address the contemporary debate about quantum individuality expressed as an opposition between those who, like Décio Krause, defend the reference of the theory to "non-individual particles", and those like Dennis Dieks, who propose instead to preserve the notion of "classical particle" as commonly applied by contemporary physicists. We will argue that these viewpoints rather than truly opposed share a common methodology which has helped to reinforce the doctrine of classical concepts that was imposed by Bohr and Dirac within the "standard" formulation --which remains the orthodox physical account of the theory of quanta. We will also discuss a recently proposed relativist yet objective relational account of quantum individuality [25] which, going back to Einstein's methodological approach, opens the doors to a completely new, truly realist understanding of quantum individuality.

DOI
10.48550/arxiv.2509.10680

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In this work we address the contemporary debate about quantum individuality expressed as an opposition between those who, like Décio Krause, defend the reference of the theory to "non-individual particles", and those like Dennis Dieks, who propose instead to preserve the notion of "classical particle" as commonly applied by contemporary physicists. We will argue that these viewpoints rather than truly opposed share a common methodology which has helped to reinforce the doctrine of classical concepts that was imposed by Bohr and Dirac within the "standard" formulation --which remains the orthodox physical account of the theory of quanta. We will also discuss a recently proposed relativist yet objective relational account of quantum individuality [25] which, going back to Einstein's methodological approach, opens the doors to a completely new, truly realist understanding of quantum individuality.
In this work we argue against the interpretation that underlies the "Standard" account of Quantum Mechanics (SQM) that was established during the 1930s by Niels Bohr and Paul Dirac. Ever since, following this orthodox narrative, physicists have dogmatically proclaimed -- quite regardless of the deep contradictions and problems -- that the the theory of quanta describes a microscopic realm composed of elementary particles (such as electrons, protons and neutrons) which underly our macroscopic world composed of tables, chairs and dogs. After critically addressing this atomist dogma still present today in contemporary (quantum) physics and philosophy, we present a new understanding of quantum individuals defined as the minimum set of relations within a specific degree of complexity capable to account for all relations within that same degree. In this case, quantum individuality is not conceived in absolute terms but -- instead -- as an objectively relative concept which even though depends of the choice of bases and factorizations remain nonetheless part of the same invariant representation.
One recent debate in philosophy of physics has centered whether quantum particles are individuals or not. The received view is that particles are not individuals and the standard methodology is to approach the question via the structure of quantum theory. I challenge both the received view and the standard methodology. I contend not only that the structure of quantum theory is not the right place to look for conditions of individuality that quantum particles may or may not satisfy, but also that there is an important role for traditional metaphysics to play. Consequently, my work brings together the philosophy of physics and traditional metaphysics literatures to shed new light on the debate over the individuality of quantum particles. I defend a set of conditions of individuality and argue that quantum particles satisfy these conditions thereby defending the view that particles are individuals in opposition to the received view. I also challenge a second feature of the standard methodology insofar as I challenge the significance of the Principle of the Identity of Indiscernibles in terms of which much discussion in the philosophy of physics literature is framed. My work is significant in a number of additional ways as well. My work implies that the dominant explanation for quantum statistics in terms of non-individuality is incorrect and it also undermines the ontic-structural realists metaphysical underdetermination challenge to the scientific realist.
In the non-reflexive formulation of quantum physics, attention is given to a metaphysical view of quantum objects (q-objects) as non-individuals, characterised as entities to which the standard notion of identity lacks sense. The reference to the nature of q-objects is usually omitted in other interpretations and the most we can find is some vague reference to “to each [quantum] system we associate a Hilbert space”, and nothing more is said about them; we need to infer from the theory their characteristics, and it gives us several alternatives. One of them, to be justified here in broad aspects, is the non-individual view. It is important to enlighten that we are not trying to just find a way to deal with quantum entities but to defend a possible ontology of non-individuals, which can be applied also to ‘particles’ arising from quantum fields. Our account is based on two assumptions: (i) the ‘classical theory of identity’ does not apply to q-objects, and (ii) their non-individuality must be attributed from the start, that is, as a primitive notion and not ‘made a posteriori’ say by assuming symmetry principles. The underlying logic is called non-reflexive because the reflexive law of identity ∀x(x=x)\forall{x{({x = x})}}∀x(x=x) is supposed not to hold for q-objects. Since all the details demand a lot of space, here we only sketch and justify our view. The references provide a more detailed account.
Particles in classical physics are distinguishable objects, which can be picked out individually on the basis of their unique physical properties. By contrast, in the philosophy of physics, the standard view is that particles of the same kind ("identical particles") are completely indistinguishable from each other and lack identity. This standard view is problematic: Particle indistinguishability is irreconcilable not only with the very meaning of "particle" in ordinary language and in classical physical theory, but also with how this term is actually used in the practice of present-day physics. Moreover, the indistinguishability doctrine prevents a smooth transition from quantum particles to what we normally understand by "particles" in the classical limit of quantum mechanics. Elaborating on earlier work, we here analyze the premises of the standard view and discuss an alternative that avoids these and similar problems. As it turns out, this alternative approach connects to recent discussions in quantum information theory.
Abstract According to classical physics particles are basic building blocks of the world. These classical particles are distinguishable objects, individuated by unique combinations of physical properties. By contrast, in quantum mechanics the received view is that particles of the same kind (“identical particles”) are physically indistinguishable from each other and lack identity. This doctrine rests on the quantum mechanical (anti)symmetrization postulates together with the “factorist” assumption that each single particle is represented in exactly one factor space of the tensor product Hilbert space of a many-particle system. Even though standard in theoretical physics and the philosophy of physics, the assumption of factorism and the ensuing indistinguishability of particles are problematic. Particle indistinguishability is irreconcilable with the everyday meaning of “particle”, and also with how this term is used in the practice of physics. Moreover, it is a consequence of the standard view that identical quantum particles remain indistinguishable even in the classical limit, which makes a smooth transition to the classical particle concept impossible. Lubberdink (1998; 2009) and Dieks and Lubberdink (2011) have proposed an alternative conception of quantum particles that does not rely on factorism and avoids these difficulties. We further explain and discuss this alternative framework here. One of its key consequences is that particles in quantum theory are not fundamental but emergent; another that once they have emerged, quantum particles are always physically distinguishable and thus possess a physically grounded identity.
According to classical physics, particles are basic constituents of the physical world. Quantum theory is much less friendly to particles; in particular, relativistic quantum field theory (RQFT) creates serious obstacles for the idea that particles are fundamental. Apparently, when moving from the domain of RQFT to that of classical mechanics (CM), particles have to emerge at some stage. It is standard to assume that this emergence has been completed at the level of quantum mechanics, halfway between RQFT and CM, even though particles of the same kind in many-particle quantum mechanics have the curious feature of being ‘entities without identity’. Against this ‘Received View’ about the nature of quantum particles we outline and defend an Alternative View (AV), in which the emergent character of particles is emphasized. According to this AV, the step to a particle theory has not yet been made in quantum mechanics: conditions have still to be satisfied in order to make the particle concept applicable. If these conditions are met, the quantum particles that emerge are distinguishable individuals possessing physically defined identities, in stark contrast to what the Received View asserts. We will compare and contrast the two Views, both from a physical and a logical/conceptual point of view. This article is part of the theme issue ‘Identity, individuality and indistinguishability in physics and mathematics’.