The Nature of Quantum Objects

November 11, 2021 - November 13, 2021
Department of Philosophy, University of Geneva


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  • SNF grant 181088


University of Warsaw
City College of New York (CUNY)
Mount Holyoke College
University of California, Davis
University of Michigan, Ann Arbor
Perugia University
Università degli Studi Roma Tre
University of Münster
University of Chicago
London School of Economics
National and Kapodistrian University of Athens
University of Parma
University of Leeds


Université de Genève
University of Geneva

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Quantum theory is the most accurate and comprehensive account of matter: no physical theory in the history of science has told us more about the material objects that constitute the world. At the same time, quantum theory is notorious for its puzzling implications about the nature of the objects it purports to describe: particles without definite locations; waves in a space with a dizzying number of dimensions; and correlations between spacelike-separated physical systems.

Philosophical engagement with quantum theory has traditionally focused on solving the quantum measurement problem, the challenge of forging the hugely successful mathematical and empirical apparatus of quantum mechanics into a physical theory––the kind of thing that is capable of explaining quantum phenomena in terms of the behavior of the material constituents of the world. While such investigations have often gone along with the articulation of proposals for the ontology of quantum mechanics, comparatively little attention has been paid to distinctively metaphysical questions about the nature of quantum objects. What are the laws governing the composition of quantum objects? Are fundamental quantum objects metaphysically independent? Are all fundamental properties of quantum objects determinate? What is the nature of locations of quantum objects? How do quantum objects persist?

The goal of this conference is bring together philosophers of physics and metaphysicians pursuing diverse approaches to such questions. 

Speakers: Tomasz Bigaj (Warsaw), Elise Crull (CUNY), David A. Glick (UC Davis), Gabrielle Kerbel & Nina Emery (Mount Holyoke), Vera Matarese (Bern), Matteo Morganti (Roma Tre), Paul M. Näger (Münster), Tom Pashby (U Chicago), Bryan W. Roberts (LSE), Vanessa Seifert (Bristol), Alessandro Torza (UNAM) and Alastair Wilson (Birmingham)

Attendance: This will be a hybrid (in-person/zoom) event. Attendance is free of charge; if you wish to attend the conference and/or join us for dinner, please fill out this Google form:

Organization: Claudio Calosi, David Schroeren, Maria Nørgaard, Ryan Miller, members of the SNF funded project “The Metaphysics of Quantum Objects” (SNF grant no. 181088, PI Claudio Calosi), Department of Philosophy, University of Geneva, Switzerland

Contact: Please direct any queries to [email protected].


(all times UTC+1:00)

Thursday, November 11, 2021

9-10:15am: Tom Pashby: Quantum Objects: Appearance and Reality
10:30-11h45am: Vanessa Seifert: Are molecules quantum objects?  
12-1:15pm: Bryan W. Roberts: Matter-Antimatter Exchange as a Spacetime Symmetry
1:15pm-2:45pm: Lunch break
2:45pm-4pm: Alessandro Torza: Derivative Metaphysical Indeterminacy and Quantum Physics
4:15pm-5:30pm: David A. Glick: Determinacy as a Desideratum

Friday, November 12, 2021

9:30-10:45am: Paul M. Näger: The Mereological Problem of Entanglement
11am-12:15pm: Elise Crull: Existence Monism from Bare Quantum Theory
12:15-1:45pm: Lunch break
1:45-3pm: Matteo Morganti: Quantum Objects and Haecceitism
3:15-4:30pm: Gabrielle Kerbel and Nina Emery: Configuration Space Realism and Fundamentality

Saturday, November 13, 2021

9-10:15am: Vera Matarese: Quantum Fictionalism
10:30-11h45am: Tomasz Bigaj: Are Quantum Objects Individuals? Why Should We Care?
12-1:15pm: Alastair Wilson: Fundamentality and Levels in Everettian Quantum Mechanics



Tomasz Bigaj: Are Quantum Objects Individuals? Why Should We Care?
There is a well-entrenched and venerated position in the philosophy of quantum mechanics, according to which quantum particles are non-individuals (as argued for by S. French, D. Krause, P. Teller, J. Arenhart among others). The reason for this assessment is the commonly accepted belief that quantum particles of the identical kind cannot be momentarily discerned by any measurable state-dependent properties. This follows from the permutation-invariance of the joint states of identical particles coupled with the standard formula for the reduced states in terms of partial traces. Consequently, quantum particles of the same type violate the Principle of the Identity of Indiscernibles (PII).  However, the connection between the validity of PII and the status of an individual is not as close as it may seem. The possibility of synchronic discernment by properties does not automatically guarantee that the discerned objects will attain the status of individuals. At the very least we should add to our discernibility-based criteria of individuality the possibility of counterfactual (transworld) and diachronic (transtemporal) identification.

Recently, an alternative conception of quantum individuation has been proposed (D. Dieks, A. Caulton, S. Saunders, following G. Ghirardi et al.). The central tenet of this approach is that absolute discernibility (discernibility by properties) is admissible even when the states and properties of systems of identical particles are limited to permutation-invariant ones. However, the supposition that quantum particles can be momentarily individuated by some measurable properties does not imply that they achieve the full status of individuals, due to the problems with counterfactual switching and reidentification over time. To that we should add that the synchronic individuation by measurable properties is typically not unique, as it depends on a selection of an orthogonal basis. We may summarize this by saying that fermions are emergent entities whose existence and properties are relativized to the choice of a basis (or a set of mutually compatible observables), and whose identity over time and in counterfactual scenarios is typically lost. All these facts put together call for a radical revision of the ontology of quantum objects. Perhaps the simple distinction individuals – non-individuals is too crude to capture the complex behavior of quantum objects according to our best theories. Maybe it is the right time to put the concept of quantum (non-)individuality to rest.

Elise Crull: Existence Monism from bare quantum theory

Recent work in fundamental mereology tends to consider the debate between priority monism and priority pluralism “the only game in town”.  Both views take metaphysical dependence relations (of some kind or other) to be primitive, and both views make important use of quantum physics.  In this talk I shall try to establish a more controversial position: Existence Monism. I do this in two (largely independent) steps: the first is to argue that quantum physics, construed in an interpretation-neutral way, raises serious problems for metaphysical dependence relations as primitive.  This undercuts the ``priority’’ qualifier. The second step is to support monism over pluralism by defending it from the significant objections raised in Calosi (2014) and Tallant & Baron (2018).  This defense will again call upon central features of interpretation-neutral quantum theory.    

David Glick: Determinacy as a Desideratum
Some have alleged that quantum theory involves metaphysical indeterminacy. However, this metaphysical claim is underdetermined—there are accounts of quantum theory that posit metaphysical indeterminacy and others that do not. Fortunately, theoretical virtues can help us to resolve this case of underdetermination. Versions of quantum theory that posit metaphysical indeterminacy will be less simple or less informative than their indeterminacy-free counterparts. Moreover, positing metaphysical indeterminacy does not provide a clear gain in explanatory power, contrary to the suggestion of Calosi and Wilson (2021). Thus, determinacy is a desideratum in an interpretation of quantum theory.

Gabrielle Kerbel and Nina Emery: Configuration Space Realism and Fundamentality
Configuration space realism is an account of quantum ontology according to which the wavefunction represents a field in a high-dimensional space. We present a version of configuration space realism that has largely been overlooked in the literature to date and argue that this version should be taken just as seriously as the standard version. Along the way we show how choosing between these different versions of configuration space realism will turn on philosophically nuanced questions about the nature of grounding, the importance of separability and locality, and the role of explanation in metaphysics and physics.

Vera Matarese: Quantum Fictionalism
Are there quantum objects? While representationalists respond in the affirmative, claiming that quantum states directly represent quantum beables, pragmatists and operationalists respond in the negative, the former interpreting quantum states only prescriptively, the latter as just calculation tools.  In this talk, I propose a fictionalist view to account for the nature of quantum objects. The core idea is that quantum objects do not physically exist, and yet they have an explanatory power that underwrites the kind of explanations normally given by representationalists.

Matteo Morganti: Quantum Objects and Haecceitism
In the debate about the metaphysical status of the entities described by non-relativistic quantum mechanics, two arguments are traditionally used in favour of the ‘Received View’ that quantum objects are non-individuals: one having to do with the Identity of the Indiscernibles, the other with quantum statistics and haecceitism. While the former has been the object of intense discussion as of late, the latter has received comparatively little attention. It basically amounts to the following: if quantum objects were individuals, then many-particle systems of ‘indistinguishable particles’ would give rise to haecceitistic differences – i.e., exactly similar physical states that only differ with respect to which particle is which; quantum statistics doesn’t exhibit such haecceitistic differences; hence, quantum objects are not individuals. This argument certainly looks compelling. However, upon scrutiny, it turns out to be less straightforward than it seems. Here, I will reconstruct the argument in detail, and look at ways to steer clear of its conclusion.  

Paul Näger: The mereological problem of entanglement
It is well-known that the entangled quantum state of a composite object cannot be reduced to the states of its parts. This quantum holism provides a peculiar challenge to formulate an appropriate mereological model: When a system is in an entangled state, which objects are there on the micro and macro level, and which of the objects carries which properties? This paper chooses a modeling approach to answer these questions: It proceeds from a systematic overview of consistent mereological models for entangled systems and discusses which of them is compatible with the quantum mechanical evidence (where quantum states are understood realistically). It reveals that entangled quantum systems neither describe undivided wholes nor objects that stand in irreducible relations. The appropriate model assumes that the entangled property is an irreducible non-relational plural property carried collectively by the micro objects, while there is no macro object. In this sense, quantum holism is an instance of property holism, not of object holism.

Tom Pashby: Quantum Objects: Appearance and Reality 
In this talk I argue against the interpretation of the quantum state of a system as describing an object. The thesis that to the quantum state there corresponds a unique physical object requires not just metaphysical realism but scientific realism. The kind of scientific realism required is evidently (what I term) an Object-Oriented Realism (OOR). Given decoherence, I argue that the Object-Oriented Realist will naturally be led to the Everett interpretation. And, given the approximate nature of the decoherence basis, the Object-Oriented Realist will be led to regard only the universal wavefunction as an object worthy of realist belief. In Wallace's (2013) Emergent Multiverse, his "real patterns" structuralist view leads to the idea that the physical objects of experience are spatio-temporal patterns (e.g., a pattern that behaves like a tiger) that can be found approximated within a branch of the universal wavefunction. So the objects of experience (the targets of ordinary realism) are spatiotemporal patterns that are FAPP definite for the branch-bound observer. But, in quantum mechanics, properties of a quantum state correspond with projectors and no spatiotemporal pattern of projectors is itself a projector. Since the patterns themselves are not properties of the wavefunction, for the Object-Oriented Realist they are not properties of any object. This leaves the Object-Oriented Realist vulnerable to the difficulties of F. H. Bradley's Absolute, which Russell (1903) diagnosed as arising from over-reliance on subject-predicate logical form, which is shared by the orthodox reading of QM. I conclude by noting that an event ontology interpretation of quantum mechanics (e.g., GRWf) would allow us to interpret quantum mechanics in terms of precisely realized spatio-temporal patterns. 

Bryan Roberts: Matter-Antimatter Exchange as a Spacetime Symmetry
I argue that the correct local spacetime symmetry group is not the Poincaré group, but its universal covering group SL(2,C). Viewing the local existence of a quantum object in spacetime as a representation of a symmetry group, this provides an elegant explanation of the relationship between matter, antimatter, and spacetime: that matter-antimatter exchange is an automorphism of the local spacetime symmetries. 

Vanessa Seifert: Are molecules quantum objects? 
Abstract TBA. 

Alessandro Torza: Derivative metaphysical indeterminacy and quantum physics 
It will be argued that quantum indeterminacy can be construed as a merely derivative phenomenon. The possibility of merely derivative quantum indeterminacy undermines both a recent argument against quantum indeterminacy due to David Glick, and an argument against the possibility of merely derivative indeterminacy due to Elizabeth Barnes.

Alastair Wilson: Fundamentality and Levels in Everettian Quantum Mechanics

Distinctions in fundamentality between different levels of description are central to the viability of contemporary decoherence-based Everettian quantum mechanics (EQM). This approach to quantum theory characteristically combines a precise fundamental reality (one universal wavefunction) with an imprecise emergent reality (multiple decoherent worlds). I explore how the Everettian appeal to fundamentality and emergence fits within extant metaphysical frameworks, identify grounding and concept fundamentality as promising analytical tools, and use them to characterize a system of explanatory levels (with associated laws of nature) for EQM. This Everettian level structure encompasses and extends the ‘classical’ levels structure comprising levels of physics, chemistry, biology, etc., which are recaptured through a correspondence with levels of explanation for the emergent quasi-classical worlds in EQM. There is however a new kind of fundamental level invoked by EQM, a level below any previously recognised classical level; I argue that this level is novel since it is best understood as physically (indeed metaphysically) non-contingent. This result blocks supervenience-based accounts of levels from applying to EQM. Another contrast with classical level structures arises from the irreducibly self-locating element to probabilities in EQM; I argue that the role of self-location gives rise to an additional novel explanatory level within the overall Everettian levels picture.

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November 8, 2021, 9:00am CET

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