SOPhiA 2022

Salzburgiense Concilium Omnibus Philosophis Analyticis

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Programm - Vortrag

On similar fermions: what's heterodox about heterodoxy?
(Philosophy of Science, Englisch)

There are largely three views on the question of whether or not Leibniz's principle of the Identity of Indiscernibles (PII) is violated by states of similar fermions: firstly, the (earliest) view that similar fermions are always qualitatively identical, so that PII is always violated; call this the no discernibility view (see French and Redhead (1988). Secondly, the (more recent) view that similar fermions are discernible in a weak sense __ the so called weak discernibility view (see Saunders (2003), (2006); Muller and Saunders (2008); Muller and Seevinck (2009)). Thirdly, the (most recent) view that similar fermions are (at least sometimes) discernible in a strong sense; call this the new discernibility view. The new discernibility view is currently advocated by, e.g., Bigaj (2015); Caulton (2014); Dieks and Lubberdink (2011), (2020); Friebe (2014), (2016); Leegwater and Muller (2020). Bigaj (2022) has recently categorized the no discernibility and the weak discernibility view as orthodox, and the new discernibility view as heterodox, thereby indicating that the latter view has something new and original about it. In this talk, I deal with the question of whether and how this categorization is justified.



As is now known, the no discernibility view relies on the semantical standard interpretation that the indices of the Hilbertspace formalism (typically (1) and (2)) refer to physical entities (i.e. particles); more specifically, that they do refer so directly (i.e. independently from properties). This semantical view has been called direct factorism. Proponents of the weak discernibility view stick to the standard semantics (i.e. direct factorism), but save PII only in a weak sense by doing so. Proponents of the new discernibility view, by contrast, reject direct factorism in one of the two following ways: Descriptive anti-factorists (Dieks and Lubberdink, Friebe) deny that the formalism_s indices have physical meaning (anti-factorism). Instead, they suppose that descriptively referring particle names can be introduced from outside the formalism (descriptive anti-factorism). Descriptive factorists (Leegwater and Muller) stick to the supposition that the formalism_s indices refer to particles (factorism), but substitute the supposition that they do refer so directly with the supposition that they do refer so descriptively (descriptive factorism). Now, it looks as if the new discernibility view, by deviating from the standard semantics, is heterodox in that it defends PII in more than just a weak sense (like proponents of the orthodox weak discernibility view do).



In this talk, I introduce two distinctions - one concerning ontology, the other concerning semantics - which show that the heterodox new discernibility view might not be as heterodox as it seems. The first distinction concerns two different interpretations of PII and, correspondingly, two different understandings of qualitative distinctness. In one interpretation, PII is supposed to work as a principle of individuation, saying that whenever two objects are numerically distinct, their numerical distinctness is grounded in their being qualitatively distinct. Correspondingly, I call it the grounding interpretation of PII. In another interpretation, PII is not supposed to work as a principle of individuation itself (i.e. objects are individuated independently from qualitative distinctness). Instead, PII is understood as an auxiliary principle which supports a principle of individuation other than PII by ensuring that a situation with two numerically distinct but qualitatively identical objects actually never occurs. Read this way, PII states that whenever two objects are numerically distinct for whatever reason (other than being qualitatively distinct), their numerical distinctness is nevertheless accompanied by qualitative distinctness. Correspondingly, I call this reading the accompanying interpretation of PII.



The two interpretations of PII differ with respect to their ontological commitments. The proponent of the accompanying interpretation is committed to an ontology which, in principle, allows for the possibility of numerically distinct but qualitatively identical objects. The reason is this: according to the accompanying interpretation, qualitative distinctness has nothing to do with individuation, so objects are individuated differently (e.g., by bare particularity). However, as soon as individuation is independent from qualitative distinctness, the possibility of numerically distinct but qualitatively identical objects immediately follows __ and must therefore be prevented by adding an auxiliary principle, such as PII in the accompanying interpretation, to one_s ontology. The proponent of PII in the grounding interpretation, by contrast, is committed to an ontology which forbids the possibility of numerically distinct but qualitatively identical objects right from the start. The reason is that as soon as individuation is tied to qualitative distinctness, the possibility of numerically distinct but qualitatively identical objects is immediately excluded __ there cannot be two objects which are qualitatively identical. Thus, investigating with which kind of ontology a view is compatible is a way of figuring out to which interpretation of PII it is committed. The results allow to determine how exactly the heterodox new discernibility view differs from the orthodox no and weak discernibility views ontologically, and thereby to determine what exactly is heterodox about the new discernibility view, ontologically speaking.



The second distinction which I wish to introduce is the distinction between semantics and metasemantics. The semantics of proper names answers the question in which way a name refers, or what the meaning of a name consists in. The metasemantics of proper names answers the question of how it comes about that a given name refers to the object it refers to, or, put differently, how the reference of a name gets fixed. Now, the following argument __ which I call the argument from metasemantics __ shows that the semantical views which are united under the heading new discernibility (i.e. descriptive anti-factorism and descriptive factorism) display some ambiguity. In a first step, it can be shown that both descriptive anti-factorists and descriptive factorists are not concerned with descriptive reference, but with descriptive reference fixing. In a second step, it can be shown that descriptive reference fixing is not sufficient for descriptive reference. This is witnessed by the so called causal theory of reference, according to which a name_s reference can get fixed either by ostension or with the help of a (definite) description, but names function as directly referring rigid designators (i.e. names which refer to the same object in every possible world) from then on. As a consequence, both descriptive anti-factorists and descriptive factorists have to prove that their proposed names do indeed refer descriptively. The argument from metasemantics shows that it is not clear whether the new discernibility view differs from the no and weak discerniblity views semantically (by deviating from the standard semantics), or metasemantically (by complementing the standard semantics with a metasemantical story). Therefore, it is not yet clear what exactly is heterodox about the heterodox new discernibility view, semantically speaking.





References



Bigaj, T. (2015). Dissecting weak discernibility of quanta, Studies in History and Philosophy of Modern Physics 50, 43-53.



- (2022). Identity and Indiscernibility in Quantum Mechanics, Palgrave Macmillan.



Caulton, A. (2014).Qualitative Individuation in Permutation-Invariant Quantum Mechanics, arXiv:1409.0247v1 _quant-ph_.



Dieks, D. and Lubberdink, A. (2011). How Classical Particles Emerge from the Quantum World, Foundations of Physics 41(6), 1051-1064.



- (2020). Identical Particles as Distinghuishable Objects, General Journal of Philosophy, https://doi.org/10.1007/s10838-020-09510-w.



French, S. and Redhead, M. (1988). Quantum Physics and the Identity of Indiscernibles, The British Journal for the Philosophy of Science 39 (2), 233-246.



Friebe, C. (2014). Individuality, distinguishability, and (non-)entanglement: A defense of Leibniz's principle, Studies in History and Philosophy of Modern Physics 48 (A), 89-98.



- (2016). Leibniz's principle, (non-)entanglement, and Pauli exclusion, DOI:10.13140/RG.2.2.20612.42883.



Leegwater, G. and Muller, F.A. (2020). The Case Against Factorism. On the Labels of -Factor &_8855; Hilbert-Spaces of Similar Particles in Quantum Mechanics, Journal for General Philosophy of Sciene, https://doi.org/10.1007/s10838-020-09514-6.



Muller, F.A. and Saunders, S. (2008). Discerning Fermions, The British Journal for the Philosophy of Science 59, 499-548.



Muller, F. and Seevinck, M. (2009). Discerning Elementary Particles, Philosophy of Science, 76: 179-200.



Saunders, S. (2003). Physics and Leibniz's Principles, in K. Brading and E. Castellani (eds.), Symmetries in Physics: Philosophical Reflections, Cambridge: Cambridge University Press.



- (2006). Are Quantum Particles Objects, Analysis, 66: 52-63.


Chair:
Zeit: 10:40-11:10, 08. September 2022 (Donnerstag)
Ort: SR 1.004

Maren Bräutigam
(Cologne University, Deutschland)



Testability and Meaning deco