Hilary Term 2025

​Week 1 (23/1): Marta Bielińska (Oxford) - Prolegomenon to an epistemology of orbifolds​

Abstract: In general relativity, spacetime is usually taken to be a (3+1)-dimensional Lorentzian manifold that is Hausdorff, paracompact, time-orientable, and so on. However, it seems that there are currently no known experiments that directly test all these spacetime properties. This raises the question of whether it is possible for our spacetime to have a different structure - for example, that of an orbifold, which is, roughly, a manifold quotiented by some group. In our talk, we will address two questions. First, is it possible to empirically verify whether one lives on a manifold or on an orbifold? Second, following up on Read and Bielińska (2022), can one identify the specific type of orbifold on which one is living; for example, is it globally or locally orientable? Our considerations begin with an examination of the topological and differentiable structures of orbifolds. We then discuss the possibility of defining field theories, such as general relativity or quantum field theory, on orbifolds. Finally, we conclude with broader philosophical reflections on epistemology of orbifolds. (Based on joint work with James Read.)​

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Week 2 (30/1): Jonathan Fay (Bristol) - On Reissner's hypothesis: Historical proposals for a Machian unification of gravity and inertia

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Abstract: The combination of Mach's hypothesis concerning the material origin of inertia and Einstein’s equivalence hypothesis on the unity of inertia and gravity raises the intriguing possibility that gravity may be explained entirely as the dynamical part of a relativized law of inertia. Shortly after the development of general relativity, it became clear that Einstein’s general covariance based approach does not reduce inertia to mass interactions. While Einstein subsequently treated "Mach's principle" as a selection criterion for models of his theory, there is an alternative research program that implements Mach's idea explicitly in its foundations. The aim of my talk is to bring attention to some of the key 20th Century papers that (retrospectively) form part of this research program, focussing in particular on Reissner (1915) and Sciama (1953). 

Although the approaches of Reissner and Sciama are quite different, they are unified insofar as they both embody this intriguing hypothesis. By looking at the common feature of such models, I draw out some of the key implications of the hypothesis, including the epochal variability of the gravitational 'constant' and a potential guarantee of the critical density condition in cosmology.

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Week 4 (13/2): Maren Bräutigam (Köln) - Leibniz's Principle and similar particles 

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Abstract: In this talk, I will give an overview of the debate on whether Leibniz's Principle of the Identity of Indiscernibles (PII), according to which qualitative difference is necessary for numerical difference, is violated by similar particles (like, e.g., two electrons). According to so-called orthodox views, PII is always violated or, at best, valid in a weak sense only. According to heterodox views, however, (a strong version of) PII is valid for similar particles in at least some cases. The main motivation for heterodox views is that orthodox arguments for the violation of PII (tacitly) rely on a certain background assumption - called factorism - which can be questioned from a physical point of view. Factorism is a semantical view concerning the quantum mechanical formalism; more specifically, it is the view that indices within this formalism have physical (not just mathematical) meaning. However, factorism yields some implausible consequences; e.g., according to one prominent argument, it hinders quantum particles from becoming localized in the classical limit. Another important concept on which heterodox views rely is a certain understanding of entanglement - called GMW-entanglement, because it goes back to physicists Ghirardi, Marinatto and Weber - which is argued to fit better for similar particles than the usual understanding in terms of non-factorizability. Since heterodox views are relatively recent, they suffer from a problem - the so-called ambiguity problem - to which a complete and satisfying solution is yet to be found. The ambiguity problem shows that individuation via properties (i.e., what heterodox views want to accomplish on an ontological level) is not unique, i.e., ambiguous. I will discuss different aspects of the ambiguity problem and propose some potential solutions.

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Week 5 (20/2): Eleanor March (Oxford) - "the logical sequence of his Principles": Understanding Du Châtelet on Newton's law of gravitation in the Principia

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Abstract: Émilie Du Châtelet (1706-1749) is perhaps equally well-known for her magnum opus, the Institutions de Physique of 1740, and for her later French translation of and commentary to Newton's Principia (first published posthumously in 1756, with the corrected edition in 1759). One of the few topics which Du Châtelet addresses in detail in both the Institutions de Physique (chapter 15) and the commentary to her translation is Newton's arguments for his law of gravitation in the Principia. To date, however, no systematic comparison of the two has been undertaken (and very little has been said on either of them separately). I reconstruct and compare these two accounts. This offers a new perspective on Du Châtelet's developing thinking on the justification of Newton's law of gravitation within the Newtonian system.

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Week 6 (27/2): Rupert Smith (Bristol) - Scientific representation and the hole argument: Insights from a structuralist approach

Abstract: Recent trends in this literature can be broadly characterised by the way they begin either from the mathematics or the metaphysics. I take Weatherall (2018) as the primary example of the mathematical approach, in which he argues that if one is only to reflect on the correct use of the mathematics, one can block or undermine the hole argument. For the metaphysical approach, I focus on a line of argument I identify in Pooley and Read (2021) in which they claim that arguments from mathematical practice fail to eliminate the relevant space of metaphysical possibilities. Specifically, they maintain that the hole diffeomorphic manifolds can represent haecceitistically different spacetimes. In response to these trends, the primary aims of this research are twofold: first, I articulate a structuralist account of scientific representation, building on Van Fraassen's structuralist empiricism (2008), that answers the demarcation problems posed by Frigg and Nguyen (2022); second, I aim to use this account to diagnose the reasons for, and provide solutions to, the recent impasse in the voluminous literature on the hole argument. While I am sympathetic to the arguments from mathematical practice, I argue that without a structuralist account of scientific representation Pooley and Read’s counterargument cannot be defused. While I am conceding this point, however, I am doing so in a minimal way: no such representation can meet the criteria of being a scientific representation. Further, if the points p and p' in the hole argument are to represent different events in spacetime, it is merely by means of stipulation. If, as I argue, scientific representation is to be understood structurally, for a manifold to be considered a model of a spacetime, it needs to include a representation relation, understood as some variety of structural mapping. Moreover, an isomorphism acting on a model would also need to have a corresponding transformation on the representation relation, which is at least sensitive to the strongest notion of structure in the manifold being considered. I conclude that, while mathematical practice alone fails to exclude the possibility of the hole diffeomorphic models representing haecceitistic differences, a structuralist account of scientific representation excludes the possibility of these classifying as scientific representations.​

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Week 7 (6/3): Wessel Vinke (Oxford) - Is there a hole in the hole argument?

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Abstract: The hole argument can be interpreted as a problem for the substantivalist. Weatherall (2018) argues that this argument derives from an incorrect use of the formalism of general relativity. It is in essence a charge of equivocation against the hole argument, as Pooley and Read (2021) have called it. Here, I present two criticisms of Weatherall's account. Firstly, interpreting the term 'sameness' or 'equivalence' as being used in different senses is unfair to the original presentation of the hole argument. Secondly, Weatherall's objection depends on an unwarranted identification of the metaphysical issue at stake with the identity map in mathematical practice. (I may also be able to present an attempt at reconciliation with Weatherall's insight.)

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Week 8 (13/3): Margot Stakenborg (Oxford) - Notions of causality in physics

Abstract: This will be half presentation, half discussion about different notions of causality. I will go over the notions of what causality is in philosophic literature, statistical definitions of causality, and discuss whether a viable notion of causation exists in fundamental physics. Critics of fundamental causation, like Bertrand Russell, argue that fundamental physical laws are time-symmetric and describe correlations rather than causal mechanisms. They claim that causation is an emergent, high-level concept rather than an intrinsic feature of physical reality. This skepticism is supported by the time-reversal invariance of classical mechanics, quantum mechanics, and general relativity, which challenges the idea of a directional causal structure at a fundamental level. However, there are forms of time-directed processes in physics suggest a causal structure, like the cosmological arrow of time, entropy, or in the definition of initial conditions of systems. I will also discuss the interventionist account of causality, by Judea Pearl. I will add to this discussion that we can also use atemporal definitions of causality to describe certain phenomena, e.g. matter causes space-time to bend, which raises the question if causality, in principle, should be time-dependent if its definition can be broadened beyond temporal constraints. I would like to facilitate a discussion on what we deem to be correct notions of causality at the end.

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