Sigma Club

In the field of quantum foundations there is a thriving research programme which involves placing quantum mechanics in a wider space of operationally defined theories in order to gain insight into its structure. There are various existing philosophical analyses of this research framework, but most have a strongly instrumentalist flavour. In this talk, I will argue that this sort of research can alternatively be understood as an implementation of structural realism, with the counterfactual features of the GPT framework encoding information about modal structure. I present a formal approach to the analysis of modal structure in the GPt framework, and demonstrate that structural realism offers new insight into the scientific value of this research and its consequences for future research programmes.

This paper criticizes the traditional philosophical account of the quantization of gauge theories and offers an alternative. On the received view, gauge theories resist quantization because they feature distinct mathematical representatives of the same physical state of affairs. This resistance is overcome by a sequence of ad hoc modifications, justified in part by reference to semiclassical electrodynamics. Among other things, these modifications introduce “ghosts”: particles with apparently unphysical properties which do not appear in asymptotic states and which are said to be purely a notational convenience. I argue that this sequence of modifications is unjustified and inadequate, making it a poor basis for the interpretation of ghosts. I then argue that gauge theories can be quantized by the same method as any other theory. On this account, ghosts are not purely notation: they are coordinates on the classical configuration space of the theory—specifically, on its gauge structure. This interpretation does not fall prey to the standard philosophical arguments against the significance of ghosts, due to Weingard. Weingard’s argumentative strategy, properly applied, in fact tells in favor of ghosts’ physical significance.

In this talk, we distinguish between different uses of mathematical limits in physics, and we determine the conditions under which an infinite limit should be understood as giving rise to an “infinite idealization”, intended as a misrepresentation of the target system by way of introducing an infinite system. We point out that when infinite limits are used as infinite idealizations they can lead one to the Paradox of Infinite Limits, which allegedly poses a threat to scientific realism. In particular, this depends on whether the idealization is essential for the explanation of the physical phenomenon under investigation. Instead, other uses of infinite limits such as approximations and abstractions do not raise any substantial problem for scientific realism. We also argue that, even in the case of “essential idealizations”, there are ways of coping with the alleged incompatibility between infinite idealizations and scientific realism, which ultimately rely on empirical considerations.

I present an analysis of classical particle indistinguishability as ‘observational indistinguishability’ in a certain mathematically precise sense. I will argue that this leads to three interesting and welcome consequences in the foundations of statistical mechanics: (1) The identification and resolution of shortcomings in the ongoing debate concerning the solution to the N! problem: the problem in statistical mechanics of justifying the inclusion of a factor N! in a probability distribution over the phase space of N indistinguishable classical particles. (2) A reinterpretation of the quotienting procedure typically used to justify the N! term and a rigorous derivation of the N! factor which does not appeal to the metaphysics of particles and which rather draws only on facts about observables. (3) A reconstruction of Gibbs' own argument as a special case of my analysis in which particles are observationally indistinguishable with respect to the Hamiltonian. I call this ‘dynamical indistinguishability’.

How can inferences from idealized models to the phenomena they represent be justified when those models deliberately distort the phenomena? Pierre Duhem considered just this problem, arguing that inferences and explanations from mathematical models of phenomena to real physical applications must also be demonstrated to be approximately correct when the (idealized) assumptions of the model are only approximately true. Despite being little discussed among philosophers, mathematicians and physicists both contemporaneous with and subsequent to Duhem took up this challenge (if only sometimes implicitly), yielding a novel and rich mathematical theory of stability with epistemological consequences.

Particles in classical physics are individuals that can be distinguished by identifying physical properties. By contrast, in quantum mechanics the “received view” is that particles of the same kind (``identical particles'') cannot be distinguished in this way. This standard view is problematic, though: not only is it at odds with the very meaning of the term ``particle'' in ordinary language, it also conflicts with how the term “particle” is actually used in the practice of present-day physics. Moreover, the indistinguishability doctrine prevents a smooth transition from quantum to classical particles (in the classical limit). We will discuss an alternative to the standard view that avoids these and similar problems. According to this proposed analysis, a particle picture is not always appropriate to represent what is usually called an “identical particle system”; but when such a picture is applicable, identical quantum particles are distinguishable no less than classical particles. As it turns out, this alternative approach connects to recent discussions concerning the question of when identical particle states should be considered to be entangled.

In science, obtaining a "robust" result is often seen as providing further support for a hypothesis. The Bayesian should have something to say about the logic underpinning this method of confirmation. Schupbach's recent explanatory account (2018) of robustness analysis (RA) is a welcome attempt to do so. Indeed, by having 'as its central notions explanation and elimination' (ibid., 286), this account seems to fit very nicely with many empirically driven cases of RA in science, thereby revealing why these cases are able to lend confirmation to a hypothesis. The subject of this talk, however, is Schupbach's further claim that his account of RA 'applies to model-based RAs just as well as it does to empirically driven RAs' (ibid. 297), since when we arrive at this claim, he and I decisively part ways. I will argue that the application of Schupbach's account to model-based RAs is considerably more complicated than he and others (such as Winsberg (2018)) suggest and relies on several non-trivial and often dubious assumptions. By making these assumptions explicit, I will show that Schupbach’s account of RA is inapplicable to many cases of model-based RA’s, contrary to what has been assumed in the literature.

In this talk, I'll review and expand on several problems faced by various forms of Everettian quantum theory, known more familiarly as many-worlds interpretations. I'll also introduce and discuss some new criticisms, one of which potentially applies to many-worlds interpretations in general, and another that's relevant to certain minimalist versions of Everettian quantum theory.

This will be a hybrid lecture: you can attend in person in our usual LAK 2.06 seminar room, or on Zoom:  Join On Zoom Meeting ID: 852 3006 9457 Passcode: 297258 ABSTRACT: It is widely claimed by physicists that symmetries have explanatory priority when it comes to the link between them and conservation principles. In the literature on Noether's first…

This will be a hybrid lecture: you can attend in person in our usual LAK 2.06 seminar room, or on Zoom:  Join On Zoom Meeting ID: 852 3006 9457 Passcode: 297258 Abstract: This talk begins with a review of the central tenets of the naturalised metaphysics of Ladyman and Ross, with particular emphasis on the negative role of intuition, and…

This will be a hybrid lecture: you can attend in person in our usual LAK 2.06 seminar room, or on Zoom:  Join On Zoom Meeting ID: 852 3006 9457 Passcode: 297258 ABSTRACT: The characteristic – Planck – energy scale of quantum gravity is utterly beyond current technology, making experimental access to the relevant physics apparently impossible. Nevertheless, low energy experiments…

This will be a hybrid lecture: you can attend in person in our usual LAK 2.06 seminar room, or on Zoom:  Join On Zoom Meeting ID: 852 3006 9457 Passcode: 297258 Abstract: It is nearly impossible to open a textbook on Newtonian mechanics without encountering the concept of inertial frames: frames which are uniquely privileged by the theory's dynamics. In…

This will be a hybrid lecture: you can attend in person in our usual LAK 2.06 seminar room, or on Zoom:  Join On Zoom Meeting ID: 852 3006 9457 Passcode: 297258 Abstract: A key scientific realist commitment is that at least some scientific expressions correspond to unobservable entities or structures out there in the world. This is usually cashed out as…

This will be a hybrid lecture: you can attend in person in our usual LAK 2.06 seminar room, or on Zoom:  Join On Zoom Meeting ID: 852 3006 9457 Passcode: 297258 Abstract: In the philosophy of quantum field theory (QFT) it is common to analyse questions concerning the interpretation of theoretical structure appearing in both high energy particle physics (HEP)…

This will be a hybrid lecture: you can attend in person in our usual LAK 2.06 seminar room, or on Zoom:  Join On Zoom Meeting ID: 852 3006 9457 Passcode: 297258 Title: Is there a problem of thermodynamic irreversibility? Abstract: No. The talk is based on this paper, and is a follow-up on Chapter 6 of Bryan's recent book Reversing…

This will be a hybrid lecture: you can attend in person in our usual LAK 2.06 seminar room, or on Zoom:  Join On Zoom Meeting ID: 852 3006 9457 Passcode: 297258 Title: Weather Probabilities are Ontic and Objective Abstract: In this talk I argue that at least some of the probabilities used to describe the weather are both ontic and…

This will be a hybrid lecture: you can attend in person in our usual LAK 2.06 seminar room, or on Zoom:  Join On Zoom Meeting ID: 852 3006 9457 Passcode: 297258 Abstract: In this talk, I will explore some consequences of abandoning operational equivalence in quantum mechanics. Two measurements are operationally equivalent if they yield the same distribution of outcomes…