**Event Categories:** BSPS Choice Group Conjectures and Refutations Popper Seminar Sigma Club

## Past Events › Sigma Club

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## Chrysovalantis Stergiou (The American College of Greece): “On Empirical Underdetermination of Physical Theories in C*Algebraic Setting”

Empirical underdetermination of physical theories by observational data lies at the heart of the debate over scientific realism. Antirealists of different strands contend that if observation cannot determine the state of a physical system then to talk about a uniquely defined state of the system is just a matter of convention. In the context of Algebraic Quantum Field Theory (AQFT) this stance is related to the claim that the physical topology of the state space is the weak*-topology and to what has become known as Algebraic Imperialism, the operationalist attitude which characterized the first steps of the theory. Aristidis Arageorgis (1995) devised a mathematical argument against empirical underdetermination of the state of a system in C*-algebraic setting which rests on two topological properties of the state space: being T1 and being first countable in the weak*-topology. The first property is possessed trivially by the state space while the latter is highly non-trivial and it can be derived from the assumption that the algebra of observables is separable.

In this talk we will reconstruct Arageorgis’ argument and examine its soundness with regard to the separability of the algebra of observables. We will show that separability is related to two factors: (a) the dimension of the algebra, considered as a vector space; (b) whether it is a C*- or von Neumann algebra. Finite-dimensional C*-algebras and von Neumann algebras are separable, infinite-dimensional von Neumann algebras are non-separable and infinite-dimensional C*-algebras can be separable. These considerations will be discussed with reference to classical systems of N particles, the Heisenberg model for ferromagnetism, the Haag-Araki formulation of AQFT and a separable reformulation of AQFT in Minkowski spacetime suggested by Porrmann (1999, 2004).

This talk is dedicated to the memory of my beloved teacher, colleague and friend Aris Arageorgis who untimely passed away in 2018.

Find out more »## Neil Dewar (Munich): “On Absolute Units”

What is the best way to characterise the intrinsic structure of physical quantities? Field’s program shows one approach (that also delivers a nominalist treatment of such quantities); in this talk, I outline how group-theoretic methods can deliver a somewhat simpler, although non-nominalist, way of doing this for scalar and vector quantities. I go on to develop a theory on how such quantities can be algebraically combined, and use this to develop a simple intrinsic treatment of Newtonian gravitation. Finally, I argue that this treatment illuminates a “third way” in the debate over absolutism and comparativism about quantities: namely, a form of anti-quidditist absolutism.

Find out more »## Miklós Rédei (LSE): “On the Tension Between Physics and Mathematics”

Because of the complex interdependence of physics and mathematics their relation is not free of tensions. The talk looks at how the tension has been perceived and articulated by some physicists, mathematicians and mathematical physicists. Some sources of the tension are identified and it is claimed that the tension is both natural and fruitful for both physics and mathematics. An attempt is made to explain why mathematical precision is typically not welcome in physics.

Find out more »## Emily Adlam (Cambridge): “Generalized Probabilistic Theories as Structural Realism”

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.

Find out more »## John Dougherty (LMU): “I ain’t afraid of no ghost”

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.

Find out more »## Patricia Palacios (Salzburg): “The Paradox of Infinite Limits: A Realist Response”

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.

Find out more »## James Wills (LSE): “Classical Particle Indistinguishability, Precisely.”

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’.

Find out more »## Samuel Fletcher (Minnesota): “The Principle of Stability”

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.

Find out more »## Dennis Dieks (Utrecht): “Identical quantum particles as distinguishable objects”

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.

Find out more »## Margherita Harris (LSE): “Model Robustness: Schupbach’s Explanatory Account of Robustness Analysis to the Rescue?”

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.

Find out more »## Jacob Barandes (Harvard): “A New Critical Analysis of Everettian Quantum Theory”

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.

Find out more »## Harvey Brown (Oxford) Sigma Club: What justifies the common claim that symmetries explain conservation principles?

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…

Find out more »## Lucy James (Lancaster) Sigma Club, Naturalised Metaphysics: The Case of Separability

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…

Find out more »## Nick Huggett (U of Illinois, Chicago) Sigma Club: Quantum gravity in a laboratory

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…

Find out more »## Caspar Jacobs (Merton College): How (Not) to Define Inertial Frames

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…

Find out more »## Tushar Menon (University of Cambridge): ‘Inferential Scientific Realism’

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…

Find out more »## Kiki Timmermans (King’s College London) Sigma Club: Analogies and Frameworks in Quantum Field 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: 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)…

Find out more »## Bryan W Roberts (LSE): ‘Is there a problem of thermodynamic irreversibility?’

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…

Find out more »## Alexander Franklin (KCL): ‘Weather Probabilities are Ontic and Objective’

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…

Find out more »## Gábor Hofer-Szabó (Hungarian Academy of Sciences): ‘Operational equivalence and causal structure’

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…

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