- Adam Caulton (Oxford)
- Niels Linnemann (Bremen)
- Michael Townsen Hicks (Birmingham)
- Marc Lange (University of North Carolina, Chapel Hill)
1000-1115: “Are Particles Characterised by a Symmetry Group? If So, Which One?” Adam Caulton, University of Oxford
Abstract: Ever since investigations into the group representation theory of spacetime symmetries, chiefly due to Wigner and Bargmann in the 1930s and ‘40s, it has become something of a mantra in particle physics that a particle is an irreducible representation of the Poincaré group (the symmetry group of Minkowski spacetime). Call this ‘Wigner’s identification’. One may ask, in a philosophical spirit, whether Wigner’s identification could serve as something like a real definition (as opposed to a nominal definition) of ‘particle’—at least for the purposes of relativistic quantum field theory. In this talk, I aim to show that, while Wigner’s identification is materially adequate for many purposes—principally scattering theory—it does not provide a serviceable definition. The main problem, or so I shall argue, is that the regime of legitimate particle talk surpasses the constraints put on it by Wigner’s identification. I aim further to show that, at least in the case of particles with mass, a promising rival definition is available. This promising rival emerges from investigations due to Foldy in the 1950s, which I will outline. The broad upshot is that the definition of ‘particle’ may well be the same in both the relativistic and non-relativistic contexts, and draws upon not the Poincaré group (or any other spacetime symmetry group) but rather the familiar Heisenberg relations.
1115-1230: “On Metaphysically Necessary Laws from Physics.” Niels Linnemann, University of Bremen
Abstract: How does metaphysical necessity relate to the modal force often associated with natural laws (natural necessity)? Fine (2002) argues that natural necessity can neither be obtained from metaphysical necessity via forms of restriction nor of relativization — and therefore pleads for modal pluralism concerning natural and metaphysical necessity. Wolff (2013) aims at providing illustrative examples in support of applying Fine’s view to the laws of nature with specific recourse to the laws of physics: On the one hand, Wolff takes it that equations of motion can count as examples of physical laws that are only naturally but not metaphysically necessary. On the other hand, Wolff argues that a certain conservation law obtainable via Noether’s second theorem is an instance of a metaphysically necessary physical law. I show how Wolff’s example for a putatively metaphysically necessary conservation law fails but argue that so-called topological currents can nevertheless count as metaphysically necessary conservation laws carrying physical content. I conclude with a remark on employing physics to answer questions in metaphysics.
1400-1515: “Are Symmetry Explanations Grounding Explanations?” Mike Hicks, University of Birmingham. PowerPoint Slides
Abstract: I aim to show that there are two sorts of symmetry explanations that are plausibly regarded as grounding explanations. The first is the explanation of symmetry principles in terms of spacetime or property structure. I will argue that symmetry principles, which are constraints on the laws, are plausibly grounded in spacetime structure. The second is the explanation of conservation laws via symmetry principles. I will argue that symmetry principles ground conservation laws.
1530-1700: “What Was the ‘Great Advance’ of 20th-Century Physics that ‘Put Symmetry First’?” Marc Lange, UNC Chapel Hill
Abstract: I will characterize the difference between the way that symmetry principles and conservation laws were generally understood before and after the great revolutions of early 20th-century physics. I will elaborate this difference in terms of explanatory priority, modal status, and counterfactual resilience. Any account of natural law, natural necessity, and scientific explanation should leave room for symmetry principles and conservation laws to play either their pre-revolutionary role or their post-revolutionary role.