Keynote speakers

Keynote speakers

Below is the list of all keynote speakers, as well as the abstracts as provided by them.

Gordon BELOT (University of Michigan, USA)

"Taking it to the limit"

Asymptotic boundary conditions and asymptotic symmetries play an important role in general relativity. As Penrose remarks, "it is only with asymptotic flatness that general relativity begins to relate in a clear way to many of the important aspects of the rest of physics, such as energy, momentum, radiation, etc." This talk will survey some of the conceptual oddities that arise in general relativity when asymptotic flatness is imposed at either spatial infinity or at null infinity: in both cases, each spacetime diffeomorphism can be viewed as a product of a gauge symmetry and a physical symmetry; in one case, the resulting group of physical symmetries is just the Poincaré group, in the other, an infinite-dimensional extension of that group; in recent years it has become clear that the ‘extra’ supertranslation symmetries that arise when asymptotic flatness is imposed at null infinity are directly related to potentially observable phenomena (the gravitational memory effect) and to subtleties surrounding soft gravitons.

Valeriya CHASOVA (Université catholique de Louvain, Belgium)

"What symmetries with DES look like and how gauge symmetries are useful for the DES" 

In the first part, I deduce what theoretical symmetries with direct empirical status (DES) look like from the requirement that they should be capable of representing empirical symmetries. This requirement implies in particular that the invariant observable dynamics and the differing observable features should be represented. I infer therefrom that a theoretical symmetry with DES, besides featuring a theoretical transformation of some variables, should also feature a couple of theoretical states consisting each of segments of solutions of the equations of motion or the field equations together with spatial distributions of values of the variables (to be) transformed. I argue for the extension of the global/local distinction to the latter component of theoretical states. I then use gauge symmetries in the second part of the talk to construct from a generic theoretical symmetry with global transformation and states, a generic theoretical symmetry with local transformation and states such that both symmetries are able to represent the same empirical symmetry. This illustrates the relevance of gauge symmetries to the DES (contra Greaves and Wallace [2014] and Teh [2016]) and allows to counter the argument (suggested by the reading of Ladyman and Presnell [manuscript January 2016]) according to which global symmetries should be used as the basis of our ontology because there can be empirical symmetries that are only representable by global and not by local symmetries. As far as the construction method that I describe works, global and local symmetries will always be on a par as to the DES, so the justification for the ontological privilege of global symmetries remains wanting.

Alexandre GUAY (Université catholique de Louvain, Belgium)

"Why gauge? Rovelli and Teh on electrodynamics"

This paper consists mainly in a discussion of Teh’s critique of Rovelli’s claim that gauge dependent quantities have a modal relational status, in particular in the context of electrodynamics. After assessing the critique and acknowledging some of its strengths, I will provide a better case study in the context of QED₂₊₁ applied to condensed matter physics. In this context, Rovelli’s claim seems more robust against Teh’s critique.

Richard HEALEY (University of Arizona, USA)

"A qualified defense of orthodoxy"

I call orthodoxy the view that while global gauge symmetries have direct empirical significance, their local counterparts do not. Greaves and Wallace have challenged this orthodoxy by developing an abstract framework for representing subsystem symmetries and applying it to argue that the localization of a subsystem global gauge symmetry inherits its direct empirical significance.

Friederich and Teh have each proposed further developments of Greaves and Wallace’s work, but arrived at contrary conclusions about the canonical instance of gauge symmetries of what the latter call Klein-Gordon-Maxwell electrodynamics.

I shall use this example as a starting point for an examination of several concepts that play important roles in the broader dispute, including subsystem, environment, direct empirical significance and symmetry itself. The examination will highlight the importance of looking beyond the mathematical models provided by a theory to what is involved in their physical application.

Suitably clarified and qualified, orthodoxy emerges unscathed from the challenge posed by Greaves and Wallace.

James LADYMAN (University of Bristol, UK)

"In what sense, if any, of 'direct empirical consequences' do local symmetries have them, and why does it matter, if at all?"

There is a tradition of saying that local symmetries in physics do not have direct empirical consequences (DEC). Greaves and Wallace argue that, in so far as this is to be understood in terms of there being a Galilean Ship Scenario (GSS), local symmetries do have DEC. Teh points out that in important cases global symmetries are not subgroups of local symmetries. This paper considers why it might be thought to matter whether local symmetries have DEC, and how symmetries in mathematics and physics relate, and whether the local versus global distinction can bear any epistemic or ontic weight. This paper argues that there are two notions of direct empirical consequence and that there is no point in wondering whether local symmetries have DEC in the weaker sense, and that Greaves and Wallace do not establish that they have DEC in the stronger sense. An analysis of GSS is given and examples are considered in relation to it. It is argued that whether or not there is a GSS cannot be used as a criterion for DEC in the stronger sense.

David WALLACE (University of Southern California, USA)

"On symmetry and observability"

Whether or not symmetry-related states of affairs are distinct, it is a commonplace that there is no observable difference between such states of affairs. But the reasons for this are somewhat elusive, leading some recent authors (notably Dasgupta) to propose building the unobservability of symmetry transformations into the definition of symmetry. I will present a fairly general argument as to why dynamical symmetries can be shown to be unobservable in at least a wide class of scenarios in classical and quantum mechanics.