## 2016-2017

29 April 2017, 3pm, LPS seminar room

**Jeff Russell (USC), “Space-Time Categories”**

Suppose we take seriously this lesson from the hole argument: there is no genuine difference between possible worlds related by a space-time diffeomorphism. In that case, what should we think the world’s genuine space-time structure is like? It won’t include facts about field-values at particular points in a manifold. Instead what we would like is a precise account of “structural roles” for things like fields in space-time. Ideas from categorical logic give us the resources to spell out such an account.

There are no readings for this meeting.

8 April 2017, 3pm, LPS seminar room

**Sean Carroll (Caltech), “Spacetime and Cosmology in Locally-Finite Hilbert Space”**

I will discuss some ideas stemming from two basic assumptions: (1) Quantum mechanics is Everettian, and there is no preferred structure on Hilbert space, only what we can derive from dynamical considerations; and (2) Hilbert space is locally finite-dimensional, i.e. regions of space are described by finite-dimensional factors. We are faced with the question of how not only quantum fields, but even space itself, emerge from the wave function, and I’ll describe some ideas in that direction, as well as some cosmological consequences.

Sean’s talk is not based on a particular paper, but he recommends these three papers (in order of decreasing readability) as background.

11 March 2017, 3pm, LPS seminar room

**Márton Gömöri (Eötvös University), “On the relation of the relativity principle and covariance”**

In its most widespread formulation, the special principle of relativity is the following statement: “The laws of physics have the same form in all inertial frames of reference.” While there is a longstanding discussion about the interpretation of the extended, general principle of relativity and its relation to the notion of general covariance, there seems to be a consensus that the above quoted special principle of relativity is absolutely unproblematic, and it is synonymous with the Lorentz covariance of the fundamental equations of physics. The talk will challenge this view through an analysis of the precise meaning of the special relativity principle, based on a precise mathematical formulation of its statement. It will be seen however that the main difficulties are not of formal/mathematical nature, but conceptual.

Please read Márton’s paper before the meeting.

25 February 2017, 3pm, LPS seminar room

**Neil Dewar (MCMP), ” Interpretation and equivalence; or, equivalence and interpretation
“**

This paper is about what it means to interpret a scientific theory (especially, a physical theory). My main contention is that a certain picture of interpretation is widespread (though implicit) in contemporary philosophy of science: a picture according to which interpretation of theories is relevantly analogous to the interpretation of foreign literature. On this “external” account of interpretation, meaning is to be imported into the equations by putting them in correspondence with some discourse whose signs and symbols are already endowed with significance. I contend that there is an alternative way of thinking about interpretation—what we can call the “internal” account of interpretation—which instead takes interpretation to be a matter of delineating a theory’s internal semantic architecture. At a minimum, I hope to show that the internal picture highlights an aspect of interpretation that we are otherwise at risk of neglecting. But I also aim to show that the internal picture offers a richer and more satisfying account of interpretation than the external picture does.

21 January 2017, 3pm, LPS seminar room

**David Wallace (USC), “Who’s afraid of coordinate systems? An essay in the representation of spacetime structure”**

Coordinate-based approaches to physical theories remain standard in mainstream physics but are largely eschewed in foundational discussion in favour of coordinate-free differential-geometric approaches. I defend the conceptual and mathematical legitimacy of the coordinate-based approach for foundational work. In doing so, I provide an account of the Kleinian conception of geometry as a theory of invariance under symmetry groups; I argue that this conception continues to play a very substantial role in contemporary mathematical physics and indeed that supposedly “coordinate-free” differential geometry relies centrally on this conception of geometry. I discuss some foundational and pedagogical advantages of the coordinate-based formulation and briefly connect it to some remarks of Norton on the historical development of geometry in physics during the establishment of the general theory of relativity.

Please read David’s manuscript before the meeting.

3 December 2016, 3pm, LPS seminar room

**Mike Schneider (UCI), on the cosmology constant problem**

This paper contends that the “Cosmological Constant Problem” (CCP) is not strictly a problem for our current theories, and so the proposed “solutions” to it cannot be solutions as such. Nonetheless, the CCP is consistently entertained as if it were a problem with a landscape of possible solutions. Given this state of affairs, I discuss how one ought to make sense of the role of the CCP in contemporary theoretical physics and generalize some lessons from it.

Please read Mike’s draft manuscript before the meeting.

15 October 2016, 3pm, LPS seminar room

**John Dougherty and Craig Callender (UCSD), on black hole thermodynamics**

Black hole thermodynamics (BHT) understands many relationships amongst black hole variables as manifestations of deep thermodynamic principles operating in the universe. BHT is widely accepted as being more than a formal analogy with thermodynamics; indeed, its identity with thermodynamics is commonly used as justification for many speculations in quantum gravity. Playing the role of philosophical gadfly, we want to pour a little cold water on the claim that BHT is more than a formal analogy. To do so, we show that BHT is often based on a kind of caricature of thermodynamics. Then we point to an important ambiguity in what systems the analogy is supposed to be between. Finally, and perhaps worst, we point out that one of the primary motivations for the theory arises from a terribly controversial understanding of entropy. BHT may be a useful guide to future physics. Only time will tell. But the analogy is not nearly as good as is commonly supposed.

Please read John and Craig’s manuscript before the meeting.