## 2014-2015

6 June 2015, 3pm, SST 777

**Nora Boyd (Pittsburgh), “Are Astrophysical Models Permanently Underdetermined?”**

Abstract: Transient underdetermination is germane to scientific practice; modelers often elaborate multiple plausible alternatives to a scientific problem and then seek empirical constraints on these models. In contrast, permanent underdetermination undercuts the aim of increasing the representational fidelity of models. Renewing pessimism that Ian Hacking raised specifically regarding modeling in astrophysics, Stéphanie Ruphy has recently argued that the field is destined to produce nothing more than permanently underdetermined models. The present paper defends astrophysics against this charge. I argue that modelers can anticipate that underdetermination will be transient when distinguishing features can be extracted from the competing alternatives, differential empirical evidence can likely be collected, and model features can be evaluated in light of such evidence. The prospects for breaking instances of purported underdetermination should be individually appraised according to this framework and considered in their appropriate scientific contexts. Applying this approach I evaluate Ruphy’s case study, challenging her claim that the features she attributes to alternative models of our galaxy are characteristic of the field. I present a further example involving two currently underdetermined models of the instability driving explosions in core-collapse supernovae. Here, astrophysicists have good reason to think that forthcoming data will discriminate between the models. This case, I argue, is similar to other prominent examples of underdetermination in representation-driven astrophysical modeling. There is good reason to expect that in many cases the underdetermination of astrophysical models is only temporary.

Please read Nora’s paper before the meeting.

25 April 2015, 3pm, SST 777

**Christian Wüthrich (UCSD), “Spacetime from Causal Sets”**

Abstract: I will illustrate how space and time vanish in causal set theory and address the central question of this research program, viz. how relativistic spacetimes re-emerge from the fundamental causal sets. Part of what I plan to talk about is covered in Section 3 of the attendant paper, which is a draft of Chapter 3 of my forthcoming book with Nick Huggett; the rest will be treated in what will be Chapter 4. Sections 1 and 2 of the paper can be read as a preparation for those who are not familiar with causal set theory, but I do not plan to discuss them in the meeting.

Please read Chris’ paper before the meeting.

11 April 2015, 3pm, SST 777

**Sybil de Clark (Arizona), “Fluctuations of the Electromagnetic Vacuum Field or radiation reaction?”**

Abstract: The fact that various physical effects usually ascribed to vacuum fluctuations can also be accounted for by the radiation reaction field suggests that perhaps, there is little evidence for vacuum field fluctuations. But is that so? Where does the underdetermination between vacuum field and radiation reaction field come from, and what can be proposed to lift it? What other evidence do we have that the vacuum field is at least partly responsible for these effects? Furthermore, vacuum fluctuations have been ascribed to the Uncertainty Relations (UR). To what extent are such claims justified, and what interpretation of the UR do vacuum fluctuations suggest?

Please read Sybil’s paper before the meeting. If the length is a concern, she suggests focusing on sections 3, 4, 5.1, and 5.2

28 February 2015, 3pm, SBSG 1321

**Ben Feintzeig (UCI) on Parochial Observables in Classical and Quantum Field Theory**

Abstract: Ruetsche (2011) argues that there is a problem of unitarily inequivalent representations in quantum theories with infinitely many degrees of freedom that leads one to choose between the following interpretive options. Either one can be a Hilbert Space Conservative and maintain that possible worlds correspond to density operators on a particular privileged Hilbert space containing a concrete irreducible representation of the algebra of observables. Or one can be an Algebraic Imperialist and hold that possible worlds are represented by the states on the abstract C*-algebra of observables, which captures the structure all representations have in common.

I will argue for a position along the lines of Algebraic Imperialism (but differing somewhat from Ruetsche’s description of that position). First, I show that unitarily inequivalent representations arise already in classical theories. It is obvious in the classical case that a Hilbert Space Conservative fails to represent all physically significant states, and this argument extends in a natural way to the quantum case. Second, I show that Ruetsche’s argument against Algebraic Imperialism, which claims that the Imperialist cannot represent all physically significant observables, fails. I show that the Imperialist can account for all of the missing observables as idealizations (in a certain precise sense) from the original abstract algebra of observables.

Please read Ben’s papers “Unitary Inequivalence, Classical Systems, and the Interpretation of Quantum Theories” and “Toward an Understanding of Parochial Observables” before the meeting.

10 January 2015, 3pm, LPS seminar room

**Casey McCoy (UCSD), “What is the Horizon Problem?”**

Abstract: Cosmological inflation is widely considered an integral and empirically successful component of contemporary cosmology. It was originally motivated by its solution of certain fine-tuning problems of the hot big bang model, particularly what are known as the horizon problem and the flatness problem. Although the physics behind these problems is clear enough, it is unclear precisely what about them is problematic, and therefore precisely which problems inflationary theory is solving. I analyze the structure of these problems, showing how they depend on explicating the sense in which flatness and uniformity are special in the hot big bang model, and the sense in which such special conditions are problematic (in cosmology). I claim that there is no un-problematic interpretation of either problem available whose solution could explain the putative empirical success of inflationary theory. Thus either a new interpretation of such fine-tuning problems is needed, or else an alternate explanation of the theory’s success that does not depend on solving these problems.

Please read Casey’s preprint before the meeting. (Casey apologizes for the length!)

6 December 2014, 3pm, LPS seminar room

**Tom Pashby (USC), “On Meyer’s The Nature of Time: Tense Primitivism, Relationism, and Physics”**

Abstract: In Ulrich Meyer’s recent monograph The Nature of Time (OUP, 2013) he proposes a novel metaphysics of time based on his work in tense logic, which he calls a ‘modal’ theory of time (due to close analogies with modal logic). Meyer claims that we should be tense primitivists, who claim that truths about the world come irreducibly tensed. I motivate this view by situating it in a tradition that includes Kant and van Fraassen (1970) and contend that Meyer’s modal theory of time can be seen as an attempt to avoid the relativized (or contingent) a priori status accorded to time by van Fraassen. To reconcile his view with special relativity Meyer argues that Minkowski’s union of space and time still leaves room to combine alternative metaphysical theories of time and space—hybrid views. According to Meyer, it is perfectly consistent to be a substantivalist about spatial points while being a relationist about instants of time. This conflicts, I claim, with a recent minority consensus in the philosophy of physics which regards temporally related events in special relativity as having an invariant partial order rather than multiple conflicting total orderings into instants. I also complain that general relativity provides further reasons to be skeptical of Meyer’s project, which accords to temporal instants a primary role. As well as positive arguments for his own view of time, Meyer also provides a novel argument against temporal relationism, a direct competitor. I point out that this argument fails to apply to its intended target, Bertrand Russell, and show how Russell’s attempted relationist account of relativistic space-times can be completed, which, I claim, leaves temporal relationism in a better position with respect to modern physics than tense primitivism.

Tom will post a pre-print closer to the meeting date.

1 November 2014, 3pm, LPS seminar room

**Sarita Rosenstock (UC Irvine) and James Weatherall (UC Irvine) on Interpretations of Yang-Mills Theory (part 1)**

Abstract: We will discuss some topics related to the interpretation of classical Yang-Mills theory. First we will describe a way of thinking about Yang-Mills theory that is motivated by a geometrical understanding of general relativity. This will count as a, broadly speaking, “fiber bundle” interpretation of the theory.

Please read Jim’s paper “Fiber Bundles, Yang-Mills Theory, and General Relativity” before the meeting.