11 February 2023

**Laura Ruetsche (Michigan), “Unborn Again: Probability in Bohmian Mechanics”**

Why are quantum probabilities encoded in measures corresponding to wave functions, rather than by a more general class of measures? Call this question *Why Born?*. Orthodox quantum mechanics has a compelling answer to *Why Born?*, I argue, but Bohmian mechanics might not. I trace Bohmian difficulties with *Why Born?* to its *antistructuralism*, its denial of physical significance to the algebraic structure of quantum observables, and propose other cases where Bohmian antistructuralism might have an explanatory cost.

If you would like to read more in advance, there are short and long versions of the manuscript available.

Past talks

14 January 2023

**Alex Franklin (Kings College London), “Incoherent? No, Just Decoherent: How Quantum Many Worlds Emerge**“

The modern Everett interpretation of quantum mechanics describes an emergent multiverse. The goal of this talk is to offer a perspicuous characterisation of how the multiverse emerges making use of a recent account of (weak) ontological emergence. This will be cashed out with a case study that identifies decoherence as the mechanism for emergence. The greater metaphysical clarity enables the rebuttal of a critique by Dawid and Thébault (2015) that casts the emergent multiverse ontology as incoherent; responses are also offered to challenges to the Everettian approach from Maudlin (2010) and Monton (2013).

3 December 2022:

**Ricardo Karam (Copenhagen), “Historical episodes of the complexification of physics“**

Complex numbers were invented (or discovered?) byItalian mathematicians in the 16th century as pragmatic tools to solve cubicequations, and not much attention was given to questions related to their “existence”.However, this changed significantly in the end of the 18th century, whencomplex numbers were given a geometrical interpretation. Such concretizationmotivated physicists to use these numbers to model all kinds of phenomena, aprocess that has been called “complexification of physics” by Salomon Bochner.The talk will present different historical episodes of the complexification, highlighting, in each case, how and why complex numbers became useful to physicists.

29 October 2022:

**Jingyi Wu (UC Irvine), “Explaining Universality: Infinite Limit Systems in the Renormalization Group Method”**

I analyze the role of infinite idealizations used in the renormalization group (RG hereafter) method in explaining universality across microscopically different physical systems in critical phenomena. I argue that despite the reference to infinite limit systems such as systems with infinite correlation lengths during the RG process, the key to explaining universality in critical phenomena need not involve infinite limit systems. I develop my argument by introducing what I regard as the explanatorily relevant property in RG explanations: the linearization* property; I then motivate and prove a proposition about the linearization property in support of my view. As a result, infinite limit systems in RG explanations are dispensable.

If you would like to read Jingyi’s paper in advance, it is available here.

]]>The ontological models framework distinguishes ψ-ontic from ψ-epistemic wave- functions. It is, in general, quite straightforward to categorize the wave-function of a certain quantum theory. Nevertheless, there has been a debate about the ontological status of the wave-function in the statistical interpretation of quantum mechanics: is it ψ-epistemic and incomplete or ψ-ontic and complete? I will argue that the wave- function in this interpretation is best regarded as ψ-ontic and incomplete. Furthermore, I will show that the probabilities in the statistical interpretation also point to the incompleteness of the theory if construed as hypothetical frequencies.

2 April 2022:

**Mahmoud Jalloh (USC), “The Π-Theorem as a Guide to Quantity Symmetries and the Argument Against Absolutism”**

In this paper a symmetry argument against quantity absolutism is amended. Rather than arguing against the fundamentality of intrinsic quantities on the basis of transformations of basic quantities, e.g. mass doubling, a class of symmetries defined by the Π-theorem is used. This theorem is a fundamental result of dimensional analysis and shows that all unit-invariant equations which adequately represent physical systems can be put into the form of a function of dimensionless quantities. Quantity transformations that leave those dimensionless quantities invariant are empirical and dynamical symmetries. The proposed symmetries of the original argument are open to counterexamples which show that they fail to be both dynamical and empirical symmetries. The amendment of the original argument requires consideration of the relationships between quantity dimensions, particularly the constraint of dimensional homogeneity on our physical equations. The discussion raises a pertinent issue: what is the modal status of the constants of nature which figure in the laws? Two positions, constant necessitism and constant contingentism, are introduced and their relationships to absolutism and comparativism undergo preliminary investigation. It is argued that the absolutist can only reject the amended symmetry argument by accepting constant necessitism, which has a costly outcome: unit transformations are no longer symmetries.

12 February 2022

**Porter Williams (USC), “The Aim and Structure of Cluster Decomposition”**

In the architecture of quantum field theory, one finds a handful of load-bearing locality or causality conditions. One of the most important is the cluster decomposition property: roughly speaking, a property intended to capture the fact that the outcome of experiments at Fermilab is independent of whatever might be happening in the accelerator tunnel at SLAC. Steven Weinberg went so far as to call it a foundational requirement of all experimental science. However, the satisfaction of cluster decomposition in quantum field theory is subtle: the mathematical statement of the principle is evidently incompatible with quantum entanglement. Nevertheless, I will ultimately conclude that something very much like Weinberg’s transcendental-ish claim is probably correct, but to get there will require disentangling the aim of the cluster decomposition property from its formal structure and elucidating a delicate relationship between the cluster decomposition property and the ubiquity of entanglement in quantum field theory.

11 December 2021

**Eddy Keming Chen (UC San Diego)**, “**The Wentaculus: Density Matrix Realism Meets the Arrow of Time**“

Two of the most difficult problems in the foundations of physics are (1) what gives rise to the arrow of time and (2) what the ontology of quantum mechanics is. They are difficult because the fundamental dynamical laws of physics do not pick out an arrow of time, and the quantum-mechanical wave function describes a high-dimensional reality that is dramatically different from the objects of our ordinary experiences. In this talk, I propose a unified solution by adopting a new theory of time’s arrow in a quantum universe—the Wentaculus [1-3]. Central to my solution are (i) Density Matrix Realism, the idea that the quantum state of the universe is objective but impure, and (ii) the Initial Projection Hypothesis, a new candidate law of nature that selects a unique initial quantum state. On the Wentaculus, the initial quantum state of the universe is sufficiently simple to be a law, and the arrow of time can be traced back to an exact boundary condition. As a bonus, we can use the theory to realize “strong determinism” as defined by Penrose [6] and remove the “fundamental nomic vagueness” of the Past Hypothesis as defined by Chen [4]. I end with some open problems for future research.

The presentation will be self-contained, but here are some optional background readings for those interested:

[1] Chen, E.K., Quantum Mechanics in a Time-Asymmetric Universe: On the Nature of the Initial Quantum State*The British Journal for the Philosophy of Science*, 2018

[2] Chen, E.K., Time’s Arrow in a Quantum Universe: On the Status of Statistical Mechanical Probabilities in Valia Allori (ed.), *Statistical Mechanics and Scientific Explanation: Determinism, Indeterminism and Laws of Nature*, World Scientific, 2020

[3] Chen, E.K., From Time Asymmetry to Quantum Entanglement: The Humean Unification*Noûs*, 2020

[4] Chen, E.K., Fundamental Nomic Vagueness*The Philosophical Review*, forthcoming

[5] Chen, E.K., The Past Hypothesis and the Nature of Physical Laws in Barry Loewer, Eric Winsberg, and Brad Weslake (eds.), *Time’s Arrows and the Probability Structure of the World*, Harvard University Press, forthcoming

[6] Penrose, R. *The Emperor’s New Mind: Concerning Computers, Minds and The Laws of Physics*, Oxford University Press, 1989, p.560 [Oxford Scholarship Online]

6 November 2021, 3pm, 777 Social Science Tower, UC Irvine

**Chip** **Sebens (Caltech), “The Fundamentality of Fields”**

There is debate as to whether quantum field theory is, at bottom, a quantum theory of fields or particles. One can take a field approach to the theory, using wave functionals over field configurations, or a particle approach, using wave functions over particle configurations. This article argues for a field approach, presenting three advantages over a particle approach: (1) photons cannot be treated as particles, (2) a classical field model of the electron is superior to a classical particle model (as regards both spin and self-interaction), and (3) field wave functionals can be used for interacting theories whereas particle wave functions cannot. The article also describes three tasks facing proponents of a field approach: (1) legitimize or excise the use of Grassmann numbers for fermionic field values and wave functional amplitudes, (2) describe how quantum fields give rise to particle-like behavior, and (3) explain the absence of electron self-repulsion in quantum electrodynamics.

Please read Chip’s paper prior to the talk.

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5 June 2021, 3pm, Via Zoom (link shared by email)

**Adam Koberinski (Waterloo / Bonn), “Lambda and the limits of effective field theory”****Abstract:** The cosmological constant problem stems from treating a semiclassical merger of quantum field theory and general relativity as an effective field theory. We argue that the problem is best understood as a *reductio ad absurdum*, and that one should reject the assumption that general relativity can generically be treated as an effective field theory. In this paper we make explicit the sensitive dependence of the cosmological constant Lambda on high-energy physics, and outline the assumptions behind naturalness and the effective field theory framework. We show that these assumptions are violated in general relativistic domains where Lambda is relevant, so one should not expect effective field theory methods to apply. We argue that the failure of naturalness signalled by the cosmological constant problem is not a deep problem for the future of physics, and highlight some current “unnatural” solutions to the problem.

———–Previous Talks———–

1 May 2021, 3pm, Via Zoom (link shared by email)

**Christopher Gregory Weaver (Illinois, Urbana-Champaign), “Hamilton, Hamiltonian Mechanics, and Causation”****Abstract**: I show how Hamilton’s philosophical commitments led him to a causal interpretation of classical mechanics. I argue that Hamilton’s metaphysics of causation was injected into his dynamics by way of a causal interpretation of force. I then detail how forces remain indispensable to both Hamilton’s formulation of classical mechanics and what we now call Hamiltonian mechanics (*i.e*., the modern formulation). On this point, my efforts primarily consist of showing that the orthodox interpretation of potential energy is the interpretation found in Hamilton’s work. Hamilton called the potential energy function the force-function because he believed that it represents forces at work in the world. Multifarious non-historical arguments for this orthodox interpretation of potential energy are provided, and matters are concluded by showing that in classical Hamiltonian mechanics, facts about the potential energies of systems are grounded in facts about forces. Thus, if one can tolerate the view that forces are causes of motions, then Hamilton provides one with a road map for transporting causation into one of the most mathematically sophisticated formulations of classical mechanics, *viz*., Hamiltonian mechanics.

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Porter Williams (USC): March 14th.

Henrique Gomes (Perimeter Institute and Cambridge University): April 18th.

Sam Fletcher (UMN): May 9th

———–Previous Talks———–

15th February 2020, 3pm LPS Seminar room

**Eugene Chua and Craig Callender (UCSD), “No Time for Time from No-Time”**

Programs in quantum gravity often involve formalisms that are supposedly fundamentally timeless, with physicists claiming that time emerges from fundamentally timeless physics. In this paper, we restrict our attention to one popular approach, the semiclassical time program, which argues that time emerges from fundamentally timeless solutions to the Wheeler-DeWitt equation after applying a series of semi-classical approximations. We think there are inherent tensions in this approach: by focusing on three major components of the semiclassical approximations – the Born-Oppenheimer approximation, the WKB approximation, and decoherence – we argue that the physical justifications for applying them are laden with time. In a variety of ways, they require systems to be in time. Either we are unjustified in applying these approximations to timeless solutions (describing timeless systems) or we must assume time in the timeless solutions. The semiclassical time approach turns out to be either unjustified or circular in deriving time from no–time.

15th February 2020, 3pm LPS Seminar room

**Mike Schneider (UCI/ Notre Dame), “Stabs in the dark sector”.**

Abstract**:** In the context of ΛCDM, our current theory of large-scale cosmology, I argue that dark energy plausibly constitutes a signpost for future fundamental physics, whereas cold dark matter does not. But such an argument has several steps, beginning with getting clear on what it means for a feature within some current theory to constitute a signpost for future fundamental physics. The view I suggest we take on this front requires, for present purposes, that ΛCDM be interpreted in accordance with some or other criteria that is argued to carry normative force. I proceed to do just this, whereupon the conclusion of my argument ultimately follows fairly quickly from the interpretation of ΛCDM I will have just given. Time pending, I will then discuss a curious upshot of the particular route taken to my conclusion: that, in contrast with dark energy, it seems we may stand to genuinely learn something about cold dark matter in virtue of achieving next-generation fundamental theory, if, after all, cold dark matter turns out to have played an important role according to which that future theory comes to be developed.

7 December 2019, 3pm, LPS Seminar room

**Mario Hubert (Cal-tech), “Why the Wave-Function has to be Psi-Ontic”**

Abstract: The PBR-theorem aimed at proving that the wave-function has to represent objective features of a physical system. There have been many attempts to interpret the wave-function as not representing the objective physical state of a quantum system by abandoning one of the assumptions of the PBR-theorem. I argue that each theory that violates either of the assumptions meets unsurmountable problems. The most severe is to give up objective reality.

9 November 2019, 3pm, LPS seminar room

**Jeff Barrett (Irvine), “****Quantum Randomness and Underdetermination”**

Abstract: We will consider the nature of quantum randomness and how one might have empirical evidence for it. We will see why, depending on one’s computational resources, it may be impossible to determine whether a particular notion of randomness properly characterizes one’s empirical data. Indeed, we will see why an ideal observer with full empirical evidence may fail to have any empirical evidence whatsoever for believing that the results of her quantum-mechanical experiments are in fact randomly determined. This illustrates a radical sort of empirical underdetermination faced by fundamentally stochastic theories like quantum mechanics.

]]>**Juliusz Doboszewski (Harvard Black Hole Initiative), “Interpreting cosmic no hair theorems”**

Cosmic no hair theorems imply that the far future of a broad class of cosmological models with accelerating expansion is locally indistinguishable from the de Sitter spacetime. I will briefly introduce these theorems and discuss what I take to be a natural interpretation of their importance, namely that the theorems succeed in establishing a form of fatalism about the far future of our universe. Then I will present various challenges to the natural interpretation (focusing mostly, but not exclusively, on black hole spacetimes), and connect some of them to philosophically interesting issues in the foundations of general relativity (including the distinction between local and global properties, conditions for being a hole free spacetime, and some form of a “singularity resolution” proposed in the context of the information loss paradox).

Please read either the published version or the penultimate draft (no paywall) of Juliusz’s paper.

27 April 2019, 3pm, LPS seminar room

**Sorin Bangu (Bergen), “Fictions in Scientific Explanation”**

Can fictions have an explanatory role in science – in physics in particular? Traditionally, the philosophy of scientific explanation (Hempel, Salmon, etc.) denied this. More recently, however, a number of authors have re-examined scientific explanation in light of its connection with understanding (Elgin, de Regt, Morrison, Bokulich, Khalifa, etc.), and are willing to accept such a role. In this paper, I aim to increase the plausibility of this second line of thinking by identifying a condition that specifies when the answer to our question can be affirmative. My proposal draws on Bogen and Woodward’s distinction between data and phenomena, and I support the position with illustrations from electrostatics and statistical mechanics.

23 February 2019, 3pm, LPS seminar room

**John Baez (UC Riverside), “Getting to the bottom of Noether’s theorem”**

In her paper of 1918, Noether’s theorem relating symmetries and conserved quantities was formulated in term of Lagrangian mechanics. But if we want to make the essence of this relation seem as self-evident as possible, we can turn to a formulation in term of Poisson brackets, which generalizes easily to quantum mechanics using commutators. The key question then becomes: when, and why, do observables generate one-parameter groups of transformations? This question sheds light on why complex numbers show up in quantum mechanics.

19 January 2019, 3pm, LPS seminar room

**Tomasz Placek (Jagiellonian University), “Interpreting non-Hausdorff (generalized) manifolds in General Relativity”**

The paper investigates the relations between Hausdorff and non-Hausdorff manifolds, as objects of General Relativity. We show that every non-Hausdorff manifold can be seen as a result of gluing together of some Hausdorff manifolds. In the light of this result we investigate a modal interpretation of a non-Hausdorff differential manifold according to which it represents a bundle of alternative spacetimes, all of which compatible with a given initial data set.

This talk is based on joint work with Joanna Luc. Please read their manuscript before the meeting.

17 November 2018, 3pm, LPS seminar room

**David Wallace (USC), “The Necessity of Statistical Mechanics”**

In discussions of the foundations of statistical mechanics, it is widely held that (a) the Gibbsian and Boltzmannian approaches are incompatible but empirically equivalent; (b) the Gibbsian approach may be calculationally preferable but only the Boltzmannian approach is conceptually satisfactory. I argue against both assumptions. Gibbsian statistical mechanics is applicable to a wide variety of problems and systems, such as the calculation of transport coefficients and the statistical mechanics and thermodynamics of mesoscopic systems, in which the Boltzmannian approach is inapplicable. And the supposed conceptual problems with the Gibbsian approach are either misconceived, or apply only to certain versions of the Gibbsian approach, or apply with equal force to both approaches. I conclude that Boltzmannian statistical mechanics is best seen as a special case of, and not an alternative to, Gibbsian statistical mechanics.

Please read David’s pre-print before the meeting.

6 October 2018, 3pm, LPS seminar room

**Chip Sebens (Caltech), “The Mass of the Gravitational Field”**

By mass-energy equivalence, the gravitational field has a relativistic mass density proportional to its energy density. I seek to better understand this mass of the gravitational field by asking whether it plays three traditional roles of mass: the role in conservation of mass, the inertial role, and the role as source for gravitation. The difficult case of general relativity is compared to the more straightforward cases of Newtonian gravity and electromagnetism by way of gravitoelectromagnetism, a special relativistic theory of gravity which resembles electromagnetism.

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**A Mini-Workshop on the Problem of Motion and Geodesic Theorems in GR**

10am: James Weatherall (Irvine), “The Motion of Small Bodies in Spacetime, or, Conservation, Inertia, and Spacetime Geometry”

11:30am: Coffee Break

11:45am: Dennis Lehmkuhl (Caltech), “The problem of motion: Einstein/Grommer and Thorne/Hartle compared”

1:15pm: Catered Lunch

2:30pm: Sam Fletcher (Minnesota), “When 2 Become 1: Approaches to the Problem of Motion”

4pm: Coffee Break

**Practical Information**

Location: The Einstein Papers Project, 363 S. Hill Ave, Pasadena, CA 91125

Local Organizer: Dennis Lehmkuhl

Parking: There is free street parking on Hill Avenue (during the weekend) and there is also a parking structure directly behind the EPP on Holliston Ave on S Holliston Ave.

5 May 2018, 3pm, LPS seminar room

**Joshua Norton (American University of Beirut), “The Hole Argument Against Everything”**

The Hole Argument was originally formulated by Einstein and it haunted him as he struggled to understand the meaning of spacetime coordinates in the context of the diffeomorphism invariance of general relativity. This argument has since been put to philosophical use by Earman and Norton (1987) to argue against a substantival conception of spacetime. In the present work I demonstrate how Earman and Norton’s Hole Argument can be extended to exclude everything and not merely substantival manifolds. These casualties of the hole demonstrate that the Hole Argument hinges essentially on our notion of determinism and not on the diffeomorphic freedom of general relativity.

Just as Earman and Norton argue that we should not let our metaphysics run roughshod over the structure of our physical theories, so I will argue that, in particular, we should not uncritically allow our metaphysics to dictate what our physical theories must determine. The central conviction which drives the arguments of this paper is that deterministic theories are not required to determine for future moments what they cannot determine for any present or past moments. I provide two arguments to the effect that a physically informed notion of determinism does not require general relativity to determine substantival facts. Consequently the Hole Argument cannot be used against substantival spacetime. The position that I advocate is an instance of “sophisticated determinism.”

A draft of Joshua’s paper can be found here.

24 February 2018, 3pm, LPS seminar room

**Lev Vaidman (Tel Aviv), “Defending the many-worlds interpretation of quantum mechanics”**

Starting from the premise that physics is deterministic and has no action at a distance, I will argue that the many-worlds interpretation is by far better than all existing alternatives. It keeps the physics part of the theory, the ontology of the universal wave function which incorporates all the worlds, very elegant. It is confirmed by experimental data with unprecedented precision. It provides a consistent connection with our experience. I will propose solutions for its alleged difficulties that the wave function in a high dimensional Hilbert space cannot correspond to our own experience of three spatial dimensions and that an experimentalist, who might have no ignorance of any detail of a quantum experiment, seems to have probabilities for different outcomes. The first difficulty is resolved by the observation that in every world the wave functions of all macroscopic objects are not entangled and thus defined in three dimension. The second is resolved by introducing the idea of probability of self-location of an observer in a particular world.

Please read Lev’s article before the meeting.

9 December 2017, 3pm, LPS seminar room

**David Wallace (USC), “Why Black Hole Information Loss is Paradoxical”**

I distinguish between two versions of the black hole information-loss paradox. The first arises from apparent failure of unitarity on the spacetime of a completely evaporating black hole, which appears to be non-globally-hyperbolic; this is the most commonly discussed version of the paradox in the foundational and semipopular literature, and the case for calling it `paradoxical’ is less than compelling. But the second arises from a clash between a fully-statistical-mechanical interpretation of black hole evaporation and the quantum-field-theoretic description used in derivations of the Hawking effect. This version of the paradox arises long before a black hole completely evaporates, seems to be the version that has played a central role in quantum gravity, and is genuinely paradoxical. After explicating the paradox, I discuss the implications of more recent work on AdS/CFT duality and on the `Firewall paradox’, and conclude that the paradox is if anything now sharper. The article is written at a (relatively) introductory level and does not assume advanced knowledge of quantum gravity.

Please read David’s preprint before the meeting.

4 November 2017, 3pm, LPS seminar room

**Marian Gilton (UCI), “Could Charge and Mass be Universal Properties?”**

There is a tradition in contemporary analytic metaphysics of looking to fundamental particle physics for an accurate list of universal properties. The central candidates for such properties are electric charge, color charge, and mass. Tim Maudlin has recently argued against a number of metaphysical theories within this tradition (Aristotelian and Platonic theories of universal properties, trope theory, the theory of natural sets, etc.) on the grounds that the general formalism of our current best fundamental physics–i.e., fiber bundles–precludes the notion of universal property used in these metaphysical theories. Consequently, Maudlin calls for a “wholesale revision” of the theory of universals. This paper argues, contra Maudlin, that the fiber bundle formalism does allow for the possibility of some universal properties, and thus a wholesale revision of this metaphysical theory is not yet warranted.

Please read Marian’s draft manuscript in preparation for the meeting.

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**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.

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**Dennis Lehmkuhl (Caltech), on the Problem of Motion**

The problem of motion of general relativity is about how exactly the gravitational field equations, the Einstein equations, are related to the equations of motion of material bodies subject to gravitational fields. This paper compares two approaches to derive the geodesic motion of (test) matter from the field equations: `the T approach’ and `the vacuum approach’. The latter approach has been dismissed by philosophers of physics because of it apparently representing material bodies by singularities. I shall argue that a careful interpretation of the approach shows that it does not depend on introducing singularities at all, and that it holds at least as much promise as the T approach. I finish with some general lessons about careful vs. literal interpretations of scientific theories.

Please read Dennis’s manuscript before the meeting.

7 May 2016, 3pm, LPS seminar room

**Bihui Li (USC), “Solutions in Constructive Field Theory”**

Constructive field theory aims to rigorously construct concrete solutions to Lagrangians used in particle physics, where the solutions satisfy some relevant set of axioms. I examine the nature of solutions in constructive field theory and their relationship to both axiomatic and Lagrangian quantum field theory (QFT). I argue that Lagrangian QFT provides conditions for what counts as a successful constructive solution, and that it provides other important information that guides constructive field theorists to solutions. Solutions matter because they describe the behavior of systems in QFT, and thus what QFT says the world is like. Constructive field theory, in incorporating ingredients from both axiomatic and Lagrangian QFT, clarifies existing disputes about which parts of QFT are relevant to philosophers and the role of rigor in these disputes.

Please read Bihui’s manuscript before the meeting.

16 April 2016, 3pm, LPS seminar room

**Julia Bursten (SFSU) on Multiscale Modeling**

Winsberg’s “handshaking” account of inter-model relations is a well-known theory of multiscale modeling in physical systems. Winsberg argues that relations among the component models in a multiscale modeling system are not related mereologically, but rather by empirically determined algorithms. I argue that while the handshaking account does demonstrate the existence of non-mereological relationships among component models, Winsberg does not attend to the different ways in which handshaking algorithms are developed. By overlooking the distinct strategies employed in different handshake models, Winsberg’s account fails to capture the central feature of effective multiscale modeling practices, namely, how the dominant behaviors of the modeled systems vary across the dierent scales, and how this variation constrains the ways modelers can combine component models. Using Winsberg’s example of nanoscale crack propagation, I distinguish two modes of handshaking and show how the different modes arise from the scale-dependent physics involved in each component model.

Please read Julia’s draft manuscript before the talk.

5 March 2016, 3pm, LPS seminar room

**Matt Leifer (Chapman), “Does time-symmetry in quantum theory imply retrocausality?”**

In [1], Huw Price argued that, under certain assumptions about the underlying ontology, an interpretation of quantum theory that is both realist and time-symmetric must be retrocausal, i.e. it must involve influences that travel backwards in time. Price’s argument is based on an analysis of a photon travelling between two polarizing beam-splitters. One of his assumptions is that the usual forward-evolving polarization vector of the photon is a beable, i.e. part of the ontology. He argues, on the basis of this and his other assumptions,

that a backward-evolving polarization vector must also be a beable.

The assumption that the forward evolving polarization vector is a beable is an assumption of the reality of the quantum state. But one of the reasons for exploring retrocausal interpretations of quantum theory is that they offer the potential for evading the unpleasant conclusions of no-go theorems, such as Bell’s theorem and, in particular, recent proofs of the reality of the quantum state [2]. In this talk, I will show how Price’s argument can, in fact, be generalized so that it does not assume the reality of the quantum state. The relationship between Price’s argument and ours bears a strong parallel to the relationship between the EPR argument and Bell’s theorem. I also reformulate the common assumptions of Price’s and our arguments to make them more generally applicable and to pin down the notion of time-symmetry involved more precisely. The notion of time-symmetry used in the argument is stronger than the notion of time-symmetry usually used in physics, but bears a family resemblance to conditions used in other no-go theorems, such as parameter independence in Bell’s theorem, and Spekkens’ notion of contextuality. All of these can be derived from the assumption that, if a theory has a symmetry in its operational predictions, then that symmetry ought to hold at the ontological level as well.

This talk is based on joint work with Matt Pusey.

[1] H. Price. Does time-symmetry imply retrocausality? How the quantum world says “maybe”. Stud. Hist. Phil. Mod. Phys., 43(2):75–83, 2012. arXiv:1002.0906

[2] For a review see M. Leifer. Is the quantum state real? An extended review of psi-ontology theorems. Quanta, 3:67-155, 2014. arXiv:1409.1570

13 February 2016, 3pm, LPS seminar room

**Richard Dawid (Stockholm) on String Dualities and Empirical Equivalence**

String dualities constitute a specific form of empirical equivalence in physics. One may argue that, after a century when empirical equivalence was primarily of interest to philosophy of science, the rise of duality in string physics marks the first time that empirical equivalence takes centre stage in physics itself. The paper will make the case, however, that the philosophical repercussions of string dualities are in fact directly opposed to the way the significance of empirical equivalence was understood throughout most of the 20th century in philosophy of science as well as physics. Comparing the canonical perspective on empirical equivalence with the role played by duality today provides an interesting indicator of the way string physics has altered the physicists’ perspective on physical theory building.

Richard expects to distribute a paper a few days before the meeting.

16 January 2016, 3pm, LPS seminar room

**Patricia Palacios (Munich) on the role of approximation in a reductive model for phase transitions**

Abstract: Phase transitions, roughly understood as sudden changes in the phenomenological properties of a system, have recently motivated a debate about reduction and emergence in the physical sciences. In this debate there are two main positions: i) Phase transitions are paradigmatic cases of emergent or irreducible behavior (Lebowitz 1999, Batterman 2000, 2002, Bangu 2011); ii) phase transitions represent a successful case of Nagelian reduction (Butterfield 2011, Menon and Callender 2011, Norton 2012). This leads one to conceive of the discussion in the following terms: Phase transitions are either non-reductive phenomena or reductive phenomena satisfying the Nagelian model of reduction. In this paper I will suggest that this dichotomy is misleading. In fact, there are good reasons for considering phase transitions as a case of reduction that does not satisfy the Nagelian model of reduction, either in its strict or more liberal versions.

21 November 2015, 3pm, LPS seminar room

**John Byron Manchak (UCI) on Epistemic Holes in Spacetime**

Abstract: A number of models of general relativity seem to contain “holes” which are thought to be “physically unreasonable”. One seeks a condition to rule out these models. We examine a number of possibilities already in use. We then introduce a new condition: epistemic hole-freeness. Epistemic hole-freeness is not just a new condition — it is new in kind. In particular, it does not presuppose a distinction between spacetimes which are “physically reasonable” and those which are not.

Please read JB’s manuscript before the meeting.

24 October 2015, 3pm, LPS seminar room

**Chip Sebens (CalTech & UCSD) on Constructing and Constraining Wave Functions for Identical Quantum Particles**

Abstract: I address the problem of explaining the symmetry dichotomy within two interpretations of quantum mechanics which clarify the connection between particles and the wave function by including particles following definite trajectories in addition to, or in lieu of, the wave function: Bohmian mechanics and Newtonian quantum mechanics. I present and examine what I take to be the most illuminating explanation of the symmetry dichotomy given in the context of Bohmian mechanics (Bacciagaluppi, 2003). If the Bohmian guidance equation is formulated as to not rely on a correspondence between particles and arguments of the wave function, then the symmetry dichotomy must be postulated for the particle velocities to be well-defined. Still, the symmetry dichotomy remains an additional postulate. I propose an explanation of the symmetry dichotomy in Newtonian quantum mechanics which parallels Bacciagaluppi’s, but is simpler and stronger. In Newtonian quantum mechanics the wave function is not part of the fundamental ontology, but simply a convenient way of describing the positions and velocities of particles. Because a world in Newtonian quantum mechanics is equally well represented by multiple points in configuration space, it turns out that any wave function constructed to describe these worlds will be either symmetric or antisymmetric. The symmetry dichotomy need not be postulated. I show that both of these explanations can be given in reduced configuration space, though doing so is only necessary if one wants to defend exotic approaches to these interpretations which take configuration space as fundamental.

The talk will be based on Chip’s draft manuscript. This project further examines the theory proposed in Quantum Mechanics as Classical Physics (arXiv) (blog post).

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**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.

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**Tomasz Bigaj (Warsaw) on “Weak discernibility for quanta: why settle for less?”**

Abstract: My talk will consist of two (connected) parts. In the first part I will share with the audience the frustrations resulting from my struggle to understand the multitude of weakly discerning quantum-mechanical relations that have recently been proposed in the literature (Muller & Saunders 2008, Muller & Seevinck 2009, Caulton 2013, Huggett & Norton 2014). On the basis of my understanding of the philosophical motivations behind the whole weak discernibility program, I will attempt to argue that virtually all the proposed methods of discerning quantum particles are fatally flawed. In the face of this setback I will subsequently try to reverse the fortunes of discernibility by arguing that even absolute discernibility of fermions and bosons of the same type is sometimes attainable if we do it right, i.e. using properly symmetrized projection operators.

Previous acquaintance with the papers cited in the abstract can be helpful but is not necessary. The second part of the talk will be loosely based on the unpublished manuscript “Quantum particles, individual properties, and discernibility”.

13 April 2014, 3pm, LPS seminar room

**Eleanor Knox (Kings College, London) on “Spacetime Structuralism or Spacetime Functionalism?”**

Abstract: I examine some currently popular articulations of ontic structural realism with respect to spacetime points, and find them lacking. Instead, I propose functionalism about spacetime itself (with at most derivative consequences for its points). This has much in common with structuralist positions, but has the virtue of usefully applying to emergent spacetimes.

Please read Eleanor’s preprint in advance of the meeting.

22 February 2014, 3pm, LPS seminar room

**Holger Lyre (Magdeburg) on “Berry phase and quantum structural realism”**

Abstract: The purpose of the talk is to analyze the phenomenon of the Berry phase, to spell out its relevance for the quantum state space structure, and to argue for a realist position about this structure. While common wisdom tells us that the quantum state space is the projective Hilbert space, the appropriate structure rich enough to account for the Berry phase turns out to be a U(1) principal bundle over that projective space. Call this the quantum bundle. The Berry phase is the only known instance of a geometric quantum holonomy that, in the absence of any further causal mechanism to bring about this phenomenon, is directly rooted in the curvature of the quantum bundle. This motivates the claim that Berry’s geometric quantum holonomy supports ontic structural realism.

Please read Holger’s preprint in advance of the meeting.

11 January 2014, 3pm, LPS seminar room

**David Wallace (Oxford) on “Thoughts on the Gauge Principle”**

Abstract: Gauge symmetry occupies a paradoxical position in contemporary physics. How can one and the same thing be (a) the third pillar of relativistic quantum field theory, alongside special relativity and quantum mechanics, and (b) a mere descriptive redundancy, indicating that we have overdescribed the theory’s degrees of freedom? Working mostly in classical field theory but motivated by its application in quantum field theory, I will attempt to get some clarity on what we are really saying about a theory conceptually and metaphysically when we say that it has gauge symmetry. Along the way I hope to shed some light on the vexed question of in what sense general relativity is also a gauge theory.

There is no reading for this meeting.

7 December 2013, 3pm, LPS seminar room

** Foad Dizadji-Bahmani (CSU Los Angeles) on “A New Model of Intertheoretic Reduction”**

Preamble/Motivation: Intertheoretic reduction is a perennial theme in philosophy of science; it is a topic that has been present since the very beginning of analytic philosophy of science. There is a striking variety of reductive claims. Some claim that the very modus operandum of science is reductive, others that the history of science is replete with reductions, others still that the putative exemplars of reduction in science are not reductions after all, and yet others that intertheoretic reduction is not possible. Tied up with intertheoretic reduction are the notions of ontological reduction and reductionism. Yet, before one can consider whether or not reductions are ubiquitous, numerous, few, or impossible; whether science aims at reduction; whether all of science does reduce to physics; and so forth, one must first settle what it is for one theory to reduce to another.

Abstract: In this paper I develop and defend a new model of intertheoretic reduction. First, I advocate a particular method for developing some such model, which is a constitutive approach in contradistinction to one based on reflective equilibrium. Second, using this method, I take the relation between the Boyles-Charles law of classical thermodynamics and the so-called kinetic theory of gases to be constitutive of reduction. Third, I discuss how this model compares to Nagel’s well-known model, and, in particular, how my model avoids many of the well-known problems with Nagel’s. Fourth, I apply the model to the relation between a) the classical 2nd Law of Thermodynamics and Boltzmannian statistical mechanics, and b) the classical 2nd Law of Thermodynamics and what in previous work I have called the Aharonov approach to quantum statistical mechanics.

This is no reading for this meeting.

2 November 2013, 4:15pm, LPS seminar room

**Kerry McKenzie (Western) on “Prescriptions on Priority”**

Abstract: In my recent work ‘Priority and Particle Physics’, I suggested that ontic structural realists could use resources gleaned from analytic metaphysics to sharpen up their fundamentality claims — most obviously that concerning the supposed priority of structures over objects. In this talk I want to reconsider that strategy, and investigate whether the fundamentality metaphysics needed for philosophy of physics can in fact be done ‘in house’. After walking us through some priority claims made by philosophers of physics, I will argue that our handling of priority could definitely use some conceptual clear-up. But I’ll also argue that the task of better articulating the concept will be largely continuous with other, antecedently familiar issues in the philosophy of science. While this seems to prise fundamentality questions a little way out of the armchair, what is noteworthy — and dare I say disappointing?! — is that the conception of ontological priority we thereby arrive at looks a lot like that defended in contemporary analytic metaphysics. The significance of this for the much-discussed antagonism between the two fields is a question I’ll leave on the table.

Readings: Although there isn’t a paper associated with the talk, Kerry suggests reading her earlier paper for background.

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