11 May 2024

**Lu Chen (USC)**, **“Algebraicism is not substantivalism”**

I defend algebraicism, according to which physical fields can be understood in terms of their structural relations without reference to a spacetime manifold, as a genuine relationalist view against the conventional wisdom that it is equivalent to substantivalism, according to which spacetime exists fundamentally. I criticize the standard version of algebraicism that is considered equivalent to substantivalism. Furthermore, I present alternative examples of algebraicism that better implement relationalism with their own advantages over the standard formalism, which I argue to be not equivalent to substantivalism.

A preprint of Lu’s talk is available here.

Past Events

27-28 October 2023

**Event: **Symmetry and Structure Workshop**Register by October 20: **https://forms.gle/r8pMXxWXALQ3MNZs8

3-4 November 2023

**Event: **Conceptual and Mathematical Foundations of Science**Register by October 27: **https://forms.gle/9FQ2YytDRWfu7Pg87

9 December 2023

**Jeffrey Barrett (UCI) and Eddy Chen (UCSD), “Algorithmic Randomness and Probabilistic Laws**“

Abstract: We consider two ways one might use algorithmic randomness to characterize a probabilistic law. The first is a generative chance* law. Such laws involve a nonstandard notion of chance. The second is a probabilistic* constraining law. Such laws impose relative frequency and randomness constraints that every physically possible world must satisfy. While each notion has virtues, we argue that the latter has advantages over the former. It supports a unified governing account of non-Humean laws and provides independently motivated solutions to issues in the Humean best-system account. On both notions, we have a much tighter connection between probabilistic laws and their corresponding sets of possible worlds. Certain histories permitted by traditional probabilistic laws are ruled out as physically impossible. As a result, such laws avoid one variety of empirical underdetermination, but the approach reveals other varieties of underdetermination that are typically overlooked.

A preprint is available: https://arxiv.org/pdf/2303.01411.pdf

13 January 2024

**Lev Vaidman (Tel Aviv), “Transfer of quantum information in teleportation”**

Abstract: The controversial issue of information transfer in quantum teleportation procedure is analyzed in the framework of the many-worlds interpretation of quantum mechanics. In contrast to the claims of Deutsch & Hayden 2000, it is argued that quantum information, considered as a measurable property for an observer in a particular world, is transferred in a nonlocal way in the teleportation process. This, however, does not lead to action at a distance on the level of the universe which includes all parallel worlds.

Preprint: https://philsci-archive.pitt.edu/21447/

~~24 February 2024~~ **TALK POSTPONED TO 28 September 2025**

**Joshua Eisenthal (Caltech)**, **“The Absolute Motion Detector”**

Abstract: Following the proliferation of non-Euclidean geometries in the nineteenth century, the “problem of space” emerged as the problem of demarcating which mathematical geometries were candidate physical geometries. By around 1900, a consensus formed around the following purported solution. The possibility of measuring spatial magnitudes depends on the possibility of moving rigid bodies (such as rulers and compasses) without changing their dimensions. As only the constant curvature geometries could represent this kind of rigid transport, only these geometries were candidate physical geometries — or so the argument went. However, it was only after the development of general relativity in 1915 that the physical significance of transport along affine geodesics was understood. When an object moves inertially it moves along an affine geodesic, but if this takes place in a curved space, those geodesics do not stay a fixed distance apart. Thus an extended object will experience elastic tension when it moves in a curved space, even when there are no forces acting on it. In this talk I will explore what impact this insight might have had for the nineteenth century problem of space. In particular, I will explore the consequences for the two main positions in the philosophy of geometry in this period: geometrical empiricism (the view that experiments determine which geometry is “true”) and geometrical conventionalism (the view that we ourselves must decide, based on simplicity and convenience, which geometry is best to use).

13 April 2024

**Eleanor March (Oxford)**, **“Are Maxwell gravitation and Newton-Cartan theory theoretically equivalent?”**

Abstract: A recent flurry of work has addressed the question whether Maxwell gravitation and Newton-Cartan theory are theoretically equivalent. I defend the view that there are plausible interpretations of Newton-Cartan theory on which the answer to the above question is ‘yes’. Along the way, I seek to clarify what is at issue in this debate. In particular, I argue that whether Maxwell gravitation and Newton-Cartan theory are equivalent has nothing to do with counterfactuals about unactualised matter, *contra* the appearance of previous discussions in the literature. Nor does it have anything to do with spacetime and dynamical symmetries, *contra* recent claims by Jacobs (2023). Instead, it depends on some rather subtle questions concerning how facts about the geodesics of a connection acquire physical significance, and the distinction between dynamical and kinematical possibility.

A preprint of Eleanor’s paper is available here.

]]>Date: **27-28 October 2023**

Place: Social and Behavioral Sciences Gateway, Room 1321 (campus map)

Time: 9am – 5:30pm Friday; 9am-1:30pm Saturday, with refreshments beginning at 8:30 both days.

Logistics: Paid parking is available in the Social Science Parking Structure.

Précis: This one-and-a-half day workshop will return to the themes of last year’s Math-First Structural Realism Workshop. Our focus this year will be on what is distinctively *mathematical* about math-first structural realism. Topics will include how to characterize mathematical structure, what mathematical equivalence results tell us about structure in the world, and how symmetry can be used to probe structure.

Speakers will include David Wallace (University of Pittsburgh), Thomas Barrett (UC Santa Barbara), Neil Dewar (Cambridge University), David Baker (University of Michigan), Clara Bradley (UC Irvine), JB Manchak (UC Irvine), Toby Meadows (UC Irvine), and James Weatherall (UC Irvine). Kerry McKenzie (University of California, San Diego) and Emily Adlam (Chapman) will participate as invited discussants.

**Schedule **(subject to change)

Friday October 27

8:30am: Continental Breakfast

9am: Opening Remarks by Jim Weatherall

9:15am: David Wallace

10:15am: JB Manchak

11:15am: Coffee Break

11:30am: Thomas Barrett

12:30pm: Lunch

1:30pm: Toby Meadows

2:30pm: Dave Baker

3:30pm Coffee Break

3:45pm Hans Halvorson

4:45pm General Discussion

Saturday October 28

8:30am: Continental Breakfast

9am: Neil Dewar

10am: Clara Bradley

11am: Coffee Break

11:15am: James Weatherall

12:15pm: Lunch

12:30pm: Brown bag discussion over lunch

The event is co-organized by Clara Bradley and James Weatherall. It is hosted by the Southern California Philosophy of Physics Group with generous support from the Department of Logic and Philosophy of Science at the University of California, Irvine. For further information, please contact the organizers at cbradle1@uci.edu and weatherj@uci.edu, respectively.

]]>3 June 2023

**Helen Meskhidze (UCI), “Torsion in the Classical Spacetime Context**“

Teleparallel gravity, an empirically equivalent counterpart to General Relativity, represents the influence of gravity using torsional forces. It raises questions about theory interpretation and underdetermination. To better understand the torsional forces of Teleparallel gravity, we consider a context in which forces are better understood: classical spacetimes. We propose a method of incorporating torsion into the classical spacetime context that yields a classical theory of gravity with a closed temporal metric and spacetime torsion. We then prove a result analogous to the Trautman degeometrization theorem, that every model of Newton-Cartan theory gives rise, non-uniquely, to a model of this theory.

Helen’s paper is available here.

Past talks

6 May 2023** **

**Eugene Chua (UCSD), “T Falls Apart: On the Status of Classical Temperature in Relativity”**

Abstract: I argue that the classical temperature concept falls apart in special relativity by examining four consilient procedures for establishing classical temperature: Carnot processes, thermometers, kinetic theory, and black-body radiation. I show that their relativistic counterparts demonstrate no such consilience. I suggest two interpretations for this situation: eliminativism akin to simultaneity, or pluralism akin to rotation.

March 18 2023

**Event: Math-First Structural Realism Workshop. **

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.

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.

]]>Précis: This one-day workshop will bring together scholars from the U.S. and U.K. to discuss ideas stemming from David Wallace’s recent paper, “Stating Structural Realism: Mathematics-First Approaches to Physics and Metaphysics“. Speakers will include Eleanor Knox (Kings College, London / University of Pittsburgh), Alexander Franklin (Kings College London / University of California, Irvine), Katie Robertson (University of Birmingham), Alastair Wilson (University of Birmingham), Kerry McKenzie (University of California, San Diego), and Tushar Menon (Cambridge / Australian Catholic University). McKenzie will introduce the event and James Weatherall will moderate a roundtable discussion, which will include all speakers and David Wallace (University of Pittsburgh).

Place: Social and Behavioral Sciences Gateway, Room 1321 (campus map)

Time: 9:30am – 5pm, with refreshments beginning at 9.

Logistics: Paid parking is available in the Social Science Parking Structure.

**Schedule **(subject to change)

9am: Continental Breakfast

9:30am: Opening Remarks by Kerry McKenzie

9:45am: Eleanor Knox

10:45am: Alexander Franklin

11:45am: Catered Lunch

1pm: Katie Robertson & Alastair Wilson

2pm: Kerry McKenzie

3pm Coffee Break

3:15pm Tushar Menon

4:15pm Comments and Replies by David Wallace

4:30pm Roundtable Discussion

The event is co-organized by Kerry McKenzie and James Weatherall. It is hosted by the Southern California Philosophy of Physics Group with generous support from the Department of Logic and Philosophy of Science at the University of California, Irvine. For further information, please contact the organizers at kmckenzie@ucsd.edu and weatherj@uci.edu, respectively.

]]>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.

]]>

**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
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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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