https://account.philosophyofphysics.lse.ac.uk/index.php/lse-j-pp/issue/feedPhilosophy of Physics2024-04-25T17:11:42+01:00Prof David Wallacedavid.wallace@pitt.eduOpen Journal Systems<p><em><span style="font-weight: 400;">Philosophy of Physics </span></em><span style="font-weight: 400;">is an open access journal publishing the best work in all areas of the philosophy of physics. PoP aims to be a flagship journal for the field and to span the various different axes of philosophy of physics: metaphysical, historical, mathematical, practice-oriented (and more). It is intended for all researchers in philosophy of physics and for interested readers in cognate disciplines, including outside philosophy. It is published by LSE Press on behalf of the <a href="http://philosophyofphysics.org/" target="_blank" rel="noopener">Philosophy of Physics Society</a>. Publication of accepted articles is free and authors retain copyright under a Creative Commons license.</span></p>https://account.philosophyofphysics.lse.ac.uk/index.php/lse-j-pp/article/view/131On Coordinates and Spacetime Structure2024-04-12T23:45:54+01:00Thomas William BarrettJ. B. Manchak<p>Philosophers and physicists often claim that the “privileged coordinates” of a physical theory provide a window into its structure. The purpose of this paper is to examine whether this is the case. We show that there are general relativistic spacetimes that admit the same privileged coordinates but have different structure, and we infer from this that privileged coordinates do not provide a perfect guide to underlying structure. We conclude by isolating the conditions under which privileged coordinates <em>do</em> perfectly reflect structure.</p>2024-07-19T00:00:00+01:00Copyright (c) 2024 The author(s)'https://account.philosophyofphysics.lse.ac.uk/index.php/lse-j-pp/article/view/109How are Entanglement Entropies Related to Entropy Bounds?2024-02-03T20:08:55+00:00Emily Adlam<p>In this paper we seek to understand what current knowledge of entanglement entropies suggests about the appropriate way to interpret the covariant entropy bound. We first begin by arguing that just as in the classical case, a universal bound on the von Neumann entropy could have either an epistemic or ontological origin. We then consider several possible ways of explaining the bound as a consequence of features of the entanglement entropy. We discuss consider area laws in condensed matter and quantum field theory, arguing that they suggest an epistemic reading of the bound. We also discuss the ‘spacetime from entanglement’ programme, arguing that entanglement alone may not be able to full ground spacetime topology, but it could potentially play a role in determining the spacetime metric, in which case it would potentially support a more ontological reading of the bound.</p>2024-07-02T00:00:00+01:00Copyright (c) 2024 The author(s)'https://account.philosophyofphysics.lse.ac.uk/index.php/lse-j-pp/article/view/103Algebraicism is not Substantivalism2024-03-14T09:00:18+00:00Lu Chen<p>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 conceptual advantages over substantivalism or its standard algebraic counterpart.</p>2024-08-12T00:00:00+01:00Copyright (c) 2024 The author(s)'https://account.philosophyofphysics.lse.ac.uk/index.php/lse-j-pp/article/view/91Einstein Against Singularities: Analysis versus Geometry2023-10-10T16:34:05+01:00John D. Norton<p>Einstein identified singularities in spacetimes, such as at the Schwarzschild radius, where later relativists only find a coordinate system assigning multiple values to a single spacetime event. These differing judgments derive from differences in mathematical methods. Later relativists employ geometrical structures to correct anomalies in the coordinate systems used in analytic expressions. Einstein took the analytic expressions to be primary and the geometrical structures as mere heuristics that could be overruled if physical assumptions required it. Einstein’s non-geometric methods had a firm base in the history of mathematical methods. They continued the non-geometric orientation of Christoffel, Ricci and Levi-Civita. Einstein’s insistence that singularities must be eliminated marked a departure from earlier tolerance of singularities. It was founded upon his long-term project of eliminating arbitrariness from fundamental physical theories. However, Einstein was willing to theorize with singularities only temporarily if they were the least arbitrary approach then available.</p>2024-07-29T00:00:00+01:00Copyright (c) 2024 The author(s)'https://account.philosophyofphysics.lse.ac.uk/index.php/lse-j-pp/article/view/90The Open Systems View2024-03-25T14:44:24+00:00Michael E. CuffaroStephan Hartmann<p>There is a deeply entrenched view in philosophy and physics, the closed systems view, according to which isolated systems are conceived of as fundamental. On this view, when a system is under the influence of its environment this is always described in terms of a coupling between it and a separate system, which taken together are isolated. There is an alternative, the open systems view, according to which systems interacting with their environment are conceived of as fundamental, and the environment’s influence is represented via the dynamical equations that govern the system of interest’s evolution. In this paper we propose (although the formalism is not original to us) a theoretical framework which we call the general quantum theory of open systems (GT), within which one can make sense of the dynamics of open quantum systems in fundamental terms, and we argue that the open systems view, as formalized in GT, is fundamental in quantum theory.</p>2024-05-23T00:00:00+01:00Copyright (c) 2024 The author(s)'https://account.philosophyofphysics.lse.ac.uk/index.php/lse-j-pp/article/view/81On Norton’s “…Shook…” and Myrvold’s “Shakin’…”2023-09-28T03:16:07+01:00Wayne C. MyrvoldJohn D. NortonNorton’s and Myrvold’s recent analyses of fluctuations and Landauer’s principle are compatible.2023-11-17T00:00:00+00:00Copyright (c) 2023 The author(s)'https://account.philosophyofphysics.lse.ac.uk/index.php/lse-j-pp/article/view/80On the Geometric Trinity of Gravity, Non-Relativistic Limits, and Maxwell Gravitation2024-04-25T17:11:42+01:00Eleanor MarchWilliam J. WolfJames Read<p>We show that the dynamical common core of the recently-discovered non-relativistic geometric trinity of gravity is Maxwell gravitation. Moreover, we explain why no analogous distinct dynamical common core exists in the case of the better-known relativistic geometric trinity of gravity.</p>2024-08-16T00:00:00+01:00Copyright (c) 2024 The author(s)'https://account.philosophyofphysics.lse.ac.uk/index.php/lse-j-pp/article/view/77Structuralism as a Stance2023-07-31T21:22:10+01:00Kerry McKenzie<p>In this paper, I argue that ontic structural realism is best understood not as a thesis or doctrine concerning how the world fundamentally is, but rather as a “stance” in the sense of van Fraassen (2002). I do so via an argument analogous to that which van Fraassen offers for why materialism should be regarded as a stance; namely, that by thinking of it as such we have a better explanation of the behavior of the putative doctrine’s adherents. In particular, I argue that thinking of structuralism as a stance best explains the toleration of disagreement within the structuralist community with respect to whether quantum fields ought to be classified as “objects” or “structures.” I close by offering a preliminary characterization of what the structuralist stance could consist in, arguing that it should be thought of as a sort of methodological orientation or injunction; namely, the injunction to foreground, when doing metaphysics, that the language of physics is mathematics.</p>2024-01-29T00:00:00+00:00Copyright (c) 2024 The author(s)'https://account.philosophyofphysics.lse.ac.uk/index.php/lse-j-pp/article/view/74Robustness and the Event Horizon Telescope: the case of the first image of M87*2023-07-25T09:40:03+01:00Juliusz DoboszewskiJamee Elder<p>We examine the justification for taking the Event Horizon Telescope’s famous 2019 image to be a reliable representation of the region surrounding a black hole. We argue that it takes the form of a robustness argument, with the resulting image being robust across variation in a range of data-analysis pipelines. We clarify the sense of “robustness” operating here and show how it can account for the reliability of astrophysical inferences, even in cases—like the EHT—where these inferences are based on experiments that are (for all practical purposes) unique. This has consequences far beyond the 2019 image.</p>2024-03-28T00:00:00+00:00Copyright (c) 2024 The author(s)'https://account.philosophyofphysics.lse.ac.uk/index.php/lse-j-pp/article/view/70Cluster Decomposition and Two Senses of Isolability2023-06-13T15:43:30+01:00Porter WilliamsJohn DoughertyMichael E. Miller<p>In the framework of quantum field theory, one finds multiple load-bearing locality and causality conditions. One of the most important is the cluster decomposition principle, which requires that scattering experiments conducted at large spatial separation have statistically independent results. The principle grounds a number of features of quantum field theory, especially the structure of scattering theory. However, the statistical independence required by cluster decomposition is in tension with the long-range correlations characteristic of entangled states. In this paper, we argue that cluster decomposition is best stated as a condition on the dynamics of a quantum field theory, not directly as a statistical independence condition. This redefinition avoids the tension with entanglement while better capturing the physical significance of cluster decomposition and the role it plays in the structure of quantum field theory.</p>2024-07-24T00:00:00+01:00Copyright (c) 2024 The author(s)'https://account.philosophyofphysics.lse.ac.uk/index.php/lse-j-pp/article/view/65Is the Deutsch-Wallace Theorem Redundant?2023-05-31T11:09:30+01:00Eleanor March<p>I defend the Deutsch-Wallace (DW) theorem against a dilemma presented by Dawid and Thébault (2014), and endorsed in part by Read (2018), and Brown and Porath (2020), according to which the theorem is either redundant or in conflict with general frequency-to-chance inferences. I argue that neither horn of the dilemma is well-posed. On the one hand, the DW theorem is not in conflict with general frequency-to-chance inferences on the most natural way of stating the theorem. On the other hand, the DW theorem is crucial for establishing the Born rule as a prediction of Everettian quantum mechanics (EQM), and so cannot be redundant within the theory.</p>2024-06-11T00:00:00+01:00Copyright (c) 2024 The author(s)'https://account.philosophyofphysics.lse.ac.uk/index.php/lse-j-pp/article/view/58On the Analogies Between Gravitational and Electromagnetic Radiative Energy2023-08-13T12:03:18+01:00Henrique GomesCarlo Rovelli<p>We give a conceptual exposition of aspects of gravitational radiation, especially in relation to energy. Our motive for doing so is that the strong analogies with electromagnetic radiation seem not to be widely enough appreciated. In particular, we reply to some recent papers in the philosophy of physics literature that seem to deny that gravitational waves carry energy.</p> <p>Our argument is based on two points: (i) that for both electromagnetism and gravity, in the presence of material sources, radiation is an effective concept, unambiguously emerging only in certain regimes or solutions of the theory; and (ii) similarly, energy conservation is only unambiguous in certain regimes or solutions of general relativity. Crucially, the domain of (i), in which radiation is meaningful, has a significant overlap with the domain of (ii), in which energy conservation is meaningful. Conceptually, the overlap of regimes is no coincidence: The long-standing question about the existence of gravitational waves was settled precisely by finding a consistent way to articulate their energy and momentum.</p>2024-01-31T00:00:00+00:00Copyright (c) 2024 The author(s)'https://account.philosophyofphysics.lse.ac.uk/index.php/lse-j-pp/article/view/54On Penrose’s Analogy between Curved Spacetime Regions and Optical Lenses2023-05-20T15:47:19+01:00Dennis LehmkuhlChristian RökenJuliusz Doboszewski<p>We present a detailed analysis of Penrose’s gravito-optical analogy between the focusing effects of particular families of Ricci- and Weyl-curved spacetime regions on the one hand, and anastigmatic and astigmatic optical lenses on the other. We put the analogy in its historical context, investigate its underlying assumptions, its range of validity, its proof of concept, and its application in Penrose’s study of the notion of energy flux in general relativity. Finally, we examine the analogy within the framework of Norton’s material theory of induction.</p>2024-04-10T00:00:00+01:00Copyright (c) 2024 The author(s)'https://account.philosophyofphysics.lse.ac.uk/index.php/lse-j-pp/article/view/48In Which Sense Can We Say That First-Class Constraints Generate Gauge Transformations?2023-03-27T18:30:42+01:00Álvaro Mozota Frauca<p>In this paper, I consider a recent controversy about whether first-class constraints generate gauge transformations in the case of electromagnetism. I argue that there is a notion of gauge transformation, the extended notion, which is different from the original gauge transformation of electromagnetism, but at the same time not trivial, which allows the making of that claim. I further argue that one can expect that this claim can be extended to more general theories, and that Dirac’s conjecture may be true for some physically reasonable theories and only in this sense of gauge transformation. Finally, I argue that the extended notion of gauge transformation seems unnatural from the point of view of classical theories, but that it nicely fits with the way quantum versions of gauge theories are constructed.</p>2024-07-11T00:00:00+01:00Copyright (c) 2024 The author(s)'https://account.philosophyofphysics.lse.ac.uk/index.php/lse-j-pp/article/view/46 How Oriented Causation Is Rooted into Thermodynamics 2023-03-26T22:39:53+01:00Carlo Rovelli<p>The notions of <em>cause</em> and <em>effect</em> are widely employed in science and commonly understood as temporally ordered: causes precede effects. I discuss why and how these notions are rooted into thermodynamics. The entropy gradient (i) explains in which sense interventions affect the future rather than the past, and (ii) underpins the time orientation of the subject of knowledge as a physical system. Via these two distinct paths, it is the entropy gradient, and only the entropy gradient, the source of the time orientation of causation, namely the fact the cause comes before its effects.</p>2023-12-22T00:00:00+00:00Copyright (c) 2023 The author(s)'https://account.philosophyofphysics.lse.ac.uk/index.php/lse-j-pp/article/view/45Is the Metric Signature Really Electromagnetic in Origin?2023-03-24T16:09:16+00:00Lu ChenJames Read<p>The program of “pre-metric electromagnetism,” developed by Hehl and collaborators, seeks to derive certain aspects of the spacetime geometry of the world (in particular, metrical signature) from elementary, empirically informed axioms regarding electromagnetic fields. The program should, therefore, be of profound interest to both empiricist and relationalist philosophers. Up to this point, however, pre-metric electromagnetism has received very little attention within the philosophy of physics; this paper seeks to rectify the situation, by engaging in a detailed foundational study of the program. In particular, in this article, we (a) present a streamlined version of the program, identifying key input assumptions, (b) consider the connections between this program and other notable projects in the foundations of spacetime theories, for example, (i) the dynamical approach to spacetime and (ii) constructive axiomatics, and (c) consider in detail the extent to which this program can be generalized beyond electromagnetism. In achieving these tasks, we hope to open up to philosophers an extraordinarily fecund—but lamentably little-known!—project within the foundations of physics.</p>2023-11-28T00:00:00+00:00Copyright (c) 2023 The author(s)'https://account.philosophyofphysics.lse.ac.uk/index.php/lse-j-pp/article/view/44Are Entropy Bounds Epistemic?2023-03-19T21:53:30+00:00Emily Adlam<p>Entropy bounds have played an important role in the development of holography as an approach to quantum gravity, so in this article we seek to gain a better understanding of the covariant entropy bound. We observe that there is a possible way of thinking about the covariant entropy bound which would suggest that it encodes an epistemic limitation rather than an objective count of the true number of degrees of freedom on a light-sheet; thus we distinguish between ontological and epistemic interpretations of the covariant bound. We consider the consequences that these interpretations might have for physics and we discuss what each approach has to say about gravitational phenomena. Our aim is not to advocate for either the ontological or epistemic approach in particular, but rather to articulate both possibilities clearly and explore some arguments for and against them.</p>2023-11-22T00:00:00+00:00Copyright (c) 2023 The author(s)'https://account.philosophyofphysics.lse.ac.uk/index.php/lse-j-pp/article/view/29Geometrogenesis in GFT: An Analysis2023-01-25T20:42:42+00:00Álvaro Mozota Frauca<p>In this paper I introduce the idea of geometrogenesis as suggested in the group field theory (GFT) literature, and I offer a criticism of it. Geometrogenesis in the context of GFT is the idea that what we observe as the big bang is nothing else but a phase transition from a nongeometric phase of the universe to a geometric one, which is the one we live in and the one to which the spacetime concepts apply. GFT offers the machinery to speak about geometric and nongeometric phases, but I argue that there are serious conceptual issues that threaten the viability of the idea. Some of these issues are directly related to the foundations of GFT and are concerned with the fact that it isn’t clear what GFT amounts to and how to understand it. The other main source of trouble has to do with geometrogenesis itself and its conceptual underpinnings, as it is unclear whether it requires the addition of an extra temporal or quasitemporal dimension, which is unwanted and problematic.</p>2023-11-17T00:00:00+00:00Copyright (c) 2023 The author(s)'https://account.philosophyofphysics.lse.ac.uk/index.php/lse-j-pp/article/view/28Scope of the action principle2023-01-08T16:55:40+00:00Ward StruyveLaws of motion given in terms of differential equations can not always be derived from an action principle, at least not without introducing auxiliary variables. By allowing auxiliary variables, e.g. in the form of Lagrange multipliers, an action is immediately obtained. Here, we consider some ways how this can be done, with illustrations from the literature, and apply this to Bohmian mechanics. We also discuss the possible metaphysical status of these auxiliary variables. A particularly interesting approach brings the theory in the form of a gauge theory, with the auxiliary variables as gauge degrees of freedom.2023-11-17T00:00:00+00:00Copyright (c) 2023 The author(s)'https://account.philosophyofphysics.lse.ac.uk/index.php/lse-j-pp/article/view/26How Haag-Tied is QFT, Really?2023-01-08T17:06:10+00:00Chris MitschMarian GiltonDavid Freeborn<p>Haag’s theorem cries out for explanation and critical assessment: It sounds the alarm that something is (perhaps) not right in one of the standard ways of constructing interacting fields to be used in generating predictions for scattering experiments. Viewpoints as to the precise nature of the problem, the appropriate solution, and subsequently-called-for developments in areas of physics, mathematics, and philosophy differ widely. In this paper, we develop and deploy a conceptual framework for critically assessing these disparate responses to Haag’s theorem. Doing so reveals the driving force of more general questions as to the nature and purpose of foundational work in physics.</p>2024-06-12T00:00:00+01:00Copyright (c) 2024 The author(s)https://account.philosophyofphysics.lse.ac.uk/index.php/lse-j-pp/article/view/24UnBorn: Probability in Bohmian Mechanics2022-12-13T20:21:59+00:00Laura Ruetsche<p>Why are quantum probabilities encoded in measures corresponding to wave functions, rather than by a more general class of measures? Call this question W<small>HY</small> B<small>ORN</small>? I argue that orthodox quantum mechanics has a compelling answer to W<small>HY</small> B<small>ORN</small>? but Bohmian mechanics might not. I trace Bohmian difficulties with W<small>HY</small> B<small>ORN</small>? to its <em>antistructuralism</em>, its denial of physical significance to the algebraic structure of quantum observables, and I propose other cases where Bohmian antistructuralism might have an explanatory cost.</p>2023-11-17T00:00:00+00:00Copyright (c) 2023 The author(s)'https://account.philosophyofphysics.lse.ac.uk/index.php/lse-j-pp/article/view/17Recovering General Relativity from a Planck Scale Discrete Theory of Quantum Gravity2022-12-13T17:11:16+00:00Jeremy ButterfieldFay Dowker<p>An argument is presented that if a theory of quantum gravity is physically discrete at the Planck scale and the theory recovers General Relativity as an approximation, then, at the current stage of our knowledge, causal sets must arise within the theory, even if they are not its basis.</p> <p>We lay out this argument in two claims. Roughly speaking, the first claim is that causal sets can recover continuum Lorentzian manifolds; and the second claim is that no other proposal for a set of discrete data that conforms to our sense of “fundamental discreteness at the Planck scale” is known to be able to recover continuum Lorentzian manifolds. To support this second claim, we show, in particular, that an apparent alternative discrete data set to causal sets, viz., a certain sort of combinatorial Lorentzian simplicial complex, cannot recover General Relativistic spacetimes in the appropriately unique way; for it cannot discriminate between Minkowski spacetime and a spacetime with a certain sort of gravitational wave burst.</p>2024-05-10T00:00:00+01:00Copyright (c) 2024 The author(s)'https://account.philosophyofphysics.lse.ac.uk/index.php/lse-j-pp/article/view/12Reopening the Hole Argument2023-01-25T20:32:47+00:00Klaas Landsman<p>This expository paper relates the Hole Argument in general relativity (<small>GR</small>) to the well-known theorem of Choquet-Bruhat and Geroch (1969) on the existence and uniqueness of globally hyperbolic solutions to the Einstein field equations. Like the Earman–Norton (1987) version of the Hole Argument (which is originally due to Einstein), this theorem exposes the tension between determinism and some version of spacetime substantivalism. But it seems less vulnerable to the campaign by Weatherall (2018) and followers to close the Hole Argument on the basis of “mathematical practice,” since the theorem only talks about isometries and hence does not make the pointwise identifications via diffeomorphisms that Weatherall objects to. Among other implications of the theorem for the philosophy of <small>GR</small>, we reconsider Butterfield’s (1987) influential definition of determinism. This should be amended if its goal is to express the idea that <small>GR</small> is deterministic in the absence of Cauchy horizons, although its original form does capture the way <small>GR</small> is indeterministic in their presence! Furthermore, in <small>GR</small> isometries come out as gauge symmetries, as do Poincaré transformations in special relativity.</p> <p>Finally, I discuss some implications of the theorem for the philosophy of science: Accepting the determinism horn still requires a choice between Frege-style abstractionism and Hilbert-style structuralism; and, within the latter, between structural realism and empiricist structuralism (which I favor).</p>2023-11-17T00:00:00+00:00Copyright (c) 2023 The author(s)'https://account.philosophyofphysics.lse.ac.uk/index.php/lse-j-pp/article/view/8Information is Physical: Cross-Perspective Links in Relational Quantum Mechanics2022-12-13T19:58:37+00:00Emily AdlamCarlo Rovelli<p>Relational quantum mechanics (RQM) is an interpretation of quantum mechanics based on the idea that quantum states do not describe an absolute property of a system but rather a relationship between systems. There have recently been some criticisms of RQM pertaining to issues around intersubjectivity. In this article, we show how RQM can address these criticisms by adding a new postulate which requires that all of the information possessed by a certain observer is stored in physical variables of that observer and thus is accessible by measurement to other observers. This makes it possible for observers to reach intersubjective agreement about quantum events that have occurred in the past. We suggest a possible ontology for a version of RQM employing this postulate; this ontology upholds the principle that quantum states are always relational, but it also postulates a set of quantum events that are not strictly relational. We show that the new postulate helps address the preferred basis problem in RQM.</p>2023-11-17T00:00:00+00:00Copyright (c) 2023 The author(s)https://account.philosophyofphysics.lse.ac.uk/index.php/lse-j-pp/article/view/7The Local Validity of Special Relativity, Part 2: Matter Dynamics2023-07-21T15:46:15+01:00Samuel C. FletcherJames Owen Weatherall<p>In this two-part essay, we distinguish several senses in which general relativity has been regarded as “locally special relativistic.” In Part 1, we focused on senses in which a relativistic spacetime may be said to be “locally (approximately) Minkowskian.” Here, in Part 2, we consider what it might mean to say that a matter theory is “locally special relativistic.” We isolate and evaluate three criteria in the literature and show that they are incompatible: matter theories satisfying one will generally violate others. We then consider what would happen if any of those criteria failed for a given theory.</p>2023-11-17T00:00:00+00:00Copyright (c) 2023 The author(s)'