James Read

Realism about general relativity (GR) seems to imply realism about spacetime curvature. The existence of the teleparallel equivalent of general relativity (TEGR) calls this into question, for (a) TEGR is set in a torsionful but flat spacetime, and (b) TEGR is empirically equivalent to GR. Knox (Stud Hist Philos Sci Part B Stud Hist Philos Mod Phys 42(4):264–275, 2011) claims that there is no genuine underdetermination between GR and TEGR; we call this verdict into question by isolating and addressing her individual arguments. In addition, we anticipate and evaluate two further worries for realism about the torsionful spacetimes of TEGR, which we call the ‘problem of operationalisability’ and the ‘problem of visualisability’.

The nodes of the ‘geometric trinity’ are: (i) general relativity (in which grav itational effects are a manifestation of spacetime curvature), (ii) the ‘teleparallel equivalent’ of general relativity (which trades spacetime curvature for torsion), and(iii) the ‘symmetric teleparallel equivalent’ of general relativity (which trades spacetime curvature for non-metricity). Onepopularreformulationof(iii)is‘co incident general relativity’, but this theory has yet to receive any philosophical attention. This article aims both to introduce philosophers to coincident general relativity, and to undertake a detailed assessment of its features.

String field theory is supposed to stand to perturbative string theory as quantum field theory stands to single-particle quantum theory; as such, it purports to offer a substantially more general and powerful perspective on string theory than the perturbative approach. In addition, string field theory has been claimed for several decades to liberate string theory from any fixed, background spatiotemporal commitments—thereby (if true) rendering it ‘background independent’. But is this really so? In this article, we undertake a detailed interrogation of this claim, finding that the verdict is sensitive both to one’s understanding of the notion of background independence, and also to how one understands string field theory itself. Although in the end our verdicts on the question of the background independence are therefore somewhat mixed, we hope that our study will elevate the levels of systematicity and rigour in these discussions, as well as equip philosophers of physics with a helpful introduction to string field theory and the variety of interesting conceptual questions which it raises.

We discuss affinities and differences between (i) the hole argument in general relativity and (ii) Putnam’s model-theoretic argument against metaphysical realism (‘Putnam’s paradox’). Following Pooley (The Reality of Spacetime, University of Oxford, 2002), we maintain that the hole argument is not a special case of Putnam’s paradox. This notwithstanding, both of these arguments have been responded to through meta-linguistic means. While van Fraassen (Philosophical Perspectives 11:17–42, 1997) claims that Putnam’s paradox dissolves due to our inability to identify a function mapping our theories to objects in the world independent of our total language, Bradley and Weatherall (Philosophy of Science 89(5): 1223–1232, 2022) maintain that the language of general relativity does not allow for the hole argument to be formulated. We compare these responses and assess the extent to which either is successful, concluding that we find van Fraassen’s argument more persuasive precisely because of the greater generality of Putnam’s paradox.

We consider the distinction between ‘qualified’ and ‘unqualified’ approaches introduced by Read (2020a) in the context of the dynamical/geometrical debate. We show that one fruitful way in which to understand this distinction is in terms of what one takes the kinematically possible models of a given theory to represent; moreover, we show that the qualified/unqualified distinction is applicable not only to the geometrical approach (which is the case considered by Read (2020a)), but also to the dynamical approach. Finally, having made these points, we connect them to other discussions of representation and of explanation in this corner of the literature.

Historically, a great deal of attention has been addressed to the question of what it would take to test experimentally the metrical structure of spacetime. Arguably, however, consideration of this question has been at the expense of comparable investigations into what it would take to test other structural features of spacetime. In this article, we critique and expand substantially upon an article by Hadley (Hadley in Class Quantum Gravity, 19:4565–4571, 2002), which constitutes one of the best-known paper-length studies of what it would take to test the orientability of spacetime. In so doing, we seek to clarify a number of matters which remain unclear in the wake of Hadley’s article, thereby allowing the literature on this topic to progress. More positively, we also present, compare, and evaluate a number of other potential approaches to testing the orientability of spacetime which have arisen in the recent physics literature.

Famously, Adrian Moore has argued that an absolute representation of reality is possible: that it is possible to represent reality from no particular point of view. Moreover, Moore believes that such absolute representations are a desideratum of physics. Recently, however, debates in the philosophy of physics have arisen regarding the apparent impossibility of an absolute representation of certain aspects of nature in light of our current best theories of physics. Throughout this article, we take gravitational energy as a particular case study of an aspect of nature that seemingly does not admit of an absolute representation. There is, therefore, a prima facie tension between Moore’s a priori case on the one hand, and the state-of-play in modern physics on the other. This article overcomes this tension by demonstrating how, when formulated in the correct way, modern physics admits of an absolute representation of gravitational energy after all. In so doing, the article offers a detailed case study of Moore’s argument for absolute representation, clarifying its structure and bringing it into contact with the distinction drawn by philosophers of physics between coordinate-freedom and coordinate-independence, as well as the philosophy of spacetime physics.

A ‘‘duality’’ is a formal mapping between the spaces of solutions of two empirically equivalent theories. In recent times, dualities have been found to be pervasive in string theory and quantum field theory. Naïvely interpreted, duality-related theories appear to make very different ontological claims about the world—differing in, for example, spacetime structure, fundamental ontology, and mereological structure. In light of this, duality-related theories raise questions familiar from discussions of underdetermination in the philosophy of science: in the presence of dual theories, what is one to say about the ontology of the world? Int his paper, we undertake a comprehensive and nontechnical survey of the landscape of possible ontological interpretations of duality-related theories. We provide a significantly enriched and clarified taxonomy of options—several of which are novel to the literature.

Despite its being one of Roger Penrose’s greatest contributions to spacetime physics, there is a dearth of philosophical literature on twistor theory. The one exception to this is Bain (2006)—but although excellent, there remains much to be said on the foundations and philosophy of twistor theory. In this article, we (a) present for philosophers an introduction to twistor theory, (b) consider how the spacetime–twistor correspondence interacts with the philosophical literature on theoretical equivalence, and (c) explore the bearing which twistor theory might have on philosophical issues such as the status of dynamics, the geometrisation of physics, spacetime ontology, the emergence of spacetime, and symmetry-to-reality inferences. We close with an elaboration of a variety of further opportunities for philosophical investigation into twistor theory.

Over the past decade, the physics literature on torsionful non-relativistic gravity has burgeoned; more recently, philosophers have also begun to explore this topic. As of yet, however, the connections between the writings of physicists and philosophers on torsionful non-relativistic gravity remain unclear. In this article, we seek to bridge the gap, in particular by situating within the context of the existing physics literature a recent theory of non-relativistic torsionful gravity developed by philosophers Meskhidze and Weatherall (Philos Sci, https://doi.org/10.1017/psa.2023.136, 2023) we also discuss the philosophical significance of that theory.

Canonically, ‘classic’ tests of general relativity (GR) include perihelion precession, the bending of light around stars, and gravitational redshift; ‘modern’ tests have to do with, _inter alia_, relativistic time delay, equivalence principle tests, gravitational lensing, strong field gravity, and gravitational waves. The orthodoxy is that both classic and modern tests of GR afford experimental confirmation of that theory _in particular_. In this article, we question this orthodoxy, by showing there are classes of both relativistic theories (with spatiotemporal geometrical properties different from those of GR) and non-relativistic theories (in which the lightcones of a relativistic spacetime are ‘widened’) which would also pass such tests. Thus, (a) issues of underdetermination in the context of GR loom much larger than one might have thought, and (b) given this, one has to think more carefully about what exactly such tests in fact _are_ testing.

In a recent article, Halvorson and Manchak (Br J Philos Sci, Forthcoming) claim that there is no basis for the Hole Argument, because (in a certain sense) hole isometries are unique. This raises two important questions: (a) does their argument succeed?; (b) how does this formalist response to the Hole Argument relate to other recent responses to the Hole Argument in the same tradition—in particular, that of Weatherall (Br J Philos Sci 69(2):329–350, 2018)? In this article, _ad_ (a), we argue that Halvorson and Manchak’s claim does not go through; _ad_ (b), we argue that although one _prima facie_ plausible reading would see Halvorson and Manchak as filling an important hole (no pun intended) in Weatherall’s argument, in fact this reading is implausible; there is no need to supplement Weatherall’s work with Halvorson and Manchak’s results.

Supposing that one is already familiar with special relativistic physics, what constitutes the best route via which to arrive at the architecture of the general theory of relativity? Although the later Einstein would stress the significance of mathematical and theoretical principles in answering this question, in this article we follow the lead of the earlier Einstein (circa 1916) and stress instead how one can go a long way to arriving at the general theory via inductive and empirical principles, without invoking presumptions concerning the geometrical structure of the final theory. We focus on the construction of the kinematical structure and the terms describing the coupling of matter to gravity. General covariance, understood and employed as a straightforward extrapolation of empirical considerations, is central to our derivation, together with what we dub the `Methodological Equivalence Principle'. We argue that our approach has a number of virtues, both for one's understanding of the general theory of relativity, but also for pedagogy, since it stresses---to the greatest extent possible (a lesson which we inherit from Bell, [1976])---both the methodological precedence of dynamical considerations to interpretative issues and the theoretical continuity between general relativity and its precursors. We conclude by comparing our approach to other philosophical approaches to general relativity and discussing the significance of empirically motivated methodological principles in the philosophy of science.

Recent work in the physics literature demonstrates that, in particular classes of rotating spacetimes, physical light rays in general do not traverse null geodesics. Having presented this result, we discuss its philosophical significance, both for the clock hypothesis (and, in particular, a recent purported proof thereof for light clocks), and for the operational meaning of the metric field. 1Introduction 2Fletcher's Theorem 2.1Maudlin on the clock hypothesis in special relativity 2.2Fletcher’s result in special relativity 2.3Fletcher’s theorem in general relativity 3Electromagnetism and the Geometrical-Optical Limit 3.1Maxwell’s equations in curved spacetime 3.2The geometrical-optical limit 3.3Rotating spacetimes 3.4Aren’t Gödel spacetimes unphysical? 4The Clock Hypothesis and Chronogeometry 4.1Natural and mathematical observations 4.2Clock registry discord 4.3Chronogeometry 5Conclusion.

It is plausible that the models of scientific theories correspond to possibilities. But how do we know which models of which scientific theories so correspond? This paper provides a novel proposal for guiding belief about possibilities via scientific theories. The proposal draws on the notion of an effective theory: a theory that applies very well to a particular, restricted domain. We argue that it is the models of effective theories that we should believe correspond, at least in part, to possibilities. It is thus effective theories that should guide modal reasoning in science.

We explore the significance of physical theories set in Euclidean spacetimes. In particular, we explore the use of these theories in contemporary physics at large, and the sense in which there can be a notion of temporal evolution in these theories. Having achieved these tasks, we proceed to reflect on the lessons that one can take from such theories for Knox’s ‘inertial frame’ version of spacetime functionalism, which seems to issue incorrect verdicts in the case of theories with Euclidean metrical structure.

What, if anything, would be wrong with replacing the light postulate in Einstein’s 1905 formulation of special relativity with a ‘sound postulate’, stating that the speed of sound is independent of the speed of the source? After reviewing the historical reasons underlying the particular focus on light in the special theory, we consider the circumstances under which such a theory of ‘sonic relativity’ would be justified on empirical grounds. We then consider the philosophical upshots of ‘sonic relativity’ for four contemporary areas of investigation in the philosophy of spacetime: global versus subsystem symmetries, dynamical versus geometrical approaches to spacetime, the possibility of a preferred frame in theories of quantum gravity, and spacetime functionalism.

Consensus in the contemporary philosophical literature has it that conserved quantity theories of causation such as that of Dowe [2000]—according to which causation is to be analysed in terms of the exchange of conserved quantities (e.g., energy)—face damning problems when confronted with contemporary physics, where the notion of conservation becomes delicate. In particular, in general relativity it is often claimed that there simply are no conservation laws for (say) total-stress energy. If this claim is correct, it is difficult to see how conserved quantity theories of causation could survive. In this article, we resist the above consensus and defend conserved quantity theories from this conclusion, at least when focusing on the apparent problems posed by general relativity. We argue that this approach to causation can continue to be defended in general relativity, once one appreciates (a) the availability of approximate symmetries in generic general relativistic spacetimes, and (b) the role of modelling and idealisation in that theory. Given these points, conserved quantity theories of causation must stand or fall on other grounds.

In a recent article in this journal, Sus purports to account for what have been identified as the ‘two miracles’ of general relativity—that (1) the local symmetries of all dynamical equations for matter fields coincide, and (2) the symmetries of the dynamical equations governing matter fields coincide locally with the symmetries of the metric field—by application of the familiar result that every symmetry of the action is also a symmetry of the resulting equations of motion. In this reply, we argue that, while otherwise exemplary in its clarity, Sus’ paper fails in this regard, for it rests upon a illegitimate application of the aforementioned result. Thus, we conclude, pace Sus, that these two miracles persist in general relativity.