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22SupertasksStanford Encyclopedia of Philosophy. 2022.A supertask is a task that consists in infinitely many component steps, but which in some sense is completed in a finite amount of time. Supertasks were studied by the pre-Socratics and continue to be objects of interest to modern philosophers, logicians and physicists. The term “super-task” itself was coined by J.F. Thomson (1954). Here we begin with an overview of the analysis of supertasks and their mechanics. We then discuss the possibility of supertasks from the perspective of general relat…Read more
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41A Hierarchy of Spacetime Symmetries: Holes to HeraclitusBritish Journal for the Philosophy of Science. forthcoming.
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53On automorphism criteria for comparing amounts of mathematical structureSynthese 201 (6): 1-14. 2023.Wilhelm (Forthcom Synth 199:6357–6369, 2021) has recently defended a criterion for comparing structure of mathematical objects, which he calls Subgroup. He argues that Subgroup is better than SYM \(^*\), another widely adopted criterion. We argue that this is mistaken; Subgroup is strictly worse than SYM \(^*\). We then formulate a new criterion that improves on both SYM \(^*\) and Subgroup, answering Wilhelm’s criticisms of SYM \(^*\) along the way. We conclude by arguing that no criterion that…Read more
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12On the (In?)Stability of Spacetime InextendibilityPhilosophy of Science 1-12. forthcoming.Leibnizian metaphysics underpins the universally held view that spacetime must be inextendible – that it must be “as large as it can be” in a sense. But here we demonstrate a surprising fact within the context of general relativity: the property of inextendibility turns out to be unstable when attention is restricted to certain collections of “physically reasonable”spacetimes.
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399Closing the Hole ArgumentBritish Journal for the Philosophy of Science. forthcoming.The hole argument purportedly shows that spacetime substantivalism implies a pernicious form of indeterminism. We show that the argument is seductive only because it mistakes a trivial claim (viz. there are isomorphic models) for a significant claim (viz. there are hole isomorphisms). We prove that the latter claim is false -- thereby closing the debate about whether substantivalism implies indeterminism.
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55Why Be regular?, part IStudies in History and Philosophy of Science Part B: Studies in History and Philosophy of Modern Physics 65 (C): 122-132. 2019.
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43A remark on ‘time machines’ in honor of Howard SteinStudies in History and Philosophy of Science Part B: Studies in History and Philosophy of Modern Physics 67 111-116. 2019.
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30Some “No Hole” Spacetime Properties are UnstableFoundations of Physics 48 (11): 1539-1545. 2018.We show a sense in which the spacetime property of effective completeness—a type of “local hole-freeness” or “local inextendibility”—is not stable.
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23General Relativity as a Collection of Collections of ModelsIn Judit Madarász & Gergely Székely (eds.), Hajnal Andréka and István Németi on Unity of Science: From Computing to Relativity Theory Through Algebraic Logic, Springer. pp. 409-425. 2021.One usually identifies a particular collection of geometric objects with the models of general relativity. But within this standard collection lurk ‘physically unreasonable’ models of spacetime. If such models are ruled out, attention can be restricted to some sub-collection of ‘physically reasonable’ models which can be considered a variant theory of general relativity. Since we have yet to identify a privileged sub-collection of ‘physically reasonable’ models, it is helpful to think of ‘genera…Read more
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11On Feyerabend, general relativity, and 'unreasonable' universesIn Karim Bschir & Jamie Shaw (eds.), Interpreting Feyerabend: Critical Essays, Cambridge University Press. 2021.I investigate the principle *anything goes* within the context of general relativity. After a few preliminaries, I show a sense in which the universe is unknowable from within this context; I suggest that we 'keep our options open' with respect to competing models of it. Given the state of affairs, proceeding counter-inductively seems to be especially appropriate; I use this method to blur some of the usual lines between 'reasonable' and 'unreasonable' models of the universe. Along the way, one …Read more
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22Space and TimeIn Sven Ove Hansson & Vincent F. Hendricks (eds.), Introduction to Formal Philosophy, Springer. pp. 487-496. 2012.Here, formal tools are used to pose and answer several philosophical questions concerning space and time. The questions involve the properties of possible worlds allowed by the general theory of relativity. In particular, attention is given to various causal properties such as “determinism” and “time travel”.
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62Paradox Regained? A Brief Comment on Maudlin on Black Hole Information LossFoundations of Physics 48 (6): 611-627. 2018.We discuss some recent work by Tim Maudlin concerning Black Hole Information Loss. We argue, contra Maudlin, that there is a paradox, in the straightforward sense that there are propositions that appear true, but which are incompatible with one another. We discuss the significance of the paradox and Maudlin's response to it.
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68Essay Review: Topics in the Foundations of General Relativity and Newtonian Gravitation TheoryDavid Malament, Topics in the Foundations of General Relativity and Newtonian Gravitation Theory. Chicago: University of Chicago Press , xii+349 pp., $55.00 (review)Philosophy of Science 79 (4): 575-583. 2012.
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67Malament–Hogarth MachinesBritish Journal for the Philosophy of Science 71 (3): 1143-1153. 2020.This article shows a clear sense in which general relativity allows for a type of ‘machine’ that can bring about a spacetime structure suitable for the implementation of ‘supertasks’. 1Introduction2Preliminaries3Malament–Hogarth Spacetimes4Machines5Malament–Hogarth Machines6Conclusion
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61Would two dimensions be world enough for spacetime?Studies in History and Philosophy of Science Part B: Studies in History and Philosophy of Modern Physics 63 100-113. 2018.We consider various curious features of general relativity, and relativistic field theory, in two spacetime dimensions. In particular, we discuss: the vanishing of the Einstein tensor; the failure of an initial-value formulation for vacuum spacetimes; the status of singularity theorems; the non-existence of a Newtonian limit; the status of the cosmological constant; and the character of matter fields, including perfect fluids and electromagnetic fields. We conclude with a discussion of what cons…Read more
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67Here we provide a proof that there exist closed timelike curves in Gödel spacetime with total acceleration less than 2π(9 + 6√3)^1/2. This answers a question posed by David Malament.
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102On force in cartesian physicsPhilosophy of Science 76 (3): 295-306. 2009.There does not seem to be a consistent way to ground the concept of “force” in Cartesian first principles. In this article, I first review the literature on the subject. Then, I offer an alternative interpretation of force—one that seems to be coherent and consistent with Descartes’ project. Not only does the new position avoid the problems of previous interpretations, but it does so in such a way as to support and justify those previous interpretations. *Received June 2007; revised June 2009. †…Read more
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44On the Inextendibility of Space-TimePhilosophy of Science 84 (5): 1215-1225. 2017.It has been argued that spacetime must be inextendible – that it must be “as large as it can be” in some sense. Here, we register some skepticism with respect to this position.
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80Is the Universe As Large As It Can Be?Erkenntnis 81 (6): 1341-1344. 2016.In this note, we cast doubt on the requirement of spacetime inextendibility; it is not at all clear that our universe is “as large as it can be.”
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45Time Travel: Why It May Not Pay to Work out All the KinksPhilosophy of Science 78 (5): 1037-1045. 2011.Here, we hypothesize that a smooth nongeodesic closed timelike curve is never most efficient with respect to total acceleration if a kink is permitted at the initial point. We support our hypothesis in a variety of ways. Most notably, we show Malament's opposing conjecture concerning Gödel space-time to be false.
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72On Gödel and the Ideality of TimePhilosophy of Science 83 (5): 1050-1058. 2016.Gödel's remarks concerning the ideality of time are examined. In the literature, some of these remarks have been somewhat neglected while others have been heavily criticized. In this note, we propose a clear and defensible sense in which Gödel's work bears on the question of whether there is an objective lapse of time in our world.
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59Global Spacetime StructureCambridge University Press. 2013.This exploration of the global structure of spacetime within the context of general relativity examines the causal and singular structures of spacetime, revealing some of the curious possibilities that are compatible with the theory, such as `time travel' and `holes' of various types. Investigations into the epistemic and modal structures of spacetime highlight the difficulties in ruling out such possibilities, unlikely as they may seem at first. The upshot seems to be that what counts as a `phy…Read more
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93On the Possibility of Supertasks in General RelativityFoundations of Physics 40 (3): 276-288. 2010.Malament-Hogarth spacetimes are the sort of models within general relativity that seem to allow for the possibility of supertasks. There are various ways in which these spacetimes might be considered physically problematic. Here, we examine these criticisms and investigate the prospect of escaping them
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146No no-go: A remark on time machinesStudies in History and Philosophy of Science Part B: Studies in History and Philosophy of Modern Physics 42 (1): 74-76. 2011.We present a counterexample to Krasnikov's much discussed time machine no-go result. In addition, we prove a positive statement: a time machine existence theorem under a modest "no holes" assumption.
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158Can we know the global structure of spacetime?Studies in History and Philosophy of Science Part B: Studies in History and Philosophy of Modern Physics 40 (1): 53-56. 2009.Here, we briefly review the notion of observational indistinguishability within the context of classical general relativity. We settle a conjecture given by Malament (1977) concerning the subject and then strengthen the result considerably. The upshot is this: There seems to be a robust sense in which the global structure of every cosmological model is underdetermined
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125What Is a Physically Reasonable Space-Time?Philosophy of Science 78 (3): 410-420. 2011.Cosmologists often use certain global properties to exclude "physically unreasonable" cosmological models from serious consideration. But, on what grounds should these properties be regarded as "physically unreasonable" if we cannot rule out, even with a robust type of inductive reasoning, the possibility of the properties obtaining in our own universe?
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83On Space-Time Singularities, Holes, and ExtensionsPhilosophy of Science 81 (5): 1066-1076. 2014.Here, we clarify the relationship among three space-time conditions of interest: geodesic completeness, hole-freeness, and inextendibility. In addition, we introduce a related fourth condition: effective completeness.
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110Is prediction possible in general relativity?Foundations of Physics 38 (4): 317-321. 2008.Here we briefly review the concept of "prediction" within the context of classical relativity theory. We prove a theorem asserting that one may predict one's own future only in a closed universe. We then question whether prediction is possible at all (even in closed universes). We note that interest in prediction has stemmed from considering the epistemological predicament of the observer. We argue that the definitions of prediction found thus far in the literature do not fully appreciate this p…Read more
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26Time machinesStudies in History and Philosophy of Science Part B: Studies in History and Philosophy of Modern Physics 48 (2): 124-127. 2014.
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Areas of Specialization
General Relativity |
Areas of Interest
General Relativity |
PhilPapers Editorships
General Relativity |