Experiences of motion and change are widely taken to have a ‘flow-like’ quality. Call this ‘temporal qualia’. Temporal qualia are commonly thought to be central to the question of whether time objectively passes: (1) passage realists take temporal passage to be necessary in order for us to have the temporal qualia we do; (2) passage antirealists typically concede that time appears to pass, as though our temporal qualia falsely represent time as passing. I reject both claims and make the case (...) that passage-talk plays no useful explanatory role with respect to temporal qualia, but rather obfuscates what the philosophical problem of temporal qualia is. I offer a ‘reductionist’ account of temporal qualia that makes no reference to the concept of passage and argue that it is well motivated by empirical studies in motion perception. (shrink)

Relativity theory is often said to support something called ‘the four-dimensional view of reality’. But there are at least three different views that sometimes go by this name. One is ‘spacetime unitism’, according to which there is a spacetime manifold, and if there are such things as points of space or instants of time, these are just spacetime regions of different sorts: thus space and time are not separate manifolds. A second is the B-theory of time, according to which the (...) past, present, and future are all equally real and there is nothing metaphysically special about the present. A third is perdurantism, according to which persisting material objects are made up of different temporal parts located at different times. We sketch routes from relativity to unitism and to the B-theory. We then discuss some routes to perdurantism, via the B-theory and via unitism. (shrink)

A variety of ideas arising in decoherence theory, and in the ongoing debate over Everett's relative-state theory, can be linked to issues in relativity theory and the philosophy of time, specifically the relational theory of tense and of identity over time. These have been systematically presented in companion papers (Saunders 1995; 1996a); in what follows we shall consider the same circle of ideas, but specifically in relation to the interpretation of probability, and its identification with relations in the Hilbert Space (...) norm. The familiar objection that Everett's approach yields probabilities different from quantum mechanics is easily dealt with. The more fundamental question is how to interpret these probabilities consistent with the relational theory of change, and the relational theory of identity over time. I shall show that the relational theory needs nothing more than the physical, minimal criterion of identity as defined by Everett's theory, and that this can be transparently interpreted in terms of the ordinary notion of the chance occurrence of an event, as witnessed in the present. It is in this sense that the theory has empirical content. (shrink)

Questions about the metaphysics of causation may be usefully divided as follows. First, there are questions about the nature of the causal relata, including (1.1) whether they are in spacetime immanence), (1.2) how fine grained they are individuation), and (1.3) how many there are adicity). Second, there are questions about the metaphysics of the causal relation, including (2.1) what is the difference between causally related and causally unrelated sequences connection), (2.2) what is the difference between sequences related as cause to (...) effect, and those related as effect to cause or as joint effects of a common cause direction), and (2.3) what is the difference between sequences involving the cause, and those involving mere conditions selection). (shrink)

This paper is an enquiry into the logical, metaphysical, and physical possibility of time travel understood in the sense of the existence of closed worldlines that can be traced out by physical objects. We argue that none of the purported paradoxes rule out time travel either on grounds of logic or metaphysics. More relevantly, modern spacetime theories such as general relativity seem to permit models that feature closed worldlines. We discuss, in the context of Gödel's infamous argument for the ideality (...) of time based on his eponymous spacetime, what this apparent physical possibility of time travel means. Furthermore, we review the recent literature on so-called time machines, i.e., of devices that produce closed worldlines where none would have existed otherwise. Finally, we investigate what the implications of the quantum behaviour of matter for the possibility of time travel might be and explicate in what sense time travel might be possible according to leading contenders for full quantum theories of gravity such as string theory and loop quantum gravity. (shrink)

I formulate a theory of persistence in the endurantist family and pose a problem for the conjunction of this theory with orthodox versions of special or general relativity. The problem centers around the question: Where are things?

This paper argues that the most famous objection to backward time travel can carry no weight. In its classic form, the objection is that backward time travel entails the occurrence of impossible things, such as auto-infanticide—and hence is itself impossible. David Lewis has rebutted the classic version of the objection: auto-infanticide is prevented by coincidences, such as time travellers slipping on banana peels as they attempt to murder their younger selves. I focus on Paul Horwich‘s more recent version of the (...) objection, according to which backward time travel entails not impossible things, but improbable ones—such as the string of slips on banana peels that would be required to stop a determined auto-infanticidal maniac from murdering her younger self—and hence is itself highly improbable. I argue that backward time travel does not entail unusual numbers of coincidences; and that, even if it did, that would not render its occurrence unlikely. (shrink)

It is a central aspect of our ordinary concept of time that history unfolds and events come into being. It is only natural to take this seriously. However, it is notoriously difficult to explain further what this `becoming' consists in, or even to show that the notion is consistent at all. In this article I first argue that the idea of a global temporal ordering, involving a succession of cosmic nows, is not indispensable for our concept of time. Our experience (...) does not support the existence of global simultaneity and arguments from modern physics further support the conclusion that time should not be seen as a succession of cosmic nows. Accordingly, I propose that if we want to make sense of becoming we should attempt to interpret it as something purely local. Second, I address the question of what this local becoming consists in. I maintain that processes of becoming are nothing but the successive happening of events, and that this happening of events consists entirely in the occurring of these events at their own spacetime locations. This leads to a consistent view of becoming, which is applicable even to rather pathological spacetimes. (shrink)

This essay offers a reaction to the recent resurgence of presentism in the philosophy of time. What is of particular interest in this renaissance is that a number of recent arguments supporting presentism are crafted in an untypically naturalistic vein, breathing new life into a metaphysics of time with a bad track record of co-habitation with modern physics. Against this trend, the present essay argues that the pressure on presentism exerted by special relativity and its core lesson of Lorentz symmetry (...) cannot easily be shirked. A categorization of presentist responses to this pressure is offered. As a case in point, I analyze a recent argument by Monton (2006) presenting a case for the compatibility of presentism with quantum gravity. Monton claims that this compatibility arises because there are quantum theories of gravity that use fixed foliations of spacetime and that such fixed foliations provide a natural home for a metaphysically robust notion of the present. A careful analysis leaves Monton's argument wanting. In sum, the prospects of presentism to be alleviated from the stress applied by fundamental physics are faint. (shrink)

But this picture of a ‘block universe’, composed of a timeless web of ‘world-lines’ in a four-dimensional space, however strongly suggested by the theory of relativity, is a piece of gratuitous metaphysics. Since the concept of change, of something happening, is an inseparable component of the common-sense concept of time and a necessary component of the scientist's view of reality, it is quite out of the question that theoretical physics should require us to hold the Eleatic view that nothing happens (...) in ‘the objective world’. Here, as so often in the philosophy of science, a useful limitation in the form of representation is mistaken for a deficiency of the universe. (shrink)

This article deals with the question of what time reversal means. It begins with a presentation of the standard account of time reversal, with plenty of examples, followed by a popular non-standard account. I argue that, in spite of recent commentary to the contrary, the standard approach to the meaning of time reversal is the only one that is philosophically and physically viable. The article concludes with a few open research problems about time reversal.

State-reduction and the notion of actuality are compared to passage through time and the notion of the present; already in classical relativity the latter give rise to difficulties. The solution proposed here is to treat both tense and value-definiteness as relational properties or facts as relations; likewise the notions of change and probability. In both cases essential characteristics are absent: temporal relations are tenselessly true; probabilistic relations are deterministically true. The basic ideas go back to Everett, although the technical development (...) makes use of the decoherent histories theory of Griffiths, Omnès, and Gell-Mann and Hartle. Alternative interpretations of the decoherent histories framework are also considered. (shrink)

Existing puzzles about coinciding objects can be divided into two types, corresponding to the manner in which they bear upon the endurantism v. perdurantism debate. Puzzles of the first type, which involve temporary spatial co-location, can be solved simply by abandoning endurantism in favor of perdurantism, whereas those of the second type, which involve career-long spatial co-location, remain equally puzzling on both views. I show that the possibility of backward time travel would give rise to a new type of puzzle. (...) The new puzzles confront perdurantists and can be solved just by shifting to endurantism. (shrink)

Time is what clocks are used to measure. Information about time tells the durations of events and when they occur and which events happen before which others, so time plays a very significant role in the universe’s structure, including the structure of our personal lives. But carefully describing time’s properties has led to many unresolved issues, both philosophical and scientific.

There is a philosophical tradition of arguing against presentism, the thesis that only presently existing things exist, on the basis of its incompatibility with fundamental physics. I grant that presentism is incompatible with special and general relativity, but argue that presentism is not incompatible with quantum gravity, because there are some theories of quantum gravity that utilize a fixed foliation of spacetime. I reply to various objections to this defense of presentism, and point out a flaw in Gödel's modal argument (...) for the ideality of time. This paper provides an interesting case study of the interplay between physics and philosophy. (shrink)

Yuri Balashov has argued that endurantism isuntenable in the context of Minkowskispacetime. Balashov's argument runs through twomain theses concerning the relation ofcoexistence, or temporal co-location. (1)Coexistence must turn out to be an absolute or objective matter; and inMinkowski spacetime coexistence must begrounded in the relation of spacelikeseparation. (2) If endurantism is true, then(1) leads to absurd conclusions; but ifperdurantism is true, then (1) is harmless. Iobject to both theses. Against (1), I arguethat coexistence is better construed as beingrelative to a (...) hyperplane of simultaneity.Against (2), I argue that the consequences of(1) given endurantism are no worse than theconsequences of (1) given perdurantism. (shrink)

An introduction to the theories of endurantism and perdurantism, and persistence more broadly.

Although C. D. Broad's notion of Becoming has received a fair amount of attention in the philosophy-of-time literature, there are no serious attempts to show how to replace the standard 'block' spacetime models by models that are more congenial to Broad's idea that the sum total of existence is continuously increased by Becoming or the coming into existence of events. In the Newtonian setting Broad-type models can be constructed in a cheating fashion by starting with a Newtonian block model, carving (...) chips off the block, and assembling the chips in an appropriately structured way. However, attempts to construct Broad-type models in a non-cheating fashion reveal a number of problematic aspects of Becoming that have not received adequate attention in the literature. The paper then turns to an assessment of the problem and prospects of adapting Becoming models to relativistic spacetimes. The results of the assessment differ in both minor and major ways from the ones in the extant literature. Finally, the paper describes how the causal set approach to quantum gravity promises to provide a mechanism for realizing Becoming, though the form of Becoming that emerges may not conform to any of the versions discussed in the philosophical literature. (shrink)

Special relativity has been understood by many as vindicating a tenseless conception of time, denying the existence of tensed facts and a fortiori objective temporal passage. The reason for this is straightforward: both passage and the obtaining of tensed facts require a universal knife-edge present moment—yet this structure is not easily reconcilable with the relativity of simultaneity. The above being said, the prospects for tense and passage are sometimes claimed to be improved on moving to cosmological solutions of general relativity. (...) In this paper, we evaluate in detail these arguments, finding that there remain several open questions to be addressed if the introduction of tensed facts into the relativistic context is to be compelling. Moreover, we argue that, even setting aside these issues, objective tense stands and falls in relativity for exactly the same reasons that it does in classical philosophical discussions on the matter. (shrink)

Continental philosophy of science has developed alongside mainstream analytic philosophy of science. But where continental approaches are inclusive, analytic philosophies of science are not–excluding not merely Nietzsche’s philosophy of science but Gödel’s philosophy of physics. As a radicalization of Kant, Nietzsche’s critical philosophy of science puts science in question and Nietzsche’s critique of the methodological foundations of classical philology bears on science, particularly evolution as well as style (in art and science). In addition to the critical (in Mach, Nietzsche, Heidegger (...) but also Husserl just to the extent that continental philosophy of science tends to depart from a reflection on the crisis of foundations), other continental philosophies of science include phenomenology (Husserl, Bachelard, Merleau‐Ponty, etc.) and hermeneutics (Heidegger, Gadamer, Heelan, etc.), especially incorporating history of science (Nietzsche, Mach, Duhem, Butterfield, Feyerabend, etc.). Examples are drawn from the philosophy of sciences (chemistry, geology, and biology) other than physics. (shrink)

A short review of some recent developments in the philosophy of physics is presented. I focus on themes which illustrate relations and points of common interest between philosophy of physics and three of its `neighboring' elds: Physics, metaphysics and general philosophy of science. The main examples discussed in these three `border areas' are decoherence and the interpretation of quantum mechanics; time in physics and metaphysics; and methodological issues surrounding the multiverse idea in modern cosmology.

The aim of this essay is to introduce philosophers of science to some recent philosophical discussions of the nature and origin of the direction of time. The essay is organized around books by Hans Reichenbach, Paul Horwich, and Huw Price. I outline their major arguments and treat certain critical points in detail. I speculate at the end about the ways in which the subject may continue to develop and in which it may connect with other areas of philosophy.

The aim of this doctoral dissertation is to closely explore the nature of Einstein’s block universe and to tease out its implications for the nature of time and human freedom. Four questions, in particular, are central to this dissertation, and set out the four dimensions of this philosophical investigation: (1) Does the block universe view of time follow inevitably from the theory of special relativity? (2) Is there room for the passage of time in the block universe? (3) Can we (...) distinguish past from future in the block universe? (4) Is there room for human freedom in the block universe? Although the answer of most philosophers would be yes, triple no, my own answer, controversially, is no, triple yes. -/- I thereby challenge the status quo with respect to each of these metaphysical questions, and argue that none of these questions can be answered from looking at physics alone. Physics may constrain our metaphysics, but it certainly does not settle it. What is needed in order to answer these questions, are additional metaphysical assumptions that fall outside the scope of modern physics. My primary goal in this dissertation, therefore, is not to settle the debates on the nature of time and human freedom, but to clarify them by expliciting the metaphysical assumptions that are otherwise left implicit. (shrink)

The relational approach to tense holds that the now, passage, and becoming are to be understood in terms of relations between events. The debate over the adequacy of this framework is illustrated by a comparative study of the sense in which physical theories, (in)deterministic and (non)relativistic, can lend expression to the metaphysics at issue. The objective is not to settle the matter, but to clarify the nature of this metaphysics and to establish that the same issues are at stake in (...) the relational approach to value-definiteness and probability in quantum mechanics. They concern the existence of a unique present, respectively actuality, and a notion of identity over time that cannot be paraphrased in terms of relations. (shrink)

Two symmetry arguments are discussed, each purporting to show that there is no more room for a preferred division of spacetime into instants of time in general relativistic cosmology than in Minkowski spacetime. The first argument is due to Gödel, and concerns the symmetries of his famous rotating cosmologies. The second turns upon the symmetries of a certain space of relativistic possibilities. Both arguments are found wanting.

Time travel has been a staple of science fiction. With the advent of general relativity it has been entertained by serious physicists. But, especially in the philosophy literature, there have been arguments that time travel is inherently paradoxical. The most famous paradox is the grandfather paradox: you travel back in time and kill your grandfather, thereby preventing your own existence. To avoid inconsistency some circumstance will have to occur which makes you fail in this attempt to kill your grandfather. Doesn't (...) this require some implausible constraint on otherwise unrelated circumstances? We examine such worries in the context of modern physics. (shrink)

This essay aims to provide a self-contained introduction to time in relativistic cosmology that clarifies both how questions about the nature of time should be posed in this setting and the extent to which they have been or can be answered empirically. The first section below recounts the loss of Newtonian absolute time with the advent of special and general relativity, and the partial recovery of absolute time in the form of cosmic time in some cosmological models. Section II considers (...) the beginning and end of time in a broader class of models in which there is not an analog of Newtonian absolute time. As we will see, reasonable physical assumptions imply that the universe is finite to the past, and Section III turns to consideration of the “beginning” itself. We critically review conventional wisdom that a “singularity” reveals flaws in general relativity and briefly assess ways of avoiding the singularity. (shrink)

Presentists have typically argued that the Block View is incapable of explaining our experience of time. In this paper I argue that the phenomenology of our experience of time is, on the contrary, against presentism. My argument is based on a dilemma: presentists must either assume that the metaphysical present has no temporal extension, or that it is temporally extended. The former horn leads to phenomenological problems. The latter renders presentism metaphysically incoherent, unless one posits a discrete present that, however, (...) suffers from the same difficulties that the instantaneous present is prone to. After introducing the main phenomenological models of our experience of time that are discussed in the literature, I show that none of them favors presentism. I conclude by arguing that if even the phenomenology of time sides against presentism, the latter metaphysical theory has no scientific evidence in its favor and ought to be dropped. (shrink)

Metaphysicians who are aware of modern physics usually follow Putnam (1967) in arguing that Special Theory of Relativity is incompatible with the view that what exists is only what exists now or presently. Partisans of presentism (the motto ‘only present things exist’) had very difficult times since, and no presentist theory of time seems to have been able to satisfactorily counter the objection raised from Special Relativity. One of the strategies offered to the presentist consists in relativizing existence to inertial (...) frames. This unfashionable strategy has been accused of counterfeiting, since the meaning of the concept of existence would be incompatible with its relativization. Therefore, existence could only be relativistically invariant. In this paper, I shall examine whether such an accusation hits its target, and I will do this by examining whether the different criteria of existence that have been suggested by the Philosophical Tradition from Plato onwards imply that existence cannot be relativized. (shrink)

In this paper I consider two objections raised by Nick Smith (1997) to an argument against the probability of time travel given by Paul Horwich (1995, 1987). Horwich argues that time travel leads to inexplicable and improbable coincidences. I argue that one of Smith's objections fails, but that another is correct. I also consider an instructive way to defend Horwich's argument against the second of Smith's objections, but show that it too fails. I conclude that unless there is something faulty (...) in the conception of explanation implicit in Horwich's argument, time travel presents us with nothing that is inexplicable. (shrink)

Some have thought that the process of the expansion of the universe can be used to define an absolute ‘cosmic time’ which then serves as the absolute time required by tensed theories of time. Indeed, this is the very reason why many tense theorists are happy to concede that special relativity is incompatible with the tense thesis, because they think that general relativity, which trumps special relativity, and on which modern cosmology rests, supplies the means of defining temporal becoming using (...) cosmic time. I argue that cosmic time is not up to the task, and that these tense theorists should rethink their strategy in dealing with the theories of relativity. Introduction The Mellor-Rees argument against tense theories Can expansion combat such wrinkles? Event and creation horizons Bursting the balloon. (shrink)

Gödel's philosophical views were to a significant extent influenced by the study not only of Leibniz or Husserl, but also of Kant. Both Gödel and Kant aimed at the secure foundation of philosophy, the certainty of knowledge and the solvability of all meaningful problems in philosophy. In this paper, parallelisms between the foundational crisis of metaphysics in Kant's view and the foundational crisis of mathematics in Gödel's view are elaborated, especially regarding the problem of finding the “secure path of a (...) science” for both mathematics and philosophy. Gödel's temporal subjectivism and metaphysical conceptual objectivism are presented as positively or negatively motivated by Kant's viewpoints. A remark on Gödel's collapse of modalities (in accordance with the collapse of objective time) is added. (shrink)

L'éternalisme implique une forme exotique d'éternité : toute entité, aussi éphémère soit-elle et quelle que soit sa localisation dans le temps, existe relativement à toute autre localisation temporelle. Cet essai vise, premièrement, à défendre l'éternalisme en exhibant les difficultés rédhibitoires du présentisme et du non-futurisme, et deuxièmement à examiner de quelle manière l'éternalisme pourrait être amendé à l'aune d'une affirmation que l'on trouve sous la plume de certains physiciens, à savoir que, fondamentalement, le temps n'existe pas. La disparition du temps (...) est-elle compatible avec la thèse éternaliste ? Enfin, en guise de conclusion, nous examinerons brièvement une conséquence curieuse de l'éternalisme : bien que mortels, nous sommes des êtres éternels. (shrink)

Kurt Gödel made many affirmations of robust realism but also showed serious engagement with the idealist tradition, especially with Leibniz, Kant, and Husserl. The root of this apparently paradoxical attitude is his conviction of the power of reason. The paper explores the question of how Gödel read Kant. His argument that relativity theory supports the idea of the ideality of time is discussed critically, in particular attempting to explain the assertion that science can go beyond the appearances and ‘approach the (...) things’. Leibniz and post-Kantian idealism are discussed more briefly, the latter as documented in the correspondence with Gotthard Günther. (shrink)

The essay centers on Gödel's views on the place of our intuitive concept of time in philosophy and in physics. It presents my interpretation of his work on the theory of relativity, his observations on the relationship between Einstein's theory and Kantian philosophy, as well as some of the scattered remarks in his conversations with me in the seventies — namely, those on the philosophies of Leibniz, Hegel and Husserl — as a successor of Kant — in relation to their (...) conceptions of time. (shrink)

Gödel’s philosophical conceptions bear striking similarities to Cantor’s. Although there is no conclusive evidence that Gödel deliberately used or adhered to Cantor’s views, one can successfully reconstruct and see his “Cantorianism” at work in many parts of his thought. In this paper, I aim to describe the most prominent conceptual intersections between Cantor’s and Gödel’s thought, particularly on such matters as the nature and existence of mathematical entities (sets), concepts, Platonism, the Absolute Infinite, the progress and inexhaustibility of mathematics.

I wish to discuss a supposed implication of one sort of time travel. The sort of time travel is time travel into one’s past along a closed timelike curve. The implication is that in spacetimes with CTCs there can be no temporal passage or “flow” of time. I will argue that the implication does not hold.

This thesis is about the conceptualization of persistence of physical, middle-sized objects within the theoretical framework of the revisionary ‘B-theory’ of time. According to the B-theory, time does not flow, but is an extended and inherently directed fourth dimension along which the history of the universe is ‘laid out’ once and for all. It is a widespread view among philosophers that if we accept the B-theory, the commonsensical ‘endurance theory’ of persistence will have to be rejected. The endurance theory says (...) that objects persist through time by being wholly present at distinct times as numerically the same entity. Instead of endurantism, it has been argued, we have to adopt either ‘perdurantism’ or the ‘stage theory’. Perdurantism is the theory that objects are four-dimensional ‘space-time worms’ persisting through time by having distinct temporal parts at distinct times. The stage theory says that objects are instantaneous temporal parts (stages) of space-time worms, persisting by having distinct temporal counterparts at distinct times. In the thesis, it is argued that no good arguments have been provided for the conclusion that we are obliged to drop the endurance theory by acceptance of the B-theory. This conclusion stands even if the endurance theory incorporates the claim that objects endure through intrinsic change. It is also shown that perdurantism and the stage theory come with unwelcome consequences. -/- Paper I demonstrates that the main arguments for the view that objects cannot endure in B-time intrinsically unchanged fail. Papers II and III do the same with respect to the traditional arguments against endurance through intrinsic change in B-time. Paper III also contains a detailed account of the semantics of the tenseless copula, which occurs frequently in the debate. The contention of Paper IV is that four-dimensional space-time worms, as traditionally understood, are not suited to take dispositional predicates. In Paper V, it is shown that the stage theory needs to introduce an overabundance of persistence-concepts, many of which will have to be simultaneously applicable to a single object (qua falling under a single sortal), in order for the theory to be consistent. The final article, Paper VI, investigates the sense in which persistence can, as is sometimes suggested, be a ‘conventional matter’. It also asks whether alleged cases of ‘conventional persistence’ create trouble for the endurance theory. It is argued that conventions can only enter at a trivial semantic level, and that the endurance theory is no more threatened by such conventions than are its rivals. (shrink)

Eternalism is a metaphysical view regarding the nature of time. It posits the equal existence of all times: the past, the present, and the future. Every event, from the big bang to the heat death of the universe, including our births and deaths, is equally real. -/- Under standard eternalism, temporal locations are somewhat akin to spatial locations. No place is exclusively real. When someone says that they stand ‘here’, it is clear that the term ‘here’ refers to their position. (...) ‘Back’ and ‘front’ exist as well. Eternalists stress that ‘now’ is indexical in a similar way. It is equally real with ‘past’ and ‘future’. Events are classified as past, present, or future from some perspective. -/- Eternalism is contrasted with presentism, which maintains that only present things exist and with the growing block view (also known as possibilism or no-futurism), which holds that past and present things exist but not future ones. The moving spotlight view suggests that all times exist but that the present is the only actual time. This view can be termed eternalist, but it preserves a non-perspectival difference between past, present, and future by treating tense as absolute. Additionally, the moving spotlight view retains some characteristics of presentism by maintaining that the ‘now’ is unique and privileged. -/- Broadly speaking, presentism is a common-sensical view, and so aligns with our manifest image of time. This view is, however, at odds with the scientific image of time. The primary motivation for eternalism arises from orthodox interpretations of the theories of relativity. According to them, simultaneity is relative, not absolute. This implies that there is no universal ‘now’ stretched out across the entire universe. One observer’s present can be another’s past or future. Assuming the universe is four-dimensional spacetime, then all events exist unconditionally. -/- The classical argument for eternalism was devised in the 1960s by Rietdijk in 1966 and Putnam in 1967, with subsequent follow-ups by Maxwell in 1985, Penrose in 1989, and Peterson and Silberstein in 2010. This argument and its ramifications remain the subject of ongoing debate. They shall be further explored in this entry, including their relation to other issues in the metaphysics of time and the philosophy of physics. (shrink)

Thinking about time travel is an entertaining way to explore how to understand time and its location in the broad conceptual landscape that includes causation, fate, action, possibility, experience, and reality. It is uncontroversial that time travel towards the future exists, and time travel to the past is generally recognized as permitted by Einstein’s general theory of relativity, though no one knows yet whether nature truly allows it. Coherent time travel stories have added flair to traditional debates over the metaphysical (...) status of the past, the reality of temporal passage, and the existence of free will. Moreover, plausible models of time travel and time machines can be used to investigate the subtle relation between space-time structure and causality. -/- It surveys some philosophical issues concerning time travel and should serves as a quick introduction. It includes a new and improved way to define a time machine. (shrink)

The aim of this paper is to make presentism a dynamic view of reality by basing it on a notion of dynamic existence, that is, on a notion of existence which has a dynamic character. The paper shows that both of the notions of existence which are used in metaphysical theories of time have a static character and, while such a notion is useful for eternalists, it is useless for presentists if they want to make their view able to remain (...) in agreement with our everyday experience and self-consistent. It is demonstrated that both empirical and theoretical arguments indicate that the presentist should replace the notion of this static existence with the notion of a dynamic existence and that this maneuver allows the presentist to treat his/her existential thesis as equivalent to the thesis that time flows. Not only does this strategy allow us to express presentism in a simple, homogenous way which remains in agreement with our experience, but also permits us to solve some of the difficult problems which presentism faces, such as, for example, the objection of triviality and the question about the rate of time passage. Moreover, such an approach to presentism allows us to solve fundamental metaphysical problems concerning time such as the problem of the openness of the future and the fixity of the past, direction of causation, and relations between presentism and persistence through time by endurance. (shrink)

The debate about the passage of time is usually confined to Minkowski‟s geometric interpretation of space-time. It infers the block universe from the notion of relative simultaneity. But there are alternative interpretations of space-time – so-called axiomatic approaches –, based on the existence of „optical facts‟, which have thermodynamic properties. It may therefore be interesting to approach the afore-mentioned debate from the point of view of relativistic thermodynamics, in which invariant parameters exist, which may serve to indicate the passage of (...) time. Of particular interest is the use of entropic clocks, gas clocks and statistical thermometers, which suggest that two observers in Minkowski space-time could agree on an objective passing of time. (shrink)

In a recent publication in the European Journal for Philosophy of Science, Romero and Pérez claim to reveal new trouble for the already difficult life of presentism in relativistic spacetimes. Their argument purports to demonstrate the impossibility of postulating a viable present in the presence of black holes, in particular the Schwarzschild geometries. I argue that their argument is flawed, and that the Schwarzschild geometries they consider offer no novel threats to presentism. However, if we consider more general black holes, (...) different and more potent threats may be lurking in the dark. I discuss these threats and sketch how a presentist may respond, thus painting a more balanced picture of the way the existence of black holes might impact presentist metaphysics. At present there is no decisive verdict from black holes, but it turns out a close scrutiny of the developments in the relevant physics will be needed to see whether their import will remain so inconclusive. (shrink)

The physicist's conception of space-time underwent two major upheavals thanks to the general theory of relativity and quantum mechanics. Both theories play a fundamental role in describing the same natural world, although at different scales. However, the inconsistency between them emerged clearly as the limitation of twentieth-century physics, so a more complete description of nature must encompass general relativity and quantum mechanics as well. The problem is a theorists' problem par excellence. Experiment provide little guide, and the inconsistency mentioned above (...) is an important problem which clearly illustrates the intermingling of philosophical, mathematical, and physical thought. In fact, in order to unify general relativity with quantum field theory, it seems necessary to invent a new mathematical framework which will generalise Riemannian geometry and therefore our present conception of space and space-time. Contemporary developments in theoretical physics suggest that another revolution may be in progress, through which a new kind of geometry may enter physics, and space-time itself can be reinterpreted as an approximate, derived concept. The main purpose of this article is to show the great significance of space-time geometry in predetermining the laws which are supposed to govern the behaviour of matter, and further to support the thesis that matter itself can be built from geometry, in the sense that particles of matter as well as the other forces of nature emerges in the same way that gravity emerges from geometry. Scientific research is not a process of steady accumulation of absolute truths, which has culminated in present theories, but rather a much more dynamic kind of process in which there are no final theoretical concepts valid in unlimited domains. (David Bohm). (shrink)

Hilary Putnam argued that the special theory of relativity shows that there can be no temporal becoming. Howard Stein replied by defining a becoming relation in Minkowski spacetime. Clifton and Hogarth extended and sharpened Stein’s results. Game over? To the contrary, it has been argued that the Stein-Clifton-Hogarth theorems actually support Putnam’s contention, in that if an apparently minimal condition is put on the becoming relation, then these theorems entail that the becoming relation must be the universal relation. I recount (...) this dialectic in some detail and then try to define and defend a becoming relation based on a present that does indeed consist of more than one point or event but still satisfies the sort of objectivity requirements that Stein-Clifton-Hogarth require of a becoming relation. This present is not a global hyperplane or surface, however; it is a local structure. I close with some methodological remarks about the relation between the present and the real and about the importance of the specious or psychological present. (shrink)

The block universe theory of time is commonly said to be incompatible with temporal becoming. This confuses Maudlin who upholds both eternalism and passage. The aim of this paper is to answer Maudlin’s plea for clarification by distinguishing four degrees of temporal becoming. After discussing their respective compatibility with the block universe, I show that Maudlin asks much less from temporal becoming than most philosophers of time. Consequently, his form of becoming is compatible with the block universe, whereas the stronger (...) forms of becoming are not. (shrink)