The idea that episodic memory is a form of mental time travel has played an important role in the development of memory research in the last couple decades. Despite its growing importance in psychology, philosophers have only begun to develop an interest in philosophical questions pertaining to the relationship between memory and mental time travel. Thus, this paper proposes a more systematic discussion of the relationship between memory and mental time travel from the point (...) of view of philosophy. I start by discussing some of the motivations to take memory to be a form of mental time travel. I call the resulting view of memory the mental time travel view. I then proceed to consider important philosophical questions pertaining to memory and develop them in the context of the mental time travel view. I conclude by suggesting that the intersection of the philosophy of memory and research on mental time travel not only provides new perspectives to think about traditional philosophical questions, but also new questions that have not been explored before. (shrink)

In "Changing the Past" (2010), Peter van Inwagen argues that a time traveler can change the past without paradox in a growing block universe. After erasing the portion of past existence that generates paradox, a new, non-paradox-generating block can be "grown" after the temporal relocation of the time traveler. -/- I articulate and explore the underlying mechanism of Van Inwagen's model: the time traveler's control over the location of the objective present. Van Inwagen's model is aimed at (...) preventing paradox by changing the past, but it achieves something broader than paradox avoidance: it gives tools for a new model of time travel. I use van Inwagen's tools to develop a new kind of time travel in which in which the location of the objective present is shifted by the time traveler. I call this type of time travel Movable Objective Present, or MOP. After defining MOP, I argue that it is compatible with any theory of time that accepts hypertime, including presentism and moving spotlight theory. (shrink)

Mental time travel is defined as projecting the self into the past and the future. Despite growing evidence of the similarities of remembering past and imagining future events, dominant theories conceive of these as distinct capacities. I propose that memory and imagination are fundamentally the same process – constructive episodic simulation – and demonstrate that the ‘simulation system’ meets the three criteria of a neurocognitive system. Irrespective of whether one is remembering or imagining, the simulation system: acts on (...) the same information, drawing on elements of experience ranging from fine-grained perceptual details to coarser-grained conceptual information and schemas about the world; is governed by the same rules of operation, including associative processes that facilitate construction of a schematic scaffold, the event representation itself, and the dynamic interplay between the two ; and is subserved by the same brain system. I also propose that by forming associations between schemas, the simulation system constructs multi-dimensional cognitive spaces, within which any given simulation is mapped by the hippocampus. Finally, I suggest that simulation is a general capacity that underpins other domains of cognition, such as the perception of ongoing experience. This proposal has some important implications for the construct of ‘MTT’, suggesting that ‘time’ and ‘travel’ may not be defining, or even essential, features. Rather, it is the ‘mental’ rendering of experience that is the most fundamental function of this domain-general simulation system enabling humans to re-experience the past, pre-experience the future, and also comprehend the complexities of the present. (shrink)

Introduction: Time travel and the mechanics of narrative -- Macrological fictions: evolutionary utopia and time travel (1887-1905) -- Historical interval I: the first time travel story -- Relativity, psychology, paradox: Wertenbaker to Heinlein (1923-1941) -- Historical interval II: three phases of time travel--the time machine -- The big time: multiple worlds, narrative viewpoint, and superspace -- Paradox and paratext: picturing narrative theory -- Theoretical interval: the primacy of the visual in (...) time travel narrative -- Viewpoint-over-histories: narrative conservation in Star Trek -- Oedipus multiplex, or, the subject as a time travel film: Back to the future -- Conclusion: The last time travel story. (shrink)

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)

I start off by relating the standard philosophical account of what time travel is to models of time travel that have recently been discussed by physicists. I then discuss some puzzles associated with time travel. I conclude that philosophers’ arguments against time travel are relevant when assessing the likelihood of the occurrence time travel in our world, and are relevant to the assessment whether time travel is physically possible.

The present paper offers a philosophical discussion of phenomena which in the empirical literature have recently been subsumed under the concept of ‘mental time travel’. More precisely, the paper considers differences and similarities between two cases of ‘mental time travel’, recollective memories (‘R-memories’) of past events on the one hand, and sensory imaginations (‘S-imaginations’) of future events on the other. It develops and defends the claim that, because a subject who R-remembers a past event is experientially (...) aware of a past particular event, while a subject who S-imagines a future event could not possibly be experientially aware of a future particular event, R-memories of past events and S-imaginations of future events are ultimately mental occurrences of two different kinds. (shrink)

Notoriously, the Einstein equations of general relativity have solutions in which closed timelike curves occur. On these curves time loops back onto itself, which has exotic consequences: for example, traveling back into one's own past becomes possible. However, in order to make time travel stories consistent constraints have to be satisfied, which prevents seemingly ordinary and plausible processes from occurring. This, and several other "unphysical" features, have motivated many authors to exclude solutions with CTCs from consideration, e.g. (...) by conjecturing a chronology protection law. In this contribution we shall investigate the nature of one particular class of exotic consequences of CTCs, namely those involving unexpected cases of indeterminism or determinism. Indeterminism arises even against the backdrop of the usual deterministic physical theories when CTCs do not cross spacelike hypersurfaces outside of a limited CTC-region|such hypersurfaces fail to be Cauchy surfaces. We shall compare this CTC-indeterminism with four other types of indeterminism that have been discussed in the philosophy of physics literature: quantum indeterminism, the indeterminism of the hole argument, non-uniqueness of solutions of differential equations and lack of predictability due to insuffcient data. By contrast, a certain kind of determinism appears to arise when an indeterministic theory is applied on a CTC: things cannot be different from what they already were. Again we shall make comparisons, this time with other cases of determination in physics. We shall argue that on further consideration both this indeterminism and determinism on CTCs turn out to possess analogues in other, familiar areas of physics. CTC- indeterminism is close to the epistemological indeterminism we know from statistical physics, while the "fixedness" typical of CTC-determinism is pervasive in physics. CTC- determinism and CTC-indeterminism therefore do not provide incontrovertible grounds for rejecting CTCs as conceptually inadmissible. (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)

In this paper I defend two conclusions: that time travel journeys to the past are not undertaken freely and, more generally, that nobody is free between the earliest arrival time and the latest departure time of a time travel journey to the past. Time travel to the past destroys freedom on a global scale.

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)

Episodic memory (memories of the personal past) and prospecting the future (anticipating events) are often described as mental time travel (MTT). While most use this description metaphorically, we argue that episodic memory may allow for MTT in at least some robust sense. While episodic memory experiences may not allow us to literally travel through time, they do afford genuine awareness of past-perceived events. This is in contrast to an alternative view on which episodic memory experiences present (...) past-perceived events as mere intentional contents. Hence, episodic memory is a way of coming into experiential contact with, or being again aware of, what happened in the past. We argue that episodic memory experiences depend on a causal-informational link with the past events being remembered, and that, assuming direct realism about episodic memory experiences, this link suffices for genuine awareness. Since there is no such link in future prospection, a similar argument cannot be used to show that it also affords genuine awareness of future events. Constructivist views of memory might challenge the idea of memory as genuine awareness of remembered events. We explain how our view is consistent with both constructivist and anti-causalist conceptions of memory. There is still room for an interpretation of episodic memory as enabling genuine awareness of past events, even if it involves reconstruction. (shrink)

The paper discusses radical constructivism about episodic memory as developed by Kourken Michaelian under the name of “simulationism”, a view that equates episodic memory with mental time travel. An alternative, direct realist view is defended, which implies disjunctivism about the appearance of remembering. While admitting the importance of mental time travel as an underlying cognitive mechanism in episodic memory, as well as the prima facie reasonableness of the simulationist’s critique of disjunctivism, I formulate three arguments in (...) defense of disjunctivism, which thus appears to be a feasible alternative to radical constructivism. (shrink)

Is time travel just a confusing plot device deployed by science fiction authors and Hollywood filmmakers to amaze and amuse? Or might empirical data prompt a scientific hypothesis of time travel? Structured on a fascinating dialogue involving  ...

Future-biased individuals systematically prefer positively valenced events to be in the future (positive future-bias) and negatively valenced events to be in the past (negative future-bias). The most extreme form of future-bias is absolute future-bias, whereby we completely discount the value of past events when forming our preferences. Various authors have thought that we are absolutely future-biased (Sullivan (2018:58); Parfit (1984:173) and that future-bias (absolute or otherwise) is at least rationally permissible (Prior (1959), Hare (2007; 2008), Kauppinen (2018), Heathwood (2008)). The (...) permissibility of future-bias is often held to be grounded in the structure of the temporal dimension. In this paper I consider several proposals for grounding the permissibility of such preferences and evaluate these in the light of the preferences we would have, and judge that we should have, in various time-travel scenarios. I argue that what we learn by considering these scenarios is that these preferences really have nothing to do with temporal structure. So if something grounds their permissibility, it is not temporal structure. (shrink)

ABSTRACTEpisodic memory is the ability to revisit events in one's personal past, to relive them as if one travelled back in mental time. It has widely been assumed that such an ability imposes a metaphysical requirement on selves. Buddhist philosophers, however, deny the requirement and therefore seek to provide accounts of episodic memory that are metaphysically parsimonious. The idea that the memory perspective is a centred field of experience whose phenomenal constituents are simulacra of an earlier field of experience, (...) yet attended to in a way that presents them as happening again, is, I suggest, a better one than that the memory perspective consists in taking as object-aspect the subject-aspect of the earlier experience, or the idea that it consists in labelling a representation of the earlier experience with an I-tag. (shrink)

This paper brings two fresh perspectives on Lewis’s theory of time travel. First: many key aspects and theoretical desiderata of Lewis’s theory can be captured in a framework that does not commit to eternalism about time. Second: implementing aspects of Lewisian time travel in a non-eternalist framework provides theoretical resources for a better treatment of time travel to the future. While time travel to the past has been extensively analyzed, time (...) travel to the future has been comparatively underexplored. I make progress on this topic. Along the way, I discuss Lewis’s lesser-known time travel oeuvre, especially his volume of correspondence and lectures on the topic collected in Beebee and Fisher (2020) and Janssen-Lauret & MacBride (forthcoming). Lewis’s body of unpublished work on time travel yields fruitful insights into his broader thinking on the subject. (shrink)

In no possible world does a time traveler succeed in killing herearlier self before she ever enters a time machine. So if many,many time travelers went back in time trying to kill theirunprotected former selves, the time travelers would fail inmany strange, coincidental ways, slipping on bananapeels, killing the wrong victim, and so on. Such cases producedoubts about time travel. How could ``coincidences'' beguaranteed to happen? And wouldn't the certainty of coincidentalfailure imply that (...) time travelers are not free to killtheir earlier selves? But if so, what would inhibit theirfreedom? Despite initial appearances, these and other doubtsmay be answered: the possibility of time travel survives yetanother challenge. (shrink)

Darwin and feminism: preliminary investigations into a possible alliance -- Darwin and the ontology of life -- The Nature of culture -- Law, justice, and the future -- The Time of violence: Derrida, deconstruction, and value -- Drucilla Cornell, identity, and the "Evolution" of Politics -- Philosophy, knowledge, and the future -- Deleuze, Bergson, and the virtual -- Merleau-Ponty, Bergson, and the question of ontology -- The thing -- Prosthetic objects -- Identity, sexual difference, and the future -- (...) The Time of thought -- The Force of sexual difference -- (Inhuman) forces: power, pleasure, and desire -- The future of female sexuality. (shrink)

This paper suggests that time travelling scenarios commonly depicted in science fiction introduce problems and dangers for the time traveller. If time travel takes time, then time travellers risk collision with past objects, relocation to distant parts of the universe, and time travel-specific injuries. I propose several models of time travel that avoid the dangers and risks of time travel taking time, and that introduce new questions about (...) the relationship between time travel and spatial location. (shrink)

We standardly evaluate counterfactuals and abilities in temporally asymmetric terms—by keeping the past fixed and holding the future open. Only future events depend counterfactually on what happens now. Past events do not. Conversely, past events are relevant to what abilities one has now in a way that future events are not. Lewis, Sider and others continue to evaluate counterfactuals and abilities in temporally asymmetric terms, even in cases of backwards time travel. I’ll argue that we need more temporally (...) neutral methods. The past shouldn’t always be held fixed, because backwards time travel requires backwards counterfactual dependence. Future events should sometimes be held fixed, because they’re in the causal history of the past, and agents have evidence of them independently of their decisions now. We need temporally neutral methods to maintain connections between causation, counterfactuals and evidence, and if counterfactuals are used to explain the temporal asymmetry of causation. (shrink)

There is an extensive literature on time travel in both philosophy and physics. Part of the great interest of the topic stems from the fact that reasons have been given both for thinking that time travel is physically possible—and for thinking that it is logically impossible! This entry deals primarily with philosophical issues; issues related to the physics of time travel are covered in the separate entries on time travel and modern (...) physics and time machines. We begin with the definitional question: what is time travel? We then turn to the major objection to the possibility of backwards time travel: the Grandfather paradox. Next, issues concerning causation are discussed—and then, issues in the metaphysics of time and change. We end with a discussion of the question why, if backwards time travel will ever occur, we have not been visited by time travellers from the future. (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)

Ryan Wasserman explores a range of fascinating puzzles raised by the possibility of time travel, with entertaining examples from physics, science fiction, and popular culture, and he draws out their implications for our understanding of time, tense, freedom, fatalism, causation, counterfactuals, laws of nature, persistence, change, and mereology.

This paper explores what the metaphysics of time travel might teach us about moral responsibility. We take our cue from a recent paper by Yishai Cohen, who argues that if time travel is metaphysically possible, then one of the most influential theories of moral responsibility (i.e., Fischer and Ravizza’s) is false. We argue that Cohen’s argument is unsound but that Cohen’s argument can serve as a lens to bring reasons-responsive theories of moral responsibility into sharper focus, (...) helping us to better understand actual-sequence theories of moral responsibility more generally and showing how actual-sequence theorists should respond to a recent criticism. (shrink)

In this paper I give consideration to some apparent impossibilities for the time travelers to the past. After criticizing the views of D. Lewis and K. Vihvelin, I will show in what sense they are really impossible.

A recent account of presentist time travel involves a causal relation between events at two different and discontiguous times, and presentists cannot have such causal relations because presentism rules out the existence of at least one of the two relata in such a relation due to it being non-present. Additionally, presentists cannot have parodies of such causal relations for use in time travel stories because parodies are subject, at least, to the same limitations as the things (...) being parodied. So, the presentist has not successfully given an internally consistent account of presentist time travel. (shrink)

Many defenders of the possibility of time travel into the past also hold that such time travel places no restrictions on what said time travelers can do. Some hold that it places at least a few restrictions on what time travelers can do. In attempting to resolve this dispute, I reached a contrary conclusion. Time travelers to the past cannot do other than what they in fact do. Using a very weak notion of (...) can, I shall argue that the correspondingly strong cannot do otherwise applies in the case of backwards time travel. I defend this result from objections. (shrink)

The paper first tries to explain how the possibility of "time travel" arises in the Godel universe. It then goes on to discuss a technical problem conerning minimal acceleration requirements for time travel. A theorem is stated and a conjecture posed. If the latter is correct, time travel can be ruled out as a practical possibility in the Godel universe.

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.

The subject of time travel has been receiving increasing attention in the recent philosophical literature. Most of the articles that deal with it have been concerned to defend the logical consistency of time travel against those who claim that it entails one or more contradictions. Two sorts of defences have been offered. The first sort of defence involves showing that time travel does not entail those consequences which other philosophers allege it does entail. The (...) second sort of defence involves an admission that time travel does indeed involve that which its opponents allege it does involve, e.g., being in more than one place at a time, but arguing that such consequences in no way vitiate the logical consistency of this notion.My first aim in this paper is to provide a defence of time travel of the second sort. More specifically, I want to cut the ground from under an argument which might run thus:Time travel entails that certain effects can precede their causes.It is logically impossible for an effect to precede its cause. (shrink)

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)

Theodore Sider has recently produced an argument which he takes to show that three-dimensionalism is incompatible with the possibility of time travel. I wish to argue that there is indeed a problem for the three-dimensionalist who wishes to countenance time travel, but that Sider has misdiagnosed it. I show why his putative challenge fails, and furthermore that if it were to succeed this would be as problematic for a wide class of four-dimensionalist positions, including Sider’s own, (...) as it would be for three-dimensionalism. Finally, I present the problem that the possibility of time travel genuinely poses for the three-dimensionalist. (shrink)

In 1987, Roy Sorensen coined the term 'parahistory' to denote the study of genuinely anachronistic artefacts delivered by time travel.¹ 'Parahistory' would thus stand to history rather as parapsychology is claimed to stand to psychology, i.e. the parahistorian would study historical data that were obtained through channels that orthodox science does not recognise. How might one establish credentials as a time traveller? What sort of evidence could a time-traveller point to in support of claims that would (...) presumably command a great deal of scepticism? While successful predictions might be one confirmatory tool, supporting evidence needn't take the form of predictions. (Although Sorensen offers an intriguing argument that a Humean about miracle-testimony would be obliged to reject any testimony to the occurrence of time travel.) Perhaps artefacts that time travellers retrieve from other times (past or future) could usefully supplement testimonial or predictive evidence for the parahistorian. However, this paper will argue, any appeal to past-artefactual evidence for parahistorical claims faces a dilemma that threatens to undermine its value: appeals to past-artefact evidence must either collapse into appeals to predictive evidence or see their value diminished by such past artefacts' necessarily exhibiting contradictory indicators of age and period. (shrink)

There is no possible world in which someone travels back in time and kills herself as a baby. All possible worlds are internally consistent; the one just described would not be. For this reason, autoinfanticide is metaphysically impossible. This metaphysical impossibility is philosophically intriguing because unlike most impossible events, we can vividly picture how it might look. Time travel itself seems possible, and for those who arrive in the past with proper equipment and training, the actual infanticide (...) should not be difficult. The considerations in this paper have led me to conclude that there are indeterministic worlds in which instances of autoinfanticide have a chance of succeeding, sometimes even a high chance. Some may be tempted to resist this conclusion, uncomfortable with the notion that something metaphysically impossible can have a positive chance. Understandably, they expect something which happens at no world to also have no chance of happening. However, no plausible theory of chance fits these preconceptions. (shrink)

The possibility of time travel, as permitted in General Relativity, is responsible for constraining physical fields beyond what laws of nature would otherwise require. In the special case where time travel is limited to a single object returning to the past and interacting with itself, consistency constraints can be avoided if the dynamics is continuous and the object's state space satisfies a certain topological requirement: that all null-homotopic mappings from the state-space to itself have some fixed (...) point. Where consistency constraints do exist, no new physics is needed to enforce them. One needs only to accept certain global topological constraints as laws, something that is reasonable in any case. (shrink)

I have used a time travel story to model the “Latin” version of the Trinity. William Hasker’s “A Leftovian Trinity?” criticizes my arguments. This piece replies.

This is a paper about time travel and what it teaches us about freedom. I argue that cases of time travel bring out an important difference between two ways of thinking about “the past”—either in terms of time itself, or in terms of causation. This ambiguity naturally transfers over to our talk about things like fixity, determinism, and incompatibilism. Moreover, certain cases of time travel suggest that our freedom is not constrained by the (...) temporal past _per se_, but by our own causal histories. This, in turn, raises a number of interesting questions about the formulation of incompatibilism and the broader debate over freedom. (shrink)

THE PURPOSE OF THIS ARTICLE IS TO SHOW HOW HUME’S SCEPTICISM ABOUT MIRACLES GENERATES "EPISTEMOLOGICAL" SCEPTICISM ABOUT TIME TRAVEL. SO THE PRIMARY QUESTION RAISED HERE IS "CAN ONE KNOW THAT TIME TRAVEL HAS OCCURED?" RATHER THAN "CAN TIME TRAVEL OCCUR?" I ARGUE THAT ATTEMPTS TO SHOW THE EXISTENCE OF TIME TRAVEL WOULD FACE THE SAME METHODOLOGICAL PROBLEMS AS THE ONES CONFRONTING ATTEMPTS TO DEMONSTRATE THE EXISTENCE OF PARANORMAL EVENTS. SINCE HUMEAN SCEPTICISM EXTENDS (...) TO THE STUDY OF PARANORMAL EVENTS (PARAPSYCHOLOGY), HUMEANS ARE COMMITTED TO SCEPTICISM ABOUT THE STUDY OF TIME TRAVEL ("PARAHISTORY"). (shrink)

Is time-travel possible? Like most intriguing problems that lie within the shared locus of physics, metaphysics and logic, this question admits of many interpretations, each of which engenders a different line of research. At its most anemic, the issue can be just: Is it possible to tell a story about travel into the past that contains no explicit contradictions? Under the stimulation of physical concerns it may develop into a more challenging problem: Do the laws of physics, (...) as best we understand them, admit of solutions that contain closed time-like curves? And next: Would it be physically possible for a massive object to travel along one of those curves into its own local past? Then: Are the known facts about our universe consistent with it being such a world? And finally: Is time-travel in our universe technologically possible? When prodded in this direction our original question arrives at last on the drawing boards of the engineers, having passed successively through the precincts of the theoretical physicists, the mathematicians, and the astronomers. (shrink)

Kourken Michaelian is one of the principal architects in the emerging field of philosophy of memory. His book Mental Time Travel: Episodic Memory and Our Know...