Time travel is metaphysically possible. Nikk Effingham contends that arguments for the impossibility of time travel are not sound. Focusing mainly on the Grandfather Paradox, Effingham explores the ramifications of taking this view, discusses issues in probability and decision theory, and considers the potential dangers of travelling in time.

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)

If recent cosmological reasonings are correct, our universe is expanding irreversibly into oblivion—a conclusion that might well inspire feelings of insignificance and futility. Can we perhaps find a sense of meaning by seeing ourselves as participants in intergalactic morality? In this paper I examine the way in which moral rules come into being, exist, and cease to exist—and conclude that there is an intergalactic morality in which we can participate and through which we can feel a sense of (...) significance in our rapidly dissipating universe. (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.

ABSTRACT In their contribution to the first part of this special issue Craig Bourn and Emily Caddick Bourne claim to have solved a puzzle I put forward in my ‘An Insoluble Problem’. Here I argue that their attempt fails.

In this paper, I argue that the thesis that time travel is logically possible, is inconsistent with the necessary truth of any of the usual ‘open futureobjective present’ models of the universe. It has been relatively uncontroversial until recently to hold that presentism is inconsistent with the possibility of time travel. I argue that recent arguments to the contrary do not show that presentism is consistent with time travel. Moreover, the necessary truth of other open future-objective present (...) models which we might, prima facie, have supposed to be more amenable to the possibility of time travel, turn out also to be inconsistent with this possibility. (shrink)

This article examines continuity and change in Star trek’s expression of the American Frontier Myth, moving from an American ideal of imperialist expansion across an unlimited feminized landscape and destruction of Indians and animals in the myth’s early form, to one of benevolent redemption of the Other as misguided or evil alien in the unlimited expanse of outer space in early Star Trek. Analysis of symbol and narrative in Star Trek Voyager show further change, as feminist and environmental ethics are (...) included. Now, movement is toward earth rather than away from it, raced and gendered Others are often internalized rather than projected onto Indians and aliens, and nature is vulnerable and spiritual rather than unlimited and inert. Though women and nature are still linked and idealized as selfless givers, progress is also made as women gain equal rank and air time and men take on some traditionally feminine roles. (shrink)

Current models of autobiographical memory suggest that self-identity guides autobiographical memory retrieval. Further, the capacity to recall the past and imagine one’s self in the future can influence social problem solving. We examined whether manipulating self-identity, through an induction task in which students were led to believe they possessed high or low self-efficacy, impacted episodic specificity and content of retrieved and imagined events, as well as social problem solving. Compared to individuals in the low self efficacy group, individuals in the (...) high self efficacy group generated past and future events with greater specificity, positive words, and self-efficacious statements, and also performed better on social problem solving indices. A lack of episodic detail for future events predicted poorer performance on social problem solving tasks. Strategies that increase perceived self-efficacy may help individuals to selectively construct a past and future that aids in negotiating social problems. (shrink)

It is possible to wholly exist at multiple spatial locations at the same time. At least, if time travel is possible and objects endure, then such must be the case. To accommodate this possibility requires the introduction of a spatial analog of either relativising properties to times—relativising properties to spatial locations—or of relativising the manner of instantiation to times—relativising the manner of instantiation to spatial locations. It has been suggested, however, that introducing irreducibly spatially relativised or spatially adverbialised properties (...) presents some difficulties for the endurantist. I will consider an objection according to which embracing such spatially relativised properties could lead us to reject mereology altogether in favour of a metaphysics according to which objects are wholly present at every space-time point at which they exist. I argue that although such a view is coherent, there are some good reasons to reject it. Moreover, I argue that the endurantist can introduce spatially relativised or adverbialised properties without conceding that objects lack spatial parts. Such a strategy has the additional advantage that it allows the endurantist not only to explain time travel, but also to reconcile our competing intuitions about cases of fission. (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)

What is it to remember an episode from one’s past? How does episodic memory give us knowledge of the personal past? What explains the emergence of the apparently uniquely human ability to relive the past? Drawing on current research on mental time travel, this book proposes an integrated set of answers to these questions, arguing that remembering is a matter of simulating past episodes, that we can identify metacognitive mechanisms enabling episodic simulation to meet standards of reliability sufficient for (...) knowledge, and that the subjective experience of reliving the past is a precondition for the reliability of simulational remembering. The resulting account of memory, memory knowledge, and their evolution will be of interest both to philosophers interested in empirically-informed approaches to memory and to psychologists interested in the philosophical implications of empirical memory research. (shrink)

Humans have cognitive mechanisms that allow them to keep track of time, represent past events, and simulate the future, but these capacities have intrinsic constraints. Here, we explore the role of material culture as an extension of internal time representations through anthropological and archeological case studies, focusing on Upper Paleolithic material culture. We argue that calendars complement and extend internal time representations, because they enable humans to project past events into the future more accurately than is possible with episodic memory (...) alone, making them one of the factors that significantly improved foraging success during the Upper Paleolithic. We discuss the implications of the epistemic use of material culture for our understanding of the causes of shifts in human behavior during the Upper Paleolithic. (shrink)

The goal of this paper is to defend the general tenet that time travelers cannot change the past within B-theoretical models of time, independently of how many temporal dimensions there are. Baron Pacific Philosophical Quarterly, 98, 129–147 offered a strong argument intended to reach this general conclusion. However, his argument does not cover a peculiar case, i.e. a B-theoretical one-dimensional model of time that allows for the presence of internal times. Loss Pacific Philosophical Quarterly, 96, 1–11 used the latter model (...) to argue that time travelers can change the past within such model. We show a way to debunk Loss’s argument, so that the general tenet about the impossibility of changing the past within B-theoretical models is maintained. (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.

Journal Name: Semiotica Issue: Ahead of print.

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)

A comparison of a recent paper by Giora Hon in this journal with a book I wrote several years ago, on Gödel's philosophy of time, reveals that the substance, and indeed many of the words themselves, appearing in Hon's essay are in fact original to my book—the ideas of which he sadly failed to understand.

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)

In his thought-provoking, carefully crafted, and impressively researched article, Don Scheid makes a compelling argument for an indefinite detention paradigm for “mega-terrorists.” Scheid's proposa...

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)