I argue that the theory of moral responsibility defended by John Martin Fischer and Mark Ravizza is incompatible with the metaphysical possibility of time travel.

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)

If time travel is possible, presumably so is my shooting my younger self ; then apparently I can kill him – I can commit retrosuicide. But if I were to kill him I would not exist to shoot him, so how can I kill him? The standard solution to this paradox understands ability as compossibility with the relevant facts and points to an equivocation about which facts are relevant: my killing YS is compossible with his proximity but not with his (...) survival, so I can kill him if facts like his survival are irrelevant but I cannot if they are relevant. I identify a lacuna in this solution, namely its reliance without argument on the hidden assumption that my killing YS is possible: if it is impossible, it is not compossible with anything. I argue that this lacuna is important, and I sketch a different solution to the paradox. (shrink)

David Lewis’s analysis of “can” in “The Paradoxes of Time Travel” has been widely accepted both as a definitive analysis of “can” and as a successful resolution of the Grandfather Paradox for time travel. I argue that the central feature of his analysis puts it on all fours with a fallacy frequently imputed to fatalists such as Richard Taylor. I go on to consider two moves that might be made to avoid the fallacy, arguing that one of them leads to (...) the unavailability of an all-things-considered “can” and the other to a new primitive modality, not analyzable in Lewis’s way. (shrink)

I argue that, contrary to an idea to be found in popularizations of time travel, one cannot more easily multiply oneself by taking younger versions of oneself back in time than by travelling back in time on one’s own. The reason is that the suggested multiplication of the traveller is, from a global perspective, only apparent.

H. G. Wells’ Time Traveller inhabits uniform Newtonian time. Where relativistic/quantum travelers into the past follow spacetime curvatures, past-bound Wellsians must reverse their direction of travel relative to absolute time. William Grey and Robin Le Poidevin claim reversing Wellsians must overlap with themselves or fade away piecemeal like the Cheshire Cat. Self-overlap is physically impossible but ‘Cheshire Cat’ fades destroy Wellsians’ causal continuity and breed bizarre fusions of traveler-stages with opposed time-directions. However, Wellsians who rotate in higher-dimensional space can reverse (...) temporal direction without self-overlap, Cheshire Cats or mereological monstrosities. Alas, hyper-rotation in Newtonian space poses dynamic and biological problems,. Controllable and survivable Wellsian travel needs topologically-variable spaces. Newtonian space, not Newtonian time, is Wellsians’ real enemy. (shrink)

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 paper focuses on problems for time travel that specifically concern continuous time-travel to the past, problems to do with potential collisions with past obstacles such as former time-slices of the time traveler herself. These problems have not been discussed nearly as much as other questions about time travel, such as the Grandfather Paradox. Here I focus on discussions by Bernstein, Dowe, Grey and Le Poidevin. After examination, I conclude that only the problems of turning around in time have any (...) merit and present a new proposal of my own for turning around in time without collisions. I assume a Lewisian framework throughout. (shrink)

Here I defend the compatibility of presentism and time travel against a few objections. Keller and Nelson argue that, if presentism is at all plausible, presentism and time travel are as compatible as eternalism and time travel. But Miller and Sider are not convinced. I reply that for their concerns to have merit, Miller and Sider must assume presentists are committed to positions they need not be; I explain why presentists are not so committed and, in the process, defend Keller (...) and Nelson’s position that there is no roadblock to presentist time travel that does not also apply to eternalist time travel. (shrink)

The possibility of continuous backwards time travel—time travel for which the traveler follows a continuous path through space between departure and arrival—gives rise to the double-occupancy problem. The trouble is that the time traveler seems bound to have to travel through his or her younger self as the trip begins. Dowe and Le Poidevin agree that this problem is solved by putting the traveler in motion for a gradual trip to the past. Le Poidevin goes on to argue, however, that (...) the gradual trip gives rise to the Cheshire cat problem, a concern about whether the traveler survives the gradual trip. We address the Cheshire cat problem by proposing and considering new continuity constraints on identity over time. Along the way, we come upon an endurantist conception of temporal parts. (shrink)

Time passes, and the inexorability of its passing has deep emotional significance. One of the main themes of this thesis involves an investigation into the metaphysical nature of the passage of time. What sort of metaphysical account of passage should be given? And do our emotional responses to temporal passage have metaphysical implications? The other main theme of the thesis is the issue of the metaphysics of persistence. When a thing is present at more than one time, what is the (...) metaphysical underpinning of its persistence? Some subsidiary issues, which are nevertheless important in their own right, are also discussed. There are interesting connections between the issues of persistence and these further issues, which include the nature of vagueness, and the distinction between intrinsic and extrinsic properties. (shrink)

I distinguish paradoxes and hypodoxes among the conundrums of time travel. I introduce ‘hypodoxes’ as a term for seemingly consistent conundrums that seem to be related to various paradoxes, as the Truth-teller is related to the Liar. In this article, I briefly compare paradoxes and hypodoxes of time travel with Liar paradoxes and Truth-teller hypodoxes. I also discuss Lewis’ treatment of time travel paradoxes, which I characterise as a Laissez Faire theory of time travel. Time travel paradoxes are impossible according (...) to Laissez Faire theories, while it seems hypodoxes are possible. (shrink)