This paper is dedicated to articulating the ethical puzzles that arise from the possibility of time travel. I divide the puzzles into three different categories: permissibility puzzles, obligation puzzles, and conflicts between past and future selves. In each category, I suggest that ethical problems involving time travel are not as dissimilar to parallel “normal” ethical puzzles as one might think.

This paper addresses a worry about backwards time travel. The worry is that there is something mysteriously inexplicable about the combination of commonplace events that will inevitably conspire to prevent the time traveler from doing something impossible such as killing her younger self. The worry is first distinguished from other problems for backwards time travel concerning its alleged impossibility or improbability. It is then shown that the worry is misplaced: there is in fact no real problem here. Yet the worry (...) has been widely expressed—so a suggestion is also made as to why it is so easy to get into the position of thinking that there is a genuine problem here, when in fact there is not. Finally, in light of the resolution of the inexplicability worry, a new way of dealing with the other two problems for backwards time travel—concerning its alleged impossibility and improbability—is proposed. (shrink)

Do time travellers retain their normal freedom and abilities when they travel back in time? Lewis, Horwich and Sider argue that they do. Time-travelling Tim can kill his young grandfather, his younger self, or whomever else he pleases—and so, it seems can reasonably deliberate about whether to do these things. He might not succeed. But he is still just as free as a non-time traveller. I’ll disagree. The freedom of time travellers is limited by a rational constraint. Tim can’t reasonably (...) deliberate on killing his grandfather, certain that he’ll fail. If Tim follows his evidence, and appropriately self-predicts, he will be certain he won’t kill his grandfather. So if Tim is both evidentially and deliberatively rational, he can’t deliberate on killing his grandfather. This result has consequences. Firstly, it shows how evidential limits in the actual world contribute to our conception of the future as open. Secondly, it undercuts arguments against the possibility of time travel. Thirdly, it affects how we evaluate counterfactuals in time travel worlds, as well as our own. I’ll use the constraint to motivate an evidential and temporally neutral method of evaluating counterfactuals that holds fixed what a relevant deliberating agent has evidence of, independently of her decision. Using this method, an agent’s local abilities may be affected by what happens globally at other times, including the future. (shrink)