Time Travel, Coincidences and Counterfactuals∗ Theodore Sider Philosophical Studies 110 (2002): 115–138 1. Failures in autoinfanticide

Imagine you had a time machine. Nothing would stop you from going back in time and killing yourself as an infant, before you ever entered the time machine. But then a contradiction would ensue: you would never have entered any time machine since you were killed before doing so (let “killing ” be understood throughout as implying permanent death), and yet you would have entered a time machine, in order to travel back in time to kill yourself. Some conclude that time travel is impossible, since it would lead to this contradiction. There is nothing special about autoinfanticide: similar problems arise when-ever a time traveler resolves to go back in time and do something that did not in fact occur. A time traveler who remembers owning a 1974 Plymouth Gold Duster could, it would seem, go back into the past and prevent herself from ever owning such a ne automobile; a time traveler could, it would seem, go back and prevent Lincoln from giving the Gettysburg address, and so on. But autoinfanticide is an especially vivid example. As it stands, this argument is very weak. All it shows is that autoinfanticide is impossible, as are related scenarios, such as one in which an address is given but in which someone travels back in time and prevents that address from being given. The impossibility of a certain kind of time-travel scenario does not impugn the possibility of time travel in general, any more than the existence of an impossible story about an empty box containing a gurine impugns the possibility of boxes. We have admitted the possibility of time travel, though not the possibility of autoinfanticide. But these possible time travelers who do not kill their earlier selves: some have the desire as well as the means. What stops them? No one thing. Some have a sudden change of heart. Some fear awful forces they think would be unleashed by a violation of the laws of logic. Some attempt the deed but fail for various reasons: non-lethal wounds, slips on banana peels