Talk about time travel is puzzling even if it isn't obviously contradictory. Philosophers however are divided about whether time travel involves empirical paradox or some deeper metaphysical incoherence. It is suggested that time travel requires a Parmenidean four-dimensionalist metaphysical conception of the world in time. The possibility of time travel is addressed (mainly) from within a Parmenidean metaphysical framework, which is accepted by David Lewis in his defence of the coherence of time travel. It is argued that time travel raises (...) formidable difficulties which are not satisfactorily resolved by Lewis's ingenious defence of time travel. Objections to time travel considered include: (1) travel to other times is impossible because there is nowhere (or “nowhen”) to go to; (2) the problem that upon setting out on a journey to the past a time machine will collide with itself; (3) time travel generates a mysterious temporal dualism between experiential time and physical time; (4) travel to the past permits reverse causation, raising the possibility of causal loops and attendant problems arising, for example, from the prospect of empirical contradiction and the possibility of someone being one of their ancestors. (shrink)

This idea of time travel has long given philosophers difficulties. Most recently, in his paper ‘Troubles with Time Travel’ William Grey presents a number of objections to time travel, some well known in the philosophical literature, others quite novel. In particular Grey's ‘no destinations’ and ‘double occupation’ objections I take to be original, while what I will call the ‘times paradox’ and the ‘possibility restriction argument’ are versions of well known objections. I show how each of these can be answered, (...) thereby defending the plausibility of time travel. (shrink)

Are there difficulties raised by the idea of backwards time travel—travel to earlier times—that are peculiar to objects? By ‘object’ in this context I mean something that takes up space, that typically prevents other items in the same category from occupying the same space, and for which it is generally thought appropriate to talk in terms of persistence conditions. One such problem is raised in H. G. Wells’ The Time Machine, but highlighted in the philosophical literature only very recently, by (...) William Grey. Consider Tim, who boards his time machine and, at 12 noon precisely, presses the button to send him back into the past. At any moments after noon, both Tim and the machine have ceased to exist. (shrink)