Exploring Time Travel

3040 Words7 Pages

An essential requirement for the possibility of time travel is the presumption that future and past were somehow real. But according to one popular view only the present is real, and to suppose that the past or future are also real is to suppose that the past and the future are also present -- a contradiction. According to this sort of Heraclitean metaphysical conception, the future is genuinely open: there is no realm of determinate future fact, no denizens of the future to identify or talk about, though of course -- in the fullness of time -- there will be. Travel to the future on this view would be ruled out because there is simply nowhere to go.

The past, though, is spoken of as fixed and determinate and not subject to change. Travel into the past would appear to make it accessible in a way that would enable the traveler to effect changes -- that is, to change things that are fixed and determinate and so not subject to change. Aristotle endorsed this popular view when he said that changing the past is beyond even the power of God. It was for this reason, Aristotle said, that 'no one deliberates about the past, but about what is future and capable of being otherwise' (Nichomachean

Ethics, 1139b6).

This is called the "no destination" objection to time travel. This view rejects the possibility of travelling to future because future is non-existent, therefore there is nowhere to travel to. Travel to past is also rejected, as the traveler cannot possibly go back in time and change it.

To travel is to change position with time. Travel through space is the successive occupancy of spatial positions. Similarly, time travel requires the successive occupancy of temporal positions. But that seems to amount to either the trivi...

... middle of paper ...

...e-time.

Travel to the past requires reverse causation. Reverse causation raises the possibility of causal loops and the attendant problems that arise, for instance, if someone were to be one of their ancestors. Although this may not be self-contradictory it does lead to intolerable restrictions on the range of possibility, and the range of efficacious choice available to an agent. Dum and Jocasta in Harrison's story, for example, cannot have a daughter. Tim cannot shoot his grandfather or press a button, though he can shoot grandfather's twin and press a physically indistinguishable button which is not wired up to send a detonating signal into the past. These empirical paradoxes arise as soon as reverse causation is allowed because reverse causation makes past times causally accessible. They are some of the intolerable consequences of countenancing time travel.

More about Exploring Time Travel

Open Document