The philosophy of time is one of the trickier aspects of philosophy in my opinion, but there is an extent to which the layperson is exposed to some rudimentary ideas. The most prominent is the use of time travel as a plot device in science fiction (and sometimes other genres as well), the use of which raises some interesting questions. Pop culture references to time travel generally don’t take account of the problems that it entails, but I think there is an underlying assumption that is somewhat revealing.
Time travel is widely appealing for one main reason: People like do-overs. Think about it: Chances are that you can remember some event in your life that you wish you could go back and change. Time travel makes the idea of this possible in fiction, but it also carries with it paradoxes. The primary one is sometimes called the “Grandfather Paradox“:
- Using time travel, you go back in time and murder your grandfather before he meets your grandmother.
- Since your grandfather is prevented from starting the causal chain that results in your birth, you are not born.
- But since you are not born, you are unable to go back and murder your grandfather.
The paradox is thus that the event performed while traveling in the past prevents itself from occurring. This is true of any account where an individual goes back in the past for the purpose of changing it; they will inevitably change the past, which then negates the reason for going back in time at all, hence depriving the individual of the reason to travel back in time.
Here is where I think there may be a presumption of dualism or where dualism might be useful in explaining this (for fictional purposes, of course). If materialism is true and my memory is merely an artifact of the physical states in my brain that mental states supervene on, then the paradox cannot be resolved because my brain states will change as a result of my action. For instance, if I go back in time to stop myself from saying something incredibly stupid to my wife (a not infrequent occurrence, I am willing to admit), then I will wipe the memory of having said the stupid thing from my brain, thus eliminating my reason to travel back.
On the other hand, assume that dualism is true and that mental states do not merely supervene on physical states. There is then a case that can be made for a continuity of subjective memory that can be made: if I go back in time and stop myself from saying a stupid thing to my wife, then the memory of the stupid thing can still be retained in my memory with a continuity of the events that occur. At time t1 I remember the event at t0; I then return to t0 and change the events; at time t1´ (the identical moment as t1 but with the resultant outcome from the change of events) I remember the event, but the event has not actually occurred. This may sound rather strange, but I think it somewhat plausible. (Of course, if I want to forget that I said the stupid thing, this won’t help me at all.)
Of course, this is rather a summary thought, but I think there is some promise in such an account. In fact, I see more echoes of dualism in other strange features of some science fiction – but that’s for another time.