In discussing the nature of time we noted that unless a time traveler goes to other universes time must be something like a dimension, and thus that something we might call a timeline exists from the distant past through the present. We might ask whether the line continues into the future, but that is already part of the more basic question: is it fixed, or mutable?
Advocates of fixed time theory maintain that time is immutable, that the past cannot be changed. What escapes notice in this is that it also means that the future cannot be changed, either. It is easy enough to suppose that everything James Cole does in the past in 12 Monkeys he was destined to do in the past because he had already done it, but what is overlooked is that for the young James Cole watching in the airport, everything he is going to do in the future is equally destined. Thus when the fixed time theorist says that you cannot kill your own grandfather because we already know that you did not do so, implicit in that is that you have no control over your destiny, that all your future choices are already made, that you are fated to a life you have not yet chosen but cannot avoid choosing.
Most of us intuitively balk at this idea that we have no free will; it seems as if we do. That, though, is an inadequate basis for concluding that we do. It is certainly arguable that we will do what we, by heredity and environment, are programmed to do, and that this feels like freedom because all the constraints are internal, within our own personalities. It is similarly possible that the entire universe is so programmed, that just as billiard balls deflect at predictable angles everything in the universe will follow a predetermined sequence of events. The problem is that once time travel is introduced you have the possibility of an instability in the programming process. What is to prevent the program from looping with the command A=A+1, or A=-A, for causes in the future to have effects in the past that alter those causes in the future? Fixed time advocates assert that this cannot happen, but the basis for that assertion is circular, that if it did, it would change the past, and since you cannot change the past, whenever you travel to the past you begin a trip you have already completed.
Yet even given a deterministic model of human choice, it is difficult to imagine that no trip to the past would ever alter events in a way that would change the factors determining those choices. If on Monday you ate a hamburger and got sick, on Tuesday you might send a message to yourself that says “don’t eat the hamburger”, and if having received the message you chose not to eat the hamburger you did not get sick, then on Tuesday you would not send that message. Fixed time advocates assert that you could not do this–either you could not choose to send the message, or having received it you could not choose not to eat the hamburger. On the other hand, if having turned right on Broad Street you later discovered that there was a terrible accident to the left on Broad Street which you avoided, you could send yourself a message that said, “don’t turn left on Broad Street,” and your previous self could receive that message and obey it, because that does not change what he would have done anyway. At this point, it appears that the universe, or whatever it is that prevents certain willed acts but not others, has sufficient intelligence to foresee what acts in the future will alter the past and which will not. It suddenly seems to become a matter of divine intervention, of God under a pseudonym preventing catastrophe.
To the fixed time advocate, though, time is not at all like a sequence of choices, but like a puzzle that fits together only one way, and we discover how it fits as we live through it. The events in our lives are like tiles in a mosaic being constructed by someone else, but that there is no one doing the construction and no one planning the pattern, and yet somehow it all fits properly.
Fixed time thus poses some intellectual problems in regard to choices and future events which it tends to gloss. It creates a world in which I cannot help writing this article and you cannot help reading it, because we are destined to do what we do not know we have already done in the future. We have no control; it is an illusion. We cannot even control whether or not we believe in fixed time.