This is a post about time travel philosophy and Doctor Who.
A ‘fixed point in time’ is not a very coherent or logical idea. If time can be rewritten, what constitutes a fixed point? What makes it so? What measure of what degree does it have to reach before it becomes a fixed point? Are there different grades of fixed point?
This seems to me a burning example of Doctor Who dues ex machina. Even the concept that time can be rewritten has major philosophical problems.
Consider the fact that time travel, like spatial travel (for example, walking to the other side of your room), requires a destination. If you are moving into the future, then the future must have a secure physical point in which to arrive. The present is your starting point. For a future-destination to exist, it must mean that every future event is predetermined, otherwise the future will simply consist of a series of possibilities. There is nothing to travel to. This is what William Grey refers to as a “‘no-destination’ objection to time travel”.
So either Doctor Who adopts a fatalist (you have no free will! Everything is decided! Lie down and eat for the rest of your life, it’s fate!) approach, or it adopts a Heraclitean point of view, in which the future and the past don’t exist, but the future is still very open. In the Heraclitean view, time can be rewritten — or, more accurately, ‘written’, because it doesn’t exist yet.
Fatalism causes problems for many time travel philosophers, as it seems like a pretty solid conclusion. Fatalism also seems like a pretty solid reason to not do anything for the rest of your life, and to an extent we are all fatalists. The past is unchangeable by nature; Richard Taylor elegantly notes “all men are fatalists as they look back on things … we are never in the least tempted to try and modify it”.
So why do we even bother thinking about time travel? There are a thousand reasons to refute it: identity crisis, filial paradoxes, time loops, the logically pernicious self-inhibitor (of course!). But to the layman, time travel is consistent with physical theories. It is its logical impossibilities which prove its greatest flaw. The way we view time provides the greatest hurdle, next to actually constructing the TARDIS.
We must rework our view of time if we want to believe in time travel, but it doesn’t require imagining it as a big ball of wibbly wobbly time-y wimey stuff. In fact, it would be useless to do that. To the redshirt, time is basically the ordering of sequential events in causal order, aka. linear. It is the time traveller’s personal timeline which is not linear, but the time traveller does not travel within the confines of external time. Let me expound.
Imagine time passes at a rate of X. I am currently travelling at the rate of X, along with everything else in the world. We are all travelling through time simultaneously, at the same speed. But to reach something further than the present, I have to travel faster than X. X, we imagine, is external (public) time: the global fixed rate of time that, in the current world, everybody experiences. The Doctor exists within global time, but travels faster: in personal time. Personal time is how fast the traveller moves.
At 12:00, it takes external time 2 hours to reach 2:00. In the Doctor’s time, it takes him 2 minutes in the TARDIS to reach 2:00. External time is 2 hours, personal time is 2 minutes. So now we have reconstructed our view of time to encompass two possible timestreams without the requirement of an extra dimension: external and personal.
Assuming time travel is physically possible, we return to the question: what is a fixed point in time? The answer is: a fixed point in time is not conceptually possible in a world which allows for time travel and the rewriting of time. Even concepts of soft determinism which I have not covered would not allow for this; with a basic knowledge of time travel theory, a fixed point is simply not compatible with a time-travel-yet-rewritable universe.
But based on this discussion, a time-travel universe must involve fixed points: it must be a fatalist world, in which everything has already been decided. So either every event in Doctor Who is a fixed point, or the Doctor is simply a raving lunatic, and everybody he knows is a hallucination.