Tiredblogging: The Anchoring Of The Thread (or, Towards A Grand Unified Theory Of Time-Travel In Doctor Who)
I’ve been wanting to write this post for a week now, and been putting it off until I’m less tired. But then I realised that if I hadn’t been less tired in a week, I probably wouldn’t be any time soon. So, here’s my Grand Unified Theory Of Time In Doctor Who, as written by someone who had to take four goes to type the word time because he’s so tired.
I’d been thinking about this for a while (and talked about bits of it with Plok while he was here), but this blog post by Eliezer Yudkowsky, about causality and time travel, gave me the final key. You might want to read that before we go ahead. I’ll wait.
OK, so one of the big things in Doctor Who since Moffat took over is the way that time can be changed, pretty much willy-nilly, when in the old series the rule was, more or less, “you can’t change history, not one line!”
Now, there are various explanations that can be used of this, not least the one I use, which is “they’re two different series with only the loosest possible connection.”
But suppose you want to reconcile them. The usual fanwank explanation is “the Time War” — and I’m going to use that, too. But that doesn’t actually *explain* anything. So I’m going to try.
And I think it can be done.
First, we assume that the uni/multiverse is — or started as — something like the timeless universe of Julian Barbour, or the ultimate ensemble of Max Tegmark. A timeless configuration space of every existing possibility, all equally existent. Every instant of time, existing simultaneously.
In one of these instants, exists an intelligent race. They’re known by various names, such as the Great Houses, but we can call them the Time Lords, because along with them comes the existence of time.
You see, time isn’t something that exists in itself. Time is just another word for the increase in entropy between different states in the configuration space. But since we can (as far as we know) draw a line between any two states, why should entropy increase?
Well, probabilistically, it’s simple. If you take any random point in a configuration space — whatever the point — and make a random perturbation to it, the result will, in the huge majority of cases, have more entropy than the original position. So a random walk among configurations will lead to an increase in entropy.
But we’re not talking about a random walk — we’re talking about a lawlike universe. And if you draw a line between the start and end points, why does it have to have that direction? Why not say that the end is the start and the start is the end?
Well, you can — but not in a universe containing intelligence. Intelligence is, fundamentally, the creation of an isomorphism between one structure (e.g. a brain) and another (e.g. a universe) such that the first can predict the second.
In order to do this, information has to pass from the universe to the brain — and by doing so, entropy in the universe has to increase proportionally.
So in any universe which contains intelligence, that intelligence, at any given point, will have knowledge of a universe which has slightly less entropy than the one in which it’s existing, and so perceive entropy as always increasing. Hence — arrow of time.
So with our Time Lords comes an arrow of time.
Now, what do we know of the Time Lords? Firstly, that they put all of history in place with the Anchoring Of The Thread (see the Book Of The War) and secondly that they could travel through time.
As Yudkowsky points out, if you’re looking at the standard formulation of causality, using Directed Acyclic Graphs, as formulated by Judea Pearl, then you can *either* have cause and effect, *or* you can have a consistent, single-history universe which contains time travel, but you can’t have both.
So, assuming for the moment that current understanding is more-or-less correct, and the universe can be understood or modelled as a computation, then we have a rough idea of what sort of process the Anchoring Of The Thread must have been — a brute-force sweep through all possible events, noting the ones that fit the consistent history the Time Lords wanted, which were then forced together — possibly just by the Time Lords’ perception — into one history. This allowed consistent time travel throughout their history, without the possibility of paradox (or of wiping themselves out of history) but with the disadvantage that there was actually no such thing as cause-and-effect — effects *appeared* to follow causes, but that’s only because they’d been put in that position by the Time Lords.
(It’s possible that Time Lords themselves (and their companions when in a TARDIS?) had the ability to alter the universe on the fly with their perceptions. If so this would mean that time-travellers were the only beings in the universe with true free will — and would explain the changes to time-travellers’ biodata (a concept often mistranslated as ‘DNA’ in the new series). It’s also possible that the computation that put history in place had something to do with the calculations of Logopolis.)
Then comes the Time War. The Time Lords are destroyed. They’re no longer there to perceive the universe, and without their computation to keep it in place, there can’t be a consistent timeline any longer.
However, there *are* still intelligences — humans, Daleks and so on — and at least some of them have time machines. This means that time must still exist. Without the influence of the Time Lords, that means that we have a universe where the past and future are both malleable — but where effects have causes, and thus actions have consequences.
So because the Time Lords have been destroyed, free will has been given to the inhabitants of the universe. They’re no longer just puppets acting out a script planned by superpowerful gods, but people whose actions *matter*. Given the Doctor’s known attitude toward free will, the question is possibly not so much why he destroyed the Time Lords (if, indeed, it was ‘really’ him who did so), as why he didn’t do it much earlier.
And as a side-note, the fact that the universe no longer runs to a fixed plan with an intelligence behind it might go some way to explaining the incoherence of many post-Time War stories…
I hope that makes some kind of sense, or at least the right kind of nonsense. I can’t actually see right now, I’m so tired, so it may not. There’ll be another Who post, on Kinda, on the Mindless Ones tomorrow or Friday, and a Beach Boys post this weekend.