(An enormous influence on this was Justin B. Rye's 'SF Chronophysics' webpage and others. Seriously, his writing is fun and fascinating the whole way through. Snarky, though.)

See, the way time works in Doctor Who does make sense, if you look at it the right way.

Not maths-sense, of course. (Yet, hopefully.) But there are curiously recurring patterns to what's possible and not, over thousands of works of fiction that probably didn't all painstakingly work out continuity with each other.

I've added an additional constraint for myself — no extra dimension of 'metatime'. It just feels unsatisfying. Not sure why. Maybe because it's just 'time, again'. Ends up needlessly familiar.

And so, of course, I wrote a song about it.

There are three main points, I think.

0. The metaphor is threads and knitting. You take a thread, bring it out and weave it into its own future or past. There can be closed loops or loose ends.

1. The Web of Time is sort of self-healing, but it can't heal everything. It tries to choose the closest self-consistent loop, and deduplicates similar-enough timelines, but sometimes the difference is just too great. Then, the timeline that was undone — or caused its own undoing — becomes inactual.

2. Inactual and not-yet-definitely-actual futures can affect their past, either to avert themselves or make sure they come true. It depends. But they can't continue beyond the loop-point until they have evidence that they're actual. (A time traveller falls through to the nearest seemingly actual one.)

   (So, when you unwrite a timeline, you don't make it not have existed. I mean, it does exist, since you were probably there at some point! Instead, you stop it from unfolding further. In an actual timeline, people that were dead yesterday stay dead tomorrow. Averting that is the whole point.)

3. Consciousnesses are more than four-dimensional. They can reach across to inactual timelines and pull together impossible memories. Arguably, they don't even necessarily exist in one main rigid timeline. It's more interesting than that.

You might say that any rigid imagining closes off narrative possibility. This whole thing is not a prescriptivist theory; nobody follows it; if something doesn't fit, I'll have to rework it eventually. But 'the exact sort of thing that one opposes [explanatory] land grabs in order to allow' can still be too boring in comparison.

Maybe, though, to work it probably just needs to also be a good metaphor for something. Be a heightened or literalised version of a thing that really happens (false pasts and lost futures?). If you don't get bogged down in fixed points and limitation effects, it might actually make more narrative and emotional sense this way.

And, even if they're all entirely wrong, there's something in having an idea about what the characters think. It's an aesthetic goal, and a really beautiful thing. Makes them more alive, maybe.