To start with, let’s look at Millennium Elephant’s response.
Now, I actually agree with the vast majority of what Millennium is saying here – only really disagreeing with the assertion that free will exists, which I think is a debatable proposition (but he’s intelligent enough to say “Though if we are wrong about that it makes no difference because all our actions, including believing we have free will, are all pre-determined anyway!” – acceptance of the possibility that one *could* be wrong is, to my mind, the basis for all rational discussion). I’m also less convinced of the Copenhagen interpretation than he is – but like him, don’t actually see it as incompatible with the many-worlds interpretation, but rather that they’re both metaphors for what’s Actually Going On, which is some not-readily-describable combination of the different interpretations.
(Luckily, for the purposes of this series of essays, I’m more interested in what’s interesting than what’s right – I’m trying to play with a whole bunch of interrelated ideas here, about canon and continuity, time and hypertime).
However, what I *do* disagree with is the assertion that, for Doctor Who at least, the Copenhagen Interpretation makes us more responsible for the consequences of our actions than the variant of the Many Worlds interpretation that I have been referring to (with a hat tip to Messrs. Morrison & Waid) as Hypertime (Doctor Who fans may be familiar with a similar-but-possibly-distinct idea under the name of The Fugue).
I’m going to attempt to show this, in the time-honoured tradition of Doctor Who fans, by referring to a single line from one story – in this case 1985’s Attack Of The Cybermen, where the Doctor refers to ‘the web of time’ in passing.
Now that line has got a lot of attention in various fanfics and spinoffery in the twenty-four years since the episode was transmitted, and there’s a reason for that – the image of time as a web, rather than the more conventional line, says quite a lot.
And this image is compatible both with the ‘hypertime’ view, and with actions carrying a *lot* of weight.
Imagine that time *is* like a web – all the points of all the multiple universes are connected to other points. A normal person’s life follows a line from one point to another to a third, and will always be a consistent timeline, because they’re only travelling forward at a rate of sixty seconds per minute.
Now imagine that every time you make a decision, you strengthen one connection (the one where you make that decision) but break other connections from that point – from a point of view outside time (and such a point of view exists in Doctor Who, though I suspect not in reality, whatever that is) – something like the collapse of the waveform in the Copenhagen Interpretation, but this is breaking off connections between different objectively-existing universes.
This would mean that everyone had a consistent history – once you’ve broken a connection, there are universes you ‘can’t get to from here’, those that directly contradicted the past decision. But it would also mean that the Doctor had an awesome responsibility as a time traveller, and his decisions would matter not only for him but for all the universe.
For the other thing about a web, along with its interconnectedness, is its fragility.
Every time the Doctor makes a decision, he breaks and makes connections between different points of time – those he’s been to before and will be again. He can alter some things – so long as there’s a way for a consistent timeline to route through all the points he’s visited. So he can save a life that wasn’t saved before, because there is a consistent universe where that person was saved, but he can’t kill Hitler in 1933, because there’s no way to make that consistent with the universes he’s visited in the past.
Because the Doctor is very aware of something – as he travels up and down his ‘timeline’ in the web of time, he’s selecting a smaller and smaller number of possible timelines, and condemning more and more to impossibility. That’s bad enough in itself, but we all do that every time we make a decision.
But he could – all too easily – break a segment of his own timeline off altogether. If he makes the wrong decisions at points A and B, then the whole section of his timeline between those points could become completely detached from the rest of the web, inaccessible from either past or future. Which would of course mean condemning all the inhabitants of that fragment of the web of time to nonexistence… the more he interferes – the more he does *anything* – the more likely this becomes, but he can’t use that as an excuse *not* to intervene.
(And of course from there we can get to all sorts of story possibilities like villains trying to make ‘pocket timelines’ to control, people in broken-off fragments trying to rejoin their fragment to reality, the Doctor unable to save entire planets because doing so would break the last connection between universes, and so on).
This would also, of course, help explain why the rest of the Gallifreyans never meddle (with the exception of all the meddlers). It’s just too dangerous – making choices has *too many* consequences.
(I’m not suggesting that this is the case in real-world physics, of course – in fact I think it’s nonsensical for multiple different reasons – but I think it *is* the case in my own Doctor Who ‘canon’…)