Science of Discworld III

The Time Machine , as we’ve said, was the absolute classic time travelogue, showing us the large picture from prehistory to the social consequences of the capitalism that the socialist Wells wanted to criticise. Then the cooling Sun, the great crabs on a post-diluvian beach … lovely. But Stephen Baxter’s modern sequel The Time Ships shows us how clever the Morlocks will be, how the Traveller is really a little bit prurient about the little Eloi girl from the future – a resonance with Lewis Carrol’s Alice – who is innocent and a bit stupid.
    It’s like a historical novel that puts all the little sexy and despicable bits into the great tapestry of history. Such literary exercises add colour and flavour to history, just as Damasio has shown that we do with our own personal memories. The pleasure this exercise gives us shows how our human minds read history: in the large without flavour, in the small with the kind of colour that we paint on to our own small reminiscences. So historical romance is just that: romantic painting of the little, interesting items, whose causality might affect the big picture, but doesn’t.
    What does it mean, then, to ask whether time knits up any changes, or whether mischievous butterflies are ultimately responsible for the fall of empires?
    Here fictional conventions cease to fit the real world. From the point of view of the wizards, Roundworld time is a one-dimensional sequence that they can access two-dimensionally like a book. For narrative reasons, we have to depict it like this because of all those thin-thread-of-causality historical stories that our minds find so congenial. In a fictional context, we have little choice. However, here we want to think about the nature of causality and free will in the ‘real’ universe, which – as we’ve made clear throughout the Science of Discworld series – does not have any narrativium. In that context,we have to understand that this simple image of Roundworld history is a fraud. The Trousers of Time also work well as a story, but as genuine physics they are a fraud: you can’t be pushed from one leg to the other by an event. Worse, you can’t tell that there has been such an event. As far as you are concerned, this is the world. It doesn’t have ‘ifs’ in its past.
    None of this stops us using ‘what ifs’ (which by nature are fictions, not facts) to think about history. We can still ask, in our minds, what would have happened if, say, Lincoln had survived … but in the real world he didn’t, and we can’t run a mock-up of ‘if he did’ in the real world: only in our heads.
    Science runs into precisely this difficulty. For instance, the main problem in testing medical treatments is that we can’t both give Mrs Jones the treatment and not give Mrs Jones the treatment, simultaneously, and compare the results. We can do it sequentially, but then the second treatment (whether it is placebo or real treatment) is of a different Mrs Jones, one who’s had the first treatment. So what the testers do is to have quite a large panel, do treatment first on some, placebo first on others – and they should perhaps do two placebos on a few, and two treatments on a few others.
    What time-travel stories do, in our minds, is the same kind of test: ‘What would happen if Leonardo had really seen a submarine working?’ or equivalently ‘Did Leonardo see a submarine working?’ In The Science of Discworld , and more explicitly in The Science of Discworld II , we asked whether the interesting stories that we make up have some kind of coherent explanation, something like ‘evil’ – which we personified in the second book as Elves. To what extent do such concepts relate to the real rules of the real world? Now we argue that we cannot know if any answer we get is useful; we can’t even know whether we’ve got an answer at all. And that this is precisely why Dennett’s kind of free will is the only one worth having. It’s prospective, giving each of us the chance to make little items of an otherwise inevitable future evitable.
    When we look back on something we’ve changed by that kind of an act of free will, it’s just as causal as everything else – and if the universe is in any sense determinate, then it is determinate in that sense. Think of Odysseus looking back at what happened as his ship failed to be caught by the Sirens. His men didn’t hear them, and he, who could hear them, couldn’t act to steer the ship. So he