Science of Discworld III

your morning newspaper be called? Would it be different? Would you still be having much the same breakfast ritual, bacon and eggs and a sausage perhaps? What about the World Wars? Hiroshima?
    A very large number of stories have been written with this kind of theme: Wilson Tucker’s The Lincoln Hunters is set in such an ‘alternat(iv)e universe’ and tackles the Lincoln question.
    Curious things happen in our minds when they are presented with any fictional world. Consider for a moment the London of the late nineteenth century. It did have Jack the Ripper, and we can wonder about the real-world puzzle of who he was. It had Darwin, Huxley and Wallace, too. But it did not have Sherlock Holmes, Dracula, Nicholas Nickleby, or Mr Polly. Nevertheless, some of the bestportrayals of the Victorian world are centred around those characters. Sometimes the fictional portrayals are intended to paint a humorous gloss on the society of the period. The Flintstones put just such a gloss on human prehistory, so much so that in order to think rationally about our evolution we must excise all those images, which is probably an impossible task.
    Sherlock Holmes and Mr Polly were Victorians in just the same sense that the tyrannosaur and triceratops in Jurassic Park were dinosaurs. When we envisage Triceratops , we cannot avoid the memory of that warty purple-spotted Jurassic Park skin, as the beast lies on its side, breathing stertorously. And Tyrannosaur , in our mind’s eye, is running after the jeep, bobbing its head like a bird. When we envisage late nineteenth-century Baker Street it’s very difficult not to see Holmes and Watson (probably in one of their filmic versions) hailing a four-wheeler, off to solve another crime. Our pictures of the past are a mixture of real historical figures and scenarios peopled by fictional entities, and it’s difficult to keep them apart, especially as films and TV series acquire better technologies to latch into those spurious pictures in our heads.
    The 1930s philosopher George Herbert Mead made much of the rather obvious point that the present, in a causal world, does not only determine (‘constrain’ if you prefer) the future, it also affects the past, in just this sense: if I discover a new fact about the present, then the (conceptual) past that led up to the new present must also have been different. Mead thereby enabled a rather cute way of seeing how good the portrayals of Sherlock Holmes, or of the Jurassic Park tyrannosaur, are. If my picture of the present isn’t altered at all by the presence or absence of Sherlock Holmes in the 1880s, or if my construction of the present by evolutionary processes isn’t altered at all by seeing Jurassic Park , then these are consistent inventions.
    Dracula and the Flintstones are inconsistent inventions: if they really existed in our past, then the present isn’t what we think it is. Much of the fun of ‘worlds of if’ stories, and of many consistentfictions like The Three Musketeers , is that they show closed-loop causalities in our apparent past. Whether or not D’Artagnan had aggregated the Musketeers and thereby brought into being much of the causal history of seventeenth-century France, children of later centuries would learn the same history in the textbooks. Ultimately, consistent historical fictions make no difference.
    In The Science of Discworld II we played with this idea in several ways: the presence of the Elves was, surprisingly, consistent with our history; stopping them led to stagnation of humans and had to be reversed. In this book the meddling of the Unseen University wizards, in Victorian history this time, is trying to create an apparently internally caused history in which Darwin wrote The Origin of Species and not Theology of Species . We are going to use this trick to illuminate the causalities of human history.
    In order to do this convincingly, we must make the Discworld intrusions consistent, but even then we must address the convergence/divergence problem, which is this. Would such a meddled-with world converge on to ours, demonstrating that history is stable, or would any tiny difference start a divergence that became wider and wider, proving history to be unstable?
    Most people think the latter. Indeed, even the wildly imaginative physicists who believe that a new world history is created by each and every decision in this universe, spawning new universes in which the other choices were implemented, don’t