The Science of Discworld Revised Edition

aliens crash-land at Roswell? Could an anti-matter warp drive ever be invented? Could we ever have the ultra long-life batteries that Scully and Mulder must be using in those torches of theirs?
    We could have taken that approach. We could, for example, have pointed out that Darwin’s theory of evolution explains how lower lifeforms can evolve into higher ones, which in turn makes it entirely reasonable that a human should evolve into an orangutan (while remaining a librarian, since there is no higher life form than a librarian). We could have speculated on which DNA sequence might reliably incorporate asbestos linings into the insides of dragons. We might even have attempted to explain how you could get a turtle ten thousand miles long.
    We decided not to do these things, for a good reason … um, two reasons.
    The first is that it would be … er … dumb.
    And this because of the second reason. Discworld does not run on scientific lines. Why pretend that it might? Dragons don’t breathe fire because they’ve got asbestos lungs – they breathe fire because everyone knows that’s what dragons
do
.
    What runs Discworld is deeper than mere magic and more powerful than pallid science. It is
narrative imperative
, the power of story. It plays a role similar to that substance known as phlogiston, once believed to be that principle or substance within inflammable things that enabled them to burn. In the Discworld universe, then, there is narrativium. It is part of the spin of every atom, the drift of every cloud. It is what causes them to be what they are and continue to exist and take part in the ongoing story of the world.
    On Roundworld, things happen because the
things
want to happen. 1 What people want does not greatly figure in the scheme of things, and the universe isn’t there to tell a story.
    With magic, you can turn a frog into a prince. With science, you can turn a frog into a Ph.D and you still have the frog you started with.
    That’s the conventional view of Roundworld science. It misses a lot of what actually makes science tick. Science doesn’t just exist in the abstract. You could grind the universe into its component particles without finding a single trace of Science. Science is a structure created and maintained by people. And people choose what interests them, and what they consider to be significant and, quite often, they have thought narratively.
    Narrativium is powerful stuff. We have always had a drive to paint stories on to the Universe. When humans first looked at the stars, which are great flaming suns an unimaginable distance away, they saw in amongst them giant bulls, dragons, and local heroes.
    This human trait doesn’t affect what the rules
say
– not much, anyway – but it does determine which rules we are willing to contemplate in the first place. Moreover, the rules of the universe have to be able to produce everything that we humans observe, which introduces a kind of narrative imperative into science too. Humans think in stories 2 . Classically, at least, science itself has been the discovery of ‘stories’ – think of all those books that had titles like
The Story of Mankind, The Descent of Man
, and, if it comes to that,
A Brief History of Time
.
    Over and above the stories of science, though, Discworld can play an even more important role: What if? We can use Discworld for thought experiments about what science might have looked like if the universe had been different, or if the history of science had followed a different route. We can look at science from the outside.
    To a scientist, a thought experiment is an argument that you can run through in your head, after which you understand what’s going on so well that there’s no need to do a real experiment, which is of course a great saving in time and money and prevents you from getting embarrassingly inconvenient results. Discworld takes a more practical view – there, a thought experiment is one that you can’t do and which wouldn’t work if you could. But the kind of thought experiment we have in mind is one that scientists carry out all the time, usually without realizing it; and you don’t need to do it, because the whole
point
is that it wouldn’t work. Many of the most important questions in science, and about our understanding of it, are
not
about how the universe actually is. They are about what would happen if the universe were different.
    Someone asks ‘why do zebras form herds?’ You could answer