The Science of Discworld

by Terry Pratchett

  First published in Great Britain in 1999

  This revised edition published in 2002 by Ebury Press

  3579 10 8642

  Copyright © Terry and Lyn Pratchett, Joat Enterprises, Jack Cohen 1999

  Line drawings Copyright © Paul and Sandra Kidby 1999

  Cover illustrations by Paul Kidby

  Terry Pratchett, Ian Stewart and Jack Cohen have asserted their right under the Copyright, Designs and Patents Act 1988 to be identified as the authors of this work.

  All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, electronic, mechanical, photocopying, recording or otherwise, without prior permission from the publisher.

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  A CIP catalogue record for this book is available from the British Library.

  ISBN 0 09 188657 0

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  CONTENTS

  The Story Starts Here ...

  1. Splitting the Thaum

  2. Squash Court Science

  3. I Know My Wizards

  4. Science and Magic

  5. The Roundworld Project

  6. Beginnings and Becomings

  7. Beyond the Fifth Element

  8. We Are Stardust (or, at least we went to Woodstock)

  9. Eat Hot Naphtha, Evil Dog!

  10. The Shape of Things

  11. Never Trust a Curved Universe

  12. Where Do Rules Come From?

  13. No, It Can't Do That

  14. Disc Worlds

  15. The Dawn of Dawn

  16. Earth and Fire

  17. Suit of Spells

  18. Air and Water

  19. There Is a Tide . . .

  20. A Giant Leap for Moonkind

  21. The Light You See the Dark By

  22. Things that Aren't

  23. No Possibility of Life

  24. Despite Which

  25. Unnatural Selection

  26. The Descent of Darwin

  27. We Need More Blobs

  28. The Iceberg Cometh

  29. Going for a Paddle

  30. Universals and Parochials

  31. Great Leap Sideways

  32. Don't Look Up

  33. The Future is Newt

  34. Nine Times out of Ten

  35. Still Bloody Lizards

  36. Running from Dinosaurs

  37. I Said, Don't Look Up

  38. The Death of Dinosaurs

  39. Backsliders

  40. Mammals on the Make

  41. Don't Play God

  42. Anthill Inside

  43. Ook: a Space Odyssey

  44. Extel Outside

  45. The Bleat Goes On

  46. Ways to Leave Your Planet

  47. You Need Chelonium

  48. Eden and Camelot

  49. As Above, So Below

  THE STORY STARTS HERE ...

  ONCE UPON A TIME, there was Discworld.

  There still is an adequate supply. Discworld is the flat world, carried through space on the back of a giant turtle, which has been the source of — so far — twenty-seven novels, four maps, an encylopaedia, two animated series, t-shirts, scarves, models, badges, beer, embroidery, pens, posters, and probably, by the time this is published, talcum powder and body splash (if not, it can only be a matter of time).

  It has, in short, become immensely popular.

  And Discworld runs on magic.

  Roundworld — our home planet, and by extension the universe in which it sits, runs on rules. In fact, it simply runs. But we have watched the running, and those observations and the ensuing deductions are the very basis of science.

  Magicians and scientists are, on the face of it, poles apart. Certainly, a group of people who often dress strangely, live in a world of their own, speak a specialized language and frequently make statements that appear to be in flagrant breach of common sense have nothing in common with a group of people who often dress strangely, speak a specialized language, live in ... er ...

  Perhaps we should try this another way. Is there a connection between magic and science? Can the magic of Discworld, with its eccentric wizards, down-to-Earth witches, obstinate trolls, fire-breathing dragons, talking dogs, and personified DEATH, shed any useful light on hard, rational, solid, Earthly science?

  We think so.

  We'll explain why in a moment, but first, let's make it clear what The Science of Discworld is not. There are several media tie-in The Science of … books at the moment, such as The Science of the X-Files and The Physics of Star Trek. They will tell you about areas of today's science that may one day lead to the events or devices that the fiction depicts. Did aliens crash-land at Roswell? Could an antimatter 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.* 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.* 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 this by an analysis of zebra sociology, psychology, and so on ... or you could ask a question of a very different kind: 'What would happen if they didn't?' One fairly obvious answer to that is 'They'd be much more likely to get eaten by lions.' This immediately suggests that zebras form herds for self-protection — and now we've got some insight into what zebras actually do by contemplating, for a moment, the possibility that they might have done something else.

  Another, more serious example is the question 'Is the solar system stable?’, which means 'Could it change dramatically as a result of some tiny disturbance?' In 1887 King Oscar II of Sweden offered a prize of 2,500 crowns for the answer It took about a century for the world's mathematicians to come up with a definite answer: 'Maybe'. (It was a good answer, but they didn't get paid. The prize had already been awarded to someone who didn't get the answer and whose prizewinning article had a big mistake right at the most interesting part. But when he put it right, at his own expense, he invented Chaos Theory and paved the way for the 'maybe'. Sometimes, the best answer is a more interesting question.) The point here is that stability is not about what a system is actually doing: it is about how the system would change if you disturbed it. Stability, by definition, deals with 'what if?'.

  Because a lot of science is really about this non-existent world of thought experiments, our understanding of science must concern itself with worlds of the imagination as well as with worlds of reality. Imagination, rather than mere intelligence, is the truly human quality. And what better world of the imagination to start from than Discworld? Discworld is a consistent, well-developed universe with its own kinds of rules, and convincingly real people live on it despite the substantial differences between their universe's rules and ours. Many of them also have a thoroughgoing grounding in 'common sense', one of science's natural enemies.

  Appearing regularly within the Discworld canon are the buildings and faculty of Unseen University, the Discworld's premier college of magic. The wizards* are a lively bunch, always ready to open any door that has 'This door to be kept shut' written on it or pick up anything that has just started to fizz. It seemed to us that they could be useful ...

  Clearly, as the wizards of Unseen University believe, this world is a parody of the Discworld one. If we, or they, compare Discworld's magic to Roundworld science, the more similaritiesa and parallels we find. And when we didn't discover parallels, we found that the differences were very revealing. Science takes on a new character when you stop asking questions like 'What does newt DNA look like?' and instead ask 'I wonder how the wizards would react to this way of thinking about newts?'

  There is no science as such on Discworld. So we have put some there. By magical means, the wizards on Discworld must be led to create their own brand of science, some kind of pocket universe' in which magic no longer works, but rules do. Then, as the wizards learn to understand how the rules make interesting things happen — rocks, bacteria, civilizations, we watch them watching ... well, us. It's a sort of recursive thought experiment, or a Russian doll wherein the smaller dolls are opened up to find the largest doll inside.

  And then we found that ... ah, but that is another story.

  TP, IS, & JC, DECEMBER 1998

  PS We have, we are afraid, mentioned in the ensuing pages Schrödinger's Cat, the Twins Paradox, and that bit about shining a torch ahead of a spaceship travelling at the speed of light. This is because, under the rules of the Guild of Science Writers, they have to be included. We have, however, tried to keep them short.

  We've managed to be very, very brief about the Trousers of Time, as well.

  PPS Sometimes scientists change their minds. New developments cause a rethink. If this bothers you, consider how much damage is being done to the world by people for whom new developments do not cause a rethink.

  This second edition has been changed to reflect three years of scientific progress ... forwards or backwards. (You will find both.) And we've added two completely new chapters: one on the life of dinosaurs, because the existing chapter on the death of dinosaurs seemed a bit depressing; and one on cosmic disasters, because in many ways the universe is depressing.

  The Discworld story has proved more robust than the science. As should be expected. Discworld makes so much more sense than Roundworld does.

  TP, IS & JC, JANUARY 2002

  In a manner of speaking. They happen because things obey the rules of universe. A rock has no detectable opinion about gravity.

  It took three years for this sentence to sink in. When it did, we wrote The Science of Discworld II: The Globe.

  Like the denizens of any Roundworld university, they have unlimited time for research, unlimited funds and no worries about tenure. They are also by turns erratic, inventively malicious, resistant to new ideas until they've become old ideas, highly creative at odd moments and perpetually argumentative — in this respect they bear no relation to their Roundworld counterparts at all.

  ONE

  SPLITTING THE THAUM

  SOME QUESTIONS SHOULD NOT BE ASKED. However, someone always does.

  'How does it work?' said Archchancellor Mustrum Ridcully, the Master of Unseen University.

  This was the kind of question that Ponder Stibbons hated almost as much as 'How much will it cost?' They were two of the hardest questions a researcher ever had to face. As the university's de facto head of magical development, he especially tried to avoid questions of finance at all costs.

  'In quite a complex way.' he ventured at last.

  'Ah.'

  'What I'd like to know,' said the Senior Wrangler, 'is when we're going to get the squash court back.'

  'You never play, Senior Wrangler,' said Ridcully, looking up at the towering black construction that now occupied the centre of the old university court.*

  'I might want to one day. It'll be damn hard with that thing in the way, that's my point. We'll have to completely rewrite the rules.'

  Outside, snow piled up against the high windows. This was turning out to be the longest winter in living memory — so long, in fact, that living memory itself was being shortened as some of the older citizens succumbed. The col
d had penetrated even the thick and ancient walls of Unseen University itself, to the general concern and annoyance of the faculty. Wizards can put up with any amount of deprivation and discomfort, provided it is not happening to them.

  And so, at long last, Ponder Stibbons's project had been authorized. He'd been waiting three years for it. His plea that splitting the thaum would push back the boundaries of human knowledge had fallen on deaf ears; the wizards considered that pushing back the boundaries of anything was akin to lifting up a very large, damp stone. His assertion that splitting the thaum might significantly increase the sum total of human happiness met with the rejoinder that everyone seemed pretty happy enough already.

  Finally he'd ventured that splitting the thaum would produce vast amounts of raw magic that could very easily be converted into cheap heat. That worked. The Faculty were lukewarm on the subject of knowledge for knowledge's sake, but they were boiling hot on the subject of warm bedrooms.

  Now the other senior wizards wandered around the suddenly-cramped court, prodding the new thing. Their Archchancellor took out his pipe and absent-mindedly knocked out the ashes on its matt black side.

  'Um ... please don't do that, sir,' said Ponder.

  'Why not?'

  'There might be ... it might... there's a chance that...' Ponder stopped. 'It will make the place untidy, sir,' he said.

  'Ah. Good point. So it's not that the whole thing might explode, then?'

  'Er ... no, sir. Haha,' said Ponder miserably. 'It'd take a lot more than that, sir —’

  There was a whack as a squash ball ricocheted off the wall, rebounded off the casing, and knocked the Archchancellor's pipe out of his mouth.

  'That was you. Dean,' said Ridcully accusingly. 'Honestly, you fellows haven't taken any notice of this place in years and suddenly you all want to — Mr Stibbons? Mr Stibbons?'