The Science of Discworld IV Read online

  CONTENTS

  * * *

  Cover

  About the Book

  About the Authors

  Also by Terry Pratchett, Ian Stewart & Jack Cohen

  Title Page

  PROLOGUE: WORLDS, DISC AND ROUND

  1. GREAT BIG THING

  2. GREAT BIG THINKING

  3. SEEPAGE BETWEEN WORLDS

  4. WORLD TURTLES

  5. MAGIC ISN’T REAL

  6. REALITY ISN’T MAGIC

  7. AMAZING GLOBE

  8. BEMUSING GLOBE

  9. UNHOLY WRIT

  10. WHERE DID THAT COME FROM?

  11. A VERY INTERESTING CASE

  12. LONG ARM OF THE LORE

  13. RINCEWIND’S ADVENTURES IN ROUNDWORLD

  14. A BETTER MOUSETRAP

  15. CASE FOR THE PLAINTIFFS

  16. SPHERICALITY SURELY IS EVERYWHERE

  17. THE WIZARD FORMERLY KNOWN AS THE DEAN

  18. BYE-BYE BIG BANG?

  19. DOES GOD WIGGLE HIS FINGERS?

  20. DISBELIEF SYSTEM

  21. THE TURTLE MOVES!

  22. FAREWELL, FINE-TUNING

  23. OVER-ZEALOUS ZEALOT

  24. NOT COLLECTING STAMPS

  EPILOGUE: L-SPACE

  INDEX

  Copyright

  About the Book

  Order in Court!

  On Discworld an almighty row is brewing…

  The Omnians want control of Roundworld – its very existence makes a mockery of their religion. The wizards of Unseen University, however, are extremely reluctant to part with it. After all, they created it!

  Enter Roundworld librarian, Marjorie Daw (accidentally, through L-space). Perhaps, with her Jimmy Choos and her enquiring and logical mind, she can help? Especially as she’s the sort of librarian who thinks that the Bible should be filed under Science Fiction and Fantasy.

  Lord Vetinari presides over the tribunal. People on both sides are getting extremely angry. There are some very big questions being asked – and someone’s got some explaining to do…

  The fourth in the Science of Discworld series, JUDGEMENT DAY sees Terry Pratchett, Professor Ian Stewart and Doctor Jack Cohen create a mind-mangling mix of fiction, cutting-edge science and philosophy in an attempt to answer the REALLY big questions – this time taking on God, the Universe and, frankly, Everything Else.

  Proceed with caution, you may never look at your universe(s) in the same way again.

  About the Authors

  Sir Terry Pratchett is the acclaimed creator of the global bestselling Discworld series; the first Discworld book, The Colour of Magic, was published in 1983. In all, he is the author of fifty bestselling books. His novels have been widely adapted for stage and screen, and he is the winner of multiple prizes, including the Carnegie Medal, as well as being awarded a knighthood for services to literature. Worldwide sales of his books now stand at 75 million.

  Professor Ian Stewart is the author of many popular science books and appears frequently on radio and television. He is an Emeritus Professor of Mathematics at the University of Warwick. He was awarded the Michael Faraday Medal for furthering the public understanding of science, and in 2001 became a Fellow of the Royal Society.

  Dr Jack Cohen is an internationally renowned reproductive biologist. He has retired to a small thatched cottage in Dorset. He writes, ponders, and plays with microscopes in a rather grand ‘garden shed’. He also throws boomerangs, but doesn’t catch them as often as he used to. In addition, he still enjoyes lecturing and continues to have a passion for the public understanding of science.

  BY THE SAME AUTHORS

  TERRY PRATCHETT

  The Discworld® series

  THE COLOUR OF MAGIC • THE LIGHT FANTASTIC • EQUAL RITES • MORT • SOURCERY • WYRD SISTERS • PYRAMIDS • GUARDS! GUARDS! • ERIC (illustrated by Josh Kirby) • MOVING PICTURES • REAPER MAN • WITCHES ABROAD • SMALL GODS • LORDS AND LADIES • MEN AT ARMS • SOUL MUSIC • INTERESTING TIMES • MASKERADE • FEET OF CLAY • HOGFATHER • JINGO • THE LAST CONTINENT • CARPE JUGULUM • THE FIFTH ELEPHANT • THE TRUTH • THIEF OF TIME • THE LAST HERO (illustrated by Paul Kidby) • THE AMAZING MAURICE AND HIS EDUCATED RODENTS (for younger readers) • NIGHT WATCH • THE WEE FREE MEN (for younger readers) • MONSTROUS REGIMENT • A HAT FULL OF SKY (for younger readers) • GOING POSTAL • THUD • WINTERSMITH (for younger readers) • MAKING MONEY • UNSEEN ACADEMICALS • I SHALL WEAR MIDNIGHT (for younger readers) • SNUFF

  The Science of Discworld series

  (with Ian Stewart and Jack Cohen)

  THE SCIENCE OF DISCWORLD

  THE SCIENCE OF DISCWORLD II: THE GLOBE

  THE SCIENCE OF DISCWORLD III: DARWIN’S WATCH

  Other books about Discworld

  TURTLE RECALL: THE DISCWORLD COMPANION … SO FAR

  (with Stephen Briggs)

  NANNY OGG’S COOKBOOK

  (with Stephen Briggs, Tina Hannan and Paul Kidby)

  THE PRATCHETT PORTFOLIO (with Paul Kidby)

  THE DISCWORLD ALMANAK (with Bernard Pearson)

  THE UNSEEN UNIVERSITY CUT-OUT BOOK

  (with Alison Batley and Bernard Pearson)

  WHERE’S MY COW? (illustrated by Melvyn Grant)

  THE ART OF DISCWORLD (with Paul Kidby)

  THE WIT AND WISDOM OF DISCWORLD (compiled by Stephen Briggs)

  THE FOLKLORE OF DISCWORLD (with Jacqueline Simpson)

  MISS FELICITY BEEDLE’S THE WORLD OF POO

  (assisted by Bernard and Isobel Pearson)

  Discworld Maps and Gazetteers

  THE STREETS OF ANKH-MORPORK

  (with Stephen Briggs, painted by Stephen Player)

  THE DISCWORLD MAPP (with Stephen Briggs, painted by Stephen Player)

  A TOURIST GUIDE TO LANCRE – A DISCWORLD MAPP

  (with Stephen Briggs, illustrated by Paul Kidby)

  DEATH’S DOMAIN (with Paul Kidby)

  THE COMPLEAT ANKH-MORPORK (with the Discworld Emporium)

  A complete list of Terry Pratchett ebooks and audio books as well as other books based on the Discworld series – illustrated screenplays, graphic novels, comics and plays – can be found on www.terrypratchett.co.uk

  Non-Discworld books

  THE DARK SIDE OF THE SUN • STRATA

  THE UNADULTERATED CAT (illustrated by Gray Jolliffe)

  GOOD OMENS (with Neil Gaiman)

  THE LONG EARTH (with Stephen Baxter)

  A BLINK OF THE SCREEN: COLLECTED SHORT FICTION

  Non-Discworld novels for younger readers

  THE CARPET PEOPLE • TRUCKERS • DIGGERS • WINGS • ONLY YOU CAN SAVE MANKIND • JOHNNY AND THE DEAD • JOHNNY AND THE BOMB • NATION • DODGER

  Ian Stewart

  CONCEPTS OF MODERN MATHEMATICS • GAME, SET, AND MATH • DOES GOD PLAY DICE? • ANOTHER FINE MATH YOU’VE GOT ME INTO • FEARFUL SYMMETRY • NATURE’S NUMBERS • FROM HERE TO INFINITY • THE MAGICAL MAZE • LIFE’S OTHER SECRET • FLATTERLAND • WHAT SHAPE IS A SNOWFLAKE? • THE ANNOTATED FLATLAND • MATH HYSTERIA • THE MAYOR OF UGLYVILLE’S DILEMMA • HOW TO CUT A CAKE • LETTERS TO A YOUNG MATHEMATICIAN • TAMING THE INFINITE (alternative title: THE STORY OF MATHEMATICS) • WHY BEAUTY IS TRUTH • COWS IN THE MAZE • MATHEMATICS OF LIFE • PROFESSOR STEWART’S CABINET OF MATHEMATICAL CURIOSITIES • PROFESSOR STEWART’S HOARD OF MATHEMATICAL TREASURES • SEVENTEEN EQUATIONS THAT CHANGED THE WORLD (alternative title: IN PURSUIT OF THE UNKNOWN)

  JACK OF ALL TRADES (science fiction ebook)

  THE GREAT MATHEMATICAL PROBLEMS

  (alternative title: VISIONS OF INFINITY)

  SYMMETRY: A VERY SHORT INTRODUCTION

  Jack C
ohen

  LIVING EMBRYOS • REPRODUCTION • PARENTS MAKING PARENTS • SPERMS, ANTIBODIES AND INFERTILITY • THE PRIVILEGED APE

  STOP WORKING AND START THINKING (with Graham Medley)

  Jack Cohen and Ian Stewart

  THE COLLAPSE OF CHAOS

  EVOLVING THE ALIEN

  (alternative title: WHAT DOES A MARTIAN LOOK LIKE?)

  Ian Stewart and Jack Cohen

  FIGMENTS OF REALITY

  WHEELERS (science fiction) • HEAVEN (science fiction)

  PROLOGUE

  * * *

  WORLDS, DISC AND ROUND

  There is a sensible way to make a world.

  It should be flat, so that no one falls off accidentallyfn1 unless they get too near the edge, in which case it’s their own fault.

  It should be circular, so that it can revolve sedately to create the slow progression of the seasons.

  It should have strong supports, so that it doesn’t fall down.

  The supports should rest on firm foundations.

  To avoid an infinite regression, the foundations should do what foundations are supposed to do, and stay up of their own accord.

  It should have a sun, to provide light. This sun should be small and not too hot, to save energy, and it should revolve around the disc to separate day from night.

  The world should be populated by people, since there is no point in making it if no one is going to live there.

  Everything should happen because people want it to (magic) or because the power of story (narrativium) demands it.

  This sensible world is Discworld – flat, circular, held up by four world-bearing elephants standing firmly on the back of a giant space-faring turtle and inhabited by ordinary humans, wizards, witches, trolls, dwarves, vampires, golems, elves, the tooth fairy and the Hogfather.

  But—

  There is also a stupid way to make a world. And sometimes, that is necessary.

  When an experiment in fundamental thaumaturgy on the squash court of Unseen University ran wild and threatened to destroy the universe, the computer Hex had to use up a huge quantity of magic in an instant. The only option was to activate the Roundworld Project, a magical force field that – paradoxically – keeps magic out. When the Dean of Unseen University poked his finger in to see what would happen, Roundworld switched on.

  Roundworld isn’t entirely sure which bit of itself its name applies to. Sometimes the name refers to the planet, sometimes to the entire universe. There have been a few mishaps along the way, but the Roundworld universe has now been running fairly successfully for thirteen and a half billion years; all of it started by an old man with a beard.

  In the absence of magic, and lacking natural narrativium, the Roundworld universe runs on rules. Not rules made by people, but rules made by Roundworld itself; which is weird, because Roundworld has no idea what its rules ought to be. It seems to make them up as it goes along, but it’s hard to be sure.

  Certainly, it doesn’t know what size it ought to be. From outside, as it gathers dust on a shelf in Rincewind’s office, the Roundworld universe – a globe about 20 centimetres in diameter – resembles a cross between a foot-the-ball and a child’s snowstorm toy. From inside, it appears to be somewhat larger: a sphere whose radius is about 400 sextillion kilometres. As far as its only knownfn2 inhabitants can tell, it may be much larger still; perhaps even infinite.

  Such a huge universe seems to be cosmic overkill, because those inhabitants occupy only the tiniest part of its awe-inspiring volume, namely the surface of an approximate sphere a mere twelve thousand kilometres across.

  The wizards call this sphere Roundworld too. Its inhabitants call it Earth, because that’s what the surface is usually made of (except for the wet, rocky, sandy and icy bits): a typically parochial attitude. Until a few centuries ago they thought that Earth was fixed at the centre of the universe; the rest, which revolved around it or wandered crazily across the sky, was of minor importance since it didn’t contain them.

  Roundworld the planet, as the name suggests, is round. Not round like a disc, but round like a foot-the-ball. It is younger than Roundworld the universe: about one third of its age. Though cosmically minuscule, the planet is fairly big compared to its inhabitants, so that if you live there, and you’re stupid, you can be fooled into imagining that it’s flat.

  To prevent the planet’s inhabitants falling off, the rules state that a mysterious force glues them on. Thankfully, there are no world-bearing elephants. If there were, the inhabitants would be able to walk round their world to the point where it meets an elephant. This world-bearing beast of immense power would appear to be lying on its back, its feet in the air. (Paint the soles yellow and you wouldn’t be able to see it floating in a bowl of custard …)

  Roundworld’s rules are democratic. Not only does this mysterious force glue people to their world: it glues everything to everything else. But the glue is weak, and everything can – and usually does – move.

  This includes Roundworld the planet. It does have a sun, but this sun does not go round the planet. Instead, the planet goes round the sun. Worse, that doesn’t create day and night; instead, it produces seasons, because the planet is tilted. Also, the orbit isn’t circular. It’s a bit squashed, which is typical of Roundworld’s jerry-built construction. So to get day and night, the planet has to spin as well. It works, in its way: if you’re really stupid, you can be fooled into imagining that the sun goes round the planet. But – wouldn’t you just know it – the spin also prevented Roundworld from being a sensible sphere, because when it was molten it got sort of squashed, just like its orbit … oh, forget it.

  As a consequence of this hopelessly bungled arrangement, the sun has to be enormous, and a very long distance away. So it has to be ridiculously hot: so hot that special new rules have to come into play to allow it to burn. And then almost all of its prodigious energy output is wasted, trying to warm up empty space.

  Roundworld has no supports. It appears to think it’s a turtle, because it swims through space, tugged along by those mysterious forces. Its human inhabitants are not bothered by a sphere that swims, despite the absence of flippers. But then, people turned up at most four hundred thousand years ago, one hundredth of a per cent of the lifetime of the planet. And they seem to have turned up by accident, starting out as little blobs and then spontaneously becoming more complex – but they argue a lot about that. They’re not terribly bright, to be honest, and they only started to work out modern scientific rules of the universe they live in four hundred years ago, so they’ve got a lot of catching up to do.

  The inhabitants refer to themselves optimistically as Homo sapiens, meaning ‘wise man’ in an appropriately dead language. Their activities seldom fit that description, but there are occasional glorious exceptions. They should really be called Pan narrans, the storytelling ape, because nothing appeals to them more than a rollicking good yarn. They are narrativium incarnate, and they are currently refashioning their world to resemble Discworld, so that things do happen because people want them to. They have invented their own form of magic, with spells like ‘make a dugout canoe’, ‘switch on the light’, and ‘login to Twitter’. This kind of magic cheats by using the rules behind the scenes, but if you’re really, really stupid you can ignore that and pretend it’s magic.

  The first The Science of Discworld explained all that, and much more, including the giant limpet and the ill-fated crab civilisation’s great leap sideways. An endless series of natural disasters established something that the wizards intuitively knew from the word go: a round world is not a safe place to be. Fast-forwarding through Roundworld history, they managed to skip from some not very promising apes huddled around a black monolith to the collapse of the space elevators, as some presumably highly intelligent creatures, having finally got the message, fled the planet and headed for the stars to escape yet another ice age.

  They couldn’t really be descended from those apes, could they? The apes seemed to have on
ly two interests: sex, and bashing each other over the head.

  In The Science of Discworld II, the wizards were surprised to find that the intelligent star-farers were indeed descended from the apes – a strange new use of the word ‘descend’, and one that caused serious trouble later. They found that out because Roundworld had taken the wrong leg of the Trousers of Time and had therefore deviated from its original timeline. Its ape-derived humans had become barbarians, their society vicious and riddled with superstition. They would never leave the planet in time to escape their doom. Something had interfered with Roundworld’s history.

  Feeling somehow responsible for the planet’s fate, much as one might worry about a sick gerbil, the wizards entered their bizarre creation, to find that it was infested by elves. Discworld’s elves are not the noble creatures of some Roundworld myths. If an elf told you to eat your own head, you’d do it. But going back in time to when the elves had arrived, and kicking them out, just made everything worse. The evil had gone, but it had taken with it any shred of innovation.

  Examining Roundworld’s history on what ought to have been its correct timeline, the wizards deduced that two key people – prominent among those very few wise ones – had never been born. This omission had to be repaired to get the planet back on track. They were William Shakespeare, whose artistic creations would give birth to a genuine spirit of humanity, and Isaac Newton, who would provide science. With considerable difficulty, and some interesting failures along the way requiring ceilings to be painted black, the wizards nudged humanity back onto the only timeline that would save it from annihilation. Shakespeare’s A Midsummer Night’s Dream tipped the tables decisively by exposing the elves to ridicule. Newton’s Principia Mathematica completed the job by pointing humanity at the stars. Job done.

  It couldn’t last.

  By the time of The Science of Discworld III, Roundworld was in trouble again. Having safely entered its Victorian era, which should have been a hotbed of innovation, it had once more departed from its proper history. New technology was developing, but at a snail’s pace. Some vital spur to innovation had been lost, and the gerbil of humanity was sick once more. This time, a key figure had written the wrong book. The Reverend Charles Darwin’s Theology of Species, explaining the complexity of life through divine intervention, had been so well received that science and religious belief had converged. The creative spark of rational debatefn3 had been lost. By the time the Reverend Richard Dawkins finally wrote The Origin of Species (by Means of Natural Selection &c &c &c …) it was too late to develop space travel before the ice came down.