The Science of Discworld Revised Edition

BY THE SAME AUTHORS:
    TERRY PRATCHETT
    THE CARPET PEOPLE • THE DARK SIDE OF THE SUN • STRATA
    TRUCKERS • DIGGERS • WINGS • ONLY YOU CAN SAVE MANKIND •
    JOHNNY AND THE DEAD • JOHNNY AND THE BOMB
    THE UNADULTERATED CAT (with Gray Jolliffe) • GOOD OMENS (with Neil Gaiman) •THE PRATCHETT PORTFOLIO (with Paul Kidby)
    T HE D ISCWORLD ® SERIES:
    THE COLOUR OF MAGIC • THE LIGHT FANTASTIC • EQUAL RITES •
    MORT • SOURCERY • WYRD SISTERS • PYRAMIDS • GUARDS! GUARDS!
    ERIC (with 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 AMAZING MAURICE AND HIS EDUCATED RODENTS •
    THE SCIENCE OF DISCWORLD II (with Ian Stewart and Jack Cohen)
    THE COLOUR OF MAGIC (graphic novel)
    THE LIGHT FANTASTIC (graphic novel)
    MORT: A DISCWORLD BIG COMIC (with Graham Higgins)
    SOUL MUSIC: The illustrated screenplay
    WYRD SISTERS: The illustrated screenplay
    MORT – THE PLAY (adapted by Stephen Briggs)
    WYRD SISTERS (adapted by Stephen Briggs)
    GUARDS! GUARDS! (adapted by Stephen Briggs)
    MEN AT ARMS (adapted by Stephen Briggs)
    THE DISCWORLD COMPANION (with Stephen Briggs)
    THE STREETS OF ANKH-MORPORK (with Stephen Briggs)
    THE DISCWORLD MAPP (with Stephen Briggs)
    A TOURIST GUIDE TO LANCRE a Discworld Mapp (with Stephen Briggs and Paul Kidby) • DEATH’S DOMAIN (with Paul Kidby) • NANNY OGG’S COOKBOOK
    IAN STEWART
    CONCEPTS OF MODERN MATHEMATICS • GAME, SET, AND MATH
    THE PROBLEMS OF MATHEMATICS • 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
    JACK COHEN
    LIVING EMBRYOS • REPRODUCTION • PARENTS MAKING PARENTS
    SPERMS, ANTIBODIES AND INFERTILITY • THE PRIVILEGED APE
    STOP WORKING AND START THINKING (with Graham Medley)
    IAN STEWART AND JACK COHEN
    THE COLLAPSE OF CHAOS • FIGMENTS OF REALITY
    WHEELERS • EVOLVING THE ALIEN



‘
Any sufficiently advanced technology is indistinguishable from magic
’
    A RTHUR C. C LARKE
    _____
    ‘
Any technology distinguishable from magic is insufficiently advanced
’
    G REGORY B ENFORD
    _____
    ‘
The reason why truth is so much stranger than fiction is that there is no requirement for it to be consistent
.’
    M ARK T WAIN
    _____
    ‘
There are no turtles anywhere
’
    P ONDER S TIBBONS

THE STORY STARTS HERE …
    O NCE 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 power 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 D EATH , 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 have been several media tie-in
The Science of
… books, such as
The Science of the X-Files
and
The Physics of Star Trek
. They tell you about areas of today’s science that may one day lead to the events or devices that the fiction depicts. Did