The Science of Discworld Revised Edition

a sun into my world?’ said Ponder.
    ‘Some suns,’ said Ridcully.
    ‘
Mine
bounced off,’ said the Dean.
    ‘And created this rather embarrassingly large hole here,’ said the Archchancellor. ‘And incidentally knocked a huge lump out of the place.’
    ‘But at least
bits
of my sun
burned
for a long time,’ said the Dean.
    ‘Yes, but
inside
the world. That doesn’t count.’ Ridcully sighed. ‘Yet your machine, Mister Stibbons, says a sun sixty miles across won’t work. And that’s ridiculous.’
    Ponder stared hollow-eyed at his world, wobbling around like a crippled duck.
    ‘There’s no narrativium,’ he said dully. ‘It doesn’t know what size a sun should be.’
    ‘Ook,’ said the Librarian.
    ‘Oh dear,’ said Ridcully. ‘Who let him in here?’
    The Librarian was informally banned from the High Energy Magic building, owing to his inherent tendency to check on what things were by tasting them. This worked very well in the Library, where taste had become a precision reference system, but was less useful in a room occasionally containing bus bars throbbing with several thousand thaums. The ban was informal, of course, because anyone capable of pulling the dooknob
right through
an oak door can obviously go where he likes.
    The orangutan knuckled over to the dome and tasted it. The wizards tensed as delicate black fingers twiddled the knobs of the omniscope, bringing into focus the furnace that had exploded yesterday. It was a tiny point of light now, surrounded by coruscating streamers of glowing gas.
    The focus moved in to the glowing ember.
    ‘Still too big,’ said Ridcully. ‘Nice try, old chap.’
    The Librarian turned towards him, the light of the explosion moving across his face, and Ponder held his breath.
    It came out in a rush.
    ‘Someone give me a light!’
    The globes on his desk rolled off and bounced on the floor as he tried to grab one. He held it as the Senior Wrangler obligingly lit a match, and waggled it this way and that.
    ‘It’ll work!’
    ‘Jolly good!’ said Ridcully. ‘What will?’
    ‘Days and nights!’ said Ponder. ‘Seasons, too, if we do it right! Well done, sir! I’m not sure about the wobble, but you might have got it just right!’
    ‘That’s the kind of thing we do,’ said Ridcully, beaming. ‘We’re the chaps for getting things right, sure enough. What things did we get right this time?’
    ‘The spin!’
    ‘That was
my
sun that did that,’ the Dean pointed out, smugly.
    Ponder was almost dancing. And then, suddenly, he looked grave.
    ‘But it all depends on fooling people down there,’ he said. ‘And there isn’t anyone down there … H EX?’
    There was a mechanical rattle as H EX paid attention.
    +++Yes? +++
    ‘Is there any way we can get on to the world?’
    +++ Nothing Physical May Enter The Project +++
    ‘I want someone down there to observe things from the surface.’
    +++ That Is Possible. Virtually Possible +++
    ‘Virtually?’
    +++ But You Will Need A Volunteer. Someone To Fool +++
    ‘This is Unseen University,’ said the Archchancellor. ‘That should present
no
problem.’
    1 A magical accident had once turned the University’s Librarian into an orangutan, a state which he enjoyed sufficiently to threaten, with simple and graphic gestures, anyone who suggested turning him back. The wizards noticed no difference no difference now. An orangutan seemed such a
natural
shape for a librarian.

SIXTEEN
EARTH AND FIRE

    WE DON’T KNOW if the Earth is a typical planet. We don’t know how common ‘aqueous’ planets with oceans and continents and atmospheres are. In our solar system, Earth is the only one. And we’d better be careful about phrases like ‘earthlike planet’, because for about half of Earth’s history it has not been the familiar blue-green planet that we see in satellite photos, with its oxygen atmosphere, white clouds, and everything else that we are used to. In order to
get
an earthlike planet, in today’s sense, you have to start with an unearthlike planet and wait a few billion years. And what you get is quite different from what, only a few decades ago, we
thought
the Earth was like.
    We thought it was a very stable place – that if you could go back to the time when the oceans and continents first separated out, they’d have been in the same places they are now. And we thought that the interior of the Earth was pretty simple.
    We were wrong.
    We know a lot about the surface of the Earth, but we