Science of Discworld III

because it wasn’t their natural habitat, but also because most of the students who frequented it used the floor as a filing cabinet and, distressingly, as a larder. Pizza is quite hard to remove from a sole, especially the cheese.
    In the background – always in the background in the High Energy Magic Building – was Hex, the university’s thinking engine.
    Occasionally, bits of it, or possibly ‘him’, moved. Ponder Stibbons had long ago given up trying to understand how Hex worked. Possibly Hex was the only entity in the university who understood how Hex worked.
    Somewhere inside Hex magic happened. Spells were reduced, not to their component candles and wands and chants, but to what they meant . It happened too fast to see, and perhaps too fast to understand. All that Ponder was certain about was that life was intimately involved. When Hex was thinking deeply there was a noticeable hum from the beehives along the back wall, where slots gave them access to the outside world, and everything completely ceased to work if the ant colony was removed from its big glass maze in the heart of the machine.
    Ponder had set up his magic lantern for a presentation. He liked making presentations. For a brief moment in the chaos of the universe, a presentation made everything sound as if it was organised.
    ‘Hex has run the history of Roundworld against the last copy,’ he announced, as the last wizard sat down. ‘He has found significant changes beginning in what was known as the nineteenth century. Slide, please, Rincewind.’ There was some muffled grumbling behind the magic lantern and a picture of a plump and elderly lady appeared on the screen. ‘This lady is Queen Victoria, ruler of the Empire of the British.’
    ‘Why is she upside down?’ said the Dean.
    ‘It could be because with a globe there is technically no right way up,’ said Ponder. ‘But I’m hazarding that it got put in wrong. Next slide, please. With care.’ Grumble, click. ‘Ah, yes, this is a steam engine. The reign of Victoria was notable for great developments in science and engineering. It was a very exciting time. Except … next slide, please.’ Grumble, click.
    ‘Wrong slide, that man!’ said Ridcully. ‘It’s just blank.’
    ‘Aha, no, sir,’ said Ponder, gleefully. ‘That is a dynamic way of showing you that the period I just described turns out not, in fact, to have happened. It should have, but it didn’t. On this version of the Globe, the Empire of the British did not become as big, and the other developments were all rather muted. The great wave of discovery flattened out. The world settled down to a period of stability and peace.’
    ‘Sounds good to me,’ said Ridcully, and got a chorus of ‘hear, hears’ from the other wizards.
    ‘Yes, Archchancellor,’ said Ponder. ‘And, then again, no . Getting off the planet, remember? The big freeze in five hundred years’ time? No land life form surviving that was bigger than a cockroach?’
    ‘No one bothered about that?’ said Ridcully.
    ‘Not until it was too late, sir. In that world as we left it, the first humans walked on the Moon less than seventy years after they flew at all.’
    Ponder looked at their blank faces.
    ‘Which was quite an achievement,’ he said.
    ‘Why? We’ve done that ,’ said the Dean.
    Ponder sighed. ‘Things are different on a globe, sir. There are no broomsticks, no magic carpets, and going to the Moon is not just a case of pushing off over the edge and trying to avoid the Turtle on the way down.’
    ‘How did they do it, then?’ said the Dean.
    ‘Using rockets, sir.’
    ‘The things that go up and explode with lots of coloured lights?’
    ‘Initially, sir, but fortunately they found out how to stop them doing that. Next slide, please …’ A picture that might have been a pair of old-fashioned pantaloons appeared on the screen. ‘Ah, this is our old friend, the Trousers of Time. We all know this. It’s what you get when history goes two ways. What we have to do now is find out why they split. That means I shall have to—’
    ‘Are we near the point where you mention quantum?’ said Ridcully, quickly.
    ‘I’m afraid it is looming, sir, yes.’
    Ridcully stood up, gathering his robes about him. ‘Ah. I think I heard the gong for dinner, gentlemen. Just as well, really.’
    The moon rose. At midnight, Ponder Stibbons read what Hex had written, wandered across the dewy lawn to the Library, woke the Librarian, and asked