The Science of Discworld Revised Edition

said the Dean.
    ‘Cloud, sir, in fact,’ said Ponder.
    ‘Well, we can all make clouds of gas –’
    ‘Er … it’s water vapour, sir,’ said Ponder.
    He reached over and adjusted the omniscope.
    The room was filled with the roar of the biggest rainstorm of all time.
    By lunchtime it was a world of ice.
    ‘And we were doing so well,’ said Ridcully.
    ‘I can’t think what went wrong,’ said Ponder, wringing his hands. ‘We were getting seas!’
    ‘Can’t we just warm it up?’ said the Senior Wrangler.
    Ponder sat down on his chair and put his head in his hands.
    ‘Bound to cool a world down, all that rain,’ said the Lecturer in Recent Runes, slowly.
    ‘Very good … er, rocks,’ said the Dean. He patted Ponder on the back .
    ‘Poor chap looks a bit down,’ hissed the Senior Wrangler to Ridcully. ‘I don’t think he’s been eating properly.’
    ‘You mean … not chewing right?’
    ‘No eating
enough
, Archchancellor.’
    The Dean picked up a piece of paper from Ponder’s crowded desk.
    ‘I say, look at these,’ he said.
    On the paper was written, in Ponder’s very neat handwriting:
    THE RULES
    1 Things fall apart, but centres hold
.
    2 Everything moves in curves
.
    3 You get balls
.
    4 Big balls tell space to bend
.
    5 There are no turtles anywhere
.
    6 … It’s so depressing
.
    ‘Always been a bit of a one for rules, our Ponder,’ said the Senior Wrangler.
    ‘Number Six doesn’t sound incredibly well formulated,’ said Ridcully.
    ‘You don’t think he’s going a bit bursar, do you?’ said the Lecturer in Recent Runes.
    ‘He always thinks everything has to
mean
something,’ said Ridcully, who generally took the view that trying to find any deep meaning to events was like trying to find reflections in a mirror: you always succeeded, but you didn’t learn anything new.
    ‘I suppose we could simply heat the thing up,’ said the Senior Wrangler.
    ‘A sun should be easy,’ said Ridcully. ‘A big ball of fire should be no problem to a thinking wizard.’ He cracked his knuckles. ‘Get some of the students to put Mister Stibbons to bed. We’ll soon have his little world all warm or my name’s not Mustrum Ridcully.’
    1 Omnianism had taught for thousands of years that the Discworld was in fact a sphere, and violently persecuted those who preferred to believe the evidence of their own eyes. At the time of writing, Omnianism was teaching that there was something to be said for every point of view.

FOURTEEN
DISC WORLDS

    TO THE WIZARDS of Unseen University, the heavens include two obviously different types of body: stars, which are tiny pinpricks of light, and the sun, which is a hot ball, not too far away, and passes over the Disc during the day and under it at night. It’s taken humanity a while to realize that in our universe it’s not like that. Our Sun is a star, and like all stars it’s
huge
, so those tiny pinpricks must be a very long way off. Moreover, some of the pinpricks that seem to be stars aren’t: they betray themselves by moving differently from the rest. These are the planets, which are a lot closer and a lot smaller, and together with the Earth, Moon, and Sun they form the solar system. Our solar system may
look
like a lot of balls whizzing around in some kind of cosmic game of pool, but that doesn’t mean that it started out as balls or rock and ice. It is the outcome of a physical process, and the ingredients that went into that process are not obliged to resemble the result that comes out.
    The more we learn about the solar system, the more difficult it is to give a plausible answer to the question: how did it start? It is not the ‘answer’ part that gets harder – it’s the plausibility. As we learn more and more about the solar system, the reality-check that our theories have to pass becomes more and more stringent. This is one reason why scientists have a habit of opening up old questions that everybody assumed were settled long ago, and deciding that they weren’t. It doesn’t mean that scientists are incompetent: it demonstrates their willingness to contemplate new evidence and re-examine old conclusions in its light. Science certainly does not claim to get things right, but it has a good record of ruling out ways to get things wrong.
    What must a theory of the formation of the solar system explain? Principally, of course, the planets – nine of them, dotted rather randomly in space; Mercury, Venus, Earth, Mars, Jupiter, Saturn,