The Science of Discworld Revised Edition

creatures like them to live. There was air to breathe, animals and plants to eat, water to drink, land to stand on, and caves to get out of the rain and the lions. They
did
know that it was changeable, chaotic, unpredictable …
    They didn’t
know
that Up There – the rest of the universe – isn’t like that. Most of it is empty space, a vacuum. You can’t breathe vacuum. Most of what isn’t vacuum is huge balls of overheated plasma. You can’t stand on a ball of flame. And most of what isn’t vacuum and isn’t burning is lifeless rock. You can’t eat rock. 1 They were going to learn this later on. What they
did
know was that Up There was, in human timescales, calm, ordered, regular. And predictable, too – you could set your stone circle by it.
    All this gave rise to a general feeling that Up There was different from Down Here for a
reason
. Down Here was clearly designed for
us
. Equally clearly, Up There wasn’t. Therefore it must be designed for
somebody else
. And the new humanity was already speculating about some suitable tenants, and had been ever since they’d hidden in the caves from the thunder. The gods! They were Up There, looking Down! And they were clearly in charge, because humanity certainly wasn’t. As a bonus, that explained all of the things Down Here that were a lot more complicated than anything visible Up There, like thunderstorms and earthquakes and bees. Those were under the control of the gods.
    It was a neat package. It made us feel important. It certainly made the priests important. And since priests were the sort of people who could have your tongue torn out or banish you into Lion Country for disagreeing with them, it rapidly became an enormously popular theory, if only because those who had other ones either couldn’t speak or were up a tree somewhere.
    And yet … every so often some lunatic with no sense of self-preservation was born who found the whole story unsatisfying, and risked the wrath of the priesthood to say so. Such folk were already around by the time of the Babylonians, whose civilization flourished between and around the Tigris and Euphrates rivers from 4000 BC to 300 BC . The Babylonians – a term that covers a whole slew of semi-independent peoples living in separate cities such as Babylon, Ur, Nippur, Uruk, Lagash, and so on – certainly worshipped the gods like everyone else. One of their stories about gods is the basis of the Biblical tale of Noah and his ark, for instance. But they also took a keen interest in what those lights in the sky
did
. They knew that the Moon was round – a sphere rather than a flat disc They probably knew that the Earth was round, too, because it cast a rounded shadow on the Moon during lunar eclipses. They knew that the year was about 365¼ days long. They even knew about the ‘precession of the equinoxes’, a cyclic variation that completes one cycle every 26,000 years. They made these discoveries by keeping careful records of how the Moon and the planets moved across the sky. Babylonian astronomical records from 500 BC survive to this day.
    From such beginnings, an alternative explanation of the universe came into being. It didn’t involve gods, at least directly, so it didn’t find much favour with the priestly class. Some of their descendants are still trying to stamp it out, even today. The traditional priesthoods (who then and now often included some very intelligent people) eventually worked out an accommodation with this godless way of thinking, but it’s still not popular with postmodernists, creationists, tabloid astrologers and others who prefer the answers you can make up for yourself at home.
    The current name for what has variously been called ‘heresy’ and ‘natural philosophy’ is, of course, ‘science’.
    Science has developed a very strange view of the universe. It thinks that the universe runs on
rules
. Rules that never get broken. Rules that leave little room for the whims of gods.
    This emphasis on rules presents science with a daunting task. It has to explain how a lot of flaming gas and rocks Up There, obeying simple rules like ‘big things attract small things, and while small things also attract big things they don’t do it strongly enough so as you’d notice’, can have any chance whatsoever of giving rise to Down Here. Down Here, rigid obedience to rules seems notably absent. One day you go out hunting and catch a dozen gazelles; next day a lion catches
you
. Down Here the