The Science of Discworld

by Terry Pratchett

  'Who the hell are you?' said the king. 'What are you doing here? Eh? Guards! I deman...’

  The insistent message from his eyes finally battered through to his brain. Mort* was impressed. King Olerve had held on to his throne for many years and, even when dead, knew how to behave.

  'Oh,' he said. 'I see. I didn't expect to see you so soon.'

  YOUR MAJESTY, said Death, bowing, FEW DO.

  The king looked around. It was quiet and dim in this shadow world, but outside there seemed to be a lot of excitement.

  'That's me down there, is it?'

  I'M AFRAID SO, SIRE.

  'Clean job. Crossbow, was it?'

  Our earthly fears about death have led to some of our strangest reifi-cations. Inventing the concept 'death' is giving a name to a process — dying — as if it's a 'thing'. Then, of course, we endow the thing with a whole suite of properties, whose care is known only to the priests. That thing turns up in many guises. It may appear as the 'soul', a thing that must leave the body when it turns it from a live body into a dead one. It is curious that the strongest believers in the soul tend to be people who denigrate material things; yet they then turn their own philosophy on its head by insisting that when an evident process — life — comes to an end, there has to be a thing that continues. No. When a process stops, it's no longer 'there'. When you stop beating an egg, there isn't some pseudo-material essence-of-eggbeater that passes on to something else. You just aren't turning the handle any more.

  Another 'thing' that arises from the assumption that death exists is whatever must be instituted in the egg/embryo/foetus in order to turn it into a proper human being, who can die when required. Note that in human myth and Discworld reality it is the soulless ones, vampires and their ilk, who cannot die. Long before ancient Egypt and the death-god Anubis, priests have made capital out of this verbal confusion. On Discworld, it's entirely proper to have 'unreal' things, like Dark, or like the Tooth Fairy in Hogfather, which play their part in the plot.* But it's a very strange idea indeed on planet Earth.

  Yet it may be part of some process that makes us human beings. As Death points out in Hogfather, humans seem to need to project a kind of interior decoration on to the universe, so that they spend much of the time in a world of their own making. We seem — at least, at the moment — to need these things. Concepts like gods, truth* and soul appear to exist only in so far as humans consider them to do so (although elephants are known to get uneasy and puzzled upon finding elephant bones in the wild — whether this is because of some dim concept of the Big Savannah In The Sky or merely because it's manifestly not a good idea to stay in a place where elephants get killed is unknown). But they work some magic for us. They add narrativium to our culture. They bring pain, hope, despair, and comfort. They wind up our elastic. Good or bad, they've made us into people.

  We wonder if the users thought that that cold-focusing mirror worked some magic for them. We can think of several ways in which it might appear to. And some very clever friends of ours are persuaded that souls might exist, too. Nearly everything is a process on some level. To a physicist, matter is a process carried out by a quantum wave function. And quantum wave functions exist only when the person you're arguing with asserts that they don't — so maybe souls exist in the same way.

  In this area, we have to admit the science doesn't know everything. Science is based on not knowing everything. But it does know some things.

  And if so: congratulations! You are a human being, thinking narratively.

  Light on the Disc travels at about the same speed as sound. This does not appear to cause problems.

  And a terrible thing it is, akin to a state of horrible depression. Hence the affliction of Captain Vimes in Guards! Guards! Who needs a couple of drinks simply to become sober.

  Well … most people.

  'Desperate' is another privative — it means 'no hope'.

  Death’s apprentice — well, he’d have to train a successor. Not in case he dies: so he can retire. Which he does (temporarily) in Reaper Man.

  Indeed, it is a 'fundamental constant' of the Discworld universe that things exist because they’re believed in.

  'Truth' is a privative in the same way that 'sober' is — until you invent lies, you don’t know what the truth is. Nature appears to, otherwise animals would not have invested so much effort on very effective camouflage.

  TWENTY-THREE

  NO POSSIBILITY OF LIFE

  IT WAS DIFFICULT EATING SANDWICHES that you couldn't see. Rincewind was aware that back in the real world the Librarian was handing them to him, and he had to take it on trust that they were going to be cheese and chutney. As it turned out, he detected a hint of banana, too.

  The wizards were shocked. It's terrible to find that you can't do what you like with your own universe.

  'So we can't just magic life into the Project?' said the Dean.

  Tin afraid not, sir,' said Ponder. 'We have quite a lot of control over things, but only in a very subtle way. I have gone into this'

  'I don't call moving huge worlds very subtle,' said the Dean.

  'In Project terms, even moving the moon into place took a hundred thousand years,' said Ponder. 'Time prefers to move faster in there. It's amazing what you can move if you give it a little push for that long.'

  'But we've done so many things —’

  'Just moved things around, sir.'

  'Seems a shame to have made a world and there's no one to live on it,' said the Senior Wrangler.

  'When I was small, I had a model farmyard,' said the Bursar, looking up from his reading.

  'Thank you, Bursar. Very interesting,' said the Archchancellor. 'All right, let's play by the rules. What do you have to move around to get people?'

  'Well ... bits of other people, my father told me,' said the Dean.

  'Bad taste there, Dean.'

  'Many religions start with dust,' said the Senior Wrangler. 'And then you bring it alive in some way.'

  'That's pretty hard even with magic,' said the Archchancellor. 'And we can't use magic.'

  'Up in Nothingfjord they believe that all life was created when the god Noddi cut off his ... unmentionables and hurled them at the sun, who was his father,' said the Senior Wrangler.

  'What, you mean his ... underwear?' said the Lecturer in Recent Runes, who could be a bit slow.

  'First of all we can't physically exist inside the Project, secondly that sort of thing is unhygienic, and thirdly I doubt very much if you'll find a volunteer,' said the Archchancellor sharply. 'Anyway, we're men of magic. That is superstition.'

  'Can we make weather, then?' said the Dean.

  'I think HEX can let us do that,' said Ponder. 'Weather is only pushing stuff around.'

  'So we can aim lightning at anyone we don't like?'

  'But there isn't anyone on the world, whether we like them or not,' said Ponder wearily. 'That's the point.'

  'And while the Dean can make enemies anywhere, I think that, ah, Roundworld would test even his powers,' said Ridcully.

  'Thank you, Archchancellor'

  'Happy to oblige, Dean.'

  HEX's keyboard clattered. The quill pen began to write.

  It began:

  +++ I Don't Think You Are Going To Believe This +++

  Thunderstorms tore the air apart, far out to sea.

  The air blinked. The storm was gone. The shoreline looked different.

  'Hey, what happened?' said Rincewind.

  'Everything all right?' said Ponder Stibbons in his ear.

  'What happened just then?'

  'We've moved you forward in time a little,' said Ponder The tone of his voice suggested that he dreaded being asked why.

  'Why?' said Rincewind.

  'You'll laugh when I tell you this ...'

  'Oh, good. I like a laugh.'

  'HEX says he's detecting life all round you. Can you see anything?'

  Rincewind looked around warily. The sea was sucking at the shore, which had a
bit of sand on it now. Scum rolled in the waves.

  'No,' he said.

  'Good. You see, there can't be any life where you are,' Ponder went on.

  'Where am I exactly?'

  'Er ... a sort of magical world with no one in it but yourself’

  'Oh, you mean the sort everyone lives in,' said Rincewind bitterly. He glanced at the sea again, just in case.

  'But if you wouldn't mind having a look ...' Ponder went on.

  'For this life that can't possibly exist?'

  'Well, you are the Professor of Cruel and Unusual Geography.'

  'It's the cruel and unusual geography that's bothering me,' said Rincewind. 'Incidentally, have you looked at the sea lately? It's blue.'

  'Well? The sea is blue.'

  'Really?'

  The omniscope was once again the centre of attention.

  'Everyone knows the sea is blue,' said the Dean. 'Ask anyone.'

  'That's right,' said Ridcully. 'However, while everyone knows the sea is blue, what everyone usually sees is a sea that's grey or dark green. Not this colour. This is virulent!'

  'I'd say turquoise,' said the Senior Wrangler.

  'I used to have a shirt that colour,' said the Bursar.

  'I thought it might be copper salts in the water,' said Ponder Stibbons. 'But it isn't.'

  The Archchancellor picked up HEX's latest write-out. It read:

  +++ Out Of Cheese Error +++

  'Not helpful,' he muttered.

  'Thank goodness he's still operating the Project,' said Ponder, joining him. 'I think he's got confused.'

  'It's not his job to be confused,' said Ridcully. 'We don't need a machine for being confused. We're entirely capable of confusin' ourselves. It is a human achievement, confusion, and right at this minute I feel I am winning a prize. You, Mister Stibbons, said there was no possibility of life turnin' up inside the Project.'

  Ponder waved his hands frantically. 'There's no way that it can! Life isn't like rocks and water. Life is special!'

  The breath of gods, that sort of thing?' said Ridcully.

  'Not gods as such, obviously, but...’

  'I suppose from the point of view of rocks, rocks are special,' said Ridcully, still reading HEX's output.

  'No, sir. Rocks don't have a point of view.'

  Rincewind lifted up a shard of rock, very carefully, ready to drop it immediately at the merest suggestion of tooth or claw.

  'This is silly,' he said. 'There's nothing here.'

  'Nothing?' said Ponder, inside the helmet.

  'Some of the rocks have got all kind of yuk on them, if that's your idea of a good time.'

  'Yuk?'

  'You know ... gunge.'

  'HEX seems to be suggesting now that whatever is showing up is, and is not, life,' said Ponder, a man whose interest in slime was limited.

  'That's very cheering.'

  'There seems to be a particular concentration not far from you ... we're just going to move you so that you can have a look at it...'

  Rincewind's head swam. A moment later, the rest of his body wanted to join it. He was underwater.

  'Don't worry,' said Ponder, 'because although you're at a very great depth, the pressure can't possibly hurt you.'

  'Good.'

  'And the boiling water should feel merely tepid.'

  'Fine.'

  'And the terrible upflow of poisonous minerals can't harm you because of course you're not really there.''So, all in all, I'm laughing,' said Rincewind gloomily, peering at the dim glow ahead of him.

  'It's gods, definitely,' said the Archchancellor. 'Gods have turned up while our back was turned. There can be no other explanation.'

  'Then they seem rather unambitious,' sniffed the Senior Wrangler. 'I mean, you'd expect humans, wouldn't you? Not ... blobs you can't see. They're not going to bow down and worship anyone, are they?'

  'Not where they are,' said Ridcully. 'The planet's full of cracks! You shouldn't get fire under water. That's against nature!'

  'Everywhere you look, little blobs,' said the Senior Wrangler. 'Everywhere.'

  'Blobs,' said the Lecturer in Recent Runes. 'Can they pray? Can they build temples? Can they wage holy war on less enlightened blobs?'

  Ponder shook his head sadly. hex's results were quite clear. Nothing solid could cross the barrier into Roundworld. It was possible, with enough thaumic effort, to exert tiny pressures, but that was all. Of course, you could speculate that thought might get in there, but if that was the case the wizards were thinking some very dull thoughts indeed. 'Blobs' wasn't really a good word for what were currently floating in the warm seas and dribbling over the rocks. It had far too many overtones of feverish gaiety and excitement.

  'They're not even moving,' said Ridcully. 'Just bobbing about.'

  'Blobbing about, haha,' said the Senior Wrangler.

  'Could we ... help them in some way?' said the Lecturer in Recent Runes. 'You know ... to become better blobs? I fear we have some responsibility.'

  'They may be as good as blobs get,' said Ridcully. 'What's up with that Rincewind fellow?'

  They turned. In its circle of smoke, the suited figure was making frantic running motions.

  'Do you think, on reflection, that it might not have good idea to miniaturize his image in Roundworld?' said Ridcully.

  'It was the only way we could get him into that little rock pool HEX wanted us to look at, sir,' said Ponder. 'He doesn't have to be any particular size. Size is relative.'

  'Is that why he keeps calling out for his mother?'

  Ponder went over to the circle and rubbed out a few important runes. Rincewind collapsed on the floor.

  'What idiot put me in there?' he said. 'Ye gods, it's awful! The size of some of those things!'

  'They're actually tiny,' said Ponder, helping him up.

  'Not when you are smaller than them!'

  'My dear chap, they can't possibly hurt you. You have nothing to fear but fear itself’

  'Oh, is that so? What help is that? You think that makes it better? Well, let me tell you, some of that fear can be pretty big and nasty —’

  'Calm down, calm down.’

  'Next time I want to be big, understand?'

  'Did they try to communicate with you in any way?'

  'They just flailed away with great big whiskers! It was worse than watching wizards arguing!'

  'Yes, I doubt if they are very intelligent.'

  'Well, nor are the rock pool creatures.'

  Tin just wondering,' said Ponder, wishing he had a beard to stroke thoughtfully, 'if perhaps they might ... improve with keeping ...'

  TWENTY-FOUR

  DESPITE WHICH ...

  THAT BLUE IN THE ROUNDWORLD SEA isn't a chemical — well, not in the usual 'simple chemical' sense of the word. It's a mass of bacteria, called cyanobacteria. Another name for them is 'blue-green algae', which is wonderfully confusing. Modern so-called blue-green algae are usually red or brown, but the ancient ones probably were blue-green. And blue-green algae are really bacteria, whereas most other algae have cells with a nucleus and so are not bacteria. The blue-green colour comes from chlorophyll, but of a different kind from that in plants, together with yellow-orange chemicals called carotenoids.

  Bacteria appeared on Earth at least 3.5 billion years ago, only a few hundred million years after the Earth cooled to the point at which living creatures could survive on it. We know this because of strange layered structures found in sedimentary rocks. The layers can be flat and bumpy, they can form huge branched pillars, or they can be highly convoluted like the leaves in a cabbage. Some deposits are half a mile thick and spread for hundreds of miles. Most date from 2 billion years ago, but those from Warrawoona in Australia are 3.5 billion years old.

  To begin with, nobody knew what these deposits were, In the 1950s and 1960s they were revealed as traces of communities of bacteria, especially cyanobacteria.

  Cyanobacteria collect together in shallow water to form huge, floating mats, like
felt. They secrete a sticky gel as protection against ultraviolet light, and this causes sediment to stick to the mats. When the layer of sediment gets so thick that it blocks out the light, the bacteria form a new layer, and so on. When the layers fossilize they turn into stromatolites, which look rather like big cushions.

  The wizards haven't been expecting life. Roundworld runs on rules, but life doesn't — or so they think. The wizards see a sharp discontinuity between life and non-life. This is the problem of expecting becomings to have boundaries — of imagining that it ought to be easy to class all objects into either the category 'alive' or the category 'dead'. But that's not possible, even ignoring the flow of time, in which 'alive' can become 'dead' — and vice versa. A 'dead' leaf is no longer part of a living tree, but it may well have a few revivable cells.

  Mitochondria, now the part of a cell that generates its chemical energy, once used to be independent organisms. Is a virus alive? Without a bacterial host it can't reproduce, but neither can DNA copy itself without a cell's chemical machinery.

  We used to build 'simple' chemical models of living processes, in the hope that a sufficiently complex network of chemistry could 'take off' — become self-referential, self-copying — by itself. There was the concept of the 'primal soup', lots of simple chemicals dissolved in the oceans, bumping into each other at random, and just occasionally forming something more complicated. It turns out that this isn't quite the way to do it. You don't have to work hard to make real-world chemistry complex: that's the default. It's easy to make complicated chemicals. The world is full of them. The problem is to keep that complexity organized.

  What counts as life? Every biologist used to have to learn a list of properties: ability to reproduce, sensitivity to its environment, utilization of energy, and the like. We have moved on. 'Autopoeisis' — the ability to make chemicals and structures related to one's own reproduction — is not a bad definition, except that modern life has evolved away from those early necessities. Today's biologists prefer to sidestep the issue and define life as a property of the DNA molecule, but this begs the deeper question of life as a general type of process. It may be that we're now defining life in the same way that 'science fiction' is defined — it's what we're pointing at when we use the term.*