Terry Pratchett & Ian Stewart & Jack Cohen - The Science Of Discworld

Terry Pratchett - The Science of DiscworldTerry Pratchett, Ian Stewart and

Jack

Cohen – The Science of Discworld

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THE STORY STARTS HERE

ONCE UPON A TIME, there was Discworld. There still is an adequate supply.

Discworld is the flat world, carried through space on the back of a giant

turtle, which has been the source of - so far - twenty-three novels, four

maps,

an encylopaedia, two animated series, t-shirts, scarves, models, badges,

beer,

embroidery, pens, posters, and prob-ably, by the time this is published,

talcum

power and body splash (if not, it can only be a matter of time).

It has, in short, become immensely popular.

And Discworld runs on magic.

Roundworld - our home planet, and by extension the universe in which it sits

—

runs on rules. In fact, it simply runs. But we have watched the running, and

those observations and the ensuing deductions are the very basis of science.

Magicians and scientists are, on the face of it, poles apart. Certainly, a

group

of people who often dress strangely, live in a world of their own, speak a

specialized language and frequently make statements that appear to be in

flagrant breach of common sense have nothing in common with a group of people

who often dress strangely, speak a specialized language, live in ... er ...

Perhaps we should try this another way. Is there a connection between magic

and

science? Can the magic of Discworld, with its eccentric wizards,

down-to-Earth

witches, obstinate trolls, fire-breathing dragons, talking dogs, and

personified

DEATH, shed any useful light on hard, rational, solid, Earthly science?

We think so.

We'll explain why in a moment, but first, let's make it clear what The

Science

of Discworld is not. There are several media tie-in The Science of... books

at

the moment, such as The Science of the X-Files and The Physics of Star Trek.

They will tell you about areas of today's science that may one day lead to

the

events or devices that the fiction depicts. Did aliens crash-land at Roswell?

Could an anti-matter warp drive ever be invented? Could we ever have the

ultra

long-life batteries that Scully and Mulder must be using in those torches of

theirs?

We could have taken that approach. We could, for example, have pointed out

that

Darwin's theory of evolution explains how lower lifeforms can evolve into

higher

ones, which in turn makes it entirely reasonable that a human should evolve

into

an orangutan (while remaining a librarian, since there is no higher life form

than a librarian). We could have speculated on which DNA sequence might

reliably

incorporate asbestos linings into the insides of drag-ons. We might even have

attempted to explain how you could get a turtle ten thousand miles long.

We decided not to do these things, for a good reason ... um, two reasons.

The first is that it would be ... er ... dumb.

And this because of the second reason. Discworld does not run on scientific

lines. Why pretend that it might? Dragons don't breathe fire because they've

got

asbestos lungs - they breathe fire because everyone knows that's what dragons

do.

What runs Discworld is deeper than mere magic and more pow-erful than pallid

science. It is narrative imperative, the power of story. It plays a role

similar

to that substance known as phlogiston, once believed to be that principle or

substance within inflammable things that enabled them to burn. In the

Discworld

universe, then, there is narrativium. It is part of the spin of every atom,

the

drift of every cloud. It is what causes them to be what they are and continue

to

exist and take part in the ongoing story of the world.

On Roundworld, things happen because the things want to hap-pen. [1] What

people

want does not greatly figure in the scheme of things, and the universe isn't

there to tell a story.

With magic, you can turn a frog into a prince. With science, you can turn a

frog

into a Ph.D and you still have the frog you started with.

That's the conventional view of Roundworld science. It misses a lot of what

actually makes science tick. Science doesn't just exist in the abstract. You

could grind the universe into its component par-ticles without finding a

single

trace of Science. Science is a structure created and maintained by people.

And

people choose what interests them, and what they consider to be significant

and,

quite often, they have thought narratively.

Narrativium is powerful stuff. We have always had a drive to paint stories on

to

the Universe. When humans first looked at the stars, which are great flaming

suns an unimaginable distance away, they saw in amongst them giant bulls,

dragons, and local heroes.

This human trait doesn't affect what the rules say - not much, anyway - but

it

does determine which rules we are willing to con-template in the first place.

Moreover, the rules of the universe have to be able to produce everything

that

we humans observe, which introduces a kind of narrative imperative into

science

too. Humans think in stories. Classically, at least, science itself has been

the

dis-covery of 'stories' - think of all those books that had titles like The

Story of Mankind, The Descent ofMan, and, if it comes to that, A Brief

History

of Time.

Over and above the stories of science, though, Discworld can play an even

more

important role: What if? We can use Discworld for thought experiments about

what

science might have looked like if the universe had been different, or if the

history of science had followed a different route. We can look at science

from

the outside.

To a scientist, a thought experiment is an argument that you can run through

in

your head, after which you understand what's going on so well that there's no

need to do a real experiment, which is of course a great saving in time and

money and prevents you from get-ting embarrassingly inconvenient results.

Discworld takes a more practical view - there, a thought experiment is one

that

you can't do and which wouldn't work if you could. But the kind of thought

experiment we have in mind is one that scientists carry out all the time,

usually without realizing it; and you don't need to do it, because the whole

point is that it wouldn't work. Many of the most important questions in

science,

and about our understanding of it, are not about how the universe actually

is.

They are about what would happen if the universe were different.

Someone asks 'why do zebras form herds?' You could answer this by an analysis

of

zebra sociology, psychology, and so on ... or you could ask a question of a

very

different kind: 'What would hap-pen if they didn't?' One fairly obvious

answer

to that is 'They'd be much more likely to get eaten by lions.' This

immediately

suggests that zebras form herds for self-protection - and now we've got some

insight into what zebras actually do by contemplating, for a moment, the

possibility that they might have done something else.

Another, more serious example is the question 'Is the solar sys-tem stable?',

which means 'Could it change dramatically as a result of some tiny

disturbance?'

In 1887 King Oscar II of Sweden offered a prize of 2,500 crowns for the

answer

It took about a century for the world's mathematicians to come up with a

definite answer: 'Maybe'. (It was a good answer, but they didn't get paid.

The

prize had already been awarded to someone who didn't get the answer and whose

prizewinning article had a big mistake right at the most interesting part.

But

when he put it right, at his own expense, he invented Chaos Theory and paved

the

way for the 'maybe'. Sometimes, the best answer is a more interesting

question.)

The point here is that stability is not about what a system is actually

doing:

it is about how the system would change if you disturbed it. Stability, by

definition, deals with 'what if?'.

Because a lot of science is really about this non-existent world of thought

experiments, our understanding of science must concern itself with worlds of

the

imagination as well as with worlds of real-ity. Imagination, rather than mere

intelligence, is the truly human quality. And what better world of the

imagination to start from than Discworld? Discworld is a consistent,

well-developed universe with its own kinds of rules, and convincingly real

people live on it despite the substantial differences between their

universe's

rules and ours. Many of them also have a thoroughgoing grounding in 'common

sense', one of science's natural enemies.

Appearing regularly within the Discworld canon are the buildings and faculty

of

Unseen University, the Discworld's premier col-lege of magic. The wizards[2]

are

a lively bunch, always ready to open any door that has 'This door to be kept

shut' written on it or pick up anything that has just started to fizz. It

seemed

to us that they could be useful ...

If we, or they, compare Discworld's magic to Roundworld sci-ence, the more

similarities and parallels we find. Clearly, as the wizards of Unseen

University

believe, this world is a parody of the Discworld one. And when we didn't

discover those, we found that the differences were very revealing. Science

takes

on a new character when you stop asking questions like 'What does newt DNA

look

like?' and instead ask 'I wonder how the wizards would react to this way of

thinking about newts?'

There is no science as such on Discworld. So we have put some there. By

magical

means, the wizards on Discworld must be led to create their own brand of

science

- some kind of pocket universe' in which magic no longer works, but rules do.

Then, as the wizards learn to understand how the rules make interesting

things

happen -rocks, bacteria, civilizations - we watch them watching ... well, us.

It's a sort of recursive thought experiment, or a Russian doll wherein the

smaller dolls are opened up to find the largest doll inside.

And then we found that ... ah, but that is another story.

TP, IS, & JC, DECEMBER 1998

PS We have, we are afraid, mentioned in the ensuing pages Schrodinger's Cat,

the

Twins Paradox, and that bit about shining a torch ahead of a spaceship

travelling at the speed of light. This is because, under the rules of the

Guild

of Science Writers, they have to be included. We have, however, tried to keep

them short.

We've managed to be very, very brief about the Trousers of Time, as well.

ONE

SPLITTING THE THAUM

SOME QUESTIONS SHOULD NOT BE ASKED. However, someone always does,

'How does it work?' said Archchancellor Mustrum Ridcully, the Master of

Unseen

University.

This was the kind of question that Ponder Stibbons hated almost as much as

'How

much will it cost?' They were two of the hardest questions a researcher ever

had

to face. As the university's de facto head of magical development, he

especially

tried to avoid questions of finance at all costs.

'In quite a complex way.' he ventured at last.

'Ah.'

'What I'd like to know,' said the Senior Wrangler, 'is when we're going to

get

the squash court back.'

'You never play, Senior Wrangler,' said Ridcully, looking up at the towering

black construction that now occupied the centre of the old university

court.[3]

'I might want to one day. It'll be damn hard with that thing in the way,

that's

my point. We'll have to completely rewrite the rules.'

Outside, snow piled up against the high windows. This was turn-ing out to be

the

longest winter in living memory - so long, in fact, that living memory itself

was being shortened as some of the older citizens succumbed. The cold had

penetrated even the thick and ancient walls of Unseen University itself, to

the

general concern and annoyance of the faculty. Wizards can put up with any

amount

of deprivation and discomfort, provided it is not happening to them.

And so, at long last, Ponder Stibbons's project had been author-ized. He'd

been

waiting three years for it. His plea that splitting the thaum would push back

the boundaries of human knowledge had fallen on deaf ears; the wizards

considered that pushing back the boundaries of anything was akin to lifting up

a

very large, damp stone. His assertion that splitting the thaum might

significantly increase the sum total of human happiness met with the

rejoinder

that everyone seemed pretty happy enough already.

Finally he'd ventured that splitting the thaum would produce vast amounts of

raw

magic that could very easily be converted into cheap heat. That worked. The

Faculty were lukewarm on the sub-ject of knowledge for knowledge's sake, but

they were boiling hot on the subject of warm bedrooms.

Now the other senior wizards wandered around the suddenly-cramped court,

prodding the new thing. Their Archchancellor took out his pipe and

absent-mindedly knocked out the ashes on its matt black side.

'Um ... please don't do that, sir,' said Ponder.

'Why not?'

'There might be ... it might... there's a chance that...' Ponder stopped. 'It

will make the place untidy, sir,' he said.

'Ah. Good point. So it's not that the whole thing might explode, then?'

'Er ... no, sir. Haha,' said Ponder miserably. 'It'd take a lot more than

that,

sir -'

There was a whack as a squash ball ricocheted off the wall, rebounded off the

casing, and knocked the Archchancellor's pipe out of his mouth.

'That was you. Dean,' said Ridcully accusingly. 'Honestly, you fellows

haven't

taken any notice of this place in years and suddenly you all want to - Mr

Stibbons? Mr Stibbons?'

He nudged the small mound that was the hunched figure of the University's

chief

research wizard. Ponder Stibbons uncurled slightly and peered between his

fingers.

'I really think it might be a good idea if they stopped playing squash, sir,'

he

whispered.

'Me too. There's nothing worse than a sweaty wizard. Stop it, you fellows.

And

gather round. Mr Stibbons is going to do his pres-entation.' The

Archchancellor

gave Ponder Stibbons a rather sharp look. 'It is going to be very informative

and interesting, isn't it, Mister Stibbons. He's going to tell us what he

spent

AM$55,879.45p on.'

'And why he's ruined a perfectly good squash court,' said the Senior

Wrangler,

tapping the side of the thing with his squash racket.

'And if this is safe? said the Dean. 'I'magainst dabbling in physics,'

Ponder Stibbons winced.

'I assure you, Dean, that the chances of anyone being killed by the, er,

reacting engine are even greater than the chance of being knocked down while

crossing the street,' he said.

'Really? Oh, well ... all right then.'

Ponder reconsidered the impromptu sentence he'd just uttered and decided, in

the

circumstances, not to correct it. Talking to the senior wizards was like

building a house of cards; if you got anything to stay upright, you just

breathed out gently and moved on.

Ponder had invented a little system he'd called, in the privacy of his head,

Lies-to-Wizards. It was for their own good, he told him-self. There was no

point

in telling your bosses everything; they were busy men, they didn't want

explanations. There was no point in bur-dening them. What they wanted was

little

stories that they felt they could understand, and then they'd go away and

stop

worrying.

He'd got his students to set up a small display at the far end of the squash

court. Beside it, with pipes looping away through the wall into the High

Energy

Magic building next door, was a termi-nal to HEX, the University's thinking

engine. And beside that was a plinth on which was a very large red lever,

around

which someone had tied a pink ribbon.

Ponder looked at his notes, and then surveyed the faculty.

'Ahem ...' he began.

'I've got a throat sweet somewhere,' said the Senior Wrangler, patting his

pockets.

Ponder looked at his notes again, and a horrible sense of hope-lessness

overcame

him. He realized that he could explain thaumic fission very well, provided

that

the person listening already knew all about it. With the senior wizards,

though,

he'd need to explain the meaning of every word. In some cases this would mean

words like 'the' and 'and'.

He glanced down at the water jug on his lectern, and decided to extemporize.

Ponder held up a glass of water.

'Do you realize, gentlemen,' he said, 'that the thaumic potential in this

water

... that is, I mean to say, the magical field generated by its narrativium

content which tells it that it is water and lets it keep on being water

instead

of, haha, a pigeon or a frog ... would, if we could release it, be enough to

move this whole university all the way to the moon?'

He beamed at them.

'Better leave it in there, then,' said the Chair of Indefinite Studies.

Ponder's smile froze.

'Obviously we cannot extract all of it,' he said, 'But we -'

'Enough to get a small part of the university to the moon?' said the Lecturer

in

Recent Runes.

'The Dean could do with a holiday,' said the Archchancellor.

'I resent that remark, Archchancellor'

'Just trying to lighten the mood, Dean.'

'But we can release just enough for all kinds of useful work,' said Ponder,

already struggling.

'Like heating my study,' said the Lecturer in Recent Runes. 'My water jug was

iced up again this morning.'

'Exactly!' said Ponder, striking out madly for a useful Lie-to-Wizards. 'We

can

use it to boil a great big kettle! That's all it is! It's perfectly harmless!

Not dangerous in any way! That's why the University Council let me build it!

You

wouldn't have let me build it if it was dangerous, would you?'

He gulped down the water.

As one man, the assembled wizards took several steps back-wards.

'Let us know what it's like up there,' said the Dean.

'Bring us back some rocks. Or something,' said the Lecturer in Recent Runes.

'Wave to us', said the Senior Wrangler. 'We've got quite a good telescope.'

Ponder stared at the empty glass, and readjusted his mental sights once more.

'Er, no,' he said. 'The fuel has to go inside the reacting engine, you see.

And

then ... and then ...'

He gave up.

'The magic goes round and round and it comes up under the boiler that we have

plumbed in and the university will then be lovely and warm,' he said. 'Any

questions?'

'Where does the coal go?' said the Dean, 'It's wicked what the dwarfs are

charging these days.'

'No, sir. No coal. The heat is ... free,' said Ponder. A little bead of sweat

ran down his face.

'Really?' said the Dean. 'That'll be a saving, then, eh, Bursar? Eh? Where's

the

Bursar?'

'Ah ... er ... the Bursar is assisting me today, sir,' said Ponder. He

pointed

to the high gallery over the court. The Bursar was standing there, smiling

his

distant smile, and holding an axe. A rope was tied around the handrail,

looped

over a beam, and held a long heavy rod suspended over the centre of the

reaction

engine,

'It is ... er ... just possible that the engine may produce too much magic,'

said Ponder. 'The rod is lead, laminated with rowan wood. Together they

naturally damp down any magical reaction, you see. So if things get too ...

if

we want to settle things down, you see, he just chops through the rope and it

drops into the very centre of the reacting engine, you see.'

'What's that man standing next to him for?'

'That's Mr Turnipseed, my assistant. He's the backup fail-safe device.'

'What does he do, then?'

'His job is to shout "For gods' sakes cut the rope now!" sir.'

The wizard nodded at one another. By the standards of Ankh-Morpork, where the

common thumb was used as a temperature measuring device, this was health and

safety at work taken to extremes.

'Well, that all seems safe enough to me,' said the Senior Wrangler.

'Where did you get the idea for this, Mister Stibbons?' said Ridcully.

'Well, er, a lot of it is from my own research, but I got quite a few leads

from

a careful reading of the Scrolls of Loko in the Library, sir.' Ponder

reckoned

he was safe enough there. The wizards liked ancient wisdom, provided it was

ancient enough. They felt wisdom was like wine, and got better the longer it

was

left alone. Something that hadn't been known for a few hundred years probably

wasn't worth knowing.

'Loko ... Loko ... Loko,' mused Ridcully. 'That's up on Uberwald, isn't it?'

That's right, sir.'

'Tryin' to bring it to mind,' Ridcully went on, rubbing his beard. 'Isn't

that

where there's that big deep valley with the ring of moun-tains round it? Very

deep valley indeed, as I recall.'

'That's right, sir. According to the library catalogue the scrolls were found

in

a cave by the Crustley Expedition -'

'Lots of centaurs and fauns and other curiously shaped magical whatnots are

there, I remember reading.'

'Is there, sir?'

'Wasn't Stanmer Crustley the one who died of planets?'

'I'm not familiar with -'

'Extremely rare magical disease, I believe.'

'Indeed, sir, but -

'Now I come to think about it, everyone on that expedition con-tracted

something

seriously magical within a few months of getting back,' Ridcully went on.

'Er, yes, sir. The suggestion was that there was some kind of curse on the

place. Ridiculous notion, of course.'

'I somehow feel I need to ask, Mister Stibbons ... what chance is there of

this

just blowin' up and destroyin' the entire university?'

Ponder's heart sank. He mentally scanned the sentence, and took refuge in

truth.

'None, sir.'

'Now try honesty, Mister Stibbons.' And that was the problem with the

Archchancellor. He mostly strode around the place shout-ing at people, but

when

he did bother to get all his brain cells lined up he could point them

straight

at the nearest weak spot.

'Well ... in the unlikely event of it going seriously wrong, it ... wouldn't

just blow up the university, sir'

'What would it blow up, pray?'

'Er ... everything, sir.'

'Everything there is, you mean?'

'Within a radius of about fifty thousand miles out into space, sir, yes.

According to HEX it'd happen instantaneously. We wouldn't even know about it.'

'And the odds of this are ... ?'

'About fifty to one, sir.'

The wizards relaxed.

'That's pretty safe. I wouldn't bet on a horse at those odds,' said the

Senior

Wrangler. There was half an inch of ice on the inside of his bedroom windows.

Things like this give you a very personal view of risk.

TWO

SQUASH COURT SCIENCE

A SQUASH COURT CAN BE USED to make things go much faster than a small rubber

ball ...

On 2 December 1942, in a squash court in the basement of Stagg Field at the

University of Chicago, a new technological era came into being. It was a

technology born of war, yet one of its consequences was to make war so

terrible

in prospect that, slowly and hesitantly, war on a global scale became less

and

less likely.[4] At Stagg Field, the Roman-born physicist Enrico Fermi and his

team of scientists achieved the world's first self-sustaining nuclear chain

reaction. From it came the atomic bomb, and later, civilian nuclear power.

But

there was a far more significant consequence: the dawn of Big Science and a

new

style of technological change.

Nobody played squash in the basement of Stagg Field, not while the reactor

was

in place - but a lot of the people working in the squash court had the same

attitudes as Ponder Stibbons ... mostly insatiable curiosity, coupled with

periods of nagging doubt tinged with a flicker of terror. It was curiosity

that

started it all and terror that concluded it.

In 1934, following a lengthy series of discoveries in physics related to the

phenomenon of radioactivity, Fermi discovered that interesting things happen

when substances are bombarded with 'slow neutrons' - subatomic particles

emitted

by radioactive beryl-lium, and passed through paraffin to slow them down.

Slow

neutrons, Fermi discovered, were just what you needed to persuade other

elements

to emit their own radioactive particles. That looked interesting, so he

squirted

streams of slow neutrons at everything he could think of, and eventually he

tried the then obscure element uranium, up until then mostly used as a source

of

yellow pigment. By something apparently like alchemy, the uranium turned into

something new when the slow neutrons cannoned into it - but Fermi couldn't

work

out what.

Four years later three Germans - Otto Hahn, Lise Meitner, and Fritz Strassmann

-

repeated Fermi's experiments, and being better chemists, they worked out what

had happened to the uranium. Mysteriously, it had turned into barium,

krypton,

and a small quan-tity of other stuff. Meitner realized that this process of

'nuclear fission' produced energy, by a remarkable method. Everyone knew that

chemistry could turn matter into other kinds of matter, but now some of the

matter in uranium was being transformed into energy, something that nobody

had

seen before. It so happened that Albert Einstein had already predicted this

possibility on theoretical grounds, with his famous formula - an equation

which

the orang-utan Librarian of Unseen University[5] would render as 'Ook'.[6]

Einstein's formula tells us that the amount of energy 'contained' in a given

amount of matter is equal to the mass of that matter, multi-plied by the

speed

of light and then multiplied by the speed of light again. As Einstein had

immediately noticed, light is so fast it does-n't even appear to move, so its

speed is decidedly big ... and the speed multiplied by itself is huge. In

other

words: you can get an awful lot of energy from a tiny bit of matter, if only

you

can find a way to do it. Now Meitner had worked out the trick.

A single equation may or may not halve your book sales, but it can change the

world completely.

Hahn, Meitner and Strassmann published their discovery in the British

scientific

journal Nature in January 1939. Nine months later Britain was at war, a war

which would be ended by a military appli-cation of their discovery. It is

ironic

that the greatest scientific secret of World War II was given away just

before

the war began, and it shows how unaware politicians then were of the

potential

-be it for good or bad - of Big Science. Fermi saw the implications of the

Nature article immediately, and he called in another top-ranking physicist,

Niels Bohr, who came up with a novel twist: the chain reaction. If a

particular,

rare form of uranium, called ura-nium-235, was bombarded with slow neutrons,

then not only would it split into other elements and release energy - it

would

also release more neutrons. Which, in turn, would bombard more uranium-235

...

The reaction would become self-sustaining, and the potential release of

energy

would be gigantic.

Would it work? Could you get 'something for nothing' in this way? Finding out

was never going to be easy, because uranium-235 is mixed up with ordinary

uranium (uranium-238), and getting it out is like looking for a needle in a

haystack when the needle is made of straw.

There were other worries too ... in particular, might the experi-ment be too

successful, setting off a chain reaction that not only spread through the

experiment's supply of uranium-235, but through everything else on Earth as

well? Might the atmosphere catch fire? Calculations suggested: probably not.

Besides, the big worry was that if the Allies didn't get nuclear fission

working

soon then the Germans would beat them to it. Given the choice between our

blowing up the world and the enemy blowing up the world, it was obvious what

to

do.

That is, on reflection, not a happy sentence.

Terry Pratchett & Ian Stewart & Jack Cohen - The Science Of Discworld

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