Terry Pratchett - The Science of Discworld I

Thinking is required if our language isn't to fool us. However, as 'focusing the cold' shows, we sometimes don't stop to think.

We've done it before. At the start of the book, we mentioned phlogiston, considered by early chemists to be the substance that made things burn. It must do: you could see the phlogiston coming out as flames, for goodness' sake. Gradually, however, clues that supported the opposite view accumulated. Things weigh more after they've burned than they did before, for instance, so phlogiston seemed to have negative weight. You may think this is wrong, inci­dentally; surely the ash left by a burnt log weighs a lot less than the log, otherwise nobody would bother having bonfires? But a lot of that log goes up in smoke, and the smoke weighs quite a bit; it rises not because it's lighter than air but because it's hot. And even if it were lighter than air, air has weight, too. And as well as the smoke, there's steam, and all sorts of other junk. If you burn a lump of wood, and collect all the liquids, gases, and solids that result, the final total weighs more than the wood.

Where does the extra weight come from? Well, if you take the trouble to weigh the air that surrounds the burning wood, you'll find that it ends up lighter than it was. (It's not so easy to do both of these weighings while keeping track of what came from where -think about it. But the chemists found ways to achieve this.) So it looks as if something gets taken out of the air, and once you're real­ized that's what's going on, it's not hard to find out what it is. Of course, it's oxygen. Burnt wood gains oxygen, it doesn't lose phlo­giston.

This all makes far more sense, and it also explains why phlogis­ton wasn't such a silly idea. Negative oxygen, oxygen that ought to be present but isn't, behaves just as nicely as positive oxygen in all the balancing equations that chemists used to check the validity of their theories. So much phlogiston moving from A to B has exactly the same effect on observations as the same amount of oxygen mov­ing from B to A. So phlogiston behaved just like a real thing, with that embarrassing exception that when your measurements became accurate enough to detect the tiny amounts involved, phlogiston weighed less than nothing. Phlogiston was a privative.

A difficult but stubborn feature of human thinking is involved in all this: it's known as 'reifying': making real. Imagining that because we have a word for something, then there must exist a 'thing' that corresponds to the word. What about 'bravery' and 'cowardice'? Or 'tunnel'? Indeed, what about 'hole'?

Many scientific concepts refer to things that are not real in the everyday sense that they correspond to objects. For instance, 'grav­ity' sounds like an explanation of planetary motion, and you vaguely wonder what it would look like if you found some, but actually it is only a word for an inverse square law attractive relationship. Or more recently, thanks to Einstein, for a tendency of objects not to move in straight lines, which we can reify as 'curved space'.

For that matter, what about 'space'? Is that a thing, or an absence?

'Debt' and 'overdraft' are very familiar privatives, and the think­ing problems they cause are quite difficult. After all, your overdraft pays your bank manager's salary, doesn't it? So how can it fail to be real? Today's derivatives market buys and sells debts and promises as if they were real, and it reifies them as words and numbers on pieces of paper, or digits in a computer's memory. The more you think about it, the more amazing the everyday world of human beings becomes: most of it doesn't actually exist at all.

Some years ago, at a science-fiction convention held in The Hague, four writers who made lots of money from their books sat in front of an audience of mostly impecunious fans to explain how they'd made huge income from their books (as if any of them really knew). Each of them said that 'money isn't important', and the fans became quite rude at this perfectly accurate statement. It was nec­essary to point out that money is like air or love, unimportant if you've got enough of it, but desperately important if you haven't [30] 'Desperate' is another privative - it means 'no hope'. , Dickens recognized this: in David Copperfield Mr Micawber remarks 'Annual income twenty pounds, annual expenditure nine­teen nineteen six, result happiness. Annual income twenty pounds, annual expenditure twenty pounds ought and six, result misery.'

There's no symmetry between having money and not having it, but the discussion had gone off the rails because everyone had assumed that there was, so that 'having money' was the opposite of 'having no money'. If you must find an opposite, then 'having money' is opposite to 'being in debt'. In that case, 'rich' is like 'knurd'. In any event, making the comparison between money, love, and air lowered the debating temperature considerably. Air isn't important if you've got it, only if you haven't; the same goes for money.

Vacuum is an interesting privative. Cut-me-own-Throat Dibbler could sell vacuum-on-a-stick. Vacuum in the right place is valuable.

Many people on Earth sell cold- on-a-stick.

Discworld does a marvellous job of revealing the woolly think­ing behind our assumptions about absence, because in Discworld privatives really do exist. The dark/light joke in Discworld is silly enough that everyone gets the point, we hope. Other Discworld uses of privatives, however, are more subtle. The most dramatic, of course, is Death, many people's favourite Discworld character, who SPEAKS IN CAPITAL LETTERS. Death is a seven-foot-tall skeleton, with tiny points of light in his eye sockets. He carries a scythe with a blade so thin that it's transparent, and he has a flying horse called Binky. When Death appears to Olerve, king of Sto Lat, in Mort, it takes the king a few moments to catch up on current events:

'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 [31] 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. 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 [32] Indeed, it is a 'fundamental constant' of the Discworld universe that things exist because they're believed in. . But it's a very strange idea indeed on planet Earth.