The Science of Discworld Revised Edition

strange about this. ‘Cold’ is the normal state of the universe, after all, even though as a
thing
it does not exist. Er … we’re not going to get past you on this one, are we, Archchancellor?)
    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