Terry Pratchett - The Science of Discworld I

'What You Get Is What You're Given And It's No Good Whining.'

Not while these are still in the polar bear.

This figure replaces the previously favoured value of about 20 billion years. Recently lots of scientists collectively decided it should be 15 billion instead. (For a while some stars seemed to be older than the universe, but the age of those stars has also been downsized.) In other circumstances they might well have settled for 20 billion. If this worries you, substitute the term 'a very long time'.

Indeed, impeccable Discworld thinking is that no matter how big the uni­verse grows, it's always the same size.

Of which there were quite a number, given HEX's unusual construction. In addition to AND, OR and their, combinations and variants, HEX could call up MAYBE, PERHAPS, SUPPOSE and WHY. HEX could think the unthinkable quite easily.

Silicon might also be able to do this, but nowhere near as readily; if you want other exotic lifeforms you have to start thinking in terms of organized vortices in the upper reaches of a sun, weird quantum assemblages in interstellar plasma, or completely implausible creatures based on non-material concepts such as information, thought, or narrativium. DNA is a different matter entirely: you could surely base lifeforms on other carbon-rich molecules. We can do it now, in laboratories, with minor variants of DNA.

Ask Mummy or Daddy if you have no idea what we're talking about.

There also ought to be 'Population III' stars, older than Population II and consisting entirely of hydrogen and helium. These would explain the occurence of some heavy elements in Population II. However, nobody has ever found a Population III star. This may be because they were short-lived. Or, a more recent theory: very soon after the Big Bang there were heavy elements around, even before any stars formed. So when the first stars condensed, they already were Population II. This contradicts what we say in the main text - lies-to-children, of course.

'Most civilizations' is admittedly not the same as 'most people'. 'Most people' through the history of the planet have not needed to concern themselves with what shape the world is, provided it supports, somewhere, the next meal.

This rule does require some special assumptions, such as the chronic and irreversible stupidity of humanity.

As Nanny Ogg always says, 'He's just a big softy.'

Omnianism had taught for thousands of years that the Discworld was in fact a sphere, and violently persecuted those who preferred to believe the evidence of their own eyes. At the time of writing, Omnianism was teaching that there was something to be said for every point of view.

A magical accident had once turned the University's Librarian into an orangutan, a state which he enjoyed sufficiently to threaten, with simple and graphic gestures, anyone who suggested turning him back. The wizards noticed no difference now. An orangutan seemed such a natural shape for a librarian.

Moreover, until the last few decades of human history, most women did not cycle. Nearly all the time, they were either pregnant or lactating. And for the great apes, the cycle is a week or so longer than for humans, and for gibbons it's shorter. So it looks as though the relation with the Moon is coincidental.

A phrase meaning 'I'm not sure you know this.'

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.

Everyone knows what science fiction is - until you start asking questions like 'Is a book set five years in the future automatically SF? Is it SF just because it's set on another world, or is it simply fantasy with nuts and bolts on the out­side? Is it SF if the author thinks it isn't? Does it have to be set in the future? Does the presence of Doug McClure mean that a movie is SF, or merely that the men-in-rubber-monster-suits quotient is going to be high?' One of the best SF books ever written was the late Roy Lewis's The Evolution Man; there is no technology in it more sophisticated than a bow, it's set in the far past, the characters are barely more than ape-men ... but it is science fiction, nonethe­less.

They were fortunate, given the names of some places in Australia, that they ended up merely sounding like a minor Star Trek species.

'Reddish-brown'.

... which had engrossed wizards for many years. The debate ran like this: it was quite easy to turn someone into a frog, and fairly easy to turn them into, say, a white mouse. Strangely, considering the basic similarity of size and shape, turning someone into an orangutan took a vast amount of power and it was only an explosion in the intense thaumic confines of the Library which had managed the trick. Turning someone into a tree was much, much harder even than that, although turning a pumpkin into a coach was so easy that even a crazy old woman with a wand could do it. Was there some kind of framework into which all this fitted?

The current hypothesis was that most Change spells unravelled the vic­tim's morphic field down to some very basic level and then 'bounced' them back. A frog was quite simple, so they wouldn't have to bounce far. An ape, being quite human-like in many respects, would mean a very long return jour­ney indeed. You couldn't turn someone into a tree because there was no way to get there from here, but a pumpkin could be turned into a wooden coach because it was quite close to it in vegetable space.

The wizards agreed that this all seemed to fit nicely, and was therefore true.

If William of Occam had been a wizard at Unseen University, he would have grown a beard.

The quantity of bacon per trotter is on average slightly more than one quar­ter of the amount per head.

Wizards seldom bothered to look things up if they could reach an answer by bickering at cross-purposes.

To the best of our knowledge, based on deduction from the available evi­dence. Certainly it was a big extinction - far bigger than the one that killed off (or helped to kill off) the dinosaurs. We remember the dinosaur one because they've had such good PR people.