The Science of Discworld IV Judgement Da - By Terry Pratchett, Ian Stewart Page 0,39

at this point, be telling themselves that it wasn’t happening, and – like your world’s fictional Alice, who you will doubtless know of – will assume they would shortly wake up. Quite possibly at the entrance to a rabbit hole. It seems that you, as a librarian, are excellent at assessing data. Cataloguing and indexing in your mind. All very impressive.’

‘Well, I did go to Roedean, and that counts for something … And if I were Alice, Mr Archchancellor, Wonderland would most certainly have shaped up, in no short measure.’ Miss Daw’s voice faltered, and she went on, ‘You know everything, don’t you?’

‘Certainly not. But because what you call Earth lies in a subordinate plane, we can by accident or intent find a way into the place, sometimes in the flesh, but mostly via a variety of devices: crystal balls and so on. It is not intrusive – we may not be good at names, but we are very good at surreptition, and we use such instruments sparingly. Excuse me, come!’

This was in response to a knocking on the door, the sound level of which had caused bits of plaster and miscellaneous debris to settle gently to the floor; indeed, a scattering of dust tumbled onto the Earth itself, causing Marjorie to giggle.

EIGHT

* * *

BEMUSING GLOBE

Roundworld is called Roundworld because, er, it’s round.

From outside. As the wizards perceive it.

From inside … well, that’s a good question.

In the Science of Discworld series, the name does double duty for our planet and our universe. The planet is indeed round – ish – though at various times in history and in various cultures this was not appreciated and other shapes were favoured. The universe … well, we don’t really know what shape that is. Round is an obvious possibility, perhaps too obvious. If you not only have a point of view, but are one, and you can see equally far in every direction, the entire visible world automatically looks round. With you at the centre! Amazing.

In the absence of narrativium, Roundworld does not know what shape it ought to be. Somehow the actual shape, of planet, universe, and everything else for that matter, has to be a consequence of those mysterious rules. But there isn’t a rule that says ‘make planets round’. There isn’t even a rule that says ‘make planets’. The rules as we currently conceive of them say obscure things like iħ∂Ψ/∂t = ĤΨ.fn1 This perverse lack of human focus in the rules drives the wizards mad. Though they do like the fancy symbols, which are obviously magical.

Even worse: the rules are not written down. They are not even implicit in narrativium, since there is none, not until human beings invent it for themselves. The rules operate (we think) behind the scenes; an occasional truly sapient human can draw back the veil and glimpse nature’s cogwheels spinning. So the creatures that live in or on Roundworld (that’s us) play a lengthy guessing game in which they make up rules that seem to work, and then argue about whether they really do. This game has gone by many names: religion, philosophy, natural philosophy, science, or just The Truth. We are still playing it.

In this chapter, we’ll deal with the shape of our planet. The answer is common knowledge, so we’ll focus on the imaginative alternatives that have at times been proposed, the processes that led to the current answer, and the lengths to which some people have gone to deny it. We’ll leave the shape of the universe to chapter 16. That’s a much harder problem, in part because we can’t stand outside the universe and look at it. However, until the 1960s we had the same problem concerning our planet, and that did not stop scientists pinning down its shape and size. Also how old it is, although the accepted scientific figure for the age of the Earth remains contentious in some quarters because some people don’t like the answer, and of course that is all you need to prove it must be wrong.

The ancient Greeks started out thinking the world was flat, but they revised their opinion when they began to appreciate indirect evidence to the contrary. Like several earlier cultures, they were aware that the Moon is a sphere. Superficially, it may look like a flat disc viewed sideways on, but because of its phases, simple geometry reveals that it must be roughly spherical. The Sun, which is difficult to look at without blinding yourself, is a disc that