The Science of Discworld IV Judgement Da - By Terry Pratchett, Ian Stewart Page 0,49

would put any airline that flew significantly slower than the rest out of business. Anyway, most long-haul aircraft are made by the same small number of companies.

It is therefore possible to draw up a reliable list of approximate distances (which are proportional to the times) between selected cities: say Cape Town, Honolulu, London, Los Angeles, Rio de Janeiro and Sydney. Simple geometry – you can draw triangles with a ruler – reveals that if the world is a plane, then Honolulu, Rio de Janeiro, Cape Town and Sydney (in that order) must lie along a path that is very close to a straight line. The travel times along that path are 13, 8 and 14 hours respectively, a total of 35 hours. Since the path is almost straight, and distances are proportional to times, that total time must be pretty close to the time it should take to travel directly from Honolulu to Sydney.

However, the actual figure is 14 hours.

Even allowing for minor errors in the approximations, the discrepancy is far too large, so the hypothesis of a flat planet must be rejected. The figures can’t lie: not even the most dedicated conspiracy theorist would suggest that global corporations are conspiring to lose large sums of money.

fn1 This is Schrödinger’s equation, the one that says a cat can be both alive and dead. Do you see why? Isn’t it obvious? Oh, since you insist. Let Ψ = A (alive) to deduce that iħ∂A/∂t = ĤA. Then let Ψ = D (dead) to obtain iħ∂D/∂t = ĤD. Add these two equations and rearrange to get iħ∂(A+D)/∂t = Ĥ(A+D). That’s a cat that’s alive and dead, and it satisfies the same equation. (To preserve unitarity, a few 1/√2’s are also needed … but you know that.)

fn2 Command Module Pilot James Lovell.

fn3 This tale is probably untrue, but it’s a good story, so it survives – much like the story of a flat Earth. Never underestimate the power of narrativium.

fn4 Archbishop James Ussher’s scripture-based calculation that the Creation dates to the night before Sunday, 23 October 4004 BC is a little bit too recent because of archaeological records that are hard to dismiss. A retreat by 4000 years neatly avoids the issue. Ussher’s date is so precise because he figured that Creation happened exactly 4000 years before the birth of Christ. Why the deity is so obsessed with decimal reckoning in multiples of one planetary orbit is not explained.

fn5 A poor choice for any cult. The most effective way of spreading a belief is to tell adherents to teach it to their children.

NINE

* * *

UNHOLY WRIT

The door was opened by Ponder Stibbons, a busy young man who seemed to be central to just about everything that was happening in the university. He was, Marjorie considered, one of those most useful people: a housetrained near-nerd, conscientious to the point of insanity but not any further, apparently.

‘It is the Omnians again, Archchancellor. They have issued a writ against us for ownership of Roundworld since, they say, it is clearly bound up with their religion. They are rather acerbic on the subject, Archchancellor,’ said Ponder, looking nervously at Marjorie. He added, ‘They are demanding the artefact and are hinting at dire action if it isn’t handed over to them.’

Ponder stayed silent then, because Ridcully himself had remained silent, and if you are a wizard you can apprehend the subtle signs of the volcano stirring. He carefully took a few steps backwards, just in case, and when the Archchancellor spoke it was almost a sullen growl.

‘Mister Stibbons, turn the writ over to Mister Slant, will you? And then make it clear to him, as our legal representative in the mundane world, that wizards react somewhat erratically when it comes to threats. Acerbic is only a beginning. Thank you, Mister Stibbons, and you may go.’

Marjorie had been watching all this with a kind of weird fascination. This place was certainly magical; occasionally you saw the wretched squid somewhere about the place, and candles were lit with a wave of the hand, though curiously enough created mundanely by servants. The magic was there but apparently like, for example, a really good bank balance: ready for use if required, and otherwise barely noticed.

As Ponder Stibbons rushed off, she drew breath and said, ‘Mustrum, since I am your guest, do you not mind telling me what that just now was all about? It sounded deeply interesting!’

‘My dear Miss Daw …’

Before Mustrum could articulate a further word, Marjorie said in a friendly