`So why'd Darwin write this theology book instead?' the Chair of Indefinite Studies persisted.
`I don't know, sir, but as I wrote on page 4, I'm sure you recall, it was the wrong book at exactly the right time. Nevertheless, it made sense. There was something in it for everyone. All the technomancers had to do was leave a place in their science for the local god, and all the priests had to give up were a few beliefs that none of the sensible ones believed anyway-'
`Such as what?' said the Dean.
`Well, that the world •was created in a week and isn't very old,' said Ponder.
`But that's true!'
`Once again, only on the outside, Dean,' said Ponder smoothly. `As far as we can tell, Theology of Species polarised intellectual opinion in a curious way. In fact, haha, it equatorialised it, you might say.'
`I don't think we would,' said Ridcully. `What does the word mean?'
`Ah ... er, on a globe, the equator is an imaginary line around the middle,' said Ponder. `What happened was that the bulk of the technomancers and the priests got behind the ideas expressed in Darwin's book, because they gave everyone pretty much what they wanted. Quite of few of the technomancers had a strong belief in the god, and most of the brighter priests could see big flaws in the dogma. Together, they were a very large and influential force. The hard-line religionists and the unbending technomancers were marginalised. Out in the cold. Polarised, in fact.' This rather neat pun, although he said it himself, failed to get even a groan of acknowledgement, so he went on: `They didn't agree with the united group and they certainly didn't agree with one another. And, thus, happy compromise ruled. For well over sixty years.'
`That's nice,' said the Lecturer in Recent Runes.
`Er ... yes, sir, and then again, no,' said Ponder. `Technomancy doesn't work well in those circumstances. It can't make real progress by consensus. Hah, being led by a bunch of self-satisfied old men who are more interesting in big dinners than asking questions is a recipe for stagnation, anyone can see that.'
The wizards nodded sagely.
`Very true,' said Archchancellor Ridcully, narrowing his eyes. `That was an important point which needed to be made.'
`Thank you, Archchancellor.'
`And now it needs to be apologised for.'
`Sorry, Archchancellor.'
`Good. So, Mr Stibbons, what do-'
There was a rattle from Hex's writing engine. The spidery arms wove across the paper and wrote:
+++ The Chair of Indefinite Studies is correct +++ The wizards clustered round.
`Right about what?' said Ponder.
+++ Charles Darwin of Theology of Species was for much of his life a Rector in the Church of England, a sub-set of the British nation +++ the computer scrawled. +++ The chief function of the priests of that religion at the time was to further the arts of archaeology, local history, lepidoptery, botany, palaeontology, geology and the making of fireworks +++
`Priests did that?' said the Dean. `What about the praying and so on?'
+++ Some of them did that too, yes, although it was considered to be showing off. The God of the English did not require much in the way of sacrifice, only that people acted decently and kept the noise down. Being a priest in that church was a natural job for a young man of good breeding and education but no very specific talent. In the rural areas they had much free time. My calculations suggest that Theology of Species was the book that he was destined to write. In all the histories of third-level phase space, there is only one in which he writes The Origin of Species +++
`Why is that?' said Ponder.
+++ The explanation is complex +++
`Well, out with it,' said Ridcully. `We're all sensible men here.'
Another piece of paper slid off Hex's tray. It read: +++ Yes. That is the problem. You understand that every possibility of choice gives birth to a new universe in which that choice is manifest? +++
`This is the Trousers of Time again, isn't it?' said Ridcully.
+++ Yes. Except that every leg of the Trousers of Time branches into many other legs, and so do those legs and every following leg, until everywhere is full of legs, which often pass through one another or join up again +++
`I think I'm losin' track,' said Ridcully.
+++ Yes. Language is not good at this. Even mathematics gets lost.
But a little story might work. I will tell you the story. It will be not completely inaccurate +++
`Go ahead,' said Ridcully.
+++ Imagine an unimaginably large number +++
`Right. No problem there,' said Ridcully, after the wizards had consulted among themselves.
+++ Very well +++ Hex wrote. +++ From the moment that the Roundworld universe was made, it began to split into almost identical copies of itself, billions of times a second. That unimaginably large number represents all possible Roundworld universes that there are +++
`Do all these universes really exist?' said the Dean.
+++ Impossible to prove. Assume that they do. In all those universes there are hardly any in which a man called Charles Darwin exists, takes a momentous ocean voyage, and writes a hugely influential book about the evolution of life on the planet. Nevertheless, that number is still unimaginably large +++
`But imagined by a smaller imagination?' said Ridcully. `I mean, is it half as many as the other unimaginable number?'
+++ No. It is unimaginably large. But compared to the first number, it is unimaginably small +++
The wizards debated this in whispers.
`Very well,' said Ridcully, at last. `Keep goin' and we'll kind of join in when we can.'
+++ Even so, it is not so unimaginable as the number of universes in which the book was The Origin of Species. That number is quite strange and can only be imagined at all in very unusual circumstances +++
`It's unimaginably larger?' said Ridcully.
+++ just unimaginably unique. The number one. Gentlemen. All by itself. One is one and all alone. One. Yes. In third-level phase space there is only one history where he gets on the boat, completes the voyage, considers the findings and writes that book. All the other alternative Darwins either did not exist, did not stay on the boat, did not survive the journey, did not write any book at all or wrote, in a large number of cases, Theology of Species and entered the Church +++
`Boat?' said Ponder. `What boat? What've boats got to do with it?'
+++ I explained, in the successful timeline which led to humanity leaving the planet, Mr Darwin makes a significant voyage. It is one of nineteen pivotal events in the history of the species. It is almost as important as Joshua Goddelson leaving his house by the back door in 1734 +++
`Who was he?' said Ponder. `I don't recall the name.'
+++ A shoemaker living in Hamburg, Germany +++ wrote Hex.
+++ Had he left his house by the front door that day, commercial nuclear fusion would not have been perfected 283 years later +++ `That was important, was it?' said Ridcully.
+++ Vastly. Major technomancy +++
`Did it need much in the way of shoes, then?' said Ridcully, mystified.
+++ No. But the chain of causality, though complex, is clear +++ `How hard is it to get on this boat?' said the Dean. +++ In the case of Charles Darwin, very hard +++ `Where did it go?'
+++ It sailed from England to England. But there were crucial stops along the way. Even in those histories where he did embark on the boat, he did not complete the voyage and complete The Origin of Species in every case but one +++
`Just one version of history, you say,' said Ponder Stibbons. `Do you know why?'
+++ Yes. It is the one where you intervene +++ `But we haven't intervened,' said Ridcully.
+++ In a primitive subjective sense this is the case. However, you are going to will have already soon +++ Hex wrote.