The Science of Discworld I

21. THE LIGHT YOU SEE THE DARK BY

THERE WAS NO DARK. This came as such a shock to Ponder Stibbons that he made HEX look again. There had to be Dark, surely? Otherwise, what was there for the light to show up against?

Eventually, he reported this lack to the other wizards.

'There should be lots of Dark and there isn't,' he said flatly. There's just Light and ... no light. And it's a pretty strange light, too.'

'In what way?' said the Archchancellor.

'Well, sir, as you know[25], there's ordinary light, which travels at about the same speed as sound... '

'That's right. You've only got to watch shadows across a land­scape to realize that.'

'Quite, sir ... and then there's meta-light, which doesn't really travel at all because it is already everywhere.'

'Otherwise we wouldn't even be able to see darkness,' said the Senior Wrangler.

'Exactly. But the Project universe has just got the one sort of light. HEX thinks it moves at hundreds of thousands of miles a sec­ond.'

'What use is that?'

'Er... in this universe, that's as fast as you can go.'

'That's nonsense, because...' Ridcully began, but Ponder held up a hand. He had not been looking forward to this one.

'Please, Archchancellor. It's doing the best it can. Just trust me on this one. Please? Yes, I can see all the reasons why it's impossi­ble. But, in there, it seems to work. HEX has written pages of stuff about it, if anyone's interested. Just don't ask me about any of it. Please, gentlemen? It's all supposed to be logical but you'll find your brain squeaking around until the ends point out of your ears.'

He placed his hands together and tried to look wise.

'It really is almost as if the Project is aping the real universe...'

'Ook.'

'I beg your pardon,' said Ponder. 'A figure of speech.'

The Librarian nodded at him and knuckled his way across the floor. The wizards watched him carefully.

'You really believe that that thing,' said the Dean, pointing, 'with its moon-hating water and worlds that go around suns...'

'As far as I can see from this,' interrupted the Senior Wrangler, who'd been reading HEX's write-out on the more complex physics of the Project, 'if you were travelling in a cart at the speed of light, and threw a ball ahead of you ...' he turned over the page, read on silently for a moment, creased his brows, turned the page over to see if any enlightenment was to be found on the other side, and went on '... your twin brother would ... be fifty years older than you when you got home ... I think.'

'Twins are the same age,' said the Dean, coldly. 'That's why they are twins.'

'Look at the world we're working on, sir,' said Ponder. 'It could be thought of as two turtle shells tied together. It's got no top and bottom but if you think of it as two worlds, bent around, with one sun and moon doing the work of two ... it's similar.'

He fried in their gaze.

'In a way, anyway,' he said.

Unnoticed by the others, the Bursar picked up the write-out on the physics of the Roundworld universe. After making himself a paper hat out of the title page, he began to read ...