In late 1998, though, a team of astronomers led by John Webb made a very accurate study of the light emitted by extremely distant, but very bright, bodies called quasars. They found subtle changes in certain features of that light, called spectral lines, which are related to the vibrations of various types of atom. In effect, what they seem to have discovered is that many billion years ago, much further back than the Oklo reactor, atoms didn't vibrate at quite the same rate as they do today. In very old gas clouds from the early universe, the fine structure constant differs from today's value by one part in 50,000. That's a huge amount by the standards of this particular area of physics. As far as anyone can tell, this unexpected result is not due to experimental error. A theory suggested in 1994 by Thibault Damour and Alexander Polyakov does indicate a possible variation in the fine structure constant, but only one-ten thousandth as large as that found by Webb's team. It's all a bit of a puzzle, and most theorists sensibly prefer to hedge their bets and wait for further research. But it could be a straw in the wind: perhaps we will soon have to accept that the laws of physics were subtly different in the distant reaches of time and space. Not turtle-shaped, perhaps, but... different.

IT DID NOT TAKE LONG for the faculty to put its col­lective finger on the philosophical nub of the problem, vis-a-vis the complete destruction of everything.

'If no one will know if it happens, then in a very real sense it wouldn't have happened,' said the Lecturer in Recent Runes. His bedroom was on one of the colder sides of the university.

'Certainly we wouldn't get the blame,' said the Dean, 'even if it did.'

'As a matter of fact,' Ponder went on, emboldened by the wiz­ards' relaxed approach, 'there is some theoretical evidence to suggest that it could not possibly happen, due to the non-temporal nature of the thaumic component.'

'Say again?' said Ridcully.

'A malfunction would not result in an explosion exactly, sir,' said Ponder. 'Nor, as far as I can work out, would it result in things ceas­ing to exist from the present onwards. They would cease to have existed at all, because of the multidirectional collapse of the thau­mic field. But since we are here, sir, we must be living in a universe where things did not go wrong.'

'Ah, I know this one,' said Ridcully. 'This is because of quantum, isn't it? And there's some usses in some universe next door where it did go wrong, and the poor devils got blown up?'

'Yes, sir Or, rather, no. They didn't get blown up because the device the other Ponder Stibbons would have built would have gone wrong, and so ... he didn't exist not to build it. That's the theory, anyway.'

'I'm glad that's sorted out, then,' said the Senior Wrangler briskly. 'We're here because we're here. And since we're here, we might as well be warm.'

'Then we seem to be in agreement,' said Ridcully. 'Mr Stibbons, you may start this infernal engine.' He nodded towards the red lever on the plinth.

'I was rather assuming you would do the honours, Archchancellor,' said Ponder, bowing. 'All you need to do is pull the lever. That will, ahem, release the interlock, allowing the flux to enter the exchanger, where a simple octiron reaction will turn the magic into heat and warm up the water in the boiler.'

'So it really is just a big kettle?' said the Dean.

'In a manner of speaking, yes,' said Ponder, trying to keep his face straight.

Ridcully grasped the lever.

'Perhaps you would care to say a few words, sir?' said Ponder.

'Yes.' Ridcully looked thoughtful for a moment, and then bright­ened up. 'Let's get this over quickly, and have lunch.'

There was a smattering of applause. He pulled the lever. The hand on a dial on the wall moved off zero.

'Well, we're not blown up after all,' said the Senior Wrangler. 'What are the numbers on the wall for, Stibbons?'

'Oh, er ... they're ... they're to tell you what number it's got to,' said Ponder.

'Oh. I see.' The Senior Wrangler grasped the lapels of his robe. 'Duck with green peas today, gentlemen, I believe,' he said, in a far more interested tone of voice. 'Well done, Mr Stibbons.'

The wizards ambled off in the apparently slow yet deceptively fast way of wizards heading towards food.

Ponder breathed a sigh of relief, which turned into a gulp when he realized that the Archchancellor had not, in fact, left but was inspecting the engine quite closely.

'Er ... is there anything else I can tell you, sir?' he said, hurriedly.

'When did you really start it, Mister Stibbons?'

'Sir?'

'Every single word in the sentence was quite short and easy to understand. Was there something wrong about the way I assembled them?'

'I ... we ... it was started just after breakfast, sir,' said Ponder meekly. 'The needle on the dial was just turned by Mr Turnipseed by means of a string, sir'

'Did it blow up at all when you started it up?'

'No sir! You'd ... well, you'd have known, sir!'

'I thought you said back there that we wouldn't have known, Stibbons.'

'Well, no, I mean...'

'I know you, Stibbons,' said Ridcully. 'And you would never test something out publicly before trying it to see if it worked. No one wants egg all over their face, do they?'

Ponder reflected that egg on the face is only of minor concern when the face is part of a cloud of particles expanding outwards at an appreciable fraction of the speed of dark.

Ridcully slammed his hand against the black panels of the engine, causing Ponder visibly to leave the ground.

'Warm already,' he said. 'You all right up there, Bursar?'

The Bursar nodded happily.

'Good man. Well done, Mister Stibbons. Let's have lunch.'

After a while, when the footsteps had died away, it dawned on the Bursar that he was, as it were, holding the short end of the string.

The Bursar was not, as many thought, insane. On the contrary, he was a man with both feet firmly on the ground, the only diffi­culty being that the ground in question was on some other planet, the one with the fluffy pink clouds and the happy little bunnies. He did not mind because he much preferred it to the real one, where people shouted too much, and he spent as little time there as possi­ble. Unfortunately this had to include mealtimes. The meal service on Planet Nice was unreliable.

Smiling his faint little smile, he put down his axe and ambled off. After all, he reasoned, the point was that the wretched thing stayed out of the ... whatever it was, and it could certainly do a simple job like that without his watching it.

Unfortunately Mr Stibbons was too worried to be very obser­vant, and none of the other wizards bothered much about the fact that everything which stood between them and thaumic devastation was blowing bubbles into his glass of milk.