Terry Pratchett - Science of Discworld

'No.'

The point is that to the victims, the experience felt real. Even though logic told them it couldn't have happened, they either did­n't apply the logic, or they did but still remembered the experience vividly. We deduce that the human mind sometimes has vivid mem­ories that do not correspond to real events. Of course we must also observe that just because some alien abductions aren't real, that doesn't imply they all aren't. However, if we can find a sensible mechanism for otherwise reasonable people believing that they really were carted off in a UFO, then the burden of proof shifts dra­matically and evidence of abduction stronger than sincere expressions of belief becomes necessary.

Reports of alien abductions are not new. Back in the Middle Ages, however, they would have been either flights on witches' broomsticks or encounters with fabulous creatures like the succubus, a demon in a woman's body who allegedly had sex with men while they slept. The witches of Discworld employ broomsticks for transport only. The sex bit doesn't appeal to them at all, except for Nanny Ogg, of course.

Folk tales of succubi and their like can be found worldwide. In Newfoundland people tell of an ancient hag sitting on their chests at night, and in Vietnam they speak of the 'grey ghost'. What seems to be going on is some common mental pattern, overlaid with cul­tural influences. That's why abductions by witches riding broomsticks have gone out of vogue, but abductions by aliens rid­ing UFOs are flavour-of-the-decade.

Susan Blackmore thinks that all of these experiences are, and were, caused by 'sleep paralysis'. This is a feature of the mind that prevents sleeping people from moving their limbs as they would if they were acting out their dreams. Such a 'mental switch' is impor­tant for any animal that dreams: you don't really want to go sleepwalking out of your cosy burrow and straight down a preda­tor's throat. Plenty of mammals dream, most of us have seen a cat or dog asleep with its legs twitching, and the evidence from record­ings of the brain's electrical activity is that the animals are engaged in something that closely resembles the brain activity of a dreaming human. We can't be sure whether cats have visual dreams like we do, but sleep and dreaming take place in primitive parts of the brain, so they probably go back a long way in our evolutionary his­tory. At any rate, if the sleep paralysis system malfunctions, people who are partially awake may undergo sleep paralysis. Experiments show that in such cases they typically get a strong impression that 'somebody is there'.

This feature of the human mind may go back to the time, just after the meteorite hit, when the nocturnal mammals suddenly awoke in a world without dinosaurs. Their senses of hearing and sight, previously separate from each other because they had evolved at very different periods and in very different circumstances, would have become linked together. When their ears heard something strange, their visual sense would kick in and make them feel that they could see what was causing it. We inherited this tendency, but we interpret it in terms of the current culture: bogeymen, witches, maybe even dragons a few centuries ago, aliens with big black eyes today. The sexual link is straightforward, too: dreams about sex are very common anyway.

Oh, yes, one more thing: since we've all watched Close Encounters, we know exactly what an alien must look like ... just as everyone used to know that witches soared through the air on a broomstick. So our visual system knows what shape it should give to whatever it sees when we get that funny feeling that something is haunting us. And flying saucers have come on nicely, too, from being the rivet-studded things that were all the rage in galactic cir­cles in the early Fifties.

Stories of people seeing ghosts may well have the same explana­tion. You've read the tales, you know what a ghost ought to look like (maybe you watched Ghostbusters or a Stephen King movie), and you're trying to sit up all night in the Haunted House. You're think­ing about ghosts, about headless horsemen and Elizabethan ladies who walk through walls and go transparent, and then you start to doze off because it's 2 am and you've been up all night... The sleep paralysis circuit glitches ... Aaaaagh!

THE ARCHCHANCELLOR WAS RATHER QUIET OVER TEA.

Eventually he said, 'Can we stop this project, Ponder?'

'Er ... are you sure, sir?' 'Well, what is it achieving? I mean, really'? Y'know, I thought, all you had to do is get a world working, and before you could say "creation" there'd be some creature who'd stand up, getting a grip on its surroundings, gaze with a certain amount of intelligence and awe at the infinite sky and say...'

‘...that thing's getting bigger, I wonder if it's going to hit us,' said Rincewind.

'Rincewind, that remark was extremely cynical and accurate.'

'Sorry, Archchancellor.'

Bonder's lips were moving quietly as he worked things out.

'We could start running it down, yes. The thaumic reactor hasn't been putting so much into it in the last week. We've nearly used up the fuel.'

'Really?'

'The squash court will have a rather high thaumic index, sir, so whoever goes in to pull the switch will suffer a certain amount of...'

There was the sound of something spinning. The wizards looked at Rincewind's chair, which finally fell over on to the flagstones. Of its former occupant there was no sign, although there was the dis­tant sound of a slamming door.

The Dean sniffed.

'Strange behaviour,' he said.

'I suggest we give it one more day of our time,' said Ridcully. 'I was hoping we might create a world, gentlemen, but instead it's clear to me that any life in this universe has to get used to living in ... in some kind of huge celestial snow globe. Fire and ice, ice and fire. Gentlemen, round worlds are intrinsically flawed. If there's any hidden gods on ours, they're pretty damn well hidden.'

'The Omnians say "Don't play God. He always wins",' said the Senior Wrangler.

'I dare say,' said Ridcully 'So ... one more day, gentlemen? And then we can get on with something sensible.'

The red sun rose quickly over the parched veldt. The apes stirred in their cave, which was little more than a rocky overhang, and saw the big black rectangle looming over them.

The Dean tapped it with his pointer

'Do try to pay attention today, will you?' He turned and chalked rapidly across the blackboard. 'Here we have R ... O ... C ... K, rock. Can anyone tell me what you do with it? Anyone? Anyone? Look, stop doing that, will you?' He tried to hit an ape with his vir­tual pointer, and then flung it away in disgust. It vanished.

'Filthy little devils,' he muttered.

'Not getting anywhere, Dean?' said Ridcully, appearing beside him.

Wo, Archchancellor. I've tried to explain to them that they've probably got just a few million years, and that's pretty hard to do in sign language, let me tell you. But the only word they know is S-E-X, and they don't waste time spelling it, oh no! For this I skipped breakfast?'

'Never mind. Let's see how the Senior Wrangler's getting on.'

'They're just bad copies of humans, if you ask me...'

The wizards vanished.

One of the apes knuckled over to the blackboard, and watched it disappear from view as HEX completed the spell.

He hadn't the faintest idea what had been happening, but he had been impressed by the stick that had been waved about. That seemed to have gone now. That didn't worry the ape, which knew about things vanishing, often, these days, a member of the clan would vanish overnight, with a lot of snarling in the shadows.