Permutation City

by Greg Egan

Paul counted – and for argument’s sake, tried to defend his own perspective, tried to imagine the outside world actually cycling through fragments of time drawn from ten distinct periods. The trouble was … this allegedly shuddering universe contained the computer which ran the whole model, the infrastructure upon which everything else depended. If its orderly chronology had been torn to shreds, what was keeping him together, enabling him to ponder the question?

But given a large enough collection of truly random numbers, there was no reason to believe that it wouldn’t include, purely by accident, hidden patterns as complex and coherent as the ones which underlay him. And wouldn’t those patterns, however scrambled they might be in real time, be conscious of themselves, just as he’d been conscious, and piece their own subjective world together, just as he had done?

Had the world shrunk to the size of his skull – and vanished from time altogether, except for the fifty computers which contributed at any one time to what he called ‘the present’? Maybe not – although in the eyes of some hypothetical space traveller the whole planet was virtually frozen in time, and flat as a pancake. Relativity declared that this point of view was perfectly valid – but Paul’s was not. Relativity permitted continuous deformation, but no cutting and pasting. Why not? Because it had to allow for cause and effect. Influences had to be localized, travelling from point to point at a finite velocity; chop up space-time and rearrange it, and the causal structure would fall apart. What if you were an observer, though, who had no causal structure? A self-aware pattern appearing by chance in the random twitches of a noise machine, your time coordinate dancing back and forth through causally respectable ‘real time’? Why should you be declared a second-class being, with no right to see the universe your way? Ultimately, what difference was there between so-called cause and effect, and any other internally consistent pattern?

Then he whispered, ‘This is dust. All dust. This room, this moment, is scattered across the planet, scattered across five hundred seconds or more – but it still holds itself together. Don’t you see what that means?’ The djinn reappeared, but Paul didn’t give him a chance to speak. The words flowed out of him, unstoppable. He understood. ‘Imagine … a universe entirely without structure, without shape, without connections. A cloud of microscopic events, like fragments of space-time … except that there is no space or time. What characterizes one point in space, for one instant? Just the values of the fundamental particle fields, just a handful of numbers. Now, take away all notions of position, arrangement, order, and what’s left? A cloud of random numbers. ‘That’s it. That’s all there is. The cosmos has no shape at all – no such thing as time or distance, no physical laws, no cause and effect. ‘But … if the pattern that is me could pick itself out from all the other events taking place on this planet … why shouldn’t the pattern we think of as ‘‘the universe’’ assemble itself, find itself, in exactly the same way? If I can piece together my own coherent space and time from data scattered so widely that it might as well be part of some giant cloud of random numbers … then what makes you think that you’re not doing the very same thing? ’

‘What difference? We perceive – we inhabit – one arrangement of the set of events. But why should that arrangement be unique? There’s no reason to believe that the pattern we’ve found is the only coherent way of ordering the dust. There must be billions of other universes coexisting with us, made of the very same stuff – just differently arranged. If I can perceive events thousands of kilometres and hundreds of seconds apart to be side by side and simultaneous, there could be worlds, and creatures, built up from what we’d think of as points in space-time scattered all over the galaxy, all over the universe. We’re one possible solution to a giant cosmic anagram … but it would be ludicrous to believe that we’re the only one.’

So long as the flesh-and-blood man had no way of knowing the truth, it was meaningless to talk about ‘two different people’ in ‘two different worlds’. The two patterns of thoughts and perceptions had effectively merged into one. If the Copy had been allowed to keep on running after the visitor had learnt that he was flesh and blood, their two paths would have diverged again. But the Copy had been shut down; it had no future at all in its original world, no separate life to live. So the two subjective histories remained as one. Paul had been a visitor believing he was a Copy. And he’d also been the Copy itself. The patterns had merged seamlessly; there could be no way of saying that one history was true and the other false. Both explanations were equally valid. Once, preparing to be scanned, he’d had two futures. Now he had two pasts.