Greg Egan - Quarantine

A single branch of reality, in the middle of a huge void-but beyond that void, an infinite thicket. Isn't that exactly what I suspected, the first time I smeared and collapsed? But —

'How can we be… surrounded by all of this, and not detect it?'

'To detect a state you have to collapse it to reality. How can you do that to a state which doesn't partake in the collapse?'

'Then how do you know that these states exist?'

'Laura knows.'

'How?'

'The uncollapsed parts of superspace aren't uninhabited. There's intelligent life spread across the eigenstates. When one civilization discovered the depleted region you inhabit, they studied the borders — cautiously — and then took steps to seal off the region.'

'By creating The Bubble?'

'Yes. But before The Bubble was put into place, one individual decided to explore further — to enter the region itself.'

'And … Laura's seen this alien? It sought her out and made contact — because she doesn't collapse the wave?'

The spokesperson smiles. 'No. Laura is the explorer. Or at least, the explorer shaped her, to become the closest thing to itself that it could achieve. It crossed the depleted region and interacted with your reality. In doing so, it was collapsed — destroyed — but it arranged the collapse in a way that coded part of its complexity into Laura's genes. When she's collapsed, Laura can barely function — because most of her brain is taken up with pathways that only work when she's smeared. But when she is smeared, she is, in effect, the explorer reborn.'

'Laura is the avatar of a Bubble Maker?' A distracting voice whispers: Believe it, or you're dead for sure. 'Why did she stay in the Hilgemann? Why has she stayed here? Surely she could escape — '

'She has escaped. She's explored most of the planet.'

'Most of the planet? But they caught her, twice — '

'Yes, they caught her near the Hilgemann — but not because she was trying to escape permanently. She never intended to be collapsed anywhere, except in her room — but out of all the trips she made, those two went wrong. The Hilgemann was a safe, convenient base; she was left unobserved long enough to smear to a degree of complexity which enabled her to mount expeditions. From that point on, she could keep herself uncollapsed, in the same way that you have.'

'So why go back to the Hilgemann at all? Why not stay unobserved forever, smeared forever?'

'Smearing is an exponential process. Within a day or two, remaining unobserved would have required her to suppress the collapse of everyone on Earth. And after a day or two of that — '

She hesitates.

'What?'

The depleted region would be filled. Humanity would: unnel through the Bubble and make contact with the rest:: superspace. What would happen then is hard to predict, rut one possibility is that the wave function in this region — ould never be collapsed again.'

I struggle to comprehend this. The whole world smeared, permanently? How — when all the co-existing possibilities must include states that cause a collapse? But: he only collapse that works is one that makes itself real. A Aorld in which no collapse becomes real is just as consistent on those terms as one with a unique reality.

'So… Laura didn't stay smeared, to avoid dragging us into this catastrophe?'

'Exactly. And this is what you have to understand about Ensemble: anyone who uses it can do the same.'

'You mean, I might — '

'Anyone who smears for too long; the time scale is a matter of days. Laura has no wish to deprive you of the option of leaving The Bubble — but nor does she wish to force this on you. Your own smeared selves may not show the same respect.'

'My smeared self has always done exactly what I've wanted.'

'Of course. You hold him hostage; this world is inimical to him. He relies on your cooperation. But each time you smear and collapse, as well as choosing outcomes that satisfy you, he's able to improve himself — selecting changes in your brain which make him more sophisticated, more complex. He's evolving, gaining strength.'

A chill passes through me. 'Then… will he even let me remember you saying that?'

'Laura guarantees it.'

I shake my head. 'Laura says this, Laura says that. Why should I believe anything you've told me? Why should I even believe that you are what you say you are?'

She shrugs. 'You will believe, one way or another; there must be eigenstates in which you do. As for what I am — I'm a set of perceptions which happens to convince you. Nothing more, nothing less.'

I spray her with tranquillizer. She smiles as the mist settles on her skin, then she purses her lips and gently exhales. The cloud of tiny droplets reappears in front of her, then rushes towards me, shrinking, and — before I can put up a gloved hand to shield myself — flows back into the nozzle of the can.

I sag to my knees. She vanishes.

After a while, I climb to my feet and make my way out of the building.

Half-way across the city, the van comes to a halt. The horn sounds, then someone shouts urgently, 'Nick! Come out! Something's happened!' I recognize Lui's voice.

I hesitate, confused and angry. Has he gone mad? Is he trying to sabotage everything? If I stay in the van, maybe I can still return to ASR safely. But then it sinks in: he wouldn't be here without a good reason. I must already be collapsed.

I clamber out. He's standing in front of the van with outstretched arms, blocking its way. A group of cyclists pass us, staring; I feel like I'm standing naked on the street — observable again, vulnerable again to the same contingencies as everyone else. We're on the outskirts of the city centre; I blink at the jewelled buildings looming ahead. It's hard to accept that I've been delivered back into the ordinary world, without a jolt, without a premonition.

Lui says, 'They know you're missing.'

'How? Why couldn't I stop it?'

He shakes his head angrily. 'I don't know why. Too many people involved. That isn't important; it's happened.'

'What do you mean, too many people?'

'They found a bomb. About twenty minutes ago.'

'Oh, shit. The Children. Po-kwai…?'

'She's fine. They defused it. Nobody's been hurt — but the building went on full alert, they swept every corner … you can imagine. They found three other devices. And they found you missing. Maybe you just couldn't juggle all the possibilities — keeping the bombs undetected and unexploded. I don't know. But you have to leave the city.'

'What about you? And the others?'

'I'm going to stay. The Canon will have to keep a low profile — but they still don't know we exist. I expect ASR will assume that the Children got to you somehow. A puppet mod …'

'If the Children had put a puppet mod in my skull, I would have stayed in the fucking building and made sure that the bombs went off.'

He scowls impatiently. Okay. I don't know what ASR will think. It doesn't matter. You have to leave. The rest of the Canon aren't implicated; we can look after ourselves.' He steps away from the van; it speeds off into the darkness. Then he takes a card from his shirt pocket and hands it to me. 'Five hundred thousand dollars. Pure, anonymous credit, drawn on an orbiting account. Go to the harbour, not the airport; ASR will find it harder to pull strings there. And with this, I expect you can out-bribe even them.'

I shake my head. 'I can't go.'

'Don't be stupid. If you stay, you're dead. But with the eigenstate mod, the Canon stands a chance of staying one step ahead. You did get it?'

I nod. 'Yes. But you can't use the mod; the risk is too great.'