Грег Иган - Dark Integers

Yuen hesitated. “Yes and no. Any cluster of near-side truth values it injects into the far side will have a non-smooth border, so they’ll be able to remove it with sheer computing power. In that sense, they’ll never be defenseless. But I don’t see how there’s anything they can do to prevent the attacks in the first place.”

“Short of wiping us out,” Campbell said.

I heard an infant sobbing. Alison said, “That’s Laura. I’m alone here. Give me five minutes.”

I buried my head in my arms. I still had no idea what the right course would have been. If we’d handed over Campbell’s algorithm immediately, might the good will that bought us have averted the war? Or would the same attack merely have come sooner? What criminal vanity had ever made the three of us think we could shoulder this responsibility on our own? Five thousand people were dead. The hawks who had taken over on the far side would weigh up our offer, and decide that they had no choice but to fight on.

And if the reluctant cabal had passed its burden to Canberra, to Zurich, to Beijing? Would there really have been peace? Or was I just wishing that there had been more hands steeped in the same blood, to share the guilt around?

The idea came from nowhere, sweeping away every other thought. I said, “Is there any reason why the far side has to stay connected ?”

“Connected to what?” Campbell asked.

“Connected to itself. Connected topologically. They should be able to send down a spike, then withdraw it, but leave behind a bubble of altered truth values: a kind of outpost, sitting within the near side, with a perfect, smooth border making it impregnable. Right?”

Yuen said, “Perhaps. With both sides collaborating on the construction, that might be possible.”

“Then the question is, can we find a place where we can do that so that it kills off the chance to use Tim’s method completely—without crippling any process that we need just to survive?”

“ Fuck you , Bruno!” Campbell exclaimed happily. “We give them one small Achilles tendon to slice… and then they’ve got nothing to fear from us!”

Yuen said, “A watertight proof of something like that is going to take weeks, months.”

“Then we’d better start work. And we’d better feed Sam the first plausible conjecture we get, so they can use their own resources to help us with the proof.”

Alison came back online and greeted the suggestion with cautious approval. I drove around until I found a quiet coffee shop. Electronic banking still wasn’t working, and I had no cash left, but the waiter agreed to take my credit card number and a signed authority for a deduction of one hundred dollars; whatever I didn’t eat and drink would be his tip.

I sat in the café, blanking out the world, steeping myself in the mathematics. Sometimes the four of us worked on separate tasks; sometimes we paired up, dragging each other out of dead ends and ruts. There were an infinite number of variations that could be made to Campbell’s algorithm, but hour by hour we whittled away at the concept, finding the common ground that no version of the weapon could do without.

By four in the morning, we had a strong conjecture. I called Sam, and explained what we were hoping to achieve.

He said, “This is a good idea. We’ll consider it.”

The café closed. I sat in the car for a while, drained and numb, then I called Kate to find out where she was. A couple had given her a lift almost as far as Penrith, and when their car failed she’d walked the rest of the way home.

For close to four days, I spent most of my waking hours just sitting at my desk, watching as a wave of red inched its way across a map of the defect. The change of hue was not being rendered lightly; before each pixel turned red, twelve separate computers needed to confirm that the region of the border it represented was flat.

On the fifth day, Sam shut off his computers and allowed us to mount an attack from our side on the narrow corridor linking the bulk of the far side with the small enclave that now surrounded our Achilles’ Heel. We wouldn’t have suffered any real loss of essential arithmetic if this slender thread had remained, but keeping the corridor both small and impregnable had turned out to be impossible. The original plan was the only route to finality: to seal the border perfectly, the far side proper could not remain linked to its offshoot.

In the next stage, the two sides worked together to seal the enclave completely, polishing the scar where its umbilical had been sheared away. When that task was complete, the map showed it as a single burnished ruby. No known process could reshape it now. Campbell’s method could have breached its border without touching it, reaching inside to reclaim it from within—but Campbell’s method was exactly what this jewel ruled out.

At the other end of the vanished umbilical, Sam’s machines set to work smoothing away the blemish. By early evening that, too, was done.

Only one tiny flaw in the border remained now: the handful of propositions that enabled communication between the two sides. The cabal had debated the fate of this for hours. So long as this small wrinkle persisted, in principle it could be used to unravel everything, to mobilize the entire border again. It was true that, compared to the border as a whole, it would be relatively easy to monitor and defend such a small site, but a sustained burst of brute-force computing from either side could still overpower any resistance and exploit it.

In the end, Sam’s political masters had made the decision for us. What they had always aspired to was certainty, and even if their strength favored them, this wasn’t a gamble they were prepared to take.

I said, “Good luck with the future.”

“Good luck to Sparseland,” Sam replied. I believed he’d tried to hold out against the hawks, but I’d never been certain of his friendship. When his icon faded from my screen, I felt more relief than regret.

I’d learned the hard way not to assume that anything was permanent. Perhaps in a thousand years, someone would discover that Campbell’s model was just an approximation to something deeper, and find a way to fracture these allegedly perfect walls. With any luck, by then both sides might also be better prepared to find a way to co-exist.

I found Kate sitting in the kitchen. I said, “I can answer your questions now, if that’s what you want.” On the morning after the disaster, I’d promised her this time would come—within weeks, not months—and she’d agreed to stay with me until it did.

She thought for a while.

“Did you have something to do with what happened last week?”

“Yes.”

“Are you saying you unleashed the virus? You’re the terrorist they’re looking for?” To my great relief, she asked this in roughly the tone she might have used if I’d claimed to be Genghis Khan.

“No, I’m not the cause of what happened. It was my job to try and stop it, and I failed. But it wasn’t any kind of computer virus.”

She searched my face. “What was it, then? Can you explain that to me?”

“It’s a long story.”

“I don’t care. We’ve got all night.”

I said, “It started in university. With an idea of Alison’s. One brilliant, beautiful, crazy idea.”

Kate looked away, her face flushing, as if I’d said something deliberately humiliating. She knew I was not a mass murderer. But there were other things about me of which she was less sure.

“The story starts with Alison,” I said. “But it ends here, with you.”