Oceanic by Greg Egan Page A

to give them something to think about.” I was still hoping that the downed jets were unintended, but we had no choice but to retaliate.
    “Yeah.” Alison’s image was live now; I saw her reach down for her mouse. She said, “It’s not responding. The net’s too degraded.” All the fancy algorithms that the routers used, and that we’d leveraged so successfully for our imaging software, were turning them into paperweights. The internet was robust against high levels of transmission noise and the loss of thousands of connections, but not against the decay of arithmetic itself.
    My watch went dead. I looked to the laptop; it was still working. I reached over and hit a single hotkey, launching a program that would try to reach Alison and the others the same way we’d talked to Sam: by modulating part of the border. In theory, the hawks might have moved the whole border – in which case we were screwed – but the border was vast, and it made more sense for them to target their computing resources on the specific needs of the assault itself.
    A small icon appeared on the laptop’s screen, a single letter A in reversed monochrome. I said, “Is this working?”
    “Yes,” Alison replied. The icon blinked out, then came back again. We were doing a Hedy Lamarr, hopping rapidly over a predetermined sequence of border points to minimize the chance of detection. Some of those points would be missing, but it looked as if enough of them remained intact.
    The A was joined by a Y and a T. The whole cabal was online now, whatever that was worth. What we needed was S, but S was not answering.
    Campbell said grimly, “I heard about the planes. I’ve started an attack.” The tactic we had agreed upon was to take turns running different variants of Campbell’s border-jumping algorithm from our scattered machines.
    I said, “The miracle is that they’re not hitting us the same way we’re hitting them. They’re just pushing down part of the border with the old voting method, step by step. If we’d given them what they’d asked for, we’d all be dead by now.”
    “Maybe not,” Yuen replied. “I’m only halfway through a proof, but I’m ninety percent sure that Tim’s method is asymmetrical. It only works in one direction. Even if we’d told them about it, they couldn’t have turned it against us.”
    I opened my mouth to argue, but if Yuen was right that made perfect sense. The far side had probably been working on the same branch of mathematics for centuries; if there had been an equivalent weapon that could be used from their vantage point, they would have discovered it long ago.
    My machine had synchronized with Campbell’s, and it took over the assault automatically. We had no real idea what we were hitting, except that the propositions were further from the border, describing far simpler arithmetic on the dark integers than anything of ours that the far side had yet touched. Were we crippling machines? Taking lives? I was torn between a triumphant vision of retribution, and a sense of shame that we’d allowed it to come to this.
    Every hundred meters or so, I passed another car sitting motionless by the side of the highway. I was far from the only person still driving, but I had a feeling Kate wouldn’t have much luck getting a taxi. She had water in her backpack, and there was a small shelter at the spot where we’d parked. There was little to be gained by reaching my office now; the laptop could do everything that mattered, and I could run it from the car battery if necessary. If I turned around and went back for Kate, though, I’d have so much explaining to do that there’d be no time for anything else.
    I switched on the car radio, but either its digital signal processor was too sophisticated for its own good, or all the local stations were out.
    “Anyone still getting news?” I asked.
    “I still have radio,” Campbell replied. “No TV, no internet. Landlines and mobiles here are dead.” It was