Accelerando

stranded in an industrial park) is converted into computronium. And it's

not just the inner system. The same forces are at work on Jupiter's

moons, and those of Saturn, although it'll take thousands of years rather

than mere decades to dismantle the gas giants themselves. Even the

entire solar energy budget isn't enough to pump Jupiter's enormous mass

to orbital velocity in less than centuries. The fast-burning primitive

thinkers descended from the African plains apes may have vanished

completely or transcended their fleshy architecture before the solar

Matrioshka brain is finished.

It won't be long now…

* * *

Meanwhile, there's a party brewing down in Saturn's well.

Sirhan's lily-pad city floats inside a gigantic and nearly-invisible sphere in Saturn's upper atmosphere; a balloon kilometers across with a shell of fullerene-reinforced diamond below and a hot hydrogen gas bag above. It's one of several hundred multimegaton soap bubbles floating in the sea of turbulent hydrogen and helium that is the upper atmosphere of Saturn, seeded there by the Society for Creative Terraforming, subcontractors for the 2074

Worlds' Fair.

The cities are elegant, grown from a conceptual seed a few megawords long. Their replication rate is slow (it takes months to build a bubble), but in only a couple of decades, exponential growth will have paved the stratosphere with human-friendly terrain. Of course, the growth rate will slow toward the end, as it takes longer to fractionate the metal isotopes out of the gas giant's turbid depths, but before that happens, the first fruits of the robot factories on Ganymede will be pouring hydrocarbons down into the mix. Eventually Saturn – cloud-top gravity a human-friendly 11 meters per second squared – will have a planet wide biosphere with nearly a hundred times the surface area of Earth. And a bloody good thing indeed this will be, for otherwise, Saturn is no use to anyone except as a fusion fuel bunker for the deep future when the sun's burned down.

This particular lily-pad is carpeted in grass, the hub of the disk rising in a gentle hill surmounted by the glowering concrete hump of the Boston Museum of Science. It looks curiously naked, shorn of its backdrop of highways and the bridges of the Charles River – but even the generous kiloton dumb matter load-outs of the skyhooks that lifted it into orbit wouldn't have stretched to bringing its framing context along with it. Probably someone will knock up a cheap diorama backdrop out of utility fog, Sirhan thinks, but for now, the museum stands proud and isolated, a solitary redoubt of classical learning in exile from the fast-thinking core of the solar system.

'Waste of money,' grumbles the woman in black. 'Whose stupid idea was this, anyway?' She jabs the diamond ferrule of her cane at the museum.

'It's a statement,' Sirhan says absently. 'You know the kind, we've got so many newtons to burn we can send our cultural embassies wherever we like. The Louvre is on its way to Pluto, did you hear that?'

'Waste of energy.' She lowers her cane reluctantly and leans on it. Pulls a face: 'It's not right.'

'You grew up during the second oil crunch, didn't you?' Sirhan prods. 'What was it like then?'

'What was it…? Oh, gas hit fifty bucks a gallon, but we still had plenty for bombers,' she says dismissively.

'We knew it would be okay. If it hadn't been for those damn' meddlesome posthumanists -' Her wrinkled, unnaturally aged face scowls at him furiously from underneath hair that has faded to the color of rotten straw, but he senses a subtext of self-deprecating irony that he doesn't understand. 'Like your grandfather, damn him. If I was young again I'd go and piss on his grave to show him what I think of what he did. If he has a grave,' she adds, almost fondly.

Memo checkpoint: log family history, Sirhan tells one of his ghosts. As a dedicated historian, he records every experience routinely, both before it enters his narrative of consciousness – efferent signals are the cleanest

– and also his own stream of selfhood, against some future paucity of memory. But his grandmother has been remarkably consistent over the decades in her refusal to adapt to the new modalities.

'You're recording this, aren't you?' she sniffs.

'I'm not recording it, Grandmama,' he says gently, 'I'm just preserving my memories for future generations.'

'Hah! We'll see,' she says suspiciously. Then she surprises him with a bark of laughter, cut off abruptly:

'No, you'll see, darling. I won't be around to be disappointed.'

'Are you going to tell me about my grandfather?' asks Sirhan.

'Why should I bother? I know you posthumans, you'll just go and ask his ghost yourself. Don't try to deny it! There are two sides to every story, child, and he's had more than his fair share of ears, the sleazebag. Leaving me to bring up your mother on my own, and nothing but a bunch of worthless intellectual property and a dozen lawsuits from the Mafiya to do it with. I don't know what I ever saw in him.' Sirhan's voice-stress monitor detects a distinct hint of untruth in this assertion. 'He's worthless trash, and don't you forget it. Lazy idiot couldn't even form just one startup on his own: He had to give it all away, all the fruits of his genius.'

While she rambles on, occasionally punctuating her characterization with sharp jabs of the cane, Pamela leads Sirhan on a slow, wavering stroll that veers around one side of the museum, until they're standing next to a starkly engineered antique loading bay. 'He should have tried real communism instead,' she harrumphs: 'Put some steel into him, shake those starry-eyed visionary positive-sum daydreams loose. You knew where you were in the old times, and no mistake. Humans were real humans, work was real work, and corporations were just things that did as we told them. And then, when she went to the bad, that was all his fault, too, you know.'

'She? You mean my, ah, mother?' Sirhan diverts his primary sensorium back to Pamela's vengeful muttering. There are aspects to this story that he isn't completely familiar with, angles he needs to sketch in so that he can satisfy himself that all is as it should be when the bailiffs go in to repossess Amber's mind.

'He sent her our cat. Of all the mean-spirited, low, downright dishonest things he ever did, that was the worst part of it. That cat was mine, but he reprogrammed it to lead her astray. And it succeeded admirably. She was only twelve at the time, an impressionable age, I'm sure you'd agree. I was trying to raise her right. Children need moral absolutes, especially in a changing world, even if they don't like it much at the time. Self-discipline and stability, you can't function as an adult without them. I was afraid that, with all her upgrades, she'd never really get a handle on who she was, that she'd end up more machine than woman. But Manfred never really understood childhood, mostly on account of his never growing up. He always was inclined to meddle.'

'Tell me about the cat,' Sirhan says quietly. One glance at the loading bay door tells him that it's been serviced recently. A thin patina of expended foglets have formed a snowy scab around its edges, flaking off like blue refractive candyfloss that leaves bright metal behind. 'Didn't it go missing or something?'

Pamela snorts. 'When your mother ran away, it uploaded itself to her starwhisp and deleted its body. It was the only one of them that had the guts – or maybe it was afraid I'd have it subpoenaed as a hostile witness. Or, and I can't rule this out, your grandfather gave it a suicide reflex. He was quite evil enough to do something like that, after he reprogrammed himself to think I was some kind of mortal enemy.'

'So when my mother died to avoid bankruptcy, the cat… didn't stay behind? Not at all? How remarkable.'

Sirhan doesn't bother adding how suicidal. Any artificial entity that's willing to upload its neural state vector into a one-kilogram interstellar probe three-quarters of the way to Alpha Centauri without backup or some clear way of returning home has got to be more than a few methods short in the object factory.

'It's a vengeful beast.' Pamela pokes her stick at the ground sharply, mutters a command word, and lets go