Diaspora

polysaccharide and builds another structural unit.'

Paolo glanced at the library again, for a simulation of the process. Catalytic sites strewn along the sides of each unit trapped the radicals in place, long enough for new bonds to form between them. Some simple sugars were incorporated straight into the polymer as they were created; others were set free to drift in solution for a microsecond or two, until they were needed. At that level, there were only a few basic chemical tricks being used… but molecular evolution must have worked its way up from a few small autocatalytic fragments, first formed by chance, to this elaborate system of twenty thousand mutually self-replicating structures. If the 'structural units' had floated free in the ocean as independent molecules, the 'lifeform' they comprised would have been virtually invisible. By bonding together, though, they became twenty thousand colors in a giant mosaic.

It was astonishing. Paolo hoped Elena was tapping the library, wherever she was. A colony of algae would have been more 'advanced'—but this incredible primordial creature revealed infinitely more about the possibilities for the genesis of life. Carbohydrate, here, played every biochemical role: information carrier, enzyme, energy source, structural material. Nothing like it could have survived on Earth, once there were organisms capable of feeding on it—and if there were ever intelligent Orpheans, they'd he unlikely to find any trace of this bizarre ancestor.

Karpal wore a secretive smile.

Paolo said, 'What?'

'Wang tiles. The carpets are made out of Wang tiles.'

Hermann beat him to the library, again. 'Wang as in the twentieth-century mathematician, Hao Wang. Tiles as in any set of shapes which can cover the plane. Wang tiles are squares with various shaped edges, which have to fit complementary shapes on adjacent squares. You can cover the plane with a set of Wang tiles, as long as you choose the right one every step of the way. Or in the case of the carpets, grow the right one.'

Karpal said, 'We should call them Wang's Carpets, in honor of Hao Wang. After twenty-three hundred years, his mathematics has come to life.'

Paolo liked the idea, but he was doubtful. 'We may have trouble getting a two-thirds majority on that. It's a bit obscure.'

Hermann laughed. 'Who needs a two-thirds majority? If we want to call them Wang's Carpets, we can call them Wang's Carpets. There are ninety-seven languages in current use in C-Z—half of them invented since the polis was founded. I don't think we'll be exiled for coining one private name.'

Paolo concurred, slightly embarrassed. The truth was, he'd completely forgotten that Hermann and Karpal weren't actually speaking Modern Roman.

The three of them instructed their exoselves to consider the name adopted: henceforth, they'd hear 'carpet' as 'Wang's Carpet'—but if they used the term with anyone else, the reverse translation would apply.

Orlando's celebration of the microprobe discoveries was very much a carnevale-refugee affair. The scape was an endless sunlit garden strewn with tables covered in food, and the invitation had politely suggested attendance in strict ancestral form. Paolo politely faked it, simulating most of the physiology but running the body as a puppet, leaving his mind unshackled.

He drifted from table to table, sampling the food to keep up appearances, wishing Elena had come. There was little conversation about the biology of Wang's Carpets; most of the people here were simply celebrating their win against the opponents of the microprobes—and the humiliation that faction would suffer, now that it was clearer than ever that the 'invasive' observations could have done no harm. Liesl's fears had proved unfounded; there was no other life in the ocean, just Wang's Carpets of various sizes. Paolo, feeling perversely even-handed after the fact, kept wanting to remind these smug movers and shakers: There might have been anything down there. Strange creatures, delicate and vulnerable in ways we could never have anticipated. We were lucky, that's all.

He ended up alone with Orlando almost by chance; they were both fleeing different groups of appalling guests when their paths crossed on the lawn.

Paolo asked, 'How do you think they'll take this, back home?'

'It's first life, isn't it? Primitive or not. It should at least maintain interest in the Diaspora, until the next alien biosphere is discovered.' Orlando seemed subdued; perhaps he was finally coming to terms with the gulf between their modest discovery and Earth's longing for world-shaking results. 'And at least the chemistry is novel. If it had turned out to be based on DNA and protein, I think half of Earth C-Z would have died of boredom on the spot. Let's face it, the possibilities of DNA have been simulated to death.'

Paolo smiled at the heresy. 'You think if nature hadn't managed a little originality, it would have dented people's faith in the charter? If the solipsist polises had begun to look more inventive than the universe itself… '

'Exactly.'

They walked on in silence, then Orlando halted, and turned to face him. 'There's something I've been meaning to tell you. My Earth-self is dead.'

'What?'

'Please, don't make a fuss.'

'But… why? Why would he?' Dead meant suicide; there was no other cause. 'I don't know why. Whether it was a vote of confidence in the Diaspora'—Orlando had chosen to wake only in the presence of alien life—'or whether he despaired of us sending back good news, and couldn't face the waiting, and the risk of disappointment. He didn't give a reason. He just had his exoself send a message, stating what he'd done.'

Paolo was shaken. 'When did this happen?'

'About fifty years after the launch.'

'My Earth-self said nothing.'

'It was up to me to tell you, not him.'

'I wouldn't have seen it that way.'

'Apparently, you would have.'

Paolo fell silent, confused. How was he supposed to mourn a distant version of Orlando, in the presence of the one he thought of as real? Death of one clone was a strange half-death, a hard thing to come to terms with. His Earth-self had lost a father; his father had lost an Earth-self. What exactly did that mean to him?

What Orlando seemed most concerned about was the culture of Earth C-Z. Paolo said carefully, 'Hermann told me there'd been a rise in emigration and suicide. But morale has improved a lot since the spectroscope picked up signs of Orphean water, and when they hear that it's more than just water—'

Orlando cut him off sharply. 'You don't have to talk things up for me. I'm in no danger of repeating the act.' They stood on the lawn, facing each other. Paolo composed a dozen different combinations of mood to communicate, but none of them felt right. He could have granted his father perfect knowledge of everything he was feeling—but what exactly would that knowledge have conveyed? In the end, there was fusion, or separateness. There was nothing in between.

Orlando said, 'Kill myself—and leave the fate of the Coalition in your hands? You must he out of your fucking mind.'

They walked on together, laughing.

Karpal seemed barely able to gather his thoughts enough to speak. Paolo would have offered him a mind graft promoting tranquillity and concentration—distilled from his own most focused moments—but he was sure that Karpal would never have accepted it. He said, 'Why don't you just start wherever you want to? I'll stop you if you're not making sense.'

Karpal looked around the white dodecahedron with an expression of disbelief. 'You live here?'

'Some of the time.'

'But this is your homescape? No trees? No sky? No furniture?'

Paolo refrained from repeating any of Hermann's naive-robot jokes. 'I add them when I want them. You know, like… music. Look, don't let my taste in decor distract you—'

Karpal made a chair and sat down heavily.

He said, 'Hao Wang proved a powerful theorem, twenty-three hundred years ago. Think of a row of Wang