Phase Space by Stephen Baxter Read Free Book Online Page A

encased by some smart membrane that held the whole thing in place and collected solar energy and regulated temperature and stuff. It looked like a little clone of Earth, in fact, and Greenberg thought it was somehow appropriate that today that tired, depopulated old Earth itself was over somewhere the far side of the sun, invisible, forgotten, the last traces of man being scraped off by the returned glaciers.
    Under the pulsing surface of Ra he could make out dark brown shapes, graceful and lithe: people, Weissmans, whole schools of them flipping around the interior. And now here came a child, wriggling up to the membrane, pushing its disturbingly human face up to the wall, peering out – with curiosity or indifference, he couldn’t tell which – at the stars. It broke his unreconstructed twentieth-century heart to see that little girl’s face stuck on the end of such a fat, unnatural body.
    An adult came by and chivvied the kid away, into the deeper interior; Greenberg saw their sleek shapes disappear into the misty blue.
    The Weissmans had been working on making their environment as simple and durable as they could. They were planning for the long haul, it seemed. So, the whole rock had been transformed into this spherical ocean, and the biosphere had been cut down to essentially two components: Weissmans, post-humans, swimming around in a population of something that was descended from blue-green algae. The algae, feeding on sunlight, were full of proteins, vitamins and essential amino acids. And the humans ate the algae, drank the water, breathing in oxygen, breathing out carbon dioxide to feed the algae.
    When people died their bodies were allowed to drift down to the centre of the world, where supercritical water reactors worked to break down their residues and return their body masses to the ecosystem.
    The loops were as closed as they could be. The loss that entropy dictated was made up by the energy steadily gathered by that smart membrane, and a few nanobugs embedded there. Greenberg understood that research was going on to eliminate the last few technological components of the system: maybe those supercritical water reactors could be replaced by something organic, and maybe even the surface membrane and the last nanobugs could be done away with. For instance, a few metres of water would serve as a radiation shield.
    It was a kind of extreme end result, Greenberg supposed, of the technology evolution that had begun all the way back with John Glenn in his cramped little Mercury tin can, breathing in canned air for his few orbits of the home planet.
    But the Weissmans were not much like John Glenn.
    He didn’t know any of their names. He didn’t care to. For a long time now, longer than he cared to think, there had been hardly anybody alive who remembered him from one waking period to the next, from one of his ‘days’ to another. Hell of a thing. He preferred to talk to the machines, in fact.
    Greenberg didn’t even know if the Weissmans were still human any more.
    The last of the true humans, as he recognized them, had been leaving the system for millennia.
    It had been necessary. For a time, as the human population grew exponentially, it looked as if even the solar system’s vast resources were in danger of depletion.
    So somebody had to leave, to open up the loops once more.
    There was a whole variety of ways to go, all of them based on pushing people-laden rocks out of the system. You could mount a big mass driver on the back of your rock and use its substance as reaction mass. Close to the sun, you could use its heat to just boil off volatiles. You could use a solar sail. You could use Jupiter’s powerful electromagnetic field as a greater mass driver. And so on. There was even a rumour of an anti-matter factory, out in the Kuiper Belt somewhere.
    Greenberg’s favourite method was the most resolutely low-tech. Just nudge your rock out of its stable orbit, let it whip through the gravity fields of