Phase Space

by Stephen Baxter

  To Greenberg’s great surprise, Ra’s inhabitants had become rich.

  The first justification for opening up the rocks had been to make them serve as short-term resource factories to aid in the colonization of the Moon, Mars and beyond. But it wasn’t working out like that. Sure, the gravity well colonies were in place, but they were hardly thriving; they were always going to be dependent on key volatiles shipped in from somewhere else. And they didn’t have much to trade; Ra could purchase high-grade metals much more cheaply from other rocks.

  There were actually more humans living in the rocks now than on the Moon or Mars. And Ra had more trade with other rocks than anybody else – even Earth …

  He saw there was one articulated joint on the splitter boom that was giving particular problems; its prophylactic cover had been taken off, revealing a knobby joint with big, easily replaced parts, already half-dismantled, like the knee joint of a T Rex.

  The youngsters were talking about more advances in technology. Like nanotech miners which would chomp their way through the rock without any human intervention at all. Greenberg kind of hoped it wouldn’t be for a while, though; he preferred machinery big enough to see, and wrestle with. It gave him a purpose, a reason to use the upper-body strength he’d brought up from Earth.

  The workers got out of the way of him, and, whistling, he moved into the balky joint with his vacuum line.

  Screw Mars, he thought as he worked; he liked it here.

  The remnant of the cloud moulded itself into a flattened, rotating disc. Solid particles condensed: ices of water and hydrocarbons in the cooler, outer rim, but only rocky debris in the hot, churning heart of the nebula. Planetesimals formed, massive, misshapen bodies that collided and accreted as they raced around the new sun.

  And, out of the collisions, planets grew: rocky worlds in the hot centre, volatile-fat giants further out. A powerful wind blew from the sun, violently ejecting the amniotic remnants of the birth cloud. Planetesimals rained down on the surfaces of the new worlds, leaving scars that would persist for billions of years.

  The gravity of young Jupiter plucked at the belt of planetesimals further in, preventing their coalescence into larger bodies. So, in the gap between Jupiter and Mars, the planetesimals survived as asteroids: rocky chunks closest to the sun, volatile-rich snowballs at the outer rim, moulded by impacts with each other, melted by radioactivity and electrical induction.

  And it was to the asteroids that the starship came: after billions of years drifting like a seed between the stars, still running from the supernova, exhausted, depleted, its ancient machinery cradling the generations that swarmed within, evolving, never understanding their plight.

  Scale: Exp 3

  The nanobugs woke him; with reluctance he swam up from dreams of sunlit days with his daughters on the beaches of Galveston.

  He emerged into a gritty, unwelcome reality. Here he was: half a man, with his whole lower body replaced by the gleaming box he called his PMU, pipes and tubes everywhere, still rattling around inside his clumsy old hab module.

  Not that there could be much left of his original home. That old NASA stuff had mostly worn out after a decade, let alone a thousand years. But the Weissmans, or anyhow the robots they’d assigned to keeping him alive, quietly rebuilt this old box around him, just as they rebuilt him continually, nanobugs crawling through his body while he slept away the years.

  Well, the hell with it. He dug out a packet of food – the label reassured him it was chicken soup, and as far as he was concerned that was what it was – and he shoved it into the rehydration drawer of his galley.

  He moved to a window, the little nitrogen reaction-control squirters on his PMU hissing softly. The window gave onto a shaft cut through the regolith, which had a massive lid that would swing down on him in case of a solar flare or some such. It gave him a good view of the surface of Ra-Shalom, and a slice of the night side of Earth, and a handful of stars.

  Water-blue light glared out of Ra.

  When he’d first come here, Ra had been just a lump of dirty carbonaceous stone. Now, the old craters and ravines transformed into a patchwork of windows, roofed over with some kind of smart membrane.

  Greenberg could see into the lens-like surface of one of the crater windows. And right now, a few minutes from the aerobraking of Toutatis, the Weissmans were swimming up from the big spherical ocean they were building in the hollowed-out interior of Ra, swimming up to watch a light show hardly any of them understood, probably.

  The Weissmans came in a variety of shapes. There were even still a few standard-issue four-limbed humans around. But the most common morphology was something like a mermaid, with the legs – useless, heavy distractions in microgravity – replaced by a kind of fish tail, useful for swimming around in the air, or the interior ocean. A lot of them had gills and never came out of the water at all, and some were covered in fur that streamlined and warmed their bodies.

  The Weissmans had done away with every part of the body which wasn’t needed in microgravity. And some had gone further. Some didn’t have hands, or arms. In an age of ubiquitous and one hundred per cent reliable machinery – machinery which could manufacture other machinery – human beings, it seemed, didn’t need to be toolmakers any more.

  To Greenberg, they looked like nothing so much as seals.

  It was their choice, or their progenitors anyhow. But what Greenberg couldn’t figure was what they did all day.

  Greenberg himself still had work to do, in these rare intervals of wakefulness: monitoring Ra’s external systems, checking the import of volatile and metal-rich cargoes.

  But maybe the Weissmans were just being kind. There were probably gigantic smart systems that backed up every action he took. He was a kind of museum piece, he supposed: the first human to rendezvous with an asteroid, all those years ago, a living totem for the Weissmans of Ra.

  He finished the soup and let go of the packet, and a domestic bot – a fussy little bastard like a trash can with attitude thrusters – came hissing out of its corner and grabbed the bag.

  Greenberg felt sour, grumpy and isolated.

  He studied Earth, which swam past on one of its closest approaches to the rock in years.

  He remembered from his first orbital missions aboard Shuttle, all those centuries ago, how the coastal rims of the continents would just glow with artificial light. Greenberg had supposed, then, that it would go on, that the Earth would just get richer and fatter and brighter.

  But it hadn’t worked out that way. Earth, in fact, grew darker every time he looked.

  Once the expansion into the near-Earth rocks had begun, it wasn’t long before a move further out followed: first to Phobos and Deimos, the captured asteroids that circled Mars, and then out into the main belt itself. Vesta, one of the biggest of the main belt rocks, had been the first to be extensively colonized, and now it was the hub of further expansion, little archipelagos of busy mines and colonization, scattered across the belt.

  And, so Greenberg understood, there were some pioneers who had gone even farther afield: to the comets out in the Oort Cloud, and the Kuiper Belt, where billions of ice moons the size of Ganymede swam through the darkness.

  Of course the techniques they used nowadays made Ra look primitive. Those universal fabricators, for instance, that sucked in asteroid ore at one end and pumped out whatever you wanted at the other, using something called molecular-beam epitaxy to spray atoms and molecules directly onto a substrate. Greenberg didn’t understand any of these new gadgets, even the stuff you could see.

  It was strange for Greenberg to remember now how much agonizing there had been when he was growing up about the depletion of Earth’s resources, the need to close the loops of mass and energy, as if Earth itself was one big CELSS. Nobody worried about that any more; the solar system had worked out to be just too rich in resources; those loops would stay open for a long time yet.

  It took a long time for the economics and demographics and such to
work out, but it had all been pretty much inevitable, it seemed to Greenberg. It was just so much cheaper to send resources skimming between the rocks than to haul them out of the planets’ big gravity wells. The colonies on Mars and the Moon had shrivelled and died, and Earth – growing poorer, its population steadily declining – had turned into a kind of huge theme park: a museum of the human species, but studded with pits of abject poverty, in the darkened ruins of the old cities. Nobody knew what was happening in those pits.

  And nobody much cared, because beyond old Earth there were too many people even to count.

  If you knew where to look, the sky was full of inhabited rocks, with their little orbital necklaces of solar power stations, and habitats studding their surfaces or buried inside, green and blue, the old colours of life. It was estimated that for every person alive when Greenberg was born, there were a billion human souls now. That was a hell of a thought. And when he considered some of the assholes he used to have to work with back in those days, a dismaying one.

  In Ra there was a whole bunch of little Weissmans, though not all of them used Mike’s old name any more, and so in his head Greenberg thought of them all as Weissmans; it made it easier to love them. Mike would have been pleased, anyhow. There were no Greenbergs, though. His line had finished with a great-grandchild, a male, who had got caught up in the New AIDS epidemic of the twenty-second century, and died childless. It was ironic. Here was Greenberg, perhaps the oldest surviving human, and not one of all those teeming trillions floating around the system could claim direct descent from him.

  On the other hand, by the laws of statistics, there ought to be a billion Einsteins out there. Nobody knew what they were all doing. They sure weren’t working together.

  All those pious dreams of the space buffs of some kind of giant solar-system civilization had never been remotely likely. There were just too many people. The human race had gathered into a billion small-town-sized tribes and splintered, shaping and seeking goals unimaginable to an Earth-born geezer like him.

  It seemed to him, in fact, that he was watching the end of the species, as a unitary whole: two million years out of Africa, the race had escaped from the cradle and was growing, to where the hell nobody could even guess.

  … And now here came Toutatis on its aerobraking pass.

  The rock looked like a comet glowing in the thin upper air of Earth, streaking by in a perfect straight line below Greenberg. It made the cities and oceans of Earth glow like the day – it must have been a remarkable sight from down there – and asteroid light played on his own face, the ancient bones of his eye sockets.

  The encounter was over in seconds. The trail of scorched air soon dissipated and dimmed, and Toutatis, its orbit subtly altered, passed on towards its next encounter. It was going to take fifty years to nudge Toutatis into its final low Earth orbit, but planning projects on that kind of time scale didn’t seem to trouble the inhabitants of Toutatis, or anybody else.

  The show was over. The people of Ra-Shalom drifted away from their blue watery windows, and returned to their mysterious business within.

  Greenberg had never meant to live for a thousand years. It was ridiculous. Nobody else had stuck around like this. It was just that he would have had to have chosen when to die, and that was something he had never expected to face when he grew up, and he just had no instinct for it.

  Anyhow, if he let himself die, he would have missed this.

  Greenberg, with a sigh, turned away from the window and went to his instrument consoles.

  It was a massive asteroid, big enough to have dragged itself into a sphere, with planet-like layers of internal structure, rich in metals, rocks and volatiles. It was bathed by the light of a sun only three times as far away as from Earth.

  The guardians considered carefully. It was, after all, to be the repository of all that was left of their designers’ species, until even this new young sun guttered and died.

  They were machines designed to plan for billions of years. They had already nursed their fragile cargo across such deserts of time. Now, looking to the future, they must plan for evolution, even the loss of mind.

  It was a good home, rich in energy and resources.

  The guardians were satisfied. They closed themselves down.

  Within the rock, history continued.

  Scale: Exp 4

  It was to be quite a day, as the last of Ra’s ore was transmuted, and Greenberg made sure the Weissmans woke him up to see it. In the event he nearly missed it, it took so long to put him together again.

  Greenberg’s window was the same old tunnel through fused regolith, but the view beyond changed as he watched, the last of the grey-black old crap literally dissolving before his eyes, to be replaced by a sharp, tight blue curve of watery horizon.

  Too damn sharp, he thought. He wondered if those asshole nanobugs had changed his eyes on him again while he’d slept. But even his naps lasted a century at a time, longer than he had once expected to live; they had time.

  Anyhow, his new eyes showed him a blue world, the landscape softly pulsing, with Greenberg’s NASA-style space station hab module stuck stubbornly to the side under its crust of regolith, like a leech clinging to flesh. Ra was just water now, 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.r />
  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 Jupiter and Saturn a few times, and you could slingshot your way out of the system for free. Of course it might take you ten thousand years to reach your destination, at Barnard’s Star or E Eradini or E Indi. But what the hell; you probably had with you more water than in the whole of the Atlantic Ocean.

  Greenberg accepted the necessity of the migration. But to him it had been a drain, not just on the system’s titanic population, but on the human spirit.

  The solar system had been left a drab, depopulated place. All the engineering types had gone, leaving behind the navel-gazing seals of Ra, and similar relics scattered around the system.

  The Weissmans, turned in on themselves, had their own interests. They were probing into a lot of areas well beyond his expertise. Like the possibility of tapping into zero-point field energy, the energy of the vacuum itself, so dense you could – it was said – boil all the oceans of Earth itself with the energy contained in a coffee cup of empty space. Then there was the compact energy stored in topological defects, little packets of space that had gotten tangled up and folded over in the Big Bang, containing some of the monstrous primeval energies within, just waiting to be tapped and opened up …