Phase Space. Stephen Baxter
none of that made a difference here, in the ancient system of Sol, the dead heart of human expansion. It was hard for him to trace the passing of the years because so little changed any more, even on the heroic timescales of his intervals of consciousness.
Conditions in a lot of the inhabited rocks had converged, in fact, so that the worlds came to resemble each other. Most of them finished up with the kind of simple, robust ecosystem that sustained Ra, even though their starting points might have been very different. It was like the way a lot of diverse habitats on Earth – forests and jungles and marshes – would, with the passage of time, converge into a peat bog, the same the world over, as if they were drawn to an attractor in some ecological phase-space.
And most of the rocks, drifting between uninhabited gravity wells, were about as interesting as peat bogs, as far as Greenberg was concerned.
Meanwhile, slowly but inexorably, life was dying back, here in the solar system. which had once hosted billions of jewel-like miniature worlds.
There were a lot of ways for a transformed asteroid to be destroyed: for instance, a chance collision with another object. Even a small impact on a fragile bubble-world like Ra could puncture it fatally. But nobody around seemed capable of pushing rocks aside any more.
But the main cause of the die-back was simple ecological failure.
An asteroid wasn’t a planet; it didn’t have the huge buffers of mass and energy that Earth had. A relatively small amount of matter circulated in each mass loop, and so the whole thing was only marginally stable, and not always self-recovering.
It had even happened here, on Ra-Shalom. Greenberg had woken once to find concentrations of the amino acid called lysine had crashed. The Weissmans were too busy on dreaming their cetacean dreams to think too much about the systems that were keeping them alive. Many died, before a new stability was reached. It drove Greenberg crazy.
But the Weissmans didn’t seem too upset. You have to think of it as apoptosis, they said to him. The cells in the hands of an archaic-form human embryo will die back in order to sculpt out tool-making fingers. Death is necessary, sometimes, so that life can progress. It is apoptosis, not necrosis …
Greenberg just couldn’t see that argument at all.
And in the meantime, Ra was still on its course to become the next dinosaur killer. The predictions just got tighter and tighter. And still, nobody seemed to be concerned about doing anything about it.
When what the Weissmans said to him made no sense at all – when they deigned to speak to him – Greenberg felt utterly isolated.
But then, all humans were alone.
Nobody had found non-terrestrial life anywhere, in the solar system or beyond, above prokaryotes: single-celled creatures without internal structures such as nuclei, mitochondria and chloroplasts. Mars was typical, it had turned out: just a handful of crude prokaryote-type bugs shivering deep in volcanic vents, waiting out an Ice Age that would never end. Only on Earth, it seemed, had life made the big, unlikely jump to eukaryotic structure, and then multi-celled organisms, and the future.
It seemed that back when he was born Earth had been one little world holding all the life there was, to all intents and purposes. And it would have stayed that way if his generation and a couple before, Americans and Russians, hadn’t risked their lives to enter space in converted ICBMs and ridiculous little capsules.
Makes you think, he reflected. The destiny of all life, forever, was in our hands. And we never knew it. Probably would have scared us to death if we had.
For if we’d failed, if we’d turned ourselves to piles of radioactive ash, there would now be no life, no mind, anywhere.
Gravitational tweaks by Earth and Venus gradually wore away the asteroid’s energy, and its orbit diminished. The process took a hundred million years.
At last, the asteroid with its fragile cargo settled into a circle, a close shadow of Earth’s orbit. Its random walk across the solar system was complete.
The inhabitants adapted. They even flourished, here in the warmer heart of the solar system.
For a time, it seemed that a long and golden afternoon lay ahead of the refugees within the rock. Once more, they forgot what lay beyond the walls of their world …
But there seemed to be something in the way.
Scale: Exp 6
We have an assignment for you.
He came swimming up from a sleep as deep as death. He wondered, in fact, if he was truly in any sense alive, between these vivid flashes of consciousness.
… And Earth, ocean-blue, swam before Ra, a fat crescent cupping a darkened ocean hemisphere, huge and beautiful, just as he’d seen it from a Shuttle cargo bay.
In his vision there was water everywhere: the skin of Earth, the droplet body of Ra-Shalom, and in his own eyes.
We have an assignment for you. A mission.
‘What are you talking about? Are you going to push this damn rock out of the way? I can’t believe you’ve let it go this far.’
This has happened before. There has been much apoptosis.
‘Hell, I know that …’
He looked up at a transformed sky.
Everywhere now, the stars were green.
There was old Rigel, for instance, one of the few stars he could name when he was a kid, down there in Orion, at the hunter’s left boot. Of course all the constellations had swum around now. But Rigel was still a blue supergiant, sixty thousand times more luminous than the sun.
But now even old Rigel had been turned emerald green, by a titanic Dyson cloud twice the diameter of Pluto’s orbit.
Not only that, the people up there were starting to adjust the evolution of their giant star. Rigel only had a few million years of stable life – compared to Sol’s billions – before it would slide off the Main Sequence and rip itself apart as a supernova.
But the people up there were managing Rigel, managing a goddamn supergiant, deflecting its evolution into realms of light and energy never before seen in the history of the universe. And that emerald colour, visible even to a naked archaic human eye, was the symbol of that achievement.
It was a hell of a thing, a Promethean triumph, monkey paws digging into the collapsing heart of a supergiant.
Nobody knew how far humans had got from Earth, or what technical and other advances they had achieved, out there on the rim. But if we don’t have to fear supernovas, he thought, we need fear nothing. We’ve come a long way since the last time I climbed into the belly of a VentureStar, down there at Canaveral, and breathed in my last lungful of sea air …
… an assignment, the Weissmans were saying to him.
Earth swam close, and was growing closer.
We want to right the ancient necrosis as far as we can. We want you to help us.
‘Me? Why me?’
It is appropriate. You are an ambassador from exponent zero. This is a way of closing the loop, in a sense. The causal loop. Do you accept?
‘I don’t know what you’re talking about. I accept. I don’t know what you mean …’
… The walls of the hab module dissolved around him. Suddenly he didn’t have hold of anything, and he was falling.
Oh, shit, he thought.
But there were