Solaris Rising (47 page)

But even this wouldn’t last forever.

Why had we come?

It was simple, really. We knew something, a single cosmic truth, one that we had discovered through patient scientific observation. It was one of the oldest pieces of information known to the species, something so elementary, so easily grasped, so familiar to any child, that it seemed self-evidential.

Before the Commonwealth, before our emergence into space, our ancestors had peered into the night sky. They mapped the starry whirlpools of other galaxies, at first mistaking them for nearby nebulae, formations of spiralling gas. Later, their instruments had shown them that galaxies were in fact very distant assemblages of stars, countless billions of them. And these galaxies were located far beyond our own Milky Way, out to the horizon of observations, out to the very edge of the visible universe. They were also receding. Their light was shifted into red, evidence of a universal cosmic expansion.

Backtracking this expansion, our ancestors deduced that the universe must have emerged from a single dimensionless point of spacetime, less than fourteen billion years ago. With a singular absence of poetry they labelled this birth event the Big Bang.

Quite a lot has happened since that discovery. We have settled interstellar space and spread our influence through a wide swathe of the galaxy. Our science is vastly more sophisticated. We don’t think of the birth event as a ‘bang’ at all, or even an ‘event’ in the accepted sense. But we continue to preserve the notion that our universe was once infinitely small, infinitely dense, infinitely hot, and that there is no sense in which anything can be said to have happened ‘before’ this eyeblink epoch.

Our Earthbound ancestors made this discovery using telescopes of glass and metal, recording spectral light onto silvery plates activated by crude photochemistry. That they were able to do it at all is a kind of miracle. Of course, it’s much, much simpler now. A child, with the right demands, could reveal this truth of cosmic expansion in a single lazy afternoon. The night sky is still aspray with galaxies, and each and every one of them still feels that tug of cosmic expansion.

There’s a catch, though. The galaxies aren’t just rushing away from each other, like the blasted fragments of a bomb. If they were, then their mutual self-gravity would eventually retard the expansion, perhaps even bring the galaxies crashing in on each other again.

Instead, they’re speeding up. Eight billion years into the universe’s life, something began to accelerate its expansion. Our ancestors called this influence ‘dark energy’. They measured it long before they had even the sketchiest understanding of what might be motivating it. Our understanding of the underlying physics would be unrecognisable to them, but we still honour their name. And dark energy changes everything. It’s the reason we came to this miserable and desolate point in space, around a dense dead star that will soon leave the galaxy altogether.

It’s the reason we came to leave Vashka’s message, engraved into the crust of a world made of star-fired diamonds.

I circled
Sculptor
, taking care to keep away from the banks of gamma-ray lasers that were even now etching Vashka’s patterns. The ship’s orange peel orbit brought it over every part of Pebble eventually, the lasers sweeping like spotlights, and when we were done there would be no part of the planet’s surface that hadn’t been touched. The lasers took the raw diamond of her crust, melting and incinerating it to leave elegant chains of symbolic reasoning, scribed from the sky in canyon-wide lines. The chains of argument formed a winding spiral, quite distinct from the surface track of our orbit. That spiral converged on a single spot on the planetary surface, the entry point to a cavern where the entire statement had been duplicated for safekeeping.

In truth we were finished; had been so for many orbital cycles. What
Sculptor
was doing now was completing the tidying-up exercise after another uplink from home. We were finishing off the ninth draft, and now home wanted us to begin again on the tenth.

We’d left the Commonwealth with what appeared to be a complete, self-consistent statement of physics and cosmology, encoded in terms that ought to be decipherable by any starfaring intelligence. But by the time
Sculptor
arrived, the eager minds back home had had second thoughts. A tweak here, an edit there. The first and second drafts had been simple enough, and there’d been no cause for concern. But by the time we were on the fifth and sixth edits, some of us were having qualms. The changes were progressively more sweeping. We’d had to begin almost completely from scratch – lasering the planet back to a blank canvas before starting over, changing our story. As fluent with physics as I was, the level of encoding had long ago slipped beyond my ready comprehension. I had to take Vashka’s word that this was all worthwhile. She seemed to think it was.

But then she would, wouldn’t she? This entire project was Vashka’s idea. Always a perfectionist, she wasn’t going to settle for second best.

The problem was that we couldn’t stay here forever. Which was where my own narrow expertise came in.

For thousands of years we’ve been crossing interstellar space using momentum-exchange drives – long enough that it’s easy to think that the technology is routine and safe. For the most part, that’s exactly what it is. Give or take a few tens of kilometres per second, the stars and planets of the Commonwealth are all co-moving in the same spiral arm, travelling at the same speed with respect to the galactic core. Interstellar transits proceed without incident. We steal momentum from the universe, but we give it back before the universe gets irritated. The net momentum deficit between a ship starting its journey around one star, and the same ship ending its journey around another, is close enough to zero to make no difference. Momentum – and by extension kinetic energy – has neither been created nor destroyed.

But that’s not true here. Because the Pebble and its pulsar are hurtling away from the galaxy at twelve thousand kilometres per second, we haven’t actually
stopped
. We started off at zero relative to the Commonwealth, and we’re still travelling at a good clip away from it.

Which means that a momentum debt is still waiting to be repaid.

The engines were a dull red when we arrived, but with each day that we
delay
paying that debt, they glow a little more intensely. That’s the universe reminding us, in an accumulation of microscopic thermal fluctuations, that we owe it something.

Leave it long enough, and the antimomentum cores will undergo catastrophic implosion.

But that wasn’t going to happen today, or tomorrow, or for months in the future. As much as I’d hoped to find some problem or trend that could be used to justify our early departure, nothing was amiss. The cores were progressing according to expectations. Loimaa’s thousand days might be a stretch too far, but I had to admit that we were good for at least the next two or three hundred. And if and when the cores started deviating, I’d be able to give Captain Reusel plenty of warning.

That didn’t mean I felt easy about it.

Yet I’d turned things over in my head long enough, and knew that twisting the facts, over-stressing the hazards, wasn’t an option. Reusel would see through that in a flash.

As would Vashka.

My suit picked up a proximity signal. I used the thrusters to spin around, in time to see another suit looping out from behind
Sculptor
. Like mine, it was an upright armoured bottle with manipulators and steering gear. The ident tag told me exactly who it was.

“Come to talk me into lying?” I asked.

“Not at all. I know you better than that, Nysa. You’d never lie, or read anything into the data that wasn’t really there. That would take…” Vashka seemed to trail off, as if her thoughts had carried her in a direction she now regretted.

“Imagination?”

“I was going to say, a streak of unprofessionalism that you don’t have.”

“Yes. I always was the diligent plodder, while you made the wild, intuitive leaps.”

“I didn’t mean it that way.”

“But it’s not too far off the mark. Oh, don’t worry. I’m not offended. It’s basically the truth, after all. I’m very good with fixing engines and making them work a bit better. That’s a rare skill, one worth cherishing. But it can’t be compared with what you’ve done, what you’ve brought into being. No one had ever thought of anything like this before you did, Vashka. It’s all yours.”

“It was a shared enterprise, Nysa.”

“Which wouldn’t have happened without your force of will, your imagination.”

Vashka took her time in answering. “Until it’s done, and we’re on our way home, there are more important things to think about than credit and glory.”

“Well, I’ve good news for you. My report will conclude that proceeding with the tenth draft is an acceptable risk. And you’re right. It never occurred to me to bend the facts.”

“I’m… happy,” Vashka said, as if she feared a trap in my words.

“It won’t be perfection,” I added. “It’ll be a step in that direction. But don’t delude yourself that this is the end. As soon as we’re back on Pellucid, you’ll be wishing you changed this or deleted that. It’s human nature. Or yours, anyway.”

“Then perhaps I’ll program my stasis berth so that I never wake up.”

It was a flip response, something that – had it come from anyone else – I’d have been more than willing to dismiss as bravado. But with Vashka, I was prepared to believe quite the opposite. She would easily choose death over living with the knowledge of irreversible failure.

Always and forever.

“I’d best get back inside,” I told her.

The day she first explained it to me we were in our old house, the one we bought together during our time at the academy, the one that overlooked the bay, with the ground floor patio windows flung open to salt-tang sea breezes and hazy morning sunshine. I was doing dance exercises, going through the old motions of stretching and limbering, but still listening to what she said. I’d made the mistake of only half-listening before, nodding in the right places, but from bitter experience I knew that Vashka would always catch me out.

It wasn’t that I didn’t care. But I had my area of obsession and she had hers, and it was increasingly clear that the two only slightly intersected.

“Dark energy is the killer,” she said. “Right now we hardly feel it. It’s making all the galaxies accelerate away from each other, but the effect is small enough that people argued over it for a long time before convincing themselves it was real.” Vashka was standing at the door, doing stretching exercises of her own. Whereas mine were in the service of art, hers served no higher purpose other than the toning of her body, a maintenance routine to keep the machine in working order.

I knew enough about cosmology to ask the easy questions. “The Milky Way’s just one galaxy in the Local Group. Won’t the gravitational pull of nearby galaxies always outweigh the repulsion caused by dark energy?”

Her nod was businesslike, as if this objection was no more than she’d anticipated. “That’s true enough, and most galaxies are also bound into small groups and clusters. But the gravitational pull
between
groups and clusters is much too weak to resist dark energy over cosmological time. At the moment we can see galaxies and galaxy clusters all the way out to the redshift horizon, but dark energy will keep pushing them over that edge. They’ll be redshifted out of our range of view. Nothing in physics can stop that, and there’s nothing we can ever do to observe them, once they’ve passed over the horizon.”

“Which won’t happen for a hundred billion years.”

“So what? That only seems like a long time if you’re not thinking cosmologically. The universe is
already
thirteen billion years old, and there are stars now shining that will still be burning nuclear fuel in a hundred billion years.”

“Not ours.”

“We don’t matter. What does is the message we leave to our descendants.”

She didn’t mean descendants of humanity. She meant the alien beings who would one day supplant us, in whatever remained of the galaxy that far downstream. Carriers of the flame of sentience, if that doesn’t sound insufferably pompous.

“Fine,” I said. “The dark energy pushes all those galaxies out of sight. But the local group galaxies are still bound.”

“That’s irrelevant. For a start, they can’t be used to detect the expansion of the universe, for the same reason that dark energy doesn’t disrupt them – their short range attraction predominates over long range cosmological effects. But it’s worse than that. In six or seven billion years, the local group galaxies will have merged with each other, pulled together by gravity. There’ll just be a single super-galaxy, where once there was the Milky Way, Andromeda, the Clouds of Magellan, all the other galaxies in our group. This isn’t speculation. We’ve seen galactic mergers across all epochs. We know that this is our fate, and we know that the mixing process will erase the prior histories of all the involved galaxies.”

“I accept this,” I said. “But if aliens arise in that super-galaxy, tens of billions years from now, they’ll have billions of years to consider their situation. Our technological science is a few thousand years old. Isn’t it presumptuous of us to assume that they won’t be capable of making the same discoveries, given time?”