Stephen Baxter - Space

He started talking about how he had traveled here.

“They put me through a whole series of Saddle Point jumps, taking me across the geography of the Galaxy… First I headed toward Scorpio. Our Sun is in the middle of a bubble in space, hundreds of light-years across — did you know that? A vacuum blown into the galactic medium by an ancient supernova explosion. But the Saddle Point leaps got longer and longer…”

With the Sun already invisible, he had been taken out of the local bubble, into a neighboring void the astronomers called Loop One.

“I saw Antares through the murk,” he said, “a glowing red jewel set against a glowing patch of sky, a burst of young stars they call the Rho Opiuchi complex. Hell of a sight. I looked back for the Sun. I couldn’t find it. But I saw a great sheet of young stars that slices through the galactic plane, right past Sol. They call that Gould’s Belt, and I knew that was where home was.

“And when I looked ahead, there was a band of darkness. I was reaching the inner limit of our spiral arm, looking into the rift between the arms, the dense dark clouds there. And then, beyond the rift, I arrived here — in this place, with the Neandertals…”

“And the stars.”

“Yes.”

While she slept, the stars had continued to migrate. Now they had all swum their way up toward that Sagittarius Arm horizon, the way Malenfant said they were heading. The opposite horizon looked dark, for all its stars had fled. All the stars in the sky, in fact, had crowded themselves into a disc, centered on a point some way above the brighter horizon — at least she guessed it was a disc; some of it was below her horizon. And the colors had changed; the stars had become green and yellow and blue.

Now, in what situation would you expect to see the stars swimming around the sky like fish?

“This is the aberration of starlight, isn’t it, Malenfant? The distortion of the visible universe, which you would see if—”

“If you travel extremely quickly. Yes,” he said softly.

She understood the principle. It was like running in the rain, a rain of starlight. As she ran faster, the rain would hit her harder, in her face, her body. If she ran extremely fast indeed, it would be as if the rain were almost horizontal…

“We’re on a starship,” she breathed.

“Yeah. We’re moving so fast that most of the stars we see up ahead must be red giants, infrared sources, invisible to us in normal times. All the regular stars have been blue-shifted to invisibility. Wherever we’re going, we’re traveling the old-fashioned way: in a spaceship, pushed up to relativistic speeds. And we’re still accelerating.”

She sat up and dug her fingers into the grass. “But it doesn’t feel like a starship. Where is the crew? Where are we going? What will happen when we get there?”

“When I found you, I hoped you were going to tell me.” He got to his feet. “What do you think we should do now?”

She shrugged. “Walk. There’s nothing to stay for here.”

“Okay. Which way?”

She pointed to the glowing Sagittarius Arm horizon, the place the stars were fleeing, their putative destination.

He smiled. “And add a couple of kilometers an hour to our eighty percent of light speed? Why not? We’re walking animals, we humans.”

Malenfant picked up a sack that turned out to contain his ancient space suit, the wreck she had spent hours fixing up on the Cannonball. Obeying some obscure impulse for tidiness, he scuffed over his dirt-scraped star map. Then they set off.

They passed the Neandertal family, who sat just where they had yesterday.

When Madeleine looked back, the Neandertals were still sitting, unmoving, as the humans receded and the stars flowed overhead.

The next time she woke, there was only a single source of light in the sky. It was a small disc, brighter than a full Moon, less bright than the Sun seen from Earth, tinged distinctly bluish.

Aside from that the cloudless sky was utterly empty.

Malenfant was standing before her, staring at the light. Beyond him she could see Neandertals, a family group of them, standing too, staring into the light, their awkward heads tipped back. Shadows streamed from the light, shadows of people and trees, steady and dark.

She stood beside Malenfant. “What is it? Stars?”

He shook his head. “The stars are all blue-shifted to invisibility. All of them.”

“Then what—”

“I think that’s the afterglow.” The background heat of the universe, left over from the Big Bang, stretched to a couple of degrees above absolute zero. “We’re going so fast now, just a tad lower than light speed, that even that has been crumpled up by aberration, crushed into a tiny disc. Some spectacle, don’t you think?” He held his hand up before him, shading the universe-Sun; she saw its shadow on his face. “You know, I remember the first time I left Earth, en route to the Saddle Point. And I looked back and saw the Earth dwindle to a dot of light smaller than that. Everything I’d ever known — five billion years of geology and biology, of sliding continents and oceans and plants and dinosaurs and people — all of it was crammed into a splinter of light, surrounded by nothing. And now the whole damn universe, stars and galaxies and squabbling aliens and all, is contained in that little smudge.”

He told her he thought they were riding an antimatter rocket.

“…It explains what the Gaijin were doing on Io, tapping the energy of Jupiter’s magnetosphere. Probably turned the whole moon into one big atom smasher, and picked the antimatter out of the debris.” The antimatter rocket could be a kind called a beam-core engine, he speculated. “It’s simple, in principle. You just have your tanks of atoms and antiatoms — hydrogen, probably, the antistuff contained in a magnetic trap — and you feed it into a nozzle and let it blow itself up. The electrons make gamma rays, and the nuclei make pions, all high energy stuff. Some of the pions are charged, so that’s what you throw out the back as your exhaust… There are other ways to do it. I don’t imagine the Gaijin have a very advanced design.”

“It must have taken the Gaijin a long time, an immense project, to assemble the antimatter they needed.”

“Oh, yeah. Hauling those superconductor cables all the way out from Venus, and everything. Big engineering.”

“But,” Madeleine said deliberately, “there is no way you could haul all of this—” She indicated the plain, the trees. “ — a ship the size of a small moon up to relativistic speeds, all the way to the Galaxy core. Is there?”

He looked into the sky. “I saw a study that said you would need a hundred tons of antimatter to haul a single ragged-assed astronaut to Proxima Centauri. At the time it would have taken our biggest atom smasher two centuries to produce so much as a milligram. I doubt that whatever the Gaijin built on Io was so terribly advanced over that. So — no, Madeleine. You couldn’t haul a small moon.”

She studied her hand, pinched the flesh. The pinch hurt. “What are we, Malenfant? You think we’re some kind of simulations running inside a giant computer?”

“It’s possible.” His voice contained a shrug, as if it didn’t matter. “It only takes a finite number of bits to encode a human being. That’s because of uncertainty, the graininess of nature… If not for that, the Saddle Point gateways wouldn’t be possible at all. On the other hand—” He dug into the ground until he came up with a stone the size of his thumbnail. “ — if the universe was the size of this rock, then each star would be the size of a quark. There are orders of magnitude of scale, structure, beneath the level of a human. Maybe we’re real, but shrunken down somehow. Plenty of room down there.”