Ultima

by Stephen Baxter

  “And now, here on Per Ardua, we’re seeing the same thing over again. How long would it take? How much time has elapsed here since humans arrived? How far into the future have we been projected, ColU? More than millions of years, more than hundreds of millions . . .”

  The ColU simulated a sigh. “I apologize for my reticence. You have asked these questions many times before. I can make only rough guesses based on the data I have so far, the evidence from the geology here, the biology—even from the evolution of the star itself. I will be able to make much more accurate estimates of the date when I see the dark-side sky, and I can gather astronomical data. But of course there is an upper bound.”

  Stef frowned. “An upper bound? How can there be an upper bound on the future—what upper bound?”

  “The End Time,” the ColU said simply.

  That was when Mardina and Chu burst into the camp, scuffed and dusty and breathing hard.

  Mardina said, “You keep saying you want to see the sky, ColU.”

  “Yes—”

  “Well, your luck is in. You can see it from the slope, not much of a climb from here. Chu, get him into his pack.”

  “See what?” Stef demanded. “The stars?”

  Mardina gave her only a quizzical look. “Sort of. See for yourself. Come on! And where’s my mother?”

  • • •

  The four of them, Stef, Chu, Mardina and Beth, stood on a hillside, looking out over the night lands of Per Ardua, over an ocean of dark. Only the faintest reflected glow from the summit above reached them here.

  And above them, in a terminator sky marred for once only by scattered cloud . . .

  Not stars, no, Stef saw. Not just stars. It was a band of light, an oval, an ellipse—no, surely it was a disc tipped away from her, all but edge on. The overall impression was of a reddish color, but bright white sparks were scattered over the pink, like shards of glass on a velvet cushion. There was a brighter blob at the center, and lanes of light sweeping around that core. As eyes adapted to the low light she saw finer detail, what looked like turbulent clouds in those outer lanes, and here and there a brighter spark, almost dazzling. And when she looked away from this tremendous celestial sculpture, she could see stars—ordinary stars, isolated sparks scattered thin, though many of them seemed reddish too. But the sky was dominated by the great ellipse.

  And, oddly, the thing she noticed next was Mardina’s hand slipping into Chu’s, and squeezing tight.

  Stef said sharply. “You know, ColU, you should have warned us about all this.”

  “But I was never sure. I can never lead; I can only advise.”

  “It’s a galaxy,” Beth said, a little wildly. “Even I know that much. Like our Galaxy, the Milky Way . . . But what the hell’s it doing up there? Is it our Galaxy?” She shook her head. “I grew up on Per Ardua, remember, on the day side. I never even saw the stars until I got to Mercury. Has Proxima been—I don’t know—flung out of the Galaxy somehow, so we see it from the outside?”

  “Nothing like that,” the ColU said gently.

  “That’s not our Galaxy at all,” Stef snapped. “That’s Andromeda, isn’t it? Bigger than ours, I think. The two galaxies were the biggest of the local group. Now, when I was a kid playing at astronomy with my father, on the rare nights we had clear skies in Seattle—”

  And, in some realities, with her impossible sister Penny by her side.

  “—we used to look for Andromeda. Fabulous in a telescope, but you could just see it even with the naked eye. A smudge of light. Now that, I would say,” and she started taking rough sightings of the width of the object with her thumb, “is, what, thirty times the apparent diameter of Earth’s sun?”

  “More like forty,” the ColU said.

  Mardina was staring at her. “So how did that thing get so big?”

  “It didn’t. It got closer.” Stef closed her eyes, remembering her own basic astronomy classes from long ago. “In my time Andromeda was two and a half million light-years away. Right, ColU? But even then we could see it was approaching our Galaxy. The two star systems were heading for a collision, which—well, which would be spectacular. Now, as I recall, the best predictions for the timing of that collision were way off in the future. Four billion years or more?”

  “More like four and a half,” the ColU said.

  Stef squinted. “So if that beast, which is around two hundred thousand light-years across, is that apparent size in the sky, I could estimate its current distance—”

  “Done,” the ColU said. “Colonel Kalinski, I now know we have traveled—or rather the Hatches have taken us—some three and a half billion years into the future. That is, after the epoch from which we set out.”

  Beth, Mardina, Chu just stared at each other, and then into the slate hanging from Chu’s neck, as if the ColU’s mind resided there, as if behind a human eye.

  But Stef understood immediately. “Yes, yes. So the collision is still a billion years away—”

  “If it were to happen at all,” the ColU said enigmatically.

  “I wonder what it must have done to cultures that emerged after our own, to have that hanging in the sky. Growing larger century by century. How many religions rose and fell in its light, awed and terrified?”

  “We’ll never know, Stef Kalinski,” the ColU murmured.

  “And, over three billion years—that’s presumably more than enough time for all the processes we’ve seen here on Per Ardua to have come about. For almost every trace of humanity to have eroded away. Even for species from two different star systems to find a way to evolve into one.”

  Mardina looked around the strange sky. “I don’t understand. Three and a half billion years . . . It’s meaningless. Where is Terra? Where’s the sun?”

  “I’m afraid I’m not sure,” the ColU said. “The sun and the Alpha Centauri system, the Centaur’s Hoof, were once near neighbors. But by now they will have wandered far from each other, as the Galaxy has turned on its axis. Earth, Terra, and the other planets will still orbit the sun. But Earth is probably lifeless; the sun, slowly heating, will have sterilized the inner planets—oh, as much as two or three billion years ago. But the aging sun has not yet entered its terminal cycle, the red giant phase when the sun will swell and swallow the inner worlds.”

  Earth lifeless. Suddenly Stef shivered, despite the comparative warmth of her clothing. To be alone on this world was one thing. To be taken out of one reality stream and dumped in another was extraordinary. But to be stranded in a future so remote that Earth was dead, that presumably nothing like the humanity she had known could still survive . . .

  “This is terrifying,” she murmured.

  “Indeed, Colonel Kalinski,” the ColU said.

  Chu was looking around the sky. “I rode on starships,” he said slowly. “I was held in slave pens. But when I passed windows, I glimpsed the skies of many worlds. And this is quite different. I mean, even aside from the approaching star storm, Andromeda. The stars seem more dim, more sparse.”

  “That’s a good observation,” the ColU said. “Even in our time the great ages of star making were ending. Now there are fewer young stars, more aging ones.”

  Chu asked, “And where are the other stars of the Centaur’s Hoof? They should be two brilliant lanterns in the sky.”

  “Even Alpha Centauri has evolved with time,” the ColU said sadly. “Its stars were older than the sun. The brightest of the main pair will have lapsed into its red giant stage perhaps half a billion years ago, sterilizing any worlds in its own system, and its partner’s, before collapsing to a white dwarf—and Proxima will have become decoupled from its weakening gravity field. The lesser of the main pair would have had many billions of years left before it, too, entered its terminal phase. Smaller stars last longer. Proxima, the runt of the litter, would likely have lasted for six trillion years before running out of its
carefully processed hydrogen fuel. But Proxima, now, is alone.”

  “You say would,” Stef said. “Would have lasted trillions of years. And you seemed remarkably precise in your estimate of the date, given only a cursory look at this sky above us—”

  “As I told you, I do have more information,” the ColU said. “About the future of the universe, gathered during the long years of my journey home to Earth in the Malleus Jesu. Subtle signs of times to come: evidence of titanic future events, smeared across the sky of the present. Events whose date I was able to estimate. Once I saw that Andromeda was so close, once I realized roughly what epoch this is, it was easy to deduce that they would have brought us, not to some arbitrary earlier point, but to this point in time. This most special time of all. With more observation, especially of the cosmic background radiation, I will be able to be more precise still—”

  “They,” Stef snapped. “They brought us here. You mean the Hatch builders. Who Earthshine called the Dreamers.”

  “The Dreamers—yes.”

  Chu asked now, “And what is so special about this time, this future, this age?”

  “Nothing.” The ColU sighed. “Nothing, save that it is the last age of all.”

  “The End Time,” Stef said.

  She saw Mardina place her hand on her belly, over her unborn child.

  That was when Titus and Clodia came clambering up the slope. “Here you are. Camp discipline: leave a note before you all clear off next time.”

  Beth said, “We’re stargazing. Looking at that.” She pointed up at Andromeda.

  Titus snorted. “Who cares about lights in the sky? I’ve got something much more important to show you. Come see what we found!”

  66

  It was a walk of around three kilometers—two of Titus’s Roman miles.

  They came down off the flank of the mountain and made their way along a dry, shadowed valley. The going was easy, even for Stef, who had walked little save around one campsite after another since the expedition set off. Titus and Clodia both carried torches of dry stems bundled up and dipped in pots of marrow; they burned, if fitfully. But the glow from Andromeda was surprisingly bright, especially from that brilliant central core. Billions of suns in lieu of moonlight, Stef thought idly.

  And, as Titus had predicted, when she came to the structure Titus and Clodia had found, Stef too forgot the wonders of the sky. She even forgot, for a while, the ColU’s dark and still obscure mutterings about the End Time.

  It was another ellipse, tilted like Andromeda in the sky—but this one, much longer than it was wide, was cut into the ground. And as Stef approached the cut she saw that in fact she was looking into a circular tube, a cylinder—no, a tunnel; it was big enough to be called that—several meters in diameter, that slid into the ground at a shallow angle, making this elliptical cross-section where it met the flat ground surface.

  The ColU had his bearer, Chu, walk around this formation, studying it closely.

  But Titus warned them all sternly not to step into the tunnel, onto the smooth, curved interior. “We were wandering around at random, hoping to find a convenient river or some such to carry us further on our way . . . Then we found a kind of way marker. Solid granite, and barely eroded.”

  “We are all but beyond the terminator weather here,” the ColU said. “Weathering, erosion, will be slow. The marker, like this structure, could be extremely old.”

  “Well, the marker had a distinctive arrow; you couldn’t mistake its meaning. Which led us straight to this.”

  “Remarkable,” the ColU said. “Remarkable. And for us to have happened on such a structure so close to where we crossed the terminator—it cannot be chance; the cold side of this world must be laced with such constructs.”

  “I don’t understand,” said Stef. She walked closer to the ellipse lip. “I see a tunnel.” She glanced back at their mountain for reference. “Pointing pretty much southeast—that is, away from the substellar—”

  “And directly toward the antistellar,” the ColU said.

  “A tunnel sloping down at a pretty shallow angle.” She took Clodia’s torch and held it up. The tunnel continued dead straight, into the ground, beyond the glow cast by the flickering torch. “Some kind of transport system?”

  Titus grinned. “You philosophers haven’t spotted the most interesting thing about it. I told you to stay off the surface. Why? Because it is perfectly slippery—less friction than the smoothest ice, I would say. Though I can tell you it is no colder than the rest of the world—I touched it with my hand; I dared that. But if you were to step on it—” He took a pebble and set it carefully on the sloping surface of the cylinder. It seemed to rest still, just for a moment, and then began to slide into the mouth of the cylinder, picking up speed gradually until it disappeared into the shadows. “See?” Titus grinned. “You would fall on your backside and you would slither off out of sight, forever.”

  “Not forever,” the ColU said. “Titus, I daresay you’ve tried this experiment a few times. When exactly did you drop your first rock down this shaft?”

  “Actually it was a spare torch. I wanted to see how far it extended . . .”

  They compared times. Titus always kept a careful check on times when marching or scouting. He had dropped the torch about an hour and fifteen minutes earlier.

  “Good,” said the ColU. “We won’t have long to wait.”

  Stef frowned. “Wait for what? This enigmatic manner of yours is irritating, ColU.”

  “I’m sorry. When I was a mere farm machine, you know, people rarely listened to my speculations—”

  “Spill it, tin man.”

  “Colonel Kalinski, I think this is a gravity tunnel. It’s an old idea, dating back to contemporaries of Newton.”

  “Never mind the history lesson. Just tell us.”

  “Imagine a tunnel dug through the ground, in a dead straight line between two points on a planet’s curving surface. The tunnel is straight, but you can see that it will seem to dive down into the ground at one point, and then climb up again at the destination.”

  Stef nodded. “I get it. So if you line the tunnel with a frictionless surface, and climbed on a sled—”

  “You would slide down into the ground, reaching some maximum speed at the midpoint of the tunnel, until slowing to the other end. It would feel as if you had descended a slope and climbed another, but in fact you would have followed the tunnel’s straight line all the way. Do you see, Stef Kalinski? The passage is energy free, once the tunnel is cut. Powered by gravity alone. And if you built a network of tunnels, and made them durable enough—”

  “You’ve built a transport system that could last a billion years.” Stef grinned at the audacity of it. “All but indestructible, and free. I love it. So the people who built this, whether they were our descendants or not, must have been pretty smart.”

  The ColU said, “They may not have been people at all. This is Per Ardua. Remember we had evidence that there was a builder Culture that achieved planetary engineering. Maybe this is somehow a legacy of that.”

  Titus was frowning. “I am trying to work this out. So my torch will have slid along this tunnel to the terminus. And then, with nobody to collect it—or so I presume—it will have started to slide straight back again. You say we must wait only a few minutes, ColU. Do you mean until my torch returns? But how can you know that? You don’t know how long this tunnel is . . .”

  “It doesn’t matter,” the ColU said. “It’s an odd quirk of physics. The time the journey takes only depends on the density of the planet, the gravitational constant . . . Even if you could cut a tunnel right through the center of the planet—”

  “Which would have been handy getting from substellar to antistellar,” Stef said drily.

  “Even then, though you’d have reached much higher speeds at the midpoint, the journey time there and back wou
ld be the same.”

  Titus said, “All this sounds like philosophical trickery to me. And how long is this magic transport time you predict, O glass demon?”

  The ColU said, “Just wait . . . About this long.”

  And, right on cue, a bundle of reeds came sliding up out of the mouth of the tunnel. As it slowed to a halt, Titus carefully reached down and swept it up with his one good hand. “Ha! A fine trick, demon. But now we have some planning to do. Come! Let us return to camp.”

  • • •

  The first trip through the gravity tunnel, Titus decreed, was to be made by sled, Beth’s cart, with the runners they had made to replace the axles and wheels on the undersurface. Of course they had anticipated having to drag the cart over farside ice, but Stef could see that this arrangement ought to work even better in the frictionless tunnel.

  So they wheeled the cart the couple of miles to the tunnel mouth, established a temporary camp, spent a day fixing up the cart with its sled rails. They ate and slept, according to Titus’s stern orders.

  Titus decreed that the first to take a trial trip through the tunnel would be himself with his daughter Clodia—and the ColU and Stef, who might be able to interpret the experience, and what they found on the far side. The pregnant Mardina, the baby’s father, Chu, and prospective grandmother Beth, would not be split up come what may; they would be staying behind.

  They were evidently going to have to do some fancy work getting the crew loaded on at one end of the tunnel, and successfully off at the other before the sled started to fall back, without any outside help. Before they hauled the cart over to the tunnel Titus had them practice the art. They had most success with Titus and Clodia leaping out at the destination, carrying rope to tie up the cart, while Stef stayed in the cart cradling the ColU.

  Then the cart crew bundled up in their warmest gear—they were after all going an unknown distance deeper into the chill of farside—and loaded food, water, blankets, material for a fire, and a few of their precious tools, onto the cart itself. Beth, Mardina and Chu had an easy enough time pushing the cart over the lip of the sloping tunnel, and held it steady while the passengers climbed aboard.