Ultima

by Stephen Baxter

  Then Titus ceremoniously lit a torch and held it aloft. “Onward, and into the unknown!”

  The support crew let go of the cart. Slowly, almost imperceptibly, it began to slip down the slope.

  Stef glanced back at the grinning, somewhat anxious faces of her companions. “It’s taking an embarrassingly long time to get going,” she said. “I feel like the King of Angleterre in his coronation carriage.”

  “We will be in the dark soon enough,” the ColU said. “But remember, even if the torch were to fail, it is only forty minutes to complete the one-way trip to the far end.”

  Now the mouth of the tunnel was all around them, swallowing them up, their speed gradually increasing. The dark was deepening now. The movement was utterly smooth, and entirely silent.

  Stef felt a frisson of fear. “It’s like a roller-coaster ride. Magic Mountain at Disneyland. None of you have the faintest idea what I’m talking about, do you?”

  Titus, cradling his torch with his burly body, was suspicious. “I don’t understand. We are moving quite rapidly already. And yet there is not a breath of wind.”

  “As I anticipated,” the ColU said smoothly.

  Stef snarled, “What now, ColU? I wish you’d be open with us.”

  “I apologize, Colonel Kalinski. There could be no air resistance in here. Otherwise, you see, the friction would slow us; we might pass the midpoint but would not reach the tunnel end, and would slip back, eventually settling at the center, the lowest point. Human engineering designs based on this idea always imagined a vacuum tunnel.”

  Titus took a deep breath. “We’re in no vacuum.”

  “I think there is an invisible subtlety to the design. The air we breathe is carried with us—perhaps the tunnel air is held aside. Given time, Stef Kalinski, you and I could no doubt investigate the engineering. Whatever the detail, it must be robust to have survived a billion years . . .”

  The dark was deep now. They didn’t seem to be moving at all, and Stef soon lost track of time. In the light of the torch, Clodia cuddled closer to her father.

  Stef, unable to resist it, moved closer to the big Roman too.

  Titus said, “I am sorry I do not have a hand for you to hold, Stef.”

  She clutched his stump of an arm and rested her head on his shoulder. “This will do.”

  “It won’t be long,” the ColU murmured, from the dark. “Just forty minutes. Not long.”

  • • •

  They emerged on an icebound plain.

  Stef walked a few steps, away from the tunnel mouth and the disgorged cart. She swung her arms, breathing in deeply; the cold stung her mouth, and her breath steamed. “This is the far side, all right. Just the way I remember it.”

  She looked around. Andromeda still hung huge and looming in a crystal-clear sky; there wasn’t a shred of terminator-weather cloud here. In the crimson galaxy light, the land seemed featureless, flat. But there was a peculiarly symmetrical hillock in the ice a few hundred meters away, like a flattened cone, or a pyramid with multiple flat sides—or like a tremendous jewel, she thought. Could it be artificial? There was no other feature in the landscape to draw her eye.

  She walked that way, trying to place her booted feet on ridges in the ice to avoid slipping.

  Inevitably Titus called after her. “Don’t go too far!”

  She snorted. “I’m hardly likely to have marauding barbarians leap out at me, legionary.”

  “You might slip and break your brittle old-lady bones. And with my single arm it would be a chore for me to have to carry you back to the cart and haul you home.”

  “I’ll try to be considerate.”

  The ColU called, “In fact, Colonel Kalinski, would you mind carrying my slate for a closer inspection? And if you could find a way to bring back a sample of that formation . . .” With surprising grace on the ice, Clodia jogged out to hand Stef the slate, and a small hammer from their rudimentary tool kit.

  As Stef approached the pyramidal structure, she listened to the ColU’s analysis.

  “I can deduce our change in position quite clearly from the shift in the visible stars’ position. Andromeda has shifted too of course, but that is too large and messy an object to yield a precise reading . . .”

  The closer she got, the less like a geological formation the pyramid seemed. It was too precise, too sharply defined for that. She supposed there might be a comparison with something like a quartz crystal. But she had an instinct that there was biology at work here, something more than mere physics and chemistry. She took panoramic and close-up images. The pyramid looked spectacular and utterly alien, sitting as it was beneath a sky full of galaxy. Then she bent to chip off a sample from one gleaming, perfect edge.

  Titus called, “How far have we traveled then, glass demon?”

  “Not very far at all, Titus Valerius. Only a hundred kilometers—just a little more. That’s perhaps sixty Roman miles. Not very far—but that means we were never very deep under the surface. Two hundred meters at the lowest point, perhaps.”

  With her sample of what felt like water ice tucked into an outer pocket, Stef headed carefully back to the group.

  “Not very far, as you say, demon. But we know this tunnel is not the only one of its kind in the planet.”

  “Quite so, legionary. There will be many such links, perhaps a whole network, perhaps of varying lengths.”

  “Yes. And a way for us to go on, deeper into the dark. There must be another entrance close by—all we need do is find it. And then—”

  “And then we can proceed in comparative comfort, if we’re lucky, all the way to the antistellar,” said the ColU. “For that central locus must be a key node of any transport network.”

  Stef had got back to the cart, within which the ColU sat, bundled against the cold. “You want me to put some of this sample in your little analysis lab?”

  “Yes, please, Stef Kalinski. Titus Valerius, let us consider. If this length of tunnel is typical, at sixty miles or so, and if we have a journey of less than six thousand Roman miles to complete to the antistellar—”

  “We’ll need a hundred hops. And if each hop takes us two-thirds of an hour, as you said, that will take, umm . . .”

  “Sixty, seventy hours,” Stef said. “I always was good at mental arithmetic. Even allowing for stops, and for hauling the cart between terminals, that’s only a few days.”

  “It may be hard work,” Titus said. “But we will not freeze to death, or starve, or die of thirst on the way.” He nodded. “Excellent! But you know, Stef, I, Titus Valerius, anticipated that we would find some such fast road as this.”

  “You did? How?”

  “Because, if not, we would have encountered Ari Guthfrithson and the Inca woman walking back the other way. Would we not? For if we could never have mastered this world of ice on foot, and I suspect that is true, they could surely not. Clever fellow, aren’t I, for a one-winged legionary? Now then—Clodia, come with me. We will do a little scouting before we return. Let’s see if we can find the terminal of the next link, somewhere in the direction of the antistellar . . .” He glanced up at the sky, taking a bearing from Andromeda. “That way. Come now! And you, Stef Kalinski, you and your old-lady bones stay put in this cart.”

  “With pleasure, legionary.”

  As they walked away, she heard father and daughter laughing.

  “It’s good to hear them happy,” Stef said. “Suddenly a journey that did look impossible has become achievable.”

  “You too should be happy,” the ColU whispered.

  “I should?”

  “For the discovery you have just made.”

  “What discovery? The pyramid?”

  “It’s no pyramid, Stef Kalinski. It’s nothing artificial, and nor is it a merely physical phenomenon, as I’m sure you guessed. It is life, Stef Kalinski. Life. An ambas
sador, perhaps, from a colder world than this . . .”

  As they sat huddled together in the cart, the ColU spoke of Titan, moon of Saturn.

  • • •

  Titan was a mere moon, a small world subsidiary to a giant, but a world nevertheless—and a very cold one. Its rocky core was overlaid by a thick shell of water, a super-cold ocean contained by a crust of ice as hard as basalt was on Earth. And over that was a thick atmosphere, mostly of nitrogen, but with traces of organics, methane, ethane . . .

  “But it is those organic traces that made Titan so interesting,” the ColU said. “On a land of ice rock, where volcanoes belch ammonia-rich water, a rain of methane falls, carving river valleys and filling seas. And in those seas—”

  “The probes found life. I remember the reports. Some kind of slow-moving bugs in the methane lakes.”

  “Yes, life based—not on carbon, as ours is—but on silicon. Just as carbon-carbon bonds, the backbone of your chemistry, Stef Kalinski, can be made and broken in room-temperature water, so silicon-silicon bonds can be made in the cold methane of Titan’s lakes. A form of life not so very unlike ours superficially, but with a different biochemistry entirely—and very slow moving, low in energy, slow to reproduce and evolve. We found nothing but simple bugs on Titan, simpler than most bacteria—not much more complicated than viruses.

  “But Titan is not the only cold world. Here at Proxima, while the Earth-like Per Ardua was the planet that caught all the attention—”

  “Ah. Proxima d.”

  “Yes. It was a Mars-sized world just outside the zone that would have made it habitable for humans, like Per Ardua.”

  “So far as I know it was never even given a decent name. Nobody cared about it—or the other Proxima worlds.”

  “They did not. But it was very like Titan—another common template for a world, it seems. And room for another kind of life.

  “Stef Kalinski, Earthshine has spoken of a panspermia bubble, of worlds like Earth and Per Ardua linked by a common chemistry carried by rocks between the stars, worlds with cousin life-forms. But there could be other bubbles, worlds with different kinds of climate, different kinds of biochemistries, yet linked in the same way. Maybe one bubble could even overlap another, you see—for clearly a stellar system may contain more than one kind of world.”

  Stef was starting to understand. “You always speak in riddles, ColU, whether you intend to or not. But I think I see. The sample I brought you—”

  “The pyramid-beast over there has a silicon-based biochemistry very similar to that recorded on Titan, but not identical. Maybe it is a visitor from Proxima d, do you think? Somehow hardened to withstand what must be for it a ferocious heat, even here on Per Ardua’s dark side. As if a human had landed on Venus. But it is here, and surviving. And with more time still . . .”

  “Yes, ColU?”

  “Stef Kalinski, we have seen that, given billions of years, life-forms from across the same panspermia bubble can integrate, grow together.”

  “The Earth ants in the Arduan stromatolite.”

  “Exactly. Now, is it possible that given tens of billions, hundreds of billions of years, even different kinds of life could mix and merge? Your fast, quick kind, and the slow-moving Titanian over there? Could that be the next stage in the evolution of the cosmos itself? You already share a world, you see.”

  “It’s a fantastic thought,” she said slowly. “But it’s never going to happen. Is it, ColU? Because this is the End Time, according to you. There will be no tens or hundreds of billions of years—”

  “I’m afraid not, Colonel Kalinski. Here on the dark side I have been able to make quite precise assays of the sky: the state of the stars, the proximity of Andromeda—even the background glow of the universe as a whole, which contains warp-bubble clues to its future.”

  “Hmm.” She looked up into the dark. “Well, it is marvelous seeing, for an astronomer. And you’ve come to a conclusion, have you?”

  “I have. And a precise estimate of the time remaining.”

  Stef felt chilled, as if she’d been given bad news by a doctor. “You’re going to have to explain all this to the others, you know. In language they can understand.”

  “Yes, Colonel Kalinski. Of course. And the importance of finding Earthshine soon, by the way, is only increased.”

  Stef could hear the others returning, father and daughter laughing, full of life and energy. And she looked across at the silicon-life explorer from Proxima d, the ice giant. “I wonder if that thing can see us . . . Just tell me,” she said. “How long have we got?”

  “A year,” the ColU said flatly. “No more. The data’s still chancy.”

  And Stef immediately thought of Mardina, and the baby.

  She pursed her lips and nodded. “A year, then. For now, not a word. Come on, let’s get ready to go on.”

  67

  The party gradually penetrated deeper into the cold of the Per Ardua farside.

  The forty-minute tunnel hops all felt much the same to Beth, but in the short intervals during which they trekked from one tunnel exit to the entrance of the next, always following trails carefully scouted out by Titus with Clodia or Chu, Beth did get glimpses of parts of her world she had never seen before. After all, during the years she’d spent growing to a young adult on Per Ardua, she had never gone farther than the tall forests that screened the terminator zone.

  Stef and the ColU had made such a journey as this once before, with Beth’s father and Liu Tao, in a purloined ISF rover. That party had followed a more or less direct course to the antistellar, cutting over the ice surface of a frozen ocean. The gravity tunnels, however, naturally enough, stuck to continental land, detouring around the shores of frozen oceans. As a result the journey was longer than a direct route, and was taking longer than the handful of days that Titus and the ColU had first estimated—but still it would be brief enough.

  And while Stef in that earlier party had spent mind-numbing days crossing geometrically perfect ice plains, now Beth saw more interesting features. Eroded mountain ranges from which glaciers spilled like huge, dirty tongues. Places where earthquakes or other geological upheavals had raised and cracked the ice cover, creating frozen cliffs that gleamed a deep blue in the light of their torches.

  Yet even these features were probably impressively old, the ColU said. There would always be a lot of weather activity at the terminator, where the warm air and water from the day side spilled into the cold of the night. But here in the dark, weather would always be desperately rare: no clouds, no fresh falls of snow or hail. Even meteor impacts would be infrequent in such an elderly system as this, with much of the primordial debris left over from the planets’ formation long since swept up. So they drove across a sculpted but static landscape—and a landscape bathed in the complex, red-tinged light of an aging Andromeda.

  Sometimes they saw more “Titanians,” enigmatic, sharp-edged pyramids standing like mute monuments. But the ColU assured them that the Titanians, in their way, on their own timescale, could be exploring just as vigorously as the humans.

  Beth noticed, however, that Stef barely glanced at the sky, or the icebound landscape, or even the Titanians. As they traveled, and in the “evenings” as they rested, Stef sat huddled with the ColU at the back of their sled-cart, or in a corner of their shelter, talking softly, Stef making occasional notes on the glowing face of her slate. Everybody knew what they were discussing: the ColU’s ideas about the fate of the world. Beth tried to read Stef’s expression. There was nothing to be discerned from the ColU’s neutral tone.

  At last, one evening, after they had cleared away their meal, with them all bundled in their warmest clothes, their feet swathed in layers of socks, gathered around the warmth of the kernel stove, Stef announced that they needed to talk about the End Time.

  “In a way,” Stef began cautiously, “the idea that the world
will have an end—that the universe itself will end, and relatively soon—ought to feel natural to us.

  “We have no direct experience of infinity, of eternity. Our own lives are short. And the scientists in my Culture proved quite definitively that eternity doesn’t lie behind us, that our universe had a beginning, a birth in a cataclysmic outpouring of energy. Why, then, should we imagine that eternity lies ahead of us, an unending arena for life and mind?”

  Beth was sitting beside her pregnant daughter. Now, under a blanket, she took her daughter’s hand, and Mardina squeezed back. Mardina’s eyes were wide in the firelight, her expression blank. This was not a conversation either of them wanted to be part of, Beth was sure.

  The ColU was on Chu’s lap, next to Stef. Titus Valerius sat beside the slave boy, listening intently.

  And Titus was skeptical. “Well, we Romans had no trouble imagining eternity. Or at least, we failed to anticipate an end. Because we never anticipated the Empire to end—do you see? Unbounded and eternal . . .”

  That sounded magnificent in the legionary’s guttural soldier’s Latin, Stef thought. Imperium sine fine.

  The ColU said, “Our own Culture, mine and Stef’s and Beth’s, had its own account of an undying empire—but an empire of scientific logic. We thought we could know the future by looking out at the universe, working out the physical laws that govern it—and then projecting forward the consequences of those laws.

  “The universe only has so much hydrogen—the stuff that stars are made out of. The hydrogen will, or would have, run out when the universe is ten thousand times as old as it is now. No more stars. After the stars there would be an age of black holes and degenerate matter—the compressed, cooling remnants of stars—and the galaxies, huge and dim, would begin to break up. There would be a major transition when protons began to decay—that is, the very stuff of which matter is made . . . In the end everything would dissolve, and there would be nothing left but a kind of sparse mist, of particles called electrons and positrons—a stuff called positronium—filling an expanding, empty universe. Even so, it was possible that minds could survive. Minds more like mine than yours, perhaps. Thoughts carried on the slow wash of electrons—thoughts that might take a million years to complete.”