Ring xs-4

by Stephen Baxter

  “Let’s suppose there is a wormhole mouth inside this tiny construct,” Mark said. “A wormhole so fine it’s just a thread… but it leads across space, to the interior of the neutron star. Lieserl, I think the neutron superfluid in here isn’t some human reconstruction — I think it’s a sample of material taken from the neutron star itself.”

  Lieserl, involuntarily, glanced around the chamber, as if she might see the miniature wormhole threading across space, a shining trail connecting this bland, human environment with the impossibly hostile heart of a neutron star.

  “But why?”

  “Isn’t it obvious?” Uvarov snapped.

  Mark was smiling at her; evidently he had worked it out too.

  She felt slow, stupid, unimaginative. “Just tell me,” she said dully.

  Mark said, “Lieserl, the link is there so the humans who built this base could reach the interior of the neutron star. I think they downloaded equipment into there: nanomachines, ’bots of some kind — maybe even some analogue of humans.

  “They populated the neutron star, Lieserl.”

  Uvarov rumbled assent. “More than that,” he rasped. “They engineered the damn thing.”

  Closed timelike curves, Spinner-of-Rope.

  The nightfighter arced through the muddled, relativity distorted sky; the neutron star system wheeled around Spinner like some gaudy light display. Behind her, the huge wings of the Xeelee nightfighter beat at space, so vigorously Spinner almost imagined she could hear the rustle of immense, impossible feathers.

  She felt her small fingers tremble inside gloves that suddenly seemed much too big for her. But Michael Poole’s hands rested over hers, large, warm.

  The ship surged forward.

  We are going to build closed timelike curves…

  Ignoring the protests of her tired back, Louise straightened up and pushed herself away from the Deck surface. She launched into the air, the muscles of her legs aching, and she let air resistance slow her to a halt a few feet above the Deck.

  Once this had been a park, near the heart of Deck Two. Now, the park had become the bottom layer of an improvised, three-dimensional hospital, and the long grass was invisible beneath a layer of bodies, bandaging, medical supplies. A rough rectangular array of ropes had been set up, stretching upwards from the Deck surface through thirty feet. Patients were being lodged loosely inside the array; they looked like specks of blood and dirt inside some huge honeycomb of air, Louise thought.

  A short distance away a group of bodies — unmoving, wrapped in sheets — had been gathered together in the air and tethered roughly to the frame of what had once been a greenhouse.

  Lieserl approached Louise tentatively. She reached out, as if she wanted to hold Louise’s hand. “You should rest,” she said.

  Louise shook her head angrily. “No time for that.” She took a deep breath, but her lungs quickly filled up with the hospital’s stench of blood and urine. She coughed, and ran an arm across her forehead, aware that it must be leaving a trail there of blood and sweat. “Damn it. Damn all of this.”

  “Come on, Louise. You’re doing your best.”

  “No. That isn’t good enough. Not any more. I should have designed for this scenario, for a catastrophic failure of the lifedome. Lieserl, we’re overwhelmed. We’ve converted all the AS treatment bays into casualty treatment centers, and we’re still overrun. Look at this so-called hospital we’ve had to improvise. It’s like something out of the Dark Ages.”

  “Louise, there’s nothing you could have done. We just didn’t have the resources to cope with this.”

  “But we should have. Lieserl, the doctors and ’bots are operating triage here. Triage, on my starship.”

  …And it didn’t help that I diverted most of our supply of medical nanobots to the hull… Instead of working here with the people — crawling through shattered bodies, repairing broken blood vessels, fighting to keep bacterial infection contained within torn abdominal cavities — the nanobots had been press-ganged, roughly — and on her decision — into crawling over the crude patches applied hurriedly to the breached hull, trying inexpertly to knit the torn metal into a seamless whole once more.

  She clenched her hands into fists, digging her nails into her palms. “What if the Xeelee are studying us now? What will they think of us? I’ve brought these people across a hundred and fifty million light years — and five million years only to let them die like animals…”

  Lieserl faced her squarely, her small, solid fists on her hips; lines clustered around her wide mouth as she glared at Louise. “That’s sentimental garbage,” she snapped. “I’m surprised at you, Louise Ye Armonk. Listen to me: what is at issue here is not how you feel. You are trying to survive — to find a way to permit the race to survive.”

  Lieserl’s stern, lined face, with the strong nose and deep eyes, reminded Louise suddenly of an overbearing mother. She snapped back, “What do you know of how I feel? I’m a human, damn it. Not a — a — ”

  “An AI?” Lieserl met her gaze evenly.

  “Oh, Lethe, Lieserl. I’m sorry.”

  “It’s all right, Louise. You’re quite right. I am an artifact. I have many inhuman attributes.” She smiled. “For instance, at this moment I have two foci of consciousness, functioning independently: one here, and one down on the planet. But…” She sighed. “I was once human, Louise. If briefly. So I do understand.”

  “I know, Lieserl. I’m sorry.” Louise had never found it easy to express affection. With a struggle, she said: “In fact, you’re one of the most human people I’ve ever met.”

  Lieserl looked around at the makeshift hospital, following the soft cries of the wounded. “Louise,” she said slowly, “I have a long perspective. Think of the story of the race. Our timelines emerged from the oceans, and for millions of years circled the Sun with Earth. Then, in a brief, spectacular explosion of causality, the timelines erupted in wild scribbles, across the Universe. Humanity was everywhere.

  “But now, our possibilities have reduced.

  “Louise, all the potential paths of the race — all the time lines, running from those ancient oceans of the past, through millions of years to an unknown future — all of them have narrowed to a single event in spacetime: here, on this ship, now. And that event is under your control.”

  Lieserl’s face loomed before Louise now, filling her vision; Louise looked into her soft, vulnerable eyes, and — for the first time, really she had a sudden, deep insight into Lieserl’s personality. This woman really is ancient — ancient, and wise.

  “Louise, you are not a woman — or rather, you are more than a woman. You are a survival mechanism: the best to be found, for this crucial instant, by our genes, and our culture, and our minds. If you didn’t have the strength within you now, to deliver us through this causal gateway to the future, you would not have been chosen. But you do have the strength to continue,” Lieserl said. “To find a way through. Look within yourself, Louise. Tap into that strength…”

  There was a deep, almost subsonic groan, all around Louise. It sounded like thunder, she thought.

  It was the sound of metal, under immense stress.

  She pulled away from Lieserl and twisted in the air. She looked across at the section of hull breached by the arc of string. The patch that had been applied across the string damage gleamed brightly, fresh and polished, at the center of the grass-coated hull surface. A stress failure — another breach of the lifedome — would kill them all. But the patch looked as if it was holding up okay… not that a visual inspection from this distance meant anything.

  As if on cue, a projection of Mark’s head materialized before her. “Louise, I’m sorry.”

  “What is it?”

  “Come with me. We need to talk.”

  “No,” she said. Suddenly, she felt enormously weary. “No more talk, Mark. I’ve done enough damage already.”

  Behind her, Lieserl said warningly: “Louise…”

  “I heard what you sai
d, Lieserl.” Louise smiled. “But it’s all a little too mystical for a tired old engineer like me. I’m going to stay here. Help out in the hospital.”

  Lieserl frowned at her. “Louise, you’re an engineer, not a doctor. Frankly, I wouldn’t want you treating me.”

  Mark smiled. “Besides, we don’t have time for all this self pity, Louise. This is important.”

  She sighed. “What is?”

  He whispered, in a surprisingly unrealistic hiss, “Didn’t you hear the hull stress noise? Spinner is moving the ship again.”

  Think of spacetime as a matrix, Michael Poole whispered. A four-dimensional grid, labeled by distance and duration. There are events: points in time and space, at nodes of the grid. These are the incidents that mark out our lives. And, connecting the events, there are trajectories.

  The starbow across the sky broadened, now. That meant her speed had reduced, since the relativistic distortion was lessened. Spinner called up a faceplate display subvocally. Yes: the ship’s velocity had fallen to a fraction over half lightspeed.

  Trajectories are paths through spacetime, Poole said. There are timelike trajectories, and there are spacelike trajectories. A ship going slower than light follows a timelike path. And, Spinner, we — all humans, since the beginning of history — work our snail-like way along timelike trajectories into the future. At last, our world lines will terminate at a place called timelike infinity at the infinitely remote, true end of time.

  But “spacelike” means moving faster than light. A tachyon — a faster-than-light particle — follows a spacelike path, as does this nightfighter under hyperdrive.

  She twisted in her seat. Already the neutron star system had vanished, into the red-shift distance. And directly ahead of her there was a cloud of cosmic string; space looked as if it were criss-crossed by fractures, around which blue shifted star images slid like oil drops.

  Poole’s hands, invisible, tightened around hers as the ship threw itself into the cloud of string.

  We know at least three ways to follow spacelike paths, Spinner-of-Rope: three ways to travel faster than light. We can use the Xeelee hyperdrive, of course. Or we can use spacetime wormholes. Or, Poole said slowly, we can use the conical spacetime around a length of cosmic string…

  Think of the gravitational tensing effect that produces double images of stars around strings. A photon coming around one side of the string can take tens of thousands of years longer to reach our telescopes than a photon following a path on the other side of the string.

  So, by passing through the string’s conical deficit, we could actually outrun a beam of light… There was string all around the ship, now, tangled, complex, an array of it receding to infinity. A pair of string lengths, so twisted around each other they were almost braided, swept over her head. She looked up. The strings trailed dazzling highways of refracting star images.

  Behind her the huge wings spread wide, exultant.

  This damn nightfighter was made for this, she thought.

  Under Poole’s guidance, Spinner brought the craft to a dead halt; the discontinuity wings cupped as they tore at space. Then Spinner turned the craft around rapidly — impossibly rapidly — and sent it hurtling at the string pair once more. The nightfighter soared upwards, and this time the two strings passed underneath the ship’s bow.

  …And if you can move along spacelike paths, Spinner-of Rope, you can construct closed timelike curves.

  The neutron star system was old.

  Once the system had been a spectacular binary pair, adorning some galaxy lost in the sky. Then one of the stars had suffered a supernova explosion, briefly and gloriously outshining its parent galaxy. The explosion had destroyed any planets, and damaged the companion star. After that, the remnant neutron star slowly cooled, glitching as it spun like some giant stirring in its sleep, while its companion star shed its life-blood hydrogen fuel over the neutron star’s wizened flesh. Slowly, too, the ring of lost gas formed, and the system’s strange, spectral second system of planets coalesced.

  Then human beings had come here.

  The humans soared about the system, surveying. They settled on the largest planet in the smoke ring. They threw microscopic wormhole mouths into the cooling corpse of the neutron star, and down through the wormholes they poured devices and — perhaps — human-analogues, made robust enough to survive in the neutron star’s impossibly rigorous environment.

  The devices and human-analogues had been tiny, like finely jewelled toys.

  The human-analogues and their devices swarmed to a magnetic pole of the neutron star, and great machines were erected there: discontinuity-drives, perhaps powered by the immense energy reserves of the neutron star itself.

  Slowly at first, then with increasing acceleration, the neutron star — dragging its attendant companion, ring and planets with it — was forced out of its parent galaxy and thrown across space, a bullet of stellar mass fired at almost light speed.

  “A bullet. Yes.” In the pod, Uvarov mused. “An apt term.”

  Lieserl stared at the swirling, unresolved pixels inside the Virtual image’s clear tetrahedral frame. “I wonder if there are still people in there,” she said.

  Mark frowned. “Where?”

  “People-analogues. Inside the neutron star. I wonder if they’ve survived.”

  He shrugged, evidently indifferent. “I doubt it. Unless they were needed for maintenance, they would surely have been shut down after their function was concluded.”

  Shut down… But these were people. What if they hadn’t been “shut down”? Lieserl closed her eyes and tried to imagine. How would it be, to live her life as a tiny, fish-like creature less than a hair’s-breadth tall, living inside the flux-ridden mantle of a neutron star? What would her world be like?

  “A bullet,” Uvarov said again. “And a bullet, fired by our forebears — directly at the heart of this Xeelee construct.”

  She opened her eyes.

  Mark was frowning. “What are you talking about, Uvarov?”

  “Can’t you see it yet? Mark, what do you imagine the purpose of this great engineering spectacle was? We already know from the Superet data, and the fragments provided to us by Lieserl — that the rivalry between humanity and Xeelee persisted for millions of years. More than persisted — it grew in that time, becoming an obsession which — in the end — consumed mankind.”

  Lieserl said, “Are you saying that all of this — the discontinuity engines, the hurling of the neutron star across space — all of this was intended as an assault on the Xeelee?”

  “But that’s insane,” Mark said.

  “Of course it is,” Uvarov said lightly. “My dear friends, we’ve plenty of evidence that humanity isn’t a particularly intelligent species — not compared to its great rivals the Xeelee, at any rate. And I have never believed that humanity, collectively, is entirely sane either.”

  “You should know, Doctor,” Mark growled.

  “I don’t understand,” Lieserl said. “Humans must have known about the photino birds — damn it, I told them! They must have seen what danger the birds represented to the future of all baryonic species. And they must have seen that the Xeelee — if remote and incomprehensible — were at least baryonic too. So the goals of the Xeelee, if directed against the birds, had to be in the long-term interests of mankind.”

  Uvarov laughed at her. “I’m afraid you’re still looking for rational explanations for irrational behavior, my dear. Lieserl, I believe that the Xeelee grew into the position in human souls once occupied by images of gods and demons. But here, at last, was a god who was finite — who occupied the same mortal realm as humans. A god who could be attacked. And attack we did: down through the long ages, while the stars went out around us, all but ignored.”

  “And so,” Mark said grimly, “we fired off a neutron star at the Ring.”

  “A spectacular gesture,” Uvarov said. “Perhaps humanity’s greatest engineering feat… But, ultimately, futile. For how could a me
re neutron star disrupt a loop of cosmic string? And besides, the Xeelee starbreaker technology was surely sufficient to destroy the star before — ”

  “But it didn’t work,” Lieserl said slowly.

  Mark had been staring at the sensor ’bot; the squat machine had come to a halt before the chair, its sensor arms suspended in the air. “What do you mean?”

  “Think about it,” she said. “The neutron star is heading away from the site of the Ring. And it’s clearly not been disrupted by starbreakers.”

  “Yes. So something went wrong,” Uvarov said. “Well, the precise sequence hardly matters, Lieserl. And — ”

  It happened in a heartbeat.

  The light died. The ancient structure was flooded with darkness.

  Louise and Mark left the improvised hospital and found an abandoned house. The house was bereft of furniture, its owners gone to live in the zero-gee sky (but, of course, the zero-gee dwellings were gone now, Louise noted morosely, swept out of the sky by the cosmic string incursion).

  Mark quickly created a Virtual diagram in the air: a geometrical sketch of lines and angles, lettered and arrowed.

  Louise couldn’t help but smile. “Lethe, Mark. At a time like this, you give me a diagram Euclid would have recognized.”

  He looked at her seriously. “Louise, working out the spacetime geometry of a cosmic string is a hard problem in general relativity. But, given that geometry, all the rest of it is no more than Pythagoras’ theorem…

  “As near as I can figure out, this is what Spinner is up to.” There was a pair of tubes in the air, glowing electric blue, like neon. “We are flying around a pair of cosmic strings. Now, here are the angle deficits of the strings’ conical spacetimes.” Wedges of air, like long cheese slices, were illuminated pale blue; one wedge trailed each string length.

  “Okay. Here comes the Northern.” The ship was represented by a cartoon sketch of a sycamore seed in black. “You can see we’re traveling on a curving path around the string pair, going against the strings’ own rotation.”