Ring xs-4

by Stephen Baxter

  Now the seed arced into the wedge-shaped angle deficit glow of one of the strings. As soon as it had entered the boundary it vanished, to reappear instantly at the far side of the deficit.

  Mark snapped his fingers. “See that? Faster-than-light travel: a spacelike trajectory right across the deficit.”

  Now the little ship-model came arcing back and flickered through the second string’s angle deficit. “Louise, the strings are traveling just under the speed of light — within three decimal places of it, actually. Spinner has the Northern traveling at a little over half lightspeed. The turning curves, and the accelerations, are incredible… The domain wall inertial shielding seems to be working pretty well, although there’s a little leakage.”

  Louise nodded. “Right. Which is why the Northern is complaining.”

  “Yeah. Louise, the Northern wasn’t designed for this — and neither was our bastardized lash-up of Northern and nightfighter. But there’s nothing we can do. We’ll just have to pray the whole mess holds together until Spinner-of-Rope finishes her joy-riding…

  “Anyway, the trajectory she’s following is quite precisely machined… We’re passing from side to side of the string pair in light-minutes, but we’re crossing light-years thanks to the spacelike savings. Louise, I think Spinner-of-Rope is assembling closed timelike curves, from these spacelike trajectories.”

  Louise stared at the seed-craft; she felt an impulse to reach out and pluck it from the air. “But why, Mark? And how?”

  “I know what a closed timelike curve is,” Spinner said. Again she dragged the ship to a halt and whirled its nose around toward the string; although she was still shielded from the impossible accelerations she felt herself gasp as the Universe lurched around her. “The original mission of the Great Northern, with its wormhole, was to follow a segment of a closed timelike curve…”

  Yes. A closed timelike curve is a circle in time. By following a closed timelike curve all the way to its starting point, you would at last meet yourself, Spinner-of Rope… Closed timelike curves allow you to travel through time, and into the past.

  Again the nightfighter hurled itself at the cosmic string pair; again Spinner hauled at the waldoes, dragging the ship around. The huge wings beat at spacetime.

  She screamed, “How much longer, damn it?”

  Spinner, each traverse around the string pair is taking us a thousand years into the past. But we need to travel back through a hundred millennia, or more…

  “A hundred traverses,” she whispered.

  Can you do it, Spinner? Do you have the strength?

  “No,” she said. “But I don’t think I have much choice, do I?”

  Lieserl looked around the darkened chamber, confused. The ’bot’s brilliant lantern had been extinguished. Suddenly the walls were dim gray sheets, closing over her head, claustrophobic.

  “Lieserl.” Mark’s face loomed before her, erupting out of the darkness; his blue eyes, white teeth were vivid. He moved with nanosecond speed, the slowness of humanity finally abandoned.

  Dimly, she was aware of poor Uvarov sitting in the pod. He was frozen in human time, and unable to follow their high speed insect-buzz. “What is it? What’s happened?”

  “The ’bot has failed. Lieserl, it was controlled by the ship’s processors. The download link from the ship must have gone down…”

  Immediately, she felt that loss of processor support. She felt as if her mind had been plunged into a twilight cavern, echoing; she felt herself drift away.

  “They’ve abandoned us.”

  “Probably they had no choice, Lieserl.”

  I am to experience death, then. But — so suddenly?

  Lieserl would survive, of course — as would Mark, as projections on board the Northern. But this projection — she, this unique branch of her ancient consciousness — couldn’t be sustained solely by the limited processors on the pod.

  She felt a spasm of regret that she would never be able to tell Louise and Spinner-of-Rope about the wonderful little people embedded inside the neutron star flux.

  She reached for Mark. Their environment suits melted away; desperately they pressed their bodies against each other. With deep, savage longing, she sought Mark’s warm mouth with her lips, and -

  “Lethe. And we can’t even talk to her.” Louise looked out of the house and across the lifedome, in the vague direction of the nightfighter cage. “Mark, Spinner is a smart woman, but she’s no expert on string dynamics. And she’s out there without significant processor support. I don’t see how she’s even calculating the trajectories we’re following.”

  Mark frowned. “I — wait.” He held up a hand, and his expression turned inward, becoming blank.

  “What is it?”

  “We’ve stopped. I mean, the traverses around the string pair have been halted.” He thought for a moment. “Louise, I counted a hundred and seven complete circuits…”

  “Louise? Mark?”

  The voice sounded out of the air close to Louise’s ear. “Yes, Trapper-of-Frogs. I hear you. Where are you?”

  “I’m in the forest. I — ”

  “Yes?”

  “I think you’d better get up here.”

  Louise looked at Mark; he was frowning, and no doubt some sub-projection of him was already with Trapper.

  “Why?” Louise asked. “What’s wrong. Trapper?”

  “Nothing’s wrong. Not exactly. It’s just — different…”

  Michael Poole’s invisible ghost-touch evaporated. Spinner-of-Rope lifted her hands from the waldoes.

  Her job was done, then. She pulled her fingers inside the body of her gloves and balled her stiff hands into fists, digging her nails into the palms of her hands. She felt herself shudder, from fear and exhaustion. There was a stabbing in the small of her back, and across her shoulder blades, just below her neck; she twisted in her couch and flexed her spine, trying to work out the stiffness.

  Then she looked out, beyond the construction-material cage, for the first time.

  31

  “Dr. Uvarov. Dr. Garry Uvarov.”

  The voice, flat and mechanical, roused him from a broken sleep.

  He opened his mouth to reply, and ropy saliva looped across his lips. “What is it now?”

  “Is there anything you require?” The voice, generated by the pod’s limited processors, didn’t even bear a semblance of humanity, and it came — maddeningly! — from all around him.

  “Yes,” he said. He felt himself shivering, distantly; he felt cold. Was the power in here failing already?

  How long had it been, since his abrupt abandonment by Lieserl and Mark Wu?

  “Yes,” he told the pod again. “Yes, there is something I require. Take me back to the Northern.”

  The pod paused, for long seconds.

  Uvarov felt the cold settle over his bones. Was this how he was to die, suspended in the thoughts of an idiot mechanical? Was he to suffer a final betrayal at the hands of technology, just as the AS nanobots had been slowly killing him for years?

  Well, if he was to die, he would take with him one deep and intense regret: that he had not lived to see the conclusion of his grand design, his experiment at extending the natural longevity of his race. He knew how others had seen him: as obsessed with his eugenics objectives, as a monomaniac perhaps. But — ah! What an achievement it would have been! What a monument…

  Ambition burned within him still, intense, almost all consuming, betrayed by the failure of his body.

  His thoughts softened, and he felt himself grow more diffuse, his awareness drifting off into the warm, comfortable caverns of his memory.

  The pod spoke again. “I’m unable to comply with your request, Doctor. I can’t obtain a fix on the Northern. I’m sorry. Would you like me to — ”

  “Then kill me.” He twisted his head from side to side, relishing the stabs of pain in his neck. “I’m stranded here. I’m going to die, as soon as my supplies run out. Kill me now. Turn off the damn power.”<
br />
  “I can’t comply with that, either, Dr. Uvarov.”

  But Uvarov was no longer listening. Once more he felt himself falling into a troubled — perhaps final — sleep, and his ruined lips moved slowly.

  “Kill me, you damn mechanical…”

  32

  The torus of ragged, fragmented string loops was gone. Now, cosmic string crossed the cavity: great, wild, triumphant whorls of it, shining a false electric blue in the sky dome’s imager.

  This one, tremendous, complex, multiple loop of string filled the cavity at the bottom of the gravity well. This was — astonishingly, unbearably — a single object, an artifact, at least ten million light-years across.

  Louise Ye Armonk — with Mark, Lieserl and Morrow — hovered on zero-gee scooters, suspended beneath the crown of the skydome. Beneath Louise — she was distantly aware — the layers of forest were filled with the rich, comforting noises: the calls of birds and monkeys and the soft burps of frogs, sounds of busy life which persisted even here at the end of time…

  Beyond the clear dome, string filled the Universe.

  Here, a hundred thousand years into the past, the galaxies still fell, fragmenting and blue-shifted, into the deepest gravity well in the Universe. And the Northern had emerged from its jaunts through the string loop’s spacetime defects to find itself once more inside a star-walled cavity, at the bottom of this Universal well.

  There the similarity ended, though, Louise thought. The cavity walls were much smoother than in the future, containing rather fewer of the ragged holes she’d noted… The walls looked almost artificially smooth here, she thought uneasily.

  And, of course, there was the Ring, whole and magnificent.

  The Ring was a hoop woven from a billion-light-year length of cosmic string. The Northern was positioned somewhere above the plane of the Ring. The near side of the artifact formed a tangled, impenetrable fence over the lifedome, twisted exuberantly into arcs and cusps, with shards of galaxy images glittering through the morass of spacetime defects. And the far side of the object was visible as a pale, hard band, remote across the blue-shifted sky.

  The rough disc of space enclosed by the Ring — a disc no less than ten million light-years across, Louise reminded herself — seemed virtually empty. Perhaps, she mused, in this era the Xeelee were actively working to keep that central region clear.

  …Clear, Louise saw as she looked more carefully, save for a single, glowing point of light, right at the geometric center of the Ring. She saw how Lieserl was staring into that point of light, her mouth half-open.

  Spinner-of-Rope’s precipitate action had delivered them, back through time, to another snapshot-timeslice of this war in Heaven… and this was, it seemed, an era not far removed from the Ring’s final fall.

  She was aware of their eyes — Mark’s, Lieserl’s, Morrow’s resting on her, expectantly. On her.

  Remember what Lieserl said, she told herself. I’m a survival mechanism. That’s all. I have to keep functioning, for just a little while longer… She reached deep inside her.

  She clapped her hands. “All right, people — Mark, Lieserl. Let’s do some work. I think it’s obvious we’ve delivered ourselves right into the middle of a war zone. We know that, at this moment, the photino birds must be hitting this Ring from all sides — because, within a hundred thousand years, we know that the Ring is going to be destroyed. That gives me the feeling that we don’t have much time, before one side or other notices we’re here…”

  “I think you’re right, Louise,” Mark said. Both the Virtuals, on high-capacity data links to the central processors, were working on different aspects of the situation. “I don’t think we should be fooled by the fact that most of the action in this incredible war seems to be occurring at sublight velocities, so that — on this scale it has all the pace of an ant column crossing the Sahara. Let’s not forget the Xeelee have a hyperdrive — which we’ve stolen — and, for all we know, so do the photino birds. We could be discovered at any time.”

  “So give me a summary of the environment.”

  Mark nodded. “First of all, our position in time: Spinner-of-Rope constructed enough closed timelike paths for us to have traveled a hundred thousand years into the past, back from the era to which our first journey brought us.” He raised his face to the skydome and rose into the air by a few feet, absently forgetting to take his Virtual-scooter with him. “The Ring is complete in this era, as far as we can tell. Its mass is immense — in fact we’re suffering inertial drag from it. Kind of a lot of drag, in fact… We’re being hauled around, through space, by the Ring. Spinner-of-Rope seems to be compensating…”

  “Lieserl. Tell me what you have.”

  Lieserl seemed to have to tear her eyes away from that tantalizing point of light at the heart of the Ring. She looked down at Louise.

  “I have the Ring, Louise. We have been restored to an era before its destruction. Bolder’s Ring is a single loop of cosmic string… but an immense one, no less than ten million light-years across and with the mass of tens of thousands of galaxies, united into one seamless whole. The string is twisted over on itself like wool wrapped around a skein; the Ring’s topography is made up of string arcs moving at close to lightspeed, and cusps which actually reach light speed. The motion is complex, but — as far as I can tell it’s non-intersecting. The Ring could persist forever.

  “Louise, there is no way this monster could have formed naturally. Our best theories say that any natural string loops should be a mere thousand light-years across.” She looked up, and the blue false color of the string images caught her profile, picking out the lines around her eyes. “Somehow — ” she laughed briefly ” — somehow the Xeelee found a way to drag cosmic string across space — or else to manufacture it on a truly heroic scale — and then to knit it up into this immense artifact.”

  Louise stared up at the Ring, tracing the tangle of string around the sky, letting Lieserl’s statistics pour through her head. And I might have died without seeing this. Thank you. Oh, thank you…

  “The cosmology here is… spectacular,” Lieserl said, smiling. “We have, essentially, an extremely massive torus, rotating very rapidly. And it’s devastating the structure of spacetime. The sheer mass of the Ring has generated a gravity well so deep that matter — galaxies — is being drawn in, toward this point, across hundreds of millions of light years. Even our original Galaxy, the Galaxy of mankind, was drawn by the Ring’s mass. So we know that the Ring was indeed the ‘Great Attractor’ identified by human astronomers.

  “And the rotation has significant effects. Louise, we’re on the fringe of a Kerr metric — the classic relativistic solution to the gravitational field of a rotating mass. In fact, this is what’s called a maximal Kerr metric: because the torus is spinning so fast the angular momentum far exceeds the mass, in gravitational units…

  “As Mark said, the Ring’s rotation is exerting a large torque on the ship. This is inertial drag: the twisting of spacetime around the rotating Ring.”

  Morrow frowned. “Inertial drag?”

  Lieserl said, “Morrow, naive ideas of gravity predicted that the spin of an object wouldn’t affect its gravitational field. No matter how fast a star rotated, you’d be attracted simply toward its center, just as if it wasn’t rotating at all.

  “But relativity tells us that isn’t true. There are nonlinear terms in the equations which couple the rotating mass to the external field. In other words, a spinning object drags space around with it,” she said. “Inertial drag. And that’s the torque the Northern is experiencing now.”

  “What else?” Louise asked. “Mark?”

  He nodded. “The first point is, we’re drowning in radio wavelength photons — ”

  That was unexpected. “What are you talking about?”

  “I mean it,” he said seriously, turning to face her. “That’s the single most significant difference in our gross physical environment, compared to the era we came from: we’re now im
mersed in a dense mush of radio waves.” He looked absent for a moment. “And the intensity of it is increasing. There’s an amplification going on, slow, but significant on the timescales of this war; the doubling time is around a thousand years. Louise, none of this shows up in the future era. By then, the radio photons will be gone.”

  Louise shook her head. “I can’t make sense of this. What’s causing the amplification?”

  He shrugged, theatrically. “Beats me.” He glanced around the sky. “But look around. The Ring is contained in a shell of galactic material, Louise. The frequencies of the radio waves are below the plasma frequency of the interstellar medium. So the waves are trapped in this galaxy-walled box. We’re inside an immense resonant cavity, ten million light years across, with reflecting walls.”

  Morrow looked beyond the skydome uncertainly. “Trapped? But what happens when — ”

  Lieserl cut in, “Mark, I think I’ve figured it out. The cause of the radio-wave amplification.”

  He glanced at her. “What?”

  “It’s the inertial drag. We’re seeing super-radiant scattering from the gravitational field. A photon, falling into the Ring’s gravity well, is coupled to the Ring by the inertial drag, and is then thrown out with additional energy — ”

  “Ah. Right.” Mark nodded, looking distant. “That would give an amplification of a few tenths of one percent each traverse… just about fitting my observations.”

  Morrow frowned. “Did I understand that? It sounds as if the photons are doing gravitational slingshots around this Ring.”

  Louise smiled at him, sensing his fear. “That’s right. The inertial drag is letting each photon extract a little energy from the Ring; the radiation is amplified, and the Ring is left spinning just a fraction slower…

  “Lieserl. Tell us more about the spacetime metric.” She looked up, at the point of light at the heart of the Ring. “What do we see, there, at the center?”

  Lieserl looked up, her face composed. “I think you know, Louise. It is a singularity, at the center of the Ring itself. The singularity is hoop-shaped, a circular flaw in space: a rip, caused by the rotation of the immense mass of the Ring. The singularity is about three hundred light-years across — obviously a lot smaller than the diameter of the material Ring…