Ring xs-4

by Stephen Baxter

  “If the Ring were spinning more slowly, the Kerr metric would be quite well behaved. The singularity would be cloaked in two event horizons — one-way membranes into the center — and, beyond them, by an ergosphere: a region in which the inertial drag is so strong that nothing sublight can resist it. If we were in an ergosphere, we’d have no choice but to rotate with the Ring. In fact, if it weren’t rotating at all, the Kerr field would collapse into a simple, stationary black hole, with a point singularity, a single event horizon and no ergosphere.

  “But the Ring is spinning… and too rapidly to permit the formation of an event horizon, or an ergosphere. And so…”

  Louise prompted, “Yes, Lieserl?”

  “And so, the singularity is naked.”

  Michael Poole sat with his legs crossed comfortably on the shoulder of the nightfighter. His gaze was on Spinner’s face, steady, direct.

  The Ring is a machine, whose sole purpose is to manufacture that naked singularity. Don’t you see? The Xeelee constructed this huge Ring and set it spinning — in order to tear a hole in the Universe.

  Spinner-of-Rope enhanced the false-color of the central singularity in her faceplate imager. The flaw looked like a solid disc — a coin, perhaps — almost on edge toward her, but tipped slightly so that she could see its upper surface.

  In that surface, white starlight swam. (White?)

  She said to Poole, “The Xeelee built all of this — they modified history, disrupted spacetime, drew in galaxies to their destruction across hundreds of millions of light-years — just for this?”

  Poole lifted his eyebrows. It is the greatest baryonic artifact, Spinner-of Rope. The greatest achievement of the Xeelee…

  The singularity was like a jewel, surrounded by the undisciplined string scribble of the Ring itself.

  “It’s very beautiful,” she conceded.

  Poole smiled. Ah, but its beauty lies in what it does…

  He turned his gaunt, tired face up to the singularity. Spinner-of-Rope, humans have imputed many purposes to this artifact. But the Ring is not a fortress, or a last redoubt, or a battleship, or a base from which the Xeelee can reclaim their baryonic Universe, he said sadly. Spinner, the Xeelee know they have lost this war in Heaven. Perhaps they have always known that, even from the dawn of their history.

  “I don’t understand.”

  Spinner, the singularity is an escape hatch.

  Lieserl and Mark turned to each other, inhumanly quickly. They stared into each other’s eyes, as if exchanging data by some means invisible to humans, their blank expressions tike mirror images.

  “What is it?” Louise asked. “What’s happened?”

  Pixels, defects in the Virtual projection, crawled across Mark’s cheek. “We need Spinner-of-Rope,” he snapped. “We can’t wait for the repairs to the data links. We’re trying to find bypasses — working quickly — ”

  Louise frowned. “Why?”

  Mark turned to her, his face expressionless. “We’re in trouble, Louise. The cops are here.”

  Spinner-of-Rope asked, “How do you destroy a loop of cosmic string ten million light-years across?”

  It isn’t so difficult… if you have the resources of a universe, and a billion years, to play with, Spinner-of Rope. Poole, perched on the shoulder of the nightfighter, pointed at a hail of infalling galaxies swamping a nearby section of the Ring. If the Ring tangles — if cosmic string self-intersects — it cuts itself, he said. It intercommutes. And a new subloop is formed, budding off the old. And perhaps that subloop, too, will self-intersect, and split into still smaller loops… and so on.

  Spinner nodded. “I think I understand. It would be an exponential process, once started. Pretty soon, the Ring would decay into the torus of debris we found will find a hundred thousand years from now…”

  Yes. No doubt the motion of the Ring has been designed by the Xeelee so that it does not cut itself. But all one need do is start the process, by disrupting the Ring’s periodic behavior. And that is evidently what the photino birds are endeavoring to do, by hurling galaxies — like thrown rocks at the Ring.

  Spinner sniffed. “Seems kind of a crude technique.”

  Poole laughed. Baryonic chauvinism, Spinner-of-Rope? Besides, the birds have other mechanisms. I —

  “…Spinner. Spinner-of-Rope. Can you hear me?”

  Spinner sat bolt upright in her couch and clutched at her helmet. “Lieserl? Is that you?”

  “Listen to me. We don’t have much time.”

  “Oh, Lieserl, I was beginning to think I’d never — ”

  “Spinner! Shut up, damn you, and listen.”

  Spinner subsided. She’d never heard Lieserl use a tone like that before.

  “Use the waldoes, Spinner. You have to get us out of here. Take us straight up, with the hyperdrive, over the plane of the Ring. Have you got that? Use the longest jump distance you can find. We’ll try to patch subroutines into the waldoes, but — ”

  “Lieserl, you’re scaring the pants off me. Can’t you tell me what’s wrong?”

  “No time, Spinner. Please. Just do it…”

  The Universe darkened.

  For a bleak, heart-stopping instant Spinner thought she was going blind. But the telltales on the waldoes still gleamed at her, as brightly as ever.

  She looked up. There was something before the ship, occluding the blue-shifted galaxy fragments, hiding the Ring.

  She saw night-dark wings, spread to their fullest extent, looming over the Northern.

  Nightfighters.

  She twisted in her seat. There were hundreds of them — impossibly many, dark lanterns hanging in the sky.

  They were Xeelee. The Northern was surrounded.

  Spinner screamed, and slammed her fists against the hyperdrive waldo.

  The ’fighters moved through electric-blue cosmic string like birds through the branches of a forest. There were so many of them in this era. They were cool and magnificent, their nightdark forms arrayed deep into space all around her. Lieserl stared at the swooping, gliding forms, willing herself to see them more clearly. Had any humans ever been closer to Xeelee than this?

  The Xeelee moved in tight formation, like bird-flocks, or schools of fish; they executed sudden changes of direction, their domain wall wings beating, in squads spanning millions of miles — absolutely in unison. Now Lieserl saw how ’fighters should be handled, in contrast to Spinner’s earnest, clumsy work. The nightfighters were sculptures of space-time, with a sleek beauty that made her shiver: this was baryonic technology raised to perfection, to a supreme art, she thought.

  She was struck by the contrast between this era and the age of devastation — of victory for the photino birds — to which the Northern had first brought them. Here, the Ring was complete and magnificent, and the Xeelee, in their pomp, filled space. Already, she knew, the final defeat was inevitable, and the Xeelee were, in truth, huddling inside their final redoubt. But still, her heart beat harder inside her as she looked out over this, the supremacy of baryonic life.

  The overlapping lengths of string slid down, smoothly, past the lifedome, as the Northern climbed. The nightfighters swooped like starlings through the string, and around the Northern — no, Spinner realized suddenly; the nightfighters were flickering across space.

  “They’re using their hyperdrive,” she breathed.

  Yes. Poole stared up at the nightfighters, his lined face translucent. And we’re hyperdriving too. You’re pushing it, Spinner; we’ve never tried jumps of this scale, even in test. Do you know how fast you’re traveling? Ten thousand light years with every lump… But even so, the Xeelee are easily keeping pace with us.

  Of course they are, Spinner thought. They are Xeelee.

  These ’fighters could have stopped the Northern at any time — even destroyed it. But they hadn’t.

  Why not?

  The ship was rising high above the plane of the Ring. The tangle of string fell away from the foreground, and she could see easily now t
he million-light-year curve of the structure’s limb. And at the heart of the Ring, the singularity seemed to be unfolding toward her, almost welcoming.

  The Xeelee ’fighters rose all around her, like leaves in a storm. They can’t believe we’re a threat. I guess humans never were a threat, in truth. Now, it’s almost as if the Xeelee are escorting us, she thought.

  “Lieserl,” she said.

  “I hear you, Spinner-of-Rope.”

  “Tell me what in Lethe’s name we’re doing.”

  “You’re taking us out of the plane of the Ring…”

  “And then?”

  “Down…” Lieserl hesitated. “Look, Spinner, we’ve got to get away from the Xeelee, before they change their mind about us. And we’ve nowhere else to run, not in all of the Universe.”

  “And this is your plan?” Spinner was aware of the hysteria in her own voice; she felt fear spread through her stomach and chest, like a cold fluid. “To fly into a singularity?”

  Mark punched his thigh. “I was right, damn it,” he said. “I was right all along.”

  The tension was a painful presence, clamped around Louise’s throat. “Damn it, Mark, be specific.”

  He turned to her. “About the significance of the radio energy flux. Don’t you see? The photino birds have manufactured this immense cavity, of stars and smashed-up galaxies, to imprison the Ring.” He glanced around the skydome. “Lethe. It must have taken them a billion years, but they’ve done it. They’ve built a huge mirror of star stuff, all around the Ring. It’s a feat of cosmic engineering almost on a par with the construction of the Ring itself.”

  “A mirror?”

  “The interstellar medium is opaque to the radio energy. So each radio photon gets reflected back into the cavity. The photon orbits the Ring — and on each pass it’s super-radiant amplified, as Lieserl described, and so sucks out a little more energy from the inertial drag of the Ring’s rotation. And then the photon heads out again… but it’s still trapped by the galaxy mirror. Back it goes again, to receive a little more amplification… Do you see? It’s a classic example of positive feedback. The trapped radio modes will grow endlessly, leaching energy from the Ring itself…”

  “But the modes can’t grow indefinitely,” Morrow said.

  “No,” Mark said. “The process is an inertial bomb, Morrow. All that electromagnetic pressure will build up in the cavity, until it can no longer be contained. And in the end — probably only a few tens of millennia from now — it will blow the cavity apart.”

  Louise glanced around the sky, seeing again the smooth distribution of galaxies she’d noted earlier. “Right. And, in a hundred thousand years, the Northern will fly right into the middle of the debris from that huge explosion.”

  Now the ship had sailed high above the plane of the Ring; Louise could see the whole structure, laid out before her like the rim of a glimmering mirror, with the sparkle of the singularity at its heart.

  Lieserl said, “Louise, the hostile photino bird activity we’ve noted before — the direct assault on the Ring itself with lumps of matter — is spectacular, but Mark’s right: this radio bomb trick is what will truly bring down the Ring.” A subtle smile played on her lips. “It’s damn clever. The birds are draining the Ring itself, drawing energy out of the gravitational field using inertial drag. They’re going to use the Ring’s own mass-energy to wreck it.”

  Subvocally, Louise checked her chronometer. Less than twenty minutes had elapsed since Mark and Lieserl had ordered Spinner to start moving the ship, but already they must have crossed eight million light-years — already they must be poised directly above the singularity.

  “Mark. Where are we going?”

  Poole, evidently trying to calm Spinner, told her what would happen to the nightfighter as it approached the disc singularity.

  A timelike trajectory could reach the upper surface of the disc, Poole told her. A ship could reach the plane of the singularity. But — so said the equations of the Kerr metric — no timelike trajectory could pass through the singularity loop and emerge from the other side.

  “So what happens? Will the ship be destroyed?”

  No.

  “But if the ship can’t travel through the loop — where does it go?”

  There can be no discontinuity in the metric, you see, Spinner-of-Rope. Poole hesitated. Spinner-of-Rope, the singularity plane is a place where universes kiss.

  “Lethe,” Louise said. “You’re planning to take us out of the Universe?”

  Mark swiveled his head toward her, unnaturally stiffly; the degradation of the image of his face — the crawling pixel-defects, the garish color of his eyes — made him look utterly inhuman. “We’ve nowhere else to run, Louise. Unless you have a better idea…”

  She stared up at the singularity. The AIs, working together at inhuman speed, had come up with a response to this scenario. But are they right? She felt the situation slipping away from her; she tried to plan, to come to terms with this.

  Lieserl said drily, “Of course, timing is going to be critical. Or we might end up in the wrong universe…”

  Morrow clung to his scooter, his eyes wide, his knuckles bloodless. “What in Lethe’s name are you talking about now?”

  Mark hesitated. “The configuration of the string is changing constantly. It’s a dynamic system. And that’s changing the topology of the Kerr metric — it’s changing the basis of the analytical continuation of space through the singularity plane…”

  “Damn you,” Morrow said. “I wish you’d stick to English.”

  “The singularity plane is a point at which this Universe touches another smoothly. Okay? But because of the oscillations of the Ring, the contact point with the other universe isn’t a constant. It’s changing. Every few minutes sometimes more frequently — the interface changes to another continuation region — to another universe.”

  Morrow frowned. “Is that significant for us?”

  Mark ran a hand through his hair. “Only because the changes aren’t predictable, either in timing or scope. Maybe the changes cycle round, for all I know, so if we wait long enough we’ll get a second chance.”

  “But we don’t have time to wait.”

  “No. Well, we’re not exactly planning this… We won’t be able to choose which universe we end up in. And not every universe is habitable, of course…”

  Louise pressed her knuckles to her temples. Good point, Mark. We’ve decided to commit ourselves to crashing out of our Universe, and we have half the Xeelee nightfighters in creation on our tails already… and now you bring me this. What am I supposed to do about it?

  “Tell me what you see through there right now,” she said. “Tell me about the universe on the other side of the Kerr interface.”

  “Now?” Mark looked doubtful. “Louise, you’re asking me to come up with an analysis of a whole cosmos — based on a few muddled glimpses — in a few seconds. It’s taken all of human history even to begin a partial — ”

  “Just do it,” she snapped.

  He studied her briefly, his expression even. “Some of the twin universes feature a degree of variation to our physical laws. That’s no great surprise; the constants of physics are just an arbitrary expression of the way the symmetries at the beginning of time were broken… But even those universes with identical laws to ours can be very different, because of changed boundary conditions at the beginning of time — or even, simply, from being at a different stage of their evolutionary cycles to ours.”

  “And in this particular case?” she asked heavily.

  He closed his eyes. Louise could see that stray pixels, yellow and purple, were again migrating across the Virtual images of his cheeks. His eyes snapped open, startling her. “High gravity,” he said.

  “What?”

  “Variation of the laws. In the neighboring universe, the constant of gravity is high — enormously high — compared to, uh, here.”

  Morrow looked nervous. “What would that mean? Would we be c
rushed?”

  More pixels, glitches in the image, trekked across Mark’s cheeks. “No. But human bodies would have discernible gravity fields. You could feel Louise’s mass, Morrow, with a pull of about half a gee.”

  Morrow looked even more alarmed.

  “Stars could be no more than a mile wide, and they would burn for only a year,” Mark said. “Planets the size of Earth would collapse under their own weight immediately…”

  Lieserl frowned. “Could we survive there?”

  Mark shrugged. “I don’t know. The lifedome would implode immediately under its own weight. We’d need to find a source of breathable air, and fast. And we’d have to live in free fall; any sizeable mass would exert unbearably high gravitational forces. But maybe we could make some kind of raft of the wreckage of the Northern…”

  Lieserl looked up into the singularity plane, and her expression softened. “We know there have been human assaults in the Ring — like the neutron star missile. So perhaps we are not the first human pilgrims to fall through the Ring. Mark, you said the bridge to the other universe goes through cycles. I wonder if there are humans on the other side of that interface even now, clinging to rafts made from wrecked warships, struggling to survive in their high-gravity world…”

  Mark smiled; he seemed to be relaxing. “Well, if there are, we won’t meet them. That continuation has closed off; a new one is opening… Wherever we’re going, it won’t be there.”

  Louise glanced up at the false-color sky. “…I think it’s time to find out,” she said.

  The Northern reached the zenith of its arc, high over the plane of the Ring.

  Spinner felt as if she were suspended at the top of some huge cosmic tree, a million light-years high. The ship was poised above the singularity’s central, glittering pool of muddled starlight, and beyond that, at the edge of her field of view, was the titanic form of the Ring itself.