Ring xs-4

by Stephen Baxter

  “But the graphic is enough to show you an important feature of this motion. It’s non-intersecting… The string is not cutting itself at any point in the periodic trajectory. If it did, it would bud off smaller sub-loops, which would oscillate and cut themselves up further, and so on… the string would rapidly decay, shrivelling through a thousand cuts, and leaking away its energy through gravitational radiation.”

  Spinner wished, suddenly, that she wasn’t human: that she could watch the motion of this loop unfold, without having to rely on Mark’s gaudy projections. How wonderful it would be to be able to step out of time!

  …Close your eyes, Spinner.

  “What?”

  You can step out of time, just as you desire. Close your eyes, and imagine you are a god.

  …And here, in her mind’s eye — so much more dramatic than any Virtual! — came the knot of string, sailing out of space. The knot wriggled like some huge worm, closed on itself as if swallowing its own tail.

  The knot struck the rim of this defenseless galaxy and scythed toward the core, battering stars aside like blades of grass.

  It was a disturbing, astonishing image. She snapped open her eyes, dispelling the vision; fear flooded her, prickling over her flesh.

  She wasn’t normally quite so imaginative, she thought drily. Maybe her companion had had something to do with that brief, vivid vision…

  She returned her attention to the harmless-looking Virtual display. Now Mark showed Spinner the loop’s induced magnetic field, a yellow glow of energy which sleeved the fake blue of the string itself.

  “As it hauls through the galaxy’s magnetic field, that string is radiating a lot of electromagnetic energy,” Mark said. “I see a flood of high-energy photons…”

  Cosmic string wasn’t actually one-dimensional; it was a Planck length across, a fine tube containing charged particles: quarks, electrons and their antiparticles, gathered into super-heavy clusters. As a result, string acted as a superconducting wire.

  The string knot was cutting through this galaxy’s magnetic field. As it did so immense electrical currents — of a hundred billion billion amps or more — were induced in the string. These currents generated strong magnetic fields around the string.

  The string’s induced field was stronger than a neutron star’s, and dominated space for tens of light-years around the knot.

  Mark said, “The string has a maximum current capacity. If it’s overloaded, the string starts to shed energy. It glows with gamma radiation. And the lost energy crystallizes into matter: ions and electrons, whispering into existence all along the length of the string.” Spinner saw representations of particles — out of scale, of course — popping into existence around the string image. “So the string is glowing as brightly as a star.”

  “Yes,” Louise put in. “But the distribution of the radiation is odd, Mark. Look at this. The radiation is beamed forward of the loop’s motion — parallel to that forward spike of gravitational radiation.”

  “Like a searchlight,” Morrow said.

  Or a spear…

  She heard Morrow saying, “Mark, what is driving the string? What is impelling it through space, and into this galaxy?”

  “Gravitational radiation,” Mark said simply.

  Louise said, “Morrow, gravity waves are emitted whenever large masses are moved through space. Because the loop is asymmetrical it’s pushing out its gravitational radiation in particular directions — in spikes, ahead of and behind it. It is pushing out momentum… It is a gravitational rocket, using its radiation to drive through space.”

  Mark said, “Of course the gravitational radiation is carrying away energy — the string is shrinking, slowly. In the end it will collapse to nothing.”

  “But not fast enough to save this galaxy,” Uvarov growled.

  “No,” Louise said. “Before it has time to decay away, the string is going to reach the core — and devastate the galaxy.”

  Close your eyes.

  Spinner-of-Rope shivered. Once again the voice had come from her left — from somewhere outside her suit. She stared at the Virtual image in her faceplate, not daring to look around.

  Close your eyes. Think about your vision again — of the string loop, cutting through the stars. It frightened you, didn’t it? What did that image mean, Spinner-of-Rope? What was it telling you?

  Suddenly she saw it.

  “Mark,” she said. “This is not just a gravitational rocket.”

  “What?”

  “Think about it. The string knot must be a missile.”

  The galaxy images dimmed, leaving Mark and Lieserl suspended in a crimson-tinged darkness. Then, against that background, new forms began to appear: speckles of light, indistinct, making up the ghostly outline of a torus, its face tipped open toward her.

  “Of course this is a false color representation,” Mark said. “The images have been reconstructed from gravity wave and gamma ray emissions…”

  The torus as a whole reminded her, distantly, of Saturn’s rings; it was a circle which spanned the galaxy-walled cavity.

  At first she thought the component speckles were mere points of light: they were like stars, she thought, or diamonds scattered against the velvet backdrop of the faded galaxy light. But as she looked more closely she could see that some of the nearer objects were not simple points, but showed structure of some kind.

  So these weren’t stars, she thought, and nor was this some attenuated galaxy: there were only (she estimated quickly) a few thousand of the shining forms, as opposed to the billions of stars in a galaxy… And besides, this cavity spanning torus was immense: she could see how the blood-dark corpses of galaxies sailed through its sparse structure.

  She knew that the Galaxy of humans had been a disc of stars a hundred thousand light-years in diameter. This torus must be at least a hundred times as broad — more than ten million light-years across.

  She turned to Mark; he studied her face, a certain kindness showing in his eyes now. “I know how you’re feeling. It’s magnificent, isn’t it?”

  “It can’t be the Ring,” she said slowly. “Can it? As far as we know, Jim Bolder reported a solid object — a single, continuous artifact.”

  “Look more closely, Lieserl. Cheat a little; enhance your vision. What do you see?”

  She turned her head and issued brisk subvocals. A section of the torus exploded toward her; the fragments, rushing apart, gave her a brief, disorienting impression of sudden velocity.

  Her view steadied. Now, it was as if she was within the torus itself, and the sparkling component objects were all around her.

  The fragments weren’t simple discs — or ellipses, or any of the shapes into which a star or galaxy might be distorted by the presence of others. She could see darkness within the heart of these objects.

  The fragments were knots.

  “Mark — ”

  “You’re looking at loops of cosmic string,” he said calmly. “This immense torus is made up of string knots, Lieserl ten thousand of them, each a thousand light years across.”

  She was aware of her hand convulsing closed around his. “I don’t understand. This is — fantastic. But it isn’t the Ring Bolder described.”

  He looked distant, wistful. “But it must be. We know we’ve come to the right place, Lieserl. This is undoubtedly the site of the Great Attractor: the loops, together, have sufficient mass to cause the local streaming of galaxies.

  “And we know this assemblage must be artificial. Primeval string loops could have formed during the formation of the Universe, after the singularity. But there should have been no more than a million of them — in the entire Universe, Lieserl — spaced tens of millions of light-years apart. It simply isn’t possible for a collection of ten thousand of the damn things to have gathered spontaneously within a cavity a mere ten million light-years across…”

  “But,” Lieserl said patiently, “but Bolder said the Ring was solid. If he was right — ”

  “
If he was right then the Ring has been destroyed, Lieserl. These loops are rubble. We’re looking at the wreckage of the Ring. The photino birds have won.” He turned to her, his face a sculpture, expressionless, obviously artificial. “We’re too late, Lieserl.”

  She felt bewildered. “But if that’s true — where are we to go?”

  Mark had no answer.

  Louise said, “What are you talking about, Spinner?”

  “Can’t you see it?” She closed her eyes and watched, once again, as the string loop punched through the fragile superstructure of the galaxy. “Mark — Louise this string loop was aimed, quite precisely. It’s a weapon. It is blasting through this galaxy with its gravitational rockets, destroying all in its path with focused beams of electromagnetic and gravitational energy…”

  Louise snapped, “Mark?”

  Mark hesitated. “We can’t prove she’s right, Louise. But the chances of the loop hitting such a precise trajectory at random are tiny…”

  “It seems crazy,” Morrow said. “Who would dare use a thousand-light-year loop of cosmic string as a weapon of war?”

  Uvarov grunted. “Isn’t that obvious? The very entities we have come all this way to seek, from whom we hope to obtain shelter — the Xeelee, Morrow; the baryonic lords.”

  “But why?” Mark asked. “Why destroy a galaxy like this?”

  “In defense,” Uvarov snapped.

  “What?”

  “Isn’t that clear too? The Xeelee were masters of the manipulation of spacetime. Their weaponry consisted of these immense structures of spacetime flaws. And the flaws have been used against the weapons of their enemies — like this galaxy.”

  There was silence for a moment. Then Morrow said, “Are you insane, Uvarov? You’re saying that this galaxy has been hurled like some rock — deliberately?”

  “Why not?” Uvarov replied calmly. “The photino birds are creatures of dark matter — which attracts baryonic matter gravitationally. We can easily imagine some immense dark chariot hauling at this fragile galaxy, hurling it hard through space…

  “Think of it. The photino birds must have begun to engineer the deflection of this galaxy’s path many millions of years ago — perhaps they were intent on launching this huge missile at the Ring long before men walked on the Earth. And the Xeelee must have been preparing their counter, this loop of string, over almost as great a timescale.”

  Now Spinner-of-Rope felt a bubble of laughter, wild, rise in her own throat. She had an absurd image of two giants, bestriding the curving Universe, hurling galaxies and string loops at each other like lumps of mud.

  “We are truly in the middle of a war zone,” Uvarov said coldly. “This galaxy, with the bullet of cosmic string aimed so accurately at its heart, is merely one incident among ten million in a huge battlefield. To our fleeting perceptions the field is frozen in time — we buzz like flies around the bullet as it hurtles into the chest of its target — and yet the battle rages all around us.”

  Don’t be afraid.

  Spinner closed her eyes and thought of the forest dream man, smiling at her from his tree and eating his fruit…

  I know who this is, she realized suddenly. I’ve seen his face, in Louise’s old Virtuals…

  “I know you,” she told him.

  Yes. Don’t be afraid, said Michael Poole.

  28

  Louise Armonk asked Spinner to take the nightfighter to the source of Mark’s anomalous hydrogen-band signal.

  She showed Spinner some data on the signal. “Here’s a graphic of the main sequence, Spinner-of-Rope.” A bar-chart, in gaudy yellow and blue, marched across Spinner’s faceplate. “We’re getting pretty excited about this. For one thing it’s periodic — the same pattern recurs every two hours or so. So we’re pretty sure it has to be artificial. And look at this,” Louise said. A sequence of thirty bars, buried among the rest, was now highlighted with electric blue. “Can you see that?”

  Spinner looked at the ascending sequence of bars, trying hard to share Louise’s excitement. “What am I looking for, Louise?”

  She heard Louise growl with impatience. “Spinner, the amplitude of these pulses is increasing, in proportion with the first thirty prime numbers.”

  The electric-blue bars were split into discrete blocks, now, to help Spinner see the pattern. She counted the blocks: one, two, three, five, seven…

  She sensed an invisible smile. Just like a child’s puzzle, isn’t it?

  “Oh, shut up,” she said easily.

  “What was that?”

  “Nothing… I’m sorry, Louise. Yes, I see it now.”

  “Look what’s exciting about finding this sequence of primes is that it means the signal is almost certainly human.”

  “How do you know that, just from this pattern?”

  “We don’t know for sure, of course,” Louise said impatiently. “But it’s a damn good clue, Spinner-of Rope. We’ve reason to believe the prime numbers are of unique significance to humans.

  “The primes are fundamental structures of arithmetic — at least, of the discrete arithmetic which seems to come naturally to humans. We are compact, discrete creatures: I’m here, you are out there somewhere. One, two. Counting like this seems to be natural to us, and so we tend to think it’s a fundamental facet of the Universe. But it’s possible to imagine other types of mathematics.

  “What of creatures like the Qax, who were diffuse creatures, with no precise boundaries between individuals? What of the Squeem, with their group minds? Why should simple counting be natural to them? Perhaps their earliest forms of mathematics were continuous — or perhaps the study of infinities came naturally to them, as naturally as arithmetic to humans. With us, Cantor’s hierarchy of infinities was quite a late development. And — ”

  Spinner barely listened. Humans? Here, at the edge of time and space? “Louise, have you decoded any of the rest of it?”

  “Well, we can figure some of it out,” Louise said defensively. “We think, anyway. But remember, Spinner, we may be dealing with humans from a culture far removed in time from our own — by millions of years, perhaps. The people of such a distant future could be almost as remote from us as an alien species. Not even Lieserl has been able to help us work this out…

  “But you’ve made some progress. Right?”

  Louise hesitated. “Yes. We think it’s a distress call.”

  “Oh, great. Well, we’re certainly in a position to help out god-humans from five million years after our birth.”

  “Who knows?” Louise said drily. “Maybe we are. Anyway, that’s what we’re going to find out.”

  …There was motion at Spinner’s left. She turned.

  Suddenly, the forest-dream man was visible. He was sitting there, quite casually — outside the cage — on the construction-material shoulder of the nightfighter. He wore no environment suit, nothing but a plain gray coverall. His hands were folded in his lap. Light — from some unseen source — caught the lines around his mouth, the marks of tiredness in his eyes.

  At last he had emerged. Gently, he nodded to her.

  She smiled.

  “…Spinner?”

  “I’m here, Louise.” She tried to focus her attention on her tasks; she reached for the hyperdrive waldo. “Are you ready?”

  “Yes.”

  The nightfighter flickered through hyperspace. Traveling at more than a hundred thousand light-years per hour, the Northern edged around the torus of fragmented string loops, like a fly around the rim of a desert.

  The journey took ten hours. As it neared its end Spinner-of Rope took a brief nap; when she woke, she had her suit’s systems freshen her skin, and she emptied her bladder.

  She checked a display on her faceplate. Twenty jumps to go. Twenty more seconds, and -

  Something vibrant-blue exploded out of space at her, ballooning into her face.

  She cried out and buried her faceplate in her arms.

  It’s all right, Poole said softly.

  “I
’m sorry, Spinner-of-Rope,” Louise Armonk said. “I should have warned you…”

  Spinner lowered her arms, cautiously.

  There was string, everywhere.

  A tangle of cosmic string, rendered electric blue by the faceplate’s false coloring, lay directly ahead of the ship. Cusps, moving at lightspeed, glittered along the twisted lengths. She leaned forward and looked up and down, to left and right; the threads of string criss-crossed the sky as far as she could see, a textured wall across space. Looking deeper into the immense structure. Spinner saw how the individual threads blurred together, merging into a soft mist at infinity.

  The string loop was a barrier across the sky, dividing the Universe in two. It was quite beautiful, she thought — but deadly. It was a cosmic web, with threads long enough to span the distances between stars: a web, ready to trap her and her ship.

  And, she knew, this was just one thousand-light-year fragment, among thousands in the torus…

  “Lethe,” she said. “We’re almost inside this damn thing.”

  “Not quite,” Louise said. Her voice, nevertheless, was tight, betraying her own nervousness. “Remember your distance scales, Spinner. The string loops in this toroidal system are around a thousand light-years across. We’re as far from the edge of that loop as the Sun was from the nearest star.”

  “Except,” Mark Wu cut in, “that the loop has no easily definable edge. It’s a tangle. Cosmic string is damn hard to detect; the display you’re looking at, Spinner, is all Virtual reconstruction; it’s just our best guess at what lies out there.”

  “Then are we at risk by being here?” Spinner asked.

  Of course, Michael Poole said.

  “No,” Louise said.

  “Yes,” Mark said. “Come on, Louise. Spinner, we’re working to minimize the risks. But the danger is there. Spinner, you need to be ready to react — to get us out of here, quickly. We have escape routines laid into the waldoes, for both hyperdrive and discontinuity drive.”