25

“I don’t know why you had to drag me up here, into the forest,” Louise grumbled. “Not now. Couldn’t you wait until you were sure of your data?”

Mark said, “But the data — ”

“Is partial, and incomplete, and hardly conclusive. What have you got — just two double images?”

“But the spectral match of the double galaxy images is almost perfect, in each case. I tell you it must be string,” Mark insisted.

“And I’m telling you that’s impossible,” Louise growled. She felt her irritation rise. “How could there be cosmic string in the middle of a void like this?”

Uvarov raised his skull-like face and cackled, relishing the conflict.

The three of them were suspended just below the forest skydome. Louise was on a zero-gee scooter, and Uvarov had been strapped into a stripped-down life support chair attached to three of the flexible little scooters.

Mark, irritatingly, was choosing to manifest himself as a disembodied head, twice life-size, hovering in the air. “How’s Spinner-of-Rope?” he asked Louise.

She grunted. “Bearing up. We’re thirty-three days into the mission, now thirty-three days for Spinner in that couch. And the last ten of them inside this damn hole in the sky.”

“Well, this is really a pretty exciting part of the journey,” Mark said. “We’re crossing the edge of the greatest cosmological void ever detected: more than two hundred million light-years across. As far as we can tell, we’re the only scrap of baryonic matter in all that immensity. That’s an exciting thought even without my evidence of cosmic string…”

“Not exciting for Spinner,” Louise said drily. “For her this void is nothing but sensory deprivation.”

“Hmmm,” said Uvarov. “The Universe as an immense sensory deprivation tank… maybe that’s a good image to sum up the photino birds’ cosmic handiwork.”

Now schematic graphics of remote galaxies — sheets of them, at the boundary of the huge void — peppered the dome with splashes of false color; here and there fragments of text and supplementary images were interspersed amid the insect like galactic swarms.

Mark’s head swiveled around toward Louise. “Look, I’m sorry you don’t think it’s appropriate for me to have dragged you up here. Maybe I should have waited for proof of the string’s existence. Well, I didn’t realize we were out here to do science. I thought we were trying to find ways to stay alive — to anticipate what we’re up against. And that means reacting — and thinking, Louise — as quickly and as flexibly as possible. All right, maybe I’m guessing. But — what if it is cosmic string out there? Have you thought about that?”

Louise turned her face, uncertainly, up to the dome. “If it is string — here — then, perhaps, we’re heading into something even more extraordinary than we’ve anticipated.”

Uvarov chuckled. “Perhaps we should stick to the facts, my dear Mark.”

“There are no facts,” Louise said. “Only a handful of observations. And — across distances measured in hundreds of millions of light-years, and taken from a platform moving through a hyperdrive journey — they’re damned imprecise observations at that.”

Uvarov turned his head to the Virtual. “Tell me about your observations, then. Why are these double images so all-fired important?”

“I’ve been taking observations of the far side of the void,” the Virtual said. “I’ve been looking for evidence of gravitational tensing… The distortion of light from distant objects by the gravitational field of some huge, interposed mass. I wasn’t looking for strings specifically. I was trying to see if I could detect any structure within the void — any concentrations of density.”

“Are the strings so massive, then, that they can distort light so far?”

Louise said, “It isn’t really as simple as that, Uvarov. Yes, strings are massive: their width is only the Planck length, but their density is enormous — a one-inch length would have a mass of around ten million billion tons… a string stretching from Sol to Saturn, say, would have around one Solar mass. We expect strings to be found either in loops thousands of light-years across, or else they will be endless — stretched right across the Universe by the expansion from the singularity.”

Uvarov nodded. “Therefore, if they are so massive, their gravitational fields are correspondingly huge.”

“Not quite,” Louise said. “Strings are very exotic objects. They aren’t like stars, or planets, or even galaxies. They simply aren’t Newtonian objects, Uvarov. The relativistic gravitational fields around them are different.”

Uvarov turned to her. “Are you telling me the strings are antigravitational, like the domain walls of the nightfighter’s discontinuity-drive wings?”

“No…”

Far enough from a loop — a finite length of string — the mass of the string would attract other bodies, just as would any other massive object. But an observer close to a string, either a loop or part of an infinite string, would not experience the gravitational effects to be expected from such massive concentrations of matter.

Louise said, “Uvarov, gravitational attraction works by distorting spacetime. Spacetime is flat if no heavy objects are present; an object will sail across it in a straight line, like a marble across a tabletop. But the spacetime close to a Newtonian object, like a star, is distorted into a well, into which other objects fall. But close to a string, spacetime is locally flat — it’s what’s called a Minkowski spacetime. Objects close by aren’t attracted to the string, despite the huge mass…”

“But,” Mark said, “the spacetime around a string is distorted. It is conical.”

Uvarov frowned. “Conical?”

“Imagine spacetime as a flat sheet. The presence of the string removes a slice from that sheet — like a slice of a pie, cut out of spacetime. What’s left of the spacetime is joined up — the hole left by the missing slice is closed up so that the spacetime is like a cone. Still flat, but with a missing piece.

“If you were to draw a circle around a string, you would find its circumference shorter than you would expect from its radius — it’s just like drawing a circle around the apex of a cone.”

“And this small spacetime defect is sufficient to cause the double images you speak of?”

“Yes,” Mark said.

A cosmic string wasn’t visible directly. But its path could be made visible, by a track of double images of remote objects, separated by about six arc seconds, along the length of the string.

Louise said, “Uvarov, imagine two photons setting off toward us from a remote galaxy, beyond a string. One of them comes to us directly. The second, passing on the far side of the string, travels through the conical defect. The second photon actually has less distance to travel to reach us, thanks to the defect; its journey time is less than the first’s by around ten thousand years. Hence, the double images.”

Uvarov grunted. “Louise, you have explained to me how the network of strings was the web around which the galaxies coalesced. I do not understand how this can be, if the gravitational effects of these strings are so slight.”

Louise sighed. “The strings are primeval objects: they were formed within an invisible fraction of a second after the Big Bang itself, during the symmetry loss caused by the decomposition of the unified superforce. Since then, the expansion of the Universe has stretched the strings. So the strings are under great tension — a tension caused by the expansion of the Universe itself… The strings whip through space, at close to the speed of light.

“Where the strings pass, their conical defects cause them to leave a wake. Matter falls in toward the two-dimensional, sheet-like path swept out by the string. And it’s this infalling that caused the formation of the baryonic matter structures we observe now: clusters of galaxies, in threads and sheets.”

“In fact,” Mark said, “the wake is itself observable. Or should be. It imposes a slight Doppler shift on the microwave background radiation. I should be able to see a slightly brighter sky on one side of the invisible string than on the other…”

“And have you seen this?” Uvarov snapped.

“No,” Mark admitted. “Damn it. The Northern couldn’t be a much worse platform for this kind of measurement; the microwave Doppler is below my level of resolution.”

“But do you think you’ve found some image pairs,” Uvarov persisted.

“Yes,” Mark said, sounding excited again. “Two pairs so far, and a few other candidates. The two pairs are aligned, just as you’d expect them to be if a string is the cause…”

“Enough,” Uvarov snapped. He raised his chair into the air above them and prowled across the underside of the sky-dome, his ravaged profile silhouetted against the false colors of the galaxies. “Now tell me what this means. Let us accept, Louise, that your Virtual lover has found a fragment of this — string. So what? Why should we care?”

“We’re in a void, Uvarov,” Louise said patiently. “We’d expect to find string at the heart of huge baryonic structures — like the Great Wall, for instance, a sheet of clusters half a billion light-years long, which — ”

“But we are not at the heart of such a huge baryonic structure. Is that your point, Louise?”

“Yes. That’s the point. There’s no reason why we should find string here, in this void, away from any concentrations of matter.”

“I see. There is nothing out there but dark matter,” Uvarov growled quietly. “Nothing but the photino birds, and their even more exotic cousins — and whatever they’ve chosen to build, here at the heart of their dark empire, far from any baryonic structure.”

Uvarov wheeled to face Louise, his scooters spurting puffs of reaction gas. “If it exists, will the string have any effect on the photino birds?”

“Possibly,” Mark said. “Strings are gravitational defects. Dark matter is influenced by gravity…”

Uvarov nodded. “So perhaps the string is here to do damage to the photino birds. Is that possible? Perhaps the string has been moved here deliberately.”

“I hadn’t thought of that, but I guess it’s possible.” Mark peered up into the dome, his eerie, disembodied head looking bizarre. “Yes. If someone is waging war on the photino birds, then maybe they are using lengths of cosmic string as weapons. Think of that. And more: who in this Universe is capable of such an act, but the Xeelee themselves?

“Lethe — fighting wars with bits of cosmic string. How have they the audacity to even imagine such weapons?”

Louise looked up into the dome’s sketchy, gaudy rendering of the Universe. Suddenly these scraps of data seemed pathetic, their understanding hopelessly limited. Were the final wars for the destiny of the Universe being played out between Xeelee and photino birds, somewhere in this huge void, even now, as she stared up in her blindness and ignorance?

“Keep gathering your data, Mark,” she said. “In another few days we’ll be out of this damn void.”

“We’re like rats, crossing the rim of some huge war zone,” Mark said, his huge face expressionless. “We can barely comprehend the visions around us. And we’re heading for the final battlefield…”

Suspended between Decks, in the middle of a cloud of floating chickens, Mark and Lieserl made love.

Afterwards, Lieserl rested her head against Mark’s bare chest. His skin, under her cheek, was rough, covered in short, tight-curled dark hairs, and slick with sweat — in fact she could taste the sweat, smell its salty tang. She felt a pleasant, moist ache in her thighs.

“I still feel breathless. Maybe I’m too old for this,” she said.

Mark nuzzled her hair. “Then make yourself younger.”

“No.” She pressed her face against his chest. “No, I don’t want to change anything. Let’s keep it just the same, Mark; let’s keep it real.”

“Sure.”

She was silent for a moment. Then, despite herself, she added, “And it is bloody real, you know. A magnificent illusion.”

She felt him smile.

“I told you, I’ve put a lot of time into getting it right,” he said. “This and coffee.”

She laughed, and pulled herself away; her skin parted from his with a soft, moist sucking sound. “I wonder if anyone was watching us.”

Mark stretched; the chickens, fluttering and clucking, swam clumsily through the air away from his arms. He glanced around. “I don’t see anyone. If there was, do you care?”

“Of course not. It might have done them good, in fact. Shaken them up a bit more.”

Lieserl rolled in the air, reached behind her back and began to straighten her hair. The Decks wheeled slowly around her, an immense box of green-furred walls. After the surrender of the Temples, the coming of zero-gee had, slowly, made inroads into the life of the people — the Undermen, as Spinner-of-Rope still called them — who lived here between the Decks. The most noticeable was the cultivation of all of the available surfaces of the Decks; now, the walls and ceilings were coated with meadows, patches of forests, fields of wheat and other crops. The trees grew a little haphazardly, of course, but they were being trained to emerge straight. And, without the pressure of walking feet, the grass in the parks and other areas was beginning to look a little wild.

A huddle of people had gathered under what had been the roof of Deck Two — the underside of Deck One. Mark — or rather a second projection of him — was taking the hesitant, young-old people through a literacy and Virtual usage program. And elsewhere, Lieserl knew, the infrastructure of the Decks was being upgraded to remove the Decks’ enforced reliance on pictograms.

These initiatives gladdened Lieserl. She remembered the world of her brief childhood, drenched in Sunlight and data and Virtuals and sentience: perhaps the most information rich environment in human history. The contrast with the stunted, data-starved environment of the Decks was poignant.

In one spot, close to the surface, she saw Milpitas and Morrow, toiling together. The two old men were constructing a sphere of water, bound together in a frame of wood and reeds: a zero-gee water garden, Morrow had called it. Lieserl remembered his smile. “All part of Milpitas’ therapy,” he’d said.

The whole environment made for a charming prospect: the Decks had evolved away from the bleak, iron-walled prison they’d been under the Planners during the long flight, and turned into a green-lined sylvan fantasy. There were trees growing at you out of the sky, for Life’s sake. And some inspired soul had liberated boxes of wild flower seeds from the Northern’s long-term stores; now the inverted meadows were, more often than not, peppered with bluebells.

The old floors were still coated with the old, boxy homes and factories, of course. But many of the homes had been abandoned; they sat squat on the surface like empty shells. Instead, new homes had been established in the air: rangy, open dwellings, loosely anchored to whichever surface was nearest, or fixed on thin, impossibly fragile spindles.

She held Mark’s hand and drifted through the chicken cloud, drinking in the fowls’ childhood, farmyard smell (…or at least a Virtual, cleaned-up version of it). “You know,” she said, “maybe zero-gee was the best thing that could have happened to this society. Slowly the Decks are turning into a decent place to live.”

Mark grunted. “But it’s taken a long time. And sometimes I think this is all a little unreal.”

“What is?”

He waved a hand. “The strange, aerial society that’s been established here. I mean, beyond these walls of grass there is nothing — nothing but an intergalactic desert, across which we’re fleeing in search of protection from an alien species with whom man has been at war for megayears…”

Across the Universe we flee, Lieserl thought, with chicken eggs and bluebells…

“Maybe that’s true,” she said. “But so what? Is it a bad thing? What can the people here do, but live their lives and maintain the lifedome’s infrastructure? An awareness of what’s outside — of the Universe as megayear celestial battlefield, across which we’re fleeing — is like a morbid, paralyzing awareness of death, it seems to me. Mark, we’re bystanders in the middle of a war. I suspect the last thing any of us needs is a sense of perspective.”

He grinned, and laid his hands on her bare hips. His eyes were alive, vibrant blue, within his coffee-dark face. “You’re probably right.” He pulled her to him, and she could feel the firmness of a new erection against her own pad of pubic hair. “What can any of us do, but follow our instincts?”

She felt a small, contained part of herself open up in his warmth. Sex — even this Virtual reconstruction of it — was wonderful, and, remotely, she was reminded once more of how much had been kept from her during her brief, engineered life. She’d gained five million years of sentience, but had been deprived of her ancient, human heritage.

She lifted her arms and wrapped them around Mark’s neck. “You should be careful with me,” she said. “I’m an old lady, you know…”

He bent his head to hers and kissed her; she ran her tongue over the sharpness of his teeth.

Around them, the chickens rustled softly, detached feathers drifting through the air like snow.