Second Genesis

CHAPTER 1

The tree named Yggdrasil plunged toward the heart of the galaxy at very nearly the speed of light, safe within a cone of shadow from a sleet of radiation that otherwise would have charred it to ash in microseconds.

It still clutched the remains of a comet in its roots, so water was not yet a problem. But light and gravity were strangely wrong, interfering with its tropisms.

Yggdrasil was a very confused tree.

Ahead, always, was a funnel of dancing sparks. Behind was a terribly bright light. Yggdrasil’s senses told it that it was in the terrifying grip of a one-g gravitational field that was tugging it toward that unnatural sun. It had been trying for twenty years to escape. But when it tried to turn the reflective surfaces of its leaves toward the perpendicular, something always frustrated it.

Yet, wonder of wonders, Yggdrasil never fell. An equal and opposite force applied to a small region of its central trunk prevented that. Yggdrasil knew in its vegetable fashion that a girdle of foreign substance encircled its waist, but its senses were not adequate to tell it about the tether and the gargantuan turnbuckle that anchored the girdle.

A strange thing had happened to the stars as well. They swarmed around the tree in rainbow hoops of color—violet, then blues, greens, and yellows ahead; orange and progressively darker reds behind. Both ahead and behind, blind disks had blossomed as the stars marched in both directions through the spectrum and disappeared. The rearward blind spot was larger. Over the years it had kept expanding, compressing the rainbow hoops and pushing them forward until now they circled the coruscating funnel of sparks like concentric halos.

Scores of times Yggdrasil had tried to pick a yellow target star, only to have it change colors and vanish from the universe.

Only the odd pursuing sun had not dopplered through the spectrum. It remained fixed in color and distance, seeming to grow ever brighter against the expanding dark region behind it.

Fretting, Yggdrasil tried to concentrate on growing one of its branches. Its crown—since it had been prevented from spinning—was no longer perfectly symmetrical, and this was a branch that needed to catch up. Fortunately, the direction of the tug of gravity was always a guide. Growth, Yggdrasil knew in its simple wisdom, was supposed to be perpendicular.

There was commensal life within the cavities of the errant branch, but it was too insignificant to be noticed. Yggdrasil ignored it. The only verities were light, gravitation, and water.

“I think Yggdrasil needs a tranquilizer again,” the tree systems officer said. “It’s starting to show signs of trauma.”

Bram set down the carton of housewares he had been packing and turned to face her. “Are you sure?” he said.

“I’m afraid so, Captain,” she said. “The monitors indicate enzymatic reactions in the heartwood, and gallic acid’s showing in the contents of the parenchymal cells.”

Mim, coming through into the observation veranda with another armload of empty cartons, heard the exchange, “Oh, no!” she exclaimed. “Right in the middle of moving week!”

Bram shot her an affectionate glance. Mim was well past middle age now—the mirror showed fewer gray hairs every day—but her handsome face still preserved some of the lines it had acquired during their four decades together. To Bram’s way of thinking, the lines gave her a strength of character and a beauty that he had come to love; it was hard to imagine Mim without them, but youthing was inevitable, and he supposed he would have to get used to it.

“Have you tried readjusting the auxin balance?” Bram said.

The tree systems officer looked worried. “We’re close to the limit on that, Captain,” she said. “Any more might be dangerous. Yggdrasil knows it’s edge-on to something that looks like a sun to it and that half of its crown’s in shadow. We can only deceive it so far, then the separate deceptions start to contradict each other. Too many auxins on the lit side, and we could have a very sick tree.”

She waited diffidently for his response. The tree systems officer was a grandchild of Jao and Ang, and like many of her contemporaries she tended to treat Bram like a monument. She had not even been born yet when he had begun the immortality project. But Bram knew that she was a first-rate botanist, and he trusted her judgment.

Bram sighed. “All right. I suppose we’d better keep Yggdrasil tranquilized at least through moving week. We can’t afford a delay. The branch we’re living in is getting a bit bosky. And we’re already ten degrees out of plumb.” His eyes crinkled humorously. “Besides, we’d have a mutiny on our hands if we held up Bobbing Day.”

“Very good, Captain,” she said without cracking a smile. She turned smartly on her heel and left.

Bram watched her go. She had made him feel old and hoary. There was no reason for it, he told himself. His apparent age was down to somewhere in the midforties by now. But his body still carried the memory of being much older, and it showed sometimes in the way he moved and in the habit of protective postures. That, too, would pass with time, Bram supposed.

“The new ones are so earnest,” Mim said, reading his thoughts.

“I just wish they wouldn’t call me ‘Captain’ all the time.”

She laughed. “But you are captain this year. And you’ve been elected seven times. That’s more than anybody.”

“It’s only ancestor worship,” he said. “Exaggerated respect for all the old father figures. And mother figures,” he added hastily.

“Then why was Jao elected only once?” she teased him.

“And never again—I know, it was a disaster! Jao’s the first one to tell you that himself.”

“Jao never wanted to be captain in the first place. I sometimes suspect he sabotaged his first term on purpose so they’d never ask him again. But pity poor Smeth. He keeps campaigning, and he hasn’t been elected once yet.”

“Save your pity. Give him time. He has the next five hundred years to round up the votes. I’ll bet that by the time we get to the Milky Way, he’ll hold the record for being elected the most often. Because by then he’ll be the only one who wants the job.”

She giggled appreciatively, though she never would have hurt Smeth’s feelings by doing it in his presence.

“And when you remember how he kept telling everybody that he had no intention of coming with us—that he wouldn’t trust his life to an overgrown plant and a jerry-built ramscoop drive!”

Smeth had been a surprise to both of them. Bram had been sure that Smeth would stay behind. By the time the probe project had reached fruition, Smeth had accreted a huge department, with more than a hundred humans beneath him. He had attached himself like glue to the Nar organizational superstructure, and the Nar, thinking they were stepping softly on human sensibilities, funneled everything through him, snowballing his authority. He had nothing to gain by deserting the new egalitarian society that human immortality had brought about. With eternity ahead of him, he had nowhere to go but up.

But when the day had come to board Yggdrasil or be left behind, Smeth had showed up at the shuttleport with a small bag of personal belongings and a string of six biosynthetic walkers, led by a Nar porter bearing his library, instruments, and accumulated records.

“I guess he decided that it was better to be a big floater in a small pool,” Bram said.

“Or maybe he simply couldn’t bear the idea of all of us leaving without him.”

Bram nodded. “After he saw the stampede that developed.”

Smeth had not been the only surprise. More than five thousand people had elected to go along on the genesis quest—almost a third of the human race. The project had tapped a deep longing. The Nar had not underestimated the strength of the buried feelings unearthed in their pets. About ten years into the project, they had begun a program to gather all candidates from the farther worlds, and it had taken another twenty years to bring them all in. Those who had waited too long or who had changed their minds at the last minute had been out of luck.

“Well, I’m glad he decided to come along. It wouldn’t be the same without him.”

“Yes. I have to admit he’s improving.”

Mim fell silent. Bram knew she was thinking about Olan Byr. Immortality had come too late for Olan. The project had been a long, hard one, even with the blueprints of Original Man to work from and the full cooperation of the Nar. There had been times when Bram had thought that he himself would grow too old to benefit from it.

Mim had had fifty years to get over her grief for Olan. Forty of them had been spent with Bram. By the time they had drifted together, she had been too old for children. But her fertility had returned during the last few years, and lately she had been thinking about having a baby after she grew another ten or fifteen years younger. But only if tree demographics permitted, she was always quick to add whenever the subject came up. Yggdrasil could easily support another twenty thousand humans—in fact, about five hundred babies had been born already. But everyone was aware that a long trip lay ahead of them.

Bram reached for her hand, and they exchanged smiles. “Go ahead,” she said. “I’ll finish the packing. You’d better see to Yggdrasil’s tranquilizer. If the drinks get sloshed over the rims of all the glasses on All-Level Eve, Marg will have a fit.”

“Life would certainly be simpler,” he said, “if we didn’t have to rotate our environment thirty degrees every year to keep Yggdrasil from getting lopsided.”

She squeezed his hand. “But it wouldn’t be half as much fun,” she said.

It was an hour’s ride to the trunk even by slingshot, but Bram always enjoyed the view. There was no real reason to make the trip—the tree systems staff was fully competent and, in fact, knew more about the operation of the tree than he did—but the approaching tree-turning maneuver made a good excuse for the excursion.

He reeled in an empty travelpod, eased it through the lips of the gasket, and clambered inside. The absurdly simple arrangement made the expense of air locks for the external travel system unnecessary; otherwise, twelve air locks would have had been installed. The main rack of cables, like an abacus one hundred fifty miles long, was anchored at a new terminus every year, thirty degrees farther along the rim of the tree’s crown, leaving a couple of permanent cables behind for standby access to the abandoned branch.

So far, the only major internal fast-transit system was limited to one branch—the one the human population would be living in during the half millennium when they were coasting between galaxies, and Yggdrasil could be allowed to have its normal one-g spin again. But that was one hundred and twenty degrees away at the moment, its halls and compartments standing on their heads, its pools drained, and everything important either moved or lashed down.

Bram took a moment to check out the pod’s systems. Nothing could go wrong, of course; there was an FM rescue beeper in every pod that would quickly summon help in an emergency. But for someone serving as year-captain, it would be embarrassing to be stranded halfway along the guide rope and have someone come to fetch him.

He made sure the air bladder carried enough reserve for the hour’s trip and that the emergency bottle under the seat was full. He squinted through the hyaloid membrane of the docking chamber’s blister and sighted upward along the elastic cable. The several hundred feet of it that he could see before it came invisible against the distant trunk were reassuringly opaque, indicating that the molecular structure was in a mostly crystalline state.

He grinned as he prepared to change that. He got the little bottle of boron trifluoride out of the dashboard and applied a few drops with an eyedropper to the elastomer line, just forward of the bowline knot that hitched it to an interior stanchion.

The pod gave a shudder as the line began to contract. Bram could see the triggered section turning transparent as its molecular structure became amorphous. The transparent portion shot outward, erasing the cable from sight. A few minutes later, when enough miles of cable had been triggered to overcome the one-g force stretching the line, the pod picked up speed, burst through the gasket, and flew up the guideline toward Yggdrasil’s distant trunk.

Bram held on. He was glad the process wasn’t instantaneous. He wouldn’t have fancied a snapped neck. There was a lot of energy stored in a hundred and fifty miles of superelastic line. As it was, the pod would accelerate at a comfortable rate, never passing two g’s at its zenith, then slow to a bounce as the trailing cable began to tighten.

The organic elastomer, with a stretch ratio of over a thousand to one, was a by-product of the exodus research program and, by departure time, had already found wide industrial application on the Father World. The raw materials came from Yggdrasil itself—derived from the adaptive mechanism by which a tree with a three-hundred-mile diameter synchronized the turgor movements of its leaves.

Bram gazed unabashedly through the transparent skin of his rubbery container and admired the outside view.

Straight up, of course, was a silhouette of Yggdrasil’s trunk seen against the swirling blizzard of sparks created by the ramscoop field some hundreds of miles in front of the tree.

The silhouette was a short, thick bar, lacking detail. The shower of light was pretty—even jolly—but Bram knew that its beauty was a lie. It was the emblem of instant death—the visible by-product of the inferno of radiation pouring into the probe’s magnetic funnel. At more than ninety-nine percent of the speed of light, here in the thick of the galaxy where the H-II clouds were dense, some two hundred trillion hydrogen atoms slammed into every square inch of the electromagnetic shield every second. Even allowing for a gamma factor of twenty thousand—the last figure Jao had given him—that worked out to twenty billion high-energy collisions per second within the ship’s relativistic time frame.

If that shield were to fail for even a fraction of a second at this velocity, five thousand humans would die before their nervous systems were able to register the fact. And Yggdrasil would turn to stardust.

Bram shuddered. As frightening as that umbrella of sparks was, at least it hid the nothingness beyond—the blind spot where the crowded wavelengths of light pushed past the visible spectrum and wiped the stars from the universe. The blind spot behind, eerily framing the artificial sun of the fusion stage of the drive, was bad enough.

He let his eyes follow the long, mirror-bright shaft downward to where the fusion flames burned. The waste light had enough red in it for Yggdrasil to carry on photosynthesis, enough ultraviolet for human sunbathers to tan themselves by behind the lenticels of the recreation areas.

The long shaft threaded a dangerous course between Yggdrasil’s twin domes. At its closest point it passed within forty miles of the trunk, and Yggdrasil itself had provided extra protection there—growing a shield of adventitious leaves with their silvery reflective sides facing out. The star tree could handle anything up through x-rays.

The material part of the shaft was its least important aspect. In fact, its tremendous length could not have held up under even moderate lateral stress. It was there to provide support for the winding coils that deflected the roaring streams of ionized hydrogen in their constricted path from the collection area forward to the ignition cage aft.

For a moment Bram tried to imagine what the whole crazy travel arrangement would look like to a hypothetical observer outside the craft—provided that the observer could see by undopplered light. Or, more to the point, provided that the observer was in the same relativistic frame, matching the spacecraft’s course in velocity and direction. Otherwise, the collection of shapes on their long skewer would be foreshortened by a factor of twenty thousand, turning them into a stack of paper-thin disks pierced by a thumbtack.

He decided it would look like a post horn straddled by a leafy dumbbell.

Bram had seen a post horn once, at one of Olan Byr’s memorial concerts. The ancient instruments, from lyres to sousaphones, had been part of Olan’s legacy. He had been tireless in commissioning reproductions from hints in man’s digitally transmitted art masterpieces, dictionary sketches, and clues in the musical notation itself. The post horn was based on one played by an angel in an Annunciation. It was a long, straight tube of brass, tall as the man who played it, with a flaring bell at one end and the smaller flare of a mouthpiece at the other.

Bram closed his eyes for a moment and savored the eccentric image.

The post horn that dragged Yggdrasil by the collar was twelve hundred miles long, with its slender tube aligned along g forces to keep it straight. The bell was an insubstantial net of superfilament, several hundred miles in diameter, that kept its shape by virtue of an independent spin at its rim. Around the bell was a multicolored cascade of sparks, like trumpet notes made visible. A miniature sun burned blindingly in a magnetic cage at the mouthpiece, like a divine breath. And from the flared mouthpiece issued a thin pencil of inspired light as the hadronic photons, their work done, decayed and wreaked havoc with whatever interstellar debris was still left behind in the wake of the probe’s sweep.

Pleased with the image, he conjured up the other component of the queer hybrid vehicle.

Yggdrasil would make a compressed sort of dumbbell, he decided, with a short, thick handle and rather flattened hemispheres. More like a pair of fat wheels lying athwart the long axis of the probe. One hemisphere was silver with a green rim facing the fusion fire. The other was brown, laced through with the crystal sparkle of cometary ice and showing an arc of green where Yggdrasil’s root system had decided to help out with the photosynthesis.

The looming reality of a wall of foliage rushing past him only a few miles away dissipated the image, and Bram turned his eyes to the view he loved best.

Between the rushing walls of Yggdrasil’s twin hemispheres, a spectacular slice of sky was visible. A rainbow of stars made a dazzling arch across the void. Optical effects had crowded the bands of color so close together that the effect was like strands of matched jewels, jumbled together in overlapping profusion.

It was so beautiful that it hurt.

Bram studied the ribbon of stars. Was it narrower than the last time he had looked? It was hard to tell. But the yellow band seemed to have moved a degree forward, and the dull, ominous blanket of reds that faded into the blind spot seemed to have been dragged along by the rainbow hem.

A star whizzed by, changing from purple to blue to green, then to yellow, orange, and red before it was swallowed by the blind spot.

The star must have been very close—only a few light-days away. At the present gamma, Yggdrasil swept across a light-year in about thirty minutes. That was fast enough to make the nearer stars move at a crawl, changing their colors as they lined up against the background rainbow.

A second violet star popped out of nothingness, riffled through the spectrum, and vanished to the rear.

The first star’s companion! Yggdrasil was skirting a double star system.

Bram tried not to worry. Even here in the depths of the galaxy the stars were light-months apart. A collision would be most improbable, Jao had assured him. Even if Smeth’s instruments were to show Yggdrasil heading straight toward a star emerging from a dust cloud, there would be minutes—perhaps hours—to change course. A lateral nudge of less than half a degree, projected over a minute or two of travel, would always give them margin to spare.

He drank in the glittering, spectacle again, wondering how much longer he would be able to enjoy it. As Yggdrasil’s speed increased, eventually the stellar rainbow would shrink into a thin gold rim framing the forward blind spot, and the vortex of hydrogen influx would make it invisible from any part of the tree. He had tried to get a time estimate from Jao, but Jao had been vague. They were slicing the remainder of the speed of light so thin at this point, Jao said, that measurements were meaningless.

He looked up through the top of the pod and saw the trunk rushing toward him. A cluster of external housings was directly above: upside-down bubbles with suspended catwalks. Ten or twenty miles to his left, he saw a portion of the tremendous crystalline girdle that circled Yggdrasil’s waist and the secondary tether that would keep Yggdrasil from sliding forward along the shaft during deceleration mode. The tether was of woven viral monofilament a half mile thick, and the double bowline knot that fastened it had been tied, with much tricky maneuvering, by a pair of space tugs. Tension would only make it stronger; with the enormous forces involved, nobody wanted to take chances with extraneous fittings.

Bram noticed that at the moment Yggdrasil was floating free within its circlet; its momentum was temporarily matched with that of the probe.

The trunk filled his view, and then the taffy pull of the counterline slowed the travelpod to a bobbing stop about a half mile below the entry blister.

Bram uttered a mild expletive as he found that the fist-size electric trolley that was supposed to wind him in the rest of the way was out of order.

For a moment he was tempted to exercise a year-captain’s prerogatives and signal the hub to reel him in. But he was only a couple of hundred feet from his destination, and the pod’s weight was negligible added to his own, even under one-g acceleration. A half hour’s worth of muscle power would do it.

With a sigh, he bent to the two-handed windlass and began cranking.

“That ought to do it,” Bram agreed.

He tore his gaze away from the massive helical housing of the high-capacity pump. There was a final gurgle that shook the floor as the last of a half million gallons of chemical solution was forced deep into Yggdrasil’s sapwood.

The tree systems officer and her hovering assistant gave him bland stares. “I thought the best way to calm Yggdrasil down would be to smooth out the peaks and valleys in phytochrome balance,” the TSO said with professional briskness. “There was too extreme a swing between the two pigment forms, and it was driving Yggdrasil crazy.”

She gauged his expression for signs of comprehension, apparently decided in his favor, and went on. “You see, the problem is the growing Doppler shift. Unfortunately, all the far-red light comes from the same direction as the fusion light, so that side of the tree’s overstimulated. The phytochrome keeps changing back and forth between the far-red-absorbing form and the sunlight-absorbing form, then back again.”

Her assistant, even younger than she was, nodded agreement. They were both being patient with the old dodderer.

“Yes, yes,” Bram said quickly. “I’m sure you took the right approach.”

The assistant cleared his throat and glanced at his boss before speaking. “And at the same time, there’s the problem of blue light tropisms at the opposite side of the tree. Where the band of up-shifted light is. Yggie’s hormones are working overtime to cope. And you can imagine what that does to his biorhythms.”

“I can understand why your department was so concerned,” Bram told them in his best sober manner.

They both beamed at him.

“So we added a healthy dose of vitamin A to the tranquilizer to damp down beta-carotene activity,” the assistant finished triumphantly.

“Fine,” Bram said with a judicious nod. He looked around for a way to make his escape. “Well, that seems to take care of it, so I’ll—”

“Of course, you’ll want to review our total hormone strategy while you’re here, Captain,” Jao’s granddaughter said. “Shall we start with the tree-turning maneuver?”

Bram gave in to the inevitable and let her lead him over to the far end of the hollow, where a battery of young technicians, wearing the leaf tabards that seemed to be the working costume of the new generation, busily tended the array of giant fermentation tanks where hormone synthesis started.

A half hour later, his eyes slightly glazed, Bram found himself blessedly alone in the brilliant corridor that ran through the trunk’s heartwood. Alcoves branched off on either side, each with its neatly painted street sign. Here, forty miles beneath Yggdrasil’s bark, a lot of specialized work went on—plastics manufacturing using leaf sugars as feedstock, the Message broadcasting facility whose vital work could not be interrupted by yearly bough migrations, the central observatory.

There was also a recreation complex with guest suites, increasingly popular with the younger set and the advanced retroyouth crowd, with facilities for sports, swimming, and small-craft sailing. After Yggdrasil left the galaxy and acceleration ceased, it would be a center for such weightless pursuits as flying, flat-trajectory handball, three-dimensional ballet, and, Bram didn’t doubt, free-fall sex.

Bram paused to look at the bulletin board. Some members of the trunk staff were choosing up sides for a game of teamball in what would eventually be the flydome. Bram was tempted to join them. But he knew that he’d be invited only through courtesy and deference to his position. At his present chronological age, he’d only be a liability to whatever team was willing to suffer him; better stick to playing with his peers on the occasional Tenday.

Feeling pleasurably sorry for himself—refraining from reminding himself that he was not as old as he had been twenty years ago—he gave the bulletin board a regretful last glance and set off down the long arcade toward the observatory.

At least that was one treat he could give himself.

Jun Davd looked up from his work and smiled at Bram with a third set of teeth that were as white and flawless as they had been when he had grown them a quarter century ago.

“Nice of you to play truant just so’s you can come visit an old man,” he said.

“The captain never plays truant,” Bram said, smiling back. “Everything I do is always in the line of duty.”

He raised both hands, and they touched palms in the old gesture.

Jun Davd chuckled. “So your duty brought you up to Yggdrasil’s attic to rummage through the stars.”

He was bent, frail, attenuated, but in remarkably good shape. Bram guessed that his biological age was down to about eighty. There were even traces of gray in the cap of white curls. Flesh was returning to the dark, mummified face, filling in the wrinkles. They had gotten to Jun Davd just in time.

“Is that what they look like now?” Bram asked, gesturing at the extrapolated display Jun Davd had been studying when he came in. The screen showed a splendid panorama of multicolored stars, glowing clouds, and luminous streamers swimming past in relative motion. Quite a few of the stars had disks.

“More or less,” Jun Davd said. “The computer’s having a hard time keeping up. That nice orange star you see coming toward you has been reconstructed from gamma rays in the ten-to-the-minus-six-nanometer range. The light that kills. The rear view’s even more of a challenge. We’re seeing those stars by ultralong radio waves—past the hundred-kilometer range. We’ve got almost a thousand miles of wire with a weight on the end trailing behind us for a dipole antenna, and I really could use a couple of thousand miles more except that I haven’t been able to figure a way to keep the drive from melting it, and I’ve got I don’t know how many thousands of stiff wires making pincushions out of Yggdrasil’s crown and root ball, but you can appreciate that definition’s still a problem. I’m afraid the computer’s taking a lot of artistic liberties.”

“Stop complaining. You’re living in an astronomer’s paradise.”

He grinned, young teeth white in the ancient face. “Don’t I know it. On my way to the galactic core to make direct observations of whatever the dust clouds are hiding. The old director, Pfaf-tlk-pfaf, would’ve given one of his fingertips for the chance!”

“I wonder what he’s doing now,” Bram started to say before he remembered.

It was strange to think that the old Nar, Pfaf-tlf-pfaf, had been dead for almost fifty thousand years. And that the immortal humans whom Yggdrasil had left behind were, presumably, still alive—unless the Father World had been hit by a wandering planetoid.

A wave of nostalgia washed over Bram as he remembered how kind the old director had been to a little boy who wanted to learn about the stars and how patient a human astronomy apprentice named Jun Davd had been in explaining all the wonders of the stellar universe.

“Sometimes I wish I’d followed my instincts back then and chosen astronomy as my career,” Bram said.

“I’m awfully glad you didn’t,” Jun Davd said tartly. “Where would I be now?”

It was a sobering thought. The two of them contemplated it in respectful silence for a moment, then Jun Davd went on more equably.

“It’s not too late, you know. You can have an infinity of careers if you wish. Why don’t we take up our lessons where we left off? In five hundred years you might make a pretty fair astronomer.”

“Are you offering me a job, Jun Davd?”

The dark face creased in mirth. “I’m going to need a good assistant. We’d better learn all we can about the Milky Way before we arrive there—including how to use its H-II regions and the hypermass at its core to match our impetus and bring us to a nice safe stop.” His voice was rich with enthusiasm. “Imagine being able to study a galaxy from the outside before making it your home! What an incomparable opportunity!”

Jun Davd had retired, still a junior apprentice, before the immortality project had borne fruit. He had hung on longer than most, and the Nar compassionately had looked the other way, but the day finally had come when he’d had to admit to himself how feeble he had become. He had been miserable in retirement. When Bram, with immortality finally in his pocket, had sought him out, he had jumped at the chance to join the expedition as chief astronomer, with the chance to run things to suit himself. In one swoop he had gone farther than he had in an entire lifetime on the Father World, and he had unlimited vistas before him. Bram sometimes thought that it was this, as much as the immortality treatment itself, that had rejuvenated Jun Davd.

It would be different now for humans on the Father World. Now it was the Nar who were the mayflies.

Their society had had fifty thousand years to adjust to the new truth. How had it transformed itself? Bram wondered. He would never know. And every hour another few years passed on the world he had left.

He shook off the thought and returned to the conversation.

“Are you sure we’ll find a hypermass to brake by when we get there?” he said.

Jun Davd looked at him reproachfully. “You’re forgeting all I taught you. Scratch a galaxy like ours and you’ll find a hypermass at the center. Relic of the quasar epoch. It’s a necessary consequence of the way galaxies are formed.”

“I know. A giant black hole.”

Jun Davd nodded. “A black hole with a mass of anywhere up to several hundred million swallowed suns. The centers of galaxies are violent places, and they’re very crowded. They stir up brews of colliding suns and relativistic electrons. They throw off x-ray jets. Sometimes they explode. The different events depend on the size and spin of the black hole and what it has to feed on and the way it chooses to express itself. And maybe the normal galaxies we see are simply the violent ones in a quiet phase of their history.”

“You paint a vivid picture. What kind of core are we diving into now?”

Jun Davd did not smile. “One that worries me,” he said.

Bram was instantly alert. “What do you mean?”

“For one thing, there are more young stars than theory predicts. And the infrared radiation getting through the dust clouds keeps increasing the farther in we travel, especially at the wavelengths associated with star formation. There are too many stars being born in there.”

Bram searched his rusty memory. “You told me yourself, years ago, that emissions at around the hundred-micron wavelength increase at a fairly uniform rate as you go in.”

“You don’t take my meaning. At this point we’re seeing by light that won’t reach the Father World for another fifty thousand years. We’ve jumped fifty thousand years into their future—and the future of those former selves of ours that made those infrared observations. The process, whatever it is, is speeding up. Something odd is happening behind those dust clouds. Something recent.”

“What do you think it is?”

Jun Davd switched off the display showing the outside stars and punched in a new code. A galaxy appeared within the screen, shining by the glossy light of computer simulation. It was a very pretty spiral with a regular shape. A second galaxy appeared to its left—another spiral, slightly smaller.

“You’re looking at our galaxy the way it appeared some hundreds of millions of years ago, before we collided with the Bonfire. The smaller spiral is the Bonfire as it must have looked before the encounter tore it all out of shape. You’re about to see a computer reenactment.”

“I’m impressed.”

“It wasn’t as big a job as you think. The basic computer model is an old one. I brought it aboard with my data files. I first ran into it as a young astronomy student. All I did was feed in a lot of updated data, including the fifty thousand years’ worth we’ve collected on our trip so far.”

“Go ahead. I’m ready.”

Jun Davd set the display going with a final poke of his finger. The point of view rotated slightly to give more of a side view, and the smaller galaxy that was the Bonfire began moving toward the larger one. Their directions of rotation were opposite, like two wheels rolling toward each other.

“They’re going to grind together with a lot of extra kinetic energy,” Bram commented.

“Watch it here. We’ve got some tidal forces coming into play.”

The larger galaxy began to draw long streamers out of the Bonfire. At the same time its own spiral structure began to stretch and deform.

“I’m going to punch in a couple of overlays at this point,” Jun Davd said. “The red lines are infrared, the white ones radio.”

His long gnarled fingers played over the touch pad, and a pair of overlapping contour maps appeared, more or less conforming to the optical shapes, surrounding them with concentric squiggles and squeezing close together at the centers of the galaxies and in the areas of encounter.

The two galaxies continued to tear at each other as their arms brushed and mingled. It was not a head-on collision, but it was damaging enough. Gauzy ribbons that must have contained millions of stars were stripped away and left to evaporate into space. The computer could not infer the collisions of individual stars—such collisions would have been rare even if the two galaxies had fully interpenetrated—but it could visualize the effects of the gas clouds slamming together.

“Tremendous rise in temperature,” Jun Davd said. “And intense radio emissions.”

The superimposed contour maps writhed, grew brighter, pulsed faster and faster.

“Now, watch closely,” Jun Davd said.

The spiral arm closest to the encounter flared and turned blue as millions of new stars were born out of the clouds of disrupted gas. The Bonfire sailed past, now a blazing blob of light that had lost its spiral shape. The larger galaxy squeezed, then stretched, responding to the gravitational tug. The coils on the opposite side, now released, loosened and changed their pitch. The blue arm tried to follow the Bonfire, reaching after it and losing more stars in the process.

“Now you know why Skybridge is blue,” Jun Davd said.

“I can see that the passing of the Bonfire rejuvenated the nearer spiral arm as a stellar nursery,” Bram said. “But what has that got to do with the interior of the galaxy?”

“Keep looking at the radio and infrared maps,” Jun Davd said.

Over an interval that must have represented a period of hundreds of millions of years after the encounter, the heat and the radio activity pulsed inward, like ripples from a stone seen in reverse. As the computer simulation neared the present, Bram could see the pattern of infrared intensity settle into the profile he was familiar with, growing stronger as it approached the central regions.

But there was more to it than that—a winking of blue light in a shell that followed the wake of the wave and shrank toward the galactic hub.

“It’s the infall of that peeled-off gas, touching off another era of star formation,” Jun Davd said. “By now, it’s in the core, feeding the black hole. Or maybe I should say overfeeding it.”

“We can handle it even if it does turn out to be bigger than we expect. After all, even a black hole with a few billions of solar masses can’t have a diameter of more than a fraction of an astronomical unit, and when we swing around it, we’ll make sure to stay a safe distance from the accretion disk.”

“You’re considering the black hole solely as a gravitational entity. I’m more concerned with what it might be doing in there.”

“Such as?”

Jun Davd added a couple of worried furrows to the fan of deep creases in his forehead. “You saw what our encounter with the Bonfire did to the outer geometry of the galaxy. I’m wondering if it stirred up things in the inner regions as well.”

“That happened hundreds of millions of years ago.”

“Exactly,” Jun Davd said, showing his perfect teeth in a mirthless grin. “Time enough for it to ripen.”

“Jun Davd says it’s thick in there,” Bram said.

“Don’t I know it.” Jao sighed. “We’re picking up gamma too fast. The ramscoop uses whatever falls into it, and I don’t dare monkey with the fields this close to the bend in our hyperbola.”

“But we still haven’t reached the limits of our projected gamma for leaving the galaxy?”

“No, but I’d hoped to make up most of the difference on the way out. We don’t want to be going too fast for the hypermass to grab us. And I don’t want to get too close to a thing like that.” He scratched his ribs reflectively. “Now I’m going to have to shave it finer than I like in there.”

“Jun Davd says the black hole’s going to be a lot bigger than we expected.”

Jao brightened. “That’ll be a help. Stronger gravity to swing us around. Stronger magnetic field to transfer rotational energy. Bigger radius to keep us from getting pulled apart by tidal effects.”

“Now you’re doing what I did, according to Jun Davd—thinking of the black hole only as a gravitational resource and not paying enough attention to whatever mischief it might be causing among all those close-packed stars and dust clouds.”

“Astronomers worry too much.”

“The centers of galaxies are active places. And this one’s more active than most. I’m not just thinking about radiation, I’m thinking about material particles. Are we going to be in danger?”

Jao sucked thoughtfully at his upper lip. The bushy gray mustache there was beginning to turn a faded orange. “Barring the chance of hitting a star or planet, our magnetic fields and our relativistic state of grace ought to do a pretty good job of protecting us. Do you have any idea of how much energy we’re carrying at this point? The universe is in more danger from us than we are from it!”

Bram refrained from smiling. “What about a dust particle?”

“Tear it apart. Whip it on through. Use it.”

“Can we handle that stew of radiation coming from the central parsec?”

“Handle it?” Jao snorted. “We’ll use it.”

Bram said nothing and waited. After a moment Jao flushed.

“All right,” he said. He squatted and scratched a diagram on the smooth wood of the floor with a stylus from his wrist pouch. Bram bent over to see.

There was an obtuse angle with a dot gouged at its vertex. Intersecting the dot was a shallow arc whose horns curved well forward of the dot to embrace the angle.

“This is us, here,” Jao said, tapping the dot. He traced the two lines forming the angle with his stylus. “Our umbrella is opened out to about this angle now, and it’ll keep opening out farther as we pick up speed. Theoretically, if we reached gamma infinity, the cone of the field would open all the way out to a flat disk, but the point is that the field thrives on anything that’s thrown at it. It all goes to feed the engine and make more gamma and a wider intake area. So we have nothing to worry about from up front. And from the rear, of course, all the dangerous wavelengths are dopplered down past the radio end of the spectrum by now.”

“And from the sides?” Bram prompted, though the answer was plain to see in the diagram.

Jao grinned hugely. “You’ve just taken a ride outside,” he said. “You saw for yourself how far forward the star-bow is displaced by now.” He tapped the two horns of the arc with his stylus. “By the time we hit the core, we’ll be snug within what amounts to a dopplered lens with a curvature that looks like this. Any hard radiation forward of the red-shifted meniscus intersects the nappe of the cone made by the field.”

“How long before we swing around the galactic center?”

“At the rate we’re picking up speed in this hydrogen soup, probably in the next few days.”

“Should I cancel Bobbing Day?”

“Don’t even whisper such a thing!” Jao exclaimed in mock horror. “I’ll try to slow us down as much as possible by avoiding the thickest parts of the H-II clouds. With any luck, we’ll squeak through Bobbing Day and All-Level Eve before Yggdrasil starts to squeak and groan.”

“And then?”

“Then we batten down.”

“How much longer can we broadcast the Message?”

“Let’s go see Trist and ask him.”

The Message Center was in the thickest part of the trunk, near the spreading root system, for maximum protection. It was, after all, the most important part of the treeship and the ultimate reason for the mission.

Bram looked down the length of the enormous cylindrical cavity, which was brilliantly lit by the abundant electrical power that was a by-product of the fusion drive. The circular tracks that had been worn all the way around the walls marched dizzyingly into the distance till they blended together. They had been scraped into the wooden surface over a period of time by the necessity of pushing thousands of pieces of heavy equipment another thirty degrees farther along every year.

The equipment itself—data banks, towering stacks of naked capacitors, oscillators, control elements for the thousands of phased array antennae planted in Yggdrasil’s crown and roots—made several broad avenues down the center of the chamber’s temporary floor, leaning crazily inward.

A work gang of young huskies had already started the next move, sweating and hauling at the heavy housings with levers, ropes, and their own backs and shoulders. It was a tremendous job once a year, but it was a lot easier than carting everything across space from bough to bough.

They found Trist in a control booth, eating a tomato sandwich with one hand and tracing geometric diagrams on a touch screen with the other. His face lit up with pleasure when he saw them.

“What brings you two to the upper depths?” he asked.

“We’re going around the bend a little earlier than we thought,” Jao said. “The skipper wanted a status report on the Message.”

Trist took a bite of his sandwich, then put it down. “We’ll be completing one last abbreviated cycle sometime later today, and I think that about finishes it.” He shrugged. “Of course, I’ll keep it going till we’re out of the galaxy. Beamed backward in the microwave frequencies. But it’ll be a very long shot, no pun intended.”

“Your signals have dopplered too far to be receivable, is that it?” Bram said.

“No, that’s not the real problem. Even with a gamma factor of twenty thousand, we’re still intelligible, pulse by pulse. The microwaves focused sternward lengthen into radio waves, and the long waves we send ahead of us compress into microwaves for anyone who happens to be listening on the radar frequencies. With the frequency continually adjusted for Doppler shift, of course. No, the trouble is the pulses are too far apart now because of time dilation. We’ve got a problem of information density.”

“How long is your abbreviated cycle?”

“Twenty days.” Trist grimaced. “We’re down to the genetic code for the Nar themselves, plus a minimum number of simple organisms from which a biologically sophisticated civilization might cobble together a supporting mini-ecology. Plus a Great Language module, of course. And a Small Language dictionary with human loan words. And a capsule history. And a highly abridged cultural package.” He peered at Bram. “We’ve got a touch symphony by your touch brother Tha-tha in the cultural package, by the way.”

Bram found himself looking past Trist, through the window of the control booth, at what he could see of the library. Miles of shelves, containing everything the Nar knew about themselves and their world. The old touch sagas were there, unintelligible to any race but the Nar. The message of Original Man was there in its entirety.

Not all of it could be broadcast, of course. But the Nar had wanted the departing humans to have it all. In the fullness of time, it might come in handy.

Out of it all, a Nar committee had prepared their Message. Or rather a series of Messages, progressively edited. The first took a year to broadcast. Now the Message was down to twenty days.

But if a touch symphony by Tha-tha was still included, then there must also be plans for a touch reader. A future generation of reincarnated Nar, here in the inner galaxy, might yet have access to a smattering of their heritage.

Jao was already figuring in his head. “Twenty days,” he said. “That works out to almost a thousand years for receiving it—with no repeats. The Message of Original Man had only a fifty-year cycle, and it was received by a very patient folk.” He shook his shaggy head. “I can see why you think the program’s finished, Trist.”

“And on our way out of the galaxy,” Trist said, “if our gamma’s up to what you say it’s going to be, we’ll have a Message cycle of close to four thousand years. With the tail out of range of the head.”

“It’s probably moot at this point, anyway,” Jao said. “If there’s other life in the galaxy, we wouldn’t find it this close to the center. Too much radiation in these skies. If we have managed to seed the galaxy with secondhand Nar, we must have done it farther out, with the unabridged Message.”

He cocked his head as a happy thought occurred to him. “That might have been forty or fifty thousand years ago, as the galaxy ticks. They might already have spread like crazy from thousand of foci. They wouldn’t have been too far behind the Father World—hell, they started with a technological civilization! And they’d know their progenitors were only a galactic blink away, waiting to embrace them with all five arms—not like us poor spawn of a vanished species! What an incentive! By now they’d have met, merged. And when we burrow out of this nest of stars, we’ll be traveling through a solid pavement of Nar.”

“Don’t get carried away,” Trist said dryly. “Our lateral transmissions cut a swath that’s only a few thousand light-years wide. The message has probably swept about two percent of the stars in this galaxy. That’s a lot of stars, but it’s hardly at the saturation point.”

Jao waved his arms impatiently. “What are you talking about? With the effective diameter of the phased array in the crown and all the power we’ve got to play with, we can beam to the opposite edge of the galaxy.”

“If we could cut through the dust clouds,” Trist said patiently. “But that’s not the point. For each cycle of the Message, I try to aim the lateral beams at some thick cluster of stars a couple of thousand light-years away and hold them there while I compensate for the changing Doppler. By the time the beam spreads much beyond that, any civilization that’s searching for intelligent signals starts getting smaller and smaller cross sections of the Message. You reach the point where you get a thin slice that doesn’t look like an intelligent signal. And even if you suspect that it is, you scan and you get other thin slices that you can’t put together.”

Jao gave Bram a disgruntled look. “Any advanced civilization doing a sky search would run a continuous survey if they’re worth their salt. They’d sweep up and down the spectrum and run a computer program to put it all together.”

“Maybe,” Trist said.

Jao brightened. “Look at it this way. Two percent of the stars in this galaxy comes to—what—four billion stars. Say two percent of those have planets with conditions that support life—”

“Don’t get reckless,” Trist said.

“Two percent,” Jao said firmly. “All right, that’s eighty million target stars. And say that one-tenth of one percent of them have advanced societies with a little genetic engineering capability and a normal amount of curiosity.”

“How about one one-thousandth of one percent?” Trist suggested mildly.

“Sure. Why not? I won’t quibble. I’m a very unimaginative guy. That makes eight hundred little Nar factories. Hell, make it one ten-thousandth of one percent! We’re still in business!”

“It only has to happen once,” Bram said. “Once out of those four billion stars we’ve touched. Those are the odds the Nar were willing to settle for. They knew it could happen. It happened once with Original Man.”

“More than once, maybe,” Trist suggested.

“That’s a thought!” Bram laughed.

“On the way out of the galaxy,” Trist said, “how about using the phased array in eavesdropping mode for a few thousand years between Message cycles? See what may have developed.”

“It’s all right with me,” Bram said. “But you’d better take it up with the next year-captain.”

“That might be Smeth. He’s campaigning already. He’s concentrating on the new crop of voters this time. He’s got them hornswoggled. The young ones flock around him to listen to his tales of the good old days, when a small band of dedicated humans under his guidance as chairman of the physics department ran the Father World and decided to initiate a grand project to return humankind to its home in the Milky Way.”

“He asked for my vote,” Bram said.

“What did you tell him?”

“I said he could have it.”

Jao, impatient at the digression, had perked up his ears at the mention of eavesdropping mode.

“Yah,” he said. “Good idea. See what intelligent transmissions we pick up. Plug in a program to look for the patterns of touch-reader transmissions. That way we know they’re Nar. You know, even if there’s no other intelligent life in the galaxy and this whole errand was a flop, the Nar must’ve spread over a sphere of a couple of thousand light-years by now, anyway. Hey, in the last fifty thousand years, maybe they sent more message probes after us. Maybe one with a second human crew. If they’ve developed a better drive and were willing to boost at slightly over one gravity, maybe they’re ahead of us. Maybe we’ll find them waiting for us in the Milky Way with a million years of civilization behind them, Or maybe the Nar have been spreading themselves at the edge of lightspeed! Why not? A few thousand years of developing the hadronic photon drive and it might be cheap enough for colony ships. Who needs probes? Who needs errandpersons? At one and a tenth g’s, they could already have settled an arc of space with its leading edge ahead of us.” He looked around wildly. “They could be all around us right now!”

“Don’t get carried away,” Trist said. “Next you’ll have them traveling faster than light.”

“Faster than light? Why not? Einstein is as Einstein does. The Nar arrived at their relativity by a different route. Maybe we humans missed something. You know, for the Nar, mathematics is a sensory experience. They count with the surface of their bodies. Whole digital operations, faster than you can whistle. They can plug as many Nar into a problem as they want—subunits, everything—and feel their way to a solution. Who’s to say they haven’t tackled the faster-than-light problem?”

“Here’s where he drags out the tachyons,” Trist said with a tolerant smile at Bram.

“Go ahead, laugh, but they could’ve reached the other side of the galaxy by now,” Jao insisted.

“If you’re still beating the dead carcass of your Klein universe with its inside-out tachyons, I thought we settled that thirty years ago when we ran it through the computer and kept running up against the problems of nonorientability and self-intersection no matter how many dimensions you cared to postulate.”

“We only ran it up to thirteen dimensions,” Jao protested. “We never solved it for a general case.”

Bram intervened to squelch the familiar squabble before it could get started.

“Whatever’s happening out there in the galaxy—whether the Nar really needed us or not, or whether other intelligent life forms exist and the Message got through to one of them, or eighty million of them by now—it doesn’t matter anymore. We’ve done our part of the job. We can go home now.”

CHAPTER 2

Home.

Bram leaned back in his chairpuff and savored the idea of it, as he had done for most of his life. When he had been a small child, it had been bright, real, and immediate. Later it had become an abstraction, an impossibility. The adult Bram had known too much to believe in it. Now it was tangible again.

From the wooden corridor outside his apartment came the sounds of revelry: Bobbing Day celebrants on their way to the All-Level Eve festivities in the Forum—some of them already tipsy, by the sound of it. Mim was in the next room, getting dressed. Shortly she would join him, and they would go down together to be a part of the merrymaking. A year-captain could not afford to be absent.

But for these few moments of solitude he could think about home. For that, after all, was what the annual tree-turning celebration was all about—though it had grown lately into a tradition of its own.

Home.

Thirty-seven million years ago there had been an intelligent species that called itself the human race—Original Man. They had dwelt, by all the evidence, on a planet of a yellow sun in a rather isolated galaxy that they called the “Milky Way,” part of a sparse cluster consisting basically of two big spirals and their attendant swarms of small satellite galaxies.

Whether or not human beings still existed there was impossible to know, of course, when the very light that arrived from the Milky Way was thirty-seven million years old. But it was unlikely in the extreme. It was to be presumed that those humans were long extinct—gone the way of other species before them. Or that in the immensity of time they had evolved out of all recognition, into some new species that could no longer be considered human.

But before they had vanished or changed, they had left their mark on the universe.

The heights they must have reached had been dazzling, for they had learned how to tame whole stars and squander their energy. The energy, in unimaginable quantities, had been spent on the ultimate purpose of every species—to perpetuate itself.

Only this species had defeated the final enemy—the witless yawn of time.

Transformed into radio waves, the energy had been sprayed in the direction of the local universe that contained the richest clusters of galaxies—galaxies by the thousands, each containing hundreds of billions of suns.

It had taken all of that thirty-seven million years for the radio waves, expanding at the speed of light, to reach the galaxy where the Father World resided—a sprung spiral that those far-away, long-ago humans had known as the Whirlpool. There, a race of intelligent decapods who called themselves the Nar had intercepted the radio waves and deciphered them.

And a treasure trove had spilled out.

The lessons in genetic engineering alone had transformed the Nar civilization and given it abundance. Terrestrial starches and sugars had provided cheap energy and construction materials in the form of cellulose and exotic plastics. The bioengineering techniques, adapted to the Father World’s life forms, had boosted the food supply and led to a host of biological devices that had taken the place of inefficient machinery. The genetic blueprint for a fast-growing tree called a poplar, included in the kit, had paved the way for the great living spaceships like Yggdrasil which plied the spaceway at up to one-seventh the speed of light and, with their world-size environments, made interstellar exploration at last practical and inexpensive.

But the centerpiece of the great Message was the genetic blueprint for humankind itself.

A mere millennium later—a drop in the bucket of cosmic time—the Nar bioengineers had created the second human race and nurtured several generations of it. A modest cultural package included in the Message had even given the new humans the sketch of a human society to enclose them.

Bram closed his eyes and remembered what it had been like to grow up as a small human child in a world of frondlike giants who towered so far above a little boy that even their girdle of waistline eyes—the closest thing to a face that a Nar possessed—loomed higher than his own eye level.

To be something between a house pet and the echo of demigods. To be loved and pitied as someone whose physical limitations would forever bar him from full closeness in the Nar touch group that had adopted him, and would forever bar him from full membership in the wider Nar society beyond.

For humans were handicapped. By their nature they were unable to speak the Great Language in all its tactile richness. Humans had to make do with the crude unenhanced sounds of the Small Language, or their own Inglex or Chin-pin-yin. And they were painfully short-lived. They died after only a century or two, long before they could earn the honorifics that would gain them an adult’s place in an adult’s word.

Still, he had been cherished. The new people born aboard Yggdrasil would never know what it was like to have Nar touch brothers.

Bram let the noise of the revelers in the outside corridor fade from his consciousness, and let the old memories wash over him.

“Bram-bram, guess what?” Tha-tha had said to him that day, in the blend of Inglex and the Small Language they used when speaking to one another.

Tha-tha was Bram’s favorite touch brother, even though you weren’t really supposed to have favorites.

“What?” he said absently, staring longingly through an oval casement at the sunny world outside.

It was a splendid morning, early in the season when the lesser sun left the night sky and spent most of its time in the day. The bay was bright and cloudless, the sky a vivid lavender blue, and Bram could see the sparkling water, full of Nar bathers and colorful little V-winged pleasure boats.

He turned to contemplate with disfavor the beehive chamber where he and his touch brothers had their lessons and naps. Ranged along the far curve of the wall were the miniature tilt-top body readers against which Tha-tha and the others pressed their outspread upper tentacles—the star-shaped upper surfaces scaled down to child’s size—and his own little desk with its reading screen and big-buttoned board that took the place of the others’ touch pads. There was the toy box, filled with baby things that most of them professed to have outgrown—the spongy alphabet-letters for Bram, and the pyramids and cones and involute spheroids of various textures, and the small furry, mock-alive things that went through their limited tactile sequence when you squeezed them in the right place.

Two of the young decapods were wrestling, roiling boisterously around on the floor, their stubby little tentacles entwined as they tested one another’s strength. Roughhousing like this was apt to go on when there was no big Nar around to supervise them. For the moment, the old foster-tutor, Voth, had left them to their own devices; they were supposed to be quietly using the touch readers or otherwise usefully occupying their time, but it was hard to concentrate when the weather was so fine and the smell of the salt ocean was in the air, and the whole world seemed to have gone swimming.

Bram gave a tragic sigh. Lessons were all right, he supposed, but some days it was better to be outside.

Tha-tha sidled closer to him, piping happily, “Voth says I can have my own grownup-size reader! And library access to grownup touch scores—the easy ones, anyway. And a real composition matrix!”

“You’re too little,” Bram said scornfully.

Actually Tha-tha, during the past year, had shot up a full foot above Bram’s mop of rust-colored hair. But the slender decapod form did not yet outmass him, and besides, in Bram’s perceptions, what really counted was eye level, and Tha-tha’s five mirror-eyes, equally spaced around the narrow waistline from which upper tentacles and lower limbs sprouted, still only came to somewhere around Bram’s ribcage.

“No, really. Voth says I’m getting very proficient. He submitted one of my toccatas; and they said that even though it wasn’t full span, it used areas just like an adult!”

In his eagerness to communicate, Tha-tha had wrapped one of his tentacles around Bram’s forearm, and Bram could feel the velvety nap of the limb’s underside writhing with effort.

“I didn’t see what was so special about it,” Bram said stubbornly.

Bram knew that Tha-tha was very talented—the most talented of all the younglings in his group. Bram had tried to Understand the little toccata that Tha-tha had composed, and had stretched himself across the five-pointed star of one of the readers to let his human skin sample its rippling patterns of cilia movement. But as always, the meaning had eluded him; it had only been something that tickled in structured rhythms.

“Anyway,” Bram said, casting about for the perfect squelch, “it was nothing but a lot of squares inside squares that kept marching off the edge. I can make a touch reader do that!”

In fact, Bram had an unusual facility with the Great Language for a human of any age. He was able to manipulate a cilia board well enough to reproduce a few basic commands, and when Voth absentmindedly pressed a limb against his skin, he was often able to recognize some of the simpler morphemes, like numbers.

Tha-tha said, with a baffled earnestness that showed in the slow beat of his tentacle lining, “But it’s not the shapes that count, Bram-bram. You can have outlines with nothing inside. It’s the meaning they enclose that’s important.”

Bram felt all the blood drain from his face. He was numb all over, as he had been the time he had slipped on a sheet of winter ice and come down flat on his belly and had all the wind knocked out of him.

“It is so the shapes that count,” he insisted feebly. “You can tell lots of things from the shapes.”

Tha-tha belatedly remembered that he had been admonished by Voth to make allowances for his four-limbed brother. He damped down the cilia movement in the tentacle that held Bram’s arm and concentrated on the fluting sounds of the Small Language coming from deep within his central gullet.

“Never mind, Bram-bram, Su-su didn’t understand it either.” He gestured with a couple of spare limbs toward one of the wrestling brothers. Su-su was squealing in simpleminded triumph. He had his opponent pinned, with all five of the upper tentacles wrapped up in a tight bundle by Su-su’s encircling grip and the lower limbs off the floor, flailing wildly for purchase.

Bram’s features screwed up, and he found himself ready to cry. Tha-tha, trying to be kind, had just made it worse. Everybody liked Su-su, but he wasn’t much in the brains department. He had trouble doing the simplest arithmetic and, Bram gathered, even the Great Language had been slow to develop in him. He communicated in the Small Language and in tactile baby talk, and it was obvious that Voth was becoming concerned about him.

“Leave me alone!” He jerked his arm out of Tha-tha’s grasp and stomped over to his desk reader. It was the only one with a vision screen. The others’ touch readers didn’t need them, Tha-tha said, because the Great Language, even in its juvenile form, provided a sort of perception that was like pictures, only better—just as it was faster to count in the Great Language with its racing ranks of cilia than on a human-style keyboard. The visual cross-connection had something to do with the way the Nar brain worked. Bram’s touch brothers were capable of appreciating the pictures of his vision screen, but most of the time they watched them without much interest, just to be polite.

Savagely, Bram punched buttons almost at random, but his small fingers were cleverer than his rage, and he found himself looking at some of his favorite sequences from the history lessons about Original Man.

Here were the human race’s achievements in all their splendor and glory, as imagined by human artists with the help of computer reconstructions drawn from clues in the great Message, and interspersed with everyday scenes of the Father World and its family of planets.

Bram caught his breath at the sight of the shining cities as they must have been, with their pyramids and cathedrals and the cloud-reaching spires that were very much like the tall calcified spirals of the cities that the Nar had grown with the aid of humankind’s bioengineering legacy.

The pictures shuffled, and he saw the forests of giant trees grown on comets in the deep beyond the Lesser Sun. And the living spaceships derived-from them—great twinned hemispheres of foliage and roots, hundreds of miles in diameter, voyaging to the nearer stars.

And here was a simulation of a star itself being enclosed in a sort of sphere—the supposition was hazy—and its energy being transformed into the radio waves of the human Message and traveling across the void between galaxies. The Nar themselves couldn’t do anything like that, and would not be able to match such power for tens of thousand of years, if ever.

And now there was another uniquely human glory—music. The scene shifted to the concert hall that the Nar had grown for their wards in the human Compound. The camera panned across the rapt faces of the audience as they listened to a scrap of their heritage—a grand songfest called “The Messiah,” which had been lovingly reconstructed from the computer readouts of the Message. A mighty chorus of human voices rang out, singing “Wonderful! Marvelous!” in recognizable Inglex, while tears rolled down the faces of the listeners.

Bram was fighting his own tears. He put his palms flat against the screen, trying to absorb the experience directly.

Nothing! There never was! Only the hard smooth surface of the screen with the miniature people in it, and the massed voices coming from the speaker. It could not compare with the touch symphonies that so entranced Tha-tha and kept him stretched out on the star-shaped body reader for hours—and that he had tried without success to explain to Bram.

Bram gave a choked sob and felt the hot tears come.

What good was it? What good was it to be a human and talk with your voice, when the Nar could talk with their whole bodies? It was only sounds … or symbols which, when you came down to it, could always be transcribed into sounds.

He began beating on the machine with his small fists, screaming and kicking at it while his touch brothers stopped what they were doing and stared at him in horrified silence.

Tha-tha warbled tentatively, “Bram-bram.”

“Go away!” Bram screamed. “Go away, all of you! I hate you!”

He was still having his tantrum when Voth came in. The old teacher stood in the tall doorway regarding the scene, his cluster of upper limbs writhing thoughtfully. Tha-tha ran in a five-legged scramble over to him and whispered something with one outstretched tentacle, Voth dipping an upper limb to listen.

“All right, Tha-tha, you can take your brothers to the beach now,” Voth said aloud in his deep tones. “I’m putting you in charge. Tell the door proctor I said it was all right.”

As the little decapods swarmed confusedly around Tha-tha and flowed in an intertangled mass out the door, Voth went over to Bram and swept him up in his tentacles.

Bram made a great gulping sound. “Oh, Voth!” he sobbed.

“Hush, little one. It’s all right.”

He let the little boy cry himself out in his warm clasp, then set him down and lowered himself to eye level. “How would you like to go to the observatory with me and see our friend Jun Davd?” he said. “We can take a ride in the bubble car and buy some polysugar candy, and Jun Davd will let you look through his telescope.”

Bram rubbed his eyes with both fists. A small coil of rebellion still burned within him. “I want to go by myself,” he said.

Voth acted not at all surprised. “You’ve never traveled alone before,” he said. “It’s a very long way to go. You’d have to ask directions in the Small Language, make yourself understood. And—” He paused delicately. “Since you can’t imprint your Word directly, you’d have to use a credit transfer device, and use it correctly.”

Bram said stubbornly, “Jun Davd is my human friend, and I want to go see him by myself.”

Voth thought it over. “All right. I guess you’re old enough. But promise me to be careful.”

Bram hugged Voth around the middle where the skirt of walking members flared outward; the waxy integument was smooth and unyielding, not at all like the warm fluffy lining of the petallike arms. “I promise,” he said.

“There are no human conveniences after the departure terminal,” Voth said, becoming brisk. “Jun Davd will see that you’re fed. Remember not to eat anything till you get there—not even polysugar. Not even if some well-meaning person offers you something. Many of the Folk do not realize that human and Nar chemistry are different.”

“I know, Voth.”

“Here’s a touch token for when you get on the bubble car. Do you know how to make it say what you want?”

Voth handed him a small flat wedge with one ciliated surface, the kind Nar used in special circumstances when credit delegation was more convenient.

“Yes,” Bram said. He demonstrated with a deft flutter of fingertips. Numbers were easy.

“Good. Even a lot of grownup humans never learn how to do that.”

He escorted Bram down the spiral ramps to the street; this was an old defunct orthocone whose lower septa had long since been scooped of life and its nutrient pool filled in, allowing a ground-level entrance to be added beneath the original overbridge. He hailed a pentapedal carrying-beast and gave it detailed directions to the terminal before lifting Bram to the passenger howdah. Bram looked about eagerly. The white sun-bleached spires and filigree bridges of the city spread endlessly and magically before him; he had every intention of countermanding Voth’s instructions as soon as the beast was out of sight, and doing a little roundabout sightseeing on his way to the terminal. He knew he could do it. The transport creatures responded to voice as well as touch.

A string of bubble cars passed overhead on their invisible cable. Bram gawked at them, hardly able to believe that soon he would be traveling in one without supervision, just like an adult Nar. Even Tha-tha had never been allowed to do that.

“I’ll call ahead and have them tell Jun Davd you’re coming,” Voth said. He tapped one of the upright limbs that formed the framework of the howdah and Bram felt himself rising high into the air as his vehicle straightened its five stiltlike legs. A moment later the beast was trotting down the causeway that led toward the terminal. Bram turned back once to wave to Voth. The old decapod waved back in imitation of the human gesture. Bram thought that somehow Voth seemed sad, but he couldn’t imagine why.

“Do you think we could look at Original Man’s galaxy now, Jun Davd?” Bram asked.

“In a little while,” the tall man said—tall for a human, though Jun Davd would hardly have topped Voth’s brachiating midsection, even on tiptoes. “But first I’m going to give you some lunch.”

“I’m not hungry, Jun Davd, honest.” He looked around impatiently at the enormous chalky chasm that housed the observatory’s big eye. Massive machinery loomed overhead in steel cradles. The interior extruded convoluted catwalks of polycarbonate that reached every nook and cranny. Across the immense floor was the eye itself, a great bowl of living jelly that seemed to Bram to be the size of a swimming pond. Aproned Nar attendants, some of them wearing optical girdles, glided silently about, seeing to its needs.

“I promised Voth-shr-voth I’d feed you,” Jun Davd said, smiling down at him. “Don’t worry—your galaxy won’t go away.”

Bram smiled back. Jun Davd was very nice, with a kindly, creased face that was several shades darker than Bram’s, almost the color of stained wood. His hair was a bush of pure white. He was old for a human, and had risen as high as a human being could go—to a shadowy status somewhere between an apprentice and an intern.

“All right, Jun Davd,” Bram said. He took the slender gnarled hand and let himself be led from the fascinating chamber to the cubbyhole where Jun Davd worked and lived amidst a clutter of instruments and a spartan few personal possessions.

They were stopped several times along the way by Nar personnel who wanted to greet the little boy and inquire after the absent Voth-shr-voth. During the past year they had become accustomed to the sight of the human child who was brought by his Nar guardian from time to time to be shown some of the distant wonders trapped by the big eye’s living system of mirror optics, and to be given some rudimentary tutoring in astronomy by Jun Davd. Voth-shr-voth was held in high esteem, and every courtesy was extended to him—though why he was encouraging a fruitless interest in astronomy in his human ward was unclear, since Voth himself was renowned for his bioengineering achievements, and presumably if he wanted to make a place for the boy, he would do it in his own touch group.

Bram presented the palms of his hands to meet the proffered tentacle tips and answered their inquiries gravely and politely. A nudge from Jun Davd reminded him to add the honorific; it was hard to remember that the eminent Voth-shr-voth was the plain old Voth whom Bram had known since his nursery days, when his own principal gene mother, mama-mu Dlors, had given over the largest part of his care.

Even the observatory’s director, the venerable Pfaf-tlk-pfaf, showed Voth a special deference. Voth was several centuries older than the director, and near to the time of his Change. Bram didn’t know exactly what the Change was, but it had something to do with why you hardly ever saw a lady Nar, except for the rare infirm and draped individual being carried in a biolitter, and why there was no such thing as a little girl Nar, only touch brothers. Bram had asked about it, but Nar grownups were always evasive, the way mama-mu Dlors always changed the subject when he asked how human babies were assembled.

“Pfaf-tlk-pfaf is very busy now,” Jun Davd told Bram, “but perhaps he’ll be able to see you for a few minutes later on.”

“And then will he show me the galaxy of Original Man with the big eye?” Bram asked.

“We’ll see. The big eye is doing some very important work at the moment—a survey of the heart of this galaxy, the one we live in.”

“But you promised.”

“All in due course. First, lunch.”

A short while later, Bram pushed away his half-finished bowl of chimerical soycorn porridge and wiped his lips on the damp cloth Jun Davd gave him. “All through,” he said.

“Would you like a sweetcrisp?”

“No, thank you. Can we see it now?”

Jun Davd went over to a keyboard that had been haywired to a Nar touch pad. An oval screen lit up with fuzzy visual patterns generated by an interface program that Jun Davd had written himself. No one but Jun Davd could make sense of it, but Bram had resolved that some day he would learn to read it, too.

“The big eye’s still busy,” Jun Davd said, “but I can give you the last stored view. We swung that way about a Tenday ago.”

Bram was disappointed. “I wanted to have a really now look, not a picture.”

Jun Davd laughed. “You couldn’t tell the difference. Anyway, there’s no such thing as a really now look. The light from Original Man’s galaxy left there thirty-seven million years ago, and the images are all processed one way or another.”

“I can so tell the difference. It isn’t the same thing.”

Jun Davd’s expression sobered. He squatted on his haunches to look into Bram’s eyes. “I understand, Bram. You want to feel that you’re seeing the actual light of home. But even the big eye only collects photons one at a time and assembles them into an image. Do you understand what I’m saying?”

“I guess so,” Bram said reluctantly. He brightened. “Could we see it with your telescope—the little one?”

The telescope that Jun Davd tended in an adjacent structure was small only by comparison with the big eye; it was a huge drumlike object mounted on rocker beams. With it you could see the planets of the lesser sun, and even the gas giant that revolved around Juxt, the closest extrasystem star, almost a light-year away.

“No, it’s too small,” Jun Davd said. “You know that, Bram. I’ve explained it all before. Compared to the Milky Way, even our neighbor galaxy, the Bonfire, is practically next door. The Milky Way is so far away that when the light we detect first left it, there weren’t even any Nar here on the Father World—just the little seashore creatures that were their ancestors. So we can never see Original Man’s galaxy as it is now.”

“We could if we waited another thirty-seven million years,” Bram said reasonably.

“I guess we could at that,” Jun Davd laughed. “Come around then and I’ll show it to you. In the meantime…”

He busied himself at the human-style keyboard and a sea of stars appeared in the oval screen. After a lot of jiggling, a fuzzy dot centered itself, grew in size, and sharpened into the image of a feathery coil of light with a golden yolk at the center.

Bram caught his breath. Jun Davd had shown him more spectacular sights through the telescope, but there was none that caused the sudden gripping pain in his small chest that the sight of humankind’s home always did. If he had been allowed to, he could have sat and looked at it for hours, making up stories in his head.

“Jun Davd,” he said at last, “do you think Original Man could speak the Great Language?”

The old apprentice looked at him sharply. “No, I’m quite sure he couldn’t. They were the same as us, those prototype humans who sent the Message—or we’re the same as them, with a few bad genes edited out, of course. Why do you ask?”

“They—they rose so high. Higher than the Nar. Everybody says so, even Voth. How c-could they, if they were like us?”

All of sudden salt tears were rolling down his cheeks. He tried to stop them and smile at Jun Davd, but the smile only made things worse.

Jun Davd took him by the shoulders and turned him gently around to face him. “What happened today, Bram?” he asked softly.

Between sobs, Bram told him about Tha-tha’s promotion to an adult touch reader while he, Bram, couldn’t even understand a toccata on a child’s reader. About the growing facility of his touch brothers in the Great Language while he himself had a growing sense of being left behind. About the feeling of increasingly being left out of things, even though Tha-tha and the others always tried to remember to speak aloud for his benefit.

“I see,” Jun Davd said grimly. “And you wonder what kind of place the world holds for you, especially when you look around at older humans like me and see the limits on how far we can go. I know how you feel, Bram. I was a protégé of the old director—the one before Pfaf-tlk-pfaf—just as you’re a protégé of Voth, and even though he was very close to the Change when I was growing up, he saw to it that I was firmly established before his final metaplasis, and Pfaf-tlk-pfaf has honored his wishes. On the whole, it’s been a good life—the best, I think, that’s reasonably possible.”

Bram flung his arms around Jun Davd’s neck. Hugging a human being was different than hugging a Nar. Human beings had bones that you could feel through the skin. “Why do I have to be different, Jun Davd?” he wailed. “I asked Voth once, and he said it was because I was made of human stuff instead of Nar stuff.”

Jun Davd disengaged him gently and held him at arm’s length so that he could look into his face. “Voth-shr-voth was right; you’re different just because you’re a human being. That doesn’t mean you’re better and it doesn’t mean you’re worse. Only a different sort of person. That’s why Voth started to bring you here to the observatory when he first saw that you were interested in where humans come from—so that you could have some sense of your own heritage and be proud of it, not think of yourself as some kind of flawed Nar. I think it would break Voth’s heart to have you apprenticed here instead of with his own touch group, but he was willing to take the chance of losing you so that you could be happy and fulfilled.”

“I’m sorry I cried, Jun Davd.”

“That’s all right, Bram. You cry whenever you feel like it. That’s part of being human, too.”

“I thought that … maybe if Original Man could speak the Great Language, I could learn how someday, too.”

“They reached the heights their own way, Bram. The human way, not the Nar way. And whatever heights the second human race reaches here in this galaxy, we’ll do as humans, too.”

Bram looked at the tiny glowing helix displayed in the viewer. “I’m going to go there someday,” he said with a child’s seriousness.

“You know that’s not possible, Bram. We’ve discussed it often enough. We can reach a few of the nearer stars within a human lifetime—though we’d be very, very old by the time we got much farther than Juxt or Next. And the Nar can travel about ten times farther within their lifetimes. But the limit will always be about a hundred light-years—maybe a few thousand light-years within our own galaxy if we ever learn to travel at relativistic speeds. But that’s a lot different from crossing the void between galaxies—especially galaxies that aren’t even in our own cluster. No, child, it’s a fine thing to be able to look through a telescope at these distant objects, but they can never be reached across an ocean of time, any more than you or I could return to our own egghood. Voth wants you to be happy in your life. And that means making your way here, in the real world, as best you can.”

It was one of those adult speeches that Bram had learned to shut his ears to. His eyes had never left the golden spiral in the screen.

“I didn’t mean right now, Jun Davd,” he said complacently. “I meant someday.”

The someday never came. Bram became immersed in life. As his touch brothers outdistanced him, he spent more and more time with friends from the human enclave and shared their purely human concerns. By adolescence, few of the humans had much in common with their Nar touch brothers anymore, and Bram was no exception. Tha-tha made an effort to keep in touch with him—still peeled down his waxy outer integument and unfolded his inner surfaces while they jabbered away in their childhood patois of Inglex-laced Small Language—but Tha-tha had his own Nar life to live, a life that grew ever more incomprehensible to Bram.

It didn’t matter. Bram, full of the juices of youth, had the heady excitement of human society to sample. All around him was a ferment of art, music, literature, fashion-people busily assimilating the sketchy outlines of human culture as it had been transmitted in the Message, and building on it. People doing things!

He left mama-mu Dlors’ nest and moved into the bachelor lodge. He was on his way to an adult life with new freedom to explore. He forgot childish dreams; the visits to Jun Davd at the observatory became less frequent and finally ceased entirely. Astronomy was a dead end for humans anyway, as Jun Davd’s example had shown. Bioengineering was where the honors lay—where there was a hope of practical results that could have a recognizable impact on the miniature human communities scattered through the Father World. A human named Willum-frth-willum had even been granted a Nar-style honorific for his contributions to the development of viral monofilament, and then had gone on to achieve celebrity among his fellow human beings for recreating additional terrestrial life forms, such as the tomato, by working backward from existing genes of human foodstuffs included in the Message. There was an old human saying to the effect that the invention of a new sauce contributes more to human welfare than the discovery of a new star; how much more important, then, was it to bring more variety to the limited human diet? When it came time for Bram to make a career choice, Willum-frth-willum’s shining example was already there before him.

So Bram made his adult compromise with life. Voth’s bioengineering touch group had always been waiting with open tentacles to take him in as a sponsored human; he was under the mantle of the great Voth-shr-voth, after all. But Bram proved to have a natural talent for the work, and soon he was holding his own. He had a greater affinity for the Great Language than most humans—he could even manipulate a touch reader well enough to call forth basic menus, and could find his way around the files with a minimum of help. In no time at all he was given greater responsibility, formed genuine working relationships with the Nar juniors, and was allowed to run his own subprojects.

Bram threw himself into his work; it was solid and useful, gave form and purpose to his life, and gave him status in the human community.

He avoided Jun Davd; he could not have said why. Every once in a while he would find himself staring at the blank patch of night sky that contained the faraway galaxy of the first human race. But you couldn’t see anything without a telescope. Bram would shake off an obscure, nagging sense of loss—a feeling he was not willing to examine—and allow the realites of daily life to absorb him.

There was a brief affair with Mim—but they lived in two different worlds now. He was part of the larger concerns of the Father World—minor though his role at the biocenter was. Mim had withdrawn more and more into the purely human ambience of the Compound, where a feverish minority of Resurgists tried to ignore the Nar civilization that supported them, and worked to recreate a semblance of an imagined human past. Eventually Bram lost Mim to an older man—Olan Byr, a musician like herself, who had made a name for himself as a tireless interpreter of the old music.

In due course, Bram formed a relationship with an exciting young woman named Kerthin, a sculptress with some radical ideas about human ascendancy in the sea of Nar that submerged them. Bram was entranced by her; he tried to show her that his thinking was as advanced as hers, but she laughed at him, told him that he was stuffy and conventional, but that she liked him anyhow.

Bram was ready to settle down by then; he formally proposed a visit to the gene co-op with Kerthin. Preliminary gene mapping had given him every reason to hope that the two of them would be allowed to contribute a preponderant number of their genes to a composite genome and rear the child as their own. It would be the final step in the settled existence he had contrived for himself.

But Kerthin was evasive. She teased Bram about being too complacent. There were still great things to be done, she told him. She was not ready to settle down.

For the human race had reinvented politics.

The human population of the Father World, small as it still was, had grown to the point where it supported a remarkable number of factions, calling themselves by such names as Partnerites, Schismatists, Resurgists, Ascendists. Kerthin’s friends were a fanatical splinter group of the staid, old Ascendist party.

Unwillingly, Bram was drawn into the conspiratorial schemes of Kerthin and her friends, at first only to keep an eye on Kerthin, and later to protect a startling secret he had uncovered through his work at the Nar biocenter.

Human beings were meant to be immortal!

Bram’s unusual facility with touch readers had provided the key. While rummaging through the old files, he had discovered that the original human genome constructed by Nar bioengineers was incomplete. A codicil to the great Message of Original Man, received some fifty years into the second cycle of the transmission, had contained instructions for a synthetic virus able to infect human cells with the disease of eternal life. The tailored DNA had the ability to insinuate itself into human nucleotides and turn off a “death gene”—a genetic switch that expressed itself after a certain number of cell generations. The information had rested in the files for a thousand years—either unrecognized, or interdicted because of environmental dangers associated with it.

Bram shuddered to think what Kerthin’s wild-eyed friends might do with such information. At best they would use it to inflame human passions, to put an end to the trust between human and Nar. Bram did not believe that the information had been hidden on purpose. He believed in the good will of the Nar, and he waited for the opportune moment to bring the matter up with Voth. But first he wanted to be sure.

While Bram was still trying to decide what to do, a starship arrived from Juxt One. Aboard it, having traveled for seven years, was the Ascendist messiah for whom Kerthin and her friends had been waiting.

His name was Penser, and what he preached was a mindless violence that he described as a “cleansing.” The universe belonged to man by right, he told his disciples, and could not be shared with the Nar. He dismissed Nar largess. “To share is weakness,” he said. “To accept is weakness.” He advocated taking by force what the Nar were giving voluntarily. On Juxt One he had stirred his followers to acts of sabotage in which Nar had been killed. The abortive revolution had been hushed up by the horrified human settlers, and had not been recognized for what it was by the peaceable and unsuspecting Nar. Penser had fled under a false identity stolen from one of his disciples.

Now Penser proposed to hijack one of the great living starships and, with a few hundred followers, use it to take over a thinly inhabited moon of Jumb, the gas giant orbiting the Lesser Sun. The small Nar population there would be deported—killed if they resisted; the human colonists, Penser believed, would have no option but to go along with his plans once the deed was done.

The takeover would be accomplished before the Nar on nearby Ilf, the Lesser Sun’s principal inhabited planet, realized what was happening. After that, according to Penser, the Nar commonwealth would accept the situation to prevent useless further violence.

“They’ll let the humans have their one little world,” Kerthin assured Bram, mouthing Penser’s words.

The seized moon was to be the focal point from which humans would crowd the Nar out of the cosmos. Penser intended to step up the human breeding rate without bothering about gene editing. Humans could easily outbreed the Nar. “Do you realize that the human population of the universe could be doubled every twenty years?” Kerthin had said, her eyes shining.

Other worldlets would be taken over, one at a time—each as an accomplished fact to be presented to the Nar, with the dust allowed to settle between conquests and the Nar encouraged to believe that this time was the last. Penser had studied the ancient history of Original Man. Hitler, Napoleon, and Alexander had failed because they had bitten off more than they could chew. By the time the Nar woke up, Penser said, the human race would be ready to swallow Ilf—even scour the Father World itself!

But the starship hijacking went horribly wrong. The Nar, with a casual swipe of their great powers, put a stop to the mutiny and took all the humans aboard into custody—Penser’s followers and innocent passengers alike, making no distinction between them. Bram was one of the innocent bystanders caught up in the net.

It was very bad. Penser was dead—a suicide. But there were dead Nar, as well. Among them was Bram’s old tutor, Voth-shr-voth.

Voth’s death was a particular atrocity to the Nar. He had died under torture when Penser’s henchmen had attempted to force him—as the space tree’s acting biologist-to override the tree’s tropisms and make it spread the leaves of its light-sail on a course to the target moon.

Worse than that, Voth’s death had interrupted the final flowering of his life—his terminal change from male to female. All of Voth’s budding children had died with him when he had failed to reach a breeding pool in time.

The Nar had not understood until this time that their pets could bite. Their civilization ground briefly to a halt while they met in one of their grand touch conclaves to decide what to do about the human species.

Tentacle pressed to tentacle, radio sleeves linking the parallel meetings on all the nearby worlds, the entire Nar race became a single immense organism whose process of deliberation passed human understanding. The humans at the center of the vast tribunal—a sea of living Nar that stretched mile upon mile—waited and shuddered.

It was the Day of Wrath.

The humans were heard. When it was Bram’s turn to speak, he told them about the immortality virus that had been withheld from all the generations of reconstituted man, condemning humans to short, unfulfilled lives in a long-lived Nar society. He told them of his childhood dream of returning home—home to the distant, unreachable galaxy where the first human race once had dwelt, and from which the tremendous Message of Original Man had been sent. His touch brother, Tha-tha, emerged from the packed throng to speak to him directly, and perhaps to intercede for him. “It is true, then, Bram-bram,” he asked sadly, “that all your life you felt you had no place here?”

All around Bram, other humans were simultaneously unburdening themselves to the collective Nar consciousness: Partnerites telling of their struggles to be accepted in a society that saw them as ephemeral mutes; Resurgists admitting why they had given up and surrendered to a daydream of past human glory; even some Penserite radicals attempting to explain why they had been driven to violence in their effort to find a place for humans in a Nar universe.

Perhaps the Nar had never before realized the depths of human alienation and anguish. But they were getting an earful now. The sea of tentacles seethed. Bram could not read what was happening out there. No human could. But he could sense a great surge of sorrow and revulsion, distress and pity.

The human race might get off lightly, he dared to hope. The present generation might be allowed to live out their lives comfortably—under closer supervision, of course. It was even possible that the human species need not vanish from the universe a second time; limited breeding or in vitro gene assembly might keep a few dozen specimens around as curiosities for future generations of Nar to gawk at.

But the Nar, in a huge tide of nonmammalian empathy, were more compassionate than Bram could have imagined.

When the verdict was announced, the human race found that it had been sentenced to immortality.

The Nar had no use for immortality themselves; for them an eternity without aging and what lay at the end of it was an eternity without fulfillment. So perhaps they simply had not realized what such a gift would mean to humankind.

Bram was put in charge of a human-run project to reconstruct the virus; the Nar, with exquisite tact, had recognized that this must be a human achievement, not an act of charity. It would be the work of years or decades, even with Original Man’s blueprint. For Bram would have to find an alternate route to the same result to avoid the biological dangers associated with the immortality nucleotides—dangers that, some thought, may have contributed to the demise of Original Man.

But immortality was only part of the Nar gift—a means to an end. With the complete gift, the Nar gave Bram back his dream.

The Nar species was on the verge of an enormous technological leap. Travel between stars, until now, had meant riding the worldlet-size space-dwelling trees that were part of Original Man’s bioengineering bequest. They had replaced the first crude boron fusion-fission starships of the Nar’s early space age, and could travel at up to one-seventh of the speed of light. With them, the Nar could spread slowly from star to star and hope to populate the galaxy in a million years or two.

But only recently a conceptual breakthrough had raised the possibility of a relativistic spacecraft that could reach the core of the galaxy in only fifty thousand years. With it, the Nar could do on a smaller scale what Original Man had done so grandly—use it as a robot beacon to broadcast their own genetic code to the billions of stars that would come within its range, If the probe hit the jackpot only once or twice, then the Nar race could spread from new foci, sending brothers among the stars who would be waiting to greet them.

To this lofty purpose, the Nar species had allocated a tremendous share of the wealth of their civilization. The robot spacecraft project had been given a timetable that might make it a reality in only a few centuries—a fraction of a Nar lifetime.

Now, in an act of stunning generosity, the Nar decided to speed up the timetable—and bequeath the relativistic engine to the human race.

With it, those humans who wished to—the restless ones, the unhappy ones, the adventurous ones—could return to their mythical home in another galaxy. The trip would take thirty-seven million years of real time, of course, but it had been calculated that by traveling within one hundred millionth of one percent of the speed of light, the time dilation factor predicted by the theory of relativity would have a value of approximately seventy thousand. So to the travelers, the journey would seem to last only about five hundred and forty years.

And when you had eternity to play with, that didn’t seem like too high a price to pay.

To reach that tremendous terminal velocity—to become pregnant with enough kinetic energy to coast between the galaxies in a fuel-less void—the ramjet craft would first have to dive to the heart of the departure galaxy, gulping the rich H-II clouds as it went, then let the gravitational center of the galaxy sling it above the plane and out into emptiness.

So it all worked out to everybody’s benefit. The humans would be able to do the Nar’s little chore for them on the way home.

One problem remained. Robot ramjets were not very hospitable to life. They were hot! And even if a way were found around that problem, there was still the question of living space and a reliable supportive environment for a substantial fraction of the human race on a trip that would last for more than five hundred years.

How would it be managed?

It was simple. The spacecraft would tow a tree.

Mim appeared in a stunning green off-the-shoulder party dress with a five-pointed hem that, though it was a bit old-fashioned compared to some of the newer styles, suited her very well. Over it she wore a short pleated chlamys that left her right arm bare—an old cellist’s habit.

She bent over the chairpuff and kissed Bram lightly above one eyebrow. “What are you sitting here brooding about?” she said.

“Oh, I was just thinking about the Father World,” Bram said, getting up. “It seems very far away now.”

“It is far away! Tens of thousands of light-years away!”

“Which means that tens of thousand of years have passed since we left. We’re in their historical past, Mim. After only a couple of decades of travel. I wonder if they’ve forgotten us.”

“Not a chance. The Nar never forget anything.”

“All the Nar we knew are dead now. But there ought to be some fifty-thousand-year-old humans that we used to know walking around. I wonder what it’s like to be fifty thousand years old. We’re still under a hundred.”

“And getting younger every day,” she reminded him.

“Yes. I wonder if fifty thousand years is long enough for a human being to learn the Great Language. Jao swears that it’s possible, with cortical transplants, electronic interfacing, and prosthetic touch sleeves.”

“It must be a very different society from the one we grew up in,” she commented.

“We’ll never know,” he said. “The people who stayed behind made their choice and we made ours. Speaking of which…”

He inclined an ear to the noise in the outside corridor. Some drunk was singing a Bobbing Day carol—off key—and his friends were making it worse by attempting harmony. Mim winced.

“Yes, we’re developing our own traditions, aren’t we? How would you like to try to explain All-Level Eve to the folk back home?”

“It’s all very natural to the younger set. Mim, do you realize that there are children who’ve been born on Yggdrasil—who’ve never known anything else? Some day they’ll outnumber us old-timers. By the time we get to the Milky Way—”

She took his arm. “Right now we’d better worry about getting to the Forum. It wouldn’t do for the year-captain to be late.”

He smiled at her and drew her a little closer. Together they stepped out into the corridor and let the crowd carry them along.

CHAPTER 3

The Bob dangled from five hundred feet overhead, its displacement showing just how badly askew the wooden chasm of the Forum was. Its carved onion shape, taller than two men, had been repainted in gaudy green and vermilion stripes by this year’s Bobbing Day committee. Though it was only about twenty degrees out of plumb—Yggdrasil had prematurely swung the bough ten degrees toward the true before being checked—that was enough to hang it above the chalked line at a point that was nearly two hundred feet from the painted bull’s-eye in the center of the floor.

“I don’t like sitting this close to it,” Mim said, taking a sip of her All-Level Eve cocktail. “I always think it’s going to fall and roll right over us.”

“It would roll in a circle,” Orris said. “That’s why it’s that shape.”

“It won’t roll at all because it’s not going to fall,” Marg said firmly. “I won’t allow anything to spoil Bobbing Day.”

Everybody at the table laughed. Marg was still the commanding presence she had always been. She was large, formidable, and matronly at this stage of her youthening, and poor Orris seemed a collection of sticks beside her.

“You’d better have a word with the acrobats, then,” Bram teased her. “If the one on top isn’t careful, he’s liable to get himself brained.”

They all looked across to where the acrobats were forming a human pyramid, no more than thirty feet from their table. There were six of them: five brawny lads in loincloths and a little lightweight fellow in rainbow skin-tights at the apex. They had managed to hoist the little fellow high enough to reach the Bob and set it spinning.

“Who are they?” Trist asked. “I think I recognize the one at the bottom right.”

“They all work together in the glucose-extraction plant. Nice boys. They’ve been practicing for months.”

Next to Trist, who had been holding her hand as if they were still in their early bonding years together, Nen said, “We all have to congratulate you, Marg. This is one of the best All-Level Eves ever. The decorations, the food, the entertainment—everything!”

Marg flushed with pleasure, and Orris beamed proudly. “Everybody on the committee worked very hard,” Marg said.

Bram looked around the Forum at Marg’s handiwork. The immense arena was lit by torches in wall brackets that cast a resinous red glow around the perimeter, where almost the entire population of the tree, with the exception of the few hundred who remained on duty tonight, were seated at tables, each defined by a circle of light cast by a sputtering resin stick. Garlands of silver leaves crisscrossed the walls, making a pattern of reflections.

There was no way to decorate so vast an area as the main floor of the ellipse, so Marg had very wisely left it in darkness, except for a central blaze of illumination where colored spotlights mounted high on the walls picked out the bull’s-eye where the Bob would come to rest. A few reddish glints here and there, where leaf arrangements had been strategically placed, gave an abstract geometric shape to the pool of darkness. More spotlights were aimed at the Bob itself and followed the entertainers.

The final touch, lending a sense of awe and mystery to the annual rite of rotation, was the beam of sullen, red-shifted light from the starbow, filtering down from a lenticel somewhere high above. On past All-Level Eves, the starlight had been jolly, multicolored, but now the surrounding vault of higher frequencies had contracted to a point forward of the direct line of vision from here, leaving only the bloody light that preceded darkness.

“Yes, here’s to the committee,” Bram said, raising his glass. “What else are you going to have in the way of entertainment?”

“Oh, we’ll have pattern dancing—three very talented couples from hydroponics—and some people who sing, and some very clever body puppets.” Marg turned to scold Mim. “And I’m very disappointed in you, Mim. I thought you were going to play the cello for us tonight.”

“Oh, nobody wants to hear concert music tonight,” Mim said. “This is an evening to have fun in. Besides, some of these people have been waiting a whole year for a chance to be on stage.”

The acrobats had given the little fellow a boost that allowed him to do a backflip past the onion bulge of the Bob, and now he hung by one knee from the suspending cord and swung the Bob in greater and greater arcs while the audience clapped and cheered.

Across the table from Bram, Ang dug her fingers into Jao’s beefy arm. “He’s going to swing right over us!” she squealed.

“Somebody pass the poor fellow a drink, then.” Jao belched. He took a mighty gulp from his glass and set it down. He squinted critically at the surface of his. drink. “Still an ellipse,” he said. “You know, it’s an awesome thought. At the very moment the Bob becomes plumb, five thousand ellipses in five thousand glasses are going to become five thousand circles.”

“And we’ll stop being all tipsy,” Ang said.

“Ah, that’s where you’re wrong,” Jao said with a sly wink at the company. “The geometry of alcohol is not the same as the geometry of space. The object of All-Level Eve is for the people to become progressively more tipsy while the environment becomes progressively less so.”

“In that case, you’re doing very well,” Mim said with a laugh.

Out on the floor of the Forum, the rainbow-clad acrobat had dropped lightly to the shoulders of his fellows, to the applause of the surrounding ring of revelers. Noisemakers razzed and rattled. The human pyramid disassembled itself, acknowledged the applause with outflung arms and a curtsy, and tripped offstage. A singing duo took their place—a man and woman in clown costume: she with enormous quilted breasts, he with a braided rag phallus that trailed on the floor—and began singing bawdy songs to the rowdy encouragement of the onlookers.

“Who’s the Momus?” Trist asked.

“Don’t you recognize him?” Marg replied. “It’s Willum-frth-willum.”

“He’s lost considerable dignity.”

“He doesn’t need it anymore. He’s got his youth to look forward to.”

“I didn’t know he had such a good singing voice,” Mim said.

“He’s kept it hidden all these years.”

A lot of table hopping was going on as the time grew near for the swing of the Bob. People made their way across the tilting floor to drop off little Bobbing Day gifts, drink a toast with friends, embrace and kiss.

“It seems as if there’s always been a Bobbing Day,” Mim said, leaning against Bram’s shoulder. “I can hardly remember how it got started. What are we going to do when we leave the galaxy and stop accelerating and there’s no more annual tree turning?”

“We’ll think of something,” Bram said. “Human beings will always celebrate some sort of a year-festival.”

“It’s going to be a long, featureless ride between the galaxies,” Jao said. “Nothing to mark the years.”

“Sounds dull,” Orris said. “But like Bram says, we’ll think of something. We ought to appoint a revels committee to look into it.” He looked fondly at Marg. “We’re putting you in charge of it.”

“Almost time,” Bram said, feeling his waistwatch with his fingertips. Some of the younger generation had taken to wearing timepieces on their wrists—clever little holo displays that showed the ten hours of the day visually, in human numerals—but for Bram, old habits died hard.

At this moment, in the heart of the tree, Jao’s granddaughter would be checking and rechecking her meters, adjusting the voltages and gas pressures that would tickle Yggdrasil into one-twelfth of a revolution—or, rather, the portion of those thirty degrees it had not already anticipated. Once, early in the voyage, the humans had tried to accomplish the maneuver by brute force, using the plentiful hydrogen trapped by the drive section. But Yggdrasil had fought back and returned to starting position four times before the humans finally gave up. It was better to trick Yggdrasil into following its own imperatives.

“Too bad your granddaughter can’t be with us tonight,” he said to Jao. “She missed the festivities last year, too; seems to me she ought to be able to alternate with other staffers in tree systems.”

“Oh, Enyd? Don’t waste your time feeling sorry for her. She could be here if she wanted to. No sense of fun, that girl, She’s happier pushing her buttons. Sometimes I wonder if she’s really our granddaughter.” He clapped a hairy hand on Ang’s haunch. “What do you think, pet? Is she a case of mislabeled genes?”

“Oh, Jao!” Ang exclaimed. “She’s just a little serious, that’s all.”

“Here comes Smeth,” Trist said. “Rounding up votes, no doubt.”

Bram looked across the torch-lit perimeter. Smeth’s gangling form could be discerned threading a route through the tables, lurching awkwardly across the tilted floor. A party of young constituents tried to detain him, but Smeth seemed distracted; he exchanged a few words, made a gesture declining an invitation to sit down, and kept coming.

“Something on his mind,” Nen said. “And it isn’t votes.”

“Now, Jao,” Ang said. “Remember you’re not on duty tonight. You said yourself that your deputy can handle anything that comes up.”

Jao patted her hand. “Wild forces couldn’t drag me away.”

Smeth stumbled the last few yards and loomed over the table.

“Sit down, Smeth,” Orris said. “Have a drink.”

“Uh, thanks, but I just wanted to have a word with Jao,” Smeth said.

“I knew it!” Ang said.

“Nothing wrong with the drive?” Jao said. “Everything working all right?”

“The drive’s fine … uh … at least it’s coping with everything the core’s throwing at us.”

“Oh?” Jao’s tufted eyebrows went up. He rose from his seat and steered Smeth by the elbow to a little distance away. Bram could see them talking earnestly, heads close together.

Jao came back to the table while Smeth waited. “Look, I’m just going down to the remote bridge for a few minutes—we’ve got the one in this bough hooked up now. Never fear—I’ll be back in plenty of time for the turning. Marg, mix me up a libation.”

“Do you want me to come with you?” Bram offered.

“No … I’m just going to take some readings. Sit tight and enjoy the festivities. You too, Trist—no, don’t get up.”

He rejoined the fidgeting Smeth, and the two of them left.

Ang had begun a litany of complaint about Smeth. “…always dragging Jao off for some nonsense. Just because he lives for his work, he thinks everyone else does. I hope that when he gets young again, he’ll find some woman who’ll take him in hand.” Marg listened sympathetically.

Mim asked Bram unobtrusively, “Why does Smeth look so worried? I know he’s a fusspot, tending his engines and guarding the sacred fusion flame like some kind of keeper of the mysteries, but he’s got Jao worried, too.”

Bram told her about Jun Davd’s concern over the gas infall that had made the center of the galaxy a denser place than it ought to be. “Galactic cores are active places, but this one may be more active than most. More collisions between stars. More stars exploding or being ripped apart by tides and feeding the black hole. Smashed stars forming a soup that circles the hole at tremendous speeds, creating more turbulence, more friction, stronger magnetic fields.”

Mim gave a shudder. “And we’re heading toward that?”

“We’re bending ourselves around it at a safe distance. Smeth may want Jao to alter our trajectory somewhat, based on what he can deduce from the junk falling into our scoop.”

“Is that what he meant by coping with what the core’s throwing at us?”

“Probably. We’ve run into the fringes of gas jets so far, and a couple of minor storms of relativistic electrons.”

“Storms?”

“Caused by shock waves in the plasma. They accelerate the stripped electrons. Gives the ramscoop quite a diet.”

“Oh, dear, I don’t like the sound of that!”

“Don’t worry. The more energy that’s thrown at us, the stronger our fields are. The chief effect is the spurts of extra acceleration it’s caused, before feedback can compensate. You’ve probably noticed times during these past weeks when you’ve felt heavier.”

“I thought it was old age delaying its farewells.”

He smiled. “No. There’ve been some episodes of minor accidents and breakage that no one paid attention to. Fortunately, outside travel isn’t allowed without a tether, for vehicles or people. Otherwise…”

“Otherwise; what?”

“Somebody could’ve gotten left behind. Traveling at almost the speed of light in some heavy weather. Not that they’d know anything. The instant they left the shadow of our intake area—”

“Please, I don’t want to know about it!”

“Sorry. But as I was saying, the chief effect is extra acceleration. And that may have put us a few days ahead of schedule on our black hole flyby.” He hesitated. “I’ve been thinking about sending everybody to the trunk when the time comes, to wait it out.”

Mim looked alarmed. “Will that be necessary?”

“Oh, I doubt there’s any real danger. If we ever ran into something we couldn’t handle, the trunk wouldn’t be any safer than an outer bough. But while I’m still year-captain, everybody’s safety is my responsibility, and moving to the trunk would put us in toward the center of our umbrella, where the field is strongest, just while we’re swinging around.”

He caught Trist looking at him from across the table. Trist compressed his mouth as a signal for Bram to shut up.

“That wouldn’t make you very popular,” Mim said. “Everybody’s getting settled into their new quarters, unpacking and sweeping out rooms they haven’t seen for twelve years, and tomorrow morning the floors will finally be level.”

Bram left it there. Across the table, Trist said loudly, “Who wants another drink? I think we’ve got time for one more before Leveltide.”

“Look,” Orris said. “Here come the clowns!”

Jao still hadn’t returned when the Bob began to swing.

“Twenty … nineteen and a half … nineteen…” the crowd chanted in unison, counting the degrees as the bulbous painted shape followed the chalk line toward the bull’s-eye in the center of the Forum. Globular membrances lit from within by a coating of biolights drifted down, released from somewhere high above. Hitherto invisible sparklers were touched off, making a star pattern on the floor. To one side, the clowns were still gamely performing their skit, though nobody was watching: Two of them wearing twelve-foot body puppets were vying for possession of a papier-mâché imitation of the Bob, while three more, making a Nar with too many legs, danced around them, trying to make peace.

“Where is he?” Ang fretted. “He’s going to miss it.”

“Never mind,” Trist said gallantly. “I’ve saved an extra kiss for you. Jao’ll have to kiss Smeth. It’ll serve him right.”

“Five…” the crowd chanted. “Four…”

Bram could feel the faint trembling in the floor as Jao’s granddaughter, a hundred and fifty miles overhead in the trunk, began to cancel inertia in order to bring the Bob precisely level. He had to admit that she was an artist at it. In some previous years, before she had become tree systems officer, the Bob had been as much as three or four degrees off. Everybody had had to make the best of it—the clowns would rush out with a big, round target-painted rug and wrestle it into place under the Bob while people egged them on, and Yggdrasil would gradually be corrected over the next few days. But Jao’s granddaughter—he must remember that her name was Enyd—never missed.

“Here’s to all you lovely people and another safe year,” Marg said, raising her glass.

The Bob settled into place, swinging in a small diminishing arc that finally came to rest. More sparklers went off, and noisemakers raised a din. People were shaking hands, kissing, embracing.

Bram felt the shudder.

Others must have felt it, too. Around the arena there was a sudden dip in the noise level, then, as people decided they had been mistaken, things warmed up again.

Trist was staring at the Bob, his eyebrows knit together. Bram followed his lead. The Bob had started swinging again, making a small ellipse that finally settled precisely over the center of the bull’s-eye once again and hovered there, trembling, only a few feet above the floor.

“Your granddaughter’s losing her touch,” Orris teased Ang. “She usually gets it on the first try.”

Bram and Trist exchanged glances. Orris had missed the point, and so had most of the others at the table and in the festivities beyond. The babble of happy ringside voices continued undiminished.

It was not some small adjustment in the angle of radius that had set the Bob swaying again. If that had been the case, the Bob would not have returned to the same spot.

No, something had bumped Yggdrasil here in the interstellar night. Something violent enough to buffet a planetoid-size object stubborn with relativistic mass.

Bram rose to his feet. “I think I’d better—”

And then the thing struck again, knocking him off his feet.

Nobody could miss it this time. People went sprawling, tables overturned, and drinks went flying. Some reflex screaming was going on. The Bob swung in great pendulum arcs over the heads of the crowd. Some wall torches fell to the floor, and a few quick-witted people moved to stamp out the flames. The electric lights flickered, dimmed, then grew bright again.

And from above, where the red-shifted light had been filtering through the lenticule, there was a sudden hideous flare as great snakes of fire flashed by and dopplered through the spectrum.

Orris, white-faced, said, “What’s happening?”

“Everybody better stay put,” Bram said. “There’s a lot of broken glass around.” People were milling around, but the situation seemed to be coming under control again. “Orris, you look after things here. Trist, I’ll need your help.” Trist nodded and rose.

And then, suddenly, Jao was at Bram’s elbow, his forehead bleeding from a gash where he must have fallen against something.

“Better come to the bridge,” Jao said. “Jun Davd’s trapped in the trunk, but I’ve got him on the fiber-optic link. And Smeth’s in touch with his black gang in the engine section.”

“What’s wrong?” Bram asked.

“The galaxy is exploding.”

Bram stared straight ahead into a representation of hell.

The viewscreen that showed the spectrum-corrected forward view was a smear of red-hot coals punctuated by glaring white intersections and eerie violet blobs that throbbed at the headachy limits of vision.

At the center of the screen, a multicolored vortex of fire swirled around a tiny central blaze of eye-hurting brightness. Time was speeded up enough so that Bram could see the crushed stars breaking up, lengthening, feeding their substance into the rushing swirl of light.

Another flattened whirlpool flamed at the edge of the screen, tilted just enough to reveal a similar blinding center. The second vortex seemed even bigger, more violent, than the first.

The whole screen pulsed. At regular intervals of a few seconds, brightness swelled, the field of coals seemed to ripple, and a dazzling shower of sparks danced in front of the view. Each time this happened, Bram felt the floor beneath him shudder, heard the vast creak and groan of the wooden worldlet around him.

“It’s not a literal view, of course,” Jun Davd’s calm voice came over the communications link. “It’s the entire electromagnetic spectrum done in visible light. But I’ve done it in a logarithmic progression, so you can more or less trust your eyes between blue-green and yellow-orange. Then it really starts to stretch out. In the blues, you’re seeing by x-rays. In the far violet, between four thousand and forty-five hundred angstroms, you’re seeing by gamma radiation. And those dull reds are very long radio waves. I had to do it that way so you could make some sense of the view. The dust obscures everything. But infrared gets passed from particle to particle, and some of the energetic gamma punches through.”

“Thank you, Jun Davd,” Bram said. “You must have stayed up all night to do that.”

Jun Davd chuckled. “I don’t imagine there was much sleep for anybody.”

That was true enough. Bram rubbed at his grainy eyes with a fist. They were red, burning. All his joints were stiff.

The others in the long, sweeping loggia that served as this bough’s bridge had suffered equally from lack of sleep. Smeth looked bedraggled, his salt-and-pepper hair sticking up in tufts. Jao and Trist moved as if they had weights attached to their feet, and Bram could see the weary, drawn faces of the people hunched over the monitors.

Mim gave him a wan smile. She was still in her party dress. She had stayed here through the long night, making herself useful. Marg was here, too. She had put Orris to work cleaning up the shambles of the festivities, then she had gotten busy organizing hot food and drink for those on duty.

The bridge itself was fully functional, with everything plugged in, though a lot of unopened cases were still shoved against the rear wall, and some of the equipment was dispersed helter-skelter wherever convenient.

A great gout of incandescence leaped out of the screen. Bram flinched. It reached toward him, a violet serpent with a beady red and orange gut showing through, and writhed offscreen. Bram turned his head to look out the observation wall and saw a cross section of fire flash by, flaring from yellow to red in seconds. Yggdrasil gave a lurch.

“What was that?” Bram said.

“Jet,” Jun Davd said. “I’d estimate it at about twenty-five light-years long and still growing. It’s moving at about three-fourths of the speed of light, but of course it’s emitting a lot of relativistic electrons that are traveling faster.”

Smeth looked around, strain showing on his face. “We swallowed some of the fringes. That was the bump you felt.”

“What caused it?” Bram asked.

Jun Davd’s composure was undisturbed despite the backhand swipe the cosmos had just taken at him. “It’s that black hole we’re heading toward. If you’ll keep your eye on it, you can see the process as it gets ready to toss the next one at us. The hole must be spinning very fast. It must have a very strange geometry—sliced off flat at the poles, but with the curvature of its circumference undisturbed. The gas and dismantled stars flowing into it would have a very strong magnetic field. You can’t anchor a magnetic field in a black hole, but some of the field lines would penetrate the accretion disk and attach themselves very close to the event horizon. Then it’s crack the whip—a million stars at a time.”

“Why are we heading directly toward it?” Bram asked Jao. “I thought we were on a course that gave it a wide berth.”

“We were,” Jao said, his face grim.

“We still are,” Jun Davd’s voice said. “That object you see is not the black hole at the center of the galaxy.”

“What is it, then?” Bram said, but he was afraid he already knew.

“It’s another black hole—in orbit around the galaxy’s central hypermass. The black hole at the center of the galaxy has a second black hole as its satellite.”

Except for those who were not able to leave their monitor boards, everyone on the bridge had gathered around the viewscreen showing Jun Davd’s display. Nobody was doing much talking.

Bram stared, fascinated, at the flat, double-ended funnel of fire that was sucking in the stars. You couldn’t see the black hole itself, of course. You couldn’t even see the accretion disk. But you could see those whirlpools of superheated gas by the inferno of radiation they gave off as they fell down that cosmic drain. And that intense, tiny blaze at the center was where the condensed matter crossed the static limit and doomed itself to leave the universe forever.

Jun Davd’s model of binary black holes explained a lot of things. It explained the rolling yawn of the satellite hole: that was caused by the precession of its spin axis. And it explained those fingers of fire across the bed of coals: the satellite hole was sweeping out the rotating gas cloud of its primary. The geometry of space-time must be very complicated in there. Eventually the orbit of the satellite hole would decay, and it would fall into its primary.

And that would make quite a splash! If anyone in the nearby universe was trying to prove the existence of gravity waves, it would make his day.

“How did it happen?” Bram said.

“The black hole may have been snatched from the Bonfire when the two galaxies met,” Jun Davd said. “That might help to explain why the Bonfire lost its shape.”

Jao spoke wonderingly. “That would have been quite a meal for our galaxy to digest. First it nibbles around the edges. Then it reaches in and pulls out a plum.”

Jun Davd cackled appreciatively. “The stolen hole would have fallen to the center, sweeping up stars and gas,” he went on. “By the time it took up residence as part of a binary pair, it would have been quite massive. We can assume, from the present remnants of the Bonfire, that its central black hole could not have been much more than a hundred million solar masses. However, the satellite hole appears to be three or four times that mass. In fact, I’d put it at a fourth to a third the size of its primary, which I now estimate at well over a billion solar masses—much bigger than I expected. Or…”

“Or?” Bram prompted.

“Alternatively, the orbiting black hole might have been born right here in the galactic nucleus—maybe with the help of turbulence caused by the passing of the Bonfire.”

“You don’t sound very convinced.”

“The dust is certainly thick enough and stellar collisions frequent enough to aggregate a second black hole of a few thousand solar masses. A single collision would be enough to start the process if the stars were massive enough to begin with.”

“But we’re dealing with a hole of three or four hundred million solar masses.”

Jao burst in: “Why stop at one orbiting black hole? Why not a whole planetary system of them?”

“Exactly,” Jun Davd said. “Of course, a number of additional black holes may exist. In fact, I’d be surprised if they didn’t. And two or more of them may have consolidated to form a larger hole. But nothing big enough to explain what we’re facing here.”

“What, then?”

“What we’ve got here is a binary system, not a planetary system. Both of them have a very rapid spin, they’re very close—only a few diameters apart—and one is at least a fourth the size of the other. In fact, they fit almost perfectly the picture of contact binaries.”

Bram struggled to remember his rusty astronomy. “Contact binaries. When the primordial cloud gains too much angular momentum as it condenses and relieves itself by forming a disk. And the disk condenses into a companion, not a planetary system, because it contains too much material and the lines of magnetic force aren’t strong enough to cause spin-down and the spiraling outward of the disk.” He frowned as if Jun Davd could see him. “But you’re describing the formation of stars.”

Jun Davd’s disembodied voice said, “What, essentially, are black holes?”

Outside the observation wall, the flickering tongue of ionized gas continued to rattle through the spectrum, a slice at a time. How long had Jun Davd said it was? Twenty-five light-years. It had grown another light-year while they were talking.

The viewscreen gave him a better impression of what the tongue was doing. It appeared as a mottled serpent swinging laterally away from them on its whiplash path, swallowing stars as it went.

Bram saw something that must have been a supernova—a wink of brilliant light, that was gone in an instant, on Yggdrasil’s speeded-up time scale. Then another flash and another, each of them bathing space in a cosmic instant of inconceivable radiation, each blowing most of its substance off to add more fuel to whatever was happening here in the heart of the galaxy, leaving its core behind as a neutron star.

Chain reaction!

In the galaxy outside, perhaps forty or fifty days had gone by in the last few minutes. Supernovae weren’t supposed to occur that close together. They were supposed to occur once every century or two.

Now he could see another cosmic jet forming at the hub of whirling gases that marked the central black hole. It whipped around, growing by the light-year, ready to slap Yggdrasil when it was long enough.

“Jun Davd,” Bram said, feeling sick, “how long can these jets grow?”

Jun Davd’s voice was grave. “Millions of light-years in the most extreme cases we know. More often, a few tens of thousands of light-years.”

“And in this case? From what you’ve been able to observe?”

“Long enough to reach the edge of the galaxy. That’s what you wanted to know, isn’t it?”

“And they’re growing at seventy-five percent of the speed of light?”

“They’ll slow down a bit as they proceed outward. Some of them will fall back.”

Bram grasped at a slender hope. “Then there would be time to warn the Father World, wouldn’t there? We could stop broadcasting the Message and use our radio beacon to beam a warning. We know they’re listening to the center of the galaxy. They’d have at least twelve thousand years to get ready. Maybe … maybe build a fleet of ships to migrate. Or … or set up ramjet screens for whole planets.”

“The primary threat isn’t the jets themselves,” Jun Davd said gently. “It’s the wave front of radiation coming from the events that have already begun here in the central region—and that travels at the speed of light.” He went on as if he were giving one of his lectures. “The jets themselves contribute to that wave front—relativistic aberration makes them radiate most intensely in the direction of their motion. But they’re only a part of the story. The supernovae are adding their increment of radiation. But, chiefly, it’s coming from that whirligig of black holes and their accretion disks. The soup of matter that engine is feeding on is getting progressively thicker—it’s now a self-sustaining process—and friction is causing the smaller, four-hundred-million-sun hole to spiral inward at an increasing rate.”

How can he be so calm, Bram wondered.

Jun Davd’s voice remained steady. “The radiation is pulsing outward in a series of shells that at this point are only light-days apart. You’ve noticed the flickering of the viewscreen and the rhythmic surges of acceleration as our engine harvests H-II pushed by that broom of photons. I’ve been taking measurements over the last shipboard hour, and those pulses are coming closer together.”

Bram snatched at another straw. “The inverse-square law! By the time the shells of radiation reach the outskirts of the galaxy—”

“They’ll still be fatal,” Jun Davd said flatly. “In any case, no life anywhere in the galaxy will be able to survive the final event, when the two black holes merge.”

A stunned silence pervaded the bridge. Everybody had been listening, of course—trying not to let it all sink in, taking refuge in Jun Davd’s lucid exposition, clinging to some last atom of hope that out of his calm parade of revelations would come the one final fact that was a reprieve for the Father World and its two races.

Now people avoided looking at one another, as if in some obscure shame.

Out of the silence came a strange sound—one that became a shocking sound a moment later as people on the bridge realized that it was the sound of Jun Davd sobbing.

Bram shocked them further by putting the question that sooner or later would have to be asked.

“Will Yggdrasil survive?”

Jun Davd needed a moment to regain control of his voice, “We are now disposing of more energy than is available to the entire Nar civilization. The fields are still holding. We are protected for the time being. But I don’t know if we can handle something on the scale of a climactic merger of the primary hole and its satellite.”

There was a delayed moan of grief from someone on the bridge. Grief for the loss of the Nar and all their works. These were superb people, Bram’s racing mind said. Personal fear would come later.

Jun Davd took refuge in more pedantry. “When two black holes become one, the resulting event horizon has a greater area than the sum of the areas of the event horizons of the original holes. It does not attain its final shape immediately. During the fraction of a second when the collapse takes place, there is a shifting and complicated topography. The geometry of space-time around it is … irregular. The mathematics to describe it does not exist. And the … distorted … event horizon vibrates. The gravity waves generated by two vibrating masses equivalent to a billion and a half suns will be tremendous. What that will do to the surrounding plasma, you can well imagine. Next, angular momentum will increase abruptly at the same time that queer event horizon expands—and because the conjugate hole is spinning rapidly, the accretion disk will be embedded well below the static limit, transferring mechanical energy and magnetic force. A tremendous explosion of gamma radiation will travel outward at the speed of light, followed by a sphere of stripped matter traveling at relativistic speeds. We can hope to outrun the matter. But our ability to survive the shell of radiation may depend on our distance from the core when it overtakes us.”

There was one last question for Bram to ask.

“How soon before the holes merge?”

“We’ll be lucky to make it around the core.”

“We’re making a run for it, anyway,” Jao said.

“That we are,” Bram agreed. “All we can do is to pour on the gravities.”

He lay propped on the floor pad, feeling the oppressive weight on his chest, his shoulders, his neck as he tried to hold his head up. All down the length of the observation loggia, dozens of people lay similarly sprawled on pads, working prone, their instruments on the floor beside them. Bram had ordered everybody to crawl, not walk, if they absolutely had to move about. The bulk of the population of the tree were in their quarters, lying down. It was still half a day till periastron, and they would remain there until then.

Jao said, “No, that’s not all we can do. Bram, I’ve got to ask you about something.”

“Ask away.”

“There’s a decision to make about the core maneuver.”

“Why ask me? I’m only year-captain. Discuss it with Jun Davd.”

“I’ve already discussed it with Jun Davd. But it’s not strictly a technical decision. It involves the lives of everyone aboard. Jun Davd says you’re the only one who can make the decision, and I agree.”

With a sinking feeling, Bram said, “Go ahead.”

“We’ve got to get in and out of the galactic core fast. There’s no way we can simply back up, the laws of physics being what they are. We’ve got to use the mass at the center to bend our path in a hyperbola and swing around and out. Now our patron mass turns out to be two masses, very close together—right—but for the purposes of our hyperbolic orbit, we’re treating it as a single mass.”

“Yes,” Bram said, wondering what Jao was driving at.

“Even if there were some magical new law of physics that would let us dump all our inertia at once and come to a dead stop without rattling the glassware, it wouldn’t do us a bit of good. Because we’d have to back out from a standing start and build up all our lovely gamma factor all over again, and that would take us fifty thousand years longer than whipping around the focus of the hyperbola. So we’re committed.”

“Yes, certainly. Everyone understands that.”

Jao tried to wave a leaden hand, gave up the effort. “We also have to add a vector to angle the outward path somewhat above the plane of the galaxy if we want to aim at the Milky Way. That makes it even more tricky, but I won’t go into that now.”

“Yes, yes,” Bram said, wishing Jao would get to the point.

“So, as you said, we decided to pile on all the acceleration that Yggdrasil will bear in the hope of beating the merger of the two black holes and the final explosion by the widest margin possible. But the extra speed means we need an even tighter hyperbola—we’ve got to brush that doomsday engine ever closer, and that has its own dangers.”

“We all decided to take the risk.”

“Otherwise,” Jao said, ignoring the interruption, “we’d escape the galaxy, all right, and save our own skins. But we’d sail on out into intergalactic space and miss our target.” He looked around and lowered his voice. “Of course, there may be some who are frightened enough of the core maneuver to want to do that on purpose.”

“If you’re asking—”

“Bram, there’s a way we can pick up some extra velocity without adding more g’s and taking the risk of cracking Yggdrasil’s branches—to say nothing of our own sacroiliacs.”

“Go on.”

Jao hitched himself closer on his elbows. He took another look around the bridge to make sure that he would not be overheard.

“We use the satellite hole as a gravity machine.”

“What?”

“We’re already going to pick up the rotational energy of the primary hole. It’s got a rotation parameter of point nine nine eight, and it’s doing weird things to the space around it, and the field lines from the accretion disk are going to reach out with magnetic fingers and fling us along by our own magnetic field. Now, what I’m saying is that we can refine our orbit and loop around the satellite hole, and pick up its orbital energy. It’s whizzing around its primary at a ferocious rate at this point. We could pick up fifty thousand g’s of acceleration without it costing us a thing. We wouldn’t even feel it!”

“We’d have to fly between the two holes to make that loop.”

“Uh huh.”

“Jun Davd says they’re only a few diameters apart at this stage. And they’re spiraling closer. The final dive could happen at any moment.”

“He thinks we have enough time to squeak through.”

Bram’s heart was pounding. “He said that at the present high rate of spin, the static limit is well above the edge of the accretion disk. The region between them must be very weird. We could get sucked into the hole with no warning. Into either one of the holes.”

“Yah. That’s why he says it’s your decision.”

Bram was going to ask for an estimate of their chances. But that would be begging the question—asking Jao and Jun Davd to make the decision.

“Do it,” he said.

Jao nodded and crawled off on his elbows and knees to confer with Smeth.

The ghost of a star drifted by, a ball of red so dull as to be at the limits of visibility. The universe outside the long observation wall was no longer blind; it was filled with a meaningless red fog that showed a suggestion of vast billows, specks, twisting sheets. The phantom star cleared a tunnel ahead of it, but that was an illusion; actually, the star was going the other way, and the tunnel, of course, was its wake.

“Can you see it?” Jun Davd’s voice said over the loudspeaker.

“Yes,” Bram called to the directional pickup.

“Interesting,” Jun Davd said. “I wasn’t sure it would be visible. That shows you how chaotic the galaxy’s final act has become. Imagine the odds against encountering a fellow traveler at anything like a fraction of our relativistic speed! I wish I had a window here.”

“There isn’t that much to see, Jun Davd. Just red mist.”

“Yes, a pale reflection of events behind us. Supernova explosions proceeding outward, perhaps. Possibly local turbulence in those expanding jets, sending shock waves in the opposite direction. Puffs of stripped matter, relativistic electrons, moving inward to add to the mischief. The death throes of a galaxy.”

Mim’s hand sought Bram’s. Her floor mat was pulled up close to his. He had tried to make her nap, but she was unable to. The party dress was bedraggled. It had been a long time since she or anyone else had eaten; Marg and her helpers had had to give up when acceleration increased.

“Easy,” Bram said. “Remember, the Father World is still alive at this moment. Nothing will happen to them for almost fifty thousand years.”

“Oh, Bram, it’s so awful! Isn’t there anything we can do?”

He shrugged. “You heard Jun Davd. The first shells of radiation are already on their way. The big one will be right behind us. We can use the Message beacon to send a warning as soon as we swing around the core, but our warning would reach them only a few years before the radiation front did. It would almost be cruel. Then what? Suppose they managed to fit out a few space arks with ramjet drives to save a few thousand Nar and humans. They have no time to build up their gamma to the point we have, and they can’t outrun the expanding shell. They can’t reach another galaxy, anyway, not in a million years of subjective time, because they can’t use the H-II in the inner galaxy to accelerate the way we did.”

“It’s all so ironic,” she said bitterly. “We were supposed to ensure the survival of the Nar species. We came all this way. And now it’s all gone for nothing. Instead of broadcasting their Message, all we can do is to give them their death sentence.”

He squeezed her hand. There was absolutely nothing he could say.

The people around him, fanned out on mats in front of the forward viewscreen, didn’t have much to say, either. Where two people lay together, they might murmur at each other at intervals, but mostly they watched the view painted by Jun Davd’s computer.

Other screens around the bridge, and the screens in the living quarters where the bulk of the people lay waiting it out, had now been plugged into Jun Davd’s program. Some of the people watching with Bram and Mim had access to their own screens, but there seemed to be a compulsion to watch in groups.

“Hold on, everybody,” Jao’s voice said over the loudspeakers. “We just have to give it one more nudge.”

The tree lurched. Tortured wood fibers groaned. Something somewhere gave with a snap. Interior lights flickered.

“How did Yggdrasil come through that?” Bram asked the tree systems center through the portable console on the floor next to his head.

The voice of Jao’s granddaughter, Enyd, answered. “We’re all right. We lost a few minor branches—all deadwood, anyway. Yggdrasil’s reacting to the increased g-forces by acting to strengthen its compartments, but it won’t last long enough to cause any serious imbalance.”

“How are you people doing in there?” he asked.

Her voice softened, lost its formality. “We’re all right, Captain,” she said.

He switched off. The view in the forward screen was astonishing. A maelstrom of star-stuff churned around and around, fast enough to see. The private whirlpool of the satellite hole could be seen at this flattened angle of approach as an eddy in the main vortex—an eddy that itself circled around the main swirl of gases, dragging streamers with it. The tilt of its precession gave a peek into its heart of brightness every time it came around. Rags of plasma glittering with embedded stars enclosed the double whirlpool like a disintegrating bird’s nest made of fire.

The background stars were squashed, stretched around the immediate vicinity of the holes, their light bent. A circle of splashed stars followed the smaller hole around, snapping back when it had passed.

Nowhere could Bram see a path through the torrent of radiance. The concentric swirls of gas seemed to make one bean-shaped disk whose irregular contour, twisting with the secondary hole, smoothed out almost to an oval with distance from the dual center.

The sky around that cosmic gullet—if you could call it a sky—was crowded with stars of every possible color, jammed so closely together that in places the blackness of space seemed to be nothing more than pavement showing through. Gigantic irregular blobs of glowing gas wandered among the stars, grazing on them. Every once in a while, the flash of a supernova explosion, speeded up twenty thousand times, could be seen through an en-gorged blob. The blobs had an average drift toward the black holes; the ones closest to the double maelstrom bulged yearningly toward it.

A cloud rushed toward them. “Hold on again,” Jao’s voice said. “We’re going through.”

The tree shook as the fields compensated. Weight fluctuated. Bram hoped nobody was moving about; otherwise, there might be broken bones that couldn’t be attended to for some hours. Starfog enveloped them, dimming the fire ahead but not hiding it. Violet stars bobbed by, bloating themselves on the feast of gas; their violet color was the computer program’s translation of the x-rays kindled by that rain of starmist.

Outside the clear elastic windows, the cloud manifested itself only as a dull red flicker—random flashes caused by encounters of gas molecules with relativistic electrons and orphaned protons that happened to be traveling in the same direction as Yggdrasil.

They broke through the cloud a minute later, into the awful radiance of the galaxy’s inner heart. The whirlpool was just ahead, a roaring cataract of flame.

“Here we go!” Jao’s voice said.

An enormous force seized the tree. Abruptly, weight was gone. Yggdrasil’s acceleration was insignificant within that tremendous grip; it was like rowing upstream against a waterfall.

“Stay down!” Bram shouted.

His voice cut through the sudden babble, and people who had started to move clung to their mats. Bram thumbed the intercom switch and repeated his warning for those in their quarters.

Tidal forces changed their orientation as Yggdrasil, now in orbit around the outside hole, swung loose on its tether. The probe, uselessly spitting hadronic photons, must similarly have been trying to align its axis with its strange new parent body.

Bram fervently and irrationally hoped the probe’s drive was pointed down, not up. Not that it would significantly matter in these few minutes and in view of the greater forces acting on the vehicle. In any case, he reminded himself, breaking free of orbit now would be every bit as deadly as diving into the black hole itself.

Equipment went sliding and crashing. People gasped as they felt the tidal pseudogravity change its direction. The hole didn’t care which axis it struck through the wider diameter of the dumbbell-shaped body it had captured, but Yggdrasil, bless it, did, and the tree’s struggle to “remember” its Bobbing Day vertical saved the humans from injury.

“Hold on to something if you can!” Bram shouted. “Try to stay in contact with the floor!”

Yggdrasil held together. Jun Davd had done his calculations well. The smaller black hole, with a solar-system-size circumference of over a billion and a half miles, was big enough, and their orbital distance from it great enough that tidal forces could not pull the tree apart. And the size of an individual human being was too insignificant to matter. Bram could feel the differential in the tug between his head and his feet, but it was no worse than the second-rate artificial gravity to be found in a spinning space vehicle that happened to have a diameter of only forty or fifty feet.

“Here comes the fun part,” Jao said over the loudspeaker.

Yggdrasil swooped around the focus of its orbit. It was now attaining the inside loop of its curve. It was no longer speeding around the black hole in a direction contrary to the hole’s own path around the parent hole, but was picking up fifty thousand g’s worth of acceleration from the hole’s orbital motion.

All for free, as Jao had pointed out. It was fifty thousand gravities that would have crushed them to paste if they had not been in free fall around the body that was providing it.

The only scary part of it was the fact that the inside loop was taking the treeful of humans between the two black holes.

“Oh, Bram,” Mim whispered, squeezing his hand in a death grip. “Can such things be?”

The screen was blinding, even though it showed a bowdlerized version of the radiance outside. They passed between cascades of fire that sheeted to infinity. The eye followed those ravening walls along a path of bent light that made nonsense of perspective—on and on past the point where they should have recurved and eclipsed themselves.

At the center of each infinity, the fires poured into an iris: nothingness surrounded by violet inferno.

“I wasn’t sure we’d be able to see the holes themselves,” Jun Davd’s awed voice said. “I thought the accretion disks and the surrounding infall would block them from sight. But geometry doesn’t mean anything here. We’re within a few billion miles of each of them—less than a light-day away. If you’re willing to accept an arbitrary definition of distance in the vicinity of gravitational fields like these, that is.”

Bram’s fear that there would be no path between the two accretion disks proved to be unfounded. What had appeared from a distance to be a merging of the twin vortices was a less substantial barrier up close. The accretion disks traded material, it was true, but the gaseous zone between them was tenuous enough to pass through. And Yggdrasil wasn’t going to be here long enough to worry about orbital decay. As they plunged between the fountaining sheets of flame, a curtain seemed to open up continually before them.

There was a moment when a giant eye looked in at them through the observation wall. People cried aloud in wonder. In the yawning eternity that the hole’s gravity had made of time, light was downshifted even more than Yggdrasil’s tremendous speeds had done thus far. Theoretically, there should have been nothing visible.

And nothing was what they were seeing.

Then the hole flung them away. The tree whipped around the loop, its path bent back on itself, and headed out of the galaxy. The transfer of orbital energy had been tremendous, and the hole’s precession had given the tree the additional vector that would angle its path above the ecliptic.

The weight of acceleration returned. People picked themselves up and started to move about. The g-forces were back to normal now. There was no need to force the pace. Whatever the danger from the front of radiation that would inevitably overtake them at some undetermined time in the years ahead, they had successfully navigated between those terrible whirlpools without being caught in the ultimate collapse.

Bram helped Mim to her feet. Together they went to the view wall. Other people were lined up along the safety rail, looking out.

There was something to see now, for the first time since the starbow had moved out of sight.

The universe was filled with light. Light of all colors, in wisps and ribbons and streamers.

An elongated blob of mottled blues and greens stretched, writhed, broke up into smaller blobs of violet and orange. A long pennant of pale blue flapped and disintegrated into a thousand filaments. Iridescent tendrils reached after the craft and fell behind. The striations of color played against a background of white radiance that cast long multiple shadows behind the people at the rail.

Yggdrasil was riding the shock waves out of the galactic center. In the nearby volume of space, collimated beams of accelerated matter were traveling in the same relativistic frame as Yggdrasil and shedding some of their radiation in the visible part of the spectrum.

The grateful tree dwellers drank in the spectacle, chattering happily after the tension of the past hours. Nobody was stopping to think about what it meant.

“It’s beautiful,” Mim said.

Bram said nothing. It was the beauty of death.

“It’s hard to believe two hundred thousand years have gone by since we left the galaxy,” Marg said. The tiny curved smile on her lips indicated an attempt at whimsy. “You don’t look a day older, Mim. In fact, quite the reverse.”

Mim, holding the new baby, beamed. “I’m going to name her Lydis,” she said. “It comes from the tonality that Beethoven chose for a quartet movement he intended as a song of thanksgiving.”

“Very appropriate,” Orris said, “seeing that she was born on Safepassage Day.”

“I was going to wait a few more years before getting pregnant,” Mim said. “But then I decided I was young enough.”

“You’re not going to get much younger,” Marg said. “None of us are.”

Marg’s own baby was two years old now. She and Orris had finally taken the plunge when Jun Davd had announced that they had officially left the exploding galaxy behind. There had been a rash of births that year.

“Oh, I don’t know.” Jun Davd laughed, trying to extricate a gnarled finger from the baby’s grip. “Some of us elders still have quite a few years to go before we lose our wrinkles.”

Bram, hovering proudly over Mim and the baby and trying not to look too smug, said, “I don’t like to think of it as two hundred thousand years. Let the outside universe take care of itself. I prefer to count it in Safepassage Days—three more of them. We’re all still alive, and we’re even ahead of schedule.”

The first Safepassage Day had been celebrated the year after the black hole maneuver. Nobody had thought it up—it had just seemed to happen by itself. It came the day after Bobbing Day, and the two holidays had naturally merged into one extended festivity. A new set of rituals had quickly sprung up around Safepassage Day, with gift giving, overeating, and much hilarity. Bobbing Day was still observed, though the reason for it was now gone, with Yggdrasil under spin. It was mostly for the children, who celebrated with miniature trees, candy, and little gaily painted plumb bobs.

“Yes,” Trist said. “We picked up a tremendous boost not only from Jao’s gravity machine, but from all that dense stuff the ramscoop swallowed on the way out.” He grinned at Jao. “Jao, my hairy friend, what’s your refined estimate of our terminal velocity, and how long before we reach the galaxy of Original Man?”

Jao fidgeted on a seating puff next to the maternal nest. Mim had passed the baby to a cooing, clucking Ang, and he was afraid that he was going to be asked to hold it.

“Well,” he said, “there’s still a lot of plus and minus in the observations, but Jun Davd’s latest figures show us coasting at within a hundred millionth of one percent of the speed of light. That means we should cover thirty-seven million light-years in about five hundred and twenty-eight years, our time.”

There was a harrumph from the fringe of the little group, where Smeth had parked himself at a safe distance from the baby.

“Not precisely,” he said. “The ramscoop is still on standby. We’re bound to pick up a stray hydrogen cloud or two, even between galaxies. We still may shave a few years from that estimate.”

Smeth had finally been elected year-captain. He took it very seriously, even though there wouldn’t be much to do during the next five hundred years. He was driving everyone crazy, poking his nose into the cellulose plant, the glucose-processing operation, housing expansion, and the kitchens.

“How about it, Jao?” Bram asked.

Jao scowled. “I hope not,” he said. “We’ve got too much velocity to shed as it is. The Milky Way was supposed to be a pretty fair match for our galaxy in mass and configuration. Nobody figured on binary black holes and core explosions.”

“How are you going to brake?”

Jao shrugged. “We’ll spiral in, spiral out. We’ve got thirty-seven million years to figure out an approach. By that time the Milky Way’s own hypermass may have grown some.”

There was an uneasy shifting in the circle of people around Mim’s nest. Jun Davd said quickly, “A larger black hole at the center of a galaxy should in itself present no dangers. In any case, with a normal accretion rate, no black hole could swallow its galaxy within the probable lifetime of the universe.”

“Hey, hear that, little Lydis?” Trist said with theatrical heartiness. “Your new home is going to be around for what passes for forever!”

People made themselves laugh, but a small pall had invaded the maternity chamber. Bram knew that everyone was thinking about the Nar and their vanished civilization.

His eyes strayed to the window wall. There was nothing to see out there anymore except Yggdrasil itself—mile after mile of great twisting subbranches and carpets of leaves, lit up by the banks of spotlights that were trained on them from the shaft of the probe: not only to give Yggdrasil a sense of its own rotation, but to provide the human passengers with a sense of place in a universe that otherwise had gone blank.

Somewhere beyond Yggdrasil’s horizons was an exploding galaxy, its light blotted out by red shift. It didn’t bear thinking about. But it was impossible to shut it out of the mind.

Nen cleared her throat. “What heights must they have reached in the fifty thousand years they had left to them?” she asked. “They spread so fast through their arm of the galaxy in that little time. Expanding their domain. As if they knew they were racing against the end of everything.”

On the way out of the galaxy, Trist had used the antenna array to monitor the radio emissions of the spreading Nar civilization until they stopped—replaced by the random radio noise of frying suns. Bram had watched Trist change, become progressively haunted during those last years, and he knew that Trist must have brought some of his despair home to Nen in their quarters at the end of each day.

“In another million years they might have started up Skybridge, toward the Bonfire,” Trist said softly.

“That wonderful web of life—it’s all gone now!” Jao’s granddaughter said with unexpected fervor. “The Nar, the humans and other organisms they brought into being, the forests of space poplars multiplying through the cometary halos from star to star!”

Bram wished the conversation hadn’t taken this turn. All this was upsetting Mim on what should have been a happy day for her.

But it was Mim herself who wouldn’t let it go. “Trist,” she said. “Do you think they ever received our warning?”

“We can’t ever know,” he said. “It couldn’t have made any difference anyway.”

Mim had retrieved the baby from Ang. Bram thought that it made a pretty picture—Mim’s dark hair spilled down around her shoulders, the baby nuzzling at her breast. Life, he thought. Life out of the ashes of universal death.

“They gave life to humankind twice, you know,” Mim said almost in a whisper. “And there’s no way we can pay the debt.”

A slow dawning overtook Bram. He smiled at Mim. “Yes,” he said. “Yes, there is.”

Halfway across the night, Yggdrasil encountered a star. It was a fading red dwarf, so dim that they were almost upon it before the sensors reacted. In minutes of treeboard time, it was light-years behind them—too quick to call the passengers for a real-time look—but Jun Davd made a record for later replay by anyone who was interested.

“It must have broken free from its parent galaxy a very long time ago,” Bram said to Mim as they watched the replay in their quarters. “Any star much higher on the main sequence would have burnt out long ago.”

“Oh, Bram,” Mim said, moved by the sight. “Could a star like that have planets? With living creatures on them?”

He touched her arm. “If so, they live in a very lonely universe. Under a sky with nothing in it except a fuzzy patch or two.”

“Like us,” Mim whispered.

“No,” Bram said, “not like us. Someday we’ll have stars in our sky again.”

CHAPTER 4

“It’ll take us about forty more years to stop,” Jao said. “But we should end up in the approximate volume of space that Original Man used to inhabit.”

People were starting to bunch around the optical boundary of the gigantic holo projection that dominated what, by convention, was the forward end of the observation lounge. More spectators were trickling into the fan-shaped chamber. Yggdrasil had just burst out of one of the globular star clusters above the plane of the Milky Way, and word was going around that there was a magnificent view to be seen.

Bram stood a little aside with the rest of the astronomy and physics group, so as not to block the view. He’d been here about a half hour now, but he still couldn’t take his eyes off the image.

The central bulge of the galaxy loomed head on out of darkness: a spectacular incandescent yolk with the flattened disk spread out around it. The fires of the nucleus glowed yellow, those of the disk shading to the paler blues of older stars. Nearer, a hail of intervening stars streamed by, Yggdrasil’s tremendous speed putting them in visible motion.

The holo vista was startlingly realistic—much more so than the kind of flat computer display Jun Davd had made do with at the beginning of the voyage. But that was hardly surprising. He’d had centuries to improve on it and five generations of brilliant engineers to assist him.

This blazing vision was everything Bram had dreamed of all his life. A knot of indescribable longing formed in his chest. It was easy to forget that this was illusion—that in deceleration mode, with the tethered tree straining forward and a torrent of hadronic photons aimed along the probe’s axis through the focus of the sheltering ramscoop fields, the scene rushing toward him was actually beneath his feet.

Jao was taking some good-natured heckling from the crowd of onlookers. “Forty years is a long time to wait,” someone said.

“We could do it faster,” Jao said. “The limiting factor is the number, of g’s we want to take over an extended period of time.”

“I don’t understand how we’ll be able to brake at all,” somebody else said, “when we’re not approaching edge-on through the spiral arms.”

“We’ve already shed some velocity diving through the globular clusters,” Jao said. “And there’s plenty of mass in the central bulge, even though it’s not as concentrated as the one that sent us on our way.” His hands sketched the glowing egg in the holo behind him. “We dive straight down through the nice, nourishing H-II regions we’re going to find in there, we make a tight demiorbit around the central three parsecs, a safe distance outside the core that contains the black hole, the central star cluster, and the rotating inner ring of ionized gas. The normal orbit at that radius—if we wanted to stay there—takes ten thousand years, so we apply vector to turn it into a powered orbit. Nevertheless, we start to spiral out in spite of ourselves, in flatter and flatter spirals that bring us into the plane of the galaxy. And the spirals are retrograde, of course, so we’re using the magnetic brake of the nucleus itself. Nothing to it! It’s as easy as tomato pie! Isn’t that so, Bram?”

Bram, startled out of his reverie, said, “Uh, certainly. The Milky Way turns out to have a very strong magnetic field at the center from what certain of our observations seem to indicate, and we ought to be able to use its rotation to slow us down considerably—just the opposite of the magnetic assist we got at departure.”

He glanced at the peculiar arc that could be seen growing out of the center of the galaxy’s golden yolk like a spray caused by a pinprick. It wasn’t a very large scale feature—only a few thousand light-years in extent—and its meaning was still being debated by the astronomy department; there was no need to go further into it at this moment.

“The galaxy’s made a quarter rotation in the last seventy-four million years,” Jun Davd interposed smoothly. “Or, rather, Original Man’s neighborhood in one of the spiral arms has. We had to allow for that, too. I hope everyone appreciates the brilliant job of orbital plotting that Jao’s department did.”

Jun Davd was as imposing as a young man as he had been when he was old. He’d become even taller with the reversal of calcium loss in his spine and carried his slim, smooth-muscled body with an easy grace that his older incarnation had only hinted at. Bram could never quite get used to seeing him without white hair, though.

“Well, I suppose if we’ve come this far, we can wait another forty years,” Jao’s heckler conceded grudgingly. Bram recognized him as one of the younger passengers who had been born on the trip. He was probably under a century old, and forty years would seem like forever to him.

“Oho, hold on minute,” Jao said with a malicious glint in his eye. “After we get to the volume of space we think Original Man’s message came from seventy-four million years ago, we still have to find the suns he used. That could take us another century or two if we don’t get lucky right away. We can do some preliminary sifting from a distance, but every time we want to stop and examine a G-type star firsthand, we’ve got to spend a year boosting down from relativistic speeds, a year boosting up to get to the next one, and at the low gamma we build up for these short hops, at least a couple of years in between. Unless you don’t mind gaining a lot of weight, that is!”

“Why do we have to find one of Original Man’s worlds at all?” grumbled the slender youth who had once been Doc Pol. Young he had become, but he hadn’t lost his grumpiness. “We’re here, we’re safe in a galaxy that isn’t exploding—why not settle down in the first G-type system we find? Put down roots. Let our descendants go gallivanting around looking for Original Man’s world if they’ve a mind to.”

There was a chorus of opposition to squelch that idea. Nobody wanted to give up on the search now that they were so close. Doc Pol hunched his faunlike head between his shoulders and looked stubborn.

“We’ve waited this long—we can wait a little while longer,” said a woman wearing one of the leaf tabards that had been popular five hundred years back. The costume placed her as one of the old hands—now a minority.

“That’s right,” another person said authoritatively. “Man’s worlds are our best bet, anyway. There’s bound to be some sort of a surviving DNA-based ecology we can adapt to instead of having to start an ecology from scratch from our vats and gardens here. In the meantime, Yggdrasil is a fine world to live on.”

“Too fine,” someone else said. “We have folk aboard who’ve never known any other world. There may be some who’ll prefer to stay in orbit with Yggdrasil. It makes a more benign environment than most planetary surfaces. I know I’d be tempted to stay myself.”

“Until one day you found yourself sailing off to the cometary halo or heading for a nearby star that Yggdrasil thought had the right absorption lines,” some wag said, and everybody laughed.

Jao’s granddaughter, Enyd, claimed attention with a frown and a gesture. She was still chief tree systems officer after all these years, still smooth, cool, and unapproachable. She picked a lover briefly every twenty years or so, but most of the time she remained seemingly wedded to Yggdrasil. The unattached men who had wooed her to no avail called her “the dryad” behind her back.

“Whatever we do, we’ll have to slow down enough to let Yggdrasil absorb a comet or two before too long,” she said. “It’s been showing the effects of drought these last few years.”

The current year-captain, a colorless hydroponicist named Ploz who’d had the support of the sociometrics clique, said with quick concern, “How critical is it?”

“We’re not losing leaves or anything like that. But the reproductive cycle is on hold. And the more recent xylem rings are getting extremely narrow—Yggdrasil’s pretty much shut down its growth these last few years.”

“How much longer before it gets critical?” Ploz persisted.

“I wouldn’t want to wait more than another century or so,” Enyd said severely.

There was a general sigh of relief. Jun Davd said, “Yggdrasil will have its comet long before then.”

Bram hung around until the press of people got too thick for comfort. Then, with a last regretful look at the galaxy’s swollen heart of fire, he elbowed his way out to make room for someone else.

“Don’t forget the meeting tomorrow,” Jao called after him. Bram waved acknowledgment.

When he emerged from the crowd, he found a delegation of four waiting to intercept him—three members of the glib younger set who seemed to be running things these days and one of the former oldsters who’d been around at the start of the journey.

Silv Jaks was the group’s spokesperson, and that was Bram’s clue that the sociometricians had taken a hand in whatever this would turn out to be. Bram wasn’t quite sure what sociometrics was, other than the fact that it had something to do with people in groups—it was one of the jargon-packed new sciences that had sprung up during the trip’s later generations—but its disciples had definite ideas about the running of the tree, and they wielded a lot of influence among the new people.

“Bram—we hoped we’d find you here,” she said briskly. “Do you have a minute to talk?”

“Sure, Silv.” Bram nodded to the group’s senior member. “Hello, Torm.”

“I’ll come to the point,” Silv said. “We represent a committee that wants you to run for year-captain this term.”

“That’s very flattering,” Bram said warily, “but I haven’t been year-captain for over two hundred years. just a working biologist and part-time astronomy assistant these days. There are plenty of qualified people around.

She set her jaw and drew a breath. “We believe you’re the candidate who’s needed at this time.”

“I thought you were going to throw your weight behind Ploz again. Everyone says he’s doing a good job.”

“He was the sort of year-captain we needed while we were still coasting. With deceleration, we’ve become a migratory society again. And there will be further upheavals as the populations of the outlying branches are assimilated into the annual branch once more. We’re going to undergo a lot of societal stress in the coming years. More important, our goal is in sight now.” She gestured past the crowds toward the overpowering panorama of the Milky Way’s bright center. “We need a renewal of our sense of purpose as a society.”

“What’s it got to do with me? It seems to me that we’ve hung on to our sense of purpose all right—even though the Father World is only a legend to most of the folk who were born between the galaxies. As to adjusting to an annual migration again, I wouldn’t worry. People manage.” He smiled reassuringly. “It might even breathe some life into All-Level Eve and Bobbing Day again.”

Silv was having none of his levity. “You’re a symbol of the old days for a lot of the people who weren’t around then. And for the original embarkees, you’re the leader who started them on this voyage. You were the first year-captain—I looked that up! We’ve run profiles of all the old leaders through the computer, and we believe you’re the one who’s best suited to bring the two moieties together.”

“The two what?”

It sounded like more of the jargon that Silv’s colleagues in the Theoretical Anthropology group were always culling out of the primal Inglex dictionary. They were always creating computer models of imaginary human societies and drawing fanciful conclusions from them. They claimed to use rigorous statistical methods, too, but from what Bram had seen, some of the more overweening practitioners of the arcane speciality had a rather shaky grasp of real math.

Silv metered her words to him carefully. “One-third of the population of the tree had been born within the last hundred and fifty years. Approximately one-fourth consists of the original embarkees and the generation immediately following, who share their values to a large degree. In between is an amorphous group who tend to be polarized in one direction or the other. Thus there has been an evolution toward endogamous moieties which—”

Torm interrupted with a twinkle. “What she’s trying to say is that the older and younger voyagers tend to divide into two groups as defined by their cross-mating practices.” He winked. “Not that I’ve noticed it myself.”

Bram laughed. “Tell that to my great-great-great-granddaughter Ame,” he said. “She’s been trying to fight off Smeth’s attentions for years.”

“Naturally, in an evolving culture the lines aren’t yet rigidly drawn,” Silv said with Signs of annoyance, “but we’ve drawn up charts and applied statistical methods, and we believe there’s a developing pattern of custom and taboo.”

Torm allowed his eyes to glaze, though not enough to be impolite. The lively old fogy of the Bachelors’ Lodge had again become the smallish, dapper young blade he must once have been. Bram would not have put it past him to have cast an eye on Silv herself for a little endogamous tumble.

“What it sublimates down to,” Torm said, “is that Silv’s crowd think I have enough influence with the old-timers to be worth cultivating and that if we can get together behind a candidate with across-the-moieties appeal, we’ll have the votes to win.”

“And that’s me?”

“You’re the only one we can agree on. If you say yes, the votes are guaranteed.”

“Will you accept?” Silv asked.

Bram looked past them at the fiery egg in the holo projection. “I’ll think it over,” he promised.

“A symbol of the old days,” Bram repeated with relish. “That’s what they’re calling me now. They want to dust me off and set me up as year-captain again.”

Mim paused in her work. She was feeding the score of a new string quartet by one of her protégés into her computer and punching in the program that would separate it into players’ parts for next Tenday’s performance. “That might not be such a bad idea,” she said.

“Oh, Mim, you know the job’s nothing but a headache,” he protested.

His daughter, Lydis, said, “What are you going to tell them?”

Lydis had hardly changed at all in the last five hundred years. She was still the same slender, dark-haired edition of her mother that she had been when she reached her final age, without an added ounce, worry line, or shift of body mass. Even her teeth seemed always to come in as identical replicas, not changing the shape of her mouth an iota. Lydis had not inherited Mim’s talent for music, though; she was a gifted and relentlessly practical engineer who had designed the hardware for some of the tree’s most important industrial biosynthesis plants. Currently she had taken an interest in piloting and was spending a lot of her time exploring the hangars where Yggdrasil’s fleet of landers was stored and practicing in the simulators.

“I haven’t decided,” Bram said. He went to the coldall and helped himself to a gourd of sapbrew. “The next few years are going to be very exciting ones for astronomy. We have the chance to study the galaxy we’re going to live in from the inside out, over a real-time frame of tens of thousands of years, so we can observe processes There’s that peculiar feature in the nucleus—the gas arc I mentioned. It suggests a powerful magnetic field, but at right angles to where one ought to be. We may find an answer in the inner parsec of the galaxy. We’ll never have the chance for a close-up view again. Jun Davd’s offered me the chance to be an important part of it. Being year-captain is time-consuming.”

He took a sip from the gourd. “And then there’s my own bioengineering project. Genesis Two. I’d have to shut that down entirely for a while.”

Mim put the string quarter score aside. “The observations will get made whether you’re there or not,” she said. “It will take years—decades—to sort them out and draw conclusions from them. You have all the time in the world. There are still tons of data from the explosion of the old galaxy that are lying there waiting for someone to go through them. Jun Davd can wait. And as for your genetics project, I know it means a lot to you, but that can wait, too. Your assistants can keep it warm. In any case, you couldn’t implement the project until we’re resettled.”

“I don’t know, Mim,” he temporized.

“I’ll tell you this,” she said. “For the last two hundred years we’ve had year-captains who immersed themselves more and more in the housekeeping details of the job. When they weren’t officious busybodies who tried to interfere with people’s lives, that is. Because for at least that long, a majority of the population have been people who think that the human past is a sort of fairy tale. They’ve never lived on a planet, never had a Nar touch brother—never even seen a real Nar, for that matter. They think that babies have always been made by two people in a nest together—not constructed out of nucleotides. They don’t have any real comprehension of the fact that the human species ceased to exist for thirty-seven million years, and that we’re here now by the grace of a wonderful race that’s ceased to exist itself, and that we escaped by the skin of our teeth, and that Yggdrasil is just a temporary habitat to get us back to the original seedbed of humanity.” She paused for breath. “Bram, do you realize that most of the people on this tree have never in their lives seen a real star—only holo projections? Maybe Silv is right. Maybe we do need to remind ourselves of what this trip is all about!”

He grinned at her. “I think you just like the privileges that go with being married to a year-captain. Like always having a meal or your sleep interrupted by some problem, and never having any privacy, and sitting through long boring meetings where everybody pushes their point of view on you for the thousandth time, and you smile and nod for the thousandth time so that nobody thinks their views are being slighted.”

She grinned back at him. “Shall I tell you why Lydis is here?”

“To check up on the old folks and make sure their synapses haven’t gotten all stuck together?”

“Oh, Bram!” Lydis said.

Mim said, “So I could ask her how she’d feel about being older sister to a new sibling. A five-hundred-year-older sister.”

’”I think it’s a wonderful idea,” Lydis said. “It’s about time. The new people hardly wait till one child is grown up before having another one. They breed like yeast. I certainly think the demographics of the tree entitle you to another baby. And I’d enjoy having a sibling.”

Both of them looked Bram’s way. He said with feeling, “Lyd is right, Mim. The end of our journey’s in sight. Yggdrasil could handle five or ten times our current population without any strain—but I doubt that even the new people can breed fast enough to fill it up before we reach home territory. You’re certainly as eligible as any centenarian to have a second child. But are you sure you don’t want to wait until we find a planet?”

“No,” she said. “Call it an act of faith.”

Bram embraced her. “Careful, oldsters,” Lydis said. “You might tempt me to have a second child, too, like my silly granddaughter.”

Mim, her dark eyes shining, said, “Think of the exciting younghood the child’s going to have. A plunge through the heart of the galaxy. The strange sights at the core. A trip to the spiral arm that was the cradle of humanity. And—and the stars coming back!” Her voice took on fervor. “A curtain of stars drawing back little by little as we slow down, stars spreading till they fill the sky again, shifting back to their true colors … until finally one day our destination star lies before us, big as a sun.”

“Yes,” Bram said, caught by the vision. It was what another child had dreamed thirty-seven million years ago in another galaxy.

Mim, warm in his arms, felt what he was thinking. “It’s come true, hasn’t it, Bram?” she said softly.

“I wonder what we’ll find there,” he said.

“You’re seeing the husk of a quasar,” Jun Davd said, “left over from the quasar epoch of the cosmos.”

He gestured toward the dizzying scene behind the observatory’s holo wall. The fabric of the universe seemed to writhe as stars were wrenched from their true positions and yanked into the illusory halo surrounding the black hole’s event horizon. Then, as Yggdrasil continued its headlong dive past the hole, the stars smeared around the heart of darkness pulled free and popped back into place. The queer stellar mirage was visible because Yggdrasil, on its first pass, was in a polar orbit—dropping down from above the nuclear bulge, where the hole’s accretion disk did not obscure the view.

You could see the inferno of light representing the disk if you stepped close to the transparent shield and looked down into the imaginary space behind the wall. But most people took a look and stepped right back again. You knew it wasn’t real, but something about it made you feel as if you were falling.

Smeth, working hard to impress Ame, cleared his throat to get noticed. “It might be a husk, but if so, it’s a husk of a hundred million solar masses. Not in the same league as the binary holes at the center of the Father World’s galaxy, but massive enough to have caused periodic core explosions of its own. We’ve detected a sort of smoke ring ten thousand light-years out that seems to be a remnant of the last explosion.” Then he made the mistake of condescending to her. “Of course,” he said importantly, “you weren’t born yet when we made the passage between Scylla and Charybdis—that’s what we old hands call the binary hole maneuver, from an old legend of Original Man—but those were the great days! You had to have been there!”

“Yes, I’ve played back the sequence many times,” Ame said offhandedly. “Jun Davd, is there any danger of the next core explosion wiping out life in this galaxy, as it did in the old one?”

Bram watched Ame with a pride of authorship he felt for all his descendants—though in Ame’s case he could claim only one thirty-second of the credit. His great-great-great-granddaughter had turned out well, he thought. She was a pert, direct, lively girl with wide green eyes and corn-colored hair. Though she was scarcely forty years old, she was a complete person with good sense and integrated views.

Her interest was in something she called reconstructive paleontology, and with a small group of similar-minded young people who styled themselves such things as comparative geologists and theoretical terralogists, she was attempting to come up with a self-consistent picture of the bygone planet, Earth, that had spawned Original Man. The store of data they had to go on was skimpy—the highly condensed primers of various descriptive sciences that had been included in the Message plus whatever clues they could gather from literary works, dictionary line drawings, parallel processes on the Father World, and similar sources. But she and her friends had been ingenious and had gone surprisingly far with their small database.

To Smeth’s chagrin, Ame had brought along two colleagues from the paleoearth department: a woman named Abiga, whose specialty was comparative geology, and a young man named Jorv, who was only in his twenties and who bubbled over with enthusiasm for something he called “deductive zoology.”

Bram felt sorry for Smeth, watching him hover and fuss around Ame. Youth had not been kind to the gawky physicist; it had robbed him of a certain acquired gravity and left him awkward and abrasive again. When Smeth had invited Ame to watch the hole approach with the astronomy and physics group, he had expected to monopolize her—and now she could not be pried loose from her chums. Smeth still was trying to figure out if Jorv was attached somehow to Abriga or whether he represented sexual competition.

As if that weren’t bad enough, Jun Davd was being courtly.

“No, we believe the Milky Way is reasonably tame now,” Jun Davd said in answer to Ame’s question. “The quasar epoch used up the tremendous quantity of material within the core that might fuel an event on that titanic a scale and stored it conveniently in the form of the black hole we’re orbiting now. The subsequent explosions—like the one that caused the ‘smoke ring’ Smeth mentioned—obviously could not have been violent enough to wipe out life in the Milky Way … though they might have had some minor effect on species.”

Ame and Jorv exchanged a peculiar glance.

“When did the last core explosion take place?” Ame asked. “Or is there any way of estimating it?”

“Yes, indeed, there is,” Jun Davd said. “We’ve been observing the so-called smoke ring over a period of more than fifteen thousand objective years during our dive into the galactic bulge. It keeps expanding and contracting to strike a balance between its rotantional velocity and the gravitational attraction of the center. From the rate of oscillation, we calculate that the last core explosion took place approximately one hundred and forty-one million years ago.” He smiled. “And I gather that Original Man evolved after that event, since he broadcast his Message only seventy-four million years ago.”

“Jun Davd,” Ame said, hesitating, “when is the next core explosion due?”

Smeth opened his mouth, but Jun Davd beat him to it.

“Theoretically, there shouldn’t be one. The last explosion should have depleted the galactic center of the necessary mass. The smoke ring’s velocity and distance suggest an ejected mass of one hundred million solar masses—and an explosion powered by converting the equivalent of ten thousand suns completely into energy. Now a black hole of one hundred million solar masses sits in the center, and except for the observed stars around it, the center should pretty well have been swept clean.” He frowned.

“But?”

“By generating artificial profiles of the twenty-one centimeter line, we’ve determined the amount of invisible matter that must be rotating around the galactic center.” He paused, decided to add to his explanation. “You see, that gave us the Doppler shift of the neutral hydrogen present.”

She seemed to know what he was talking about. “The faster the rotation, the greater the mass?”

He brightened. “Precisely. And the figure we get is two hundred million solar masses.”

“Twice what ought to be there?”

He nodded. “And we don’t know where it came from.”

“Jao has a theory about that, though,” Bram put in.

“I’ve heard about Jao’s theories, Bram-tsu.” Ame laughed. She was a dutiful descendant, always giving him an ancestral honorific in the abbreviated Chin-pin-yin form. He had told her over and over again to simply call him Bram, but like so many of the young people, she was a stickler for convention; it was as if the newest generation were trying to revive a structure of human tradition all by themselves.

Jao, hearing his name, twisted his shaggy red head around from the console he had been working. “Yah,” he said, “there has to be some kind of mechanism for renewing matter in the core of the galaxy. It doesn’t have to amount to much—about seven-tenths of a solar mass per year.”

“The problem is,” Jun Davd said indulgently, “that this hypothetical flow of matter isn’t coming from the galactic plane, and it isn’t coming from outside the galaxy, as when the Whirlpool cannibalized the Bonfire.”

“So that leaves one place, right?” Jao continued. “The nucleus of the galaxy itself. Matter just appears there.”

Smeth found his voice. “That’s preposterous!” he said. “It’s nothing more than a rehash of the old discredited theory of the continuous origin of matter!”

“No, listen, this is a new idea based on the heavy-neutrino model of the universe,” Jao insisted. “If neutrinos have mass, then they could account for ninety percent of the mass of the universe, and ordinary matter is a film wrapped around great clumps of neutrinos. And where do the clumps come from? I’m glad you asked that. They’re simply the walls of a great spongy cellular structure, one of whose bubbles is our own dear old universe. This all takes place in eleven-dimensional space-time, needless to say. The different domains are a necessary consequence of the first moments of creation—and you’ll notice that the domains would be nonregular in shape, and that fits in well with the observed fibrous structure of the universe. So how do we create matter in the nuclei of galaxies without violating baryon conservation?”

He glared around at everybody.

“I have a feeling he’s going to tell us,” Bram said.

“We don’t!” Jao proclaimed triumphantly. “We have an exchange of neutrinos and un-neutrinos through the walls of the domains. The walls leak. Why are the leaks located in the centers of galaxies? Easy. Because of the hypermasses there—the super black holes sinking deep into the plenum and stretching the warp and woof of space-time to its limits. You may well ask why no right-handed neutrinos have ever been observed, despite the predictions of theory! Because the scales are balanced in other domains, that’s why! So symmetry is preserved in the larger sense. Baryons—like protons and neutrons—can’t cross the domain walls without instantly decaying. But un-neutrinos exhibit antidecay and assemble themselves into elementary particles, in the reverse of beta decay.”

Smeth was beside himself. His face was red as a tomato, and he seemed in danger of bursting.

“You can’t do that!” he said, his voice cracking. “How can you change leptons into baryons?”

“With mesons as the mediators, naturally,” Jao said. “And while we’re at it, what do you think happened to those missing solar neutrinos you tried to detect in that chlorine tank experiment of yours back on the Father World? I’ll tell you. They were falling in, not out. They were being funneled through the domain wall to another domain. There must have been a black hole on the other side.”

Smeth opened his mouth indignantly to reply, but Ame cut in to get the subject back on track.

“So what it boils down to is that, by whatever mysterious process, there’s enough material in the center of the galaxy for another explosion, even though it shouldn’t be there?” she asked.

“Admirably put,” Jun Davd said.

“And that presumably this process acted in the past to cause periodic explosions?”

“Yes.”

Ame mulled it over. “Could core explosions be a byproduct of some other process? Or vice versa?”

Jun Davd pursed his lips. “That’s an interesting question. More interesting than you know. Why do you ask?”

“I’m trying to pin down periodicity. You said that the last core explosion in the Milky Way must have taken place one hundred and forty-one million years ago?”

“Thereabouts.”

“It’s a very interesting coincidence.”

Her zoologist friend, Jorv, nodded energetically.

“Coincidence? How?” Jun Davd asked.

“Because one hundred and thirty-nine million years ago was when the dinosaurs became extinct.”

Jorv burst out, “Practically on the heels of the explosion!”

“What is a dinosaur?” Jun Davd inquired.

“It was a very large animal that predated humans on Earth. Though they couldn’t have been as large as the Message described them—there must be some error or misinterpretation of scale. We have line sketches of several of the main types. They were the dominant form of life on Earth for about one hundred and thirty million years, then they abruptly vanished.”

“Like Original Man,” Jun Davd murmured. “I take your point.’

“How big were they?” Jao asked.

“They were built on the same general plan as human beings,” Ame said. “Four limbs, bilateral symmetry, bony skeleton—so I suppose it’s possible that they could have been as much as three or four times human size. We’ve done computer simulations of them, and with a thicker bone cross section as compared to a human, certain efficiencies in oxygenating tissues, a slower metabolism, and so forth, we think it’s possible for them to have weighed as much as a ton.”

Jao whistled. “That big?”

“The Message data has some of them attaining a length of ninety feet and weighing as much as fifty tons.” She smiled. “But of course that’s nonsense. No creature with an internal skeleton could attain that size. It would have to have some sort of exoskeleton supporting its weight like a scaffolding, or an external shell, like the orthocone creatures on the Father World—and of course, then they couldn’t be very active.”

Jorv’s boyish face had been working, and now he said, “Don’t take away my big dinosaurs, Ame! I’ve been running a different set of assumptions through the computer, and I can get bipeds up to twenty feet tall and quadrupeds twice that scale.”

“Bone is bone, and histology is histology,” Ame said tolerantly, “but if you want to postulate more efficient absorptive surfaces than human beings have, and a food intake of a quarter ton a day, and radiators to get rid of body heat, you’re welcome to your big dinosaurs.”

It was the usual sort of professional banter, but Bram could all but see Smeth’s suspicious mind working to make something more of it. Poor Smeth, he thought. The case was hopeless, but it wasn’t up to him to tell Smeth that!

“So these … dinosaurs disappeared at the approximate time of the core explosion?” Jun Davd mused. “Hmmm … allowing time for some undefined process to spread to Earth’s latitude in the galaxy at the quite reasonable rate of about one and one-half percent of the speed of light?”

“Not just the dinosaurs, Jun Davd,” Jorv said. “They disappeared completely—every last one of them—but many other land animals and most marine species disappeared at the same time. If the record that we’ve been given is correct.”

“And about one hundred fifty-five million years before that mass extinction,” Ame put in, “there was another major extinction in which half of all animal families were wiped out. And one hundred and fifty-five million is almost an exact multiple of twenty-six million.”

“What’s the significance of twenty-six million?” Jun Davd asked.

Ame and Jorv fell over themselves to be the one to tell him. Ame won out. “The geological record we got from Original Man—and you must realize it’s only a summary, without the detail we’d like—shows that there seem to be major species die-offs at intervals that work out to an average of about twenty-six million years.”

Jorv amended: “In two cases, there seems to have been a follow-up extinction of species at an interval somewhere between thirteen and fifteen million years.”

“That’s what worries me,” Ame said. “There were two cycles of extinction that followed the dinosaur disappearances that don’t appear to have affected the precursors of Homo sapiens, but add another thirteen million years to that and you get a value pretty close to the time when Original Man’s Message was cut off.”

“Jao,” Jun Davd said, turning around. “What sort of correlation can we get on that major date of one hundred and fifty-five million years prior to the last core explosion?”

Jao’s fingers flew over his board. “It’s hard to say, Jun Davd. We got one scenario that could have put another core explosion about there. You know, the one where we factored in the expanding molecular ring at the center. But we don’t know enough yet.”

Jun Davd turned back to Ame. “There’s not enough to go on,” he said. “We have one striking correlation of a core explosion with one of your two major extinctions and one more possible correspondence. But there’s been no more explosion since the dinosaurs disappeared and no periodic phenomenon that subdivides the major events into twenty-six-million-year cycles.”

“How about this?” Jao said. “Imagine something that sweeps the galaxy like the spokes of a wheel. Imagine eight spokes. Four major spokes, like the arms of a cross. And in between, four minor spokes, also arranged roughly as a cross. As Man’s sun orbits the galactic center, it encounters a spoke approximately every twenty-six million years.”

“Why eight spokes?” Jun Davd inquired.

“You have to start somewhere. Eight has a nice symmetry. Besides, it works out in lots of ways. You’ll see in a minute.”

“What do you mean?” Ame asked, leaning forward.

“Look,” Jao said. He did something to his console, and the tremendous scene behind the holo wall vanished, to be replaced by the rough scrawls Jao was tracing on his touch pad with one meaty forefinger.

“Hey, wait a minute!” Smeth protested.

“The universe won’t go away,” Jao said. “I’ll bring it back in a minute. I want everyone to see this.”

A bold vertical line in screaming orange grew in the illusory void behind the wall. “We start with a two-spoke model,” Jao said. “Two opposing arms, like a lot of cosmic phenomena. Like galactic gas jets, for example. Now we add another pair of arms at right angles.”

He slashed another orange line across the first. It wasn’t quite horizontal—apparently by design, because as everyone watched, the second pair of arms, responding to whatever crude instructions he had punched into his board, slowly turned until the adjustment was made.

“You see, there’s some repulsive force holding them equidistant from the two previous arms,” Jao said. “Like magnetism. Now we subdivide one more time.”

Two more crude slashes turned the cross into an asterisk. This time the finger-painted lines weren’t as thick, and they were a paler orange. They were also slightly out of position, but after a moment the second cross rotated with respect to the first until all the angles were equal.

“These are the baby arms,” Jao said. “They’re not full-grown yet. They’re weaker. That’s why I drew them skinny.”

Jorv, with growing excitement, said, “What did you mean when you said it works out?”

“For starts, when you multiply these twenty-six-million-year events of yours by eight, you get a figure of two hundred and eight million years. Which is a pretty good match for the length of time it takes Man’s sun to make one complete orbit around the galactic center.”

“Very suggestive,” Jun Davd said. “Eight events per solar orbit. Of course, you’re assuming either that the spokes are stationary, or the sun is stationary, or the spokes are rotating at twice the sun’s speed at the radius of the sun’s orbit.”

“Like I said, you have to start somewhere,” Jao said. “I like figures that come out even. So you begin with a nice regular series—two, four, eight. And multiples of orbital speed—which incidentally would put the end of a full-grown spoke somewhere at the rim of the galaxy.”

“Why not a ten-spoke model?” Smeth interrupted, with a sidelong glance at Ame. “You’d get a multiple of two hundred and sixty million years, which is closer to the two-hundred-and-fifty-million-year galactic year that some of us prefer!”

Jao shrugged. “Suit yourself. You could make that work, too, with a little fiddling with the relative velocities. You can work out the figures if you like. But an eight-spoke model’s more elegant.”

“I take it there’s more,” Jun Davd prompted.

Jao brightened. “Yah. Watch this.”

His thick fingers busied themselves on the board, and a bright yellow dot appeared about halfway out on one of the orange spokes. It began tracing a slow circle around the center of the geometric figure. A moment later the eight-armed figure began to revolve, too, at a somewhat faster rate, with the arms continually overtaking the dot.

“Now, let’s label the arms so we can keep track of them,” Jao said.

Letters popped up, alphabetizing the arms. Jao did not stop the process quickly enough, and a second round of letters began to subtend the first.

“That’s okay, leave it,” Jao said. “If I were laying this out flat, I’d be going past eight into the next cycle, anyway.”

Ame and Jorv were intent on the garish sketch hanging in the space before them. Bram could see Ame’s lips moving as she counted to herself.

“Now we take those forty-five-degree angles and subdivide them again,” Jao said.

Eight more lines grew within the spoked figure. These were dotted lines, even paler and more tentative than the lines of the second cross. Not all of them were full-length. Several of them still fell short of the yellow dot’s circular orbit.

“These are your follow-up extinctions,” Jao said to Jorv, “The ones you say sometimes follow the main events thirteen to fifteen million years later. They subdivide the twenty-six-million-year intervals, and they’re growing outward at different rates, so we can’t fit all of them into the picture. Yet.”

“Very thin,” Smeh said.

“So we start with what we do know. Here’s the dinosaurs.”

One of the arms of the original cross thickened and darkened to burnt orange. The tenuous dotted line following it began to blink for attention.

“Okay, anything there?” Jao asked.

Ame and Jorv looked at each other. “The Miocene crisis,” Ame said immediately. “A mass wipeout of shellfish, plankton, some land animals. But it’s only twelve million years later.”

“Close enough,” Jao said. “Now, let’s skip back one hundred and fifty-five million years to the other really major crisis. The one that wiped out half of all animal families on Earth. Have we got a secondary extinction associated with it?”

“Yes,” Ame said, catching her breath. “A bigger one this time. A very large extinction of marine organisms that could fall within a ten- to fifteen-million-year period. We couldn’t fit it into our data before without stretching it.”

“All in knowing how,” Jao said with a grin, while Smeth smoldered.

Jao thickened the axis and shaded it over to include the following arm. “Very interesting,” he said. “The two big ones are at right angles to each other. Forming two arms of the older cross. And it’s the arms sprouting in their wake that turn out to be the real killers.”

“As if whatever it is was getting stronger,” Ame suggested.

“Yah.”

“Jao—”

“Not yet. Let’s fill in as many blanks as we can first.”

Over the next several minutes they assigned eleven extinction episodes to the rotating spokes. Nine of them fit the pattern of the eight major spokes, and two fell within the secondary following position.

“How do you explain the missing pieces?” Smeth asked.

“How should I know?” Jao rumbled. “Insufficient data. Fluctuations in the strength of the spokes. Maybe factors that we haven’t figured yet. The sun catches up with a spiral arm every hundred million years or so and stays inside for ten million years. It bobs up and down through the plane in a thirty-three-million-year cycle, if it behaves like the other stars at that radius. Maybe the dust intensifies the killer effect on some passes. Maybe it does the opposite and acts as a shield. Why don’t you try to combine all the cycles and see what you can work out? The important thing is that everything we do have fits the pattern.”

His belligerence died. Like everybody else in the observatory he was staring at the one big fact that hung before them in the rotating holo image.

“The ninth extinction and the first extinction are doubled up on the same spoke,” Ame said in a half whisper.

“It came back again for a second swipe,” Jao said.

“The second visitation was the last extinction before human beings evolved.”

“The first swipe was the big double event,” Jorv said. “First the trilobites and all that plankton—ninety percent of sea life. Then half of all animal life on Earth.”

“And if there was a … a similar follow-up,” Ame said, “it would have come at just about the same time that Original Man disappeared from the universe.”

Smeth’s harsh voice grated through the ensuing silence.

“It couldn’t be. Man is an intelligent being, not a—a dinosaur! He would have found some way to protect himself. Or flee. After all, it isn’t as if the entire Milky Way was sterilized the way the Father World’s galaxy was. Some life survived each of these—extinctions and went on to evolve.”

“When the dinosaurs disappeared,” Jorv said, his young voice getting away from him, “no species of land animal weighing more than twenty pounds survived. Man’s ancestors were very small and primitive. It was the highly evolved species that went. The second time around, that was man.”

Jao stared thoughtfully at the rotating orange arms of his holo model. “Original Man had only spread a few hundred light-years. At most, a few thousand. You can’t travel faster than the speed of light. You can’t outrun something that extends to the galactic rim and sweeps the galaxy laterally. They could only have caught up with the previous killer arm.”

He retreated into gloomy contemplation. Nobody else seemed very lively, either. Bram was just about to say something, when Jun Davd did it for him.

“Let’s not jump to conclusions,” Jun Davd said. “This is all highly speculative. Jao doesn’t have a theory, just a hypothesis. We need more data. We’ll set up a long-term computer model and keep feeding our observations into it.”

Yah, I’ll get on that today,” Jao said.

Jan Davd went on, “Original Man’s sector of the galaxy is about thirty thousand light-years from the center, and on our outward spiral, we’ll sweep great areas of the disk over a real-time period of tens of millennia. We’ll be able to make observations that were not possible for Original Man, no matter how much further advanced than us he was.”

Ame and Jorv looked puzzled, and Jun Davd added gently, “The time wasn’t there for him, you see.”

As it sank in, the tension began to go out of the room. A few tentative smiles made their appearance. Ame brought her chin up and said to Bram, “You’ve brought us this far, Bramtsu. Nothing can frighten us now. This galaxy is humankind’s heritage, and we’re here to claim it.”

Smeth edged forward, trying to reestablish contact with Ame. “That’s right,” he said. “The whole thing may be nothing more than a statistical fluke, anyway.”

“There’s just one thing.” Jao’s voice brought their heads around again. “If the eight-arm model is correct, our sector of the galaxy is due for another brush soon.”

His hand swept the board, and the rotating orange lines snapped out of existence. The universe came terrifyingly back into sight, a raw torrent of light that slammed them across the eyes and turned the human figures into stark silhouettes. Yggdrasil’s plunge toward periastron had carried it past the black hole’s equator, and the accretion disk had risen out of the floor.

CHAPTER 5

“There’s a star in there somewhere,” Jun Davd said through his suit radio. “Its light may be blocked, but it’s shining its heart out in the ten-micron infrared range.”

Bram clung to a cleat with one gloved hand to keep the trunk’s slow rotation from shedding him into space and turned up the magnification of his helmet visor. “A body-temperature star,” he said. “That fits the picture, all right.”

He peered past the leafy horizon at a void that was frosty with stars again. After more than two decades of braking, the starbow had separated and strewn its baubles across the sky. The drive was off, and Yggdrasil was towing the probe now, not the other way around.

But despite the magnificence of the sprinkled stars, it was the sight in the center of his image compensator that occupied Bram’s full attention.

There was a scratch across the sky—a perfectly straight line, as if a cosmic thumbnail had scraped away the black. Next to the long scratch was a collection of bright squiggles, like cursive writing in an unknown language.

“The straight line’s about ninety million miles long,” Jun Davd said. Within the crystal bowl of the new space suit, his dark profile was intent on the distant object. “That’s about the same length as the radius of the infrared emission shell the instruments can detect. Does that suggest anything to you?”

“The only astronomical phenomenon I can think of that’s that straight and that long is a Type I comet tail,” Bram said. “Except that there’s no coma at one end. In fact, the brightest part, if I read the instruments right, is in the middle.”

“Yes,” Jun Davd agreed. “And it doesn’t extend outward from where the mass indicators say our shrouded star ought to be. It’s tangent to it.”

“So that suggests very strongly that it has something to do with the structure that’s enclosing the star. And that those curved scratches—the arcs and hooks—are part of the same manifestation.”

Jun Davd turned to face him: Somehow Jun Davd managed to be limber, even in the bulky envelope of the human-shaped space suit that had been developed during the last ten years of deceleration by a team under the direction of Lydis. He had the toe of one heavy boot hooked under the horn of a cleat to check his outward drift, and his long-limbed body swiveled halfway around at the hips with a natural grace. He was not one of those people you saw bobbing around at the end of their safety ropes and having to haul themselves in.

“I agree. I have a computer working on an analysis of the curvatures to see what kind of a three-dimensional shape we can make them fit into. But clearly, we’re looking at an artifact.”

Artifact. Bram tasted the word with disbelief. From the size of the infrared emission shell, the unseen sun ought to have been a red giant—a swallower of solar systems. An artifact of that radius at the center of the Father World’s system would have engulfed the two inner planets and the Father World itself.

“A trap around a star,” Bram said slowly. “A trap for energy. When we first began searching for an enclosed star radiating in the ten-micron part of the spectrum, I somehow visualized something like a sphere. I think we all did.” He paused to stare again at the distant wonder. “It’s hard to imagine how any rectilinear material body the size of that could maintain its shape without gravitationally collapsing.”

“There’s only one answer, then. It’s not straight.”

Bram looked again, but the line was just as straight as before. “It’s not?” he said.

“We’re looking at the illuminated limb of another geometric form,” Jun Davd said. “One that can maintain its shape. I can think of at least two: a cylinder and—”

“Yes,” Bram breathed. “A disk. A spinning disk. Seen edge-on. But it’s still unbelievable.”

“We don’t know what was possible to Original Man at the height of his glory. Perhaps, given another forty or fifty thousand years, the Nar might have learned how to utilize the total energy of a sun.”

“Do you really think that’s Man’s sun in there?”

Jun Davd wrinkled his brow. “One of the suns he used, perhaps. The sun that gave him birth, no. I can’t see him dismantling his own father world to make a beacon. There’s nothing in this system larger than an asteroid. Nothing but a swarm of comets orbiting an invisible mass. And we’re lucky he left us the comets.”

He broke off to stare across the miles at the cagework trumpet bell of the ramscoop, which was no longer bathed in the spilled energies that had made it bright. A couple of comets had already been stuffed down its throat as start-up fuel for the next intersystem hop—the hop that the absence of worlds here had made unavoidable.

A space tug floated nearby, waiting to field the next slushball to be sent onward. Two tugs, actually, with a five-mile-wide net strung between them. It was the net that was visible as a fleck of light from a reflected spotlight beam. Bram wondered if his daughter Lydis was one of the pilots.

Closer at hand, against the fibrous wall of the root system across the way, a work crew was prying another ensnared comet away from Yggdrasil—a small one, less than a mile in diameter. With his magnification up, Bram could just make out the tiny space suited figures. They were melting away the clinging ice with dozens of two-man torches. It would require exquisite nicety of timing on the part of the foreman to make sure that the frozen sphere broke loose at just the right moment to cast it toward the waiting tugs instead of outward into the dark.

Yggdrasil could spare a few comets. Scores of the captured iceballs beaded the thirsty surface of its root hemisphere. The tree was working bravely to redistribute mass, but the unassimilated treasure trove still caused a wobble in the crown that took some getting used to. There was a lot of dropped glassware in the living quarters these days, but nobody was complaining. Abundance had returned to the tree after the long drought. The pools were filled, there was boating in the lagoon again, and water sports in the spherical pond at the center of the trunk. More important was the increase in metabolic products as Yggdrasil went through a growth spurt—sugars, starches, complex resins, and new cellulose for the factories.

Bram remembered the excitement when they had entered this queer, gutted system. Four previous ten-micron emission sources had proved to be false alarms—supergiants with circumstellar emission shells that were probably heated dust grains, not worth slowing down for. But the fifth candidate had shown all the symptoms of what the search team had jokingly taken to calling “Jao’s shell.”

It was Jao who first had proposed the theory of an enwrapped star whose output—by whatever unknown means—had been translated into the cosmos-spanning radio waves of Original Man’s beacon.

“Where’s all that building material going to come from?” Smeth had scoffed.

“From the dismantled planets,” Jao had replied. “And maybe they’d have to haul over the planets from a couple of nearby systems, too. They’d be turned into some kind of supermaterial made mostly of hydrogen, carbon, and oxygen—the atmospheres of a couple of gas giants mixed with the goodies at the core, and some cometary ice—you get the picture.”

“How are you going to keep the shell from drifting off center?” Smeth had expostulated. “And if it rotates, how do you keep its substance from collecting at the equator?”

“Details,” Jao had replied airily. “We’ll worry about them later. The main thing is to look for infrared sources that fit the basic picture.”

The search area had been narrowed down to a sphere a thousand light-years in diameter. The Nar, long ago, had pinpointed an approximate location for Original Man’s sun by analyzing wave fronts on a line stretched between the Father World and the new outpost on Juxt, and they had arrived at a value for the galactic year at that radius. Jun Davd, during the thirty-seven-million-year head-on approach to the Milky Way, had refined the figure still further. When the M supergiants and the small hot objects shining through dust had been eliminated, the number of candidates was small. Even so, it was surprising to have found it, apparently, on the first try.

“I calculate a total energy output for our invisible sun of four times ten to the thirty-third power ergs per second,” Jun Davd had announced shortly after Yggdrasil had settled into a cometary orbit. “That’s based on the number of ergs per square inch falling on our collectors and applying the figure to an imaginary sphere at the radius of our own orbit. All in the deep infrared! It’s consistent with the normal output at all wavelengths of a G-type dwarf similar to both Original Man’s presumed sun and the Father World’s primary. An attractive sun for our type of life, and the Nar’s.”

Jao had worked out approximate orbital periods for the first few comets Yggdrasil had chased. “Yah,” he’d said. “The comets are moving at the right speed for the postulated mass at the center. Maybe just a little bit high—but, like I said, the beacon builders might’ve dragged in an extra gas giant or two from another system.”

It was going to be hard to pry Yggdrasil away from the comets after its long thirst. Bram—year-captain again for the fiftieth time—was under a lot of pressure to let the tree graze peaceably for a while in the outer reaches of the cometary halo. The human population of the living spaceship was now up to twenty-five thousand. It was getting a bit crowded along the axis of acceleration. The younger generation in particular had its eye on all the congenial real estate that would open up in the other branches if Yggdrasil went on permanent rotation mode.

But Bram did not dare give in. He had the feeling that if the populace spread out this time, he’d never get them back to the axis.

At Yggdrasil’s leisurely rate of travel, it would take decades to drift from star to star—centuries or even millennia to search out the G-type dwarfs in this sector of the galaxy for the traces of Original Man. The new people did not have the same sense of urgency—the idea of a goal. For them, Yggdrasil was a way of life. It was more than possible than the citizenry could vote to settle in the first system that had rocky bodies to mine, a cometary shell to seed with a crop of more Yggdrasils.

Sometimes, on bad nights, Bram had a nightmare that he would never make planetfall again.

No, he thought. The only solution was to get his little convoy under fusion acceleration as quickly as possible, investigate the mystery at the heart of this system, then boost out again at one g.

Certain it was that Yggdrasil, left to its own devices, was not going to get much of an outward kick from the starlight to be found here!

Beside him, Jun Davd said, “I saw something just then.”

Bram looked, but saw nothing except the faint scratch in the darkness and its attendant squiggles.

“Within the curve of the larger arc,” Jun Davd said.

Large, at this distance, meant nothing much more than a fairy’s hangnail, even under full magnification, but Bram stared till his eyes watered.

Then he could just make it out—the dimmest of patches, like a foggy speck in his faceplate.

“It’s leaking light,” Jun Davd said. “There are holes in it. That’s diffuse reflection on a surface. Keep watching. And if I’m not mistaken…”

As if someone had punctured the fabric of space with a pin, a star peeped forth.

“It’s not the whole star, of course,” Jun Davd mused. “It’s probably the light from no more than ten or twenty percent of its surface to judge by the apparent magnitude. But we wouldn’t have seen a disk, anyway, at this distance, just a point of light.”

Bram didn’t need a spectroscope to tell him what he was looking at. “It’s a G-type sun,” he said.

“Yes, indeed,” Jun Davd said. “Well, we’d better uproot poor Yggdrasil again and go in for a closer look.”

“It’s embarrassing,” Ame said. “I have as many children as my great-great-great-grandmother.”

She held up the twins for inspection, one in the crook of each arm. They were beginning to lose the wrinkled, recently boiled look, and it could be seen from their coloring and button features that they were going to take after Ame, not Smeth.

“Never mind, they’re beautiful babies,” Mim said, nudging Bram in the ribs to keep him quiet. “And dizygotic twins are nobody’s fault.”

Smeth puttered nearby, a fatuous grin on his face. Ame’s firm stewardship had done wonders for him; the rough edges, if not gone, were ground down a bit, and his friends pronounced him almost civilized. He and Ame had been together for ten Bobbings now. She teased him by telling him that it had simply become too much trouble keeping him at arm’s length and that she had decided that maybe he was salvagable after all, despite five hundred years of bachelordom; to which he responded by swelling with pride and pleasure.

“I’ve used up my quota on my first try,” Ame said ruefully.

One child per century was the rule nowadays, enforced by society’s unspoken displeasure. Those who had bred too thoughtlessly during the profligate days of middle-passage now sheepishly waited for the passing years to rehabilitate their reputations.

“You can have a share of mine or Lydis’s,” Mim said. “We’re not a prolific family. It all averages out.”

“Yah, you want to talk embarrassed, look at Marg and Orris,” Jao said heartily. “Five children, like clockwork. Hey, I bet they have a cesium clock hanging over their sleeping nest so they can start working on number six the nanosecond it’s licit.”

“Jao, you’re awful—stop that!” Ang exclaimed. “Excuse him, everybody.”

“Why? What did I say?” Jao said innocently.

Bram, suppressing a smile, said to Ame, “Quotas may be a thing of the past sooner than you think. We ought to be ready to leave this system in a few years, and then it’s just a question of time till we hit on a suitable planet.”

He carefully refrained from specifying the father world of Original Man. He didn’t want to appear to be too much of a visionary to these practical young people like Ame and her friends. It was generally accepted that there ought to be any number of suitable planets of G-type suns in Original Man’s neck of the galaxy that once had been used by the vanished race and that therefore would possess breathable atmospheres and benign ecologies. Any sensible person aboard ought to be ready to settle for one of these. And any one of them would be a treasure trove for the paleontologists and the archeologists and the rest of the practitioners of the new theoretical sciences.

“Yah, as soon as your cohabitant here starts up the fusion engine, we’ll be on our way,” Jao said. “How’s it going, Smeth?”

Smeth, startled out of his slack-jawed adoration of his firstborn, replied, “I’ve got a crew aboard the probe overhauling the systems now. The four-wave mirrors need realignment, and there’s been some minor damage to the web of the scoop, but it held up pretty well, considering. I’d say we ought to finish in a two of Tendays, and then we’ll be ready to travel again.”

“We ought to be able to land on the outside of whatever’s walling off the sun!” Jao said enthusiastically. “The temperature’s a nice comfortable three hundred degrees Absolute. Then we hightail it out of the system and start looking at yellow dwarfs. There’s only eight or nine possibles within a twenty-light-year radius, and I’m betting one of them is the birthplace of Original Man. The stars around him would’ve had different relative motions—the guidepost constellations in the Message are no good to us now—but they’d have the same general orbits around the galactic center, and I’m betting they didn’t drift too far apart. This beacon would’ve been one of the two or three closest.” He showed all this teeth to Ame in a gargantuan grin. “You’ll be able to multiply with a clear conscience by the time the twins are grown.”

Bram marveled that Jao was able to be so bluff and nonchalant on the subject in the face of his own tragedy. His second child, by some fluke, had proved to be immune to the immorality virus. The boy had grown into a humorous, likable chap with Jao’s talent for physics. He had made some notable contributions and had left offspring himself before dying at the age of a hundred and thirty. That had been two centuries ago. Jao and Ang had never had another child after that.

Bram thought about his own new son, Edard. He and Mim had been lucky. Edard was a fine young man, still in his twenties but already making a contribution to human culture. From the first it had been evident that he had inherited Mim’s musical talent. He had picked out tunes on the keyboard at the age of three, and by five he was well on the way to teaching himself to play Mim’s cello, when Mim had taken a hand and started giving him formal lessons. Now, Edard was devoting himself to composition. He was obsessed by the six old symphonies that had been transmitted in score in the Message of Original Man and had applied himself to the task of recreating a live symphonic texture. He was probably the first composer in the history of the tree who was in a position to do so. With the increase in population, there were now enough first-rate players for an orchestra of thirty-eight people. They gave a concert every Tenday evening. Tonight they were going to introduce Edard’s twenty-second symphony, the first in which he had totally abjured all electronic fill-ins for missing instruments and had limited himself to what the live players could produce. It promised to start a new, revolutionary trend.

Thinking of it reminded Bram to check his waistwatch for the time; the newer people might think him an old fuddy-duddy for clinging to habits learned on the Father World, but any honest person would have to admit that it was more polite to unobtrusively feel for the time with your fingertips than to read it off a visual wrist meter.

“We’d better think about going, Mim,” he said when he had a chance to get her attention. “It’s only two hours till the concert.”

Mim made the announcement general. “Sorry to rush off,” she said, “but I’m not cellist emeritus yet. I have to do my share with the others. Edard insists on a thick cello sound—he says he needs at least four.”

“I’d better go, too,” Ang said. She was in the violin section. “No, you stay a while if you like,” she said to Jao.

“I wish I could hear the concert, Mim-tsu-mu,” Ame said, “but I don’t think I’d be welcome with two yowling babies.”

“I’ll stay with you,” Smeth said.

“No, you go,” Ame told him. “Don’t you dare miss Edard’s premiere.”

“I can hear it later on tape,” he said.

“Tape?” Jao exploded. He put on an indignant expression for Mim’s benefit. “Have you been paying the remotest attention to what Ang and Mim’ve been saying? The whole point is that it’s living, breathing music. If you’re going to hear it through a speaker; Edard might as well’ve done it all on a synthesizer!”

“Since when are you the great music lover?” Smeth snapped.

Ame stopped him with a look. “You go on,” she said. “One of us ought to be there.” She apologized to Mim. “Tell Edard-tsu-hsiung I’m sorry. I’ll hear another performance of it.” The punctilious honorific she added to Edard’s name meant something like “ancestor-brother.” Immortality was stretching the language out of shape.

The door rasp sounded. “I’ll get it,” Smeth said, glad to escape.

While Mim and Ame said their good-byes, Bram heard raised voices at the door. Someone was wroth with Smeth. When leave-taking was done and Bram accompanied the two musicians to the entry chamber, he saw that the agitated caller was Jao’s granddaughter, Enyd, the tree systems officer.

“I didn’t expect to find you here, Captain,” Enyd said. “I came here to ask physics supervisor Smeth if it’s true that he plans to put Yggdrasil under acceleration again, and if so to lodge a protest.”

Smeth blustered, “The decision to reactive the drive is entirely the prerogative of—”

Bram cut him off. “Yes, it’s true, Officer Enyd. I planned to discuss it with you first thing in the morning. I apologize for the fact that word apparently got to you in a roundabout way before I had that opportunity. You should have been the first to know.”

“It was one of the technicians working on the overhaul,” Smeth fumed. “That loudmouth Perc, I’ll bet. He must have spread it all over the place. All I did was to flash the workcage to ask how soon they could promise start-up if we decided to go! But I told them to keep their mouths shut.”

“We’ll have to make an announcement,” Bram said.

“Captain, Yggdrasil’s barely had time to recover,” Enyd said. “It wants to spin normally for a while. It can’t go back so soon to the artificial rhythm of adjusting its lateral growth once every Bobbing.”

Bram looked at Mim. “Go on ahead, Mim. I’ll catch up.” Mim and Ame left after a belated, perfunctory exchange of greetings with the distracted Enyd.

“How is Yggdrasil’s ice reserve?” Bram asked, before Enyd could resume her complaints.

She hesitated, then said scrupulously, “Adequate, I suppose. But if we are to resume traveling, I would prefer to achieve satiety.”

“I’ll tell you what. When we get the fusion drive started, we’ll chase down a few more comets for Yggdrasil before proceeding inward.”

“Captain, water and trace elements aren’t the only point. Yggdrasill needs a summer season, relief from stress, time for sustained photosynthesis. I wouldn’t mind if you turned on the fusion fire for that; right now, Yggdrasil’s trying to make do with starlight … and the minor portion of infrared that it’s able to convert into the six-hundred-sixty-and seven-hundred-thirty-millimicron range.”

Her voice was almost tremulous, belying the cool, remote beauty that drove her suitors wild.

Bram spoke gravely. “I’m confident in your ability to monitor Yggdrasil’s metabolism and do whatever is necessary, Chief Officer Enyd. I’m going to ask you to keep this tree happy for two more years. That’s the time we’ll need to penetrate to the center of this system under one gravity’s acceleration. Then we can let Yggdrasil bask in the light of a real sun for a while, while we explore.”

Edard sat in the cello section with Mim and the other two cellists, but sometimes in the finicky passages he would leave off playing and beat time for the other musicians. Bram watched the slender, dark-haired figure with pride. The music was first-rate; everybody said so, Mim had told him after the rehearsals. Even the old diehard, Kesper, had said with tears in his eyes, “If Mozart had written another symphony besides the Jupiter, it would have sounded like this!”

In the seat beside Bram, Smeth was trying to suppress a cough. Jao glared at him fiercely, and Smeth grumbled, “Where’s the tune? Everybody’s playing something different.”

There were whispers of “Quiet!” from the surrounding seats, and Smeth subsided. Bram looked around the great, carved wooden chamber. Every one of the eight thousand seats was filled, and a repeat performance had been scheduled for those who were unable to get in. Edard had refused to allow a microphone pickup, saying that it would only encourage people to listen in their own chambers.

The live sound was glorious, Bram had to admit. The acoustics of the wooden cavity, refined over the centuries, helped.

Stringed instruments had come a long way in five hundred years. The new cello was like a truncated pyramid the height of a child, and the performers played it vertically instead of horizontally on a stand, as before. The bow weighed only a couple of pounds now and could be played without an elbow clamp; it was a lightweight plastic framework with its own power source to keep the continuous friction band running smoothly around its sprockets. Mim was a stickler for proper bow technique. She told her students that the bow should hardly be moved at all—just raised or lowered on the eight strings.

The music was coming to a climax. The cellos all buzzed in unison; the violins soared; the horn players raised their long, conical instruments and blared in thrilling harmony.

It was over. Bram stood with the rest and applauded. On the central platform, Edard looked flushed and pleased. Mim went over and kissed him.

“You’ve got a talented boy, all right,” Jao said. “Too bad he has no head for science.”

Bram laughed. “Are you trying to sound like Smeth?”

“I’d never say a thing like that,” Smeth protested indignantly. “I thought it was … very good.”

The applause rose, swelled. The other musicians were closing around Edard, clapping him on the back, grasping his hands. Edard looked no younger than the others, but Bram could not help reflecting on his age. What will he develop into, he thought, with all eternity ahead of him?

The audience had settled down again for the encore. Edard had wisely refrained from repeating his own music and was giving them the familiar slow movement of the Jupiter Symphony—deliberately inviting comparison, Bram thought, smiling at the arrogance of youth. He closed his eyes and listened as the long-drawn cello melody gravely climbed its steps while the violins scolded it. The audience held its breath. Even Smeth sat rapt and silent beside him.

There was a tap on his shoulder, and he turned toward the aisle to find Trist leaning apologetically toward him.

“I’m sorry,” Trist whispered, “but something’s come up. I think you’d better have a look at it. Jun Davd’s waiting for us.”

The violins had succeeded in wresting the theme back from the cellos. Bram looked longingly at the communing musicians on the platform. Mim and Edard would expect to see him backstage afterward. He gave a resigned shrug and eased his way out while people glared at him. He followed Trist up the aisle. The heavenly music floated after him. A backward glance had told him that Jao was trailing along behind, prodding a resisting Smeth.

“Now, what’s this about?” Bram said when they were out of the hall.

“We’re getting some very strange radio signals,” Trist said.

Bram stopped in his tracks. Smeth and Jao piled into him. “Intelligent?” he said.

“Let’s just say they’re nonnatural,” Trist said.

Jao’s big hand grabbed Trist by the shoulder and spun him around. “Where are they coming from?” he said hoarsely.

“From everywhere,” Trist said.

“What do you mean?” Bram said.

Trist bit his lip. “I mean from half the sky. From every star in a volume of space that—” He broke off. “Best come see for yourself.”

“But what kind of—”

“Jun Davd’s still sorting out the data the computer dumped,” Trist said. “He’ll probably have a simulation ready by the time we get there.”

And that was all they could get out of him during the trip to the Message center. It was a ride of over twenty minutes, even on the high-speed mag-lev tubeway that had finally replaced the outside slingshot pods on eight of the twelve major branches. Bram had to watch Smeth fidget and listen to Jao grumble all the way. He found it hard to contain his own curiosity, but he knew there was no point in pressing Trist.

The Message center had been gathering dust during the five centuries of coasting between galaxies, and had been reopened only in recent years, as an adjunct of the observatory. It had been thought worthwhile to begin searching for possible evidence of artificial signals as they approached the volume of space that once had held the civilization of Original Man—if they were going to have intelligent neighbors, they had better know about it—and the radio installation still held a lot of specialized equipment and the old programs that Trist had used in monitoring the Nar wavelengths on the way out of the Whirlpool galaxy. But the search program still took a back seat to the long-range radioastronomy programs that Jun Davd had set up using the Message center’s antenna ray, including the accreting computer model of Jao’s magnetic eight-spoke theory to account for the periodic extinctions of Earth’s life.

The tremendous cylindrical arcade was darkened and silent as they floated through it; with the fusion drive turned off, the tree was practicing a few small economies in its use of electric power. Far down an avenue of shadowy capacitors, Bram could see the bobbing lights of one of the skeleton maintenance crews that made periodic inspection tours here. Trist led the way in a series of shallow touchdowns. The gravity was almost nil this close to the tree’s center of rotation; they had to wait once for Smeth, who incautiously bounced too high and got himself captured by what had been the ceiling when the tree had been under acceleration.

“Here we are,” Trist said, letting them into his old office.

Jun Davd looked up at them from a jumble of printouts and scrawled summaries spread out around him on a variety of work surfaces. Screens and variously organized date windows were fine, but there was nothing like paper when you wanted to see everything at once.

“Ah, here you are,” he said. “Did you tell them?”

“Yes,” Trist said.

“Tell us?” Jao roared. “He told us nothing except that we’d better come have a look for ourselves.”

Jun Davd said imperturbably, “You know that we have a number of ingenious computer programs written by Trist, designed to search likely wavelengths for patterns of various types, with all sorts of Doppler compensations—for our motion, the motion of stars, the motions of presumed planets orbiting in a variety of presumed planes, shifts in limb brightness along the edges of the presumed planets as the planets themselves rotate around an infinite number of presumed axes … it’s all very complicated, particularly when we ourselves are moving.”

“Yes, yes,” Jao said impatiently.

“Some of the data goes back over a year—we’d already spotted the infrared emission of our invisible star and were decelerating toward it. But the computer never sounded the alarm. Neither did the technicians who conducted the occasional random sampling. But that’s not surprising. The data picture didn’t become really interesting till we came to rest.”

Seeing Jao redden toward explosion, Bram said. “Take pity on the man, Jun Davd.”

“Here it is translated into audio,” Jun Davd said. “With a little guesswork, of course.”

He flipped a switch, and the room was suddenly filled with clicks and snaps, as if a million demented children were all breaking twigs at once.

Bram felt ice down his spine. “What is it?” he said.

“It has no information-bearing content that we can see. On the other hand we can’t make it correspond to any natural radio phenomenon that we can imagine.”

Trist broke in. “So we decided it must be a by-product of some artificial process. Like back-lobe leakage from the space-based antennas of solar power satellites.”

“Then an analysis of the wave forms suggested strongly that the clicks were acoustic in nature,” Jun Davd said. “So we discarded the idea that they were some kind of static, either natural or artificial.”

Bram listened to the hard, dry snapping sounds for a moment. Regarded as actual physical noises, they were even more puzzling. “They’d have to be produced in a medium: solid, liquid, or gas,” he said.

“Ridiculous,” Smeth said. “There must be a natural explanation. Remember how pulsars fooled the early radio astronomers? It’s some property of the stars in this arm of the galaxy.”

Bram frowned. “Trist said that the signals come from everywhere. From the invisible star we’re orbiting too?”

“No. Everywhere but,” Trist volunteered.

“Now we come to the interesting part,” Jun Davd said. “Bear with me a moment. This is still very crude. But it will give you an idea.”

He fiddled with a console, and a holographic window lit up in the display board. It was a three-dimensional star map, reasonably realistic, with points of colored light scattered through the velvet darkness. A dull red bead began winking in a lower corner.

“That’s our position,” Jun Davd said. “Or the position of our infrared star. We’re somewhere in the cometary belt—we won’t quibble about half a light-year or so. And now here’s the route we took from the center of the galaxy.”

A yellow dotted line grew from the blinking bead, angling inward in the holographic illusion, and disappeared behind the windowframe on the opposite side.

“Now, all of this space is filled with these odd radio emissions—they’ve all had different times of origin and the oldest of them are presumably spreading in spheres many hundreds of light-years in diameter. Far beyond the boundaries of my little map. But that’s not what we’re concerned with. We want to show the stars of origin.”

He fiddled with the console again, and a whole swarm of stars in the center of the holo image began blinking. The swarm was in the shape of a lumpy sphere—as near to a perfect sphere as the actual distribution of stars in space could make it.

With one exception. There was a curiously flat, squashed area on the part of the sphere directly opposite the bead representing the infrared star, which hung just outside the boundary of winking stars.

“I don’t think that part of the sphere is actually flattened,” Jun Davd said. “That’s about forty light-years away—at the furthest distance from us. I think any emissions originating there have started fairly recently and simply haven’t reached us yet.”

Trist nodded in agreement. “Yes, we intersected a small chord of this … spherical volume of space on our way here, and when we crank back the data we find that we’ve witnessed several discrete jumps in the size of the globe. It seems to be growing quite uniformly, at about one-tenth of the speed of light.”

Jun Davd’s fingers flicked buttons, and a star at the surface of the shell sent a spray of three dotted lines toward the line embedded within the sphere that represented Yggdrasil’s route, making an equilateral triangle bisected at the vertex. He added three little green Yggdrasils where the dotted lines met the route.

“No reception,” Jun Davd said, tapping the first Yggdrasil at the earliest position on the route. He went on to tap the second Yggdrasil, where the bisecting line showed the shortest distance to the star. “First reception,” he said. Then he pointed to the third little tree symbol. “And we’re still receiving at the same radial distance as the previous no-reception zone, so knowing our speed and the distance covered, and throwing in a little Doppler anaylsis of about a dozen similar cases, we get a pretty good value for the rate of growth of the shell.”

“And virtually every single star within the shell is giving off radio clicks,” Trist said.

The other three looked at one another. The thought was inescapable. “Original Man?” Bram said.

“No, impossible!” Jao said.

Smeth was getting excited. Too excited. “Why are we wasting time here?” he said. “Whatever this phenomenon is, it’s growing from a center.” He squinted at the pinch of stars in the middle of the representation—a couple of yellow dwarfs, one with a smaller orange star and a red dwarf for companions; a solitary red dwarf; a blue-white giant attended by a burnt-out cinder. “Let’s investigate the center of the sphere and see if we can find out what’s causing it!”

Jao bellowed in outrage. He could see his lovely enclosed star slipping away from him. “What? That’s twenty light-years away! You’re talking seven, eight years of ship time by the time we build up enough gamma at one g! We’re here now! We can be at the center of this system in less than two years!”

Jun Davd was no help. He stood there smiling. Bram turned to Trist. “How fast did you say that sphere of clicking stars is growing? At about one-tenth the speed of light?”

“That’s right,” Trist said.

Bram exercised his prerogatives as year-captain. “In that case we can stay here and wait for it. This star is due to give off clicks any time now.”

CHAPTER 6

The sky was full of disks.

The nearest one, only a hundred million miles away, turned half the sky blind. It stood almost edge-on—seen only as a paper-thin rim faintly traced by light, sketching the partial outline of a tall ellipse whose shape could be inferred from the stars it blotted out.

It was immense. Unbelievably so. A planet would have been imperceptible against it, a sun a mere pinprick. Its diameter was, in fact, that of a planetary orbit.

Another disk, equally huge, bracketed the other side of the sky, showing as a somewhat fuller ellipse. But this one presented its inner face and was visible as a pale wash of refracted light.

Between them hung a whole collection of similar shapes, like paper cutouts all dangling at the same level from invisible threads. Directly ahead was a great illuminated circle on what must have been the opposite side of the hidden sun. A smaller circle was a black silhouette trying unsuccessfully to eclipse it. On either side of the smaller circle were attendant disks, canted inward to make narrow ovals. Their inner faces, closer to the unseen sun than the gigantic disk opposite, made brighter daubs against its inferior illumination. A bite had been taken out of the edge of one of them by the eclipsing circle.

Through the spaces between them could be seen a whole swarm of still smaller disks—if objects that were millions of miles in diameter could be called small. The glimpsed shapes were in a different plane than the outer disks; the ellipses they presented were horizontal, not vertical.

The tiny dot of a sun in the center of that bewildering arrangement had never peeped forth again in all the two years they had been traveling toward it. In view of the complicated schedule of eclipses, its brief emergence must have been an exceedingly rare event.

Bram stared over the heads of the crowd at the flat, queer shapes floating in the darkness. He swallowed hard. Reason said they could not exist. But they did.

“There can be no stranger sight in the universe,” Jun Davd said to no one in particular.

People jostled and crowded around him at the safety rail in front of the long, curving observation wall. This was a real view, not a holo. Naked space was on the other side of the transparent polycarbonate sheet, and people had been gravitating here even though Yggdrasil’s slow rotation periodically turned the scenery on its head. The holo still ran at the opposite end of the lounge, but even though it showed close-ups, there was no added detail to make it worth watching.

“It works out to an ingeniously timed energy trap,” Jao was burbling to anyone who would listen. His burly form was at the center of a knot of people, the nearer ones in danger of getting clipped by his waving hands.

“Listen to him,” Smeth grumbled to Bram. “You’d think he was taking credit for it himself. It’s nothing like the continuous bubble he theorized about.”

“…though the timing’s decayed somewhat after seventy-four million years,” Jao went on. “Otherwise, we wouldn’t be seeing the disks by so much leaked light, and we never would have seen the star itself.”

A pretty admirer who must have stretched Jao’s uxoriousness to the limit spoke up. “I know you explained it before, Jao, but it’s awfully confusing. It gives me a headache just to think about it.”

“It’s beautiful, beautiful!” Jao boomed. “Look, there are four shells of disks—an outer and inner shell in equatorial orbit, and an outer and inner shell in polar orbit. The polar shells are the itsy ones on the inside, and their main job is simply to reflect all radiation into the equatorial plane.”

“I understand that, but…”

“Each shell consists of three disks whose diameters are equal to the radii of their distance from the sun. Actually, it’s their centers of gravity that’re in that orbit. But they don’t swivel. Each one of them has exactly enough spin to make its day equal to its year, so that the flat side always faces sunward.” He frowned. “Except that one of the inner ones once got a nudge from something that messed up its synchronization—probably a solar flare. That’s why the sun was able to pop out in the equatorial plane when we were in the cometary belt.”

“But why don’t they all just crash into one another?” his admirer wailed.

“Look—each set of three consists of disks whose centers of gravity are at the points of an equilateral triangle, thus occupying the same orbit in a state of equilibrium. It’s a very stable arrangement. And the fact—now, get this—the fact that the diameter of each disk is equal to the radius of its orbit means that the zone of interception of the inner set is equal to the zone of interception of the outer set—so that when you project that cone, it’s like having a solid fence of six disks, all tangent to each other.” He smiled benignly. “Except that you don’t have to worry about them crashing together. To say nothing of all the mass you save.”

“By using littler disks?”

He nodded. “Almost all the mass of the energy trap is in the three big ninety-million-mile disks. The next shell inward—the one that orbits at thirty-six million miles—contains only about a sixth as much mass. Call it four twenty-fifths. And the ratio holds as you keep diminishing—so that all of the inner disks put together add up to less than the mass of one more big disk. Original Man was very clever. He made his fence out of geometry instead of mass.”

“It’s a fence with a lot of gaps, though, isn’t it?” said a smart aleck who looked as if he were the boyfriend of the girl or aspired to be.

“Not as much as you think,” Jao said indulgently. “Let’s figure it out. Hey, Smeth, what’s the formula for a hypocycloid—never mind, I’ll graph it.”

He grabbed for the touch pad he had dangling from a chain around his neck and poked at it with thick fingers. An electric-blue circle grew on its photoplastic surface, followed by a horizontal line that bisected it, then two curves with the same radius as the original circle that sprouted from the ends of the line and met at the top. Little boxes began to subdivide the resulting figures, getting smaller and smaller until the eye could no longer separate them. The negatively curved triangle in the center differentiated itself with a change of color. Jao’s fingers asked the touch pad a couple of questions, and he read off the answer.

“Yah,” he said. “The equatorial fence intercepts about seventy percent of the solar energy that comes its way. So does the polar shell. Together they cover somewhat more than one-fifth of the surface of an imaginary sphere enclosing the sun at any radius. I guess that was good enough to do the job.”

“What ever happened to Jao’s Bubble?” his opponent asked maliciously.

Jao was totally bland. “Oh, yah, the idea of enclosing a star inside some kind of a continuous shell. It wouldn’t work.”

“I can’t stand it!” Smeth groaned. “Now he’s going to disown the whole idea.”

“He has no shame.” Bram laughed. “Jao throws off ideas, but. he isn’t attached to them.”

Jao was lecturing the young man earnestly. “In the first place, there’s no way to keep it from drifting off center,” he said. “You might start with the star perfectly centered, but once the slightest drift started, it would keep getting worse, because the attraction from all other directions would keep decreasing…”

“That’s exactly what I told him,” Smeth complained to Bram.

“…and can you imagine the centrifugal force at the equator if the thing rotated at all? Your sphere would suffer from slump. Everything would tend to collect at the equatorial plane. No, my friend, your sphere’s a picturesque idea, but you can’t have it.”

“How does he do it?” Smeth grumbled.

“And who needs it, anyway?” Jao said before his young antagonist could open his mouth to protest. “Let’s figure out how much energy Original Man had at his disposal for his intergalactic beacon.”

He reached for his pendant touch pad again and began tapping at it one-handed without looking.

“Look at him showing off,” Smeth said in disgust. “He hits wrong numbers all the time that way, but that doesn’t stop him.”

“Each one of those big disks has a surface area of … hmm … call it six point three six quadrillion square miles. A six followed by fifteen digits. On each side. If you’re trying to make sense of a number like that, it means that—” He punched numbers again. “—one side of a disk has thirty-two million times the surface area of an ordinary planetary body like the Father World.”

“Why one side?” his admirer queried.

“We’re only concerned with the side that’s soaking up energy.”

“Oh.”

Jao continued. “We’ve already got a value for the solar constant at the distance of the cometary halo, a light-year out. Now let’s crank it back according to the inverse-square law, and we’ve got—” His fingers busied themselves again. “At ninety million miles, it works out to … hmm … one point four kilowatts per square meter … times sixteen times ten to the nineteen square meters—”

“Oh, for pity’s sake!” Smeth burst out. “All that rigamarole! He wants to say that each of the three large diskworlds receives twenty-three times ten to the twenty-first kilowatts of energy!”

“Thank you, Smeth,” Jao said equably. “Twenty-three sextillion kilowatts. And we’re not through yet. We multiply by six, and—”

“Multiply by three something, you mean,” interrupted his rival for the young woman’s attention.

“No. Don’t forget the three disks of the inner equatorial shell may be a lot smaller, but they’re closer to the star, and they intercept exactly as much solar radiation as if they were big disks in the outer orbit.”

“But—”

Jao sailed on serenely. “Which means that in the equatorial fence alone, Original Man had one hundred and thirty-eight sextillion kilowatts at his disposal to turn into radio waves.” He paused for effect. “That is ten trillion times as much power as Nar civilization produced on the Father World.”

Bram caught his breath. The figure was staggering. He had never bothered to work it out himself, though he had known it must be very high.

“They thought big, those people,” he said to Smeth. “By now the human genetic code will have reached the Virgo cluster. I always assumed that was the target. But with that kind of power, I wonder if they were aiming beyond.”

Smeth snorted. “Huh, don’t let Jao’s raving impress you too much. We don’t know how efficient those … constructions were at converting energy into the longer radio wavelengths and modulating them.”

“It hardly matters, does it?” Bram responded. “The waves will keep spreading through the universe. If they were meant to reach Virgo, the limit of their detectability must lie many times beyond it.”

Over by the view wall, Jao was unleashing one of his terrifying smiles on the girl. Though he was utterly faithful to Ang, he didn’t mind going through the motions.

Jao’s young competitor glowered and made another try at impressing the girl. “If most of the mass of the system is in the big disks,” he said belligerently, “how come the sun hasn’t drifted toward one or another of them over a period of time—just as it would toward one side of a ‘Jao’s Bubble’? Excuse me—‘Jao’s shell.’ The same thing would apply—the attraction of the other two disks would decrease with distance, and it would keep getting worse!”

He must have been a physics, apprentice. He stole a glance at the girl and went on in a classroom voice. “In a synthetic system like this one, which is essentially three big masses mutually revolving at the points of an equilaterial triangle, a mass occupying the center can’t move above or below the equatorial plane because of the combined pull of the three major components.” He stared a challenge. “But it can and will move within the plane!”

“I didn’t say most of the mass of the system was in the big disks,” Jao said kindly. “I said the big disks contain most of the planetary mass. Actually, they only mass about the same as a good-size gas giant—maybe a few tenths of one percent of the mass of the G-type star in the middle. So they’re in orbit around it in the normal way.”

“But that would mean—”

“Right. We know they’re very thin—maybe as little as fifty miles across the rim. But even so, with a diameter measured in orbital distances, that would give them a volume of maybe four thousand times the volume of your run-of-the-mill gas giant. So they’re lighter than they have any right to be.”

The boy did some quick figuring in his head. “Four thou—but that would make them lighter than air!”

“Correct. About three and a third times lighter. In fact, they have a density of only about twice that of helium, on average.”

“But that’s impossible.”

“I said on average.”

Smeth bustled over. “One might posulate that they’re hollow, or honeycombed, or a gas enclosed by a membrane. Or made of a rigid, infinite-length polymer with properties we can’t imagine.”

“What could be that light—and strong enough to maintain its shape over interplanetary distances?” the boy said.

Jao stared out the window at the strange floating circles that had taken the place of most of the sky. His face was flushed with excitement.

When he finally spoke, it was in Bram’s direction. “We’ll have to land on one of them to find out, won’t we, Captain?”

Bram kissed Mim good-bye, feeling self-conscious in front of all the spectators. A crowd of about two thousand was jammed into the cavernous hangar, waiting to see the takeoff, and the rest of the population of the tree must have been watching on their holo sets. Bram could see the camera crew perched high on the spidery platform of an interbranch shuttle vehicle, where they had an overall view.

“Be careful,” Mim said, pressing herself against the tough hide of his vacuum suit. “I wish you weren’t going this trip.”

He embraced her one-armed, his bubble helmet tucked under the other arm. “The year-captain’s expected to lead the way,” he said. “That’s why they elect him. But don’t worry. Lydis is the best landing craft pilot we have—and it’s not going to be like landing, anyway. It’ll be more like docking with a nonrotating branch. She’s practiced it in the simulator a hundred times.”

“But it’s spinning.”

“So slowly at the rim that it makes practically no difference. You’re thinking in terms of a body like Yggdrasil, with a diameter only a few hundred miles across. In this case, the spin isn’t there to provide gravity. It cancels it. So when we match for it, we’ll touch down as lightly as a leaf.”

“I’d still feel a whole lot better if I knew you were landing on the flat side.”

A few feet away, under the skeletal arch of a landing leg, Jao left off nuzzling a clinging Ang and looked across her golden head toward them.

“That’d be a lot trickier, Mim, even though it looks simpler,” Jao boomed past Ang’s ear, making her wince. “Your normal instincts don’t apply on a body as bizarre as that. Neither do your first mathematical assumptions about up and down. Landing anywhere between the hub and the rim on a disk-shaped body would give Lydis some complicated gravitational gradients to cope with. The vertical component and the horizontal component don’t behave the same way in relation to the center of gravity. And then there’d be the added factor of centrifugal force tending to make us slide outward, though we don’t think it’d exceed the diagonal gravitational vector tending to pin us down. To say nothing of all sorts of unpredictable edge effects to get past before we could cross to those interesting structures on the rim. No, Mim, this is the simplest way. We’ve got it all worked out.”

Bram had felt Mim stiffen at Jao’s mention of “sliding outward” and “edge effects.” He turned it into a joke. “What Jao’s really worried about is having to hike across a ninety-million-mile plain to get to where we’re going.”

She smiled gamely. “I guess I don’t understand physics.”

“That’s all right, Mim, I don’t understand Bach,” Jao said.

“Don’t worry, we’ll be very careful,” Bram told her, “and we’ll be locked in to Jun Davd and his computer the whole time.

The third member of the exploration team, a dour geologist, named Enry, pushed his way through the well-wishers and said apologetically to Bram, “Lydis says she’s about ready. Says it’s time to get these people out of here and climb aboard.”

Enry stood there, stolidly waiting. He was a blocky, square-jawed man who long ago had been a touch associate with a geology touch group on the Father World. Though the Father World no longer existed, Enry had never given up his speciality; he pored over the old Nar records in the library and published a monograph every quarter century or so. He was the nearest thing to an expert the tree possessed, and he handled himself well physically in the null-gravity sports at the trunk’s center. Bram had thought of him immediately when choosing the exploration team.

“All right,” Bram said. He gave Mim a final peck that turned into something more as their lips touched again, then went with Enry to pry Jao loose from Ang.

A warning blast came from a two-tone bass whistle. Exasperated monitors wearing headbadges rushed back and forth, trying to shoo lingering spectators out of the drop area.

“Behind the ropes, behind the ropes! Everybody behind the ropes! Other side of the air curtain track!” The crowd moved as sluggishly as sap. “Keep it moving, keep it moving, unless you want to breathe vacuum!”

Bram got Enry and Jao started up the landing leg ladder with their gear and was preparing to climb it himself when he became aware of a disturbance at the fringe of the retreating crowd. A small, agile figure was darting past the monitors, getting chased by them, and darting back into the forbidden area. The interloper evaded a pursuer and made a beeline for the base of the ladder.

Bram saw corn-yellow hair flying and green eyes on either side of an upturned nose and recognized his great-great-great-granddaughter. “Ame!” he exclaimed. “What are you doing here?”

“I’m going with you,” she announced. “Here, take this.”

She unslung a lumpy shoulder bag and thrust it at him. The clinking sound of some kind of equipment came from within.

“You can’t,” he said. “We don’t know what we may run into. Anyway, it’s only a scouting trip. You’ll have plenty of opportunities to go along on the later landings, like everybody else.”

“That’s the point, Bram-tsu. You ought to have a palentogist along on your first survey, and I’m the only authentic specimen you’ve got.” She grinned engagingly at him. “Besides, I’ve turned myself into a pretty fair geologist, so I’ll carry my weight.”

“We’ve got a geologist, a good one.”

“Oh, Enry knows his subject, I’ll give him that. But his subject’s the Father World. Those disks out there are something nobody’s an expert on. But my group’s been doing theoretical studies for twenty years now—you’d be surprised at some of the computer simulations we’ve come up with!” She wrinkled her nose. “We really ought to have an archeologist with us, too.”

“An archaeologist, is it? Spare me! A theoretical paleontologist’s farfetched enough on a preliminary scouting expedition like this.”

“Does that mean you’ll—”

A monitor came puffing up, a man with a broad, law-abiding face and a long-suffering expression.

“Sorry, Captain. She slipped past us. I’ll get her out of here.”

Ame turned on him. “I’m not going with you. I’m going aboard, isn’t that right, Bram-tsu Captain?”

The monitor looked doubtfully at the lightweight knee-lengths and slipover she was wearing. “If you want, I can get one of the other safety marshals and we can escort her forcibly.”

“No, it’s all right. I’ll talk to her,” Bram said. “Go on, Marshal, I’ll take responsibility for sending her back.”

The monitor raised a quizzical eyebrow and withdrew. Bram turned to Ame. “You haven’t rehearsed with us. There’s the question of equipment—”

“Oh, that! There are spare space suits in the ship, and one of them is bound to fit me—it isn’t as if they had to be custom fitted. I’ve ridden with Lydis lots of times before—on trips to other branches and even to the probe. And when it comes to that, I’ve spent as much time in vacuum as anybody. If I can climb around the branches under spin, I ought to be able to manage on one of those nice flat things out there.”

Bram refrained from bringing up Jao’s speculations on the nature of disk gravity gradients. “Are you sure you want to leave the twins alone for that long?”

“Smeth will take care of them. They adore him. He spoils them like mad. They’re two years old now—they don’t need to have me around constantly.”

Bram sighed. “Everybody and their gene sibling wanted to be included on this trip. I almost had a riot. I had to promise that if there are no problems, everyone who wants to will get a turn while we’re parked in this orbit. And here I am, giving preference to a descendant. They’ll have my hide for nepotism.”

“I can go, then?”

He gave in. “Your great-great-grandmother is the pilot. It’s her decision. If she says you can go, then you’re on. Otherwise you promise to leave quietly, all right?”

“I promise.”

Above, Jao stuck his head out of the hatch. “What’s holding you up? Lydis’s already lost a turn while you’ve been palavering.”

Ame scrambled up the landing leg ladder, with Bram behind her carrying the sack of equipment. It was bulky; he felt the handle of a digging tool through the fabric as it swung against his hip.

At the top, Bram twisted around and caught sight of Mim waving to him from the other side of the barrier. He waved back and squeezed through the hatch after Ame.

Jao filled the air lock, huge and grinning. “Stay here a minute with her,” Bram said, “while I—”

“Lydis says it’s okay,” Jao said. “Let’s get going.”

A great rumbling sound filled the bay as the curtain rolled around its track and sealed off the cylindrical launch chamber. The crowd on the other side would be streaming toward holo monitors to watch the drop as relayed by the exterior pickups.

Bram turned sternly to Ame. “You had it all arranged with her in advance, didn’t you?”

She wrinkled her nose at him. “She said you’d only be stuffy about it, and she was right.”

Bram shrugged and sealed the outside hatch, then, after herding Jao and Ame through the air lock, screwed the inner lid into place.

He looked around the dome-shaped cabin. The landing vehicle was basically a squat hemisphere supported on five arched legs. It had started out as a Nar design with the pilot’s seat in the middle, but like the rest of the considerable fleet the tree had been stocked with, its interior had been rearranged during the intergalactic crossing to give it something resembling front-back orientation, and the controls had been shifted to conform to human morphology. Lydis and her copilot sat facing one of the five bulging ports—the one that had been designated “forward.” The rear of the cabin contained passenger couches—more than the current mission profile called for—storage, equipment, and minimum amenities.

“You have exactly ten minutes to tie yourselves down,” Lydis said. “I don’t intend to sit here for another go-round.”

“Sorry,” Bram said.

He nodded to his daughter’s co-pilot, a wiry, nonchalant fellow named Zef, then helped Enry and Jao stow their gear. Ame went to a locker and helped herself to a spare vacuum suit. While she struggled to get into it, Bram hefted the clanking sack she had given him and, after a moment’s reflection, shoved it into a padded locker. “I hope there’s nothing breakable in there,” he said.

“Nothing very breakable,” she said.

They climbed onto their couches and fastened the armpits-to-hips webbing in place. Jao cranked his couch to a sitting position.

“I want all you treelubbers to lie prone for the drop,” Lydis said. “And while you’re at it, put your helmets on.”

She herself was sitting upright, as was Zef. Jao pointed that out.

“You do everything by the list when you ride with me,” Lydis said. “Otherwise, you can get out and walk.”

Grumbling, Jao complied.

“It’s surprising, the number of things that can go wrong,” Zef said cheerfully. “Why, I saw a fellow explode once because he forgot to screw his helmet on all the way and nobody’d told him the cabin wasn’t going to be pressurized that trip.”

“Oh, stow it,” Jao said. “I’m not falling for any more of your stories.”

Zef laughed. “It’s not that we care about the safety of our passengers. We just don’t want a lot of helmets floating around and bumping into things.”

Jao started to reply, but his voice was cut off as Lydis watched the passengers off the Talk circuit. Abruptly Zef dropped his smile and became all business. Bram found himself gripping the armrests of his couch. Drop must be imminent.

He was still plugged into the Listen circuit, though. He could hear Lydis talking to Jun Davd back in the observatory.

“I have your readout,” she said. “Please confirm.”

“Three minutes more and you’ll be in optimum drop position. As tangent as you can get. Do you want the computer to open the trapdoor for you?”

“No, I’d rather do it by feel. The computer doesn’t have nerves in its bottom, and it has too much faith in the invariance of mechanical systems. I’m going to have to make a lot of small burn corrections, anyway, once we’re out there. Just keep feeding me the figures.”

It was a point of pride with Lydis to be in fingertip control. She believed piloting was an art, not a science.

“A computer with nerves in its bottom!” Jun Davd chuckled. “My goodness. We’ll work on it.”

By craning his neck, Bram could see one of the duplicate screens left over from the original Nar installation, next to the observation blister closest to him. In a simplified computer cartoon it showed a great dull-red disk, slightly angled to give a sense of perspective, and a jolly little green representation of Yggdrasil, much out of scale, floating above and to one side of it. Discreetly flashing and dotted lines showed the direction of rotation of both bodies and their intersecting orbits around the rice-grain sun shining through a cluster of red lobes at the center of the system.

It obviously hadn’t been very practical to put Yggdrasil into orbit around the rim of a disk-shaped body with a circumference of two hundred seventy million miles. And parking Yggdrasil sixty degrees ahead of the disk—at the stable point which in this crazy system neatly coincided with the point of equilibrium with the disk ahead of it in orbit—would still have placed them an inconvenient forty-five million miles away from the forward edge of the disk and all of one hundred million miles away from the present “top” of the disk, which they had chosen as their likeliest base of operations.

So instead, with Jun Davd’s help, Bram had put Yggdrasil into a solar orbit that intersected the disk’s orbit at a tilted angle. It started above and behind the disk at a distance of only a few million miles, slanted down at a tangent that almost grazed their target point on the rim, and continued on past to a point ahead of the disk in orbit that would place Yggdrasil directly “above” the spot where the disk’s own slow rotation would have brought the explorers’ base of operations by that time.

Thus, for at least the first half year, travel time between Yggdrasil and the main landing site would be measured in days rather than months. At that point, Yggdrasil’s solar orbit could be converted into a powered orbit around the rim, which would take it back to its starting point for another such orbital stern chase.

Bram kept his eye on the pulsing orange line that emanated from the tiny cartoon Yggdrasil on the screen and ended tangent to the disk. It represented a vector of the momentum that would be imparted by Yggdrasil’s own orbital motion plus the added kick from Yggdrasil’s rotation at the moment of release.

Lydis would add her own increment of momentum by firing the spacecraft’s engines once she was in a position to judge how well lined up she was. Then she would have to cut it fine at the other end, killing all her pseudoorbital velocity and matching the speed of her target on the rotating edge of the disk—so that the net cancellation of both would come out even at the precise moment of touchdown.

No wonder she didn’t trust the computer.

Once launched, the complex orbital mechanics boiled down to an eyeball-and-seat-of-the-pants job, and Bram himself trusted Lydis’s instincts more than he trusted the unreeling chains of glowing figures superimposed on the computer cartoon that kept changing their final decimal places.

“Hold on to your valuables,” Zef warned through the helmet circuit.

The trapdoor beneath the spacecraft sprang open, and they fell through. Sudden weightlessness was a faint thrill along Bram’s spine till his body adjusted. He made an incautious movement and floated an inch off the couch, held down by the webbing pressing against his chest.

He lost interest immediately in the computer display and applied himself to the view outside the blister. Yggdrasil’s great gnarled branches floated by, pierced by random points of light from people’s living quarters.

The tree rose until it was a green cloud above them. It began to dwindle and in minutes was far enough away that its shape could be seen against a sprinkling of stars: a double-ended mushroom divided by darkness.

He turned his head to see how Enry was taking it and saw that the man was sweating inside his helmet. Of the four passengers, Enry was the only one who had never been away from the tree; Ame had gone on jaunts with Lydis, and Jao had gone with Bram on comet-chasing expeditions. Bram could understand how Enry felt. It was a wrenching experience to part from the entity that nutured you in blind universe.

From this angle, line of sight was out of the system, and nothing could be seen except the stars. Now, with Yggdrasil shrinking overhead, Lydis rotated the ship to point toward their destination.

An uncanny collection of glowing circles rose to fill the viewport. Here, above the equatorial plane of the system, one could look down past their scalloped fence into the inner heart where the polar disks orbited. Their tininess was an illusion of distance; they still dwarfed the enclosed sun. One of them was skewed; Jao had been right about that. A collision with a leftover planetoid or a solar flare some time in the past had altered its carefully timed spin. The sun spilled its light through like a glowing egg in a nest.

The turning of the craft continued, and now an enormous knife edge cleaved the sky: the disk that was their destination.

Lydis applied a touch of her lateral jets once more, and the turning stopped until the knife edge was suspended directly overhead, Bram studied it through the bubble dome. At the tip where the line ended was an illuminated dot, like a tiny flower on a stem.

“You can see the moon from here,” Lydis’s voice came through the suit radio. “It looks as if it’s resting on the rim from here, but of course it’s not. The structures we sighted through the big telescope are beneath it. We should begin to make them out at about a quarter million miles. They’re huge.”

The diskworld had proved to have moons—eleven of them, equally spaced, in synchronous orbit around the rim. Where the twelfth should have been, the narrow ribbon of landscape slumped suggestively across a span of twenty million miles.

The orbits of the moons were impossible—too close and too slow. “They have no right to hover like that,” Jun Davd had said.

For once, Jao had had no theories, except for a halfhearted, “Antigrav, maybe?”

“What I’m interested in is, what are they hovering over?” Jun Davd had mused. He had kept his instruments trained on the moons during Yggdrasil’s long inward sweep from the outer limits of the plundered system, and had done much juggling with computer enhancement and other techniques. Some two billion miles out, he had been rewarded. “It’s some kind of support complex,” he had announced, showing dubious pictures of a patchy grid, which might have been nothing more than the computer’s desire to please. “Roadways, maybe. Ditches or canals or the remnants of a buried transport system. Street layouts with the rubble showing differently in the infrared … casting low shadows…”

He had set a course for the largest of the complexes on the disk whose orbit they could most conveniently intercept. It struck Bram as finicky and bizarre, and Jun Davd agreed with him. But it was a planetary body with interplanetary distances; the next largest complex was a third of the way around the rim—ninety million miles away. Too far to walk. It was definitely a problem in space navigation.

“Hold on,” Lydis’s voice said. “I’m going to give you some weight now.”

There was a gentle shove on Bram’s chest, pressing him into the couch. A rain of small objects came from above; someone had forgotten to secure some minor gear. Zef turned to glare at the culprit, and Jao grinned sheepishly within his helmet.

The burn was a leisurely one, lasting a half hour at what Bram estimated to be about a quarter of a gravity. There was plenty of hydrogen and oxygen to be profligate with since Yggdrasil had drunk its fill of comets.

Lydis saw her passengers fidgeting. “I know it’s hard to lie still when there doesn’t seem to be any reason for it,” she said, “but I don’t want any mass moving around while I’m doing this.”

At last they went weightless again. “All right,” Lydis said. “You can get up now. Take off your vacuum suits if you like. I’m not going to fire the jets again for about two days.”

Everybody gratefully desuited. Jao scratched mightily. “I don’t think you were worried about leaks at all,” he said. “I think you just wanted to keep us quiet.”

“Where’d you ever get an idea like that?” Zef said.

They all crowded to an observation blister to have a look at their destination; Lydis had rolled the ship over after the main burn so that people wouldn’t have to crane their necks to look through the overhead dome.

Enry, pale, said, “How wide is the rim? It still looks like a one-dimensional line from here.”

“About fifty miles,” Jao said. “Talk about thin! We wouldn’t see it at all from this angle if it wasn’t for scattered light from over the edge.”

Ame said, with a trace of awe, “The former human race was efficient. “Just about all the working surface is on the fiat sides.”

Jao nodded. “But don’t forget, even a fifty-mile width gives a surface area on the rim alone of thirteen and a half billion square miles. That’s equivalent to the surface areas of seventy of your normal, terrestroid-style planets like the Father World. That’s a lot of elbow room, even if it is all east and west.”

“I’m glad we don’t have to dig it all up,” Ame said, with a glance at Enry to see how he was taking her presence.

Enry rose to the occasion. He was stuffy but nice. “I could use a little help,” he said.

A perfunctory laugh went around. Bram asked Lydis for a magnified view through the ship’s telescope and got nothing more than a fuzzier line topped by a blurred speck that might have been construed as a crescent.

“It’s going to be a very strange place,” he said.