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."