“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 micro
wave 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 a
s 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.
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