“Listen to your father,” Chu said.
“What do you mean, in their own way?” Nina said, subdued now.
“Even on Earth, trees and other plants had the ability to share information and plan for a common defense against their enemies,” Joorn said. “If a tree was attacked by bark beetles, for example, it could warn its fellow trees to thicken their bark or produce appropriate toxins or repellents by sending chemical signals through the groundwater or the air.”
“There’s no air in space, let alone groundwater,” Nina protested.
“In an Oort cloud filled with trillions of living things, there’d be plenty of exudations, no matter how thinned out,” Chu pointed out. “Stray water molecules from the trees’ metabolism, plant hormones, individual grains of pollen. It wouldn’t take much. One molecule per every cubic meter or so would constitute a medium for transmitting chemical messages, though perhaps at a rate imperceptible to us fast-living humans.”
“But why would people plant trees in space in the first place?” Nina asked. “The colonists on Rebirth are planting forests there, and we’ve got our own little forest for whatever wood we need right here in the ship.”
“Chu’s too young to remember,” Joorn said. “He was born on Rebirth. I was raised on Mother Earth less than a century after our expansion into space began. The answer is that lots of wood was needed for construction out there, and, just as important, in the tremendous sizes provided by Bernal’s trees. It dawned on our brave planners that wood was the ideal construction material for our new space age. It didn’t deteriorate like plastic under ultraviolet bombardment. It didn’t have to be boosted into space at great expense, let alone mined at even greater expense. And even better, it provided greater protection against killer radiation than the tin cans we were using for habitats and spaceships before then.”
Joorn paused reflectively. Chu maintained a respectful silence.
“I’m old enough to remember when the first space habitat was constructed out of vacuum-grown wood. There was a lot of hype about it, enough to fire the imagination of a small boy who wanted to be a starship pilot. And it wasn’t even made of comet-grown wood under conditions of negligible gravity. The first Oortian trees hadn’t matured yet. This one was carpentered together out of wood from the still-experimental lunar forests, under conditions of one-sixth Earth gravity. Those early trees only grew to a height of about half a mile.
“The construction of that first habitat was crude. It was polygonal rather than toroidal. They hadn’t yet thought of those enormous planters that rotate an increment at a time to make the tree grow with the proper curvature as it keeps striving toward the vertical under one-sixth gravity. So they started with eighteen straight joists made into six equilateral triangles that were about three thousand feet on a side and as wide as a football field. Then they framed the habitat by joining the triangles to make a hexagon and went on from there.”
He smiled reminiscently. “I visited the habitat when I was a young man in training. It was in orbit around Jupiter, at a relatively safe distance beyond the orbit of Himalia. It was a little disconcerting. Gravity seemed to be straight up and down when you were standing in the center of one of those football fields, but as you walked toward the next triangle, it began to feel like walking uphill. Your eyes told you that you were walking on a flat surface, but your inner ear disagreed. It kept getting steeper and steeper till you reached the next triangle, then you were walking downhill till you reached that segment’s center. People got used to it.”
Chu nodded vigorously. He was a great history buff and had always been fascinated by the romantic era of wooden habitats and wooden spaceships. His captain was a living relic, a firsthand witness of those bygone days, and whenever the duty roster made it possible, Chu enjoyed whiling away the long hours of his watch by listening to Joorn’s oft-told tales.
“The day of the wooden spaceship vanished when the Higgs drive came in,” Chu said sadly. “Just as the age of sail vanished when steam power began to replace wooden sailing ships. But change was inevitable.”
“Not quite,” Joorn said. “The first starships to Alpha Centauri and Tau Ceti, which were launched before the Higgs drive with its built-in radiation shield made wooden spaceships obsolete, were made of wood. A thickness of fifteen feet of wood was safer than a metal skin. Energetic particles were absorbed, not bounced around to create killer secondary radiation, and it was more practical than embedding the living quarters inside fifteen feet of water, which did the same thing. It could handle anything from solar flares to the sleet of gamma rays you got from interstellar travel.” He chuckled. “When the first Higgs ship made it to Alpha Centauri after a five-year trip, some sixty years after a maiden expedition had been launched in one of those old wooden ships, the would-be colonists were still less than halfway across. A rescue mission was mounted to intercept the First Centauri Expedition and transfer the colonists to a Higgs ship, leaving the old wooden hulk to drift for eternity. When the original colonists arrived at Alpha Centauri, they were surprised—and a little miffed—to find a settlement already flourishing there.”
He became serious. “Of course it was only wooden spaceships that were made obsolete by the Higgs drive,” he said soberly. “Wooden habitats were still more practical than aluminum and titanium and man-made plastics. And a lot cheaper. When your grandmother and I left Earth, the habitats orbiting Mars and the gas giants were still being constructed of giant timbers harvested in the Oort cloud and the Kuiper Belt. In the fullness of time, our colonists on Rebirth will be harvesting lumber that’s come to maturity in their Oort cloud.”
“The fullness of time’s already come to pass,” Chu reminded him. “Six billion years of it. “The human race in that galaxy has long been supplanted by whatever evolution does to a species in six billion years.”
“Yes, of course,” Joorn said. “Forgive an old man. Time tends to run together at my age.”
“On the other hand,” Chu said, “the engineered trees, or whatever they’ve evolved into, have probably filled 3C-273 and all the galaxies in our supercluster by now.”
“Our supercluster is—was—a hundred and fifty million light-years across,” Nina said, showing off. “How could randomly drifting trees disperse through an area like that, even in six billion years?”
“Good question,” Chu said. “The answer is that they didn’t randomly drift. Your grandfather can tell you about that.”
Joorn obliged. “They had light sails, and they had their plantlike volition,” he said. “All plants are phototropic, each in its own fashion. The poplar trees that these immense growths were derived from were no exception. But, with an assist from the genetic engineers of the day, they could utilize parts of the electromagnetic spectrum that ordinary plants can’t—from the long radio waves below the infrared to the x-rays and gamma rays at the top. It didn’t kill them, because they had reflective leaves that bounced the dangerous stuff back and forth till it was usable. And more to the point, the tropisms that made this possible turned their leaves into little light sails to seek promising sources of light—including supernova flashes in nearby galaxies. Trees are patient. They could build up their acceleration through light pressure over periods of hundreds of years, maybe even attaining modest relativistic speeds.”
Chu couldn’t restrain himself. “Those early genetic engineers speculated that by the time of the Big Crunch—they believed in it then—Earth life in the form of those wandering trees could spread through the entire Universe.”
“And that’s not all,” Joorn said. “Don’t forget that all trees harbor commensal life—even those early moon-nurtured trees that first seeded the Oort cloud acquired it one way or another. You saw it on Rebirth and even in our little shipboard forest. Insects. The spiders that feed on insects. Moths—you can’t escape them—and the bats that hunt moths. Tree snakes. Fungi of all types. Parasitic plants and symbiotic pl
ants. Every tree has its own rich ecology, and the Bernal trees were in effect self-contained planetoids that provided water, nutrients, and the internal atmospheres that they manufactured for their own use out of cometary ice.”
Joorn could see that Nina was getting caught up in the speculation. “And the people who harvested the trees in the Oort cloud must have lived there while they worked on them,” she offered. “They would have brought plants and animals of their own.”
“Good point, princess. The lumberjacks they sent out from Earth would have had to live there for years at a time while they trimmed branches and operated the sawmills that made the giant boards, and otherwise prepared to send their products sunward. And of course they would have had to be fed. That means cattle and other meat animals. Chickens and turkeys—”
“Little dinosaurs at first,” Chu interjected.
“Of course that would have been hundreds of years after my time,” Joorn said. “There’s no telling what might have developed afterward. But even before I departed Earth, they’d begun to employ dolphins as safety engineers on space habitats to search out leaks and cracks with their sonar and such. And they’re awfully good at holding their breath, aren’t they? As a lumber industry grew in the Oort cloud and Kuiper Belt, there must have been a need for dolphins among the personnel.”
“That’s where I draw the line,” Chu said good-naturedly. “Their sonar would be no good in a vacuum. And no matter how long they could learn to hold their breath, they have no legs. Out of their tanks, how would they get around?”
“Six million millennia of reverse evolution,” Joorn retorted. “All cetaceans once were land animals, like hippos. They’d crawled out of the sea to become mammals, then, after some millions of years, crawled back and lost their legs. Did you know that whales have vestigial leg bones?”
Nina giggled. “Can you picture Jonah or Triton running around on legs? Wearing little booties? The two dolphin safety engineers were Martin’s colleagues on his outside maintenance rounds, and Nina had become fast friends with them, even joining them in their tank for an occasional swim. Their ancestors would have populated Rebirth’s seas long ago.
Chu shrugged. “We’re getting a bit fanciful here. I’ll grant you the bugs and spiders. We’ll soon find out. We’re well within the Oort cloud now, and that object in the viewscreen is within planetary distances. Let’s have a closer look.”
He fiddled with the banks of keys, and the jiggling image jumped in size as it sprang into sharper focus.
Nina gasped. It was a tree all right. Just like the pictures she’d seen of trees on Rebirth and vanished Earth, or the tamed thirty-footers in Time’s Beginning’s forest compartment.
But not quite. It was a real tree, with the unmistakable natural shape of any plant responding to its environment. But it was designed to grow in the absence of gravity. It was almost perfectly symmetrical—two flattened spheres joined by a thick trunk, like a dumbbell. The green spheroid was the tree’s crown. The balancing brownish spheroid, clutching an outmatched globe of dirty ice that had to be a comet, was the tree’s root ball. But the root ball, too, was streaked with green—adventitious leaves that the tree had grown to take advantage of any quantum of electromagnetic energy that came its way.
“It’s a rather conflicted tree, sweetheart,” Joorn lectured. “It knows that it’s supposed to respond to gravity by growing straight up. Our ancestors chose poplar trees for their experiments. They’re fast-growing, and they grow straight—good for lumber. But the comets didn’t give them much help. Their gravity’s too feeble. The tree’s strategy was to use its rotation as a growth guide. Centrifugal force is a good substitute for gravity, right? The trees rotate along their vertical axis, and those two oblate spheres respond by growing into matching symmetrical shapes.”
Nina’s face was glowing. “Grandfather!” she exclaimed. “This is where a really, really dull subject like botany becomes an actual branch of astronomy!”
“Precisely, princess. Bear that in mind when you go back to class. Biologists are scientists too. And watch those puns.”
“I wish Martin were here to see this,” Nina said.
“He’s getting a better view,” Chu said. “Or will be. Hanging by his heels from one of the dolphin pods.”
Some of the color drained from Nina’s face. “Uncle Chu, you won’t …”
“Don’t worry, sweetheart. The Higgs drive will be turned off while Martin’s working outside, the way it always is. We’ll coast without gaining any gamma. What’s a few hours out of a billion and a quarter years, right?”
“You mean losing, not gaining,” Nina pointed out tartly. “We’ve been decelerating since midpoint.”
“Touché, little genius,” Chu said. “That’s what I meant to say.”
“We ought to be switching to the fusion drive soon anyway,” Joorn said. “We’re in the outer fringes of the Oort cloud now, but we’ll be within planetary distances before you know it. We didn’t come all this way to sterilize the planets of Sol and Alpha Centauri, assuming that some sort of bacterial life survived. And now, with these trees …”
“We don’t want to sterilize the comets either,” Chu finished for him. “I’m way ahead of you, Skipper. I’ve already warmed up the deuterium-helium-3 reaction, and it’s on standby.” He checked the figures unreeling on his screen. “And weren’t we lucky that Rebirth’s oceans turned out to be full of deuterium?”
“And that the deuterium-helium reaction turned out to be a lot less lethal than deuterium-tritium fusion. What’s our gamma now, Chu?”
“We’re down to about one-tenth of the speed of light, Skipper. We’re practically in real time now.”
“All right. Keep track of our distance from that tree. I don’t want to get any closer than twenty astronomical units with the Higgs drive still on.”
“You’ve got it, Skipper,” Chu said.
“What’s happening, Uncle Chu?” Nina said.
“We’re about to get a closer look, sweetheart,” Chu said. He punched in further instructions, and the image bloomed again. You could see that the smooth ball of the crown was actually composed of individual branches.
Nina gasped. “What are those things like midges hovering over the edge of the green ball?” She squinted. “They look like they’re sort of … flapping! Like bats.”
“That’s crazy, Nina,” her grandfather said. “Nothing can fly in a vacuum.”
“There! Look at that one down near the rim! It’s after some kind of little speck that I can’t make out! It is too! It’s flapping!”
“We’re about to find out, sweetheart,” Chu said. His hands flew over the board. The deep thrum of the Higgs drive stopped abruptly. Weight disappeared, and Nina grabbed for her armrests.
Chu tapped at the keys again. Weight returned. “It’s all yours, Skipper,” Chu said. He turned to Nina. “Hang on to your hat, sweetheart,” he said. “It’s going to be a downhill ride.”
CHAPTER 17
6,000,000,000 A.D.
The Oort Cloud
A small boy in a skinsuit that was too big for him threw an iceball at Torris as he headed for the cave mouth. He ducked without haste, and it missed him, but then two or three of the other children who were playing outside joined the sport. Another iceball grazed him, dangerously close to his airbag gasket, but by then the mothers were hauling their children back to keep them from becoming contaminated by Torris. Being Shunned meant not being noticed by other people at all, either for good or ill.
He shifted the towering load of firewood on his back for better balance. He was not banned from the communal fire, but nobody made way for him either. He’d also been lucky enough to snare a couple of fat stovebeasts, which were trying to escape from a sack dangling from his waist. Other than that, he hadn’t had much luck on his foraging expedition: a few bark hoppers that would barely fill his stomach, a sma
ll pouch of thin syrup from a worn-out stretch of root that the tribe no longer bothered to tap, and some edible seed pods from the vegetation growing on the lower branches.
He could smell roasting meat as he made his way down the main passageway, his helmet tilted back as he breathed the communal air. His mouth watered as he thought of the feast his father would be having at this hour. His father, particularly, made a point of avoiding him. He understood that, but it bothered him all the same. Neither Firstmother nor Secondmother would dare try to sneak food to him; it would be too dangerous. He understood that too.
A group of rowdy young men was blocking his way. They made no attempt to move aside for him, but some sneaked glances as he edged past them. He heard someone whisper “heretic,” followed by a whispered reply about “a woman” that sounded envious.
They resumed the loud discussion they’d been having. They were talking excitedly about the coming bride raid and the approaching foreign Tree, speculating about when it would be close enough for Claz to give his approval. All of them were armed, and they were comparing weapons and boasting about their prowess.
He longed to tell them that the people of Ning’s Tree were far more advanced than their own tribe and would probably prove to be formidable adversaries. The talk that would be generated by Ning’s return would probably spur the young bloods there to launch their own bride raid sooner than Torris’s tribe would dare risk it.
Torris wondered if Ning would be in the vanguard, if she would come looking for him, as a man might target a particular woman. He shook his head to rid himself of the insane thought. A thought as far from the natural order of things as wishing for a world without caves, where you could walk around on the surface and yet somehow breathe.
He pushed aside the translucent gut curtain that sealed the third of the three airlocks and stepped through into the communal chamber. Nobody noticed him at first; they were all gathered around the big central fire, busy eating, talking, minding the children, and jockeying for places closer to the warmth, so he was able to catch fragments of the evening’s chitchat.
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