"What do you want, Gover?"

Gover took a step closer to Rees. His stale breath cut through the wine fumes in Rees's nostrils. "Listen, mine rat, believe it or not I want to do you a favor."

"What kind of favor?"

"Things are changing here," Gover said slyly. "Do you understand what I'm saying? Things won't always be as they are now." He eyed Rees, evidently unwilling to go further.

Rees frowned. "What are you talking about? The discontents?"

"That's what some call them. Seekers of justice, others say."

The noise of the revelers seemed to recede from Rees; it was as if Gover and he shared their own Raft somewhere in the air. "Gover, I was in the Theatre of Light, that shift. Was that justice?"

Gover's eyes narrowed. "Rees, you've seen how the elite on this Raft keep the rest of us down - and how their obscene economic system degrades the rest of the Nebula's human population. The time is near when they will have to atone."

Rees stared at him. "You're one of them, aren't you?"

Gover bit his lip. "Maybe. Look, Rees, I'm taking a chance talking to you like this. And if you betray me I'll deny we ever had this conversation."

"What do you want of me?"

"There are good men in the cause. Men like Decker, Pallis-"

Rees guffawed. Decker - the huge Infrastructure worker he had encountered on his first arrival here - he could believe. But Pallis? "Come on, Gover."

Gover was unruffled. "d.a.m.n it, Rees, you know what I think of you. You're a mine rat. You don't belong here, among decent people. But where you come from makes you one of us. All I'm asking is that you come along and listen to what they have to say. With your access to the Science buildings you could be... useful."

Rees tried to clear his thinking. Gover was a vicious, bitter young man, and his arguments - the contradictory mixture of contempt and appeal to fellow-feeling he directed at Rees, for example - were simple-minded and muddled. But what gave Gover's words force was their terrible truth. Part of Rees was appalled that such as Gover could so quickly disorient him - but inside him a core of anger flared up in response.

But if some revolution were to occur - if the Labs were smashed, the Officers imprisoned - what then?

"Gover, look up."

Gover raised his face.

"See that star up there? If we don't move the Raft the star will graze us. And then we'll fry. And even if we were to survive that - look further out." He swept an arm around the red-stained sky. "The Nebula's dying and we'll die with it. Gover, only the Scientists, backed by the organization of the Raft, can save us from such dangers."

Gover scowled and spat at the deck. "You seriously believe that? Come on, Rees. I'll tell you something. The Nebula could support us all for a long time yet - if its resources were shared equally. And that's all we want." He paused. "Well?"

Rees closed his eyes. Would sky wolves discuss Gover's case as they descended on the wreck of the Raft and picked clean the bones of his children? "Get lost, Gover," he said tiredly.

Gover sneered. "If that's what you want. I can't say I'm sorry..." He grinned at Rees with something approaching pure contempt. Then he slid away through the crowd.

The noise seemed to swirl around Rees, not touching him. He pushed his way through the crush to the bar and ordered straight liquor, and downed the hot liquid in one throw.

Jaen joined him and grabbed his arm. "I've been looking for you. Where...?" Then she felt the bunched muscles under Rees's jacket; and when he turned to face her, she shrank back from his anger.

6.

THE SCIENTIST SECOND CLa.s.s STOOD in the doorway of the Bridge. He watched the new Third Cla.s.s approach and tried to hide a smile. The young man's uniform was so obviously new, he stared with such awe at the Bridge's silver hull, and his pallor was undisputable evidence of his Thousandth Shift celebration, which had finished probably mere hours earlier... The Second Cla.s.s felt quite old as he remembered his own Thousandth Shift, his own arrival at the Bridge, a good three thousand shifts ago.

At least this boy had a look of inquiry about him. So many of the apprentices the Second had to deal with were sullen and resentful at best, downright contemptuous at worst; and the rates of absenteeism and dismissal were worsening. He reached out a hand as the young man approached.

"Welcome to the Bridge," said Scientist Second Cla.s.s Rees.

The boy - blond, with a premature streak of gray - was called Nead. He smiled uncertainly.

A bulky, grim-faced security guard stood just inside the door. He fixed Nead with a threatening stare; Rees saw how the boy quailed. Rees sighed. "It's all right, lad; this is just old Forv; it's his job to remember your face, that's all." It was only recently, Rees realized a little wistfully, that such heavy-handed security measures had come to seem necessary; with the continuing decline in food supplies, the mood on the Raft had worsened, and the severity and frequency of the attacks of the "discontents" were increasing. Sometimes Rees wondered ifHe shook his head to dismiss such thoughts; he had a job to do. He walked the wide-eyed boy slowly through the Bridge's gleaming corridors. "It's enough for now if you get an idea of the layout of the place," he said. "The Bridge is a cylinder a hundred yards long. This corridor runs around its midriff. The interior is divided into three rooms - a large middle chamber and two smaller chambers toward the ends. We think that the latter were once control rooms, perhaps equipment lockers; you see, the Bridge seems to have been a part of the original Ship..."

They had reached one of the smaller chambers; it was stacked with books, piles of paper and devices of all shapes and sizes. Two Scientists, bent in concentration, sat coc.o.o.ned in dust. Nead turned flat, brown eyes on Rees. "What's this room used for now?"

"This is the Library," Rees said quietly. "The Bridge is the most secure place we have, the best protected from weather, accident - so we keep our records here. As much as we can: one copy of everything vital, and some of the stranger artefacts that have come down to us from the past..."

They walked on following the corridor to a shallow staircase set into the floor. They began to descend toward a door set in the inner wall, which led to the Bridge's central chamber. Rees thought of warning the boy to watch his step - then decided against it, a slightly malicious humor sparkling within him.

Nead took three or four steps down - then, arms flailing, he tipped face-forward. He didn't fall; instead he bobbed in the stairwell, turning a slow somersault. It was as if he had fallen into some invisible fluid.

Rees grinned broadly.

Nead, panting, reached for the wall. His palms flat against the metal he steadied himself and scrambled back up the steps. "By the Bones," he swore, "what's down there?"

"Don't worry, it's harmless," Rees said. "It caught me the first time too. Nead, you're a Scientist now. Think about it. What happened when you went down those steps?"

The boy looked blank.

Rees sighed. "You pa.s.sed through the plane of the Raft's deck, didn't you? It's the metal of the deck that provides the Raft's gravity pull. So here - at the center of the Raft, and actually in its plane - there is no pull. You see? You walked into a weightless zone."

Nead opened his mouth - then closed it again, looking puzzled.

"You'll get used to it," Rees snapped. "And maybe, with time, you'll even understand it. Come on."

He led the way through the doorway to the central chamber, and was gratified to hear Nead gasp.

They had entered an airy room some fifty yards wide. Most of its floor area was transparent, a single vast window which afforded a vertiginous view of the depths of the Nebula. Gaunt machines taller than men were fixed around the window. To Nead's untutored eye, Rees reflected, the machines must look like huge, unlikely insects, studded with lenses and antennae and peering into some deep pool of air. The room was filled with a clean smell of ozone and lubricating oil; servomotors hummed softly.

There were perhaps a dozen Scientists working this shift; they moved about the machines making adjustments and jotting copious notes. And because the plane of the Raft pa.s.sed over the window-floor at about waist height, the Scientists bobbed in the air like boats in an invisible pond, their centers of gravity oscillating above and below the equilibrium line with periods of two or three seconds. Rees, looking at the scene as if through new eyes, found himself hiding another grin. One small, round man had even, quite unselfconsciously, turned upside down to bring his eyes closer to a sensor panel. His trousers rode continually toward the equilibrium plane, so that his short legs protruded, bare.

They stood on a low ledge; Rees took a step down and was soon floating in the air, his feet a few inches from the window-floor. Nead lingered nervously. "Come on, it's easy," Rees said. "Just swim in the air, or bounce up and down until your feet hit the deck."

Nead stepped off the ledge and tumbled forward, slowly bobbing upright. He reminded Rees of a child entering a pool for the first time. After a few seconds a slow smile spread across the young man's face; and soon he was skimming about the room, his feet brushing at the window below.

Rees took him on a tour around the machines.

Nead shook his head. "This is amazing."

Rees smiled. "This equipment is among the best preserved of the Ship's materiel. It's as if it were unloaded only last shift... We call this place the Observatory. All the heavy-duty sensors are mounted here, and this is where - as a member of my Nebular physics team - you'll be spending most of your time." They stopped beside a tube ten feet long and encrusted with lenses. Rees ran a palm along the instrument's jewelled flank. "This baby's my favorite," he said. "Beautiful, isn't she? It's a Telescope which will work at all wavelengths - including the visual. Using this we can see right down into the heart of the Nebula."

Nead thought that over, then glanced at the ceiling. "Don't we ever need to look outwards?"

Rees nodded approvingly. Good question. "Yes, we do. There are ways of making the roof transparent - in fact, we can opaque the floor, if we want to." He glanced at the instrument's fist-sized status panel. "We're in luck; there are no observations currently running. I'll give you a quick guided tour of the Nebula. You should know most of what I'll tell you from your studies so far, and don't worry about the details for now..." Slowly he punched a sequence of commands into the keypad mounted below the sensor. He became aware that the lad was watching him curiously. Maybe he's never seen anyone with such rusty keyboard skills, Rees reflected, here on this Raft of a hundred supply machinesThe stab of old resentment shocked him. Never mind...

A disc of ceiling faded to transparency, revealing a red sky. Rees indicated a monitor plate mounted on a slim post close to the Telescope. The plate abruptly filled with darkness punctuated by fuzzy lens shapes; the lenses were all colors, from red through yellow to the purest blue. Once more Nead gasped.

"Let's review a few facts," Rees began. "You know we live in a Nebula, which is an ellipse-shaped cloud of gas about five thousand miles across. Every particle of the Nebula is...o...b..ting the Core. The Raft is in orbit too, embedded in the Nebula like a fly on a spinning plate; we circle the Core every twelve shifts or so. The Belt mine is further in and only takes about nine shifts to complete its...o...b..t. When the pilots fly between mine and Raft their trees are actually changing orbits...! Fortunately the gradients in orbital speeds are so shallow out here that the velocities the trees can reach are enough for them easily to fly from one orbit to another. Of course the pilots must plan their courses carefully, to make sure the Belt mine isn't on the other side of the Core when they arrive at the right orbit...

"Here we're looking through the Observatory roof and out of the Nebula. Normally the atmosphere shields this view from us, but the Telescope can unscramble the atmospheric scattering and show us what we'd see if the air were stripped away."

Nead peered closer at the picture. "What are those blobs? Are they stars?"

Rees shook his head. "They're other nebulae: some larger than ours, some smaller, some younger - the blue ones - and some older. As far as we can see with this Telescope - and that's hundreds of millions of miles - s.p.a.ce is filled with them.

"All right; let's move inwards." With a single keystroke the picture changed to reveal a blue-purple sky; stars glittered, white as diamonds.

"That's beautiful," Nead breathed. "But it can't be in our Nebula-"

"But it is." Rees smiled sadly. "You're looking at the topmost layer, where the lightest gases - hydrogen and helium - separate out. That is where stars form. Turbulence causes clumps of higher density; the clumps implode and new stars burst to life." The stars, b.a.l.l.s of fusion fire, formed dense bow waves in the thin atmosphere as they began their long, slow fall into the Nebula. Rees went on, "The stars shine for about a thousand shifts before burning out and dropping, as a cool ball of iron, into the Core... Most of them anyway; one or two of the kernels end up in stable orbits around the Core. That's where the star mines come from."

Nead frowned. "And if the path of a falling star intersects the orbit of the Raft-"

"Then we're in trouble, and we must use the trees to change the Raft's...o...b..t. Fortunately star and Raft converge slowly enough for us to track the star on its way toward us..."

"If new stars are being formed, why do people say the Nebula is dying?"

"Because there are far fewer than before. When the Nebula was formed it was almost pure hydrogen. The stars have turned a lot of the hydrogen into helium, carbon and other heavy elements. That's how the complex substances which support life here were formed.

"Or rather, it's life for us. But it's a slow, choking death for the Nebula. From its point of view oxygen, carbon and the rest are waste products. Heavier than hydrogen, they settle slowly around the Core; the residual hydrogen gets less and less until - as today - it's reduced to a thin crust around the Nebula."

Nead stared at the spa.r.s.e young stars. "What will happen in the end?"

Rees shrugged. "Well, we've observed other nebulae. The last stars will fail and die. Deprived of energy the airborne life of the Nebula - the whales, the sky wolves, the trees, and the lesser creatures they feed on - will cease to exist."

"Are there truly such things as whales? I thought they were just stories-"

Rees shrugged. "We never see them out here, but we have plenty of evidence from travellers who've entered the depths of the Nebula."

"What, as far as the Belt mine, you mean?"

Rees suppressed a smile. "No, even further than that. The Nebula is a big place, lad; there is room to hide a lot of mystery. Perhaps there are even lost human colonies; perhaps the Boneys really exist, and all those legends are true... of the subhuman whale-singers lost in the sky."

The boy shuddered.

"Of course," Rees mused, "there are puzzles about the native life of the Nebula. For example, how can it exist at all? Our records show that life in the home universe took thousands of billions of shifts to evolve. The Nebula isn't anything like that old - and will be far younger when it dies. So how did life arise?"

"You were telling me what will happen after the stars go out..."

"Yes. The atmosphere, darkened, will steadily lose heat, and - less able to resist the gravity of the Core - will collapse. Finally the Nebula will be reduced to a layer a few inches thick around the Core, slowly falling inwards..."

The young man, his face pale, nodded slowly.

"All right," Rees said briskly. "Let's look inwards now - past the Raft's level, which is a thousand miles from the edge of the Nebula - and in to the center."

Now the monitor filled up with a familiar ruddy sky. Stars were scattered spa.r.s.ely through the air. Rees punched a key-and stars exploded out of the picture. The focus plummeted into the Nebula and it was as if they were falling.

Finally the star cloud began to thin and a darker knot of matter emerged at its center.

"What you're seeing here is a layer of detritus in close orbit around the Core," Rees said quietly. "At the heart of this Nebula is a black hole. If you're not sure what that is right now, don't worry... The black hole is about a hundredth of an inch wide; the large object we call the Core is a dense ma.s.s of material surrounding the hole. We can't see through this cloud of rubble to the Core itself, but we believe it's an ellipsoid about fifty miles across. And somewhere inside the Core will be the black hole itself and an accretion disc around it, a region perhaps a hundred feet wide in which matter is crushed out of existence as it is dragged into the hole...

"At the surface of the Core the hole's gravity is down to a mere several hundred gee. At the outer edge of the Nebula - where we are - it's down to about one per cent of a gee; but even though it's so small here the hole's gravity is what binds this Nebula together.

"And if we could travel into the Core itself we would find gravity climbing to thousands, millions of gee. Hollerbach has some theories about what happens near and within the Core, a realm of what he calls 'gravitic chemistry'-"

Nead frowned. "I don't understand."

"I bet you don't." Rees laughed. "But I'll tell you anyway, so you'll know the questions to ask...

"You see, in the day-to-day turmoil of things we - even we Scientists - tend to forget the central, astonishing fact of this cosmos - that the gravitational constant is a billon times larger than in the universe from which man arose. Oh, we see the macroscopic effects - for instance, a human body exerts a respectable gravitational field! - but what about the small, the subtle, the microscopic effects?"

In man's original universe, Rees went on, gravity was the only significant force over the interstellar scale. But over short ranges - on the scale of an individual atom - gravity was so tiny as to be negligible. "It is utterly dominated by even the electromagnetic force," Rees said. "And that is why our bodies are shambling cages of electromagnetism; and attractive electrical forces between molecules drive the chemistry that sustains our being.

"But here..." He rubbed his nose thoughtfully. "Here, things are different. Here, in certain circ.u.mstances, gravity can be as significant on the atomic scale as other forces - even dominant.

"Hollerbach talks of a new kind of 'atom.' Its fundamental particles would be ma.s.sive - perhaps they would be tiny black holes - and the atom would be bonded by gravity in novel, complex structures. A new type of chemistry - a gravitic chemistry - would be possible; a new realm of nature about whose form even Hollerbach can scarcely begin to speculate."

Nead frowned. "But why haven't we observed this 'gravitic chemistry'?"

Rees nodded approvingly. "Good question. Hollerbach calculates that the right conditions must prevail: the right temperature and pressure, powerful gravitational gradients-"

"In the Core," Nead breathed. "I see. So perhaps-"

There was a soft boom.

The Bridge shifted slightly, as if a wave were pa.s.sing through its structure. The image in the monitor broke up.

Rees twisted. A sharp smell of burning, of smoke, touched his nostrils. The Scientists were milling in confusion, but the instruments seemed to be intact. Somewhere someone screamed.

Fear creased Nead's brow. "Is that normal?"

"That came from the Library," Rees murmured. "And, no, it's not b.l.o.o.d.y normal." He took a deep, calming breath; and when he spoke again his voice was steady. "It's all right, Nead. I want you to get out of here as quickly as you can. Wait until..." His voice tailed away.

Nead looked at him, half-understanding. "Until what?"

"Until I send for you. Now move."