Hollerbach said nothing; he steepled liver-spotted fingers before his face and regarded Rees gravely.

At length Rees blurted, "Am I correct?"

Hollerbach looked disappointed. "You must learn, boy, that in this business there are no right answers. There are only good guesses. You have made an empirical prediction; well, fine. Now you must check it against the body of theory you have learned."

Inwardly Rees groaned. But he went away and did so.

Later he showed his findings on the strength and direction of the Raft's gravitational field to Hollerbach. "The way the field varies is quite complex," he said. "At first I thought it might fall off as the inverse square of the distance from the center of the Raft; but you can see that's not true..."

"The inverse square law holds only for point ma.s.ses, or for perfectly spherical objects. Not for something shaped like a dinner plate, like the Raft."

"Then what is...?"

Hollerbach merely eyed him.

"I know," Rees sighed. "I should go and work it out. Right?"

It took him longer than the pendulum problem. He had to learn to integrate in three dimensions... and how to use vector forces and equipotential surfaces... and how to make sensible approximating a.s.sumptions.

But he did it. And when he'd done that, there was another problem. And another, and still another...

It wasn't all work.

One shift Baert, with whom Rees struck up a diffident friendship, offered Rees a spare ticket to something called the Theatre of Light. "I won't pretend you're my first choice companion," Baert grinned. "She was a bit better looking than you... But I don't want to miss the show, or waste a ticket."

Rees thanked him, turning the strip of cardboard over in his hands. "The Theatre of Light? What is it? What goes on there?"

"There aren't too many theatres in the Belt, eh? Well, if you haven't heard, wait and see..."

The Theatre was situated beyond the tethered forest, about three-quarters of the way to the Rim. There was a bus service from the Raft's central regions but Baert and Rees chose to walk. By the time they had reached the head-high fence which surrounded the Theatre the deck appeared to be sloping quite steeply, and the walk had become a respectable climb. Out here on the exposed deck, far from the cover of the forest canopy, the heat of the star above the Raft was a tangible thing, and both of them arrived with faces slick with sweat.

Baert turned awkwardly, slippered feet gripping at the riveted slope, and grinned down at Rees. "Kind of a hike," he said. "But it'll be worth it. Do you have your ticket?"

Rees fumbled in his pockets until he found the precious piece of cardboard. Bemused, he watched as Baert presented the tickets to a doorkeeper and then followed Baert through a narrow gate.

The Theatre of Light was an oval some fifty yards along its long axis, which ran down the apparent slope of the deck. Benches were fixed across the upper part of the Theatre. Rees and Baert took their places and Rees found himself looking down the slope at a small stage which was fixed on stilts so that it rested at the local horizontal - so at an angle to the "tilted" deck - and beyond the stage, serving as a mighty backdrop to the show, he could see the center of the Raft tip away, a vast metal slope of boxy buildings and whirling, rustling trees.

The Theatre filled up rapidly. Rees estimated there was room for about a hundred people here, and he shivered a little, uncomfortable at the thought of so many people in one place.

"Drinks?"

He turned with a start. A girl, luminously pretty, stood beside his seat with a tray of gla.s.ses. He tried to smile back and form an answer, but there was something odd about the way she was standing...

Without effort or discomfort she was standing perpendicularly to the deck; she ignored the apparent tilt of the deck and stood as naturally as if it were level. Rees felt his jaw drop, and all his carefully constructed reasoning about the illusory tilt of the deck evaporated. For if she was vertical then he was sitting at an angle with nothing at his backWith a stifled yell he tumbled backwards.

Baert, laughing, helped him up, and the girl, with an apologetic smile, presented him with a tumbler of some clear, sweet beverage. Rees could feel his cheeks burn like stars. "What was all that about?"

Baert suppressed his laughter. "I'm sorry. It gets them every time. I should have warned you, really..."

"But how does she walk like that?"

Baert's thin shoulders moved in a shrug. "If I knew it would spoil the fun. Magnetic soles on her shoes? The funny thing is, it's not the girl that knocks you over... It's the collapse of your own perceptions, the failure of your sense of balance."

"Yeah, hilarious." Rees sucked sourly at his drink and watched the girl move through the crowd. Her footsteps seemed easy and natural, and try as he might he failed to see how she kept her balance. Soon, though, there were more spectacular acts to watch. Jugglers, for instance, with clubs that swooped and soared in arcs at quite impossible angles, returning infallibly to their owners' hands.

During applause Rees said to Baert, "It's like magic."

"Not magic," the other said. "Simple physics; that's all there is to it. I guess this is making your miner's eyes pop out, eh?"

Rees frowned. On the Belt there wasn't a lot of time for juggling... and no doubt the labor of the miners was going to pay for all this, in some indirect fashion. Discreetly he glanced around at the rest of the audience. Plenty of gold and crimson braid, not a lot of black or the other colors. Upper Cla.s.ses only? He suppressed a stab of resentment and returned his attention to the show.

Soon it was time for the main feature. A trampoline was set up to cover the stage and the crowd grew hushed. Some wind instrument evoked a plaintive melody and a man and a woman dressed in simple leotards took the stage. They bowed once to the audience, climbed onto the trampoline, and together began to soar high into the starlit air. At first they performed simple manoeuvres - slow, graceful somersaults and twists - pleasing to the eye, but hardly spectacular.

Then the couple hit the trampoline together, jumped high, met at the top of their arcs - and, without touching, they twisted around each other, so that each was thrown wide.

Baert gasped. "Now, how did they do that?"

"Gravity," Rees whispered. "Just for a second they orbited around each other's center of ma.s.s."

The dance went on. The partners twisted around each other, throwing their lithe bodies into elaborate parabolae, and Rees watched through half-closed eyes, entranced. The physicist in him a.n.a.lyzed the dancers' elaborate movements. Their centers of ma.s.s, located somewhere around their waists, traced out hyperbolic orbits in the varying gravity fields of the Raft, the stage and the dancers themselves, so that each time the dancers launched themselves from their trampoline the paths of their centers were more or less determined... But the dancers adorned the paths with movements of their slim bodies so deceptively that it seemed that the two of them were flying through the air at will, independent of gravity. How paradoxical, Rees thought, that the billion-gee environment of this universe should afford humans such freedom.

Now the dancers launched into a final, elaborate arc, their bodies...o...b..ting, their faces locked together like facing planets. Then it was over; the dancers stood hand-in-hand atop their trampoline, and Rees cheered and stamped with the rest. So there was more to do with billion-strength gravity than measure it and fight itA flash, a m.u.f.fled rush of air, a sudden blossom of smoke. The trampoline, blasted from below, turned briefly into a fluttering, birdlike creature, a dancer itself; the dancers, screaming, were hurled into the air. Then the trampoline collapsed into the splintered ruins of the stage, the dancers falling after it.

The audience, stunned, fell silent. The only sound was a low, broken crying from the wreckage of the stage, and Rees watched, unbelieving, as a red-brown stain spread over the remains of the trampoline.

A burly man bearing orange braids hurried from the wings and stood commandingly before the audience. "Sit down," he ordered. "No one should try to leave." And he stood there as the audience quietly obeyed. Rees, looking around, saw more orange braids at the exits from the Theatre, still more working their way into the ruins of the stage.

Baert's face was pale. "Security," he whispered. "Report directly to the Captain. You don't see them around too often, but they're always there... undercover as often as not." He sat back and folded his arms. "What a mess. They'll interrogate us all before they let us out of here; it will take hours-"

"Baert, I don't understand any of this. What happened?"

Baert shrugged. "What do you think? A bomb, of course."

Rees felt an echo of the disorientation he had suffered when the drinks girl had walked by. "Someone did this deliberately?"

Baert looked at him sourly and did not reply.

"Why?"

"I don't know. I don't speak for those people." Baert rubbed the side of his nose. "But there's been a few of these attacks, directed against Officers, mostly, or places they're likely to be. Like this.

"Not everyone's happy here, you see, my friend," he went on. "A lot of people think the Officers get more than their share."

"So they're turning to actions like this?" Rees turned away. The red-stained trampoline was being wrapped around the limp bodies of the gravity dancers; he watched with an unshakeable sense of unreality. He remembered his own flash of resentment at Baert, not more than an hour before this disaster. Perhaps he could sympathize with the motives of the people behind this act - why should one group enjoy at leisure the fruits of another's labor? - but to kill for such a reason?

The orange-braided security men began to organize strip searches of the crowd. Resigned, not speaking, Rees and Baert sat back to wait their turn.

Despite isolated incidents like the Theatre attack Rees found his new life fascinating and rewarding, and the shifts wore away unbelievably quickly. All too soon, it seemed, he had finished his Thousand Shifts, the first stage of his graduation process, and it was time for his achievement to be honored.

And so he found himself sitting on a decorated bus and studying the crimson braids of a Scientist (Third Cla.s.s), freshly st.i.tched to the shoulder of his coverall, and shivering with a sense of unreality. The bus worked its way through the suburbs of the Raft. Its dozen young occupants, Rees's fellow graduate-apprentices, spun out a cloud of laughter and talk.

Jaen was studying him with humorous concern, a slight crease over her broad nose; her hands rested in the lap of her dress uniform. "Something on your mind?"

He shrugged. "I'm fine. You know me. I'm the serious type."

"d.a.m.n right. Here." Jaen reached to the boy sitting on the far side from Rees and took a narrow-necked bottle. "Drink. You're graduating. This is your Thousandth Shift and you're ent.i.tled to enjoy it."

"Well, it isn't precisely. I was a slow starter, remember. For me it's more like a thousand and a quarter-"

"Oh, you boring b.u.g.g.e.r, drink some of this stuff before I kick you off the bus."

Rees, laughing, gave in and took a deep draught from the bottle.

He had sampled some tough liquors in the Quartermaster's bar, and plenty of them had been stronger than this fizzing wine-sim; but none of them had quite the same effect. Soon the globe lights lining the avenue of cables seemed to emit a more friendly light; Jaen's gravity pull mingling with his was a source of warmth and stillness; and the brittle conversation of his companions seemed to grow vivid and amusing.

His mood persisted as they emerged from beneath the canopy of flying trees and reached the shadow of the Platform. The great lip of metal jutted inwards from the Rim, forming a black rectangle cut out of the crimson of the sky, its supporting braces like gaunt limbs. The bus wheezed to a halt alongside a set of wide stairs. Rees, Jaen and the rest tumbled from the bus and clambered up the stairs to the Platform.

The Thousandth Shift party was already in full swing, bustling with perhaps a hundred graduates of the various Cla.s.ses of the Raft. A bar set up on trestle tables was doing healthy business, and a discordant set of musicians was thumping out a rhythmic sound - there were even a few couples tentatively dancing, near the band's low stage. Rees, with Jaen in tolerant tow, set off on a tour of the walls of the Platform.

The Platform was an elegant idea: to fix a hundred-yard-square plate to the Rim at such an angle that it matched the local horizontal, surround it by a wall of gla.s.s, and so reveal a universe of spectacular views. At the inward edge was the Raft itself, tilted like some huge toy for Rees's inspection. As at the Theatre the sensation of being on a safe, flat surface gave the proximity of the vast slope a vertiginous thrill.

The s.p.a.ce-facing edge of the platform was suspended over the Rim of the Raft, and a section of the floor was inset with sheets of gla.s.s. Rees stood over the depths of the Nebula; it felt as if he were floating in the air. He could see hundreds of stars scattered in a vast three-dimensional array, illuminating the air like mile-wide globe lamps; and at the center of the view, towards the hidden Core of the Nebula, the stars were crowded together, so that it was as if he were staring into a vast, star-walled shaft.

"Rees. I congratulate you." Rees turned. Hollerbach, gaunt, unsmiling and utterly out of place in all this gaiety, stood beside him.

"Thank you, sir."

The old Scientist leaned towards him conspiratorially. "Of course, I didn't doubt you'd do well from the first."

Rees laughed. "I can tell you I doubted it sometimes."

"A Thousand Shifts, eh?" Hollerbach scratched his cheek. "Well, I've no doubt you'll go much further... And in the meantime here's something for you to think about, boy. The ancients, the first Crew, didn't measure time exclusively in shifts. We know this from their records. They used shifts, yes, but they had other units: a 'day,' which was about three shifts, and a 'year,' which was about a thousand shifts. How old are you now?"

"About seventeen thousand, I believe, sir."

"So you'd be about seventeen 'years' old, eh? Now then - what do you suppose these units, a 'day' and a 'year,' referred to?" But before Rees could answer Hollerbach raised his hand and walked off. "Baert! So they've let you get this far despite my efforts to the contrary-"

Bowls of sweetmeats had been set out around the walls. Jaen nibbled on some fluffy substance and tugged absently at his hand. "Come on. Isn't that enough sightseeing and science?"

Rees looked at her, the combination of wine-sim and stars leaving him quite dazed. "Hm? You know, Jaen, the stories of our home universe notwithstanding, sometimes this seems a very beautiful place." He grinned. "And you don't look too bad yourself."

She punched him in the solar plexus. "And nor do you. Now let's have a dance."

"What?" His euphoria evaporated. He looked past her shoulder at the whirl of dancing couples. "Look, Jaen, I've never danced in my life."

She clicked her tongue. "Don't be such a coward, you mine rat. Those people are just ex-apprentices like you and me, and I can tell you one thing for sure: they won't be watching you."

"Well..." he began, but it was too late; with a determined grip on his forearm she led him to the center of the Platform.

His head filled with memories of the unfortunate gravity dancers at the Theatre of Light and their swooping, spectacular ballet. If he lived for fifty thousand shifts he would never be able to match such grace.

Luckily this dance was nothing like that.

Young men eyed girls across a few yards of floor. Those who were dancing were enthusiastic but hardly expert; Rees watched for a few seconds, then began to imitate their rhythmic swaying.

Jaen pulled a face at him. "That's b.l.o.o.d.y awful. But who cares?"

In the low-gee conditions - gravity here was about half its value near the Labs - the dance had a dreamy slowness. After a while Rees began to relax; and, eventually, he realized he was enjoying himself-until his legs whisked out from under him; he clattered to the Platform with a slow b.u.mp. Jaen covered her face with one hand, suppressing giggles; a circle of laughter cl.u.s.tered briefly around him. He got to his feet. "I'm sorry-"

There was a tap on his shoulder. "So you should be."

He turned; there, with a broad, glinting grin, stood a tall young man with the braids of a Junior Officer. "Doav," Rees said slowly. "Did you trip me?"

Doav barked laughter.

Rees felt his forearm muscles bunch. "Doav, you've been an irritation to me for the last year..."

Doav looked baffled.

"...I mean, the last thousand shifts." And it was true; Rees could bear the constant sniping, cracks and cruelties of Doav and his like throughout his working day... but he would much prefer not to have to. And, since the incident at the Theatre, he had come to see how att.i.tudes like Doav's were the cause of a great deal of pain and suffering on the Raft; and, perhaps, of much more to come.

The wine-sim was like blood now, pounding in his head. "Cadet, if we've something to settle-"

Doav fixed him with a look of contempt. "Not here. But soon. Oh, yes; soon." And he turned his back and walked off through the throng.

Jaen thumped Rees's arm hard enough to make him flinch. "Do you have to turn every incident into an exhibition? Come on; let's get a drink." She stamped her way towards the bar.

"h.e.l.lo, Rees."

Rees paused, allowing Jaen to slip ahead into the crush around the bar. A thin young man stood before him, hair plastered across his scalp. He wore the black braids of Infrastructure and he regarded Rees with cool appraisal.

Rees groaned. "Gover, I guess this isn't to be the best shift I've ever had."

"What?"

"Never mind. I haven't seen you since not long after my arrival."

"Yeah, but that's not hard to understand." Gover flicked delicately at Rees's braid. "We move in different circles, don't we?"

Rees, already on edge after the incident with Doav, studied Gover as coolly as he could. There were still the same sharp features, the look of petulant anger - but Gover looked more substantial, more sure of himself.

"So you're still skivvying for those old farts in the Labs, eh?"

"I'm not going to respond to that, Gover."

"You're not?" Gover rubbed at his nostrils with the palm of his hand. "Seeing you in this toy uniform made me wonder how you see yourself now. I bet you haven't done a shift's work - real work - since you landed here. I wonder what your fellow rats would think of you now. Eh?"

Rees felt blood surge once more to his cheeks; the wine-sim seemed to be turning sour. There was a seed of confusion inside him. Was his anger at Gover just a way of shielding himself from the truth, that he had betrayed his origins...?