Rees frowned. Maybe, he thought.

But Gover had sounded very sure.

A few shifts later Hollerbach asked to see Rees.

Rees paused outside the Chief Scientist's office, drawing deep breaths. He felt as if he were poised on the Rim of the Raft; the next few moments might shape the rest of his life.

Pushing his shoulders back he entered the office.

Hollerbach was bent over paperwork by the light of a globe over his desk. He scowled up at Rees's approach. "Eh? Who's that? Oh, yes; the miner lad. Come in, come in." He waved Rees to a chair before the desk; then he rested back in his armchair, bony arms folded behind his head. The light above the desk made the hollows around his eyes seem enormously deep.

"You asked to see me," Rees said.

"I did, didn't I?" Hollerbach stared frankly at Rees. "Now then; I hear you've been making yourself useful around the place. You're a hard worker, and that's something all too rare… So thank you for what you've done. But," he went on gently, "a supply tree has been loaded and is ready to fly to the Belt. Next shift. What I have to decide is whether you're to be on it or not."

A thrill coursed through Rees; perhaps he still had a chance to earn a place here. Anticipating some kind of test, he hastily reviewed the fragments of knowledge he had acquired.

Hollerbach got out of his chair and began to walk around the office. "You know we're overpopulated here," he said. "And we have… problems with the supply dispensers, so that's not going to get any easier. On the other hand, now that I've shed that useless article Gover I have a vacancy in the labs. But unless it's really justified I can't make a case for keeping you."

Rees waited.

Hollerbach frowned. "You keep your own counsel, don't you, lad? Very well… If you were going to ask me one question, now, before you're shipped out of here — and I guaranteed to answer it as fully as I could — what would it be?"

Rees felt his heart pound. Here was the test, the moment of Rim balancing — but it had come in such an unexpected form. One question! What was the one key that might unlock the secrets against which his mind battered like a skitter against a globe lamp?

The seconds ticked away; Hollerbach regarded him steadily, thin hands steepled before his face.

At last, almost on impulse, Rees asked: "What's a gee?"

Hollerbach frowned. "Explain."

Rees bunched his fists. "We live in a universe filled with strong, shifting gravity fields. But we have a standard unit of gravitational acceleration… a gee. Why should this be so? And why should it have the particular value it does?"

Hollerbach nodded. "And what answer would you anticipate?"

"That the gee relates to the place man came from. It must have had a large area over which gravity was stable, with a value of what we call a gee. So that became the standard. There's nowhere in the universe with such a region — not even the Raft, So maybe some huge Raft in the past, that's now broken up—"

Hollerbach smiled, the skin stretching over his bony jaw. "That's not bad thinking… Suppose I told you that there has never been anywhere in this universe with such a region?"

Rees thought that over. "Then I'd suggest that men came here from somewhere else."

"Are you sure about that?"

"Of course not," Rees said defensively. "I'd have to check it out… find more evidence."

The old Scientist shook his head. "Boy, I suspect there's more scientific method in your untrained head than in whole cadres of my so-called assistants."

"But what's the answer?"

Hollerbach laughed. "You are a rare creature, aren't you? More interested in understanding than in your own fate…

"Well, I'll tell you. Your guess was quite right. Men don't belong in this universe. We came here in a Ship. We passed through something called Holder's Ring, which was a kind of gateway. Somewhere in the cosmos on the other side of the Ring is the world we came from. It's a planet, incidentally; a sphere, not a Raft, about eight thousand miles wide. And its surface has a gravity of exactly one gee."

Rees frowned. "Then it must be made of some

gas." |

Hollerbach took the orrery from the shelf and studied the tiny planets. "It's a ball of iron, actually. It couldn't exist… here.

"Gravity is the key to the absurd place we're stranded in, you see; gravity here is a billion times as strong as in the universe we came from. Here our home planet would have a surface gravity of a billion gees — if it didn't implode in an instant. And celestial mechanics are a joke. The home world takes more than a thousand shifts to orbit around its star. Here it would take just seventeen minutes!

"Rees, we don't believe the Crew intended to bring the Ship here. It was probably an accident. As soon as the increased gravity hit, large parts of the Ship collapsed. Including whatever they used to propel it through the air. They must have fallen into the Nebula, barely understanding what was happening, frantically seeking a way to stay out of the Core…"

Rees thought of the foundry implosion and his imagination began to construct a scene…

…Crew members hurried through the corridors of their falling Ship; smoke filled the passageways as lurid flames singed the air. The hull was breached; the raw air of the Nebula scoured through the cabins, and through rents in the silver walls the Crew saw flying trees and huge, cloudy whales, all utterly unlike anything in their experience , . .

"The Bones alone know how they survived those first few shifts. But survive they did; they harnessed trees and stayed out of the clutches of the Core; and gradually men spread through the Nebula, to the Belt worlds and beyond—"

"What?" Rees's focus snapped back to the present. "But I thought you were describing how the Raft folk got here… I assumed that Belt folk and the others—"

"Came from somewhere else?" Hollerbach smiled, looking tired. "It's rather convenient for us, in comparative comfort here on the Raft, to believe so; but the fact is that all the humans in the Nebula originated on the Ship. Yes, even the Boneys. And in fact this myth of disparate origins is probably damaging the species. We need to cross-breed, to expand the size of our gene pool…"

Rees thought that over. In retrospect there were so many obvious points of similarity between life here and in the Belt. But the thought of the obvious differences, of the relentless harshness of Belt life, began to fill him with a cold anger.

Why, for instance, shouldn't the Belt have its own supply machine? If they had a shared origin surely the miners were as entitled as the Raft dwellers…

There would be time to think on this later. He tried to concentrate on what Hollerbach was saying. "… So I'll be frank with you, young man. We know the Nebula is almost spent. And unless we do something about it we'll be spent too."

"What will happen? Will the air turn un-breathable?"

Holierbach replaced the orrery tenderly. "Probably. But long before that the stars will go out. It will get cold and dark… and the trees will start to fail.

"We'll have nothing to hold us steady any more. We'll fall into the Core, and that will be that. It should be quite a ride…

"If we're not to take that death ride, Rees, we need Scientists. Young ones; inquiring ones who might think up a way out of the trap the Nebula is becoming. Rees, the secret of a Scientist is not what he knows. It's what he asks. I think you've got that trick. Maybe, anyway…"

A flush warmed Rees's cheeks. "You're saying I can stay?"

Hollerbach sniffed. "It's still probationary, mind; for as long as I think it needs to be. And we'll have to fix up some real education for you. Chase Grye a bit harder, will you?" The old Scientist shuffled back to his desk and lowered himself into his seat. He took his spectacles from a pocket of his robe, perched them on his nose, and bent once more over his papers. He glanced up at Rees. "Anything else?"