"How the hell did that happen?" Barnes said.

"It was me," Beth said. "I pushed this button."

"Let's not go around pushing buttons, if you don't mind," Barnes said irritably.

"It was marked 'ROOM LIGHTS.' It seemed an appropriate thing to do."

"Let's try to stay together on this," Barnes said.

"Well, Jesus, Hat - "

"Just don't push any more buttons, Beth!"

They were moving around the cabin, looking at the instrument panel, at the chairs. All of them, that is, all except for Harry. He stood very still in the middle of the room, not moving, and said, "Anybody see a date anywhere?"

"No date."

"There's got to be a date," Harry said, suddenly tense. "And we've got to find it. Because this is definitely an American spaceship from the future."

"What's it doing here?" Norman asked. "Damned if I know," Harry said. He shrugged. Norman frowned.

"What's wrong, Harry?"

"Nothing."

"Sure?"

"Yeah, sure."

Norman thought: He's figured out something, and it bothers him. But he's not saying what it is.

Ted said, "So this is what a time-travel machine looks like.

"I don't know," Barnes said. "If you ask me, this instrument panel looks like it's for flying, and this room looks like a flight deck."

Norman thought so, too: everything about the room reminded him of an airplane cockpit. The three chairs for pilot, copilot, navigator. The layout of the instrumentation. This was a machine that flew, he was sure of it. Yet something was odd. ...

He slipped into one of the contoured chairs. The soft leather-like material was almost too comfortable. He heard a gurgling: water inside?

"I hope you're not going to fly this sucker," Ted laughed.

"No, no."

"What's that whirring noise?"

The chair gripped him. Norman had an instant of panic, feeling the chair move all around his body, squeezing his shoulders, wrapping around his hips. The leather padding slid around his head, covering his ears, drawing down over his forehead. He was sinking deeper, disappearing inside the chair itself, being swallowed up by it.

"Oh God ..."

And then the chair snapped forward, pulling up tight before the control console. And the whirring stopped. Then nothing.

"I think," Beth said, "that the chair thinks you are going to fly it."

"Umm," Norman said, trying to control his breathing, his racing pulse, "I wonder how I get out?"

The only part of his body still free were his hands. He moved his fingers, felt a panel of buttons on the arms of the chair. He pressed one.

The chair slid back, opened like a soft clam, released him. Norman climbed out, and looked back at the imprint of his body, slowly disappearing as the chair whirred and adjusted itself.

Harry poked one of the leather pads experimentally, heard the gurgle. "Water-filled."

"Makes perfect sense," Barnes said. "Water's not compressible. You can withstand enormous G-forces sitting in a chair like this."

"And the ship itself is built to take great strains," Ted said. "Maybe time travel is strenuous? Structurally strenuous?"

"Maybe." Norman was doubtful. "But I think Barnes is right - this is a machine that flew."

"Perhaps it just looks that way," Ted said. "After all, we know how to travel in space, but we don't know how to travel in time. We know that space and time are really aspects of the same thing, space-time. Perhaps you're required to fly in time just the way you fly in space. Maybe time travel and space travel are more similar than we think now."

"Aren't we forgetting something?" Beth said. "Where is everybody? If people flew this thing in either time or space, where are they?"

"Probably somewhere else on the ship."

"I'm not so sure," Harry said. "Look at this leather on these seats. It's brand-new."

"Maybe it was a new ship."

"No, I mean really brand-new. This leather doesn't show any scratches, any cuts, any coffee-cup spills or stains. There is nothing to suggest that these seats have ever been sat in." "Maybe there wasn't any crew."

"Why would you have seats if there wasn't any crew?"

"Maybe they took the crew out at the last minute. It seems they were worried about radiation. The inner hull's leadshielded, too."

"Why should there be radiation associated with time travel?"

"I know," Ted said. "Maybe the ship got launched by accident. Maybe the ship was on the launch pad and somebody pressed the button before the crew got aboard so the ship took off empty."

"You mean, oops, wrong button?"

"That'd be a hell of a mistake," Norman said.

Barnes shook his head. "I'm not buying it. For one thing, a ship this big could never be launched from Earth. It had to be built and assembled in orbit, and launched from space."

"What do you make of this?" Beth said, pointing to another console near the rear of the flight deck. There was a fourth chair, drawn up close to the console.

The leather was wrapped around a human form.

"No kidding..."

"There's a man in there?"

"Let's have a look." Beth pushed the armrest buttons. The chair whirred back from the console and unwrapped itself. They saw a man, staring forward, his eyes open.

"My God, after all these years, perfectly preserved," Ted said.

"You would expect that," Harry said. "Considering he's a mannequin."

"But he's so lifelike - "

"Give our descendants some credit for advances," Harry said. "They're half a century ahead of us." He pushed the mannequin forward, exposing an umbilicus running out the back, at the base of the hips.

"Wires ..."

"Not wires," Ted said. "Glass. Optical cables. This whole ship uses optical technology, and not electronics."

"In any case, it's one mystery solved," Harry said, looking at the dummy. "Obviously this craft was built to be a manned ship, but it was sent out unmanned."

"Why?"

"Probably the intended voyage was too dangerous. They sent an unmanned vessel first, before they sent a manned vessel."

Beth said, "And where did they send it?"

"With time travel, you don't send it to a where. You send it to a when."

"Okay. Then to when did they send it?"

Harry shrugged. "No information yet," he said.

That diffidence again, Norman thought. What was Harry really thinking?

"Well, this craft is half a mile long," Barnes said. "We have a lot more to see."

"I wonder if they had a flight recorder," Norman said.

"You mean like a commercial airliner?"

"Yes. Something to record the activity of the ship on its voyage."

"They must have," Harry said. "Trace the dummy cable back, you're sure to find it. I'd like to see that recorder, too. In fact, I would say it is crucial."

Norman was looking at the console, lifting up a keyboard panel. "Look here," he said. "I found a date."

They clustered around. There was a stamp in the plastic beneath the keyboard. "Intel Inc. Made in U.S.A. Serial No: 98004077 8/5/43."

"August 5, 2043?"

"Looks like it."

"So we're walking through a ship fifty-odd years before it's going to be built. ..."

"This is giving me a headache."

"Look here." Beth had moved forward from the console deck, into what looked like living quarters. There were twenty bunk beds.

"Crew of twenty? If it took three people to fly it, what were the other seventeen for?"

Nobody had an answer to that.

Next, they entered a large kitchen, a toilet, living quarters. Everything was new and sleekly designed, but recognizable for what it was.

"You know, Hal, this is a lot more comfortable than DH-8."

"Yes, maybe we should move in here."

"Absolutely not," Barnes said. "We're studying this ship, not living in it. We've got a lot more work to do before we even begin to know what this is all about."

"It'd be more efficient to live here while we explore it."

"I don't want to live here," Harry said. "It gives me the creeps."

"Me too," Beth said.

They had been aboard the ship for an hour now, and Norman's feet hurt. That was another thing he hadn't anticipated: while exploring a large spacecraft from the future, your feet could begin to hurt.

But Barnes continued on.

Leaving the crew quarters, they entered a vast area of narrow walkways set out between great sealed compartments that stretched ahead as far as they could see. The compartments turned out to be storage bays of immense size. They opened one bay and found it was filled with heavy plastic containers, which looked rather like the loading containers of contemporary airliners, except many times larger. They opened one container.

"No kidding," Barnes said, peering inside. "What is it?"

"Food."

The food was wrapped in layers of lead foil and plastic, like NASA rations. Ted picked one up. "Food from the future!" he said, and smacked his lips.

"You going to eat that?" Harry said.

"Absolutely," Ted said. "You know, I once had a bottle of Dom Perignon 1897, but this will be the first time I've ever had anything to eat from the future, from 2043."

"It's also three hundred years old," Harry said.

"Maybe you'll want to film this," Ted said to Edmunds. "Me eating."

Edmunds dutifully put the camera to her eye, flicked on the light.

"Let's not do that now," Barnes said. "We have other things to accomplish."

"This is human interest," Ted said. "Not now," Barnes said firmly.

He opened a second storage container, and a third. They all contained food. They moved to the next storage bay and opened more containers.

"It's all food. Nothing but food."

The ship had traveled with an enormous amount of food. Even allowing for a crew of twenty, it was enough food for a voyage of several years.

They were getting very tired; it was a relief when Beth found a button, said, "I wonder what this does - "

Barnes said, "Beth - "

And the walkway began to move, rubber tread rolling forward with a slight hum.

"Beth, I want you to stop pushing every damn button you see."

But nobody else objected. It was a relief to ride the walkway past dozens of identical storage bays. Finally they came to a new section, much farther forward. Norman guessed by now they were a quarter of a mile from the crew compartment in the back. That meant they were roughly in the middle of the huge ship.

And here they found a room with life-support equipment, and twenty hanging spacesuits.

"Bingo," Ted said. "It's finally clear. This ship is intended to travel to the stars."

The others murmured, excited by the possibility. Suddenly it all made sense: the great size, the vastness of the ship, the complexity of the control consoles. ...

"Oh, for Christ's sake," Harry said. "It can't have been made to travel to the stars. This is obviously a conventional spacecraft, although very large. And at conventional speeds, the nearest star is two hundred and fifty years away."

"Maybe they had new technology."

"Where is it? There's no evidence of new technology."

"Well, maybe it's - "

"Face the facts, Ted," Harry said. "Even with this huge size, the ship is only provisioned for a few years: fifteen or twenty years, at most. How far could it go in that time? Barely out of the solar system, right?"

Ted nodded glumly. "It's true. It took the Voyager spacecraft five years to reach Jupiter, nine years to reach Uranus. In fifteen years ... Maybe they were going to Pluto."

"Why would anyone want to go to Pluto?"

"We don't know yet, but - "

The radios squawked. The voice of Tina Chan said, "Captain Barnes, surface wants you for a secure encrypted communication, sir."

"Okay," Barnes said. "It's time to go back, anyway." They headed back, through the vast ship, to the main entrance.

SPACE AND TIME

They were sitting in the lounge of DH-8, watching the divers work on the grid. Barnes was in the next cylinder, talking to the surface. Levy was cooking lunch, or dinner - a meal, anyway. They were all getting confused about what the Navy people called "surface time."

"Surface time doesn't matter down here," Edmunds said, in her precise librarian's voice. "Day or night, it just doesn't make any difference. You get used to it."

They nodded vaguely. Everyone was tired, Norman saw. The strain, the tension of the exploration, had taken its toll.

Beth had already drifted off to sleep, feet up on the coffee table, her muscular arms folded across her chest.

Outside the window, three small submarines had come down and were hovering over the grid. Several divers were clustered around; others were heading back to the divers' habitat, DH-7.

"Looks like something's up," Harry said. "Something to do with Barnes's call?"

"Could be." Harry was still preoccupied, distracted. "Where's Tina Chan?"

"She must be with Barnes. Why?"

"I need to talk to her."

"What about?" Ted said.

"It's personal," Harry said.

Ted raised his eyebrows but said nothing more. Harry left, going into D Cyl. Norman and Ted were alone.

"He's a strange fellow," Ted said.

"Is he?"

"You know he is, Norman. Arrogant, too. Probably because he's black. Compensating, don't you think?"

"I don't know."

"I'd say he has a chip on his shoulder," Ted said. "He seems to resent everything about this expedition." He sighed. "Of course, mathematicians are all strange. He's probably got no sort of life at all, I mean a private life, women and so forth. Did I tell you I married again?"

"I read it somewhere," Norman said.

"She's a television reporter," Ted said. "Wonderful woman." He smiled. "When we got married, she gave me this Corvette. Beautiful '58 Corvette, as a wedding present. You know that nice fire-engine red color they had in the fifties? That color." Ted paced around the room, glanced over at Beth. "I just think this is all unbelievably exciting. I couldn't possibly sleep."

Norman nodded. It was interesting how different they all were, he thought. Ted, eternally optimistic, with the bubbling enthusiasm of a child. Harry, with the cold, critical demeanor, the icy mind, the unblinking eye. Beth, not so intellectual or so cerebral. At once more physical and more emotional. That was why, though they were all exhausted, only Beth could sleep.

"Say, Norman," Ted said. "I thought you said this was going to be scary."

"I thought it would be," Norman said.

"Well," Ted said. "Of all the people who could be wrong about this expedition, I'm glad it was you."

"I am, too."

"Although I can't imagine why you would select a man like Harry Adams for this team. Not that he isn't distinguished, but ..."

Norman didn't want to talk about Harry. "Ted, remember back on the ship, when you said space and time are aspects of the same thing?"

"Space-time, yes."

"I've never really understood that."

"Why? It's quite straightforward."

"You can explain it to me?"

"Sure."

"In English?" Norman said.

"You mean, explain it without mathematics?"

"Yes."

"Well, I'll try." Ted frowned, but Norman knew he was pleased; Ted loved to lecture. He paused for a moment, then said, "Okay. Let's see where we need to begin. You're familiar with the idea that gravity is just geometry?"

"No."

"Curvature of space and time?"

"Not really, no."

"Uh. Einstein's general relativity?"

"Sorry," Norman said.

"Never mind," Ted said. There was a bowl of fruit on the table. Ted emptied the bowl, setting the fruit on the table.

"Okay. This table is space. Nice, flat space."

"Okay," Norman said.

Ted began to position the pieces of fruit. "This orange is the sun. And these are the planets, which move in circles around the sun. So we have the solar system on this table."

"Okay."

"Fine," Ted said. "Now, the sun" - he pointed to the orange in the center of the table - "is very large, so it has a lot of gravity."

"Right."

Ted gave Norman a ball bearing. "This is a spaceship. I want you to send it through the solar system, so it passes very close to the sun. Okay?"

Norman took the ball bearing and rolled it so it passed close to the orange. "Okay."

"You notice that your ball rolled straight across the flat table."

"Right."

"But in real life, what would happen to your spacecraft when it passed near the sun?"

"It would get sucked into the sun."

"Yes. We say it would 'fall into' the sun. The spacecraft would curve inward from a straight line and hit the sun. But your spacecraft didn't."

"No.

"So we know that the flat table is wrong," Ted said. "Real space can't be flat like the table."

"It can't?"

"No," Ted said.

He took the empty bowl and set the orange in the bottom. "Now roll your ball straight across past the sun."

Norman flicked the ball bearing into the bowl. The ball curved, and spiraled down the inside of the bowl until it hit the orange.

"Okay," Ted said. "The spacecraft hit the sun, just like it would in real life."

"But if I gave it enough speed," Norman said, "it'd go right past it. It'd roll down and up the far side of the bowl and out again."

"Correct," Ted said. "Also like real life. If the spacecraft has enough velocity, it will escape the gravitational field of the sun."

"Right."

"So," Ted said, "what we are showing is that a spacecraft passing the sun in real life behaves as if it were entering a curved region of space around the sun. Space around the sun is curved like this bowl."

"Okay ..."

"And if your ball had the right speed, it wouldn't escape from the bowl, but instead would just spiral around endlessly inside the rim of the bowl. And that's what the planets are doing. They are endlessly spiraling inside the bowl created by the sun."

He put the orange back on the table. "In reality, you should imagine the table is made out of rubber and the planets are all making dents in the rubber as they sit there. That's what space is really like. Real space is curved-and the curvature changes with the amount of gravity."

"Yes..."

"So," Ted said, "space is curved by gravity."

"Okay."

"And that means that you can think of gravity as nothing more than the curvature of space. The Earth has gravity because the Earth curves the space around it."

"Okay."

"Except it's not that simple," Ted said.

Norman sighed. "I didn't think it would be."

Harry came back into the room, looked at the fruit on the table, but said nothing.

"Now," Ted said, "when you roll your ball bearing across the bowl, you notice that it not only spirals down, but it also goes faster, right?"

"Yes."

"Now, when an object goes faster, time on that object passes slower. Einstein proved that early in the century. What it means is that you can think of the curvature of space as also representing a curvature of time. The deeper the curve in the bowl, the slower time passes."

Harry said, "Well ..."

"Layman's terms," Ted said. "Give the guy a break."

"Yeah," Norman said, "give the guy a break."

Ted held up the bowl. "Now, if you're doing all this mathematically, what you find is that the curved bowl is neither space nor time, but the combination of both, which is calledspace-time. This bowl is space-time, and objects moving on it are moving in space-time. We don't think about movement that way, but that's really what's happening."

"It is?"

"Sure. Take baseball."

"Idiot game," Harry said. "I hate games."

"You know baseball?" Ted said to Norman.

"Yes," Norman said.

"Okay. Imagine the batter hits a line drive to the center fielder. The ball goes almost straight out and takes, say, half a second."

"Right."

"Now imagine the batter hits a high pop fly to the same center fielder. This time the ball goes way up in the air, and it takes six seconds before the center fielder catches it."

"Okay."

"Now, the paths of the two balls - the line drive and the pop fly - look very different to us. But both these balls moved exactly the same in space-time."

"No," Norman said.

"Yes," Ted said. "And in a way, you already know it. Suppose I ask you to hit a high pop fly to the center fielder, but to make it reach the fielder in half a second instead of six seconds."

"That's impossible," Norman said.

"Why? Just hit the pop fly harder."

"If I hit it harder, it will go higher and end up taking longer."

"Okay, then hit a low line drive that takes six seconds to reach center field."

"I can't do that, either."

"Right," Ted said. "So what you are telling me is that you can't make the ball do anything you want. There is a fixed relationship governing the path of the ball through space and time."

"Sure. Because the Earth has gravity."

"Yes," Ted said, "and we've already agreed that gravity is a curvature of space-time, like the curve of this bowl. Any baseball on Earth must move along the same curve of space-time, as this ball bearing moves along this bowl. Look." He put the orange back in the bowl. "Here's the Earth." He put two fingers on opposite sides of the orange. "Here's batter and fielder. Now, roll the ball bearing from one finger to the other, and you'll find you have to accommodate the curve of the bowl. Either you flick the ball lightly and it will roll close to the orange, or you can give it a big flick and it will go way up the side of the bowl, before falling down again to the other side. But you can't make this ball bearing do anything you want, because the ball bearing is moving along the curved bowl. And that's what your baseball is really doing - it's moving on curved space-time."

Norman said, "I sort of get it. But what does this have to do with time travel?"

"Well, we think the gravitational field of the Earth is strong - it hurts us when we fall down - but in reality it's very weak. It's almost nonexistent. So space-time around the Earth isn't very curved. Space-time is much more curved around the sun. And in other parts of the universe, it's very curved, producing a sort of roller-coaster ride, and all sorts of distortions of time may occur. In fact, if you consider a black hole - "

He broke off.

"Yes, Ted? A black hole?"

"Oh my God," Ted said softly.

Harry pushed his glasses up on his nose and said, "Ted, for once in your life, you just might be right."

They both grabbed for paper, began scribbling.

"It couldn't be a Schwartzschild hole - "

" - No, no. Have to be rotating - "

" - Angular momentum would assure that - "

" - And you couldn't approach the singularity - "

" - No, the tidal forces - "

" - rip you apart - "

"But if you just dipped below the event horizon ..."

"Is it possible? Did they have the nerve?"

The two fell silent, making calculations, muttering to themselves.

"What is it about a black hole?" Norman said. But they weren't listening to him any more.

The intercom clicked. Barnes said, "Attention. This is the Captain speaking. I want all hands in the conference room on the double."

"We're in the conference room," Norman said.

"On the double. Now."

"We're already there, Hal."

"That is all," Barnes said, and the intercom clicked off.

THE CONFERENCE

"I've just been on the scrambler with Admiral Spaulding of CincComPac Honolulu," Barnes said. "Apparently Spaulding just learned that I had taken civilians to saturated depths for a project about which he knew nothing. He wasn't happy about it."

There was a silence. They all looked at him.