Larry Niven: The Ringworld Engineers

The puppeteer said, “The Ringworld could not have been off center when you were here. It was twenty-three years ago.”

Louis nodded. To speak would be distracting. Only the joy of the wire now held away horror for the fate of the Ringworld natives, fear and guilt for himself. The Hindmost continued, “The Ringworld structure is unstable in the plane of its orbit. Surely you knew?”

“No!”

Louis said, “I didn’t know myself till after I was back on Earth. I did some research then.”

Both aliens were looking at him. He hadn’t really wanted that much of their attention. Oh, well. “It’s easy enough to show that the Ringworld is unstable. Stable along the axis, but unstable in the plane. There must have been something to keep the sun on the axis.”

“But it’s off center now !”

“Whatever it was stopped working.”

Chmeee clawed at the invisible floor. “But then they must die! Billions of them, tens of billions — trillions?” He turned to Louis. “I tire of your fatuous smile. Would you talk better without the droud?”

“I can talk fine.”

“Talk, then. Why is the Ringworld unstable? Is it not in orbit?”

“No, of course not. It has to be rigid. That terrific spin would pull it rigid. If you nudge the Ringworld off center it’ll fall further off center. But the equations are pretty hairy. I played around with a computer and I got numbers I’m not sure I believe.”

The Hindmost said, “At one time we thought we might build our own Ringworld. The instability is too great. Even a strong solar flare would exert enough pressure on the structure to throw it off balance. Five years later it would grind against its sun.”

“That’s the same figure I got,” Louis said. “That must be what happened here.”

Chmeee was clawing the floor again. “Attitude jets! The Ringworld engineers would have mounted attitude jets!”

“Maybe. We know they had Bussard ramjets. They used them to drive their starships. Okay, a lot of big Bussard ramjets on the rim walls would be enough to keep the Ringworld centered. The motors would fuse the hydrogen in the solar wind. They’d never ran out of fuel.”

“We saw nothing. Think how huge the motors would have to be!”

Louis chuckled. “What do you call huge? On the Ringworld? We missed them, that’s all.” But he couldn’t like the way Chmeee stood above him with claws extended.

“You accept it all so easily? There may be enough Ringworld natives to crowd the worlds of known space thousands of times over. They are more nearly your kind than mine.”

“You’re a ruthless, merciless carnivore. Try to remember,” Louis told the kzin. “Look: it’ll bother me. It’ll bother me a lot after the Hindmost turns off my droud. But it won’t kill me, because I’ll be a little bit used to it by then. Can you think of anything we can do to help them? Anything? ”

The kzin turned away. “Hindmost, how much time do they have left?”

“I will attempt to find out.”

The sun was well off center to the Ringworld. Louis guessed it might be, oh, seventy million miles from the near side, which would put it a hundred and twenty million miles from the far side. The near side would be getting nearly three times as much sunlight as the far side, and the structure rotated in seven and a half thirty-hour days. There would be weather. Plants that couldn’t take the changes would be dying. And animals. And men.

The Hindmost had finished its work at the telescope. Now it worked at the computer, out of sight behind the solid green wall. Louis wondered what else was concealed in that hidden part of the ship.

The puppeteer trotted into view. “One year and five months from now, the Ringworld will graze its sun. I expect it will disintegrate then. Given their rotational velocity, the fragments would all recede into interstellar space.”

“Shadow squares,” Louis murmured.

“What? Yes, the shadow squares would impact before the sun. Still, we should have at least a year. Plenty of time for us,” the Hindmost said briskly. “We will not touch the Ringworld surface at all. Your expedition examined the spaceport ledge, from some tens of thousands of miles away, without being fired on by the Ringworld meteor defenses. I believe the spaceport has been abandoned. We can land in safety.”

Chmeee asked, “What do you expect to find?”

“I’m surprised you haven’t remembered.” The Hindmost turned to its control board. “Louis, you’ve had enough time.”

“Wait—”

The wire in his brain went dead.

Louis watched through the wall as the puppeteer worked on his droud. He thought of death in mind-stunning numbers, and death as his own very personal experience, and death for aliens who monitored the current to his brain.

Flat heads poised and shifted and nosed the small black casing as if nibbling at a dubious meal. Long tongues and sensitive lips worked inside the casing. In a few minutes the puppeteer had reset the timer to a thirty-hour day, and cut the current by half.

The next day it was pure joy unfiltered by human sense, and nothing could actually bother him, but… Louis had trouble defining his own feelings. When the current cut off too soon that evening, depression dropped over him like thick saffron smog.

Then Chmeee stooped above Louis Wu, pulled the droud from his scalp, and set it on the stepping disc to be flicked to the flight deck. For resetting. Again.

Louis screamed and leaped. He scrambled up the kzin’s broad back via fur handholds and tried to tear his ears off. The kzin whirled. Louis found himself clinging to a great arm, found the arm slinging him across the room. He fetched up against a wall. Half stunned, with blood streaming down his torn arm, Louis turned to the attack.

He turned in time to see Chmeee leap onto the stepping disc just as the Hindmost mouthed the controls.

Chmeee crouched on the black disc, looking dangerous and foolish.

The Hindmost said, “Nothing so massive may be flicked to these discs. Do you judge me an idiot, to flick a kzin onto my own flight deck?”

Chmeee snarled, “How much intelligence does it take to sneak up on a leaf?” He flipped the droud to Louis and shambled toward his water bed.

A diversion. Chmeee had snatched the droud from Louis’s scalp just after it switched off, solely to drive Louis Wu into berserker rage, to distract the puppeteer’s attention.

The Hindmost said, “When next I alter your droud I will do it just before you plug in. Does that make you happy?”

“You know tanj well what makes me happy!” Louis held the droud tightly. It was dead, of course — dead until the timer made it live again.

“You are nearly as long-lived as we are. This is so temporary,” the Hindmost wheedled him. “You will be wealthy beyond dreams! The Ringworld spacecraft used a method of cheap, large-scale transmutation, the same that they must have used to build the Ringworld itself!”

Louis looked up, startled.

“I wish we knew the mass and bulk of the machine,” the puppeteer continued. “The Ringworld spacecraft are tremendous things. But we need not transport it. If necessary, a hologram taken by deep-radar, and holograms of the mechanism in action, should be enough to convince my subjects. Then we need only send a General Products #4 craft to pick it up.”

The alien would not expect a man deep in current withdrawal to respond to every little comment. Of course not. But from under his brows Louis watched Chmeee, to see how he would handle it.

The kzin was admirable. For a moment he froze. Then, “How did you come to lose your prerogatives?”

“The tale is complex.”