by Larry Niven
"I wonder what it looks like from the inside."
Speaker heard, and he touched a control point, and the view slid. The magnification was not yet great enough to pick up details. Bright blue and brighter white slid across the scope screen, and the blurred straight edge of a navy blue shadow …
The further rim slid into view. Here the rim wall was tilted outward.
Nessus, standing in the doorway with his heads poised above Speaker's shoulders, ordered, "Give us what magnification you can."
The view expanded.
"Mountains," said Teela. "How lovely." For the rim wall was irregular, sculptured like eroded rock, and was the color of the Moon. "Mountains a thousand miles high."
"I can expand the view no further. For greater detail we must approach closer."
"Let us first attempt to contact them," said the puppeteer. "Are we at rest?"
Speaker consulted the ship's brain. "We are approaching the primary at perhaps thirty miles per second. Is that slow enough?"
"Yes. Begin transmissions."
No laser light was falling on the Liar.
Testing for electromagnetic radiation was more difficult. Radio, infrared, ultraviolet, X-rays — the whole spectrum had to be investigated, from the room-temperature heat given off by the dark side of the Ringworld, up to light quanta energetic enough to split into matter-antimatter pairs. The twenty-one centimeter band was empty; and so were its easy multiples and divisors, which might have been used merely because the hydrogen absorption band was so obvious. Beyond that point Speaker-To-Animals was playing blind man's bluff with his receivers.
The great pods of communications equipment on the Liar's wing had opened. The Liar was sending radio messages on the hydrogen absorption frequency and others, bathing successive portions of the ring's inner surface with laser light of ten different frequencies, and sending Interworld-Morse in alternate blasts of the fusion motors.
"Our autopilot would eventually translate any possible message," said Nessus. "We must assume that their ground-based computers are at least as capable.
Speakees reply was venomous. "Can your leucotomized computers translate total silence?"
"Concentrate your sendings at the rim. If they have spaceports, the spaceports must be at the rim. To land a spacecraft anywhere else would be horribly dangerous."
In the Hero's Tongue Speaker-To-Animals snarled something horribly insulting. Effectively it ended the conversation; but Nessus stayed where he had been for hours now, with his heads poised alertly above the kzin's shoulders.
The Ringworld waited beyond the hull, a checkered blue ribbon trailing across the sky.
"You tried to tell me about Dyson spheres," said Teela.
"And you told me to go pick lice out of my hair." Louis had found a description of Dyson spheres in the ship's library. Excited by the idea, he had made the mistake of interrupting Teela's game of solitaire to tell her about it.
"Tell me now," she coaxed.
"Go pick lice out of your hair."
She waited.
"You win," said Louis. For the past hour he had been staring broodingly out at the ring. He was as bored as she was.
"I tried to tell you that the Ringworld is a compromise, an engineering compromise between a Dyson sphere and a normal planet.
"Dyson was one of the ancient natural philosophers, pre-Belt, almost pre-atomic. He pointed out that a civilization is limited by the energy available to it. The way for the human race to use all the energy within its reach, he said, is to build a spherical shell around the sun and trap every ray of sunlight.
"Now if you'll quit giggling for just a minute, you'll see the idea. The Earth traps only about half a billionth of the sun's output. If we could use all that energy …
"Well, it wasn't crazy then. There wasn't even a theoretical basis for faster-than-light travel. We never did invent hyperdrive, if you'll recall. We'd never have discovered it by accident, either, because we'd never have thought to do our experiments out beyond the singularity.
"Suppose an Outsider ship hadn't stumbled across a United Nations ramrobot? Suppose the Fertility Laws hadn't worked out? With a trillion human beings standing on each other's shoulders, and the ramships the fastest thing around, how long could we get along on fusion power? We'd use up all the hydrogen in Earth's oceans in a hundred years.
"But there's more to a Dyson sphere than collecting solar power.
"Say you make the sphere one astronomical unit in radius. You've got to clear out the solar system anyway, so you use all the solar planets in the construction. That gives you a shell of, say, chrome steel a few yards thick. Now you put gravity generators all over the shell. You'd have a surface area a billion times as big as the Earth's surface. A trillion people could wander all their lives without ever meeting one another."
Teela finlly got a full sentence in edgewise. "You're using the gravity generators to hold everything down?"
"Yeah, against the inside. We cover the inside with soil."
"What if one of the gravity generators broke down?"
"Picky, picky, picky. Well … you'd get a billion people drifting up into the sun. All the air swarming up after them. A tornado big enough to swallow the Earth. Not a prayer of getting a repair crew in, not through that kind of a storm …"
"I don't like it," Teela said decisively.
"Let's not be hasty. There may be ways to make a gravity generator foolproof."
"Not that. You couldn't see the stars."
Louis hadn't thought of that aspect. "Never mind. The point about Dyson spheres is that any sentient, industrial race is eventually going to need one. Technological civilizations tend to use more and more power as time goes on. The ring is a compromise between a normal planet and a Dyson sphere. With the ring you get only a fraction of the available room, and you block only a fraction of the available sunlight; but you can see the stars, and you don't have to worry about gravity generators."
From the control room Speaker-to-Animal snarled something complicated, a sound powerful enough to curse the very air of the cabin. Teela giggled.
"If the puppeteers have been thinking along the same lines as Dyson," Louis continued, "they might very well expect to find the Clouds of Magellan riddled with Ringworlds, edge to edge."
"And that's why we were called in."
"I'd hate to bet on a puppeteer's thoughts. But if I had to, that's the way I'd bet."
"No wonder you've been spending all your time in the library."
"Infuriating!" screamed the kzin. "Insulting! They deliberately ignore us! They pointedly turn their backs to invite attack!"
"Improbable," said Nessus. "If you cannot find radio transmissions, then they do not use radio. Even if they were routinely using radio lasers, we would detect some leakap."
"They do not use lasers, they do not use radio, they do not use hyperwave. What are they using for communicadon? Telepathy? Wntten messages? Big mirrors?"
"Parrots," Louis suggested. He got up to join them at the door to the control room. "Huge parrots, specially bred for their oversized lungs. They're too big to fly. They just sit on hilltops and scream at each other."
Speaker turned to look Louis in the eye. "For four hours I have tried to contact the Ringworld. For four hours the inhabitants have ignored me. Their contempt has been absolute. Not a word have they vouchsafed me. My muscles are trembling for lack of exercise, my fur is matted, my eyes refuse to focus, my sthondat-begotten room is too small, my microwave heater heats all meat to the same temperature, and it is the wrong temperature, and I cannot get it fixed. Were it not for your help and your suggestions, Louis, I would despair."
"Can they have lost their civilization?" Nessus mused. "It would be silly of them, considering."
"Perhaps they are dead," Speaker said viciously. "That too would be silly. Not to contact us has been silly. Let us land and find out."
Nessus whistled in panic. "Land on a world which may have killed its indigenous species? Are you
mad?"
"How else can we learn?"
"Of course," Teela chimed in. "We didn't come all this way just to fly in circles!"
"I forbid it. Speaker, continue your attempts to contact the Ringworld."
"I have ended such attempts."
"Repeat them."
"I will not."
In stepped Louis Wu, volunteer diplomat. "Cool it, furry buddy. Nessus, he's right. The Ringworlders don't have anything to say to us. Otherwise we'd know it by now."
"But what can we do other than keep trying?"
"Go on about our business. Give the Ringworlders time to make up their minds about us."
Reluctantly the puppeteer agreed.
* * *
They drifted toward the Ringworld.
Speaker had aimed the Liar to pass outside the Ringworld's edge: a concession to Nessus. The puppeteer feared that hypothetical Ringworlders would take it as a threat if the ship's course should intersect the ring itself. He also claimed that fusion drives of the Liar's power had the look of weapons; and so the Liar moved on thrusters alone.
To the eye there was no way of judging scale. Over the hours the ring shifted position. Too slowly. With cabin gravity to compensate for from zero to thirty gee of thrust, the inner ear could not sense motion. Time passed in a vacuum, and Louis, for the first time since leaving Earth, was ready to gnaw his fingernails.
Finally the ring was edge-on to the Liar. Speaker used the thrusters, braking the ship into a circular orbit around the rim; and then he sent them drifting in toward the
Now there was motion.
The rim of the Ringworld grew from a dim line occluding a few stars, to a black wall. A wall a thousand miles high, featureless, though any features would have been blurred by speed. Half a thousand miles away, blocking ninety degrees of sky, the wall sped past at a hellish 770 miles per second. Its edges converged to vanishing points, to points at infinity at either end of the universe; and from each point at infinity, a narrow line of baby blue shot straight upward.
To look into the vanishing point was to step into another universe, a universe of true straight lines, right angles, and other geometric abstractions. Louis stared hypnotized into the vanishing point. Which point was it, the source or the sink? Did the black wall emerge or vanish in that meeting place?
… from out of the point at infinity, something came at them.
It was a ledge, growing like another abstraction along the base of the rim wall. First the ledge appeared; then, mounted on the ledge, a row of upright rings. Straight at the Liar they came, straight at the bridge of Louis's nose. Louis shut his eyes and threw his arms up to protect his head. He heard a whimper of fear.
Death should have come in that instant. When it didn't, he opened his eyes. The rings were going by in a steady stream; and he realized that they were no more than fifty miles across.
Nessus was curled in a ball. Teela, her palms pressed flat against the transparent hull, was staring avidly outward. Speaker was fearless and attentive at the control board. Perhaps he was better than Louis at judging distance.
Or perhaps he was faking it. The whimper could have come from Speaker.
Nessus uncurled. He looked out at the rings, which were smaller now, converging. "Speaker, you must match velocities with the Ringworld. Hold us in position by thrusting at one gravity. We must inspect this."
Centrifugal force is an illusion, a manifestation of the law of inertia. Reality is centripetal force, a force applied at right angles to the velocity vector of a mass. The mass resists, tends to move in its accustomed straight line.
By reason of its velocity and the law of inertia, the Ringworld tended to fly apart. Its rigid structure would not allow that. The Ringworld applied its own centrifugal force to itself. The Liar, matching speed at 770 miles per second, had to match that centripetal force.
Speaker matched it. The Liar hovered next to the rim wall, balanced on .992 gee of thrust, while her crew inspected the spaceport.
The spaceport was a narrow ledge, so narrow as to be a dimensionless line until Speaker moved the ship inward. Then it was wide, wide enough to dwarf a pair of tremendous spacecraft. Ile craft were flat nosed cylinders, both of the same design: an unfamiliar design, yet clearly the design of a fusion-ramship. These ships were intended to fuel themselves, picking up interstellar hydrogen in scoops of electromagnetic force. One had been cannibalized for parts, so that it stood with its guts open to vacuum and its intimate structure exposed to alien eyes.
Windows showed around the upper run of the intact ship, allowing those eyes to gauge that ship's size. In the random starlight, the glitter of windows was precisely like crystal candy sprinkled on a cake. Thousands of windows. That ship was big.
And it was dark. The entire spaceport was dark. Perhaps the beings who used it did not need light in the "visible" frequencies. But to Louis Wu, the spaceport looked abandoned.
"I don't understand the rings," said Teela.
"Electromagnetic cannon," Louis answered absently. "For takeoffs."
"No," said Nessus.
"Oh?"
"The cannon must have been intended for landing the ships. One can even surmise the method used. The ship must go into orbit alongside the rim wall. It will not attempt to match the ring's velocity, but will position itself twenty-five miles from the base of the rim wall. As the ring rotates, the coils of the electromagnetic cannon will scoop up the ship and accelerate it to match the velocity of the ring. I compliment the ring engineers. The ship need never come close enough to the ring to be dangerous."
"You could also use the ring for takeoff."
"No. Observe the facility to our left."
"I'll be tanjed," said Louis Wu.
The "facility" was little more than a trap door big enough to hold one of the ramships.
It figured. 770 miles per second was ramscoop speed. The rines launching facility was merely a structure for tumbling the ship off into the void. The pilot would immediately accelerate away on ramscoop-fumon power.
"The spaceport facility seems to be abandoned," said Speaker.
"Is there power in use?"
"My instruments sense none. There are no anomolous hot spots, no large-scale electromagnetic activities. As for the sensors which operate the linear accelerator, they may use less power than we can sense."
"Your suggestion?"
"The facilities may still be in operational condition. We can test this by proceeding to the mouth of the linear accelerator and entering."
Nessus curled himself into a ball.
"Wouldn't work," said Louis. "There could be a key signal to start the thing, and we don't know it. It might react only to a metal hull. If we tried to go through the cannon at the speed of the Ringworld, we'd hit one of the coils and blow everything to bits."
"I have flown ships under similar conditions during simulated war maneuvers."
"How long ago?"
"Perhaps too long. Never mind. Your suggestion?"
"The underside," said Louis. The puppeteer uncurled at once.
* * *
They hovered beneath the Ringworld floor, matching velocities, thrusting outward at 9.94 meters per second. "Spotlights," said Nessus.
The spots reached across half a thousand miles; but if their light touched the back of the ring, it did not return. The spots were for landings.
"Do you still trust your engineers, Nessus?"
"They should have anticipated this contingency."
"But I did. I can light the Ringworld, if I may use the fusion drives," said the kzin.
"Do so."
Speaker used all four: the pair facing forward, and the larger motors facing back. But on the forward pair, the pair intended for emergency braking and possibly for weapons, Speaker choked the nozzle wide open. Hydrogen flowed though the tube too fast, emerged half-burnt. Fusion-tube temperature dropped until the exhaust, usually hotter than the core of a nova, was as cool as the surface of a yellow dwarf star. Light thrust for
ward in twin spears to fall across the black underside of the Ringworld.
First: the underside was not flat. It dipped and rose; there were bulges and indentations.
"I thought it would be smooth," said Teela.
"Sculptured," said Louis. "I'll make you a bet. Whereever we see a bulge, there's a sea on the sunlit side. Where we see a dent, there's a mountain."
But the formations were tiny, unnoticeable until Speaker drew the ship close. The Lying Bastard drifted in from the Ringworld's edge, half a thousand miles beneath her underbelly. Sculptured bulges and sculptured indentations, they drifted by, irregular, somehow pleasing …
For many centuries excusion boats had drifted in like manner across the surface of Earth's Moon. The effect here was much the same: airless pits and peaks, sharp-edged blacks and whites, exposed on the Moon's dark side by the powerful spotlights carried by all such boats.
Yet there was a difference. At any height above the Moon, you could always see the lunar horizon, sharp and toothy against black space and gently curved.
There were no teeth in the Ringworld's horizon, and no curves. It was a straight line, a geometer's line, unimaginably distant; barely visible as black-against-black. How could Speaker stand it? Louis wondered. Hour after hour, driving the Liar across and beneath the belly of this … artifact.
Louis shuddered. Gradually he was learning the size, the scale of the Ringworld. It was unpleasant, like all learning processes.
He drew his eyes away from that terrible horizon, back to the illuminated area below/above them.
Nessus said, "All the seas seem to be of the same order of magnitude."
"I've seen a few ponds," Teela contradicted him. "And look, there's a river. It has to be a river. But I haven't seen any big oceans."
Seas there were in plenty, Louis saw — if he was right, and those flat bulges were seas. Though they were not all the same size, they seemed evenly distributed, so that no region was without water. And — "Flat. All the seas have flattened bottoms."
