Ringworld by Larry Niven Page B

heat for power."
    "U-u-urr. I begin to understand. The more puppeteers, the more heat is produced."
    "Do you understand, then, that the heat of our civilization was making our world uninhabitable?"
    Smog, thought Louis Wu. Internal combustion engines. Fission bombs and fusion rockets in the atmosphere. Industrial garbage in the lakes and oceans. It's often enough that we've half-killed ourselves in our own waste products. Without the Fertility Board, would the Earth be dying now in its own waste heat?
    "Incredible," said Speaker-To-Animals. "Why didn't you leave?"
    "Who would trust his life to the many deaths of space? Only such a one as me. Should we settle worlds with our insane?"
    "Send cargos of frozen fertilized ova. Run the ships with crews of the insane."
    "Discussions of sex make me uncomfortable. Our biology is not adapted to such methods, but doubtless we could evolve something analogous ... but to what purpose? Our population would be the same, and our world would still have been dying of its own waste heat."
    Irrelevantly, Teela said, "I wish we could see out."
    The puppeteer was astounded. "Are you sure? Are you not subject to the fear of falling?"
    "On a puppeteer ship?"
    "Ye-es. In any case, our watching cannot increase the danger. Very well." Nessus spoke musically in his own tongue, and the ship vanished.
    They could see themselves and each other; they could see four crash couches resting on emptiness, and the refreshment console in the middle. All else was black space. But five worlds glowed in white splendor behind Teela's dark hair.
    They were of equal size: perhaps twice the angular diameter of the full Moon as seen from Earth. They formed a pentagram. Four of the worlds were circled by strings of tiny, glaring lights: orbital suns giving off artificial yellow-white sunlight. These four were alike in brightness and appearance: misty blue spheres, their continental outlines invisible at this distance. But the fifth ...
    The fifth world had no orbital lights. It glowed by its own light, in patches the shapes of continents and the colors of sunlight. Between the patches was a black that matched the black of surrounding space; and this black, too, was filled with stars. The black of space seemed to encroach on continents of sunlight.
    "I've never seen anything so beautiful," said Teela, with tears in her voice. And Louis, who had seen many things, was inclined to agree.
    "Incredible," said Speaker-To-Animals. "I hardly dared believe it. You took your worlds with you."
    "Puppeteers don't trust spacecraft," Louis said absently. There was a touch of cold in the thought that he might have missed this; that the puppeteer might have chosen someone in his place. He might have died without seeing the puppeteer rosette ...
    "But how?"
    "I had explained," said Nessus, "that our civilization was dying in its own waste heat. Total conversion of energy had rid us of all waste products of civilization, save that one. We had no choice but to move our world outward from its primary."
    "Was that not dangerous?"
    "Very. Then was much madness that year. For that reason it is famous in our history. But we had purchased a reactionless, inertialess drive from the Outsiders. You may guess their price. We are still paying in installments. We had moved two agricultural worlds; we had experimented with other, useless worlds of our system, using the Outsider drive.
    "In any case, we did it. We moved our world.
    "In later millenia our numbers reached a full trillion. The dearth of natural sunlight had made it necessary to light our streets during the day, producing more heat. Our sun was misbehaving.
    "In short, we found that a sun was a liability rather than an asset. We moved our world to a tenth of a light year's distance, keeping the primary only as an anchor. We needed the farming worlds and it would have been dangerous to let our world wander randomly through space. Otherwise we would not have needed a sun at all."
    "So," said