is why Dr. Sarton initiated his project of humanoid robots. They were substitute men, designed to enter the City instead of us - "
"Yes. R. Daneel explained this to me."
"Do you disapprove?"
"Look," said Baley, "since we're talking to one another so freely, let me ask a question in simple words. Why have you Spacers come to Earth anyway? Why don't you leave us alone?"
Dr. Fastolfe said, with obvious surprise, "Are you satisfied with life on Earth?"
"We get along."
"Yes, but for how long will that continue? Your population goes up continuously; the available calories meet the needs only as a result of greater and greater effort. Earth is in a blind alley, man."
"We get along," repeated Baley stubbornly.
"Barely. A City like New York must spend every ounce of effort getting water in and waste out. The nuclear power plants are kept going by uranium supplies that are constantly more difficult to obtain even from the other planets of the system, and the supply needed goes up steadily. The life of the City depends every moment on the arrival of wood pulp for the yeast vats and minerals for the hydroponic plants. Air must be circulated unceasingly. The balance is a very delicate one in a hundred directions, and growing more delicate each year. What would happen to New York if the tremendous flow of input and outgo were to be interrupted for even a single hour?"
"It never has been."
"Which is no security for the future. In primitive times, individual population centers were virtually self-supporting, living on the produce of neighboring farms. Nothing but immediate disaster, a flood or a pestilence or crop failure, could harm them. As the centers grew and technology improved, localized disasters could be overcome by drawing on help from distant centers, but at the cost of making ever larger areas interdependent. In Medieval times, the open cities, even the largest, could subsist on food stores and on emergency supplies of all sorts for a week at least. When New York first became a City, it could have lived on itself for a day. Now it cannot do so for an hour. A disaster that would have been uncomfortable ten thousand years ago, merely serious a thousand years ago, and acute a hundred years ago would now be surely fatal."
Baley moved restlessly in his chair. "I've heard all this before. The Medievalists want an end to Cities. They want us to get back to the soil and to natural agriculture. Well, they're mad; we can't. There are too many of us and you can't go backward in history, only forward. Of course, if emigration to the Outer Worlds were not restricted - "
"You know why it must be restricted."
"Then what is there to do? You're tapping a dead power line."
"What about emigration to new worlds? There are a hundred billion stars in the Galaxy. It is estimated that there are a hundred million planets that are inhabitable or can be made inhabitable."
"That's ridiculous."
"Why?" asked Dr. Fastolfe, with vehemence. "Why is the suggestion ridiculous? Earthmen have colonized planets in the past. Over thirty of the fifty Outer Worlds, including my native Aurora, were directly colonized by Earthmen. Is colonization no longer possible?"
"Well..."
"No answer? Let me suggest that if it is no longer possible, it is because of the development of City culture on Earth. Before the Cities, human life on Earth wasn't so specialized that they couldn't break loose and start all over on a raw world. They did it thirty times. But now, Earthmen are all so coddled, so enwombed in their imprisoning caves of steel, that they are caught forever. You, Mr. Baley, won't even believe that a City dweller is capable of crossing country to get to Spacetown. Crossing space to get to a new world must represent impossibility squared to you. Civism is ruining Earth, sir."
Baley said angrily, "And if it does? How does it concern you people? It's our problem. We'll solve it. If not, it's our own particular road to hell."
"Better your own road to hell than another's road to heaven, eh? I know how you must feel. It is not pleasant to listen to the preaching of a stranger. Yet I wish your people could preach to us, for we, too, have a problem, one that is quite analogous to yours."
Baley smiled crookedly. "Overpopulation?"
"Analogous, not identical. Ours is underpopulation. How old would you say I was?"
The Earthman considered for a moment and then deliberately overestimated. "Sixty, I'd say."
"A hundred and sixty, you