Pelorat shook his head. “There, Golan, if you will excuse my saying so, you talk like a soldier or a politician. That is not the way history works.”

Trevize took a deep breath and kept his temper. “Tell me how it works, Janov. We've got two days. Educate me.”

“You can't rely on any one myth or even on any one group. I've had to gather them all, analyze them, organize them, set up symbols to represent different aspects of their content—tales of impossible weather, astronomic details of planetary systems at variance with what actually exists, place of origin of culture heroes specifically stated not to be native, quite literally hundreds of other items. No use going through the entire list. Even two days wouldn't be enough. I spent over thirty years, I tell you.

“I then worked up a computer program that searched through all these myths for common components and sought a transformation that would eliminate the true impossibilities. Gradually I worked up a model of what Earth must have been like. After all, if human beings all originated on a single planet, that single planet must represent the one fact that all origin myths, all culture—hero tales, have in common.—Well, do you want me to go into mathematical detail?”

Trevize said, “Not at the moment, thank you, but how do you know you won't be misled by your mathematics? We know for a fact that Terminus was founded only five centuries ago and that the first human beings arrived as a colony from Trantor but had been assembled from dozens—if not hundreds—of other worlds. Yet someone who did not know this could assume that Hari Seldon and Salvor Hardin, neither of whom were born on Terminus, came from Earth and that Trantor was really a name that stood for Earth. Certainly, if the Trantor as described in Seldon's time were searched for—a world with all its land surface coated with metal—it would not be found and it might be considered an impossible myth.”

Pelorat looked pleased. “I withdraw my earlier remark about soldiers and politicians, my dear fellow. You have a remarkable intuitive sense. Of course, I had to set up controls. I invented a hundred falsities based on distortions of actual history and imitating myths of the type I had collected. I then attempted to incorporate my inventions into the model. One of my inventions was even based on Terminus's early history. The computer rejected them all. Every one. To be sure, that might have meant I simply lacked the fictional talents to make up something reasonable, but I did my best”

“I'm sure you did, Janov. And what did your model tell you about Earth?”

“A number of things of varying degrees of likelihood. A kind of profile. For instance, about 90 percent of the inhabited planets in the Galaxy have rotation periods of between twenty-two and twenty-six Galactic Standard Hours. Well—“ ”

Trevize cut in. “I hope you didn't pay any attention to that, Janov. There's no mystery there. For a planet to be habitable, you don't want it to rotate so quickly that air circulation patterns produce impossibly stormy conditions or so slowly that temperature variation patterns are extreme. It's a property that's self-selective. Human beings prefer to live on planets with suitable characteristics, and then when all habitable planets resemble each other in these characteristics, some say, ‘What an amazing coincidence,’ when it's not amazing at all and not even a coincidence.”

“As a matter of fact,” said Pelorat calmly, “that's a well-known phenomenon in social science. In physics, too, I believe—but I'm not a physicist and I'm not certain about that. In any case, it is called the ‘anthropic principle’: The observer influences the events he observes by the mere act of observing them or by being there to observe them. But the question is: Where is the planet that served as a model? Which planet rotates in precisely one Galactic Standard Day of twenty-four Galactic Standard Hours?”

Trevize looked thoughtful and thrust out his lower lip. “You think that might be Earth? Surely Galactic Standard could have been based on the local characteristics of any world, might it not?”

“Not likely. It's not the human way. Trantor was the capital world of the Galaxy for twelve thousand years—the most populous world for twenty thousand years—yet it did not impose its rotation period of 1.08 Galactic Standard Days on all the Galaxy. And Terminus's rotation period is 0.91 GSD and we don't enforce ours on the planets dominated by us. Every planet makes use of its own private calculations in its own Local Planetary Day system, and for matters of interplanetary importance converts—with the help of computers—back and forth between LPD and GSD. The Galactic Standard Day must come from Earth]”

“Why is it a must?”

“For one thing, Earth was once the only inhabited world, so naturally its day and year would be standard and would very likely remain standard out of social inertia as other worlds were populated. Then, too, the model I produced was that of an Earth that rotated on its axis in just twenty-four Galactic Standard Hours and that revolved about its sun in just one Galactic Standard Year.”

“Might that not be coincidence?”

Pelorat laughed. “Now it is you who are talking coincidence. Would you care to lay a wager on such a thing happening by coincidence?”

“Well well,” muttered Trevize.

“In fact, there's more to it. There's an archaic measure of time that's called the month…”

“I've heard of it.”

“It, apparently, about fits the period of revolution of Earth's satellite about Earth. However—”

“Yes?”

“Well, one rather astonishing factor of the model is that the satellite I just mentioned is huge—over one quarter the diameter of the Earth itself.”

“Never heard of such a thing, Janov. There isn't a populated planet in the Galaxy with a satellite like that.”

“But that's good,” said Pelorat with animation. “If Earth is a unique world in its production of variegated species and the evolution of intelligence, then we want some physical uniqueness.”

“But what could a large satellite have to do with variegated species, intelligence, and all that?”

“Well now, there you hit a difficulty. I don't really know. But it's worth examination, don't you think?”

Trevize rose to his feet and folded his arms across his chest. “But what's the problem, then? Look up the statistics on inhabited planets and find one that has a period of rotation and of revolution that are exactly one Galactic Standard Day and one Galactic Standard Year in length, respectively. And if it also has a gigantic satellite, you'd have what you want. I presume, from your statement that you ‘have an excellent possibility in mind,’ that you've done just this, and that you have your world.”

Pelorat looked disconcerted. “Well, now, that's not exactly what happened. I did look through the statistics, or at least I had it done by the astronomy department and—well, to put it bluntly, there's no such world.”

Trevize sat down again abruptly. “But that means your whole argument falls to the ground.”

“Not quite, it seems to me.”

“What do you mean, not quite? You produce a model with all sorts of detailed descriptions and you can't find anything that fits. Your model is useless, then. You must start from the beginning.”

“No. It just means that the statistics on populated planets are incomplete. After all, there are tens of millions of them and some are very obscure worlds. For instance, there is no good data on the population of nearly half. And concerning six hundred and forty thousand populated worlds there is almost no information other than their names and sometimes the location. Some galactographers have estimated that there may be up to ten thousand inhabited planets that aren't listed at all. The worlds prefer it that way, presumably. During the Imperial Era, it might have helped them avoid taxation.”