Postulate Eight, now—
He began keying in Yimot’s calculations. Several times his trembling fingers betrayed him and he made an error; but his mind was still sharp enough to tell him instantly that he had hit the wrong key, and he backed up and repaired the damage each time. Twice, as he worked, he nearly blacked out from the intensity of his effort. But he forced himself to go on.
You are the only person in the world who can possibly do this, he told himself as he worked. And so you must.
It sounded foolish to him, and madly egocentric, and perhaps a little insane. It probably wasn’t even true. But at this stage in his exhaustion he couldn’t allow himself to consider any other premise but that of his own indispensability. All the basic concepts of this project were held in his mind, and his mind alone. He had to push himself onward until he had closed the last link in the chain. Until—
There.
The last of Yimot’s numbers went into the computer.
Athor hit the key that brought the two orbits up into view simultaneously on the middle screen, and hit the key that integrated the new number with the existing patterns.
The brilliant red ellipse that was the original theoretical orbit wavered and shifted, and suddenly it was gone. So was the yellow one of the observed orbit. Now there was only a single line on the screen, a deep, intense orange, the two orbital simulations overlapping to the last decimal place.
Athor gasped. For a long moment he studied the screen, and then he closed his eyes again and bowed his head against the edge of the desk. The orange ellipse blazed like a ring of flame against his closed eyelids.
He felt a curious sense of exultation mixed with dismay.
He had his answer, now; he had a hypothesis that he was certain would stand up to the closest scrutiny. The Theory of Universal Gravitation was valid after alclass="underline" the epochal chain of reasoning on which his fame was based would not be overthrown.
But at the same time he knew now that the model of the solar system with which he was so familiar was in fact erroneous. The unknown factor for which they had sought, the invisible giant, the dragon in the sky, was real. Athor found that profoundly upsetting, even if it had rescued his famous theory. He had thought for years that he fully understood the rhythm of the heavens, and now it was clear to him that his knowledge had been incomplete, that a great strangeness existed in the midst of the known universe, that things were not as he had always believed them to be. It was hard, at his age, to swallow that.
After a time Athor looked up. Nothing had changed on the screen. He punched in a few interrogative equations, and still nothing changed. He saw one orbit, not two.
Very well, he told himself. So the universe is not quite as you thought it was. You’d better rearrange your beliefs, then. Because you certainly can’t rearrange the universe.
“Yimot!” he called. “Faro! Beenay! All of you!”
Roly-poly little Faro was the first through the door, with beanpole Yimot just behind him, and then the rest of the Astronomy Department, Beenay, Thilanda, Klet, Simbron, and some others. They clustered just inside the entrance to his office. Athor saw by the expression of shock on their faces that he must be a frightful sight indeed, no doubt wild and haggard, his white hair standing out in all directions, his face pale, his whole appearance that of an old man right on the edge of collapse.
It was important to defuse their fears right away. This was no moment for melodrama.
Quietly he said, “Yes, I’m very tired and I know it. And I probably look like some demon out of the nether realms. But I’ve got something here that looks like it works.”
“The gravitational lens idea?” Beenay said.
“The gravitational lens is a completely hopeless concept,” Athor said frostily. “The same with the burned-out sun, the fold in space, the zone of negative mass, and the other fantastical notions we’ve been playing with all week. They’re all very pretty ideas but they don’t stand up to hard scrutiny. There is one that does, though.”
He watched their eyes widen.
Turning to the screen, he began once again to set up the numbers of Postulate Eight. His weariness dropped away as he worked: he struck no wrong keys this time, he felt no aches and pains. He had moved into a realm beyond fatigue.
“In this postulate we assume,” he said, “a non-luminous planetary body similar to Kalgash, which is in orbit not around Onos but around Kalgash itself. Its mass is considerable, in fact is nearly the same as that of Kalgash itself: sufficient to exert a gravitational force on our world that causes the perturbations of our orbit which Beenay has called to our attention.”
Athor keyed in the visuals and the solar system appeared on the screen in stylized form: the six suns, Kalgash, and the postulated satellite of Kalgash.
He turned back to face the others. They were all looking at each other uneasily. Though they were half his age, or even less, they must be having as much trouble coming to an intellectual and emotional acceptance of the whole idea of another major heavenly body in the universe as he had had. Or else they simply must think he had become senile, and somehow had slipped up in his calculations.
“The numbers supporting Postulate Eight are correct,” Athor said. “I pledge you that. And the postulate has withstood every test I could apply.”
He glared at them defiantly, looking ferociously at each of them in turn, as if to remind them that he was the Athor 77 who had given the world the Theory of Universal Gravitation, and that he had not yet taken leave of his faculties.
Beenay said softly, “And the reason why we are unable to see this satellite, sir—?”
“Two reasons,” replied Athor serenely. “Like Kalgash itself, this planetary body would shine only by reflected light. If we assume that its surface is made up largely of bluish rock—not an implausible geological likelihood—then the light reflected from it would be positioned along the spectrum in such a way that the eternal blaze of the six suns, combined with the lightscattering properties of our own atmosphere, would completely mask its presence. In a sky where several suns are shining at virtually every moment, such a satellite would be invisible to us.”
Faro said, “Provided the orbit of the satellite is an extremely large one, isn’t that so, sir?”
“Right.” Athor keyed in the second visual. “Here’s a closer look. As you see, our unknown and invisible satellite travels around us on an enormous ellipse that carries it extremely far from us for many years at a time. Not so distant that we don’t display the orbital effects of its presence in the heavens—but far enough so that ordinarily there is no possibility of our getting a naked-eye view of this dim rocky mass in the sky, and very little possibility of our discovering it even with our telescopes. Since we have no way of knowing it’s there by ordinary observation, it would be only by the wildest chance that we’d have detected it astronomically.”
“But of course we can go looking for it now,” said Thilanda 191, whose specialty was astrophotography.
“And of course we will,” Athor told her. They were coming around to the idea now, he saw. Every one of them. He knew them well enough to see that there were no secret scoffers. “Though you may find the search harder than you suspect, very definitely a needle-in-a-haystack proposition. But there’ll be an immediate appropriation for the work, that I pledge you.”
Beenay said, “One question, sir.”
“Go on.”
“If the orbit’s as eccentric as your postulate supposes, and therefore this satellite of ours, this—Kalgash Two, let’s call it for the moment—Kalgash Two is extremely distant from us during certain parts of its orbital cycle, then it stands to reason that at other parts of its cycle it’s bound to move into a position that’s very much closer to us. There has to be some range of variation even in the most perfect orbit, and a satellite traveling in a large elliptical orbit is likely to have an extreme range between the farthest and the closest points of approach to the primary.”