Giskard had kept his eyes steadily on Daneel throughout his explanation and he now said, "I think the structure you have built up has serious weak points, friend Daneel, and therefore may not be very trustworthy—but even if it were all perfectly sound, surely this has nothing to do with the possible forthcoming crisis that we are laboring to understand."
Daneel said, plead for your patience, friend Giskard, and I will continue. As it happens, both the fusion process and the fission process are expressions of the weak interactions, one of the four interactions that control all events in the Universe. Consequently, the same nuclear intensifier that will explode a fusion reactor will also explode a fission reactor.
"There is, however, a difference. Fusion takes place only at ultrahigh temperatures. The intensifier explodes the ultrahot portion of the fuel that is actively undergoing fusion, plus some of the surrounding fuel that is heated to fusion in the initial explosion—before the material is blown explosively outward and the heat is dissipated to the point where other quantities of fuel present are not ignited. Some of the fusion fuel is exploded, in other words, but a good deal perhaps even most—is not. The explosion is powerful enough even so, of course, to destroy the fusion reactor and anything in its immediate neighborhood, such as a ship carrying the reactor.
"On the other hand, a fission reactor can operate at low temperatures, perhaps not much above the boiling point of water, perhaps even at room temperature. The effect of the nuclear intensifier, then, will be to make all the fission fuel go. Indeed, even if the fission reactor is not actively working, the intensifier will explode it. Although, gram for gram, I gather that fission fuel liberates less energy than fusion fuel, the fission reactor will produce the greater explosion because more of its fuel explodes than in the case of the fusion reactor."
Giskard nodded his head slowly and said, "All this may well be so, friend Daneel, but are there any fission power stations on Earth?"
"No, there aren't—not one. So Undersecretary Quintana seemed to indicate and the encyclopedia seems to agree. Indeed, whereas there are devices on Earth that are powered by small fusion reactors, there is nothing—nothing at all—that is powered by fission reactors, large or small."
"Then, friend Daneel, there is nothing for a nuclear intensifier to act upon. All your reasoning, even were it impeccable, ends in nothing."
Daneel said earnestly, "Not quite, friend Giskard. There remains a third type of nuclear reaction to be taken into consideration."
Giskard said, "What might that be? I cannot think of a third."
"It is not an easy thought, friend Giskard, for on the Spacer and Settler worlds, there is very little uranium and thorium in the planetary crusts and, therefore, very little in the way of obvious radioactivity. The subject is of little interest, in consequence, and is ignored by all but a few theoretical physicists. On Earth, however, as Madam Quintana pointed out to me, uranium and thorium are comparatively common, and natural radioactivity, with its ultraslow production of heat and energetic radiation, must therefore be a comparatively prominent part of the environment. That is the third type of nuclear reaction to be taken into consideration."
"In what way, friend Daneel?"
"Natural radioactivity is also an expression of the weak interaction. A nuclear intensifier that can explode a fusion reactor or a fission reactor can also accelerate natural radioactivity to the point, I presume, of exploding a section of the crust—if enough uranium or thorium is present."
Giskard stared at Daneel for a period of time without moving or speaking. Then he said softly, "You suggest, then, that it is Dr. Amadiro's plan to explode Earth's crust, destroy the planet as an abode of life, and, in this way, ensure the domination of the Galaxy by the Spacers."
Daneel nodded. "Or, if there is not enough thorium and uranium for mass explosion, the increase of radioactivity may produce excess heat that will alter the climate, and excess radiation that will produce cancer and birth defects, and these will serve the same purpose—if a bit more slowly."
Giskard said, "This is an appalling possibility. Do you think it can really be brought about?"
"Possibly. It seems to me that for several years now—just how many I do not know—humanoid robots from Aurora, such as the would-be-assassin—have been on Earth. They are advanced enough for complex programming and are capable, when needed, of entering the Cities for equipment. They have, it is to be presumed, been setting up nuclear intensifiers in places where the soil is rich in uranium or thorium. Perhaps many intensifiers have been set up over the years. Dr. Amadiro and Dr. Mandamus are here now to oversee the final details and to activate the intensifiers. Presumably, they are arranging matters so that they will have time to escape before the planet is destroyed."
"In that case," said Giskard, "it is imperative that the Secretary-General be informed, that Earth's security forces be mobilized at once, that Dr. Amadiro and Dr. Mandamus be located without delay, and that they be restrained from completing their project."
Daneel said, "I do not think that can be done. The Secretary-General is very likely to refuse to believe us, thanks to the widespread mystical belief in the inviolability of the planet. You have referred to that as something that would work against humanity and I suspect that is just what it will do in this case. If his belief in the unique position of Earth is challenged, he will refuse to allow his conviction, however irrational, to be shaken and he will seek refuge by refusing to believe us.
"Then, too, even if he believed us, any preparation for counter-measures would have to go through the governmental bureaucracy and, no matter how that process was speeded, it would take far too long to serve its purpose.
"Not only that but, even if we could imagine the full resources of Earth mobilized at once, I do not think Earthpeople are adapted to locate the presence of two human beings in an enormous wilderness. The, Earthpeople have lived in the Cities for many scores of decades and almost never venture beyond the City confines. I remember that well from the occasion of my first case with Elijah Baley here on Earth. And even if Earthpeople could force themselves to tramp the open spaces, they are not likely to come across the two human beings soon enough to save the situation except by the most incredible of coincidences—and that is something we cannot count upon."
Giskard said, "Settlers could easily form a search party. They are not afraid of open environments or of strange ones."
"But they would be as firmly convinced in the planet's inviolability as Earthpeople are, just as insistent on refusing to believe us, and just as unlikely to find the two human beings quickly enough to save the situation—even if they should believe us."
"What of Earth's robots, then?" said Giskard. "They swarm in the spaces between the Cities. Some should already be aware of human beings in their midst. They should be questioned."
Daneel said, "The human beings in their midst are expert roboticists. They would not have failed to see to it that any robots in their vicinity remain unaware of their presence. Nor, for this same reason, need they fear danger from any robots who might be part of a searching party. The party will be ordered to depart and forget. To make it worse, Earth's robots are comparatively simple models, designed for very little more than for specific tasks in growing crops, herding animals, and operating mines. They cannot easily be adapted to such a general purpose as conducting a meaningful search."
Giskard said, "You have eliminated every possible action, friend Daneel? Does anything remain?"
Daneel said, "We must find the two human beings ourselves and we must stop them—and we must do it now."
"Do you know where they are, friend Daneel?"
"I do not, friend Giskard."
"Then if it seems unlikely that an elaborate search party composed of many, many Earthpeople, or Settlers, or robots, or, I presume, all three, could succeed in finding their location in time except by the most marvelous of coincidences, how can we two do so?"
"I do not know, friend Giskard, but we must."
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And Giskard said, in a voice that seemed to have an edge of harshness in its choice of words, "Necessity is not enough, friend Daneel. You have come a long way. You have worked out the existence of a crisis and, bit by bit, you have worked out its nature. And none of it serves. Here we remain, as helpless as ever to do anything about it."
Daneel said, "There remains one chance—a farfetched one, an all-but-useless one—but we have no choice except to try. Out of Amadiro's fear of you, he sent an assassin robot to destroy you and that may turn out to have been his mistake."
"And if that all-but-useless chance fails, friend Daneel?"
Daneel looked calmly at Giskard. "Then we are helpless, and Earth will be destroyed, and human history will dwindle to an eventual end."
18. THE ZEROTH LAW
84.
Keldon Amadiro was not happy. The surface gravity of Earth was a trifle too high for his liking, the atmosphere a trifle too dense, the sound and the odor of the outdoors subtly and annoyingly different from that on Aurora, and there was no indoors that could make any pretense of being civilized.
The robots had built shelters of a sort. There were ample food supplies and there were makeshift privies that were functionally adequate but offensively inadequate in every other way.
Worst of all, though the morning was pleasant enough, it was a clear day and Earth's too-bright sun was rising. Soon the temperature would be too high, the air would be too damp, and the biting insects would appear. Amadiro had not understood, at first, why there should be small itching swellings on his arms till Mandamus explained.
Now he mumbled, as he scratched, "Dreadful! They might carry infections."
"I believe," said Mandamus with apparent indifference, "that they sometimes do. It isn't likely, however. I have lotions to relieve the discomfort and we can burn certain substances that the insects find offensive, although I find the odors offensive, too."
"Burn them," said Amadiro.
Mandamus continued, without changing tone, "And I don't want to do anything, however trifling—an odor, a bit of smoke—that would increase the chance of our being detected."
Amadiro eyed him suspiciously. "You have said, over and over, that this region is never visited by either Earthpeople or their field robots."
"That's right, but it's not a mathematical proposition. It's a sociological observation and there is always the possibility of exceptions to such observations."
Amadiro scowled. "The best road to safety lies with being done with this project. You said you'd be ready today."
"That, too, is a sociological observation, Dr. Amadiro. I should be ready today. I would like to be. I cannot guarantee it mathematically."
"How long before you can guarantee it?"
Mandamus spread his hands in a "Who knows?" gesture. "Dr. Amadiro, I am under the impression I have already explained this, but I'm willing to go through it again. It took me seven years to get this far. I have been counting on some months yet of personal observations at the fourteen different relay stations on Earth's surface. I can't do that now because we must finish before we are located and, possibly, stopped by the robot Giskard. That means I have to do my checking by communicating with our own humanoid robots at the relays. I can't trust them as I would myself. I must check and recheck their reports and it is possible that I may have to go to one or two places before, I am satisfied. That would take days—perhaps a week or two."
"A week or two. Impossible! How long do you think I can endure this planet, Mandamus?"
"Sir, on one of my previous visits I stayed on this planet for nearly a year—on another, for over four months."
"And you liked it?"
"No, sir, but I had a job to do and I did it—without sparing myself." Mandamus stared coldly at Amadiro.
Amadiro flushed and said in a somewhat chastened tone, "Well, then, where do we stand?"
"I'm still weighing the reports that are coming in. We are not working with a smoothly designed laboratory-made system, you know. We have an extraordinary heterogeneous planetary crust to deal with. Fortunately, the radioactive materials are widely spread, but in places they run perilously thin, and we must place a relay in such places and leave robots in charge. If those relays are not, in every case, properly positioned and in proper order, the nuclear intensification will die out and we will have wasted all these painful years of effort on nothing. Or else, there may be a surge of localized intensification that will have the force of an explosion that will blow itself out and leave the rest of the crust unaffected. In either case, total damage would be insignificant.
"What we want, Dr., Amadiro, is to have the radioactive materials and, therefore, significantly large sections of earth's crust grow—slowly—steadily—irreversibly"—he bit the words off as he pronounced them in spaced intervals—"more and more intensely radioactive, so that Earth becomes progressively more unlivable. The social structure of the planet will break down and the Earth, as an effective abode of humanity, will be over and done with. I take it, Dr. Amadiro, that this is what you want. It is what I described to you years ago and what you said, at that time, you wanted."
"I still do, Mandamus. Don't be a fool."
"Then bear with the discomfort, sir—or else, leave and I will carry on for whatever additional time it takes."
"No, no," muttered Amadiro. "I must be here when it's done—but I can't help being impatient. How long have you decided to allow the process to build? —I mean, once you initiate the original wave of intensification, how long before Earth becomes uninhabitable?"
"That depends on the degree of intensification I apply initially. I don't know, just yet, what degree will be required, for that depends on the overall efficiency of the relays, so I have prepared a variable control. What I want to arrange is a lapse period of ten to twenty decades."
"And if you allow a smaller lapse period?"
"The less the lapse period we allow, the more rapidly portions of the crust will grow radioactive and the more rapidly the planet will warm up and grow dangerous. And that means the less likely it will be that any significant number of its population can be removed in time."
"Does that matter?" murmured Amadiro.
Mandamus frowned. "The more rapidly the Earth deteriorates, the more likely it is that Earthpeople and Settlers will suspect a technological cause—and that we are the likely ones to receive the blame. The Settlers will then attack us with fury and, in the cause of their holy world, they will fight to extinction, provided only that they can inflict substantial harm on us. This is something we have discussed before and it seems we agreed on the matter. It would be far better to allow ample time, during which we can prepare for the worst and during which a confused Earth may assume that the slowly increasing radioactivity is some natural phenomenon they don't understand. That is something that has become more urgent today than yesterday, in my judgment."
"Is that so?" Amadiro, was frowning also. "You have that sour, puritanical look that makes me sure you have found a way to place the responsibility for that on my shoulders."
"With respect, sir, that is not difficult in this case. It was unwise to send out one of our robots to destroy Giskard."
"On the contrary, it had to be done. Giskard is the only one who might destroy us."
"He must find us first—and he won't. And even if he does, we are knowledgeable roboticists. Don't you think we could handle him?"
"Indeed?" said Amadiro. "So Vasilia thought and she knew Giskard better than we—and yet she couldn't handle him. And somehow the warship that was to take him into charge and destroy him at a distance could not handle him. So he has now landed on Earth. One way or another, he must be destroyed."
"He has, not been. There has been no report of it."
"Bad news is sometimes repressed by a prudent government—and Earth officials, though barbarians, might conceivably be prudent. And if our robot failed and was questioned, he would certainly go into irreversible block. That means we will have los
t a robot, something we can afford to do, but nothing more. And if Giskard should still be at large, the more reason we have to hurry."
"If we have lost a robot, we have lost more than a robot if they manage to elicit the location of this center of operations. We ought, at least, not to have used a local robot."
"I used one that was immediately available. And he will reveal nothing. You can trust my programming, I think."
"He cannot help reveal, by his mere existence, whether frozen or not, that he is of Auroran manufacture. Earth roboticists—and there are some on this planet—will be sure of that. All the more reason to make the increase in radioactivity very slow. Enough time must pass so that Earthpeople forget the incident and don't associate it with the progressive change in radioactivity. We must have ten decades at the very least, perhaps fifteen, or even twenty."
He walked away to inspect his instruments again and to re-establish contact with relays six and ten, which he still found troublesome. Amadiro looked after him with a mixture of disdain and intense dislike and muttered to himself, "Yes, but I don't have twenty more decades, or fifteen, or maybe even ten. You do—but I don't."
85.
It was early morning in New York. Giskard and Daneel assumed that from the gradual heightening of activity.
"Somewhere above and outside the City," said Giskard, "it may be dawn now. Once, in speaking to Elijah Baley twenty decades ago, I referred to Earth as the World of the Dawn. Will it continue to be so for much longer? Or has it already ceased to be that?"