Giskard said, “But this discussion is useless. It seems apparent that the crisis is nearly upon us—and since we have not even managed to work out the nature of the crisis—”
Daneel interrupted. “You are wrong, there at least, friend Giskard. I now know the nature of the crisis.”
91
One would not expect Giskard to show surprise. His face was, of course, incapable of expression. His voice possessed modulation, so that his speech sounded human and was neither monotonous nor unpleasant. That modulation, however, was never altered by emotion in any recognizable way.
Therefore, when he said, “Are you serious?” it sounded as it would have had he expressed doubt over a remark Daneel had made concerning what the weather would be like the next day. Yet, from the manner in which his head turned toward Daneel, the way in which one hand lifted, there was no doubt that he was surprised.
Daneel said, “I am, friend Giskard.”
“How did the information come to you?”
“In part, from what I was told by Madam Undersecretary Quintana at the dinner table.”
“But did you not say that you had obtained nothing helpful from her, that you supposed you had asked the wrong questions?”
“So it seemed in the immediate aftermath. On further reflection, however, I found myself able to make helpful deductions from what she had said. I have been searching Earth’s central encyclopedia through the computer outlet these past few hours—”
“And found your deductions confirmed?”
“Not exactly, but I found nothing that would refute them, which is perhaps the next best thing.”
“But is negative evidence sufficient for certainty?”
“It is not. And therefore I am not certain. Let me tell you, however, my reasoning and if you find it faulty, say so.”
“Please proceed, friend Daneel.”
“Fusion power, friend Giskard, was developed on Earth before the days of hyperspatial travel and, therefore, while human beings were to be found, only on the one planet, Earth. This is well known. It took a long time to develop practical controlled fusion power after the possibility had first been conceived and put on a sound scientific footing. The chief difficulty in converting the concept into practice involved the necessity of achieving a sufficiently high temperature in a sufficiently dense gas for a long enough time to bring about fusion ignition.
“And yet several decades before controlled fusion power had been established, fusion bombs had existed—these bombs representing an uncontrolled fusion reaction. But controlled or uncontrolled, fusion could not take place without an extremely high temperature in the millions of degrees. If human beings could not produce the necessary temperature for controlled fusion power, how could they do so for an uncontrolled fusion explosion?
“Madam Quintana told me that before fusion existed on Earth, there was another variety of nuclear reaction in existence—nuclear fission. Energy was derived from the splitting—or fission—of large nuclei, such as those of uranium and thorium. That, I thought, might be one way of achieving a high temperature.
“The encyclopedia I have this night been consulting gives very little information about nuclear bombs of any sort and, certainly, no real details. It is a taboo subject, I gather, and it must be so on all worlds,—for I have never read of such details on Aurora either, even though such bombs still exist. It is a part of history that human beings are ashamed of, or afraid of, or both, and I think this is rational. In what I did read of fusion bombs, however, I read nothing about their ignition that would have eliminated the fission bomb as the igniting mechanism. I suspect, then, that based, in part, on this negative evidence, the fission bomb was the igniting mechanism.
“But, then, how was the fission bomb ignited? Fission bombs existed before fusion bombs and if fission bombs required an ultrahigh temperature for ignition, as fusion bombs did, then there was nothing that existed before fission bombs that would supply a high enough temperature. From this, I conclude—even though the encyclopedia contained no information on the subject,—that fission bombs could be ignited at relatively low temperatures, perhaps even at room temperature. There were difficulties involved, for it took several years of unremitting effort after the discovery that fission existed before the bomb was developed. Whatever those difficulties might have been, however, they did not involve the production of ultrahigh temperatures.—Your opinion of all this, friend Giskard?”
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, “I 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.”