Cascade Point

by Timothy Zahn

  There was a mad scramble for the door, but as Carter turned to leave he found his way barred by Senator Chou. "Dr. Carter, a word with you, please."

  "I'll be up in a minute," Carter called to Rurik over Chou's shoulder. Rurik nodded and glided from the room, not bothering to use his Velcro shoes. "What is it, Senator?" Carter said when the others had gone. "Make it fast, please. I'm in a hurry."

  "What are our chances of stopping it, do you think?"

  "Is that what you wanted? I have no idea. You'll just have to wait until the rest of us know."

  "I can't wait for certainties—probabilities must do for now. I have a duty to the people of Earth. If anything goes wrong here we will have to begin taking steps to protect them, and the sooner we start the fewer will have to die."

  Carter looked at Chou with new insight. For the past several months he had seen the Senator as simply an opponent, a cardboard cutout violently and irrationally opposed to the Firefly Project. Now, suddenly, Carter saw him as a human being. "You really care about Earth, don't you?" he said softly.

  "It's my profession to care, Doctor. You may recall that I wanted the black hole placed a good distance further from Earth, where it would have been less of a danger to both the planet and the Space Colonies. I am not anti-technology, despite your side's efforts to paint me so, but I wished for a larger safety factor."

  "Senator, there wasn't a decent safety factor available. If we can't stop the runaway, Earth has had it no matter where Firefly is."

  "I don't understand."

  Carter took a deep breath. "If we can't stabilize Firefly's temperature, it will keep getting hotter and hotter. The hotter it gets, the faster it radiates its mass as energy until it basically explodes. According to current theory, in the last tenth second of its existence it will radiate with one percent of the sun's total power output."

  Chou's eyes were very wide. "Good Lord! And you allowed this—this nova to be placed in Earth orbit? You must be insane!"

  "Senator, if Firefly lets go anywhere in the solar system Earth is finished. The sun will go crazy with all that extra radiation hitting it. If the extra solar heat doesn't sterilize the inner system, the extra radiation will. But we had no real choice in the matter. I don't think more than a handful of people realize this, but if we had just ignored the black hole from the very beginning the same thing probably would have happened. Firefly was already too close to blowing. We didn't deliberately put Earth in danger, Senator; we were trying very hard to save it. And we still are. Excuse me, but I have to get to the control room."

  —

  It was an hour later before Carter was satisfied that the DeVega accelerator crews had the technique down well enough to be able to switch beam materials in the shortest possible time. The Project's chief design engineer, Felix Mahler, floated by Carter's shoulder as the control-room personnel waited for word that the changeover had been completed.

  "Santos and Trumbell are the best techs I've got," Mahler said into the brittle silence as the minutes ticked by. "If anyone can get the DeVegas going in ten minutes it's them. Matter of fact, Ray, I'll bet you they'll do it in nine."

  The speaker crackled. "Beta station; Santos. We're ready here."

  Rossetti, at the control board, didn't wait for Carter's nod. "Firing," he said.

  "Eight and a half," Mahler muttered to no one in particular. "They're better than I thought."

  Carter smiled slightly, but it was an automatic response. His full attention was on the meters that gave Firefly's luminosity and temperature, both of which had been running. The indicators jumped wildly, as always happened when a new beam was brought to strength, and Carter's heart rate jerked in sympathetic response.

  "Beam's steadying down," Rossetti muttered.

  "How's it look?" "It's hard to say, Doc. We're getting extra power just from the gravitational energy effects—since the iron atoms are heavier than neutrons—and that's fouling all our calibrations." Rossetti stared hard at the temperature indicator. "If Firefly's cooling down I can't tell from this. Not yet, anyway."

  "We could shift the feed on the other DeVegas," Mahler suggested. "That would make any temperature change more visible."

  "I'd rather not risk shutting off the neutron beams for the time that would take," Carter said. "Not until we're sure it'll do us any good. Let's give this an hour or so and see what happens."

  —

  The results after two hours were very clear. Firefly's temperature was still increasing.

  "Damn!" Carter muttered through clenched teeth. "It's got to work. Galton's numbers prove that. What's going wrong?"

  He threw a glance around the room, a glare brimming with frustration that most of the others seemed to interpret as fury. "I've looked over Galton's work, Ray," Rurik spoke up with some hesitation. "I can only think of one effect that hasn't been taken into account."

  "Well?"

  "We're dealing with iron atoms here, much larger than neutrons, and with electron clouds at—relatively—great distances. As the atoms approach Firefly, the first things to be swallowed will be an electron or two, which will leave the atom with a net positive charge. Since the black hole is also positive, the atom—the ion, now—will be deflected slightly before the nucleus gets to Firefly."

  "And some of the shots that would otherwise have hit don't make it in," Carter growled. "Makes sense. Unfortunately. Is it worth switching the other two beams, do you think?"

  "I doubt it. We'd gain a little, maybe, but most of that would be offset by the losses while the DeVegas are being altered."

  "Doc, would it help to run the beams faster?" Rossetti asked. "If the time interval between ionization and contact was smaller, the atoms wouldn't be deflected as far."

  Carter looked at Mahler and raised his eyebrows. "Possible?"

  "Sorry. These DeVegas were specially designed to deliver high-particle currents, and for technical reasons we can't boost the velocities any higher than they are now." There was a moment of silence. Then Kapoor's soft voice broke into the others' thoughts. "Dr. Carter, are you going to switch back to a neutron beam?"

  "Why? The iron atoms aren't doing any worse than the neutrons are and we'd just lose ten more minutes of beam during switchover."

  "It seemed to me, sir, that if the black hole is absorbing one or two electrons from even those atoms which are deflected—"

  Kapoor never got to finish his sentence. "My God!" Rurik exploded. "He's right, Ray. We've got to change that beam, fast."

  "Right." Carter had caught Kapoor's drift at the same time Rurik had, and his heart was pounding violently in his ears. "Felix, get your men on that beam, now."

  Mahler was already talking urgently into his intercom.

  "I don't understand, Dr. Carter," Senator Chou murmured from his left.

  Carter turned to face him. "The only thing that keeps Firefly in place is the electric field from the main plates, and for that to work Firefly has to have a heavy positive charge. Each extra electron that goes in cancels one of those charges. If the charge goes down to zero, we'll have no way of holding Firefly in the neutron beams."

  "You couldn't recapture it?"

  "Not in time. Possibly not at all."

  Mahler looked up. "Okay, Ray, Beta's down again. Santos and Trumbell will have it running with neutrons in a few minutes."

  "And I've just talked to the control room," Rossetti added. "Firefly's still holding positive charge, well within safety limits."

  Rurik leaned back in his chair. "We were lucky," he muttered to no one in particular.

  "Yes," Carter agreed. He took a deep breath and let it out slowly before continuing. "Gentlemen, we still have a crisis on our hands. We have got to find a way to get more mass into Firefly. Suggestions?"

  There was a long silence. "I don't suppose it would help to enclose Firefly in degenerate matter of some kind," Rossetti said hesitantly.

  Rurik shook his head. "We'd need better than neutron star density to make any headway—and ev
en if we could make material like that we'd never get it near Firefly. The thing's just too hot."

  Mahler looked up from a tablet he'd been writing on. "Whatever we're going to do, we have to do it fast," he announced quietly. "At the current rate of temperature increase, Firefly's radiation pressure will soon match the driving force behind the neutron beams. When that happens the DeVegas are, for all practical purposes, useless."

  Carter had to force the words out. "How long?"

  "Sixty hours. Maybe sixty-five."

  Someone muttered a shocked obscenity. Carter felt his stomach trying to curl up and die. Sixty hours! His eyes swept the room of their own volition, as if looking for a way out, and finally came to rest on Kapoor's abnormally pale face. The Indian had been right to be so gloomy, Carter thought, feeling strangely light- headed. It had been sheer folly to suppose mankind could tame even a tiny black hole. They might as well have tried to hitch a tiger to a plow....

  With a physical effort Carter shook the vertigo from his mind. He couldn't afford to go to pieces. "All right," he said. "You all know what that means. I want some ideas and some solutions. For starters"—he looked at Mahler—"I want the spare DeVega set up as close to the accelerator ring as possible." He raised a hand as the other started to object. "I know, at that distance it won't help much. But we need anything we can get, and it may at least buy us some time. Punch some holes in the shielding and collector sphere to let the beam through."

  "Right." Mahler scribbled a note. "I'll get a crew on it right now." Sliding his chair back, the engineer launched himself through the door.

  "I'm calling a recess," Carter said to the others. "We'll meet back here in an hour."

  Carter remained in his chair until the others had left, staring at the table as he gently kneaded his temples with his fingertips.

  "You look tired. You'd better get some sleep."

  Carter looked up in surprise. "I thought you'd left with the others, Senator."

  Chou shook his head, his eyes never leaving Carters face. "I meant what I said about sleep, Doctor."

  "Can't afford the time." He smiled wanly. "Why the sudden solicitude? I thought you didn't like me."

  "My likes or dislikes are of complete unimportance," Chou replied. "If anyone can come up with the solution we need, it will probably be you, and we can't afford to let your intellect break down from fatigue."

  Even to himself, Carter's laugh sounded hollow. "Some intellect. I wasted several badly needed hours with the iron atom fiasco, and damn near lost our control of Firefly in the bargain. I tell you, Senator, if we're relying on me, we might as well quit now."

  Chou was silent for a moment. "If we can't stop this, how long do we have?"

  "Until the explosion? A year, probably. If our theory is right, that is; if it isn't I have no idea. Of course, Firefly will be far too hot to approach long before that."

  "Dr. Carter... can we stop Firefly?"

  Carter shook his head slowly. "I can't see any way to do it. No way at all. My God, Senator, what's going to happen to all those people?"

  "We won't be able to evacuate them in time. Besides, where would they go? Ceres and Hestia can't absorb any excess population. Maybe we can tow the Space Colonies out of Earth orbit into the asteroid belt; they should be able to survive out there." Chou shook his head, his face a mirror of horror and pain. "But Earth has no chance."

  "No."

  Chou looked up. Carter avoided his eyes. The blame is not yours, Doctor," the Senator said. "We—mankind's leaders—made the final decision on Firefly. Ours is the responsibility. Not that laying blame helps any." He sighed. "Ironic, isn't it? For the past three centuries we have been continually worried about running out of energy, but now the final crisis arrives in the form of too much energy."

  Something brushed the edge of Carters mind. "Say that last again, will you?"

  "What? I just said our final crisis was too much energy, whereas in the past—"

  "Too much. Too much." Suddenly the fatigue was gone, dislodged from his mind by a maelstrom of new thoughts and ideas. Fumbling out his intercom, he keyed for general 'cast. "This is Carter. All senior staff, report to conference immediately."

  "Dr. Carter...?"

  Carter glanced up and smiled slightly at the Senators uneasy expression. "Don't worry, I haven't crossed my circuits; at least, not yet. You just reminded me that there are two sides to this problem and we've been ignoring one of them. Excuse me now, I have to think."

  He was still scribbling on a pad when the others arrived and took their places. "All right," he said. "First of all, has anyone else come up with anything?"

  No one spoke, but Carter could feel the drop in tension throughout the room as they realized there was a hidden promise in his question. "I don't guarantee this," he warned them, "but see what you think. So far we've been concentrating on getting more mass into Firefly. Maybe we can hit the problem from the other direction; namely, to decrease the density of the particle cloud that's keeping the neutrons out in the first place."

  "But it's not like a real, stationary cloud," Rurik objected. "It's self- regenerating, more on the order of a bathtub with a faucet at one end and a drain at the other."

  "Exactly. So we're going to enlarge the drain. What is the cloud composed of, gentlemen?"

  "Subatomic particles," Galton said. "Positive and neutral, mostly."

  "Right," Carter agreed. "Why no negative ones? Because the positive plates that hold Firefly itself in place rip away any negatives as soon as they're formed. Conversely, the plates tend to keep the positives near Firefly. The neutrals don't care either way." He handed a sketch to Mahler. "Felix, I propose setting up a pair of negatively charged plates a few meters from Firefly and where they won't block the neutron beams. What I want is to set up an extra electric field that will pull the positive particles away from Firefly without risking moving the black hole itself. Can it be done?"

  Mahler frowned at the sketch for a moment. "It'll be tricky," he said. "Any extra charge near Firefly will change the field of the main plates. What we need is stable equilibrium right at Firefly's position and a small nonzero field a few angstroms away. We'll probably need curved electrodes of some kind; the computer can figure the shape for us."

  "But be damn careful with that field," Rurik spoke up. "The black hole has got to be at a stable equilibrium point or we'll lose it."

  "I'll set up the programming myself," Mahler said, making notes beside Carter's sketch.

  "Doc, what about the neutral particles?" Rossetti asked.

  "I think we're stuck with them," Carter admitted. "But if we can decrease the density of positives even a little it may be enough." The excitement he had felt a few minutes before was wearing off and fatigue was beginning to pull at him. It was an effort to continue speaking. "If there are no further questions let's get to work. Felix, get those plates designed and built as soon as possible. The rest of you assist him or stay out of his way. That's all, then. Paul, I'll meet you in the control room in a few minutes."

  Carter had intended only to rest his eyes for a moment before rejoining the others. It was with some shock, therefore, that he dragged himself from a nightmarish dream two hours later to find himself still sitting at the deserted conference-room table. Blinking the sleep from his eyes, he pulled out his intercom. "Carter to control room," he said thickly.

  "Rurik here, Ray." "What's going on up there? Why did you let me sleep this long?"

  "We thought you needed the rest. The new electrodes have been made and tested, and Galton and Telemann have just about got them in place. There's nothing you need to do for at least a couple of more hours. Why don't you go back to sleep?"

  "In a minute." Sleep was beginning to fog his brain again, but what he had to say was vital. "Paul, when they're finished out there I want you to set up those X- ray lasers to fire at Firefly."

  "But the photons don't carry enough mass to make any real difference. Remember?"

  "Don't care about
the mass. The X-ray photons will get trapped into orbits around Firefly, either spiraling in or being absorbed by particles in the cloud. Most of those particles will be neutrals, since we're pulling away the others. Any particle that absorbs a photon will gain its kinetic energy and momentum."

  "I understand," Rurik nodded excitedly. "The neutrals will tend to move away from the black hole faster. Just like heating up a gas and making it expand, really."

  "Right. I admit it'll be a small effect—Firefly's own X-ray output is heating up that particle cloud far more than our lasers could ever hope to—but it may be worth doing, anyway."

  "Agreed. We'll get on that right away."

  Deep in Carter's subconscious the decision was made that he had done all that he could and that Firefly's fete was now in the hands of the universe. He barely managed to turn off his intercom before he was once more deeply asleep.

  —

  It was another four hours before he again awoke. This time he had the strength to go to the control room. One look at the meters was enough. "We did it," he murmured, half to himself.

  Rurik swiveled in his seat at the main board. "You're awake," he said unnecessarily. "Yes, thanks to you. Firefly's temperature is dropping steadily. We've already cut the DeVegas back to safe flux levels, and will probably be able to shut off that extra field soon. Just as well, since the two electrodes are in pretty bad shape already from radiation damage."

  "That reminds me. Did you tell me Galton was helping to install the new plates?"

  Rurik lowered his eyes. "He insisted on going. I think he felt—well, responsible for the runaway." "He's an operator, not a tech," Carter growled. "He had no business going out there." He looked around the room. "Where is he, anyway?"