"Why not?"
"Because the past for him will now contain the factors ABC plus b. In other words, ABC+b can never equal abc. That time equation wouldn't balance. So, although b can reverse his time machine and go back to his own date, he will never find the reality of the present he left. He will always land in another of the infinite number of alternate futures coexisting. ABC+b may result in abcb, abbe, babe and so on—but never in abc!"
"I get it," Conn said. "You're trying to say that by traveling back into my past, I've switched over to a different track so that I couldn't move forward again on my original track."
"I'm trying to say more than that," Rollins broke in. "I'm saying that you'll never be able to move forward on the same track twice. In other words, that time travel is impossible in the sense that a man can take a journey to the past and return to his starting present.
"You see, you could continue to shuttle back and forth between 1941 and 2941, but although for obvious reasons you'd find the same present in 1941, you'd never find the same in 2941. There are an infinite number of alternative coexistent futures. Each time you made a round trip you'd create another infinitude of alternates. Representing each trip as an equation, here's the mathematical proof of why, once you'd traveled back in Time you could never return to your starting point—"
Rollins wrote swiftly:
(1) ABC=abc
(2) ABC+b=abc+b
(3) ABC+2b=abc+2b
(4) ABC+3b=abc+3b . . .
(n) ABC+n (b)=abc+n (b)
Conn's fingers shook, but he finally managed to get the cigarette lit. The flaring match looked dull in the bright light. Conn held the match until it seared his fingers.
He dragged on the cigarette. He thought: This is a lovely mess. It serves me right—leaving Hilda and dithering about duty to a man, to an existence I'll never see again. Maybe Dunbar will send someone else back to look for me. Maybe hell send back dozens, wondering why none return. Maybe he'll figure out what Rollins here calls the joker.
And all that while he was filled with a bitter sense of futility, the nostalgia of a man lost to everything. He wasn't even a man, he thought, he was only an alternative—a mere probability that coexisted with an infinitude of other probabilities. All the probable Conns should get together, he thought grimly, and kick him.
At last he said wearily: "What about the Swasts—and the Readers—and the fighting. This tunnel system; the castle and all that?"
Rollins smiled. "I'd have to give you a thousand years of history. This is it briefly. About nine hundred years ago, America was invaded and conquered by a horde of Nagees. Their credo was the superiority of brute strength over reason. Their symbol was the swastika from which comes their present name—" "Nagee," Conn said, "or Nazi. Of course. I should have realized. But according to history Nazism never reached America. It was defeated in Europe around 1945—"
"I said this was the history of our alternate," Rollins answered. "At any rate, the few Americans who held out and fought a guerilla war became known as Readers because of their respect for learning. That's why the mere possession of books got you into trouble with the Swasts you unfortunately aided, and why they got you out of a tight spot with us. Your books and records will be invaluable for us; but I should like to ask about the cans of celluloid pictures—"
"Motion pictures," Conn said. "My notes will show you how to build a projector. They'll do more for you than all the books. What about that castle?"
"It's the last stronghold of the Swasts in America. They took possession of that building centuries ago. Originally it had been used for something important by the Readers, but unfortunately our records don't say—"
There was a sharp knock on the door and Bradley almost shot through. Nevertheless he clamped down his impatience and waited for a chance to speak.
"Listen," Conn said, "don't think I'm ungrateful, but I'd like to get out of your world. You seem to have it nicely worked out. It's a beautiful place down here, but I'd rather not stay. I'd . . . I'd like to—"
He had to stop. The memory of Hilda choked him. When he realized how near she was, how swiftly the machine in the hill could return him to her, he trembled with eagerness.
"I'd like to recharge my batteries," Conn said. "I'd like to go back into the past and stay there. You said I'd find it the same?"
"The same." Rollins nodded. "It takes time, lots of time before the alternate futures split off and differentiate. You'll find the same 1941 you left—but I'm afraid I don't know what you mean by 'recharge.'"
"Batteries," Conn repeated. He smothered a growing sense of panic. "Accumulators—you know, generators, electricity, batteries—"
Rollins shook his head sadly. "We've been trying to recapture the lost art of electrical engineering for generations," he said. "So far it's evaded us."
"Then we'll work it out together," Conn snapped. "In my records you'll find the material necessary to recapture your lost art. In a month I'll have this place electrified, and in two months I'll be going back to—"
He broke off. Rollins' face had dissolved into an expression of incredulity mixed with childish delight. He gripped Conn's shoulders and stared, eyes filling. Then stepped forward.
"In a month" Bradley said, "there won't be anything to electrify."
"What's that?" Rollins started.
"I said there won't be anything left," Bradley answered in a queer, harsh voice. "There won't be any underground—any Readers— anything. The Swasts have returned to three-level-fifteen. They're following the lead and blasting every tunnel wide open with their lances. They'll reach the city in an hour. It's all up."
Conn finally realized what Bradley meant.
"Nothing's all up," he growled. "I'm getting back to 1941 if I have to win your war for you." He slapped Bradley and Rollins smartly on the shoulders. "Pick up your faces, Readers, I've brought a few tricks with me from a thousand years ago that're going to make a hell of a lot of difference in this future. Let's go to the council room!"
V
Faces looked up from the table as they entered. Dismayed faces. Rollins rapped his knuckles on the table.
"In the emergency," he said, "David Conn will supervise defensive tactics. Please!" He held up his hand. "I understand that Conn has come to us under highly embarrassing circumstances. I have heard his story and I assure you that I have full confidence in him. I think you will, too, when you've had time to hear his explanations. For the moment I think it would be wise to have faith in his leadership."
Rollins escorted Conn to the head of the table and seated himself alongside. There were grumbles from the others and a low whistle of surprise. Eventually they all nodded.
"The first thing," Conn said swiftly, "is arms. What have you?"
"Just the lances," Bradley answered. "That's all."
"What's the mechanism of those lances—the silent explosions?
The hot-headed young man spoke up. Rollins leaned toward Conn. "Name is Wilder," he answered. "Chief technician. Be nice to him. He didn't relish those punches."
"We really don't know," Wilder was saying. "Actually the lances are no more than self-coiling spring guns. They shoot a radioactive pellet—Uranium 237. The same isotope gives us light and heat in the form of slow radiation. We treat minute particles to disintegrate on violent contact and they induce subsidiary disintegration in the surrounding area."
"I get it," Conn said. "You use spring propulsion for gradual acceleration. If you shot the particles out too hard, they'd explode at the moment of initial impulse and blow up gun and shooter."
Wilder glowered. "That's what I was about to say."
"What's the range of your lances?"
"Thirty or forty yards."
"What about explosives. Guncotton? TNT?"
All looked blank. Conn realized that this was another lost art for the Readers. He turned quickly to Bradley.
"Just what are the Swasts doing? Coming down through the tunnels after us?"
"Hell, no
!" Bradley looked furious. "They won't come into the tunnels yet, not until they're too deep for blasting. Right now they're opening up the small capillaries from the surface. Sort of plowing them open with their lances—"
He caught himself, raised his head and stared into space. Conn, too, had sensed the vibrations. Seconds later, it seemed he heard a mutter. The sound boulders make when they rumble down the slope of a distant valley.
Bradley whispered: "No! Not yet!" He leaped to his feet and tore out of the room, Conn hard on his heels. The others followed.
Outside, under the glittering cavern ceiling, the Readers were dashing about in fright. Bradley had paused with ear cocked toward the cavern entrance. Again came the muttering rumble as the earth underneath them shook. Squads of Readers, bearing lances, were sprinting down toward the entrance. Men were herding the women and children back toward the recesses. Bradley stopped one.
"What is it?" he demanded.
The man looked weary. "Swasts!" he said. He had a kid under his arm, a two-year-old that was crying lustily. "The Swasts have come down through the tunnel—all of them. Hundreds. They're outside the gate now, trying to blast through."
As he started off with the child, Conn stopped him.
"Going out the back way?" he asked, pointing toward the recesses of the arcade.
The man shook his head. "There isn't any back way," he said. "We just hide in the depths—"
"In three hundred years," Bradley said apathetically, "the Swasts have never dared to attack us at our gates. There was never any need for more than one exit—"
Conn grabbed Bradley's arm and shook the man until he appeared to waken. "How long can you hold the gate?" Conn asked. He repeated the question until Bradley answered.
"Twelve hours, maybe. The gate's strong, but not enough—"
"Twelve hours is enough time for me!" Conn shook Bradley again. "Snap out of it. I got you into this mess and I'll get you out. You're my lieutenant, understand? Go down and see to the gates. I'll be along—"
Bradley nodded mutely. Life began to flow back into his eyes. Conn gave him a push and he galloped down the cavern toward the gate.
"Rollins!" snapped Conn. "I've got to work fast. I'll need the help of every technician you can spare—plus a squad of diggers."
"You'll have them."
"Get the diggers first. I want a shaft sent up from the cavern to the surface. You can drill, blast, dig or scratch with your fingernails—I don't care how, so long as it's done in six hours."
"You're mad," Wilder snarled. "Even granting it could be done."
"It can," interrupted a young man with a snub nose. "The rock overhead and through this entire sector is honeycombed with passages and faults. It'll be dangerous—but we can do it."
"Granting that," snapped Wilder, "there's no sense creating another hazard for us and another vantage point for the Swasts. We're trying to hold them off from one entrance. You're planning another."
"That so?" Conn eyed Wilder and wanted to punch him again. "Maybe it hasn't occurred to you that we're trapped down here. If we don't do something but quick, it won't matter how many holes the cavern's got in it. We won't be alive to know the difference."
Rollins had given the order for the diggers. The snub-nosed young man ran off to supervise. Conn took Rollins and the rest of the technicians back to the lab. The same glittering light pouring through the windows gave him the impression that less than a few moments had elapsed since he'd first sat up on the cot. It was peculiar not to have a sun that moved. Phony.
Conn glanced at the lab, then at the nervous men around him. He thought: It's all my fault. If I don't use my head and figure something out, then there won't be any more phony sun, any more Readers or cavern. It's a thousand years from 1941, but I still hate the Nazis and their children's children. I hate everything they stand for. I hate the thought of what'll happen to those strong, clean people and children, those pretty girls-
He couldn't think about that. It brought Hilda to his mind again. Conn shivered and tried to concentrate on the job ahead. He had to figure something out.
"Rollins," he said, "you don't know what I mean, but we need munitions. Explosives. Could you build up big pellets of Uranium 237—sort of bombs?"
Rollins shook his head. "Impossible," he answered. "They'd burn the men to crisps before they could get near them. There's no known insulation—"
Conn said: "Yeah." He tapped his teeth with the slate pencil and stared around the laboratory, gazing abstractedly at the bottles. They were of heavy glass—so heavy they wouldn't break if you dropped them. Conn looked at the reagents. The Readers had evidently lost the art of chemical notation, but maybe they'd rediscovered the essential ingredients of what he needed. Maybe—
"Potassium nitrate?" Conn said. "Got it? Also known as—"
"Plenty," answered Rollins.
"How about sulphur? Yes? Fine. Charcoal and wax? Yes?" Conn went into action. He lined up the technicians before him. "From now on, you boys are just cooks. Is that understood? You're to follow my instructions to the letter. Make this up. Potassium nitrate, sixty-five percent. Sulphur, two percent. Charcoal, twenty percent. Plain wax to make up the rest."
Pencils squeaked on slates. Heads nodded.
"When you've compounded this I want it packed carefully into heavy pint-sized bottles," Conn went on. He picked up a specimen. "Like this. I want the mouths corked tight. Through the corks, well into the compound, and extending at least a foot outside, I want you to run a heavy candle wick. Got that?"
He started to leave while they were still nodding. At the door he paused. "One last word, boys. Treat this mixture extra gentle, please. And if you value your lives, don't let a spark of flame come near it."
He vaulted down the stairs and set off for the cavern gate. The cavern itself was deserted. All the noncombatants had withdrawn to the deep recesses. As Conn approached the gate he passed the scattered signs of hasty flight. Children's toys, a sandal, a handful of grapes, and a little portrait painted on wood. Conn wondered if the owner would live to pick it up.
The gate itself was shuddering with palsy. The muttering rumbles continued without pause now, and Conn understood that the Swasts were blasting it continually on the other side. There were no more than a hundred and fifty Readers marshaled with lances, and for the first time Conn realized how appalling the odds were. He located Bradley.
"How goes it?" he asked.
"It could be better," Bradley said. "Thank heavens there's solid rock around that gate. It'll hold for a time. These lances can't blast through rock very quickly—only earth."
"You haven't got many men," Conn said.
Bradley looked over the little army. "We've got twenty more," he answered, "but they're busy digging to the surface. What's the general idea?"
"It's old where I come from," Conn said. "When the enemy attacks and you're fighting a losing battle, the only way to make him draw off is to counterattack him where it hurts. That's what we're going to do. Any idea where it'll hurt?"
Bradley stared. "The castle?" he gasped.
"That's it," said Conn grimly.
VI
It was two hundred feet to the surface. The shaft had been started from a side of the cavern and thrust upward a zigzag course that took advantage of every rock fault and slide. Conn tugged experimentally at the rope ladder that hung down from the open mouth of the shaft above him. The ladder still quivered from the heels of the last Reader to mount.
"That's a hundred," Bradley said. He strapped his lance across his back and looked at Conn. "Now what?"
"Go on up yourself," Conn said tensely. "Keep your men under cover up there and wait for me. I'll be along in no time to speak of."
Bradley nodded and started up the ropes. In a few seconds his mounting legs disappeared in the dark shaft mouth. Conn picked up his bulging rucksack and slung it gingerly over his shoulder. In it were twenty-five pints of destruction. He didn't relish the idea of carrying it up through the
narrow, twisting shaft. That was why he wanted his little army to be in the clear in case of accidents.
The snub-nosed mine technician placed a hand on Conn's shoulder. "Be careful going up," he said. "You're not acquainted with our terrain. This is all loose granite rock. It's honeycombed with flaws and faults, and our tunnels haven't done much to strengthen it. Too much of a jar might start a slide that would result in the settling of all the rock for miles around. This cavern—everything—would be crushed."
Conn said: "Thanks for the bedtime story." He tried to make it sound funny. To Rollins he said: "Here are your orders. Hold the gate with your skeleton crew at all costs. Only send your women and children up this ladder as a last result. The Swasts would slaughter them in open country. Don't worry. I'll get you out of this mess. I swear it!"
He started up the ladder. It quivered and shook, and his rucksack thumped slightly against his back. It was pitch black in the shaft, but the Readers had coated one strand of the rope ladder with uranium. It glowed before him like a never-ending worm.
The ladder arose for seventy feet, and Conn bruised elbows and knees against the rough shaft wall. Then be came to a small shelf. He crawled over and followed the rope along the gutter of a narrow mounting tube that had razor sides. He could hear his clothing shred, and the rucksack caught on the projections and tugged at him. The glass clinked.
A rock slipped under him and he heard it go thundering down the tube. A dull muttering began and then a creak and a whisper. He thought it must be the echo of the fall, but it sounded more like the scream of rock under pressure. Conn swallowed hard and tried to climb faster. If the shifting layers of granite cut the ladder above him—
The tube ended and the ladder mounted again. Conn climbed through open space, swinging like a pendulum. He had no idea how long he struggled. He lost count of rungs. In the black nothingness he was cut off from time altogether. But at last his groping hand touched rock and he wormed his way between two flat masses of stone barely three feet apart.