Poul Anderson - The Shield of Time

“Too bad.” She leaned back on the sofa and, in her turn, smiled again. “Manse. Okay, then, those timecycles or hoppers or whatever you call them, they are what they are, and if you tried to explain, scientists today wouldn’t understand.”

“They’ve got a glimmering already. Non-inertial reference frames. Quantum gravity. Energy from the vacuum. Bell’s theorem was lately violated in the laboratory, wasn’t it? Or won’t that happen for another year or two? Stuff about wormholes in the continuum, Kerr metrics, Tipler machines—Not that I understand it myself. Physics was not my best subject at the Patrol Academy, by a long shot. It’ll be many thousands of years from now when the last discoveries are made and the first working space-time vehicle is built.”

She frowned, concentrating. “And … expeditions begin. Scientific, historical, cultural—commercial, I suppose? Even military? I hope not that. But I can see where they’d soon need police, a Time Patrol, to help and advise and rescue and … keep travelers in line, so you don’t get robberies or swindles or”—she grimaced—“taking advantage of people in the past. They’d be helpless against knowledge and apparatus from the future, wouldn’t they?”

“Not always. As you can testify.”

She started, then uttered a shaky laugh. “Hoo boy, can I ever! Are there many guys in history as tough and smart as Luis Castelar?”

“Enough. Our ancestors didn’t know everything we do, but they did know things we don’t, stuff we’ve forgotten or leave moldering in our libraries. And they averaged the same brains.” Everard sat forward in his chair. “Yes, mainly we in the Patrol are cops, doing the work you mentioned, plus conducting research of our own. You see, we can’t protect the pattern of events unless we know it well. That’s our basic job, protection. That’s the reason the Danellians founded our corps.”

She lifted her brows. “Danellians?”

“English version of their name in Temporal. Temporal’s our mutual language, artificial, developed to deal with the twists and turns of time travel. The Danellians—Some of them appeared, will appear, when chronokinesis was newly developed.”

He paused. His words turned low and slow. “That must have been … awesome. I met one once, for a few minutes. Didn’t get over it for weeks. Of course, no doubt they can disguise themselves when they want to, go among us in the form of human beings, if they ever want to. I’m not sure they do. They’re what comes after us in evolution, a million or more years uptime. The way we come after apes. At least that’s what most us suppose. Nobody knows for certain.”

Her eyes went large, staring past him. “How much could Australopithecus know for certain about us?” she whispered.

“Yeah.” Everard forced prosiness back into his tone. “They appeared, and commanded the founding of the Patrol. Otherwise the world, theirs and everybody’s, was doomed. It would not simply be wrecked, it would never have existed. On purpose or by accident, time travelers would change the past so much that everything future-ward of them would be something else; and this would happen again and again till—I don’t know. Till complete chaos, or the extinction of the human race, or something like that brought a halt, and time travel had never occurred in the first place.”

She had gone pale. “But that doesn’t make sense.”

“By ordinary logic, it doesn’t. Think, though. If you go into the past, you’re as free an agent as you ever were. What mystical powers has it got to constrain your actions that the present doesn’t have? None. You, Wanda Tamberly, could kill your father before he married. Not that you’d want to. But suppose, innocently bumbling around in a year when your parents were young, you did something that kept them from ever meeting each other.”

“Would I … stop existing?”

“No. You’d still be there in that year. You’ve mentioned a sister, though. She would never be born.”

“Then where would I have come from?” Impishness flickered: “Hardly from under a cabbage leaf!” and died away.

“From nowhere. From nothing. Cause-and-effect doesn’t apply. It’s sort of like quantum mechanics, scaled up from the subatomic to the human level.”

Almost audibly, tension crackled. Everard sought to bleed it off. “Don’t worry,” he said. “Things aren’t that delicately balanced in practice. The continuum is seldom easy to distort. For instance, in the case of you and your parents, your common sense would be a protective factor. Prospective time travelers are pretty carefully screened before they’re allowed to take off unsupervised. And most of what they do makes no long-range difference. Does it matter whether you or I did or did not attend a play at the Globe Theater one of the times when Shakespeare was on stage? Even if, oh, if you did cancel your parents’ marriage and your sister’s life—with all due respect, I don’t think world history would notice. Her husband-who-would-have-been would marry somebody else, and the somebody else would … happen … to be such a person that after a few generations the gene pool would be the same as it would have been anyway. The same famous descendant would be born, several hundred years from now. And so on. Do you follow?”

“You’re throwing me curve balls till it’s my head that’s spinning. But, oh, I did learn a little about relativity. World lines, our tracks through space-time. They’re like a mesh of tough rubber bands, right? Pull on them, and they’ll try to spring back to their proper, uh, configuration.”

He whistled softly. “You do catch on fast.”

She wasn’t relieved in the least. “However, there are events, people, situations where the balance is … unstable. Aren’t there? Like if some well-meaning idiot kept Booth from shooting Lincoln, maybe that’d change everything afterward?”

He nodded.

She sat straight, shivering, and gripped her knees. “Don Luis wanted—he wants to get hold of modern weapons—go back to Perú in the sixteenth century and … take charge of the Conquest, then stamp out the Protestants in Europe and drive the Muslims out of Palestine—”

“You’ve got the idea.”

Everard leaned farther forward and caught her hands in his. She clung. Hers were cold. “Don’t be afraid, Wanda,” he urged. “Yes, it is terrifying. It could turn out that you and I never had this talk today, that we and our whole world never were, not even a dream in somebody’s sleep. It’s harder to imagine and harder to take than the idea of personal annihilation when we die. How well I know. But it isn’t going to be, Wanda. Castelar is a fluke. By a freak of chance, he got hold of a timecycle and learned how to operate it. Well, he’s one man alone, otherwise ignorant; he barely escaped from here last night; the Patrol is on his trail. We’ll nail him, Wanda, and repair any damage he may have done. That’s what we’re for. Our record is pretty damn good, if I do say so myself. And I do.”

She gulped. “Okay, I believe you, Manse.” He felt warmth begin returning to the fingers between his.

“Good girl. You’re helping us a lot, you know. Your account of your experience was excellent, full of clues to what he’ll try next. I expect to gather more hints as new questions occur to me. Quite likely you’ll have suggestions of your own.”

Further reassurance: “That’s why I’m being this open with you. As I told you earlier, ordinarily it’s forbidden to reveal to outsiders that time travel goes on. More than forbidden; we’re conditioned against it, we’re unable to. But these are rather special circumstances, and I’m what they call an Unattached agent, with authority to waive the rules.”