Something twitched in my left cheek. “And you could stop, knowing that it was all in your grasp?”

“Yes,” He scuffed at the base of the boulder, knelt, scooped sand, sifted it through his fingers. He did not look at me. At length he said, “Was it an act of moral grandeur, I wonder, or just an act of cowardice? What do you think, Leo?”

“You tell me.”

“Do you know where my work was heading?”

“I think I knew it before you,” I said. “But I wasn’t going to point it out. I had to let you make all the decisions. You never once indicated that you saw any of the larger implications at all, Jack. As far as I could tell, you thought you were dealing with the atomic binding forces in a vacuum of theory.”

“I was. For the first year and a half.”

“And then?”

“I met Shirley, remember? She didn’t know much about physics. Sociology, history, those were her fields. I described my work to her. She didn’t understand, so I put it in simpler terms, and then still simpler terms. It was good discipline for me, verbalizing what had really been just a bunch of equations. And finally I said that what I was doing was finding out what holds atoms together internally. And she said, ‘Does that mean we’d be able to take them apart without blowing things up?’ ‘Yes,’ I said. ‘Why, we could take any atom at all and liberate enough energy to run a house on it, I suppose.’ Shirley gave me a queer look and said, ‘That would be the end of our whole economic structure, wouldn’t it? ’ ”

“It had never occurred to you before?”

“Never, Leo. Never. I was that skinny kid from M.I.T., yes? I didn’t worry about applied technology. Shirley turned me upside down. I started calculating, then got on the phone to the library and had the computer run off some engineering texts for me, and Shirley gave me a little lecture on elementary economics. Then I saw, yes, by damn, somebody could take my equations and figure out a way of liberating unlimited energy. It was E=MC2 all over again. I panicked. I couldn’t assume the responsibility for overturning the world. My first impulse was to go to you and ask what you thought I should do.”

“Why didn’t you?”

He shrugged. “It was the cheap way out. Loading the burden onto you. Anyway, I realized that you probably saw the problem already, and that you would have said something about it to me unless you felt I ought to work out the moral part by myself. So I asked for that sabbatical, and spent my time fooling around at the accelerator while I thought things over. I looked up Oppenheimer and Fermi, and the rest of the boys who built the atomic bomb, and asked myself what I would have done in their place. They worked in wartime, to help humanity against a really filthy enemy, and even they had their doubts. I wasn’t doing anything that would save humanity from clear and present danger. I was simply whipping up a gratuitous bit of research that would smash the world’s money structure. I saw myself as an enemy of mankind.”

“With real energy conversion,” I said quietly, “there’d be no more hunger, no more greed, no more monopolies—”

“There’d also be a fifty-year upheaval while the new order of things was taking shape. And the name of Jack Bryant would be accursed. I couldn’t do it. I wasn’t able to take the responsibility. At the end of that third year, I packed myself in. I walked away from my own work and came out here. I committed a crime against knowledge to avoid committing a worse crime.”

“And you feel guilty about it?”

“Of course I do. I feel that my whole life for the past decade has been a penance for running away. Have you ever wondered about the book I’ve been writing, Leo?”

“Many times.”

“It’s a kind of autobiographical essay: an apologia pro vita sua. In it I explain what I was working on at the University, how I came to realize its true nature, why I halted work, and what my attitude toward my own withdrawal has been. The book’s an examination of the moral responsibilities of science, you could say. By way of an appendix, I include the complete text of my thesis.”

“As it was the day you stopped work?”

“No,” Jack said. “The complete text. I told you the answers were in sight when I quit. I finished my work five years ago. It’s all there in the manuscript. With a billion dollars and a decently equipped laboratory any reasonably alert corporation could translate my equations into a fully functioning power system the size of a walnut that would run forever on an input of sand.”

Just then it seemed to me as if the Earth wobbled a little on its axis. I said after a long moment, “Why did you wait this long to bring the subject up?”

“That stupid newscast the other night gave me the push. The so-called man from 2999, with his idiot talk of a decentralized civilization in which every man is self-sufficient because he’s got full energy conversion. It was like having a vision of the future — a future that I helped to shape.”

“Surely you don’t believe—”

“I don’t know, Leo. It’s a load of nonsense to imagine a man dropping in on us from a thousand years ahead. I was as convinced as you were that the man was all phony… until he started describing the decentralization thing.”

“The idea of complete liberation of atomic energy has been around for a long time, Jack. This fellow’s clever enough to grab it up and use it. It doesn’t necessarily mean that he really is from the future and that your equations have actually gone into use. Forgive me, Jack, but I think you’re overestimating your own uniqueness. You’ve taken an idea out of the floating pool of futuristic dreams and turned it into reality, yes, but no one except you and Shirley knows that, and you mustn’t let his random shot fool you into thinking—”

“But suppose it is true, Leo?”

“If you’re really worried about it, why don’t you burn your manuscript?” I suggested.

He looked as shocked as if I had proposed self-mutilation.

“I couldn’t do that.”

“You’d protect mankind against the upheaval that you seem to feel advance guilt for causing.”

“The manuscript’s safe enough, Leo.”

“Where?”

“Downstairs. I’ve built a vault for it and rigged up a deadfall in the house reactor. If anyone tries to enter the vault improperly, the safeties come out of the reactor and the house blows sky high. I don’t need to destroy what I’ve written. It’ll never fall into the wrong hands.”

“Yet you assume it has fallen into the wrong hands, somewhere in the next thousand years; so that by the time Vornan-19 is born, the world is already living on your power system. Right?”

“I don’t know, Leo. The whole thing is crazy. I think I’m going crazy myself.”

“Let’s say for argument’s sake that Vornan-19 is genuine and that such a power system is in use in A.D. 2999. Yes? Okay, but we don’t know that it’s the system you devised. Suppose you burn your manuscript. The act of doing that would change the future so that the economy described by Vornan-19 would never have come into existence. He himself might wink out of existence the moment your book went into the incinerator. And that way you’d know that the future was saved from the terrible fate you had created for it.”

“No, Leo. Even if I burned the manuscript, I’d still be here. I could recreate my equations from memory. The menace is in my brain. Burning the book would prove nothing.”

“There are memory-washing drugs—”

He shuddered. “I couldn’t trust those.”

I looked at him in horror. With a sensation like that of falling through a trapdoor, I made contact with Jack’s paranoia for the first time; and the healthy, tanned extrovert of these desert years vanished forever. To think that he had come to this! Tied in knots over the possibility that a shrewd but implausible fraud represented a veritable ambassador from a distant future shaped by Jack’s own suppressed creation!