'How's that?' I said.

'What I mean is that some of the radioactivity is evenly spread throughout the time of translation as if the material tested had been reacting during backward passage through time by a constant amount. My figures show that - well, if you were to be moved backward in time, you would age one day for every hundred years. Or, to put it another way, if you could watch a time dial which recorded the time outside a "time-machine," your watch would move forward twenty-four hours while the time dial moved back a hundred years. That's a universal constant, I think, because the speed of light is a universal constant. Anyway, that's my work.'

After a few minutes, in which I chewed all this, I asked: 'Where did you get the energy needed for your experiments?'

'They ran out a special line from the power plant. Pop's a big shot there, and swung the deal.'

'Hm-m-m. What was the heaviest amount of material you sent into the past?'

'Oh' - he sent his eyes upwards - 'I think we shot back one hundredth of a milligram once. That's ten micrograms.'

'Ever try sending anything into the future?'

That won't work,' he put in quickly. 'Impossible. You can't change signs like that, because the energy required becomes more than infinite. It's a one-way proposition.'

I looked hard at my fingernails: 'How much material could you send back in time if you fissioned about… oh, say, one hundred pounds of plutonium.' Things, I thought, were becoming, if anything, too obvious.

The answer came quickly: 'In plutonium fission,' he said, 'not more than one or two percent of the mass is converted into energy. Therefore, one hundred pounds of plutonium when completely used up would send a pound or two back into time.'

'Is that all? But could you handle all that energy? I mean, a hundred pounds of plutonium can make quite an explosion.'

'All relative,' he said, a bit pompously. 'If you took all that energy and let it loose a little at a time, you could handle it. If you released it all at once, but used it just as fast as you released it, you could still handle it. In sending back material through time, energy can be used much faster than it can possibly be released even through fission. Theoretically, anyway.'

'But how do you get rid of it?'

'It's spread through time, naturally. Of course, the minimum time through which material could be transferred would, therefore, depend on the mass of the material. Otherwise, you're liable to have the energy density with time too high.'

'All right, kid,' I said. 'I'm calling up headquarters, and they'll send a man here to take you home. You'll stay there a while.'

'But - What for?'

'It won't be for long.'

It wasn't - and it was made up to him afterwards.

I spent the evening at Headquarters. We had a library there - a very special kind of library. The very morning after the explosion, two or three operators had drifted quietly into the chemistry and physics libraries of the University. Experts in their way. They located every article Tywood had ever published in any scientific journal and had snapped each page. Nothing was disturbed otherwise.

Other men went through magazine files and through book lists. It ended with a room at Headquarters that represented a complete Tywoodana. Nor was there a definite purpose in doing this. It merely represented part of the thoroughness with which a problem of this sort is met.

I went through that library. Not the scientific papers. I knew there'd be nothing there that I wanted. But he had written a series of articles for a magazine twenty years back, and I read those. And I grabbed at every piece of private correspondence they had available.

After that, I just sat and thought - and got scared.

I got to bed about four in the morning and had nightmares.

But I was in the Boss' private office at nine in the morning just the same.

He's a big man, the Boss, with iron-gray hair slicked down tight. He doesn't smoke, but he keeps a box of cigars on his desk and when he doesn't want to say anything for a few seconds, he picks one up, rolls it about a little, smells it, then sticks it right into the middle of his mouth and lights it in a very careful way. By that time, he either has something to say or doesn't have to say anything at all. Then he puts the cigar down and lets it burn to death.

He used up a box in about three weeks, and every Christmas, half his gift-wraps held boxes of cigars.

He wasn't reaching for any cigars now, though. He just folded his big fists together on the desk and looked up at me from under a creased forehead. 'What's boiling?'

I told him. Slowly, because micro-temporal-translation doesn't sit well with anybody, especially when you call it time travel, which I did. It's a sign of how serious things were that he only asked me once if I were crazy.

Then I was finished and we stared at each other.

He said: 'And you think he tried to send something back in time - something weighing a pound or two - and blew an entire plant doing it?'

'It fits in,' I said.

I let him go for a while. He was thinking and I wanted him to keep on thinking. I wanted him, if possible, to think of the same thing I was thinking, so that I wouldn't have to tell him -

Because I hated to have to tell him -

Because it was nuts, for one thing. And too horrible, for another.

So I kept quiet and he kept on thinking and every once in a while some of his thoughts came to the surface.

After a while, he said: 'Assuming the student, Howe, to have told the truth - and you'd better check his notebooks, by the way, which I hope you've impounded -'

'The entire wing of that floor is out of bounds, sir. Edwards has the notebooks.'

He went on: 'All right. Assuming he told us all the truth he knows, why did Tywood jump from less than a milligram to a pound?'

His eyes came down and they were hard: 'Now you're concentrating on the time-travel angle. To you, I gather, that is the crucial point, with the energy involved as incidental -purely incidental.'

'Yes, sir,' I said grimly. 'I think exactly that.'

'Have you considered that you might be wrong? That you might have matters inverted?'

'I don't quite get that.'

'Well, look. You say you've read up on Tywood. All right. He was one of that bunch of scientists after World War II that fought the atom bomb; wanted a world state - You know about that, don't you?'

I nodded.

'He had a guilt complex,' the Boss said with energy. 'He'd helped work out the bomb, and he couldn't sleep nights thinking of what he'd done. He lived with that fear for years. And even though the bomb wasn't used in World War III, can you imagine what every day of uncertainty must have meant to him? Can you imagine the shriveling horror in his soul as he waited for others to make the decision at every crucial moment till the final Compromise of Sixty-Five?

'We have a complete psychiatric analysis of Tywood and several others just like him, taken during the last war. Did you know that?'

'No, sir.'

'It's true. We let up after Sixty-Five, of course, because with the establishment of world control of atomic power, the scrapping of the atomic bomb stockpile in all countries, and the establishment of research liaison among the various spheres of influence on the planet, most of the ethical conflict in the scientific mind was removed.

'But the findings at the time were serious. In 1964, Tywood had a morbid subconscious hatred for the very concept of atomic power. He began to make mistakes, serious ones. Eventually, we were forced to take him off research of any kind. And several others as well, even though things were pretty bad at the time. We had just lost India, if you remember.'

Considering that I was in India at the time, I remembered. But I still wasn't seeing his point.

'Now, what,' he continued, 'if dregs of that attitude remained buried in Tywood to the very end? Don't you see that this time-travel is a double-edged sword? Why throw a pound of anything into the past, anyway? For the sake of proving a point? He had proved his case just as much when he sent back a fraction of a milligram. That was good enough for the Nobel Prize, I suppose.

'But there was one thing he could do with a pound of matter that he couldn't do with a milligram, and that was to drain a power plant. So that was what he must have been after. He had discovered a way of consuming inconceivable quantities of energy. By sending back eighty pounds of dirt, he could remove all the existing plutonium in the world. End atomic power for an indefinite period.'

I was completely unimpressed, but I tried not to make that too -plain. I just said: 'Do you think he could possibly have thought he could get away with it more than once?'

'This is all based on the fact that he wasn't a normal man. How do I know what he could imagine he could do? Besides, there may be men behind him - with less science and more brains - who are quite ready to continue onwards from this point.'

'Have any of these men been found yet? Any evidence of such men?'

A little wait, and his hand reached for the cigar box. He stared at the cigar and turned it end for end. Just a little wait more. I was patient.

Then he put it down decisively without lighting it.

'No,' he said.

He looked at me, and clear through me and said: 'Then, you still don't go for that?'

I shrugged, 'Well - It doesn't sound right.'

'Do you have a notion of your own?'

'Yes. But I can't bring myself to talk about it. If I'm wrong, I'm the wrongest man that ever was; but if I'm right, I'm the rightest.'

'I'll listen,' he said, and he put his hand under the desk.

That was the pay-off. The room was armored, sound-proof, and radiation-proof to anything short of a nuclear explosion. And with that little signal showing on his secretary's desk, the President of the United States couldn't have interrupted us.

I leaned back and said: 'Chief, do you happen to remember how you met your wife? Was it a little thing?'

He must have thought it a non sequitur. What else could he have thought? But he was giving me my head now; having his own reasons, I suppose.

He just smiled and said: 'I sneezed and she turned around. It was at a street corner.'

'What made you be on that street corner just then? What made her be? Do you remember just why you sneezed? Where you caught the cold? Or where the speck of dust came from? Imagine how many factors had to intersect in just the right place at just the right time for you to meet your wife,'

'I suppose we would have met some other time, if not then?'

'But you can't know that. How do you know whom you didn't meet, because once when you might have turned around, you didn't; because once when you might have been late, you weren't. Your life forks at every instant, and you go down one of the forks almost at random, and so does everyone else. Start twenty years ago, and the forks diverge further and further with time.