He wasn't sure Potterley knew what he was talking about. He didn't care. He needed a breather. He had to get some of this out of his clotting thoughts. . . . And he needed background for what he would have to tell Potterley next.
He went on. "It was Sterbinski who first discovered that the neutrino broke through the space-time cross-sectional barrier, that it traveled through time as well as through space. It was Sterbinski who first devised a method for stopping neutrinos. He invented a neutrino recorder and learned how to interpret the pattern of the neutrino stream. Naturally, the stream had been affected and deflected by all the matter it had passed through in its passage through time, and the deflections could be analyzed and converted into the images of the matter that had done the deflecting. Time viewing was possible. Even air vibrations could be detected in this way and converted into sound."
Potterley was definitely not listening. He said, "Yes. Yes. But when can you build a chronoscope?"
Foster said urgently, "Let me finish. Everything depends on the method used to detect and analyze the neutrino stream. Sterbinski's method was difficult and roundabout. It required mountains of energy. But I've studied pseudo-gravities, Dr. Potterley, the science of artificial gravitational fields. I've specialized in the behavior of light in such fields. It's a new science. Sterbinski knew nothing of it. If he had, he would have seen-anyone would have-a much better and more efficient method of detecting neutrinos using a pseudo-gravitic field. If I had known more neutrinics to begin with, I would have seen it at once."
Potterley brightened a bit. "I knew it," he said. "Even if they stop research in neutrinics there is no way the government can be sure that discoveries in other segments of science won't reflect knowledge on neutrinics. So much for the value of centralized direction of science. 1 thought this long ago, Dr. Foster, before you ever came to work here."
"1 congratulate you on that," said Foster, "but there's one thing-"
"Oh, never mind all this. Answer me. Please. When can you build a chronoscope?"
"I'm trying to tell you something, Dr. Potterley. A chronoscope won't do you any good." (This is it, Foster thought.)
Slowly, Potterley descended the stairs. He stood facing Foster. "What do you mean? Why won't it help me?"
"You won't see Carthage. It's what I've got to tell you. It's what I've been leading up to. You can never see Carthage."
Potterley shook his head slightly. "Oh, no, you're wrong. If you have the chronoscope, just focus it properly-"
"No, Dr. Potterley. It's not a question of focus. There are random factors affecting the neutrino stream, as they affect all subatomic particles. What we call the uncertainty principle. When the stream is recorded and interpreted, the random factor comes out as fuzziness, or 'noise' as the communications boys speak of it. The further back in time you penetrate, the more pronounced the fuzziness, the greater the noise. After a while, the noise drowns out the picture. Do you understand?"
"More power," said Potterley in a dead kind of voice.
"That won't help. When the noise blurs out detail, magnifying detail magnifies the noise, too. You can't see anything in a sun-bumed film by enlarging it, can you? Get this through your head, now. The physical nature of the universe sets limits. The random thermal motions of air molecules set limits to how weak a sound can be detected by any instrument. The length of a light wave or of an electron wave sets limits to the size of objects that can be seen by any instrument. It works that way in chronoscopy, too. You can only time view so far."
"How far? How far?"
Foster took a deep breath. "A century and a quarter. That's the most."
"But the monthly bulletin the Commission puts out deals with ancient history almost entirely." The historian laughed shakily. "You must be wrong. The government has data as far back as 3000 b.c."
"When did you switch to believing them?" demanded Foster, scornfully. "You began this business by proving they were lying; that no historian had made use of the chronoscope. Don't you see why now? No historian, except one interested in contemporary history, could. No chronoscope can possibly see back in time further than 1920 under any conditions."
"You're wrong. You don't know everything," said Potterley.
"The truth won't bend itself to your convenience either. Face it. The IJ&vernment's part in this is to perpetuate a hoax." of'Why?"
"I don't know why."
Potterley's snubby nose was twitching. His eyes were bulging. He pleaded, "It's only theory, Dr. Foster. Build a chronoscope. Build one and try."
Foster caught Potterley's shoulders in a sudden, fierce grip. "Do you think I haven't? Do you think I would tell you this before I had checked it every way I knew? I have built one. It's all around you. Look!"
He ran to the switches at the power leads. He flicked them on, one by one. He turned a resistor, adjusted other knobs, put out the cellar lights. "Wait. Let it warm up."
There was a small glow near the center of one wall. Potterley was gibbering incoherently, but Foster only cried again, "Look!"
The light sharpened and brightened, broke up into a light-and-dark pattern. Men and women! Fuzzy. Features blurred. Arms and legs mere streaks. An old-fashioned ground car, unclear but recognizable as one of the kind that had once used gasoline-powered internal-combustion engines, sped by.
Foster said, "Mid-twentieth century, somewhere. I can't hook up an audio yet so this is soundless. Eventually, we can add sound. Anyway, mid-twentieth is almost as far back as you can go. Believe me, that's the best focusing that can be done."