The Complete Stories_ Volume 1 - Isaac Asimov [17]
"I 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-burned 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