The End of Eternity - By Isaac Asimov Page 0,52

What were their views on the matter?"

Twissell's whisper carried the length of the table. "Cobwebs!"

But Sennor ignored that. He said, "Would you answer my question, Technician?"

Harlan said, "The Primitives gave virtually no thought to Timetravel, Computer."

"Did not consider it possible, eh?"

"I believethat's right."

"Did not even speculate?"

"Well, as to that," said Harlan uncertainly, "I believe there were speculations of sorts in some types of escape literature. I am not well acquainted with these, but I believe a recurrent theme was that of the man who returned in Time to kill his own grandfather as a child."

Sennor seemed delighted. "Wonderful! Wonderful! After all, that is at least an expression of the basic paradox of Time-travel, if we assume an indeviant Reality, eh? Now your Primitives, I'll venture to state, never assumed anything but an indeviant Reality. Am I right?"

Harlan waited to answer. He did not see where the conversation was aiming or what Sennor's deeper purposes were, and it unnerved him. He said, "I don't know enough to answer you with certainty, sir. I believe there may have been speculations as to alternate paths of time or planes of existence. I don't know."

Sennor thrust out a lower lip. "I'm sure you're wrong. You may have been misled by reading your own knowledge into various ambiguities you may have come across. No, without actual experience of Time-travel, the philosophic intricacies of Reality would be quite beyond the human mind. For instance, why does Reality possess inertia? We all know that it does. Any alteration in its flow must reach a certain magnitude before a Change, a true Change, is effected. Even then, Reality has a tendency to flow back to its original position.

"For instance, suppose a Change here in the 575th. Reality will change with increasing effects to perhaps the 600th. It will change, but with continually lesser effects to perhaps the 650th. Thereafter, Reality will be unchanged. We all know this is so, but do any of us know why it is so? Intuitive reasoning would suggest that any Reality Change would increase its effects without limit as the Centuries pass, yet that is not so.

"Take another point. Technician Harlan, I'm told, is excellent at selecting the exact Minimum Change Required for any situation. I'll wager he cannot explain how he arrives at his own choice.

"Consider how helpless the Primitives must be. They worry about a man killing his own grandfather because they do not understand the truth about Reality. Take a more likely and a more easily analyzed case and let's consider the man who in his travels through time meets himself--"

Harlan said sharply, "What about a man who meets himself?"

The fact that Harlan interrupted a Computer was a breach of manners in itself. His tone of voice worsened the breach to a scandalous extent, and all eyes turned reproachfully on the Technician.

Sennor harumphed, but spoke in the strained tone of one determined to be polite despite nearly insuperable difficulties. He said, continuing his broken sentence and thus avoiding the appearance of answering directly the unmannerly question addressed to him, "And the four subdivisions into which such an act can fall. Call the man earlier in physiotime, A, and the one later, B. Subdivision one, A and B may not see one another, or do anything that will significantly affect one another. In that case, they have not really met and we may dismiss this case as trivial.

"Or B, the later individual, may see A while A does not see B. Here, too, no serious consequences need be expected. B, seeing A, sees him in a position and engaged in activity of which he already has knowledge. Nothing new is involved.

"The third and fourth possibilities are that A sees B, while B does not see A, and that A and B see one another. In each possibility, the serious point is that A has seen B; the man at an earlier stage in his physiological existence sees himself at a later stage. Observe that he has learned he will be alive at the apparent age of B. He knows he will live long enough to perform the action he has witnessed. Now a man in knowing his own future in even the slightest detail can act on that knowledge and therefore changes his future. It follows that Reality must be changed to the extent of not allowing A and B to meet or, at the very least, of preventing A from seeing B. Then, since nothing in a Reality made un-Real