"One thing I have not explained is that, as we have it developed now, our time travel capability is in one direction only. We can go into the past; we cannot move futureward.
So, if any advance party is sent back and finds the situation untenable, they have no recourse other than to stay there. Our great fear is that we may have to keep readjusting the destination of the tunnels and may have to send out, and abandon, several advance parties. We hope not, of course, but it is a possibility, and if necessary it will be done. Our people, gentlemen, are quite prepared to face such a situation. We have men up in your future guarding the tunnel heads who do not expect to travel though the tunnels. They are well aware that there will come a time when each tunnel must be destroyed and that they and whoever else may not have made it through the tunnels must then face death.
"I don't tell you this to enlist your sympathy. I only say it to assure you that whatever dangers there may be we are quite willing ourselves to face. We shall not call upon you for more than you are willing to give. We shall be grateful, of course, for anything that you may do."
"Kindly as I may feel toward you," said the Secretary of State, "and much as I am disposed, short of a certain natural skepticism, to believe what you have told us, I am considerably puzzled by some of the implications. What is happening now, right here this minute, will become a matter of historical record. It stands to reason that it now becomes a part of history that you read up in the future. So you knew before you started how it all came out. You would have had to know."
"No," said Gale, "we did not know. It was not in our history. It hadn't, strange as it may sound, happened yet…"
"But it had," said Sandburg. "It must have."
"Now," said Gale, "you are getting into an area that I do not understand at all, philosophical, and physical concepts, strangely intertwined and, so far as I am concerned, impossible of any real understanding. It is something that our scientific community gave a lot of thought to. At first we asked ourselves if it lay within our right to change history, to go back into the past and introduce factors that would change the course of events. We wondered what effects such history changing would have and what would happen to the history that we already have. But now we are told that it will have no effect at all upon the history that already has been laid down. I know all this must sound impossible to you and I admit that I don't fully understand all the factors myself. The human race passed this way once before, when our ancestors were moving futureward and this thing that is happening now did not happen then. So the human race moved up to our future and the alien invaders came. Now we come back to escape the aliens and this event now is happening, history has been changed and from this moment forward nothing will be quite the same. History has been changed, but not our history, not the history that led forward to the moment that we left. Your history has been changed. By our action you are on another time track. Whether on this second time track the aliens will attack, we cannot be sure, but the indications are they will…"
"This," said Douglas flatly, "is a lot of nonsense."
"Believe me," said Gale, "it is not willing nonsense. The men who worked it out, who thought it through, are honorable and accomplished scholars."
"This is nothing," said the President, "that we can resolve at the moment. Since it is done, we can safely put it off until another day. After all, what's done is done and we have to live with it. There is one thing else that puzzles me."
"Please say it, sir," said Gale.
"Why go back twenty million years? Why so far?"
"We want to go back far enough so that our occupation of that segment of Earth's time cannot possibly have any impact on the rise of mankind. We probably will not be there too long. Our historians tell us that man, in his present state of technology, cannot look forward to more than a million years on Earth, perhaps much less than that. In a million years, in far less than a million years, we'll all be gone from Earth. We are right now, I mean we were up in our own time, if we had been left undisturbed, only a few centuries from true spaceship capability. Given a few thousand years we will have developed deep space capability and probably will be gone from Earth. Once man can leave the Earth, he probably will leave it. Give him a million years and he surely will be gone."
"But you will have impact back there," Williams pointed out. "You'll use up natural resources. You'll use coal and iron, you'll tap oil and gas. You will…"
"Some iron. Not enough that it will be noticed. With so little left up there five hundred years from now, we've learned to be very frugal. And no fossil fuel at all."
"You'll need energy."
"We have fusion power," said Gale. "Our economy would be a great shock to you. We now make things to last. Not ten years, or twenty, but for centuries. Obsolescence no longer is a factor in our economy. As a result, our manufacturing up in 2498 is less than one percent of what yours is today."
"That's impossible," said Sandburg.
"By your present standards, perhaps," admitted Gale. "Not by ours. We had to change our lifestyle. We simply had no choice. Centuries of overuse of natural resources left us impoverished. We had to do with what we had. We had to find ways in which to do it."
"If what you say about man remaining on the Earth for no longer than another million years is true," said the President, "I don't quite understand why you have to travel back the twenty million. You could go back only five and it would be quite all right."
Gale shook his head, "We'd be getting too close, then, to the forerunners of mankind. True, man as we can recognize him, rose no more than two million years ago, but the first primates came into being some seventy million years ago. We'll be intruding on those first primates, of course, but perhaps with no great impact, and it would be impossible for us to miss them, for to go beyond them would place us in the era of the dinosaurs, which would not be a comfortable time period. Not just the, dinosaurs alone, but a number of other things. The critical period for mankind, the appearance of the forerunners of the australopithecines, could not have been later than fifteen million years ago. We can't be certain of these figures. Most of our anthropologists believe that if we went back only ten million it probably would be safe enough. But we want to be sure. And there is no reason why we can't go deeper into time. So the twenty million. And there is another thing, as well. We want to leave room enough for you."
Douglas leaped to his feet. "For us!" he yelled.
The President raised a restraining hand. "Wait a minute, Reilly. Let's have the rest of it."
"It makes good sense," said Gale, "or we think it does. Consider this-just five hundred years ahead lies the invasion from outer space. Yes, I know, because of the second time track we have thrown you on, it may not happen, but our scholars think it will, they're almost sure it will. So why should you move forward to meet it? Why not go back with us? You've got a five-hundred-year margin. You could make use of it. You could go back, not in a hurry as we'll be going, but over the course of a number of years. Why not leave Earth empty and go back to make a new beginning? It would be a fresh start for the human race. New lands to develop…"
"This is sheer insanity!" shouted Douglas. "If we, your ancestors, left, you'd not be up there to start with and…"
"You're forgetting what he explained to us," said Williams, "about a different time track."
Douglas sat down. "I wash my hands of it," he said. "I'll have no more to do with it."
"We couldn't go back with you," said Sandburg. "There are too many of us and…
"Not with us. Like us. Together there would be far too many of us. There are too many of you now. Here is the chance, if you will take it, to reduce your population to more acceptable numbers. We go back twenty million years. Half of you go back nineteen million years, the other half eighteen million years. Each group of us would be separated by a million years. We'd not interfere with one another."