“Forty-one,” he told the scientist.
“Yes, so we could safely send you back for a period of twenty days with an adequate safety margin. Over fifty, it accelerates like mad. It’s simply not safe.”
“What happens, then, if you overstay your welcome? Don’t come back within that margin?”
“Then the energy required to retrieve you would exceed our capacity. The line would break. You would literally be integrated into that past time as that created person, eventually with no memories or traces that you were not native to that time and place. And if that was, say, 1820, we could not later rescue you. You could not go forward of your own present—1820—and even if there was a way, we would retrieve someone else, not you. Someone, incidentally, invariably minor and unlikely to change any events. We learned our lesson the hard way.”
“You’ve lost someone, then?”
He nodded, “An expert in Renaissance history and culture, who was also a valuable agent when he attended East European conferences, which is why he was one of the few scholars we allowed to downtime personally. He was forty-six when he went back the first time, and he stayed two weeks. Later, he needed a follow-up, so we sent him back again—and lost him. The clock, we learned, starts when you arrive the first time, and it does not reset if you return again. He, and we, assumed at the time that he had two weeks a trip. He didn’t. So he’s there now, for all time, a meek, mild Franciscan monk in a monastery in northern Italy, a pudgy little Italian native of the time. To give you a final idea of how absolute absorption is, Dr. Small was also black—in our time.”
Ron Moosic whistled. “So then how do you get the recordings and pictures?”
“They tend to have a stronger sense of shape and substance, being inanimate. We’ve discovered that recorders and the like can be retained for almost the safety period. Weapons, on the other hand, tend to be absorbed into period weapons rather quickly. One supposes that a battery-powered recorder has a minimal chance of affecting history, while a new weapon or something else of that sort could do a great deal of damage. Why and how such judgments are made by nature we don’t know at all. Why is the speed of light so absolute even time must bend before it? We don’t know. It just is, that’s all.”
“Still, the old saw about going back and killing your own father before he met your mother still holds. How can you do that and still exist? And if you didn’t exist, you couldn’t go back.”
“But you could. We haven’t actually had a test, but this absorption phenomenon seems designed mostly to counter that sort of thing. In theory, you would in fact cease to exist in the present as soon as you committed the deed, which would snap your energy link. You would then become, immediately, this wholly new personality, this created individual. Joe would become time-frame John, and it would be John, not Joe, who shot the man who would have become Joe’s father. Of course, John would create a ripple that would then wipe out Joe, or so we believe, but the deed would still be done.”
“It would seem, then, that there’s very little to worry about in all this,” Moosic commented. “The only real risk is to our time traveler, not our present.”
Silverberg sighed. “That, alas, is not entirely true. The time mechanism itself, for example, is rather bulky, much like a space suit. You don’t need it where you’re going, but you need it to keep you alive until you get there. That can fall into other hands with potentially disastrous results, as you might understand. We can take precautions on that. But for the active period in the time frame, you—the present you—are still in control. During that period, particularly in the early stages of it, you are a walking potential disaster. The fact that it was John, not Joe, who shot Joe’s father does not make Joe’s father any less dead. We haven’t yet tested it because of the dangers and unpredictability, but we suspect that if causality is challenged, in the same way light speed is challenged, then something has to give, and what gives will be time.
“We suspect, in general, a minimal disruption—if you kill Hitler, someone will arise who is substantially the same and formed by the same sort of hatreds and prejudices. If Joe’s father had sired three children in the present track, those children would still be born—to a different father, but one rather similar to the first. But there are key figures in key places at key times who might be irreplaceable. Would a Second Continental Congress without John Adams ever have declared independence? Would we have won the Battle of Saratoga and gotten French and Spanish allies if Arnold had been killed earlier? What would a contemporary Britain be like without a Churchill, or a U.S. without Roosevelt? That is why the Nobel prizes must be unawarded and this installation protected. I would rather have it melt down than have proof of what we have here leak out.”
Moosic nodded. “I think I see. So somebody could change things.”
“We believe so. The best model we have begins with the Big Bang. With all of the rest of creation, a time wave is created as a continuous stream. It might be an anomaly, might be necessary to keep everything else stable, but there it is. Think of it as a thick glob of paint on a sheet of glass. It runs down the glass, when we tilt it, at a slow and steady speed. The edge is where time is now, still running down so long as everything else is expanding, but the paint trail it left is still there. The edge, where we are now, is the sum of that trail. Alter that trail, and you will start a ripple that will run down to catch up with the leading edge. The math is rather esoteric, but the ripple will run at ten times the edge rate primarily because it’s smaller. If it’s a tiny ripple, it may resolve things and die out quickly. A big wave, though—it would change the sum of the world.”
Moosic had a sudden, uneasy thought. “What about others? Would we even know if, say, the Soviets had a project like this? They’re doing fusion research now.”
“No, there’s no way of knowing. Of ever knowing. A time war would be the most frightening thing of all. However, it would still be badly limited in several respects. It would require enormous power. It would require a country insane enough or desperate enough to risk its own lot on a new roll of the dice. And it would certainly involve few participants in any event, participants who would be limited to a small amount of time in any frame to accomplish much at all. The Soviets are our opponents. They are not mad, which is why we are all still here. Neither are the current Germans, Japanese, Chinese, or others capable of such a project. It is only the fear that someone else is doing it that keeps us funded at all, so expensive is this operation. We spend a lot of time trying to convince them that there is military potential, when actually there is not. But we don’t know, of course. And so long as NSA’s very budget is classified, we can continue to get the money. You keep us out of unfriendly hands.”
“I’ll try,” Ron Moosic assured him, shaking his head and feeling far more worried now than when he’d walked in the door. This was a bit much to digest, even after a career in high-tech environments. In a sense, there was more unsettling business going on here than at the Pentagon and Kremlin war rooms. Here, just one well-meaning scientist could obliterate all that was constant in the world. A social experimenter would be even worse.
“That’s who we fear the most,” Riggs agreed. “The Air Force boys showed it wasn’t impossible to infiltrate here, but it’s pretty near so. On the other hand, how do you really get into a guy’s head when he’s being considered for downtiming?”