
"No. Not exactly, that is. You could go back, yes, but by that time you wouldn't be you anymore. Nature
does resist tampering. We made that discovery the first time out. You're back there, and you don't fit. Time
then makes you fit. It is far easier and more efficient to integrate you into that present you're now in than it
is to change all time. It creates a curious niche for you. It adjusts a very small thing in what we call the time
frame so that you were born and raised there. In a way, it's very handy. Go back to fifteenth-century
France and you'll find yourself thinking in the local language and dialect and generally knowing your way
around. Only the massive energy link, a lifeline of sorts, between here and there keeps you from being
completely absorbed. Unfortunately, the longer you are there, the more energy is required to sustain you.
It's in some way related to the subject's age, although we haven't gotten the exact ratio. It requires more
energy to send an older person back than a younger. Someone up to about the age of fifty we can generally
sustain back there for the number of time-frame days equal to half his age. How old are you?"
"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
record-ers 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 affect-ing 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, particu-larly 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 unpredict-ability, 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