He nodded, stunned. “You could send an army back and have it pop up out of nowhere.”

“Bah! You’re hopeless! Mr. Moosic, you will never send an army back in time. We need the entire capacity of this power plant, which is capable of supplying the energy needs of roughly ten million people, just to send four people back a century, and the further back you go, the more power is required. To get one human being back to 1445 would require our total output. That and to sustain him there, anyway, for any period of time. Beyond that the energy requirements get so enormous that we’ve estimated that just to send one person back to the first century A.D. would require every single bit of power this nation could generate for three solid weeks.”

“But for only, say, a week back? Surely—”

“No, no. It’s impossible. Physics is still physics and natural law is still natural law. Just as nothing is permitted past the speed of light, no one is permitted to coexist at any point in the past where he already exists. It just won’t do it. In fact, it won’t do it within a decade of your birth date. Why we haven’t any idea.”

He thought about it, trying to accept it at least for argument’s sake. “A decade. Then you could go back and live past the time you were born.”

“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.