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.