"And if we find out," said Herb, "those guys over in the other universe can come over and help us hold the Hellhounds off while we rig up the stuff we have to have.”
"I'm afraid," said Kingsley, "we have to take the chance.”
"Chance," said the Engineer. "It's a whole lot more than chance. The place I have in mind may not even exist.”
"May not even exist?" asked Caroline and there was an edge of terror in her words.
"It is far away," said the Engineer. "Not far in space — perhaps even close to us in space. But far away in time.”
"In time?" asked Tommy. "Some great civilization of the past?”
"No," said the Engineer. "A civilization of the future. A civilization which may never exist. One that may never come to be.”
"How do you know about it, then?" flared Gary.
"I followed its world line," said the Engineer. "And yet not its actual world line, but the world line that was to come. I traced it into the realm of probability. I followed it ahead in time, saw it as it is not yet, as it may never be. I saw the shadow of its probability.”
Gary's head reeled. What talk was this? Following of probable world lines.