Manning nodded. "Like the problem of catching a lion on the Sahara Desert. You get a lion cage with an open door, electronically triggered to close at the press of a distant button. Then the laws of probability state that at any instant there exists a mathematical probability the lion is in the region of the cage. At this instant you shut the door. The lion lies within the cage, trapped."
"Stop goofing off. This is no picnic. Have you any idea of how many square light years we have to comb?"
"Cubic light years, Commodore Wilson."
"Cubic. So I'm sloppy in my speech, too? Look, Manning, all we really want from you is the overall conic volume in which the lifeships must lie. You know the course of Flight Seventy-nine. You know the standard take-off velocity of a lifeship. The forward motion plus the sidewise, escape velocity, produces a vector angle which falls in the volume of a cone because we don't know which escape angle they may have used. We can pinpoint the place of escape fairly close."
"Yeah, within a light year. Maybe two."
"And we know that the lifeship will reduce its velocity below light as soon as possible."
"Naturally."
"So somewhere on that vector cone, or within it, is a lifeship—two lifeships—traveling on some unknown course at some velocity considerably lower than the speed of light."
"We've located 'em before. We'll locate 'em again."
Wilson shook his head worriedly. "That's a lot of vacant space out there. Even admitting that we have the place pinpointed, the pinpoint is a couple of light years in diameter, and will grow larger as time and the lifeship course continues. Or," he added crisply, "shall we take a certain volume of space and assert that a definite mathematical probability exists that the survivors lie within that volume?"