"The flow of Time is from left to right," he explained. "At left is the past, at right the future. This electron, E, is moving normally along at the top of the diagram when it runs into an energy explosion at A. It reverses itself, going back through time as the positron, P, until it hits another energy explosion at B. Then it is reversed again into the right time direction, continuing as the electron E, at the bottom. You follow the line, as the pencil point does in making the Z, and it's a single body."
"But," and he drew a vertical line through the Z, "we move always forward in time. To us, the energy explosion at B happens before the one at A. Suddenly at B, a positron and an electron are created out of nothing. The electron at the top apparently has nothing to do with either of them. But the positron moves along and collides with it at A, leaving nothing there again—except, once more, an apparently unrelated electron, the one at the bottom of the diagram."
"But you're saying the same thing can exist in three places at once," I objected.
"Exactly, but in one of those places, it's traveling backward in time. So, if Summer's time reversal occurred or will occur after birth, she may be existing somewhere else, as a younger girl, right now; besides being here in the house with us."
"Your example is, as you say, at the atomic level," I said. "How can you transfer that into terms of human beings?"
"The only thing I know to do," he said, "is to create an energy explosion which I know won't hurt Summer physically, but may reverse her back to a normal direction. It would be like the energy explosion that meets the positron at B and forces it to continue existence as an electron."
"It appears to me," I said slowly, trying to grasp the concept, "that your explosion at B would have to have happened already if it were going to happen at all."