"Fantastic!" I exclaimed.
"It must be true;" he insisted. "It has to be true, unless she reversed ... will reverse ... her direction in time after birth. In that case, perhaps some baby girl here even now is Summer, living coexistently with her reversed self."
"If you're going to reverse her direction in time again and make her live normally," I said, for he already had told me this was his aim, "I don't see how you can prevent a paradox. She has already lived in the past as an adult woman. If you reverse her existence at this stage, then she can't be born, because she'd be living from her present age on, both forward and backward in time."
He shook his head.
"I don't know," he said. "Perhaps it can't be done. Perhaps it would involve a parallel time stream, if there is such a thing. All I know is that I must try. If I can, she might still consent to be my wife later, if the difference in our ages isn't too great. That would be up to her."
"I don't see how you even know where to start on such a project," I confessed.
"The chances are slim," he admitted, "but I have some hope. The only actual time reversal we know, scientifically, is at the sub-atomic level. The theory was advanced by Feynman that annihilation of an electron-positron pair upon contact might be, not actual annihilation, but a 'time reversal' of the electron. The emission of a photon of energy, in such cases, is powerful enough to cause a recoil in time, and the positron is merely the electron traveling backward through time after the energy explosion."
I looked extremely blank.
"Look," said Wyn, taking up a pencil. He drew a big "Z" on a piece of scrap paper, labelling the two arms "E" and the connecting line "P". The angles he marked "A" and "B:"