Text: If Light Doesn't Travel Backward in Time, Your Flashlight Won't Work In 1945, John Wheeler and his graduate student Richard Feynman, then at Princeton University, proposed a novel way of looking at light that gives the backward-in-time solutions of Maxwell's equations equal status with the forward-in-time solutions. John Wheeler, author of a seven-pound paperback book on gravity, is presently director of a fundamental physics research center in Austin, Texas. Richard Feynman, who received the Nobel prize for developing an improved quantum theory of electromagnetic radiation, is remembered in some circles as "the Groucho Marx of physics" for his humorous and irreverent behavior. The Wheeler-Feynman model, called the "absorber theory of radiation," makes electromagnetism a two-way street as far as the time dimension is concerned. They base their time-symmetric theory on the assumption that every light wave emitted by an atom must be absorbed by another atom and that these two events, light emission plus light absorption, should be considered as a single inseparable process. . . . According to the Wheeler-Feynman theory . . . radiation occurs in two steps. First atom A emits . . . a half-sized (retarded) wave that travels forward in time at a speed of 186,000 mps to the absorber atom B. Atom B recoils as it takes up this light's momentum. Then, stimulated by its recoil motion, atom B emites a half-sized (advanced) wave that travels backwards in time at a speed of 186,000 mps to atom A. Atom A recoils as it takes up this advanced wave's momentum. . . . in order for light to be emitted it must be connected to some future absorber by a two-way retarded-advanced wave handshake process. Because of the need for the presence of absorbers, the absorber theory predicts that if there are none in a particular direction in space, then light will refuse to shine in that particular direction! If absorber theory is correct, your flashlight would go out whenever you shine it up into the night sky in the direction of an "antiemission locus"‹a region of space entirely devoid of absorbers of light in the frequency range of your flashlight. In certain other directions, containing only a few absorber atoms, your flashlight would dim, but not go out. Only in those directions in which light was totally absorbed would the flashlight be able to shine at its full brightness. ‹ Nick Herbert, Faster than Light: Superluminal Loopholes in Physics

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