Fermi National Accelerator Laboratory
STANFORD LINEAR ACCELERATOR CENTER
SLAC, Bin 81
P.O. Box 4349
Stanford, CA 94309
(415) 926-2266 August 31, 1988
Dear Mr. Gordon,
The answer to your question is certainly no. All photons travel at the speed of light. This is a consequence of the Special Theory of Relativity and Quantum Electrodynamics obeys Special Relativity. That was the short answer. To understand why virtual electron-positron pairs don't slow the photon down is a little more complicated. The photon moves at the speed of light because it is massless. It is a non-trivial prediction of QED that the presence of virtual electron-positron pairs does not change the mass of the photon. To see how this works requires quite a bit of quantum field theory. Quantum field theory is not a field that is easily learned from a book but if you have the time you might try some of these references: The Theory of Fundamental Processes, QED: The Strange Theory of Light and Matter and Quantum Electrodynamics by Richard Feynman, Relativistic Quantum Mechanics and Relativistic Quantum Fields by Bjorken and Drell, and Quantum Field Theory by Mandl and Shaw. Most of these books should be available at a university library. The sections that are particularly relevant are those on renormalization.
Regards,
Russel Kauffman