Re: how big is the difference between classical and quantum electrodynamics ?

Hi Werner,

the situation in classical electrodynamics (ed) is very different. QED is the quantum theory of ed. In classical electrodynamics, only one solution will survive, the straight line shown in Fig. 19 - the first figure of this "mirror series". A solution of the Maxwell equations will provide you with the unique solution - Snellius' law - that the mirror will reflect light such that the angle of incidence is equal to the angle of reflection, at any rate. In the quantum situation, Snellius' law is not true any more. Deviations are possible. One has to add up all the possible deviations to obtain the final result. The classical path of the photon is the path that contributes the most on the quantum level.

The book by R. Feynman is remarkable. It is a popular book but nevertheless describes one of the approaches to QED - called the path integral approach - without giving any confusing formulae. To my knowledge, there is no comparable book. Of course, there are some elementary text books for students on QED or quantum field theory in general. Some of them are e.g.: Lewis Ryder, Quantum Field Theory; Walter Greiner, QED; F. Mandl, Quantum Field Theory. I don't know about your mathematical and physical background. These books are fairly elementary, but the subject by itself is mathematically very involved. So maybe I should recommend you some introductory books on elementary particles. These books are not so much concerned with the mathematical construction of the theory, but with physics, particle phenomenology. Some good books are e.g.: Lewis Ryder, Elementary Particles and Symmetries; B. Martin and G. Shaw, Particle Physics; D. Perkins, Introduction to High Energy Physics.

I hope I could help you and that you enjoy your further studies.
Michael