ABSTRACT
Because of the interpretation of the negative energy states as antiparticles, which travel ‘backwards’ in time, the quantum theory will require that the positive energy part vanishes for past infinity, whereas the negative energy part will be required to vanish for future infinity. The Feynman rules to convert a diagram to the solution are apparently that each line (propagator) between pointsx and y contributes G(x – y) and each cross source at a point x contributes J (x). It is straightforward to translate these Feynman rules to momentum space, by inserting the Fourier expansion of each of the terms that occur. Because of the gauge invariance, the choice of gauge has no effect on the equations of motion because the current is conserved.
