Light source reflected from mirrors or diffraction gratings seems to travel at different distances upon reaching a photomultiplier detector. Accordingly, as described by Feynman, the path of greatest distance corresponds to the highest light’s frequency, the blue end of the visible spectrum. On the other hand, the path of smallest distance corresponds to the lowest frequency, the red end of the visible spectrum.

This phenomenon seems contradictory to what the big bang theory suggests that the expansion is a red shift not a blue shift. So, what is the logical or physical or mathematical fallacy? Was the illustrative description in Feynman’s book QED on page 48 erroneous? Or could it be that the big bang theory is really a big crunch theory?