| 请教沈先生一个问题: A free electron with velocity v in Observer frame head and head collides with a photon with frequency f also in the Observer frame, please tell me what's the relationship of the final photon frequency in the Observer (still of course) with the angle theta (since the angles related to the horizontal line alpha and theta are correlated, and not necessarily to be 90 degree). In other words, what is the function of ff(f,Me,c,v,theta) looks alike? ph (F) with frequency ff | | photon with frequency f | toward O | theta electron with v move toward O ph (I) -----------------------------O-----------------------------------e (I) | alpha | | e (F) |