hi everyone, I'm a beginner in QM and I have a question. we know that when an electron is hit by a photon, it gains the photon's energy and goes up to the excited state. Here is my question: according to the compton effect, we can interpret the collision of a photon and an electron just like collision of billiard balls, energy and the momentum is conserved. So isn't it important the way the photon hits the electron, so it could slow down or speed up the electron. thanks for your help, and sorry for my bad english.