1. The problem statement, all variables and given/known data In an article, I am informed that a free electron can neither absorb nor emit a photon. I just want to know why?! Please help me. 2. Relevant equations 3. The attempt at a solution I've no idea at all. Photon is the medium boson carrying electromagnetic force, so the relationship between electron and photon is interesting. The above process is said to bef orbidden, and I think some conservation laws must be violated!