hi. I've got a quick question. So I've just read Arnold Neumaier's description on virtual particle in
physics.stackexchange.com/questions/4349/…. How wrong is it to claim that we can only see virtual particles appearing in our equations when we have at least 2 quantum objects in our system? In normal 'semiclassical' QM e.g. quantum electron in classical potential, the electron is on-shell all the time. Once resolved, I'll append the answer as a comment later.