1.) When and how did idea about radiating electrons come about, atomic theory and orbitals? 2.) Is this phenomena considered purely QM, or inter-related with some other branch of physics like SR maybe? Or perhaps it can also be defined independently using some theories and equations other than QM? 3.) What experiment best demonstrates electron radiation, most recent such experiment? 4.) If electron is indivisible smallest amount of matter, then what is the explanation as to where those radiated photons are supposed to come from?