If when you shine a photon into an atom for example, and this excites an electron to a higher energy level, do the electron(s) keep going higher the more light you shine, and is there an energy limit, if so why?
Secondly, if you then stop shining light, why will the electrons fall back to a lower level? Will they at all? And why? it seems arbitrary that they will unless acted on by something else.
If they do fall back, how long does it take till they do?
I am taking QM but have not reached this understanding yet.