Given a simple atom like the Bohr atom (and possibly generalized to any other atom), I know that an electron can transition from one energy level to another, either by absorbing or releasing a photon of a precise hf. How much time does an electron take to make a transition from one energy level to another? I know the electron cannot be found physically in the space between energy levels. Does anyone know where such calculations can be found? Usually, the effect is considered "instantaneous" but I am curious as to the actual times of transition between energy levels. Note: I didn't underline anything. I don't know why that spontaneously appears in my text.