Hi all, Whew, last question for a while: I think I already know the answer, but want to confirm (e..g, I think this thread basically answers the question, https://www.physicsforums.com/threads/propagation-of-wavefunction.152053/) As an example, let's say I have an electron (in free space or bound to an atom) that absorbs a photon and transitions to a higher energy state. I understand that in QFT, this transition is not instantaneous (although very fast) - in terms of the electron probability distribution (square of wave function) for, e.g., the bound electron case, there should be a decrease in the probability of being found in one orbital over time, with an increase in the probability of being found in a higher orbital over time (again, with the time scale of this transition being very short). Now, the question: the electron wave function will change as a result of the photon absorption - however, the propagation of the change in the wave function must not exceed the speed of light to agree with special relativity? I realize that that wave function lives in Hilbert space, so I guess what I'm asking is: the speed at which 'information' about the absorption of the photon propagates through the relevant field in spacetime should be c or less - correct? Otherwise, e.g., nearby particles (other field excitations) would feel in influence of the change faster light. Thanks!