When you hit a hydrogen atom with a photon, would it always register a hit 100% of the time? so do you have to compute for probability if it would hit it? I'd like to know if it is the photon wave function that interacts with the electron wave function so there should always be a hit all the time (because wave interacting with wave has larger scattering sections). Or do you need to imagine it as a photon particle hitting the electron particle? Then it's like imagining a rocket aimed randomly at the earth/moon and calculating the probability the rocket would hit the moon, and you know the probability is so low. If the photon and atom's electron is like this. Hit would be rare. Or do you need to imagine it as a rocket wavefunction interacting with the moon wavefunction and there is a hit all the time because the wavefunction of moon is located at all space (this is just analogy of the electron wave function occupying the orbital all at ones)?.