Could someone explain to me how the delayed choice experiment is described within the framework of the Copenhagen interpretation? (Double slit experiment with two slits open but a late decission to measure the path of the particle). I do not understand how the deterministic evolution of the wavefunction passing through both slits, fits with the fact that no interference is observed after the decision to measure the path. Can we say that the wavefunction is [itex]\psi = \psi_1 + \psi_2[/itex] (subindices for the two slits) and obeys the Schrödinger equation all the time until the measurement is done? In that case, how is it that the measurement can be only explained if [itex]\psi = \psi_1[/itex]? I am sorry to bring up this very often discussed topic, but I found only heuristic explanations to that and I would like to see something more formal.