I've read that when one performs the double slit experiment (dse) without any detectors to "see" which slit the photon goes through one gets an interference pattern. When one places a detector to see which slit the photon goes through the interference pattern disappears. My question are these. 1. Has the DSE been done with a detector on the ingoing side of the slits and then the outgoing side of the slits? 2. What exactly do the detectors do? As near as i can figure for the detector to detect it has to interact with the photon and the only way it can do that is by exchange of energy. If that is true then the photon in the experiment with the detector and the photon in the experiment without the detector likely don't have the same energy to begin with or/and end with. Or am i missing something entirely? As always thanks for reading.