Ok, so I've just started studying quantum physics with the introductory double slit experiment. I thought I had a pretty good grasp on the results of the experiment but my tutor says I don't. This is what I interpreted from the experiment: Both slits are open. We place a detector along one of the slits. The fact that we know which slit the electron went through makes it act as a particle. Now, we remove the detector. We don't know which slit the electron went through. Because of this, the electron acts as a wave and we observe an interference pattern. My tutor says that I'm missing the point and this is all bs. He said Feynman's experiment was theoretical, and has nothing to do with the main point. My tutor didn't elaborate beyond this! I'm left wondering if he's correct that I'm missing the point, and if so, what the point is?! Another person told me that the reason detection changes the result of the two slit experiment is because there are no tools capable of not interfering with the experiment. Is this true? One more question: Can we say the electron goes through one slit or does it go through both if it acts as a wave?