Hi, I was trying to learn a bit of quantum mechanics from Feynmann lectures. In the 3rd volume of the Feynmann lectures, he talks of the double slit experiment with electrons. He says that if we keep a light source near the first slit, so that every time an electron passes it scatters light and lets us know that it has passed, if the wave length of the light is small enough we will not get the interference pattern. My question is, what if we remove the light source and keep another kind of a detector, something that detects the electrons field, will we still get an interference pattern? More over is the destruction of the pattern related to the collision with photons or is it due to the very act of observation that lets the observer know which hole the electron went through?