Just a simple question. How do we know the detector isn't messing up the double slit experiment when a single photon is shot out. When there is no detector we know the interference pattern is formed even with a single photon. If we add detector to see where the photon actually went through a defraction pattern appears. As if the wave form collapsed because it was being detected. To me my first logical thought was that the detector must be somehow messing up the experiment (plugging the hole) or interfering electromagnetically somehow, because the pattern is showing exactly like there is 1 slit again. Now I realize this experiment is over 100 years old and has been retested numerous times. I am assuming the detector isn't actually messing up the experiment, but I just want to understand how the detector works and how they know it isn't contaminating the results. I have looked all over the intertubes and can find no simple explanation of this. Thank you.