This question already has an answer here:
This is my first question here. Hope it not too dull to you guys :p
I found this video on youtube. After 3:24 it says if there is an observer detecting which slit the electron goes through, there won't be an interference pattern. Has there ever been any experiment (not thought experiment) demonstrating this phenomenon really using microscopes or other detectors to see where the electron goes?
My physics teacher don't know the answer, but he took an alternative route, said if we suddenly close one of the slits, we know the electron can only go through the other, and it turns out no interference pattern shown. It sounds convincing to me and the experiment is much easier to perform. But if one can really shine a light and see the electron, he or she can alter the intensity or energy of the light to find a critical value below which the interference pattern won't be destroyed. Sounds even cooler :)