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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 :)

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Yes, of course, all these things have been experimentally done decades ago. –  Luboš Motl May 26 '11 at 15:55
    
Thank you all. @Luboš, I do believe so. Though I am not an expert in searching old physics papers.... really wonder how physicists setup those experiments. Is there any hint how to find either the papers or the video demo of the experiment? Maybe all I need is the very "key" words for Google to sift out what I want..... –  pipsi May 30 '11 at 10:21
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up vote 5 down vote accepted

This or a similar video was topic here already:

Is Dr Quantum's Double Slit Experiment video scientifically accurate?

This: ""But if one can really shine a light and see the electron, "" is the problem, in practice one had to "shoot" electrons at the electrons to "see" them. Or on could use gamma rays (Compton effect), but always this would disturb the experiment. Ther is no "eye" in the quantum world to "watch" those balls without interaction.

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Thanks, Georg. My physics teacher taught me pretty much the same idea as yours. Still I am really curious about whether and how such experiments have been done - I mean, like shooting electrons or shining gamma rays to those electrons about to pass the slits. –  pipsi May 30 '11 at 10:26
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