Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Questions about the Double Slit Experiment

  1. Feb 14, 2009 #1
    As I'm not learning quantum mechanics formally in a classroom, I have no real experience with the matter, or a teacher to whom I can pose my questions. There are a few experiments I'd like to run as well, but no way to do so. In any case, I'm hoping that someone else has run these experiments, or at least has theories as to what will happen.

    1. What happens if you run the double slit experiment, recording which particles go through which slit, look at the back wall before looking at the results of the observations, then look back at the wall? Will it start off as an interference pattern, then become a clumping pattern, since your knowledge about the particles has changed? Will it "predict" that you will look at the data, and start off as a clumping pattern? Will the fact that you've already looked at the wall lock the particles in place, so even after you look at the data, their positions won't change because you know where they landed? Or something completely different?
    2. What happens if you run the experiment with two (groups of) people, one to look at the wall and one who may or may not look at the data. Will the results always agree with each other? Does it matter if you look at the wall or the data first, even if it's two different people doing so?

    Thank you for reading, and hopefully for responding.
    Last edited: Feb 14, 2009
  2. jcsd
  3. Feb 15, 2009 #2

    Doc Al

    User Avatar

    Staff: Mentor

    The interference pattern doesn't change just because someone chooses to look or not look at the data about which slit the particles passed through. Modifying the experiment in order to record the "which way" information is what changes the interference pattern--whether or not anyone looks at that information.
  4. Feb 15, 2009 #3
    "double slit experiment" interpretations depend on "school" you are belong to.
    There are Copenhagen, Einstein, Bohmian,..... or your own.
    Physics Forum rules forbid even discussion of the validity of any of them :(((((
    So i must close my mouth.
  5. Feb 15, 2009 #4
    Don't all the interpretations agree that, as long as you modify the experiment in such a way that which-slit info is leaked out into the environment, you will not get the interference pattern. Shouldn't matter if or when or who looks at the which slit information, just that the which slit information is available is enough to remove the interference.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook