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

Delayed choice experiment

  1. Sep 6, 2012 #1
    Consider the below (figure 1), an electron gun is made to emit electrons one by one through two slits S1 and S2.
    There is a screen at the other side and a pair of telescopes (with electron detectors inside them) T1 and T2 trained on the slits S1 and S2 respectively.
    We can choose to bring down the screen even after the electron has crossed the slits.

    If we choose to keep the screen up, we get an interference pattern as more and more electrons move through the slits.
    But if we choose to remove the screen the electron is always detected either at T1 or T2 with a 50:50 chance.

    Now if we choose to insert an array of detectors in between the slits and the screen/telescopes (figure 2), the electron will be detected in only one of the detectors in the array as it moves from the slits to the screen.

    How does the detector affect the entire set up?

    Consider that we have the screen up. Since we have the detectors the interference pattern should disappear.
    If we have the screen down, then the electron shows up only at either of the telescopes.
    So wouldn't the electron be detected at the detectors which are in line with the telescopes T1 and T2.

    The question is whether there would be any difference in the detection pattern (at the detector array) depending on whether the screen is up or down?



    Attached Files:

  2. jcsd
  3. Sep 6, 2012 #2


    User Avatar
    Science Advisor
    Gold Member

    Welcome to PhysicsForums, entropy15!

    The setup you propose is not clear to me as to what you are varying that is of significance.

    The usual rule is the pattern changes according to whether or not which-slit information is available (in principle, regardless of whether the observer actually obtains it). So I am not sure I see where this element is being varied. Raising or lowering the screen doesn't change that.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook