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

Question regarding the effects of the measuring device in the double slit experiment.

  1. Jan 6, 2013 #1
    Hi, I've done a lot of personal research on the internet trying to understand what exactly is happening in this experiment but I keep seeing contrasting information about what the role of observation actually had on the experiment.

    What I understand is that when they try to figure out which slit the particles actually went through before they appear on the screen, the wave function collapses because the detectors use light to read its position and that affects the particles somehow.

    How do the detectors actually affect the position of the particle?

    Certain explanations like in this video assert that when the detectors were turned on but the data wasn't collected then the wave function still didn't collapse. He thinks its the fact that someone is consciously interpreting the experiment that affects the results. I'm pretty sure that's false but I really don't know why.

    Edit:

    Or do the detectors even affect the outcome? according to this video the delayed choice quantum eraser experiment proves that it wasn't the detector that collapsed the wave function.

    According to this article,
    "The big mind**** here is that an interference patterns appears even when the which-slit information is removed in the far future! It is as if the electron knows that IN THE FUTURE the information about which slit it went through will be erased, and decides to act differently in the present moment!"

    Does science have explanations for these phenomena other than the natural assumption that it must be the act of conscious observers affecting the results of the experiment?
     
    Last edited: Jan 6, 2013
  2. jcsd
  3. Jan 6, 2013 #2
    Re: Question regarding the effects of the measuring device in the double slit experim

    Actually, we don't know how measurement causes wavefunctions to collapse, if indeed they do collapse. At the moment, it's just a convenient description. It is probably does not require consciousness to happen (though I suppose I can't really justify that "probably"). There is something called "quantum decoherence" where a quantum system being entangled with its environment causes its wavefunction to evolve (unitarily) in a manner that looks kind of like wavefunction collapse—but it's not the same thing, and doesn't really address the fundamental issue of how a quantum state goes from a superposition of states to an eigenstate. It's called the measurement problem and at the moment all we have are number of proposed resolutions from a variety of different possible interpretations of quantum mechanics.
     
  4. Jan 6, 2013 #3
    Re: Question regarding the effects of the measuring device in the double slit experim

    In response to your edit: the mysterious nature of wavefunction collapse notwithstanding, the article containing the quotation in your edit (which you didn't actually link to, FYI) can probably be safely dismissed as garbage. Quantum physics is a fully causal theory, and suggesting the quantum eraser experiment requires the future to affect the present is utter nonsense.
     
  5. Jan 6, 2013 #4
    Re: Question regarding the effects of the measuring device in the double slit experim

    Hey thanks for the replies! I fixed my post if you wanna take a look at the article.

    Are you familiar with the delayed choice quantum eraser experiment? I haven't taken a good look at it yet because my brain is really fried tonight from trying to understand all of this. Does the experiment prove that the detectors were not the cause of the change in pattern?
     
  6. Jan 6, 2013 #5

    Drakkith

    User Avatar

    Staff: Mentor

    Re: Question regarding the effects of the measuring device in the double slit experim

    It is evidence that the formation of the interference pattern does NOT depend on WHEN either particle was detected. It only depends on whether the slit a particle goes through can be determined or not. If it can, then no interference pattern will appear. If it cannot, then an interference pattern WILL appear.
     
  7. Jan 6, 2013 #6
    Re: Question regarding the effects of the measuring device in the double slit experim

    I am familiar with the delayed choice experiment—but I don't really understand your question. I glanced at your article, and a word of advice: if you ever read anything about quantum physics that cites the movie "What the Bleep Do We Know?" you would advised to stop reading and not waste your time.
     
  8. Jan 7, 2013 #7
    Re: Question regarding the effects of the measuring device in the double slit experim

    Yea but doesn't it also mean that the detectors themselves aren't what's causing the change in pattern? In the double slit experiment when they put detectors in front of the 2 slits to see which slit it went through it made a clump pattern and went through one slit. In this experiment, they didn't do anything to see beforehand which slit it went through. They shot entangled particles at different detectors which eventually showed a pattern that changed depending on if we could know which slit it went through. It was the actual act of measurement that changed the result, not the way we measured it, right?

    Quantum_Eraser.png

    150px-Detector0RawResults.svg.png

    Also, to be clear, the detector at D0 showed a pattern that wasn't discernible until you corresponded each photon to it's entangled partner at a different detector that had it's own pattern as shown in the photo, right?
     
  9. Jan 7, 2013 #8
    Re: Question regarding the effects of the measuring device in the double slit experim

    I think you're right. Each particle goes through one of two identical detectors, one where the "which path" info is erased and one where it's not. The first path still creates an interference pattern even though it still went through a detector. This proves that the detector isn't doing something funky to the particle to collapse the wave function, no?
     
  10. Jan 8, 2013 #9

    Drakkith

    User Avatar

    Staff: Mentor

    Re: Question regarding the effects of the measuring device in the double slit experim

    The light doesn't go "through" the detector, its path ends at the detector. By detector I mean the sensor that records the light.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: Question regarding the effects of the measuring device in the double slit experiment.
Loading...