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Quantum Physics and Lack of Measurement

  1. Dec 17, 2013 #1
    So this semester our lecture explained and showed us the double slit experiment.
    And it he explained to us the uncertainty principal that the act of observation can change the result.

    However this is the part where I kind of a have a problem with..

    Since quantum physics is based on the uncertainty principle, due to our inability to measure photons without disrupting them, it feels like we are saying:

    ok, we can't measure a photons location without disrupting its destination hence it must be UNCERTAIN!
    therefore everything in the atomic level must act on the basis of probability..
    (its like saying, because we can't measure something [due to lack of technology] it must is immeasurable, hence everything is possible!)

    So it leads to another question,
    what happens to quantum physics if one day we are able to measure photons without interfering with the experiment?

    Sorry if it sounds weird, I tried my best to explain it..
  2. jcsd
  3. Dec 17, 2013 #2


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    There are a number of ways to show that technology is not the reason for the uncertainty principle or the double slit results. You can place polarizers in front of each slit which will "disrupt" photons equally. You get interference or no-interference depending on their relative angle setting. In other words, the interference appears when the polarizers are set so you do not know which one it went through (polarizers are parallel). But no interference when you do know (set as anti-parallel or crossed).

    So obviously the photon can be measured without disrupting the interference. The only thing changing is the polarizer angle.
  4. Dec 17, 2013 #3
    Uncertainty principle is not that.

    The above kind of wrong reasoning has been going on, among some teachers around the world, probably, since uncertainty principle was established.
  5. Dec 17, 2013 #4


    Staff: Mentor

    This is the beginning level where it is attempted to give pictorial vividness to the ideas.

    The real basis of QM has nothing to do with that sort of stuff.

    Here is a much better view:

    Don't worry, since you are now just at the beginning level, if you don't understand the paper - you will still probably be able to get the gist.

    And once you understand QM better you will see that it's a matter of principle, not mere technological limitations, that you can't do that. But we all must start somewhere.

    Hope you enjoy your journey.

  6. Dec 18, 2013 #5


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    Standard quantum theory says that some observables are uncertain irrespective of technology. The question is whether the standard quantum theory is the final theory of everything, or only a provisional theory waiting for a discovery of a better theory. In the latter case, it is conceivable that a future better theory will explain that uncertainties are only an artefact of primitive technology. For example, it is possible that the currently existing Bohmian formulation of quantum theory will evolve in that direction, so you might be interested to learn more about Bohmian formulation. For that purpose, you can start, e.g., with
  7. Dec 22, 2013 #6
    right, maybe non linear models.

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