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What do we mean when we say a particle is 'observed'?

  1. Jun 22, 2013 #1
    I haven't studied quantum physics academically and I have no understanding of it mathematically so forgive me if my questions are strange, nonsensical or erroneous.

    For instance in the double slit experiment when we attempt to observe the object going through a slit then the diffraction disappears.

    EDIT: And when observed does it assume a pure particle state / when unobserved does it automatically assume its dual wave-particle state. Or two borrow a term, a "wavicle"?
    Last edited: Jun 22, 2013
  2. jcsd
  3. Jun 22, 2013 #2
    I take observed to mean we made a measurement on it to determine something about its state. Like when a photon hits a polarizer: if it goes through we have observed that it is in a polarization state aligned with the polarizer. If it doesn't pass through it was polarized at a 90 degree angle. But before it hit the polarizer, it was in no definite state. For example it could have been prepared in a state polarized at some angle relative to the polarizer, which would put it in a superposition of states that will (0 degree) or will not (90 degree) pass through.

    Let me know if you don't get the above, I can break it down more if you're interested.

    Observation always doesn't imply that the observed is a particle. You can "observe" phenomena behaving as a wave.

    IDK why the double slit experiment is so popular. I think it's results are difficult for laymen to understand properly. It only made perfect sense to me after I heard about Feynman's intuition using the path integral formulation.

    Edit: Also, a lot of people get really philosophical and mystical when addressing the question "what does is mean to observe" and maybe this was the kind of answer you wanted. In my experience, the discussion that arises form playing around with and debating the interpretation of words like "observation" and "measurement" hasn't really helped my understanding of quantum physics. Rather, I think QM is best understood by analyzing the results of experiment. Especially when you have never studied the subject at all.
    Last edited: Jun 22, 2013
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