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I Spooky electrons...

  1. Dec 1, 2016 #1
    I watched a documentary about Quantum mechanics.
    There's a phenomenon which Einstien called "spooky action at a distance" states that two electrons appeared in the same event are related to each other in a spooky way,which means that if one of them has a specific state then the other one will have an opposite state.And this was found to be true in 1970s by John bell.
    My question is what kind of events can produce spooky related electrons and what states these electrons can have?
    Note:If there is something grammatically wrong or incorrect with the context please correct me because I'm working on improving my English.
    And thanks in advance. :)
     
  2. jcsd
  3. Dec 1, 2016 #2
    How much of Quantum Mechanics do you know, and from what source(s) was that information obtained? You've created this thread with an 'A' (advanced) label which may have been done in error.
     
  4. Dec 1, 2016 #3

    I don't know too much about it.
    And I think the presenter is trusted and the documentary was broadcast on the BBC.
    you think this information are wrong?
     
  5. Dec 1, 2016 #4
    Yes, I've seen that documentary before. The presenter is a Professor of Physics in the UK.

    No.

    I shall leave it at that, and someone should come along shortly to answer your queries.
     
  6. Dec 1, 2016 #5

    bhobba

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  7. Dec 1, 2016 #6

    Henryk

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    The 'spooky action at the distance" was Einstein objection to the Copenhagen interpretation of quantum theory.
    The famous Einstein Podolsky Rosen paradox was supposed to prove that quantum theory does not provide a complete description of reality.
    John Bell did not did actually prove anything, he derived an equations, Bells inequality, which would provide a definite criterion which interpretation of the quantum theory was right. The actual experimental proof is credited to Alain Aspect.
    I did read Bell's paper, it was not easy to grasp. Basically, it boils down to this:
    Suppose you create two electrons with the total spin equal zero.
    In Einstein interpretation, there are two separate particles, both have definite spin values at the moment of creation and measurement just reveals the value.
    In Copenhagen interpretations the two electrons are described by one wavefunction, which has local maxima corresponding to the apparent position of the two separate particles.
     
  8. Dec 1, 2016 #7

    Henryk

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    Sorry, I pressed something and what I was typing got posted before I finished.
    Bell derived mathematical equations in form of inequalities to set a criterion which of the interpretation was correct.
    My own understanding is as follows:
    Einstein assumed locality, that is a body like an electron was localized in space. Quantum mechanics is non-local. A localized electron can be represented by a superposition of plane waves extending from plus to minus infinity. In other words, every elementary particle exist everywhere in the universe, just not with the same probability.
    So, there is not 'spooky action at a distance' because both electrons in the EPR thought experiment are present everywhere. Measuring spin at any point collapses the wave function to a particular state.
     
  9. Dec 2, 2016 #8

    bhobba

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    That's incorrect.

    P'ease review Bell's theorem.

    Thanks
    Bill
     
  10. Dec 2, 2016 #9

    zonde

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    In experiments entangled electrons are produced by rather complicated setup using entanglement swapping. For example in this experiment https://arxiv.org/abs/1508.05949 first, two electron-photon entangled pairs are produced and then entanglement swapping is performed using both photons.

    It is easier to produce entangled photons using specific crystals that can split one high energy photon into two lower energy photons. See for example this paper: https://arxiv.org/abs/quant-ph/0205171
    Pair of entangled photons can be produced in four different entangled states:
    - both photons have the same polarization when measured in horizontal/vertical basis and the same polarization when measured in +45°/-45° basis
    - the same polarization in H/V basis, opposite in +45°/-45° basis
    - opposite polarization in H/V basis, the same in +45°/-45° basis
    - opposite polarization in H/V basis, opposite in +45°/-45° basis
     
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