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What happens when we measure spin of a fermion?

  1. Apr 2, 2013 #1

    andrewkirk

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    I am trying to understand the measurement of spin, in order to understand Bell's paper on the Einstein-Podolsky-Rosen paradox.

    When we measure the spin of a fermion in the direction of unit vector a, will the result be:

    1. a value of either +0.5 or -0.5, and upon measurement, the fermion adopts an eigenstate of the spin operator in which the spin is aligned with a

    or

    2. a value of 0.5 cos θ, where θ is the angle between a and the direction of spin the particle has adopted as a result of the measurement, and θ may be anywhere in [0, π)


    or is it something else?

    Thank you for any help.
     
  2. jcsd
  3. Apr 2, 2013 #2

    Bill_K

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    This one is correct.
     
  4. Apr 10, 2013 #3

    andrewkirk

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    Thank you Bill.
    I meant to say thanks earlier, but I got a bit carried away reading the Bell paper when I found I could actually understand it.
     
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