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Electron spin clarification

  1. Mar 12, 2015 #1
    I just want to clear up something about electron spin to see if I have it correctly. As far as I understand it is it not really spinning but it's just a convenient word and what it denotes is the the particular quantum number is either up or down. Now I think I've got it right to say that this value is not determined until it is measured and the measurement then forces the electron to choose either up or down on the axis which it is measured.

    I further understand it that once the spin is measured on a particular axis that the spin on the other two axes cannot be known. What I am not sure of is if an electron has 'spin' on three different axes at once but only one can be measured and therefore known at one time. Or if it in fact it only ever has spin on a single axis and whatever axis is measured the electron then becomes either spin up or down on that axis.

    I hope that is clear with regards to my question.
  2. jcsd
  3. Mar 13, 2015 #2
    Take a look at the "Binney's interpretation of Violation of Bell Inequalities" thread...

    The discussion there covers the question of how the axes relate to the measurement.
  4. Mar 13, 2015 #3
    I hope this helps:
  5. Mar 13, 2015 #4


    Staff: Mentor

    Quantum spin is quantised spin angular momentum in analogy with classical mechanics:

    Its like the quantum analogue of any classical thing such as momentum - its not really describable in classical terms.

  6. Mar 18, 2015 #5


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    Science Advisor

    I wouldn't say that measuring the spin on one axis implies not knowing the spin on other axes. Rather, measuring the spin in one axis implies that the spin is in a superposition state on other axes. You don't know what you would get if you measured on another axis, projecting to a particular eigenstate, but, without measuring, you do know that it is in a superposition state, which is totally different from not knowing the state at all.
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