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Measuring spin of a free electron

  1. Sep 23, 2015 #1
    Hi everybody. I have been reading about the Stern Gerlach experiment lately and a doubt has came to my mind.
    Is there any way to know the spin of an electron without forcing it to interact with a magnetic field?

    Thanks for reading.
  2. jcsd
  3. Sep 23, 2015 #2


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    If you're sticking to the spin of a single electron, I'd say no.
    Theoretically, to measure the spin of an electron would require interacting with it in a way that can in principle (however slightly) change its spin state.
    As far as I know, the only interactions capable of changing the spin-state of an electron are magnetic.

    However, if you're going to measure the spin of a whole bunch of electrons, you could at least narrow it down by showing that they are fermions (i.e., half-integer spin particles obeying the Pauli exclusion principle).
    For example, since a pair of electrons cannot occupy the same state, you could try to bring other electrons with known spin states close, and see how the repulsion between them changes depending on the spin state of the known electron. Ideally, the electron in a spin state most closely resembling the spin state of the unknown electron would have a maximum repulsion.

    There may also be quirks of statistics that will distinguish a bunch of spin-1/2 particles from a bunch of spin-3/2 particles, but I don't know enough to say just what that would be.
  4. Sep 24, 2015 #3
    Thank you very much for your anwser. That's pretty much what I thought that would happen.
  5. Sep 25, 2015 #4


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