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Visualization of electron spin

  1. May 11, 2010 #1

    zonde

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    Gold Member

    I have seen in this forum number of discussions about problems of spin visualization.
    I think the problem is that spin usually is visualized as rotating charged billiard ball. But this classical picture requires that this billiard ball after any time interval resembles itself just with different orientation in space.

    I have taken a bit different approach and I can visualize spin quite fine.
    That is instead of assuming that this billiard ball resembles itself at any time I assume that it resembles itself only after certain periods of time meaning that it has some phase space where similarities are seen when you compare the same states from phase space.
    Let me describe this with diagram (elementary 1/2 spin particle - electron):
    Code (Text):
    (P->)~(   )
    after full period (2Pi)
    (   )~(<-P)
    after full period (2Pi)
    (P->)~(   )
    Now magnetic field of particle comes from periodic displacement of charge between two points in space. Another thing as can be seen from this diagram is that particle has the same orientation in space after two periods.
    If we take spin 1 particle (photon) instead we have different diagram:
    Code (Text):
    (P->)~(   )
    after full period (2Pi)
    (   )~(P->)~(   )
    after full period (2Pi)
          (   )~(P->)~(   )
    There we have the same orientation in space after one period.

    So I thought that maybe someone will find this visualization helpful.
     
  2. jcsd
  3. Jun 29, 2010 #2
    I have a few questions.

    1. For the spin 1/2 diagram the start (P->)~( ) and end (P->)~( ) phase spaces each have two states. However, for the spin 1 diagram you have added one state to the end situation, that is, the number of states go from 2 to 3 ? Why is this ? Seems to me the spin 1 diagram should start as ( )~(P->)~( ) and then evolve over time as three states? What am I missing ?

    2. For the spin 1 diagram, the spin direction does not shift, as it does for spin 1/2 diagram ? Why is this ? I mean, many spin 1 particles (which would be bosons) have + (P->) and - (<-P) spin possibilities. So, should not the spin 1 diagram show (P->) shift to (<-P) over time, same as for spin 1/2 diagram ?

    Sorry for such simple questions, but if I know the answer I would not ask.
     
  4. Jun 29, 2010 #3

    zonde

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    Gold Member

    Idea of diagram is that at every row it shows particle in the same state as in other rows only with different spatial position (and orientation). So the empty parentheses shows place of particle for the same state period before and period after.
    Of course you can start the diagram for photon with ( )~(P->)~( ) but it does not mean 3 states.

    As I understand spin +/- for elementary bosons is usually interpreted as helicity of circular polarization. So first of all it should not change over time.
    Second, circular polarization can be explained using linear polarization and vice versa. So it depends what you take as more fundamental property of photon - circular or linear polarization. I prefer to think that linear polarization is more basic and that circular polarization is composite property of photon ensemble not single photon. And in that case helicity is not really property of single photon and there is no meaningful way to speak about +/- spin of photon as it is usually defined.

    If it's not some general knowledge but only some idea of mine then you have no other way than to ask what I mean with that. No need to apologize. :wink:
     
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