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B Particle Spin

  1. Nov 12, 2017 #1


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    Could anyone please help me understand particle spins?
    I read the 'A Brief History of Time' and now would like to understand them better. Basically from zero.
    Any resources?
    I have had a look at Wikipedia, but the language is not clear and there is too much information.
    Thank you.
  2. jcsd
  3. Nov 12, 2017 #2


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    A number of QM books start with spin, but I'm not sure you have the mathematical or physics prerequisites to study QM at undergraduate level. I'm not sure what to suggest. You might try Susskind's lectures:

  4. Nov 12, 2017 #3


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    No, I do not have much mathematical understanding, unfortunately...
    I am not really looking for uni level things and I don't want too much information
    I just would like a short and sweet understanding of spins for a high school level.
    Thank you, @PeroK.
  5. Nov 12, 2017 #4


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    That would be, I suggest, popular science. QM is a university level subject. There's not really a high-school version, as far as I know. One probem would be trying to learn Quantum Spin, Angular Momentum, Harmonic Oscillation before you've learned the much simpler classical versions.

    Another problem is that QM is based on Hamiltonian Wave Mechanics (or a more abstract mathematical formulation). You can't really take on Hamiltonian mechanics before you've learned classical mechanics.

    It's not clear to me what you would gain by jumping into QM without these prerequisites. Certainly not in the long-term.
  6. Nov 12, 2017 #5
    Do you know what the classical magnetic moment of a rotating (spinning) charge is? That we can measure magnetic moments of particles is evidence of them having intrinsic angular momentum.

    Think of orbiting electrons in an atom. They build up the angular momentum of the atom that generates the magnetic moment. Now consider subnuclear particles and grant them angular momentum. In their rest frame, that angular momentum is called spin (including that of a single electron). Things get a little more complicated if those particles are believed to have no spatial extent, but don't worry about that yet unless you want to get deeply into the math. Just think of spin as intrinsic angular momentum.
  7. Nov 13, 2017 #6
  8. Nov 13, 2017 #7


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    Although an electron (or other fundamental particle) isn't really a little ball that spins around its axis classically like a spinning baseball or the Earth's 24-hour rotation, its quantum-mechanical "spin" (intrinsic angular momentum) does contribute to an object's macroscopic angular momentum. This is demonstrated by the Einstein-de Haas effect which I discussed in this post:

  9. Nov 13, 2017 #8
    Think of it this way: spin is an intrinsic quantum number -- just like charge -- that manifests in an observer's space-time context by contributing to angular momentum. We know nothing of what spin is in a purely intrinsic context (where there are no space-time properties); all we know is how to manipulate the math.
  10. Nov 13, 2017 #9
    We do know that spin of higher electron orbitals can approach the speed limit "c" in which case, as in the example of Au, relativistic effects apply to even quantum context... which is why gold is golden.
  11. Nov 13, 2017 #10
    Spin does not have a linear "speed". Electron orbitals are not electron spin.
  12. Nov 13, 2017 #11
    But they are related...
  13. Nov 13, 2017 #12
    They are related by addition but only in a space-time context because orbital angular momentum has meaning only in a space-time context. Spin has meaning independently of that. I think the OP was interested in spin in particular not angular momentum in general.
  14. Nov 13, 2017 #13
    Start from the heart.
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