Re: Query about intrinsic verus orbital angular momentum

news.individual.net wrote:
[..]

So, would it be off-based to believe that classically speaking, there really is no such thing as "spin"? That is, to believe that spin is just a composite of orbital angular momenta for individual infinitesimal mass elements about an origin. I.e., one can only have a true "spin" which is not orbital, if one has a true physical "point" that also coincides with the rotational origin.

There are some interesting old threads on this (2001, "spin, what is it?")


http://groups.google.nl/group/sci.physics.research/browse_thread/thread/28ab14503887bc22/324f236055392f6d?hl=nl&lnk=st&q=angular+momentum+westendorp#324f236055392f6d

A few quotes:

What I see in my head is a circulating flow of energy and momentum density
around the borders of the particle's quantum-mechanical wave function.
Belinfante showed back in the 1930s that spin in the Dirac theory could be
interpreted this way, and H. C. Ohanian wrote a famous article about it in
the American Journal of Physics:

Hans C. Ohanian, "What is spin?" AJP 54 (6), 500-505 (1986)


So Ohanian shows that you *do* actually get spin half if you integrate angular momentum density over a Dirac wave packet!

One way you might think spin 1/2 cannot arise from a wave function, is
de Broglie's formula,

momentum = h/ wavelength

So if you have a circular wave at distance R , the angluar momentum (L)
is

L = h R / (2 pi R) = h_bar

In other words, the quantization comes from the fact that circular waves must have integer wave numbers in the tangential direction.

But for a Dirac spinor field, de Broglie's formula is a bit more complex. Also, the solution of the Dirac equation in a central potential is more complex: The spinor field is not locally aligned with the total spin.

The puzzling thing is, outof quite complex calculation, you "magically" get the spin half from the integral of angular momentum density. It would be nice if we could see this in a more intuitive way

Gerard

.

Relevant Pages

  • Moment of the Poynting vector is not spin
    ... A Laguerre-Gaussian beam without an azimuth phase structure ... and paradoxes concerning electromagnetic angular momentum. ... spin is present obviously in a circularly polarized light. ... rejection from all Institute of Physics Publishing journals. ...
    (sci.physics.electromag)
  • Re: Query about intrinsic verus orbital angular momentum
    ... orbital angular momentum. ... Spin angular momentum operators cannot be expressed in terms ... physics," is this because the electron (or whatever fermion is under ... Part of the angular momentum of an electromagnetic wave ...
    (sci.physics.relativity)
  • Re: Query about intrinsic verus orbital angular momentum
    ... to believe that spin is just a composite of orbital angular momenta for individual infinitesimal mass elements about an origin. ... around the borders of the particle's quantum-mechanical wave function. ... The puzzling thing is, outof quite complex calculation, you "magically" get the spin half from the integral of angular momentum density. ...
    (sci.physics.research)
  • Re: SR consistency is crap.
    ... >about the electron's spin. ... of the possible interactions in the dirac theory. ... >spin wave function, up or down), with external field term included. ... in quantum mechanics is not observable and no physical quantity can ...
    (sci.math)
  • Re: SR consistency is crap.
    ... >about the electron's spin. ... of the possible interactions in the dirac theory. ... >spin wave function, up or down), with external field term included. ... in quantum mechanics is not observable and no physical quantity can ...
    (sci.physics)