4
$\begingroup$

Are we taking the photon spin to be one to describe electromagnetic force or there is any equation (is it relativistic Schrodinger or Dirac equation?) with a solution that tells us that its value is one?

$\endgroup$
  • 3
    $\begingroup$ For measurement of the photon's angular momentum, the classic paper is by Richard Beth, published in Physical Review in 1936, doi.org/10.1103/PhysRev.50.115 $\endgroup$ – rob Nov 21 at 20:24
  • $\begingroup$ The photons are the quanta of electromagnetic field so it's in those equations that you have to look.. $\endgroup$ – lcv Nov 22 at 11:25
2
$\begingroup$

The question $\textit{why it has spin 1}$ is inappropriate. Particles, by definition, are embedded into irreducible representations of the Poincaré group, i.e., a field. Fields with distinct Lorentz representations have distinct phenomenology and so we must $\textbf{choose}$ the representation of the field in order to describe the correct phenomenology of the particle.

The photon is a particular case of this; it a boson with two degrees of freedom (two independent polarizations) which is its own antiparticle. In particular, the circular polarization of the photon is characteristic of massless spin 1 particles, since other spins like 0 or 2 have different polarization patterns. So, without going to deep into the theory, it is phenomenologically unavoidable to have a spin 1 photon.

$\endgroup$
  • $\begingroup$ How do you sync what you said with this answer (e.g. "It is also what is meant by that photons have helicity, not spin")? $\endgroup$ – bolbteppa Nov 23 at 14:57
  • $\begingroup$ Oh, in my answer I am being sloppy by using the word "spin", but just like any other massless particle the photon has helicity, which accounts for two degrees of freedom. Is that what you meant? $\endgroup$ – Masso Nov 24 at 0:43
0
$\begingroup$

Photons are spin-1 particles, they can be polarized in two different ways, circular (left und right), like electromagnetic waves. They obey the Maxwell equation $\partial_\mu F^{\mu \nu}=j^{\nu}$. The question why is not so easy to answer. The photon is the U(1) gauge boson so it has to have integer spin.

$\endgroup$
  • $\begingroup$ Why does the U(1) gauge boson have to have integer spin? $\endgroup$ – Lars D. Nov 22 at 3:31
  • $\begingroup$ Photons obey $E=pc$. EM fields obey the Maxwell equations and its solutions describe where to expect a photon. $\endgroup$ – my2cts Nov 23 at 18:03

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.