For the question What all has intrinsic spin? it was answered that

Spin is a number that tells you how the state of the object transforms under rotations.

How I imagine such rotations for photons and for electrons?

  • $\begingroup$ Imagine rotating the laboratory apparatus rather than the system (in this case, a particle) being observed. This is a “passive rotation” rather than an “active rotation”. They are equivalent. $\endgroup$ – G. Smith Jul 1 at 5:13
  • $\begingroup$ @G.Smith To 90° or 180° and in which direction(s)? $\endgroup$ – HolgerFiedler Jul 1 at 5:21
  • $\begingroup$ If the system has a particular spin, it will transform in a particular way under a rotation by any angle on any direction. The details are called the representation theory of the rotation group. The simplest rotation to consider is a 360-degree complete rotation around any axis. For systems with half-integral spin, this is not the same as no rotation! $\endgroup$ – G. Smith Jul 1 at 5:37
  • $\begingroup$ @G.Smith ... and only for special angles (180°, 360°) the state will be the same as the previous state. I guess the direction of rotation does not matter. $\endgroup$ – HolgerFiedler Jul 1 at 5:44
  • $\begingroup$ The direction doesn’t matter if you can treat space as isotopic. But if there are external fields affecting the system, though, you can’t do that. $\endgroup$ – G. Smith Jul 1 at 5:48

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