Three levels of understanding of special relativity

The first complete formulation of special relativity (SR) is that of Einstein who postulated the light speed invariance. The second level assumes the longitudinal length contractions and the slowing down of clock rates by the same factor γ
⁻¹
. This level discusses the role of different synchronizations. In the third level SR is seen as a consequence of the spin motion of the elementary particles. It seems possible to detect the privileged system S for which the electromagnetic radiation due to the spin motion of all the electrons in the universe is isotropic.