In that case, as is done in STR, the absolute nature of light expresses itself in the fact that the speed of light is the same in any inertial reference frame. [5] This is very counterintuitive.

See the article '"Frames of Reference" revisited' by Alistair Steyn-Ross and Donald G Ivey, American Journal of Physics 60 (12), 1069-1085, December 1992, which contains an annotated script of the ...