On the validity of the principle of relativity in the physical universe

We present several examples showing that a significant discrepancy exists between the principle of relativity in the real physical universe and its mathematical model, especially for high relativistic velocities. According to this principle, all inertial systems are equivalent, i.e., indistinguishable. However, a fast-moving traveler in any direction in the physical universe can readily determine that his system is not equivalent with others, since there exists a preferred cosmic reference system S 0 , associated with the cosmic microwave background (CMB) radiation, which has the same temperature 2.73 K in all directions. At high velocities with respect to S 0 , the traveler will detect strong anisotropy in this radiation, which may shift the CMB into infrared or even x-ray radiation due to the Doppler effect. A similar anisotropy appears when detecting intergalactic gas and dust, as well as light from stars and galaxies. Thus, the traveler can observe that the spectrum of galaxies on one half of the celestial sphere is shifted toward blue, while on the opposite half it is shifted toward red. Moreover, all neighboring galaxies, without exception, would be moving with respect to the traveler at high relativistic velocities in nearly the same direction. The reference system S 0 is unavoidable and cannot be overridden, eliminated, or ignored, since the CMB is present everywhere. This violates the principle of relativity in the physical universe. Since this principle is a fundamental assumption in the special theory of relativity, it is essential to verify whether the theory provides an adequate approximation of reality.