Special relativity to a first observer O, and frame S′ (pronounced "S prime") belongs to a second observer O′. Since there is no absolute reference frame in relativity theory, a concept of 'moving' doesn't strictly exist, as everything is always moving with respect to some other reference frame. Instead, any two frames that move at the same speed in the same direction are said to be "comoving". Therefore, "S" and "S"′ are not "comoving". The principle of relativity, which states that physical laws have the same form in each inertial reference frame, dates back to Galileo, and was incorporated into Newtonian physics.
Criticism of the theory of relativity Kretschmann was mistaken (subsequent papers showed that such a theory would still be usable), another argument can be made in favor of general covariance: it is a natural way to express the equivalence principle, "i.e.", the equivalence in the description of a free-falling observer and an observer at rest, and thus it is more convenient to use general covariance together with general relativity, rather than with Newtonian mechanics. Connected with this, also the question of absolute motion was dealt with. Einstein argued that the general covariance of his theory of gravity supports Mach's principle, which would eliminate any "absolute motion"