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.
Relativity priority dispute laws of physics in gravitational fields". This would leave the special theory of relativity as the unique theory of relativity. Keswani cited also Vladimir Fock for this same opinion. This series of articles prompted responses, among others from Herbert Dingle and Karl Popper. Dingle said, among other things, ".. the 'principle of relativity' had various meanings, and the theories associated with it were quite distinct; they were not different forms of the same theory. Each of the three protagonists... was very well aware of the others ... but each preferred his own views" Karl Popper says "Though Einstein appears to