I had not read GR books profoundly but I understand the basic idea - relative frames of reference and constant speed of light. Is it possible to exist absolute space, as defined below? absolute space - this is such a space and frame of reference in which all objects moves with the maximal allowed velocity - the speed of light. what that means - imagine two frames K1 and K2 that moves one according to other with velocity of v. If now we rotate K2 such that it axes coinside with x,y and z axes of K1 so that only vx is different then zero, and start to move K2 in a direction opposite to vx with velocity (c-vx), in K2 K1 will moves with the speed of light. Since that is the maximal speed there exist only one such system of reference according to which all frames moves with a velocity equal ezactly to c. an another explanation - imagine a point source of light, it irradiates photons in all directions, since according to a Frenel law (i dont remember exact definition) every point from the EM wave is a source of light, we can consider the following illustration - photons move in a 2D square lattice, after time of dt four new photons are irradiated in all four directions of the x and y axes, after time of 2dt every photon produces 4 new photons and so on: X X X X X when the number of directions is extrapolated to infinity is produced an absolute space, all photons in the world share one and the same frame of reference, am I correct? Also this space is immovable to all systems of reference.