Two branches of physics have diverged to the point that they are now in direct conflict. The theory of Special Relativity, proposed by Einstein in 1905, claimed that motion is purely relative, that for two bodies moving with constant velocities their motion is a relation between them and not a property of one or the other; there is no body absolutely at rest to which the motion of each can be referred. At that time the universe was believed to consist only of our own galaxy, the Milky Way, but in the following decades astronomical observations revealed a vast number of galaxies outside of our own stretching into the far reaches of space. Their spectral red-shifts indicated their velocities of recession from us and these were found to be proportional to their distances. This was evidence for an expanding universe in which a local rest frame is defined as that in which the galactic red-shifts and the microwave background radiation are the same in all directions. Any deviation from this isotropy would be a measure of the observer's motion through the cosmos. This is a clear conflict between theory and observation that needs to be resolved. It is found that the problem arises from an error in Einstein's original paper concerning the properties of time. He concluded that if a clock A is moved at constant velocity to a second clock B its motion causes it to run slow so that, on arrival, A's clock indicates an earlier time than B's. But if motion is purely relative the relation between A and B is symmetrical so we could equally well conclude that B's clock is slower than A's. The only possible outcome consistent with the principle of relativity is that the clocks agree when they meet. For this reason and others the effect know as time dilation is an invalid deduction from the theory. This being so a clock is unaffected by motion and remote clocks can be synchronized by transportation of a standard clock from one to the other. In this way a lattice of synchronized clocks can be set up to form a universal time scale. Combining this with the fundamental hypothesis of space-time, that the speed of light is invariant, leads to a theory based on the Voigt transformation rather than that of Lorentz. This modified theory contains a preferred inertial frame and a universal time, features that correspond to the those of the real universe. According to the Big Bang theory all matter was originally compressed into a small volume and at time zero began a uniform expansion, leading to a universe which is always homogeneous and isotropic. To an observer moving with local matter, known as the Hubble flow, the recession of the galaxies is the same in all directions. The Hubble flow defines the local rest frame and the uniform aging of all matter defines a universal cosmic time. Clearly this theory of Cosmic Space-time agrees closely with the observed properties of the universe. It is based on the Voigt transformation which differs from the Lorentz transformation only by a constant factor; consequently most of their physical properties are the same, including the invariance of the laws of physics and the equivalence of mass and energy. So nearly all the experimental and observational evidence that supports relativity theory also supports cosmic space-time. A few experiments claim to measure time dilation but this is not predicted by relativity theory so we must look elsewhere for an explanation of these results.