Einstein’s Special Theory of Relativity (SR) relates time dilation to the velocity between the observer and the observed object as if they are identical. Our new theory breaks this symmetry by relating the velocity of the object not directly to the observer, but instead to the center of gravity of object and observer. The reason why such a mass influence has not been reported might be that the mass of the observer in most experiments is much greater than that of the object, for example when earth is observing, satellites or detectors are studying nuclear masses.