Relativity

Dependence of one quantity or knowledge upon another. The Theory of Relativity formulated by Albert Einstein, based upon the principle that the universe is a four-dimensional (time-space) continuum, includes the conclusions that there is no absolute length, that unobstructed light rays have a constant velocity irrespective of the relative velocity between the observer and the source of light, that the velocity of matter can never reach the velocity of light unle the matter becomes light, that the ma of a body depends on its velocity.