Although acceleration is, by its descriptive definition, the expansion of velocity, where celeritas /kɛ’lɛritas/ or /tʃɛ’lɛritas/ is a Latin word translated as “swiftness” or “speed”, we prove that gravity is expansion (dilation) of the speed of light (celeritas c), i.e. the genesis of space in time. From this evidence, we explain the arrow of time. Implicitly, the foundation of a complex manifestation of nature is deduced to a tautological relationship between space-time variables, with the consequence of a unification of the reference measurement system. By unique relation, we connect the predictions of General and Special relativity. We introduce the scalar principle valid in all space-time dimensions of the universe.