A universe of motion compotes the physical universe, in which motion is a reciprocal relation between space and time. All motion consists of discrete units. Each individual unit of motion is a relation between one unit of space and one unit of time, a motion at unit speed. This unit speed and its constituents, clock time and clock space, are absolute magnitudes. Unit speed is identified with the speed of the physical locations of photon. Absolute magnitudes do not exclude relative magnitudes, such as material speed, coordinate space and coordinate time. Mass, invariant with speed, as reported by I. Newton, L. Oken and D.B. Larson, is another fundamental absolute physical magnitude. The contention of some teachers of the theories of relativity that mass near unit speed is a relative magnitude, not an absolute magnitude, results from the misinterpretation of the equation, E=mc^{2}. E does not denote the total energy of a moving mass, but rather only the rest energy of the mass.

## Reciprocal System of theory

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