Abstract

Pure entities consist of mass or energy without the presence of the other: the inertial rest mass is all mass and no kinetic energy ; the photon is all kinetic energy and no mass. Pure entities may be compared at the ontological level. From this analysis it is shown that Einstein’s second postulate of special relativity is actually derivative from a more fundamental attribute of all pure entities. Part two of this essay focuses on the space contraction and time dilation of moving physical objects. Arguments against attributing these changes to space and time itself are offered. Instead, the roles of kinetic energy and of de Broglie wave effects are presented as a better explanation.