Structural Differentiation Cosmology (SDC) describes the universe as a closed systemundergoing irreversible internal differentiation, grounded in the impossibility ofabsolute nothingness. Cosmic expansion and acceleration are interpreted as observationalprojections of structural evolution rather than physical expansion of spacetime. In this version, structural density C(t) is treated as a member of a class of admissiblemonotonic functions. Different structural classes give rise to distinct observationalsignatures, allowing SDC to be empirically distinguishable from standard cosmologywithout introducing new physical entities.