Structural Differentiation Cosmology (SDC) v1.7: A Single Observational Criterion Distinguishing Projection from Physical Acceleration

Structural Differentiation Cosmology (SDC) v1.7 presents a closed-universe framework in which the observed cosmic acceleration is interpreted not as physical expansion driven by dark energy, but as an observational projection of irreversible internal structural differentiation. This version explicitly formulates a single decisive observational criterion distinguishing SDC from the standard ΛCDM cosmology. Although both frameworks may reproduce the same expansion history H(z), they diverge unavoidably in the mutual consistency of independent cosmological probes—specifically between expansion-related observables and structure-growth observables—at sufficiently high redshift. The framework introduces no new physical entities, no adjustable dynamics, and no modifications of gravity. It is directly falsifiable by forthcoming observational programs including DESI, Euclid, Roman, and CMB-S4.