Article II — Spectral Finiteness without Ontological Quantization: Blackbody Radiation and the Domain of Validity of the Quantum Description

This paper revisits the historical blackbody radiation problem as a test case for the domain of validity of physical descriptions. Rather than treating the ultraviolet divergence of the Rayleigh–Jeans law as evidence of the failure of classical physics, the analysis shows that the divergence arises from an implicit assumption of an unbounded frequency domain, independent of physical realizability. By introducing a time–frequency criterion for event realization, previously developed in Article I, the radiation spectrum becomes finite without invoking ontological energy quantization. Planck’s law is thereby reinterpreted not as proof of discrete energy ontology, but as a formally correct description operating within a physically constrained domain of applicability. The work follows the historical development from Kirchhoff’s universality principle, through Wien’s empirical findings, to Planck’s original formal motivation, emphasizing that quantization emerged as a solution to spectral finiteness rather than as an explicit ontological claim.