Structural Constraints on the Gravitational Wave Spectrum from Causal Time

This work derives structural constraints on the stochastic gravitational wave spectrum from the causal structure of time in cosmology. By analyzing how global temporal accumulation operates in non-isolated expanding spacetimes, we show that distinct temporal frameworks impose opposite signs on the spectral slope. The result functions as a structural selection criterion between competing cosmological time structures, independent of source modeling, detector specifics, or phenomenological fitting.