Dimensional Projections in FRW Kinematics: The Emergence of the Dark Sector

Dark energy and the vacuum discrepancy arise from modeling cosmic expansion as a 3D fluid instead of a 2D boundary invariant. Evaluating equilibrium strictly at a radiative decoupling surface yields a mass-independent invariant: π³/15 ≃ 2.0671. Projecting this limit to the macroscopic horizon analytically derives the empirical dark energy fraction (ΩΛ = π³/45 ≃ 0.689) without free parameters. Spatial flatness fixes the complementary matter fraction (Ωm ≃ 0.311). This partition natively yields the observed onset of cosmic acceleration (zacc ≃ 0.642), relaxes early dark matter requirements, and contextualizes the H0 tension as a topological defect fraction. Macroscopic gravity emerges inherently as a boundary constraint.