Dark Energy as Residual Pressure: A Four-Dimensional Interpretation of the Measured Expansion History

This paper proposes a pressure-based interpretation of cosmic expansion in which ordinary three-dimensional space is the observable hypersurface of a larger four-dimensional expanding structure. Global expansion is driven by pressure in the four-dimensional substrate and limited by vacuum inertia plus exterior or boundary reaction pressure. Gravity is treated as local curvature within the expanding hypersurface, not as a force capable of slowing, reversing, or controlling the universe’s global expansion. Dark energy is reinterpreted as the observed residual pressure imbalance of this system, rather than necessarily as a fundamental cosmological constant or independent energy substance. The analysis is limited to post-recombination expansion history and is agnostic regarding inflation. It does not model primordial nucleosynthesis, the origin of the cosmic microwave background, or the full CMB acoustic spectrum. Instead, it focuses on directly comparable geometric expansion measurements, especially H(z), redshift, BAO, and related distance measures. A central diagnostic converts the Hubble parameter from fractional expansion rate to normalized radius-growth speed. With a = R/R0 and H = a_dot/a, measured values of H(z) become a_dot = aH(z). Representative values at z = 0, z ≈ 1.34, and z ≈ 2.34 show that although H(z) changes by more than a factor of three, the corresponding normalized growth speeds vary much less. This suggests that post-recombination expansion may be compatible with smooth pressure-driven growth of a four-dimensional cosmic radius. The next required step is a quantitative pressure-inertia expansion law relating acceleration to internal pressure, exterior reaction pressure, and effective vacuum inertial loading. The present work does not claim a complete cosmology, but establishes a measurement-facing framework for testing cosmic expansion as four-dimensional pressure flow.