We develop the interpretation that gravity arises from electromagnetic energy loading of the quantum vacuum, treated as a physical storage medium with vacuum force scale K₀ = c⁴/ (8πG). The dimensionless scalar field ψ measures the fractional loading, and the vacuum refractive index n = eᵠ follows uniquely from the multiplicative composition law via Cauchy's exponential functional equation. We interpret the full nonlinear DFD field equation as a stress–strain constitutive equilibrium of the vacuum medium, define gravitational strain and stress in analogy with continuum mechanics, and show that the vacuum exhibits reduced gravitational permittivity at low gradients — the mechanism behind flat rotation curves without dark matter. The constitutive split parameter κ = α/4 ≈ 1. 82 × 10⁻³ is derived from gauge-emergence corrections to the optical metric. Newton's constant G = c⁴/ (8πK₀) is identified as the inverse vacuum force scale, explaining both its universality and its smallness. The vacuum stiffness is topologically structured, with normalization set by H₀ through K₀ = ℏH₀²/ (8πα⁵⁷c). Companion Python module (dfdgravity. py, 35/35 validation tests passing) included. Parent theory: Density Field Dynamics (DFD) unified theory v3. 2, https: //doi. org/10. 5281/zenodo. 18066593Alpha derivation: https: //doi. org/10. 5281/zenodo. 19178465
Gary Alcock (Mon,) studied this question.