Gravity as Pressure Gradient

This paper proposes that gravity is a pressure gradient in a superfluid vacuum. The vacuum is treated as a physical medium with measurable mechanical properties — density, compressibility, and a thermodynamic equation of state. Matter is a region where vacuum energy has been reconfigured into a stable standing pattern, reducing the local contribution to ambient vacuum pressure and creating a radial pressure deficit. The surrounding medium presses inward to restore equilibrium. This inward pressure gradient is gravity. The central quantitative result is a derivation of gravitational radiation power using Lighthill's acoustic quadrupole formula, yielding the Peters (1964) result P = −(32/5)(G⁴/c⁵)(m₁m₂)²(m₁+m₂)/a⁵ with the coupling constant K = 2/3 absorbed into every empirical measurement of G. Applied to the Hulse–Taylor binary pulsar PSR B1913+16, the framework matches the observed orbital decay rate to within 0.2%. The paper extends to variable gravity via an effective refractive-index metric reproducing Schwarzschild phenomenology, frame-dragging as quantised superfluid vorticity, dark matter as a long-range logarithmic tail in the vacuum pressure profile, dark energy as residual vacuum tension, and electromagnetism as a second class of vacuum excitation with Maxwell's permittivity and permeability as mechanical properties of the medium. Eight falsifiable predictions are presented, the sharpest being the angular distribution of gravitational radiation: the framework predicts sin⁴θ (power concentrated in the orbital plane), while General Relativity predicts (1 + 6cos²θ + cos⁴θ) (power concentrated along the orbital axis). The expanding network of gravitational wave detectors will be decisive. The framework builds on the analogue gravity programme of Unruh, Visser, and Barceló; the superfluid vacuum theory of Volovik; and the logarithmic BEC cosmology of Zloshchastiev, while identifying substantive divergences from each. Open problems are discussed explicitly, including the spin-2 mode identification, the post-Newtonian extension, and the vacuum equation of state degeneracy. A companion paper, "Gravity as Acoustic Radiation Pressure: The Secondary Bjerknes Force in the Superfluid Vacuum," develops the oscillatory mechanism underlying the same framework.