This paper presents a comprehensive theoretical framework deriving gravity, inertia, and the nature of matter from hydrodynamic first principles. Starting from two foundational axioms—(1) motion is purely relative with no experimentally accessible absolute frame, and (2) oscillation traps energy into stable configurations—we demonstrate that known physics emerges as low-energy effective field theory describing collective behaviour of empty space exhibiting superfluid-like dynamics. The framework synthesises Superfluid Vacuum Theory (Volovik), Stochastic Electrodynamics (Haisch–Rueda–Puthoff), and Sakharov's induced gravity to derive: emergent Lorentz invariance from Fermi point topology; matter as self-sustaining oscillons maintained by ponderomotive forces; gravity as the Secondary Bjerknes Force (acoustic radiation pressure between resonant structures); and the Equivalence Principle as tautological rather than coincidental. Convergent validation from multiple physics disciplines: The Koide formula relating charged lepton masses (verified to 0.01% precision) is shown to be isomorphic to the Descartes Circle Theorem and to circulant matrix eigenvalues describing coupled oscillators with trigonal symmetry. The PMNS neutrino mixing matrix has been experimentally reconstructed using three coupled pendulums (Savla, 2024), demonstrating that flavour oscillations are mathematically identical to classical beat phenomena. The tensor polarisation of gravitational waves—previously considered incompatible with fluid models—is addressed through the emergent metric formalism. In Volovik's framework, the effective spacetime metric is constructed from the order parameter triad of the chiral superfluid vacuum, producing a rank-2 symmetric tensor whose perturbations carry the spin-2 quadrupole structure observed by LIGO. This is distinct from Transverse Zero Sound, which is a spin-1 (ℓ = 1) collective mode—a photon analogue, not a graviton analogue. Recent condensed matter developments support this programme: Liang et al. (2024) observed chiral graviton modes in fractional quantum Hall states, and Chojnacki et al. (2024) identified spin-nematic Goldstone bosons with graviton-like dispersion in frustrated magnets. Additional validations: Sine-Gordon breather physics explains discrete mass quantisation; Volovik's topological charge N = 3 explains exactly three generations; wave closure geometry in toroidal vortices derives the fine structure constant α ≈ 1/137 (Meucci, 2024—awaiting peer review and independent verification); the Spiral Periodic Table demonstrates the same harmonic principles (2n² shells) operating at atomic scales. Key results include resolution of the vacuum catastrophe via Gibbs–Duhem equilibrium, explanation of the hierarchy problem, and a falsifiable prediction: gravitational wave echoes from gravastar cores (distinguishing HQG from standard General Relativity). The mathematical correspondences across soliton theory, plasma physics, topology, and information theory are too precise and too numerous to be coincidental. They suggest that the Standard Model is the spectroscopy of the vacuum; General Relativity is its acoustics. This constitutes the theoretical companion to "Harrison's Theorem of Anti-gravity" (DOI: 10.5281/zenodo.18210447), which presents experimental predictions and falsification criteria. Discussion and feedback: https://github.com/Gptham123456/Hydrodynamic-Quantum-Gravity/discussions