Pressure-Mediated Gravity (PMG): A Speculative Toy Model for Emergent Gravity via Superfluid Vacuum Dynamics

We propose Pressure-Mediated Gravity (PMG) as a speculative toy model in which spacetime is treated as a superfluid vacuum medium whose density perturbations generate emergent gravitational phenomena via pressure gradients. The framework reproduces Newtonian gravity in the high-acceleration regime through a corrected depletion equation ∇²ρ = +αρ_b (attractive sign), and reproduces MOND-like scaling a ∼ √(a₀a_N) in the deep-vacuum limit. The relativistic Gross–Pitaevskii equation for a logarithmic superfluid provides a quantum mechanical foundation for the depletion dynamics. An emergent spacetime metric conformally related to Painlevé–Gullstrand form shares mathematical structure with curved spacetime solutions. Crucially, this work presents a non-relativistic toy model with significant unresolved challenges: (i) mass-proportional coupling is assumed rather than derived from vacuum microphysics, so the framework accommodates—but does not explain—the weak equivalence principle; (ii) the characteristic acceleration a₀ lacks first-principles derivation, with physically motivated parameters yielding a 44-order-of-magnitude numerical discrepancy relative to observation; (iii) the emergent metric contains a dimensional conformal factor that alters timelike geodesics without demonstrated dynamical suppression; (iv) no recovery of full general relativity (lensing, cosmology, gravitational waves) has been demonstrated; and (v) Lorentz violation constraints require unphysically small healing lengths (ξ ≲ 10⁻²⁰ℓ_P). The framework should be viewed strictly as a conceptual exploration of hydrodynamic gravity analogs inspired by laboratory analog gravity experiments—not as an established theory of nature.