Spacetime as a Causal Viscous Fluid: A Single Lagrangian for Gravity, Electromagnetism, and the Emergence of Schrödinger Dynamics

We present a deterministic field theory in which spacetime is modeled as a relativistic viscous fluid with density (x), phase (x), and four-velocity u^ (x) on a dynamical Lorentzian manifold (M, g_). Electromagnetism enters exclusively through the derivative (gauge-invariant) combination B__-qA_, structurally guaranteeing that the photon remains strictly massless. The viscous degrees of freedom (_, ) obey Israel--Stewart-type relaxation equations, rendering the system hyperbolic (causal). We prove in detail: (a) ~the equations of motion from the action principle, (b) ~U (1) gauge invariance and the Ward identity (m_=0), (c) ~recovery of free Maxwell equations in the linear limit, d) ~hyperbolicity and energy stability. We establish that total energy is exactly conserved (Bianchi identity), while the ordered (wave) energy decreases monotonically via viscous entropy production — the second law of thermodynamics in field-theoretic form. We show that the measurement independence assumption of Bell's theorem generically fails due to the non-factorization of the Gauss-constrained initial-data surface, offering a candidate mechanism for superdeterminism without ad~hoc assumptions (though the quantitative reproduction of the Tsirelson bound |S|=22 remains open). We further show that, via the Madelung transformation, the theory reproduces the Schrödinger equation in its non-relativistic limit: the phase equation becomes the continuity equation, the quantum potential emerges from the medium's gradient energy, and the medium configuration suggests a possible ontological reading as the physical pilot wave of de~Broglie--Bohm mechanics. We note that this requiredcorrecting the sign of the phase--density coupling, which independently removes a ghost in the phase sector. Preliminary numerical simulations of 1\!+\!1D and 2\!+\!1D toy models confirm Bell-bound saturation (|S|=2. 0 0. 04) ; we discuss why single-particle Schrödinger dynamics emerges while multi-particle entanglement correlations do not, tracing this to the configuration-space problem. AI Acknowledgment: The author acknowledges extensive use of Claude (Anthropic) as an AI research assistant throughout the development of this work. All scientific content, theoretical ideas, and research direction are the author's own responsibility.