Title GETT Correspondence Paper 4.2: General Relativity Correspondence II: Einstein-Domain Dynamics and Field-Equation Recovery Abstract This paper establishes the dynamical correspondence between General Expanse Tension Theory (GETT) and General Relativity (GR) within a precisely defined physical regime. Building on the geometrisation limit derived in Paper 4.1, we demonstrate that the coarse-grained dynamics of a real, covariant singlet scalar field Φ, coupled to matter via a density-dependent interaction, admit a closed macroscopic description in which spacetime curvature evolves according to Einstein-domain equations. Starting from first-principles Φ-field dynamics, we construct the effective stress-energy tensor of the coupled matter–substrate system and show that it is locally conserved under controlled coarse-graining. We then define explicit closure conditions – including mid-density coupling stability, weak coupling variation, smooth field behaviour, adiabatic evolution, and effective universality – under which the emergent metric satisfies a curvature–source relation, where all non-Einstein contributions are isolated in a physically interpretable correction tensor. We show that, within the Einstein domain, these corrections are perturbatively suppressed, yielding recovery of the Einstein field equations to leading order, with exact correspondence in the formal limit of vanishing control parameter. The effective gravitational coupling emerges from the underlying Φ–matter interaction and is shown to be approximately constant within this regime. This result establishes General Relativity as a domain-limited dynamical closure of an underlying scalar-field substrate, providing a physically grounded reconstruction in which both the success and the limitations of GR arise from explicit, testable conditions. The work reframes gravity from a fundamentally geometric theory to an emergent macroscopic manifestation of substrate dynamics, delivering a unified framework that not only reproduces Einstein’s equations but explains why and where they apply. Description This paper presents the fourth instalment of the GETT Correspondence Series, a structured programme whose objective is to reconstruct established physical theories as exact, domain-limited descriptions emerging from the General Expanse Tension Theory (GETT). The present work establishes the recovery of the Einstein field equations as a controlled, leading-order closure of a deeper scalar-field–matter system, defined by a physically explicit Lagrangian with density-dependent coupling. Scope and Objective The primary objective of this paper is to demonstrate that, under well-defined physical conditions, the coarse-grained dynamics of the underlying scalar field Φ and its coupling to matter reduce to a self-consistent curvature–source relation of the form: Gμν=8πGeff TμνeffG_{\mu\nu} = 8\pi G_{\mathrm{eff}}\,T^{\mathrm{eff}}_{\mu\nu}Gμν=8πGeffTμνeff This recovery is not assumed, but derived through: explicit construction of the effective stress–energy tensor controlled coarse-graining of microscopic dynamics and identification of a well-defined domain of validity (the Einstein domain) Core Contributions This paper makes the following key contributions: Derivation of Einstein-Domain DynamicsThe Einstein field equations are recovered as the leading-order (O(ϵ0)O(\epsilon^0)O(ϵ0)) truncation of the coarse-grained Φ–matter system, with deviations captured by a correction tensor Δμν=O(ϵ)\Delta_{\mu\nu} = O(\epsilon)Δμν=O(ϵ). Formal Closure Conditions (Theorem Hypotheses)A complete set of covariant closure conditions is defined, including: coupling stability (mid-density plateau) spatial smoothness and scale separation adiabatic evolution effective universality potential regularityThese are unified through a single dimensionless control parameter ϵ≪1\epsilon \ll 1ϵ≪1. Controlled Coarse-Graining FrameworkA Gaussian averaging kernel is introduced to define macroscopic fields. The non-commutativity of averaging and differentiation is explicitly treated, with residuals shown to scale as: O(ℓmicro/L)O(\ell_{\mathrm{micro}}/L)O(ℓmicro/L)ensuring controlled suppression in the Einstein domain. Two-Step Conservation StructureExact microscopic conservation is shown to persist under coarse-graining, yielding: ∇μTeffμν=0\nabla_\mu T^{\mu\nu}_{\mathrm{eff}} = 0∇μTeffμν=0This result is derived explicitly and is a key structural strength of the framework. Compatibility with GR Geometric StructureThe Levi-Civita connection, curvature tensors, and Einstein tensor are constructed in full consistency with standard General Relativity formulations, ensuring compatibility with canonical treatments. Derivation of Effective Gravitational CouplingA schematic derivation of the effective gravitational constant is provided: Geff∝(λ0S0v2)2/mΦ2×RG_{\mathrm{eff}} \propto (\lambda_0 S_0 v^2)^2 / m_\Phi^2 \times \mathcal{R}Geff∝(λ0S0v2)2/mΦ2×Rwith constraints on the response function R\mathcal{R}R ensuring consistency with the observed value of GGG within the Einstein domain. Domain of Validity (Einstein Domain)The regime in which General Relativity is recovered is formally defined through inequalities on dimensionless control parameters. Outside this domain, deviations arise in a controlled manner through the correction tensor. Non-Einstein Regimes IdentifiedThe framework explicitly identifies physical regimes in which closure conditions fail (e.g. low-density, non-adiabatic, or high-gradient environments), without extending into empirical claims. Conceptual Positioning This work differs from prior emergent-gravity approaches (e.g. induced gravity and thermodynamic derivations) in that: it begins from an explicit, renormalisable scalar-field Lagrangian incorporates density-dependent coupling at the field level performs controlled coarse-graining with explicit residual scaling and derives the Einstein equations as a domain-limited effective theory General Relativity is therefore interpreted not as a fundamental description, but as the leading-order closure of a deeper physical system under well-defined conditions. Structure of the Paper Sections 2–3: Definition of the underlying scalar-field–matter system Section 4: Coarse-graining framework and averaging procedure Section 5: Energy–momentum structure and conservation Section 6: Formal closure conditions (Einstein-domain hypotheses) Section 7: Emergent geometric structure and field-equation recovery Section 8: Correction tensor and higher-order deviations Section 9: Recovery of known limits Section 10: Domain of validity (formal statement) Section 11: Breakdown of Einstein closure Section 12: Correspondence audit Section 13: Outlook Significance This paper provides a fully specified, internally consistent derivation of Einstein-domain dynamics from a microscopic scalar-field framework, with: explicit control of approximations clearly defined domain of validity and direct correspondence with established General Relativity It represents a key step in the GETT Correspondence Series, establishing the dynamical and geometric foundations required for subsequent empirical and phenomenological investigations. Keywords General Relativity; emergent gravity; scalar field theory; coarse-graining; Einstein field equations; effective field theory; stress–energy conservation; gravitational coupling; domain of validity; correspondence principle