Emergence of FLRW Cosmology from Discrete Horizon Layering

We present a kinematic reconstruction in which the growth of a spherically symmetric black-hole horizon defines an effective, expanding interior geometry. Adopting an external-observer perspective, horizon growth is organized as a discrete sequence of completed incorporations of Planck units of geometric mass, used purely as a bookkeeping and causal-ordering device. Physical degrees of freedom are associated with a stretched horizon located a Planck proper distance outside the geometric event horizon, where an operational time parameter remains well defined. Using only (i) discrete horizon growth, (ii) the area–information relation, and (iii) an information-limited stacking prescription for reconstructing radial depth, we show that a homogeneous and isotropic interior geometry emerges as the continuum description of the coarse-grained horizon history. Equal increments of incorporated mass are mapped to equal increments of enclosed interior volume, fixing the radial scaling and eliminating the central density divergence that would arise from naive Schwarzschild layering. An operational identification of fractional horizon growth with fractional interior rescaling then yields a coasting expansion law, a(t) ∝ t, with H(t) = 1/t. Imposing maximal symmetry on constant-time slices selects the spatially flat representative of the FLRWfamily. The resulting interior metric is not postulated but reconstructed, and its geodesic structure is recovered from local propagation rules expressed in terms of horizon-derived mass–per–cell pointers. Effective fluid quantities, including weff = −1/3, arise only as diagnostic re-parameterizations of the reconstructed kinematics. The framework requires no bulk stress–energy tensor, Einstein field equations, or microscopic model of horizon degrees of freedom. It should be read as a constructive existence proof: given a small and explicit set of horizon-based structural inputs, a spatially flat FLRW interior with linear expansion emerges as uniquely within this reconstruction class as the natural continuum descriptor of the interior geometry.