Causal Spatial Subdivision and the Emergence of the Friedmann Equation

This work presents an independent construction of cosmological expansion dynamics based on a causal spatial subdivision defined by light-cone accessibility. Rather than assuming spacetime geometry or the Einstein field equations, the approach starts from Newtonian mechanics and energy conservation applied to a spherically symmetric subdivision cell whose boundary is determined by causal information propagation. Within this framework, space is not treated as a predefined geometric manifold, but as a physically meaningful partition into causally accessible regions. Once this causal subdivision is adopted, the dynamics of the cell boundary depend only on the mass-energy contained within the subdivision, in accordance with Newtonian gravity and the shell theorem. From this minimal set of assumptions, a cosmological expansion equation of the Friedmann form emerges naturally. In this construction, the cosmological constant does not arise as a dynamical source term or a flux across the subdivision boundary. Instead, it appears as a non-updating reference contribution associated with the subdivision structure itself and therefore remains a true constant. No time-dependent cosmological constant or external adjustment parameter is introduced. Furthermore, the condition H (t) t = 1 follows uniquely as a consistency requirement between two equivalent descriptions of the subdivision boundary: the causal horizon defined by light-cone propagation and the dynamical scale defined by the expansion rate. This relation is not imposed as an additional assumption, nor does it rely on specific cosmological models or acceleration mechanisms. Although the resulting equation is formally identical to the Friedmann equation of general relativity, the derivation presented here is logically independent of spacetime geometry and the Einstein field equations. The work therefore does not constitute a reinterpretation of general relativity, but rather an alternative, causally grounded construction of cosmological kinematics based on minimal physical principles.