Causal Percolation and the Symmetry of Horizons: From Pre-Geometry to Late-Time Fragmentation

Finite propagation speed is treated here not merely as a kinematic limit but as an ontological throttle governing when reality becomes globally coherent. Because no influence propagates instantaneously, global causal structure cannot be primitive. It must assemble through the accumulation of irreversible relational closures propagated at finite speed. This work introduces a dimensionless causal-percolation parameter, Π(τ), defined as the integrated density of irreversible closures within a causal diamond of duration τ. When Π(τ) ≪ 1, reality is subcritical: quantum, indeterminate, and lacking global objectivity. When Π(τ) ≫ 1, reality is supercritical: classical, centerless, and geometrically stable. Horizons arise wherever causal percolation is incomplete, either because causal structure has not yet formed, as in the early universe, or because global connectivity fragments at late times under acceleration. The framework reframes quantum measurement, classical emergence, spacetime geometry, and horizon thermodynamics as regime-dependent consequences of finite-speed causal percolation rather than contradictions among physical laws.