A Geometric Ratio cπ Derived from the Spacetime and Speed of Light geometry

The central new result of this version is the geometric ratio cπ = α^(61/10)/(4π A(4)^5) =1.7734573703×10^-28 — the spacetime analogue of π, derived entirely from PA axioms. Justas π is forced by Euclidean circle geometry, cπ is forced by the 1+3 spacetime ℍ geometry andthe ℂ/ℍ Hurwitz boundary. It is identified concretely in the hydrogen atom as the ratio α/(2π × d),where d is the diameter between the two antipodal electromagnetic vertices. The photoncrosses that diameter in exactly d Planck times at speed exactly 1. cπ is the completegeometric characterization of c. The value 299,792,458 m/s is its shadow in human units.