The Developmental Péclet Number: Turing Reaction-Diffusion as Drift-Diffusion, Cell Fate as Void Crossing, and the Waddington Landscape as Void Geometry

Turing's 1952 reaction-diffusion equations are drift-diffusion equations with spatial structure: the activator-inhibitor competition is governed by a Péclet number Pedev = Dₐctivator/Dᵢnhibitor, and pattern formation occurs precisely when Pedev > 1. The Waddington epigenetic landscape maps exactly onto void geometry — cell fate decisions are V* threshold crossings, differentiation is irreversible commitment above threshold, and cancer dedifferentiation is a conjugacy violation attempt. This paper derives the developmental Péclet number, maps morphogenesis milestones to Pe transitions, applies T3 (constraint cost), T10 (coupling floor for minimum morphogen concentration), and the Fantasia Bound (maximum potency × maximum commitment is impossible), and generates six falsifiable predictions extending the cross-substrate convergence of the void framework to developmental biology.