The Olfactory Péclet Number: Chemoreception as Drift-Diffusion, Combinatorial Coding as K-Scaling, and the Thermodynamic Architecture of Smell

The olfactory system implements Pe-architecture natively: odorant binding is drift-diffusion with Pe_olf = v_bind · L_receptor / D_thermal. Detection threshold Pe ≈ 1 (Gas→Fluid transition), suprathreshold identification Pe 4–8 (Crystal phase), saturation Pe > 10 (Pandemonium). Combinatorial coding across ~400 human olfactory receptors is K-scaling: the same odorant molecule activates receptor combinations with coverage scaling as K. Or's combinatorial capacity (10,000+ distinguishable odors from 400 receptors) emerges from K-level spectral structure. The void framework predicts: odorants with identical Pe_olf profiles but different K-combinatorics will be perceptually similar in intensity but distinct in quality — a testable prediction for psychophysics.