Coherence Half-Life (τ½): A Cross-Domain Measurement Framework for Structural Decay and Early Warning

This manuscript proposes Coherence Half-Life (τ½) as a candidate cross-domain observable for measuring structural decay in coherence-bearing systems. Using the Standard Coherence Fidelity Layer (SCFL), the paper defines τ½ formally, specifies a replication-ready measurement protocol (τ½-M1), and presents empirical case analyses across power systems, financial institutions, organizational collapse, computational substrates, and operational healthcare. Across the cases examined, coherence decay is consistently well-described by an exponential form, suggesting a shared structural pattern that may precede operational rupture. The manuscript does not treat this as settled law; instead, it frames τ½ as a falsifiable measurement hypothesis supported by preliminary cross-domain evidence and bounded by seven explicit falsification conditions. The work is positioned as a foundation paper: it introduces the observable, defines the epistemic limits, and outlines the pathway by which τ½ could be independently tested, replicated, and potentially developed into a standardized framework for structural early-warning measurement.