The Half Life of Fiat A Statistical History of Monetary Decay

This paper presents a statistical analysis of 21 fiat currency regimes across eight centuries and finds a universal decay constant: the mean lifespan from commodity decoupling to terminal failure is ~31 years. Using a simple exponential survival model
S(t) ≈ exp(−t/τ) with τ ≈ 31,
the analysis shows that fiat stability behaves like a relaxation process with an approximately constant half‑life, independent of ideology, geography, or institutional design.

The result is intentionally reductionist: fiat viability is treated as a temporal structural constraint, not a function of policy quality, governance competence, or macro conditions. Once a currency detaches from an invariant reference, confidence decays along a generational horizon (~30 years), after which failure modes such as hyperinflation, redenomination, or replacement become statistically unavoidable.

The framework positions fiat stability as a survival‑analysis problem, revealing consistent timing signatures across historical episodes: early collapses linked to wartime issuance, a modal decay band around 25–35 years, and a long tail of slower‑moving legacy systems. The model provides a temporal primitive for monetary drift, analogous to half‑life constants in physical and biological systems.

This is not a prediction tool or a causal theory. It is a systems‑theoretic measurement lens for quantifying confidence erosion, analyzing regime fragility, and mapping monetary decay as a universal statistical phenomenon. Applications include calibration of macro‑risk models, generational-scale hazard analysis, and comparative evaluation of fiat regimes under long‑run stress.

Scope: conceptual and statistical foundation only — no forecasts, no policy evaluation, no normative claims. The focus is purely on the invariant temporal structure of fiat decay.