Bak-Tang-Wiesenfeld self-organized criticality
The BTW sandpile (Bak, Tang, Wiesenfeld 1987) self-organizes to a critical state where avalanches of all sizes occur. The avalanche size distribution follows a power law P(s) ∝ s⁻ᵧ with γ ≈ 1.2 in 2D — a signature of self-organized criticality (SOC). No parameter tuning is needed: the system finds criticality automatically.