Field Guide · models · order, coupling & thresholds
Self-organized criticality
A system that tunes itself to the edge.
Drop grains of sand one at a time. The pile grows, steepens, and starts to slide — and the slides come in every size. Most grains do nothing; a few set off avalanches that cross the whole pile. Plot the sizes and you get a power law: no typical scale, no average avalanche, just the same statistics from the tiny to the catastrophic.
The remarkable part, named by Bak, Tang and Wiesenfeld in 1987, is the self-organized bit. Nobody set the slope to the critical angle. Fed steadily, the pile drives itself there and stays poised on the edge of stability. The same signature appears in earthquakes, forest fires, extinctions, and market crashes.
It is the deepest reason I distrust the word "outlier". In a critical system the big event is not an anomaly that broke the rules — it is the same rule that produced all the small ones, playing out at full size. Click to dump a pile and trigger one yourself.