Winter Before Autumn

This paper sets forth the conjecture that late medieval society by about 1300 was a self-organized system that approached, or had achieved, a state of criticality that persisted until at least the end of the fifteenth century. Fundamental attributes of self-organized criticality account for the resilience1 shown by late-medieval society at the time and in the aftermath of the horrific experience of the Black Death. Self-organized criticality is an emergent feature of systems composed of agents capable of complex behavior. These agents can be people, machines, or grains of sand, functioning in systems that look like societies, networks, or sand piles. The sand pile is the canonical self-organized system. As a grain of sand, multifaceted and of roughly uniform size, is dropped one at a time to create a pile of sand, the slope of the pile is formed. Below a critical threshold value for the slope, a grain of sand dropped on the pile dislodges at most a few neighboring grains in a tiny avalanche that never exceeds a very small number of grains. At or above the critical threshold value for the slope, a grain of sand dropped on the pile dislodges an unpredictable number of neighboring grains, producing an avalanche of unpredictable size. Any given single impact of a grain of sand can produce a barely noticeable ripple in the sand pile, or it can produce