Cascade

the grain wasn’t special. the pile was ready.

drop sand — the pile self-organizes to the edge of collapse

Every dropped grain follows the identical simple rule, toppling once it holds four and passing one to each neighbor, with no memory of what came before it — yet the pile spends most of its life balanced at a point where an ordinary drop can go nowhere or can cascade for a long time, and there is no way to tell which in advance. The sizes that come out follow a stark pattern: mostly nothing, occasionally enormous, nothing typical in between.

Concepts: self-organization, criticality.

An interactive you play with one thumb, on Wundr.