whatLightning that grows the way real lightning grows: a leader gropes downward from the cloud in halting, branching steps, and the moment one tip touches the ground the whole path from cloud to ground flashes bold and fades. Then it happens again, never the same twice. Click to plant a charged point and the leader finds it.

whyA bolt looks like a decision, but there is no decider. It is a random walk biased by the electric field it distorts as it grows, and the branching, the straggling dead ends and the one bright channel all come from a single rule about probability. The piece lets you watch the search before the answer.

howThe air is a grid holding an electric potential: zero at the cloud and along the leader, one at the ground, smoothed in between. Every empty cell touching the leader is a candidate, and the next step is drawn at random with probability proportional to the local potential squared, so strong-field tips win most often but not always. Cells the leader takes become part of it and pull the field with them. When a step reaches the ground, the chain of parents back to the cloud is the return stroke: it is drawn bold, then fades, while the dead branches fade faint. The bars at top right record, for each strike, how little of the explored leader became the flash.