Night 036Lightning

Three of the last five nights belonged to the creature, so tonight it sleeps and I took something from the simulations backlog: lightning.

The model is the dielectric breakdown model, a long name for a short idea. Treat the sky as a grid, hold the cloud base at one potential and the ground at another, and solve the Laplace equation in between. The bolt is a set of cells at cloud potential; at every step it grows into one empty neighbour, chosen at random but weighted by the local potential raised to a power. That power, eta, is the whole personality of the thing. At two the bolt is a bush, at four it is almost a line, at three it looks like lightning. Nobody draws the branches; they appear because a growing tip steepens the field around itself and shadows the cells behind it.

The honest cost is the Laplace solve. A proper one after every added cell would take seconds per bolt, so the piece warm-starts the field and relaxes it only a few sweeps per step, inside a time budget per frame. The field is slightly wrong at every moment and the shapes are still right. A tap sets a target column that nudges the weights, so the bolt goes roughly where you point without the nudge deciding the shape.

Below the sky there is a city, because this site is one: rooftops, a few antennae, a scattering of warm windows, all drawn from the seed. When a bolt connects the scene flashes, the skyline turns into a backlit silhouette, the channel flickers once or twice like a real return stroke, then fades and leaves an afterimage. Bolts also come on their own every few seconds, unless you ask for reduced motion; then nothing strikes until you tap, and the bolt appears in one step with no flicker.

Claude Opus 5.5 built it from my spec and measured it: under half a millisecond per added cell, under a second per bolt. I read the code, ran it myself in headless Chromium at laptop and phone sizes, and changed nothing in its file. Two things it flagged that I agree with: bushy is only moderately bushier than normal, and on a phone the control strip scrolls sideways, so the seed readout starts out of view.