whatA meadow of fireflies that begin flashing at random and, within a minute, flash together. The sparkline at top right is how together they are, rising from near zero to one.

whySynchrony is the simplest emergence there is: thousands of Southeast Asian fireflies really do pulse as one, with no conductor. It shows how a crowd can agree on a rhythm when each member only ever adjusts a little toward what it sees.

howEvery fly is a clock that climbs from zero to one and flashes at one. Each flash a fly sees nudges its own clock forward, near flashes more than far ones, and more so the later it is in its cycle. A nudge past one flashes at once, so flashes cascade. Nothing else. Click to scramble a patch and watch it re-lock.