Picture in your mind the delta of a river — the way the main channel splits into smaller rivulets and tributaries. Something similar occurs in waves as they propagate through a certain kind of medium: the path of the wave splits, breaking up into smaller channels like the branches of a tree.

This is called a branching flow, and it’s been observed in such phenomena as the flow of electrons (electric current), ocean waves, and sound waves. Now, for the first time, physicists have observed it in visible light — and all it took was a laser and a soap bubble.

Depending on the structure of the medium, different things can happen to waves travelling through; they can attenuate, disperse, bend, spread, or continue flowing.