The light is launched into the soap film through an optical fiber. <br /> <br />The optical beam propagates within the thin film, which acts as a slab waveguide with a locally varying thickness. <br /> <br />The light scatters from the thickness variations and forms the pattern of branched flow. <br /> <br />Credit: Patsyk et al, doi: 10.1038/s41586-020-2376-8.
