“…The remarkable phenomenon of branched flow, in which waves split repeatedly while travelling through a smoothly and gently disordered refracting medium, has been studied in different contexts and from different perspectives. Examples where branching occurs (mostly two-dimensonal) are: electrons issuing from a quantum point contact [1][2][3], tsunamis passing over an ocean whose depth varies [4], rogue waves [5], microwaves [6], and recently light, in beautiful experiments and simulations [7] with incident beams and plane waves confined within soap films whose thickness varies. Investigations have centred on several aspects, including: statistics [8][9][10][11][12], ray and wave descriptions [10], controlling flow along the branches [13], and persisting localisation of the branches [7].…”