Collective motion occurs inevitably in a class of populations of   globally coupled chaotic elements
  We discovered numerically a scaling law obeyed by the amplitude of collective mo tion in large populations of chaotic elements. Our analysis strongly suggests that such populations generically exhibit collective motion in the presence of interaction, however weak it may be. A phase diagram for the collective motion, which is characterized by peculiar structures similar to Arnold tongues, is obtained. 
N. Nakagawa (1), T. S. Komatsu (2) ((1) Department of Pure and Applied   Sciences, College of Arts and Sciences, University ...