Synchronization occurs when large numbers of individuals co-ordinate to act in unison. In this wide definition of the word, many different types of collective behavior are examples of synchronization. A highly aligned group of birds, fish, or particles can be said to have synchronized their direction of movement. More commonly, however, when we use the word synchronization we are thinking about time. Bank robbers synchronize their watches before a robbery, the instruments of the orchestra are synchronized by the conductor and the sound is synchronized to the pictures in a film. It is this narrower sense of the word synchronization I use in this chapter. How and why do behaviors become synchronized in time?
Given that synchronization is a specific type of collective behavior it should come as no surprise that it shares many properties with systems looked at in earlier chapters of this book. In particular, and unlike with the bank robbers or the orchestra, synchronization can be achieved without a leader or centralized control. As with other types of collective behavior, we can also build mathematical models that describe how synchronization emerges from individual interactions. Indeed, some of the models of synchronization are among the most elegant models of collective behavior and have been employed successfully in understanding a wide variety of biological and social systems.
While the instruments of a concert orchestra are, at least in part, synchronized by signals from the conductor, the applause of the audience after the performance is not usually centrally controlled. Despite the lack of a central controller, in Eastern Europe and Scandinavia this applause is often rhythmical, with the entire audience clapping simultaneously and periodically. Neda et al. (2000a, 2000b) recorded and analyzed the clapping of theater and opera audiences in Romania and Hungary and found a common pattern: first an initial phase of incoherent but loud clapping,