Introduction to the chaos focus issue on the dynamics of social systems

In social science, we consider systems that consist of an usually large number of individuals whose actions and behaviors are mediated by the interactions among them. After the change in the scientific paradigm brought in by Newton, by which every physical behavior could be predicted from very simple physical laws, people tried to apply the same simplifying principles to other sciences. The apparent similarity of social systems with some problems of interest in the physical sciences became evident quite early. In the same way that a macroscopic body, gas, solid, or liquid, which consists of many interacting units, atoms or molecules, obeys the general laws that rule their behavior, i.e., the law of perfect gases of the Dulong–Petit law for the specific heat of solids, it was naïvely expected that the general laws governing the overall behavior of a social or economical system could arise from very simple general principles....