From discourse to facts through simulation of complex systems

The Covid pandemic19 has awakened recurrent debates about the future of cities. Some speculate on a gradual abandonment of large metropolises and a return of populations to the countryside, or to small or medium-sized towns. Similar predictions invoking a trend of "counter-urbanisation" had been made in the mid-1970s but did not materialise. Before risking predictive hypotheses, a thorough analysis of the dynamics of cities is necessary. We observe how cities, which are organised in systems of cities, maintain their size relationships over time. The main explanation for this persistence lies in the importance of the interactions between cities and urban stakeholders. Dynamic models of complex systems can simulate this development. They provide elements to explain the cognitive dissonance between individual and collective ways of living in the world. They also make it possible to envisage reasoned planning for a successful ecological transition and to reduce inequalities.