Cooperation for Public Goods Driven by Noise.

Cooperation for public goods poses a dilemma, where individuals are tempted to free ride on othersu0027 contributions. Classic solutions involve costly feedback mechanisms with rewards and punishments, but there are important collective actions based on simple and cheap cues only, for example unplanned protests and revolts, as well as cooperation in other species. This is explained by an Ising model with asymmetric spin values representing defection and cooperation, and the assumption that when people share a goal in an uncertain situation, they tend to conform to their local majority. Then a critical level of noise, such as rumors that cause misunderstandings about the situation or provocations by opponents, causes the onset of collective action. The model thereby provides a parsimonious explanation without recourse to accurate monitoring, high network connectivity, reliable transmission of information, advanced cognition with memory, pro-social norms, incentives or leaders. It can incorporate leaders, though, and can express incentives and norms in terms of (local) fields to show that additional mechanisms are necessary when noise is below the critical level.