Networks on the edge

Intracontinental power grids are even more vulnerable to catastrophic failure than previously suspected, according to an analysis reported online this week in Nature Physics.

Networks - a system of connected and interdependent individual units - are themselves often linked together. Previous simulations have suggested that such ‘networks of networks’ are robust against breakdown so long as they operate below some critical point. Otherwise, a failure in one element can bring the rest crashing down. But these studies assumed that the subnetworks are positioned randomly. In the real world, mountain ranges, coastlines and transport infrastructure impose geographical constraints on the location of the nodes that ruin this simplistic view and make the subnetworks more structured. Amir Bashan, Shlomo Havlin and colleagues now show that no subcritical region of safety exists in realistic systems, and that networks of networks are always extremely vulnerable. The authors suggest that their results might also apply to some types of communication and computer networks.