Every day, we expend energy when we con­trol the net­works in our lives. For example, to drive our car, we utilize a net­work whose com­po­nents include the car's accel­er­ator, steering wheel, and brake. Knowing how much that effort "costs" can help deter­mine which com­po­nents to manipulate--and to what degree--to ensure the smoothest, safest ride as you acclerate from 55 to 90 miles per hour. Physicists now reveal a measuring device that could guide scientists in controlling real-world complex systems.

Source: Cutting costs: Sustainability matters even in complex networks