What is an ergodic social system in the novel, Hard to Be a God?

An ergodic social system is one that has its own inner "inertia" which will dominate its behavior despite any amount of benign intervention from the outside. The authors are at pains to point out that, no matter how hard the progressors from Earth may strive to accelerate the evolution of the Arkanar society, these efforts are doomed to failure. Even the noblest intentions or the most advanced technologies cannot wrest an entire civilization away from its place and time in history.