Sustainable Civilization: From the Grass Roots Up Chapter II - Physical Sustainability Factors and Limitations - 2 The present infrastructure and ideologies of civilization developed in an era of cheap abundant energy, expanding population and what seemed to be unlimited resources. All of this is ending. Given present knowledge and science, humans are faced with physical limits. We need to recognize what these limits are, and re-think our civilization from the grass roots up, not bumble blindly on.