Entropy is the measure of the disorder of a system
Design philosophy that seeks to imitate the no waste, closed loop systems seen in diverse natural systems.
Cybernetics is the interdisciplinary study of the structure of complex systems, especially communication processes, control mechanisms and feedback principles. Cybernetics is closely related to control theory and systems theory.
Systems theory is an interdisciplinary field of science and the study of the nature of complex systems in nature, society, and science. This could be a single organism or an ecosystem, any organization or society, or any electro-mechanical or informational artifact.
Significant decrease in human population and/or political/economic/social complexity over a considerable area, for an extended time.