Entropy
Entropy is a subtle and difficult concept that seems important in understanding consumption and the ability of a practice to continue over long timescales.
Erwin Schrödinger argued that life feeds on negative entropy in the 1944 book What is Life?
Kenneth E. Boulding discussed the application of the concept of entropy to energy, matter and possibly knowledge in 'The Economics of the Coming Spaceship Earth' in 1966.
If after a long time intelligent life still existed on this earth, it must still be possible to withdraw negative entropy from somewhere. This conclusion is probably trivial and saying little more than that the sun must still shine, bringing the argument back to the one about energy. But there could be more subtle and important uses of the entropy perspective independent from energy e.g., with respect to distribution of materials, and information/culture/civilization as initiaded by Boulding. tbd
- Wikipedia's entry on entropy provides various aspects and a lot of links