nicholas georgescu-roegen (a romanian-born economist whose work in the 1970s began to define this new approach) models the economy as a living system. like all life, it draws from its environment valuable (or “low entropy”) matter and energy, for animate life, food; for an economy, energy, ores, the raw materials provided by plants and animals. and like all life, an economy emits a high-entropy wake, it spews degraded matter and energy, that is... waste heat, waste gases, toxic byproducts, the molecules of iron lost to rust and abrasion. low entropy emissions include trash and pollution in all their forms. matter taken up into the economy can be recycled, using energy; but energy, used once, is forever unavailable to us at that level again. the law of entropy commands a one-way flow downward from more to less useful forms. thus, georgescu-roegen, paraphrasing the economist alfred marshall, said: “biology, not mechanics, is our mecca.”