efficiency gains. The creation of tangible, material products and services and also the creation of knowledge and culture (less tangible but not wholly intangible) require an increase in order. To increase order and fight the natural tendency to greater disorder (entropy), requires energy for useful work applied locally. Local order (products of economy and culture on planet earth in this case) will increase although the entire entropy of the universe will still increase. Earth is a closed system in thermodynamic terms. This is a technical definition which means matter cannot enter or leave the system (except in very minor ways in the case of earth) but energy can enter and leave. As a closed system, with a maximum energy inflow (and close to balancing outflows) via solar radiation (insolation), the earth has a real maximum and finite energy flow available. A portion of this will be available for useful work. Again, there will be a finite and real maximum. However, energy flow may not be the limting factor for economic grwoth. Following Liebig's Law of the minimum, there may be (and probably will be) some other limiting factor which intervenes first to limit the growth of the human economy on earth. Liebig's Law states; Growth is limited not by the total amount of resources available, but by the scarcest resource as the limiting factor. Footnote: Lay people are often confused about what "closed system" means in thermodynamic terms and think that it means nothing (neither matter nor energy) can enter