Circular Economy: Theoretical Benchmark or Perpetual Motion Machine?

“Two guiding questions to ask when assessing EOL options for waste materials or products are: How much energy is required to restore the recovered material back to the desired material or product?, and, How does this quantity compare with obtaining the desired material or product from virgin or primary sources?” operating “without the aid of any power other than that generated by the machine itself and which machine, when once started, will operate for an indefinite time” (The Inventor’s Department 1911, 443)—a machine that goes round and around indefinitely without any input of energy. The Office viewed such applications as “ . . . opposed to well-known physical laws . . . ”. Today, the dream of perpetual motion and unlimited free energy lives on, but the physical laws governing motion have, thus far, refused to yield. Perpetual motion remains a utopian ideal—a theoretical benchmark against which to pursue and measure progress, but an ideal nonetheless. It is tempting to indulge the idea of an entirely circular economy (CE) as a practically achievable reality. A CE future is one in which waste no longer exists, one where material loops are closed, and where products are recycled indefinitely— an economy that perpetually gyrates without any input of depletable resources. For real materials and processes, this is, in any practical sense, impossible. Every loop around the circle creates dissipation and entropy, attributed to losses in quantity (physical material losses, by-products) and quality (mixing, downgrading). New materials and energy must be injected into any circular material loop, to overcome these dissipative losses. If circularity is an ideal state, then to maintain credibility we should avoid giving any impression of full attainability. In other domains, we adopt the prefix “theoretical” to make this clear. Thus, the theoretical efficiency limit for an energy device is understood to be unachievable in practice. Given the impos-