Concept
In 1865 Clausius named entropy the heat transferred divided by temperature (dS = δQ/T). Boltzmann reinterpreted it as S = k ln W, where W is the number of microstates for a macrostate, giving entropy its sense of disorder or number of possible arrangements.
The second law
- Clausius statement: heat does not flow spontaneously from cold to hot.
- Kelvin-Planck statement: no engine can turn heat from a single reservoir entirely into work, so efficiency cannot exceed the Carnot limit (1 − Tc/Th).
- Entropy increase: an isolated system's entropy rises or stays constant, setting the arrow of time.
Social readings and critique
Jeremy Rifkin's Entropy (1980) argued that fossil-fuel civilisation accelerates entropy and called for a low-energy society; ecological economist Georgescu-Roegen also framed the economy as an entropic process. Yet open systems such as living things and the Earth can build local order with energy flows, so transplanting the law to society has limits.
References
- Clausius, R. (1865). Über verschiedene für die Anwendung bequeme Formen der Hauptgleichungen der mechanischen Wärmetheorie. Annalen der Physik, 201(7), 353-400.
- Atkins, P. (2010). The Laws of Thermodynamics: A Very Short Introduction. Oxford University Press.
- Rifkin, J. (1980). Entropy: A New World View. Viking.
- Georgescu-Roegen, N. (1971). The Entropy Law and the Economic Process. Harvard University Press.