The laws of thermodynamics
Sadi CarnotJames Prescott JouleRudolf ClausiusWilliam Thomson (Lord Kelvin)
This page delivers no verdict; it presents claims and evidence with their sources. No theory in science is absolute. Method
For everyone
Energy cannot be created or destroyed, only changed in form (first law). Heat does not flow by itself from cold to hot, and no engine can turn all heat into work (second law). These laws set the limits of every machine from the steam engine to the refrigerator.
For specialists
Carnot (1824) showed that the efficiency of an ideal heat engine depends only on temperatures (η = 1 − T_c/T_h). Joule's paddle-wheel experiments measured the mechanical equivalent of heat. Clausius (1850, 1865) formulated the first and second laws and defined entropy. Boltzmann gave the second law a statistical interpretation (S = k log W): it is not strict but overwhelmingly probable behaviour. Fluctuations in which entropy decreases temporarily in small systems have been observed experimentally.
Claims
- Energy is conserved in a closed system; the entropy of an isolated system does not decrease.[1]
Evidence
Supporting
Joule measured that a paddle wheel driven by falling weights heats water, with a constant ratio between work done and heat produced.[2]
Challenging
Short-lived entropy decreases, apparent "violations" of the second law, were measured in microscopic systems, in line with the statistical predictions of the fluctuation theorem.[3]
Connections
Sources
- Article (1850). Ueber die bewegende Kraft der Wärme und die Gesetze, welche sich daraus für die Wärmelehre selbst ableiten lassen. Annalen der Physik 155(3), 368–397DOI 10.1002/andp.18501550306archive
- Article (1850). On the mechanical equivalent of heat. Philosophical Transactions of the Royal Society of London 140, 61–82DOI 10.1098/rstl.1850.0004archive
- Article (2002). Experimental demonstration of violations of the second law of thermodynamics for small systems and short time scales. Physical Review Letters 89, 050601DOI 10.1103/PhysRevLett.89.050601archive
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Cite this page
Athena contributors. (2026). The laws of thermodynamics. Athena: The tree of human knowledge. Retrieved November 1, 2026, from https://latifkedi.github.io/athena/en/d/termodinamik/
@misc{athena_termodinamik,
title = {The laws of thermodynamics},
author = {{Athena contributors}},
year = {2026},
howpublished = {\url{https://latifkedi.github.io/athena/en/d/termodinamik/}},
note = {Athena: The tree of human knowledge. Accessed: 2026-11-01}
}Added: September 27, 2026 · Last changed: September 28, 2026 · Page history