Full Idea
William Thomson, Lord Kelvin, declared (in 1865) the second law of thermodynamics: mechanical work inevitably tends to degrade into heat, but not vice versa.
Gist of Idea
Work degrades into heat, but not vice versa
Source
Frank Close (Theories of Everything [2017], 3 'Perpetual')
A Reaction
The basis of entropy, which makes time an essential part of physics. Might this be the single most important fact about the physical world?
Book Reference
Close,Frank: 'Theories of Everything' [Profile Books 2017], p.28