natural process (criterion)
The standard definition, according to English chemical thermodynamicist Edward Guggenheim (1933), of what constitutes the differences between an unnatural process and a natural process, based on the Clausius inequality, for standard earth-bound systems. [1]
In science, unnatural or ‘what is unnatural’, as contrasted with natural, is defined by processes or reactions, for standard earth-bound systems, that meet the following criterion: [1]

dG > 0

This is called the Lewis inequality that are ‘thermodynamically impossible’, defined in 1923 by American physical chemist Gilbert Lewis, based on the various Gibbs inequalities, which he termed as a “universal rule” for freely reacting isothermal-isobaric processes (e.g. ones that occur between reacting humans). [2] In generalized form, what is natural for any system or body of the universe is defined or quantified those processes or reactions that meet the Clausius inequality (1856).

See also
Natural science

The following are related quotes:

“Contrary to popular belief, being alive is unnatural.”
Michael Guillen (1995), Five Equations that Changed the World (pg. 6)

1. Guggenheim, Eduard, A. (1933). Modern Thermodynamics by the Methods of Willard Gibbs (pgs. 5, 17). London: Methuen & Co.
2. Lewis, Gilbert N. and Randall, Merle. (1923). Thermodynamics and the Free Energy of Chemical Substances (pg. 160). McGraw-Hill Book Co., Inc.

Further reading

● Ball, Philip. (2011). Unnatural: the Heretical Idea of Making People (pg. 3). Vintage Books.

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