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