Thermodynamics of love (Hwang, 2001)
Above: a annotated version of American computational chemist David Hwang's 2001 article "The Thermodynamics of Love", wherein he defines people chemically as "elements" (see: human chemical element), couples as "compounds", and the process of falling in love as a chemical reaction that is quantified and governed via Gibbs free energy changes, from Libb Thims' 2015 Zerotheism for Kids lecture (part two). [1]
In famous publications, "The Thermodynamics of Love" is a 2001 article, published in the Journal of Hybrid Vigor, by American chemist and neuroscience physician David Hwang, in which a Gibbs free energy theory of mate selection is outlined, albeit in humorous form. [1]

In short, in chemistry, reaction feasibility is determined by "thermodynamics", particularly chemical thermodynamics. Subsequently, the feasibilities of the various potential processes of human mating or "love the chemical reaction" would also be determined by thermodynamics.

Hwang's human thermodynamics
Hwang, however, did more than verbally justify his thermodynamics of love theory, he described it, in rather descent form, from a chemical thermodynamic point of view. [3] In particular, thermodynamics, according to Hwang, "not only explains the spontaneity of chemical reactions", but "also applies directly to various factors determining the success of human relationships". To begin with, Hwang defines the couple forming reaction as such: a theoretical chemical reaction where two elements, "male" (M) and "female" (F), combine to form a new compound called "couple" (M-F):

M + F M-F

To visually illustrate this, Hwang used free energy vs. reaction extent plots (shown adjacent). Firstly, in regards to the plots, he states that the y-axis measures Gibbs free energy and that the x-axis measures the time progression of the reaction, Hwang defines individual elements (presumably either single unattached people or bonded couples) with a collective high free energy (G) value are relatively reactive, while a compound with a low G value is likely to be stable.

Thus, according to Hwang, a reaction in which G decreases (-sG) favors formation of product because the products have less free energy than the starting compounds and are more stable. In a reaction in which G increases (+sG), in Hwang’s view, reactants are not likely to make much chemical progress. Subsequently, according to Hwang, we can apply these concepts to our theoretical male-female reaction and thus use chemical thermodynamics to answer questions such as “are two people completely natural as a pair, or are they better off apart?”

Difficulties on theory
All-in-all, aside from a few points of argument, Hwang's take on the situation is fairly accurate. One area of difficulty in Hwang's theory is the small particle count aspect involved in the thermodynamic computations of interactions between people with systems consisting of a few humans (e.g. ten human molecules in a system).

Specifically, how do the laws of thermodynamics apply to the analysis of, for instance, two particle systems, such as two people in a regioned system? General thermodynamic analysis, e.g. gas phase systems, for instance, studies "working bodies" consisting of Avogadro's number of particles, namely 10E23 particles, i.e. atoms or molecules. There have, however, been thermodynamic studies on one-particle systems. This is an advanced topic.

Hwang free energy diagrams
Hwang's free energy plots verse extent of reaction, showing stable products (top) and unstable products (bottom).
Other
See main: Thermodynamics of love
In the 1950s, Iranian mechanical engineer Mehdi Bazargan is said to have penned an article entitled "Thermodynamics of Love"; possibly still only available in Farsi.

In circa 2000, American child prodigy turned astrophysicist Christopher Hirata penned his human chemical thermodynamics and human physics based “The Physics of Relationships” (see: relationship physics) article consisting of five parts:

1. Thermochemical Approach to RelationshipsExternal link icon (c)
2. Complex Equilibria of Men and WomenExternal link icon (c)
3. Reaction KineticsExternal link icon (c)
4. Neutron Scattering: A Cautionary TaleExternal link icon (c)
5. The Shell ModelExternal link icon (c)

on the topics of a thermochemical approach to relationships, complex equilibria of men and women, reaction kinetics, neutron scattering, and shell model, written at the age of about 18 that harks of genius ranking near to that of the great insights of German polyintellect Johann Goethe (IQ=230) and his 1796 human chemical theory. [1]

In 2003, internet writer Wild Bob, in his short article “Thermodynamics of Love”, reasoned that “people often can be heard talking about the 'chemistry' in a relationship
”, and, without going into too much detail on this postulate, concludes: [2]

“Remember, it’s not chemistry that determines long term love—it’s thermodynamics.”

Chemistry, he states, may be involved in the initial attraction, but it is “thermodynamics that determines if the relationship will last.”

In 2015, Colombian-born British writer Patrissia Cuberos published The Thermodynamics of Love: the Secret Life of a God, part one of a three-part trilogy (Book I: The Secret Life of a God; Book II: Diary of an Ex-Goddess; Book III: The Physics of Romance), wherein she applies chemistry, thermodynamics, and physics to relationship dynamics; the abstract of part one is as follows: [6]

“We live in a world of relationships: from chemical bonds to boy meets girl, to families and societies, to the laws that govern the cosmic order. The trilogy is a typical love story. Indeed, boy meets girl and a relationship develops, but we all know that as Woody Allen says ‘Sooner or later everything turns to sh*t.’ In other words, in most relationships, the initial dynamic exchange of heat-energy soon becomes the dreaded lukewarm entropy, harbinger of heat death. However, the physics that seem to doom David and Kate’s relationship to the thermodynamic trap, might be able to help them to transform it into the everlasting loop of energy exchange they have always dreamed of: a superconductive love unmarred by friction from guilt, fear and resentment. Their quest will force them to challenge, and eventually transcend their all too human feelings of inadequacy, the apparently inevitable limitations of time, and the hazy, illusory lines between dream and reality, life and death.”

(add)

Quotes
The following are related quotes:

“The thermodynamics of computation, if anyone had stopped to wonder about it, would probably have seemed no more urgent as a topic than, say, the thermodynamics of love.”
Charles Bennett (1988), “Notes on the History of Reversible Computation” [4]

“The big ideas in heat are the laws of thermodynamics. So important and far-reaching are the laws of thermodynamics that some people try to use them to explain what governments should do, why people fall in love, and why there are car wrecks.”
Bill Nye (1993), American mechanical engineer [5]

See also
Surya Pati
Chemistry of love
Physics of love
Mathematics of love

References
1. (a) Hwang, David. (2001). “The Thermodynamics of Love” (WB) (pdf), Journal of Hybrid Vigor, Issue 1, Emory University.
(b) Thims, Libb. (2007). Human Chemistry (Volume One) (Hwang diagram, pg. 116). Morrisville, NC: LuLu.
(c) Thims, Libb. (2015). “Zerotheism for Kids” (Lecture: Part Two), Aug 10.
2. (a) What is Love (top 150 definitions) – Institute of Human Thermodynamics.
(b) Wild Bob. (2003). “Thermodynamics of Love”, UnsolvedMysteries.com
3. (a) Thims, Libb. (2007). Human Chemistry (Volume One), (ch. 4: section: "Love and the Combined law of Thermodynamics", pgs. 116-19), (preview), (Google books). Morrisville, NC: LuLu.
(b) Thims, Libb. (2007). Human Chemistry (Volume Two), (pgs. 673-74). (preview), (Google books). Morrisville, NC: LuLu.
(c) Thims, Libb. (2008). The Human Molecule, (pg. 62), (preview). Morrisville, NC: LuLu.
4. Bennett, Charles H. (1988). “Notes on the History of Reversible Computation”, IBM J. Res. Develop. 32(1): 16-23.
5. Nye, Bill. (1993). Bill Nye the Science Guy’s Big Blast of Science (pg. 50). Basic Books.
6. Cuberos, P.E. (2015). The Thermodynamics of Love: the Secret Life of a God (Ѻ). Amazon Media.

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