|A modern "exchange force" view of sex, from the quark interaction scale up to the human interaction scale; the exchange force in the first four cases (human, bug, bacteria, molecular) being the electromagnetic force, mediated via the exchange of photons, the exchange force in the latter two scenarios (nuclide and quark) being the strong nuclear force, mediated by the gluon. |
In 1993, playwright Tom Stoppard debuted his play Arcadia, a modern day take on German writer Johann Goethe’s 1809 Elective Affinities, wherein he incorporates talk of “sexual energy”, “heat”, entropy via his discussion of the “second law of thermodynamics”, and human chemical affinity via his talk of “the attraction that Newton left out … all the way back to the apple in the garden”, the steam engine, upon which the laws of thermodynamics were derived, among other topics.
In 1997, American authors biologist Lynn Margulis and her son, science writer Dorion Sagan, who in their 1997 book What is Sex?, argue that sex, or specifically sexual reproduction, is “a byproduct of thermodynamic dissipation.”  They give the view that sex as has a “thermodynamic background”, in that the process of coupling is a crucial part of the energy transformation process by which (with pleasure) beings reproduce their forms and increase their complexities. In the construct of the earth system, Margulis and Sagan state, through sexual reproduction, animals evolved and mate selection began, wherein organisms, choosing some mates over others, played a role in their own evolution.  In reference to forces, they state that:
“Sex [is] a powerful and mysterious force in our lives”
From a physics point of view, however, the force of sex is not a mystery and can be explained through a number of perspectives; namely through the fundamental forces of the universe (strong nuclear, weak nuclear, electromagnetic, and gravitational) and their quantification as exchange forces, in the dynamics of the interaction and in the construct of the human chemical bond, and thermodynamic forces, in the bulk driving forces of the system.
In the 2005 book Into the Cool: Energy Flow, Thermodynamics, and Life, American authors science writer Dorian Sagan and ecological thermodynamicist Eric Schneider argue that “sex is the way living dissipative systems propagate into the future” and that “sex maintains our form of thermodynamic disequilibrium by reproducing physiological systems much like us but newer and sometimes improved.” 
|A poster for Howard Bloom's 2013 talk on sex and thermodynamics at SUNY. |
In 2013, Howard Bloom gave at talk entitled “Sex and the Second Law of Thermodynamics: How Sex Breaks the Law of Physics”, the abstract of which is as follows: 
“At the turn of the 19th century, Sigmund Freud proposed something absurd, his concept of libido, the idea that humankind was driven by sex. Was Freud crazy? Or was he right? Why? And how does our sexual obsession relate to the evolution of the cosmos? How does it relate to two rules that imply that sex should not and cannot exist: the principle of least effort and the second law of thermodynamics? Is sexual selection a least-effort proposition? Is it the most energy-efficient way to a goal? And what goal could that possibly be? Is plant sex, with its extravagant use of the advertising devices we call flowers, maximizing the universe's entropy? Is the peacock's tail a sign of a thrifty cosmos? How about your sexual and romantic obsessions as you read this sentence and secretly covet the body of a person ten feet away from you? Do these things hint that the cosmos is very different than the thermodynamics obsessive beliefs? And what does that mean for the way we look at strange things like psychology?”
The following are related quotes:
“Sex isn’t something you’ve got to play with; sex is you. It’s the flow of your life, it’s your moving self and you are due to be true to the nature of it.”— D.H. Lawrence (c.1915), Collected Poetry 
● Human reproduction reaction
1. (a) Thims, Libb. (2007). Human Chemistry (Volume One). Morrisville, NC: LuLu.
(b) Thims, Libb. (2007). Human Chemistry (Volume Two). Morrisville, NC: LuLu.
2. Margulis, Lynn and Sagan, Dorion. (1997). What is Sex? New York: Simon & Schuster.
3. Schneider, Eric D. and Sagan, Dorion. (2005). Into the Cool - Energy Flow, Thermodynamics, and Life, (section: Sex and Thermodynamics, pgs. 154-55). Chicago: The University of Chicago Press.
4. Solomon, Robert C. (1981). Love: Emotion, Myth, & Metaphor (pg.253). Prometheus Books, 1990.
5. Bloom, Howard. (2013). “Sex and the Second Law of Thermodynamics: How Sex Breaks the Law of Physics” (abs) (vid), New Paltz Evolution Studies, SUNY New Paltz CSB Auditorium, Oct 9.
● Sex – Wikipedia.