Arcadia
An opening scene from act II of a November 1998 performance of Arcadia done at Willamette University Theater. [3]
In literature thermodynamics, Arcadia is a 1993 play by British playwright Tom Stoppard in which the characters, juxtaposed between the years 1809 (date of publication of Goethe’s Elective Affinities) and 1989, attempt to interpret German scientist Johann Goethe’s 1809 affinity theory of sex, love, relationships, and death, a theory which itself is based on Swedish chemist Torbern Bergman’s 1775 textbook A Dissertation on Elective Attractions (viewed using a human chemical perspective), in the modern-day second law of thermodynamics perspective, with a mixture of chaos theory, mathematics, among other mixed topics. [1] The play alludes to a dialog on relationships and sexual energy.

American English professor Raymond J. Wilson III, in his 2003 “Gardens in Stoppard, Austen, and Goethe”, seems to have been one of the first to make a connection between Arcadia and Elective Affinities. [4]

Etymology
The enigmatic phrase En in Arcadia ego ("even in Arcadia I exist"), used in the play, made its first debut before in a painting by Itailian artist Guercino (or Giovanni Barbieri) in c.1618, featuring a skull with a bee perched on it, below which is found the riddled phrase, which loosely means that even in paradise or utopia by death and sex coexists in the balance of natural harmony.

In Guercino painting, the phrase 'Et in Arcadia ego' - meaning 'And in Arcadia I' - is found directly below the skull which in turn is facing directly toward the viewer. This clarifies to some extent the meaning of the mysterious motto. The 'ego' part (i.e. 'I' as in 'me') can be understood to refer to the skull, that is, death. So we would have: 'Even in Arcadia death'. To put it another way, 'death is also to be found in Paradise; or, in the midst of earthly delights, the transience of life cannot be disregarded'.

Dialogues
The following are noted dialogues, selected by Jay Labinger (1995): [5]

“THOMASINA: When you stir your rice pudding, Septimus, the spoonful of spreads itself round making red trails like the picture of a meteor in my astronomical atlas. But if you stir backward, the jam will not come together again. Indeed, the pudding does not notice and continues to turn pink just as before. Do you think this is odd?
SEPTIMUS: No.
THOMASINA: Well, I do. You cannot stir things apart.
SEPTIMUS: No more you can, time must needs run backward, and since it will not, we must stir our way onward mixing as we go, disorder out of disorder into disorder until pink is complete, unchanging and unchangeable, and we are done with it forever. This is known as free will or self-determination.”
— Tom Stoppard (1993), Arcadia (pgs. 4-5; first 10 minutes)

“THOMASINA: If you could stop every atom in its position and direction, and your mind could comprehend all the actions thus suspended, then if you were really, really good at algebra you could write the formula for all the future; and although nobody can be so clever as to do it, the formula must exist just as if one could.”
— Tom Stoppard (1993), Arcadia (pg. 5; first 10 minutes)

“THOMASINA: ... Newton's equations go forwards and backwards, they do not care which way. But the heat equation cares very much, it goes only one way ...
SEPTIMUS: So, we are all doomed!
THOMASINA: (Cheerfully) Yes.
SEPTIMUS: So the improved Newtonian universe must cease and grow cold. Dear me.”
— Tom Stoppard (1993), Arcadia (pgs. 87, 93)

Labinger also notes that the ending scene where Tomasina dies in a fire just before the final (1812) scene—that is she suffers her own “heat death” as Labinger puts it, he comments that a member of the audience, during his “Metaphoric Usage of the Second Law: Entropy as Time's (double-headed) Arrow in Tom Stoppard's Arcadia”, presented at Nov meeting of the Society for Literature and Science, Los Angeles, explained that he had heard that Stoppard in an interview had said that he added this touch after his son, a physics student, told him that his take on thermodynamics was rather too optimistic.

Notes
One aspect of this play that is difficult to track down is how Tom Stoppard came to be aware, if at all, about the fact that Goethe's 1809 version of science and sex, explained via chemical affinities A, and the post 1865 versions of science and sex, explained via equations that incorporate entropy S, are related via the following equations, derived in overview in 1882 by Hermann Helmholtz:

A = – ΔG

or in terms of entropy and entropy:

A = TΔS – TH

The existence of this connection is a deeply buried fact in science, especially so in 1993, at the time of penning Arcadia. It is possible, however, that this was just a fortuitous connection or guess?

Et in Arcadia ego
The phrase "Et in Arcadia ego" is quoted, in the play, by Lady Croom, the archly witty resident aristocrat of Sidley Parkin 1809, a quote from the c. 1618 paintine (above, below the skull) by Italian artist Guercino. [2]
References
1. (a) Stoppard, Tom. (1993). Arcadia. London: Faber and Faber.
(b) Stoppard, Tom. (1993). Arcadia. Samuel French, Inc.
(b) Thims, Libb. (2007). Human Chemistry (Volume One), (preview), (Google books). Morrisville, NC: LuLu.
(c) Thims, Libb. (2007). Human Chemistry (Volume Two) (section: Arcadia and Elective Affinities, pgs. 445-49) (preview), (Google books). Morrisville, NC: LuLu.
2. (a) Et in Arcadia ego (Guercino) – Wikipedia.
(b) Et in Arcadia ego – Wikipedia.
(c) Arcadia (utopia) – Wikipedia.
3. Arcadia (photos) by Chris L. Harris – Flickr.com.
4. Raymond, Wilson J. (2003). “Gardens in Stoppard, Austen, and Goethe”, in: Gardens and the Passion for the Infinite, Volume 78 (pgs. 59-). Springer.
5. Labinger, Jay A. (1995). “Metaphoric Usage of the Second Law: Entropy as Time's (double-headed) Arrow in Tom Stoppard's Arcadia”, Presented at Nov meeting of the Society for Literature and Science, Los Angeles; in: The Chemical Intelligencer (pg. 34), Oct. 31-36, 1996.

Further reading

● Stepherd-Barr, Kirsten. (2006). Science on Stage: from Doctor Faustus to Copenhagen (ch. 6: Mathematics and Thermodynamics in the Theater, pgs 128-154). Princeton University Press.

External links
Arcadia (play) – Wikipedia.
● Rich, Frank. (1993). “Critic’s Notebook; on Thermodynamics, Byron and Oh, Yes, Sex”, The New York Times, July 08.
Essay: Arcadia Notes (thermodynamics) by Carol Ann Duffy – CourseWork.info.
Arcadia (main themes) – Physics.Weber.edu.
● Arcadia: Themes, Motifs, and Symbols – SparkNotes.com.

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