2063: Carnot Cycle

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Carnot Cycle
The Carnot cycle is more properly known by its full title, the "Carnot-Tolkien-Wagner Ring Cycle."
Title text: The Carnot cycle is more properly known by its full title, the "Carnot-Tolkien-Wagner Ring Cycle."


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This comic shows a Pressure–volume diagram which is used in this case for a Carnot cycle, a theoretical thermodynamic cycle and covers most thermodynamics classes which looks very much like the figure drawn. However in this case, Randall has replaced the labels of the 4 stages of the real Carnot cycle with new ones.

Each step is explained below

Step in Comic Step in the real Carnot Cycle Explanation
1. Isometric expansion. When heated, the gas becomes larger due to increasing volume Reversible isothermal expansion of the gas at the "hot" temperature, Th (isothermal heat addition or absorption). The comic text uses a circular argument. Additionally, "isometric" (equal dimensions) could mean that the gas does not change in volume, in contrast to the change in volume here.
2. Isotonic expansion. The gas expands further due to dark energy while percent milkfat remains constant. Isentropic (reversible adiabatic) expansion of the gas (isentropic work output). Isotonic is commonly associated with sports drink (and not thermodynamics). Dark energy is hypothesized to be a cause for the expansion of the universe.
3. Isopropyl compression. While inflation is held constant, the gas contracts due to tightening interest rates. Reversible isothermal compression of the gas at the "cold" temperature, Tc. (isothermal heat rejection) Isopropyl alcohol is commonly used for cleaning. Inflation and contraction could refer to changes in gas volume, but the reference to interest rates puts them in the context of macroeconomics. Raising ("tightening") interest rates tends to reduce inflation and/or "contract" the economy. In economics (and other sciences) to better understand model parameter relations, some parameter may be held constant in theory. This could refer to the Fisher equation Holding one parameter constant is also done in the Carnot cycle (for a physical parameter): not only in theory but also in practice! (In free market economies the inflation cannot be directly held constant).
4. Decline and fall. The gas diminishes and goes into the West while remaining Galadriel, completing the cycle. Isentropic compression of the gas (isentropic work input). Galadriel is a character in The Lord of the Rings. She is one of the leading elves, a race that in the time of the book is said to be dwindling (in number and importance) in Middle Earth and migrating westward to Valinor. Galadriel is one of the last elves to leave, after successfully resisting temptation to take the One Ring and become an all-powerful queen who dominates Middle-earth, instead saying "I will diminish, and go into the West, and remain Galadriel."

Title text: Richard Wagner's Ring cycle consists of four operas. J.R.R. Tolkien wrote The Lord of the Rings. Their works are known as Literary cycles.


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The Carnot cycle is a theoretical construct from thermodynamics describing an ideal way to produce work using a temperature differential. The shape of the diagram matches diagrams of said cycle. The different stages in the Carnot cycle are either isentropic or isothermal. 'Isometric', 'Isotonic', and 'Isopropyl' all play on the 'iso' prefix. 'Isometric' also describes the shape of the diagram. 'Isotonic' seems to have something to do with muscles... which I suppose have some relation to engines as well—they both do work. 16:11, 24 October 2018 (UTC)

Indeed, isotonic and isometric are types of exercises for muscle contraction. Isotonic means that they provide constant force, isometric that they produce no movement in the joints. Maybe the joke is that this are muscle constractions on a expanding phase of a cycle 22:18, 27 October 2018 (UTC)

Did anyone notice that there is a note on the top of XKCD about how to register to vote? Zachweix (talk) 17:18, 24 October 2018 (UTC)

Randall often gives some hints to elections, in this case it's the United States House of Representatives elections, 2018 on November 6, 2018. --Dgbrt (talk) 17:30, 24 October 2018 (UTC)
There are other things being voted on, aside from the House of Representatives. One third of the United States Senate is also up for election (as happens every two years), as well as numerous state offices. 20:35, 24 October 2018 (UTC)

Please read the Editor FAQ about tables, this here was a good example where tables should not be used (check the history at this comic for the former layout.) Furthermore we should explain the comic but not the real Carnot Cycle, that's done in the Wiki link or at least it should be done in a separate chapter. --Dgbrt (talk) 18:06, 24 October 2018 (UTC)

I'm sure it doesn't need a full explanation, but because the pairings of the stages are part of the joke, I think it's necessary to explain what each stage is. But just enough to explain the contrast. –P1h3r1e3d13 (talk) 18:39, 24 October 2018 (UTC)
I agree. --Dgbrt (talk) 18:46, 24 October 2018 (UTC)
Thermodynamics is the hell! I've always hated it. But I entered the essential original terms with a short explanation. And now I feel we should reverse-translate Randalls words to the real thing, or more precise: a similar sentence using accurate words. --Dgbrt (talk) 20:36, 24 October 2018 (UTC)
Thermodynamics isn't the hell, it's unexplainable... IMHO real physicists shouldn't stuck on entropy, that's not a measurable value. It's more like... ohh, I don't want to say this here. Nonetheless I tried to give a short description on that official terms. --Dgbrt (talk) 00:37, 28 October 2018 (UTC)

Decline and Fall could also reference Evelyn Waugh - though it is a stand alone novel, his first, not part of a cycle. Arachrah (talk) 12:13, 25 October 2018 (UTC)

Randall loves tautologies (see comics 703, and 1602) should we mention that "The gas becomes larger due to increasing volume" is a tautology? 19:08, 29 October 2018 (UTC)

Inflation is probably wrong explained

One section before dark energy is mentioned, in Cosmology this energy causes the cosmic inflation. I'm sure Randall talks about this. But maybe we just should mention both. --Dgbrt (talk) 18:12, 24 October 2018 (UTC)

The cosmic inflation is badly presented at Wikipedia. There was a Nobel Prize in 2011 exactly about this, but it's hard to find this at the corresponding Wiki articles. That's because I'm linking an article from National Geographic. Nonetheless, as a physicist I'm sure not the Nobel Prize but the conclusions will be proven as over-interpreted, but that's not part of the actual explanation here. --Dgbrt (talk) 20:34, 27 October 2018 (UTC)

Is there a pun in the title text on token-ring (Tolkien ring) networks? Mlv (talk) 18:39, 24 October 2018 (UTC)

Nice idea, but I don't see that because there is no IBM here. --Dgbrt (talk) 20:40, 24 October 2018 (UTC)

Wagner Ring Cycle probably refers to a part of the Five-Minute Comics: Part 1 in which Cueball and Bach are running away from Wagner, who is on his ring cycle. (talk) (please sign your comments with ~~~~)

Decline and fall

Current explanations for this reference don't seem to adequately explain why it would be a stage in a four-part cycle. Actually, the first thing which comes to mind is the four-stage pride cycle (repentance, prosperity, pride, destruction, repentance et cetera), which is often referenced when analysing the plot of the Book of Mormon (though I don't see why it would be limited to that context). However, the precise term "decline and fall" doesn't seem to be used in the diagrams that first come up in a search for that (though it would be a fitting description for the destruction stage), and I don't know how well known that device is outside of LDS circles, so I'm not sure if that's being directly referenced.

The other thing which comes up is the lag, growth, stagnation, decline model which is often used for describing the development of a bacterial culture, though I've also been taught a remarkably similar model in the context of popularity over time of seaside resorts (with the addition of a possible rejuvenation stage), so it's not limited to biology. Although while it is a four-stage model with a "decline" stage, it's not inherently a cycle.

I suspect those might not the only things that have "decline and fall" as one of four parts ("cyclic", in either sense, or otherwise).

-- HarJIT 14:21, 27 October 2018 (UTC)

Title Text

The Name Carnot-Tolkien-Wagner Cycle is similar to other hyphenated names used for scientific hypotheses. For example, there's the Bose-Einstein condensate and the Einstein-Podolsky-Rosen Paradox (further examples in this article). Thaledison (talk) 18:18, 26 February 2019 (UTC)