Talk:Second law of thermodynamics/Archive 7

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Lead section

I added the lead rewrite template to the article in order to encourage the lead to make more sense for people without a degree in physics or engineering. The MOS recommends that leads ease a reader into a concept by starting with simple language and then gradually expanding upon the concept rather than dropping them right into the middle of it.

I notice a few years back the lead paragraph was written as:

The second law of thermodynamics states that the entropy of an isolated system never decreases, because isolated systems always evolve toward thermodynamic equilibrium, a state with maximum entropy.

What were the problems with this phrasing? That is much more clear and concise for the average reader.

If the problem is that the description is not accurate enough, what could be done instead is to describe what the law means first rather than what it states, and then incorporate the various technical interpretations of the law further down in the lead. I took a stab at this angle a bit in order to give an example of what I am talking about. Adrian (talk) 21:22, 31 October 2015 (UTC)

Recent changes do not seem to have made the intro simpler. Instead new ill-defined concepts have been introduced in the second paragraph. For example:

• the restrictive characters of the walls are changed by some external agency, making the walls less restrictive and more permeable in various ways. I learned that thermodynamic systems are either closed or open, with nothing in between. How does a wall become less restrictive other than by making a hole and changing the closed system to an open one?
• The process invariably spreads, disperses, and dissipates. A thermodynamic process is defined (in the first sentence of that article) as a passage of a thermodynamic system from an initial state to a final state. So what does it mean to say that a process spreads etc.?

I think the article should only used language which either a) has already been defined in the article (or a linked article) or b) is clearly understood by most readers. Dirac66 (talk) 22:10, 31 October 2015 (UTC)

As to the concern

I notice a few years back the lead paragraph was written as:

The second law of thermodynamics states that the entropy of an isolated system never decreases, because isolated systems always evolve toward thermodynamic equilibrium, a state with maximum entropy.

What were the problems with this phrasing? That is much more clear and concise for the average reader.

Perhaps clear and concise, but deeply misleading.

Many physicists fondly dream that there is a nice non-equilibrium thermodynamics, that 'entropy' is defined for any physical system, and that it makes sense to speak of the 'entropy of the universe' read literally. The next steps along the path of muddle are clever stories of how we know better than the second law. It is not the business of Wikipedia to foster dreams in an article on a natural science such as physics.

In P.T. Landsberg's text it is set as a student exercise to criticize that "clear and concise" statement. What's wrong with it? Thermodynamics as it is known today is defined only for systems in their states of internal thermodynamic equilibrium; this statement is sometimes called the minus first law of thermodynamics; it is a fundamental presupposition, often not stated in so many words, but still necessary. To speak of the entropy of an evolving isolated system is to encourage the dream of a thermodynamics that goes outside the limitations of the minus first law. The "clear and concise" statement goes there. Not the mandate of Wikipedia. We are not here to lure innocents into error.

It is proposed "to describe what the law means first rather than what it states". It is hard to reply to this. For brevity, perhaps I can say I think it is clever rhetoric, but unhelpful.

The "stab at this angle a bit" restricts the meaning to the case of closed systems, and then leaves out irreversible work.

As to the oft-repeated well-meaning link to the Wikipedia article on entropy, I think that article is a mess and it is better here NOT to link to it.

As to the careful considerations about "new ill-defined concepts".

I am sorry that is a problem. I am not so sure that the concepts are new or ill-defined. I think they make sense in ordinary language, as well as being well established in reliable sources. The concept of the 'wall' is deeply and widely standard. A wall is characterized by what it allows to pass, its permeability. Some walls are movable so that they allow energy to pass as work. A wall that is not movable can be made less restrictive by a thermodynamic operation that makes it movable. This allows a new freedom, of PV work. With an increase in entropy. An ideal semi-permeable wall that allows passage of one component can be made less restrictive by making it pass other components as well. An adiabatic wall can be made diathermal. I think all of these are standard usages.

I am a little surprised that is a problem that a "process spreads energy". I think a process does things, or is the host or receptacle of things happening or being done. It is being here demanded that we produce an ordinary-language layman's account of the meaning of the second law, within the space confines of a lead. The word "spread" is recommended by Guggenheim for this purpose. I recently tried to introduce the word 'dispersal', which has a Wikipedia article headed Entropy (energy dispersal) about it, though that article is disputed. I think the word is valid and useful, though my effort to use it here was struck down by an editor. The word, I think, passes the ordinary-language test with flying colours. The word 'dissipate' is more traditional than either of the foregoing, recommended by Kelvin, but reservedly objected to by Planck, who hardly offered a substitute.

For the present, in order to clear the decks, I have undone the new attempts to provide a more chatty lead.Chjoaygame (talk) 00:11, 1 November 2015 (UTC)

I appreciate the explanations. As it is currently written, I cannot wrap my head around the lead section at all. I remember thermodynamics being covered in high school and the explanation of this law was not nearly this complicated, though I understand that thermodynamics is in no way a simple idea. The paragraph you added to the lead seemed to make more sense out of things, even though it was lengthy and still contained a lot of jargon. I understand I am essentially asking someone, "Explain the laws of thermodynamics to me as if I were a child in 50 words or less with no factual inaccuracies or missing caveats." Which is certainly not an easy task to say the least. But I think something can be done to make it slightly better. Adrian (talk) 01:19, 1 November 2015 (UTC)

I forgot to say that the final state is not always the state with maximum possible entropy. I won't go into detail about that now.

Perhaps I may say a little more. I looked at the article Wikipedia:Manual of Style. I did not see the part about "The MOS recommends that leads ease a reader into a concept by starting with simple language and then gradually expanding upon the concept rather than dropping them right into the middle of it." Perhaps I did not look in the right way or the right place. I am not convinced that a small child will be interested in thermodynamics. I have to confess I did not learn of the existence of thermodynamics when I was a schoolchild. I went to a normal school and highschool.

It is said that there are more different statements of the second law than there are writers of them. The present initial lead statement is a slight re-wording of Planck's. It has the following advantages, if they may be considered as such:

1. It is expressed in terms of entropy; this is perhaps only debatably an advantage.
2. It is positive. It tells explicitly of the usual or natural case, that of a process in which the entropy does in fact positively increase.
3. It doesn't require the reader to speculate too much: he is told that several systems participate, each having its entropy initially and finally.
4. It is worded so that it is true, without exception or wriggle room.

I am sorry to read that you "cannot wrap your head around the lead". I wonder if that may be because you have prejudices from your highschool days, or from your later studies, and you disagree with the purport or content of the current lead?

I don't know if a chatty first sentence will survive here. There are often raids by experts, each knowing best.Chjoaygame (talk)Chjoaygame (talk) 04:47, 1 November 2015 (UTC)

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It's not that I have prejudices, I am not a scientist nor an expert on this subject in any regard. I support a fact-based and accurate phrasing of the law, and have no preferences in which such phrasing is more or less accurate. When I mentioned my high school, what I was referring to is that my teachers and textbooks explained it to me in a way that made sense at the time. So, it seems logical that there is some way to summarize the law that would make sense to a high school or college student who is just starting to learn about the subject. I will admit that my high school was a bit more advanced than the high schools that many of my later peers experienced, so I could be overestimating the understanding of the average high school graduate, but that kind of supports my opinion here considering I can't make heads or tails about it. If you look at the Wikipedia pages for the zeroth law of thermodynamics, the first law of thermodynamics, and the third law of thermodynamics they all have great lead sections (in my opinion) that are easy to understand and clearly describe the subject matter using terms that a person with a high school understanding of physics might understand. The first law article specifically is very succinct. They all carefully describe the law then explain how it relates to other parts of thermodynamics and what it means to us, in addition to expanding upon concepts that might be confusing to some.

In the MOS this is the particular part that I am referring to:

In general, introduce useful abbreviations, but avoid difficult-to-understand terminology and symbols. Mathematical equations and formulas should be avoided when they conflict with the goal of making the lead section accessible to as broad an audience as possible. Where uncommon terms are essential, they should be placed in context, linked and briefly defined. The subject should be placed in a context familiar to a normal reader. For example, it is better to describe the location of a town with reference to an area or larger place than with coordinates. Readers should not be dropped into the middle of the subject from the first word; they should be eased into it. (MOS:INTRO)

And to a lesser degree:

Consideration should be given to creating interest in reading more of the article. (MOS:LEAD)

I suppose I should also highlight what seems to be confusing to me about the lead section in its current state: What is a "participating body"? What is a "limiting case"? What is a "reversible process" in this context? Why is the knowledge of this law important, and how does the law affect the world as we know it? These are all questions that average readers will probably be asking.

Adrian (talk) 06:02, 1 November 2015 (UTC)

Thank you for this clarification. You make some good points.

"Readers should not be dropped into the middle of the subject from the first word; they should be eased into it."

It is said that Wiki editing guides admit of exceptions to deal with particular cases. I think there were reasons why my schoolteachers did not tell me about thermodynamics. They wanted me to matriculate, through an exam set by my local university. It might be said that someone seriously wanting to know about the second law of thermodynamics has already dived into the deep end, presumably having learnt something already about thermodynamics. I think that to try to tell about the second law to a non-swimmer is to invite muddled thinking. It is hard enough to get clear understanding of the law by physicists. There is a sad tendency to run with literal readings of Clausius' poetic or sibyllic statements about "the universe" in thermodynamic terms, as if they were useful or right. Many physicists think that the second law tells about physical systems in general, not restricted to thermodynamic systems. The second law is stated in many ways because it is understood (or misunderstood) in many ways. It is not easy to understand it immediately. The demands you make are not easy to supply.

Do you make the same demands of articles such as for example Quantum state?

To be positive, after that expression of reservations, perhaps the main use of the second law is to support the quantitative definition of entropy, the extensive state variable or function of state conjugate to temperature. Perhaps it would be a good idea to put that into the lead. I will think carefully about that. There is a new approach to this very topic, by Lieb & Yngvason, but it may be too complicated for the present article.

You were prepared to leave the reader to work out for himself that for a process in an isolated system to proceed, that system must have sub-systems separated by walls of adjustable permeability, each initially in its own state of internal thermodynamic equilibrium, and that the process is initiated by an external agent altering the permeabilities.

I think you might consider having the lead say that explicitly so that the reader is not left to work it out for himself. I think that is as near as one can get to a simple and direct statement of the law. That's why Planck put it that way. True, Planck didn't follow more recent texts that are explicit that a thermodynamic operation is needed to initiate the process; he left that implicit. And he wasn't explicit that the walls' changes of permeability are the precipitating causes of the process. But I think it helpful to spell it out, especially for a beginner.

With respect, it seems possible that your schoolteachers only bluffed you into thinking that you understood the law, when they left you finding the present simple and direct statement of it not easy to get your head around. Only recently did I read a carefully reasoned article by top expert Jos Uffink having the title "Bluff your way in the second law of thermodynamics" !! I think you do have a prejudice, that the second law is intelligible at a glance.

Perhaps that is enough chat from me for the moment.Chjoaygame (talk) 07:29, 1 November 2015 (UTC)

You're probably right, that I do have a prejudice believing that the law is intelligible at a glance. In truth, I never had an "understanding" of the second law, just some understanding of what it described, what it was used for, and why it was important. Oddly enough, the Quantum state article you linked has quite an amazing lead. It introduces a lot of concepts that are complex, expands upon the meaning of ideas, gives examples, and points me to the right direction where I can get more information about something I don't understand. It loosely violates the mathematical equation suggestions within the MOS in favor of making it more understandable since the equations are simply put, and the lead piques my interest to make me want to read more. That's the perfect model of what a lead section about such a complicated subject should look like.

I think I've contributed all that I can to this article for the time being, and may switch my gaze over to quantum physics. Adrian (talk) 08:06, 1 November 2015 (UTC)

Hmm. I see the article on the Quantum state as a masterpiece of superficially and glibly worded obfuscation, relying heavily on violation of the advice against mathematical formulas. I think by reading that article, a beginner would get not the slightest idea of what quantum state is !!

Back to the present article. I will think over your concerns, which are fair, and perhaps act on them to some extent. It seems my initial try at doing so was a failure.Chjoaygame (talk) 08:26, 1 November 2015 (UTC)

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Perhaps Wikipedia should have two articles on the second law, one for beginners and one for more advanced readers. The treatment of a difficult subject at two different levels could be similar to the two articles Quantum mechanics and Introduction to quantum mechanics. Dirac66 (talk) 11:04, 1 November 2015 (UTC)

Thank you for your comment. It's a thought. But I don't buy it. Though I think we should avoid glibbifying the second law, I also think it is not so very difficult. Quantum mechanics is far more complicated. I would like to try to negotiate a bit more along the lines that I offered in my first effort to respond to the current demand. For example, finding an acceptable wording for 'relaxing constraints'.

I think we should also add something to the lead about how the law sets up an extensive variable conjugate to temperature. And how it informs us of the sense in which a putative reaction will go, a point recently struck down.Chjoaygame (talk) 11:57, 1 November 2015 (UTC)

general derivation from unitarity of quantum mechanics

I concur with and am very happy to see the deletion of the subsection headed General derivation from unitarity of quantum mechanics.Chjoaygame (talk) 17:39, 30 November 2015 (UTC)

link to "arrow of time"

Though one often enough reads of Eddington's story that the second law somehow establishes "the arrow of time", I think Uffink's arguments<Uffink, J. (2001). Bluff your way in the second law of thermodynamics, Stud. Hist. Phil. Mod. Phys., 32(3): 305–394> are enough to dispose of that story. Rather than see it promoted as a link in the lead, I would prefer to see it criticized and debunked in the body of the article. The reason for the 'irreversibility' of natural processes does not rely on Eddington's story.Chjoaygame (talk) 18:07, 30 November 2015 (UTC)

I have only begun to read it, but it's a fascinating essay. Very heavily cited as well. Here is the link on arXiv btw. Kingsindian ♝♚ 18:53, 30 November 2015 (UTC)

I'll read it as well, thanks for the link. It's certainly a widely-held view among contemporary physicists that the arrow of time and the second law are inextricably connected. Waleswatcher (talk) 19:05, 30 November 2015 (UTC)

Well, I disagree with a lot of what he says, but even Uffink seems to agree there is a link between the second law and the arrow of time ("l do not wish to suggest that there is no connection between thermodynamics and the arrow of time"). If someone prefers, we could weaken the language to say something like "The increase in entropy accounts for the irreversibility of natural processes, and is related to the asymmetry between future and past". Waleswatcher (talk) 20:04, 30 November 2015 (UTC)

I would prefer to omit the sentence altogether from the lead. It raises too many problems. As indicated by Uffink, <Uffink, J. (2003). Irreversibility and the Second Law of Thermodynamics, Chapter 7 of Entropy, Greven, A., Keller, G., Warnecke (editors) (2003), Princeton University Press, Princeton NJ, ISBN 0-691-11338-6> irreversibility is not quite simple. As for 'the arrow of time', I say at least remove the link.Chjoaygame (talk) 20:58, 30 November 2015 (UTC)

Perhaps I may add that I also find Uffink not an ultimate universal guide, though he is very respectable.Chjoaygame (talk) 21:02, 30 November 2015 (UTC)

I should say that when I learnt the second law, the "arrow of time" aspect was very heavily emphasized - indeed, that is basically how I remember it even now. Of course, specialists may have a different view. Kingsindian ♝ ♚ 17:42, 6 December 2015 (UTC)

I would leave things as they are. The arrow of time is not now in the lead, which is probably for the best as it is not really an essential aspect of the second law and we cannot put everything into the lead. However it is in the table of contents with a very brief section and two links to more detailed articles, which is good because there will be some readers who are interested in knowing more about this related subject. Dirac66 (talk) 18:29, 6 December 2015 (UTC)

I agree with Editor Dirac66.

My view is that Uffink is right on this point. If one makes the arrow of time rely on the second law, I think one ends up muddled. Editor Kingsindian is right that one does encounter very heavy emphasis on the arrow of time story.Chjoaygame (talk) 19:27, 6 December 2015 (UTC)

different approaches

As I think this over, the idea occurs to me we might respond to fact that there are two fundamental formalisms for thermodynamics: in terms of thermodynamic states, and in terms of cyclic processes. Accordingly, there are two main forms of expression of the second law, in terms of entropy of states, and in terms of heat and work transfers. We are not forced to choose only one of them to occupy the lead.Chjoaygame (talk) 14:34, 12 December 2015 (UTC)

every natural <thermodynamic> process

Comment is needed on this latest edit. It is a another deteriorative step, changing 'every natural thermodynamic process' to 'every natural process'.

There is a very big difference between 'every natural process' and 'every natural thermodynamic process', a difference that is important for understanding the second law. Natural processes form a very wide class, including those that at no stage are anywhere near thermodynamic equilibrium. Thermodynamic processes start and finish in states of thermodynamic equilibrium. Natural thermodynamic processes are thermodynamic processes that can occur in what we take to be nature. It is only to them that the Second Law of Thermodynamics applies.Chjoaygame (talk) 07:33, 1 December 2015 (UTC)

I would suggest that you follow WP:BRD instead of the reverse. If an edit is unconstructive in your opinion, revert it, then discuss it here. The article space is what matters, talk is just to aid in this. I have reverted this, because I agree that removing the word changes the meaning, and keeping it in is not too obstrusive. Kingsindian ♝♚ 11:49, 1 December 2015 (UTC)

First, the meaning of "natural thermodynamic process" is obscure even to me, and I'm an expert in this topic. To a common reader, it's simply meaningless except insofar as It makes it sound as though the second law only applies to some special kind of processes. That implies that it's perfectly OK for entropy to decrease globally for other kinds of processes, which is the worst possible misconception we could give the reader. Second, while it's true that the most precise formulations of the second law apply only to systems that begin and end in equilibrium (because otherwise it's hard to define the change in entropy), the law is applied (correctly) all the time to other processes. In fact, in the real world, it is NEVER applied to systems that begin and end in perfect equilibrium, because there aren't any. If the second law really only applied in such cases, it would be useless as a law of physics. For those reasons I'm removing that term, and replacing "natural thermodynamic" with "real" (to distinguish from the idealized cases mentioned in the next sentence, otherwise it could just read "every"). Waleswatcher (talk) 14:08, 1 December 2015 (UTC)

I have read the foregoing comment.Chjoaygame (talk) 14:14, 1 December 2015 (UTC)

One other comment - if the issue is defining the entropy for systems that start or end out of equilibrium, there's no real problem with the way that sentence is worded, because if the entropy cannot be defined uniquely, it doesn't mean much to say that it increases (that is, you might as well define it in such a way that the statement is true). But again, these are technical issues that go far beyond the knowledge of most people reading the lede of this article, and anyway we make this point in the second paragraph. Waleswatcher (talk) 14:20, 1 December 2015 (UTC)

Perhaps I should reply.

As to "It makes it sound as though the second law only applies to some special kind of processes. That implies that it's perfectly OK for entropy to decrease globally for other kinds of processes, which is the worst possible misconception we could give the reader."

As rightly observed by Editor Waleswatcher, of course the mistake that natural thermodynamic process would see a decrease of total entropy of the participating systems is the very opposite of what is intended. As Editor Waleswatcher then rightly observes, "it's true that the most precise formulations of the second law apply only to systems that begin and end in equilibrium (because otherwise it's hard to define the change in entropy)." The purpose of the phrase "thermodynamic systems" is to focus the reader's imagination, so as to exclude processes that are not thermodynamic processes, for which entropy is undefined. The purpose is not to stimulate the envisaging of occurrences of processes in which the entropy sum decreases. It is true, as implied by Editor Waleswatcher's comment on the most precise formulations, that the second law, properly stated, restricts its purview to some special kind of processes, namely thermodynamic processes.

As to "In fact, in the real world, it is NEVER applied to systems that begin and end in perfect equilibrium, because there aren't any." In that frame of mind, thermodynamics would never be used. In practice, it is safely used when there is fair confidence in the validity of the standard presupposion, that the minus-oneth law holds near enough, that is to say, that the each of the bodies can be regarded, near enough, as being initially and finally in its own state of internal thermodynamic equilibrium. The equilibria, as Editor Waleswatcher rightly points out, are NEVER perfect; thermodynamics works when the equilibria are near enough. For most physical problems, one has to be satisfied by a theory that is near enough. The task is to find such a theory. The statement of the theory demarcates the full and empty parts of the glass, near enough. The serious drinker imbibes from the full part.

As to "if the issue is defining the entropy for systems that start or end out of equilibrium, there's no real problem with the way that sentence is worded, because if the entropy cannot be defined uniquely, it doesn't mean much to say that it increases." I think it decisively more helpful and safer to say it out loudly enough to explicitly guide the newcomer to the need to stay with the case when the entropy can be defined uniquely, and not to leave it tacit so that he has an unnecessary burden of nutting it out for himself.Chjoaygame (talk) 15:26, 2 December 2015 (UTC)

My comments. "Natural" has a natural meaning (sorry for the pun) for the layperson: it means stuff occurring in nature. The section above quotes the Guggenheim source for this point, which seems reasonably clear to me. So I don't see any problems there. I don't have any issues with "thermodynamic process" either. The fact that in the real world systems are not in equilibrium is not important: as long as there is a good approximation, we are ok. As to the unintentional misconception, I don't see any implication that entropy could decrease in processes not starting/ending in equilibirium: logically speaking it could simply be that entropy is undefined or meaningless in such processes. I think it is important to be as simple as possible, but without being inaccurate. I don't find calling them "natural thermodynamic processes" to be needlessly complex. So I generally find Chjoaygame's viewpoint reasonable. Kingsindian ♝♚ 21:45, 2 December 2015 (UTC)

I agree that "natural" has a clear meaning - and that's exactly the problem. It's not only natural processes that satisfy the second law, it's 'all' processes. Specifying "natural" gives the clear implication that 'only' natural processes satisfy the second law, and again, that's a terrible misconception (if it were true, one could build perpetual machines of the second kind, among other impossibilities). You say "The fact that in the real world systems are not in equilibrium is not important" - in that case, there's no need to say "thermodynamic", because requiring initial and final equilibrium was precisely the justification given above for saying it. Waleswatcher (talk) 00:00, 3 December 2015 (UTC)

My understanding was that the statement was accurate, this was agreed above? According to the terminology used by Guggenheim (following Planck) only natural processes occur, unnatural processes never occur, and reversible process are a fiction as a limit. So I don't see anything inaccurate here. Regarding the latter point, the 2nd law is applicable properly to thermodynamic processes. I did not mean to say that equilibrium was not important, I said (or at least meant, maybe I mangled my sentence) that the fact that in the real world equilibrium is not perfectly attained is not important; if it is approximately attained that may be enough, depending on the application. Anyway, don't use my formulation, Chjoaygame made the same point much more accurately above. I only meant to say that I agree with them on this point. Kingsindian ♝♚ 01:30, 3 December 2015 (UTC)

A lot of people will interpret "natural" as something that occurs in the natural world, as opposed to processes done in the lab or by people or machines (think of "natural" versus "artificial" flavoring). Personally, I think the best thing to do here is remove "real" and just say "all processes", and then reword the second sentence to make it clear reversible processes don't really exist. As for "thermodynamic", I of course agree with what Chjoaygame said above. That's not the issue - the issue is (at the risk of repeating myself) that (a) very few people will interpret "thermodynamic process" to mean "a process that begins and ends in equilibrium" - most will think it's a process involving heat, or something like that - and (b) no such qualifier is necessary, and so it simply creates the potential for conveying false information. Don't we want to avoid that? The second paragraph can explain how the 2nd law strictly applies only to beginning and ending in equilibrium. Waleswatcher (talk) 04:52, 3 December 2015 (UTC)

Mostly I proposed the word 'natural' because Planck used it, and the summary formulation in question is near enough Planck's. The word can be avoided by varying the formulation. For example, one might safely write along lines such as "When a thermodynamic process occurs, then the sum increases." At the same time, one might safely avoid the technical term 'thermodynamic process' in the first sentence by spelling it out in that sentence that the process begins and ends with states of thermodynamic equilibrium. In order to avoid an overloaded first sentence, one could make the initial defining statement occupy several short sentences. Accuracy must outweigh public relations and even customary Wikipedia conventions. Wikipedia rules do not require misleading grammatical forms for the sake of abbreviation. Leaving the explanation to the second paragraph would too easily be read as suggesting that strictness of statement was otiose pedantry as opposed to necessary accuracy. It is not just that the second law applies strictly to thermodynamic processes. It is that it applies only to them; it is not useful to hint at some unspecified non-strict applicability, whatever that might mean.Chjoaygame (talk) 07:25, 3 December 2015 (UTC)

I see good points in both replies, indeed I argued myself something similar to Waleswatcher when I first saw this page. However, over this discussion, I have come across to something more like Chjoaygame's position. Perhaps one can look at this from a different angle. See Newton's laws of motion. As pointed out in Uffink's article, by comparison with the second law of thermodynamics, the Newton's laws of motion are much clearer and well defined. When I see the lead for that page, it lists the three laws in fairly technical language: the first law refers to an inertial reference frame, and the second law to a vector sum, neither of which is likely familiar to a layperson. I see this as unfortunate but desirable nonetheless. I think the statement in the lead should be accurate technically, as far as possible. Our job is to elaborate the law to make it as simple as possible, but not sacrifice accuracy while doing so. Kingsindian ♝♚ 13:59, 3 December 2015 (UTC)

Well, there's obviously a balance that must be struck between accuracy and clarity/simplicity/brevity. My point is that the way the statement was worded before was both less simple and less accurate than the way it is worded now, so there is really no argument for going back to it. The reasons are (a) "natural" must exclude some processes (else it is a meaningless and unnecessary qualifier), and yet no process is exempt from the second law, (b) "thermodynamic" simply doesn't mean what Chjoaygame seems to think it means - according to our own wikipedia, it means any process involving a "thermodynamic system", and explicit includes processes where the beginning and final states are NOT in equilibrium - and (c), the second law is in fact never applied in practice to systems beginning and ending in equilibrium, nor does it in fact only apply to such systems (else it could not be a law of physics), and so we must be very careful not to give the contrary impression . Waleswatcher (talk) 14:44, 3 December 2015 (UTC)

Let me first be clear on one technical point, since I'm not an expert in this topic. The first sentence earlier read: The second law of thermodynamics states that in every natural thermodynamic process the sum of the entropies of all participating bodies is increased. Here, "natural" is used in the technical sense of Guggenheim and Planck. My impression from reading the discussion is that this is accurate. That it excludes unnatural and reversible processes is irrelevant, because they never occur. I am curious though, if the unnatural and reversible processes never occur, could we simply drop the qualifier "natural" and the statement will still be accurate? Perhaps Chjoaygame can also weigh in on this point. Kingsindian ♝♚ 15:08, 3 December 2015 (UTC)

Editor Kingsindian asks about "simply dropping" the word 'natural'. I have above suggested that it can safely be avoided, but not by simply dropping it. I suggested writing along lines such as "When a thermodynamic process occurs, then the sum increases." The point here is that it is made explicit that the law applies to processes that occur.

Editor Waleswatcher expresses several opinions in his just-foregoing comment. Opinions with which of course I disagree; indeed profoundly disagree. I think it would take us too far afield if I were right here and now to explain why. I do not foresee easy dispelling of disagreement here.Chjoaygame (talk) 15:23, 3 December 2015 (UTC)Chjoaygame (talk) 19:34, 3 December 2015 (UTC)

Thanks, I now read your earlier response more carefully, and you did indeed address this point. I am happy with a phrasing on the lines you suggest above. As to the latter point about thermodynamic processes, I agree with Chjoaygame's viewpoint, for reasons I already gave above. There is no right and wrong here, but a matter of judgement, so it is hard to say something intelligent without repeating myself. Kingsindian ♝♚ 15:37, 3 December 2015 (UTC)

Thinking this over. I wrote above: "At the same time, one might safely avoid the technical term 'thermodynamic process' in the first sentence by spelling it out in that sentence that the process begins and ends with states of thermodynamic equilibrium. In order to avoid an overloaded first sentence, one could make the initial defining statement occupy several short sentences." I would now amend that to: 'At the same time, we should avoid the technical term 'thermodynamic process' in the first sentence by spelling it out in that sentence that the process begins and ends with states of thermodynamic equilibrium. In order to avoid an overloaded first sentence, we could make the initial defining statement occupy several short sentences.' I have here used bold font to draw attention to the important change.Chjoaygame (talk) 19:26, 3 December 2015 (UTC)

To repeat - both according to my own knowledge (which is pretty extensive in this area) and according to wikipedia's own article on the topic, "thermodynamic process" does not mean a process that begins and ends in equilibrium - on the contrary, it explicitly includes processes that do not. Therefore it plainly cannot be used the way it was being used. As per the comment just above, it seems Chjoaygame now agrees with that (but perhaps Kingsindian doesn't?). As for specifying that the second law strictly only applies to such processes, I agree we should say something in the lede about that (and we do), but we must also say clearly that the law is often (actually, always!) applied to processes that do not begin and end in equilibrium. Waleswatcher (talk) 20:33, 3 December 2015 (UTC)

The lead of the Wikipedia article headed Thermodynamic process reads:

A thermodynamic process is a passage of a thermodynamic system from an initial state to a final state. In equilibrium thermodynamics, the initial and final states are states of internal thermodynamic equilibrium, each respectively fully specified by a suitable set of thermodynamic state variables, that depend only on the current state of the system, not the path taken to reach that state. In general, in a thermodynamic process, the system passes through physical states which are not describable as thermodynamic states, because they are far from internal thermodynamic equilibrium. It is possible, however, that a process may take place slowly or smoothly enough to allow its description to be usefully approximated by a continuous path of thermodynamic states. Then it may be approximately described by a process function that does depend on the path.

Newton's laws are often read as if they are treating idealized particles, though such are not actual entities. We do not emphasize that they are not actual entities when we state Newton's laws. We ought not over-emphasize that "the law is often (actually, always!) applied to processes that do not begin and end in equilibrium". As it stands, that sentence would be more misleading than enlightening to a newcomer; emphasizing it would be very likely to mislead or gratuitously puzzle. True, a thermodynamic system is an idealization, not an actual entity. An actual entity can in suitable cases be idealized as if it were a thermodynamic system. This is an approximation: where the approximation fails, the thermodynamics fails. Thermodynamics rests on the presupposition of the "minus-oneth law", that there exist systems in their own states of internal thermodynamic equilibrium. When one uses thermodynamics one is using that presupposition. Without the presupposition, one is without the law.Chjoaygame (talk) 21:48, 3 December 2015 (UTC)

I am afraid I am totally unqualified to offer an opinion on the nuances here. If you don't agree, and you feel that this is important enough, you can try an informal WP:3O, or a formal RfC. Kingsindian ♝♚ 22:12, 3 December 2015 (UTC)

It is proposed above that "we must also say clearly that the law is often (actually, always!) applied to processes that do not begin and end in equilibrium". It is appropriate to remind the reader that thermodynamics works through the presupposition of the minus-oneth law, and that this is of course never exactly obeyed in the real physical world. The reminder should, however, be worded in a way that does not suggest that the second law applies to situations of significant failure of, or departure from, the minus-oneth law.Chjoaygame (talk) 05:29, 6 December 2015 (UTC)

It may be helpful to observe that while a thermodynamic process proper refers to one that starts and ends in states of thermodynamic equilibrium, during the actual course of the process, large departures from equilibrium are permitted. Such departures, however, are not of concern for the second law.Chjoaygame (talk) 11:37, 12 December 2015 (UTC)

Yes, I think this is an important point which will not be obvious to all readers and should be in the article. Perhaps in the section on Nonequilibrium states. Dirac66 (talk) 12:27, 12 December 2015 (UTC)

Thank you for this comment. I think it important to keep clear the distinctions between equilibrium and non-equilibrium thermodynamics, and between thermodynamics and statistical mechanics. In response to your comment I have tried to clarify the section on non-equilibrium states. I would favour making the point (that equilibrium thermodynamics ignores even extreme non-equilibrium conditions during course of a process of passage from one equilibrium state to another) right in the main line of exposition, not aside in the section on non-equilibrium states. I think it remarkable that equilibrium thermodynamics permits even violent explosions during which it is utterly infeasible to define thermodynamic variables, while, mostly, non-equilibrium thermodynamics keeps to processes that stay close enough to equilibrium to allow definition of quasi-classical thermodynamic variables, though still lacking a strictly defined entropy for states.Chjoaygame (talk) 15:11, 12 December 2015 (UTC)

Minus-oneth (or minus-first) law

Editor Chjoaygame has referred several times above to a minus-oneth law of thermodynamics. If this is an important concept which can help the understanding of the second law, then it should be mentioned in this article with a link to the Wikipedia article which explains it. After some searching I find that about two weeks ago Chjoaygame added an explanation of the minus-first law at Thermodynamic equilibrium#Thermodynamic state of internal equilibrium of a system which seems adequate, so perhaps a link could be added from this article to that explanation.

As for minus-oneth versus minus-first, my own preference would be minus-first for the simple reason that first is an English word and oneth is not. However if there are sources of similar quality which use each term, then WP:NPOV would require mentioning both. Dirac66 (talk) 17:31, 6 December 2015 (UTC)

Thank you for this comment. Yes, we should have major battle over whether to talk about the minus-oneth law or the minus first law !!!! Perhaps needing administrative arbitration !!!! The sources agree with you and speak of the minus first. You prevail! No contest!

Bailyn on page 20 calls it (in CAPITAL LETTERS) "THE LAW OF EQUILIBRIUM". He spells it out in a longish indented paragraph that I will copy in here upon request. Though no request has come, I feel it would be useful that I now supply that copy. Here it is (Bailyn used small print):

THE LAW OF EQUILIBRIUM: A macroscopic, bounded, nongravitating system that is otherwise isolated or in a uniform environment attempts to reach an asymptotic state called equilibrium characterized by constant and piece-wise uniform values of its intensive state variables, unless it is already in equilibrium, in which case it will remain indefinitely in this state unless acted upon by systems with different intensive state variables, or systems in relative motion.

I don't regard this sentence as beyond criticism, but I will not criticize it here and now. It may be useful to add also here Callen's sentences on his page 15, which give one of the reasons why the existence of equilibrium states is a postulate: "In practice, the criterion for equilibrium is circular. Operationally, a system is in an equilibrium state if its properties are consistently described by thermodynamic theory."

Planck does not name it, but just says on page 3:

"§ 6. In the following we shall deal chiefly with homogeneous, isotropic bodies of any form, possessing throughout their substance the same temperature and density, and subject to a uniform pressure acting everywhere perpendicular to the surface."

Planck is a bit revanchist, revisionist, deviationist, counter-revolutionary, and backsliding, in that he presupposes empirical temperature. I think even Münster does that, at least partly! Howsoever, I think Planck's statement here is the best.Chjoaygame (talk) 21:07, 15 December 2015 (UTC)

Tisza (1966) on page 92 writes

... We now turn to the discussion of the concept of equilibrium that exhibits in a most extreme form the double aspects of simplicity and complexity.

     Virtually every thermodynamic phenomenon involves the concept of equilibrium in a more or less hidden fashion. For example, when we measure the temperature of an object we trust that thermal equilibrium is being established between the system and the instrument. Yet we have to face the embarrassing fact that there is no satisfactory empirical definition of equilibrium. The usual requirement that visible intrinsic processes should cease is only a necessary criterion that serves us well in simple situations, but we lack a practical sufficient criterion to reassure us that equilibrium is actually established on any particular level of molecular organization.

     In MTE [macroscopic thermodynamics of equilibrium] the assignment of a definite entropy value can be considered as a sort of definition of equilibrium. Of course, the cynic might interject that we explain the ill-understood concept of equilibrium in terms of a concept that we grasp even less. I propose to show that the cynic is wrong.

Callen (1985) on page 13 writes

Postulate I. There exist particular states (called equilibrium states) of simple systems, that, macroscopically, are characterized completely by the internal energy U, the volume V, and the mole numbers N₁, N₂, ..., N_r of the chemical components.

Only very few sources actually name it the minus first law. I would perhaps be a bit wary about how express it. But there is agreement that it is a presupposition, not a consequence, of the second law.

I agree it would probably help to cite it here. Gradually it can be introduced in appropriate places.Chjoaygame (talk) 19:15, 6 December 2015 (UTC)Chjoaygame (talk) 19:46, 6 December 2015 (UTC)Chjoaygame (talk) 20:12, 6 December 2015 (UTC)

At Philosophy of thermal and statistical physics#What is thermodynamics?, this is also mentioned thus:

At the very heart of contemporary thermodynamics lies the idea of thermodynamic equilibrium, a state in which no macroscopic properties of the system change over time. In orthodox versions of thermodynamics, properties such as temperature and entropy are defined for equilibrium states only. The assertion that all thermodynamic systems occupying a fixed volume will reach equilibrium in infinite time, which has been central but tacit to thermodynamics, has recently been dubbed the "minus first law of thermodynamics."

I should say that I think that claim about infinite time is wrong.Chjoaygame (talk) 22:49, 12 December 2015 (UTC)Chjoaygame (talk) 23:14, 12 December 2015 (UTC)

Thinking a bit more about it, I see there is a big mistake in the foregoing quote, that needs correction.Chjoaygame (talk) 15:56, 13 December 2015 (UTC)

The corrected version is now

At the very heart of contemporary thermodynamics lies the idea of thermodynamic equilibrium, a state in which no macroscopic properties of the system change over time. In orthodox versions of thermodynamics, properties such as temperature and entropy are defined for equilibrium states only. The idea of the existence of states of thermodynamic equilibrium has been central but tacit to thermodynamics. It has recently been dubbed the "minus first law of thermodynamics".

References

Looking at some articles about this, I judge that they are not very good.Chjoaygame (talk) 16:14, 13 December 2015 (UTC)

As it happens, I think some of the discussions, including those by Uffink and Brown, are distinctly and seriously inferior to that given by Phil Attard.Chjoaygame (talk) 16:19, 13 December 2015 (UTC)

wish to avoid conflict

Editor Kingsindian has here made a good-faith edit. His edit summary reads: "Made a stab at adding an informal description because lead was felt to be too technical".

In order to avoid conflict arising from summary undoing, I am here talking on the talk page.

I think the edit is very bad. I think that though it has some virtues, it is nonetheless a stab in the heart of the development of ideas in the literature over more than a century. Its main virtue is the words " an unrestrained expansion of a gas from one side of a container to the whole container". Perhaps best I do not expatiate too much right here and now. I will try to be brief, listing a few objections, and other ways forward.

• The concept of entropy first appeared under the name of "the thermodynamic function" at the hand of Rankine. It was later Christened and poeticized as well as logically clarified by Clausius.
• The use of the word "universe" is an invitation to drivel, a very harmful locution, that leads to endless nonsense.
• I do not like the use of the locution "Informally". I see it as an excuse for faulty writing.
• The "arrow of time" thing is misleading and according to Jos Uffink, an important current expert, wrong. For brevity, I will not expand on my objections to the rest of the sentence that it leads.

The second law stands as an ever-present lure to 'improve' and 'make and easier to understand'. It is just such improvements as made by the current good-faith stab that make it seem mysterious and even magical, hiding its true meaning.

The present lead is very spare because it is not easy to get agreement about the ordinary-language meaning of the second law. The word entropy is part of the problem.

Sadly not supplying the readily available reliable sources, I recently proposed as follows:

... It is about bodies of matter and radiation, initially each in its own state of internal thermodynamic equilibrium, and separated from one another by walls that restrict the passage of matter and energy between them. The law envisages that the restrictive characters of the walls are changed by some external agency. Thereby a process is defined, by which new equilibrium states are established. The process invariably spreads and disperses and dissipates matter and energy amongst the bodies. This is quantitatively described by increase of entropy. It is the consequence of less restriction after the change than before it. An increase of restriction has no effect on an established thermodynamic equilibrium.

I took this down because much respected Editor Dirac66 did not like it. Perhaps I may partly summarize his reasons here. He was not happy with the words "restrictive characters of the walls". Also he was not happy with the locution "The process invariably spreads, disperses, and dissipates ...".

I accept that my proposal reads a little technically. I think the second law is important enough that accuracy is at least as important as public relations (echo of Feynman).

I think my above offering says what should be said in some words or other. The language can be changed. The ideas, as pointed out by Dirac66, should be found clearly in the body of the article. The word "restrictive" is widespread in the literature. The word "spread" is recommended by Guggenheim, about as good a single authority as one might wish for. The word "dissipate" has historical sanction. The word "dispersal" is not so revered by history, but has a Wikipedia article about it that I think partly justifies it. The words spread, dissipate, and disperse, are ordinary-language words here used in more or less their ordinary-language senses.

I have it on my agenda to put the above in some form into the body of the article, to justify or partly justify its appearance, in some form, in the lead. I am sorry I haven't done it before now.Chjoaygame (talk) 23:48, 20 November 2015 (UTC)

Firstly, feel free to revert/change/whatever my edit. I don't mind. Secondly, as made clear explicitly, the description is an informal one: it is not meant to provide a formal definition of the second law, which is already present (briefly) in the first paragraph. The example comes from the class notes of an MIT course, which I cited in my edit. The notes introduces the second law with this motivating example. Nobody claimed that this is the state of the art or whatever.

For the lay reader, in my opinion, a famous law such as the second law of thermodynamics should be summarized informally in one sentence. If one recalls "The Two Cultures", by C P Snow, he gives the example of the second law of thermodynamics: it is equivalent to asking: "Have you read a work of Shakespeare?". This is my attempt. Kingsindian ♝♚ 04:29, 21 November 2015 (UTC)

Thank you for your careful response.

I have now put in a subsection that intends to offer some intuition about what the second law says. I am very sorry to say I could not find the source for my bold claim that "spread" is supported by Guggenheim. I hardly need say how sorry I am to have made that unsupported claim. I wish I could recall where I found it in what I think was a proper thermodynamic context. Perhaps in future I may be able to find support for it. I recall being very pleasantly surprised to find the word 'spread' proposed. I think it is great for the job. It is easy to find support for it in statistical mechanical accounts, but I mostly avoided them here because thermodynamics is a macroscopic subject.

I am feeling a bit better upon finding the following:

My memory was not exact.Chjoaygame (talk) 18:55, 12 December 2015 (UTC)

Now feeling much better. Found the Guggenheim reference!Chjoaygame (talk) 06:40, 20 January 2016 (UTC)

As for Editor Dirac66's concern about 'process'. I think process is also a word of the ordinary language, and I think language is flexible enough to admit that part of the essence of a process is that it does or effects or affects something. I think it can do such things as spreading, as part of the ordinary language.

I think it is unreasonable to demand a one-sentence summary for the layman, of what the second law says, informal or not. I don't like the notion "informal summary". I think such a statement is bound to mislead. There are countless attempts to do it, and they are all mischievous, in my opinion. I think that slick and quick statements create, and do not solve, problems. We don't need to add to or support such mischief. I think it is not the business of Wikipedia to mislead the layman, no matter how comforting that might be to do. Snow is wrong to compare the second law with Shakespeare. Perhaps even some physicists might appreciate Shakespeare? The ordinary person can appreciate Shakespeare, no matter what his education, whether or not it includes physics or literature. Not so for the second law. I have an idea that some physicists cling to statements such as Clausius' sibylline version. It is bad to support that. The second law deserves careful and accurate statement, no exceptions, not even for the sake of public relations.Chjoaygame (talk) 07:22, 21 November 2015 (UTC)Chjoaygame (talk) 09:26, 21 November 2015 (UTC)Chjoaygame (talk) 09:31, 21 November 2015 (UTC)

Regarding the last paragraph, I am sorry for my sloppy use of "one sentence". I meant "a few sentences". Indeed, I used more than one sentence in my "informal description". I certainly did not intend to follow Woody Allen in their description of War and Peace, "It's about Russia".

Snow's point was that the layman should have at least a rough idea of the second law. The most common formulation I am familiar with deals with the arrow of time. Maybe that is out of date and inaccurate, but then I only read about it in school and college, and haven't used it since. I can tell someone the plot of The Merchant of Venice if they ask me, even if I can't quote passages or whatever (except the famous Shylock one, partially). This is about the level of detail which is expected for the layman.

I am much too unqualified to offer too many constructive suggestions about an alternative lead, though if you present one, I can critique it for its use of technical terms. I see that you have given one in the introduction which seems fine to me at the first glance. I am not sure if it is possible or desirable to give a summary of that in the lead, but my viewpoint is that it should be done. Kingsindian ♝♚ 18:16, 21 November 2015 (UTC)

Thank you for your civil comments.

I think it significant that you can tell someone the plot of The Merchant of Venice but that you indicate you have reservations about this article. Shakespeare is celebrated for good reason. I didn't know that Woody Allen joke.

Perhaps it would help if you would very kindly be willing to say more about my new sub-section on intuitive meaning. I suppose it can be improved. Planck is not happy with the dissipation idea as being general enough, and I think he is right to a degree. The dispersal idea is better, I think, though some people are not altogether happy with it. I am keen on the very ordinary word 'spread', but it may not appeal to everyone. I am very sorry I seem to have forgotten my source for it, though I recall being very happy when I came across it.

There is another way of approaching this, in terms of "order" and "disorder", which I think is confusing and unhelpful or misleading, though it is found often enough, I would say, far too often; there are literature criticisms of it which I think are sound. I think it would be a very bad idea to try to include it, or even to mention it, in the present article, a lure for drivel. Your MIT example is the right one, I think; much more intuitively comprehensible and more logically apt.

We may compare our problem with that for the first law. What is the difference between the first law of thermodynamics and the law of conservation of energy? In a nutshell, it is that the first law is focused on internal energy, not total energy. How to convey that to the layman in very brief compass?

After looking through some standard texts, I accept Editor Dirac66's concern that in my above quoted proposal, the word 'restrict' is not well supported in this precise context in those texts. I think 'constrain' is well enough supported to replace it.

I am reluctant to try to shorten the summary beyond that, because of the big risk of misleading. The second law is not mysterious, but also, in its currently known and accepted form, it is not the answer to every question in physics, as it sometimes seems to be mistakenly seen. I think the remedy is careful statement.Chjoaygame (talk) 23:41, 21 November 2015 (UTC)

I slightly rewrote the lead so that it reads better, in my view. If I mangled the meaning inadvertently, feel free to revert/edit/discuss. Kingsindian ♝♚ 07:35, 24 November 2015 (UTC)

With respect, I am very unhappy with the improvements. I do not wish to be difficult.

I am sorry to say the improvements have gravely mangled the meaning, through being quick and efficient. The distinction between thermodynamic operations and thermodynamic processes is profound and essential to understanding. The improvements have elided it. Failure to recognize it is a main cause of faulty thinking about the law. That is why they need sentences of their own. The 'thermodynamic operation' is a technical term of a rather special kind. In the lead, for non-experts, I think it better to spell out its meaning than to use it directly as a term. 'Process' does duty both as a technical term and word of ordinary language, without too much gap between.

Again, I think it better here to speak of 'bodies' than of 'thermodynamic systems'. 'Body' is a perfectly respectable and traditional, more or less technical, term in thermodynamics.

I think it otiose to tell the reader that 'the following is more formal'. More formal than the preceding two sentences? Really? Does it matter?

Somewhere in the Wikipedia style ordinances for this kind of article, if I recall aright, one is enjoined not to give the reader orders such as 'Consider xxx'. More urgently, here it detracts from the meaning. It is important that the law is about bodies, and it is best to say so. The reader is not informed of that by an order to consider them. How does he know from such an order that just this is the subject matter of the law, no more and no less?

You feel the improvements read better. Please excuse me, but I don't think that justifies them.

I am reluctant to say so, but I think I need to: best that the improvements just be undone.Chjoaygame (talk) 14:08, 24 November 2015 (UTC)

No response from Editor Kingsindian?Chjoaygame (talk) 00:20, 27 November 2015 (UTC)

As I stated already, if I mangled the meaning, feel free to revert. My edit was meant solely as a copyedit to make the text read better. I feel the text which you added was ok. Kingsindian ♝♚ 06:59, 27 November 2015 (UTC)

Thank you for your patience and care in this. I accept that my wording can be seen perhaps as a little stark. I think the law is of stark simplicity, and it is best to present it so, leaving as little room as one can for potential mystificationisms. I think for this purpose, it is best to spell out the key points. Done.Chjoaygame (talk) 07:13, 27 November 2015 (UTC)

formerly unclear wording now clarified

Editor Waleswatcher has here deleted a paragraph from the lead, with the edit summary "deleted second paragraph of lede, which was incorrect ("increase of constraint" - like compression - does affect the equilibrium state) - and incomprehensible ("The law envisages"???))." Editor Kingsindian has here undone the deletion and requested discussion on this page.

I can see how Editor Waleswatcher might have found the former wording "incomprehensible", and how he might have misconstrued it so as to see it as "incorrect". I have accordingly offered amended wording that I hope may be comprehensible as well as easily seen as correct.Chjoaygame (talk) 13:14, 30 November 2015 (UTC)

It's a bit better, but it's still so poorly worded as to warrant deletion or a complete rewrite. This is the lede of a wikipedia article. It's supposed to be clear and accessible. The way it's worded now is convoluted and obscures the physics. I'll attempt a rewrite. Waleswatcher (talk) 14:45, 30 November 2015 (UTC)

Editor Waleswatcher has offered a re-write of the second paragraph of the lead. He objects to the paragraph as it stood. I am not impressed that his objections are reasonable or sound, nor that his re-write is a real improvement. But I also wish to avoid editorial conflict.Chjoaygame (talk) 17:54, 30 November 2015 (UTC)

One can't really argue about content on Wikipedia without a certain amount of conflict. I find the newer version easier to understand as a layperson, though I might be missing some nuances. If it is not inaccurate, then I don't really have any problems with it. The "introduction" section elaborates on this, so I don't see that anything is lost here. Kingsindian ♝♚ 18:42, 30 November 2015 (UTC)

Thanks for that. By the way, I don't know what a "natural thermodynamic process" is. Do you agree it would be better to simply say "every process" (or maybe "every real process", or "every physical process") rather than "every natural thermodynamic process"? The second law doesn't need to be qualified, at least not unless we are talking about esoterica like Poincare recurrences (which I think would be too technical for the lede). Waleswatcher (talk) 20:07, 30 November 2015 (UTC)

Guggenheim carefully and approvingly quotes Planck's use of the term 'natural process'. For me, that constitutes reliable sourcing and is valuable. 'Reversible processes' are not natural; they are limiting fictions that are often talked about.

Perhaps I should say a little more.

Serious sources on thermodynamics explicitly emphasize the walls. The walls are not just nuances; they are physically important. Statistical mechanics sources are less emphatic on walls because they have different concerns. This article is about thermodynamics. The new wording "put into contact" regrettably hides the physical importance of walls for thermodynamics. There are other important kinds of thermodynamic operation than "putting into contact"; omission of them gratuitously reduces the expression of the generality of the law. It is regrettable if not inaccurate to omit them. The new wording directly contradicts Pippard's important and valid cited comment that "it is the act of removing the wall and not the subsequent flow of heat which increases the entropy". Such a contradiction constitutes inaccuracy. The new wording "While often applied to more general processes, the law technically" is vague or evasive, and unenlightening.

In summary, though for the layman the newer version might seem easier to understand, it gives less real understanding of the thermodynamics, because it omits important things and is inaccurate. The second law is often misunderstood because it is stated in excessive abbreviation.Chjoaygame (talk) 20:43, 30 November 2015 (UTC)

The word natural just means occurring in nature. So a natural process is just a real process which can actually occur, as opposed for example to a reversible process which is an idealized limit and cannot really occur. Dirac66 (talk) 22:42, 1 December 2015 (UTC)

It seems to me that Editor Dirac66 is in agreement with Guggenheim's 5th revised edition (1967), on p. 12 as follows:

§1.12 Natural and reversible processes

We must now consider a classification of processes due to Planck^*. All the independent infinitesimal processes that might conceivably take place may be divided into three types: natural processes, unnatural processes, and reversible processes.

      Natural processes are all such as actually do occur; they proceed in a direction towards equilibrium.

      An unnatural process is one in a direction away from equilibrium; such a process never occurs.

      As a limiting case between natural and unnatural processes we have reversible processes, which consist of the passage in either direction through a continuous series of equilibrium states. Reversible processes do not actually occur, but in whichever direction we contemplate a reversible process we can by a small change in the conditions produce a natural process differing as little as we choose from the reversible process contemplated.

^* Planck, Ann. Phys. Lpz. 1887 30 563.

I suppose this would be considered a reliable source on this point.Chjoaygame (talk) 00:34, 2 December 2015 (UTC)

Yes, I concur that this appears to be a good, clear statement of my point from a well-known reliable source. Dirac66 (talk) 01:24, 2 December 2015 (UTC)