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"Thus"

Editor DavRosen's addition to the caption of the picture of the surface of the sun needs comment and I think revision, at least while the official dogma is being enforced. His newly edited sentence reads: "Nuclear fusion in the Sun converts nuclear potential energy into other forms and keeps the Sun's temperature high. Some of this energy is ultimately emitted as black-body radiation, whose net transfer to Earth is due to its lower temperature and is thus a heating process."

The official dogma (in which of course I totally and unquestioningly believe) is that net transfer of energy by means other than mechanical, between closed systems, is transfer as heat. It is fantastically proud of itself that it does not mention temperature. Silly old Clausius, silly old Kelvin, silly old Maxwell, silly old Planck. These ignorant fools thought that something qualified as a heat transfer just because it was purely driven by a temperature difference. These ignorant fools did not know that they must not talk or think about temperature until it had been defined in terms of entropy through the second law of thermodynamics. That it had already been so defined by Kelvin, in terms of Carnot's principle, a version of the second law, in 1848 before the recognition of the first law, is of course no excuse, because the first law having the number one must be considered prior to the second law which has the number 2, and because there are never excuses for departure from official dogma. Of course today we are much cleverer than they were, and we know that the official dogma is the only way to think correctly; and we are humble and do not often congratulate ourselves on how clever we are.

But, dare I say it, it seems that DavRosen might be backsliding, and saying that the transfer of energy from the sun to the earth, each for this purpose being considered as a closed system (matter not transferred between them), by radiation, a means other than mechanical, is heat because it goes down a temperature gradient. He seems to imply this 'because' by use of the words "due to its lower temperature" and "thus". What diabolical wickedness. I am so shocked by this that I will need to rest and wait for his response. I suppose my shock would be dispelled if he just removed the word "thus".

Also, Editor DavRosen's edit seems to imply that the radiation from the sun is heat because it is black-body, also seeming to imply that it is black-body. True it is more or less near (though not exactly) black-body, but thermal radiation does not need to be black-body to qualify as a mechanism of heat transfer. I think this could be remedied by changing the word "black-body" to 'thermal'.Chjoaygame (talk) 06:56, 16 July 2013 (UTC)

Okay, good discussion and points, and I do think I'm going to learn something here.

But do you agree, even if not all heating processes are due to a temperature difference, that if a given energy transfer process is due to a temperature difference and decreases the temperature of the "sender" and increases the temperature of the "receiver" then it is is a form of heat transfer process? Focusing on black-body radiation itself, its net energy transfer from the Sun to Earth occurs because the Sun is hotter, correct? That is to say, if the Earth were hotter then it would transfer more bbr to the Sun than vice-versa.

I know that you in particular understand that all energy has mass and vice-versa, and matter isn't a well-defined concept, so any definition that relies on "no transfer of matter" is not meaningful in general -- should it perhaps be "no net transfer of momentum" instead?

In any case, do you agree that not all emission of energy (and not even all emission of radiant energy) from the Sun that reaches the Earth is thermal? Even if the Sun and Earth were both somehow kept cooled to abs. zero, some particle interactions within the Sun would still occur spontaneously (familiar radioactive decay is just one example) because they do not need to draw on or cool a thermal energy reservoir, and some of their products (some massive and some massless) would escape and reach Earth and transfer some energy to it; these would likely far exceed such transfers in the opposite direction simply because there is so much more of nearly every type of particle in the Sun than in the Earth. These particles carry some momentum, all of it away from the Sun and toward the earth (not in arbitrary directions as in the thermal case) and would do some work on the Earth by displacing it in the direction of this momentum transfer, in the direction of the force they exert on Earth. Although some of that energy would be dissipated in practice, it would be possible in principle to set up a device that would reflect some of them back towards the Sun with equal and opposite momentum and no dissipative loss, for example an electric field gradient acting on an electron coming from the sun until it reverses direction and heads back. Thus these particles *could* do mechanical work on the Earth, i.e. they needn't necessarily raise the temperature of the Earth, so they don't represent heat transfer. This is why I thought the 2nd original sentence, "Consequently, heat is transported to Earth as electromagnetic radiation.", was misleading.

Do you agree that, even for nuclear fusion at the Sun's temperature, not all the converted nuclear potential energy becomes available as internal thermal energy -- i.e. some can escape just as in the previous examples without any further thermal interaction within the Sun and thus without changing its temperature? This is why I objected to the original sentence "Nuclear fusion in the Sun converts nuclear potential energy into available internal energy and keeps the temperature of the Sun very high."

I'm sure there are other ways to rewrite the caption that would address these issues, but, come to think of it, why are we using such a complicated example? Why don't we switch to a more straightforward example, of which there are plenty?

DavRosen (talk) 16:32, 16 July 2013 (UTC)

I only want to ask you to remove the word "thus", and to replace the term "black-body" with the word 'thermal'. No more than that.

My reasons are: (1) For the sake of logical consistency and simplicity in an introduction, it is better to work directly from the official definition that is routinely insisted upon here, than to use an indirect line of reasoning, relying on deductions, such as you propose. The official definition is that heat is energy transferred from one closed system to another by means other than as macroscopic work; it is its pride and joy that it doesn't mention temperature. If you don't like it, you could try to overthrow the massive, even fierce, consensus of orthodoxy that has established it here. You may have noticed that a new section, more or less to the effect that perhaps the temperature-difference definition is not as ridiculous as the official dogma insists, has just been deleted, though not because it was faulty. If you care about this, you might like to restore that deleted section. (2) Both solar and terrestrial radiation are nearly but not exactly black-body, but are thermal.

As for your extensive discussion, only a few words. In talking about particles you are leaving the macroscopic world where heat lives, and entering the microscopic world where heat is not a natural citizen, because the natural citizens there are microscopic; internal energy is still a citizen there, but not heat as defined in the macroscopic theory; microscopic stories ruthlessly use the word heat, but they don't mean it as it is meant in the macroscopic theory. So far as I know, all heat transfer is due to temperature difference, but that is not the official definition. It is a deduction from it and from some other ideas. To try to bring in here the sophisticated idea, that there is no clear definition of matter, is a mighty distraction from the main line of thinking here, which assumes the distinction between matter and energy as given. If you don't admit that matter and energy are different here, because you insist that matter is not well defined, for consistency you also have to give up the idea of heat as far far far less well defined, and there is no point in having an article on heat at all. Systematic thinking works with well defined, limited-scope theories, and does not try to fit everything into a one-size-fits-all theory. Systematic thinking about heat is macroscopic and considers matter and energy to be distinct.Chjoaygame (talk) 19:30, 16 July 2013 (UTC)

Implication word ("thus") removed. Actually I ended up rewording a lot of it, and it still needs work.

Okay, I got a little carried away with absolute truth (as-we-know-it), and I've benefited from reading your words. I'm pretty sure someone else will come along who will want to remove even more of what I've said :-)

DavRosen (talk) 21:08, 16 July 2013 (UTC)

Good work in removing the worrying word.

As you say, the picture shows something that is "complicated", not quite "straightforward". The sun-earth-outer-space compound system is a non-equilibrium one. In a crude sort of way one may think of the earth as lying 'between' the sun and outer space. The earth is heated by the sun and cooled by outer space. Radiant heat is passing in net from sun to earth and then from earth to outer space. The sun is hotter than the earth, and the earth is hotter than outer space. Also the sun is being cooled by outer space; indeed this is most of the cooling of the sun. As a very rough approximation, the thermal energy of the sun is supplied by nuclear reactions within it, and this more or less balances the heat lost by the cooling mechanisms, and the earth is in more or less a steady state of internal energy, being supplied by the sun and depleted by outer space. This is a dynamical situation, more complicated or advanced than a simple transfer of energy, between a closed system and its surroundings by mechanisms other than adiabatic work, that advances the system from an initial state of internal thermodynamic equilibrium to a final one. I am not sure that it is quite the thing to try to expound in detail in a caption of a bright coloured picture in the lead of an article about heat. In particular, the idea of available internal energy, being supplied by nuclear reactions, is a bit complicated for an introductory caption of a picture in the lead of an article about heat. I don't worry too much about this picture. It is coloured and dramatic. I don't have strong views about its appropriateness. If you feel "pretty sure someone else will come along who will want to remove even more of what I've said", you could anticipate them and put in something that you think will not make someone want to do such a thing. On the other hand, there are some very worrying problems with this article, that deserve careful and circumspect attention.Chjoaygame (talk) 14:26, 17 July 2013 (UTC)

Good points. If you draw a system boundary as the convex hull of the earth & the sun (enclosing them and the space through which they can directly exchange radiation), then within this system there's a net heat transfer from the hot sun to relatively-cool earth; of course heat also flows in and out of the system as well. Although the net energy transfer in-out of the earth system itself may be near zero, the Sun provides something just as important: it counterbalances some of the increase in entropy of the earth, i.e. increases the ability to do work on earth. I guess you could say it provides a higher-temperature heat reservoir so that some work can ultimately be extracted from the heat transfer to earth (not sure i'm saying this correctly but of course it relates to a heat engine). For example a photocell on earth can convert some of the sunlight to electric energy that can do work, or, more importantly, plants do something similar through chemical energy, etc. DavRosen (talk) 18:08, 17 July 2013 (UTC)

Tidy up

I have tidied up the lead to make it explicitly express the current orthodoxy on transfer of energy as heat. I have cited more authoritative references.Chjoaygame (talk) 22:14, 17 July 2013 (UTC)

Maybe I'm taking this too literally

"Heat in physics is defined as energy transferred between closed systems by mechanisms other than work."

but this sounds like you're claiming that heat transfer between two given systems is impossible unless both systems are each completely closed to matter transfer. Why can't there simultaneously be both heat and matter transfer between two given systems? Or do you mean that, in order for heat transfer to exist, it has to be possible to define two closed systems across whose mutual boundary the heat is being transferred? Still seems confusing to me. DavRosen (talk) 04:22, 18 July 2013 (UTC)

The definition is standardly stated in cited reliable sources for closed systems, as you may verify by reading them and other standard texts on thermodynamics. I am reporting reliable sources, not offering my own view. The situation for open systems is not simple, as you may verify by reading standard texts on thermodynamics. The present article's lead is simply silent on the case of open systems, making no claim about them. Some more on this in the article on the First law of thermodynamics#First law of thermodynamics for open systems.Chjoaygame (talk) 04:38, 18 July 2013 (UTC)

further tidy up

I have tidied up some introductory sections to remove faults which were inserted during and survived the recent flurry of edits.Chjoaygame (talk) 17:35, 19 July 2013 (UTC)

helpful intervention

We have been favoured by the helpful intervention of Editor Apteva. Some helpful comments by this editor are to be found here. I read, perhaps mistakenly, on the page User:Apteva that this editor is not an administrator but would like to be, and that he is a kind of patroller.

Particularly helpful are Editor Apteva's remarks that "the article is a mess, and needs people who have a basic understanding of heat contributing, but not by edit warring. It is a technical subject which requires the assistance of someone who is an expert." This is most helpful when juxtaposed with his further comment that "As far as the general public is concerned, anyone who has taken (and passed) even one thermodynamics course qualifies as an expert on heat and temperature," and his comment that "the editor in question has clearly studied thermodynamics, qualifying them as an expert in the subject." (I always like to see that the neutral pronoun "they" is used instead of the native English speakers' 'he', because political correctness is most important for me.) From the context, I read (perhaps mistakenly, but hard to verify because of the fancy bureaucratic language) that in this quote, by "the editor in question", Editor Apteva means Damorbel. If Editor Apteva really means all this, what he says appears to mean that the article requires the assistance of someone such as Damorbel. It is good to know that we are guided by such wisdom, by someone manifestly holier than us.

The administrative mind is a wonderful thing, for which we all may be most grateful. Yet I remain puzzled as to how Editor Apteva is qualified to force his opinions on us as he seems to have done.Chjoaygame (talk) 18:03, 19 July 2013 (UTC)

• Chjoaygame, that's not helpful. I think we and almost all the editors here are on the same page with regard to the disruptive edit-warring of Damorbel, over a long period of time, to replace some established definitions with his own throughout articles, but let's start with the assumption that anyone new who wants to help is well-intentioned. DavRosen (talk) 18:16, 19 July 2013 (UTC)

Perhaps we are all on the same page, but as a routine, Damorbel gets away with it scot free, and our being on the same page is inefficacious. There are lots of little messes left by him that I have not touched because I routinely do not respond to his depredations because if I do it is usually followed by a punitive raid from him. As for the very helpful Editor Apteva, as far as I can see he sees his role as to defend Damorbel's depredations, and somehow he seems to have some kind of power to delete efforts to do something effective to the contrary. I am puzzled about that apparent power. Can you enlighten me?Chjoaygame (talk) 19:08, 19 July 2013 (UTC)

I am definitely not defending anyone's actions. As I see it the article needs work, and edit warring is not the way to fix things. All of us have our own knowledge about subjects, but we need to support that with reliable sources. I am detecting different opinions of what the article should say, which could partly come from different definitions of the word heat. For example, the article begins by saying "in physics and chemistry, heat is". Well what is heat outside of physics and chemistry? Is this article only about heat as defined by physics and chemistry? And do those two even use the same definition for heat? I found the last section, "Usage of words" particularly confusing, even though it was certainly written to clarify the word heat. Apteva (talk) 21:44, 19 July 2013 (UTC)

Whether or not you intend it, your sanctimonious comments have an effect of defending someone's action. The depredations of the someone are a major obstacle to others trying to do useful work on the article. You should think more carefully about your actions in this. We tried to specify the article as about a single defined area, Heat (thermodynamics), because "Thermodynamics is a branch of natural science concerned with heat and its relation to energy and work". But it didn't work, largely because of some editors being dominant over others.Chjoaygame (talk) 05:20, 20 July 2013 (UTC)

• I am not commenting on who would be helpful in bringing the article up to WP:GA or WP:FA status, only commenting on what needs to be done. The lead is too long, has too many references in it, most of the article is unreferenced, and many of the references are difficult to verify. The lead is used to summarize the article, and normally only statements that would be surprising need to be referenced in the lead, with all statements in the lead supported by references in the body of the article. I see no surprising statements in the lead that require referencing in the lead. Encyclopedias need to meet the needs of all readers, and topics need to be introduced in relatively simple terms. If heat is used with more than one meaning, separate articles or separate sections of this article can be used to cover those separate meanings. It is always important to focus on content, and not on the specific contributors (WP:FOC). Comments to or about contributors belong on that contributor's talk page. What's up with the lower case section headings? Section headings are always sentence case, and begin with a capital letter. Is there some reason for deviating from that convention here? See the section about neutral section headings here: WP:TALKNEW Apteva (talk) 18:32, 19 July 2013 (UTC)

Good to have your further advice. Many thanks.Chjoaygame (talk) 18:56, 19 July 2013 (UTC)

good edit

DavRosen changed the wording from one that used the specialist term "closed" to an ordinary language usage about transfer of matter.

I think this was a very good move. The point is not whether matter transfer might happen. The point is whether it actually does happen. I regard this as a useful conceptual clarification, that opens the way to further clarity.Chjoaygame (talk) 05:26, 20 July 2013 (UTC)

Convection

Convection is a perfectly good description of the third type of heat transfer, and actually, "convective circulation" is less accurate. "Convective heat transfer" would just be saying the same thing twice. Apteva (talk) 08:21, 20 July 2013 (UTC)

Convection is a general term, and includes the transfer of matter and internal energy. The definition of heat transfer excludes transfer of matter as mechanism. To make convection into a form of heat transfer, convection needs to be stripped of its matter transfer. That is done by insisting that it be circulatory. Thus, strictly speaking, heat transfer by convection has to be specifically and exclusively by convective circulation, as explained in the article, with a reference a classic example in a classic reliable source. Convection in general carries internal energy but not heat. People who cover what they say with "actually" usually mean that they have insight superior to the delusive view of their target, who sees only the imaginary, not the actuality.Chjoaygame (talk) 10:09, 20 July 2013 (UTC)

There is no requirement that the convection be circulatory to transfer heat. It is better to just say there are three types of heat transfer, conduction, convection, and radiation. Calling two of them simple and one complex is not helpful either. Apteva (talk) 11:38, 20 July 2013 (UTC)

Careful attention to the definition accepted in the article will reveal that convection in general transfers internal energy, but not in general heat. This is because only circulatory convection excludes transfer of matter between the source and the destination of the transferred internal energy, and transfer as heat excludes transfer of matter as a mechanism.Chjoaygame (talk) 12:33, 20 July 2013 (UTC)

The mathematics of convection do not impose that the convection be circulatory. The medium that contacts the hot object does not need to return to the hot object, which is what the word circulatory means. Just say,

Heat is a means of transferring energy from a hotter object or region to a colder object or region, and can be done by conduction, convection, or by radiation. Heat is measured in joules, or in calories. In physics and chemistry heat is only the transfer of energy. Older and more common definitions of heat, such as in engineering, define heat as the energy that an object or region has due to the object or region's temperature, with the total heat being roughly proportional to the mass and temperature, in addition to the transfer of energy. A calorie is defined as the heat required to increase the temperature of one gram of water by one degree Celsius. A joule is defined using physical parameters, the work done in applying a force of one newton through a distance of one meter. One calorie is roughly or even exactly 4.184 joules (food uses the kilocalorie, calling 1,000 calories one calorie).

Apteva (talk) 19:12, 20 July 2013 (UTC)

You apparently try to apply standards of a thermodynamics textbooks to a Wikipedia article, which is discouraged. Convection is a type of motion. It may caused by whatever reason. Is includes what is called convection in thermodynamics, but is broader. It usually results in a heat transfer, but a convection is a mechanism and the heat transfer is its result. It is convective circulation a pleonasm; convective heat transfer is, contrary, perfectly meaningful: there are three types of heat transfer, and the heat is not the only thing that can be transferred. Incnis Mrsi (talk) 10:25, 20 July 2013 (UTC)

• It depends on the way you choose to specify the thermodynamic description of the system. So, you have a physical system, an exact description of which would require you to specify an astronically large amount of information. The thermodynamic description of a system is a coarse grained description of the system, what is included here is everything that is visible after the coarse graining is performed. Energy transfer that becomes invisible due to the coarse graining is by definition heat. You are free to decide how you perform the coarse graining, but this then affects the separation of energy transfer into heat and work. Also, the same physical system can be out of thermal equilibrium in one description, barring one from describing it thermodynamically at that coarse graining level, while in a more fine grained description one can see that it consists of subsystems that are in internal thermodynamic equilibrium which are not in thermal equilibrium with each other. If the latter is approximately true when the coarse graining is fine enough, one considers the system to be in local thermodynamic equilibrium. Count Iblis (talk) 10:59, 20 July 2013 (UTC)

• As Editor Incnis Mrsi rightly says, convection is a broad or general word, not specifically belonging to thermodynamics, and not restricted to transfer of energy. It just means that something is carried by bulk flow. It is not restricted to circulatory pictures, though of course, it is usually part of a circulation.

Perhaps it is discouraged by Wikipedia policy to apply the standards of a thermodynamics textbook to a Wikipedia article. Editor Incnis Mrsi is the Wikilawyer here, and would know. But the policy doesn't seem to cover this article at present. Perhaps it should, and perhaps it can be imposed on it starting now. But till that happens, the article has been more or less thermodynamical in style.

When convection includes actual transfer of matter between the source and destination of the transported internal energy, it is excluded by the strict definition of heat transfer: it is just transfer of internal energy, properly speaking; 'heat transfer' is not a thermodynamically acceptable expression for it.

Editor Incnis Mrsi says that 'convective circulation' is a pleonasm, meaning that usually convection is eventually part of a circulation, because of conservation of matter. In that sense he is right. But, in another sense, the one obviously intended here, and detailed in the article, what is eventually part of a circulation is not necessarily circulatory when taken by itself. An open thermodynamic system can be defined to include only a part of a circulation, and to exclude the rest of it. As Editor Count Iblis rightly says, "It depends on the way you choose to specify the thermodynamic description of the system."Chjoaygame (talk) 11:30, 20 July 2013 (UTC)

• It does seem at least a bit confusing to state in 1st sentence that heat is an energy transfer other than by transfer of matter (or work), and then in 2nd sentence list convection, which clearly involves transfer of matter in some way. Let's clarify the definition in our own minds and them we can decide how to write it.

To that end, a question: Suppose I have 2 systems: each is is a bottle of water at 2 diff. temps., & the process I perform is: exchange 1/4 of the water of each with one another (& allow time for temp equilibrium within each), so that after the process they each still have the same amt of water but their temperatures have changed. Can this be considered a heating process, and if not, what is it? The net result is the same as if I had transferred the heat by conduction, but I didn't.

DavRosen (talk) 19:14, 20 July 2013 (UTC)

Conduction. You placed one quarter cold water into a body of warm water, which by conduction transferred the heat from the warm water to the cooler water. The convection that resulted was not a part of the heat transfer, and just meant that the cold water was dispersed within the warm water. The lead section needs to introduce the subject in words that are clear and easy to understand, particularly the lead sentence, which is used to define the subject. Apteva (talk) 20:40, 20 July 2013 (UTC)

• Hmm, your answer doesn't seem very clear or easy to understand, but it could just be me. Are you sure the energy transfer between my two systems was simply heat conduction through the boundary of the two systems? Heat conduction would not involve transfer/exchange of matter across the boundary, but rather energy being conducted between *adjacent* matter on the two sides of the boundary where the matter itself does not move across the boundary, correct? I moved the energy across the boundary entirely by moving actual water which had an amount of energy stored within it -- where exactly did all that "conduction" happen? DavRosen (talk) 21:06, 20 July 2013 (UTC)

[sorry for the duplication of Apteva's post, but I was responding to his first version, above, while he was editing it into his version below, which I may respond to separately]

Conduction. You placed one quarter cold water into a body of warm water, which by conduction transferred the heat from the warm water to the cooler water. The convection that resulted was not a part of the heat transfer, and just meant that the cold water was dispersed within the warm water. Like Maxwell's box, let us instead assume that the two containers have chambers that can be separated with insulating and non-insulating membranes that are removed, so that the water is not moved in any way when the exchange is made, but is suddenly in contact with water of a different temperature, and will transfer heat by conduction from the warmer to the colder water. The lead section needs to introduce the subject in words that are clear and easy to understand, particularly the lead sentence, which is used to define the subject. Apteva (talk) 20:40, 20 July 2013 (UTC)

• In thermodynamics, the system(s) can be defined how ever one chooses for purposes of the analysis of interest, with a defined boundary between them. I defined the two bottles as the two systems of interest in order to talk about what energy is transferred across the boundary between them. In your answer you changed that definition and talked about transfer that occurred within one of the bottles, which is interesting but it wasn't what I wanted to know. Are you saying my definition of the two systems is inherently invalid, or that my question is meaningless or unanswerable without redefining the system boundary as you did?

(Btw, separate question about the systems as you chose to define them: you described the energy transfer between the old and new water within one bottle as conduction followed by water dispersal, but wasn't that dispersal itself part of the heat transfer mechanism? If there had been a thin, thermally conductive membrane between the new and old water, it would have taken much longer to reach equilibrium because it would stop convection across the boundary (although there would still be convection separately on each side). How do you explain how quickly it equilibrated unless you consider convection across the boundary (which, by the way, will tend to be cyclical convection in this case until equilibrium is reached, unlike my setup, where there was no cyclical transfer during the finite process that I defined.)?)

DavRosen (talk) 21:20, 20 July 2013 (UTC)

Since none of this has anything to do with article, there is no point in discussing this. To put something like this into the article would require finding this example somewhere and providing whatever explanation was presented in that source. Apteva (talk) 22:20, 20 July 2013 (UTC)

Apteva, you are the one who started this discussion in order to remove the term "convective circulation", stating the view, "Convection is a perfectly good description of the third type of heat transfer, and actually, "convective circulation" is less accurate. "Convective heat transfer" would just be saying the same thing twice.. I'm just trying to figure out exactly what definition of heat your statement is consistent with, so we can be sure we are conveying such a definition. We can't simply say something that has an apparent logical contradiction, so we we need to find a way to address or acknowledge this inconsistency if we are going to have it in the lede. Currently we state in 1st sentence that heat is an energy transfer other than by transfer of matter (or work), and then in the 2nd sentence you propose listing convection, without any qualification such as "circulation", but are you saying that convection doesn't involve transfer or matter, or that the first sentence is not stated correctly? Or that somehow it's a a different sense or type of transfer of matter, in which case we need be sure we are explaining this distinction somewhere. Chjoaygame's qualification, "convective circulation" attempted to address this this inconsistency because circulation would imply at least that there is no net transfer of matter over whole cycles. You proposed simply removing this qualification, without proposing an alternative means of resolving the inconsistency. I think you may be on to something: there may be a better way to resolve the inconsistency without simply saying "circulation". My question and followups above, about which you say "none of this has anything to do with article", were merely an attempt to identify such a means of resolving this apparent inconsistency in a way that's better and that would allow us to follow your suggestion in removing the term "circulation". DavRosen (talk) 00:06, 21 July 2013 (UTC)

I would resolve the inconsistency by clarifying the "transfer of matter" to mean into or out of the system. And I see nothing wrong with calling the third heating method "convection". If there's some confusion surrounding that word, then let's define it carefully within the article, but it seems clear enough to me. Is there anything lacking in this wording?:

In physics and chemistry, heat is energy transferred between a system and its surroundings other than by work or by the transfer of matter into or out of the system. The transfer of energy can occur by conduction, radiation, and convection.

I would also prefer replacing "its surroundings" with a second system, but that's another topic. Spiel496 (talk) 01:02, 21 July 2013 (UTC)

• That helps, but that's even more restrictive of the definition of convection (and ultimately of heat). If two rooms of my house (two systems) are at different temperatures and I remove the wall between them, how would you describe what happens? Clearly there is a lot of transfer of gas molecules back and forth between the two rooms -- what would you call this process other than a convective heating process? In order to meet your definition I would have to keep at least a thin membrane between the rooms, in which case there would be convection within each room separately, but energy would be transferred much more slowly than if I allowed this matter exchange across the boundary.

Actually, I had the word "net" in the first sentence of the article before Chjoaygame's most recent edit:

In physics and chemistry, heat is energy transferred between a system and its surroundings other than by work or the net transfer of matter.

Maybe that would help (with or without "into or out of the system" as well) but is it correct?

DavRosen (talk) 02:16, 21 July 2013 (UTC)

Editor DavRosen makes some useful points here: as to the word "net", and as to the phrase "into or out of the system".

I thought about the word net, carelessly and mistakenly believing that I was the one who had used it. I reached the conclusion that I had been mistaken to use it, that it should not be present. My reason is that a thermodynamic system is permitted to make simultaneous contact with several different subsystems of its surroundings, so that a process can involve several distinct simultaneous transfers of matter with associated internal energy transfers, and that the matter transfers can be in net zero, while the associated internal energy transfers do not have to have a zero net value. In such a scenario, non-zero net transfer of internal energy could result from a zero net transfer of matter, but such transfer would not properly be regarded as a transfer of energy as heat. Transfer of energy as heat can easily involve microscopic and perfectly balanced transfer of matter, molecules being exchanged, but such microscopic transfer is not to be regarded as a transfer between thermodynamic systems, because the latter are defined strictly macroscopically, and the details of microscopic transfers are relevant to thermodynamics only when they lead to macroscopic transfers.

As for the phrase "into or out of the system". It could be argued that it is necessary to make the meaning clearer, or that it is redundant because the phrase "between a system and its surroundings" has already made the point. That would be a matter of style of expression about which I suppose editorial opinions might vary.Chjoaygame (talk) 09:08, 21 July 2013 (UTC)

• Editor Spiel496 comments "I would also prefer replacing ″its surroundings″ with a second system, but that's another topic." In response I would say that it is often allowed that the "system" and "its surroundings" have different natures. For classical thermodynamics, the system is usually considered to start and finish the process in its own state of internal thermodynamic equilibrium, with all proper thermodynamic state variables well defined, while such a restriction is not placed on the surroundings, which are allowed arbitrary adventures in regions of it that are not in direct contact with the system. To replace its surroundings by a second system is to specialize to the case when the surroundings are also required to start and finish the process in their own state of internal thermodynamic equilibrium.

Editor Spiel496 comments "If there's some confusion surrounding that word, then let's define it carefully within the article." There is a subsection in the article that intends to define convection in general: Heat#Transfers of energy between closed systems#Transfers of energy involving more than two bodies#Convective transfer of energy. It is a subsection of the one about closed systems, with open systems being treated as exceptions, instead of being taken as a reason to start a new major section. It might be argued that it should be given its own major section with some heading such as 'Transfers of energy between open systems', but I think that may be going too far.Chjoaygame (talk) 09:08, 21 July 2013 (UTC)

Heat vs. heat flow/transfer

I think edits such as [1], while obviously incorrect, point to the necessity to explain some terminology, as it's used mostly in engineering rather than physics. First, that edit is (wrongly) trying to rename "temperature" to "heat". (I think any high-school textbook can properly explain the difference between those, so I won't delve on that here.) Secondly, that edit is trying to rename "heat" to "heat flow". The distinction between "heat" and "heat flow" (or "heat transfer", but in the sense of the physical process rather than the engineering discipline) is actually somewhat esoteric. Per [2]: "In contrast to thermodynamics, which mainly deals with homogenous systems, the so-called phases, heat transfer is a continuum theory which deals with fields extended in space and also dependent on time. This has consequences for the concept of heat, which in thermodynamics is defined as energy which crosses the system boundary. This contradiction with thermodynamic terminology can the be resolved by considering that in a continuum theory the mass and volume elements of the body are taken to be small systems, between which energy can be transferred as heat. Therefore, when one speaks of a heat flow within a solid body or fluid, or of the heat flux vector field in conjunction with the temperature field, the thermodynamic theory is not violated." Someone not using his real name (talk) 22:17, 20 July 2013 (UTC)

Minor typo from the quoted book: "can the resolved" should be "can be resolved". Please tell me the book was not written by one of our editors. Step one write WP article. Step two write book based on that article. Step three quote the book as a source for the article. So if heat is heat transfer, what is heat? (Please Do Not Answer) Apteva (talk) 22:40, 20 July 2013 (UTC)

Thanks for spotting the typo. As for the rest of your post, I think it's alas entirely nonconstructive. Someone not using his real name (talk) 22:47, 20 July 2013 (UTC)

By the way, there is an article doi:10.1119/1.1341254 which argues that "heat transfer" is an oxymoron "because heat cannot be stored". This is mostly a linguistic rather than conceptual problem though. More here: "John Jewett (26) observes that in fact heat can be a noun, but is the name of a process rather than the name of what is transferred. The main point is that using heat as a noun to designate “the heat in a body” is incorrect, and one way to avoid error is to use heat either as an adjective (e.g., “heat process”) or verb (e.g., “heat water”)." citing J. W. Jewett, “Energy and the confused student III: Language,” Phys. Teach. 46, 149–153 (March 2008) [3]. It goes a bit further to say "It is no more appropriate to speak of heat in a body than work in a body. Both statements are not sensible. As pointed out by Mark Zemansky, (24) “Heat and work are methods of energy transfer, and when all flow is over, the words heat and work have no longer any usefulness or meaning . . . and once the transfers are over, we can speak only of the internal energy of the system. It is impossible to subdivide the internal energy into two parts, one due to a heat transfer and the other to work.” cited to M. Zemansky, “The use and misuse of the word ‘heat’ in physics teaching,” Phys. Teach. 8, 295 (Sept. 1970). It concludes with "it is well to heed the words of Walter T. Grandy (28) “In the 21st century it is still common to speak of heat as if it were a ‘substance’ that flows and can be thought of as a fluid; scientifically we still use the phrase ‘heat capacity’ that connotes an amount of something, although we know better. We take note of these foibles only to emphasize that human perception remains a bit ‘fuzzy’ in discussing the concept of heat, difficult to pin down at times. Technically, however we have no trouble agreeing that heat is not a substance, but a process of energy exchange between macroscopic systems and their environments.” citing W. T. Grandy, Entropy and the Time Evolution of Macroscopic Systems (Oxford University Press, Oxford, 2008), p. 2. Some of this is probably useful to mention in the wiki article. Someone not using his real name (talk) 23:59, 20 July 2013 (UTC)

Jewett has another paragraph worth citing, pointing to the differences between common language use and the notion in physics: "Consider some phrases used in common language: “heat transfer,” “flow of heat,” and “the heat radiated outward.” These phrases refer to a transfer of energy but represent incorrect uses of the word heat. The phrases can be tested by substituting the words “energy transfer” for “heat.” Each phrase sounds awkward or redundant when this is done. For example, “heat transfer” becomes “energy transfer transfer.” Other common phrases include “the heat of the day” and “too much heat in the air.” In these uses, heat is being used to represent temperature. Another common statement is “heat rises.” In this case, heat is used to mean warm air!" 86.121.18.17 (talk) 00:10, 21 July 2013 (UTC)

The technical term heat does have some linguistic problems. One way to reduce the problem is to use terms like "[amount of] energy transfer[ed] as heat" or "[amount of] energy transfer[ed] by a heating process". Another is to talk about "[amount of] energy transferred thermally" or "[amount of] energy transferred by a thermal process". The problem with using the word "thermal" that way is keeping it from coming right before the word "energy", because then you're into a different meaning: "thermal energy transfer" could mean a transfer of thermal energy, which isn't necessarily by a heating process. DavRosen (talk) 01:41, 21 July 2013 (UTC)

Can we come up with a sentence that begins: "Heat is" for the first sentence of the article? Starting out with "In physics" is not very good. Here is another one:

Heat is energy transferred from a hotter object or region to a colder object or region, by conduction, convection, or by radiation. Older and common definitions refer to the heat contained within an object or region due to its temperature, but the modern physics and chemistry definition of heat is the energy transferred as heat.

--Apteva (talk) 02:58, 22 July 2013 (UTC)

There's no good reason to do that per WP:NOTDICT. Someone not using his real name (talk) 04:41, 22 July 2013 (UTC)

The reason is to define the topic. The topic is heat, so a logical sentence would begin, heat is. Apteva (talk) 04:45, 22 July 2013 (UTC)

We already have that in the current lead. Given that there's already a section Heat#Usage of words, it could be summarized in lead along the lines of: "In ordinary language, 'heat' has several other meanings, including temperature, and this leads to some misconceptions/confusion". That tail section could be expanded to be more explanatory with the sources given above... Someone not using his real name (talk) 04:58, 22 July 2013 (UTC)

Not temperature. That is a separate subject. And this is not a dictionary, we do not have to describe all of the uses for the word heat, we only need to describe in the lead section what ways this article uses the word heat. The first sentence should not start with "in physics" but should start "heat is". It should not start "in this article, heat is", but "heat is". If it needs to start with "in something" that really implies that we have another article about what heat is everywhere else, which is not the case. Apteva (talk) 05:18, 22 July 2013 (UTC)

This isn't an article about the word "heat", it's about a specific scientific concept and quantity, which is termed "heat" by the modern physical sciences. (It often takes many decades for definitions to filter down from the sciences into secondary and primary school classrooms, and sometimes they never do.) WP doesn't have one article per word, but rather one article per subject. That's why disambiguation pages are needed -- the same term may represent different subjects. Most of these types of articles do begin with something like "In the physical sciences, ", just to make the subject clear. Also, if the lead gives similar emphasis to two different meanings of heat, then does every remaining section of the article have to state which of the two concepts it's referring to? Almost none of the sections as they exist today would be directly applicable to your concept of heat without modification -- are you going to expand each section in order to accurately cover the concept you describe as well as the current one? The lead is supposed to summarize the article and the article isn't about your concept of heat. Anyway the concept you're describing is much closer to that of thermal energy than heat, so maybe that article would be a better place to bring up your points about colloquial usage of the word heat. DavRosen (talk) 05:21, 22 July 2013 (UTC)

There is no need to combine the two topics heat and thermal energy, but just as the article on thermal energy refers to this article, this article needs to refer to that article. That article has the sort of sentence that I am looking for, "Heat is thermal energy in the process of transfer or conversion across a boundary of one region of matter to another, as a result of a temperature difference", although the sentence can be improved quite a bit. Apteva (talk) 06:24, 22 July 2013 (UTC)

I have no objection to the idea of referring to thermal energy article from heat in some way, to help draw the distinction between them. DavRosen (talk) 15:54, 22 July 2013 (UTC)

I would oppose a reference from this this article to the one on Thermal energy. The latter's lead begins "Thermal energy is the part of the total potential energy and kinetic energy of an object or sample of matter that results in the system temperature. It is represented by the variable Q, and can be measured in Joules. This quantity may be difficult to determine or even meaningless unless the system has attained its temperature only through warming (heating), and not been subjected to work input or output, or any other energy-changing processes. Because the total amount of heat that enters an object is not a conserved quantity like mass or energy, and may be destroyed or created by many proceses, the idea of an object's thermal energy or "heat content," something that remains a measureable and objective part of the internal energy of a body, cannot be strictly upheld. The idea of a thermal (part) of object internal energy is therefore useful only as an ideal model, in special cases where the total integrated energy of heat added or removed from a system happens to stay approximately constant as heat is conducted through the system."

Most particularly I would draw attention to the sentences in purple in the above. The phrase 'thermal energy' is vague, and I think not a preferred way to go. The first law of thermodynamics relies on a quantity 'internal energy'. Very loosely speaking, 'thermal energy' has some relation with internal energy, but the same can be said of other thermodynamic functions, such as enthalpy, Helmholtz free energy, and Gibbs free energy. The phrase 'thermal energy', though used often enough, and occasionally even by respectable writers such as Maxwell, is mostly used when the speaker has not quite thought through exactly what he means. I do not favour urging our readers in that direction. If one has something definite in mind, I think it better to try to find precise words to express it.Chjoaygame (talk) 17:31, 22 July 2013 (UTC)

Just dumping a source: [4] In pages 383-384 it describes the origin of the modern definition of heat, and how people misinterpret their meaning. This would a good source for a short explanation of why people confuse the concepts. --Enric Naval (talk) 17:36, 22 July 2013 (UTC)

Physics IV for High School, 2006 "Heat: Energy transferred between a system and its surroundings due to temperature differences only. This definition of heat has some subtleties. As stated, heat is energy transferred from one system to another system (when they are in thermal contact) because of a temperature difference. Before the energy is transferred, and after the energy arrives in the system, it is not called heat (and never heat energy). More properly it is called: Thermal energy (or internal energy)" Apteva (talk) 04:56, 23 July 2013 (UTC)

The definition quoted just above is as advertised, from a high-school textbook. It is pretty nearly the definition stated in the article at Heat#Heat, temperature, and thermal equilibrium regarded as jointly primitive notions as belonging to the founders' view of heat as a notion coherent with temperature, jointly primitive for thermodynamics. It has a physical difference from the conceptually revised definition taken as currently orthodox by the present article. The difference is registered in the lead of the present article by the sentences "If the surroundings of a system can be described also as a thermodynamic system with a temperature, and it is connected to the system by a pathway for heat transfer, then, according to the second law of thermodynamics, heat flow occurs spontaneously from the hotter to the colder system. Consequently, in this circumstance, heat is transfer of energy due purely to temperature gradient or difference." The point is that the surroundings are in general not required to be constituted by a bunch of nicely behaved thermodynamic systems. They are allowed arbitrary adventures. For example, they may, other than by work or transfer of matter, pass energy to the system from a turbulently flowing thermally inhomogeneous and indeed temperatureless contact subsystem. The older definition, in terms of temperature difference, relies on the surroundings being able to be considered as a thermodynamic system with a temperature, and thus refers to a special case of the conceptually revised idea. Some years ago this was heatedly and lengthily debated here, and the present article represents the outcome of that debate.Chjoaygame (talk) 10:26, 23 July 2013 (UTC)

Reference

References

an AA battery

Chjoaygame, if not thermal energy per se, can there be any extensive state variable that represents part of the system's internal energy and that's well-defined in such a way that it goes to zero along with the Temperature? Internal energy includes all the energy within the system, some of which is independent of its temperature and can be extracted as available energy to do work without dumping any energy into a lower-temperature reservoir, correct? For example, the part of the chemical energy in a AA battery that we can extract to do work, is still stored in there, even if we bring the battery's temperature down arbitrarily close to abs. zero, right? DavRosen (talk) 22:28, 22 July 2013 (UTC)

Fair question, DavRosen. An AA battery is not a system in its own internal state of thermodynamic equilibrium, and therefore does not qualify as a system that can be the initial condition of a thermodynamic process. To get power from an AA battery, one needs to perform a thermodynamic operation, that is to say, to connect it to the load. Such a connection is a thermodynamic operation, because it changes the contact connectivity between the system and its surroundings. A process is not allowed to have within it an operation on the system's connectivity with its surroundings. Thermodynamic operations within the surroundings are permitted, indeed more or less needed. The initial condition of a thermodynamic process is best conceived of as a situation in which the system is at actual contact equilibrium with its surroundings. Then the surroundings change, for example, by a remote thermodynamic operation that eventually affects the subsystems of the surroundings that are in contact with the system. Things happen, and eventually the contacting subsystems of the surroundings settle again to a stationary state, and the system can settle to its own internal state of thermodynamic equilibrium, which is the final state of the process. These matters are not very extensively dealt with in most sources. So far as I know, probably the distinction between a process and an operation was first articulated explicitly by Tisza (Tisza, L. (1966). Generalized Thermodynamics, M.I.T. Press, Cambridge MA). The distinction is however implicit in Kelvin's reference to an "inanimate material agency". The system is not allowed to contain an 'animate agency'. That is part of its being in its own state of internal thermodynamic equilibrium. This is the reason that Carathéodory's principle is inferior to Planck's principle as an axiom for the second law. Planck's principle is that a system in its own state of internal thermodynamic equilibrium cannot do strictly isochoric adiabatic work on its surroundings, though its surroundings can do isochoric adiabatic work on it. Carathéodory's principle doesn't tell you which way is physically positive for entropy production.Chjoaygame (talk) 11:03, 23 July 2013 (UTC)

So, if a system has non-thermal(loosely speaking) energy that could be extracted as work, but only by changing the "contact connectivity", then the system can't be well-described by thermodynamics? In statistical mechanics, it appears to me that the thermal or internal energy can be defined more narrowly as something along the lines of macroscopically-uncorrelated microscopic mechanical energy, so the chemical energy simply wouldn't be included and would have no effect on the thermal behavior of the system until some process converts or releases that energy. DavRosen (talk) 15:31, 24 July 2013 (UTC)

"Classical thermodynamics" is also called equilibrium thermodynamics. One major kind of entity of interest in the theory is the single-phase system in its own state of thermodynamic equilibrium. In the absence of external force fields, such a system is spatially homogeneous with respect to the intensive thermodynamic variables. Planck's treatise on thermodynamics more or less uses the notion of a homogeneous system as primitive, instead of saying it is in its own state of internal thermodynamic equilibrium. Another major kind of entity of interest in the theory is the natural thermodynamic process. A natural thermodynamic process includes a transient departure from thermodynamic equilibrium, and during this, strictly speaking, neither the system nor its surroundings are supposed to be described by thermodynamic state variables, which always in this theory refer to strict thermodynamic equilibrium. Thus the theory does not require eternal equilibrium, in spite of its being called equilibrium thermodynamics; it is just the states that are, on every occasion that they are defined, in equilibrium.

Non-equilibrium thermodynamics is a far less well settled subject. Much is written about it, and many assumptions are made for and about it, but it remains much less settled than equilibrium thermodynamics. It is not too relevant here.

What I wrote above about the AA battery is not a full expression of the situation. I did not stipulate that I was assuming that the battery was given in an isolated state.

What I wrote above concerns an AA battery given in isolation. I focused on the fact that a well-charged AA battery in isolation is not a system in its own internal thermodynamic equilibrium, not so much that it requires a change in its contact connectivity to release its potential energy. If left to itself for long enough, it will go flat, discharging itself. That will bring it towards its own state of internal thermodynamic equilibrium, which would eventually make it a system such as is considered an initial condition for a thermodynamic process. And of course it would then obey Planck's principle, and be unable to provide work to its surroundings, though it could charged by its surroundings doing work on it if is a re-chargeable battery. It might be likened to a spring held coiled by a thin plastic cover. If the cover is ripped the spring will expand and do work on a suitable load.

If the AA battery were not given in an isolated state, it might be given that it was sitting more or less well charged in its cradle in its battery charger, with its surroundings holding its terminals at a steady voltage. Then of course no current flows, and indeed there are no flows in the battery at all, if it is a good one. Then it is in a state of contact equilibrium with its surroundings. It does not consist of a single phase. It needs to be described as consisting of several internal subsystems or phases, and its surroundings also need to have suitable structure. Without changing the contact connectivity, the battery can then be subject to thermodynamic processes, by changes in the surroundings. For example, the charger can be replaced by a load, changing only the parts of the external electrical circuitry that are not in immediate direct contact with the battery, which are perhaps copper wires. Then the battery will do work by driving an electric current through the load. If the battery is thermally isolated, then the work done on the load will be equal to the loss of internal energy of the battery. Some amount of the chemical potential energy of the battery, which is part of its internal energy, will also be expended in raising the temperature of the battery. If, alternatively, the battery is held at constant temperature, some, nearly the same amount probably, of the internal energy will be lost to the surrounding isothermal heat bath as heat.

In order to achieve your plan of not including the chemical potential energy, I suppose one would need at least to keep the battery electrically isolated. It would not be internally homogeneous, but it might have some practically permanent internal mechanical structure. But I don't see how it could be a battery if it had no internal pathways for spontaneous chemical flows. I think some of its chemical potential energy would be internally redistributed by changing its temperature, as a result of transient internal chemical reactions and flows, though if is a good battery that effect might be small enough to neglect. On a time scale that makes the spontaneous internal discharge of the battery negligibly slow, one could then treat it as a mechanical body, with pressure, volume, and temperature in its relation with its surroundings. It is important that it would probably have no strictly adiabatically isolated internal phases; then one could measure its temperature by an external contact thermometer. When it settled into its own electrically isolated state it would then have a single internal temperature that would be spatially uniform, spatially homogeneous. It would make things easy if its surroundings could be described by a single temperature and a single pressure. One could measure its internal energy relative to some chosen reference mechanical state, in the usual ways for a closed system. Carathéodory's theory seems not to allow chemical reactions (though this is not explicitly stipulated), but to allow diffusion between the internal phases. Apart from that, it covers such a system, that consists of several phases without internal adiabatically isolated compartments, for its definition of overall closed system internal energy and work. For internal energy, I suppose one could stipulate some chosen reference pressure and one could define the reference temperature as absolute zero, though this would entail a few practical problems.

I did not directly address your mention of extensive state variables. An extensive variable is a state variable that scales with the size of a homogeneous system. Internal energy is an extensive variable. Quantity of energy transferred as heat is not a state variable.

Perhaps the above could be put in a nutshell by Munster's advice, that definite meanings can be attached to words when the precise circumstances to which they refer are specified. To say something about a kind of transfer, one should specify the conditions under which it will be considered to occur.

I do not mean to suggest that these considerations are different from those for a setup for statistical mechanics.Chjoaygame (talk) 18:30, 24 July 2013 (UTC)

Archival notice, July 2013

Closed issue, not related to this article.

As you can notice, eleven threads disappeared. They now lie intact at talk:Heat/Archive 14 #Needs Revision. Contains a fundamental blunder. and below. If even Apteva switched to support a restricition, then there is no doubt that the community denies the competence of Damorbel to edit this article. The topic ban can be now considered de facto in force due to overwhelming majority support. Damorbel explicated his points, resulting discussions are fully preserved, but there is no merit to continue them further. Let’s move on, mates. Incnis Mrsi (talk) 09:04, 24 July 2013 (UTC) I concur, except that I think that it is unsafe to suppose that "The topic ban can be now considered de facto in force." I think we need strongly enforceable enactment.Chjoaygame (talk) 10:01, 24 July 2013 (UTC)

Problems with intro and other drawbacks

http://en.wikipedia.org/w/index.php?title=Heat&oldid=565886236

(1) Logical contradiction in the very first paragraph:

1. "heat is energy"
2. (in WP page energy): energy is "a conserved extensive property of a physical system"
3. "Heat is not a property or component or constituent of a system or body"

(2) "If the surroundings of a system can be described also as a thermodynamic system with a temperature, and it is connected to the system by a pathway for heat transfer, then, according to the second law of thermodynamics, heat flow occurs spontaneously from the hotter to the colder system."

The sentence starts talking about one system and ends talking about two systems. It starts talking about "surroundings" and ends with two systems. Do the two systems have common surroundings? Or is "the system" is one system and "its surroundings" is another system in question? Confusing. Also, the sentence is two miles long. Can it be simplified? Also, what the heck is "thermodynamic system with a temperature"? Is there one without temperature? Also, if the "a system" the surrounding thereof are discussed herein is a "thermodynamic system" or not?

(3) "Heat is not a property or component or constituent of a system or body; rather, it describes a process of transfer of energy.[8]"

The ref in questions actually says : "heat is not a substance, but a process of energy exchange". Two problems here: the first part of the wikipedia sentence is not cited; while the second part says not the same as the ref cited. I understand this is nitpicking, but given the complexity of the topic, I'd rather have a better support for credibility of the article, especially its intro.

(4) Ref 8 actually has a good section about the history of the concept "heat", including flogiston and caloric, among other things. Whereas our section 'History' sucks.

(5) Ref 8 has a useful remark to the end that even today serious texts may say "heat flows" or "heat capacity", but these are actually remnants of older concepts and should not be taken in their face value. Something to this end must be prominently added (e.g., in a new section "Terminology"), to avoid various confusions and misconceptions.

Staszek Lem (talk) 22:40, 7 August 2013 (UTC)

Thank you Staszek Lem for this commentary.

(1) Logical contradiction in the very first paragraph:

1. "heat is energy"
2. (in WP page energy): energy is "a conserved extensive property of a physical system"
3. "Heat is not a property or component or constituent of a system or body"

The first sentence was a sentence, not merely a string of words. The logical or grammatical complement of the sentence was "energy transferred" not 'energy'. Ordinary language is not compositional, but must be read as formed from sentences, not mere word strings. Nevertheless, I have made a change in response to your comment, from "energy transferred" to 'energy in transfer'.

Evidently the article on energy is faulty in not allowing for energy in transfer. I suppose you are free to remedy that fault.Chjoaygame (talk) 18:24, 8 August 2013 (UTC)

(2) "If the surroundings of a system can be described also as a thermodynamic system with a temperature, and it is connected to the system by a pathway for heat transfer, then, according to the second law of thermodynamics, heat flow occurs spontaneously from the hotter to the colder system."

The sentence starts talking about one system and ends talking about two systems. It starts talking about "surroundings" and ends with two systems. Do the two systems have common surroundings? Or is "the system" is one system and "its surroundings" is another system in question? Confusing. Also, the sentence is two miles long. Can it be simplified? Also, what the heck is "thermodynamic system with a temperature"? Is there one without temperature? Also, if the "a system" the surrounding thereof are discussed herein is a "thermodynamic system" or not?

Yes, the sentence does start with one system and end up talking about two, which it constructs from the one and its surroundings. In general, the surroundings are not required to have a temperature. If the surroundings do not have a well defined temperature, they do not constitute a properly defined thermodynamic system. That they should have a temperature of their own is a special case, constructed and considered here.

(3) "Heat is not a property or component or constituent of a system or body; rather, it describes a process of transfer of energy.[8]"

The ref in questions actually says : "heat is not a substance, but a process of energy exchange". Two problems here: the first part of the wikipedia sentence is not cited; while the second part says not the same as the ref cited. I understand this is nitpicking, but given the complexity of the topic, I'd rather have a better support for credibility of the article, especially its intro.

The lead is a summary and does not need (and even, some would say, should not use) a citation. I put in the citation to please a commentator on this talk page, because it seemed to have the same meaning as the sentence in the lead. I have now taken it out again in response to your complaint that it is not a literal quote of the source. If you feel like finding a place for the Grandy citation in the body of the article, you are of course free to put it in.

(4) Ref 8 actually has a good section about the history of the concept "heat", including flogiston and caloric, among other things. Whereas our section 'History' sucks.

It is always a pleasure to read helpful commentary. Of course you are free to re-write the section on 'History'.

(5) Ref 8 has a useful remark to the end that even today serious texts may say "heat flows" or "heat capacity", but these are actually remnants of older concepts and should not be taken in their face value. Something to this end must be prominently added (e.g., in a new section "Terminology"), to avoid various confusions and misconceptions.

There is a section at the end of the article about usage of language. It intends to deal with the problem to which your comment refers, as it asks for a section called "Terminology". I put it at the end because there was a complaint that it was too prominent when placed nearer the beginning of the article. Now your comment finds it not prominent enough even to be noticed.Chjoaygame (talk) 16:59, 8 August 2013 (UTC)

ease of editing

Chjoaygame has a habit of using a paragraph where a sentence will do. If you are dealing with reasonable people, your authority means nothing, only your arguments count. If you are dealing with unreasonable people, your authority means nothing and neither does your argument. The only people who are impressed by authority are proto-cult members and clerks. Most of the editors here are semi-reasonable on the short run, very reasonable on the long run, so yes, give an argument. What is this "standard undergraduate text"? Maybe we are all wrong, but we will never know it until you explain what you mean by "serious lack of understanding of the subject". PAR (talk) 20:19, 30 August 2013 (UTC)

Well, let me try once more, though I am not particularly looking forward to this discussion. In particular, you seem to overlook twice my first statement in this thread, where I cite the undergraduate text by Wolfson. Btw all other texts I have seen, for example Giancoli, use the same definition - heat is energy and not transfer. Concerning how general this definition is. We can consider an equilibrium, a quasi-equilibrium, or a (strongly) non-equilibrium situation. In reality, the heat definition as the energy to be transferred between the bodies of different temperatures is always correct in an equilibrium or quasi-equlilbrium situation, when temperatures can be defined, even if locally or instantaneously. If we are talking about non-equilibrium systems, so that temperatures or even distribution functions can not be defined, then there is no unique definition of heat. From what I know, there are research areas, in particular, consensed matter, where the issue is still debated. Therefore no definition of heat for strongly non-equilibrium systems can belong to the lede of the article. Concerning that my definition is "misguided", I do not see how the argument leading to this conclusion is valid. I was asked to provide a source, I provided a source. If someone insists Wolfson is not a reliable source, well, I do not see why but I can possibly go to the library and find more sources. If the source does not say what Chjoaygame wants to hear - well, I am sorry, but I can not help.--Ymblanter (talk) 21:42, 30 August 2013 (UTC)

We all know that all our terms are but abstractions which help us to describe what we see. It is well-known that physical concepts change over time, even lose their meaning altogether. The canonical example is wave vs. particle (which eventually turned out both). There is nothing unusual that some notions make no sense in some conditions. Therefore when making a definition, one has to clearly identify areas of its applicability or non-applicability. And this definitely belongs to the lede. But this was not my pertinacious question. Staszek Lem (talk) 22:05, 30 August 2013 (UTC)

Sure, I just oppose the statement that "heat = transferred energy" can not be a correct definition since it does not apply out of (quasi)-equilibrium.--Ymblanter (talk) 22:10, 30 August 2013 (UTC)

Ymblanter makes an important point. It is good to have someone of his stature here. To be fair, I would point out that he has perhaps not read all that has transpired here on this talk page, and perhaps has not read the whole article, of which the lead is a summary, and so some of what is here and in the lead of the article will seem to him to come out of left field from nowhere, or even to be nonsense.

As I read him, Ymblanter is making the point that there is a definition of heat that coheres with the concept of temperature. This definition is covered in the article in the section entitled Heat#Heat, temperature, and thermal equilibrium regarded as jointly primitive notions. When I first came to this article I felt that this was the proper definition. So I started where Ymblanter is now. I think I may therefore fairly say that I appreciate his viewpoint. That starting point is what might fairly be called the traditional thermodynamic approach.

But the editors here soon disabused me of my starting point. The article was, I learnt, dominated by the viewpoint that Bailyn calls the "mechanical approach" <Bailyn, M. (1994). A Survey of Thermodynamics, American Institute of Physics Press, New York, ISBN 0-88318-797-3, at page 65>. It started with writing by George H. Bryan, an example of which is Bryan, G.H. (1907), Thermodynamics. An Introductory Treatise dealing mainly with First Principles and their Direct Applications, B.G. Teubner, Leipzig. This view was also put by Max Born, who stimulated Constantin Carathéodory to write a paper in 1909, Untersuchungen über die Grundlagen der Thermodynamik, Mathematische Annalen, 67: 355–386, doi=10.1007/BF01450409. A translation may be found here. A mostly reliable translation is to be found at Kestin, J. (1976). The Second Law of Thermodynamics, Dowden, Hutchinson & Ross, Stroudsburg PA.

This 1909 Carathéodory paper was championed by Born, and it became what I think of as the currently dominant "official findings", the mechanical approach as labeled by Bailyn. Dear Ymblanter, it is not that I want to hear these official findings. It is that they have been forced on me by the consensus of editors here. The source that you cite still uses the thermodynamic approach, not the mechanical approach of the official findings.

Ymbalanter, if you want to reconstruct the article, making the thermodynamic approach the default view, you will be reversing the current consensus. Perhaps you may succeed in such an endeavor. But there are some problems in your way that we may consider on another occasion.

The thermodynamic approach is traditional, and suitable for an introductory pedagogical account, such as is cited by Ymblanter. It requires the surroundings of the system to have a temperature. The mechanical approach does not require the surroundings of the system to be defined in thermodynamic terms. Consequently, it does not require it to have a temperature.

Perhaps my just foregoing note misrepresents Ymblanter. If so, I hope he may correct me.

Reading Ymblanter again, I find that he thinks that heat is not defined in the absence of a temperature. I agree that the system must have a temperature at the initial and final states of the process, in order to qualify as a thermodynamic system, implicitly in its own internal state of thermodynamic equilibrium. But the official view is that the surroundings are not at any stage required to have a temperature. If they have a temperature, then the traditional view works. If they don't, only the official view works.

As for the last comment by Ymblanter, it is very brief and I do not know what it means. Nowhere in the article do I find in exactly so many words the formula "heat = transferred energy". This formula is obviously quick and efficient, but it does not appear in so many words in the article. I need a more exact statement to respond to. Perhaps Ymblanter will supply one for me.Chjoaygame (talk) 00:12, 31 August 2013 (UTC)

What am I missing? I thought this was cleared up.

You have a bank account, its amount can increase by payments or by interest. Is payment money? Well, yes. But there is no "payment money" or "payment" in the account, only money. You don't ask for ten dollars of payment money and two dollars of interest money when you withdraw money. You just withdraw money.

You have a lake, the amount of water in it can increase by flow from a stream or by condensation (rain). Is flow water? Well, yes. But there is no "flow water" or "flow" in the lake, only water. You don't ask for a cup of flow water and two cups of rainwater when you want water from the lake. You just withdraw water. You can ask for water to be withdrawn by evaporation and water to be withdrawn as a flow out of a another stream, but that's a different matter.

You have a thermodynamic system, the amount of energy in it can increase by work or by heat(ing). Is heat energy? Well, yes. But there is no "heat energy" or "heat" in the lake, only energy. You don't ask for a joule of heat energy and two joules of work energy when you want energy from the system. You just withdraw energy. You can ask for energy to be withdrawn as heat and energy to be withdrawn as work, but that's a different matter.

This is a semantic problem. The third example sometimes grates against the vernacular or colloquial use of the term heat. The consensus, as I see it, is that the imprecise colloquial terms are rejected. Yet the misuse of the term "heat" rather than "thermal energy" persists. PAR (talk) 08:27, 31 August 2013 (UTC)

These comments by PAR don't seem to be relevant to what Ymblanter wrote? I was asking Ymblanter what was he concerned about when he wrote "Sure, I just oppose the statement that "heat = transferred energy" can not be a correct definition since it does not apply out of (quasi)-equilibrium." I hope he will tell me, if he wants to pursue what he wrote there. Ymblanter was responding to Staszek Lem's last comment, which I think is off the main track of Ymblanter's concern.Chjoaygame (talk) 13:29, 31 August 2013 (UTC)

I now see the relevance of PAR's comment.

In its light, now reading again the remarks by Ymblanter, I see that Ymblanter means that he thinks someone here rejects the idea that heat means quantity of energy transferred as heat. He rightly thinks that no reason can justify such a rejection. He is mistaken to think someone here rejects the idea the heat means quantity of energy transferred as heat. And mistaken to think that the aforesaid someone here imagines as a reason 'that the definition does not apply out of (quasi)-equilibrium.'.

No, Ymblanter, there is no such someone here. The consensus here is that heat means quantity of energy transferred as heat. That also applies when the surroundings do not have a temperature.

I think Ymblanter's comments have two sticking points:

(1) Ymblanter wrote above: "I do not see how heat can be transfer. Heat flow is transfer." No, Ymblanter, this is a matter of language. The consensus here is that usage allows that 'energy in transfer' and 'transfer of energy' both mean 'quantity of energy transferred as heat', and are in this usage virtually synonymous. We do not insist that heat transfer requires the phrase 'heat flow'; in context, 'heat' by itself means 'transfer of energy'. These usages are not compositional. This is the point that PAR is referring to.

(2) Ymblanter wrote above: Heat is energy being transferred from one object to another because of a temperature difference alone. No, Ymblanter, this is a matter of physics. The consensus here is that this definition assumes a special case (considered in what might be called the thermodynamic approach) that requires the surroundings to have a temperature. But here we take as default the more general case in which the system has temperatures respectively in its initial and final states, but the surroundings are not required to have a temperature (as considered in what might be called the mechanical approach).Chjoaygame (talk) 21:19, 1 September 2013 (UTC)

I essentially agree with Chjoaygame. Heat is the energy transferred from one system to another that is not transferred as work, work being directly measureable. If the receiving system is in thermal equilibrium at its beginning and end points, the total energy transferred may be inferred (without reference to the concept of temperature). Heat is then the energy that can be inferred to have been transferred by subtracting the energy transferred as work from the total energy transferred. The system from which the energy is extracted need not be in equilibrium and need not have a definable temperature. We are talking first law effects here, and temperature is not defined until the second law. Please feel free to modify and/or correct. PAR (talk) 15:32, 2 September 2013 (UTC)

response

I am sorry to say, but someone here recently tried to teach me Wikipedia policies. What about WP:RS? I brought a quote from a reliable source. If this quote is not good enough, it should be countered by another quote from another reliable source (and, at best, the one which adresses the first source and explains why it is not complete). So far, both of you failed to do this. According to WP:RS, your opinions can not be used to modify the article. Let me respectfully repeat again that if the systems are strongly out of equilibrium, heat can not be defined. (The internal energy can not be separated from work).--Ymblanter (talk) 16:53, 2 September 2013 (UTC)

And, yes, temperature appears in the zeroth law.--Ymblanter (talk) 21:12, 2 September 2013 (UTC)

Thank you, Ymblanter, for your contribution here. It is good to have someone of your stature with us.

I very much sympathize with your physical view that "if the systems is strongly out of equilibrium, heat can not be defined. (The internal energy can not be separated from work)." I had a mighty battle with Editor Count Iblis, in which I put the best case I could manage in favour of your view. I cite just one part of that battle, because it was long and scattered. In the end, I have to concede that Count Iblis was right, though I do not think he put his case soundly. The view that I put followed the thermodynamic approach, but the main textbook view nowadays is the mechanical approach, though textbooks are not uniform in this.

Thus, in retrospect, I think the arguments on either side were not very well conducted. My current summary of the situation is stated above, copied here: "The consensus here is that this definition assumes a special case (considered in what might be called the thermodynamic approach) that requires the surroundings to have a temperature. But here we take as default the more general case in which the system has temperatures respectively in its initial and final states, but the surroundings are not required to have a temperature (as considered in what might be called the mechanical approach)."

The two definitions are considered in the article at some length, at Heat#Rigorous definition of quantity of energy transferred as heat and at Heat#Heat, temperature, and thermal equilibrium regarded as jointly primitive notions. A summary is offered in the article at Heat#Macroscopic view of quantity of energy transferred as heat. These sections are adequately referenced, it seems.

Therefore I do not accept your proposal "So far, none of you failed to do this." I think when you read the sections I have just cited you will come to agree that this question has been adequately considered in the article with due weight to both points of view.

Expressing it again, I think the way to make things clear it is to tell separately about the system and about its surroundings, each in its own right. In order to qualify as a thermodynamic system undergoing a thermodynamic process, the system has to be described by thermodynamic state variables for the initial and final states of the process. The surroundings are not constrained in this narrow way. I suggest that your comment about the case "if the systems is strongly out of equilibrium" does not tell separately about the system and its surroundings, each in its own right.

I think we agree here that if the system itself in the initial and final conditions respectively of the process is not in thermodynamic equilibrium, then for classical thermodynamics, it is not a thermodynamic system; heat is defined only when one is considering a thermodynamic system. We agree that in order to be a thermodynamic system, the system should be in its own internal state of thermodynamic equilibrium in the initial and final states of the process. But that does not apply to the surroundings, and the difference is there.Chjoaygame (talk) 21:30, 2 September 2013 (UTC)

Ymblanter - Sorry, cannot find the Wolfson quote in this discussion. Is it from "Essential University Physics"? - If so, I do not have access to that book, so a quote (with some context) would be helpful. PAR (talk) 05:06, 3 September 2013 (UTC)

Heat is energy being transferred from one object to another because of a temperature difference alone. This is a direct quote from Wolfson.--Ymblanter (talk) 05:28, 3 September 2013 (UTC)

The article as it stands has in the lead the following: "It can occur that the surroundings of a system can be described also as a second thermodynamic system that has its own definite temperature. In this special circumstance, if the two are connected by a pathway for heat transfer, then, according to the second law of thermodynamics, heat flow occurs spontaneously from the hotter to the colder system. Consequently, in this circumstance, heat is transfer of energy due purely to temperature gradient or difference." It seems that there is not much difference between us. Since the lead is a summary of the article, it is not customary to be very demanding of source citations in the lead, especially if there is no dispute.Chjoaygame (talk) 07:56, 3 September 2013 (UTC)

I think a response to my just above comment is due from Editor Ymblanter.Chjoaygame (talk) 09:55, 4 September 2013 (UTC)

Not really.--Ymblanter (talk) 10:13, 4 September 2013 (UTC)

Just to remind you, the original question was "is heat energy or transfer". You have written about a zillion of things, most of them wrong, but failed to answer this question. Could you please get closer to the point. My answer, supported by the quote, is "energy". I do not see how this argument can change if we take a system out of equilibrium and somehow manage to define heat in a unique way.--Ymblanter (talk) 10:52, 4 September 2013 (UTC)

Dear Editor Ymblanter, you have raised two questions. One about language, is heat energy or is it transfer. The other is about physics, for our primary definition of heat, should we take the thermodynamic approach, defining it as due to temperature difference, or the mechanical approach, defining it as a residual after work has been deducted from change in internal energy. You are now proposing to focus on just the first, as to language.

Sad to say, it seems you have been misled by a coach who verges on Wikilawyering. I am sorry to say it is only too obvious who that coach might be, someone who has been banned here for unethical behavior. You have not served your cause well by your belligerent words "I am sorry to say, but someone here recently tried to teach me Wikipedia policies. What about WP:RS? I brought a quote from a reliable source. If this quote is not good enough, it should be countered by another quote from another reliable source (and, at best, the one which adresses the first source and explains why it is not complete). So far, both of you failed to do this. According to WP:RS, your opinions can not be used to modify the article. Let me respectfully repeat again that if the systems are strongly out of equilibrium, heat can not be defined. (The internal energy can not be separated from work)." You did not enhance your position by your response: "I am afraid what you write clearly shows serious lack of understanding of the subject. Very typical for Wikipedia. I am afraid I would rather unwatch this page. Perhaps I am, being a full professor of physics in one of the top universities in the world, and having taught the subject for several years, just not qualified enough to carry out this discussion." And now after I have spent some time answering you civilly, when I say I think a reply to my just above comment is due from you, you say "Not really".

It seems you have hardly read either the article or my answers here. It seems you think that a Wikilawyering approach will serve you well. Things are not as simple as your Wikilawering coach would have you believe. It is necessary but not sufficient to have reliable sourcing. There are many reliable sources in the literature. The editors' job is to select from them with proper weight. The article has already over 50 sources, most of them weighty. The new one you propose is a lightweight. It introduces nothing that is not already carefully dealt with in the article with reference to the already present sources. The proper weight is not decided by fiat from a single editor with a single source, nor by a simple mechanical procedure of quote and counter-quote, as you suggest. Some reasoned judgment, consensus, and balance are also involved.

Now as to your specific focus. In thermodynamics, the word heat refers to a complex idea. One word is being used to express the idea when the word 'heat' appears on its own. It is more fully expressed by the phrase 'quantity of energy transferred as heat'. The phrases 'energy in transfer' and 'transfer of energy' mean the same thing. The question of 'whether heat is energy or whether it is transfer' is hardly better than your comment "(The internal energy can not be separated from work)." Internal energy is a state variable, work is a process variable. They are different in categorical nature and thereby separated. Yes, we know you meant to write that under the specified circumstances, heat transfer cannot be separated from work transfer, but that is because we know what the words mean, not because your question is well expressed. The question on which you now wish to focus, is heat energy or transfer, is more or less predicated on a sort of compositional theory of semantics. But ordinary language, including the language used here, does not have compositional semantics. Heat can be said to be both transfer and energy combined and it would be nonsensical to try to say it was one and not the other. It is as if you have asked which are you, a university staffer or a professor? You are a university professor, and those two ideas are not reasonably to be separated. It is hardly appropriate to try to impose an answer to your ill-posed question by reference to one or two literature sources. No one is suggesting that "this argument can change if we take a system out of equilibrium and somehow manage to define heat in a unique way."

If, as you suggest by your words "Not really", you do not have a response to my just above comment about your other question, as to whether our primary definition should be the thermodynamic one or the mechanical one, I am happy to let that question lapse, leaving things as they are.Chjoaygame (talk) 15:43, 4 September 2013 (UTC)

I really appreciate your attempt to teach me basic notions of Wikipedia, even if using an ad hominem attack. May be you should nominate yourself to an administrator rather than continue talking about heat. You might also note that I posed not two, like you state, but zero questions, and I am really amazed how you managed to derail the whole discussion away from them. I guess you are best left alone, since I do not see anybody else here interested in this pointless discussion. All the best.--Ymblanter (talk) 15:51, 4 September 2013 (UTC)

axiomatics

I don't see the Wolfson quote as a definition of heat, but rather a property of heat when the two systems happen to be in equilibrium. As a definition, it involves circular reasoning. Temperature is not defined until the second law, which means that heat cannot be defined until the second law, yet heat is defined in the first law, which is then used (along with the second) to define temperature. PAR (talk) 13:27, 3 September 2013 (UTC)

As I mentioned earlier, the temperature is defined in the zeroth law. Your statement that the temperature is not defined until the second law is incorrect. Apparently you are confusing entropy and temperature. My quote from Wolfson is the definition of the heat, given in that book. I suggest that if you do not like it you write to Wolfson and ask him to change the structure of the book.--Ymblanter (talk) 13:43, 3 September 2013 (UTC)

In classical thermodynamics one needs extra postulates. I have to say that I don't personally like this approach and as a consequence I am not so well versed in this compared to the statistical thermodynamics approach (e.g. as presented in the textbook by Reif). If you forget about the small details and focus on the physics, then one has to acknowledge that heat flow is always due to the systems being out of thermal equilibrium. Also, the systems will themselves be out of internal thermal equilibrium, only in the limit that the heat flow happens at a rate of zero (the quasistatic limit) can the systems remain in thermal equilibrium. But you don't want to define heat in such a way that this requires temperature to be well defined during the exchange of heat, as that would severely limit the applicability of thermodynamics when in practice there is no problem with it being undefined.

E.g. in the free expansion experiment, it's not a problem to say that Q = 0 and W = 0, despite that during the free expansion the system is very far from thermal equilibrium. And if Q were not equal to zero in a similar set-up, it would not necessarily be a problem to determine its value. Count Iblis (talk) 20:06, 3 September 2013 (UTC)

We are now talking about axiomatics in a general way. I will reply to the three comments just above.

There are several questions raised here. Perhaps the largest is the one raised by Count Iblis. He prefers, as I see it, to regard thermodynamics as a special case of statistical mechanics, in which in effect the number of microscopic degrees of freedom has reached the thermodynamic limit, while the number of macroscopic variables remains smaller. Editors PAR and Ymblanter are concerned with thermodynamics considered as a macroscopic subject from the beginning, developed from some principles, stage by stage.

The article as it stands takes the purely macroscopic approach as primary, and the statistical mechanical approach as explanatory in terms of a model. According to Lieb and Yngvason (1999), "If the law of entropy increase is ever going to be derived from statistical mechanics — a goal that has so far eluded the deepest thinkers — then it is important to be absolutely clear about what it is that one wants to derive." This is an argument for statement of thermodynamics in purely macroscopic terms, even if only to define the target at which statistical mechanics is aiming.

As for axiomatics, different developments use different axioms. Tisza (1966) compares several of them. I would comment about the remarks of Editors PAR and Ymblanter that in mathematical developments from axioms, it is often the case that several axioms are used at once, and the order in which they are stated does not have to match the order in which they are cited in a proof. Also I would say that opinions differ about exactly what the zeroth law says. The title "zeroth law" was invented some time in the nineteen twenties or early thirties. The usual summary of it was written in authoritative texts, not labeled as a numbered law, decades before. Most texts regard it as contributing to and helping to apply the definition of empirical temperature, and perhaps as helping to apply the Kelvin definition of absolute thermodynamic temperature. There are of course also various statements of the first, second, and third laws. The various usual statements of the four laws are hardly enough to support respective rigorous logical developments without supplementary axioms that might be considered too trivial to merit honorific titles and numbers as laws in their own respective rights.Chjoaygame (talk) 21:28, 3 September 2013 (UTC)

I agree with everything you say, but I don't understand the implications. Wikipedia should follow some sort of axiomatic theory, not necessarily absolutely rigorously, but at least to say that each law builds upon the previous law. If that's the case, the heat defined in terms of temperature is circular. That's all I'm saying. PAR (talk) 05:14, 4 September 2013 (UTC)

I am suggesting no particular action. I was just intending to say that I think that one may expect that different editors may have different ideas about the appropriate axioms to start with. Therefore I think it would not be feasible to get consensus about a strict axiomatic development. The present set-out is more or less the product of consensus. It is very far indeed from being an exact and rigorous development from an axiom system, but for practical purposes I think it is not too bad as a general presentation. I think we are not likely to do much better by changing its axiomatic structure. I am in favour at present of keeping the primary definition of heat the way it is now, as quantity of energy transferred by means other than transfer of energy as work or transfer of matter. I think we have reached a consensus on that. I am not in favour at present of changing the primary definition to the one proposed by Ymblanter. I think his proposed definition is already adequately represented in the article as a secondary statement about heat. I see him as having a different axiom system in mind, and so I don't reject his proposed definition; I just think it should stay in the article as a secondary statement about heat, not as a primary definition.Chjoaygame (talk) 07:49, 4 September 2013 (UTC)

Count Iblis, I am not sure our discussion makes much sense, since apparently it deviated too much from the original question, but I am not sure I buy your argument so easily. Imagine we have a medium with population inversion, which is continuously pumped and radiates. What is heat and what is work? And if the atoms get stuck in the metastable state?--Ymblanter (talk) 11:14, 4 September 2013 (UTC)

Ymblanter, I'm not an expert in laser physics, but in general, there is no unique way to split an energy transfer in "heat" and "work". This is very clear from the approach that I prefer (based on e.g. the treatment in the book by F. Reif). When given a system such as the the medium with population inversion, it is up to you to split the degrees of freedom of the system into two parts, one part will be treated statistically, the other will be kept in the thermodynamic description as "external parameters". This splitting is in principle completely arbitrary, but in practice for a thermodynamic description to be useful, you are usually forced to pick the external parameters in a certain way. Then an energy tranfer associated with a change in the external parameters is defined as work, while the rest is defined as heat. Then there are some issues here with having to use an ensemble that one has to average over to make everything well defined, but the general idea is to throw away most of the degrees of freedom of the system and attempt to describe those statistically.

In your example, you would presumably work with a Master equation describing the time evolution of the numbers of atoms in the various excited states. Then what matters for the definition of heat and work is simply what your control is over these occupation numbers. In case of a medium in ordinary thermal equilibrium, the occupation numbers are not controlled at all, they are given by the canonical distribution and any change in internal energy associated with a change in these occupation numbers is always counted as heat. In your case, this will be different depending on the control you have over the occupation numbers. Count Iblis (talk) 15:11, 4 September 2013 (UTC)

Right, this is exactly my point that it is generally difficult to separate energy into heat and work; additionally, one needs to introduce environments, and in the quantum case it becomes a nighmare and so on. (I am not an expert in laser physics either). This is why I believe it is safe to stay in the thermodynamic limit and to define heat as the energy transferred between two systems with different temperatures.--Ymblanter (talk) 15:28, 4 September 2013 (UTC)

It's not a general enough statement, it doesn't e.g. cover the case where work is converted to heat (you coud try to do that, but that would force one to appeal to resolve a complicated non-equilibrium situation in more detail so that it can be approximately described in terms of local thermal equilibrium where you then can define in some approximate way a local temperature; obviously, this is not rigorous). If you simply rub against a gas cylinder, you are performing work which is converted to heat. You can describe what happens here in terms of well defined intitial and final states of thermal equilibrium, there is no need to consider the detailed processes that occur during this transfer of energy. Count Iblis (talk) 19:27, 4 September 2013 (UTC)

• Well, if you state it like this I would probably agree.--Ymblanter (talk) 19:43, 4 September 2013 (UTC)

• Count Iblis, of course I agree with your comment "It's not a general enough statement."

But I would criticize your reasons for it. "If you simply rub against a gas cylinder, you are performing work." Yes, this is an example of isochoric work as thought of in classical thermodynamics. The classic experiments are those of Rumford, boring a cannon, and Humphrey Davey, rubbing two pieces of ice together in a vacuum; also Joule of course. Also engineers think of shaft work as a kind of isochoric work. The conceptual importance of isochoric work is well presented by Munster.

But just simply to say that heat is produced thereby is not quite by the book. At least, not until one additionally specifies that there is also a mechanism of conduction or radiation by which the internal energy added to the system by rubbing is transferred as heat to the surroundings. And even then, the internal energy that supplies the heat is just internal energy of the system, not work as such supplied by the surroundings.

The more general character that you rightly refer to is secured by a certain feature, not shared by the system, of the surroundings: in the general case they may lack a temperature where they contact the system. An example of surroundings lacking a temperature where they contact the system would be very turbulent fluid surroundings with many different remote temperature sources, or perhaps in a turbulent explosion that heats the system. During the process of transfer of energy, in classical thermodynamics, the temperature of the system is not a concern, as we all agree. But of course as you emphasize, it is strictly necessary that the system has a temperature in its initial and final states of internal thermodynamic equilibrium. But the surroundings are not required, by Reif or by others who use the Carathéodory mechanical approach, to have a temperature; this is the key to the generality that you rightly point to.Chjoaygame (talk) 00:47, 5 September 2013 (UTC)

Just to be sure we are clear about an important point:   The definition of quantity of energy transferred as heat that is given in the first sentence of the lead is in full agreement with the definition given in Count Iblis' preferred textbook, Reif. There is good consensus here about that.Chjoaygame (talk) 02:16, 10 September 2013 (UTC)

References

References