Talk:Temperature

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edit·history·watch·refresh Stock post message.svg To-do list for Temperature:

Restructure according to the guidelines proposed in Wikipedia:WikiProject Science, ie. with the following main sections:

  • Introduction : importance of temperature for life and humans; brief history of the understanding of temperature
  • Temperature in practice: (avoid theory here)
    • Types of temperature: perceived vs real, typical values, macroscopic vs microscopic, temperature of light, negative temperature
    • Units of measure
    • Temperature in the Universe: temperature changes since the big bang
    • Temperature in everyday life: common measuring devices; importance for life
    • Temperature in industry: importance in chemical processes; sample processes with very low or high temperature
    • Temperature in science: precise measuring devices; role in many scientific theories
  • Temperature theory: discuss thermodynamics, why temperature cannot go below 0...
    • Basic concepts
      • why temperature cannot go below zero under a basic definition
    • Advanced concepts
      • why temperature can go below zero under a more rigorous definition
  • History: explain how the concept of temperature evolved over time
Priority 1 (top)


The lede is wrong: temperature is not energy[edit]

It says: "absolute temperature as proportional to the average kinetic energy". This is wrong. It is only valid for an ideal gas. Temperature is not the same as energy. Adding energy to ice will melt it into water, but it can still be at the same temperature as ice. /Pieter Kuiper (talk) 00:22, 31 December 2015 (UTC)

Editor Pieter Kuiper is right that temperature is not defined by "average kinetic energy". The lead, however, does not make the mistake of defining it so. The lead sentences to which Editor Peter Kuiper objects (quoting a few words extracted from one of them) read in full: "The kinetic theory offers a valuable but limited account of the behavior of the materials of macroscopic systems, especially of fluids. It indicates the absolute temperature as proportional to the average kinetic energy of the random microscopic motions of their constituent microscopic particles such as electrons, atoms, and molecules." The proper definition of temperature is not simple, and, for the sake of brevity, the lead does not attempt it. The kinetic theory defines temperature as indicated, in its own specifically convenient way, not in the way that it is properly defined in thermodynamics.Chjoaygame (talk) 01:33, 31 December 2015 (UTC)
Not true. The lede says that the temperature is _proportional_ to energy in unspecified "fluids". This could be water. But the statement is only true for ideal gases. And even then, this talk about the "constituent particles" is so wrong. The kinetic energy of electrons is not proportional to temperature. It is amazing how wrong Wikipedia can be in the lede of a basic science concept. And Chjoaygame does not care. /Pieter Kuiper (talk) 04:12, 31 December 2015 (UTC)
Pieter, I edited that paragraph - see what you think (and please feel free to change it). As for what you say about wikipedia, you're absolutely correct. The problem seems to come down to a small number of non-expert editors, and too few experts with the time or inclination to contribute. Waleswatcher (talk) 21:20, 1 January 2016 (UTC)
Thank you, Waleswatcher, that is a huge improvement. Basically correct. One issue is that some readers will misunderstand and forget the limitation to ideal gas, but the lede is not the place to try to address this. This rest of this article has more problems (poorly organized, too long), but it would require a tremendous effort to edit it into something. And then there are so many more of this kind of articles... /Pieter Kuiper (talk) 23:13, 1 January 2016 (UTC)
Editor Pieter Kuiper wrote above "And Chjoaygame does not care." This was a gratuitous personal aspersion, contrary to Wikipedia policy.Chjoaygame (talk) 04:35, 3 January 2016 (UTC)
Some of the above comments, including the header of this section, by Editor Pieter Kuiper are substantially inaccurate or misleading, or are misquotations, as exposed by my above comments.Chjoaygame (talk) 05:35, 3 January 2016 (UTC)

It bothers me that this edit was made without achieving greater consensus on the discussion page. The previous version VERY clearly indicated that the temperature/kinetic energy relationship, which is often derived from KMT, is fundamentally limited in scope. The new version does NOT make such a clear indication. Furthermore, the new version tends to over-generalize. The kinetic-energy-only relationship is really only true for monoatomic ideal gases, not all ideal gases. Polyatomic ideal gases will exhibit intramolecular potential energy that cannot be neglected. It took many discussion threads and entries to arrive at the previous version. I am very much in favor of reverting the recent change. If the problem was with the phrase "...especially of fluids", then I am in favor of removing that phrase only, since it doesn't necessarily add to the quality of the explanation. JCMPC (talk) 03:16, 2 January 2016 (UTC)

Experiments to test it have for some systems verified the proposition that electrons moving more or less 'freely' do indeed indicate the absolute temperature. The exact scope of kinetic theory is not quite clear, I think. In Wikipedia it is not well defined with adequate support. For sure, it is good for ideal gases, and mostly for real gases in suitable circumstances. There are kinetic theories of liquids. The concept of 'kinetic energy of a particle' is partly applicable in some areas of solid state physics.Chjoaygame (talk) 04:59, 2 January 2016 (UTC)
Personally, I don't have any qualms with kinetic molecular theory. I do have problems with what I view as the over-generalization and over-emphasis of the temperature/kinetic energy relationship. In my experience, this over-emphasis stems from when and how temperature is taught in typical undergraduate curricula. Introductory courses in thermodynamics try to paint a physical picture for temperature, and this is routinely done for the first (and likely only) time using a monoatomic ideal gas since the kinetic molecular theory description of this system is fairly straightforward. Introductory textbooks are very clear in providing this context, but many students at this level are all to eager to apply the new idea and tend to ignore the context in which the concept is initially presented. A review of the talk page archives for this article reveals that this issue has been as major point of contention in the past and, if I am allowed to interpret, the consensus was to include a statement that explicitly draws attention to the potential problems with the interpretation of temperature as kinetic energy. Such a statement was in the previous version of the article. JCMPC (talk) 14:07, 2 January 2016 (UTC)
Also, to follow up on other comments, why can't electrons be influenced by the temperature? While it is often standard to ignore "thermal" motion of electrons, this is just because the typical energy gap between electronic states is substantially larger than kT. In cases where low lying electronic excited states exist, thermal excitation of electrons should be commonplace. At the very least, isn't this why metals are such good heat conductors? The highly delocalized electrons in close lying states can transport energy over long distances at a rate that is fast when compared to the transfer of energy via vibrational motion "only" in insulators. JCMPC (talk) 14:26, 2 January 2016 (UTC)
I seem to recall that electrons emitted from a hot wire have been analyzed for velocity, and found to have a Maxwell distribution that tells the temperature of the wire. I don't right now recall the exact reference.Chjoaygame (talk) 17:49, 2 January 2016 (UTC)
Though I cannot comment on the distribution law followed, what you mention is the basis for thermionic emission, which is the basis for many electron guns, which is in turn the basis for cathode ray tubes. JCMPC (talk) 20:26, 2 January 2016 (UTC)
I have now supplied references in the body of the article for the Maxwell distribution of velocities of thermionically emitted electrons.Chjoaygame (talk) 04:17, 3 January 2016 (UTC)
As for dense fluids, the following may be of interest: E. G. D. Cohen, (1984), 'The kinetic theory of fluids—an introduction', Physics Today, 37(1): 64–73; doi: 10.1063/1.2916049: "velocity correlations are, of course, also created by collisions in fluids in thermal equilibrium. The created correlations are, however, again destroyed through collisions in such a way that the Maxwell velocity distribution function is maintained. This is not true in nonequilibrium fluids."Chjoaygame (talk) 22:08, 2 January 2016 (UTC)

Are there any further thoughts on the lead? Can we add back in the caveat on KMT that was present several versions ago? The phrase "temperature is proportional to the average kinetic energy of the random microscopic motions of the constituent microscopic particles" doesn't sit well with me. In particular, this implies to me a linear relationship between temperature and kinetic energy, which I find problematic. JCMPC (talk) 22:39, 3 January 2016 (UTC)

Editor JCMPC, you are right to want to do something about it. Careful wording is needed. Some editors are by nature opposed or allergic to careful wording. In thermodynamics (I mean equilibrium thermodynamics) temperature is defined in terms of a Carnot cycle, a strictly equilibrium concept. Kinetic theory wants temperature to be defined for non-equilibrium. Logically that is not possible. Therefore they just say "Oh, forget the logic. Let's just define temperature as simply proportional to the average kinetic energy of particles that are moving more or less freely." For many purposes, they have there a very good and valuable approximation. For rigorous theory, the necessary concepts are still at the cutting edge of research, mostly beyond Wikipedia, I think.Chjoaygame (talk) 04:49, 4 January 2016 (UTC)

This paragraph is still wrong, especially because it mentions electrons: "The kinetic theory offers a valuable but limited account of the behavior of the materials of macroscopic bodies, especially of fluids. It indicates the absolute temperature as proportional to the average kinetic energy of the random microscopic motions of those of their constituent microscopic particles, such as electrons, atoms, and molecules, that move freely within the material."

The kinetic theory is pre-quantum. For electrons in metals, this would be the obsolete Drude model. In metals, the energy of electrons is typically several electronvolt, on the order of 100 times larger than what kinetic theory predicts for room temperature. Also light atoms (hydrogen in water, carbon in diamond) have kinetic energies larger than what classical theory predicted. And the classical equipartition theorem does not depend on particles moving freely within a material. /Pieter Kuiper (talk) 20:05, 4 July 2016 (UTC)

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"improve" the English by changing the physical meaning[edit]

I have undone an "improvement" in the English that made the physical meaning wrong. The absolute zero of thermodynamic temperature is the coldest possible temperature, but the lowest possible temperature either does not exist or is −∞ K. The latter is also the hottest possible temperature. 'Coldest' is the appropriate word, not 'lowest'.Chjoaygame (talk) 22:40, 10 April 2016 (UTC)

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Lead changes[edit]

Prior to making any changes in the lead of this article, please be sure to achieve consensus on the talk page first. Temperature is a very important, yet incredibly subtle, topic. As such, this is a very difficult article to get right. The article has a long (and contentious) history regarding consensus. Please respect the years of work on this page by many editors by seeking and achieving consensus before making any changes.

DePiep, my justification of "long time stable" for undoing your well-intentioned edits was to reflect the need for consensus on this page. It took a long time (and lots of discussion) to achieve consensus on the sentence you removed. As a standalone statement at the start of the article, it is clearly the most important statement in the article. It should only be replaced with the utmost caution. JCMPC (talk) 14:20, 3 August 2017 (UTC)

In that case, your es better be like "Old versio n has broad consensus" ;-) which would have triggered me into the right direction. That said, I do:n't think the older first sentence was good enough: "Temperature is an objective comparative measurement of hot or cold" [1]. Notes:
  • hot is not even an article (it's a DAB), and the DAB too says: we have no article hot (temperature) for high temperature (I'm not missing it; we also don't have fast (speed) for high speed.).
  • The "objective comparative measurement" looks good at first, but doesn't cover it. It's not comparative (compared to what? As a base! SI quantity, it is measured independently! by definition). Objective it is, that's the 'physical'. And a 'measurement' is touching it: temperature is the description of a measurement (or, of a definition).
  • As with all physical quantitys, best is to start with the (SI base) definition:
Temperature = number × unit. (we use the word temperature usually, esp in sentences, but in science one can use formally & internationally the less-known quantity symbol T). We know the number & unit notion, but helpful is to keep recognising the algebraic formula. Either in language or in symbols. Temperature is the quantity being described (measured, defined, or discussed). number & unit is the value of that quantity we point to.
Once this algebraic definition of the quantity is grasped, we can go to verbose description (which I tried in the opening sentence). With all this, it would be better to write like:
"Temperature (symbol T) is a physical quantity describing the thermodynamic energy[?], expressed as a value on a temperature scale (°C, °F, or K)." -DePiep (talk) 14:48, 3 August 2017 (UTC)
Regardless of whether or not YOU didn't think the old version was good enough, you should still obtain consensus before making such a change. All of your points have already been covered in exhausting detail, and can be found in the archives of this talk page. They will help you to understand why the opening sentence was what it was. Temperature is not a topic to be taken lightly. It is a very subtle concept to grasp if not done properly, and is routinely misunderstood. It is a very difficult task to explain what temperature is from both an intuitive standpoint as well as from a more rigorous, scientific standpoint. The opening statement was intended to better reach the general public. The rest of the article goes into the more rigorous detail. JCMPC (talk) 17:19, 3 August 2017 (UTC)
you should still obtain consensus — or I can apply BRD. Your claim 'long time stable so BOLD even BRD edits are forbidden' is incorrect. And in short: the opening sentence is too childish and off to even hint it was well fleshed out. But I'll google the archives shortly.
Meanwhile, I hereby propose to keep the change I made & motivated here. -DePiep (talk) 17:30, 3 August 2017 (UTC)
  • Restart I propose this: you JCMPC write the opening sentence as you think best. That could include some my improvements (not just reverting). After that, we'll be back here to discuss improvements. Gives time & arguing space. Deal? -DePiep (talk) 21:15, 3 August 2017 (UTC)
Please don't assume that I believe bold or BRD edits to be forbidden. That is not what I implied. My reversion of your edits is entirely in line with the notion of BRD, which is why I chose to address this issue on the Talk page rather than reverting a second time. That being said, why be bold and disrupt a long-standing consensus (even if a temporary one) when a discussion thread can be opened instead? Making a BRD edit should not come at the expense of respect for the work and established consensus of other editors.
If I were to rewrite the opening sentence as I currently think best, I would just revert once again. Ideally, if I could first establish consensus among active editors, I would prefer to go back to an opening sentence from almost a decade ago, "Temperature is a physical property of matter that quantitatively expresses the common notions of hot and cold." That being said, what was there last week wasn't so much different from this and so poorly worded that I would justify the time trying to change it, especially when a consensus had been reached among many other editors.
Regarding your proposed suggestion (14:48, 3 August 2017 (UTC)) for another new opening sentence, the idea that "Temperature is a physical quantity describing the thermodynamic energy..." is highly problematic and easily subject to error and/or misinterpretation, which is something that has been discussed at length on this talk page. Additionally, the idea that "temperature is... expressed as a value on a temperature scale" is essentially a tautology, which does not add value to the article. Furthermore, the topics of symbols and units are covered in detail throughout the article, and there is no need to include them in the opening sentence, which should be of use to a broad audience. I do not suggest sacrificing rigor, because there is plenty of that in the article, but the people who read this article the most will likely be non-experts, and it is imperative that their needs are kept in mind. The goal of tying the idea of temperature to the concepts of hot and cold, regardless of whether or not there are individual articles for "hot" or "cold," would be highly beneficial for the non-expert, which is something that has been already been discussed on the talk pages. JCMPC (talk) 04:59, 4 August 2017 (UTC)
As I said: please first create the opening sentence as you think it should be. That could include changes I edit/proposed. After that we can dive into the content issues here.
About the process: your reversal had the es: "Reverted well-intentioned edits back to an earlier version that has been stable for a long time." [2]. I repeat that "stable for a long time" is not a reason at all, so I reverted that one for good reason (I'm not supposed to understand that something else was implied). Only then did you start this talk (correct & laudable), in which real arguments came up (like the consensus you refer to). And some less usefull ("respect the years of work" [... so don't be bold] is not the way WP works). This sequence does not make me in error. -DePiep (talk) 10:14, 4 August 2017 (UTC)
"Stable for a long time" is a reason. It implies that a consensus exists. If this was not apparent, then I apologize for not using clearer phrasing, but edits summaries are limited in length and I chose my wording to be brief. To be frank, I find your sentiment that Wikipedia does not work on the basis of respect for other editors to be deplorable. It goes directly against one of the Five Pillars of Wikipedia, "Editors should treat each other with respect and civility." (WP:Five Pillars) At the risk of being less civil and diplomatic than I prefer, I shall have to be more bold. The new opening sentence isn't even complete. It is grammatically incorrect, making it impossible to determine its intended meaning. Editing the sentence to improve it would have been in vain, so I simply reverted. Incorporating the new feedback from the talk page into a revision would also be in vain because the rationale is incomplete and incoherent. It lacks structure and clarity. Beyond wanting to include something about units, symbols, and measurement theory (which is far too much detail for the opening sentence, as I have mentioned above) it makes no sense. I will repeat what I suggested in my previous comment: that we should either revert back to what it was or, if consensus among editors can be achieved, revert back to an opening sentence that was used years ago. There is nothing wrong with a bold edit. Many bold edits by many editors have made this article far better than it used to be, but bold is not the same as cavalier. JCMPC (talk) 12:36, 4 August 2017 (UTC)
Why didn't you revert or partially revert, as I proposed (twice)? -DePiep (talk) 16:48, 4 August 2017 (UTC)
You never proposed reverting.
"I propose this: you JCMPC write the opening sentence as you think best. That could include some my improvements (not just reverting)." (21:15, 3 August 2017 (UTC))
"As I said: please first create the opening sentence as you think it should be. That could include changes I edit/proposed. After that we can dive into the content issues here." (As I said: please first create the opening sentence as you think it should be. That could include changes I edit/proposed. After that we can dive into the content issues here.)
You requested that I write the opening as I see fit and specifically mentioned not reverting. I have now done this multiple times. Here is what I propose, yet again: "Temperature is a physical property of matter that quantitatively expresses the common notions of hot and cold." JCMPC (talk) 22:01, 4 August 2017 (UTC)
Yes I did, twice:
(1) [3]: I propose this: you JCMPC write the opening sentence as you think best.
(2) [4] please first create the opening sentence as you think it should be
Of course, even if you did not get my invitations: you could have (partially) revert. -DePiep (talk) 22:23, 4 August 2017 (UTC)

Editors JCMPC and DePiep have been discussing the first sentence of the lead. I will also comment.

There are two kinds of temperature scale, empirical and absolute thermodynamic. Empirical scales are of historical and practical importance. The absolute thermodynamic scale is well founded in thermodynamic theory, being based on a ratio of quantities of heat transferred. The quantities of heat are in turn based on quantities of work, which in turn is defined by mechanics, not thermodynamics. In practice, the absolute scale is most often expressed by virtually empirical procedures, such as platinum resistance.

The numerical value of an absolute thermodynamic temperature measurement is set by an arbitrarily chosen reference number for an arbitrarily chosen reference state of an arbitrarily chosen thermodynamic system, 273.16 K for the triple point of water. There is no theoretical reason why the Kelvin scale could not have settled on making the triple point of carbon dioxide the reference state of the reference system, and it could not have been given the value 1000 K. This is the reason why the word 'comparative' was included in the lead. Perhaps the word 'comparative' is not the best possible one for the purpose, but the purpose is worth its place in the sentence, I think.

The word 'objective' intends to make a contrast between the valid but imprecise and possibly subjective wording in terms of 'hot' and 'cold'. These terms have both subjective (how does it feel to me when I touch it?) and objective (which way does heat flow?) connotations; in ordinary language, the prime language of Wikipedia, the subjective connotation is part of the meaning. So the word 'objective' has a useful purpose, I think.

The grammar of the present first sentence is not comfortable. It is hardly obvious what is gained by saying that temperature is a 'physical quantity' in the first sentence. A naive reader may have little idea of the connotations of the phrase 'physical quantity'.Chjoaygame (talk) 09:13, 12 August 2017 (UTC)

Thanks, a nice reading.
In short, I think we should aim for an opening sentence that has both definitions: the scientific one and the subjective one. The two descriptions should be unconnected (don't try to describe one in terms of the other).
As for the science, one way or another we must state it is a physical quantity, i.e. a property of a body etc. Too often people jump into the measurement of it, but a temperature exists even when we do not measure it. Seconds pitfall is starting with the scale (as Chjoaygame does ;-) ) or unit. These are why describing the quantity becomes such a difficult task: the wrong end (many physical quantity article & uses suffer from this). So the setup should be like: "Temperature is a physical quantity (T) usually expressed in degrees on scale K, C, or F. It is also a subjective sense of being hot or cold." (it's about the elements to be in there, for now; not my English).
I disagree with the dumbing down argument, saying "ordinary language" cannot describe it (and no, that is not the prime language). -DePiep (talk) 10:04, 12 August 2017 (UTC)
WHil this talk is going on, Kbrose edited the lede into [5] without engaging here. First, this is bad practice, second, current text is not following from this talk. I ask Kbrose to revert and to join the talk. -DePiep (talk) 16:25, 12 August 2017 (UTC)

Several questions now arise, but I will consider just one for the moment.

Editor DePiep writes:

I disagree with the dumbing down argument, saying "ordinary language" cannot describe it (and no, that is not the prime language).

This sentence of Editor DePiep is hard to interpret. Who is doing the "saying"? Perhaps the sentence intends that Editor DePiep says that ordinary language cannot describe temperature. Then it seems that Editor DePiep asserts that ordinary language is not the primary language of Wikipedia.

Where is the "dumbing down argument"? It seems that Editor DePiep intends that use of ordinary language is dumbing down.Chjoaygame (talk) 08:11, 16 August 2017 (UTC)

Why do you address me in 3rd person? Why the 'Editor' style? -DePiep (talk) 18:25, 16 August 2017 (UTC)
This has turned out to be a long thread with several editors involved, so I assume that Chjoaygame is choosing a grammatical voice to clarify which parts of the thread are being referred to. That being said, I do agree with the concerns raised by Chjoaygame. Wikipedia is not a technical publication, and this should be reflected in the language of the articles. This does not preclude an article from using technical language, but it should certainly not be the focus of the lead (let alone the first sentence). The lead section (in particular the opening sentence, see WP:Redundancy) should be written for the non-specialist reader. This presumes that the average reader will have little-to-know technical knowledge of the subject. If technical language should not be used, then the only thing remaining is ordinary language. Furthermore, using ordinary language does not automatically make a statement incorrect or "dumbed down". Both ordinary and technical languages should be equally able to describe a topic. Technical language is advantageous because it is far more precise for a given word count, but it has the disadvantage that the non-specialist will lack the required vocabulary to interpret a given statement. Ordinary language is advantageous because it is accessible to the non-specialist, but it has the disadvantage that a larger word count is necessary for achieving the same precision as technical language. JCMPC (talk) 14:17, 21 August 2017 (UTC)

the first sentence of the new lead[edit]

The new lead starts:

Temperature is a physical quantity that expresses the subjective perceptions of hot and cold.

The article is primarily about physics. Though the terms 'hot' and 'cold' have subjective connotations, they also have solid foundations in physics, as may be checked in many reliable source physics textbooks. When two bodies are connected solely by a path that is strictly selective for heat transfer (a diathermanous path), energy will pass from the hotter to the colder. For this, it is not necessary that either body possess a temperature. Temperature does not primarily express the subjective perceptions of hot and cold. It therefore is regrettable that the rather tricky topic of subjective perceptions of hot and cold is given top priority in the first sentence of the lead.

The former version of the lead mentioned the comparative nature of temperature. This is rooted in the comparison between hot and cold. There is no uniquely suitable reference temperature, and so the numbers assigned to temperature measurements rest on comparison with an arbitrary reference temperature. In contrast, for example, the speed of light is in a sense a unique reference for speed. Besides the nonuniqueness of reference for temperature, there are empirical as well as thermodynamically absolute temperature measurements. This is the reason why earlier versions used the indefinite artic'e 'a' as the first word.

Though its appearance in the first sentence of the lead may be questioned, that temperature is a physical quantity expresses its contrast with psychophysical quantities. Likewise, that temperature is an objective measure contrasts it with subjective perceptions.

Perhaps the first sentence might read:

A temperature is a comparative physical measurement of hot and cold.

Perhaps.Chjoaygame (talk) 19:58, 25 August 2017 (UTC)

This discussion is useless. I won't go into this while Kbrose can revert into a nonsense version without engaging in this talk [6]. Why does not anyone revert Kbrose? (to be clear: hot is a DAB page. What more do you want to know about 1st sentence quality?). -DePiep (talk) 22:45, 25 August 2017 (UTC)
Sorry for the lengthy post. I wanted to address a number of questions I have all at once.
Chjoaygame, can you please elaborate on what you mean by empirical vs. thermodynamically absolute temperature measurements and the non-uniqueness of temperature? Don't the third and zeroth laws of thermodynamics, in combination with the expression of temperature as an entropy/energy derivative, uniquely fix the reference for absolute temperature just as the speed of light fixes the reference for speed? If this is the case, then wouldn't empirical temperature scales then be similar to measuring speed empirically with an arbitrary definition for a standard length and fixed unit of time? Empirical scales predated absolute, thermodynamic scales, but so did empirical measurements of speed.
Also, could you please elaborate on your comment, "For [energy transfer], it is not necessary that either body possess a temperature." If you are dealing solely with heat transfer, then mustn't the two bodies both possess a temperature, each of which is different?
Regarding psycho-physical quantities, isn't that where most physical measurements historically come from, the quantification of some perceived, subjective quality of an object? (Note that I don't mean to include things like charge or spin, which were properties that came long after the quantification other qualities and thus have an origin that is not psycho-physical.)
I would like to point out that, for me, I don't believe that the problem is about defining temperature. It is about defining temperature for the general public in a way that is the best compromise between accessibility and accuracy. For instance, the IUPAC Gold Book defines (thermodynamic) temperature as "[A] Base quantity in the system of quantities upon which SI is based," which is what I now believe DePiep may have been going for (please correct me if I am wrong). While this is certainly acceptable in a technical reference such as the Gold Book, I don't see how it is accessible to the average reader. I think the opening sentence (or two or three) should err on the side of accessibility since there is much space to achieve accuracy in the rest of the page.
What is wrong with the terms "physical property" and "physical quantity"? Don't all physical properties/quantities have to be measurable by definition, and don't all measurements have to be comparative by definition? If so, doesn't the phrase, "temperature is a physical property..." imply that temperature is measured comparatively?
How would people feel about using the phrase "...related to hot and cold" in lieu of "..of hot and cold"? Based on my above comments, I would then suggest "Temperature is a physical property related to the common notions of hot and cold." Would this fix some of the issue? For now, I will at least remove the link to the DAB page as per DePiep's comment. JCMPC (talk) 01:13, 29 August 2017 (UTC)
"can you please elaborate on what you mean by empirical vs. thermodynamically absolute temperature measurements and the non-uniqueness of temperature? Don't the third and zeroth laws of thermodynamics, in combination with the expression of temperature as an entropy/energy derivative, uniquely fix the reference for absolute temperature just as the speed of light fixes the reference for speed? If this is the case, then wouldn't empirical temperature scales then be similar to measuring speed empirically with an arbitrary definition for a standard length and fixed unit of time? Empirical scales predated absolute, thermodynamic scales, but so did empirical measurements of speed."
All of these comments are fair. The thermodynamic definition of temperature is not as an entropy/energy derivative, using the third law; it is in terms of heat engines and the triple point of water. Though some mathematical developments assume entropy as given, its measurement usually relies on temperature. One can do a lot of thermodynamics with empirical temperatures and empirical entropies, as some reliable sources emphasize. The indefinite article 'a' is a short word, and it leaves open the possibilities. It may cause some readers to think about the topic. Why not use it?
"could you please elaborate on your comment, "For [energy transfer], it is not necessary that either body possess a temperature." If you are dealing solely with heat transfer, then mustn't the two bodies both possess a temperature, each of which is different?"
This comment raises an important point of principle. The new first sentence of the article on heat dumbs it out. It is important for the logic of thermodynamics that the definition of heat not refer to nor implicitly rely on any notion of temperature. The thermodynamic definition of temperature then relies explicitly on that of heat. Circular thinking is thereby avoided. Strictly speaking, thermodynamic temperature is defined for a body in its own internal state of thermodynamic equilibrium. Heat transfer is admitted to occur between bodies that are not in their own internal states of thermodynamic equilibrium, and do not possess temperatures. Relative hotness is defined by the direction (sense) of heat transfer, logically prior to the notion of temperature.
"Regarding psycho-physical quantities, isn't that where most physical measurements historically come from, the quantification of some perceived, subjective quality of an object? (Note that I don't mean to include things like charge or spin, which were properties that came long after the quantification other qualities and thus have an origin that is not psycho-physical.)"
Since it is mentioned in these comments that there is a subjective quality of a body that reflects hotness and coldness, it is reasonable in these comments to distinguish psychophysical measurements from physical measurements. It is easy to do psychophysucal experiments that display big gaps between them for hotness and coldness. Such a distinction might reasonably be called metaphysical. But I don't think it necessary in the first sentence of the lead to burden the reader with such metaphysical considerations. I think one use of the word physical should be enough in one sentence to indicate that the article is primarily about physics.
"I would like to point out that, for me, I don't believe that the problem is about defining temperature. It is about defining temperature for the general public in a way that is the best compromise between accessibility and accuracy. For instance, the IUPAC Gold Book defines (thermodynamic) temperature as "[A] Base quantity in the system of quantities upon which SI is based," which is what I now believe DePiep may have been going for (please correct me if I am wrong). While this is certainly acceptable in a technical reference such as the Gold Book, I don't see how it is accessible to the average reader. I think the opening sentence (or two or three) should err on the side of accessibility since there is much space to achieve accuracy in the rest of the page."
I am not persuaded that there is a need to err on the side of accessibility. It is not evident to me that "related to the common notions of hot and cold" offers more accessibility than "of hot and cold". It think it is reasonable to tacitly assume that the latter phrase is related to common notions. What other notions of hot and cold would occur to the average reader, unless he is inclined to metaphysical reading?
Editor DePiep distinguishes between 'comparative measurement' and 'physical property'. He prefers the latter in the first sentence of the lead. I get the feeling that he doesn't like to emphasize the comparative aspect of temperature measurement and the measurement aspect of physical properties. I think "physical measurement" gives a better slant than "physical property".
"What is wrong with the terms "physical property" and "physical quantity"? Don't all physical properties/quantities have to be measurable by definition, and don't all measurements have to be comparative by definition? If so, doesn't the phrase, "temperature is a physical property..." imply that temperature is measured comparatively?"
Not all physical properties are directly measureable by definition. Some properties of light beams can be found only by very elaborate calculation, based on direct measurement. The phrase "comparative measurement" was insisted upon by an enthusiastic editor. I was taught that measurement can be either by effect or by comparison. I agree with that teaching. I am not sure whether the insistent editor had that distinction in mind, but I did not try too hard to oppose him. Temperatures are in a sense less obviously raw primary physical properties than for example lengths and masses. It might be proposed that the thermodynamic definition of temperature is by effect, to do with heat engines, as well as with the triple point of water, but in practice that definition is not common, and comparison is the usual way, for example platinum resistance. If it is really objectionable to put it in the first sentence of the lead, I would not insist on the word "comparative", but I think it has some merit. To a certain kind of trained mind, "the phrase, "temperature is a physical property..." impl[ies] that temperature is measured comparatively?" But the implication may not occur to the mind of the average reader. The term 'physical property' is rather abstract, while 'comparative measurement' has a more concrete slant, perhaps being more accessible to the average reader.
"How would people feel about using the phrase "...related to hot and cold" in lieu of "..of hot and cold"? Based on my above comments, I would then suggest "Temperature is a physical property related to the common notions of hot and cold." Would this fix some of the issue?"
I would prefer 'A temperature is a comparative physical measurement of hot and cold.' Next preference 'A temperature is a physical measurement of hot and cold.'Chjoaygame (talk) 07:11, 29 August 2017 (UTC)


Thanks Chjoaygame for clarifying your points. I only have few (hopefully small) comments in response.
When commenting on physical properties/quantities being measurable, I didn't mean to imply only direct measurements. Most physical properties, like those you mentioned, are only indirectly measurable. Many empirical measurements of temperature are indirect as they consist of measuring lengths or volumes.
I suppose I don't have the same objection to cyclical definitions as long as they are presumed to make up some axiomatic system, i.e. postulates. The cyclical definitions create relationships between abstract entities that are then used to build up some the system. But, I agree that such definitions should be avoided in the context of an encyclopedic entry. That approach would be best suited to a full treatment of a subject.
My suggestion to use "related to hot and cold" as opposed to "of hot and cold" was not to make it more accessible, but to address some of your concerns by slightly softening the connection between temperature and the notions of hot and cold as psychophysical sensations. Not sure if that makes sense.
I am certainly not opposed to explicit mention of things like "measurement" or "comparative" as long as things don't get overly verbose. I think both of your suggested opening sentences are fine. Of the two, I prefer the first. Also, I do like including the article, "a", at the beginning. To me, it helps to create a subtle distinction between this article and the article on thermodynamic temperature. JCMPC (talk) 16:09, 29 August 2017 (UTC)
Thank you for these comments. Concern to avoid circular definitions has been a staple of the talk pages on heat and temperature. My impression is that undefined primitive terms may use circular thinking, to express relations amongst presupposed ideas. Such circularity is informal and perhaps even necessary. It intends merely to suggest basic intuitions that are hardly expressed precisely in words. It is not logical development. Starting from that informal basis, formal definitions and axiomatic development should avoid circularity. As for thoughts of psychophysics, my feeling is that they don't need expression in the first sentence of the lead. Hot and cold have directly physical meaning, found in reliable sources of thermodynamics, as well as psychophysical meaning.Chjoaygame (talk) 02:13, 30 August 2017 (UTC)

──────────────────────────────────────────────────────────────────────────────────────────────────── I see that Chjoaygame is pestering the talk pages of physics articles again. Be aware that this editor may be your worst Wikipedia nightmare. Don't feed Chjoaygame. Chjoaygame is issued a topic ban in quantum physics. It is mostly an accident that Chjoaygame is not so far issued a topic ban in thermodynamics as well. YohanN7 (talk) 13:24, 5 September 2017 (UTC)