Wikipedia:Articles for deletion/Thermal energy


 * The following discussion is an archived debate of the proposed deletion of the article below. Please do not modify it. Subsequent comments should be made on the appropriate discussion page (such as the article's talk page or in a deletion review).  No further edits should be made to this page.

The result was no consensus. There's substantial disagreement on whether this should be turned into a WP:DAB page or kept as is. But, that discussion can continue on the article talk page. The only thing that would require admin (and thus, WP:AfD) involvement would be an outright deletion, and that's clearly not being argued by anybody. -- RoySmith (talk) 12:53, 23 April 2018 (UTC)

Thermal_energy
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There is no well-defined or accepted concept of "thermal energy" in physics or thermodynamics. The article lacks reliable sources, and been tagged as needing them since at least 2014.  Waleswatcher  ( talk ) 02:00, 28 March 2018 (UTC)


 * Speedy keep. MIT, Leipzig University and the Norwegian University of Science and Technology, among others, think there is something to it. (Also that disreputable rag the Encyclopaedia Britannica.) Clarityfiend (talk) 02:21, 28 March 2018 (UTC)


 * None of those three sources supports Thermal energy as a rigorous concept in thermodynamics. The first is a press release using the term in a general sense.  The second is about Internal energy.  The third uses the term in a general sense.  For Britannica, see below.  A reliable source would be (say) a textbook on thermal or statistical physics.   Waleswatcher  ( talk ) 03:42, 28 March 2018 (UTC)


 * KEEP. The notion that this is not a defined term is kind of strange, and the idea to delete the article is absurd. Many physics texts define it quite distinctly, and Encyclopedia Britannica thinks so too. Calculating the total thermal energy of a system is a frequent exercise in problems. The concept of thermal energy comes directly from the equipartition theorem and is usually defined defined in terms of kT.  It is essentially provided by   (dS/dU)V,N = T–1 (PS: d = delta)  Kbrose (talk) 03:16, 28 March 2018 (UTC)


 * If "many physics texts define it", please list a few. Encyclopedias are not reliable sources per wiki policy as I understand it - they are tertiary, not secondary.  In fact there are no reliable sources for this concept that I know of, nor have any been added to the article after four years, because the concept of "thermal energy" (as opposed to internal energy U that you refer to, or heat or temperature or work) turns out not to make sense.  I say this as a professional physicist with expertise in this area.  I could explain the physics here, but my understanding is that it would not really be appropriate.  Material without reliable sources is supposed to be deleted, is it not?   Waleswatcher  ( talk ) 03:32, 28 March 2018 (UTC)

By the way, I have no problem if "thermal energy" is simply synonymous with internal energy, in which case we can just redirect to there rather than delete. That seems to be Kbrose's view, and is the subject of this source Leipzig University as cited by Clarityfiend.  Waleswatcher  ( talk ) 03:47, 28 March 2018 (UTC)


 * Disambiguate As I understand it; change in thermal energy is used as a synonym for change in internal energy, where thermal energy describes the internal kinetic energy of particles in a system which, when averaged, becomes temperature. It's a useful concept for students trying to relate stat mech to classial thermo.

However, this is not a rigorous concept used in fundamental equations (I'm curious why not - is it redundant with an understanding of temperature?). I think an ideal article would explain this, then disambiguate. SpaceInnovader (talk) 00:24, 29 March 2018 (UTC)


 * 'Delete/Disambiguate: Use it as a disambiguation article. It can point to heat, internal energy, Helmholtz free energy, etc. --MaoGo (talk) 08:01, 28 March 2018 (UTC)
 * Keep. Even when this notion covers no well-defined or accepted concept in physics, it is in my perception a broadly (ab)used term (e.g. in connection with sustainability, stability, resilience, ...). Retreating to sound terms of thermodynamics, or a pure DAB possibly would not properly handle the expectations of interested readers. I am roughly aware of the tedious task to watch over a page like this. Purgy (talk) 12:34, 28 March 2018 (UTC)
 * But that is not what the article is (currently) about - it says nothing about "sustainability, stability, resilience". Instead, it (falsely and without reliable sources) states it's about a concept in thermodynamics and gives a specific and (naively) reasonable sounding definition.   Waleswatcher  ( talk ) 12:41, 28 March 2018 (UTC)


 * Comment Kardar's textbook uses "thermal energy" as a synonym for the Boltzmann constant times the absolute temperature (p. 243). So do Huang and Reichl and Kittel and Myers and Reif. Landau and Lifshitz do the same, but work in units where $$k_B = 1$$ (volume 5, Eq. 80.16). Ashcroft and Mermin also use the term (e.g., p. 20 of the 1976 edition). It is definitely, definitely a thing that physicists say, and that is enough reason to have a page about it. However, the current article is not very good, and the easiest fix might be to turn it into a redirect or a disambiguation page. XOR&#39;easter (talk) 15:57, 28 March 2018 (UTC)
 * Note: This discussion has been included in the list of Science-related deletion discussions. XOR&#39;easter (talk) 16:04, 28 March 2018 (UTC)
 * Thanks for this, it's very useful to have real references to discuss. It's true that kT is sometimes referred to as "thermal energy" and that makes perfect sense in context (kT is indeed an energy, and it sets the characteristic scale for the energies in thermal systems), but that is not at all what the current article is describing, nor does it correspond to the internal energy that Kbrose defined, nor does it correspond to the concept "defined" in the Britannica article.  So this simply illustrates the problem.  Perhaps another solution besides a DAB is to describe the various ways this term can be used...  but would that meet wiki's notability guidelines?   Waleswatcher  ( talk ) 17:48, 28 March 2018 (UTC)
 * FYI, We already have an article kT (energy) which can and should be included on a DAB page if that's what we wind up with. --Steve (talk) 01:53, 29 March 2018 (UTC)
 * That should probably include Geothermal energy too. Clarityfiend (talk) 06:19, 29 March 2018 (UTC)


 * Make it a DAB per Mao suggestion, pointing in particular to heat ("thermal energy" when it's flowing), internal energy ("thermal energy" when it's not flowing), and kT (energy) (cf XOReaster comment). I would concede Kbrose's point that people sometimes discuss "thermal energy of a mode" in the sense of "thermal-equilibrium average energy in a mode", but I think the internal energy link would cover that case well enough. --Steve (talk) 16:32, 28 March 2018 (UTC)


 * Keep. Thermal energy could be defined as temperature times entropy. This is no more or less meaningful than Helmholtz free energy which is the internal energy minus the thermal energy. It is important to note that thermal energy is not a conserved quantity, but that does not mean that it is meaningless. Kinetic energy is not conserved; neither is potential energy. But people still talk about them and we have articles on them. JRSpriggs (talk) 23:46, 28 March 2018 (UTC)
 * You can define whatever you want. Wikipedia, however, is supposed to be based on reliable sources, not original research or ad hoc definitions.    Waleswatcher  ( talk ) 00:10, 29 March 2018 (UTC)
 * This is not a reason to delete the article. If you think that thermal energy is ill-defined, are you going to delete the article for heat as well, which is typically even more confused than thermal energy? For more rigorous, and more recent and modern usage of the term, you might like Hans Fuchs (The Dynamics of Heat). Daniel Schroeder also defines it quite definitively, which I believe used to be a reference to the article, but which probably fell victim to previous bouts of deletions (by you?). Frankly, the article used to be quite reasonably sourced, before people started swamping it with all kinds of crap. Kbrose (talk) 19:54, 31 March 2018 (UTC)
 * Heat is a standard thermodynamic concept that appears in every textbook. As far as I cam see Fuchs never uses the term "thermal energy" without "flux" or "current" attached, in which case he is simply discussing heat without using the standard term.  Again, heat is well-defined, but it is a transfer of energy, not a property of a system.  Waleswatcher  ( talk ) 01:15, 2 April 2018 (UTC)
 * Kbrose, I think Waleswatcher's complaint was specifically that JRSpriggs wrote "thermal energy could be defined as T×S", but didn't say that it actually is defined as T×S by reliable sources. So Waleswatcher read the sentence as implying that JRSpriggs had just creatively made up the T×S definition off the top of their head. JRSpriggs or Kbrose, can you please confirm one way or the other?
 * Kbrose, would you mind telling us the definition of "thermal energy" used by Hans Fuchs and/or Daniel Schroeder? Is it something distinct from internal energy and kT (energy) and other articles we already have? You wrote above that it's defined by "(dS/dU)V,N = T–1", but I don't get it, are you saying that thermal energy is the reciprocal of temperature? I find that weird, the units are wrong, and also intuitively one would expect higher internal energy at higher temperature. Sorry if you already explained this somewhere. Thanks in advance, --Steve (talk) 01:59, 1 April 2018 (UTC)
 * By the way, the actual answer to this is that Schroeder mentions thermal energy just once, at the very beginning of his book (p.15) where he is building intuition. He defines it as N*f*(1/2)k*T, where N is the number of molecules and f is the number of degrees of freedom per molecule.  Of course this is a fine definition as far as it goes, but it obviously isn't very general (for instance, it refers to molecules).  Schroeder doesn't point this out, but for real molecular gases f is a function of T even in the gas phase, and that formula cannot be applied at all at a phase transition or to other phases.  Schroeder says he will return to this formula later when he proves the equipartition theorem, but when he does so he only ever refers to standard thermodynamic variables (like the internal energy U).  As far as I can see (and according to the index) he never mentions thermal energy anywhere other than around p 15.   Waleswatcher  ( talk ) 01:46, 2 April 2018 (UTC)
 * You can write (dS/dU)V,N—1 = T, if the inverse is confusing. But you cannot invert the partial differential. It tells you directly that you measure temperature to evaluate changes in thermal energy. But T is intensive while T.E. is extensive. Isn't that a most intuitive definition? It is exactly what it has meant since the days of Joule. That also implies that it is perfectly to ok to define thermal energy as the product of temperature and a change in entropy, as stated above. Thermodynamics only ever deals with a small part of internal energy, and it only ever describes CHANGES in internal energy, even when the system undergoes a nuclear reaction in the process. So, internal energy is often defined in a very restrictive manner, depending on the area of study. Only for the ideal gas is the internal energy identical to its thermal energy. Thermal energy expressions occur in a vast number of physical formalisms, the term ex/kT is ever present. So why would it be so undefined ? I would say it is the very definition in most text books, not just a few. But often it is not emphasized, because it is so fundamental, perhaps, not terribly interesting. There is way more confusion about the term heat in text books than thermal energy, because heat is actually differently defined in physics than in engineering, and the public certainly has a heated opinion about many other topics.
 * So, given the preponderance of usage of thermal energy as a valid physics concept, I move to end this discussion and fix the article instead. Kbrose (talk) 17:22, 1 April 2018 (UTC)

For years the article defined thermal energy as "the internal energy present in a system due to its temperature" or as the average kinetic energy per particle. That definition was never supported by any reliable sources, despite a request dating back to at least 2014. There is a reason no sources were ever supplied - you cannot define such a quantity in any real system (for instance, because of the latent heat of phase transitions). Even in idealized systems that definition is either not applicable or simply equal to the internal energy. Regarding the discussion here, Kbrose seems to be engaging in original research, which has no place on wikipedia (or perhaps s/he is suggesting thermal energy should be identified as heat, I can't really tell). The other commentators in favor of keeping the article have variously suggested kT, ST, and the internal energy U as definitions of thermal energy - which is fine, I have no objection if the page remains and just says that the term can refer to any of those (with sources, of course).  Waleswatcher  ( talk ) 01:15, 2 April 2018 (UTC)  Relisted to generate a more thorough discussion and clearer consensus.

Please add new comments below this notice. Thanks,  Sandstein   11:14, 5 April 2018 (UTC)


 * Disambiguate: Although I've seen this term used in textbooks, there aren't significant papers or other sources that use thermal energy, and it covered by heat and temperature. Elliot321 (talk &#124; contribs) 17:30, 5 April 2018 (UTC)

 Relisted to generate a more thorough discussion and clearer consensus.
 * Keep: Widely used concept so it is desirable that Wikipedia has an article. Wikipedia has an article on the luminiferous aether even though it has been determined that it doesn’t exist. Similarly, an article on fictitious forces even though they are fictitious. Wikipedia has articles on these concepts because they qualify as adequately notable. Dolphin  ( t ) 07:59, 9 April 2018 (UTC)

Please add new comments below this notice. Thanks,  Sandstein   11:17, 13 April 2018 (UTC)
 * Speedy Keep meets Notability standards Felicia (talk) 01:13, 16 April 2018 (UTC)
 * Just to be clear, I don't think anyone is arguing that "thermal energy" is non-notable per se; the debate concerns whether "thermal energy" refers to a distinct concept, different from the concepts discussed in other articles. (see WP:NAD / WP:CFORK - if a single concept is referred to with multiple different words or phrases, we generally only have one article for it.) :-D  --Steve (talk) 02:47, 16 April 2018 (UTC)


 * Speedy Keep This concept ("heat energy" as some physics texts call it) draws an important distinction from other forms of energy such as macroscopic kinetic energy, macroscopic potential energy, electric potential energy, radiant energy, chemical energy, mass-energy equivalence E = mc², etc. It is part of the internal energy U of a substance, namely the part that does not involve chemical reactions or conversion of mass to energy but only the transfer of heat between substances at different temperatures; equivalently, the part governed by the equipartition theorem. Vaughan Pratt (talk) 20:22, 16 April 2018 (UTC)
 * You say it is "only the transfer of heat between substances at different temperatures". If so, it is not distinct from heat, and it is only defined as a transfer of energy (which is not at all how the article defined it).  You also say something rather different, that it is part of the internal energy.  That's closer to what the article (used to) assert, but the difficulty is that there is simply no way to define what part that is.  That is why thermal energy (as distinct from heat, or internal energy) just isn't a thing (in general, in thermodynamics).   Waleswatcher  ( talk ) 21:44, 16 April 2018 (UTC)


 * The above discussion is preserved as an archive of the debate. Please do not modify it. Subsequent comments should be made on the appropriate discussion page (such as the article's talk page or in a deletion review). No further edits should be made to this page.