Talk:Kelvin

Plural usage

As a mechanical engineer with a B.S. and M.S. from MIT with a specialization in Thermodynamics, I must emphatically assert that the usage of the Kelvin scale when spoken or written is always singular (e.g. "77 kelvin"). This is confirmed by Wiktionary "...[kelvin] (usually as postpositioned adjective) A unit for a specific temperature on the Kelvin scale.

   Ice melts above 273.15 kelvin.
   Water boils above 373.15 kelvin."  — Preceding unsigned comment added by 2601:6:3280:483:4593:DD0:2C31:EA0D (talk) 19:27, 2 May 2015 (UTC) 

I have a proposal and am interested in what others think. I note that the BIMP and the NIST seem to have both ducked the issue of plural usage of kelvin when reporting temperatures. This Kelvin article currently ducks the issue too and the conspicuous absence sticks out like sore thumb. This article tells that kelvin in its plural form is kelvins, but it currently entirely avoids the topic of plural usage. From what I can see, plural usage is currently a free-for-all. It seems that intervals, e.g., “the difference between our two readings was 50 kelvins” is most commonly expressed using the plural form. This makes sense to me and and seems consistent with the rules of English usage. However, it seems that both forms are used in the expression of specific temperature values. One can as easily find "a temperature of 300 kelvin" as one can find "a temperature of 300 kelvins." I just now googled on sun "5800 kelvin" and got 963 hits. I got 458 hits on sun "5800 kelvins". I'm sure Wikipedia contributors have opinions as to what is the “proper” way to express temperatures but personal opinions are a dime a dozen. I wonder if any prominent scientific journals have specific editorial guidelines on this issue. So…

I've got a suggestion and a question. Perhaps this article should address the issue of plural usage by noting that both forms are currently used and there is no officially endorsed form. As regards my question, does anyone know of a suggested editorial practice by a reputable scientific publishing organization regarding the expression of kelvin temperatures? Greg L (my talk) 05:22, 4 April 2007 (UTC)

We don't talk about "centigrades" or "Fahrenheits" when giving temperatures, so why should we say "Kelvins?" Seems to me that the unit in all of these cases is the degree; the terms centigrade, Fahrenheit, Kelvin, etc. simply give the point of reference from which the measurement of degrees starts. True, since the size of a centigrade degree is different from that of a Fahrenheit degree, there is some justification for recognizing that uniqueness in an abbreviated form by saying "Kelvins," but it comes down to a personal preference, I suppose, for the "degrees Kelvin" form. As to capital letters, I think it's good to remember that Kelvin, Ohm, Volta, etc., were people--yes, it's nice to honor them, but it's also helpful to recall that they were human, and we are dealing with results of human endeavors--i.e., they might have made some wrong assumptions, and we should always be careful of following blindly. Personally, I am dead set against counting instances and going with the majority on ANY question whatsoever. Remember, half the folks out there are by definition below average.  :) As a historian, I have NEVER tried to settle a dispute by counting the number of sources on either side of the question. The question is how good the sources are, not how many idjots took the easy way out and copied a bad source without checking it. Terry J. Carter (talk) 18:25, 4 July 2008 (UTC)

If you look at the documents mentioned in the following footnote on the meter page: Meter#cite_note-7, they write 273.16 kelvins.

The Metric Conversion Act of 1975 gives the Secretary of Commerce of the US the responsibility of interpreting or modifying the SI for use in the US. The Secretary of Commerce delegated this authority to the Director of the National Institute of Standards and Technology (NIST) (Turner, 2008). In 2008, the NIST published the US version (Taylor and Thompson, 2008a) of the English text of the eighth edition of the Bureau International des Poids et Mesures (BIPM) publication Le Système International d’ Unités (SI) (BIPM, 2006). In the NIST publication, the spellings "meter," "liter," and "deka" are used rather than "metre", "litre", and "deca" as in the original BIPM English text (Taylor and Thompson, 2008a, p. iii). The Director of the NIST officially recognised this publication, together with Taylor and Thompson (2008b), as the "legal interpretation" of the SI for the United States (Turner, 2008).

If there is any official guidelines I would expect the NIST and BIPM would be aware of it? I would guess you say 3.4 kelvins, and 0.9 kelvin.
—Apis (talk) 05:38, 30 January 2009 (UTC)

We don't say Celsiuses or Fahrenheits because we say degrees Celsius or degrees Fahrenheit. The plurality of degrees is what leads people to want to use a plural. I don't think it's a problem. As long as the abbreviated form doesn't get corrupt, e.g. as we sometime see in "kms/h" instead of "km/h", for example. Jdpipe (talk) 04:22, 27 July 2009 (UTC)

BIPM quote:

"over a wide temperature range from a few kelvins to above 550 K." 

from "SI-App2-kelvin.pdf"

189.129.53.203 (talk) 13:51, 12 September 2022 (UTC) baden k.

History of Kelvin scale

There seems to be an issue with the history of the Kelvin scale, which I reverted. The 1848 paper does deal with the need for an absolute thermometric scale, so I'm not sure what the point of the edit was. There were also some typoes present, and items removed without explanation. So, let's discuss what is thought to be needed before reinstating this change. Tarl N. (discuss) 03:16, 13 June 2019 (UTC)

Let me be specific about what I don't like:

• Change of "engineer and physicist" to "physicist". He's remembered today primarily as a physicist, but recognition in his own time was for his engineering skills. So I think that description is appropriate.
• Parenthetical statement in lead about why he was awarded the title. We generally prefer to avoid parenthetical statements in the lede.
• Celcius. It's tricky wording to begin with (we used to have the terms degree Celsius and degree Kelvin, now it's the kelvin alone), the mispelling doesn't help. I think we should leave it as is. The point is that one unit of Celsius (called a degree) is equivalent to a difference of one Kelvin, the question is the phraseology.
• In his 1848 paper, he made clear the need for an absolute scale. Maybe we need to reword it to avoid implying that he had it entirely worked out in 1848, but we don't need to complicate it with later 1851 paper which still didn't have all the details worked out. The point to get across is when the work started.

Tarl N. (discuss) 03:23, 13 June 2019 (UTC)

I simply thought I would share what I have learned:

• Kelvin thought of himself as a physicist, and the engineering got added in because the engineer initially running the project (Preece, if memory serves me) screwed up the Atlantic cable project; Kelvin was brought in to fix it, which he did. He was a physicist who for a time did engineering, but he was not an engineer. I don't know where you got that idea, but it is wrong.
• The writing is not perfect; I felt that correct information is more important that great wording (to which I am sensitive).
• Please feel free to revise. At least distinguish between recognizing the need for an absolute scale (I did explain what such a scale means) and actually finding one. — Preceding unsigned comment added by WMSwiki (talk • contribs) 04:48, 13 June 2019 (UTC)

My two cents. The first thing to remember is that the article is about the unit of measurement, not about Kelvin himself, so details about his schooling and preferred rather than professional titles are really not germane here. (Technically, if one trains to be an engineer but doesn't make a living at it, they are not an engineer, but if one works as an engineer, they are one regardless of training. To some it just comes naturally.)

Great wording can be all the difference between something that is coherent and understandable, and something either incomprehensible or something that may mean multiple things depending upon how you look at it. With this particular topic, it's very difficult to avoid those dual meanings and make it fully understandable to the general masses. Great care should be taken to make sure of both.

Mostly, we need sources to verify what you learned. The info must come from somewhere, so it is always advisable to cite those sources for any info you add. I hope that helps. Zaereth (talk) 20:32, 13 June 2019 (UTC)

triple point of water

The redefinition of SI results in the triple point of water now becoming an empirically determined value. I think the current lead is perhaps misleading in that it could be read to indicate that the triple point of water is still exactly 0.01 Celsius, when this is no longer the case. Thus I changed the lead. Please let me know if you feel that this is incorrect. 2601:184:407F:8921:646B:30F2:10C3:559E (talk) 03:10, 7 July 2019 (UTC)

Potential new sections, Implications of 2019 revision and motivation for using an absolute scale

Do you think we should create a section on the mathematical implications of assigning an exact value the the Boltzmann constant?

Do you think we should create a section on the the motivation for creating an absolute temperature scale at all, rather than sticking with scales that have some other starting point? This has the potential to get into puff piece territory, but I could also imagine this being one of the main questions people have when looking this subject up. Ava Eva Thornton (talk) 07:29, 18 February 2022 (UTC)

I don't know much about the first part of your question, as I don't speak math very fluently. Possibly could be of value if you can translate it to English for all us non-mathematicians out here.

The second part of your question is something that interests me very much, as I'm always wanting to know why. It may be a little much or off topic for this article, but I think it would be perfect for the absolute scale article. I know Kelvin was a pioneer in both deep cold and deep vacuum measurements, along with Edison and several others. (They each began using the Torr scale very early in their research, so the concept was not new.) Both are quantities you can assign a known minimum to, and in both you start to get wonky readings at extreme lows without having a fixed zero-reference to compare against. It's not necessarily that an absolute scale is better than a relative one, because it all depends on what you're measuring for. (See discussion at Talk:Absolute scale) We live in a pressurized atmosphere at temperatures above freezing, so for day-to-day measurements a relative scale is better. For example, with things like tire pressure or blood pressure, the absolute pressure is not very critical. It's far more important to know the difference between them and atmospheric pressure, because that is a far better indication of burst pressure. With lighting, aeronautics, or barometry, an absolute scale is far more accurate for the necessary info. When it comes to deep cold or deep vacuum measurements, it starts to become really apparent that you need an absolute scale so you have a fixed reference point that doesn't change.

Also, I think the section on orders of magnitude could be toned down a little. It would probably read better as a list, so it doesn't clutter up the table of contents as much. Zaereth (talk) 04:08, 2 March 2022 (UTC)

1 Kelvin

I don't see why there should be a (rather lengthy) section on 1 Kelvin in this article. More appropriately it should be in a separate article, much like absolute zero.
—DIV (137.111.13.4 (talk) 03:47, 9 May 2022 (UTC))

Bloat

The user Ava Eva Thornton (talk · contribs) added a huge volume of content in this article, not all of it useful. Compare what the article used to look like vs. what it looks like now. While, some the content is mostly tangential, usually quantitative information. I have already deleted a section that was purely WP:OR that added no useful information about the 2019 definition. The "Multiples" section is mostly WP:IINFO, and I recommend either converting it into a table like Metre#SI prefixed forms of metre, or deleting it outright; "1 kelvin" should probably be deleted for the same reason. –LaundryPizza03 (dc̄) 19:55, 13 July 2022 (UTC)

The Multiples section should simply go away. The 1 Kelvin section has interesting information, but isn't specific to the Kelvin scale, so should probably be moved to another article. Tarl N. (discuss) 20:26, 13 July 2022 (UTC)

The 1 Kelvin section probably belongs in the Absolute zero#Very low temperatures section, which it at least partially overlaps. Tarl N. (discuss) 20:33, 13 July 2022 (UTC)

Conversion Table Placement

The Conversion Table is placed in (adjacent to) the "Practical uses" section, but has nothing to do with the section's content. A better placement would be desirable.

189.250.250.12 (talk) 13:16, 12 September 2022 (UTC) baden k.

Make the range of Kelvin immediately clear

In the intro, can it be made immediately obvious that a characteristic of Kelvin is that its lowest possible value is 0, because it is tied to kinetic energy? i.e. Kelvin's values range from 0 on upwards; there is never a negative Kelvin value (if this is true). Such basic things about the nature and usage and consequences of concepts are nice to make immediately clear, for anyone who doesn't really need to know more than that, but does need to know and understand such implications for usage. And then anyone who wants to go further for the sake of knowledge or the nuances of those reasons can delve into the further details.

I'll write what I might suggest for such an addition later, if I remember. GabeGibler (talk) 23:25, 17 February 2023 (UTC)

I agree. The lede is a little backwards in its presentation, which doesn't help really clarify immediately what this thing is. The most important information for building context is actually in the last sentence of the first paragraph, when it should really be the first. That it's an SI unit or who it's named after is really secondary to that. For all intents and purposes, Kelvin is just another name for Celsius (absolute), that is, it's based on the Celsius scale, but starts at absolute zero rather than the freezing point of water. If you want to try to improve it, you are most welcome to give it a shot. Zaereth (talk) 01:08, 18 February 2023 (UTC)

I took a stab. I think the 0 K - 273.15 K - 273.16 K sentence should explain the range pretty well. Although maybe it's hard to understand? Mathnerd314159 (talk) 05:06, 24 April 2023 (UTC)

Lead structure

@NebY I don't think your lead structure is "much-improved". My two-paragraph structure has a simple, logical structure: one paragraph for the current definition and one paragraph for the historical definitions. This makes the key points clear. In contrast, your structure is fragmented - the historical context abruptly ends and then switches to discussing the 2019 redefinition in a new paragraph. Putting the 2019 redefinition using the Boltzmann at the start of a new paragraph is confusing to readers as they wonder why this is a new topic and how it is related to kelvins. In contrast, my second paragraph seamlessly integrates all of the historical definitions without disrupting the flow of the text. Two paragraphs is also more concise than 3 - following your logic, every sentence would be in its own paragraph because these "brief paragraphs" would somehow make it less intimidating. But of course this is flawed as breaking up paragraphs with random breaks makes it less readable and more intimidating.

My structure introduces the precise, current definition of the scale early, following MOS:LEADSENTENCE: "If its subject is definable, then the first sentence should give a concise definition." (Per Wikipedia:Wikipedia_is_not_a_dictionary#Good_definitions it is actually two sentences with two definitions, as the kelvin and Kelvin scale are highly related topics). In contrast, if someone needs to identify the current definition of the Kelvin scale in your structure, they would have to look at the beginning and end of the first paragraph and also search through the end of the third paragraph. This disjointed definition is not suitable for grasping the concept of the kelvin. It is not accessible, not early, and not clear. Mathnerd314159 (talk) 18:36, 2 May 2024 (UTC)

To address the concern about the 2019 definition not appearing immediately, I have just edited the infobox to add a line "2019 definition" that gives out the Boltzmann constant in terms of J/K.

I had done many of the edits to try to simplify the lead. I am afraid if we overload new readers by immediately in the first paragraph getting into very technical Boltzmann constant (which itself requires a large amount of explaining and background knowledge), then we risk loosing them completely.

The historical definition using the melting point of ice is something that won't loose new readers because it is more relatable too. Even though the kelvin is no longer precisely defined by the melting point, that is still a good-enough and concise definition for practical purposes. As the "2019 definition" section now explains:

"For practical purposes, the redefinition was unnoticed; enough digits were used for the Boltzmann constant to ensure that 273.16 K has enough significant digits to contain the uncertainty of water's triple point and water will still freeze at 0 °C to a high degree of precision." Em3rgent0rdr (talk) 20:04, 2 May 2024 (UTC)

References

Upon rereading the intro a few times, I would suggest the name origin "It is named after Belfast-born University of Glasgow scientist William Thomson, 1st Baron Kelvin (1824–1907)" could be moved to the very end of the introduction instead of being in the first paragraph, because its name itself has little to do with what it is. Em3rgent0rdr (talk) 20:11, 2 May 2024 (UTC)

Here's my advice. Shorter is not always better, and being too brief is always a problem with technical and scientific articles. Technicians and scientists invariably write for technicians and scientists, leaving out much of the background information necessary for the general reader to follow smoothly, hence the term "techniquese". There is such a thing as too brief.

Explaining complex things to people who have no background knowledge of it is one of the greatest challenges in writing. It shouldn't focus on the number of paragraphs as much as getting the point across as concisely yet precisely as possible.

The lede should be written at around a 6th grade level, which doesn't mean dumbing it down or oversimplifying, but explaining it in terms that a 6th grader should be expected to understand. It doesn't need to be overly detailed, because it's just a summary of the body, but should give the basic gist of what the body contains in easily understandable terminology.

Things like the history are not as important as what the subject is. That should be answered in the first paragraph. But what if I don't know what absolute zero means? If I have to click on that wikilink you've already lost me down the rabbit hole, so that doesn't work either. Imagine trying to explain it to a 6th grader in a way they'll comprehend precisely what the subject is.

For comparison, a very well-written article is Honey. It's not overly technical in the lede, but saves that for the body, yet gives all the pertinent info needed to get a good understanding of the subject in a very logical order. Not too long and not too short either. I hope that helps. Zaereth (talk) 20:38, 2 May 2024 (UTC)

I've tried taking your advice and tried to explain just enough as to why things were done. Those are significant changes, so I understand if other editors revert it or make more changes. Em3rgent0rdr (talk) 00:50, 3 May 2024 (UTC)

I think it reads much better that way. By that, I mean it's more cohesive and flows a lot better, and those are important factors for both comprehension and in keeping the average reader's interest.

That said, I would eliminate the first sentence of the second paragraph altogether. I had to read it twice to figure out what it was saying, and it seems redundant considering the following sentence says basically the same thing.

For this sentence, "...the 2019 redefinition of the SI base units now defines the kelvin by setting the Boltzmann constant to exactly 1.380649×10−23 joules per kelvin", I would probably clarify that it's defining temperature as a product of energy, so I might change it to read: "...the 2019 redefinition of the SI base units now defines the kelvin in terms of energy by setting the Boltzmann constant to exactly 1.380649×10−23 joules per kelvin", or something like that. Just so the reader has enough context to connect the dots.

The only thing else I wonder is if a short sentence, maybe at the end of the second paragraph, comparing kelvin to other absolute scales (Rankine, which is the same principal but based on the Fahrenheit scale) would be helpful to the reader, or would it just confuse the issue? Zaereth (talk) 01:24, 3 May 2024 (UTC)

Of course, there have been some changes while I was writing the above, so many of those suggestions may no longer apply, but it looks like you got the gist. Zaereth (talk) 01:36, 3 May 2024 (UTC)

Thanks, I've incorporated the "now defines the kelvin in terms of energy" and sorry I did make quite more changes while you were typing. I'll sleep now and won't edit it for the next day or so to give others a chance to edit. Em3rgent0rdr (talk) 03:24, 3 May 2024 (UTC)

Mathnerd314159, we're writing for one of the largest audiences in the world, and we don't know why our readers are here or how they got here. We do know that it's extraordinarily unlikely that they'll be reading Wikipedia in order to do anything that requires the value of the Boltzmann constant. Laboratories measuring temperature in their experiments, industries measuring process temperatures, manufacturers of temperature measurement equipment and others will at intervals want to ensure their instrumentation's good. For this, there's a worldwide system of certification ultimately traceable back to national and international standards - see Traceability#Measurement - which since 2019 can if necessary be completely independently established. That's an extraordinary achievement, finally liberating international metrology from the International Prototype of the Kilogram and the isotopes of water, and it's quite rarefied; it makes no difference to those laboratories, industries and manufacturers. Likewise, what the Boltzmann constant is, how it's used to define the kelvin or what particular numeric constant is used in that definition aren't going to be at all meaningful to our readers until they understand a bit more about what the kelvin is. Indeed, once they've understood that bit more about the kelvin, they may well still not have the slightest interest in the Boltzmann constant, and we should respect that, not insist that they read all the digits before going further.

Instead, we talk about the idea of absolute temperature, and about the close but shifting relationship between the kelvin and the more familiar degree Celsius. Especially in the lead, we can use paragraphs to make it easier for readers to judge what they might choose to read and what they might skip; in that way and others, we respect our readers and their various interests and abilities - they're not all mathnerds and that's fine. As MOS:INTRO says, It is even more important here than in the rest of the article that the text be accessible. Editors should avoid lengthy paragraphs and overly specific descriptions – greater detail is saved for the body of the article. NebY (talk) 18:01, 3 May 2024 (UTC)

I don't agree with you that the SI definition of the kelvin and its numerical constant is meaningless or useless to most readers. Looking at the other base SI units:

• Second says "historically defined as 1/86400 of a day", then SI as the second paragraph (B-class)
• Metre gives SI as the second sentence (B-class)
• Kilogram alludes to the SI definition in a sentence in the second paragraph and explains that a Kibble balance can be used to realize this definition. (Good article)
• Ampere says 1 coulomb/s and SI is the second paragraph (C-class)
• Mole (unit) has SI as the second sentence (C-class)
• Candela doesn't have SI in the lead, but its definition is complex (B-class)

So the trend is that the SI definition is somewhere in the lead, generally the second paragraph. If the SI definition was lengthy or complex I could see omitting it but for kelvin it is actually shorter than e.g. the definition of the second so MOS:INTRO does not justify leaving it out.

I am OK with what Em3rgent0rdr did, defining the Kelvin scale as "0 K = absolute zero and 1 K = 1 °C" is reasonable, historical, and it avoids duplicating the Boltzmann constant. It is sort of circular, since Celsius is now defined in terms of kelvins instead of the basic 0 = freezing 100 = boiling, but ampere/coulomb is viciously circular and the discussion seems to have left it that way. I did some rearrangement again since I still think the Kelvin scale should be explicitly defined with a sentence like "The Kelvin scale is...".

You do bring up a good point with the traceability. There is some stuff [1] [2] [3]. Expanding the article with how the kelvin is practically realized and used would bring the different definitions into context and make their relative importance more clear. Mathnerd314159 (talk) 21:56, 3 May 2024 (UTC)

Sadly, Wikipedia is not a good guide as to what's meaningful to readers! Our articles don't always develop with such a coherent view and as you've found (and thanks for that survey), most of our articles on base units aren't rated highly. Of course, it varies from one unit to another how much explanation of the concept's needed, roughly in the order you've given: the second is a familiar unit in common parlance and in other systems, while the very idea of the mole is unfamiliar to many and the candela is indeed complex.

Still, looking at Kilogram - assessed as a GA in 2008, before the redefinition - I notice a three-paragraph lead with the middle paragraph describing the manner in which the kilogram's defined and the significance of such a definition without actually providing any of the constants or formulae involved. What's more, the reader can skip that paragraph after reading the first few words, carry on to the next paragraph and still gain from the article. In that way it's doing a good job of talking to a wide range of readers.

I'm sure we can improve on the current lead. At the moment,[4] the first of two short paragraphs manages to repeat 273.15 three times, and the second then throws in 273.16. So many numbers don't make for easy reading, and as Kilogram shows, we can communicate a great deal without supplying a lot of quantities. NebY (talk) 16:22, 4 May 2024 (UTC)

I'm not well versed in the subject myself except for it's practical importance, in that, at very cold temperatures just as in very deep vacuums relative scales tend to break down, hence having an absolute scale becomes a necessity then. So I don't have have much input to give beyond advice about writing in general. But along those lines I would make this suggestion: the last few days the article has become very unstable, which can be confusing or even frustrating for the reader. Perhaps it would be better to finish this discussion and hammer out all the details first, and when everyone has come to a consensus, then implement the changes to the article. We can copy/paste it right here and do all the wordsmithing until it's just right, without disrupting all those readers out there. Not to mention, it's hard to discuss something when that something is in constant flux, (see my last comment). To discuss, it's important to give people time to respond.

That said, it's refreshing to see people actually discussing a subject in a collaborative manner rather than a combative one, for a change, so thanks for that. Zaereth (talk) 22:15, 3 May 2024 (UTC)

I agree - the recent speed of editing makes it hard to discuss issues and hard even to spot a version one might like; it's also difficult to see when to edit, as another editor might or might not be in the middle of a batch of little changes, even about to revert themselves. Also, let's not put each other under pressure to respond quickly, for fear something will seem to be agreed nem con; we can take it easy. NebY (talk) 15:49, 4 May 2024 (UTC)

Drafting

Combining some of the recent improvements with some earlier ideas, I'd like to float the following draft; it's not perfect (no Wikipedia lead is ever perfect) but you'll recognise some of the principles from the discussion above. I've removed the refs for two reasons: they make talk-page drafting awkward, especially as many will be unresolved, and it's not actually necessary to source a lead when it's summarising sourced content, so we may do without them anyway.

Draft

The kelvin, symbol K, is the base unit of measurement for temperature in the International System of Units (SI). The Kelvin scale is an absolute temperature scale that starts from 0 K as the coldest possible temperature, absolute zero. It is named after the nineteenth-century British scientist Lord Kelvin who first developed it, and was formally added to the International System of Units in 1954. The Kelvin scale was developed from the Celsius scale (symbol °C). A change of 1 K exactly equals a change of 1 °C, but absolute zero, -273.15 °C, is 0 K. Any temperature in degrees Celsius can be converted to kelvin by adding 273.15. The Celsius, Fahrenheit, and Rankine scales are now defined in terms of the Kelvin scale. The kelvin itself is now defined in terms of energy by setting the Boltzmann constant to exactly 1.380649×10−23 joules per kelvin; every 1 K change of thermodynamic temperature corresponds to a thermal energy change of exactly 1.380649×10−23 J.

NebY (talk) 17:00, 4 May 2024 (UTC)

i like that draft. I would change ". A change" into ", such that a change" Em3rgent0rdr (talk) 17:30, 4 May 2024 (UTC)

Thanks! It would be grammatically jarring, even wrong, to use "such that" without a preceding noun or noun phrase. "in such a way that" would be grammatical but a bit longwinded, and "so" logically incomplete, but "so that" or a semicolon would work. NebY (talk) 12:58, 6 May 2024 (UTC)

I don't like splitting the definition of the Kelvin scale into pieces. You can't define a scale without two pieces of information, in this case the start and the increment. So I would keep ", then rises by exactly 1 K for each 1 °C" after "absolute zero".

I don't like "it is named after". For one, it is passive voice. The 1954 CGPM meeting named it. That's why my version puts it down below, in line with the history.

You stated you didn't like the duplication of 273.15, this does remove one instance but there are still 2 left. Personally I liked having it 3 times, I think some schoolchildren will need it to be repeated to get it through their heads that this number is important. But if avoiding duplication is really a goal then I would say to go further and remove the absolute zero = -273.15 °C, just have a sentence "Any temperature in degrees Celsius can be converted to kelvin by adding 273.15." Also, it is incorrect to say that the Kelvin scale was developed from the Celsius scale, as my recent additions of the history show. Rather, the Kelvin scale was developed from thermodynamic principles, and then the arbitrary increment parameter was chosen to agree with the Celsius scale. So I would change that mini-paragraph to "The Kelvin scale was designed to be easily converted from the Celsius scale (symbol °C). Any temperature in degrees Celsius can be converted to kelvin by adding 273.15."

I added the "absolute Celsius" reference because it provides a third definition, besides "SI unit" and the scale start and increment - a simple mnemonic to remember what the Kelvin scale is. I think adding a redirect from "Absolute Celsius" to here would make sense and having a sentence in the lead would explain the context of that redirect to readers. So I don't see why you removed it.

I also don't like the phrasing "are now defined" - it begs the question of "since when?". In my phrasing it is chronological, there is the definition of the kelvin in 1954 and the redefinition in 2019 and one can conclude that the scales were redefined between those two points and the 2019 definition is the current definition. I don't have sources handy but I would suspect that the range 1954-2019 for redefining Celsius is about as precise as one can get because it was a gradual process of updating the definitions book by book.

And 273.16 K being the triple point of water is an important definition, it is probably more important than the 2019 one at present. As those NIST pages I linked say, there is essentially no realization of the new 2019 definition at this point, everyone still uses triple point cells and there are no plans to change over for the foreseeable future. So again I object to removing it.

So after going through those, I put what we seem to be in agreement about into the article. It is not a huge change but it is a little improvement. Mathnerd314159 (talk) 05:59, 7 May 2024 (UTC)

Add expression of kelvin in terms of SI defining constants h, ΔνCs, and k

The stable (April 30th) section on "2019 redefinition" said:

"The unit J/K is equal to kg⋅m²⋅s⁻²⋅K⁻¹, where the kilogram, metre and second are defined in terms of the Planck constant, the speed of light, and the duration of the caesium-133 ground-state hyperfine transition respectively. Thus, this definition depends only on universal constants, and not on any physical artifacts as practiced previously."

(Note I did do some rearrangement and tweaks to that section, which is why I've copied that stable version here.)

Out of curiosity, I looked at Caesium standard#Summary which gives an expression of the kelvin in terms of the SI defining constants (h, Δν_Cs, and k) to be:

1 kelvin = ⁠13.80649/6.09110229711386655⁠ h Δν_Cs/k

I want to put this into the "2019 redefinition" section, because it gives exactly what kelvin is in terms of the defining constants. Currently kelvin's article only provides the indirect definition by putting kelvin in the denominator of k_B ≝ 1.380649×10⁻²³ J/K. So I'm thinking to make kelvin's article a little more about kelvin (this article is titled "kelvin" and not "Boltzmann constant"), I'd like to add this expression to the "2019 redefinition" section (and maybe also in the "extradata2" field of its infobox unit). But per Zaereth's request to slow down editing the page directly, I'm posting in this talk first. Em3rgent0rdr (talk) 00:25, 4 May 2024 (UTC)

I'm just making a note that the SI brochure page 133 gives

1 kelvin = ⁠13.80649×10⁻²³/(6.62607015×10⁻³⁴)(9192631770)⁠ h Δν_Cs / k

so could cite that part. (The rest of the derivation is just multiplying the denominator numbers to get 6.09110229711386655 and cancelling the exponents.) Em3rgent0rdr (talk) 03:04, 4 May 2024 (UTC)

It seems fine, I would use the SI brochure's version. Or maybe group the constants with their numbers like

$$1{\text{ kelvin}}={\frac {h}{6.62607015\times 10^{-34}}}{\frac {\Delta \nu _{\text{Cs}}}{9192631770}}{\frac {13.80649\times 10^{-23}}{k}}$$

Also, the main point of contention has been the lead, I for one appreciate your edits and I wouldn't interpret Zaereth's request to include edits to the rest of the article. Mathnerd314159 (talk) 05:15, 4 May 2024 (UTC)

I spent some time trying to figure out a good way to do show this, and ended up with putting discussion of the dependencies as caption to the SI units diagram, using blackened arrows for the kelvin-specific dependencies so is easier to trace: https://en.wikipedia.org/w/index.php?title=Kelvin&diff=1222200283&oldid=1222153908 Em3rgent0rdr (talk) 14:52, 4 May 2024 (UTC)