Talk:Planck constant

Plaque?
Why is the image of the Plaque on this page? It has nothing to do with the article. It should either be on Max's article or the Humboldt University article.


 * I moved the plaque image about the university to the Max Planck page into the section that actually talks about him at the university.


 * I moved it back - please read the plaque, it celebrates the discovery of Planck's constant, the subject of this article. PAR (talk) 01:59, 13 March 2013 (UTC)


 * It may "celebrate" the discovery of Planck's constant, but it is not a picture of Planck's constant, and thus it would be appropriate in the "history" section, and not in the info box. Geoffrey.landis (talk) 16:33, 8 April 2022 (UTC)

Significance of the Value
"In a unit system adapted to atomic scales, the electronvolt is the appropriate unit of energy and the Petahertz the appropriate unit of frequency. In such an atomic units system, Planck's constant is indeed described by a number of order 1."

Is it me or is the claim that h is of order 1 a bit circular? The Petahertz is the "appropriate" unit of frequency because it's related to the energy by Planck's constant. By this same argument, the Megaelectronvolt (MeV) is the proper energy unit for the atomic nucleus, and the Zettahertz (1021 Hz) is the "appropriate" unit of frequency, and in these units Planck's constant is also of order one. In fact, for a baseball, the appropriate energy is a Joule and the "appropriate" frequency is 1033 Hertz, yielding h of order 1 in those units as well.

The rest of the section is fine, but I think the implication that atomic scales are somehow special is misleading. Ragnarstroberg (talk) 02:24, 2 April 2013 (UTC)

RELATED, YET DIDNT FIND NEW THREAD This may or may be the time or place, yet I've been intending to note, whether peer reviewed or not, the page for "h bar" or Plancks Constant (~6.626x10^34) / 2Pi is WRONG; It's h/4Pi, like any undergrad Chem/Phys/Engr keeps at arms length, even if they only jammed textbooks in their heads. The following rant was blasted to my FB wall & I still stand true; Thx!:

Why do Wikipedia & Google FAIL at h/4pi, roughly equalling h bar, 5.20410333x10^Рѕњ34? "Is there no....." hope in truth & ".....chivalry" (-Perry Ferral)?, I'm throwing Penn & Teller's "red card" on B.S.! 70+ years of University texts since Maxwell Planck & likely, enough to crush concrete @ 3.75 Tons /in^2 (on W-C, C-C, CN:, C-B, OsB4, OsB6, WB4, WB6, etc) worth of ISBN that Northrop, Grumman, Boeing, JPL, Bechtel, Brookhaven, LBL, CNSI, Nobel, USPTO, UCS, FLIR, Indigo, Bayer, Alfa-Aesar, Merck, Applied Materials, Alcoa, Kaiser, Musk Co's, Easton, Fischer, Edmonds, Asus, Apple, Microsoft, HP, Agilent, Intel, AMD, Nvidia, Komatsu, Liebherr, Komatsu, Lufthansa, Ford, Mercedez, GMC, VW, Rolls-Royce, Bentley, Ferrari, Genesis, Subaru, S-4, Dulce. etc..... likely, WILL NOT HIRE, unless owned (seva-Sanskrit)! Muhahaahaaa..... Okay, now what (Okinawa)? Wiki & Google; Shokai de nai!, Hakujin (JP), xiao rien (CN), ce fu (FR) ('Hacked genius dirty souled looney binned cooks") search engines amidst! Ikh zog nor ("I'm just saying" - Yiddish)..... 3~* & =^P!

Please peer review & rebuild Bastille! — Preceding unsigned comment added by 2604:2D80:ED00:2F00:7D98:2AA9:8B3B:AF55 (talk) 11:51, 15 February 2023 (UTC)

missing constant definition
In the part about the Bohr radius there is an equation:


 * $$E_n = -\frac{h c_0 R_{\infty}}{n^2}$$

What is "c sub 0"?

Should it be:


 * $$E_n = -\frac{h \varepsilon_0 R_{\infty}}{n^2}$$

using the permittivity of free space?

Where else is this equation explained/documented? It seems to appear here without any citation.三人莫然 (talk) 18:09, 13 June 2013 (UTC)

I don't know this formula off the top of my head, but the units are correct with a velocity (and would not be with permittivity) since the Rydberg constant has units of inverse meters. I'm going to get rid of the subscript on $$ c_0 $$ since c itself is generally defined as the speed of light in vacuum.

I just realized that $$ c_0 $$ is used throughout this article. I don't really want to change all of it in case that was intentional, but it seems very non-standard. Does anyone have a good explanation for why this would be the case? Ponderomotive (talk) 15:52, 25 November 2013 (UTC)


 * Not that non-standard judging by gbook results. Using this notation for speed of light in free space allows c to be used for speed of light in some other medium.  It also seems to be useful in discussions involving the possibility of non-constant speed of light.  Spinning  Spark  17:41, 25 November 2013 (UTC)

I would generally consider consistency with the rest of Wikipedia to be the most relevant figure of merit, but I do agree that there is some precedent for alternate definitions. Since it is defined in the article, I suppose there is no ambiguity. Ponderomotive (talk) 19:01, 25 November 2013 (UTC)


 * Absolutely not, we should always refer out to reliable sources in our work. Self-referencing to other Wikipedia articles will inevitably end up spreading inaccuracies and misunderstandings from article to article.  Inevitable because many of Wikipedia's millions of articles are very poor quality.  And from here the disinformation spreads to the rest of the internet as it gets copied from page to page and then the whole world ends up believing it just because it is written in Wikipedia.  Spinning  Spark  00:25, 26 November 2013 (UTC)


 * I agree citations should certainly not be other wiki articles. I'm just not a huge fan of changing the definition of a parameter partway through an article or between closely related articles. Ponderomotive (talk) 22:09, 26 November 2013 (UTC)


 * I agree that c is well understood as the value for the speed of light in vacuum in physics. Nobody thinks that the formula "E=mc2" means that the energy changes depending on whether you're in space or underwater! It is possible to define c as the speed of light in a medium other than vacuum, but this is uncommon, and I would agree with using "c" and not "c0" here. Geoffrey.landis (talk) 16:38, 8 April 2022 (UTC)

about unit
should not the unit of h to be J.second/cycle? since the energe E=hv while v has unit cycles/second, only when the unit is J.second/cycle, then E=hv can have unit J. otherwise, the unit will become J.cycle.
 * similarly, the reduce plank's constant should have unit J.second/radian. Jackzhp (talk) 17:29, 26 September 2013 (UTC)
 * Radians and cycles are not really units. The NIST guide to the SI system says
 * The radian and steradian are special names for the number one that may be used to convey information about the quantity concerned. In practice the symbols rad and sr are used where appropriate, but the symbol for the derived unit one is generally omitted in specifying the values of dimensionless quantities.
 * They have units of m/m in terms of base units, that is, they are dimensionless.  Spinning Spark  23:40, 26 September 2013 (UTC)

Historically inaccuracy in introductory paragraph.
The second sentence of the article says, "The Planck constant was first described as the proportionality constant between the energy (E) of a photon and the frequency (ν) of its associated electromagnetic wave" But, that can't be true because photons were not yet known to physics when Planck first calculated the value of h.129.42.208.183 (talk) 17:02, 16 October 2013 (UTC)
 * True enough. It's a constant that relates frequency of a field to the size of lumps (quanta) of energy that can be added or subtracted from the field by a charged oscillator. The idea that these "lumps" or quanta of energy were themselves particles with any type of independent reality, as we all know, came five years later. And nobody really believed it until Compton, working 22 years later. I'll see what I can do with the text.  S  B Harris 00:56, 17 October 2013 (UTC)


 * Were not Planck's original plots of Energy v. inverse wavelength rather than frequency?  Spinning Spark  11:14, 13 November 2013 (UTC)

This article discusses quantization of energy as a general phenomenon, but it is really only appropriate to discuss quantization in reference to bound states. In the case of free particles, arbitrary energies are allowed. Probably because the historical development dealt primarily with bound state electrons, we now essentially define a photon by the amount of energy at a given frequency corresponding to a bound state transition (which has a characteristic decay lifetime). In this way we can still talk of virtual photon exchange via electromagnetic forces, but these forces can take on arbitrary amplitudes. This is discussed to some extent at the beginning of Ch. 15 in Jackson. This may be sufficiently subtle as to not be worth mentioning in the article, but I would be interested to hear someone more versed in quantum mechanics weigh in on the issue. Ponderomotive (talk) 17:26, 25 November 2013 (UTC)

Gordons
I have removed this from the table as uncited. I can find no trace of "Gordons" as a unit of energy in reliable sources. I have tried numerous search terms in Google, gbooks and Scholar. The reference in Units of energy is to Convenient Units for Efficient Mathematics but I cannot find any trace of this document either - no publisher, author, link, or other citation details are given. I therefore think it should be left out pending presentation of a source. And just a minor point, Planck's constant would be in units of G-s if Gordons are units of energy, not in just Gordons.  Spinning Spark  11:14, 13 November 2013 (UTC)


 * Given that, I think you've made the right call by reverting my edit. Thanks!  Garamond Lethe t c  11:22, 13 November 2013 (UTC)


 * An also consider the fact that the first mention of Gordons on Wikipedia was added on 1 April 2013. This is long term vandalism by someone who snickers at their own joke. Headbomb {talk / contribs / physics / books} 11:09, 14 November 2013 (UTC)

mole of photons is not necessary for sensory experience
The statement

"everyday experience is not concerned with individual photons any more than with individual atoms or molecules. An amount of light compatible with everyday experience is the energy of one mole of photons"

is incorrect or misleading since around 100 photons impinging the retina can result in a conscious event. The argument in the article surrounding this claim also is unreferenced.

Spope3 (talk) 21:55, 15 May 2014 (UTC)


 * The article does not actually say that a mole of photons is the smallest detectable amount. It says it is comparable with everyday experience.  In a similar vein, one could talk of a pound weight being comparable with everyday experience, even though weights far smaller than a pound are human detectable.  I'm not sure what "argument" you think needs citing.  If you mean the actual value of a mole of photons, references verifying that are easy to find: here's one .  Spinning  Spark  00:31, 16 May 2014 (UTC)

By "surrounding argument" I mean the entire paragraph containing the sentence I quoted. "Comparable with everyday experience" is too vague to be informative. A "mole" is a number selected to be useful to (some) chemists, and has little to do with everyday experience. And, there are no references. So we don't know if a published source has ever chosen to make a similar argument about moles and everyday experiences, in addition to obvious counterexamples.

Spope3 (talk) 06:10, 18 May 2014 (UTC)


 * Perhaps a compromise: instead of using the technical term mole, say something like "Human beings and the everyday objects they deal with are made of large numbers of quantum particles (atoms), of the order of 1022 particles, so the energy fluxes significant on a human scale are composed of similarly large numbers of photons." -- Chetvorno TALK 07:29, 18 May 2014 (UTC)


 * By the way, Spope3, your example of the eyes responding to 300 photons is the exception; the eye is an extremely sensitive receptor.  If you want to toast a marshmallow, get a suntan, run a small appliance (which run on virtual photons provided through the power cord), pound a nail (virtual photons again), or make a cellphone call, you are talking about electromagnetic fluxes at least of the order of 1015 photons. -- Chetvorno TALK 07:29, 18 May 2014 (UTC)
 * However, photon reception by the eye is probably the pinnacle of "everyday interaction" with photons. As an example, the paragraph seems very ill-concieved, besides reeking of original research. (Even the 10^15 you mention in the last sentences is many orders of magnitude away from 10^22.) It is somewhat beyond me why anyone would opt for light to make an example about everyday things consisting of many particles, instead of a more conventional baryonic option, e.g. the number of atoms in a human cel, or whatever. The whole paragraph just seems like a very bad idea.TR 09:21, 19 May 2014 (UTC)
 * A baryonic example like a mole of carbon atoms (or a mole of potatoes) is great for explaining what a mole is, but this is not the mole article and that is not what is trying to be explained. I think photons were chosen because an energy quantity is needed to highlight the smallness of the Planck constant.  Perhaps an example in terms of heat might be better and easier for the reader to grasp.  Spinning  Spark  09:41, 19 May 2014 (UTC)
 * I see why an energy related quantity would be preferable. Heat might indeed be better. An example with a referencable source would be even better. The current phrasing with the first sentence focusing on that green light is chosen because the eye is most sensitive to it is unfortunate.
 * Even better than an energy example, would be an actual action example. It is because typical everyday actions are large that planck's constant is small. Actions are a bit more abstract though.TR 10:07, 19 May 2014 (UTC)
 * For concreteness sake, an example based on the energy needed to complete an everyday task (e.g. lift a spoon) might be better.TR 10:11, 19 May 2014 (UTC)
 * That's a good idea. Here's a source describing a pendulum oscillator.  Spinning  Spark  11:06, 19 May 2014 (UTC)
 * 74.111.160.142 (talk) 12:13, 19 October 2015 (UTC)Do you normally throw 10g spoons at 6.57267 km/s?

I rephrased to clarify that this is not the minimum of human perception. -- Beland (talk) 15:23, 16 November 2018 (UTC)

Probable typos - W90, F90, and p-90
There appears to be a subscript "90" on a lot of the symbols on this page starting with the 8th hit for "90" which is W 90, which is the symbol for Watts.

There are also several " p-90 " or similar references which are very confusing due to the minus sign. I suspect that all of these "90"s should be removed, or corrected (if they are part of a latex format), but I don't want to mess it up in case I don't know some subtlty of the jargon.)

Find "90" on the page and find next several times to see them all.

Can someone who knows what they're doing pls verify that at least the W 90 and F 90 are wrong and perhaps correct this page?

Rainbow Sally (talk) 14:23, 7 August 2014 (UTC)


 * It is not wrong, see conventional electrical unit. SpinningSpark 01:25, 8 August 2014 (UTC)

Unicode ℎ not h
Should the Unicode sign ℎ (U+210E) for the Plank Constant be used instead of an italic lower-case h character? --NoahSpurrier (talk) 06:58, 10 December 2014 (UTC)


 * I'd suggest not using it on WP at this stage – it carries the risk of lack of font support on many systems with no visible benefit. Besides, the semantics associated with Unicode symbols are very fuzzy (not prescriptive); one seems to be free to choose which symbol to use for a given meaning. It is unclear to me why a special symbol should be defined by Unicode when it is known as a standard "h"; there are any number of similar symbols that do not to my knowledge have special Unicode symbols defined for them (e.g. c, &pi;). —Quondum 16:42, 10 December 2014 (UTC)
 * Agree.Chjoaygame (talk) 17:50, 10 December 2014 (UTC)

Definitia constantei h rezulta imediat din relatiile energetice ale procesului de anihilare electron-pozitron. Wpe=(k*Qe^2)/Re=Me*c^2=h*Ffae. Rezulta h=(k*Qe^2)/(Re*Ffae), in care k este constanta interactiunilor electrice =9*10^9 (N*m^2)/C^2, Qe=1,602*10^-19 C, Re=2,81743810^-15 m, Ffae=1,237268*10^20 Hz, este frecventa fotonului gama de la anihilarea electronului cu pozitronul. — Preceding unsigned comment added by 2A02:2F0B:840E:E300:9417:5314:4085:490D (talk) 09:34, 21 October 2018 (UTC)

Value section edits by IP
The following edit is being made by an anonymous IP without any explanation:

It has been reverted at least twice, once by me and once by Hroðulf. I'm not following why these edits are being made, but if the IP wants to add information to the article, then perhaps that is a good way to proceed. Isambard Kingdom (talk) 15:44, 1 March 2015 (UTC)


 * Yes, I think the previous version, in which the units are given in terms of "action" (energy multiplied by time or momentum multiplied by distance) is much more common and physically intuitive than 91.122.2.96's description in terms of "areal momentum". 91.122.2.96, since your changes are controversial you need to discuss them on this page first. -- Chetvorno TALK 18:39, 1 March 2015 (UTC)


 * Oh no. The areal momentum guy is back. Time to protect the article again. AManWithNoPlan (talk) 19:17, 1 March 2015 (UTC)
 * Technically he is correct, the units are "areal momentum" (kg m^2 s^-1) and not (kg rad s^-1), however angular momentum is not (kg rad s^-1)74.111.160.142 (talk) 12:34, 19 October 2015 (UTC).

perceiving weak stimuli
Editor Lycurgus is rightly concerned for precision and accuracy.

Nevertheless, his edit here reads in part: "the neural mechanism would be excessively noisy if a single photon could be perceived." I think this is perhaps editorial argumentation/guesswork and may be original research. The experiments that claim to show perception of very weak stimuli are done with a silent or dark background. What is occasionally perceptible then may have little to do with ordinary perception against ordinary backgrounds. The cited source says that it has shown that one quantum is enough to give rise to perception. The matter is, however, not quite as simple as this might make it seem. There are more recent sources I have glimpsed but not examined closely that I think may perhaps partly disagree. The movement of the eardrum may be regarded as a quantum collective phenomenon and so considered in terms of phonons, which are quanta. Perhaps Editor Lycurgus will tell us more of his thinking.Chjoaygame (talk) 13:51, 1 January 2016 (UTC)


 * Acknowledged, may respond further later. 108.183.102.223 (talk) 03:11, 3 January 2016 (UTC)

Missing references to proofs of UV catastrophe
The text states: "The black-body problem was revisited in 1905, when Rayleigh and Jeans (on the one hand) and Einstein (on the other hand) independently proved that classical electromagnetism could never account for the observed spectrum. These proofs are commonly known as the "ultraviolet catastrophe", a name coined by Paul Ehrenfest in 1911." I know of one proof we saw at university, but I am interested to read their independent original proofs that classical electromagnetism could never account for the spectrum. Sadly the statement does not reference the original derivations. The works of Rayleigh are on archive.org, but I'm having trouble locating both proofs. Its also unclear if Einsteins proof was also published in 1905 or a different year?

Can anyone help me locate these? — Preceding unsigned comment added by 213.219.148.2 (talk) 05:08, 25 May 2018 (UTC)

Values given for h and h-bar are inconsistent, and h does not match NIST value.
The value given for h divided by the value given for h-bar is 2*3.141592537 instead of 2*pi. NIST gives h as 6.626 070 040 x 10-34 J*s, and h-bar as 1.054 571 800 x 10-34 J*s, indicating that the value in the main article is wrong. — Preceding unsigned comment added by Pciszek (talk • contribs) 18:06, 11 June 2018 (UTC)


 * Also this article https://www.sciencenews.org/article/official-redefining-kilogram-units-measurement says "After May 20, the value of the Planck constant will be fixed at exactly 6.62607015e-34" CaGlwwWEDymzc7KBQC8u (talk) 17:18, 16 November 2018 (UTC)


 * Yes, the unit of kilogram is redefined as of 2018-11-16 (see definition here https://www.bipm.org/utils/en/pdf/CGPM/Draft-Resolution-A-EN.pdf, and news of the vote here https://www.nytimes.com/aponline/2018/11/16/world/europe/ap-eu-france-updating-the-kilo-the-latest.html), by defintion of the Planck constant to be exactly 6.62607015⋅10−34 J⋅s . DarkoS (talk) 19:37, 16 November 2018 (UTC)

E
This symbol should be defined when it first appears.Lewis Goudy (talk) 11:56, 5 October 2019 (UTC)

Uncertainty Relation
The section of the article on the uncertainty relation seems to be dubious at best. There is no Energy-Time measurement uncertainty in Quantum Mechanics, though there are similar looking formula that maybe could be noted. After this the section seems to become very vague and confusing, with little actual information, and possibly some false statements. For example I am not sure what quantization has to do with "either-or" (I have never heard this phrase before). I feel like this section could probably be cleaned by making sure everything is coming out of a decent QM book.--128.84.127.175 (talk) 17:12, 19 October 2019 (UTC)
 * I agree, the sentence
 * "The either-or nature of uncertainty forces measurement attempts to choose between trade offs, and given that they are quanta, the trade offs often take the form of either-or (as in Fourier analysis), rather than the compromises and gray areas of time series analysis."
 * seems to be vague pompous bloviation. Rewrote it to make a clearer point. --ChetvornoTALK 21:51, 21 October 2019 (UTC)

"Planck action" listed at Redirects for discussion
An editor has asked for a discussion to address the redirect Planck action. Please participate in the redirect discussion if you wish to do so. Utopes (talk / cont) 20:32, 8 April 2020 (UTC)

h*c "not expressible as a finite decimal" in value box note 3
At the moment, this page lists the value of h*c in Joule seconds as 1.98644568E-25. A note says that this is not expressible as a finite decimal, and has therefore been approximated to 8 decimal places. This doesn't sound correct to me. Both the non-reduced Planck constant h and the speed of light c are defined exactly in the J s unit system, at 9 significant figures. Therefore, their product can be expressed as a finite decimal with no more than 18 significant figures. I understand the "not expressible as a finite decimal" argument for the reduced constant hbar and hbar*c, but not for the purposes of hc. — Preceding unsigned comment added by 94.197.213.230 (talk) 16:36, 15 July 2020 (UTC)


 * Not only is the value of h*c expressible as a finite decimal, the truncated value quoted is wrong 1n full it should be 1.9864458571489287 x 10^-25 Js, the quoted value is 1.98644568×10^−25 — Preceding unsigned comment added by 2A00:23C6:8303:1200:89F:D81A:EEBC:65EB (talk) 18:29, 22 August 2020 (UTC)


 * Both fixed —Quondum 19:28, 22 August 2020 (UTC)


 * FYI, I think the value for hc in eV*um is also incorrect. I think the value should be 1.239 841 984 332 (exactly), which, rounded to 8 decimal places would be 1.239 841 98 not 1.239 841 93 as the table lists.  (Honestly, at only 12 decimal places, it would probably be useful to have the exact value.)  I might have made a mistake, so please double-check.  — Preceding unsigned comment added by 67.184.158.199 (talk) 03:58, 7 December 2020 (UTC)

Note 2 is self-contradictory
It says the value is exact, but rounded to 9 digits. Well, is it exact or is it rounded? Somebody please fix this. Betaneptune (talk) 21:07, 5 February 2021 (UTC)
 * The note has been removed. We do not need exhaustive details in the table; a shorthand hint "..." is sufficient to suggest that the value is known to infinite precision but not all digits are listed, with more detail in the text.  —Quondum 23:15, 30 April 2021 (UTC)

Strange units in Diagram
In fig. #2 (caption: "Intensity of light emitted from a black body. ...") the y axis is labeled "spectral energy density" with unit kJ/m3nm. Can anybody explain what this means? -- Wassermaus (talk) 16:28, 22 July 2021 (UTC)

A Well Structured Exposition
As a casual Wikimedia user I rarely contribute to Content nor Talk in topics that are generally beyond my depth. But in this particular page on Planck's Constant I am moved to add an observation that the page has high educational value which I think comes from its 'didactic' flow that can perhaps be emulated in other expositions at Wikimedia. Hats off to all the contributors to this page.

My appreciation arises from (1) Its non - distracted sequential focus on the 'constant' that keeps the reader's attention in coherent state throughout. (2) At every apparent digression (subsection) it actually provides further insight into the import of the 'constant'. (3) It also provides its significance in empirical practice and (4) Is up-to-date in various standardization practices of Physics that now regard the 'constant' as arbiter of palpable reality in Mass, Distance and Time and the like.

I hope Wikimedia 'gods' notice this observation and share it with contributors. Very frequently, especially in subjects prone to arbitrary abstraction (Algebra/Geometry etc), articles are usually angled towards a first author's preferences/bias, followed by objections back and forth until they all tire of the edit war and leave a final version in a disjointed Truce, and the 'Topic' remains in a state of suspended incoherence, even a decade later, sometimes.

From my experience, whenever concluding a Thesis, coherence is arrived at at the very end when synchronizing initial to final viewpoints on a topic, by editing the Thesis in a sequence that is reverse to that of the exposition; so perhaps a way to emulating this admirable result on 'Planck_constant' would be in requiring a 'Synopsis' section as a device that might guide collective contributors into achieving that elusive coherence?

I'm sure that haggling over a relevant 'Synopsis' in Talk would be well worth it in the end.Mkhomo (talk) 19:58, 27 January 2022 (UTC)

Formatting question
I'm noticing that sometimes s is used and that sometimes Hz^-1 is used. Is there any reason why? They seem to be identical to me. 68.132.68.254 (talk) 01:32, 23 July 2022 (UTC)

Constant value defined in terms of Planck units
A recent edit by removed the column in the values table giving the value in Planck units. I'm not sure I agree with that deletion, but I thought I'd ask for discussion here before restoring it. PianoDan (talk) 16:26, 25 July 2022 (UTC)


 * I don't have strong feelings about it, but it does seem like one of those ideas where if you already understand the topic (Planck and other natural units), then you don't need a column in a table, and if you don't already understand it, the column does nothing to edify you. XOR&#39;easter (talk) 21:09, 25 July 2022 (UTC)

"quantum of action": meaning
Historically I understand that the Planck constant h was referred to as "the quantum of action", but Wilczek refers to the reduced Planck constant ħ by this name (see first sentence here). Should we include this alternate meaning in this article? —Quondum 00:13, 4 November 2022 (UTC)


 * Actually I learned today that $$\hbar = h$$, Bunker, P. R., Ian M. Mills, and Per Jensen. "The Planck constant and its units." Journal of Quantitative Spectroscopy and Radiative Transfer 237 (2019): 106594. These are the same value in different angular frequency units. Johnjbarton (talk) 15:56, 6 September 2023 (UTC)
 * Unfortunately this is not true in the current SI, in which angles are dimensionless. There is a lot of discussion on whether the angular dimension should be included in the SI in Metrologia. Relevant to this case, see for example https://iopscience.iop.org/article/10.1088/1681-7575/ab931e Jähmefyysikko (talk) 17:30, 6 September 2023 (UTC)

Reduced Planck constant
@Reuqr as you see I merged your recent work on reduced Planck with the section of that name from the body of the article. I think the section needs to be cleaned up a bit. Maybe you can see how to do that better than I can.

I also reduced the lead paragraph to just the essentials needed to summarize the article. Johnjbarton (talk) 17:11, 6 September 2023 (UTC)


 * Would it be appropriate to say that some sources refer to both $$h$$ and $$\hbar$$ as the Planck (or Planck's) constant? It would be easy to read our current text as implying only the latter. The only one I've been able to see online so far (I've not tried to find each one online) is the Great Soviet Encyclopedia quoted at the Free Dictionary, which says $$h$$ is the Planck constant and $$\hbar$$ is also called that. Reuqr@undefined, you've seen and cited many works that call $$\hbar$$ the Planck constant; do they also call $$h$$ the Planck constant, or have another name for it, or not name it at all? NebY (talk) 15:23, 26 September 2023 (UTC)

Team-B-Vital Improvement Drive
Hello all!

This article has been chosen as this fortnight's effort for WP:Discord's #team-b-vital channel, a collaborative effort to bring Vital articles up to a B class if possible, similar to WP:Articles for Improvement. This effort will run for up to a fortnight, ending early if the article is felt to be at B-class or impossible to further improve. Articles are chosen by a quick vote among interested chatters, with the goal of working together on interesting Vital articles that need improving.

Thank you!  Rema goxer  (talk) 22:46, 20 September 2023 (UTC)

hc not useful in table.
Again I removed 'hc' from the table. It is off topic. Nothing in the article refers to hc. The entry in the table is not helpful to readers interested in nature of the Planck constant.

If 'hc' is important then we should have a section named something like the "The combination $$\hbar c$$ explaining the (encyclopedic) importance of hc. Johnjbarton (talk) 14:27, 2 October 2023 (UTC)

"Significance" section is unreferenced.
I reorganized the table of contents and moved the entire (now defunct) measurement section to kilogram.

A glaring problem is the lack of any reference in the "Significance" section. I almost deleted it, but given that the history section drones on and on I think it is important that we explain why this thing deserves so much attention. Johnjbarton (talk) 15:24, 14 October 2023 (UTC)

Seconds vs. per hertz
Template:physconst, following NIST, has a preference for units of J/Hz and J.s for h and h-bar, resp.:

I sense this might be related to the preference for units of angular frequency and frequency -- see footnote "b": "The SI unit of frequency is hertz, the SI unit of angular velocity and angular frequency is radian per second...". Does anyone know a source confirming it? I've tried searching in the CODATA 2018 bibliography but didn't find anything specific. fgnievinski (talk) 04:31, 6 November 2023 (UTC) Complementing the above, the units of h-bar, in full, would be J⋅s/rad, although "rad" is often ommitted; see further discussion: Radian. fgnievinski (talk) 05:18, 7 November 2023 (UTC)


 * The NIST site actually contradicts itself on the same page.
 * https://www.nist.gov/si-redefinition/meet-constants
 * Under "h: the Planck constant:
 * "In the revised SI, the Planck constant h is equal to exactly 6.626 070 15 × 10-34 Joule seconds."
 * but in the wallet card image the values you quote are shown. Johnjbarton (talk) 15:04, 7 November 2023 (UTC)
 * SI gives h in J*s.
 * https://www.bipm.org/en/measurement-units/si-defining-constants
 * D B Newell et al 2018 Metrologia 55 L13
 * "The CODATA 2017 values of h, e, k, and NA for the revision of the SI"
 * DOI 10.1088/1681-7575/aa950a
 * only lists h and in J*s. Johnjbarton (talk) 15:14, 7 November 2023 (UTC)
 * Thank you for digging this up. However, in the (current) SI, rad can be removed and inserted at will; furthermore, Hz can be used instead of s^-1 whenever rotational frequency is implied. So, the NIST is not exactly in self contradiction, it's just slightly inconsistent.
 * It seems NIST stopped midway through making angle an explicit dimension, see "Implications of adopting plane angle as a base quantity in the SI" https://iopscience.iop.org/article/10.1088/0026-1394/53/3/998 (esp. section "Note on the units for the Planck constant, h, and ħ"):
 * Similarly, instead of the quantities action and angular momentum having the same units, as is the case within the current SI, angular momentum could become action per unit angle, in direct analogy to linear momentum being action per unit length, and energy being action per unit time. The change would consequently be beneficial in terms of dimensional analysis, in addition to providing a better description of some physical quantities.
 * Within the current SI system, both h and ħ have the units kg·m^2·s^−1, or J·s. The question arises as to whether this would or should change if angle became a base quantity. Simplistically, if we consider E=h·f and E=ħ·ω as the fundamental equations involving h and ħ, the change in status of angle would leave the units for h unchanged, while, for ħ, we would need to either assign ħ the units of angular momentum, kg·m2·s^−1·rad^−1, or modify the equation to E=η·ħ· ω. (...)
 * In our view, the Planck constant h is fundamentally a measure of action (Quincey 2013), and should therefore have the units of action, kg·m^2·s^−1, or J·s, units that hold whether or not angle is considered a base quantity. (...)
 * The decision on the best units for ħ would be more of a free choice. There would be an argument for giving ħ the units of angular momentum [kg·m2·s^−1·rad^−1], while h retains those of action [kg·m^2·s^−1], so that the familiar equations E=h·f and E=ħ·ω can be retained, and the role of ħ as the natural unit of angular momentum is highlighted. h and ħ would then be related by the equation ħ=ηh/2π.
 * where η=1/rad (see: Radian). fgnievinski (talk) 05:29, 8 November 2023 (UTC)
 * Seems to me that these Hz, sec, rad, points ought to be called out in the article in a section under Dimensions. Johnjbarton (talk) 16:31, 8 November 2023 (UTC)
 * I also find the above clarification useful pedagogically but I'm afraid it doesn't reflect the prevailing consensus.
 * I've searched on Google Books and didn't find many textbooks espousing Quincey and Brown's interpretation:
 * On the other hand, searching on the Web reveals interest in the topic, as demonstrated by questions in discussion forums:
 * Redoing the search on Google Scholar brings up a lot more hits,  including some older and well cited papers:
 * A B Torrens 1986 Metrologia
 * G R Freeman 1987 Metrologia
 * P J Mohr & W D Phillips 2015 Metrologia
 * P R Bunker & P Jensen 2020 JQSRT
 * All in all, I think the view above, that h has dimensions of action and ħ has dimension of angular momentum, forms a "significant minority", thus worthy of inclusion, as per WP:DUE. fgnievinski (talk) 05:04, 9 November 2023 (UTC)
 * All in all, I think the view above, that h has dimensions of action and ħ has dimension of angular momentum, forms a "significant minority", thus worthy of inclusion, as per WP:DUE. fgnievinski (talk) 05:04, 9 November 2023 (UTC)

Quantum of action vs quantum of angular momentum.
I've removed this footnote:


 * The quantum of action, a historical name for the Planck constant, should not be confused with the quantum of angular momentum, equal to the reduced Planck constant.

In the lead "quantum of action" is referenced to Planck's Nobel. I think we should have a ref for the quantum of angular momentum on:
 * Bohr also introduced the quantity, now known as the reduced Planck constant or Dirac constant, as the quantum of angular momentum.

And I think the two identifications should be in the lead. Johnjbarton (talk) 00:50, 6 December 2023 (UTC)

Symbol for frequency
I studied physics at university. I have never seen Planck's equation written E = hf. I know it as E = hν (Greek letter nu).

Elsewhere in the article, nu is used. Why is "f" used here? Should it be changed to nu?

Marchino61 (talk) 10:01, 1 June 2024 (UTC)


 * I have seen $$hf$$ $$\hbar\omega$$ and $$h\nu$$ all used and all three are used in the article. Since the sources are not consistent there is no reason to be consistent in the article. Ideally we could have a reference which discusses these conventions. Johnjbarton (talk) 13:46, 1 June 2024 (UTC)

Nicholson's contribution
The § History §§ Development and application §§§ Atomic structure subsubsection opens with this:

But the § Reduced Planck constant ℏ §§ History subsection says:

With a note explaining:

Can we please resolve this contradiction about Nicholson's contribution? — UnladenSwallow (talk) 15:17, 2 June 2024 (UTC)


 * The lengthy footnote in the § Reduced Planck constant ℏ §§ History section is inappropriate. The footnote cites historians then precedes with analysis that contradicts them. I have deleted the footnote and removed the claim about Bohr being "first".
 * I have to say that the footnote was wonderfully documented with many citations! I am sure this was a sincere effort to "get it right", but Wikipedia requires reliable sources. Johnjbarton (talk) 00:18, 3 June 2024 (UTC)
 * I made some addition edits to the Bohr section as well. Johnjbarton (talk) 17:26, 3 June 2024 (UTC)