Wikipedia talk:WikiProject Physics/Archive December 2022

Do we need Galilean non-invariance of electromagnetism?

The page Galilean non-invariance of classical electromagnetism is a bit odd. (1) why restrain it to classical electromagnetism (2) weird lead and writing in general (also headers that should be sub headers and so on) (3) it seems it could be merged into electromagnetism or Galilean invariance or something like that. As it is, the article seems too specific unless it is there for historical issues but then the history part is missing. Any thoughts are welcome. See also the talk. ReyHahn (talk) 09:38, 28 November 2022 (UTC)

Yeah I would AfD it. The article seems to be based on this obscure reference [1]. The opening sentence is already outrageously wrong: If Galilean transformations were invariant for not only mechanics but also electromagnetism, Newtonian relativity would hold for the whole of the physics. The subject is quite weird, deserving no more of a footnote in treatments of classical electromagnetism. The entire contents of the article are a violation of WP:NOTTEXTBOOK. To top off, its last reference [2] is hair-raising crackpottery. Tercer (talk) 10:26, 28 November 2022 (UTC)

As well as I know the story, it was this non-invariance that was important in developing special relativity. As noted, though, one does have to be careful with WP:NOTTEXTBOOK. Including the appropriate history, which might not be done well otherwise, could be enough to fix it. Some of the history is in Lorentz transformation, but maybe not all of it. The again, Lorentz transformation might be the place to fix it. We could even redirect this to a section in that page. Gah4 (talk) 16:25, 28 November 2022 (UTC)

I agree with taking it to AfD, basically because it has nothing usefully salvageable. There is a core idea that is valid and well-understood [although not by me], essentially that there is a broad class of diffeomorphisms that respect Maxwell's equations in terms of the EM 2-form and charge–current 3-form. The Galilean transformations are not special [whether they are included or not; I suspect not, as per Gah4]. This could be started as a section in Classical electromagnetism, but not through a merge. The concept is a bit counterintuitive, and I'm no expert. but even John Baez has made reference to this. —Quondum 17:17, 28 November 2022 (UTC)

Thanks you for your feedback. A deleting discussion has been created Wikipedia:Articles for deletion/Galilean non-invariance of classical electromagnetism.--ReyHahn (talk) 13:44, 1 December 2022 (UTC)

Drafts at AfC of proposed fermions

There is a set of drafts at AfC about or related to fermions, mostly those proposed to solve the fermion doubling problem. Are there enough sources for these to have separate articles, rather than expanding "Fermion doubling"? And if so, is there any way to make these articles at all comprehensible to the general science reader?

• Draft:Stacey fermion
• Draft:SLAC fermion
• Draft:Domain wall fermion
• Draft:Overlap fermion
• Draft:Ginsparg–Wilson equation
• Draft:Twisted mass fermion
• Draft:Wilson fermion

StarryGrandma (talk) 23:48, 4 December 2022 (UTC)

Absent evidence that any of these actually exist, having more than one article on them would be excessive in my view. JRSpriggs (talk) 01:32, 5 December 2022 (UTC)

I suspect it's an attempt to remove the wall of redlinks at Fermion_doubling#Resolutions_to_fermion_doubling. Primefac (talk) 14:19, 5 December 2022 (UTC)

86400 s = 360.9856...°

The second sentence of the lead of Day now reads "In terms of Earth's rotation, the average day length is 360.9856...°." In case anyone is interested in assessing this "improvement", which is being defended. —Quondum 01:45, 5 December 2022 (UTC)

Although the reasoning behind these changes is correct – indeed Earth rotates 360° in a sidereal day and ~361° in a solar day – such an explanation does not belong in the lead section, and definitely not in its second sentence. The purpose of the lead section is to give a summary-style overview of the topic, not defend a specific point (even if said point is factually correct); statements such as The reason why it is roughly 1° greater than 360° and If the Earth's orbit was perfectly circular, and the Earth had no tilt have a noticeably different tone than expected for an encyclopedic lead (especially for an article on a less technical subject matter). A reworded version explaining this nuance, ideally reading less like an annotated text, might be appropriate later in the article (section Apparent and mean solar day).

As such, I support reversion of these changes to the lead, but would encourage constructive edits clarifying this in the appropriate subsection. ^Complex/_Rational 02:53, 5 December 2022 (UTC)

@Tdadamemd19: Please add your opinion. —Quondum 03:04, 5 December 2022 (UTC)

The content is good, but it was out of place in the lede. I moved it down into a more appropriate section.--Srleffler (talk) 04:00, 5 December 2022 (UTC)

The article claims that "the average day length is about 360.9856°". I suspect Quondum's point is that a day is equal to 24 hours (86400 s), not 361 deg, because a time can never be equal to an angle. There can be a correspondence between time and angle, but never equality. Dondervogel 2 (talk) 09:02, 5 December 2022 (UTC)

There were several issues, including the unencyclopedic language equating a length of time to an angle, and the detailed technical point hitting you in the face in the lead (an apparent failure to understand the purpose of the lead). I do not have the patience at the moment to deal with someone who, after a obviously good-faith edits, decided on a BRR sequence instead of a WP:BRD approach (and the strongly worded edit comments about the article don't help). Making others aware of it seemed better than me being confrontational.

I confess that my patience is strained because of a editor who has expressed puzzlement in a revert about a statement (I presume this one) where I refer to "the (mistaken) intuition that 1 cyc = 2π rad". However, that would best be a separate thread. —Quondum 14:56, 5 December 2022 (UTC)

Add ronna- and quetta- to units articles?

Should we add today's four new SI prefixes (quecto-, ronto-, ronna- and quetta-) to our various articles on units of measurement? For example, Tonne now lists ronnatonne and quettatonne with their equivalents. I recently reverted the addition[3] of a table ranging from quectocandela to quettacandela, calling them fantasy units and a waste of our readers' attention, but now regarding Tonne, {{Quantities of bytes}} and others, I'm told[4] we should include the prefixes even if no-one uses them, and now I'd be glad to see some consensus either way. NebY (talk) 23:13, 18 November 2022 (UTC)

OK, now they're just messing with us. --Trovatore (talk) 19:31, 19 November 2022 (UTC)

There is an obvious and clear precedent for including all prefixed forms of a unit in tables: most of the "yotta-" prefixes. Nobody uses yottametres, at that scale it's light-years/parsecs/redshifts. Nobody uses yottagrams, at that scale it's probably Earth masses. Yet metre and kilogram have and have long had them listed in neat little tables. Quondum added the new prefixes immediately to {{SI multiples}}, and the new "ronna-" and "quetta-" forms were added to {{Quantities of bytes}} by three separate editors: myself, Dondervogel 2, and Anthonyryan1. They were added to Tonne by myself and I am a Green Bee. The consensus NebY seeks is present and obvious: it is in favour of adding the prefixes in question. Double sharp (talk) 23:18, 18 November 2022 (UTC)

For information: {{SI multiples}} is used[5] in 11 units articles and 5 orders-of-magnitude articles to make tables listing units from eg quectoampere to quettaampere. NebY (talk) 23:35, 18 November 2022 (UTC)

I echo Double sharp here: in terms of tables, these should be complete where the article lists prefixed units for official (i.e. SI) cases. Tonne is not an SI unit; that table could be trimmed after megatonne. Candela is an example where one might not include a table at all. The purpose of an encyclopedia is to (reliably) inform – in this case, about the existence of the SI units, which includes all prefixed forms – not to present only what is familiar or common. Relatable examples include the electron mass of 0.9 rontograms and Jupiter at 2 quettagrams. One motivation of the prefixes was to get ahead of the existing very real trend of invention of ad-hoc prefixes (hella-, bronto-, ...), which shows that they are of interest to the average joe. —Quondum 00:23, 19 November 2022 (UTC)

I think gigatonnes are common enough to include, but yes, agreed on cutting the table early for tonnes. Double sharp (talk) 01:21, 19 November 2022 (UTC)

Done. Google ngram (only one result for "teratonne", none for "petatonne"). —Quondum 01:49, 19 November 2022 (UTC)

@Quondum: thank you for doing that and resolving one of the contentions. I'm glad you mention Candela as an article where might not have a table. Do you think the underlying principle might be that the four SI units that have physiological weighting factors (candela, lumen, lux and sievert) are only used within comparatively narrow ranges? In my experience their use is roughly bounded by physiological relevance, after all. NebY (talk) 15:52, 19 November 2022 (UTC)

I agree with that thought. There is no conceivable use for quettacandelas, even in principle.--Srleffler (talk) 23:26, 19 November 2022 (UTC)

My suggested rule of thumb here is based on the presence or absence of "yotta", as I've never actually seen it used in practice. If it already isn't there, then there's clearly a precedent that a complete set is not needed. But if it already is there, then there's a clear precedent to show a complete set. Double sharp (talk) 00:24, 20 November 2022 (UTC)

NebY, I'd go along with that (say 10–15 orders of magnitude). I'm not an expert, though. —Quondum 02:42, 20 November 2022 (UTC)

This is a long-winded concurrence with keeping all prefixes on official SI units and trimming to in-use cases for other units. My opinion is that the extreme units are merely distracting when they are so rarely used that they would be viewed as cheeky or intentionally obscure even in a scientific or technical publication. Writing that the electron mass is 0.9 rg or that Andromeda Galaxy is 24 Zm away is distracting and not done in practice without further explanation, not even written out as rontograms or zettameters, and readers should be given a clue that this is the case. The use of bold to imply what's not common practice is extremely helpful, so I'll keep my complaints about rare prefixes to a murmur. Any reason not to use this bolding method in metre and second? For other-than-base units, it does the job to show commonly used cases and point out that all the SI prefixes are technically allowed.

Also, unless someone persuades me it's not helpful, I suggest adding SI units to the many articles that lack them, as we come across them, along with the conventional units like light-years. For example, the distance to Sirius is at present given only in parsecs and light-years, with 8.1×10¹⁶ m left as homework. This makes comparison difficult, e.g. comparing to the distance to the Sun.

On the lighter side, see this xkcd essay for a bit of fun with extremes of luminous intensity. –MadeOfAtoms (talk) 09:51, 20 November 2022 (UTC)

I by "common practice" guess you mean "familiar to the man in the street", and sure, "commonly used units" could be bolded in Metre and Second. Judging what is obscure in scientific circles is trickier. Combination units can use prefixed units that do not normally occur standalone. For example, despite the elementary charge being 160 zC (no direct use for yC or below), the non-SI D might (I guess) over time be replaced by the similarly sized qC·m because this is now conveniently sized as a unit of electric dipole moment of particles or atoms. We can't readily judge what is "strange" if used in scientific literature. The only real value I see in a table is: it allows quick visual relative placement, and it familiarizes the eye to the combinations (e.g., when I see something unfamiliar like 'mT', I might not immediately recognize even what sort of unit it.) In this context and use, including all makes sense, even though the last few might be very obscure. It also has value in introducing people to the new prefixes. —Quondum 15:33, 20 November 2022 (UTC)

@MadeOfAtoms: I fear that if you started adding metre distances to stars and galaxies, you'd find yourself sharply reverted. Once we appreciate that even Sirius is hundreds of thousands times more distant than the sun, light-year and parsec are more useful for describing and differentiating between stars, and are the conventional units. You'd be going against the documentation and functionality of the infobox too, but perhaps more importantly you'd be spending that most important resource, the attention of our readers. NebY (talk) 16:27, 20 November 2022 (UTC)

I'm with MadeOfAtoms (talk · contribs) on this. Seeing some distances in light-years, some in parsecs and some in astronomical units is confusing. A conversion to SI units would be helpful. Dondervogel 2 (talk) 20:49, 20 November 2022 (UTC)

I'd say that making distances more comparable is off-topic for this thread (though not necessarily without merit). —Quondum 21:31, 20 November 2022 (UTC)

@Quondum: By "common practice" I don't have a precise meaning in mind, but how reliable sources use each unit is a verifiable approach. "Common" will always be open to judgement and have grey areas, and combination units do make it trickier. A solution like the common units in bold in kilogram multiples seems like an excellent one to use for more unit articles. Kilogram specifies criteria for inclusion as "common", whose details can then be a separate discussion if anyone disagrees. Regarding SI units added pervasively: thanks NebY for the convincing advice. Even though the ideal of specifying a common unit is attractive to many like me and Dondervogel 2, I'll leave it to the reliable sources and the most focused editors of each article to select the most helpful set of units. If there's much more to say, let's start a new thread per Quondum's note. –MadeOfAtoms (talk) 00:14, 21 November 2022 (UTC)

I don't see the harm in documenting them in areas specific to SI units. However, I think it's far too early to use them in articles outside of that. We should, as always, follow our sources. If our sources are using parsecs, light-years and so on, then our articles should respect that choice of unit. This is, functionally, almost the same thing that's been going on with WP:COMPUNITS (and the attempts to force "gibibytes", "mebibytes", et al. into articles where the sources have never or very rarely use those terms). —Locke Cole • t • c 19:53, 21 November 2022 (UTC)

I never said we should actually use those units. We don't use any of the yotta- units either, because even though that prefix was adopted in 1991, those units are not used in practice. I merely claim that any case where they are mentioned is a precedent for adding the ronna- and quetta- units which are in the same situation. Double sharp (talk) 20:05, 21 November 2022 (UTC)

That seems perilously close to the common argument that if we've included fact A we should also include much more recondite fact B (re which the editor happens to be a fan), or more generally that however far we've stretched, we should stretch further. "Yottabyte" itself is very rare - a company name, a storage architecture that could scale to yottabytes but never has - and hardly makes the case for going further. It's not as if bits and bytes pass Quondum's test of being SI units either, not even being listed in the SI Brchure as Non-SI units that are accepted for use with the SI. NebY (talk) 16:31, 22 November 2022 (UTC)

If byte multiples are cited by BIPM as the raison d'être for the existence of the new prefixes, that alone seems reason enough to extend the byte template to include them. Dondervogel 2 (talk) 16:42, 22 November 2022 (UTC)

Did the BIPM refer to bytes, and did it refer to bits? NebY (talk) 17:18, 22 November 2022 (UTC)

The news release at Nature.com is entitled How many yottabytes in a quettabyte? Extreme numbers get new names and includes the words "Today, the driver is data science, says Richard Brown, a metrologist at the UK National Physical Laboratory in Teddington. He has been working on plans to introduce the latest prefixes for five years, and presented the proposal to the CGPM on 17 November. With the annual volume of data generated globally having already hit zettabytes, informal suggestions for 10²⁷ — including ‘hella’ and ‘bronto’ — were starting to take hold, he says. Google’s unit converter, for example, already tells users that 1,000 yottabytes is 1 hellabyte, and at least one UK government website quotes brontobyte as the correct term" Dondervogel 2 (talk) 19:36, 22 November 2022 (UTC)

Thanks. From that article we have

- annual total world byte generation set to reach 1 yottabyte in the 2030s

- new prefixes for 1,000 and 1,000,000 times that only named to stop other names

- no use case for the new little-end prefixes

- no mention of bits

- entire Latin alphabet consumed, so no more new prefixes ever.

That's a relief, we don't need to worry about unlimited expansion of the tables, but all in all it makes

- some case for expanding the byte article

- a much weaker case for expanding byte templates, adding unused stuff to various articles, the MOS etc

- not much case at all for expanding bit templates. NebY (talk) 21:05, 22 November 2022 (UTC)

• The case for expanding the byte template seems every bit as strong as the case for expanding the byte article. I don't understand the argument for expanding one and not the other.
• I've seen the terms ronnabit and quettabit used in foreign language articles, but not yet in English. Nevertheless, once prefixes are defined by the BIPM they are applicable to all units of the International System of Quantities, including the bit and the byte. So while I accept the case for expanding the bit template is weaker than that for byte, it remains a strong case.

Dondervogel 2 (talk) 21:26, 22 November 2022 (UTC)

A BIPM document by the proposer of the new prefixes (Richard J. C. Brown) indeed notes that there wasn't any driver for the small-end prefixes, and that they were only included because it was considered foolish and unbalanced to only extend the range at one end. It explicitly mentions that bits and bytes are the main driver for the large-end prefixes: The main pressure for new SI prefixes comes currently from outside the SI, from information technology and data storage; in particular from ‘units’ for describing digital information and data size, such as ‘bit’, ‘byte’ and ‘octet’. ... Given the accelerating growth of data production rates and data storage requirements this field will soon require prefixes to cover orders of magnitude in excess of yottabytes. The popular scientific literature is already speculating on what these might be. In New Scientist, Brown suggests that ronto- and quecto- would make sense in radio astronomy, where such scales are needed, but a physicist (Mike Merrifield) points out that most astronomers just use janskys instead. But that's not relevant to the question of the byte and bit articles and tables, where none of the negative-power prefixes were included to begin with, and none were proposed for inclusion. This document says that the letter "B" is the last available, yielding one more potential prefix pair, but that might've changed since in the more recent Nature article Dondervogel 2 linked, Brown notes that B is also unavailable. Double sharp (talk) 21:35, 22 November 2022 (UTC)

I can't see what the aversion to a few items in a table is. If the table lists the prefixed forms, why leave off the last two? I see an irrational aversion to embracing change in so many places. To put things in perspective: the CGPM "owns" (is the defining authority for) some non-metric symbols such as tonne, dalton, day, but has not said which prefixed forms of these are valid (except that minute, hour and day may not be prefixed), and it is not for us to synthesize these forms. It does not "own" the byte or bit, but other bodies such as the IEC do lay down standards for these. If the IEC has said that nonfractional metric prefixes (in general) apply to the byte (which would need checking), then this includes ronna and quetta, and we should include these in any table as per Double sharp's rule of thumb. As far at the templates for binary prefixes are concerned, most who value their sanity have learned to steer clear of them. No debate around them is likely to be balanced. —Quondum 03:48, 23 November 2022 (UTC)

AFAICS nobody is proposing to add the obvious analogous binary prefixes robi- and quebi- to tables. They have been mentioned as the natural analogues in a consultation paper, but have not been adopted by the relevant authority for those prefixes. I did put in a brief cited mention at Byte to explain that situation, but left them out of the table precisely because they haven't been adopted. Double sharp (talk) 08:27, 23 November 2022 (UTC)

For the record, there was one good faith attempt to extend the binary prefixes, but it was reverted. Dondervogel 2 (talk) 09:14, 23 November 2022 (UTC)

OK, thanks. I stand corrected: AFAICS there is no consensus to add the obvious analogous binary prefixes robi- and quebi- to tables, whereas there is for the decimal prefixes ronna- and quetta- in cases where yotta- is already there. Double sharp (talk) 11:17, 23 November 2022 (UTC)

Surely the reason not to add these is because the IEC hasn't defined them yet? Barnards.tar.gz (talk) 11:16, 24 November 2022 (UTC)

Correct. That is the reason there is no consensus for adding them. Dondervogel 2 (talk) 11:23, 24 November 2022 (UTC)

I see the templates as providing handy guides in articles/MOS/etc to help readers understand text in those articles/MOS/etc. Handy guides that relate to what we might be reading are better than ones that also tell us about things that aren't actually to be found in use in our articles or elsewhere. As for disliking change, changes in templates aren't detectable on article/MOS watchlists so template editing carries an extra layer of responsibility, though minor in these cases compared to some. NebY (talk) 18:40, 23 November 2022 (UTC)

The templates have long included the yotta- forms that do not have any actual use. (Unsurprisingly, as that prefix was adopted before WP even existed.) It would seem quite clear from the evidence that how you see the templates is inconsistent with how they have long been actually used. Double sharp (talk) 22:49, 23 November 2022 (UTC)

OK, Double sharp, I'm not convinced but I'm happy to say no more about extension of the bit & byte templates. I'm only back because Litre just popped up on my watchlist. Its table has gained quectolitre, rontolitre, ronnalitre and quettalitre, with equivalences from thousand cubic picometres to cubic gigametre.[6] It already went from yoctolitre to yottalitre. Does that settle it or should we take the same approach to that as you and Quondum did to tonne? NebY (talk) 18:06, 28 November 2022 (UTC)

@NebY: There are actual uses of the extreme small prefixes with the litre, e.g. femtolitre, attolitre, zeptolitre, yoctolitre. So, even though litre is a non-SI unit accepted for SI use (like tonne), there seems to be enough of a case to keep the whole set. (The large prefixes appear to be uncommon, but it seems sensible to show a symmetrical range.) Double sharp (talk) 18:31, 28 November 2022 (UTC)

Thanks for those. "1 yL can contain ~100 metal atoms..." I am awestruck. I haven't tried to figure what a quectolitre might contain, but that is simply beautiful. NebY (talk) 18:47, 28 November 2022 (UTC)

The table does not need two sides; it can be presented as a single range running from something small up to around gigalitre. It is already too wide. This sort of nixes the symmetry argument. —Quondum 18:50, 28 November 2022 (UTC)

What an improvement! A straightforward sequence is so much more readable than a symmetry of powers. NebY (talk) 19:53, 28 November 2022 (UTC)

@NebY: Metals are nowhere near the smallest atoms. Helium is one of the smallest atoms, and its atomic radius is 31 pm. Plugging that into the formula for the volume of a sphere, we get the volume of a helium atom as 1.25 × 10⁻²⁸ litres, which gives a sensible use for quectolitres. Naturally, an alpha particle (helium nucleus) will have even smaller volume. Double sharp (talk) 19:00, 28 November 2022 (UTC)

FWIW, I would limit Litre to 18 orders of magnitude, from nL to GL. I understand you *can* go further but don't see a strong case for it, because use is so rare. The same logic applies to Tonne (nt to Gt). Dondervogel 2 (talk) 19:14, 28 November 2022 (UTC)

Quetta sounds cool! I am a Green Bee (talk) 10:35, 19 November 2022 (UTC)

I created an article for ronna. If consensus is to delete the article the content in the article for ronna can be merged with the content for metric prefixes. WalkingRadiance (talk) 21:09, 6 December 2022 (UTC)

I removed the redirect from ronna to the article for the prefix ronna and added the link to ronna in the SI prefixes template. WalkingRadiance (talk) 21:09, 6 December 2022 (UTC)

Wind Generated surface waves: Unsourced, seemingly contradictory claims.

Talk:Gravity_wave#Unsourced,_seemingly_contradictory_claims_(frequency_times_period_should_be_2π). Annette Maon (talk) 11:25, 8 December 2022 (UTC)

There is no problem. (Pet gripe: This will remain confusing until they redefine the system of quantities and quantity names relating to angles.) —Quondum 13:47, 8 December 2022 (UTC)

Photoelectron Article?

Hello! I'm just curious why there isn't an article about photoelectrons. There is an article on the photoelectric effect, but not on the particles themselves. ERBuermann (talk) 19:22, 8 December 2022 (UTC)

@ERBuermann, we do have an article on the particles - see electron, linked in the first sentence of the article. StarryGrandma (talk) 20:02, 8 December 2022 (UTC)

That reply could be confusing (and perhaps unfairly tongue-in-cheek): here, "an article" refers Electron, but "the article" refers to Photoelectric effect. A photoelectron is just an electron. Photoelectric effect is the only article that should contain information on the term "photoelectron". —Quondum 21:17, 8 December 2022 (UTC)

Ok, thank you! ERBuermann (talk) 02:30, 9 December 2022 (UTC)

Roche limit

This article is a mess, and has accumulated lots of garbage since the FA demotion in 2007.

• The mathematical description needs to be condensed by removing unnecessary derivation and textbook-like language.
• There are loads of unsourced content with plenty of likely OR; some of the citations should be inline for clarity and to prevent the article from attracting further OR.
• I recently removed a section consisting only of data tables based on unsourced and often conjectural data; and an incoherent section connecting the topic to the Hill sphere, that was also severely damaged during an attempted copyedit in January 2021.

–LaundryPizza03 (dc̄) 08:35, 19 November 2022 (UTC)

I took a machete to it. Some portions of the removed material can perhaps be restored if edited for tone first, but honestly, I think we'd get a cleaner result by starting from scratch and clearly identifying what the important ideas are, rather than throwing things in as they spring to mind. XOR'easter (talk) 16:21, 10 December 2022 (UTC)

Pervasive angle vs. count confusion

As I darkly hinted in a previous thread, WP has accumulated a number of errors related to the mistaken understanding that 1 cyc = 2π rad, or equivalently, that 1 Hz = 2π rad/s. In the collapsed section here, I give a nonexhaustive list of related articles, highlighting example dubious content related to this issue. Note: The unit cycle per second is implicitly defined by the SI. I understand that the revolution was defined by a historical version of ISO 80000-3, and is still effectively defined by NIST SP 811. The associated quantity rotation is still defined by ISO 80000-3:2019. Both cycle and revolution are inherently counts (albeit not restricted to integers), not angles.

list of nitpicks by mainspace name (article/dab/redirect)

Angle The turn, also cycle, revolution, and rotation, is one complete circular movement or measure, i.e. going around in a circle once and returning to the same point. A turn is abbreviated cyc, rev, or rot depending on the application. A turn is equal to 2π or tau radians. fixed Angle of rotation A clockwise rotation is considered a negative rotation, so that, for instance, a rotation of 310° (counterclockwise) can also be called a rotation of –50° (since 310° + 50° = 360°, a full turn). Angular frequency ... the units of angular measure (cycle or radian) ... clarified Angular momentum Maybe okay; far too long and rambling for me to check thoroughly. Angular wavenumber Redirects to Wavenumber. If the two distinct concepts of wavenumber (spatial frequency) and angular wavenumber were clearly separated in the article, it would not be as bad, but the article keeps referring to both. Cycle Cycle (geometry) or revolution, a unit of plane angle equivalent to 360 degrees fixed Cycle (geometry) Redirects to Turn (angle). What does a cycle mean in geometry, if anything? Cycle (unit) Redirects to Turn (angle), which is inconsistent with the definition of a cycle (as at Frequency or Cycle per second), and indeed as mentioned in the SI. redirect changed Cycle per second Fairly consistent crossing this off Degree (angle) The turn (or revolution, full circle, full rotation, cycle) is used in technology and science. One turn is equal to 360°. cleaned Frequency Fairly consistent crossing this off Normalized frequency (signal processing) normalized frequency (f') is a quantity having dimension of frequency expressed in units of "cycles per sample". ... analogous to the concept of natural units in physics". fixed Period seems okay crossing this off Radial frequency Redirects to Angular frequency. What is "radial frequency" and does it belong? Radian Mostly consistent if messy. I repaired stuff like turns (complete revolutions) and One revolution per second is equivalent to 2π radians per second. Radian per second This is because one cycle of a rotating object is an angular rotation of one turn (360 degrees), which equals 2π radians. fixed Revolutions per minute Fairly consistent crossing this off (I'm not going to fight about the plural in the title) Rotation around a fixed axis 1 revolution = 360° = 2π rad fixed Rotational frequency Redirects to Frequency (which is fine), but editors periodically redirect it to Angular frequency. swapped with Rotational speed Rotational speed Mostly consistent, but evidently written by someone who thinks that a quantity symbol refers to the numeric values of a quantity, excluding its unit (i.e. the complete quantity divided by a selected unit, indicated by a subscript in the article). Also, using the the symbol ωcyc for a frequency? cleaned Torque Largely corrected, but not checked for consistency. Somewhat rambling. Turn (angle) I cannot find adequate notable definitions of the turn as a unit, especially that distinguishes whether it is a unit of angle or of rotation (note: rotation is defined by ISO 80000-3 as the count of complete revolutions, not as an angle). Wave vector I've separated the definition of angular wavevector from that if the wavevector, but the rest of the article is confused still, using phrases like 'physics definition' that arose from before my partial edits, and is similar to the problem at Wavenumber. Wavenumber In the physical sciences, the wavenumber (also wave number or repetency[1]) is the spatial frequency of a wave, measured in cycles per unit distance (ordinary wavenumber) or radians per unit distance (angular wavenumber). The topic is unclear: wavenumber or angular wavenumber? Violates WP:DICTIONARY: "However, articles rarely, if ever, contain more than one distinct definition or usage of the article's title."

How would this best be addressed? It seems as though we need an essay in WP space that addresses this clearly, which could be linked from the top of the relevant talk pages, or alternatively that something like this may belong in mainspace to serve as a reference for readers. (I also would not object to help in cleaning the articles up.) —Quondum 20:41, 10 December 2022 (UTC)

I don't see your point. A full rotation of something is an angular change of 2π radians. They are the same thing. A rotation, cycle, turn, etc. is an angular change. A "cycle" is a unit of angle equal to 2π radians.--Srleffler (talk) 06:26, 11 December 2022 (UTC)

I think Quondum's point is that while a cycle may be represented by an angle, that does not make it equal to one. Consider a traffic light cycle comprising 4 phases

1. red
2. red-amber
3. green
4. amber

If each phase lasts 10 s, the period is 40 s and the frequency is 1/(40 s) = 25 mHz (0.025 cycles per second), but there is no angle in sight. Dondervogel 2 (talk) 10:40, 11 December 2022 (UTC)

Agreed, the angle is not obvious in this case. Since the behaviour is periodic, however, you can describe it completely with Fourier series, the variable of which looks a whole lot like an angle. EM waves don't actually involve a physical angle either; the angle is a construct that makes the math easier to understand. Anything that has a frequency has an angle, whether physical or abstract.--Srleffler (talk) 21:05, 11 December 2022 (UTC)

Srleffler, your statement is directly analogous to saying that because the size of a circle is the same thing however you look at it, its circumference and radius are equal, because these are two ways to measure its size. In the same way, the rotation and angular displacement describe the same thing, but are different quantities. Perhaps to take it to a more familiar example: if you believe that 1 cyc = 2π rad (as you have just stated), and we have that in describing a sine wave, we have f = 1 cyc/s = 1 Hz, and ω = 2π rad/s, as well as that ω = 2πf, at least one of these equations is in error. Which one is it? —Quondum 13:40, 11 December 2022 (UTC)

OK, I see where you are coming from now. I don't think the distinction is as clear-cut as you do, but helping people to not confuse frequency and angular frequency is a good thing. Be careful that in introducing this distinction you don't make things less clear rather than more.

The error in your example is that when an angular variable appears in an expression outside of a trig function, the formula is always unit-specific. You can't substitute an angle in degrees into a formula that expects an angle in radians. Similarly you can't substitute an angle in cycles into a formula that expects an angle in radians. --Srleffler (talk) 21:01, 11 December 2022 (UTC)

This description of an "error" does not apply in either the SI or the mathematical context. The SI pretty much covers everything outside of trig functions and very little with them. Mathematicians define trig functions to take unitless real numbers. In spirit I agree with you, but I'm not going into that here. This is only a nitpick, since I don't actually see the relevance here. —Quondum 23:55, 11 December 2022 (UTC)

My take on this is that any periodic dynamical system can have a period and a frequency associated with the periodic behavior, e.g., periodic finite state systems, oscillations in cellular automata, or rotating systems. But only those systems with the concept of an angle, such as rotating systems or the possibly the angle coordinates of an action-angle representation of a Hamiltonian system, would have a notion of associating cycles with radians or degrees. So whether 1 cycle is equal to 2 pi radians is context dependent. In the gravity wave example above, in the simple harmonic approximation of wave dynamics, it's easy to map to an angle variable and make the association. But for the full nonlinear dynamics, associating an angle becomes more problematic and it is best to just stick to cycles. --{{u|Mark viking}} {Talk} 19:06, 11 December 2022 (UTC)

The current SI brochure distinguishes the quantitities (frequency, angular velocity, angular frequency and activity) and their respective units thus:

"The SI unit of frequency is hertz, the SI unit of angular velocity and angular frequency is radian per second, and the SI unit of activity is becquerel, implying counts per second. Although it is formally correct to write all three of these units as the reciprocal second, the use of the different names emphasizes the different nature of the quantities concerned. It is especially important to carefully distinguish frequencies from angular frequencies, because by definition their numerical values differ by a factor1 of 2π. Ignoring this fact may cause an error of 2π. Note that in some countries, frequency values are conventionally expressed using “cycle/s” or “cps” instead of the SI unit Hz, although “cycle” and “cps” are not units in the SI. Note also that it is common, although not recommended, to use the term frequency for quantities expressed in rad/s. Because of this, it is recommended that quantities called “frequency”, “angular frequency”, and “angular velocity” always be given explicit units of Hz or rad/s and not s−1."

I read that as acknowledging the use of "cycle" for frequency but not for angular frequency or angular velocity. NebY (talk) 20:03, 11 December 2022 (UTC)

I read the SI brochure the same as you do, NebY. But given that it is only an acknowledgement and that the standards bodies seem to be progressively standing back from dictating anything about this, I think I should walk back my hard-line interpretation. If we adopt this approach, it has implications on what we say about these as units, and in particular that no article should treat "cycle" etc. as definitively a unit of angle (or any given quantity). It would help to highlight the conflicting variations of usage of these unstandardized units in our articles if possible. —Quondum 00:41, 12 December 2022 (UTC)

References

Creation of article for First Light Fusion

Please excuse my ignorance putting this here. I came across a Youtube video about First Light Fusion's project (Their website) and wanted to look up what their progress was from a hopefully unbiased Wikipedia point of view. Wikipedia searches seem to suggest there is a little about them in Fusion power but not much. If I understand correctly, they are going down a unique path and have made a reasonable amount of progress. It appears that they achieved fusion in 2022. I am thinking this is an article that needs creating but I am not confident to do so myself with this being a complex topic and I only have an amateur understanding on the subject material. Is this a suitable article for yourselves to create?

I think the article should be created by someone, if this is not the place and you are not the group to request it from, can anyone point me in the right direction? Many thanks GQsm ^{Talk | c} 16:21, 21 December 2022 (UTC)

It is not the function of Wikipedia to report on the latest developments in physics or any other field. We only cover material for which there are reliable secondary sources. That is, the original research must be published in a form which is subject to peer review and then, when the community accepts it as probably true, covered by review articles (the "secondary" sources, also peer reviewed) or other encyclopedias ("ternary" sources). So asking us to cover it is quite premature. Come back in a few years. JRSpriggs (talk) 17:20, 21 December 2022 (UTC)

There are numerous mentions within Wikipedia, including at the dab page First Light. A redirect or two is surely warranted right now. Inertial fusion power plant mentions it as an example, Department of Engineering Science, University of Oxford lists it as one of its spin-offs, and Fusion rocket includes a somewhat gratuitous external link. Fusion power, Ronald A. Roy, and Zap Energy also have mentions. There is plenty of peer-reviewed papers, and the company First Light Fusion Ltd exists. I think there's probably enough there for an article if someone wanted to give it a try. Or maybe just expand a little at somewhere like Inertial fusion power plant with a plan to possibly split it out later. Lithopsian (talk) 17:39, 21 December 2022 (UTC)

Disambiguation of links to Interaction

Could you help to disambiguate some of the links to Interaction? This list shows the 200+ articles with links to the disambiguation page. It would help readers to link to a more specific article. Some are chemistry related and others biology, physics, mathmatics or other sciences. Any help with sorting these out would be appreciated.— Rod ^talk 12:39, 22 December 2022 (UTC)

Inconsistencies related to mechanical energy

The following paragraph was inserted at Conservation law#Approximate laws on November 13. (See the diff.)

There are also conservation laws which appear approximate, but only because microscopic details are neglected. For instance, the conservation of mechanical energy was often considered to be non-exact because forces such as friction appear to convert mechanical energy into other forms. However, a close inspection of friction reveals that only conservative forces are involved (electromagnetic forces), and the heat energy produced by friction is actually mechanical in nature (in the form of kinetic and potential energy). In this manner, it was realized that mechanical energy, as defined as the sum of kinetic and potential energies, is in fact fully conserved in all circumstances. It is only macroscopic energy which is not. Source: The Feynman Lectures on Physics

This text was posted in one of a number of recent edits by Logic314. (Logic314 has attributed the edits to the Feynman Lectures on Physics, Volume 1. I don’t have a copy.) This paragraph is inconsistent with a number of Wikipedia articles that have Top importance on the project’s importance scale. Here are five examples:

In Mechanical energy Wikipedia says "The principle of conservation of mechanical energy states that if an isolated system is subject only to conservative forces then the mechanical energy is constant." In contrast, in the new paragraph quoted above, Wikipedia now says “In this manner, it was realized that mechanical energy, as defined as the sum of kinetic and potential energies, is in fact fully conserved in all circumstances”.

In Conservative force Wikipedia says the total work done by a conservative force in moving a particle between two points is independent of the path taken; Wikipedia also says frictional force is an example of a non-conservative force. In contrast, in the new paragraph quoted above, Wikipedia now says “a close inspection of friction reveals that only conservative forces are involved (electromagnetic forces), and the heat energy produced by friction is actually mechanical in nature (in the form of kinetic and potential energy). ... mechanical energy ... is in fact fully conserved in all circumstances ...“

In Friction Wikipedia says “Friction is a non-conservative force – work done against friction is path dependent. In the presence of friction, some kinetic energy is always transformed to thermal energy, so mechanical energy is not conserved.” In contrast, in the new paragraph quoted above, Wikipedia now says “forces such as friction appear to convert mechanical energy into other forms. However, a close inspection of friction reveals that only conservative forces are involved (electromagnetic forces), and the heat energy produced by friction is actually mechanical in nature (in the form of kinetic and potential energy). ... mechanical energy ... is in fact fully conserved in all circumstances ...“

In Inelastic collision Wikipedia says “An inelastic collision, in contrast to an elastic collision, is a collision in which kinetic energy is not conserved due to the action of internal friction.” In contrast, in the new paragraph quoted above, Wikipedia now says “a close inspection of friction reveals that only conservative forces are involved”. The implication appears to be that all collisions are elastic because mechanical energy is always conserved.

In First law of thermodynamics Wikipedia explains that when a body absorbs sensible heat or latent heat, its internal energy increases, regardless of whether the source of the heat is friction, combustion, electric current etc. In contrast, in the new paragraph quoted above, Wikipedia now implies that when a body absorbs heat generated by friction, its microscopic mechanical energy increases to match the reduction in macroscopic mechanical energy so that mechanical energy is conserved. Logic314 has not mentioned internal energy so it is unclear to me how Feynman describes the energy absorbed by a body as a result of combustion or an electric current. The first law of thermodynamics is intimately connected to the concept of internal energy.

Logic314 appears to believe their edits represent a profound change to Wikipedia’s coverage of the subject, and Feynman’s view on this matter is an amazing discovery. I disagree because Logic314’s edits merely alter the definition of the mechanical energy of a body so that, as well as macroscopic kinetic and potential energies, it also includes sufficient of the body’s internal energy that mechanical energy is conserved even in the presence of friction, and therefore friction can be declared a conservative force. Logic314’s law of conservation of mechanical energy is little different to Wikipedia’s law of conservation of energy. Logic 314 has conceded that point because they have written “When everything is considered, conservation of mechanical energy is a complete exact conservation law, and is in fact equivalent to the full conservation of energy”. See Logic314’s diff.

The limited applicability of the principle of conservation of mechanical energy plays an important role in mechanics, particularly for students. It is important for students to realize that conservation of mechanical energy is a principle that is very easily applied quantitatively, but it is only applicable when all forces are conservative. When a non-conservative force is at work, we must rely on conservation of Momentum which is usually the next topic to be studied. Students are entitled to ask "If mechanical energy is always conserved, why do we need conservation of momentum?"

I have challenged some of the edits made by Logic314. See my diff 1 and diff 2. In particular, see Logic314's explanation at Talk:Conservation law#Conservation of mechanical energy. Logic314 has not returned to this topic for more than a week so I am raising the matter for consideration by the Physics community.

The question for the Physics community is What should be done about the inconsistencies introduced by Logic314’s edits at Conservation law?

1. Should we ignore the inconsistencies?
2. Should we establish a project to adjust other articles such as Mechanical energy, Conservative force, Friction, First law of thermodynamics to make them consistent with Feynman and Logic314’s recent edits?
3. Should we adjust the text posted by Logic314 to make it an alternative viewpoint about conservation laws rather than the one-and-only explanation of conservation of mechanical energy, thereby giving it due weight but not undue weight?
4. Should we revert Logic314's edits at Conservation law? Dolphin (t) 02:55, 22 November 2022 (UTC)

Disregarding sources for now, from a physicist's standpoint the theories you apply depend on the context. On a human scale, conservation of mechanical energy is approximately true (or sometimes even just not true at all). At the atomic/subatomic level, as Logic314 points out, conservation of mechanical energy holds true since mechanical energy is redefined to include all energy. Therefore, on articles where "mechanical energy" is defined as ${\frac {1}{2}}mv^{2}+V({\overrightarrow {r}})$, the law holds approximately true no questions asked. On articles where "mechanical energy" is defined as $<\psi |{\hat {H}}|\psi >$ then yes, the law is absolute.

To answer your question then using this framework - the article mechanical energy should be kept as is, especially as the article has an entire section named "conversion". Friction is explicitly about the macroscopic phenomenon and hence should also be kept as is. The first law of thermodynamics relies on the concept of temperature (hence heat energy) as separate from mechanical work, hence it should also be kept as is. Conservative force is a bit more iffy, because it's hard to say if you can even define a force at the relevant scale.

Overall, therefore, I suggest we modify Logic314's original version to make it clear that there are two different definitions of mechanical energy being operated under (and I believe Feynman does make it clear that he doesn't mean all energy when he talks about mechanical energy in anywhere else but the relevant semantic curiosity). @Logic314 Fermiboson (talk) 18:47, 22 November 2022 (UTC)

If you define "mechanical energy" so broadly as to encompass everything including relativistic mass-energy, then the conservation of "mechanical energy" is as exact as the conservation of energy. I don't think that's a particularly profound statement. What matters is explaining the concepts (heat is the jiggling of molecules, etc.), not the presence or absence of a particular adjective on a certain page of a specific book. I think that most instances of "mechanical energy" in physics writing would mean "the kinetic and potential energy of macroscopic bodies due to their bulk behavior", i.e., not including heat, chemical bonding, etc. My impression of introductory thermodynamics texts is that they contrast "heat" and "work" or "mechanical work". But that's not a hard-and-fast rule by any means. XOR'easter (talk) 21:09, 3 December 2022 (UTC)

@Fermiboson, Caltech has kindly put the Feynman Lectures online. Section 14-4 of Volume I is titled "Nonconservative forces" (Section 14-3 is "Conservative forces"), and doesn't mention "mechanical energy" at all, or refer to "macroscopic" energy. The conclusions in the paragraph added above are the conclusions of the editor, not Feynman. I think the edit could be reverted. StarryGrandma (talk) 00:14, 4 December 2022 (UTC)

I support reversion. Xxanthippe (talk) 00:19, 4 December 2022 (UTC).

It seems to me that undergraduate mechanics texts (e.g., David Morin's Introduction to Classical Mechanics), as well as sources aimed at a broader audience, define mechanical energy or total energy as the sum of kinetic and potential energy and do not mention internal energy. Although I have not exhaustively cross-referenced or studied Feynman's lectures in detail, it appears that these changes reflect a minority viewpoint – WP:UNDUE weight – and thus I also support reversion. Nonetheless, a cited endnote mentioning this alternate definition could be appropriate; using endnotes to clarify nuances, exceptions, or less widespread viewpoints is fairly common practice. ^Complex/_Rational 02:42, 4 December 2022 (UTC)

This is not an undue issue because, as XOR mentioned, it's fairly obvious once you make the underlying assumptions known. It's just not an assumption that people generally make. I think @ComplexRational's solution is a good one. In any case, it's been more than a week, so any dispute should have petered out. Fermiboson (talk) 10:33, 4 December 2022 (UTC)

This discussion thread has been in existence for 5 weeks. The consensus is that the paragraph in question is problematical and should be removed. For example, the cited source (Feynman) does not define or use the expression “mechanical energy”, and does not mention “macroscopic energy”.

I will remove the offending paragraph and give consideration to an endnote that will explain Feynman’s explanation of how friction can be considered a conservative force. Dolphin (t) 08:29, 27 December 2022 (UTC)