The dictionary definition of OV at Wiktionary (also ㍵) says:

• (ōbui)

1. unit of basal body temperature, 0 being 35.5 °C and 50 being 38 °C, used for fertility awareness

However Wiktionary has no references. I cannot find references elsewhere. Maybe they exist but searching for "OV", especially when including "ovulation" gives many false positives. Can you find a reference for the existence and meaning of this unit, preferably in a language I can understand, such as English or Spanish? I guess most references are in Japanese, that I don't understand. -- Error (talk) 10:44, 8 July 2024 (UTC)[reply]

"*Women's thermometers use the "OV value" so that slight changes in body temperature can be read."

"This is a value that divides the range of 35.5 to 38.0°C into 50 equal parts."

Original source: [1]

Translated source:[2] OptoFidelty (talk) 01:06, 10 July 2024 (UTC)[reply]

It was rejected as promotional material. --Error (talk) 23:46, 10 July 2024 (UTC)[reply]

I learned of the "hillocks of Hiss" from the wikipedia article on Tubercle Tubercle#Ears

From looking at other sources, I see they're also spelt "hillocks of his" -- What I cannot find out, and what I'm asking y'all is, *why* they are called 'Hiss/His' are they named for a person?140.147.160.225 (talk) 12:02, 8 July 2024 (UTC)[reply]

Presumably named for Wilhelm His Sr. or Wilhelm His Jr.. --Amble (talk) 16:47, 8 July 2024 (UTC)[reply]

In a book on the pathophysiology of orbital diseases I found this sentence:^[3]

In 1868, Hiss demonstrated that shortly after gastrulation, a different type of cell was formed between the ectoderm and the paraxial mesoderm on both sides of the neural tube.⁹

I bet this is the same His(s) as that of the hillocks. Given their bios, this would then be His Sr. The reference 9 is to the textbook Human Embryology, for which the restrictive snippet view fails to reveal more, but the 1868 publication is almost certainly Untersuchungen über die erste Anlage des Wirbelthierleibes.  --Lambiam 17:23, 8 July 2024 (UTC)[reply]

thanks so much Lambiam and Amble! -- any chance you could add a footnote or ref to the Tubercle article so future folks won't be as stymied as I was? 140.147.160.225 (talk) 12:04, 9 July 2024 (UTC)[reply]

I found this further confirmation:

The most important theory arose in 1855 when Wilhelm His named six cartilaginous hillocks as the original auricular structures.

Source: Jack Davis (1997). Otoplasty. Springer, p. 24. ISBN 978-1-4612-7484-1.

You should be able to add a footnote (with ref) to the Tubercle article yourself.  --Lambiam 14:36, 9 July 2024 (UTC)[reply]

Now done, also added to the His Sr article. Alansplodge (talk) 13:24, 10 July 2024 (UTC)[reply]

If aliens took a spherical Kuiper belt object with the composition of Saturn's highest-water-content ring and the perihelion of Pluto, and reshaped it into a cube, how massive would it have to be for humans to detect the shape change before gravity reverted it? NeonMerlin 05:49, 10 July 2024 (UTC)[reply]

Sounds like one for Randall Munroe. 41.23.55.195 (talk) 06:04, 10 July 2024 (UTC)[reply]

There are two sensible ways how the shape could be detected: a light curve or an occultation. A light curve uses the fact that for a non-spherical shape (or a spherical shape with non-uniform albedo) the brightness varies as the object spins on its axis. Professional telescopes have other things to do than collecting light curves of KBOs, but if this thing is at least around 500 km in size, it gets into range of bigger amateur telescopes. Some of those occasionally take light curves of some KBOs. But you can't really prove a cubical shape this way, as the light curve can also be explained with a funny albedo variation.

An occultation happens when this object passes in front of a background star. Multiple observers on the ground on Earth can detect the exact times when the star disappears behind the KBO and reappears later. With enough observations, one can see the silhouette of the KBO and confirm it's cubical. Around 10 observers in the occultation path, the width of which equals the diameter of the KBO, should be enough. The KBO doesn't have to be bigger than 50 km or so. Those observers are typically amateur astronomers, whose telescopes don't need to be big enough to see the KBO; seeing the background star with sufficiently short integration time (sub-second) is enough. The difficulty is knowing the orbit of the KBO accurately enough to predict the occultation and finding enough telescopes in the occultation path. PiusImpavidus (talk) 08:51, 10 July 2024 (UTC)[reply]

If I drank a 0,5 l bottle of 5,3% beer and another 0,5 l of a 4,9% beer, would it be correct to say that I drank 1 litre of 10,2% beer from physiological and chemical perspective? 212.180.235.46 (talk) 07:48, 10 July 2024 (UTC)[reply]

No, not from any perspective, physiological, chemical, or mathematical. You don't add the percentages, you take the mean. (5.3 + 4.9) / 2 = 5.1% by volume. AndyTheGrump (talk) 08:00, 10 July 2024 (UTC)[reply]

But, you can't exactly take the mean of the percentage-by-volume, because the mixture of ethanol and water causes a nonlinear volumetric change... For example, our article about alcohol by volume states: "The phenomenon of volume changes due to mixing dissimilar solutions..." is its partial molar property. The volume change is small, but non-zero... and it makes the ABV of the mixed drink non-equal to the arithmetic mean of its constituent ingredients. Our universe is amazingly complicated! Nimur (talk) 16:56, 10 July 2024 (UTC)[reply]

However, if the bottles are marked with their alcohol content in Alcohol units, you can add those. {The poster formerly known as 87.81.230.195} 151.227.226.178 (talk) 14:47, 10 July 2024 (UTC)[reply]

The formulas given at Standard drink § Calculation of pure alcohol mass in a serving ignore the nonlinearity, though. They are equivalent to taking the average ABV percentage (weighted by volume) and using that for the sum of the volumes.  --Lambiam 20:31, 10 July 2024 (UTC)[reply]

But is the inaccuracy significant in the context of people drinking (say) beer in pints and halves and estimating their likely degree of insobriety? Personal physiological factors are likely (in my experience as a trained beer drinker (really!)) to outweigh the physical chemistry aspects. {The poster formerly known as 87.81.230.195} 94.6.82.201 (talk) 06:56, 11 July 2024 (UTC)[reply]

I will ignore the mass/volume difference of alcohol and water. So assume that a liter is a kilogram, and alcohol by volume equals alcohol by mass.

0.5 liters of 5.3% alcohol contains 0.0265 liters of alcohol. 0.5 x 0.053 = 0.0265.

0.5 liters of 4.9% alcohol contains 0.0245 liters of alcohol. 0.5 x 0.049 = 0.0245.

So 0.0265 + 0.0245 = 0.051 liters of alcohol. You had three and a half tablespoons of alcohol.

If you drink one liter of 10.2% alcohol, you consume 0.1 liters of alcohol. Tenth of a liter is a deciliter, right? Which is twice the amount of your two pints above.

In practice, effects of alcohol intake will depend on things like how quickly you gulp the beer vs. hard spirits, how often you will need to drain the weasel, and such.

(Which is AndyTheGrump correctly said above; just showing the math.) 85.76.166.151 (talk) 16:34, 11 July 2024 (UTC)[reply]

The laws of gravity are presumably the same throughout the universe: the force is proportional to the product of the masses and inversely proportional to the square of the distances. So why do we observe very different structures at different scales? Solar systems involve a few discrete objects orbiting a sun, galaxies have various shapes but often spirals, and then over larger distances the distribution of galaxies is like a 3-D network of filaments. I believe that simulation models can produce all these different structures, but I am hoping for some intuitive explanation of why the different outcomes. One possibility might be that things happen relatively faster over small distances, and that the universe would also develop into something like a giant solar system given more time. Another possibility is that some processes happening only at the local scale (e.g. nuclear fusion in stars) interfere with what would happen if gravity alone were operating. Or is it something else entirely? Thanks. JMCHutchinson (talk) 12:01, 11 July 2024 (UTC)[reply]

The small-scale stuctures, such as the discrete objects in solar systems and the spiral structure of galaxies (even the disk itself) arise due to non-gravitational processes. When a cloud of ordinary (baryonic) gas collapses its density and temperature increase and it gives off an increasing amount of electromagnetic radiation, this leads to a loss of energy (radiative cooling) that speeds up the collapse and leads to the formation of small-scale structures. Dark matter, which is only subject to gravity, does not do that and there is no comparable small-scale structure in the dark-matter distribution. There are purely gravitational cooling mechanisms such as violent relaxation but they are much less effective than radiative cooling and operate on larger time scales. The time since the Big Band has been sufficient for galaxies and clusters of galaxies to form (less massive objects form first, more massive objects later), but not yet for objects on larger mass scales (superclusters exist but they are not bound objects yet). This is the reason why matter on the largest scales is organised in filaments but not in bound, more or less spherical objects. Finally, the presence of dark energy and the consequent accelerating expansion of the Universe set an upper limit to the mass of bound objects that will ever form — I don't know what that limit is but I guess it is in the supercluster range. --Wrongfilter (talk) 12:27, 11 July 2024 (UTC)[reply]

This is a very clear answer and exactly what I wanted. Thanks! JMCHutchinson (talk) 17:20, 11 July 2024 (UTC)[reply]

Hi. I've noticed that the term "neuroplastic pain" has 700 thousand hits on Bing search, but there is no article or redirect for it on Wikipedia. However, it seems similar to nociplastic pain, but I'm not completely sure. Is here anyone with medical background who could confirm/decline this? --Pek (talk) 16:35, 11 July 2024 (UTC)[reply]

It seems to be an incipient medical term, with 107 Google Scholar results. Just glancing down the squibs Google provides shows that it is listed separately, for instance, "Nociplastic pain is hypothesized to differ from nociceptive and neuroplastic pain...". Neuroplastic pain appears to be a sequela of neuropathic pain. The results from the Google Scholar and regular searches show a lot of scammy stuff, and I worry that creating a redirect (to neuropathic pain) may be a bad idea. Conversely, without good sourcing, an article may be impossible to create at this time. I would take this to WT:WikiProject Medicine. Abductive (reasoning) 21:36, 12 July 2024 (UTC)[reply]

Our article Velocity factor states: The velocity factor...is the ratio, of the speed at which a wavefront (of an electromagnetic signal)...passes through the medium, to the speed of light in vacuum. So it seems that the velocity of an electromagnetic wavefront does depend on the medium.

However, our article Front velocity states: The earliest appearance of the front of an electromagnetic disturbance (the precursor) travels at the front velocity, which is c, no matter what the medium. Similarly, our article Wavefront states: Wavefronts travel with the speed of light in all directions in an isotropic medium. So it seems that the velocity of an electromagnetic wavefront does not depend on the medium.

I wonder whether this is a contradiction between our articles (if so then how should they be corrected?), or - probably - I miss something here (if so then what do I miss?)... HOTmag (talk) 21:00, 11 July 2024 (UTC)[reply]

I have corrected the sentence in wavefront — the article talks about waves in general, not specifically about electromagnetic waves (in which case it should have been the speed of light in the medium). The "front" discussed in front velocity is not the same thing as a wavefront (= a surface of constant phase) but, as in your quote, the earliest appearance of an electromagnetic disturbance (again one could talk about non-em disturbances but we won't). For instance, some switches on a lightbulb a distance ${\displaystyle s}$ from me. The question is "At what time can I know the lightbulb is on?" and the answer is ${\displaystyle s/c_{\mathrm {vac} }}$. The reasoning is that because this is a discontinuous signal (the mathematical formulation involves the Heaviside function) the spectrum of the signal includes all frequencies, in particular very high ones. In most (any?) media the refractive index approaches 1 for very high frequencies, i.e. the propagation speed approaches the vacuum speed of light for high frequencies. Therefore, the high-frequency part of the signal arrives first, and the bulk of the signal later. Due to this dispersion, the temporal/spatial shape of the wave signal changes as it propagates (think of what sound does on a frozen lake). --Wrongfilter (talk) 05:52, 12 July 2024 (UTC)[reply]

Thank you for correcting our article Wave front.

Regarding our article Front velocity: As opposed to other readers (including me), you've understood that it refers to a beam of light containing the whole spectrum. However, if the beam of light contains, not the whole spectrum, but e.g. two types of waves only, e.g. red and blue, then the front velocity of this beam of light does depend on the medium, right?

Here is the full quote, from our article Front velocity: the wave discontinuity, called the front, propagates at a speed less than or equal to the speed of light c in any medium. In fact, the earliest appearance of the front of an electromagnetic disturbance (the precursor) travels at the front velocity, which is c, no matter what the medium.

Is the claim in this quote correct, as far as my red-blue example mentioned above is concerned? In my example, "the earliest appearance of the front" of this electromagnetic disturbance is the appearance of the blue wave, right? If it is, then shouldn't the paragraph be corrected, for all readers to understand that it only refers to a beam of light containing the whole spectrum? HOTmag (talk) 08:55, 12 July 2024 (UTC)[reply]

The spectrum is the Fourier transform of the disturbance. A discontinuous disturbance has signal at all frequencies, not just "red" and "blue". These things are not independent. --Wrongfilter (talk) 09:16, 12 July 2024 (UTC)[reply]

Got it, thank you.

So, If I want the value of the speed of light to be independent of medium, I must refer to the front velocity of a beam of light containing the highest frequencies possible, right?

If your answer is positive, then how can the formula ${\displaystyle p=\gamma mv}$ be justified, when applied to a red light moving in water? In this case, ${\displaystyle v<c,}$ so ${\displaystyle \gamma }$ is a finite number, while ${\displaystyle m=0,}$ so according to this formula, we get ${\displaystyle p=0,}$ which is false...

I'm pretty confused now. Unless no mass is allowed to be attributed to the light, not even a zero-mass, so my last question will vanish. Am I right? HOTmag (talk) 10:14, 12 July 2024 (UTC)[reply]

I'm not letting myself get drawn into the mass debate again. Light is complicated, light in matter is even more complicated. If you want the momentum of a photon, use ${\displaystyle \hbar k}$. --Wrongfilter (talk) 10:25, 12 July 2024 (UTC)[reply]

Thank you. What about my only question still left, in my second sentence? "If I want the value of the speed of light to be independent of medium, I must refer to the front velocity of a beam of light containing the highest frequencies possible, right?" HOTmag (talk) 10:53, 12 July 2024 (UTC)[reply]

I don't see the point of that sentence. Why would you "want the value of the speed of light to be independent of medium"? The front velocity looks like an interesting theoretical curiosity with little actual physical relevance. --Wrongfilter (talk) 11:13, 12 July 2024 (UTC)[reply]

I've only wanted to know if, the only way to define the well known speed of light - usually denoted by c - must rely on the vacuum, or the speed of light can also be defined without the concept of vacuum? Assuming we don't want to define it numerically (299,792,458 m/s), nor by ratios between other physical constants.

So according to your previous clarifications, I thought that perhaps the speed of light could be defined as the front velocity of a beam of light containing the highest frequencies possible... HOTmag (talk) 12:39, 12 July 2024 (UTC)[reply]

You are perhaps falling into the trap of thinking that the speed of light in a vacuum, c, is determined by a property of light (in the sense of e-m radiation). It is not: it is (as a limit) a fundamental property of Spacetime, to which light and everything else (though not spacetime itself) has to conform, including other massless 'particles' which must perforce travel at it in a vacuum. It just so happens that it is easiest to observe (and measure) using light, and was thus discovered and named. Or so I understand the matter. {The poster formerly known as 87.81.230.195} 94.6.82.201 (talk) 07:37, 13 July 2024 (UTC)[reply]

Oh, of course I've always knwon that c is just a limit being a fundamental property of Spacetime. But instead of using the complicated expression: "a limit being a fundamental property of Spacetime", I used the common term "speed of light", as most people do (including you - as I guess), just for the sake of convenience and simplicity. That said, I only asked if this limit - which I called "the speed of light" for the sake of convenience and simplicity, could be defined - without the concept of vacuum - as the front velocity of a beam of light containing the highest frequencies possible. HOTmag (talk) 22:33, 13 July 2024 (UTC)[reply]

According to the uncertainty principle the electron has a momentum :
${\displaystyle \Delta p_{e}={\tfrac {h}{4\pi \Delta x_{e}}}{\text{ , }}}$
${\displaystyle \Delta x_{e}=10^{-10}{\text{m (can be found from liquid hydrogen density)}}}$ .

To conserve the atom momentum zero , the proton must have a momentum  :
${\displaystyle \Delta p_{p}=-\Delta p_{e}}$.
So ${\displaystyle \Delta x_{p}=\Delta x_{e}}$ and the proton must also smear to atom's full size.

But Rutherford scattering experiment shows that a size of a nucleus is ${\displaystyle 10^{5}}$ smaller. Why does the uncertainty principle fail? — Preceding unsigned comment added by U240700 (talk • contribs) 08:54, 12 July 2024 (UTC)[reply]

You seem to be confusing the (expectation) values of the momenta and their uncertainties. Conservation of momentum demands ${\displaystyle \langle p_{p}\rangle =-\langle p_{e}\rangle }$ and says nothing about the uncertainties. --Wrongfilter (talk) 09:24, 12 July 2024 (UTC)[reply]

Uncertainty ${\displaystyle \Delta p_{e}}$ means that ${\displaystyle p_{e}}$ can take any value within ${\displaystyle \Delta p_{e}}$. So taking the intervals like ${\displaystyle p_{e}=0{\text{ ... }}\Delta p_{e}}$ or ${\displaystyle p_{e}=0.5\Delta p_{e}{\text{ ... }}1.5\Delta p_{e}}$ is suitable for the order of magnitude. U240700 (talk) 12:19, 12 July 2024 (UTC)[reply]

The total momentum in quantum mechanics is conserved meaning that

${\displaystyle {\hat {\mathbf {p} }}_{e}+{\hat {\mathbf {p} }}_{p}=0}$,

or

${\displaystyle <({\hat {\mathbf {p} }}_{e}+{\hat {\mathbf {p} }}_{p})^{2}>=(\Delta \mathbf {p} _{e})^{2}+(\Delta \mathbf {p} _{p})^{2}+2<\Delta {\hat {\mathbf {p} }}_{p}\Delta {\hat {\mathbf {p} }}_{e}>=0}$.

This equality holds because electron and proton momentums are anticorrelated. Ruslik_Zero 21:00, 12 July 2024 (UTC)[reply]

Last equation confirms only that ${\displaystyle \Delta p_{p}=-\Delta p_{e}}$. How does it prove or disprove ${\displaystyle \Delta x_{p}=\Delta x_{e}}$? U240700 (talk) 00:54, 13 July 2024 (UTC)[reply]

Your value ${\displaystyle \Delta x_{e}}$ comes from a different experiment, not Rutherford's, and is therefore not relevant here. It applies, for instance, to a measurement of the average charge density in an atom. This would be a low-energy experiment, taking care not to disturb the electronic structure of the atom. The uncertainty principle does not stop you from setting up an experiment to measure the instantaneous position of an electron more precisely, but the concomitant momentum uncertainty would likely ionise the atom. Rutherford's alpha particles had energies in the MeV range, if I'm not mistaken, much higher than the binding energies of electrons in atoms. They could in principle — I don't know how, and Rutherford's experiment is certainly not set up to do so — be used to locate electrons to much smaller ${\displaystyle \Delta x_{e}}$ than the value you give. --Wrongfilter (talk) 03:53, 13 July 2024 (UTC)[reply]

I have no questions for ${\displaystyle \Delta x_{e}}$, I have a question for ${\displaystyle \Delta x_{p}}$. The proton is located in center of atom in very small boundaries (${\displaystyle 10^{-15}{\text{ m}}}$) . It violates the uncertainty principle. The proton must be smeared over ${\displaystyle 10^{-10}{\text{ m}}}$ and (like the electron) be detected (materialized) everywhere , not just in center. U240700 (talk) 06:57, 13 July 2024 (UTC)[reply]

Okay, like you I got too hung up on the location of protons and electrons. The Rutherford experiment does not actually measure the location of nuclei, it measures their size. The experiment does not tell you where the nuclei are (not even in relation to their electron shell). Putting them at the centre of atoms is subsequent model building. --Wrongfilter (talk) 09:14, 13 July 2024 (UTC)[reply]

The momenta of the proton and electron are only equal and opposite if the total momentum of the atom is zero. In that case, the position of the atom is completely indeterminate. In order for the atom to be localized, it must have some uncertainty in the total momentum, which means that you can't equate the momentum uncertainties of the proton and electron in this way. The proton can have a larger momentum uncertainty, and a smaller position uncertainty, than the electron. (Note also that the uncertainty principle is an inequality, and it's worth calling out that the ground state is a minimum uncertainty state.) --Amble (talk) 00:35, 16 July 2024 (UTC)[reply]

Rutherford scattering experiment did not actually measure the position of nucleus. It only measured differential cross-section, which appeared to be one of a point-like charge. Where this nucleus is located is absolutely irrelevant. Ruslik_Zero 20:20, 18 July 2024 (UTC)[reply]

What procedure did Anders Gustaf Ekeberg use to isolate metallic tantalum? Double sharp (talk) 09:11, 13 July 2024 (UTC)[reply]

If you can read Swedish, I think this is the original publication in which Ekeberg announced his discovery of tantalum. If you can't, maybe someone who knows Swedish and has some familiarity with the terminology of analytical chemistry will be kind enough to summarize the procedure, which I think is described in the later half of the article; on p.78 I see Detta nya metallämnet ("this new metallic substance").  --Lambiam 11:26, 13 July 2024 (UTC)[reply]

Unfortunately, the Scandinavian languages are something I never looked deeply into. Though it's starting to seem clear that I'm going to need to look into Swedish to study this period of chemical history. :) Double sharp (talk) 12:19, 13 July 2024 (UTC)[reply]

This ref:

• Ekeberg, Anders (1802). "Of the Properties of the Earth Yttria, compared with those of Glucine; of Fossils, in which the first of these Earths in contained; and of the Discovery of a metallic Nature (Tantalium)". Journal of Natural Philosophy, Chemistry, and the Arts. 3: 251–255.

might be an English translation (or at least contain discussion of it). DMacks (talk) 22:42, 13 July 2024 (UTC)[reply]

It is a strongly abridged extract of the second half of Ekeberg's article, referring to the newly discovered metal with the incorrrect name tantalium. It does not give the isolation procedure of the elemental metal but only some of its physical properties as well as chemical properties distinguishing it from tin, tungsten and titanium.  --Lambiam 09:37, 14 July 2024 (UTC)[reply]

Boo:( DMacks (talk) 18:48, 14 July 2024 (UTC)[reply]

A German translation of the original paper is here. AstroLynx (talk) 19:29, 14 July 2024 (UTC)[reply]

{{ec}} If anyone wants to have a go at manual- or machine-translation from Swedish, I uploaded what en:tantalum and sv:tantal appear to identify as the original article as File:Ekeberg-1802.pdf. My naive first pass with Acrobat was able to do some extraction, but had trouble with some of the diacritical marks and correctly representing them in my system's font, and also gave too many disjointed text fields to make it bulk-selectable. DMacks (talk) 19:32, 14 July 2024 (UTC)[reply]

Thanks. The German translation AstroLynx points to can be copy-pasted from the generated PDF, so here's a somewhat cleaned-up reading of the relevant bit:

Dieser neue Metallstoff zeichnet sich durch seine Unauflöslichkeit in alle Säuren, wie man ihn auch mit denselben behandelt, aus. Das einzige Auflösungsmittel, das ich auf denselben wirksam gefunden habe, ist das ätzende fixe Laugensalz, so daß, wenn man das Erz mit demselben brennt, und das Gemenge mit Wasser auszieht, ein großer Theil in der laugensalzigen Lauge aufgelöst wird. Aus derselben kann er durch eine Säure gefällt werden, aber der Niederschlag wird nicht wieder aufgelöst, wie viele Säure man auch zugießen mag. Abgeseihet und getrocknet erscheint er als ein Pulver von ausgezeichneter Weiße, welche Farbe er auch beym Glühen behält. Wenn der Theil des gebrannten Klumpens, welcher von der laugensalzigen Lauge nicht aufgenommen ist, mit Säure ausgezogen wird, bleibt ein weißes Pulver von gleicher Beschaffensheit nach. Seine eigenthümliche Schwere, nach dem Glühen, war 6,500. Vor dem Blaserohre wird er leicht vom Borax und Phosphorsalze aufgelöst, gibt den Flüssen aber keine Farbe. Auf einem Heerde von Kohlengestäbe in einem Ziegel, ohne Zusaß der Hitze, welche zu einer Braunsteinprobe erfordert wird, ausgefeßt, untergeht er eine Art von Verfrischung, bey welcher er zu einem grünlich harten Klumpen zusammensiedet, welcher auf der Oberfläche einen metallischen Glanz hat, aber im Bruche nur matt glänzt und schwarze grün aussieht. Auf diesen haben Säuren keine weitere Wirkung, als daß fie ihn wieder zu der weißen Halbsäure verwandeln. Das Verhalten bey der Verfrischung und die eigenthümliche Schwere, gaben mir Anleitung, diesen besondern Körper unter die Metalle zu rechnen.

It sounds like the English abridgement omitted to notice the word Erz there. That makes the procedure sensible: it seems that Ekeberg converted the ore via alkaline digestion to Ta₂O₅ (certainly a mixture with Nb₂O₅, though he wouldn't know that), then attempted to reduce it with carbon. This actually should have a quite poor yield under his likely experimental conditions, but clearly, it was enough for him to draw the correct conclusion. I'm extremely impressed. (V, Nb, and Ta are quite a pain to reduce from the oxides to the elemental metals, especially if you want a reasonably pure product.) Double sharp (talk) 10:05, 15 July 2024 (UTC)[reply]

Was the grünliche harte Klumpen (impure) elemental tantalum? It is a pity Ekeberg did not give its specific mass, unlike for the ore, or other physical properties.  --Lambiam 18:04, 15 July 2024 (UTC)[reply]

"Get more energy out than you put in." (https://astronaerospace.com/) Is this legit? Has this been demonstrated or are they just good at making slick CGI animations (better than at spelling)? Thank you. Hevesli (talk) 16:33, 15 July 2024 (UTC)[reply]

I wasted several seconds looking at it. It's what we call a solidworks engine. take any positive displacement pump, add fuel and oxidiser, hey presto semi believable engine animation. The total absence of technical info in the youtube I saw is a bit of a giveaway. "Get more energy out than you put in." yeah and I've got a bridge to sell you. Greglocock (talk) 05:54, 16 July 2024 (UTC)[reply]

An exception might be a hydrogen bomb. ←Baseball Bugs ^{What's up, Doc?} carrots→ 06:17, 16 July 2024 (UTC)[reply]

I don't think the H-bomb is considered a "holy grail". The term has been used for nuclear fusion as a source of "clean energy", where the hope is that "we can obtain more energy than we put in".^[4] In this context, the wording "obtain more energy than is put in" is IMO somewhat justifiable: after all, E = mc² gives mass–energy equivalence, not mass–energy equality. Claiming to obtain more energy than is put in for combustion engines is not justifiable.  --Lambiam 13:03, 16 July 2024 (UTC)[reply]

Moved to here from the Mathematics section of the Reference desk —  --Lambiam 13:23, 16 July 2024 (UTC).[reply]

Julian day says that the next Julian period will begin in AD 3268. When representing dates after this period begins, do mathematicians/astronomers/etc. reset the date count to 1 in 3268, or do they continue incrementing dates unchanged from 3267? If this is answered in the article, I missed it. Nyttend (talk) 21:57, 15 July 2024 (UTC)[reply]

I'm not convinced this is a math question, so perhaps it should be migrated to the science or computing desk. Are there people who actually need to keep track of dates that far in the future? --RDBury (talk) 02:14, 16 July 2024 (UTC)[reply]

I would suggest asking the question again some time after the year, say, 3250, when the people in charge have started thinking about it. Personally, I would think that resetting would be rather inconvenient and serve no practical purpose. --Wrongfilter (talk) 12:21, 16 July 2024 (UTC)[reply]

nasa.gov already has free Julian astrometry to day ~5,373,483 (Anno Domini 9999, if they ever go to 9,999,999.999999999 you could get major solar system object positions till December 20th 22666 AD (a Thursday)). Sagittarian Milky Way (talk) 18:10, 16 July 2024 (UTC)[reply]

Wikipedia lists many observable astronomical events that will occur in the next Julian period, so presumably some astronomers are already thinking about it and may even have developed a convention. I don't know, though, whether they are "the people in charge".  --Lambiam 13:19, 16 July 2024 (UTC)[reply]

The people in charge would be one of the IAU commissions. --Wrongfilter (talk) 13:46, 16 July 2024 (UTC)[reply]

No resetting: the Julian date is a continuous count. The epoch is fixed to the beginning of the current Julian period, it doesn't float to the beginning of the Julian period of times in the distant future. See for example "The Julian and Modified Julian Dates" by Dennis McCarthy from the USNO: "The Julian day number (JD) is the number assigned to a day in a continuous count of days beginning with the Julian day number 0 assigned to the day starting at Greenwich mean noon on 1 January 4713 B.C., in the Julian calendar extrapolated backwards ('proleptic')." Similarly, if you look into the IAU's SOFA software, it uses a fixed epoch, and defines the range of valid dates for the conversion routines [5], [6]: "The earliest valid date is -68569.5 (-4900 March 1). The largest value accepted is 10^9." This shows the understanding that Julian dates corresponding to future Julian periods are expected to be counted from the current epoch, without resetting. --Amble (talk) 16:18, 16 July 2024 (UTC)[reply]

Could you find a specific citable source for no-reset? I'm uncomfortable citing the software, and I can't find the quote in McCarthy. Nyttend (talk) 21:44, 18 July 2024 (UTC)[reply]

The JPL Horizons On-Line Ephemeris System is software I guess but doesn't reset and uses the best ephemerides known to man (same ones the Astronomical Almanac uses) Sagittarian Milky Way (talk) 01:46, 19 July 2024 (UTC)[reply]

I'd recommend going with the McCarthy article and/or the IAU resolutions from 1997. For McCarthy, look in the last paragraph, just before the acknowledgements, pg. 330. [7] For the IAU resolutions, look at resolution B1 and the appendix here: [8]. --Amble (talk) 16:12, 19 July 2024 (UTC)[reply]

This is a small park on the Homer Spit. We mostly have Sitka Spruce as far as evergreens around here, so I suspect these are specimen trees, probably some kind of pine tree but I'm not sure what kind. They aren't very big but that may be because they are out of their usual range. Just Step Sideways ^{from this world ..... today} 20:37, 17 July 2024 (UTC)[reply]

Looks like shore pine. --Amble (talk) 22:30, 17 July 2024 (UTC)[reply]

After ec, shore pines? Mikenorton (talk) 22:32, 17 July 2024 (UTC)[reply]

That does seem likely, the needles and cones look the same. Just Step Sideways ^{from this world ..... today} 18:42, 18 July 2024 (UTC)[reply]

Scene in Laramie, Wyoming, USA. I'd like to put it into Commons categories for the trees along the street — particularly the big prominent one near the centre — but I don't know anything about this kind of thing. Nyttend (talk) 08:04, 18 July 2024 (UTC) PS, I was guessing blue spruce for the big one at the centre, but the shape is quite different from those of the trees pictured in that article. Nyttend (talk) 08:20, 18 July 2024 (UTC)[reply]

A zoom-in on the image shows some distinctive spruce cones, and it is certainly blue-ish (Caveat: the blue spruce is an uncommon specimen tree in the UK and I'm not sure that I've ever seen one in person). Alansplodge (talk) 10:53, 18 July 2024 (UTC)[reply]

Speaking as a regular WP:Wikiproject Plants contributor, I would prefer that users didn't assign species categories to images such as this unless they were absolutely certain of the identification. Ideally, the image would include the label from the arboretum or botanical garden. Abductive (reasoning) 21:11, 20 July 2024 (UTC)[reply]

For deriving the Lorentz transformations, our article Derivations of the Lorentz transformations relies on their linearity. How do we know they must be linear? Our article answers: Since space is assumed to be homogeneous, the transformation[s] must be linear. I wonder, how their linearity is deduced from the homogeneity of space, before we've found how they will look like...

For the time being, I'm adding an Einsteinian source for this claim in the article, even though I don't know how Einstein derived this claim. HOTmag (talk) 23:41, 18 July 2024 (UTC)[reply]

The Lorentz transformations are linear transformations by definition. The linearity comes from their domain being a linear "Newtonian" spacetime isomorphic to the product of Euclidean 3-space and a linear time axis.  --Lambiam 09:48, 19 July 2024 (UTC)[reply]

Thanks. However, rather than assuming linearity - from the very beginning (as you do), Einstein's claim I've quoted from our article - derives linearity - from the homogeneity of spacetime. My question was: how can the quote be justified. HOTmag (talk) 10:02, 19 July 2024 (UTC)[reply]

This is the article in which Einstein introduced the special theory of relativity. His spacetime is flat, and the reference frame of a stationary observer is basically the same as for Lorentz, so space is an Euclidean 3-space. The "homogeneity" is that the laws of physics are invariant under an isometric transformation of space. Just homogeneity is not enough; to reach the conclusion, the flatness is essential.  --Lambiam 00:19, 20 July 2024 (UTC)[reply]

Let's assume that the space is flat, and that the laws of physics are invariant under an isometric transformation of space. How do you infer from these assumptions, that the Lorentz transformations (which are actually not isometric) are linear? This is what I can't understand yet... HOTmag (talk) 18:35, 20 July 2024 (UTC)[reply]

So I get that in around 100 billion years, our observable universe will be limited to the Local Group due to Hubble expansion (bummer), but would that include the Virgo Cluster? Some sources say that they would join due to gravity (https://astronomy.swin.edu.au/cosmos/V/Virgo+Cluster, https://en.wikipedia.org/wiki/Observable_universe) but I'm also reading responses saying the Hubble expansion is more powerful and therefore Virgo would end up outside of the observable universe. I realize there a lot of variables that we don't know or could change. 184.96.249.124 (talk) 02:28, 19 July 2024 (UTC)[reply]

Virgo cluster is receding from us unfortunately. In 100 billion years it would be more than 300 million light years away. Ruslik_Zero 19:24, 19 July 2024 (UTC)[reply]

The fact that it is receding now does not necessarily imply that it will continue to recede forever. The Andromeda galaxy and the Milky Way once receded from each other but have by now turned around and are approaching each other. Every bound object (more exactly, "virialised object"), say a cluster or group of galaxies, has formed out of an initially expanding, but overdense region of the Universe that through the action of gravity has by now recollapsed (a "little crunch", if you will). Throwing a stone up in the air is a pretty good analogy: When I do that on earth, the stone will first move upwards (recede from me) but then it will invariably turn around and fall back down. When I do it on a sufficiently small asteroid, throwing the stone with the exact same force, it may well escape to infinity and never come back. What the analogy does not capture is the effect of Dark Energy, which prevents structures on very large scales from recollapsing, and, as I wrote in another recent thread, I do not know where the limit is. The article Laniakea Supercluster suggests that this structure is not bound, i.e. will not recollapse. You may want to have a look at the references therein. --Wrongfilter (talk) 08:44, 20 July 2024 (UTC)[reply]

Thank you but I know all of these. However it is well known that Virgo supercluster (as any supercluster) is not gravitationally bound. The present recessional velocity of the Virgo cluster is more that 1000 km/s. There is not nearly enough mass to even slow this expansion rate. If fact this velocity is already increasing due to the cosmic repulsion. Ruslik_Zero 21:11, 21 July 2024 (UTC)[reply]

I thought that natural immunity via infection from COVID was roughly comparable to immunity via vaccination. However, I just read this article, Study suggests reinfections from the virus that causes COVID-19 likely have similar severity as original infection, which seems to suggest that natural immunity via infection doesn't provide much protection - at least in regard to severe infections. Am I understanding the article correctly? A Quest For Knowledge (talk) 06:07, 19 July 2024 (UTC)[reply]

That would match the experience of people I know who've caught it twice. HiLo48 (talk) 06:12, 19 July 2024 (UTC)[reply]

I'm not sure the results of the study support a statement like "immunity via infection doesn't provide much protection - at least in regard to severe infections" given that only about "a quarter of individuals with either a moderate or severe first infection coinciding with hospitalization also were hospitalized at the time of reinfection", although the difference might not be due to their immune responses. Sean.hoyland (talk) 06:56, 19 July 2024 (UTC)[reply]

The unpredictability of viral infection and immune response at the individual level is quite impressive. I got an AstraZeneca shot, a Moderna shot about 6 months later and a Moderna booster 6 months after that or thereabouts and I didn't experience any symptomatic Covid infections, despite being surrounded by people with active infections quite often. Then finally, a couple of months ago, I had my first symptomatic SARS-CoV-2 infection. And despite having lived through decades of dengue seasons and thousands of mosquito bites in various places during dengue outbreaks without any symptomatic dengue infections, I had my first dengue infection a month after Covid. Hats off to scientists trying to make sense of these immensely complex systems. Sean.hoyland (talk) 07:47, 19 July 2024 (UTC)[reply]

SARS-CoV-2 is a quickly mutating virus with many variants. The immunity provided after infection by one variant is strongest for that specific variant. Evading immunity is a driving factor in the evolution of the virus, which is why we may expect recurring waves, as we are used to for influenza. Next to reinfection with a different variant, the immunity after infection or after vaccination wears off after a couple of months. I have taken all shots and booster shots as soon as they were made available, yet I have been symptomatic twice. Since the vaccines are developed mostly for specific variants, and one usually does not determine the specific variant responsible for the infection of a symptomatic patient, I doubt that there are studies that have determined whether vaccination provides the same level of protection as that after infection. I'm not sure, but so many factors play a role that I think it will be very difficult to collect the data necessary for drawing a conclusion.  --Lambiam 09:29, 19 July 2024 (UTC)[reply]

The immune system having a sort of predictive system via somatic hypermutation complicates matters. I think labs at La Jolla Institute for Immunology have done some work on comparing the immune responses to infection vs vaccination, immune memory etc. Sean.hoyland (talk) 09:57, 19 July 2024 (UTC)[reply]

See also COVID-19 immunity: Infection compared with vaccination (Feb 2022) from the British Society for Immunology. Alansplodge (talk) 10:49, 19 July 2024 (UTC)[reply]

HOTmag (talk) 12:44, 19 July 2024 (UTC)[reply]

It is locally linear but coefficients will depend on coordinates. Ruslik_Zero 19:29, 19 July 2024 (UTC)[reply]

Locally linear, so it's not linear. Thank you. HOTmag (talk) 18:15, 20 July 2024 (UTC)[reply]

https://en.wikipedia.org/wiki/Lorentz_transformation says Frames of reference can be divided into two groups: inertial (relative motion with constant velocity) and non-inertial (accelerating, moving in curved paths, rotational motion with constant angular velocity, etc.). The term "Lorentz transformations" only refers to transformations between inertial frames, usually in the context of special relativity. Greglocock (talk) 04:25, 20 July 2024 (UTC)[reply]

I'm not asking about the Lorentz transformations. HOTmag (talk) 18:16, 20 July 2024 (UTC)[reply]

I learnt in school that different types of elements can bond in different ways, like non-metal atoms bond covalently together while a non-metal atom with a metal atom bond ionically, but why is that? Also, what factor(s) determine why some elements (like hydrogen) share/transfer 1 electron, while others (like carbon and nitrogen) and share/transfer 2 or 3 electrons? Bestfweind (talk) 04:58, 20 July 2024 (UTC)[reply]

More than anything else, it's the number of valence electrons that each atom has, and the number that it needs. Hydrogen needs just one extra valence electron to have a full outer shell, so two hydrogens share a single electron. Nitrogen needs three, so two nitrogens share three electrons. Nyttend (talk) 07:00, 20 July 2024 (UTC)[reply]

Also, you may be thinking of common compounds such as table salt, sodium chloride, which involves an alkali metal (at the left end of the periodic table) and a halogen (near the right end). Like the other alkali metals, sodium has just one valence electron, so it's highly electropositive (ready to give up an electron), and like the other halogens, chlorine needs just one valence electron, so it's highly electronegative (ready to gain an electron), and it's extremely easy to create an ionic bond between atoms that are both highly electropositive/negative and that need to give/take the same number. Nyttend (talk) 07:06, 20 July 2024 (UTC)[reply]

The bond is better described as ionic when one atom is much more electronegative than the other. In something like table salt you can approximate the valence electron of Na as having passed completely to the Cl, although in reality it's not a complete transfer. Covalency happens when the electronegativities are similar. It is all a continuum from one to the other: Na–Cl will be more ionic than Li–Cl, which will in turn be more ionic than C–Cl.

The first-row elements B–Ne have a larger tendency towards multiple bonding than their higher homologues in lower rows, because their atoms are so small that non-bonding pairs of electrons result in significant repulsion. It's less of an issue for things like Al–Ar. Double sharp (talk) 07:24, 20 July 2024 (UTC)[reply]

Our Double bond rule is quite light on cited content for the concept itself, and gives (with cite, that I can't access) a different rationale. Please update if you've got a ref. DMacks (talk) 03:02, 21 July 2024 (UTC)[reply]

doi:10.1002/anie.198402721. I've updated the page. :) Double sharp (talk) 03:46, 21 July 2024 (UTC)[reply]

Thanks! I keep meaning to split up that hybrid (ha!) of an article, but obviously keep never getting around to it. DMacks (talk) 04:37, 21 July 2024 (UTC)[reply]

When there are evidence in support of Big Bang, why do people believe in God? CometVolcano (talk) 16:41, 20 July 2024 (UTC)[reply]

What better explanation of the Big Bang is there? You did note who first proposed it (second sentence of article)? -- Verbarson  ^talk_edits 17:28, 20 July 2024 (UTC)[reply]

It also depends on how one defines "God". ←Baseball Bugs ^{What's up, Doc?} carrots→ 18:04, 20 July 2024 (UTC)[reply]

God could have started things off with a big bang. The two are not mutually exclusive. There are physics Nobel laureates who are Christians, e.g. Charles H. Townes. Clarityfiend (talk) 02:40, 21 July 2024 (UTC)[reply]

Also renowned cosmologist and Quaker George F. R. Ellis. Clarityfiend (talk) 03:32, 21 July 2024 (UTC)[reply]

See Religious interpretations of the Big Bang theory. Double sharp (talk) 04:09, 21 July 2024 (UTC)[reply]

If a belief is not falsifiable, evidence seems irrelevant. Sean.hoyland (talk) 11:41, 21 July 2024 (UTC)[reply]

Since it doesn't only refer to an object's length, but also to any abstract length, so why isn't this general fact mentioned in the lead of the article Length contraction, nor in (most of) the common literature discussing the phenomenon of length contraction?

Explanation: The lead of our article claims the following: If we (travel on a train and) observe a moving "object" (e.g. a moving building), for which ${\displaystyle L}$ is the object's length measured in the object's reference frame, then we will meausre the object's length to be shorter, i.e. ${\displaystyle L/\gamma .}$ So, why does the lead of our article (as well as the professional literature discussing this phenomenon) only mention an "object", even though this is also true for abstract lengths? Just substitute "distance" (e.g. between two buildings) for "object", and you'll get the following true analogous sentence: If we (travel on a train and) observe a moving distance (e.g. a distance between two co-moving buildings), for which ${\displaystyle L}$ is the distance's length measured in the distance's reference frame (i.e. in the reference frame of the buildings), then we will meausre the distance's length to be shorter, i.e. ${\displaystyle L/\gamma .}$

Indeed, our article contains some hints, e.g. in the chapter "Basis in relativity": Here, "object" simply means a distance with endpoints that are always mutually at rest, i.e., that are at rest in the same inertial frame of reference. Yet, this general fact is neither mentioned nor implied, neither in the lead - nor in the chapters that prove the length contraction - nor in (most of) the common professional literature. HOTmag (talk) 19:26, 20 July 2024 (UTC)[reply]

The phrase "any length in the moving object's reference frame" is ambiguous. Supposedly it is the length of some (other) object. Is it co-moving with the first object? By "a moving object measures (some length)", do you mean, "an observer to whom this moving object is at rest measures (some length)"? It is not very clear.  --Lambiam 20:20, 20 July 2024 (UTC)[reply]

There once was a fellow called Fisk
Whose fencing was strikingly brisk
So fast was his action
That FitzGerald contraction
Reduced his rapier to a disk
—I thought this was an original Lear, but can't find it. It was printed in our physics books at school in the 1970s.Martin of Sheffield (talk) 20:48, 20 July 2024 (UTC)[reply]

My answers to all of your questions are positive.

Let's focus on the following concrete example: If a moving observer measures a given distance between two trees to be one mile long, then we measure this distance to be shorter, i.e. ${\displaystyle 1/\gamma }$ mile long, right? So, why isn't this fact mentioned in the article? It only mentions an "object's length", which really includes the observer's length, yet not any abstract length, e.g. a distance between two trees and likewise. The phenomenon of length contraction is not only about an object's length, right? HOTmag (talk) 22:04, 20 July 2024 (UTC)[reply]

If the observer is moving along a row of trees, the trees are moving relative to the observer, so this moving observer will observe length contraction by a factor of ${\displaystyle \gamma ^{{-}1}}$ for the distance between successive trees, compared to this distance as measured by an observer in whose frame of reference the trees are not moving. So, if "we" are the latter observer, we measure this distance to be longer, by a factor of ${\displaystyle \gamma ,}$ than the length reported by the moving observer. If, on the other hand, the trees are moving with the observer, who (from their point of view) is standing still among a row of trees while seeing us whizz along in a rocket, this observer, who is moving only relative to us and not to the trees, will not observe length contraction for the distance between successive trees, whereas to us in the rocket the trees are moving, so we measure the inter-tree distance to be shorter by a factor of ${\displaystyle \gamma ^{{-}1}.}$ Do you feel our article should explicitly mention the fact that length contraction is not observed by an observer in whose frame of reference the object is not moving?  --Lambiam 06:32, 21 July 2024 (UTC)[reply]

I'm really referring to the latter case you've mentioned, in which the trees are co-moving with the observer, who sees them at rest. It's only us who see, both the observer and the trees, co-moving at the same velocity.

As for your last question: No, I don't want our article to mention the obvious fact that no length contraction is observed by any observer in whose frame of reference the object being measured is at rest. However, I do want the lead of our article, as well as the professional literature discussing the phenomenon of length contraction, to mention that this phenomenon is not only about a given object's length but also about a given abstract length.

Let me explain my point: The lead of our article claims (in my own words) that: if we (travel on a train and) observe a moving "object" (e.g. a moving tree), for which ${\displaystyle L}$ is the object's length measured in the object's reference frame, then we will meausre the object's length to be shorter, i.e. ${\displaystyle L/\gamma ,}$ right? I guess you agree (if not to my exact own words then to their content). So, why does the lead of our article (as well as the professional literature discussing this phenomenon) only mention an "object", even though this is also true for abstract lengths? Just substitute "distance" (e.g. between two trees) for "object", and you'll get the following true analogous sentence: If we (travel on a train and) observe a moving distance (e.g. a distance between two co-moving trees), for which ${\displaystyle L}$ is the distance's length measured in the distance's reference frame (i.e. in the reference frame of the trees), then we will meausre the distance's length to be shorter, i.e. ${\displaystyle L/\gamma ,}$ right? This was my question from the very beginning. HOTmag (talk) 07:57, 21 July 2024 (UTC)[reply]

Certainly two trees set a distance apart is an object that has length. They don't have to be touching anymore than the solar system's planets do. Modocc (talk) 11:22, 21 July 2024 (UTC)[reply]

I think the term "system's length" is more appropriate, than the term "object's length", as far as a distance (between two trees or two planets and the like) is concerned. Have you ever called the solar system "an object"? HOTmag (talk) 11:58, 21 July 2024 (UTC)[reply]

Our solar system is a physical object. As are galaxies and our universe. Of course, these kinds of objects have spatial dimensions and a time dimension. Modocc (talk) 12:11, 21 July 2024 (UTC)[reply]

Which name is more appropriate: a "solar system" or a "solar object"?

On the other hand, which name would you prefer: a "system" consisting of two trees, or an "object" consisting of two trees? HOTmag (talk) 13:14, 21 July 2024 (UTC)[reply]

Depends on the physical context. The term "system" regarding physical objects tends to be more abstract and typically refers to processes like with manufacturing and computers. An atmospheric cloud is both a system of particles and an object. Modocc (talk) 13:24, 21 July 2024 (UTC)[reply]

Back to the trees observed by an observer on a moving train, who sees them co-moving and measures the distance between them: They are pretty wide, so the length being measured is not required to include their width, but only the distance between them, i.e. excluding them. This distance is influenced by the effect of length contraction. Would you call this distance an "boject", a "system", or simply a "distance"? The same question may be asked about the distance between two stars, excluding them. HOTmag (talk) 14:10, 21 July 2024 (UTC)[reply]

The length between buttons is the same as the distance between them. With relativity the measured contraction is not an "effect", it is a change in coordinates. The stationary Earth is an oblique sphere, but with reference frame Lorentz boosts it is pancake-shaped instead. Of course, isometries of Minkowski spacetime are defined by the Poincaré group and its subgroup the Lorentz group. Modocc (talk) 14:39, 21 July 2024 (UTC)[reply]

With relativity the measured contraction is not an "effect". I've never disagreed. I called it "effect", just because it's called "effect" - in the lead of our article Length contraction - and in common speech.

The length between buttons is the same as the distance between them. This is exactly what I'm claiming from the very beginning. That's why I'm asking, why the lead of that article - only attributes that contraction to objects - and not also to distances as in your example of a distance between two buttons. HOTmag (talk) 17:02, 21 July 2024 (UTC)[reply]

Right. Matter is composed of various objects and referring to distances between their elements is simply redundant when length suffices, especially when talking about object velocities. Modocc (talk) 17:46, 21 July 2024 (UTC)[reply]

Referring to distances between their elements is simply redundant when length suffices. Does mentioning "length" alone, suffice? Our article is not satisfied with mentioning "length" alone, and mentions an "object's length", so I asked: Why "object's length" only, and not also a "distance's length", as in your example of a distance between two buttons. This distance has nothing to do with matter, because it excludes the buttons. HOTmag (talk) 18:35, 21 July 2024 (UTC)[reply]

The distance between buttons is spacial is it not. They are embedded in actual space. Thus the distances between the ends of rulers are the same as their lengths. Modocc (talk) 18:47, 21 July 2024 (UTC)[reply]

is it not. Yes it is.

the distance between the ends of a ruler is the same as the ruler's length. Your argument is the following: With regard to length contraction, OBJECT includes a ruler, whereas RULER includes any abstract length, Hence OBJECT is supposed to include any abstract length...

Just as, with regard to time dilation, OBJECT includes a clock, whereas CLOCK includes any abstract time, hence OBJECT is supposed to include any abstract time......

According to your explanation, the leads of our articles Length contraction and Time dilation, should've used, either the terms "object's length" and "object's time", respectively, or the terms "ruler's length" and "clock's time", respectively, or "length" alone and "time" alone, respectively.

However, this is not the case. The lead of our article Length contraction attributes "length" to an "object", rather than to a "ruler", whereas the lead of our article Time dilation attributes "time" to a "clock", rather than to an "object". How do you justify this asymmetry, between length contraction and time dilation? HOTmag (talk) 19:38, 21 July 2024 (UTC)[reply]

Rulers and clocks are objects that measure space and time. With relativity their asymmetric reference frame dependencies are a consequence of a coordinate change given the supposed existence of SR and GR's spacetime which conserves the distances of its worldlines. It is by no means a classical model. Modocc (talk) 20:02, 21 July 2024 (UTC)[reply]

When I recently asked you about how "you justify this asymmetry between length contraction and time dilation", I didn't refer to what you're calling now "their asymmetric reference frame dependencies", but rather to the asymmetry between - how the lead of our article length contraction attributes "length" to an "object" rather than to a "ruler" - and how the lead of our article time dilation attributes "time" to a "clock" rather than to an "object".

Please notice, that according to your explanation in your previous response, the leads of those articles should've used, either the terms - "object's length" and "object's time" - respectively, or the terms - "ruler's length" and "clock's time" - respectively, or "length" alone and "time" alone respectively. However, this is not the case in the leads of those articles. My recent question was: Why, and it only referred to the leads of those articles (as well as to the common professional literature). HOTmag (talk) 20:36, 21 July 2024 (UTC)[reply]

Our articles state: "Length contraction is the phenomenon that a moving object's length is measured to be shorter than its proper length, which is the length as measured in the object's own rest frame." and "Time dilation is the difference in elapsed time as measured by two clocks, either because of a relative velocity between them (special relativity), or a difference in gravitational potential between their locations (general relativity). When unspecified, "time dilation" usually refers to the effect due to velocity." Both descriptions refer to measurements of objects in relative motion. Modocc (talk) 21:05, 21 July 2024 (UTC)[reply]

As you quote, the lead of our article length contraction states: "Length contraction is the phenomenon that a moving object's length is measured to be shorter than its proper length", right? So the lead of this article attributes "length" to one "object", instead of attributing length measurement to two "rulers" - a stationary one and a moving one, right?

On the other hand, as you quote, the lead of our article time dilation states: "Time dilation is the difference in elapsed time as measured by two clocks", right? So the lead of this article attributes time measurement to two "clocks" - a stationary one and a moving one, instead of attributing time to one "object", right? My question was: How do you justify this asymmetry between the leads of those articles. HOTmag (talk) 21:46, 21 July 2024 (UTC)[reply]

The first article does not attribute "length" to an "object". Objects have lengths as a property and there are different ways to measure them. In addition, not all objects tick in any obvious way and measure time, so of course clocks are mentioned. Twins do attain different ages per the Twin paradox. :-) Modocc (talk) 22:01, 21 July 2024 (UTC)[reply]

The first article does not attribute "length" to an "object". Objects have lengths as a property. Maybe you didn't interpret me well. By "to attribute X to Y" I mean "to mention X as the property of Y". The expression "a person's feelings" attributes feelings to a person, just as the expression "an object's length" attributes "length" to an "object". Both lengths and feelings are properties attributed to an object/person - respectively, i.e. a length/feeling is a property - an object/person has - respectively.

not all objects - [mark and] tick [moments] in any obvious way - and measure time, so of course clocks are mentioned [in the lead of our article time dilation]. The same is true for rulers: Not all objects - mark and tick centimeters in any obvious way - and measure length, so rulers should apparently have been mentioned in the lead of our article length contraction. So why weren't they mentioned in that lead, even though they should've been mentioned in that lead, just as clocks are mentioned in the lead of our article time dilation? HOTmag (talk) 23:30, 21 July 2024 (UTC)[reply]

IMHO the articles' ledes are fine, as is, and they appear to be written in accordance with the literature and my understanding of it. Without going into what would amount to original research I don't believe I have anything more to contribute here today. Modocc (talk) 23:41, 21 July 2024 (UTC)[reply]

Why, even though plastics degrade slowly, over hundreds to thousands of years, microplastic particles detach from its parent body (often bottles), contaminating the surrounding area, but glass bottles, for example, seemingly don't have such property? 212.180.235.46 (talk) 10:58, 21 July 2024 (UTC)[reply]

Because plastics degrade and glass doesn't. See Polymer degradation. Alansplodge (talk) 11:08, 21 July 2024 (UTC)[reply]

I'm not sure where to start. This work defines 12 basic colors. Some are named, and I tried to match them up to sRGB equivalents...

However, I'm no expert on colors.

The original is written in the 1880's, and the author was connected with commercial printers in the US.
It seems reasonable to assume the basic colors were originally intended to match up with available basic pigments available at the time of publication.

So what are the likely 12 original colors (ideally based on pigments that would be generally available to a printer in the US) as modern (and sRGB equivlants?)

The page on Wikisource: s:Page:The color printer (1892).djvu/23 , someone on commons tried to tweak the colors in s:File:The color printer (1892) - Basic tones.svg ShakespeareFan00 (talk) 16:15, 21 July 2024 (UTC)[reply]

The author writes, "These colors were adopted because the writer believes that a greater variety of mixed colors can be produced from this selection than from any other containing the same number; besides, these colors are not only the most useful, but also, the most common, and best known among printers." So they were obviously widely available as printing inks, although I doubt they were thought of as "basic" pigments. We have a List of inorganic pigments; I expect most of these 12 are among them. Even if identified, it may not be obvious how to place them in sRGB colour space.  --Lambiam 19:23, 21 July 2024 (UTC)[reply]