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July 16

Next Julian period

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

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)

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)

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)

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)

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)

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

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 [1], [2]: "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)

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)

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)

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. [3] For the IAU resolutions, look at resolution B1 and the appendix here: [4]. --Amble (talk) 16:12, 19 July 2024 (UTC)

July 17

Identify some trees?

some kind of pine

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)

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

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

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

July 18

Identify some more trees?

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)

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)

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)

Lorentz transformations.

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)

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)

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)

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)

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)

July 19

Virgo Cluster in Observable Universe

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://wiki.riteme.site/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)

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)

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)

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)

COVID - Natural Immunity vs Vaccination

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)

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

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)

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)

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)

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)

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)

Is the relativistic transformation, between two non-rotating non-inertial reference frames, linear?

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

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

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

https://wiki.riteme.site/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)

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

July 20

Element bonding

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)

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)

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)

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)

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)

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

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)

@DMacks: Also, I added a link to double bond rule in kainosymmetry, where this (together with other unusual features of first-row elements) is discussed. Double sharp (talk) 06:10, 23 July 2024 (UTC)

Big Bang vs supernatural creation

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

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)

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

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)

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

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

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

If image sleuths were to discover that the unexplained "Little Red Dots" observed by the JWST,^[5] as seen from the solar system against the cosmic expanse, actually spell out a message in a well-known two-dimensional barcode, namely, "Of course I exist, you blockheads. Yours forever, God", would this seem relevant evidence?  --Lambiam 12:09, 22 July 2024 (UTC)

Carl Sagan postulated a somewhat similar idea in one of his books. However, there's also the logic problem postulated in the Hitchhiker's Guide. ←Baseball Bugs ^{What's up, Doc?} carrots→ 19:40, 22 July 2024 (UTC)

Most people who believe in a god believe in the same one as their parents, implying that they do so because of what some would call cultural influences, but which I call love bombing and brainwashing from birth. HiLo48 (talk)

"Of course I exist, you blockheads. Yours forever, God" - I guess it could be evidence of something, trickster djinns, the breaking of the 4th wall between simulator and simulated etc. They could simply arrange in person book signings for their best-selling books, go on some podcasts etc. Sean.hoyland (talk) 07:35, 23 July 2024 (UTC)

Nay I say! No sceptic can deny the uncontrovertably unfalsifiable revelation that the number pi found in epiphany when expanded to sufficiently many decimal places actually contains the message "Of course I exist, you blockheads. Yours forever, God", perfectly encoded in ASCII, itself proof of a divine miracle predating knowledge that humans gained no earlier than 1963 as attested by these witnesses. Philvoids (talk) 20:54, 24 July 2024 (UTC)

I will add that the big bang is what happened after the creation, but was not the singularity that was the start of the Universe. So creation is at time 0. Big bang in the interval (0,CMB visibility] Graeme Bartlett (talk) 01:59, 23 July 2024 (UTC)

That claim definitely needs a Reliable source. HiLo48 (talk) 02:11, 23 July 2024 (UTC)

It is stated in our article on the Big Bang, with sources (see the "Singularity" section), that some authors use "Big Bang" to just mean the initial singularity and others include some periods after it. I'd argue that the name Big Bang nucleosynthesis sort of implies that at least the first few minutes (when deuterium, helium, and lithium are synthesised) can be taken as part of the "Big Bang". Double sharp (talk) 06:03, 23 July 2024 (UTC)

And Creation? There is no science behind that at all. HiLo48 (talk) 06:36, 23 July 2024 (UTC)

Graeme Bartlett said that "creation is at time 0". That's a clearly scientific definition, though I suppose you can call it instead the initial singularity, if you like that name better. I suppose physics before the quark epoch is not yet empirically testable, in the sense that current accelerators cannot reach the energies needed to explore electroweak unification, but that's a matter of our current level of technology. Double sharp (talk) 08:47, 23 July 2024 (UTC)

It's also a matter of theory — beyond a certain point we need a theory of quantum-gravity to proceed, and that does not exist yet. The "Big Bang" singularity is an extrapolation based on known physics, which is known (pun...) to not be applicable to those conditions. So the evidence for a "Big Bang" is not quite what OP appears to imagine it to be. --Wrongfilter (talk) 09:58, 23 July 2024 (UTC)

A very good point indeed. My apologies; once quarks stop being confined, it's not something I know much about anymore. :) Double sharp (talk) 03:29, 24 July 2024 (UTC)

A common mistake, made by people at both sides of the controversy, is that God and religion are not meant to provide answers about the physical world. God is not meant to be an answer to the origin of the universe, the origin of life or any such question that requires a scientific answer. “Give to Caesar what belongs to Caesar, and to God what belongs to God” Cambalachero (talk) 03:45, 24 July 2024 (UTC)

And that statement is just an opinion or point of view. What does "meant" mean? See Proximate and ultimate causation and Meaning of life. Graeme Bartlett (talk) 07:54, 25 July 2024 (UTC)

How about: A great deal of unnecessary conflict has been created by people who assume that 2000-3000 year old Hebrew literature is the same genre as nineteenth-century scientific journals, and can therefore be understood using exactly the same assumptions and literary methods. -- Verbarson  ^talk_edits 20:54, 25 July 2024 (UTC)

Yes, the thousands years old Hebrew literature was written at a time when humans understanding of the nature was rudimentary and primitive, when people thought the Earth was the center of the universe and concept of atoms, subatomic particles and periodic table did not exist. --CometVolcano (talk) 16:01, 26 July 2024 (UTC)

Democritus: Say what? Clarityfiend (talk) 08:41, 27 July 2024 (UTC)

Aristarchus: Hmm? Double sharp (talk) 08:45, 27 July 2024 (UTC)

From well before these guys. Graeme Bartlett (talk) 12:24, 27 July 2024 (UTC)

Indeed. *facepalm* Double sharp (talk) 14:04, 27 July 2024 (UTC)

At that time, humans had no understanding of the nature of the universe. They did not know there are many galaxies in the universe. It was not untill the Great Debate (astronomy) humans did not know that Milky Way is one of billions of galaxies in the universe. --CometVolcano (talk) 19:25, 27 July 2024 (UTC)

And a generation (or two) ago scientists hadn't noticed the 95% of the universe we now call dark energy and dark matter. Just imagine what our grandchildren will discover (and how condescending they might be about our ignorance). -- Verbarson  ^talk_edits 21:48, 27 July 2024 (UTC)

+1 Double sharp (talk) 04:07, 28 July 2024 (UTC)

Length contraction

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 $L$ 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. $L/\gamma .$ 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 $L$ 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. $L/\gamma .$

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)

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)

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)

Our articles say that Lear died in 1888 and Length contraction wasn't postulated by George FitzGerald until 1889. AlmostReadytoFly (talk) 11:11, 22 July 2024 (UTC)

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. $1/\gamma$ 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)

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 $\gamma ^{{-}1}$ 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 $\gamma ,$ 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 $\gamma ^{{-}1}.$ 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)

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 $L$ 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. $L/\gamma ,$ 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 $L$ 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. $L/\gamma ,$ right? This was my question from the very beginning. HOTmag (talk) 07:57, 21 July 2024 (UTC)

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)

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)

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)

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)

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)

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)

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)

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)

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)

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)

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)

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)

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)

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)

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)

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)

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)

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)

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)

July 21

Microplastics detachment

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)

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

Glass in the sea does degrade too. As it washes up and down on a beach, the surface becomes rough. Graeme Bartlett (talk) 12:20, 22 July 2024 (UTC)

Also, most glass bottles are made from materials that, when worn down into particles, are virtually identical to natural sands, so do not contaminate the marine environment. See also Sea glass (which I have always known as drift glass). {The poster formerly known as 87.81.230.195} 94.2.67.235 (talk) 00:27, 23 July 2024 (UTC)

Colors. (The Color Painter)

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)

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)

I wouldn't sadly know where to start looking for information as to common printing inks in the 1880's, but from initial reading around, I'm finding that the articles on pigments don't necessarily have sample colors on them. ShakespeareFan00 (talk) 17:10, 22 July 2024 (UTC)

You probably know this already, but 'The Printer's Manual: An Illustrated History: Classical and Unusual Texts on Printing from the Seventeenth, Eighteenth, and Nineteenth Centuries' by David Pankow says that Earhart's 12 colors came from "twelve stock inks". Maybe they had the same names that he used...not that that helps you get closer to your objective in any way whatsoever. Sean.hoyland (talk) 17:23, 22 July 2024 (UTC)

Wasn't there a museum that kept a collection of old pigments / inks? ShakespeareFan00 (talk) 19:46, 24 July 2024 (UTC)

The Forbes Pigment Collection at the Harvard Art Museums.[6] Their online CAMEO database, of which the Forbes Pigment Database is a section, runs on MediaWiki. DMacks (talk) 23:53, 25 July 2024 (UTC)

Thanks. So it's a case of working out what the stock inks were. In the scan some of the color samples like Vermillion and Rose Lake seem to be different from what I was finding with those names. And whilst the work says it used zinc white, using an approximation I found for that as an HTML triplet, gave colors that were too desturated compared to whats in the scan. Some degree of pigment fading or color change is not unepexected in a more than 100 year old work, but it would be nice to try and figure out collectively what the originals might have been :) ShakespeareFan00 (talk) 19:45, 24 July 2024 (UTC)

Vermilion is actually not one specific colour but a colour family. The pigments are very likely still available today – if not as commercial printing inks, then as artists' paints. There is no guarantee, though, that two colours with the same name from different producers are identical. Also, there is no guarantee that the colours you see on your screen are the same as those on the physical pages of the book. The average RGB triple for the scan of the colour labeled BLUE is (63, 125, 161), or  #3f7da1 , which is not very blue, more like  steel blue , so the scanned B values are perhaps systematically too low.  --Lambiam 00:12, 25 July 2024 (UTC)

July 24

The challenge of space surgery

What are the main challenges of performing surgery in outer space? Have there been any actual attempts to do so either on animals or on humans (other than in fairly controversial Russian disaster movies), and if so, were they successful? 2601:646:8082:BA0:55D1:7827:9FF8:5400 (talk) 08:32, 24 July 2024 (UTC)

The challenges in a zero-gravity setting are manifold. Surgery commonly induces some bleeding. In Earth-bound surgery, gravity keeps the blood from floating away. Free-floating blood droplets will present an unacceptable risk, so foolproof procedures need to be developed to prevent the blood or other bodily fluids from escaping. Free-floating surgical instruments are also not acceptable, but tethering them is awkward. AFAIK no surgery has been attempted under zero-gravity conditions, whether experimental or out of necessity.  --Lambiam 10:40, 24 July 2024 (UTC)

What, not even cutting off a rat's tail, as claimed in the above-mentioned Russian movie? 2601:646:8082:BA0:55D1:7827:9FF8:5400 (talk) 11:11, 24 July 2024 (UTC)

(Zero) Gravity

Before the Russkies went and actually filmed a movie in space, how did moviemakers film zero-gravity scenes for older movies set in space (such as You Only Live Twice, Apollo 13, Moonraker, Deep Impact, Armageddon, Space Odyssey 2001 (what, no article?!), Mission to Mars and Gravity)? Did they film the scenes in the pool, or did they use the Vomit Comet, or what? 2601:646:8082:BA0:55D1:7827:9FF8:5400 (talk) 09:03, 24 July 2024 (UTC)

The article is at 2001: A Space Odyssey.  --Lambiam 10:15, 24 July 2024 (UTC)

Space Odyssey 2001 was directed by Sham Lee Qbrick. Clarityfiend (talk) 11:02, 25 July 2024 (UTC)

For some techniques, see 2001: A Space Odyssey § Zero-gravity effects and Technologies in 2001: A Space Odyssey. Other films have used CGI; see e.g. Gravity (2013 film) § Visual effects.  --Lambiam 10:25, 24 July 2024 (UTC)

The weightless scenes in Apollo 13 were filmed in short sections on a Reduced-gravity aircraft (see Apollo 13 (film)#Filming). Deor (talk) 13:47, 24 July 2024 (UTC)

Yes, the Vomit Comet as noted above. ←Baseball Bugs ^{What's up, Doc?} carrots→ 18:48, 24 July 2024 (UTC)

July 25

Vicarization

Greetings! I was reading the https://wiki.riteme.site/wiki/Fauna_of_Puerto_Rico article and came across the above word, it is blue-linked to "Speciation" but I cannot find that word on the speciation article. I couldn't find a definition in several dictionaries i checked either...Do you know what this word means? could it be made more clear in the article?140.147.160.225 (talk) 18:47, 25 July 2024 (UTC)

The link should be to Allopatric speciation. To my ignorant mind it appears that the correct word is "vicariance", not "vicarization". --Wrongfilter (talk) 19:06, 25 July 2024 (UTC)

Yes. VICARIANCE n. (biology) The separation of a group of organisms by a geographic barrier, resulting in differentiation of the original group into new varieties or species [7] Philvoids (talk) 12:07, 26 July 2024 (UTC)

thanks so much! I've updated the article 140.147.160.225 (talk) 18:42, 29 July 2024 (UTC)

Fels-Naptha

At Talk:Fels-Naptha I raised the issue that the article makes that unsourced claim that "Fels-Naptha once contained naphtha, a skin and eye irritant", but I was unable to find any source showing that Fels-Naptha (note the single "h") soap used to have Naphtha (note the two "h"s) in it, when it was removed, or why it was removed. This may be an urban myth. Can anyone find a source for those claims? --Guy Macon Alternate Account (talk) 19:52, 25 July 2024 (UTC)

Following up links in the references of that article and of Naphtha leads to several sources that state naphtha was dropped from the ingredients, at least one saying this was due to fears it might be carcinogenic. I don't know if any of those sources count as 'Reliable', and none give their sources. This seems unsurprising given the degree to which naphtha was and is used in many products and processes.

'Naptha' seems merely to be a common variant spelling, particularly in product names, presumably because the string -phth- is uncommon in English and likely to be mispronounced and misread by non-chemists. {The poster formerly known as 87.81.230.195} 94.2.67.235 (talk) 20:49, 28 July 2024 (UTC)

July 26

Absorption of matter, without changing the absorber's restmass. Possible?

When a stationary system absorbs a new stationary body, the system's restmass increases by the new body's restmass.

Something similar happens when an electron absorbs light. See Wikisource: The free electrons absorb some of the ultraviolet energy that initially set them free and form an ionized layer.

However, when a stationary body collides with a moving body, the stationary body gains kinetic energy, without changing this body's restmass.

Can a moving body be absorbed by an absorber (like in the first case), but with the absorber's restmass remaining the same as before (like in the second case)? HOTmag (talk) 12:35, 26 July 2024 (UTC)

A free electron cannot absorb light. Ruslik_Zero 13:24, 26 July 2024 (UTC)

Photons caught by a trap increases its mass. As Ruslik_Zero points out, photons interacting with free electrons are not absorbed. Instead they interact elastically, but inelastic collisions are always additive increasing the invariant mass of the absorber. Modocc (talk) 14:26, 26 July 2024 (UTC)

Must the answer to the question in the title be negative?

As for free electrons absorbing light, I've struck it out, but is the book "Electronics Technician" wrong? It's quoted in Wikisource: [8]: The free electrons absorb some of the ultraviolet energy that initially set them free and form an ionized layer.

HOTmag (talk) 14:46, 26 July 2024 (UTC)

Not wrong. The electrons were bonded so the photons' energies broke them without changing their intrinsic rest masses. Modocc (talk) 15:38, 26 July 2024 (UTC)

Ok, so I've just added back the first comment about free electrons absorbing light (I've also added your clarification). Anyway, I'm still curious to know the answer to the question in the title. HOTmag (talk) 16:27, 26 July 2024 (UTC)

In Compton scattering, a free electron gains energy and momentum from a photon, but it does not "absorb" it. --Wrongfilter (talk) 16:52, 26 July 2024 (UTC)

Right, matter absorbs radiation per Quantum electrodynamics. Its rest mass increases unless the energy gets scattered elsewhere. Modocc (talk) 18:06, 26 July 2024 (UTC)

The electron's mass does not increase. --Wrongfilter (talk) 18:26, 26 July 2024 (UTC)

With Compton scattering, it cannot absorb the photon. Modocc (talk) 18:29, 26 July 2024 (UTC)

Who said it does? I'm out. --Wrongfilter (talk) 18:31, 26 July 2024 (UTC)

Sorry. I certainly did not nor did I say the electron's mass increased! And when I realized I simply repeated what you said I was going to fix that. Modocc (talk) 18:35, 26 July 2024 (UTC)

Right, the mass of the bound masses increases and with respect to electrons only their energy increases. Modocc (talk) 18:38, 26 July 2024 (UTC)

HOTmag, as I was trying to say, bound matter's rest mass increases unless the energy absorbed by it gets emitted again. Modocc (talk) 18:49, 26 July 2024 (UTC)

In general, the energy of waves are absorbed: See Absorption (acoustics) and Absorption (electromagnetic radiation). Also, all matter is thought to be comprised of matter-waves. Perhaps that helps. Modocc (talk) 19:50, 26 July 2024 (UTC)

To sum up, electrons' masses are intrinsic and elemental, but the bound rest masses of objects are not. Both absorbed light and matter can increase the latter's (bound rest masses) mass as you observed, but neither can increase the former's mass (the electron's). Thus the answer is no, absorbers do not absorb matter without increasing their rest masses unless they release it, like you noted with particle annihilation, if only because their masses are not as elemental as their constituents... Modocc (talk) 00:24, 27 July 2024 (UTC)

Let me be more clear, now without mentioning photons:

When a stationary system absorbs a new stationary body, the system's restmass increases by the new body's restmass.

However, when a stationary body collides with a moving body, the stationary body gains kinetic energy, without changing this body's restmass.

Can matter be absorbed by an absorber (like in the first case), but with the absorber's restmass remaining the same as before (like in the second case)? HOTmag (talk) 19:30, 27 July 2024 (UTC)

The first case, absorption, always adds rest mass (the second case changes the object's KE, but not its rest mass like within particle accelerators). Modocc (talk) 20:11, 27 July 2024 (UTC)

I didn't ask about the first case, i.e. about a stationary system absorbing a stationary body so that the whole system's restsmass increases, nor about the second case in which the restmass doesn't change.

I wonder, why there can be no third case, i.e, a case in which a system (whether a stationary one or a moving one) absorbs a moving body, so that the system's kinetic energy increases but the whole system's restsmass doesn't change. Is there any reasoning or explanation behind this fact of absence of such a third case? HOTmag (talk) 21:56, 27 July 2024 (UTC)

When an object is at rest its KE is zero, but conservation of energy requires that every object's total energy to be the sum of its parts. We call it rest mass and absorption(s) increases it. Modocc (talk) 22:36, 27 July 2024 (UTC)

I think the conservation of energy is not sufficient for the full explanation: Without the conservation of momentum, one can still argue, that before the absorptoin, the absorber was at rest - hence carried no kinetic energy, while the other body about to be absorbed carried some kinetic energy. After the absorption, the whole system remained surprisingly with the same mass as before, but gained the absorbed body's kinetic energy. What's wrong with that? The wrong thing is my neglecting the conservation of momentum. HOTmag (talk) 00:58, 28 July 2024 (UTC)

The absorbed body adds, at a minimum, a mass-energy equal to KE/c² to the absorber which gains its KE. In addition, for the n-body system, its rest mass and total energy is conserved and unchanged whether they are far apart or bonded together, or internalized and perhaps superimposed. To calculate their combined rest mass one simply adds up their energies in its center-of-momentum frame. In this reference frame the momentum vanishes and their total energy is therefore its rest mass. Modocc (talk) 03:25, 28 July 2024 (UTC)

As to your first sentence about adding a mass $E_{K}/c^{2}$ to the absorber: Please notice, that without the conservation of momentum, one can still argue that before the absorption, the body about to be absorbed carried a total energy $E$ that included - both an internal energy $E_{0}$ - and a kinetic energy $E_{K}$ equivalent to a mass of the size $E_{K}/c^{2}$ you've mentioned. After the absorption, the whole system remained surprisingly with the same mass as before, whereas the absorbed body's internal energy $E_{0}$ was not added to the absorber's internal energy as an addition of the size $E_{0}$, but rather the absorbed body's total energy $E$ was added to the absorber's kinetic energy as an addition of the size $E$. What's wrong with that, without assuming the consevation of momentum, which may actually be not conserved (as you can see in my following thread)?

As to your last claim that "for the n-body system, its rest mass and total energy is conserved and unchanged whether they are far apart or bonded together": AFAIK, what's conserved is the mass-energy as a whole, but the mass alone doesn't have to be conserved: Check: an electron-positron pair, becoming energy alone, without conserving the mass alone (unless one attributes mass to photons, which is a controversial and debatable possibility). HOTmag (talk) 07:11, 28 July 2024 (UTC)

Energy contributes to the rest mass. For example, the gluons' energy within the proton contributes to its overall rest mass. It's a widely accepted concept. Modocc (talk) 12:35, 28 July 2024 (UTC)

Not always. Check: an electron-positron pair, becoming energy alone, without contributing any mass to the light emitted (unless one attributes mass to photons, which is a controversial and debatable possibility). HOTmag (talk) 12:38, 28 July 2024 (UTC)

The rest mass of the 2-body system is conserved. Modocc (talk) 12:54, 28 July 2024 (UTC)

Before the electron and the positron annihilated each other and became energy, the system's rest mass was positive, but after they annihilated each other, the system became light carrying no restmass. HOTmag (talk) 13:24, 28 July 2024 (UTC)

The light carries only energy and momentum yes, but there is a center-of-momentum reference frame in which the particle-waves' momentum vanishes, but their energy, their 2-body rest mass, does not. Modocc (talk) 13:44, 28 July 2024 (UTC)

Yes, their energy does not vanish, but their 2-body restmass does vanish, once they annihilate each other and become light, which actually carries no restmass, so the energy they carried before they annihilated each other does not contribute any mass to the light emitted. HOTmag (talk) 17:19, 28 July 2024 (UTC)

Place the event in an opaque container. Both the container's total energy and momentum are unaffected because its rest mass includes the photons. Modocc (talk) 19:55, 28 July 2024 (UTC)

Yes, when a photon is absorbed it contributes to the absorber's restmass.

However, when an electron-positron pair becomes light in the free space, the pair's restmass vanishes.

This proves that restmass alone, in the free space (rather than in an opaque container), doesn't have to be conserved.

Indeed, restmass is conserved if one assumes both the conservation of energy and the conservation of momentum, but if one only assumes the conservation of energy without assuming the conservation of momentum, then one can still argue, that although any massive body about to be absorbed carries a total energy $E$ that includes - both a kinetic energy $E_{K}$ - and an internal energy $E_{0}$ equivalent to restmass, still after the absorption, the absorber remains surprisingly with the same restmass as before, whereas the absorbed body's internal energy $E_{0}$ is not added to the absorber's internal energy as an addition of the size $E_{0}$, but rather the absorbed body's total energy $E$ is added to the absorber's kinetic energy as an addition of the size $E$. What's wrong with that, without assuming the consevation of momentum, which may actually be not conserved (as you can see in my following thread)? HOTmag (talk) 22:35, 28 July 2024 (UTC)

The container need not contain free space and even if it does as a system its total energy still does not change. Think also of the atmospheric cloud. It consists of enormous numbers of massive and massless particles moving at various velocities, but it is nearly stationary to you and the clouds' total energy that can be calculated is called rest mass. Modocc (talk) 23:00, 28 July 2024 (UTC)

Yes, the container, as well as the atmospheric cloud, are systems each of which conserves the restmass. However, in my previous response I didn't talk about any container, nor about any atmospheric cloud. I only said, that "when an electron-positron pair becomes light, [not in a container nor in an atmospheric cloud, but rather] in the free space, then the pair's restmass vanishes". This proves that restmass alone, in the free space (rather than in a container or in an atmospheric cloud), doesn't have to be conserved. Then I added the crucial last paragraph in my previous response. HOTmag (talk) 06:45, 29 July 2024 (UTC)

We've had the two-photon thing before. --Wrongfilter (talk) 09:32, 29 July 2024 (UTC)

Yes, I remember, but this time I'm talking with Moddoc about an electron-positron pair, which is another issue. HOTmag (talk) 10:54, 29 July 2024 (UTC)

How many photons do you think come out of an electron-positron annihilation event? --Wrongfilter (talk) 11:13, 29 July 2024 (UTC)

2. HOTmag (talk) 12:54, 29 July 2024 (UTC)

July 27

Grooming behavior

In videos of grooming monkeys put all the trash they clean into own mouth, as if eating it, rather than throwing out (same happens when a pet monkey is grooming a human). Why do they do that and isn't harmful for their health? 212.180.235.46 (talk) 10:00, 27 July 2024 (UTC)

How would they know any different? ←Baseball Bugs ^{What's up, Doc?} carrots→ 11:41, 27 July 2024 (UTC)

If they find lice, these are delicious and nutritious. Also yummy and more important are flakes of salt (dried-up sweat). Dandruff is harmless. If it was generally harmful to their health, evolution would have weeded out this specific behaviour long time ago.  --Lambiam 12:32, 27 July 2024 (UTC)

I guess when you are a social animal, putting parasites you have found back on the ground probably isn't a good idea. This is, however, what my dog does with ticks. But the ticks are apparently not delicious, even for fire ants. Sean.hoyland (talk) 05:23, 28 July 2024 (UTC)

Also, small things sometimes (often?) have some antibacterial and antifungal things in their biological toolkits to help them stay alive. Maybe eating them can be beneficial. Sean.hoyland (talk) 05:36, 28 July 2024 (UTC)

What's the opposite of "sticky"?

When a given object tends to get attached to close objects, it may be called "sticky". What about the opposite phenomenon? i.e. How should a given object be called, when it's "reluctant" to get attached to close objects? Even if all objects are at rest, so the adjective "elastic" is not sufficient for describing the opposite of "sticky". HOTmag (talk) 20:20, 27 July 2024 (UTC)

Repulsive, eg. the wall repels objects and the suffix -phobic is used in chemistry, eg. hydrophobic. Modocc (talk) 20:33, 27 July 2024 (UTC)

Thank you. HOTmag (talk) 22:01, 27 July 2024 (UTC)

There is non-stick, which describes objects made of (or coated with) a material with a very low coefficient of friction. Mikenorton (talk) 20:39, 27 July 2024 (UTC)

Thank you. HOTmag (talk) 22:02, 27 July 2024 (UTC)

Hoban (1975) used the term "anti-sticky". [9]  Card Zero  (talk) 03:42, 29 July 2024 (UTC)

"anti-sticky" is good. I guess you could write "not sticky" as "$\neg$ sticky", a downside being that it looks like a stick being described as stick-like. Sean.hoyland (talk) 07:06, 29 July 2024 (UTC)

Thank you. HOTmag (talk) 13:11, 29 July 2024 (UTC)

Teflon? Teflon-like? Huldra (talk) 21:59, 29 July 2024 (UTC)

Also nonadhesive. Modocc (talk) 11:12, 30 July 2024 (UTC)

Slippery Doug butler (talk) 11:24, 30 July 2024 (UTC)

July 28

What is the geological composition of Lascaux?

I am an artist currently working on a project themed around prehistory and I'd like to know about the geological composition of Lascaux (as well as other early human settlements and pre-human geography in general), so I can better represent it. Additionally, is there any sort of database I can use for these purposes? Aedenuniverse (talk) 01:20, 28 July 2024 (UTC)

See karst. Not sure that helps much. Sean.hoyland (talk) 06:05, 28 July 2024 (UTC)

Specifically, it is reported as being calcarenite from the upper Coniacian. Sean.hoyland (talk) 06:10, 28 July 2024 (UTC)

The function of Lascaux is a topic of academic debate, but it was not a settlement. It, and similar caves, are not suitable for serving as dwellings. Human groups of that time lived in tents or the open air, and may occasionally have found shelter in much shallower caves.  --Lambiam 12:02, 28 July 2024 (UTC)

Conserving the kinetic energy, without conserving the momentum. Possible?

There being no external forces, inelastic collisions conserve the whole system's momentum, without conserving the whole system's kinetic energy.

What about the opposite physical process? I.E. is there any physical process, e.g. with external forces, which conserves the whole system's kinetic energy, without conserving the whole system's momentum? HOTmag (talk) 07:27, 28 July 2024 (UTC)

Resolved

I've just thought about it:

The whole system is: a single elastic body.

The physical process is as follows: the single elastic body collides with an elastic wall, being the external force.

Result: the single elastic body is pushed back to the oppposite direction, with the same speed as before the elastic collision took place.

Therefore: the elastic body's kinetic energy is conserved, yet the elastic body's momentum is not. QED. HOTmag (talk) 10:05, 28 July 2024 (UTC)

Nah, you've ignored newton 3. QED Greglocock (talk) 23:47, 28 July 2024 (UTC)

Why do you think I ignored it? I think I didn't. HOTmag (talk) 06:47, 29 July 2024 (UTC)

My second thought is to underline 3 words in my response below. Ignoring what is happening by calling one involved object "the whole system" is disingenuous. Philvoids (talk) 18:21, 29 July 2024 (UTC)

The decision of what the "whole system" is, depends on our choice. Here is a typical example: If two perfectly elastic bodies collide with each other, we can choose, whether to call the two-body system: "the whole system", in which case no external force is involved - hence the momentum is conserved in our "whole system" chosen, or to call one colliding body alone "the whole system", in which case the other body exerts an external force on our "whole system" chosen - hence the momentum is not conserved in our "whole system" chosen. This is how all of physics works, with no exceptions. HOTmag (talk) 20:39, 29 July 2024 (UTC)

The wall will gain some momentum. In a multi body collision the centre of gravity of the system remains at constant velocity (N1) in the absence of external forces. You are 100% wrong, and are just making up random explanations to cover up your lack of understanding. I'll be ignoring you from now on. Greglocock (talk) 23:54, 29 July 2024 (UTC)

I'm referring to a very specific reference frame, which is the wall's reference frame, in which every observer referring to the elastic body as "the whole system" attributes no change to the wall's momentum.

I'm bad at analyzing personal comments, so I'm letting the users decide who is right and who is wrong.

HOTmag (talk) 09:18, 30 July 2024 (UTC)

If you're analysing a collision, you can't just pick one of the things that's colliding and call it the whole system. If it was the whole system, there would be nothing else for it to collide with. "The whole system" is not a reference frame. It's the whole set of objects, by definition; you can't pick and choose which objects it includes. AlmostReadytoFly (talk) 09:57, 30 July 2024 (UTC)

A side note: I've never claimed that "the whole system" is a reference frame.

As to your main response: Can you give any example of a two-body system, for which our referring to one of them as the "whole system" may contradict the laws of physics? AFAIK, there is no example of this kind. Recommendation: before you try to think about such an example, take another look at the example I've already given in my previous-previous response (i.e. the one beginning with "The decision"). HOTmag (talk) 10:35, 30 July 2024 (UTC)

If you have a two-body system, the two bodies are the system. If you say you have a one body system, then say that that body collides with something else (e.g. a wall), you're contradicting yourself. AlmostReadytoFly (talk) 11:30, 30 July 2024 (UTC)

Maybe the expression "the whole system" confuses you. I can replace it by the expression "the sub-system chosen", in which case no contradiction follows, even according to your attitude.

One contradicts oneself when one says "x" and then says "not x". My analysis is not the case, even when the expression "whole system" is used, but I'm changing it for you, to avoid confusion. HOTmag (talk) 12:32, 30 July 2024 (UTC)

"When I use a word," Humpty Dumpty said in rather a scornful tone, "it means just what I choose it to mean——neither more nor less."

If you just want a physical process where a body keeps its kinetic energy but not its momentum, consider a body in a circular orbit. AlmostReadytoFly (talk) 13:00, 30 July 2024 (UTC)

(ec)

All types of collision (inelastic or elastic) conserve momentum. Total kinetic energy would be conserved (meaning no release of sound or heat) only in an impractical perfectly elastic collision. To identify a process that conserves a system's kinetic energy but may be affected by external forces, one needs firstly to clarify whether the system shall qualify as an Isolated system where thermodynamic laws apply. The Second law of thermodynamics observes that the entropy of isolated systems left to spontaneous evolution cannot decrease, as they always tend toward a state of thermodynamic equilibrium where the entropy is highest at the given internal energy. Philvoids (talk) 10:10, 28 July 2024 (UTC)

July 29

Access to reference 9 in Petrichor

Garg, Anu (2007). The Dord, the Diglot, and an Avocado Or Two: The Hidden Lives and Strange Origins of Words. Penguin. p. 399. ISBN 9780452288614.

Do you have access to the page 399? I would like to find out what it says about the two researchers, Isabel Bear and Dick Thomas. (In ruwiki the same source is cited and it is written that Thomas was from UK, whereas the enwiki says they are both from Australia).

Thank you in advance for your help. Gryllida (talk, e-mail) 00:41, 29 July 2024 (UTC)

The ref says, "In 1964, two Australian researchers, I.J. Bear and R. G. Thomas..." but does not provide any further biographical informaion about either one. Our article links to enwiki articles about each of them: Isabel Joy Bear and Richard Grenfell Thomas. Bear's article makes a strong claim for her being Australian, even though she did work for a few years in the UK. Thoman's article does not have any hint of any national connection other than Australia. DMacks (talk) 01:02, 29 July 2024 (UTC)

Thanks, Bear's article says "In the 1950s Bear moved to the United Kingdom, where she worked at the Harwell Science and Innovation Campus. She moved to the University of Birmingham, where she worked as a postdoctoral researcher in the department of metallurgy. Whilst working in Birmingham Bear became interested in solid-state chemistry. Bear joined the Council for Scientific and Industrial Research (CSIRO) in 1953, [...]" -- does it mean she apparently worked in the UK between 1950 and 1953?

The Nature paper was in 1964. Gryllida (talk, e-mail) 04:05, 29 July 2024 (UTC)

Yes, Reference [3] after the first sentence in your quote says explicitly "

In the UK (1950-53)

During three years in the UK she was employed first as an Experimental Scientist in the Metallurgy Division of the Atomic Energy Research Establishment at Harwell, and later as a Research Assistant in the Metallurgy Department of Birmingham University." AlmostReadytoFly (talk) 15:45, 29 July 2024 (UTC)

The fastest Internet speed during rain?

So ChatGPT says the fastest Internet speed during rain is fiber topics, then cabled Internet, then mobile wireless Internet. I just want a 2nd opinion if anyone agrees or disagrees? Specifically, ChatGPT said:

• Most Affected: Mobile wireless internet is the most affected by rainy weather due to signal attenuation.
• Moderately Affected: Cabled internet can be affected if the infrastructure is old or damaged, but it is generally more resilient than mobile wireless internet.
• Least Affected: Fiber optic internet is the least affected by rain due to its well-protected, light-based transmission system.

Thanks. 66.99.15.162 (talk) 19:36, 29 July 2024 (UTC).

Fibre optic cable is always the fastest. The bot is right that wireless technology suffers from rain by signal attenuation, which, provided the protocol is designed to make use of good conditions, can slow down internet speed in rain. Some attenuation isn't too bad, as it reduces interference between nearby cellphone towers, without significantly affecting signal strength on short distances. Once the transmitter reaches maximum power, more rain reduces possible speed.

Wired technology is generally unaffected by rain, unless there's so much rain that it enters the cabinets housing routers etc. or causes landslides, ripping the cables apart. Maybe ChatGPT thinks (to the extend that machines can think) that copper cable networks tend to be older than fibre optic networks and therefore more susceptible to such water intrusion.

Copper networks are typically faster than wireless for the same reason as why speaking tubes are better than providing everybody with a megaphone: the more people shout over the same medium, the more confusion. PiusImpavidus (talk) 09:47, 30 July 2024 (UTC)

The speed of mobile wireless Internet access depends more on the generation of broadband cellular network technology deployed locally (2G, 3G, 4G, 5G) than on the weather conditions. If there is no cellular coverage, the only solution is satellite Internet access, which can stream at a high rate but has a high latency. In all cases (wireless, cable, fiber) the bandwidth may depend on the contract with the provider – often one can opt for a subscription with a higher rate at a higher cost. And in all cases the actual latency and streaming rate may be much lower than the promised one.  --Lambiam 09:57, 30 July 2024 (UTC)

Historic (pre-1800s) Wildfires in California

I read that historically, about 2-4 million hectares would burn a year in California, https://www.propublica.org/article/they-know-how-to-prevent-megafires-why-wont-anybody-listen and https://www.sciencedirect.com/science/article/abs/pii/S0378112707004379. A claim made in the sources was that smoke was a feature of the landscape, rather than an oddity as it is now. If the "extreme" modern season tends to be around 2 million ha with moderate air quality impact, what would be some rough estimates for the average pm2.5 levels across pre-1800s California in late summertime? Takedalullaby (talk) 21:01, 29 July 2024 (UTC)