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November 3

Empty calories

I read a statement by a Dr. Rosen in an article on yahoo!life[1]. She states that diet sodas "are loaded with empty calories". Is that true? Thank you. Hevesli (talk) 10:22, 3 November 2022 (UTC)[reply]

According to Coca-cola, their diet coke has only one calorie per 330 ml can, so more just empty I would have thought, apart from E numbers. Mikenorton (talk) 10:42, 3 November 2022 (UTC)[reply]

I wonder if that particular quote was taken out of context by the article writer. It would seem to apply better to non-diet drinks. Alansplodge (talk) 13:51, 3 November 2022 (UTC)[reply]

Yes, the usual meaning of "empty calories" is calories consumed without benefit of any other nutrients such as vitamins or protein. Abductive (reasoning) 03:50, 4 November 2022 (UTC)[reply]

Cooling hot oven racks

Situation: I start heating up my oven, and at one point take two oven racks out when they are quite hot. I hold one with my one hand steadily (in a mitten), and another with another hand (in mitten), shaking it vigorously so that the individual rods vibrate. Will there be an appreciable difference in cooling rate between the two? --Ouro (blah blah) 18:09, 3 November 2022 (UTC)[reply]

The "standard equations" for such scenarios tend to be large and painful to solve. I pulled up my go-to reference - Incropera et al., Fundamentals of Heat and Mass Transfer, (my copy is a 7th edition). As you would expect, arrays of long-cylindrical-metal-rods are solved around Page 618. Rather than quote a complicated equation out of context, it's worth saying that the math is complicated. It would take six hundred and seventeen pages of preparatory explanation to do it justice (... that's why this equation is on Page 618). "Will there be an appreciable difference in cooling rate?" Yes. "Exactly how appreciable?" ... So, let's break this down: what is the metal made of? What is the air made of? How hot is the metal? How hot is the air? How precisely can you measure temperature? How many places (throughout your scenario) are you using a simplifying assumption? (Did you extract the rail from the oven in zero seconds, or in finite time? Is air viscous, or not viscous? When a steel rod vibrates, to what extent do you assume the displacement to be infinitesimal? Exactly how round are the metal rods that constitute your oven-rack?) We can literally (literally) spend hundreds of pages - hundreds of thousands of complicated mathematical words to talk about all the details. Golly, even I had to actually look up Nusselt number to refresh my memory - and I'm some kind of scientist - not just anyone, either - I happen to be the original author of the Official Wikipedia Science Reference Desk Mathematical Model And Numerical Simulator For How Much My Coffee Has Gone Cold As I Expend Time Answering Thermal Physics Questions On The Science Reference Desk!

The more pertinent questions revolve around a more general question: which of these complicated details of engineering and physics are relevant to your scenario?

Are you simply baking cookies? Few of these details materially affect the quality of your cookies.

Nimur (talk) 18:34, 3 November 2022 (UTC)[reply]

And don't forget that by shaking one hand, you are likely causing minor vibrations in the rest of your body so that the other hand is not "steady". AND the waving of the one rack will produce air currents that will blow past the other rack..... --User:Khajidha (talk) (contributions) 18:55, 3 November 2022 (UTC)[reply]

Nimur... I do not need to be baking anything, that's just something I thought of... I just wondered... I can appreciate the diversity of variables that need to be taken into account and am thankful for Your answer - doing justice to the complexity of the problem. Appreciable would mean in excess of a few percent I'd say. Thanks.

Khajidha... of course. Then again, it's just a thought exercise (a WP:RD exercise if you will).

Thanks friends --Ouro (blah blah) 19:13, 3 November 2022 (UTC)[reply]

Right-o - it's just that it's hard to say confidently whether we're looking at differences in - let's just pick one quantifiable parameter, cooling rate - of a few parts per hundred, or a few parts per million. It's hard to know - confidently - whether we can safely ignore some effects!

The beauty, and the curse, of the mathematics that model convective heat transfer is that they are highly sensitive (in the mathematical sense of that word). Small changes can be amplified by physical processes that are governed by nonlinear equations.

It is no coincidence that heat transfer is studied as a part of statistical physics. It is also no coincidence that convective heat transfer relates strongly to turbulent flow.

Your thought-experiment is a great one - but to really do it justice, we do need to start with much simpler thought-experiments. By this, I mean that we have to spend a pretty significant amount of study before we can come to any conclusion, if we care about a scientifically valid answer - let alone one that is accurate and precise enough to say "yeah, that's an effect whose size is, say, 3% to 5%."

Otherwise, we're kind of just not doing science - we're just guessing.

There is a lot of stuff in our universe - basically, the entire set of topics that we call experimental physics - where we can perform a controlled experiment more easily than we can answer from a theoretical perspective. But, a true experimental physicist cares about controlling the experiment so that they can draw some kind of generalizable conclusion. This is exactly how we end up with thousand-page textbooks where we can say, "hm, for a rack made out of an array of rods, use Equation 9.34 from the chapter on Free Convection." I mean, a correct answer does exist - a correct answer can exist - and that's what separates real physicists from postmodernist nihilists. We (physicists) subscribe to a world-view in which we believe we can find out truth and assign a number to it. They (post-modernist nihilists) tell us that truth defies understanding, let alone quantification.

"Neither of these world-views is more correct," say the post-modernist nihilists.

"Post-modern nihilists are in no position to tell us about correctness," retort the physicists.

Only... the experimental physicist has the fortitude of moral character, nay, the intellectual resolve, to spend thousands of hours slogging through the work to prove the philosophers are wrong.

So, uhm, ... let's get crackin' on that!

Nimur (talk) 21:11, 3 November 2022 (UTC)[reply]

Yes, waving them around will increase the rate of cooling. That's because as well as radiative and convective heat loss you also get conductive heat loss into cooler gas. That's why car radiators have fans. Greglocock (talk) 21:45, 3 November 2022 (UTC)[reply]

Car radiators use the simplifying assumption that the gas outside the engine cowling will be cooler, so they use a fan to impel cool gas across the radiator. Ambient air outside can be approximated as an infinite cold reservoir. So, it is thermodynamically efficient for the engine to spend a few extra joules (... which needs energy, which means burning more fuel, which adds extra heat), and then convert this surplus heat energy into kinetic energy in the fan, and we assert that the fan shall impel cold air toward the radiator, improving net efficiency during normal operation in normal, specified conditions.

Fans, like all non-perpetual motion machines, need energy to spin - and in this case, the energy comes from the engine, and so ... amazingly, adding the fan to the automobile engine causes heat to be added to the universe. It only so happens that the automobile engine is designed to put this heat "somewhere else". Somebody, (an engineer, perhaps) had to study those horrible airflow and convection equations to make sure this actually has a net cooling effect on the portion of the machine we care about! Does the fan actually cool the engine if... the outside air temperature is in Flagstaff, Arizona, in the summer, while driving 400 kilograms of astrophysicists up a steep hill, or is this contrived situation a case of inversion in parameters, in which the existence of this cooling-fan actually adds heat to the radiator?

What about other scenarios - where the normal operation of the system does not necessarily rely on forced air cooling? What if we designed for maximum efficiency with passive cooling - a fan would move us away from maximum efficiency!

Would a cooling fan be of any assistance in, say, an airplane engine? ...Or a coal-fired powerplant turbine? Would it cool the metal any faster if the "oven" were an iron smelter? How about a blast furnace (where cold air is added to increase the net temperature)? How about a sports car with a turbocharger, where cold air is blown at the engine intake by a fan? It really, really matters where the fan is and where the air goes - turbocharging an engine usually makes it get hotter, because cold air does more than convect - it can combust!

How about if the "cylindrical metal tube" is radiating into a cooling fluid that radiates into the vacuum of space (... or is exposed to direct sunlight in the vacuum of space), fluctuating between 4 and 280 kelvins, depending on the time of the month? How many billions of dollars does it cost if a simplified assumption flips the sign of the cooling rate, and what is the impact to weather forecasting for half a planet for the next two decades?

The scenarios are diverse, and in this diversity, the magnitude of the rate of cooling changes dramatically. In fact, even the sign of the value changes. So, it's never so simple unless we know what the scenario is doing!

Nimur (talk) 16:10, 4 November 2022 (UTC)[reply]

"What if we designed for maximum efficiency with passive cooling" For interest, this is exactly the case for Formula One (and other) racing car engines, which is why, when they return to their pits, team personnel have to direct externally driven cooling fans into their air intake ducts. {The poster formerly known as 87.81.230.195} 5.64.163.219 (talk) 08:15, 5 November 2022 (UTC)[reply]

In the case of practical engines, and particularly turbines, cooling is not just part of the Carnot cycle, but is also for engineering purposes. Differential expansion and contraction modified the clearances and if the oil gets too hot it looses its lubricating properties. Martin of Sheffield (talk) 08:24, 5 November 2022 (UTC)[reply]

A steadily held hot rod mainly cools by transferring heat to the surrounding air. Since the rate of heat flow is proportional to the difference in temperature between the rod and the air, the heat flow will thereby decrease and the cooling slows down more than necessary. This can be avoided by replacing the warm air continually by fresh cold air. One way of accomplishing this is by aiming a ventilator at the rod. Another way is swinging the rod through the air. Shaking it will mainly have an effect if the absolute displacement is considerable. --Lambiam 21:43, 3 November 2022 (UTC)[reply]

Just to add another important perspective here, and add on a bit to the excellent (though a bit TLDR) responses by Nimur above; when you wave the rack through the air, you're basically trying to take advantage of convection to the heat transfer situation. We can confidently say yes to the notion that it will cool off faster. The devil is in the details, however; if it cools an extra 0.01 kelvin per hour, that's hardly worth the effort spent doing it. The problem is that fluid dynamics is a famously impenetrable science to work in theoretically. You would need something akin to Newton's laws of motion and the work equation and the law of conservation of energy and the like for fluids (rather than objects). For objects, these are simple three-variable equations that any middle schooler can solve. For fluids, we've got the equations, its just that no one can solve them. No really, the fluid equivalent of all of the dynamics and kinematics equations you learned in high school physics are called the Navier–Stokes equations; actually solving them in three dimensions represents one of the Millennium Prize Problems, which tells you they are still unsolved. The issue is that Navier-Stokes doesn't play well with turbulence, and that's why we have the Navier–Stokes existence and smoothness problem. Since solving "how much energy is carried away by convection" requires us to accurately model fluid dynamics around your waving oven grid, and that flow will be turbulent, not only do we not have solutions for such a model; we don't even know whether or not they exist. --Jayron 32 12:30, 4 November 2022 (UTC)[reply]
I'll work on brevity, (but not today)! Nimur (talk) 16:11, 4 November 2022 (UTC)[reply]

I got my brevity down pat, Nimur, but you forget it if you do such excellent work. I am reading through your answers, friends, and thanks. Of course we could have (should have) started off much simpler, with say - one rod (one wire) that is shaken or not and then to measure the heat transfer away from the object... and then somehow transpose that (with all the details like material, make-up, design details, etc.) and work upwards towards the oven rack. And Jayron you're absolutely spot on about fluid dynamics being difficult - I know. Thanks anyway, you got me a lot to think about. --Ouro (blah blah) 18:18, 4 November 2022 (UTC)[reply]

One thing that is still true; you can work this stuff out empirically. You can shake rods of different thicknesses at different speeds in different environments, you can plot the results on graphs and interpolate and extrapolate the data to develop models of cooling that don't depend on knowing anything about fluid dynamics. Newton himself developed Newton's law of cooling using carefully controlled experiments. However, the problem is that you can't work from first principles to develop a theory of cooling that would work here, in the same way that we have good theories explaining things like balls rolling down hills and hockey pucks colliding on ice. Even though the same principles apply to describe colliding hockey pucks and cooling off waving chunks of metal in the air, the math is just too intractable using the tools we have today to do so. --Jayron 32 18:37, 4 November 2022 (UTC)[reply]

But what is the sound of one hand shaking? (My Zen master suggests that this question may not even exist.) MinorProphet (talk) 01:31, 10 November 2022 (UTC)[reply]

Kem Kem Leptocleidid.

When is the new leptocleidid plesiosaur from the Kem Kem going to be given a name? CuddleKing1993 (talk) 21:27, 3 November 2022 (UTC)[reply]

If you mean a binomial name, it is not so simple as naming a new-born baby. The first issue is the assignment of a genus. Do all fossils from this group belong to the same genus? And if so, is it one of the known genera, or a new one? Such questions require careful study. If this can be resolved, the questions repeat at the species level. --Lambiam 22:12, 3 November 2022 (UTC)[reply]

The ICZN, International Commission on Zoological Nomenclature, maintains the process for assigning binomial names; they don't name the organisms themselves but they do set the standards for how things are supposed to be named, and they do adjudicate disputes. The process is described in a document called the International Code of Zoological Nomenclature (also abbreviated ICZN). The process of granting the name does take time, so it's hard to predict "when" such a name will be published. It depends a bit both on the discoverer of the species (who has the right to name it) and to the publisher of the work in which it is named. As Lambiam notes above, what needs to be done first is to figure out what the taxonomy/cladistics of the species is; such as to which genus it should belong, or does it represent a new genus; should it be a species on its own, or a subspecies, to which family should it belong, and so on up the line. That kind of determination takes real labor and work on the part of scientists who need to look at the fossils, analyze them, and come to conclusions. --Jayron 32 12:16, 4 November 2022 (UTC)[reply]

In the past discoverers would name specimens without taking such careful precautions. But this led to many cases of multiple names being given to what turned out to be the same thing. Which meant standards had to be set up for which name was to be used going forward. Usually strict priority is the determining factor, but there have been exceptions that were explicitly made for good reasons (if the oldest name was never used after its initial publication and a later name was used in numerous publications, it would be counterproductive to insist on strict priority). --User:Khajidha (talk) (contributions) 13:41, 4 November 2022 (UTC)[reply]

November 4

fungal infections from ancient tombs

I've been seeing stories[2][3] that after 12 research scientists entered the 500 year old tomb of Casimir IV Jagiellon, 4 of them died days later, and another 6 died months later. It is speculated that the deaths may have been due to a fungal infection caused by exposure to Aspergillus while in the tomb. My question is about the specific incident involving the King of Poland's tomb in the 1970s. I've had a difficult time finding contemporary accounts or any reliable sources to confirm these deaths. Any additional info would be greatly appreciated. mikeu ^talk 23:28, 4 November 2022 (UTC)[reply]

This is already mentioned in the article you link, in the section Tomb, with a reference cited to a reliable source. {The poster formerly known as 87.81.230.195} 5.64.163.219 (talk) 08:19, 5 November 2022 (UTC)[reply]

Specifically; this. Alansplodge (talk) 12:32, 5 November 2022 (UTC)[reply]

Yes, I saw that. If ten out of twelve researchers died after entering the tomb it would be an extraordinary occurrence. I would expect it to have been covered in the news, yet the ProQuest historic news database does not return any results. It would be of great scientific interest, but Scholar lacks any hits. One source that I linked to mentions a "Dr. B. Symk" who survived. Scholar shows one paper by the author about microbiology but nothing about this dramatic incident. All of the sources that I've found repeat the same vague claim without details or reference to a primary source. --mikeu ^talk 14:31, 5 November 2022 (UTC)[reply]

What I understand from an article in the English edition of the printed magazine Poland (volume 351, no. 3, 1987) with the title "Anathemas, Microbes and Scholars", is that the role of prof. Bolesław Szyk, a microbiologist from the Kraków Agricultural Academy, was that he examined the microbes in the tomb.^[4][5] One may assume that as a microbiologist he understood the risks and took proper precautions, unlike the hapless archaeologists. The snippet view makes it hard to see the full story. The author of the article is science journalist Zbigniew Święch,^[6] who has an article on the Polish Wikipedia. He wrote a book with the title Klątwy, mikroby i uczeni,^[7] which in English means Anathemas, Microbes and Scholars, the same as the title of the magazine article. --Lambiam 02:44, 6 November 2022 (UTC)[reply]

The Polish Wikipedia also has an article on Klątwy, mikroby i uczeni, which turns out to be a series of three books. The first book in the series is devoted to "the curse of Casimir Jagiellon". --Lambiam 02:54, 6 November 2022 (UTC)[reply]

November 5

Nature versus nurture

It is often said that the heritability of IQ increases with age and was/is greatest in school. This worries me a bit, it looks very much like an artifact. Where the children receive by force a same way of life, the way of life changes nevertheless depending upon family etc.. Have the intelligence researchers considered this? 2A02:908:424:9D60:0:0:0:F38B (talk) 00:02, 5 November 2022 (UTC)[reply]

What do you mean by "receive by force a same way of life"? ←Baseball Bugs ^{What's up, Doc?} carrots→ 00:23, 5 November 2022 (UTC)[reply]

The evidence is increasingly pointing to intelligence being all nurture, no genetics. Abductive (reasoning) 01:02, 5 November 2022 (UTC)[reply]

What evidence? ←Baseball Bugs ^{What's up, Doc?} carrots→ 01:37, 5 November 2022 (UTC)[reply]

I'm not sure that is correct; see e.g. this article. See also Heritability of IQ. The present scientific consensus in the "nature versus nurture" debate appears to be that when it comes to intelligence as measured by IQ tests, both are an important factor. --Lambiam 08:20, 5 November 2022 (UTC)[reply]

They are forced to go to school, to learn and so on. They hang out in classes, they have the same environment. 2A02:908:424:9D60:0:0:0:F38B (talk) 08:14, 5 November 2022 (UTC)[reply]

And they all make the same grades? ←Baseball Bugs ^{What's up, Doc?} carrots→ 18:26, 5 November 2022 (UTC)[reply]

Some monozygotic twins get separated at birth and are raised in different environments; see e.g. this article, "Personality traits, mental abilities and other individual differences: Monozygotic female twins raised apart in South Korea and the United States".^[8] --Lambiam 08:24, 5 November 2022 (UTC)[reply]

Here is a popular articel about that study from one of the autores. 2A02:908:424:9D60:0:0:0:F38B (talk) 00:04, 6 November 2022 (UTC)[reply]

Heritability is the proportion of the total variation that is explained by the genetic variation. If the environment is more variable in a way that causes an increase in total variation, the heritability will be lower even though the mechanisms underlying the genetic effects are unchanged. Geneticists are very well aware of this. Heritability of IQ in adults is surprisingly high, about 0.75. The figure is smaller in children, probably because children of the same age vary in how developed they are. Jmchutchinson (talk) 16:03, 5 November 2022 (UTC)[reply]

Concerns about page for Thermal Medicine

Hey all, Straight to the topic: I'm concerned about this page: https://en.wikipedia.org/wiki/Society_for_Thermal_Medicine

Basically, we don't have a thermal medicine page, and googling thermal medicine leads you to it.

The page is at best subpar for what Wikipedia would consider an acceptable medicine article, and I'm concerned that it presents a health risk. Even though the page is referenced, the references are from a time when p-hacking and using "researcher degrees of freedom" was rampant, and I'm not sure they represent the scientific consensus on the subject.

Any suggestions? Thanks!

Best regards, Victor ~victorsouza (talk) 22:06, 5 November 2022 (UTC)[reply]

I'm not convinced that the Society for Thermal Medicine meets WP:NORG; with a quick web search I can't find any significant, independent coverage on it (except maybe this), and none of the sources currently in the article appear to help establish its notability. Also, I'm pretty sure there is an article about thermal medicine: Hyperthermia therapy. Shells-shells (talk) 00:11, 6 November 2022 (UTC)[reply]

Considerable swaths of text are verbatim or almost verbatim copies of passages on the history page of the Society for Thermal Medicine. --Lambiam 01:44, 6 November 2022 (UTC)[reply]

November 6

entropy

How might the universe look if the second law of thermodynamics worked in reverse? Instead of the universe's entropy increasing over time, entropy would generally decrease over time in this alternate universe. Might life have still come into existence, and if so how might it be different? I heard about an MIT study about how the universe's increasing entropy might make the development of life inevitable, which got me interested in this question. How might stars, galaxies, planets etc might look if they even exist at all? 2600:4040:1014:7300:594B:5953:EE8F:274C (talk) 00:49, 6 November 2022 (UTC)[reply]

Take a film of the universe and play it in reverse. --Lambiam 01:18, 6 November 2022 (UTC)[reply]

See "Entropic Time (Backwards Billy Joel Parody)" (A Capella Science) on YouTube DMacks (talk) 22:17, 6 November 2022 (UTC)[reply]

Your question doesn't make sense in physics, because this event didn't happen. In France we say "with if we put Paris in a bottle".

But in mathematics you can define this kind of postulate and pose a problem in this new theoretical set. Malypaet (talk) 18:07, 6 November 2022 (UTC)[reply]

This would make the universe unstable. Ruslik_Zero 18:43, 6 November 2022 (UTC)[reply]

This question comes up from time to time. See Wikipedia:Reference desk/Archives/Science/2019 February 9#Arrow of Time, making the point that time may well be a two-way street. 79.76.42.157 (talk) 13:56, 8 November 2022 (UTC)[reply]

first law

Along a similar note, how might the universe look if it was possible to create energy out of nothing or destroy energy? 2600:4040:1014:7300:594B:5953:EE8F:274C (talk) 01:14, 6 November 2022 (UTC)[reply]

This question is unanswerable. If the law of conservation of energy is broken, all physical laws as we know them are broken, since this implies that the laws of physics are not constant but change with time (see Conservation of energy § Noether's theorem). --Lambiam 01:29, 6 November 2022 (UTC)[reply]

It don't get it. I was thinking that the conservation-laws are a inference from symmetry properties. For instance, conservation of Impuls is a conclusion of the possibility to go in every direction in space. 2A02:908:424:9D60:0:0:0:F38B (talk) 11:36, 8 November 2022 (UTC)[reply]

So anything might be possible in that case (and its impossible to predict) because the laws of physics can change over time. — Preceding unsigned comment added by 2600:4040:1014:7300:594B:5953:EE8F:274C (talk) 02:05, 6 November 2022 (UTC)[reply]

You're waaay over in the region of speculative science fiction or magic rather than anything that can be answere in the science reference desk. NadVolum (talk) 11:54, 6 November 2022 (UTC)[reply]

Unit in physics and multiplication by time

In several definitions of physical quantities, we find a multiplication by a second (J.s, A.s) when we refer to a quantity dependent on the time which flows towards the future and therefore expressed by the division of a second. Mathematically, I understand the operation, because it ultimately consists in removing any reference of this magnitude to time. In physics, the division of time on a quantity relates to associating a time interval which flows towards the future with this one (J/s, C/s, m/s), this is regularly experienced. On the other hand in physics, the multiplication of time on a quantity would consist in associating a time interval which flows towards the past, except that has never been experienced (except by reversing the progress of a video!). How can we allow ourselves to use this kind of notion in physics when it only comes under the domain of mathematics or science fiction? Malypaet (talk) 02:49, 6 November 2022 (UTC)[reply]

I don't know where you get this idea of an association of multiplication or division with time flowing or the past or future. In the case of corn in a field on can have corn per hectare or total corn in the field. Both figures are useful for different purposes but there is no flow involved. In the same way for fuel in a car one can have the total number of litres and kilometres per litre which together give an idea of how far it can go between refills. Speed can be measured in kilometres per hour and together with a distance that can give how long it'll take to arrive. The multiplication or divisions involved imply nothing about the future or the past. NadVolum (talk) 11:46, 6 November 2022 (UTC)[reply]

You write "Speed can be measured in kilometres per hour" : km/h, this is not a division ? You write "how long it'll take to arrive", this has no thing to do with the futur ? If you don't have the base of language or in physics, don't loose your time here and mine too ! Malypaet (talk) 17:58, 6 November 2022 (UTC)[reply]

You can also ask how long it took to arrive. Past tense. --Wrongfilter (talk) 19:23, 6 November 2022 (UTC)[reply]

Yes, but "how long" is between start to end (end is the futur of start), with a speed for a distance divided by (from end minus start ). what you means with "Past tense", is a replay in your imagination, as in a dream (as in mathematics), you're telling a story that happened in the past, it's not the same as reversing time. Reversing time was never experimented in reality (physics), a time action event from end to start. Exept if you can give me an exemple or pointing me on a publication ? Malypaet (talk) 08:29, 7 November 2022 (UTC)[reply]

Being rude towards those who can (or at least try) help you may turn out counterproductive... --CiaPan (talk) 21:12, 6 November 2022 (UTC)[reply]

Sorry, you are right Malypaet (talk) 08:12, 7 November 2022 (UTC)[reply]

Also have you tried figuring out how your idea of flow, the future and the past apply to the corn and land area, and are they really all that relevant? I put them in as things which don't slot into your model and therefore you might feel freer to think about NadVolum (talk) 11:47, 7 November 2022 (UTC)[reply]

Talking for nothing Malypaet (talk) 13:21, 7 November 2022 (UTC)[reply]

I feel the OP would benefit from a course in calculus explaining the operator ρ/ρt that means the differential with respect to time of anything that varies with time, evaluated at one given instant in time. Becoming able to understand Maxwell's equations that employ differential operators to reveal the interdependence of electric and magnetic fields, and their importance in the technologies of Electromagnetism (light, radio, TV, radar) should remove any doubt that physicists "can allow themselves" to use these calculations. Of course they are aware that any practical measurement of a ρ/ρt value will require collecting values of the varying quantity during a finite time span which may be as short as measurement accuracy allows. For example: two photographs of a car showed it was at time(hh:mm:ss)/distance: 6:00:00 / 5 miles and 6:00:01 / 5-1/60 miles. The photographs are enough to convict the driver of exceeding by 10 mph the local speed limit of 50 mph but nothing is, nor can, be implied about his behavior before or after the measurement. After calculating velocity = ρ (position)/ρt for a car one may further calculate its acceleration = ρ (velocity)/ρt = ρ² (position)/ρt², also applicable to a given instant with no implications for the past or future. Philvoids (talk) 16:08, 7 November 2022 (UTC)[reply]

"with no implication for the past"? It is obvious, the past is over, we cannot act on it. But, a position, a speed, a direction, and an acceleration allows you to know where you will be in 10 minutes, so a precise implication on the future, remove some of this information, there will always be an implication on the future, even vague. Too focused on equations, makes you forget the meaning of things. Malypaet (talk) 21:36, 7 November 2022 (UTC)[reply]

Your advice is noted. The example of instantaneous measurements taken of a car was wasted if you think they predict whatever the driver may do later. I think a person seeking late in life to reform the physics that they neglected or forget will not be helped by more rambling debate and that this one may now be closed, citing the rule here: "We don't answer requests for opinions, predictions or debate." Philvoids (talk) 15:19, 8 November 2022 (UTC) [reply]

From their user page: "Currently I am interested in the origins of Einstein's theory of relativity and want to participate in discussions on this vast subject, to perhaps correct it." I dare say we can safely ignore this guy.--User:Khajidha (talk) (contributions) 21:48, 7 November 2022 (UTC)[reply]

Here can we speak freely of science ? "Einstein's theory of relativity": It's questionable science or dogma ? Malypaet (talk) 22:05, 7 November 2022 (UTC)[reply]

Maxwell was a professor of natural philosophy, at the time when nature and physics were linked. I reread his original article "A Dynamical Theory of the Electromagnetic Field". His text is as powerful as his equations. You should read it. Malypaet (talk) 22:00, 7 November 2022 (UTC)[reply]

Cats' eyes

I have two cats; each cat has eyes that reflect in a different color. One reflects red, the other green. I had assumed eye reflection color would be species dependent, but evidently it is not. What determines the color of eye reflection? 136.56.52.157 (talk) 03:09, 6 November 2022 (UTC)[reply]

Humans can have red/pink, green, blue, black etc eyes. Even purple I think.

. Sagittarian Milky Way (talk) 03:14, 6 November 2022 (UTC)[reply]

Humans have only red, because we lack the tapetum lucidum. Foxes eyes reflect green; supposedly a murder case hinged on this fact, as the shooter claimed he was aiming at a fox at night and accidentally shot a person. Your cat may be explained further down in the tapetum lucidum article, or s/he might have a damaged or missing tapetum lucidum in one eye. Abductive (reasoning) 03:34, 6 November 2022 (UTC)[reply]

Interesting article, thanks for the link. Accordingly, green reflection ("eyeshine") is normal for cats, and blue-eyed cats are an exception, glowing red. In my case, the cat with red eyeshine does indeed have blue eyes. The article doesn't explain why a blue iris would affect eyeshine color; presumably it is coincidentally caused by genetics. 136.56.52.157 (talk) 04:31, 6 November 2022 (UTC) ... Edit: I should clarify that each cat has same color in both eyes; but one cat reflects green in both, the other (blue-eyed cat) reflects red in both -- sorry for the confusion.[reply]

I wonder if blue-eyed cats don't see as well in the dark (?). 136.56.52.157 (talk) 04:51, 6 November 2022 (UTC)[reply]

If the cat's eyes really don't reflect green from any angle then I would say, yes, their night vision is impaired. Supposedly cats can detect a single photon under the right circumstances, while our detection level is something like 4 photons. Cat vision says their night vision is about seven times more sensitive than ours. Abductive (reasoning) 08:56, 6 November 2022 (UTC)[reply]

Dubious animal with only one layer of cells

I remember reading about an animal that may or may not actually exist. It was microscopic and had only a single layer of cells in its body. It was like a sausage in shape, with a pore and extra cillia on each endd Quick Trundleteacher (Talk) (Inputs) 18:52, 6 November 2022 (UTC)[reply]

Are you maybe thinking of rotifers?--User:Khajidha (talk) (contributions) 11:10, 7 November 2022 (UTC)[reply]

Perhaps Placozoa (or Myxozoa, some of which are unicellular)? --Amble (talk) 19:02, 7 November 2022 (UTC)[reply]

Choanoflagellate can be a ball shape of a single layer of cells, not classed as an animal. Embryos may be a single cell layer, eg the sponge embryo. Graeme Bartlett (talk) 21:06, 7 November 2022 (UTC)[reply]

Jiufotang Dinosaurs

Why is there such a lack of variety of non avian dinosaurs in the Jiufotang formation compared to the Yixian formation which has iguanodonts, compsognathids, therizinosaurs, sauropods, ornithomimosaurs and troodontids, while the Jiufotang only has microraptorines, ceratopsians, ankylosaurs, and proceratosaurs which the Yixian also has? CuddleKing1993 (talk) 19:44, 6 November 2022 (UTC)[reply]

I can't answer myself, but Jehol Biota may contain some clues. {The poster formerly known as 87.81.230.195} 5.64.163.219 (talk) 08:12, 7 November 2022 (UTC)[reply]

November 7

Lens related question

The complete range of n for which a convex lens comprises of ( 2n-1) different transparent materials forming (2n-1) images ( n is a positive integer). Options: (1) n≥0 (2) n≥2 (3) n≥1, (4) n≥ 1/2 Exclusive Editor _{Notify Me!} 13:13, 7 November 2022 (UTC)[reply]

Please do your own homework.

Welcome to the Wikipedia Reference Desk. Your question appears to be a homework question. I apologize if this is a misinterpretation, but it is our aim here not to do people's homework for them, but to merely aid them in doing it themselves. Letting someone else do your homework does not help you learn nearly as much as doing it yourself. Please attempt to solve the problem or answer the question yourself first. If you need help with a specific part of your homework, feel free to tell us where you are stuck and ask for help. If you need help grasping the concept of a problem, by all means let us know. AndrewWTaylor (talk) 14:14, 7 November 2022 (UTC)[reply]

What insect is this?

My brother randomly capture it in a water plastic bottle? We are in Indonesia if that helps.

https://i.postimg.cc/KcsC631Y/20221108-002246.jpg

https://i.postimg.cc/y8053fvJ/20221108-002339.jpg

https://i.postimg.cc/FKm6yjBT/20221108-002347.jpg Salbazier (talk) 17:39, 7 November 2022 (UTC)[reply]

Looks like an ant. ps last image is the clearest. Graeme Bartlett (talk) 21:30, 7 November 2022 (UTC)[reply]

Vesbius purpureus? See, for example, the Biodiversity of Singapore. But make sure you compare with other images too, including photographs. We have no article on the species or on the genus Vesbius which belongs to the Harpactorini, a tribe of the Harpactorinae, a subfamily of the assassin bugs. ---Sluzzelin talk 21:46, 7 November 2022 (UTC)[reply]

White dust around air purifiers

I've tried multiple air purifiers in the living room, brand name ones and highly rated models, with the correct CADRs for the room, and they, probably because of tall the air circulation around the units, all result in white dust on surfaces around the units. If these machines are so good at cleaning the air, why do they make their surroundings so dusty?

I tend to operate the machines at just below the top speed. The air quality indicators on the new machines all indicate good quality in general, although the current Winix does turn red from time to time, usually when I use the stove, so I'd turn it up when it does. 74.64.73.24 (talk) 21:01, 7 November 2022 (UTC)[reply]

In general, there is a very big difference between a room that has appropriately-filtered air (possibly maintained by a moveable or installed air filtration system); and a cleanroom that is engineered to have very few or zero airborne particulates.

Air purifiers remove dust; but they do not prevent dust from existing. Dust floating around in the air can be conceptualized as a mixture at some sort of stoichiometric equilibrium: we can remove dust, and new dust can be added, and the relative rate of adding and removing dust yields a sort of equilibrium with some amount of dust floating around, just like those rate-equations we used to do for wet chemistry. Each "specie" of dust has its own rate-equation; an air filter machine just nudges that equilibrium around a bit, with a different effect-size for all the diverse species and sizes of dust.

To summarize this in a dramatic and oversimplified fashion: if your room has a floor (in other words, if - when you stand - you are not standing on the steel grates that cover your laminar flow exhaust ports), you shouldn't expect a dust-free volume of air - no matter how many large, powerful air purification appliances you employ.

Here's an array of fun further reading:

Health and Environmental Effects of Particulate Matter (PM)
Particle Pollution and Your Health - "The size of particles is directly linked to their potential health concern ... Larger particles are of less concern"
Indoor Air Pollution: Introduction for Health Professionals (in which our esteemed experts tell us how cleaning the air can actually stir up extra dust - hey, we were just talking about turbulence and rate-inversion and sign-flipping in sensitive systems a few days ago!)
And, of course, one of my favorite picture-books: Wolf's Microchip Manufacturing, which has a whole lot of cool photos of air filters —

Long story short - a very large majority of the dust you can see floating around is physically too large to harm your health. These particles can't get into the tiny spaces inside your lungs; they can't get inside your bloodstream. Air filters (the kind of appliances you buy at the store - whether they are built to the "HEPA" standard or to any other standard) aren't necessarily trying to get rid of "all the dust you can see" - they are trying to get rid of those airborne particulate materials that are most harmful to human health.

If you need to get rid of airborne dust for some other reason — (let's say that you want to make sure there is no radioactive dust that could contaminate your fragile low-noise amplifiers, or avoid any airborne particulates that could smudge up your photolithography mask, or embed in your aluminum sputterer, or any of the other unusual things that you might do in your lab, and absolutely should not do at home, no matter how tempting — but these are scenarios where we say, "yes, we really want exactly zero dust in the air and we will pay any amount of money to do it") — then your air filtration system is going to look and behave a lot differently from even a professional-grade air filter designed to improve healthy air-quality.

Nimur (talk) 21:54, 7 November 2022 (UTC)[reply]

More specific to the original query, unless there is some other source of "white dust", it is most likely dead skin cells. Logically, the reason there is an accumulation near the filters, is that the filter's fan attracts the particles in the air, but some are heavy enough to fall before being sucked in, or they bounce off the grating in front. (Just guessing -- no source). 136.56.52.157 (talk) 19:22, 8 November 2022 (UTC)[reply]

What? Why would the effective power of the fan be lessened as the particle got closer? If it was strong enough to haul a skin cell from across the hall, how could it be too weak to finish the job? Matt Deres (talk) 21:35, 9 November 2022 (UTC)[reply]

It's my understanding that dust often accumulates on surfaces, especially wherever the air is circulated such as with box fans, because of static cling. Indeed, according to the Lifehacker website: [9] which cites the Readers Digest, spraying a diluted solution of antistatic fabric softener on surfaces ought help reduce the dust from accumulating in your home, but I don't know how effective it is. -Modocc (talk) 23:17, 9 November 2022 (UTC)[reply]

November 8

Animals with bony tongues

Are/were there animals whose tongues contain bone(s), except Osteoglossiformes? 212.180.235.46 (talk) 12:19, 8 November 2022 (UTC)[reply]

While it is not strictly within the tongue, many vertebrates have a hyoid bone or analogues, which among other functions, support the tongue. --Jayron 32 14:20, 8 November 2022 (UTC)[reply]

Hall of mirrors

The front page of this morning's Daily Mail has on it a picture of the front page of this morning's Daily Mail, which of course includes a picture of the front page of this morning's Daily Mail, and so ad infinitum. Is there a name for this phenomenon? 79.76.42.157 (talk) 13:35, 8 November 2022 (UTC)[reply]

See Droste effect (and also mise en abyme and infinity mirror). ---Sluzzelin talk 13:42, 8 November 2022 (UTC)[reply]

Or more generally, Recursion. --Jayron 32 16:00, 8 November 2022 (UTC)[reply]

How many replications before it disappears into the pixels? ←Baseball Bugs ^{What's up, Doc?} carrots→ 16:41, 8 November 2022 (UTC)[reply]

What are you talking about? You can zoom in forever, see here! ---Sluzzelin talk 17:35, 8 November 2022 (UTC)[reply]

Temporary place to see that front page. --174.89.144.126 (talk) 20:14, 8 November 2022 (UTC)[reply]

Looks like the answer is 3. ←Baseball Bugs ^{What's up, Doc?} carrots→ 21:43, 8 November 2022 (UTC)[reply]

Many years ago I came across a a pdf named A Primer to Contemporary Self-Reference by Thomas Bolander. I saved it on my PC and still have it, but it seems to have disappeared from the interwebs. I can only suggest Uroboros as a starting point. May your journey be fruitful and not end up deep in your own fundament. MinorProphet (talk) 01:47, 10 November 2022 (UTC)[reply]

November 9

Arsenic compound used in WWI weapons

Zone Rouge says:

Some areas where 99% of all plants still die remain off limits (for example, two small pieces of land close to Ypres and Woëvre), as arsenic constitutes up to 175,907 mg/kg of soil samples.

I found that the source of this arsenic was from detonators:

A study, published in 2007, claimed the levels of arsenic, used in the detonators, were between 1,000 and 10,000 times the level usually found in the ground.[10]

What was the chemical compound containing arsenic that was used in WWI-era detonators?

Helian James (talk) 00:12, 9 November 2022 (UTC)[reply]

That seems to be a typo or misunderstanding. It should have been detonations, not detonators. Recovered chemical weapons in World War I were detonated there after the war. See:

Thouin, Hugues; Le Forestier, Lydie; Gautret, Pascale; Hube, Daniel; Laperche, Valérie; Dupraz, Sebastien; Battaglia-Brunet, Fabienne (15 April 2016). "Characterization and mobility of arsenic and heavy metals in soils polluted by the destruction of arsenic-containing shells from the Great War". Science of The Total Environment. 550: 658–669. doi:10.1016/j.scitotenv.2016.01.111. ISSN 0048-9697.
Masini, Giovanni; Saglietti, Ivo (28 December 2017). "The endless battle". InsideOver. IL GIORNALE ON LINE S.R.L.

--136.56.52.157 (talk) 04:04, 9 November 2022 (UTC)[reply]

The chemicals include diphenyl-chloroarsine and diphenylcyano-arsine

Flyn, Cal (10 August 2021). "Plants, Heavy Metals, and the Lingering Scars of World War I". Atlas Obscura. --136.56.52.157 (talk) 04:33, 9 November 2022 (UTC)[reply]

This publication is the source of the value 175,907 mg/kg. The number seems ridiculously precise to me. --Lambiam 10:28, 9 November 2022 (UTC)[reply]

Why question their results when the precision of the measured data is lab dependent and any less precise value(s) than they report are not maximums of their empirical data sets? Modocc (talk) 14:26, 9 November 2022 (UTC)[reply]

See False precision --136.56.52.157 (talk) 15:01, 9 November 2022 (UTC)[reply]

For more on that subject, see today's xkcd. --174.89.144.126 (talk) 23:11, 9 November 2022 (UTC)[reply]

The question/possibility of false precision was raised by Lambiam, but he did not substantiate why it seems to be the case with the published source. Modocc (talk) 15:08, 9 November 2022 (UTC)[reply]

I'll let @Lambiam: respond specifically; in the meantime read False precision. Regardless of the source, there are many variables that would affect the data (minute changes from day to day, variability of sample locations, etc.). At best, one can obtain an average or mean with a margin of error. The entire volume of soil in the study area surely isn't exactly 175,907 mg/kg without variation. 136.56.52.157 (talk) 16:38, 9 November 2022 (UTC)[reply]

Yes, I know that empirical data sets that are produced are affected by circumstances and methodologies (and subject to peer-review) and are reported on accordingly. With sampling, it's likely that localized contamination is higher than what was sampled, but the authors are reporting on what was found. Not what could be found. Modocc (talk) 17:07, 9 November 2022 (UTC)[reply]

A specific measurement on a specific sample taken on a specific date might be "accurate" but meaningless. 136.56.52.157 (talk) 17:17, 9 November 2022 (UTC)[reply]

Empirical recorded maximums are typically not meaningless though. Modocc (talk) 17:30, 9 November 2022 (UTC)[reply]

That data might make sense in its original context, but journalists using it for a general media article is nonsensical. 136.56.52.157 (talk) 19:03, 9 November 2022 (UTC)[reply]

The cited 2007 article is behind a paywall (and the DailyMail is not a reliable source the last time I checked and it's not cited). Modocc (talk) 19:49, 9 November 2022 (UTC)[reply]

If they had divided the soil sample into three equal parts after thoroughly mixing it and then had tested these parts separately, they might have found three values like {175,837 mg/kg, 175,893 mg/kg, 175,921 mg/kg}. There is no way the spread would have been in the order of 1 mg/kg. Copying the number as read off a measuring device in a table as one of the entries among the 14 samples tested is one thing; reporting it that way in the abstract is something else. --Lambiam 19:33, 9 November 2022 (UTC)[reply]

Suppose the mixing you suggest is inadequate and its all found only in one subsample (in 1/3 the sample), the result for the entire sample is still the same as reported. The question regarding its meaningfulness depends on its distribution in the soil, how many samples per area were measured, and whether or not any of the data can be considered as outliers, none of which is in the paper's abstract and which is the only part available to me. I have not nor plan to review their results. Modocc (talk) 20:05, 9 November 2022 (UTC)[reply]

November 10

Benzene ring

Many, many moons ago (I would have been about 15) our chemistry teacher told us about the benzene ring. But because my mathematics was abysmal, bordering on non-existent, I soon came to the unhappy conclusion that I was never going to realise my boyhood dream: to be some sort of chemist, preferably of the organic type. Even the concept of a mole did my head in. About a decade later (having pursued a somewhat different career path) I came across Kekulé's fabled constitutional wander, and began to understand how utterly important his insight was.

Can anyone explain in plain language why the benzine ring appears to be so fundamental to org. chem.? Almost every diagram of any complex molecule I come across on WP seems to include it almost as a matter of course. What makes it so bindable, as it were? Is there anything else quite so widespread?

Our teacher also suggested The Peptide Link™ as the name of a funky jazz beat combo, but it seems never to have taken off. MinorProphet (talk) 02:24, 10 November 2022 (UTC)[reply]

Articles: cyclic compound, aromatic compound, aromaticity. Very technically, a "benzene ring" is only C₆H₆. There are lots of compounds containing a ring structure that isn't a "benzene ring", although they can be modeled as starting from a benzene ring and then substituting atoms of the ring with other things. Aromatic rings, of which the benzene ring is an example, are very stable chemically because the electrons of the atoms in the ring "overlap" and are delocalized throughout the ring, in a great demonstration of quantum chemistry and the wave–particle duality of electrons. This confers increased stability, which is often a desirable property. Not all "common" molecules contain ring structures. For instance carbohydrates often can adopt a cyclic form, but can freely convert between this and a linear form. Fatty acids are linear molecules, and only some of the proteinogenic amino acids contain rings. --47.147.118.55 (talk) 05:22, 10 November 2022 (UTC)[reply]