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June 9

Determine a fluorescent lamp fixture's voltage requirement

I have a 6 W UV-C tube with a fluorescent lamp fixture. The seller says it's for 110 V. However, it failed to turn on after proper installation. The seller returned money to me and let me keep it. I now have a 220 V transformer. How do I know if it's safe to test if the fixture was actually a 220 V one? -- Toytoy (talk) 15:06, 9 June 2022 (UTC)[reply]

According to customer service at Amerlux, a light manufacturer, the ballast is voltage rated, not the fluorescent tube. She also noted that a UVC tube is ultraviolet only. It will not fluoresce, so it will not produce visible light. I assume that you know that and you were trying to use it for a different purpose than lighting a room. 97.82.165.112 (talk) 18:17, 9 June 2022 (UTC)[reply]

A fluorescent UVC lamp will give off some visible light, as the spectrum of the glowing gas is quite complicated. PS do not let UVC irradiate you for long as it will cause sunburns even on the eye. You can also smell the ozone produced. Graeme Bartlett (talk) 01:13, 10 June 2022 (UTC)[reply]

History and Future of the Sunda trench between the Australian Plate and the Sunda Plate?

I'm trying to get a feeling for what the portion of the planet north of the currently extant Australian plate looked like while Australia was farther south. Is there any way to know whether there were more islands (to the size of Papau New Guinea?) that were subducted into the Sunda Trench or not? Also as the Australian plate moves north, is there any way to know whether Australia would subduct into the Sunda trench presumably raising the Java, Borneo, etc (and as such perhaps causing some of the islands to join) or whether you'd end up with the Australia plate staying on the surface and causing a massive crunch.Naraht (talk) 15:10, 9 June 2022 (UTC)[reply]

Continents and islands never subduct. They just collide with each other. So, Australia will collide with islands lying between it and the Asia and then with Asia itself. This collision will raise a new great mountain belt. As to the past, some island have been probably accumulating at the North margin of the Australia as it moved North. I also should note that New Guinea is a part of the Australian continent, not a true island. Ruslik_Zero 21:02, 9 June 2022 (UTC)[reply]

Only limited amounts of continental material are ever subducted due to their relative buoyancy, a result of their much lower density than oceanic crust. The northern part of the Australian continent has been colliding with the Pacific Plate since the Late Cretaceous. This has led to the progressive accretion of several terranes representing island arcs and microcontinents. This paper looks at that history and where these bits and pieces have ended up in terms of the present geology of New Guinea. Mikenorton (talk) 22:32, 9 June 2022 (UTC)[reply]

Further west, in the Timor area, the oceanic crust that used to lie north of the Australian continent has now been completely consumed by subduction along the Sunda Trench system and there is ongoing collision, involving some subduction of the Australian continental margin, according to this study on that region. The collision caused by the continental margin entering the Sunda Trench is diachronous, propagating steadily westward with time. Mikenorton (talk) 22:51, 9 June 2022 (UTC)[reply]

From studying the papers, it feels like the Australian Plate is undergoing two *different* type of collisions. On the east side of the northern edge, New Guinea has crunched into quite a bit of land on its way north but at this point, only New Britain and New Ireland are going to be crunched in the near term. After that, it will simply continue north, however, that depends on whether the Philippines are moving east fast enough to get in the way or not.

OTOH, in the west, the Australian Plate will continue to subduct but this is causing the Sunda plate to rotate counter clockwise slightly, but the continent itself is heading just enough east of directly north that it won't necessarily crunch the islands farther west in on the Sunda Trench.

Feels like any the Techtonics of the Sunda plate and the Philippines are more complicated than anywhere else on the Planet.Naraht (talk) 15:11, 10 June 2022 (UTC)[reply]

I think that's a fair description. The long term effect of the collision with the Sunda Plate and all those other minor plates to the east is hard to predict. Mikenorton (talk) 19:36, 10 June 2022 (UTC)[reply]

Big Ear's design and Wow signal

Per Wow! signal, prior to detecting it, the Big Ear was assigned to the scientific search for extraterrestrial intelligence (SETI). Then, per article, due to Big Ear's design it couldn't fully pinpoint the signal's place of origin. So why was Big Ear assigned to SETI if it lacked the basic ability to determine signal's right ascension (which looks essential in such activity)? Poor decision? Thanks. 212.180.235.46 (talk) 16:54, 9 June 2022 (UTC)[reply]

Every position measurement has some measurement uncertainty (see the quoted errors on the right ascension and declination values in the article). "Normally" there would be a single contiguous error ellipse centred on one point, and one would look for an optical counterpart within that ellipse. Here, the uncertainty is spread over two non-contiguous ellipses – that might look weird at first glance, but it's just an extension (induced by the design of the telescope) of the ordinary measurement uncertainty. Not a big deal, really. --Wrongfilter (talk) 17:34, 9 June 2022 (UTC)[reply]

You can find some details here: [1]. The telescope had two feed horns that looked in slightly different directions. The signal processing equipment was capable of distinguishing a signal in one horn from a signal in the other. The problem is that the program that made a record of the data simply didn't include this information. That's something you'd obviously want to have, and it was added in a later version of the software. This does seem to be a poor decision, and the report's author agrees: it is listed among the "especially important changes done later that should have been done earlier". But it's not a limitation of the Big Ear, it's just an oversight in the data recording software that could have been (and should have been, and later was) easily remedied. --Amble (talk) 18:46, 9 June 2022 (UTC)[reply]

Let me try an clarify my previous answer a bit more, in light of Amble's excellent findings. Obviously, noone would buy a bathroom scale that tells you "you weigh 75kg or 90kg". The difference is that, even with the measures mentioned by Amble, which could have identified the horn that detected the signal, we still wouldn't know where the signal came from. A paper referenced in the article (Caballero 2022) lists 38 stars in the positive horn and 28 stars in the negative horn (already reduced to G-type and early-to-mid K-type stars). So, identifying the horn reduces the uncertainty and the number of stars to investigate by a factor of two, which is great but does not fully solve the problem. --Wrongfilter (talk) 20:55, 9 June 2022 (UTC)[reply]

You can understand why this extra record wasn't usually necessary by thinking about what happens when the telescope would scan across a normal radio source. One horn crosses the position of the source and sees the signal, then the other horn. The radio sources are in discrete locations on the sky and sparse enough to avoid "confusion", so you see two bumps, one after the other, and it's completely obvious which bump came from which horn. The Wow! signal only has one bump. You can look at the right distance before and after it, and where you'd expect to see another bump, there's no signal. Either the first horn saw it, and it turned off before the second horn got there, or else the first horn saw nothing, and it turned on before the second horn got there. So the record for this signal had an ambiguity that wasn't present in the record for normal radio sources on the sky. --Amble (talk) 21:22, 9 June 2022 (UTC)[reply]

June 10

Simulate heavy weight with levels.

In the gym, people normally pick x kg of iron weights when they want to exercise lifting x kg. Wouldn't it make financially sense to use a level to increase the load, (say increase by 10x putting the weight at 10 cm of a 1 m level) and use a 5 kg weight to lift 50 kg? --Bumptump (talk) 18:17, 10 June 2022 (UTC)[reply]

Do you mean a lever? You could also use a pulley or gears to get mechanical advantage. Weight machines do use various kinds of mechanical advantage: see [2] for example. However, if you change the mechanical advantage, you'll also change the distance the weights need to travel as the user completes the motion. For example, if you make 5 kg of weights feel like 50 kg, the weights will also need to move through 10 times as great a distance. Making the machine 10x as large will have implications for its cost, space requirements, and safety, which you'd have to balance against the cost of the weights themselves. --Amble (talk) 18:48, 10 June 2022 (UTC)[reply]

If you really want to reduce the need for weights, you can make an exercise machine with other forms of resistance, like friction or springs. --Amble (talk) 19:12, 10 June 2022 (UTC)[reply]

June 11

Have atoms with g orbitals been experimentally created?

It is my understanding that no currently known chemical elements have electrons on g orbitals in the ground state, and it is theorized that the 8th period will contain such elements. I'm curious, however: has anyone created excited atoms with electrons on g orbitals? As a layperson, I imagine no, since it would require pushing electrons up at least two energy levels from the highest ground state for currently discovered elements (from 7p to 8s to 5g), and I'm not even sure if current superheavy elements were synthesized as complete atoms or bare nuclei. - Linneris (talk) 09:18, 11 June 2022 (UTC)[reply]

When someone takes a bell and knocks it with a hammer, the bell will get into an excited state and start ringing. It is a bit unusual to describe this by saying they created an excited bell. Electron excitation is a common process, but if the excitation energy is too high, the electron flies off and the atom becomes ionized. Otherwise, with lower energy, the electron settles (usually for a brief instant) into a higher orbital, which can be the g-orbital. This happens all the time. Since this is a quantum system, more properly speaking this is a superposition of eigenstates, somewhat like the ringing of an excited bell is a superposition of the fundamental and overtones. When superheavy elements are synthesized, this happens in a highly energetic environment by bombarding already heavy nuclei with a beam of nuclei, brought to a very high speed in a particle accelerator. It is all very messy; the most meaningful statement one can make about whether the new element was formed as complete atoms or bare nuclei is that neither is the case (and no atomic physicist cares). The new nucleus as originally formed by fusion will emit some neutrons before it is stable long enough (still very short) that it can be identified as having a specific atomic weight. --Lambiam 10:33, 11 June 2022 (UTC)[reply]

To answer the final part of your question, Linneris, the conventional chemistry of superheavy elements is normally accessible despite their short half-lives: see nobelium for an example. Its solution chemistry in the +2 or +3 oxidation states (but otherwise with the expected set of electrons) is relatively well-known. Chemists do care.... Mike Turnbull (talk) 12:07, 11 June 2022 (UTC)[reply]

Exciting electrons to 'high' energy levels is surprisingly easy. Electrons that are still in orbitals - that is, still in a bound state - are by definition at lower energy than free electrons. If you have enough energy available to ionize an atom, then you need less energy than that to kick an electron up to an arbitrarily high-energy orbital. (The 'difficult' bit is often setting up your experiment to only supply enough energy for the appropriate excitation, rather than full ionization.)

There's a whole field of study devoted to Rydberg atoms: atoms with one or more of their electrons in highly-excited states, with very large principal quantum numbers (n). You can get delightfully weird behavior, where you start blurring the distinction between an 'orbital' and an 'orbit'. TenOfAllTrades(talk) 13:33, 11 June 2022 (UTC)[reply]

Actually the 8-th period begins with the element 119, which has not been created yet. So, the answer is no. Ruslik_Zero 15:00, 11 June 2022 (UTC)[reply]

As others (inluding the OP) have mentioned, creating an electron configuration with an electron higher than the atom's neutral ground state (where the Aufbau principle predicts the electrons would be) is not intrinsically difficult. Excited states, by promotion of an electron to a higher orbital, are common. Where things get more interesting is actual reduction—forcing extra electrons in, to make anions—that crosses into the next principal energy level. That the H^2– ion (no, that's not a superscript/subscript transposition!) can be made is interesting several ways.doi:10.1126/science.191.4226.463. DMacks (talk) 17:05, 11 June 2022 (UTC)[reply]

Why is there comparatively so much junk DNA?

Why do so many living beings seem to have such a comparatively large amount of DNA that can mutate, for example, without this leading to functional impairments?
What evolutionary advantage does this have?--2A02:908:422:9760:0:0:0:82C8 (talk) 14:17, 11 June 2022 (UTC)[reply]

Non-coding DNA#Junk DNA will get you started. (See also selfish genetic element.) TenOfAllTrades(talk) 14:29, 11 June 2022 (UTC)[reply]

Neat roads in Japan

Why do roads in Japan, the roads themselves and the markings, always look so neat? Do they use different materials, do they repair them regularly, are they in a temperature sweet-spot (neither snow nor heatwaves, that implies neither salt in winter and less tyre attrition)? Do lighter vehicles contribute to this? Or is it just my Western impression based on typical images? --Bumptump (talk) 16:02, 11 June 2022 (UTC)[reply]

Search the web for "japan road quality" and you'll see a lot of answers. It's a combination of material selection, construction methodology, and standards. --jpgordon^{𝄢𝄆𝄐𝄇} 16:39, 11 June 2022 (UTC)[reply]

Yep, but the problem is more what Finlay says: "to find a reference that's worthwhile"--Bumptump (talk) 16:58, 11 June 2022 (UTC)[reply]

It's my understanding (but I've failed to find a reference that's worthwhile) that Japan generally doesn't use road salt much. Instead, as with places like Norway, when the roads get cold and snowy enough, people in affected areas change to winter or studded tires. This was, apparently, an issue when Japanese car makers began to export cars to the UK. They figured this would be straightforward, as the climate in northern Honshu is fairly similar to the UK's, and both countries drive on the left. But British weather is very changeable (there isn't a consistent "ice season"), so winter or snow tires are very rare the UK (you'd fit them and then a week later it would be 8C and raining). So the UK uses a lot of road salt (applied as the weather forecast demands). The mostly Japanese-spec cars didn't have the additional undersealing that winter salt demands, and so initially had a bad reputation for rusting. -- Finlay McWalter··–·Talk 16:41, 11 June 2022 (UTC)[reply]

It is also notable that studded tires also cause road damage. When they were first introduced in Ontario, where I live, this became obvious when the lane markings rapidly disappeared from many roads, and studded tires were banned in response. (They were later allowed in Northern Ontario only.) If Japan avoids salt damage but their roads somehow stand up to studded tires, this is also notable. --174.95.83.56 (talk) 22:27, 11 June 2022 (UTC)[reply]

Per Snow tire#Asia, Japan has banned studded tires on paved roads and vehicles either use winter tires or snow chains. Pinguinn 🐧 09:33, 13 June 2022 (UTC)[reply]

No snow in Japan? The macaques are very disappointed in you. Fgf10 (talk) 08:32, 12 June 2022 (UTC)[reply]

Japan has also hosted a couple of Winter Olympics. --←Baseball Bugs ^{What's up, Doc?} carrots→ 13:25, 12 June 2022 (UTC)[reply]

So has subtropical Sochi. Hardly a good measuring stick. Fgf10 (talk) 16:10, 12 June 2022 (UTC)[reply]

See also POROUS ELASTIC ROAD SURFACE AS URBAN HIGHWAY NOISE MEASURE in Japan, but use seems limited. Alansplodge (talk) 13:51, 12 June 2022 (UTC)[reply]

Road wear and tear is exponential with weight. Maybe cab-behind-engine-not-over-miniRV-behind-that 18-wheelers with the American sized 53 foot trailer aren't as popular there? Japanese car tax laws are so F-450 discouraging that kei cars became very popular. Tokyo is not mild in summer, it's hot and humid. Sagittarian Milky Way (talk) 02:54, 14 June 2022 (UTC)[reply]

According to this, the max trailer length in Japan is 12 metres (40 ft) and max gross weight is 20 tonnes (25 t on designated roads). Alansplodge (talk) 13:36, 14 June 2022 (UTC)[reply]

In the US max gross weight is at least 36.29 tonnes in all states (15.42 tonnes per tandem axle plus 5.44 on steering axle). Some states much more. Sagittarian Milky Way (talk) 06:00, 15 June 2022 (UTC)[reply]

June 13

Enola Gay traveled 18.5 km in 44 seconds after dropping the atomic bomb over Hiroshima

Atomic_bombings_of_Hiroshima_and_Nagasaki#Bombing_of_Hiroshima says: Little Boy containing about 64 kg (141 lb) of uranium-235 took 44.4 seconds to fall from the aircraft flying at about 9,400 meters (31,000 ft) to a detonation height of about 580 meters (1,900 ft) above the city. Enola Gay traveled 18.5 km (11.5 mi) before it felt the shock waves from the blast. That is over 940 mph, but the top speed of Enola Gay is 339 mph. Is that a mistake? Vpab15 (talk) 15:27, 13 June 2022 (UTC)[reply]

"before it felt the shock waves" is the key statement -- the shockwave has its own travel time. So, 44 seconds of head start, plus relative position head start, plus distance travelled by the bomb (can be part of that relative position, but remember to include it), plus the relative overtake speed of shockwave versus plane-in-a-dive-to-add-speed. It seems plausible. This page says the goal was to achieve at least 7 miles of separation. (editing to add: 509th_Composite_Group#Atomic_bomb_missions says it was "a minute", no firm precision, after the blast before the shockwave reached the aircraft -- point being, more time elapsed post-blast than pre-blast) — Lomn 15:39, 13 June 2022 (UTC)[reply]

Yep, this is an important point. The blast wave propagates outward at speeds roughly comparable to the speed of sound, at least initially: about 700 mph, or about 300 m/s.

So the aircraft gets a head start of 44 seconds from the time it takes for the bomb to fall, plus the time-of-flight for the blast wave. Even if the Enola Gay were hovering in place directly over the detonation, that's another 30 seconds or so for sound (and the blast) to climb back up again. Assuming the pilots were travelling at a brisk pace away from the detonation, they'd be moving close to half the speed of sound. It would take a while for the blast to overtake them.

11.5 miles at 339 mph is almost exactly 2 minutes of flight time. I can't bring myself to do the pencil-and-paper work, but it strikes me as plausible that they had sufficient head start. TenOfAllTrades(talk) 16:21, 13 June 2022 (UTC)[reply]

The blast wave propagates outward at speeds roughly comparable to the speed of sound, at least initially: about 700 mph, or about 300 m/s. Is that correct? A blast wave starts with a shock wave which can go (much) faster than the speed of sound. Whether that was the case for those bombings, I do not know (the speed depends on how much energy was released and the gas properties). The later, non-shock wave does propagate at the speed of sound with a relatively linear behavior (= the speed does not depend on the amplitude). Tigraan^{Click here for my talk page ("private" contact)} 09:10, 15 June 2022 (UTC)[reply]

Thanks for the reply and the link. However, it says As it turned out, with the first bomb, which was dropped on Hiroshima, they did get approximately 6 to 7 miles away from the blast, following this procedure. That is significantly less than the 11.5 miles mentioned in the wiki article. Any idea which one is correct? Vpab15 (talk) 16:26, 13 June 2022 (UTC)[reply]

Two different statements. "Away from the blast" suggests distance from the point of explosion at the time of explosion, which is relevant for surviving the flash. But the initial question is about surviving the shock wave, which has the additional travel time (and therefore distance). — Lomn 18:05, 13 June 2022 (UTC)[reply]

(edit conflict) A careful reading of the escape tactics link shows that the bomb traveled onwards for 21⁄4 miles before detonating. In the meantime Enola Gay had performed a diving turn to go as fast as possible in the other direction. The bomber was therefore nearly 7 miles away from the detonation. As TenOfAllTrades pointed out, Enola Gay continued to fly at around half the speed of sound away from the expanding blast front which was itself traveling at around the speed of sound. By the time the blast reached the 6 or 7 mile point, Tibbits had already put another 3 miles or so between him and the explosion. The blast finally caught up with him at 111⁄2 miles from the point of detonation. Martin of Sheffield (talk) 18:13, 13 June 2022 (UTC)[reply]

That makes sense. Thanks all for your replies. Vpab15 (talk) 21:26, 14 June 2022 (UTC)[reply]

June 14

Scientific Notation base

Does anyone have an opinion (or a factual argument) about whether the term "Scientific Notation" always implies base 10, or if it can be used with any base? Our article is somewhat ambiguous on the question. (I have started a thread on its talk page.) Stated another way, if I say "binary scientific notation", is that a fine way to refer to a representation of the form m × 2ⁿ, or a fine way although a pedant might complain, or a not-so-fine way, or a total howler? (To be on the safe side I can definitely say "binary exponential notation", but I'm still wondering about "scientific notation".) —scs (talk) 02:53, 14 June 2022 (UTC)[reply]

As the term "scientific notation" is commonly used, the base is always 10, as stated explicitly here. However, not everyone agrees.^[3] People who understand both scientific notation and binary notation will also understand what is meant by "binary scientific notation", and the term can be found used.^[4][5][6] There are also uses of "hexadecimal scientific notation" in the literature.^[7][8][9] --Lambiam 03:46, 14 June 2022 (UTC)[reply]

I searched in onelook.com for "scientific notation". Every dictionary where I found a definition indicated that it meant base 10. However, one of them—Merriam-Webster—includes a couple of example sentences collected automatically(!) from the Internet, and one of those is an article in Ars Technica by Jim Salter. Talking about the confusion based on describing amounts of storage in multiples of powers of 1024 or of 1000, he writes: "Filesystems almost universally use the powers of two (standard scientific notation), whereas storage device specifications are almost universally in powers of ten." So this sentence that M-W found to illustrate their definition does not actually conform to it. And in my opinion Salter was wrong to use those words that way and Steve is loony to ask his question. --174.95.83.56 (talk) 05:43, 14 June 2022 (UTC)[reply]

Doesn't the first sentence of the last section (Other bases) sum it up pretty well: "While base ten is normally used for scientific notation, powers of other bases can be used too". In other words ten is the default unless explicitly stated otherwise. Martin of Sheffield (talk) 08:13, 14 June 2022 (UTC)[reply]

Just an opinion: the answer is that a pedant might complain. I'm a pedant (in this question, and many others). If the analogy to scientific notation is important to you, I'd suggest calling it "generalized scientific notation" for bases other than ten.

(There is another class of pedant of the opinion that adding an adjective to a noun never extends the noun's meaning, but only restricts it. They're wrong, but it may be easier to cater to their preferences than to get into the seven millionth "a dwarf planet is a planet by definition!" argument). IpseCustos (talk) 08:30, 14 June 2022 (UTC)[reply]

Thanks, all — this is just the sort of reference information I was looking for. (My hunch about usage is basically confirmed — but I wanted something more than just my own hunch.) —sc "loony" s (talk) 11:38, 14 June 2022 (UTC)[reply]

If you represent a number as m×10^n with 10 being the binary representation of two and m and n also in binary, you have scientific notation in binary. But if you write m×2^n with m and n in decimal, you use a mixed system. My computer can also use a mixed system. When it says my file is 513kiB in size, 513 is decimal, but the ki prefix stands for 1024 and is part of a binary system. Imperial units also form a mixed system. PiusImpavidus (talk) 16:38, 14 June 2022 (UTC)[reply]

Good point. I tend to write m×2ⁿ where m is base 2 and n is base 10, which I guess is extra mixed. And then, in C, printf's %a format boils down to m×2ⁿ with m in base 16, which I find really annoying... —scs (talk) 17:52, 14 June 2022 (UTC)[reply]

Parkinson

Does Parkinson’s disease damage the ability to think and reason? --62.18.86.132 (talk) 21:27, 14 June 2022 (UTC)[reply]

Yes, Parkinson's disease#Neuropsychiatric mentions some cognitive challenges. Larry Hockett (Talk) 21:32, 14 June 2022 (UTC)[reply]

Path of moon

For any given point on earth, are there any parts of the sky that the Moon does not pass through at some time? When was this proven? Thanks. — Preceding unsigned comment added by 86.186.37.132 (talk) 21:48, 14 June 2022 (UTC)[reply]

The path of the Moon is near the ecliptic so there are definitely parts of the sky that it would not pass through. It stays within a band circling the Earth that is +/- 5 degrees from the ecliptic.[10] --mikeu ^talk 22:01, 14 June 2022 (UTC)[reply]

Thank you. Presumably this was fully known to all ancient civilisations and would have been written down at some early time in history. 86.186.37.132 (talk) 22:09, 14 June 2022 (UTC)[reply]

You are welcome. I assume so, but couldn't find a reference. I suspect that it was so obvious it was noticed before written history. --mikeu ^talk 22:14, 14 June 2022 (UTC)[reply]

Yes, so how long would one have to observe, to know that this was true? A year? 86.186.37.132 (talk) 22:21, 14 June 2022 (UTC)[reply]

It would only take months to notice but I would give it a year or so to confirm that there is a pattern that repeats. After that it becomes pretty obvious. --mikeu ^talk 22:37, 14 June 2022 (UTC)[reply]

Thank you. Of course, ancient civilisations had no concept of the earth or, therefore, the notion of "any given point on earth". So that must have come later. 86.186.37.132 (talk) 22:41, 14 June 2022 (UTC)[reply]

Ancient civilisations had words for Earth (𒅕𒍢𒁴, ארץ, γῆ) and a concept of "a point on Earth", which is meaningful regardless of whether your mental model is that of a flat Earth or a globe. For any given point on Earth, such as where some ancient stargazer may have had their domicile, the major part of the sky is Moon-free all year round. The Moon is never anywhere near the North Star. This cannot be "proven"; our best astronomical models, combined with our understanding of the laws of physics, can at best tell us not to expect the Moon venturing out of its orbit any time soon. --Lambiam 02:54, 15 June 2022 (UTC)[reply]

It's hard to figure what the IP meant by "of course", since it's demonstrably false. He might mean "earth as we now understand it", but that's true of lots of ancient concepts. --←Baseball Bugs ^{What's up, Doc?} carrots→ 04:43, 15 June 2022 (UTC)[reply]

You may be interested in Lunar distance (astronomy) in which people as early as 4th century BC observed that moon was in a different place in the sky when observed from different places on Earth. So they were able to work out how far away the Moon was at that time. Graeme Bartlett (talk) 05:21, 15 June 2022 (UTC)[reply]

Thank you, that's exactly what I was looking for. I agree "prove" is the wrong word. I meant that ancient people did not have astronomical knowledge from all over the earth as they never travelled that far or had the technology to gather it. 86.186.37.132 (talk) 07:28, 15 June 2022 (UTC)[reply]

You are actually talking about the Zodiac, that part of the sky which the Sun (and also the Moon) travels through. It appears to be of great antiquity, going back to at least Babylonian astronomy -- Verbarson ^talk_edits 08:58, 15 June 2022 (UTC)[reply]

You don't have to observe the Moon simultaneously from different places on Earth to get a distance. Just observe it from a single place over a few days and make use of the Earth's rotation and you can get a parallax measurement. You still need the radius of the Earth.

The Moon moves along the ecliptic, plus or minus 5 degrees as the orbital plane of the Moon isn't exactly aligned with the orbital plane of the Earth, plus or minus 1 degree due to parallax. PiusImpavidus (talk) 09:18, 16 June 2022 (UTC)[reply]

June 15

Scrutinizing claims about 'child marriage' according to medical sciences

Probably this was needed to be on this sciences board but rest of the connection is with humanities so I have posted an input request @ Wikipedia:Reference desk/Humanities#Scrutinizing claims about 'child marriage' according to medical sciences.

Thanks for inputs

Bookku, 'Encyclopedias = expanding information & knowledge' (talk) 09:19, 15 June 2022 (UTC)[reply]

Maxwell's Demon

Can someone explain to be how Maxwell's Demon is a useful or meaningful thought experiment? As far as I can see, either the "demon" obeys the laws of physics (requiring energy to perform work, etc), in which case this is no more a violation of the laws thermodynamics than e.g. me pumping air into a tyre. Or alternatively, the demon isn't bound by the laws of physics, in which case all that the thought-experiment proves is that something that breaks the laws of thermodynamics breaks the laws of thermodynamics, which is a pointless tautology. From the article, I see some people have already made similar criticisms, but despite that "The concept of Maxwell's demon has provoked substantial debate in the philosophy of science and theoretical physics, which continues to the present day". Iapetus (talk) 12:09, 15 June 2022 (UTC)[reply]

Whether it is useful or meaningful is up for debate but even if not it is part of the history of science. We no longer use the phlogiston theory to explain combustion but Wikipedia has an article on the subject because it is notable, not because it is currently useful. Mike Turnbull (talk) 13:49, 15 June 2022 (UTC)[reply]

That response seems a little misdirected — I don't see the slightest indication that Iapetus doesn't think Wikipedia should have an article on Maxwell's Demon. --Trovatore (talk) 16:56, 15 June 2022 (UTC) [reply]

Thought experiments that pose hypothetical questions are valuable in education to encourage reasoning. They include Schrödinger's cat, illustrating quantum indeterminacy through the manipulation of a perfectly sealed environment and a tiny bit of radioactive substance, and Maxwell's demon, which attempts to demonstrate the ability of a hypothetical finite being to violate the 2nd law of thermodynamics. The article is rated C-class, meaning it is substantive but might still be improved. Maxwell's concept of 1867 is still a fruitful sourcee for experimental work that includes an experimental realization of a Szilárd engine. Philvoids (talk) 14:16, 15 June 2022 (UTC)[reply]

Trovatore is correct - I'm not disputing that Wikipedia should have an article on it. My question is why was it (and apparently still and is) considered worthy of "substantial debate in the philosophy of science and theoretical physics", when it looks to me to be so obviously a flawed concept. Iapetus (talk) 08:51, 16 June 2022 (UTC)[reply]

The point of a thought experiment is usually to clarify the properties of a model or theory and to clarify hidden assumptions. Therefore, getting the correct result is often less important than understanding how that result comes about. Maxwell's demon seems to show an inconsistency between elementary mechanics and the laws of thermodynamics. Is there really an inconsistency? Why not? What hidden assumptions are being made? How can they be clarified and corrected? Are there other situations where we may be making a similar assumption? Thinking about these questions in the case of Maxwell's demon has led to important developments in understanding measurement, information, and computation as physical processes. --Amble (talk) 16:30, 15 June 2022 (UTC)[reply]

Einstein's most famous thought experiment, chasing a beam of light, changed the laws of physics of space and time as they were understood at the time.^[11] His thought experiment of a person floating in a box and then falling to the floor led to the even much more revolutionary concept of a curved spacetime continuum. His later thought experiments regarding "spooky action at a distance" did not change the laws of quantum physics – which Einstein had helped establish – but were fruitful in helping to push the understanding of the theory and forced theoretical and experimental physicists to be much more precise. When Maxwell conceived of his thought experiment the second law of thermodynamics was not nearly as firmly established as it is now. I think it was triggered by Kelvin's formulation of the law: It is impossible, by means of inanimate material agency, to derive mechanical effect from any portion of matter by cooling it below the temperature of the coldest of the surrounding objects.^[12] [My emphasis by underlining. --L.] Whatever the case, as pointed out by Philvoids above and also explained in our article, Maxwell's thought experiment has proved a fruitful driver for important theoretical and experimental work. --Lambiam 17:08, 15 June 2022 (UTC)[reply]

Why would a demonic sorter sorting be useful? Ha. I'm too often not all that helpful, but scientists are well-known, because of a lack of knowledge, for being myopically dead wrong, but slog on because they believe they are not since their work is useful. The noble objective, obviously, was/is simply an entropy-busting sort, but the suggested means to that end, a hypothetical gate-keeping demon, does allow for knocking down their strawman and the promulgation of that knowledge. BTW, I've just started playing Wordle and found that the word "youth" is a nice followup to "raise". -Modocc (talk) 18:43, 15 June 2022 (UTC)[reply]

Why would chasing a beam of light be useful? The question completely ignores the nature and purpose of a thought experiment and therefore is myopically dead wrong, perhaps because of a lack of knowledge. Many people are myopically dead wrong because of a lack of knowledge. This is so common that it usually does not draw any attention, unless, of course the mistaken person is a scientist. --Lambiam 20:56, 15 June 2022 (UTC)[reply]

Thought experiments are common too, but note that "The noble objective, obviously, was/is simply an entropy-busting sort..." It's why the demon has drawn attention. Modocc (talk) 21:26, 15 June 2022 (UTC)[reply]

The undisguisedly ignoble objective of the EPR paradox was to bust quantum mechanics. While not successful in that respect, it instigated, among other things, the discovery of Bell's theorem. --Lambiam 10:53, 16 June 2022 (UTC)[reply]

I think^[opinion] that the Maxwell demon is a bad illustration of a good point. The better illustration is the Brownian ratchet, unfortunately that one was produced later and is therefore less famous. The point is that if you apply macroscopic intuition to microscopic events, you can easily imagine a device that violates the second law. Introducing a "demon" muddles the waters, because the demon needs to violate certain rules (of biology for starters) to exist, and the argument becomes "yes but ignore that, just look at thermodynamics and there is a problem". Tigraan^{Click here for my talk page ("private" contact)} 09:21, 16 June 2022 (UTC)[reply]

June 16

Can optical illusions be used for medical purposes?

I stumbled upon this picture: https://twitter.com/SteveStuWill/status/1537102642345746435

And I did see curly green lines instead of the straight ones which they really are. For military duty we were asked to look at a picture filled with colored dots and asked if we could see a number. The color blind couldn't, the others said "that's obviously a 9". I think the test had no false negatives and no false positives.

Such tests are very simple and cheap while at the same time testing a full range of brain functions in a few seconds. Listening, understanding, looking, explaining, and let's not forget turning light into an image and minimizing the image to what is being asked, it's almost absurd what our brains can do. And it's not a vague Rorschach test, the answer to each picture is just Yes or No.

It might be possible that if you don't see curly lines, there's an 80% chance that you will be diagnosed with Alzheimer disease within 10 years. Or maybe people answering No to picture 3, 5 and 8 show a more than average shortage of vitamin X after a blood test. I have no medical background but I think such correlations are very well possible.

I wonder if someone researched to see if optical illusions are not just funny on Twitter, but could actually be helpful in a doctor's office. Joepnl (talk) 01:29, 16 June 2022 (UTC)[reply]

The test you did in the military was likely some version of the Ishihara test. Without needing much specialized training from the examiner, it gives a >99% correct classification of the various color-blindness tests. It is very cheap, quick, and not very invasive for the patient.

Such a test is really an outlier within all diagnosis tests, both in ophtalmology and in all of medicine. The usual status is either that there is no test with really great stats of precision and recall (= many false positives and/or false negatives), or that the test is highly invasive. For instance, breast cancer screening can be done by three tests: self-examination by the patient, which is not very invasive but is not very reliable; mammography, which is more invasive but more reliable; and biopsy, which is super-invasive but super-reliable.

The Ishihara test works very well because the underlying condition has one single symptom, it is (almost) binary (most people with color vision deficiency are entirely color-blind, not kind-of-have-difficulty-to-separate-color-partially-blind), and the symptom is constantly present among affected individuals (so that no special conditions are required to do the test).

Without a medical background, I can understand why a visual test showing colored stuff detects color-blindness. But when it comes to detecting vitamin deficiency etc. it’s hard to see how that could be diagnosed with visual tests. I suppose that some medical problems that are not directly vision-related cause some vision changes and that a diagnosis test could be based on that; but I expect that the average such test would have abysmal precision and/or recall. Tigraan^{Click here for my talk page ("private" contact)} 09:10, 16 June 2022 (UTC)[reply]

The trick image seen by the OP is an example of contradictory patterns that compete in the viewer's mind for recognition. That describes many "impossible" objects that can be drawn. The artist M. C. Escher was able to fill art galleries with such Trompe-l'œil illusions. These optical illusions work for the majority of normal people and are of no use to indicate ill health as the OP speculates. Please leave the design and use of images for medical tests to qualified medical practitioners. Such images are entirely different and include the Ishihara tests for colour vision, the Rorschach tests for examining pareidolia (seeing an object, pattern, or meaning where there is none), your opthalmologist's Snellen chart for visual acuity or an Amsler grid for macular degeneration. A claim to diagnose future Alzheimer's disease or some unspecified vitamin deficiency using only an image would be so extraordinary that without extraordinary evidence the notion must be rejected. Philvoids (talk) 11:07, 16 June 2022 (UTC)[reply]

The fact that an optical illusion is an extremely simple and quick test is why I'm asking. Posters in the waiting room of the GP, "if you don't see curly lines, please tell the doctor", something like that. Don't know which illusions to use, don't know which diseases to detect, but an extremely wild guess is that patients suffering from migraine or epilepsy have different answers than patients who don't. I'm sure blindness is one, but who knows what an illusion can also detect? Compare the story of a girl who got advertisements for diapers, just the words she typed in a search engine was enough to guess she was pregnant before she knew herself. I was hoping someone did the research and did find a huge correlation with a vitamin deficiency. Joepnl (talk) 12:02, 16 June 2022 (UTC)[reply]

What do plants do to counter animal-waste?

Plants have been crapped on for as long as plants and animals have been around. We know for humans, we have chemicals and non-chemicals to fight bacteria and viruses. Non-chemicals such as macrophages, lysozymes, and white blood cells, and chemicals such as H2O2 and HOCl. What do plants have for chemicals and non-chemicals to fight that? Also, plants can sometimes be urinated on, but I think, mammalian urine does more good than bad. It has fertilizer properties, as well as cations and anions which can be for nutrition. So I imagine urinating on plants is not an issue. 67.165.185.178 (talk) 02:41, 16 June 2022 (UTC).[reply]

Plant cuticle resists penetration of foreign matter. The waxes are fairly inert. Though if a plant is buried under a cowpat, it won't get any light. It may grow a new shoot to get around the problem. Graeme Bartlett (talk) 04:07, 16 June 2022 (UTC)[reply]

Could racism and cruelty be caused by infections from bacteria or viruses?

Could evil emotions be caused by infections that either affect our hormones or get in our brains? To be objective, I should ask,could good emotions like kindness, patience and honesty also be caused by infections? ..We often observe that a child's ethics or lack of can be learned from the example given by their parents, but how do we know that the child's ethics aren't passed on from a pathogen given to the child by a parent? Also, what about low average intelligence, could that be caused by infections?Rich (talk) 05:40, 16 June 2022 (UTC)[reply]

See Nature versus nurture. --←Baseball Bugs ^{What's up, Doc?} carrots→ 06:21, 16 June 2022 (UTC)[reply]

It is well known that some infections (meningitis!) can cause lasting neurological impairments that diminish the patient's intelligence. Some pathogenic microorganisms are known to affect the behaviour of infected animals. Spinochordodes tellinii and Paragordius tricuspidatus are extreme examples, inducing suicide by drowning in infected grasshoppers and crickets. Another well-studied example is Toxoplasma gondii, that makes infected mice lose their fear of cats. Dicrocoelium dendriticum makes an infected ant climb night after night to the top of a blade of grass and sit there till dawn, until it is eaten by a grazing animal. For humans, there is evidence that some gut bacteria, usually considered non-pathogenic, may contribute to autism, while others may relieve anxiety and depression.^[13] So, yes, at least in theory it is conceivable that some infectious agents have effects on the relative strengths of various emotions. --Lambiam 10:42, 16 June 2022 (UTC)[reply]

Toxoplasma gondii infection in mice lowers general anxiety, increases explorative behaviors and surprisingly increases a general loss of aversion to predators without selectivity toward cats. I mean to point out that it's beyond the scope of a virus, bacteria, or even an intracellular parasite, to select for the recognition of some complex entity like a cat, even in a mouse, never mind in humans with all our abstract and creative ideas. It's debatable whether there are any such things as grandmother cells (used for recognition of grandmothers), and even if there are, it would be extraordinary for a microorganism to be able to target them, since they probably have no predictable characteristics, and their locations probably vary from person to person, if they exist. Even then, the infection could only cause an unreasoning disgust about, say, Samoan people (which I mention since "racism" is in the post's title), which is not at all the same thing as interfering with the host's ethics. That is to say, a good person ought to be able to use reason to overcome any irrational visceral disgust. I might find myself having to carry a sick bag whenever hanging out with my Samoan best friend, and perhaps we'd tend to prefer to be online buddies, but this needn't affect my ethics or my politics. This kind of gut feeling can prompt racism or cruelty, but doesn't directly control it. Card Zero (talk) 11:39, 16 June 2022 (UTC)[reply]

Electric animals

I've just been playing Let's Go Pikachu on my Switch tonight. It got me thinking. We have loads and loads of aquatic animals that can use electrical discharges for attack and defense, right? Why is it that we don't have any terrestrial animals that can also do that (say, if a lion could emit an electric arc to paralyze and drop a zebra, or a bug where it's jaws were like the two terminals of a stun gun)? Or not any that I'm aware of. Maybe I'm wrong? Was there a little jungle bird somewhere a few years ago that could emit electricity if touched? I may have dreamed that. Is there a physical reason why that couldn't happen on land? --Iloveparrots (talk) 07:22, 16 June 2022 (UTC)[reply]

Actually, thinking about it further. We have stun guns, that require skin contact. We have tazers that rely on shooting out wires at a distance to deliver an electric attack. But I don't think we have a weapon (yet?) that can deliver a targeted electric discharge at a chosen target across a distance? Is that right? Which leads me to believe that this is is difficult, if not impossible? So, probably the same in nature? But less evolutionary complex than an organism that can emit two electrode terminals somehow? So one of my points upthread may be invalid. --Iloveparrots (talk) 07:33, 16 June 2022 (UTC)[reply]

Further research. Ignore the "little bird" claim above. I was thinking of the hooded pitohui, which emits a neurotoxin, not electricity in defense. But yeah, I'm still curious as to why electric animals don't exist on land. --Iloveparrots (talk) 07:46, 16 June 2022 (UTC)[reply]

Dammit, you got my hopes up that there was an electric oriole. Card Zero (talk) 11:00, 16 June 2022 (UTC)[reply]

Electroreception and electrogenesis claims that The capabilities are found almost exclusively in aquatic or amphibious animals, since water is a much better conductor of electricity than air. That sentence is unsourced, and I kind of doubt it when it comes to shock-stunning prey, which requires physical contact anyway. Of course, it is tempting to believe that there is a simple physical reason of water vs. air, but it seems like physicist’s speculation to me. Tigraan^{Click here for my talk page ("private" contact)} 08:37, 16 June 2022 (UTC)[reply]

Water (in particular seawater) is a decent electrical conductor, air is not. It's far worse than any land animal. So a land animal trying to send an electric discharge through air, will instead send it though its own body. Feathers and fur are decent insulators too, so the attacking land animal has to penetrate the victims skin with its teeth or claws before it can deliver an electric discharge. As it has to bite the victim already, the costly electric tissue has limited added value. PiusImpavidus (talk) 09:42, 16 June 2022 (UTC)[reply]

An electrical discharge through normal, non-ionized air takes the form of an electric spark, "created when the applied electric field exceeds the dielectric breakdown strength of the intervening medium. For air, the breakdown strength is about 30 kV/cm at sea level." 30 kV is about 35 times the voltage Electrophorus voltai, "the strongest bioelectricity generator in nature", is capable of generating. The advantage for the electric eel of delivering a shock is largely that it can stun its prey before engaging in physical contact. --Lambiam 10:03, 16 June 2022 (UTC)[reply]

But as Tigraan says above, electric eels (and electric catfish) don't have ranged weapons. I note that the article "Electroreception and electrogenesis" is talking about those two things as related. It has most to say about electroreception. This looks like a clue. Platypuses have electroreception (and sometimes wander about on land, particularly the big Tasmanian ones) so I can imagine them having evolved electric weapons, if they had undergone enough evolution. If only the world had been dominated by platypuses at any time, in greater variety. The connection to water might be due to the advantage water's conductivity confers on electroreception, which then provides an evolutionary pathway to weaponization. Card Zero (talk) 11:13, 16 June 2022 (UTC)[reply]

As a not-entirely irrelevant sidetrack, Iloveparrots, although it is of course (science-) fiction, you might be interested in reading Naomi Alderman's 2016 novel The Power, which utilises this idea. {The poster formerly known as 87.81.230.195} 90.201.73.162 (talk) 11:06, 16 June 2022 (UTC)[reply]