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November 23

Rescue Request

🆘 Please excuse me, I really need to ask this question to several Wikipedia Oracles so I have to use an automatic translator, sorry... By the way, there are links leading to texts, I think you will only need an automatic translator to understand...

[==]Request for rescue[==]

🆘 Hello dear pythias, (by the way I'm impressed with the volunteering! , anyway: ) having made a summary I put below, I don't know what to do. What should I ask/implement/recommend to the authorities or public services: one of the items in particular from the list in my final message to Bertrouf? To choose between them? And which authorities or public services should I ask? I'm not going to dial 112 / 911 ... 2A01:CB0C:38C:9F00:8886:DD15:2880:78CB (discuss) November 20, 2021 at 03:05 (CET)

"

[==] disassembling the brain [==]

Hello, I would like to have your opinion on this text, please https://www.youtube.com/watch?v=Ieuc3ABCMMA? If you agree, which authority should I contact? 2A01:CB0C:38C:9F00:3995:A59E:126B:3055 (discuss) October 19, 2020 at 07:36 (CEST)

Sorry, usually a question that starts with "what is your opinion" or "what do you think" is not answered on the oracle. And furthermore: {{SAV|Youtube}} We invite you to rephrase your question (at worst, there is the "Report" button below the video). _Bertrouf October 19, 2020 at 09:36 (CEST)

And to which authority should I apply for a judgment in order, in case of a favorable opinion, to realize, please? 2A01:CB0C:38C:9F00:3995:A59E:126B:3055 (discussion) October 19, 2020 at 1:38 PM (CEST)

Sorry, but I still don't understand your question. What do you want to achieve? Do you want to have the YouTube video removed? Do you want to do a medical analysis? Do you want to dissect or freeze a child (huh {{surprise}}?)? Want to appeal to a judge in court? Do you want to create an article about cryonics? In short, your question is unclear. _Bertrouf October 19, 2020 at 5:37 PM (CEST)

(Actually I had adapted the text of my video for children) I would like to get the process I described done, please. 81.254.12.248 (discuss) October 19, 2020 at 6:38 PM (CEST)

Hello, I don't think your process is feasible in the current state of science. Moreover if it is to transfer consciousness/mind into a machine, I don't think that knowing the completeness of all the neuronal connections can reproduce a consciousness. Eystein (discussion) October 20, 2020 at 14:56 (CEST)

Actually, I wanted to excite each of the neurons individually by a neuron exciter once the impulse it should make has been calculated by a computer using a simulation of the brain known from disassembly. 81.254.12.248 (discuss) October 21, 2020 at 2:20 PM (CEST)

Exactly: the current 'exciters' are the arrays of microelectrodes able to contact up to a thousand neurons at the same time. To measure or excite the 100 billion neurons of a brain you will have to use 100 million of these arrays and of course in three dimensions. Moreover it is likely that the state of excitation of the neurons at a certain moment has very little to do with the function of the brain, which is determined rather by the individual threshold of excitability stored in each synapse. As there are well within 10 thousand synapses on a single neuron you can see that there will not be so many authorities ready to spend all this money. But in any case you can look in Scientific_Research#Financing_of_Research, the chapter on the financing of scientific research. The tendency being towards private funding, it would be advisable for you to emphasize to potential investors all the money that will be made with your invention the day it will be put on the market. 2003:F5:6F03:6D00:D025:35D7:937:D52F (discussion) October 21, 2020 at 20:24 (CEST) Marco PB

In fact, since the brain is demonstrated, one can only have to use exciters in two dimensions.2A01:CB0C:C45:E000:CDE2:B43:D65D:2173 (discussion) October 21, 2020 at 22:44 (CEST)

[==]High tech, neurons [==]

Sorry for the inconvenience, I would like to know if my essay posted here https://www.youtube.com/watch?v=Ieuc3ABCMMA can work, please? 2A01:CB0C:38C:9F00:353A:F859:81D1:E460 (talk) 19:08, 3 November 2020 (UTC)

To be honest, it's not clear what you are proposing and what you are trying to achieve. Reconstructing the connections of a (human?) brain in a computer simulation in order to obtain (or inflict) consciousness, similar to the notion of brain in a tank? What does this have to do with children? Should they understand the trial? Or do the brains to be dismantled have to be children's brains? Do you know that "nerve cell" and "neuron" mean the same thing? Removing the outer membrane is an effective way to destroy it. Connections are made through synapses; they are not like electrical connections; knowing which neurons connect to which neurons does not give enough information to simulate the activity of the network formed by the neurons.  --Lambiam 23:49, 4 November 2020 (UTC)

2A01:CB0C:38C:9F00:353A:F859:81D1:E460-Why are you posting on YouTube? Can't you ask a question directly to the reference/science desk? Is it important for YouTube to serve as a conduit? Bus stop (talk) 03:08, 5 November 2020 (UTC)

:

Actually, I was hoping that my essay could be read by everyone, including children. I would like to use the simulation to inject the consciousness function back into the real original set of neurons, please?2A01:CB0C:38C:9F00:E450:3436:FE14:781F. (talk) 00:01, 11 November 2020 (UTC)

Actually, I'd like to know if there is a way to extract the entire data set?

Not with the current technology.  --Lambiam 11:07, 12 November 2020 (UTC)

And what do we do about my process? Do we tell the authorities about it? - Previous comment unsigned added by 37.166.33.181 (talk) 14:03, 14 November 2020 (UTC)

To this same question I told you a few weeks ago on the French oracle that in order to emulate the functioning of a specific brain it is necessary not only to know which of the 100 billion neurons is connected to which other, but also to know the specific excitability threshold of each of the 10,000 or so synapses belonging to each neuron. And it is quite possible that the excitability state of the synapses is lost at death.

Even if you can measure every neuron in a frozen brain to see how they are connected, it will not help you reconstruct, restore or even emulate the consciousness of the deceased, no matter what technology you use. And as long as no authority is interested in realizing your idea.

But if you can first develop a concrete process and show that 1) it is feasible and 2) that it works, you will find here some suggestions concerning the financial aspect: Funding of science. 2003:F5:6F0B:1E00:C990:B89E:5A87:5709 (talk) 21:49, 14 November 2020 (UTC) Marco PB

[deterioration of neurons during embalming, cryonics, Sokushinbutsu, plastination, brain under BrainEx machine: pictures please? (sorry for my English) [==]

Hello, sorry to bother you, I have an urgent need, but I don't speak English very well, can I speak in Esperanto please? (eo) Per kon'i la teknik'o'n la mal'plej difekt'ant'a'n (vid'i on Bild'o'j), oni pov'os aplik'i unu'n de la strategi'o'j kiu'j est'as teori'it'a'j pri Cryonics? 2A01:CB0C:C45:E000:B879:DC16:6186:289E (talk) 00:59, 25 September 2021 (UTC)

Estas neniu ligo al la Bild'o'j. Kial ĉi tio estas tiel urĝa? Ĉu vi ankaŭ afiŝis la demandojn "High technology, neurons" ĉi tie kaj ĉi tie? Via obseda serĉo kondukos nenien.  --Lambiam 09:00, 25 September 2021 (UTC)

[==] Cryonics / Embalming [==]

Hi, I hope I'm not interrupting, I would have liked to have a list of leads for cryonics that (leads) are not prevented from working for embalmed people, please? You'd be pulling a hell of a thorn out of my side...37.170.29.222 (discuss) June 23, 2021 at 4:05 pm (CEST)

Hello. No, you are not disturbing anyone, only volunteers answer here. On the other hand I am not sure I understood the question. We agree that you want to know the difference between cryonics and embalming? Cryonics freezes, embalming dries (desiccation). For the result, in both cases the cells are destroyed. Whether the future will offer technologies to revive the spirit depends on who believes in it. _Bertrouf June 24, 2021 at 10:06 am (CEST)

[==]Embalming?[==] (Sorry for the repost, last time I forgot something)

Hi, I hope I'm not disturbing you, could I have your opinion on the text I posted here https://www.dailymotion.com/video/x8343fi (password: a single space) please? 37.172.223.200 (discussion) August 2, 2021 at 5:17 PM (CEST) Should we call the H.A.S. and ask them to request final embalming for people dying in France please? 37.172.223.200 (discuss) August 2, 2021 at 7:08 pm (CEST)

Hello, I believe we tried to bring you answers in week 42 2020 [1], but the conclusion was that your text made no sense. Eystein (discussion) August 3, 2021 at 10:39 (CEST)

Actually, I went into more detail right after the original text. 37.164.150.43 (discuss) August 3, 2021 at 14:05 (CEST)

That question there, is that you too? _Bertrouf August 3, 2021 at 14:59 (CEST)

I quote from the article the Human Brain, "consisting of about 170 billion cells including 86 billion neurons on average that can each form 5-60,000 synapses. In order to measure the number, to count them by hand, one by one, at the speed of one neuron per second, it would take about 2700 years. This is what makes me say that your idea is unrealistic. Eystein (discussion) August 3, 2021 at 3:29 PM (CEST)

Hello, I had actually hoped for a robot. And I had resigned myself to the 3,000 year duration. 37.165.145.24 (discuss) August 3, 2021 at 20:36 (CEST)

P.S.: I just saw the answer to the question I forgot about on That question from "That question, is that you too?" (Bertrouf). I would have to go and see an image of neurons after embalming to see their state ... By the way, among the different embalming techniques, isn't there one that doesn't destroy neurons? Like a substance eliminating putrefactive agents? What about plastination or sokushinbutsu, please? Maybe it could be performed post-mortem, possibly on the brain alone ... 37.165.145.24 (discuss) August 3, 2021 at 9:01 pm (CEST)

P.S.2 Would you mind if I asked about techniques to preserve neurons without too much deterioration after death, please? Remark: I have already seen a photograph of a preserved elephant brain, it seems to me that it must have been in a jar, among other animal brains I believe preserved in a jar, and from this I draw the conclusion that they were embalmed. And it didn't look disintegrated.

37.165.145.24 (discuss) August 4, 2021 at 02:19 (CEST)

Unfortunately, to the best of my knowledge, I don't think there are any reliable techniques for keeping anything for these kinds of durations without damaging what you want to measure. And more generally, even if it were possible, even if you had a complete map of the synaptic connections and their electrical potential at a given time, it would not allow you to reconstruct memory, consciousness etc. Eystein (discussion) August 5, 2021 at 11:30 (CEST)

[==] embalming, cells, neurons [==]

Hello, you had told me once that embalmed neurons were deteriorated. Could you ask someone in the field to provide me with images so that I can see the extent of the damage, please? 92.148.82.16 (discuss) October 14, 2021 at 01:19 (CEST)

I invite you to go to a funeral home or hospital with a morgue, ask to speak to a fr:thanatopractor and see how he or she can answer your questions. He or she may have some reference books to suggest. I have no particular knowledge of medicine. _Bertrouf October 14, 2021 at 10:56 (CEST)

[==] Embalming continued [==] Hello, excuse me for bothering you, in fact, after I typed "embalmed cells" [sic] (I made a mistake because just before I had typed "embalmed neurons"), in short, on Google, I saw in 17th position a result containing "[...]cell structure remain intact", under a heading Good bye, Lenin: how Russian specialists have at en.rbth.com: I clicked on it and then I saw, at https://fr.rbth.com/histoire/79513-corps-lenine-comment-embaumer , in the 7th post-introduction paragraph "embalm the body so that the shapes and cell structure remain intact" but just after I read that this was the Challenge -so I don't know if they really succeeded in embalming without destroying the cells- Conclusion: hopefully I have scrambled here https://www. dailymotion.com/video/x853ycf (put a space at the request of the password) [Inserting, in the discussion, an Addition for Wikipedia Oracles: select the text next to or at the bottom and drag the selection down to see all the text], I said to myself do we have to call immediately the authorities to ask them to practice a definitive embalming preserving the cellular structure on each deceased person, please? 81.49.93.152 (discuss) October 29, 2021 at 22:21 (CEST)

But I don't know! Wikipedia:Reference desk/Science/ _Bertrouf November 8, 2021 at 11:01 (CET)

Hello, excuse me for rearranging, I'm contacting you because I can't figure out what the urgency is right now among :

-asking the authorities to prevent the putrefaction of the deceased by a means leaving not too much deterioration of the neurons as the Russians claimed they did for Lenin (if such a means is indeed known)

-determine the known means of preventing putrefaction that deteriorates the neurons the least if it is sufficient among cryonics with a cryopreserver, final embalming, sokushinbutsu, plastination, (BrainEx related to the immune system)? )

-searching for a way to prevent putrefaction leaving the neurons not too deteriorated (new cryopreservative, new embalming technique, or a technique other than those known)

- Can you not take me for a madman please, but while I was in the anguish that neither cryonics nor embalming could not deteriorate too much the neurons, it passed through my head while I needed a plan B the idea of a dismantling of the brain carried out on a voluntary person or in coma without hope of awakening, but I have just remembered that we were not yet able to do it.

- By the way, if we put the BrainEx on for example the whole body of a living person, I don't know what happens in case of cardiac arrest ...

(to the line)

By the way, I sent a letter at the beginning of October to the Ministry of Health, to the Ministry of Defense, and to the SDIS 59 and 62 in which I asked for a vision-conference to discuss all together what to do, but the Ministry of Defense and the 2 SDIS did not answer me ... 92.148.81.56 (discuss) November 18, 2021 at 02:23 (CET)

[Amendment to the last message I sent to Bertrouf: there is a new Canadian-Quebec embalming technique described here https://ici.radio-canada.ca/nouvelle/1068136/nouvelle-technique-uqtr-medecine-embaumement-sel ] "

2A01:CB0C:38C:9F00:8886:DD15:2880:78CB (discuss) November 20, 2021 at 03:05 (CET)

• I don't know about the French side, but here on en.wp it is customary NOT to post the same question to two branches of the Reference Desk. Since this is (at least primarily) a Science question, I'll remove it from the Miscellaneous desk. —Tamfang (talk) 02:44, 23 November 2021 (UTC)

I fear that you may be approaching this whole process at too crude a level. There is a hypothesis which proposes that thoughts and consciousness are emergent not from the network of brain cells (neurons) and their connections (synapses), but at the much more microscopic level of the complex frameworks of microtubules within all of those cells, see the article Orchestrated objective reduction.

If this is the case, then the approach you suggest is like trying to replicate all the texts of all the books in a library merely by reproducing their titles, Dewy decimal codes and shelf positions. {The poster formerly known as 87.81.230.195} 90.205.225.31 (talk) 05:14, 24 November 2021 (UTC)

• I added ":fr:" to some of the links here, but I suspect the auto-translation wrecked some of them even so. —Tamfang (talk) 02:59, 27 November 2021 (UTC)

Hollow planet?

Hi all. Not a scientist, so go easy on me. If volcanoes having been belching out material onto the Earth's crust since the planet came to exist, does that mean the sphere of the planet is growing and conversely, some of its lower strata are becoming less densely packed with material? --Dweller (talk) Old fashioned is the new thing! 13:53, 23 November 2021 (UTC)

The Earth's mantle is, effectively, a liquid. If you were to suck water from the bottom of your bathtub and spray it on the top, it wouldn't leave a hollow layer at the bottom of the tub - the water would fall down under gravity. So it is with the mantle - material is always rising and falling, driven by the heat of the core and the cooling effect of the surface - but it can't sustain voids (larger than the microscopic) - see mantle convection. This is the downfall of any kind of hollow Earth theory - rock seems solid on a human scale and human timescale, but on geological scales, it's treacle. -- Finlay McWalter··–·Talk 14:41, 23 November 2021 (UTC)

(edit conflict) No, for a couple of reasons 1) The material that comes to the surface through volcanos is basically all fairly close to the surface anyways. It's from the Asthenosphere, which only goes down about 200 km below the surface, a very small fraction of the earth's radius of 6,350ish km. 2) The asthenosphere-lithosphere system is basically a closed system whereby the earth's crust is recycled via the process of plate tectonics. Wherever volcanoes are erupting magma, somewhere else on earth subduction is consuming the earth's crust into the asthenosphere and producing more magma. There are going to be some local variations due to the differences between continental (granitic) and oceanic (basaltic) crusts, but that's a level of complexity we don't need to answer your question. The entire system is in dynamic equilibrium, roughly speaking, so that for each bit of magma erupting on the surface, there's a commensurate amount of crust being recycled via subduction. --Jayron32 14:43, 23 November 2021 (UTC)

Fantastic answers, both of you. Completely intelligible, even by an ignoramus. Thank you, Jayron32 and Finlay McWalter --Dweller (talk) Old fashioned is the new thing! 14:57, 23 November 2021 (UTC)

Have we actually checked that there's nothing at Sun–Earth L3 Lagrange point?

It is a common science fiction trope that Sun–Earth L3 Lagrange point would be the perfect place to stash away a hostile alien base or spaceship since it is always hidden from us by the sun.

Now, I don't actually believe there are hostile aliens hiding behind the sun, but a question occurs... have we actually checked?
If yes, when and how? If not, do we have the means to check (even if inadvertently through other scientific work) without launching a purpose built mission? Melmann 22:13, 23 November 2021 (UTC)

According to Lagrange point, yes, we've checked. It shouldn't be that hard anyway, given all the space probes that have already been launched. Also, the L3 point is unstable, so anything parked there would not stay there for very long unless it was artificially kept there. Double sharp (talk) 22:33, 23 November 2021 (UTC)

There is no Counter-Earth there, but a teapot may escape detection.  --Lambiam 22:48, 23 November 2021 (UTC)

A deadly alien teapot bristling with instruments of mass pouring. Clarityfiend (talk) 01:09, 24 November 2021 (UTC)

Sooner or later, some wag will put a china teapot in elliptical orbit between Earth and Mars, and then where will we be? —Tamfang (talk) 03:09, 27 November 2021 (UTC)

See also Counter-Earth#Scientific_analysis.

There's certainly nothing planetary-sized there; anything really big would have given itself away through its gravitational effects on other more-easily-observable bodies.

There's also nothing there that's really electromagnetically 'loud'; we would have incidentally caught something like that as the Sun wobbles back and forth a bit and occasionally gives a reasonable clear line-of-sight to L3.

Finally, certain space-based observing missions would have seen any moderately large objects hanging out at L3. The STEREO observing mission, during its early months, would have been able to see objects down to about 100 miles in diameter lurking at L3.

As Lambiam says, though, it's well-nigh impossible to prove a negative, and as far as I can tell, this is one that we haven't had any need to expend a lot of effort on. If the starship Enterprise were sitting at L3 right now, we wouldn't have any easy way to know. If it helps you sleep at night, though, we probably would have been able to see the Death Star. So there's that. TenOfAllTrades(talk) 12:43, 24 November 2021 (UTC)

In the early days of the Superman saga, the planet Krypton was on the opposite side of the sun from us, hence we couldn't see it, hence its name "Krypton" (as in "hidden"). ←Baseball Bugs ^{What's up, Doc?} carrots→ 06:56, 25 November 2021 (UTC)

Oh hey look, Category:Counter-Earths. —Tamfang (talk) 03:12, 27 November 2021 (UTC)

November 24

Subatomic Particles

What are subatomic particles made of? — Preceding unsigned comment added by 173.26.107.224 (talk) 02:32, 24 November 2021 (UTC)

Read Subatomic particle for some opinions on the matter. ←Baseball Bugs ^{What's up, Doc?} carrots→ 02:56, 24 November 2021 (UTC)

These are not so much (subjective) opinions as different (objective) aspects resulting from different angles in approaching the subject, much as in the parable of the blind men and an elephant.  --Lambiam 08:07, 24 November 2021 (UTC)

I was at first going to suggest that they're made of even smaller particles, and that those particles are made of yet smaller particles, and so on. Kind of a turtles all the way down argument. ←Baseball Bugs ^{What's up, Doc?} carrots→ 11:31, 24 November 2021 (UTC)

Quantum field theory avoids that problem. --Jayron32 13:12, 24 November 2021 (UTC)

Earbuds sound

While typically headphones could be regarded as superior to earbuds, could it be argued that, in the absence of noise or low noise, earbuds deliver sound more efficiently and clearly because they face directly the ear canal instead of hanging around auricle, like headphones? 212.180.235.46 (talk) 17:22, 24 November 2021 (UTC)

The best earbuds are better than some headphones and vice versa. So one should compare the best ones in a given narrow price range. Such a comparison has to be based, I think, on the subjective judgements of listeners. I expect some such comparisons have been made. While I'm not aware of any and their results, I cannot offhand think of an argument why earbuds should be expected to come out on top. As we hear sounds naturally, they come to us from around our auricles; pumping them straight into the ear canal may have an unnatural effect. I'm not saying that it has (more so than earphones), but I cannot rule it out. Headphones also offer more room for including microelectronics for processing the signal for a better listening experience.  --Lambiam 08:47, 25 November 2021 (UTC)

November 25

What is this physical process called?

My hole-y couscous

I’ve noticed that when I add my couscous to rapidly boiling water and then rapidly cool it by removing it from the heat, the parts where the boiling was most prominent becomes little cavities once it cools. What is this process called and what is happening to produce the holes? Viriditas (talk) 00:46, 25 November 2021 (UTC)

Nucleate boiling likely applies here. Vapor bubbles are being generated from nucleation sites (probably small surface cavities that increase the fluid's contact area with the heating surface, causing water at those sites to vaporize faster) forming dense bubble columns. The fluid/couscous not in the path of these columns also should cool slightly faster, causing it to solidify around the nucleation jets. JoelleJay (talk) 06:20, 25 November 2021 (UTC)

Additionally, a larger rising steam bubble forms a channel that subsequently formed steam tends to follow as the path of least resistance, thereby maintaining it, much like flowing water may carve out a channel, or a conductive channel formed in lightning is not only used by the initial discharge but reused by quickly following strokes. So, next to possible preferred nucleation sites of the cookware, spontaneous symmetry breaking may also play a role.  --Lambiam 07:54, 25 November 2021 (UTC)

Thank you. I’ve read the linked article and it says that the process is complex, they have trouble developing models, there are contradictory results, and more research is needed. Is there a reason this is poorly understood? Also, what accounts for the chaotic pattern of the bubble cavities? If I did this over and over again, and performed the same procedures, such as using the same amount of couscous, the same pot, stirring it the same number of times, etc, would the bubble holes always appear in different spots? Is there an approximate number that should arise each time? Or is this more a function of my stove and cookware? Viriditas (talk) 21:59, 25 November 2021 (UTC)

Second batch for comparison

A cursory visual inspection suggests that the hole-y pattern does not emerge from a Poisson point process: there are too few holes very close to each other, and also very few close to the border. This is your opportunity to conduct a scientific study in your kitchen lab. The number and distribution of the holes may be influenced by the granularity, composition and other aspects of the couscous, the amounts of couscous and water, the heat level and the cookware. So, for a first series of tests, try to introduce as little variation between runs as possible. Intuitively, I expect the number to show little variation and to follow a Poisson distribution. If the pattern repeats – more precisely, if the similarity between successive patterns is larger than expected for a non-repeating pattern – nucleation is the most likely dominant factor. If the positions of the holes in successive patterns are not correlated, symmetry breaking is a good explanation.  --Lambiam 23:23, 25 November 2021 (UTC)

Lambiam, I posted the photo of the second batch up above. Any comments? Viriditas (talk) 22:11, 28 November 2021 (UTC)

I didn't count them, but their numbers can't be very different. Just offhand, based merely on a visual impression, it appears to me that knowing the positions of the holes in one instance of the process gives very little information for where they'll appear in the next instance – apart from the fact that they are again sparse in a border zone. As before, they also seem neatly separated. It occurred to me that if bubbles, as they rise up (along a z coordinate) from a nucleation site, at the same time perform a random walk in the x and y directions, it may be very hard to distinguish this from the explanation as a symmetry-breaking process based on the lack of similarity. The main giveaway that I see is that, again, the pattern does not look like an instance of a Poisson point process. I'd expect nucleation sites to form a Poisson point field, and a random walk then only increases the Poisson-pointness, so that you expect to see more clustering, arising purely by chance, than seen in these images.  --Lambiam 23:57, 28 November 2021 (UTC)

So, does this mean we are living in a simulation? Just kidding. Thanks for your help with this, Lambiam. Viriditas (talk) 22:01, 29 November 2021 (UTC)

Where do microrobots go after finish its job?

I learn that microrobots can also be used to target/ treat cancer cells from research site. Rizosome (talk) 03:33, 25 November 2021 (UTC)

From the linked article (emphasis mine): "These micromotors can penetrate the mucus of the digestive tract and stay there for a long time. This improves medicine delivery," Gao says. "But because they're made of magnesium, they're biocompatible and biodegradable." And from the original article: The micromotors have been eventually cleared by the digestive system via excrement, without any adverse effects. JoelleJay (talk) 06:28, 25 November 2021 (UTC)

This line answered my question: "cleared by the digestive system via excrement". Rizosome (talk) 01:10, 26 November 2021 (UTC)

Resolved

Mr Ruthven

Is mentioned in HMS Waterwitch (1866) as having had the idea of driving ships with waterpumps, as mentioned. Lacking a link, I seem to be unable to find which Mr Ruthven that is, or, barring the wikipedia does not have an article about said individual, I would like to inquire as to who this Mr Ruthven is - anyone an idea? Regards, --G-41614 (talk) 14:47, 25 November 2021 (UTC)

Here's something. They don't seem to be certain about the first name, though... --Wrongfilter (talk) 15:31, 25 November 2021 (UTC)

This seems interesting. According to this, John is the son of the inventor, Morris West Ruthven, see also here. I leave it to you to actually read these references and figure out who was involved with the good ship Waterwitch. --Wrongfilter (talk) 15:38, 25 November 2021 (UTC)

Thank you very much, this does help and, after only a first glance, appears to answer my question. Regards, --G-41614 (talk) 16:36, 25 November 2021 (UTC)

Day length of a retrograde planet

If a planet orbits a star every 15hours but the planet itself is rotates around itself every 30hours in retrograde direction, what is the average "day"/"night" length on the planet? Jo-Jo Eumerus (talk) 17:12, 25 November 2021 (UTC)

Its day should be 30 hours, while its year should be 15 hours. ←Baseball Bugs ^{What's up, Doc?} carrots→ 18:11, 25 November 2021 (UTC)

You may find Mercury (planet) interesting. ←Baseball Bugs ^{What's up, Doc?} carrots→ 18:23, 25 November 2021 (UTC)

That doesn't answer my question; I am not asking about the rotation period but about the day/night duration. Jo-Jo Eumerus (talk) 20:12, 25 November 2021 (UTC)

The general formula for the synodic period $T$ is:

$T={\frac {T_{o}T_{sd}}{T_{o}-T_{sd}}}$,

where $T_{o}$ is the orbital period and $T_{sd}$ is the sidereal period. The sigh of $T_{sd}$ corresponds to the prograde/retrograde case. So, in this case, when $T_{sd}=-30$ hours and $T_{o}=15$ hours, we have $T=-15*30/(15+30)=-10$ hours. Ruslik_Zero 20:52, 25 November 2021 (UTC)

Note that the formula can be rewritten in the form

$\left|{\frac {T}{T_{\operatorname {o} }}}-{\frac {T}{T_{\operatorname {sd} }}}\right|=1,$

which has an obvious and easy to remember interpretation: the number of turns during a period $T$ in the synodic view differs by exactly $1$ from that number in the sidereal view, because the respective reference frames then rotate exactly one turn with respect to each other. The tricky part is to figure out the sign of the difference.  --Lambiam 22:45, 25 November 2021 (UTC)

If you're standing at a fixed point of the equator of this fictitious planet, holding a clock which allows for a 30-hour day, and forgetting about twilight and such, shouldn't a single day be exactly 30 hours? 15 hours of sunlight and 15 hours of night? ←Baseball Bugs ^{What's up, Doc?} carrots→ 23:28, 25 November 2021 (UTC)

No because it is orbitting the star twice in the time, in the opposite direction, so the star appears to move faster in th sky. Graeme Bartlett (talk) 04:18, 26 November 2021 (UTC)

So if its sun is overhead at high noon on one day of that 30-hour clock, it won't be overhead at high noon the next day? ←Baseball Bugs ^{What's up, Doc?} carrots→ 04:23, 26 November 2021 (UTC)

Yes if 30 hours is mean solar time not sidereal/(real) but only by definition. Retrograde and years close to 1 day (and orbit ellipticity) can really screw things up. There are even places on Mercury where the sun decelerates and goes back — setting the same side it rose (east or west, I forgot which). The Sun can only reverse direction once a year but that's like 0.5 average days between noons (net noons, not gross). Or 1.5 actual rotations. Sagittarian Milky Way (talk) 05:40, 26 November 2021 (UTC)

Would the Reference desk/Mathematics be a better place for this? -- Q Chris (talk) 08:13, 26 November 2021 (UTC)

Maybe. I'm curious how close to the sun that planet would have to be, to circle it once every 15 hours. ←Baseball Bugs ^{What's up, Doc?} carrots→ 14:11, 26 November 2021 (UTC)

Kepler's third law gives the answer: 0.014 AU, i.e. 2.1 million kilometers. We know many exoplanets with orbital periods on the order of days (e.g. Hot Jupiters). --Wrongfilter (talk) 14:30, 26 November 2021 (UTC)

So if the hypothetical object were that close to the sun, it would almost be "in" it. ←Baseball Bugs ^{What's up, Doc?} carrots→ 14:40, 26 November 2021 (UTC)

If it were our Sun (with a diameter of nearly 1.4 million kilometers), yes, but the OP specified a hypothetical planet orbiting a star (its sun), and many exoplanets may orbit stars much smaller than the Sun, including Red dwarfs and White dwarfs, and even Neutron stars which are very small indeed by comparison. {The poster formerly known as 87.81.230.195} 90.205.225.31 (talk) 15:48, 26 November 2021 (UTC)

The formula can just be rewritten as $1/T=1/T_{sd}-1/T_{o}$ – an algebraic sum of angular frequencies. Ruslik_Zero

In fact the situation is similar to that of Venus: $T_{o}=225$ days and $T_{sd}=-243$ days with $T=-117$ days. Ruslik_Zero 21:03, 26 November 2021 (UTC)

November 26

Why isn't hydrogen peroxide used for wastewater treatment?

The U.S. primarily uses chlorine gas, U.K. primarily uses ozone, for water sewage disinfection. My environmental chem textbook talks about the 2, as well as chlorine dioxide. Basically, using chlorine gas causes all kinds of small chemicals like chloroform and trihalomethanes as byproducts. But nobody talks about hydrogen peroxide as sewage disinfectant. It kills viruses and bacteria, and it eventually decomposes to water and oxygen. My gut reaction is... it must be really expensive? Also, is anyone from a country or municipality that uses disinfection other than chlorine or ozone? 67.165.185.178 (talk) 02:39, 26 November 2021 (UTC).

Apparently membrane filters and UV light can be used too, but our article tells me that sewage water usually isn't disinfected at all, which matches my experience from visiting the local wastewater processing facility some years ago. PiusImpavidus (talk) 09:13, 26 November 2021 (UTC)

Right, in my area sewage discharges not suitable for drinking water, but discharging it to rivers that eventually reach the Gulf of Mexico. And we get out water from Lake Michigan which is not discharged from our sewage. So, I am also curious if any jurisdiction in the world, treats sewage water all the way back to drinkable water? 67.165.185.178 (talk) 13:24, 26 November 2021 (UTC).

See reclaimed water. Mikenorton (talk) 15:31, 26 November 2021 (UTC)

Hydrogen peroxide is one of several chemicals used in advanced oxidation processes, a step in wastewater reclamation. Some issues are mentioned in the section Advanced oxidation process § Current shortcomings. See also Hydrogen peroxide § Disinfectant, which states that hydrogen peroxide is used in certain wastewater treatment processes to remove organic impurities, and that it is seen as an environmentally safe alternative to chlorine-based bleaches, as it degrades to form oxygen and water and it is generally recognized as safe as an antimicrobial agent by the U.S. Food and Drug Administration. The cost difference with chlorine-based treatment does not have to be large for a water management authority, often hard-pressed for money, to engage in penny-pinching and opt for the cheaper solution.  --Lambiam 10:03, 26 November 2021 (UTC)

But I also feel like the process to make mass hydrogen peroxide is a overwhelm compared to making chlorine. 67.165.185.178 (talk) 13:25, 26 November 2021 (UTC).

Poisonous plants examples.

Q1. It is possible to be poisoned to death, from drinking the milk of cows, that ate poisonous plants. Such is the example of the plant white snakeroot because it contains tremetol. This is how Abraham Lincoln's mother died. Are there any other examples? Basically, these plants must not be poisonous to cows.

I don't know of other examples involving cow milk, but for a related item see mad honey. AFAIK, the bees are not affected by the grayanotoxins, though we obviously are. For some reason, I thought locoweed poisoning could be passed through to us via livestock, but that doesn't seem t be the case. Matt Deres (talk) 18:24, 26 November 2021 (UTC)

Q2. Same question, but cases where the cow'w body digested the plant to no longer be poisonous in their cow milk.

Q3. It is possible to have a skin irritation just by standing under a poisonous tree when it rains. The only example I have is the manchineel tree, probably the most poisonous tree species in the world. But eating its fruit is a lot more toxic. Any other examples?

Q4. Most of the poisons are biological compounds, such as alkaloids, cardiac glycosides, neurotoxins, ribosome-inactivating proteins, and saponins. The infamous ricin falls under ribosome-inactivating proteins and the poison that killed Socrates, coniine, is an alkaloid. What are inorganic chemical examples, besides calcium oxalate? And coumarins. 67.165.185.178 (talk) 02:46, 26 November 2021 (UTC).

Reason drawings of cubes tend to slant left

More common

Less common

After drawing File:Snake_cube_solution.svg, I found with a cursory search on Commons and Google that simple diagrams of cubes made by drawing two squares and joining corresponding vertices tend to slant left, as in above images.

Is there a psychological reason for this preference? (I can understand the preference for the viewpoint from above as gravity causes most things to be viewed from above.)

Thanks,
cmɢʟee⎆τaʟκ 10:02, 26 November 2021 (UTC)

Maybe because we write from left to right? Also, the second item in your "more common" illustration looks like an Escher drawing. ←Baseball Bugs ^{What's up, Doc?} carrots→ 14:09, 26 November 2021 (UTC)

Yes, that's an Impossible object. Sorry I mean it's a drawing of an Impossible object. I wonder how do people who write right to left draw cubes? Martinevans123 (talk) 14:12, 26 November 2021 (UTC)

Top-left lighting discusses part of this. Bazza (talk) 14:42, 26 November 2021 (UTC)

Also if the majority of people see the right and top of the cube in front before the opposite (?) then the right, top, front, north, east and up come before their opposites in Western culture (e.g. right hand of God). And a right-handed person can draw diagonal northeast arcs just by swinging the wrist in a normal writing position which is closer to drawing a northeast line than northwest. Sagittarian Milky Way (talk) 15:18, 26 November 2021 (UTC)

You're saying it's (partly) a product of handedness? Is there any empirical evidence? Thanks. Martinevans123 (talk) 15:23, 26 November 2021 (UTC)

Two guesses of things that might at least subtly increase the percentage of northeast chirality in the cubes OP has seen. Right, up, front, north and east also have some sort of priority in coordinates cause they got to be the positive sides, if an intelligent species was 90% left-handed and somehow underground 90% of the time for gamma ray reasons or something like that then left and down may have priority instead and their analog of church Latin wouldn't have a negative word (sinister) that also means left. Sagittarian Milky Way (talk) 17:35, 26 November 2021 (UTC)

That's not really the sort of "empirical evidence" I was thinking of. But thanks anyway. Martinevans123 (talk) 19:04, 26 November 2021 (UTC)

Most of the pictures in the article 3D projection also show the right and top sides if possible. Technical drawing surely has also settled on a convention of which sides to show if taking the shortcut of only drawing the orthographic projection from one side of a Cartesian axis instead of both. Sagittarian Milky Way (talk) 19:55, 27 November 2021 (UTC)

I'm interested in why the original poster calls that slanting left because I would describe them as pointing right.--Khajidha (talk) 18:14, 26 November 2021 (UTC)

The front face slants left w.r.t. the back face. The back face slants right w.r.t. the front face.  --Lambiam 01:20, 27 November 2021 (UTC)

Thank you very much, everyone who replied. Handedness and writing direction are both good explanations. It was also eye-opening to realise my own bias in calling it slanting left and right. Cheers, cmɢʟee⎆τaʟκ 22:02, 27 November 2021 (UTC)

Resolved

Proton decay with naked senses

If the easiest to notice proton in the human body decayed while a human with good [sense] was paying attention to [sense] what would they notice? Is this proton in the eyes or nervous system? Maybe in a rhodopsin molecule in a dark-adapted eye? What would be the detection mechanism? (Cherenkov radiation? A shower of descendant xyz particles similar to a cosmic ray in air? Direct nervous system stimulation somehow?) Sagittarian Milky Way (talk) 18:00, 26 November 2021 (UTC)

Did you really mean to use the proton as an example, Sagittarian Milky Way? According to the article, proton decay is hypothetical and the minimum half-life is a factor of about 10²⁴ longer than the age of the universe! So a bit difficult to speculate what would happen if one did decay.... Mike Turnbull (talk) 18:32, 26 November 2021 (UTC)

Yes but there has been a cumulative ~10³⁰ times age of the universe years worth of chances for a proton to decay in a man since the 18th century.

I cannot assign a meaning to this sentence. How much is "one year worth of chances" worth, in terms of probability? Where does the number 10³⁰ come from?  --Lambiam 01:04, 27 November 2021 (UTC)

If you're confused by something I didn't say clear enough it doesn't mean I'm an imbecile. If the proton half-life is 10²⁴ times the age of the universe then about 6.93x10^-25*100% of your protons decay in 13.8 billion years or ~6.93x10^-33 in 138 years or ~1.612x10^-32 in 321 years (since 1701.0 AD) but multiply by 7x10²⁷ atoms in a 70kg human body then multiply by the average number of protons per atom (~0.24*8+0.12*6+0.62*1+0.011*7+0.0022*20+0.0022*15+0.00033*19+0.00038*16+0.00037*11+0.00024*17+0.00007*12+0.0000067*26+0.000012*9+0.0000031*30+0.000058*14+0.000007*31+0.00000033*37+0.00000033*38+0.0000003*35+0.000000045*82+0.000000104*29+0.00000015*13+0.000000045*48≈3.44) then multiply by some sort of representative population of the world for that time period let's say 1 billion (too low but 70kg is too high) and you get 388,000 proton decays in the human species after 1700. If it'd take ~10²⁴ times the age of the universe to see one proton decay then that much proton decay would take about 10^29.6 times the current age of the universe (but you'd have to pick a new proton to watch 388,000 times, as the proton has only one life to give, not 388,000. Of course it could be anything from over 100,000 to exactly zero. And maybe not something that'd cause one to suspect proton decay if it was sensed, if a spot of skin itches I don't suspect proton decay. Sagittarian Milky Way (talk) 03:56, 27 November 2021 (UTC)

I know it's only a hypothesis and has never been detected by anything (or if it has then non-proton decay reasons must be more likely as a single event over 50% likely to be proton decay would surely be physicist-interesting enough to be in the article). Sagittarian Milky Way (talk) 20:01, 26 November 2021 (UTC)

And some physicists predict gamma rays will come out, a particle who's interactions with flesh are surely not unknown speculation. Sagittarian Milky Way (talk) 20:07, 26 November 2021 (UTC)

We are hit all the time by gamma rays arising from cosmic radiation. A couple of gamma photons once every so many lifetimes of the universe won’t make much of a noticeable difference.  --Lambiam 01:17, 27 November 2021 (UTC)

Yeah but you have 2*10**28 protons, you'd only have to wait a few thousandths of the current age of the universe. Or maybe up to infinity. How bright would it be if it was in the eyeball? Could you hear it if it was on a cochlea hair or eardrum? Sagittarian Milky Way (talk) 03:56, 27 November 2021 (UTC)

I estimate the energy of the photons to be about 75 pJ or about 470 MeV, which is very high for a single photon but not a whole lot on a macroscopic scale. While their wavelength is not in the range of visible light, they might excite the neurons of one or two rods of the retina, but not of the cochlear hair cells.  --Lambiam 00:54, 28 November 2021 (UTC)

Curbing SARS-CoV-2 mutations

Are there any official plans on how to curb the ongoing mutations of SARS-CoV-2? Particularly, does the emergence of a variant of concern entail some preventive measures or is it just another blah-blah term? 212.180.235.46 (talk) 20:24, 26 November 2021 (UTC)

I don't know about officials, but vaccine manufacturers have plans. Novavax is working on adapting its vaccine "in weeks", Moderna says it will develop one, BioNTech says it could ship one in 100 days if its old vaccine isn't good enough, AstraZeneca is collecting data on how well its existing vaccine performs against the new variant.  Card Zero  (talk) 00:04, 27 November 2021 (UTC)

COVID variants

And, speaking of COVID variants, has the WHO said anything about how they intend to give them short names after they run out of Greek letters? --184.144.99.241 (talk) 20:54, 26 November 2021 (UTC)

Maybe they could name them after COVID deniers. ←Baseball Bugs ^{What's up, Doc?} carrots→ 23:19, 26 November 2021 (UTC)

They could name them after numbers. You know, like $e$, $\pi$, ${\sqrt {2}}$ and so forth. There are lots of those, even more than there are integers. 2601:648:8202:350:0:0:0:69F6 (talk) 00:01, 28 November 2021 (UTC)

Too late - $\pi$ will come next, after $\mathrm {o}$(omicron).--Verbarson (talk) 15:49, 29 November 2021 (UTC)

That's pi, the letter. After that we could have pi, the number, followed by pie, the dessert, whose symptoms can be be improved by scooping ice cream on top of the patient. DMacks (talk) 02:24, 30 November 2021 (UTC)

November 27

How does my cat tell time so well?

So I was browsing the web one day and saw the following suggestion:

"Have a pill you have to take the same time every day? Give your dog or cat a treat right before you take it. You may forget, but they won't."

I tried it and they were right. The cat comes looking for a handout every day at 6PM.

The thing is, the cat is never off by more than five minutes either way! How do they tell time so accurately? 01:06, 27 November 2021 (UTC)2600:1700:D0A0:21B0:7013:8442:84B6:D144 (talk)

It's just a good sense of timing. See Time perception. Many animals can do this. I guess humans don't much need to so they don't try. I stopped wearing a wristwatch a few years ago and my sense of timing markedly improved, and I was surprised to find I can now consistently judge half an hour to within a minute.--Shantavira|^{feed me} 09:38, 27 November 2021 (UTC)

It could also have to do with where you are physically when you take the pill. Anytime we walk over near where we keep the cat food, the cat gets interested. ←Baseball Bugs ^{What's up, Doc?} carrots→ 22:16, 28 November 2021 (UTC)

Which is the most postponed space project?

I didn't find my answer in List of NASA cancellations.

I strongly believe James Webb Space Telescope. I am referring my postponed word to launch date only. Rizosome (talk) 01:52, 27 November 2021 (UTC)

November 28

Many world interpretation

Is the MWI an actual fleshed out theory, at least mathematically? I mean does it really say that the whole universe evolves by the Schrödinger equation with a single time parameter t that reaches everywhere? Asking because I just saw this claiming time could flow forwards in some places while backwards in others. What I'm trying to understand is whether there is really supposed to be something like "branching" or if that is just a metaphor. Thanks. 2601:648:8202:350:0:0:0:69F6 (talk) 00:07, 28 November 2021 (UTC)

According to a section in our article, Many-worlds interpretation#Debate whether the other worlds are real, some physicists see it as "real" and others "unreal". I guess that most people without a deep understanding of quantum physics are in a third "don't care" category! Mike Turnbull (talk) 19:02, 28 November 2021 (UTC)

I did read the article, but I'm asking less about the reality of the alternate worlds, than whether there is a reasonably complete theory that describes them (let's say it's ok to ignore general and maybe special relativity) even if they are fictional. I guess it is a question about mathematical physics (whether someone has worked out certain QM equations even if they don't describe reality) than scientific physics (how one describes the real universe(s)). 2601:648:8202:350:0:0:0:69F6 (talk) 23:21, 28 November 2021 (UTC)

Why didn't bones evolve with carbon ?

Carbon makes any object sustain more tensile and yield strength. So Why can't bones evolve with carbon instead of calcium? Rizosome (talk) 02:38, 28 November 2021 (UTC)

Carbon in any old form or (allotrope) doesn't make objects stronger, only certain ones like diamond and carbon fibre. Natural Diamond is made under immense temperatures and pressures deep in the Earth (and though very hard, is also quite brittle); carbon fibre is constructed artificially, and as far as I'm aware could not be made by natural biological processes, or at least ones that are likely to be achievable through evolution. {The poster formerly known as 87.81.230.195} 90.205.225.31 (talk) 07:27, 28 November 2021 (UTC)

Graphite is the form of carbon that is stable under normal conditions and it is a very soft and weak material. Carbon, as part of compounds, forms part of the hard supporting structure in many types of animal - see chitin, calcite and aragonite. Mikenorton (talk) 11:31, 28 November 2021 (UTC)

This sentence answered my question: Carbon, as part of compounds, forms part of the hard supporting structure in many types of animal - see chitin, calcite and aragonite. Rizosome (talk) 01:45, 29 November 2021 (UTC)

Also relevant; your bones DO contain carbon. Bone is about 30% collagen and other proteins, which is mostly carbon. --Jayron32 02:14, 29 November 2021 (UTC)

And without that protein, the bones would probably not be resilient enough to function properly. There's an old demonstration of this where you soak one chicken bone in vinegar for a significant time (removing the calcium, phosphorus, and other mineral components) and bake another in an oven (burning off the protein portion). The first becomes rubbery, the second becomes brittle. --Khajidha (talk) 23:52, 29 November 2021 (UTC)

Also note that the mineralogical components of bone also contain carbon in the form of carbonates. --Khajidha (talk) 23:56, 29 November 2021 (UTC)

S2 / Sagittarius A* acceleration

I'm reading about S2 (star) and I noted the line that it experiences "acceleration of about 1.5 m/s2 (almost one-sixth of Earth's surface gravity)." I was wondering, disregarding all the horrible radiation, the fact that you'd in orbit around a black hole which would tear us to bits, and stuff what would happen if you were somehow replace S2 with Earth. Would you feel it? Like, would sitting on the side of the planet facing in the direction of the acceleration feel heavier than sitting on the opposite side? Or at least, would it be measurable? Essentially I'm wondering if our entire planet was accelerated suddenly would we notice or because we're small and our planet is big we wouldn't? Would any of this be different if we were in orbit around S2 instead of simply taking the place of it? 194.72.22.84 (talk) 10:17, 28 November 2021 (UTC)

I'll assume we can model the gravitational effect of the black hole as that of a hugely massive body in Newtonian spacetime. An observer in free fall near the Earth, whether falling down or circling it, does not directly experience the acceleration in their reference frame, but they may be able to measure the minute differences related to the distance to the Earth's centre. The acceleration in a stationary frame of a small body in orbit around a much more massive body is given by $a=cr^{{-}2},$ in which $r$ is the distance to the centre of gravity, which we may put at the centre of the larger body. (The value of $c=GM,$ in which $M$ is the mass of the larger body, is further irrelevant.) For a difference $\Delta r$ in distance, the difference in acceleration is given, to a first approximation, by $\Delta a={\tfrac {da}{dr}}\Delta r=-2ar^{{-}1}\Delta r.$ This can also be found by integration of the tidal force across that distance. Using $a=1.5\,\mathrm {m} ,$ $r=18\times 10^{12}\,\mathrm {m}$ (the pericentre distance of S2) and $\Delta r=12.756\times 10^{6}\,\mathrm {m}$ (twice the Earth's equatorial radius), we find $\Delta a\approx -2.1\times 10^{{-}6}\,\mathrm {m} \mathrm {s} ^{{-}2}\approx -{\tfrac {1}{4{,}600{,}000}}g.$ Perhaps measurable with precision instruments, but not something an observer might feel.  --Lambiam 11:58, 28 November 2021 (UTC)
[Corrected 11:58, 29 November 2021 (UTC); the earlier value of $\Delta r$ was off by a factor of $1000$. --.L]

Why are humans so bad at climbing/walking downwards?

I was on a walk with some snow-covered steep paths and it occurred to me how much better were are at walking/scrambling up than down. Going up I rarely had to worry about whether I had a firm foothold. I could feel when it was ok to transfer weight to the front foot, and if I slipped at all a quick scrabble and I was ok. When I have previously slipped on very steep slopes I end up on all fours with little impact and can easily grab something and continue.

On the other hand when descending I found I was deliberately having to test whether my front (lower) foot would lose grip. If it did I was in a very precarious position with no instinctive scrabble to recover. When I have previously had bad slips I have ended up falling heavily on my backside, and my hands have not been in a position to grab anything until I'm slipping faster. I have ended up with bruises and cut hands before now. In fact this is so obviously a difficult way that my instinct is to descend backwards if anything is very steep and treacherous, where I gain the advantages of moving forwards but go much slower.

My dog, on the other hand, appears to be as sure footed ascending and descending head first. My first thought was that this is a side effect from when we moved to two legged walking. However I would have thought evolutionary pressure would have led to safe descent as well as ascent. I also wonder whether it is part of a much older evolutionary legacy, because as far as I know there are no primates which will descend trees head first, though many other animals can. - Q Chris (talk) 16:42, 28 November 2021 (UTC)

The easiest explanation is that it is a trade-off. For short bursts of speed, many land animals outdo humans, but in endurance running Homo sapiens outdoes many of its prey animals. Evolution may have favoured this trait over handling steep descents quickly. Also, I suppose that someone who is used to barefoot walking may be more confident while descending, as the grip of their unshod sole may be better and they also get a more informative feedback.  --Lambiam 18:03, 28 November 2021 (UTC)

Our bipedalism does put us at a disadvantage. A dog's centre of gravity is lower than ours, and they have four potential points of ground contact. Also our feet are flat with no claws, and almost all of a human foot is forward of the leg and ankle (which results in the foot mechanics of going uphill being different to going down). The reason why we haven't evolved to be good at descending slippery slopes is presumably because 1) much of human evolution occurred in parts of the world with little or no snow, and 2) descending slippery slopes isn't an important attribute for us to have - as Lambiam states, we evolved as endurance hunters for whom running quickly isn't important (and we have good brains and can invent arrows and poison darts etc. that, at least for hunting purposes, circumvent the need to run down slopes quickly). PaleCloudedWhite (talk) 18:47, 28 November 2021 (UTC)

How often did bipedal savannans hunt and gather on slopes? Sagittarian Milky Way (talk) 00:57, 29 November 2021 (UTC)

The same reason why it's easier to back down a ladder than to go forward down a ladder: our knees only bend in one direction. This gives us a stable pose where the forward foot is higher than the rear foot. There's no similar pose where the forward foot is lower than the rear foot, because that would require the knee to bend in the opposite direction. --Amble (talk) 18:55, 28 November 2021 (UTC)

In some circumstances it helps to descend an uneven slope sideways with the upper knee more bent and the body leaning upslope, which reduces the discrepancy of feet placements and helps with balance: it's tiring to perform for an extended period, however. {The poster formerly known as 87.81.230.195} 90.205.225.31 (talk) 00:24, 29 November 2021 (UTC)

This explains why descending facing forward is harder with the current, actual build of the species, but not why evolution did not take a path towards faster secure forward descent.  --Lambiam 11:38, 29 November 2021 (UTC)

As you yourself implied above, the results of evolution by natural selection are often compromises between several competing 'pressures', so what alternative body plan evolvable in only a few million years could a primate, moving from a predominently arborial lifestyle to a predominently ambulatory one, have arrived at that better facilitated forward downhill movement without detracting from the more common requirement of out-running prey over long distances on relatively level savannah? {The poster formerly known as 87.81.230.195} 90.205.225.31 (talk) 23:36, 29 November 2021 (UTC)

Sure. I thought that part was already well covered. One other interesting point is that I always find it much more efficient to go down an uneven trail with a galloping motion than walking. It turns out there's an interesting paper on the mechanics of this motion: [2]. --Amble (talk) 17:06, 29 November 2021 (UTC)

November 29

How can a magnet be used to alter a current?

Current through a circuit, like a flashlight, and current through a wire? So that's DC and AC. Magnets can interfere with the electromagnetic field, right. 67.165.185.178 (talk) 05:27, 29 November 2021 (UTC).

That's right. Dynamos and Power stations use magnets to generate electrical current. Do you have a more specific question?--Shantavira|^{feed me} 09:22, 29 November 2021 (UTC)

Yea, but I don't think electric current is the word I'm looking for, that makes it seems like magnets create or destroy electricity from nothing. 67.165.185.178 (talk) 14:01, 29 November 2021 (UTC).

Electric power plants make electricity by spinning one or more magnets near large amounts of wire, if the motion stopped the electricity would turn off. Sagittarian Milky Way (talk) 17:17, 29 November 2021 (UTC)

Whether the current is DC or AC depends on the power source. Flashlights typically operate on batteries, which are used to power DC circuits. The current through a wire can be of either type. Faraday's law of induction describes how a magnetic field interacts (a more neutral term than "interferes"; the interaction can be useful) with an electric circuit. It requires the magnetic flux to vary in time. A stationary permanent magnet has no effect on a stationary electric circuit.  --Lambiam 11:31, 29 November 2021 (UTC)

Weird, I thought magnets influence DC motors more than AC motors? 67.165.185.178 (talk) 14:01, 29 November 2021 (UTC).

What kind of influence are you thinking of? Among electrical motors, the difference between motors powered by DC sources and AC sources is slight; the former type has an additional commutator that makes the direct current appear to the coils of the motor as if it alternating. It is not apparent to me why that difference should be of any importance when magnet enter the scene.  --Lambiam 23:51, 29 November 2021 (UTC)

Okay here's an answer I got from a retired electrical engineer: for dc motors, the magnetic flux lines have to intersect a coil of wire at the correct angle at a certain rate of speed, while alternating north and south poles to excite electrons in the wire coil to create measurable current flow. a motor just reverses the process. ac motors are a little different. alternating current is always rising and falling the magnet would have to be synchronized in reversing poles to affect the ac motor. 67.165.185.178 (talk) 05:53, 30 November 2021 (UTC).

November 30

Rockets with solid rocket boosters launching crewed spacecraft

One of the reasons Ares I was canceled was because it was determined that launching a crewed spacecraft on a solid rocket was unsafe. Similarly, the Space Shuttle's SRBs were considered unsafe (and given that the Challenger disaster happened, those fears had basis). However, the Boeing Starliner is launched on the Atlas V in a configuration that uses solid boosters; similarly, the cancelled Hermes spaceplane was planned to be launched on the Ariane 5, which also uses solid boosters. How come launching crewed spacecraft on solid rockets or rockets with solid rockets is often considered unsafe, but this was not considered to be the case for the Atlas V launching Starliner? Is it the size of the boosters, or is it another factor? Narutolovehinata5 (talk · contributions) 00:19, 30 November 2021 (UTC)

As far as I am aware, the cancelation of Ares I had nothing to do with safety concerns of the SRBs. In fact, Ares I was seen as having a potential higher safety rating than EELV launchers, such as the Atlas V. --OuroborosCobra (talk) 00:30, 30 November 2021 (UTC)

According to this Scott Manley video, one factor for the cancellation of the Constellation program was that an Air Force study claimed that if there was a need to abort due to a problem with the rocket (i.e. an explosion), the capsule's parachutes would be burned by burning debris. Narutolovehinata5 (talk · contributions) 00:45, 30 November 2021 (UTC)

I don't know if solid boosters are less safe: they are just way less efficient (have lower specific impulse) than liquid boosters. The Space Shuttle SRB failure resulted from notoriously ignoring signs of burn-through in the O-rings, which in turn resulted from human normalization of deviance within the contracting organization. Liquid boosters can also be throttled, turned on and off, etc., unlike solid boosters that are basically giant sparklers that can't be extinguished once lit. But if anything, liquid boosters are less reliable than solid boosters, because of the complicated turbines, pumps, cryogenics, etc. in them. Remember also the near-fatal LOX tank explosion on Apollo 13.

The US crewed spaceflight programs prior to the Shuttle all used liquid boosters, but (iirc) 1960s-70s Soviet crewed launches used supplemental solid boosters similar to what the Shuttle eventually used. I suspect this was because NASA was by then better equipped than the Soviets to surmount the hellishly difficult technical challenges of making cryogenic boosters (particularly using liquid hydrogen) reliable. 2601:648:8202:350:0:0:0:69F6 (talk) 00:34, 30 November 2021 (UTC)

As a correction, the Vostok/Voshkod/Soyuz boosters all use kerolox engines, they never used solid rockets to launch crew. Even the Buran's boosters (which were later adapted into the Zenit rocket) used kerolox, not solid propellant. Narutolovehinata5 (talk · contributions) 00:47, 30 November 2021 (UTC)

Let's not forget per-spaceflight JATO units and the shenanigans people got up to with those. See the JATO_Rocket_Car urban legend. 41.165.67.114 (talk) 06:19, 30 November 2021 (UTC)