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September 29

Are there any pathogens where the fraternal birth order effect makes a difference?

It's been established that the more older brothers a boy has, the more likely he is to be gay:

http://www.pnas.org/content/early/2017/12/05/1705895114

This fact, combined with Greg Cochran's theory about a pathogen being response for male homosexuality, makes me wonder:

Are there any pathogens where the fraternal birth order effect makes a difference? Specifically, are there any pathogens where the more older brothers a boy or man has, the more likely he is to be affected by this pathogen?

Basically, I am asking this question in order to get a rough idea of the likelihood of Greg Cochran's theory actually being correct. Also, No, I'm certainly not trolling; rather, I am trying as best as an amateur can in figuring out the truth behind this issue. Futurist110 (talk) 01:11, 29 September 2018 (UTC)

It doesn't sound like much of a "theory" where Cochran is concerned,

Can you please elaborate on this part? Futurist110 (talk) 01:30, 3 October 2018 (UTC)

but the association of homosexuality with a female anti-neuroligin 4 Y-linked (NLGN4Y) antibody is fascinating. This makes it sound like the antibody could be a simple case of an Rh factor like phenomenon; however, bear in mind that evolutionarily this "problem" could easily be "fixed" (women could express NLGN4Y anywhere in their bodies - big toe, salivary gland, wherever - and then it would end up being recognized as a self antigen and homosexuality would go away). This would indicate that far from being some insoluble design issue, homosexuality has been preserved by natural selection even in the face of a readily available mutation (putting some random enhancer on the DNA next to it). Which would mean that some very immediate selective benefit for homosexuality has to exist from the perspective of the mother.

Are you sure that a selective benefit has to have occurred? I mean, couldn't there be a gay germ instead which likewise evolves along with humans--thus ensuring that any immunity that humans will develop to this pathogen will become meaningless? Futurist110 (talk) 01:30, 3 October 2018 (UTC)

That said, Cochran's speculation isn't necessarily wrong -- anything is possible in biology, always. One can imagine that a foreign antigen could influence rejection of some other protein, like lone star tick causing meat allergy. The antigen could, in theory, be just about anything - mosquito saliva, rose thorns, or a virus. But the problem is, I am not aware of any demonstration that homosexuality has ever not existed in any human society, so how can it be an environmental factor?

I have heard either Cochran or someone else previously make the claim that homosexuality (or at least male homosexuality) doesn't appear to exist in hunter-gatherer populations. Futurist110 (talk) 01:30, 3 October 2018 (UTC)

It could be interesting to look into whether this particular neuroligin is responsible for the specificity of synapses between potential pheromone receptors (some orthologs are allegedly pseudogenes, but I'm suspicious of selenocysteine involvement) in the vomeronasal organ, and GnRH-expressing neurons that pass through the terminal nerve to the hypothalamus. If this antibody response can alter the determination of which odor is a pheromone, then it should be able to condition recognition of one sex rather than another. Wnt (talk) 01:50, 29 September 2018 (UTC)

Can this antibody response also alter the blueprint of one's body that one has in one's brain? Basically, I'm wondering if this antibody response could likewise cause gender dysphoria. Futurist110 (talk) 01:30, 3 October 2018 (UTC)

Here is a list of possible ways that natural selection can select for homosexuality as a trait that increases the success of an individual in reproducing and passing their genes on to the next generation: [ https://sites.psu.edu/evolutionofhumansexuality/2014/03/05/selection-for-homosexuality/ ]. --Guy Macon (talk) 04:38, 29 September 2018 (UTC)

Relevant articles: biology and sexual orientation and environment and sexual orientation. --47.146.63.87 (talk) 22:12, 29 September 2018 (UTC)

@Guy Macon: That article looks like a good review of at least most of the leading ideas. Problem? (a) Heterozygous advantage implies there is a "gay gene", which would have been mapped and cloned by now. People have tried hard and failed to map any one locus on the chromosome. (b) Altruism seems iffy in the article itself, as it is hard to explain how the homosexual can improve transmission of his genes that much in third parties; but see below. (c) A polygenic trait seems like a winner --- however, if women can simply express this neuroligin to prevent this antibody effect, then they can have a single gene trait that overrides it all, which is why I got excited to see the article. And (d) antagonistic pleiotropy only would make sense if the antibody response could also improve reproductive success (how?)

However, this paper introduces another possibility, which is that the mother could be selecting for her success, not the offspring's. It is always easier to tell somebody else to be altruistic than to be altruistic yourself, and so I think this might change some of the numbers, but I haven't looked into the math of altruism. Wnt (talk) 00:05, 30 September 2018 (UTC)

Diamond valuation

Is there someplace online where you can get a general idea of the value of a daimond (or even minor gemstones like, say, citrine)? I was reading about the 4Cs and am trying to figure out valuation by altering certain digits. Say how much would something like this cost? Color: I; Clarity: SI2; CTW: 0.200; Cut: RoundLihaas (talk) 09:41, 29 September 2018 (UTC)

This was the first hit on google for "diamond valuation", and puts your diamond's value at $147.42. 2400:D400:9:1268:306:200:0:10B0 (talk) 10:12, 29 September 2018 (UTC)

It's not clear from your post whether you're buying or selling. The price of a synthetic gemstone will generally be much lower than that of a "natural" one. Whether buying or selling, if you want a "natural" stone, you will likely get widely varying prices from different establishments; the market is intentionally opaque and full of collusion so you'll give up and just take whatever price is offered. (For instance, several of the largest U.S. jewelry store chains are owned by the same company.) --47.146.63.87 (talk) 22:07, 29 September 2018 (UTC)

This is a very old article but still relevant.[1] 173.228.123.166 (talk) 22:19, 29 September 2018 (UTC)

There is a company called the Jewelry Exchange in Redwood City, California that advertises "diamonds guaranteed to appraise for double". That ridiculous slogan indicates that diamond prices are mushy and subjective, as opposed to gold prices, for example. Cullen³²⁸ Let's discuss it 22:23, 29 September 2018 (UTC)

That's what I head, especially if they are lab made vs. natural.

Thanks, anywasy, yall.Lihaas (talk) 22:59, 29 September 2018 (UTC)

We have an article, though it's in bad shape. (No Cal resident? As the article says, their headquarters are down here, so here their ads always tout "The Jewelry Exchange in Tustin". I think they've been running the same TV ad for over 20 years.) --47.146.63.87 (talk) 08:11, 30 September 2018 (UTC)

September 30

Pianos vs motor vehicles: moving parts

A dear friend of mine, who's a highly experienced piano teacher, has told me that a piano has more moving parts than a motor car. I wonder if this would depend on the type of piano and the type of car. Or maybe it's absolutely correct. Or maybe not. Can someone shed light on this for me? -- Jack of Oz ^{[pleasantries]} 00:19, 30 September 2018 (UTC)

It could well be true. Start counting the moving parts in a typical car, and they might fall short of 88, or whatever the magic number would be. ←Baseball Bugs ^{What's up, Doc?} carrots→ 01:38, 30 September 2018 (UTC)

I can tell you it's way more than just the 88 keys. And I'm sure any car would have way more than 88 moving parts. -- Jack of Oz ^{[pleasantries]} 02:06, 30 September 2018 (UTC)

Have you asked your friend to "prove it"? Or might that be a sensitive issue? ←Baseball Bugs ^{What's up, Doc?} carrots→ 02:13, 30 September 2018 (UTC)

Do you count the cams on a cam shaft or the wheel weights on the wheel? Technically, every part on a car is a moving part if the car is moving, no??? ;) Wnt (talk) 01:59, 30 September 2018 (UTC)

A piano can also be moved via its wheels, but I'm not so sure the basic chassis of either a car or a piano would count as a "moving part". ←Baseball Bugs ^{What's up, Doc?} carrots→ 02:13, 30 September 2018 (UTC)

These items claim that a piano has about 12,000 while a car has about 10,000. Piano and [2] ←Baseball Bugs ^{What's up, Doc?} carrots→ 02:16, 30 September 2018 (UTC)

Our piano article cites a promotional website from Steinway & Sons, a piano building firm of international repute. The source claims: "There are 12,116 individual parts that make up a Steinway grand piano." This is not the same as 12,000 moving parts.

In any event, the number of parts - moving or otherwise - is a poor proxy for the mechanical complexity of a system. Not all moving parts are equal in complexity.

Personally, I find the non-moving part of the piano to exude more complexity: for example, the curved hardwood that forms the distinctive casing, or rim, of a grand piano commands a five-figure premium over the straight wall of an upright piano; and in both types of piano, the soundboard must be crafted in a manner that simultaneously satisfies strict engineering requirements and artful imprecision. As discussed in our article on piano acoustics, it is the inharmonicity of a piano - "not because of a lack of precision" - that give each instrument it timbre - and why it takes so much effort for electronic synthesizers to produce an authentic piano sound!

Nimur (talk) 03:24, 30 September 2018 (UTC)

Nobody mentioned complexity. Just numbers of moving parts. -- Jack of Oz ^{[pleasantries]} 03:43, 30 September 2018 (UTC)

{{ec}} with Nimur (had trouble tracking down the piano-article ref to verify) As a quick guesstimate, I count 15 moving parts in the action of a grand piano key, which gives 1320 total. That does not include the mechanism of shifting the set of hammers for the soft pedal, holding up all the dampers for the sustain pedal, etc. but those are likely^[SWAG] only a few tens each for the whole instrument or at most a few extra per key. DMacks (talk) 03:54, 30 September 2018 (UTC)

• Cars would generally be seen as having more, because the manufacturing processes used involve assembling together smaller parts. Consider a piano action vs. an engine cylinder. 88 keys, 11 parts in a piano action per key; 8 cylinders (or 4) - we can simplify this to "Does a car have more than 11 moving parts per cylinder?" Maybe 22 in Europe. Now the parts of that action are largely wooden, with many separate holes drilled into a piece of wood for each lever. The levers are few, but complex. But the car has separate parts, each staying separate until assembled by a mechanic in a garage (I'm counting parts which would be separated during repair as being "separate parts"). We have as many parts as a piano action just for each engine valve on an OHV engine. If you start counting balls in ball bearings, then it's far more. Andy Dingley (talk) 09:49, 30 September 2018 (UTC)

Small numbers of parts are replaced in routine car maintenance but a full restoration that considers all its parts happens only rarely, if ever, to a car or a piano. One cannot meaningfully compare counts of "moving parts" without an even-handed definition of what constitutes a moving part. Some extreme views are possible e.g.

• Every separable part that moves relative to another separable part when the piano/car is taken into use. The count includes screws holding the piano lid to its hinge, and every ball in the car wheel bearings.

• Literally every separable part because pianos and cars both have continual motions, both vibratory and planetary, relative to the fixed stars. The count includes every screw on both sides of the piano lid hinge and every chassis fastener in the car.

• A conceptual moving part counts as a single part regardless of its actual construction. For piano, key+hammer+string counts as 3, for car drivechain+camshaft+valve counts as 3.

A moderate view can be to count Every saleable replaceable part that moves in contact with another saleable replaceable part during normal continual use of the piano or car. For the car, the dealer's parts list is a guide. We may assume that a piston (with rings, gudgeon, connecting rod and big end shells) or a wheel bearing (preassembled with rollers and oil seals) count each as one. A piano key action should be separated into parts than a qualified repairer would consider replacing. This piano repairer estimates 12,000 action components. DroneB (talk) 19:59, 30 September 2018 (UTC)

Every component of every link in the timing chain would give you about a thousand moving parts. Your excellent attempt at stratifying the terminology is important, in this trivial problem.Greglocock (talk) 22:53, 30 September 2018 (UTC)

That's the 2nd example of intellectual snobbery on this thread. It says more about the writers of such things than anything else. -- Jack of Oz ^{[pleasantries]} 08:47, 1 October 2018 (UTC)

The Question is the famous comparing Apples and oranges nonsense. A Piano is meant to play 88 notes with a volume and dampening like the pianist intends, a engine is meant to provide a predefined jet flexible, efficient and secure transformation of fuel to rotation and Torque. The answer always causes the new question: "Yes/No, so what?" --Kharon (talk) 21:02, 1 October 2018 (UTC)

The OP raised the question because his friend made a statement about it. It seems like a reasonable question to ask. A more apples-and-apples question might compare a piano to a harpsichord. But the apples-and-oranges nature of the question is the point. ←Baseball Bugs ^{What's up, Doc?} carrots→ 21:20, 1 October 2018 (UTC)

Kharon, it depends on one's perspective. Yours is not useful here. Keep it simple. A piano is an object composed of many parts, some of which move when the object is in operation. A car is an object composed of many parts, some of which move when the object is in operation. How do the numbers of moving parts compare? -- Jack of Oz ^{[pleasantries]} 09:28, 2 October 2018 (UTC)

We may simplify the comparison to count the numbers of parts that move simultaneously. The wretched inadequacy of my piano playing ability is apparent when I encounter the 7 - gasp 7 -note chord in the 10th bar of Debussy's Clair de Lune. Although the piano is capable of playing all its 88 notes simultaneously under protest (from anyone within earshot), it will never Deo volente be asked to do so. The designer of the Yamaha PortaSound PSS-280 electronic keyboard seems in agreement because this instrument simply refuses to emit more than 7 piano notes at once. Can it be mere serendipity that an East German car was marketed with a 3-cylinder 2-stroke engine that has exactly 7 moving parts? Enough has been said and now like God we should rest on the 7th. DroneB (talk) 14:05, 2 October 2018 (UTC)

The seventh? DMacks (talk) 14:30, 2 October 2018 (UTC)

_{I fear the seventh both because 7 8 9, and to face an unlucky number 13 is risky. So I'll quietly take the fifth. DroneB (talk) 16:56, 2 October 2018 (UTC)}

Ok Jack of Oz. Let me help you on your perspective then. The Volkswagen Group 7993ccm W16 engine is a 16 cylinder 64 valve quad-turbocharged engine, that you can find in the Bugatti Veyrons and Bugatti Chirons and some Bentley models. It should beat any piano regarding number of moving parts since it already has almost as many valves (64) as a piano has keys. Given all the additional moving parts (for example in the fuel injection for 16 cylinders, oilpumps, fuelpumps, waterpumps, power generator, Starter (engine), Distributor, turbochargers etc.) a piano misses, lots of engines probably have more and a few very likely even more that double the moving parts. Btw. a 16 cylinder is not even the top of existing, build combustion engines in cylinder count. And your dear friend compared a piano to a whole car?

B.t.w. why are these pianos so damn expensive? Just cut a tree and you have enough material for the frame and mechanics for 5-10 pianos. How does Steinway get away with asking 81 000 $ for a single one? ---Kharon (talk) 14:37, 2 October 2018 (UTC)

Yeah, a Steinway is just a tree cut into pieces and re-arranged. --jpgordon^{𝄢𝄆 𝄐𝄇} 14:10, 3 October 2018 (UTC)

How does Barnes and Noble get away with asking $10 for a book? The price of paper and ink is not even a tenth of that. Tigraan^{Click here to contact me} 16:10, 3 October 2018 (UTC)

Somewhat bringing this back to the original topic, have you seen what those damn Germans are up to? Steel etc is a little bit more expensive than wood, still how on earth can they can justify that price tag for a BMW i8. I mean they aren't as bad as the Italians or ole Musky, but still..... Nil Einne (talk) 17:02, 6 October 2018 (UTC)

Berry

What berry is it? Grows this month along a public sidewalk in Warsaw, quite small, about the size of a blackcurrant. I'm planning to pick them for eating, if they're non-toxic, so would like to know the species with absolute certainty. Brandmeister^talk 15:51, 30 September 2018 (UTC)

Looks a bit like a cotoneaster - if so the berries are not considered edible. Mikenorton (talk) 20:49, 30 September 2018 (UTC)

I agree, looks very like a cotoneaster to me. DuncanHill (talk) 23:57, 30 September 2018 (UTC)

I disagree. The leaves in the picture are obtuse - not "ovate to lanceolate in shape". The fruits are borne singly or pairs close to the stem in the pictures - not on a corymb. I will try to track down a better candidate. 196.213.35.147 (talk) 13:37, 1 October 2018 (UTC)

Looks like it could be a cotoneaster after all. I'm going with Cotoneaster microphyllus var. glacialis 196.213.35.147 (talk) 14:01, 1 October 2018 (UTC)

"These berries are, however, of only doubtful or low toxicity" from Poisonous Plants in Britain and their effects on Animals and Man by the UK Ministry of Agriculture, Fisheries and Food.

Also "...as so often, the berries aren’t pleasant to eat. With the Cotoneaster, it is not so much that the taste is unpleasant, though it is, it is that the berries aren’t at all juicy and the texture is powdery. Even birds aren’t that anxious to eat the berries" ';'The Poison Garden Website. Alansplodge (talk) 14:47, 2 October 2018 (UTC)

Why do tinyish spiders often rappel when chased indoors?

Why don't they just jump off without expelling silk? They probably can't fall as fast as freefall while making silk and such a small creature might not even be injured by terminal velocity. Or did blowing away in the wind on a 1-thread parachute save more spider lives than "freefall and run" in its original outdoor habitat and the instinct remains? Sagittarian Milky Way (talk) 20:01, 30 September 2018 (UTC)

Our article ballooning (spider) may help. Mikenorton (talk) 20:57, 30 September 2018 (UTC)

You refer to "its original outdoor habitat". I very much doubt whether a spider, whether spiderling or adult, has either any concepts of "outdoors" and "indoors", or the perceptual abilities to tell the differences bearing in mind their size relative to a human-dimensioned structure. {The poster formerly known as 87.81.230.195} 90.217.102.65 (talk) 09:33, 1 October 2018 (UTC)

It goes without saying, as it is implied in OP's "and the instinct remains".

But even if spiders could distinguish indoors from outdoors (which should be possible, as there are so many differentiating factors they could evaluate: average wind speed, temperature, direction and intensity of infrared radiation and polarized light, smell), why should they just jump off without expelling silk? How could this be a selective advantage? Freefall speed is not the only relevant factor, another would be for example that the thread gives the spider a chance to withdraw from any less than optimal landing place, like water or perhaps the vicinity of predators and carnivorous plants or fire. 194.174.73.80 (talk) 13:31, 1 October 2018 (UTC) Marco Pagliero

If you really are asking how it could be a selective advantage, that's obvious: freefall speed could be the most important factor. I've no idea whether it is, but for what it's worth, the ballooning article doesn't seem to give any indication that the spiders can direct their flight. That would seem to imply that the other factors you mention are not significant. Henry^Flower 14:49, 1 October 2018 (UTC)

Please, you apparently did not read carefully the original question: it asks, why do small spiders "often rappel when chased indoors". Rappel has nothing to do with ballooning but instead describes a spider dropping e.g. from the ceiling on a line of silk. Even if the spider has no control on the direction, the thread allows it to stop and even to reverse the fall if it wishes so. In the context of rappel (not ballooning), my suggestions are of course significant.

And secondly you did not read carefully my own question, which read: "How could it be a selective advantage for a spider to just jump off without expelling silk?", this is the opposite of the question you seem to believe you are answering.

While for your post to be significant at all you should prove or at least make credible that such small animals as "tinyish spiders" can indeed be damaged when free falling from any height (We are not talking of Migale or Tarantula). 194.174.73.80 (talk) 16:35, 1 October 2018 (UTC) Marco Pagliero Berlin

"Migale"? Is there an article? ←Baseball Bugs ^{What's up, Doc?} carrots→ 16:40, 1 October 2018 (UTC)

Sorry, "Migale" is not English, you are looking for Mygalomorphae 194.174.73.80 (talk) 16:51, 1 October 2018 (UTC) Marco Pagliero Berlin

Marco, you've misunderstood completely. Not producing silk maximises freefall speed and so allows the fastest escape from the chaser. There's a fairly obvious selective advantage to that. (The ballooning issue is not so relevant, but you got that wrong too: SMW asked about "blowing away in the wind on a 1-thread parachute".) Henry^Flower 20:41, 1 October 2018 (UTC)

No, the question was "Why do tinyish spiders often rappel when chased indoors", while the parachute sentence you are citing was enbedded in a tentative response to this question but it doesn't imply the tinyish spiders SMW is chasing do actually try to balloon away (see the next sentence: 'can't fall as fast as freefall while making silk'). So I ask again, why should it be an advantage to spring without a thread beeing indoors if it is an advantage to spring with a thread beeing outdoors?

Your 'fairly obvious selective advantage' is not meaningful: whether you see the landing speed or the freefall speed as important, chased spiders never try to escape by ballooning but either by running or by rappeling, so your argument is pointless: ballooning is not a strategy for escaping when beeing chased and is not initiated by jumping without a fixed thread.

Well, even I can be wrong, so I'd like SMW to confirm whether he has ever seen a chased spider actually try to escape by 'blowing away in the wind on a 1-thread parachute' (Even our article on ballooning doesn't suggest anything like this) 194.174.73.80 (talk) 16:16, 4 October 2018 (UTC) Marco Pagliero Berlin

That was my mistake, I didn't know that thing baby spiders do to disperse was multiple threads. I have never actually seen a spider balloon but one of those nasty ballooners blew in my face once. That was my guess of why they have the rappelling instinct even though there's no wind - that they'd either cut the thread if wind gave them enough sideways momentum and squirt more thread to be blown away on or they'd glue it to the wall weakly enough that it breaks off if the spider brakes suddenly in the first quarter cycle of swinging in the wind like a pendulum. And then blow away on that thread. Sagittarian Milky Way (talk) 19:53, 4 October 2018 (UTC)

It doesn't have to be a selective advantage in all circumstances. It only has to be a selective advantage in a sufficient number of instances to provide a meaningful impetus to survival and reproduction. Bus stop (talk) 16:57, 1 October 2018 (UTC)

File:Amrum.grass.jpg

The dunes concerned.

Location known, but wanted to check something. The grass here gives way to a different cover, over what I am thinking is the landward portion of dunes?

Which articles should I look at to epxand the description? — Preceding unsigned comment added by ShakespeareFan00 (talk • contribs) 22:52, 30 September 2018 (UTC)

The green and purple stuff? Heather - so see Ericaceae, Erica, and Calluna vulgaris. DuncanHill (talk) 23:54, 30 September 2018 (UTC)

This paper should help narrow the options down. Mikenorton (talk) 16:57, 1 October 2018 (UTC)

This one may be more helpful (by the same botanist). Mikenorton (talk) 17:05, 1 October 2018 (UTC)

Thanks caption updated accordingly, if someone wants to review. ShakespeareFan00 (talk) 09:04, 2 October 2018 (UTC)

October 1

Toluene, water and isopropanol miscibility

I mixed one part toluene with one part 70% isopropanol and it separated into two phases. How do I determine what is in the lower phase? I'm guessing it's the water? — Preceding unsigned comment added by 185.230.100.66 (talk) 16:56, 1 October 2018 (UTC)

Density density density. More dense liquid sinks, less dense liquid floats. If you google fotr density of isopropanol water you will find various tables and specific values covering a wide range of percents. "70%" happens to be a standard product, and is directly available from simple product literature (i.e., no need to use scientific journals or paywalled sources), and probably even in the snapshot that Google provides on its list of hits. Of course our toluene article has the density of that pure substance. But once mixed, the more the IPA migrates into the toluene, the lower the %IPA in the aqueous phase and the denser the aqueous phase becomes. DMacks (talk) 17:59, 1 October 2018 (UTC)

Proportion of predicted progeny for a test cross of ABC/abc involving linkage

help i embarrassed myself as a tutor today. I don't have time to draw a diagram and a picture of the question would not be free content. Suppose there are three loci, A, B and C on a single chromosome, where A/B are 20 map units apart, and B/C are 10 map units apart:

• A — 20 — B — 10 — C •

Suppose we have a rat with the following genotype:

A B C
———
a b c

The question asks for the proportion of progeny with the genotype Aabbcc.

Whichever way I did it, I did not get 9%, which is what was shown on the answer key:

The only way to produce Aabbcc progeny is through Abc and abc gametes.

Assuming no double crossovers between same loci (but allowing for double crossovers between different loci): the gamete frequency for abc is 0.9 * 0.8 * 0.5 = 36% (chance of no crossover betwen either pairs of loci * half the gametes) and for Abc is 0.2 * 0.9 * 0.5 = 9% (chance of crossover between A/B * chance of no crossover between B/C * half the gametes) so the expected frequency should be 3.24%.

How is the answer key (9%) correct? Yanping Nora Soong (talk) 18:11, 1 October 2018 (UTC)

• Disclaimer: I just discovered the topic of crossovers (but not probabilities).

There is an error in your reasoning when you assumed the first gamete must be abc and the second Abc (it can be the other way around) so you miss a factor of two. (Out of the 36 outcomes when you cast two dice, only one is a double 1, but two contain one 1 and one 2 - if that is not obvious to you, or for further reading, see [3].)

Furthermore, the probability of crossover is not strictly proportional to the distance so it is not exactly 80% and 90% chances of no crossover. The formula at Centimorgan#Relation_to_the_probability_of_recombination should be valid only if double crossovers are allowed (since at infinite distance the probability of recombination tends to 1/2, which comes from the fact that an odd or even number of crossovers is equally likely), but yours (P = d/100) is pretty much never right I think (except for small-d approximations). Using the article formula I get crossover properties of P10=9.06% and P20=16.48% (instead of 10% and 20%).

Your reasoning for gamete frequencies seems correct to me and gives $P(abc)=(1-P_{20})*(1-P_{10})*0.5=37.97\%,P(Abc)=P_{20}*(1-P_{10})*0.5=7.49\%$. The final probability of genotype is then $P(Abc+abc)=2*P(Abc)*P(abc)=5.69\%$. While it brings one closer to the result, that is still not the answer key. Tigraan^{Click here to contact me} 14:21, 2 October 2018 (UTC)

It's been a while since I've dealt with something like this but since we are talking about rats, which don't naturally self fertilise, have I misunderstood something or is there no way to give a single progeny diploid genotype frequency based on the question as worded? There is only one rat mentioned. We have no idea what the genotype of the other parent is. It could be anything e.g. abc|abc, ABC|ABC, a'b'c'|A'B'C'. You could only give a range from 0% (if the other parent has none of those alleles) to the maximum possible (assuming the most favourable parent to produce that combination when mating with the parent who's genotype is mentioned). Are you sure that the question didn't say something like 'assume both parents are ABC|abc' or 'if the rat self fertilises' (which is a very odd suggestion but I'm sure far from the weirdest test question) or something which would clarify the situation? Nil Einne (talk) 19:26, 2 October 2018 (UTC)

Your original calculation came up with a 9% figure for Abc. So the way to get the book's answer is to suppose they threw in the word "backcross" somewhere, or a comment about the phenotype of the other parent being abc, etc. The assumption of no double crossovers between adjacent genes is reasonable, though the statement that they are 20 and 10 centimorgans apart (rather than having this observed probability of recombination) would make it an approximation. Wnt (talk) 01:45, 3 October 2018 (UTC)

I asked my genetics professor from eight years ago, and she made me realize I confused a test cross with a self-cross. Oops. Yanping Nora Soong (talk) 16:31, 3 October 2018 (UTC)

Remember that providing key question details in the subject heading only on the RD is quite confusing since it's fairly common that people will only skim over or even just not notice the heading. Nil Einne (talk) 19:33, 3 October 2018 (UTC)

Indeed so! Also, people tend not to Wikilink from headers since it is "frowned upon", whereas if the OP had linked test cross in the question, he or she might well have gotten to his own answer in the process. Wnt (talk) 01:51, 4 October 2018 (UTC)

I wrote this question from my phone, which is quite different in "feel" than writing from my laptop. Yanping Nora Soong (talk) 15:46, 4 October 2018 (UTC)

I didn't intend to criticize anyone but myself for not RTFQ. Wnt (talk) 12:28, 6 October 2018 (UTC)

October 2

Why did it take so long to invent the heavy plough?

The heavy plough is hailed as one of the most revolutionary technological advances in the history of agriculture. But, from what I've read, the heavy plough is, quite literally, just a heavier version of the regular plough. Why did it take so long to invent, then? — Preceding unsigned comment added by 90.69.6.163 (talk) 10:05, 2 October 2018 (UTC)

The Plough invention described was replacement of the simple ard by the carruca turnplough around the 7th century, though a heavy iron moldboard plow was already developed in China's Han Empire in the 1st and 2nd century. The carruca may have been introduced to the British Isles by the Viking invasions of England in the late 9th century. The article Iron Age gives estimated dates for the spread of iron tool- and weapon-making around the World but cannot explain "Why not earlier?". DroneB (talk) 13:09, 2 October 2018 (UTC)

See https://www.deere.com/en/our-company/history/john-deere-plow/. The main rise of technology came with the rise of industrialization and mass transport. Maybe someone already invented it in the roman empire but no one cared because it was slave work anyway and much cheaper to buy additional slaves to do double the work. --Kharon (talk) 15:01, 2 October 2018 (UTC)

• What relevance does John Deere (who were one of the inventors of the steel plough) have, a thousand years after the invention discussed here? Andy Dingley (talk) 22:38, 2 October 2018 (UTC)

"The scratch plow which preceded the wheeled plough had been ideal for the light sandy soils of Southern Europe" which means that the heavy plow was probably not necessary in Italy. Ruslik_Zero 12:28, 3 October 2018 (UTC)

• It isn't merely heavier. It's also wheeled and (most importantly) uses a more robustly constructed share and mouldboard, capable of turning a furrow, not merely acting as a harrow. Which also requires a greater investment of iron, still a highly valuable material in this period. Additionally it also requires a team of draft oxen to pull it (oxen rather than horses at that time). You can't pull it with a donkey, or a couple of friends. Andy Dingley (talk) 22:38, 2 October 2018 (UTC)

Can anyone identify this caterpillar (Vietnam)

Hi

I was wondering if anyone could identify this caterpillar? A colleague/friend is on a work trip to Vietnam and took this photo.

Hermitical (talk) 23:10, 2 October 2018 (UTC)

I spent quite a lot of time looking at images of caterpillars in Vietnam and found several that looked like your image, but on all occasions the photographer simply said "wow, look at the hairy caterpillar, I wonder what it is?", even one guy who had happily identified all the birds that he saw. So, unfortunately there's nothing to go on. Mikenorton (talk) 17:54, 5 October 2018 (UTC)

October 3

What are the odds of conceiving the exact same embryo in these two scenarios?

Here are the two scenarios:

In the first scenario, you conceive an embryo through intercourse. Meanwhile, in the second scenario, you conceive an embryo through in vitro fertilization (IVF). Let's say that the second scenario happens in a parallel universe at the exact same time that the first scenario occurs in this universe.

Anyway, what are the odds that the two embryos conceived in these two parallel universes would be the exact same embryo? Futurist110 (talk) 01:59, 3 October 2018 (UTC)

Depends on who is the father of the child. 86.152.81.16 (talk) 10:21, 3 October 2018 (UTC)

175983257964128056 to 1. — Preceding unsigned comment added by 82.38.221.49 (talk) 12:23, 3 October 2018 (UTC)

An interesting question, but I don't know how you'd get to the answer. I assume from your premise that the gametes in each universe would be identical (otherwise you are asking the usual question of what would have happened if another sperm had won the race). But is there any detectable effect of the procedure? Well, the in vitro fertilization article has two sections about suspected issues ranging from birth defects to hypertension. Whether these are accompanied by any subtler, non-medical change to the offspring is another question. Wnt (talk) 12:40, 3 October 2018 (UTC)

• If you are asking about embryo development differences between IVF and the ol' way, ask it, instead of masking the question in a layer of probability. (I cannot answer that.)

If the real question is about the probabilities that offspring of the same parents has the exact same genetic code... That is the Shannon entropy of offspring DNA. There's a good argument for why DNA entropy is not well-defined but I guess you could easily produce something that looks like a definition; for instance, "for every gene with multiple alleles, estimate the prevalence of each allele, and compute the entropy by assuming genes to be independent (which they obviously are not in reality)". Tigraan^{Click here to contact me} 16:26, 3 October 2018 (UTC)

100% odds, as there is always going to exist a sector within that parallel universe where the required conditions for the exact copy to arise will be met. Count Iblis (talk) 17:34, 3 October 2018 (UTC)

Inheritance of hair color

I'm interested in under exactly what circumstances a child inherits a specific hair color from its parents. In general, how well understood is the genetics of this? A more specific question is, what hair color would a child of a red-haired father and a blond-haired mother inherit? FreeKnowledgeCreator (talk) 02:33, 3 October 2018 (UTC)

You might find Human hair color helpful. It appears that there are other factors than the visible hair colour that have to be taken into account when attempting such predictions. Richard Avery (talk) 08:51, 3 October 2018 (UTC)

Thank you. It's disappointing to see, however, that the article's section on "Genetics and biochemistry of hair color" is uncited. I'm presuming my more specific question doesn't have a clear-cut answer? FreeKnowledgeCreator (talk) 09:28, 3 October 2018 (UTC)

"There is very little known about hair color inheritance but there are some interesting theories" from The Stanford Department of Genetics.

A better referenced article is Red hair color: The myth from John H. McDonald, University of Delaware. Alansplodge (talk) 12:25, 3 October 2018 (UTC)

A newspaper article from April this year: Scientists discover dozens of new genes for hair colour

The research the article describes seems to be Genome-wide association meta-analysis of individuals of European ancestry identifies new loci explaining a substantial fraction of hair color variation and heritability. Alansplodge (talk) 12:33, 3 October 2018 (UTC)

Does the MRI produce radiation?

I've been under the impression that MRI is dangerous because of a potential radiation exposure. However yesterday I talked to a radiation technician and she said: "No, MRI is all magnetic." I could have found out myself, I want a verification, but it will take longer, so please advise. Thanks. AboutFace 22 (talk) 13:19, 3 October 2018 (UTC)

Have you read our article on MRI? Plenty of verification there. --Shantavira|^{feed me} 13:25, 3 October 2018 (UTC)

If you have concerns about safety, you should ask to speak to the radiologist (who is a medical doctor), not just to the technician who operates the machines.

To clear up the basic physics: an MRI works by emitting and detecting radio-frequency radiation while exposing the test-subject to a powerful static magnetic field. An MRI does emit radiation.

Not all radiation is medically harmful. Review the definition of radiation - the transmission of energy - which takes many forms, including electromagnetic waves of all different types. Consider that ordinary light-bulbs emit large amounts of electromagnetic radiation in the visible light spectrum. Medical harm is caused when the radiation is especially strong, or if it has other special physical properties - like the ability to ionize or otherwise disrupt a material.

Certain categories of radiation are particularly noteworthy for their adverse medical effects on humans: among them are ionizing radiation and the radiation of particles from certain nuclear processes. Broadly speaking, an MRI does not emit ionizing radiation. An MRI does radiate energy in the form of a powerful electromagnetic wave, but it is at a frequency that is generally considered safe for human exposure.

MRIs are classified, by the FDA, as a radiation emitting product. This is accurate from a physical point of view.

Properly-maintained machines are safe and legal for medical use in the United States, subject to many special considerations. In addition to the machine itself, a patient in a normal clinical setting might also be exposed to radiation from other sources at the clinic, including other lab equipment and radiological materials used for diagnostic processes.

One last note: technicians in the clinic are not necessarily experts on the theory of the machine - they are trained in operating it. So, they might not be the best resource for explaining how the machine works.

Nimur (talk) 13:42, 3 October 2018 (UTC)

Or even better, talk to a health physicist (a physicist, not a physician) who understands specifically the medical physics of what the various machines do produce and whether it's a problem. Nor would I undervalue the knowledge of a good operator.

MRI machines do have hazards (magnetism, cryogenics, induced currents), but they're well understood and don't have long-term risks. But (simply put) if you make it in and out of the machine without an obvious accident, you're not going to develop unwanted Superpowers down the line. Andy Dingley (talk) 13:59, 3 October 2018 (UTC)

We have a well referenced and reassuring article Safety of magnetic resonance imaging but there is also in-hospital gossip and sensational reports such as "Man dies after being sucked into MRI scanner at Indian hospital" that serve to maintain awareness of the overriding danger of an MRI scanner which is not radiation but its strong magnetic field that can snatch up a steel Wheelchair with its patient. DroneB (talk) 16:23, 3 October 2018 (UTC)

To the average person, "radiation" means ionizing radiation. Or, more accurately, "scary evil invisible manmade stuff that can KILL YOU AT ANY TIME! RUN AWAY!" --47.146.63.87 (talk) 07:12, 4 October 2018 (UTC)

I appreciate the explanations, so the technician was correct. I work at a place where there is an MRI machine, or at least it is my impression, but there are no radiological MD. They transmit images electronically to a large medical center. They simply do not have enough volume. I will find out if they have an MRI machine though. Thanks very much to Nimur, Dingly, DroneB. AboutFace 22 (talk) 16:54, 3 October 2018 (UTC)

They tell you not to bring objects attractable by magnets and electronics that are keeping people alive like pacemakers into the area right? Those are a lot more important than the radiation. Once there was an accident where some idiot turned on the MRI while a steel gas tank (O2? or would that rust like hell or spontaneously explode?) was in the room and it flew towards the magnet and hit the machine at high speed. Sagittarian Milky Way (talk) 18:12, 3 October 2018 (UTC)

You don't "turn on" an MRI machine's magnet. The main magnetic field is either a superconducting magnet, or else (rarely) a permanent magnet using rare earth magnets. Neither of these are switchable. This is why MRI machines are kept in their own rooms (or rooms beyond rooms) and there's a "quarantine" system so that magnetic objects aren't taken beyond the door. When they are, accidents happen. Andy Dingley (talk) 20:49, 3 October 2018 (UTC)

To be pedantic, you don't in normal operation. If things go pear-shaped a magnet quench occurs, which is very expensive. And obviously the machine is shut off in a more orderly fashion for service, to be moved, or whatever. Also for educational purposes: the above poster is discussing how the MRI room is enclosed in a Faraday cage, to contain the field of the magnet as well as keep out interference. --47.146.63.87 (talk) 07:12, 4 October 2018 (UTC)

I remember being told that MRI scanners used to be called NMR scanners (nuclear magnetic resonance) and they changed the name from NMR to MR (I guess MRI was after that) to avoid scaring people with the word "nuclear" (associated with radioactivity). 173.228.123.166 (talk) 00:41, 6 October 2018 (UTC)

Yes, and outside of medicine, "NMR" is still the usual term. --47.146.63.87 (talk) 06:48, 7 October 2018 (UTC)

bug ID

https://postimg.cc/RJnzmp7v

North/Central Europe. Is it parasitoid? Thank you everyone Asmrulz (talk) 13:47, 3 October 2018 (UTC)

Looks like a woodlouse to me. Rojomoke (talk) 15:44, 3 October 2018 (UTC)

Oniscus asellus? Mikenorton (talk) 16:24, 3 October 2018 (UTC)

How far from Earth before the densest air stops being equatorial?

I imagine it might vary somewhat with things like solar activity, time of day and atmospheric tides (perihelionic New Moon perigean spring tides are the strongest and about as far from the atmosphere's equatorial bulge as can be, sometimes both Sun and Moon are equatorial at the same time leaving only the miniscule tides of things like Venus) Sagittarian Milky Way (talk) 18:01, 3 October 2018 (UTC)

Earth atmosphere is not an equally round sphere but more like a drop with a tail in the direction opposite to its orbit vector around the sun, Just like a comet tail but much shorter, because the earth gravitation is way stronger than a comets one. Never the less the "tail" of the Earth actually also causes some Atmospheric escape. Because the Earth axis is slightly tilted and the atmosphere "drop" is shaped mostly by gravity and solar winds, the shape of the atmosphere is not "equatorial" at all. --Kharon (talk) 22:29, 3 October 2018 (UTC)

Maybe Wikipedia could get an article on Equatorial air mass, so users like Kharon would have the opportunity of understanding questions like the one above and spare us all of some nonsense answer. Apart from that, the Air mass article has links in the right direction. Doroletho (talk) 22:47, 3 October 2018 (UTC)

The equaterial air mass occupies the lower Troposphere which extends from sea level to typically a few hundred meters to 2 km (1.2 mi; 6,600 ft) altitude. It is the stagnant air of the doldrums or the equatorial trough, distinguishable from the tropical air of the trade-wind zones (Grimes, A., 1951: Compendium of Meteorology, p. 881). At the altitude of the Tropopause 17 kilometres (11 mi) above equatorial regions, there is virtually no water vapor or variation in weather or temperature, and therefore no part of the mass of the Stratosphere to receive the Bergeron classification Equatorial. DroneB (talk) 17:27, 5 October 2018 (UTC)

vision is by far the most used of the five senses?

I just read a phrase in an ophthalmology book and I'm absolutely not sure about it: "vision is by far the most used of the five senses". Is it really correct? I would say that the hearing or smelling is the most used since they are open involuntarily unlike the eye that at night close as well as many times a day when blinking the eyelids. Isn't it? — Preceding unsigned comment added by 93.126.116.89 (talk) 18:40, 3 October 2018 (UTC)

It is the most used in sense that humans receive more than 90% of information from vision. Ruslik_Zero 20:52, 3 October 2018 (UTC)

Vision records the largest volume of data in humans. In that sense its most used but its not active when we sleep and you wont wake up from light but certainly from sound. So sound is used around the clock without brake. "Most used" is an incomplete quantification because its missing in what regard. Time? Data volume? Sensitivity? --Kharon (talk) 22:44, 3 October 2018 (UTC)

What's the relation between fire and electricity?

I'm looking for differences between fire that comes from an electricity (for example electrical stove) and fire that comes from a real fire. If your religion would tell you that you aren't allowed to use fire for cooking did you used electricity or did you not use it. Kindly let's put aside our opinion about religion at all and try to answer scientifically about the question and give a reason why to resemble or not resemble between the two. I've red a lot of articles on wikipedia and I'm really confused and I believe that great part of it is because I don't have enough (deep) background or 'infrastracture' in sciences. Then please try to explain me in simple words as simple as possible and I'll appreciate it a lot. 93.126.116.89 (talk) 18:52, 3 October 2018 (UTC)

Fire is a rapid chemical reaction in which other elements combine with oxygen to form new molecules consisting of the other elements and the newly-added oxygen. Electricity (in the sense used to create heat) is the passage of electricity through an element that resists, but does not totally block, the passage of electricity. No chemical reactions occur in the electric heating appliance (although chemical reactions may be occurring at the power station where the electricity is being generated). A practical difference is that the gases created during fire are not entirely safe. While a small fire, such as a modern gas kitchen stove, can be used in a room with no planned, active ventilation, a larger fire, such as that needed to heat a house, must be vented to the outdoors with a chimney or equivalent measures. Jc3s5h (talk) 19:01, 3 October 2018 (UTC)

Thank you for your answer. Just to clarify that I understood you answer let me ask something please. you said "No chemical reactions occur in the electric heating appliance". But if I'm not mistaken, physically or microscopically, the eating occurs by the action of electrons moving in the metal very fast and that's what causes heating. isn't it? or maybe I didn't understand your words? 93.126.116.89 (talk) 19:44, 3 October 2018 (UTC)

Electric cookers (with some modern exceptions, such as the microwave oven and the induction hob) work by resistive Joule heating. Electric current in a metal wire flows because the electrons are no longer attached to each atom of the metal but can move quite freely within the metal, between the atoms. They collide with the atoms though, which loses their energy as vibrations, which we then detect outside as heat.

This is not fire though. Fire is a chemical reaction, usually an oxidation and the combination of some fuel with the oxygen in the air as the oxidiser. Each reaction releases a certain amount of energy (this depends on the chemistry involved) and this energy is seen as heat.

Although the end result of both is heat, the mechanisms to produce it are unrelated. Andy Dingley (talk) 20:44, 3 October 2018 (UTC)

A simple Chemical reaction is when two substances combine to produce new substance(s). What we call Fire is commonly the Flame that we see when such a reaction happens to be strongly exothermic (releases heat energy). Familiar examples are whenever a Fuel is consumed by burning in air. Use the links in bold to read more detailed articles. Chemists describe the reactions in burning by equations such as the example below. It describes the burning of hydrogen gas whose end product is simply water; this is a chemist's explanation of the conflagration in the Hindenburg disaster.

2H
₂ + O
₂ → 2H₂O

Be careful with the expression electric fire which in British English means a heating appliance that is powered by electricity. There should be no chemical reaction of fire in such an appliance (room heater, cooker, hairdryer, clothes iron, toaster, etc.) They have internal resistive heating wires made of some metal alloy e.g. Nichrome and this alloy material does not change during the lifetime of the appliance.

Examples of relations between fire and electricity are 1. Electricity in the form of a spark can trigger the start of a fire, as when lightning starts a forest fire, provided there is fuel available for the fire. 2. Fire can be used to heat water to drive a steam generator, thus converting the energy in a fuel to electric power. DroneB (talk) 21:57, 3 October 2018 (UTC)

Chemical reactions can also change a reactant into a simpler substance. Digestion furnishes lots of such examples. As the article says, a chemical reaction involves a transformation of one or more chemicals into other chemicals. There is something of a similarity, at the level of physics, between redox reactions and electric current, since both involve a flow of electrons or other charge carriers, though this doesn't mean they're the exact same thing. Living systems demonstrate this link quite well: your cells produce electric charge gradients by using enzymes to pump ions around, all fueled by the release of chemical energy stored in the food you consume. --47.146.63.87 (talk) 07:26, 4 October 2018 (UTC)

The religious issue you raise can get quite thorny. See Electricity on Shabbat for the example of Orthodox Judaism. --47.146.63.87 (talk) 07:26, 4 October 2018 (UTC)

US Patent no. 7872576 introduces a notion that a manually operated switch whose effect is by design incompletely predictable can somehow reduce the personal responsibility of operating an electric light (said to be a no-no for some Jews on the Sabbath or holy days) or of actions such as discontinuation of life support for terminally ill patients, triggering of a lethal dose in a death sentence, or discharging of a weapon. The article KosherSwitch does not show how this alleged Sabbath-compliant (Shomer Shabbat) device works or address the question of what degree of pseudorandomity is close enough to unpredictable randomity (in the sense of Schrödinger's cat experiment) to impress the God of Abraham as Exculpatory evidence. DroneB (talk) 10:57, 4 October 2018 (UTC)

• Feel free to ask away question about the physics if the above is insufficient. When it comes to the religious law part, I think the correct answer here is the same as for actual law: consult with whoever you feel has actually the authority to make judgement of whether a given course of action is or is not compatible with your religion, rather than asking a bunch of random internet folks. As evidenced by Activities_prohibited_on_Shabbat#Igniting_a_fire, a statement that is scientifically correct ("there is no fire in incandescent light bulbs" is pretty much uncontroversial when "fire" is meant to mean flame) does not necessarily translate into religious rule (at least according to some Orthodox Jew authorities, light bulbs violate the no-fire rule, but of course "fire" in a religious sense might be more than a bunch of chemical reactions). Tigraan^{Click here to contact me} 15:33, 4 October 2018 (UTC)

One way to distinguish fire and electricity is that fire generates waste heat, while electricity is (conceptually, at least) entirely capable of being exploited for work (physics). For example, a coal fired power plant might generate a large amount of heat, but to use this for power generation it must run a boiler or other heat engine which cannot exceed the Carnot efficiency. The remainder of the heat will go out as steam from a cooling tower or warmed water flowing down a formerly cool river. Also, unlike many combustion reactions that are subject to a key temperature threshold (fire point), there is no practical lower threshold for electricity. (Some reactions, such as the hardening of tung oil on a piece of furniture, are essentially a slow, continuous form of combustion; hence rags soaked in that oil can undergo spontaneous combustion in a hot attic) It seems worth noting that small amounts of electricity are always around us - in the nervous systems of people and pets, in static electricity from dry clothes, in eddy currents generated when the magnet holding a cabinet shut is pulled away or put back, or in the corrosion of bimetallic objects that inadvertently become batteries.

That said, there is also a distinction to be made between electricity and a spark made by electricity. Flipping an ordinary light switch produces an electrical arc that has some similarities to fire (other than in not being self sustaining). For example, a room flooded with natural gas might not catch on fire until a light switch is flipped to start the fire (see the distinction between flash point and autoignition point). There is no inherent reason why flipping an electrical switch should produce such an arc; it's just crude design. I don't know much about it, but there are various mentions of arcless electrical switches online, and if a religion were to spur people to redesign their home electrical systems to avoid generating potential ignition sources at any moment in their operation it may not be a bad thing. Wnt (talk) 10:30, 5 October 2018 (UTC)

I know of some Sabbath observers who take the light bulbs out of their refrigerators, so they can open the fridge door on Sabbath without making it turn the light on and off. 173.228.123.166 (talk) 00:45, 6 October 2018 (UTC)

File:Leech crawling.webm

File:Leech crawling.webm is described as a leech, but it looks more like a Bipalium planarian in light of its head. Anyone know what it actually is? Jo-Jo Eumerus (talk, contributions) 19:24, 3 October 2018 (UTC)

Yes, it resembles a Bipalium flatworm. Ruslik_Zero 20:50, 3 October 2018 (UTC)

October 5

When do fetuses/babies start feeling pain?

And how can we scientifically test this? --Qlearn (talk) 01:15, 5 October 2018 (UTC)

Start reading the references in our article on nociception, and read our article on clinical research ethics. Reputable scientists will not harm humans - especially not young ones - to satisfy curiosity. There would have to be a very good reason to study the problem, and the methods would necessarily be non-invasive and subject to review by an ethics committee.

Here's a peer-reviewed article authored by a couple of medical doctors from Stanford: Towards a Physiology-Based Measure of Pain..., (2011).

Just up the road from their lab is the Pediatric Pain Management facility at the Lucile Packard Children's Hospital. They are a real working clinic and they also publish active scientific research. They publish a guide for parents to help understand pain and related symptoms in children, including those that are too young to verbalize their reports. If scientific publications aren't your forte, they even have a video explaining how things work in simple words that even a child can understand.

So the short summary is, real scientists and clinicians do care about this kind of question, but they approach the topic with appropriate sensitivity and decorum.

Nimur (talk) 03:30, 5 October 2018 (UTC)

I have the impression the OP wants to know an age-threshold, when fetus are developed enough to feel and perceive pain. This is a recurrent issue in abortion debates and the basis for fetal-pain laws in Utah (who would trust Stanford scientists more than Utah Republicans in such matters?) requiring doctor to use anesthesia during some abortions (that is, given to the mother for reaching the fetus).

For a scientific review of the evidence around fetal pain see: [4]

The nociception article could be complemented with a section about fetal pain--Doroletho (talk) 10:50, 5 October 2018 (UTC)

One can set a lower limit by making the quite reasonable assumption that there is no pain before the nerve cells (including the pain receptors) start connecting to each other and sending signals. If I remember correctly, this happens after the first trimester and before the third trimester. --Guy Macon (talk) 17:48, 5 October 2018 (UTC)

Ideal pattern for a camera trying to focus automatically

What kind of pattern is a camera looking for in order to focus automatically? What pattern could I print on paper to best maintain the focus of an auto-focusing camera? — Preceding unsigned comment added by 185.230.100.66 (talk) 04:11, 5 October 2018 (UTC)

We have an article Autofocus. The whole business is complex but basically lots of sharp edges help. Dmcq (talk) 10:36, 5 October 2018 (UTC)

The article autofocus focuses on focus technology. --Doroletho (talk) 10:35, 5 October 2018 (UTC)

If you want a practical answer, use a Datacolor SpyderLensCal Autofocus Calibration Aid, available here:[5] I would be interested in seeing an engineering analyses comparing various autofocus test patterns --Guy Macon (talk) 17:57, 5 October 2018 (UTC)

If you want a pattern to test autofocus instead of a pattern that will "best maintain the focus of an auto-focusing camera", look here:[6] --Guy Macon (talk) 18:02, 5 October 2018 (UTC)

Stink but serious

I have noted that some flatulence is close to odorless at 1st (will not go into detail as to how I know that) but after couple of seconds start to stink. I guess there is some reaction behind that, but what it can be? — Preceding unsigned comment added by 37.26.148.231 (talk) 07:54, 5 October 2018 (UTC)

Fascinating observation. Looking into this a moment, I see that the odor of flatus is very largely attributed to hydrogen sulfide ([7]). And in fact the detection of sulfur odor requires binding of the sulfur containing compound to copper before it can interact with the odorant receptor. ([8]) As the GPCR cascades are rapid and work rapidly for other odors, I assume that once the OR is bound there ought not be any noticeable delay (caveats about biology being immune to theory applying as always). But copper is a trace element and its binding to H2S seems like the sort of thing that no specific catalyst may exist to speed up, so you plausibly could be observing the rate of that reaction directly. But I don't know that, and there may be data on how quickly H2S is smelled elsewhere. But I do seem to recollect experiencing a brief delay in noticing sulfur odors with other compounds... but I never thought about it! Wnt (talk) 10:06, 5 October 2018 (UTC)

Related: https://www.peoplespharmacy.com/2012/09/03/bismuth-helps-combat-smelly-gas/ --Guy Macon (talk) 17:34, 5 October 2018 (UTC)

Much thanks! — Preceding unsigned comment added by 77.126.11.38 (talk) 18:39, 5 October 2018 (UTC)

Something that seems obvious to me, but maybe I'm missing something: it takes time for gas to travel to your nose. Flatulence is a mixture of gases, most of which are odorless to humans. As mentioned, hydrogen sulfide is the main gas responsible for the odor of flatulence. To smell something, you need to expel H2S, and then it has to find its way to your nose. --47.146.63.87 (talk) 07:28, 6 October 2018 (UTC)

I was assuming the OP had come up with some pleasant way to pass the time which, occasionally, gave him an opportunity for research under conditions where this interval was negligible. ;) Wnt (talk) 12:18, 6 October 2018 (UTC)

Could a cell phone case actually make the device more fragile?

I have dropped unintendedly my phone several times without any damage to the phone proper (just the cover would crack a little bit more after each strike). When hitting the ground, the phone would normally burst open, the cover and battery would fly off. Until its original cover broke up completely, I did not use any case. But after being forced to replace the cover I decided to put it in a rubber case, which held the phone together after a fall. And just one fall was enough to crack the whole screen. I wonder whether this case actually transmitted the shock instead of dissipating it. Are phones designed this way? Does some official instruction mentions the fact that cases can damage your phone? --Doroletho (talk) 11:06, 5 October 2018 (UTC)

A supplier of impact resistant smartphone cases claims the material they use is "ultra efficient, absorbing and dissipating impact force and stopping that force from passing into your device, whilst at the same time ensuring the device continues to work as intended. Less efficient materials let the force pass straight through to your phone giving minimal protection, increasing the likelihood of damage, and can even negatively affect phone performance." Cell phone cases are also available to protect the screen aginst scratches and to block harmful Electromagnetic Radiation (EMF) and RFID. DroneB (talk) 11:42, 5 October 2018 (UTC)

Angular Momentum of Electrons

How is the angular momentum of electrons calculated? —Eli355 ( talk • contribs ) 14:18, 5 October 2018 (UTC)

... The angular momentum of an electron is calculated very carefully, using the excruciating mathematics of quantum mechanics. We have an article on spin, including a very detailed encyclopedic introduction to its mathematical formulation - but beware: these calculations are not easy. The angular momentum of an electron can be calculated by anybody - but it is usually calculated by people who have spent a few years of full-time formal mathematical study in preparation for the difficult math that follows.

As I frequently remark: perhaps our reader is some sort of extreme genius who is able to skip past the several years of preparatory work that most very smart physicists require - but if the reader is a mere mortal like the rest of us, the best place to start is an elementary physics book like Tipler's Physics for Scientists and Engineers. Start at page one of the first book, and by the time you reach the third book, (Volume 3, Chapters 34 through 41), you'll be ready to follow exactly the calculations for electron angular momentum that are covered in there. Chapters 35 (Applications of the Schrödinger equation) and 41 (Elementary particles...) both work the math in detail.

Nimur (talk) 15:20, 5 October 2018 (UTC)

From Electron: "The issue of the radius of the electron is a challenging problem of the modern theoretical physics. The admission of the hypothesis of a finite radius of the electron is incompatible to the premises of the theory of relativity. On the other hand, a point-like electron (zero radius) generates serious mathematical difficulties due to the self-energy of the electron tending to infinity." Now think about what "spin" and "angular momentum" mean if the radius is zero. (head explodes). --Guy Macon (talk) 17:41, 5 October 2018 (UTC)

"You can think of quantum spin as just like a spinning top, except there is no top." I saw that somewhere but I don't remember where. --47.146.63.87 (talk) 07:25, 6 October 2018 (UTC)

Does electron spin have any connection at all with classical angular momentum? Thanks. (Not the OP). 173.228.123.166 (talk) 00:29, 6 October 2018 (UTC)

I don't think so but it might have an axis direction of the clockwise pole which is analogous to planets spinning but not literally spinning like a little electron ball. Sagittarian Milky Way (talk) 04:24, 6 October 2018 (UTC)

I should remind everyone that the angular momentum of electron is not same as its spin. It also includes the orbital angular momentum. Ruslik_Zero 07:22, 6 October 2018 (UTC)

Which of the three links on the disambiguation page you just linked to are you referring to? --Guy Macon (talk) 18:31, 6 October 2018 (UTC)

I'm sure he's referring to angular momentum operator, specifically, L. He's stating that J=S+L i.e. total angular momentum = spin + orbital angular momentum. 139.194.67.236 (talk) 02:56, 7 October 2018 (UTC)

As an aside, I don't have the impression that the math in this stuff is really that bad? Some basic calculus and linear algebra, is there more? It's hard for me to tell because the articles I look at are full of physics jargon that I don't understand. But that's separate from the math context. 173.228.123.166 (talk) 08:15, 7 October 2018 (UTC)

October 6

KosherSwitch

As I discussed at Talk:KosherSwitch#Patent, I am having a bit of trouble figuring out [ https://patentimages.storage.googleapis.com/48/4f/8c/b1df4e115e8359/US7872576.pdf ]. In particular, I am having trouble with

"FIG. 3 shows an embodiment of the present invention including a device having one pair consisting of one transmitter positioned opposite one receiver. FIG. 5 shows an embodiment of the present invention including a device having two pairs, each pair consisting of a transmitter positioned opposite a receiver."

What is the point of the two transmitters and receivers (which anyone else would call light sources and light detectors)? Figure 7 shows one or the other being blocked. Why?

Because this is the refdesk (and because the religious aspects may be the reason for the two sets of light sources and light detectors); here is what I think is going on (and I know nothing about this other than what I found doing a web search):

• Orthodox Jews are (usually) not allowed to light a candle of blow out a candle on the sabbath.

• If an Orthodox Jews opens a window on a windy day, knowing that doing so will blow out a candle, this is considered indirectly blowing out the candle. I think that the rules are a bit different between direct and indirect, but I am not clear how.

• An Orthodox Jew can light a candle before the sabbath and use it for illumination after the sabbath starts. Starting a fire that is not allowed, but the fire itself is. Likewise with electric lights.

• An Orthodox Jew can light a short candle, knowing that it will burn out during the sabbath. This is not considered putting the fire out. Based upon this, it appears that setting a timer before the sabbath to start/stop an electrical appliance during the sabbath is allowed, and there are smart phone apps and wireless relays that are used to do things like cook a dinner on an electric stove.

• If an Orthodox Jews opens a window on a non-windy day without knowing whether wind is in the forecast and later a wind blows out the candle, that is allowed. And he isn't required to close the window if he sees a wind coming up.

• I am not clear about what happens if he knows that there is a 90% chance of wind, and whatever the rule is on that appears to be at the heart of whether the KosherSwitch is allowed.

Clearly there ate a lot of complexities that are going right over my head on this: see [9][10][11][12] --Guy Macon (talk) 07:56, 6 October 2018 (UTC)

The implicit reasoning is that one can disown responsibility for exactly what occurs after one starts a random process because only the omniscient God can know it. The notion is similar to the medieval imposition of a Trial by ordeal: the end result was considered a "judgement of God" because one believed that God would miraculously intervene on behalf of an innocent accused (Secular objections that no such God exists, that the process is not random but pseudorandom meaning predetermined, or that human motivation cannot be so easily hidden from an omniscient God who does not intervene on human command are all notwithstanding.) The KosherSwitch arrangement with one Tx/Tx pair provides a delay from action to intended result of a duration that is pseudorandom if relying only on binary logic circuitry, or a greater degree of randomness could be introduced by means the patent hints about e.g. room temperature, room sound level etc. The notional divine intervention is to hinder a "succesful" transmission, or choose not to do so. The point of introducing two Rx/Tx pairs is to give an apparent symmetry of alternate possible divine interventions. In other words, there is no correlation between the binary result and God's choice whether to intervene. DroneB (talk) 11:55, 6 October 2018 (UTC) This response introduces only one reference link to the discussion subject that Guy Macon could have allowed to proceed at Talk:KosherSwitch#Patent where it belongs. DroneB (talk) 11:55, 6 October 2018 (UTC)

(joke) I have heard preachers say that we should leave things to God's choice, but they never liked it when I proposed taking all of my money and throwing it in the air rather than putting it in the collection plate. I figure that whatever God wants he can keep and whatever comes down is mine... --Guy Macon (talk) 19:01, 6 October 2018 (UTC)

This reminds me of the news report on the front page of the Guardian about thirty years ago describing a new Brazilian watch giving the prayer times and direction to Mecca anywhere in the world. The publication date was Saturday, April 1. 86.152.81.16 (talk) 11:56, 6 October 2018 (UTC)

There is certainly no reason why one of the wearable GPS toys that large corporations sell to track their chattels couldn't be programmed to do that right now. Wnt (talk) 12:14, 6 October 2018 (UTC)

While we're off topic ... is there any rule against turning up a stove that is already on, or a light bulb on a dimmer switch? Because then there could be a bunch of appliances automatically set to come on at a very low level every seven days, where the "off" just means "very low". Wnt (talk) 12:26, 6 October 2018 (UTC)

Apparently not allowed. See [13]

I don't think there are uniform "rules" for any of this stuff. It's a matter of interpretation and interpretations vary. 173.228.123.166 (talk) 14:02, 6 October 2018 (UTC)

I have been down the rabbit hole for hours, reading about rabbinic interpretations when my original aim was simply to add a section describing the electronics inside the KosherSwitch. There are some rules that come straight from the old testament and everyone agrees on. There are some that come from rabiis (often rabbis who lived centuries ago) that everyone agrees on. There are some rules that only one rabbi teaches. And then there are rules that are hotly debated. The whole thing reminds me of Wikipedia policies. :) --Guy Macon (talk) 19:01, 6 October 2018 (UTC)

Is there some reason you're trying to figure out from the patent what the purposes of the various functions are rather then their website [14] (also the FAQ entries)? When I looked at it when someone brought up the switch a few days ago it seemed to explain at a basic level why they were doing stuff in certain ways. The manufacturer is obviously not unbiased and wouldn't be an RS for much but you've brought this to the RD rather than keeping it to the article talk page so I presume aren't simply looking for RS. In particular their religious reasoning should be treated with care (including [15] and the FAQ) but it at least lets you try and understand why they're doing what they're doing from their POV. One thing I don't think they dealt with is the pseudorandom issue, at least that I saw, still it sounds like your confusion is much more than that. Note they do deal with issues like advantages over times (basically obvious stuff, saving electricity and not having to be bound by the exact times of the timer). As 173 has said, and is clear from our article IIRC, obviously not everyone agrees whether the KosherSwitch is okay, as with most things surrounding interpretations of most religious laws. Nil Einne (talk) 16:57, 6 October 2018 (UTC)

My aim is to add a good engineering description of the electronics with, if I can, a description of why they did it that way in a NPOV manner -- carefully avoiding implying that they are right or wrong about what is allowable under Jewish law. Neither the "how" page or the FAQ appear to explain the reasoning or operation of the variation where there are two light sources and two light detectors. The one-detector version is called the "classic" but I am not sure whether the two-detector version is shipping, planned, or just something they threw into the patent. -- The religious aspects are interesting, but I am only going to edit the engineering description, other than removing things that clearly violate our NPOV or BLP policies. --Guy Macon (talk) 19:01, 6 October 2018 (UTC)

(Didn't properly read above reply) I belatedly realised I forgot to mention is if this is something do with the article, ignoring whether or not the RD is a good place to handle that, I'm not sure why the patent was brought up anyway. The patent is definitely not a good source for the article, as it's WP:Primary and as clear from the first post, requires a lot of interpretation which we shouldn't be doing. In fact, in some ways it's worse than the webpage. Nil Einne (talk) 15:47, 7 October 2018 (UTC)

d-orbital overlap in primitive metal lattice

My inorganic chemistry text book has this practice problem. You can see figure 3.66 here. The answer to the first part is fine enough. What I'm confused with is the Self-test 3.17. If I imagine a primitive unit cell like this one, with transition metal atoms at each of the verticies, then it seems to me the atoms should be able to overlap their d-orbitals with their nearest neighbors along all 3 axes. That could involve sigma, pi and delta bonding, and all d-orbitals would be able to participate. The answer guide however says, "The d_x2_-y2 and d_z2 have lobes pointing along the cell edges to the nearest neighbor metals". Now I can kind of understand what they mean if they consider the orientation of the orbitals to be constrained in exactly the way they are shown in figure 3.66. But in a primitive structured metal there would be no reason that I can see for them to be stuck in that orientation when they could much more efficiently form bonds with their neighbors by rotating 45°. 139.194.67.236 (talk) 08:42, 6 October 2018 (UTC)

I'm not sure precisely what you're suggesting, but I should note that our article on titanium(II) oxide says that it is "non-stoichiometric" with many vacant sites in the crystal, and that "careful annealing" can produce a monoclinic form. I looked this up, though, and it is "monoclinic" in the sense that the vacancies in the rock salt lattice have been put into regular positions. [16] Looking at that structure I don't see a way for the atoms to get at one another more efficiently; the vacancies maybe have something to do with tweaking the Ti-O bond length to an optimal value? Also, the Ti atoms seem to be making about 14 contacts each there (five to oxygen) which perhaps coincidentally would fill out a shell of 18 in a simple-minded way. But the original diagram illustrates that the lobes make good overlap in this overall geometry, and none of this really changes that. Wnt (talk) 12:11, 6 October 2018 (UTC)

My question relates to the Self-Test 3.17 portion; "which d-orbitals can overlap in a metal having a primitive structure?" The answer to that self-test given in my answer guide seems to assume that in a metal the atoms would still be locked into the relative orientations that they take in TiO, but I see no reason what that would be the case. 139.194.67.236 (talk) 00:28, 7 October 2018 (UTC)

That makes sense. I should say that I'm actually having a hard time finding good examples - this site says only polonium crystallizes in a simple cubic structure, with which the Wikipedia article agrees. And that's only one allotrope of it. And it's scarcely a metal, being a chalcogen. Just searching for the simple cubic I find the book's case more often [17][18] where indeed dxz, dyz, dxy are the stable ones but in a structure of alternating ions. Now there is a paper I found when searching "polonium d orbitals" on Google Scholar, but it uses some strange new perversion of the web where the direct link gets a "not found" even though clicking the link from the search result finds it - despite having scripts off. The name is "A study of the mechanical and structural properties of polonium" and it says polonium is an "s²p⁴ structure, with a large splitting between the s and p energy levels". Not surprising for a chalcogen, I suppose. I don't necessarily understand every last syllable, but the bottom line is that the only simple cubic metal in existence gets that way using p_x, p_y, and p_z orbitals. So you might have a point about the d orbitals ... but it seems moot either way. Wnt (talk) 01:32, 7 October 2018 (UTC)

Ok, thanks. That's very helpful. A lot of the questions in this text seem to be like that: they're so esoteric and involve such purely theoretical scenarios that they can't just be looked up as such, and whoever wrote the answer guide seems to have just ran through the questions quickly and just guessed where they weren't sure, confident that the questions and their short answers were vague enough to ensure they're not even wrong. I suppose in a classroom setting that would help generate discussion when going through these problems, but I'm just reading by myself at home and I don't find them very useful.

In this particular case though, there are other examples of metals that form primitive unit cells, but they do so at elevated temperatures and pressures. Ca-III is one example. I can't find any information of their d-orbital orientations though (calcium doesn't have any occupied d-orbitals anyway). 139.194.67.236 (talk) 02:28, 7 October 2018 (UTC)

Dead ants in my home

I have strange little problem that I can't explain and I'm curious about it. In a ground-floor bathroom in my home, dead ants just keep appearing. Not just a few, but hundreds at a time. I vaccuum them up and then several days later they will be back. They never appear gradually, only a whole bunch showing up all at once, usually overnight. I have never seen a live ant in the area. I have never used any insecticides. I live in New Jersey, USA and they are the normal small black ants that are most common around here. Is this some kind of ant cemetery where they bring their dead? (But not immediately when they die - they would have to be accumulating bodies for a couple of days then dropping them off in a mass burial). What's going on here? And how do I stop it? Deadantspilingup (talk) 17:56, 6 October 2018 (UTC)

According to this National Geographic article ants regularly clear out their dead, so you are, perhaps, just the "lucky" recipient. Mikenorton (talk) 18:03, 6 October 2018 (UTC)

"Bring out your dead!" (Clang!) Obviously you have some live ants in close proximity. If I were in your situation, I would call a pest-control company, who could do some spraying and hopefully drive the living ones away and/or kill them. ←Baseball Bugs ^{What's up, Doc?} carrots→ 18:24, 6 October 2018 (UTC)

Indeed, from that article your bathroom must be right next to the nest for it to be a convenient disposal site. Mikenorton (talk) 18:39, 6 October 2018 (UTC)

Although I called it a "ground-floor bathroom", my property is sloped and the bathroom is actually about 3 feet above ground with nothing but cement foundation underneath. I have checked outside multiple times to see if there were ants climbing up the cement to find a way inside (finding a crack in the siding, or whatever), but I've never seen any. If there is a nest somewhere that is clearing out their dead by putting them in my bathroom, they certainly aren't doing it the easy way. Deadantspilingup (talk) 19:30, 6 October 2018 (UTC)

I say again: Call an exterminator. You'll be glad you did. ←Baseball Bugs ^{What's up, Doc?} carrots→ 19:33, 6 October 2018 (UTC)

Point taken. But I think I'll first try those bait traps where they take poisoned food back to the nest. Hopefully the little buggers get real hungry carrying their dead siblings to the cemetery. Deadantspilingup (talk) 19:40, 6 October 2018 (UTC)

It's worth a shot. ←Baseball Bugs ^{What's up, Doc?} carrots→ 19:43, 6 October 2018 (UTC)

Stating something kind of obvious, but you may not have thought about it: if you have some kind of camera you can set up to record continuously, you can use that to find out where they're coming from. I'm not sure the bait idea will work; I recall reading that colonial ants generally avoid areas containing dead members of the same species, because of the potential for disease. So, they might not take food from the area. --47.146.63.87 (talk) 05:41, 7 October 2018 (UTC)

This happened to my laundry a while ago. Eventually I found an ants nest in the ceiling, and they were pushing dead ants out the manhole. This might also happen though a light fitting. or air vent. Graeme Bartlett (talk) 08:58, 7 October 2018 (UTC)

What will be the most correct definition for light?

93.126.116.89 (talk) 09:45, 7 October 2018 (UTC)
The light is a result of energy?
"The light is a result of chemical reaction (fire) or physical energy (electricity)" is correct? 93.126.116.89 (talk) 23:41, 6 October 2018 (UTC)

That definition does not describe light specifically. Fire and electricity can also produce heat, which is different from light. Light is electromagnetic radiation with wavelenghts visible to the human eye (sometimes ultraviolet or infrared 'light' is also included). - Lindert (talk) 23:57, 6 October 2018 (UTC)

And light can be produced in many other ways than chemical reaction or electricity. "physical energy" is too vague to say what it includes. PrimeHunter (talk) 00:28, 7 October 2018 (UTC)

To expand on those replies, the statement is wholly wrong. Light is produced when something emits a photon. The photon is the gauge boson of the electromagnetic interaction. Photons are produced in an electromagnetic interaction. All baryons radiate photons all the time. That includes you and pretty much everything you interact with daily. Those photons are of too low a frequency for your eyes to detect, but if something gets hot enough, the photon frequency increases until they become visible. This is what happens in a fire, or an incandescent light bulb, or the Sun. Other processes also produce photons, one example being when electrons and holes recombine in a light-emitting diode.

Where do the photons come from? Well, they come from nowhere. They are created ex nihilo. However, for real (that is, non-virtual) photons, the energy of the photon does have to come from somewhere. If this bothers you, you are in good company. Niels Bohr reputedly said, "anyone who is not shocked by quantum theory has not understood it." But the universe doesn't care what we think about it. --47.146.63.87 (talk) 05:38, 7 October 2018 (UTC)

"Those photons are of too low a frequency for your eyes to detect, but if something gets hot enough, the photon frequency increases until they become visible." Does it mean that colors that we see in daily life contains high frequency photons? Id so, why does it happens, here is the color can be the coldest in the world and almost no energy in it?! And as I understand there should be some energy to make photons in high frequency. Isn't it? 93.126.116.89 (talk) 09:45, 7 October 2018 (UTC)

All photons have energy. Photon energy is directly proportional to the frequency. Visible light is in a small frequency interval around 430–750 terahertz. The frequency and energy of a photon can both be billions of times larger and smaller than this. See Electromagnetic spectrum. PrimeHunter (talk) 11:43, 7 October 2018 (UTC)

This Media:Plutonium_pellet.jpg is a lump of plutonium that is glowing orange black-body radiation because it surface has been heated to about 2500K, from natural decay. If you heated, say steel, in any manner to 2500K, it would glow with a similar colour, even after the source of the heat has been removed. This Media:Gaseous_tritium_light_source.jpg is tritium. The tritium emits electrons, which strike phosphor on the inside of the glass. This energises electrons in the atoms. They then loose that energy, emitting photons on specific frequencies. LongHairedFop (talk) 13:19, 7 October 2018 (UTC)

Erie-builts in Russia?

Were the Kharkiv Locomotive Factory 2D100 and 10D100 engines (as used on the TE3 and TE10 locomotives respectively) based on Fairbanks-Morse engine designs such as those used in their Erie-built series of locomotives? 2601:646:8A00:A0B3:AC2E:3471:38A3:4615 (talk) 02:01, 7 October 2018 (UTC)

Antarctic rescue

Were Kharkovchanka off-road vehicles ever used in rescue missions in Antarctica? 2601:646:8A00:A0B3:AC2E:3471:38A3:4615 (talk) 02:20, 7 October 2018 (UTC)

Read the article, follow the ref. Use Google Translate if you don't read Russian. --Guy Macon (talk) 06:03, 7 October 2018 (UTC)

not quite a rescue mission, but here one V. Sanin recounts how he and a couple of coworkers got lost in a snow-storm and found their way back thanks to Kharkovchanka's chain tracks. ~~

Kharkivchanka is due to some over-eager Western editor who sympathizes with the Ukies. The Ukrainian for Kharkovite _FEM is Kharkiv'yanka, not Kharkivchanka, and this is what the Ukie article calls it. Someone please fix. Aecho6Ee (talk) 15:55, 7 October 2018 (UTC)

Questions of Our Expanding Universe

Many currently published theoretical physicists reference a universe that is expanding at an increasing rate and which has been doing so since the 'Big Bang' that first created the universe 13.7bn years ago. They also reference the fact that when we 'look out into the universe around us' we see everything moving away from us. From these two ideas follow my two questions: 1. If everything is moving away from us, then that means, does it not, that we are at the 'centre' of the universe? If we are not at the centre then we must surely observe things moving towards us too. 2. If the universe's expansion since the Big Bang has been continuously accelerating then surely it must have been expanding very slowly indeed at the beginning if it is still expanding now. And because the universal constant, c, (incidentally, the speed at which light travels) is finite and known, then after such a long period of time surely terminal velocity of matter would have been reached. Jeremy — Preceding unsigned comment added by 82.34.208.156 (talk) 08:11, 7 October 2018 (UTC)

One of the easier ways of thinking about this is to consider evenly spaced dots on the surface of an inflating balloon - all of them spread away from each other and none of them get closer. It's not a perfect analogy, but it may help. Mikenorton (talk) 08:24, 7 October 2018 (UTC)

Edit conflict: The way in which the universe is expanding is not like an explosion where everything moves outward from a definite center. You can imagine it like this: take a balloon and draw two dots on it with a sharpie. The balloon is a 3D object but its surface is 2D. The relationship between the two points can be described in terms of their relative locations in that 2D space. Now blow the balloon up. As far as the two dots on the 2D surface of the balloon are concerned, they are moving away from each other, but there is no "center" of the balloon's 2D surface. We can mathematically describe objects in a space of more than 3 dimensions. For example, we can add a 4th axis to a regular Euclidean space. Then we can imagine an surface that is exactly 1 unit from the origin at every point. That object is a 3-sphere, the 4 dimensional analogue of sphere. The 3-sphere is 4D but its surface is 3D. If we "blow up" the 3-sphere in a way analogous to how we blew up the 3D balloon, we increase the volume of the 3-sphere's 3D surface in a way analogous to the 2D surface of the balloon increasing. And that's basically what's happening to our universe. The volume of our 3D space is increasing in all directions, all the time. It's not expanding out from any center that exists within out 3D space, and it's not expanding "into" anything. 139.194.67.236 (talk) 08:32, 7 October 2018 (UTC)

The OP's post contains only one question and its second section just states a deduction. In the expanding universe described by the above models, galaxies recede from us at velocities proportional to their distances from Earth. Astronomers observe galaxies' resulting Redshifts due to the Doppler effect. The limiting velocity c relative to Earth corresponds to the finite spherical size of our Observable universe. A different location in the Universe has its own observable spherical volume, different from ours. DroneB (talk) 14:05, 7 October 2018 (UTC)

Dark Energy

We read that Dark Energy constitutes approx. 68% of all energy in the universe (baryonic (real) matter, dark matter and dark energy). Well isn't that percentage quite obviously the ratio of the surface area of a sphere to its volume? In other words Dark Energy is not yet 'seen' because we're not looking in the right place. We 'expect' to find it on the surface of the universe and we need to look inside / under the 'surface'. [Analogously it would be like calculating the mass of our Earth as that land which we 'see' only on its surface]. — Preceding unsigned comment added by 82.34.208.156 (talk) 08:21, 7 October 2018 (UTC)

That's numerology and not even enough digits to indulge in good numerology. Plus the ration of a volume and an area is a length not a number. Dmcq (talk) 10:12, 7 October 2018 (UTC)

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