Wikipedia:Reference desk/Archives/Science/2016 November 14

= November 14 =

Feynman Lectures. Lecture 35. Ch. 35–4 The chromaticity diagram
Trying to understand the diagram on Fig. 35–4, I assume that to find this diagram one take a rectangular coordinate system XYZ with axes of 3 unreal colors, then plot a plane x+y+z=1, then take a XY view (view from Z axis). Is it correct? Why one didn't take as 3 colors green, red and blue (then the axes x and y on Fig. 35–4 would concurrent at point B )? Username160611000000 (talk) 11:37, 14 November 2016 (UTC)
 * See our article on the CIE xyY color space, which includes the derivation. The co-ordinate system is based on the exact properties of the eye's cone cells and the plane is chosen so that all points on that plane have the same Luminance (brightness). - X,Y and Z are red, green and blue, but defined by the optimum wavelength of the three different types of cone cells. Don't forget, the laws of physics don't define what "red" or "green" are. These are just names that we've given to the qualia corresponding to various frequencies of light hitting our retinas, and although it makes our models much simpler to assume these are three distinct points, in reality each type of cell has a complicated broadband response. As for why we don't have a 3-dimensional RGB colour space, this is possible (see right), but it doesn't actually include every colour - there are colours that we can see but which can't be produced as a combination of red, blue and green (no matter what wavelengths you choose as your starting point). These exist outside the triangle that Feynman draws. We can see them, but we can't reproduce them on a TV or monitor. (A real example: the British Rail blue used on UK trains from about 1965-1985 often looks wrong in photographs - in many light conditions, it appears either too intense or too washed out) Smurrayinchester 12:31, 14 November 2016 (UTC)
 * but it doesn't actually include every colour Why? E.g. defining axes like this https://s.sender.mobi/u/image/2016/11/14/2GgCxGh5B/feyn.PNG, we obtain same picture (some colors will contain negative values of 3 main colors).Username160611000000 (talk) 14:10, 14 November 2016 (UTC)


 * The RGB is just one example of a color gamut for there is no canonical or universal choice of primaries. One can include more than just three even, for there are different color gamuts depending on the media being used with some being more inclusive than others. -Modocc (talk) 15:52, 14 November 2016 (UTC)

Thank you very much. I think I understand diagram. But what I noticed: the wavelength varies nonuniformly on the curve ... Username160611000000 (talk) 16:29, 14 November 2016 (UTC)


 * We can see them, but we can't reproduce them on a TV or monitor. (A real example: the British Rail blue used on UK trains from about 1965-1985 Suppose, the three pigments in the human's cones are magenta (absorbs green), cyan (absorbs red), yellow (absorbs blue). Then how can human see lights that are outside of red-green-blue triangle on the diagram? How to use Fig. 35–8? It means that eye  in 1.75 times better recognizes 4500 Å (curve B) than 5300 Å (curve G) at equal brightness (equal brightness  is adjusted by the flicker system ), or what? Username160611000000 (talk) 09:56, 16 November 2016 (UTC)
 * Because our eye cells don't simply react to a single frequency of light. Instead, each one has a complicated, overlapping response (and although the diagram doesn't show it clearly, there are also secondary resonance peaks - the colour violet (a monochromatic colour with a wavelength around 400 nm) looks like magenta (a secondary colour corresponding to a combination of blue and green light) because our red cone cells have a second resonance at violet frequencies - see Violet light.) In general, the perception of colour is a complicated topic that has more to do with biology, neurology and psychology than physics, and I think Feynman is muddying the waters a bit by going into so much detail about it in a physics course. Smurrayinchester 12:13, 16 November 2016 (UTC)
 * The pigment has a color (as well as any other substance in the universe), so it has no other choice but to follow the rules. If we have only one pigment, then we get one curve. It means that light of wavelength 5500 Å and 50 % brightness makes some signal 1,16 (vertical axis). Lower wavelength but higher brightness can produce same signal. E.g. with 4500 Å the signal = 0.1 . But it will be the same green color, just darker, because we can get same signal with 5500 Å and 5% brightness. Or brain can interpret lower signal as different wavelength? Username160611000000 (talk) 14:21, 16 November 2016 (UTC)
 * I don't follow you. The cone cells may have a "colour", but as we explained, colour is a complicated thing. The cells absorb light over a range of wave lengths, and those ranges overlap. So pure yellow light, for instance, has a wavelength of about 580nm, which means it is absorbed by both the "green" and "red" cone cells. When both these cells trigger (and blue does not), and produce roughly equal signals, your brain generates the qualia of yellowness. A person who only has green cells is colour-blind, and cannot differentiate between two different wavelengths of light. Smurrayinchester 22:27, 16 November 2016 (UTC)
 * If the color is complicated, we will talk about wavelength. Feynman says in last paragraph of Ch.36–6 that there are 3 pigments, but in some proportions in each cone cell. Is it correct?
 * The cells absorb light over a range of wave lengths, and those ranges overlap. So what? The pigment absorbs some wavelengths. When we see a yellow flower, this means the flower absorbs wavelengths 390-500 nm, and 500 nm is approximate: the flower can absorb 510 nm but very poor. A similar situation is with the pigment1). The single pigment does not give different reactions on different wavelengths (as you said, the brain can't interpret lower signal from one type of pigment as different wavelength). I'm driving at point that pigments have some points on the chromaticity diagram, not necessary red-green-blue, but still three points. The pigment can absorb range of wavelengths - it's a line on the diagram that can be reduced to point in the middle of the line. Or pigments can be thought as spots on the diagram?
 * All that I wrote was my guess, so you are free to correct me. Username160611000000 (talk) 07:52, 17 November 2016 (UTC)


 * Here is a diagram that includes the maximum sensitivities of the eyes' different cones and rods to specific wavelengths: 420, 498, 534, 564. On the chromaticity diagram, our responses to any monochromatic light AKA spectral color falls specifically on the curved edge which is called the spectral locus, everything else in between such as absorption of white light with equal luminosity is in the interior. The article on spectral color has a better diagram of the colors and a chart showing the spectral colors that we can perceive. Note that the red segment is nearly flat on the CIELUV's uniform chromaticity scale diagram, but has longer wavelengths than the peak sensitivities 534 and 564 of the M and L cones. Eriko Self, Ph.D. in his article on Color Vision Deficiencies presents a brief Overview of Human Color Vision that shows some of the complexity of the neural signal processing. Modocc (talk) 15:02, 17 November 2016 (UTC)

1) A pigment OPN1LW, if will be extracted or synthesized, will reflect strongly 390-500 nm and 680-740 nm, and absorb strongly 500-680 nm . It will be seen as blue substance (one point on chromaticity diagram), but give a signal in negative color yellow (also one point on chromaticity diagram).

Pain and fever relief
I was browsing through our articles on common OTC analgesics (aspirin, paracetamol, ibuprofen, etc.) and noticed that, besides all being pain-relievers, they also all reduce fever. Is it understood why that would be? Are there any analgesics that don't also reduce fever? Are there any antipyretics that don't reduce pain? It seems like there would be a market for a non-antipyretic analgesic if one existed. I'm having trouble Googling the subject. Matt Deres (talk) 17:43, 14 November 2016 (UTC)


 * The short answer is that generally NSAIDs are drugs that block cyclooxygenase - either COX-1, COX-2, or (typically) both - which generates prostaglandins. Antipyretics block fever by opposing prostaglandin action in the hypothalamus.  The specifics....... there are a lot of specifics, starting with how paracetamol works, which is probably a few Ph.D. theses' worth of confusion in its own right.  There are also many different prostaglandins with subtly different effects.  There are a variety of other, related enzymes that drugs can interfere with, like Arachidonate 5-lipoxygenase which tie into this pathway.  Even cannabis ties into something related.  I'll pause here for the moment... Wnt (talk) 19:00, 14 November 2016 (UTC)


 * Cool - thank you for the explanation! Matt Deres (talk) 01:31, 16 November 2016 (UTC)


 * "Are there any analgesics that don't also reduce fever?" Yes, all opioids. This is because they act on opioid receptors on neurons, which don't have anything to do with fever. As to why NSAIDs reduce both pain and fever, Wnt went into the biochemistry. From an evolutionary perspective, fever, pain, and inflammation are all responses to an insult to the body, so overlap in their biochemical pathways makes sense. --47.138.163.230 (talk) 10:57, 17 November 2016 (UTC)

Projected disappearance of vestigial organs
Has it been estimated when approximately in the future vestigial organs (some or all) in humans such as coccyx or wisdom tooth will completely gone away? Brandmeistertalk  19:09, 14 November 2016 (UTC)


 * Possibly never. If the existence of the organ has no measurable deleterious effect on fitness, they will only be lost if mutations that cause their absence undergo fixation. If the mutations that complete the loss of coccyx also have rare deleterious effects themselves (such as the case with congenital caudal regression syndrome), then they most likely will not fix. In the case of a mutation that truly has no deleterious effect, the expected time to fixation of a new allele, should it fix, is a number of generations equal to four times the effective population size of the human race, or 40,000 generations, or about a million years. Again, if and only if the mutation has no deleterious side effects, and it is only a single mutation that is required to abolish the vestigial organ, and this is a statistical estimate so it could take shorter, longer, or just never happen. Someguy1221 (talk) 21:49, 14 November 2016 (UTC)


 * Furthermore, certain stages of development serve as precursors of or necessary conditions for the development of other organs, which is why we still have rudimentary gills. Also, organs like the appendix may be called vestigial, but they apparently may serve a role in immunity/maintaining the gut flora.  See also exaptation; organs can become repurposed, such as the pineal eye. μηδείς (talk) 01:19, 15 November 2016 (UTC)


 * I think that a distinction needs to be drawn between vestigial organs that are selected against directly versus those which might have been casualties of some other evolutionary trend. I mean, solely as an anecdote - I'm unaware of any work along this line - for me wisdom teeth are simply third molars, with no particular problems.  I know I also grew to full size rapidly, by 15 rather than 18, which was more common among earlier humans, so I tend to be suspicious that all the wisdom tooth troubles people have is simply the result of a slowed overall growth.  If that were true, it would follow that an effective evolutionary response might be to eliminate the teeth, but it might also be to delay their eruption or tweak the rate of jaw growth relative to the rest of the body, or many other things.  Now it's practically impossible to really predict these things in the future, and almost impossible to avoid getting caught up in "just-so stories" even when trying to explain why things evolved as they did in the past, so this remains all behind a thick curtain of unjustifiable speculation.  But at some point it might become possible to model, with unimaginably advanced software and hardware, what any given mutation will do to morphology, and taking the odds of each mutation, and modelling them all, one might begin to predict most likely scenarios. Wnt (talk) 14:19, 15 November 2016 (UTC)

Correlation between penis size and cultural acceptance of nudity--sexual selection?
It is my understanding that even in tropical regions, nudity is rarely practiced anymore. However, I have heard it was quite prevalent in the time of Christoper Columbus. So, has there been study of penis size among ethnic groups that practiced nudity within the last few centuries vs. those that did not, like in colder countries? After all, insofar as a woman or her family would wish to select a mate for her based on penis size(idk), it would really only work if most men went naked. 144.35.45.62 (talk) 21:22, 14 November 2016 (UTC)


 * On the contrary - clothing was designed and used to emphasise and exaggerate penis size. Even tribes who wore little else tended to have a penis sheath, and in European culture the codpiece became a male emblem of pride. Not that penis size was likely to be the main thing a woman looked for - the ability to protect and feed the family was more important - so strength and hunting prowess. Wymspen (talk) 21:51, 14 November 2016 (UTC)


 * Practically all penises, when fully extended, are the same length - 6 3/4 inches, although a few are shorter.  Anything longer would cause problems and it doesn't happen. 92.8.63.27 (talk) 12:41, 15 November 2016 (UTC)
 * on all of that.  The article titled Human penis size disagrees, with cited references, with just about everything you just stated. -- Jayron 32 12:51, 15 November 2016 (UTC)
 * If the IP had ever seen any of John Holmes (actor)'s work, he might revise his comments. ←Baseball Bugs What's up, Doc? carrots→ 20:50, 15 November 2016 (UTC)


 * I would argue that masturbation is the human animal’s most important adaptation. The very cornerstone of our technological civilization. Our hands evolved to grip tools, all right including our own. You see, thinkers, inventors, and scientists are usually geeks, and geeks have a harder time getting laid than anyone. Without the built-in sexual release valve provided by masturbation, it’s doubtful that early humans would have ever mastered the secrets of fire or discovered the wheel. And you can bet that Galileo, Newton, and Einstein never would have made their discoveries if they hadn’t first been able to clear their heads by slapping the salami (or “knocking a few protons off the old hydrogen atom”). The same goes for Marie Curie. Before she discovered radium, you can be certain she first discovered the little man in the canoe. 64.170.21.194 (talk) 06:42, 17 November 2016 (UTC)

Are there indeed only 3 anatomical planes?
It's used to teach that there are 3 anatomical planes: Transverse plane (horizontal + sagittal axes), sagittal plane (vertical + sagittal axes) and frontal (aka coronal) plane (horizontal + vertical). Now my question is what about oblique plane? If we take one of the planes and just divert it a little bit, then it becomes to oblique plane. In this case what are the names of the axes referred as? 93.126.88.30 (talk) 21:36, 14 November 2016 (UTC)


 * See Anatomical plane. You could, in theory, have an infinite number of different planes - but that is mathematics rather than anatomy. Wymspen (talk) 21:56, 14 November 2016 (UTC)
 * Thank you. I have already saw this article before I came here and it didn't answer on my question. On what do you base your opinion that the other planes are in theory and math rather than in anatomy? Of course that there are in anatomy oblique plane and in order to understand what I'm talking about just put this two words on Google (oblique plane). 93.126.88.30 (talk) 07:08, 15 November 2016 (UTC)


 * Oblique planes are used in MRI brain imagining to better resolve certain structures, such as the hippocampus. They are just called oblique coronal planes. (Source: my brain imaging collogues, but found something about it here as well.) Fgf10 (talk) 08:00, 15 November 2016 (UTC)