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February 9

Neurotransmitters, part 3

Does prolactin counteract the effects of dopamine (either through suppressing its release, through blocking its signalling and/or through exerting an opposite effect on the brain)? Does it counteract the effects of oxytocin? 2601:646:8080:FC40:B8B0:B42B:BB0C:97BA (talk) 22:18, 9 February 2024 (UTC)

Oxytocin stimulates prolactin secretion, while prolactin, once a threshold is reached, stimulates dopamine release, which has an inhibitory effect on prolactin secretion (PMID 22129099, PMID 18477617).  --Lambiam 14:15, 10 February 2024 (UTC)

Thanks! And a related question: does prolactin then inhibit D4 receptors? (Yes, this has to do with my personal research about introversion -- I'm trying to see whether or not increased prolactin levels would be pleasurable for an introvert from the deep end of the scale!) Also, does prolactin either stimulate or inhibit oxytocin? 2601:646:8080:FC40:9D4E:C237:28BF:6A78 (talk) 03:59, 11 February 2024 (UTC)

Autism vs. introversion

Two questions in one: (1) how can they tell for sure between autism and just an extreme case of introversion (given that 3 of the 4 diagnostic symptoms, of which only 2 are needed to diagnose autism -- in fact, all of them except stimming -- can also be associated with introversion)? And (2) how does autism specifically affect oxytocin signalling in the brain? 2601:646:8080:FC40:B8B0:B42B:BB0C:97BA (talk) 23:14, 9 February 2024 (UTC)

As to (2), here is a review article, "Oxytocin and Autism Spectrum Disorders", PMID 28766270. Several studies have reported a tendency of lower oxytocin levels in children on the autism spectrum, but the causal connection is not clear. In summary, autism is not well understood, and more research is needed.  --Lambiam 14:25, 10 February 2024 (UTC)

Not sure why the two should be confused at all, they're very different. Being an introvert is something they would diagnose for? Do they diagnose being an extrovert as well? What is the opposite of autism if they think that way? NadVolum (talk) 20:41, 11 February 2024 (UTC)

Do you not think a psychiatrist would never mistake an extreme case of introversion (a normal condition) for autism and misdiagnose someone when in fact the person doesn't actually have anything to be diagnosed with??? After all, as I pointed out, 3 out of the 4 diagnostic symptoms for autism can also be observed in introverts -- and now that I think of it, even stimming might not always be a reliable symptom of autism, in some cases (although uncommonly) what is thought of as "stimming" might actually be just a reflexive pain response (because, in introverts, over-stimulation -- such as being at a big loud party -- can in some cases cause physical pain, such as a headache!) Not to mention that there's also the possibility of malicious diagnosis (although that's probably another topic for another time)! 2601:646:8080:FC40:8443:5BCE:DED0:5463 (talk) 03:27, 12 February 2024 (UTC)

You appear to be assuming that autism is an all-or-nothing condition; but Biology is complicated and messy.

It's often thought (rightly or wrongly) that everyone is on a "spectrum", with most (the "neurotypical") at various low values on it and some at higher values which correlate with greater interactional (with the material world and/or other people) difficulties.

If this is so, inevitably the threshold value for "having autism" (or whatever) will in part be a matter of subjective judgement that may vary between medical practioners, and will evolve as medical science advances. Moreover, some people (including myself) may consistently exhibit some cognition and behaviour which, if more pronounced, would qualify as autism. Lastly, I doubt that anyone scores exactly the same "spectral value" all the time. 90.199.107.217 (talk) 07:29, 12 February 2024 (UTC)

Right, and that brings us back to the same question: where exactly is the line between just strongly pronounced introversion on one hand and high-functioning autism on the other? 2601:646:8080:FC40:99FE:A33D:618C:8AB5 (talk) 11:51, 12 February 2024 (UTC)

As indicated, there isn't a line - see idiot savant. Reticence is not an indicator of anything - for example, an individual may not speak for weeks on end (apart from things like asking for a newspaper in a shop) but may be active on social media. 2A00:23D0:EF3:2001:F9CC:1EC8:88FD:4354 (talk) 14:24, 12 February 2024 (UTC)

The big difference is that with autism people tend to lack understanding of other people's feelings and have to follow rules to get on with them, whereas introverts have no special problem that way but feel general socializing is a drag. If 'strongly pronounced introversion' is leading to real problems for a person it would practically always be because of some other problem that has developed from it like being very anxious in social circumstances. NadVolum (talk) 18:15, 12 February 2024 (UTC)

OK, I see your point, but there's still room for ambiguity: suppose a hypothetical scenario with a person who's not only on the deep end of the scale in terms of introversion, but also has a high score for assertiveness (unlikely because introversion tends to correlate with low assertiveness, but still possible) and low scores for cooperation and sympathy -- might a person with that combination of personality traits not be misdiagnosed with autism without actually having it? Or is this combination of personality traits in itself diagnostic of autism? 2601:646:8080:FC40:A0EA:E55B:2645:FEAF (talk) 03:14, 14 February 2024 (UTC)

Lots of company heads are like that. They can cope with meetings fine because they're achieving something - and they'll push to get things done instead of just waffling. Getting people to work with you when you don't understand feelings is a lot more difficult though. And understanding peoples feelings doesn't necessarily mean having problems firing them if needed and that can be helped by not getting too friendly. NadVolum (talk) 13:51, 14 February 2024 (UTC)

Socialising is an integral part of our lives. While some of us have no issues around it, for many it can be daunting. Social anxiety can cause symptoms such as feeling sick, trembling, or even dizziness. It is estimated that 12 per cent of the general population is diagnosed with the disorder at some point in their lives. If you are struggling and not sure how to get help, my support pack Social Anxiety has lots of advice. - Deirdre, Sun on Sunday, 28 January 2024. [1]. 2A00:23D0:5D3:5601:71F9:9EF3:5186:F60D (talk) 16:05, 15 February 2024 (UTC)

Planck's law 1901 article conundrum

In my personal popularization of Planck's 1901 paper on Planc's law, I have a sticking point. I am ok up to the equation (9):
(9)     ${\frac {1}{\vartheta }}={\frac {DS}{DU}}$
But between:
$S=k${$(1+{\frac {U}{h\nu }})log(1+{\frac {U}{h\nu }})-{\frac {U}{h\nu }}log{\frac {U}{h\nu }}$}
And
Substitution in (9) gives:
${\frac {1}{\vartheta }}={\frac {k}{h\nu }}log(1+{\frac {h\nu }{U}})$
Between these 2 equation I don't find?
(After to the end it is ok)
I arrive to this point:
$S=klog(1+{\frac {U}{h\nu }})+{\frac {kU}{h\nu }}log(1+{\frac {h\nu }{U}})$
Apparently, that suppose:
$S-klog(1+{\frac {U}{h\nu }})={\frac {U}{\vartheta }}$
But I'm stuck there and it is not clearer in Planck's following manuscripts.
Any idea ?
Malypaet (talk) 23:18, 9 February 2024 (UTC)

I think you've made a math error in there somewhere. Taking the derivative of S with respect to U gives:

${\frac {1}{\vartheta }}=k[{\frac {1}{h\nu }}ln(1+{\frac {U}{h\nu }})-{\frac {1}{h\nu }}ln({\frac {U}{h\nu }})]$

Which only takes a little poking with log identities to yield the desired result. PianoDan (talk) 02:27, 10 February 2024 (UTC)

An error, sure.

But how do you go from Planck:

$S=k${$(1+{\frac {U}{h\nu }})$$log(1+{\frac {U}{h\nu }})-{\frac {U}{h\nu }}log{\frac {U}{h\nu }}$}

to your formula "taking the derivative of S with respect to U"?

${\frac {1}{\vartheta }}=k[$${\frac {1}{h\nu }}$$ln(1+{\frac {U}{h\nu }})-{\frac {1}{h\nu }}ln({\frac {U}{h\nu }})]$

You cannot simply replace $S$ with ${\frac {U}{\vartheta }}$ to get your result, isn't it?
Malypaet (talk) 09:29, 10 February 2024 (UTC)

I think I've asked before: Do you know what the derivative of a function is and how to compute it? --Wrongfilter (talk) 09:36, 10 February 2024 (UTC)

I only ask to relearn, Planck integrates where pianodan takes the derivative? Malypaet (talk) 11:17, 10 February 2024 (UTC)

Planck isn't integrating here either. PianoDan (talk) 17:32, 10 February 2024 (UTC)

${\frac {1}{\vartheta }}={\frac {{\text{d}}S}{{\text{d}}U}}$

$~~~~={\frac {\text{d}}{{\text{d}}U}}~k\!\left((1+{\frac {U}{h\nu }})\log(1+{\frac {U}{h\nu }})-{\frac {U}{h\nu }}\log {\frac {U}{h\nu }}\right)$

$~~~~=~...$

 --Lambiam 14:39, 10 February 2024 (UTC)

$=k[(0+{\frac {1}{h\nu }})log(1+{\frac {U}{h\nu }})-{\frac {1}{h\nu }}log({\frac {U}{h\nu }})]$

$=\cdots$

Many thanks Lambiam, that’s all I was missing.
Now with Planck's 1901 paper, for me everything is clear from start to finish and in detail.

I will be able to simplify it and make it more realistic, without resonators.

(°—′)
Malypaet (talk) 18:51, 10 February 2024 (UTC)

February 10

Rotating a magnetic field

I've been thinking about a superconducting electric coil with some current, creating a stable magnetic field. Now assume an axis through the middle of that coil. My intuition tells me that rotating the coil around this axis should be inconsequential. But assume an axis perpendicular to the first one. If I rotate the coil around this axis (and, I assume, the magnetic field with it), a distant observer would see a regularly fluctuating magnetic field - and, I again assume, because auf the unity of electric and magnetic fields, this would appear as an electromagnetic wave. Is this correct? If so, where is the energy carried by the wave coming from? Is the magnetic field dissipating? Or do I need to put energy into the system to keep rotating the coil? Thanks! --Stephan Schulz (talk) 13:53, 10 February 2024 (UTC)

Assuming that the setup indeed creates a changing magnetic field, by Lenz's law this induces an opposing current which (as in an induction brake) should counteract the rotation.  --Lambiam 15:00, 10 February 2024 (UTC)

An ordinary permanent magnet is a cheaper and more convenient alternative to a super-conducting coil. Spinning the magnet about its transverse axis will induce eddy currents in any nearby metal objects, which will oppose the rotation of the magnet and remove energy by resistive heating of the metal - this is induction braking. In the absence of any nearby metal objects, then there will indeed be braking associated with the energy and angular momentum carried away by the radiated field. However it is necessary to spin the magnet very fast or be very far from metal for the radiation braking to be significant compared with the induction braking, requiring something of the order of ω = c / d where ω is the angular frequency of the rotation and d is the distance from metal. catslash (talk) 18:09, 10 February 2024 (UTC)

Thank you - and of course. I should have thought of that! --Stephan Schulz (talk) 05:07, 11 February 2024 (UTC)

An example of such a strong, rapidly spinning permanent magnet with no metal anywhere near would be a pulsar. There is, however, some interesting plasma physics happening in the pretty good vacuum of the near field, so although there are no metals, there are electric currents. And pulsars do spin down. PiusImpavidus (talk) 11:57, 11 February 2024 (UTC)

A perhaps overly complicated analysis:

If an electrically small loop carrying $I$ amp-turns d.c. around an area $A$, spins with an angular frequency $\omega$ about its diameter on (say) the z-axis, then the resulting electromagnetic field is

$\mathbf {E} ={Z}_{0}IA\left(\left({\frac {1}{ikr}}+{\frac {1}{(ikr)^{2}}}\right){\frac {y\mathbf {\hat {z}} -z\mathbf {\hat {y}} }{r}}+i\left({\frac {1}{ikr}}+{\frac {1}{(ikr)^{2}}}\right){\frac {-x\mathbf {\hat {z}} +z\mathbf {\hat {x}} }{r}}\right)ik^{3}{\frac {e^{-ikr}}{4\pi }}$

$\mathbf {H} =IA\left(\left({\frac {1}{ikr}}+{\frac {1}{(ikr)^{2}}}+{\frac {1}{(ikr)^{3}}}\right)(\mathbf {\hat {x}} +i\mathbf {\hat {y}} )-\left({\frac {1}{ikr}}+{\frac {3}{(ikr)^{2}}}+{\frac {3}{(ikr)^{3}}}\right){\frac {x+iy}{r^{2}}}\mathbf {r} \right)ik^{3}{\frac {e^{-ikr}}{4\pi }}$

where $k={\frac {\omega }{c}}$ is the wavenumber, $\mathbf {r} =x\mathbf {\hat {x}} +y\mathbf {\hat {y}} +z\mathbf {\hat {z}}$ and $r=\|\mathbf {r} \|$ is the distance from the loop. Then the time-averaged Poynting vector (giving the electromagnetic power flow) is

$\mathbf {P} ={\frac {1}{2}}\mathrm {Re} (\mathbf {E} \times \mathbf {H} ^{*})={\frac {{Z}_{0}I^{2}A^{2}k^{4}}{32\pi ^{2}r^{3}}}\left({\frac {r^{2}+z^{2}}{r^{2}}}\mathbf {r} +2\left({\frac {1}{rk}}+{\frac {1}{(kr)^{3}}}\right)\mathbf {r} \times \mathbf {\hat {z}} \right)$

and integrating the radial component of this over the sphere of all directions gives the total radiated power

$P=\int _{0}^{\pi }\int _{0}^{2\pi }(\mathbf {P} \cdot \mathbf {\hat {r}} )r\sin(\theta )\partial \phi r\partial \theta ={\frac {{Z}_{0}}{6\pi }}\left(IA\left({\frac {\omega }{c}}\right)^{2}\right)^{2}$

Similarly, the time-averaged Maxwell stress tensor (giving the momentum flow) is

$\mathbf {T} ={\frac {1}{2}}\mathrm {Re} \left(\varepsilon _{0}\mathbf {E} \mathbf {E} ^{*}+\mu _{0}\mathbf {H} \mathbf {H} ^{*}-{\frac {1}{2}}\mathbf {I} (\varepsilon _{0}(\mathbf {E} \cdot \mathbf {E} ^{*})+\mu _{0}(\mathbf {H} \cdot \mathbf {H} ^{*}))\right)=\mathrm {complicated}$

and integrating this to get the total radiated angular momentum gives

$\mathbf {\tau } =\int _{0}^{\pi }\int _{0}^{2\pi }\mathbf {r} \times (\mathbf {T} \cdot \mathbf {\hat {r}} )r\sin(\theta )\partial \phi r\partial \theta ={\frac {{Z}_{0}}{6\pi \omega }}\left(IA\left({\frac {\omega }{c}}\right)^{2}\right)^{2}\mathbf {\hat {z}}$

But conservation of angular momentum demands a torque of $-\mathbf {\tau }$ on the source, and that will absorb a power of $\omega (\mathbf {\tau } \cdot \mathbf {\hat {z}} )$ from the rotation, exactly accounting for the radiated power $P$, meaning that no power is derived from the current (the radiation resistance is zero) - as expected.

The $c^{4}$ in the denominator means that $P$ is really small for feasible $IA$ and $\omega$.

catslash (talk) 01:34, 19 February 2024 (UTC)

February 11

Collision analysis

A bus of mass 25 tons starts to travel along a straight road from A to B at 50 mph. At the same time a bee of mass 2.5 grams starts to fly from B to A along the same road at 5 mph. Eventually the bee and the bus collide.

Assume the bee impacts a surface of the bus which is flat and at right angles to its direction of travel, such as the windscreen, and the bee sticks to this surface.

Then the bus will be slowed by a tiny amount reflecting the relative masses / momenta of the bee and bus. In addition, relative to A, the velocity of the bee changes from -5 mph to +50 (approximately) mph during the collision. So at some stage during the collision the bee must be stationary. This can only be when the bee is in contact with the bus.

The question is : Why is the bus not stationary at the same time?

Does it make any difference to the situation if the bee is replaced by either a perfectly elastic object, or a perfectly rigid object, of the same mass?

And does it make any difference if the collision is considered at the level of the individual atoms involved? Ionlywanttoknow (talk) 18:40, 11 February 2024 (UTC)

If you define the direction from A to B as positive, the bee is changing from a speed of -5 mph to +50 mph. Regardless of the exact nature of that change, in order to get from -5 to +50, at some point the speed must pass 0.

The bus's speed is changing from +50 mph to +49.999999... mph. That change does not pass through zero, so the bus is never stationary.

You could get into more details of the interaction, but that's the basic point. PianoDan (talk) 20:11, 11 February 2024 (UTC)

There's two explanations. If you're thinking of absolutely rigid bodies then the bee is never stationary, it immediately switches between going in one direction and the other. In the physical world there is always an bit of elasticity so the bus atoms can keep going forwards whilst the bees ones slow down and reverse as the bee is squashed against the windscreen. NadVolum (talk) 20:30, 11 February 2024 (UTC)

This follows from the Intermediate value theorem. Ruslik_Zero 20:35, 11 February 2024 (UTC)

There is no intermediate value of speed in the case of rigid bodies. NadVolum (talk) 21:06, 11 February 2024 (UTC)

Here is the argument: The intermediate value theorem tells you that the speed of the bee is zero at some points in time. By assumption, the bee and the bus move at the same speed when they are in contact. So the bus must move at speed zero at that point in time. So far, so good. But we are talking about points in time. Speed, being distance per time, is not well-defined for an individual point. You need an "expanse of time" to have speed. --Stephan Schulz (talk) 10:20, 12 February 2024 (UTC)

The intermediate value theorem is valid for continuous functions. For rigid bodies, the speed is discontinuous (acceleration infinite), so the IVT does not apply. As was said above, real bodies are always elastic to some point, which causes gradual changes of the speed and keeps the accelerations finite. --Wrongfilter (talk) 12:06, 12 February 2024 (UTC)

Why is the bus not stationary? Because it is moving at 50 mph! For the bus to decelerate from 50 mph to stationary in the brief duration of this collision would take a very, very large force. So large it could not possibly occur in a collision with a small object. Dolphin (t) 06:19, 12 February 2024 (UTC)

The meaning of "why" in the question is unclear. However, one of many ways to see that the bee+bus system cannot be stationary is that its kinetic energy would be zero, violating the law of conservation of energy. In the idealized analysis, the bee is treated as if it is a point particle. In a more refined analysis, the collision takes some time; the drama unfolds in about half a millisecond. Halfway through the process, the front part of the insect has already been squashed and splotched across the bus, co-moving with it at almost 50 mph. Shockwaves through its body may have caused parts of its now liquefied internals to erupt through its rear, moving even faster than the bus. Other parts of the bee are still moving in the original direction, towards the bus. If we zoom in to the elementary particle level, we run into the fundamental limit of quantum uncertainty: we cannot assert meaningfully that any part of the bee is stationary at any time.  --Lambiam 13:30, 12 February 2024 (UTC)

By the way you might like to read Windshield phenomenon about why this hasn't been happening much recently. NadVolum (talk) 17:01, 12 February 2024 (UTC)

According to the reincarnated bee (murmuring something about local inertial frames not accelerating) it was the bus that stopped and the road reversed and took the bus+bee to the land of honey. Modocc (talk) 14:18, 13 February 2024 (UTC)

February 12

Hospital Gangrene

Is there is Wikipedia on Gangraena nosocomialis or hospital gangrene, predominant up until about 1870-1880. I can't seem to locate anything although it might on under some different name. scope_creep^Talk 09:29, 12 February 2024 (UTC)

Here ? Heihaheihaha (talk) 10:29, 12 February 2024 (UTC)

Hospital gangrene redirects to Necrotizing fasciitis. The historical use of the term can perhaps not be precisely related to current terminology, including many cases that could have been treated non-surgically by suitable antiseptic wound dressing and administering antibiotics if they had been available at the time.  --Lambiam 13:08, 12 February 2024 (UTC)

Strange "mitotic phase" of oocytes in rabbit's primary follicle

Two months ago, I posted a question on StackExchange but no one answered me there. It's about a primary follicle (Inferred from the number of layers of granular layer cells), whose oocyte seems to be undergoing division, which is supposed not to happen at this stage by my textbook. I've asked my histology teacher and got no answer. My initial idea was whether it is possible to have multiple oocytes simultaneously in the follicles of rabbits. I've tried to google and searche on PubMed, I didn't find relevant evidence there. The full size picture is provided here, which may provide more information.

The question is: how to explain this phenomenon? I did not observe this phenomenon in other many slices. Heihaheihaha (talk) 10:26, 12 February 2024 (UTC)

Interesting. Following. Zarnivop (talk) 10:21, 13 February 2024 (UTC)

Rabbits have a couple of wrinkles not found in all mammals, induced ovulation and embryonic diapause, could these be related? Abductive (reasoning) 12:20, 13 February 2024 (UTC)

February 13

UV index

This thing interests me, and I don't know it (it's not homework): in which time of the year is the UV index highest in any given place? Is it arund the summer solstice, which is in June in northern hemisphere and in December in southern hemisphere, or is it in July in northern hemisphere and in January in southern hemisphere, when temperatures are highest? --40bus (talk) 15:58, 13 February 2024 (UTC)

See Ultraviolet index. I expect the UV Index at any geographical position to be at its annual highest value when the sun is at the greatest elevation - the summer solstice. Dolphin (t) 16:27, 13 February 2024 (UTC)

But the high-latitude ozone hole peaks in early spring, in low latitude the Sun height changes of Earth's axis cause smaller incoming solar radiation changes than elsewhere cause trigonometry so the strong 1-year wet and dry season cycle and milder seasonal ozone strength cycle might overpower the small axis tilt effect and make it not the time of highest noon Sun (which is not the solstice less than 23.44 degrees from the Equator. Sagittarian Milky Way (talk) 18:00, 13 February 2024 (UTC)

Sun Safety Monthly Average UV Index 2006-2023 from the United States Environmental Protection Agency shows similar results for June and July. Alansplodge (talk) 12:41, 15 February 2024 (UTC)

Some relevant considerations also are to be found in that article Record solar UV irradiance in the tropical Andes. As can be expected, peak values were measured between the end of December, and January (2004). --Askedonty (talk) 13:38, 15 February 2024 (UTC)

Peak rain time is afternoon, Andes might often pierce the clouds, the ITCZ usually lags the Sun zenith latitude and it only has to be sunny in late December once to be a record. Sagittarian Milky Way (talk) 14:12, 15 February 2024 (UTC)

Yes, that's why the team hit bonanza. But no residual glacier, which is a course other latitudes tend to be following lately [2]. --Askedonty (talk) 14:52, 15 February 2024 (UTC)

Also the Sun is closest to Earth in early January. Sagittarian Milky Way (talk) 14:57, 15 February 2024 (UTC)

However the zenith noon latitude is only December solstice at the Tropic of Capricorn, slightly norther it'll be zenith twice a year and the early January one will be at the nearest part of Earth's orbit but not even get peak doldrums. Also it's dry as fuck there. Atacama Desert, nothing to block UV not even tropospheric ozone pollution. Sagittarian Milky Way (talk) 15:05, 15 February 2024 (UTC)

In NYC the summer month percent of possible sunshine is 57 59 63 (frontal thunderstorms decline after June, frontless land heating thunderstorms likely peak July). Avg UV index 7 8 8 8 6 MJJAS according to Wikipedia, maybe enough of the country is similar to make June and July the national average peak. Sagittarian Milky Way (talk) 14:19, 15 February 2024 (UTC)

Wilson-Effect

Does the Wilson-Effect apply to other properties or just hight (how large somebody is)? 2A02:8071:60A0:92E0:C1E2:268B:CB67:A6BA (talk) 22:07, 13 February 2024 (UTC)

What Wilson effect? There's one concerning sun spots: Wilson effect. There's one concerning inheritability of IQ: [3]. You seem to be talking about yet another one. Please try to ask a proper question. --Wrongfilter (talk) 22:22, 13 February 2024 (UTC)

This refers to an increase in heritability of IQ with age, not of height:

Thomas J. Bouchard (October 2013). "The Wilson effect: The increase in heritability of IQ with age". Twin Research and Human Genetics 16(5):923–30. PMID 23919982

Reportedly, looking at a proxy for general cognitive ability instead of IQ, some researchers found the opposite effect for the age bracket of 50–69 years:

Matthew A. Sarraf, Michael Anthony Woodley of Menie, Mateo Peñaherrera-Aguirre (February 2023). "The anti-Wilson effect: The decrease in heritability of general cognitive ability, as proxied by polygenic expressivity, with advanced age". Personality and Individual Differences 202:111969. doi:10.1016/j.paid.2022.111969

 --Lambiam 09:22, 14 February 2024 (UTC)

I've known about that for a long time and am surprised it still is just a citation in Heritability of IQ and not even named there. Yes I would expect height to follow a similar pattern but haven't seen anything about it. NadVolum (talk) 14:12, 14 February 2024 (UTC)

Children develop at different rates for all sorts of reasons, including non-genetic reasons like nutrition. So children of a particular age are more variable in IQ and height than older age groups that have reached full adulthood. This is what causes the heritability to be higher in older age groups; there is less non-genetic variation, so the proportion of total variation explained by genetic variation is higher. Hence I would expect the Wilson effect to exist in most traits that show developmental changes with age during childhood. A character like baldness might show the opposite pattern. JMCHutchinson (talk) 22:18, 14 February 2024 (UTC)

February 15

Is salted whipped butter more friable and/or sticks less to bread?

If so then why? Solid pieces of unsalted whipped butter seem to fall off less often.Sagittarian Milky Way (talk) 01:06, 15 February 2024 (UTC)

Than what? Salted whipped butter? Unsalted unwhipped butter? Salted unwhipped butter? {The poster formerly knwn as 87.81.230.195} 176.24.45.226 (talk) 12:06, 15 February 2024 (UTC)

Salted whipped butter vs unsalted whipped butter Sagittarian Milky Way (talk) 14:22, 15 February 2024 (UTC)

Take it with a grain of salt: my short answer without references. When pressed and/or placed onto bread, some of the butter liquefies and is wicked into the bread giving it additional contact and surface tension (see Capillary action) causing the butter to stick. At the point the bread becomes saturated, the butter tends to slide off because a fluid film forms between the saturated bread and the intact butter solids. Added salt suppresses the melting points of solids such as ice, so it likely significantly speeds up the end result.

Modocc (talk) 14:50, 15 February 2024 (UTC)

Taken unsalted, your answer may stick better.  --Lambiam 17:17, 15 February 2024 (UTC)

Magnetic compass

Not homework but I'd like to know how to answer this at the level of an introductory E&M physics class or that sort of thing. Basically a magnetic compass is a magnetized needle with a pivot in the middle, sitting in the Earth's magnetic field. The needle has mass M and length L and I guess we can ignore most subtleties.

My question is, how do you calculate the torque around the pivot, at least dimensionally? My first thought was that it would be quadratic in L (by integrating along the needle) but maybe that's wrong, and I just don't understand magnets well enough.

Oh yes, I guess the needle material itself needs to have some physical magnetization parameters specified. How would I find those, for whatever permanent magnet material is generally used in not-fancy compasses? Do fancy ones use fancier materials like rare earth magnets?

Motivation for asking: if I get a small cheap compass, say 1 inch in diameter, it will tend to get stuck easily, because the torque from the magnet isn't enough to overcome the friction in the pivot. Compasses with better (lower friction) pivots cost more. If I get one of similar quality that's 2 inches diameter, it will have 2x the friction in the pivot (because the needle is twice as heavy) but I wondered if it would have 4x the torque, similar to a moment of intertia calculation. That is, I'm wondering whether big cheap compasses work better than small cheap compasses.

Someday I'll try to work through a textbook on this magnetism stuff. Thanks. 2601:644:8501:AAF0:0:0:0:2F14 (talk) 03:55, 15 February 2024 (UTC)

The torque depends on the magnetic moment, which for a permanent magnet is the remanence times the volume (I think; you should read the articles to check). catslash (talk) 11:13, 15 February 2024 (UTC)

That's

${\boldsymbol {\tau }}={\frac {\text{vol}}{\mu _{0}}}\mathbf {B} _{\text{rem}}\times \mathbf {B} _{\text{earth}}$

catslash (talk) 12:08, 15 February 2024 (UTC)

I asked about this in 2019 and didn't get a good answer. Sagittarian Milky Way (talk) 14:29, 15 February 2024 (UTC)

Since the earth's magnetic field and the permeability of free space are outside our control at present, it seems we just need to maximize the volume of the compass magnet and the remanence of it's material. catslash (talk) 14:43, 15 February 2024 (UTC)

Increasing the needle's mass M by increasing its width or thickness increases its magnetic torque by the same factor, which does not help if the stickiness is due to pivot Stiction (static friction) whose resistance to motion is proprtional to the weight of the needle. Increasing needle mass instead by increasing its length moves the effective centers of application of torque further from the pivot, thereby adding a further increase in the moment of the torque to give faster settling. Another way to overcome stiction is to vibrate the compass. Philvoids (talk) 14:14, 17 February 2024 (UTC)

February 16

Tertiary color

There are 3 primary colors and (3*2)/2 = 6/2 = 3 secondary colors. Then the number of tertiary colors should be (3*2*1)/6 = 6/6 = 1. Wikipedia's article List of colors by shade says that in theory this color should be black, but that in practice it is brown because blue pigments are so weak. Why is blue so weak?? Georgia guy (talk) 17:09, 16 February 2024 (UTC)

Color is such an interesting topic, because there are so many different ways to approach this complex subject!

If we take a very bland and scientific approach - like the one you might find in the main article about color mixing - you'll see a different (and more precise) way of describing the phenomenon. It also includes a link to a few useful citations.

We have to be careful to distill your question to its core, practical application, and to make sure we lay out some reservations: the observation is not universally true; but it manifests in some examples like mixing paints (especially the kind of paint you might buy in an art store). I'm trying to avoid weasel-words, and also trying to avoid being unnecessarily technical here, but it's important that we're scientifically accurate!

If somebody - like an artist who mixes paint - describes "blue" as "weaker" (... in the context of how it qualitatively affects the outcome when mixing paints) - then they are probably dancing around the topic of opacity as it affects mixing pigments.

If this is what they mean, we can study scientific explanations for why the paint has this particular opacity. I'm reluctant to use a word like "weak" or "strong" here - we might disagree on which word is more apt - but it's helpful to know that most paints (like the ones you find in an art store) contain a chemical mixture of pigment in a binder (or sometimes a solvent). The material is not "pure" pigment - it's a mixture. The color of the mixture can be made more- or less- opaque by adjusting the concentration of the pigment. Bafflingly, we might say that blue pigments are stronger, so paint companies can use less pigment in their paint to obtain a qualitatively equivalent amount of color , ... which makes for a bizarre reversal of qualitative language use..., which is confusing, and it's why we probably shouldn't use words like "weaker" or "stronger" when we're being scientific in our discussions about color.

All this aside, it would be misplaced if I attacked the fundamental premise here (as somebody who spends a lot of time scientifically studying color, and human perception of color, it's very tempting to shout ..."there's no such thing as a primary or secondary color...!" But ... human perception is involved here, so ... it's more complicated than that, too!) Rather, I think what I would say is - "this simple model of color-primaries is useful only in very simplified cases, like kindergarten-level paint-mixing examples." We do not have to work very hard to find examples where the simple model is insufficiently detailed to describe behaviors that are plainly visible to (most) everyone! In fact, you found such an example!

Nimur (talk) 17:32, 16 February 2024 (UTC)

If you go back to that table you'll see that black is an absence of color. Mixing pigments removes color components. Additive colors are probably more what you want if you want to talk about a 'tertiary' color and that would be white or a pale color. NadVolum (talk) 23:01, 16 February 2024 (UTC)

A tertiary color is an intermediate color resulting from an even mixture of a primary and a secondary color, i.e. a mixture of the primaries in 3:1:0 proportion resulting in a less saturated form of the dominant primary color of the mixture. Philvoids (talk) 01:41, 17 February 2024 (UTC)

Note that this is given as a more recent "alternative definition" conflicting with the more traditional (and quite different) one of a mixture in a 1:2:1 proportion.  --Lambiam 09:34, 17 February 2024 (UTC)

Using the RGB additive colour model, here are the three maximally light 1:2:1 mixtures:

     

and here are the six maximally light 3:1:0 mixtures:

           

Brown is more like a (not maximally light) 4:2:1 mixture:  .
 --Lambiam 09:56, 17 February 2024 (UTC)

What about yellow? Zarnivop (talk) 10:34, 17 February 2024 (UTC)

As an even mixture of R and G, it is a secondary colour in the RGB model.  --Lambiam 13:28, 17 February 2024 (UTC)

  Yes, or a primary color in subtractive color systems or 575–585 nm spectral wavelength. Philvoids (talk) 13:50, 17 February 2024 (UTC)

February 19

Why the physical and chemical properties of element 0 is very hard to find?

Why the physical and chemical properties of element 0 (neutronium) is very hard to find (e.g. it should be as noble as helium and neon, and should be gas in the room temperature, maybe neutronium is ideal gas)? The half-life of the free neutron is longer than the half-life of the longest- lived isotope of the elements with atomic number >= 107, and some physical and chemical properties of the elements with atomic number >= 107 are already known. 61.224.147.34 (talk) 07:50, 19 February 2024 (UTC)

If you look at our article your will read it is a "hypothetical substance". But see Neutron#Neutron compounds, the conditions to form these are not available in the Solar System, so anything known would be hypothetical. Perhaps some clues can be gleaned by neutron star collisions. Neutrons stored in a bottle would be a dilute gas. They do not interact with light, and so is transparent. Graeme Bartlett (talk) 08:42, 19 February 2024 (UTC)

I don't think neutrons can be stored in a bottle. Since neutrons are neutral they do not feel the electromagnetic Coulomb barrier that keeps atoms and molecules in the bottle. For the same reason it makes little sense to talk about "chemical properties". These are determined by the electrons in atoms; neutronium has no electrons, and neutrons cannot capture electrons to form negative ions. --Wrongfilter (talk) 09:03, 19 February 2024 (UTC)

See ultracold neutrons#Reflecting materials for what to make your neutron storage bottle from. It appears that beryllium is best. (But it's not transparent) Graeme Bartlett (talk) 09:37, 19 February 2024 (UTC)

That's very interesting, thanks! Pity the article doesn't provide enough information to understand how that works. --Wrongfilter (talk) 09:52, 19 February 2024 (UTC)

Apparently it works by the strong interaction, as expected. Which basically illustrates why element 0 doesn't really have chemical properties; it has no electrons, which would be needed for such things like forming bonds and a normal condensed phase. Double sharp (talk) 10:24, 20 February 2024 (UTC)

Has any gluon's velocity ever been measured?

I'm asking, because for the time being, only two particles, considered to have no mass, have been detected, one of which has empirically turned out to have a velocity, being (or sufficiently close to) the well known constant velocity C, if that particle (namely photon) is in a medium, being (or sufficiently close to) an absolute vacuum. So my question is: what about the other particle (namely gluon), as far as its measured velocity (especially in a vacuum) is concerned? HOTmag (talk) 13:04, 19 February 2024 (UTC)

The scale at which gluons operate (see Strong interaction § Behavior of the strong interaction} is less than 0.8 fm = 0.8×10⁻¹⁸ m. At the speed of light, the time scale is less than 3×10⁻²⁷ s or 3 rontoseconds. The inverse of the hyperfine transition frequency of ¹³³Cs used in atomic clocks is about 0.1 nanoseconds or 0.1×10⁻⁹ s, 16 orders of magnitude larger. I do not think technology is up to measuring such short time spans. Apart from technological limitations, I think there are also fundamental limitations baked into the laws of physics as we understand them, such as quantum uncertainty. I can't think of any kind of experimental setup that might clock a gluon as being at some definite position. Bounds on gluon mass will have to be deduced from energy budget calculations of high-energy collisions.  --Lambiam 17:59, 19 February 2024 (UTC)

Thank you for your (disappointing) reply. I hoped the gluon's velocity could be measured somehow, because I wanted to make sure that the well known hypothesis - stating that no massless particle can be a tachyon - could be emprically proved also for particles other than photons, but according to your reply I understand we will have to stay in the boundary of photons alone for emprically proving this hypothesis - which I suspect is not sufficiently reliable while it has been empirically proved for photons only. That no massive paricle can be a tachyon, is a well established fact, or rather a mathematicllay proved fact - deriving from the relativistic equation of momentum, but this fact cannot be mathematically proved for massless particles, for which we can only rely on experiments, which have actually been carried out for photons only, unfortunately, as I understand from your reply. What a pity... HOTmag (talk) 08:00, 20 February 2024 (UTC)

February 20

The increasing role of relativistic effects in heavy elements, since the speed of the 1s electron is not far less than c (speed of light)

The increasing role of relativistic effects in heavy elements, since the speed of the 1s electron is not far less than c (speed of light). Thus if the reciprocal of the fine-structure constant is 299792458 rather than 137, then the physical properties and the chemical properties of the elements in the period 8 will be completely different? 125.230.19.122 (talk) 07:01, 20 February 2024 (UTC)

I suppose by changing α you really mean changing c, implicitly using atomic units. (See this Physics Stack Exchange answer for the subtleties involved in such "alternate-physics" discussions.) So this really amounts to increasing the speed of light until relativistic effects are no longer important. In that case, not only is period 8 probably completely different, but also differences should be noticeable in periods 6 and 7. Without relativistic effects, mercury would be solid at room temperature, and lead-acid batteries would not work (because relativistic effects stabilise Pb^II relative to Pb^IV; without them, Pb would be much more like Sn than it really is). Double sharp (talk) 07:56, 20 February 2024 (UTC)

steel flexture lifetime

I was watching this video [4] when I noticed that at 0:30 they claim: "Infinite lifetime", "no friction, no wear".

I think this is a flexure mechanism, and I'm not too familiar with them. But I do know a little bit about springs, and springs have a finite design lifetime, because every time a spring is compressed fatigue is introduced. Springs "wear", in other words.

Since springs have a finite lifetime, and undergoes wear during operation, wouldn't the same principle apply to the device shown in the video? OptoFidelty (talk) 21:33, 20 February 2024 (UTC)

They also advertize their gear as "frictionless" on the very first frame, which I think is not physically possible.  --Lambiam 01:22, 21 February 2024 (UTC)

According to Plasticity (physics) however, load should not exceed the yield strength associated with a given material for it to retain its plasticity. It's a simple rule that may be perhaps not practical to observe in most real-life situations; and it always ended in failure at some point in all situations I studied, but that might be a matter of scale. Then the video is about a product intended to be used in a very sterile, quiet, and, finally, previsible environment. Thus, the notion of fatigue as we know it must also have a subjective dimension in it in some way. --Askedonty (talk) 01:27, 21 February 2024 (UTC)

Steel has a so-called endurance limit for stress, and according to this there is no limit to the fatigue life if you stay under it. According to an experienced test engineer, this is more a result of poor test technique than physics. Ultimately if you keep flexing steel, migration of discontinuities will continue, they will form cracks and then it breaks. Sorry, no refs. Greglocock (talk) 08:24, 21 February 2024 (UTC)

I would be very cautious about any claims within this advert since, as far as I can see, it indirectly claims to be breaking the laws of physics. Electric fan and direct radiant heaters already convert well over 90% of their drawn electrical energy to heat, so the inferences that these devices can heat a room much more quickly ("in seconds" – how many seconds?) much more cheaply ("for pennies" – how many pennies?) than existing devices seem dubious. {The poster formerly known as 87.81.230.195} 176.24.45.226 (talk) 15:21, 22 February 2024 (UTC)

What advert are you talking about? The OP posted a video about a steel flex mechanism with no electric heater mentioned. Philvoids (talk) 21:06, 22 February 2024 (UTC)

Plus heat pumps are far better at heating than directly converting electric currents into heat. NadVolum (talk) 22:50, 22 February 2024 (UTC)

February 22

Aliens have killed themselves

There are reasons to think that extraterrestrial life should be common, but so far we have never find any. The Fermi paradox provides several possible explanations for it, such as that aliens may self-destruct after discovering atomic power or other advanced technologies. But today I was thinking, should that be an obstacle? Let's say that the Klingons started an atomic war and killed themselves before we could get anywhere near a Star Trek situation. Shouldn't we still be able to detect anyway an exoplanet with an atmosphere polluted with high levels of radiation, that could not be explained by natural processes? Wouldn't other ways of an alien civilization to self-destruct (chemical war, mere pollution, etc) leave detectable clues as well?

I don't think I need to explain that such a discovery (a world where life existed, and more, intelligent life!) would still be a revolutionary one, even if there was nobody left by now. Cambalachero (talk) 18:15, 22 February 2024 (UTC)

Well, for one, the Fermi paradox presumes that civilisations spread through the galaxy. If they self-destroy before reaching that phase (as we very well might still do, assuming we even are civilised to begin with), then they are much less frequent, and hence much harder to detect. Also, we can sometimes get some spectroscopic data for some exoplanet atmospheres, but I doubt we can distinguish between radioactive and other isotopes that way. --Stephan Schulz (talk) 18:54, 22 February 2024 (UTC)

That depends on the method of spectroscopy, element, and compound. Infrared techniques and microwave techniques, or redshifted forms of them, are molecular spectroscopy, see infrared spectroscopy and microwave spectroscopy. These are tools for measuring molecular vibrations and molecular rotations, respectively, and the masses of the atoms within the compounds play a major factor in the spectral signature. The frequencies of their absorptions are inversely proportional to the square root of the reduced mass of the system. In a diatomic molecule, for example, a significant change in the mass of of the atoms by isotopic substitution is easily detectable, and is often used as a tool in studying molecular systems by intentionally substituting for isotopes. Take the case of HCl; it's infrared spectrum is made up of doublets due to the presence of both chloride-35 and chloride-37 isotopes, which exist in known ratios (under natural conditions) reflected in the relative intensities of the doublet peaks. If that ratio were to be different, that would at least indicate something unusual had happened. The difference in frequency there is fairly small, but the difference in frequency between HCl and DCl is quite large and incredibly easy to detect. While it would be harder to detect than chlorine-37, HCl composed of chlorine-36 could, if detected, be an indicator of the use of nuclear weapons, since our underwater testing of nuclear weapons produced a great deal of chlorine-36. That's just one example, though. I'll bet a careful examination of the isotopic products of a nuclear exchange was done, others examples could be found, and a potential model for IR/MW examination for extra-terrestrial nuclear weapons use could be designed. --OuroborosCobra (talk) 19:29, 22 February 2024 (UTC)

Good point - I had only thought about atomic spectra. --Stephan Schulz (talk) 19:39, 22 February 2024 (UTC)

Also, going by our own example, it wouldn't take much to cause the collapse of a single-system technological civilization at our own level or beyond (which needn't cause total extinction), and any effects detectable at long range would be short lived in astronomical terms. Such civilizations might arise not uncommonly Galaxy-wide, but too far separated in time for their technological eras to overlap. {The poster formerly known as 87.81.230.195} 176.24.45.226 (talk) 19:27, 22 February 2024 (UTC)

There is no way of establishing ferm lower bounds on most of the variables featuring in the Drake equation. If a technologically advanced civilization arises about once every million years in our galaxy and then inevitably blows itself up, the signature of the calamity will have disappeared by the time we examine the planet.  --Lambiam 22:49, 22 February 2024 (UTC)

The Fermi Paradox has always struck me as being misnamed. The idea that the galaxy should be full of aliens rests on so many assumptions that it us not having found evidence of any (let alone evidence that they have visited us) hardly seems to constitute a "paradox". Iapetus (talk) 10:55, 23 February 2024 (UTC)

It has that in common with many puzzling facts named "paradoxes": Antarctic paradox, Denny's paradox, Elevator paradox, Potato paradox, Willpower paradox. Informally, the term paradox is often used to describe a counterintuitive result. Case in point: our page Counterintuitive redirects to the article Paradox.  --Lambiam 13:52, 23 February 2024 (UTC)

Our article Date of Easter talks about the "Easter paradox", meaning that it is not observed on the Sunday after the full moon, or it is observed on the Sunday after the "wrong" full moon. Kepler gave the answer to that: "Easter is a feast, not a planet." Incidentally, following the introduction of a new table acceptable to everyone Special:Permalink/1188536894#The Reichenau Primer (opposite Pangur Bán) it is anticipated that this year's divided celebration (split between 31 March and 5 May) will be the last. It was the 31 March celebration ordered by the Romanian Orthodox Church which led to the peasants' revolt and the disappearance of the Gregorian Easter from Orthodox eastern Europe (barring Finland, where the government offers the Orthodox church there money to keep the Gregorian Easter, to which their response is "Why not?") 81.154.229.214 (talk) 17:19, 23 February 2024 (UTC)

February 23

Does a photon measure set its velocity as plus C, i.e. from the left to the right, or as minus C, i.e. from the right to the left?

Two observers looking at each other, see a photon move between them on their axis of right/left. Observer A sees the photon move at plus C, i.e. from the left to the right. So, observer B, who looks at observer A, must see the photon move at minus C, i.e. from the right to the left. But what about what the photon sees when measuring setting its velocity? Will the photon set its velocity as plus C, i.e. from the left to the right, or it will set its velocity as minus C, i.e. from the right to the left? HOTmag (talk) 01:18, 23 February 2024 (UTC)

A photon cannot measure its own velocity, not just because it is not a physicist, but mainly because it has no proper time. Any two events along a lightlike curve have $\Delta \tau =0$ and the photon cannot derive a speed from that. --Wrongfilter (talk) 07:05, 23 February 2024 (UTC)

Thx.

I apologize, because I was probably wrong with choosing my words. Actually, instead of "measuring" I meant "setting". Anyway, please notice, that according to the principle of the constancy of the speed of light, the photon doesn't have to measure anything - e.g. its speed, because (even without being a physicist or a human being) the photon has already set its speed as carrying the absolute value of C, hasn't it? I assume you agree it has (without measuring anything), so the only question remaining is about whether the direction set by the photon is plus C - i.e. from the left to the right, or the other way around - i.e. minus C. I hope my question is clearer now. HOTmag (talk) 07:47, 23 February 2024 (UTC)

(ec) $\Delta \tau =0$ implies that there is no direction. The photon cannot say that it was first here, then there, or the other way round because it is here and there at the same time. --Wrongfilter (talk) 07:56, 23 February 2024 (UTC)

There is no physical concept of a particle "setting" its velocity. Velocity is a vector quantity; a description of the measure of a velocity requires a frame of reference. The velocity of a particle does not depend on the selected reference frame; it is only the description of its measure that does depend on it. Photons can do many things; selecting a reference frame for describing the measure of its velocity is not one of them.  --Lambiam 13:12, 23 February 2024 (UTC)

The entire Universe is split into the two half-universes occupied repectively by observers A and B. Any observer distinguishes "right" or "left" relative to a personal baseline such as the separation of their eyes. An observer can quantify the travel of a photon only after its arrival at a destination target is timed. Then if the source of the photon is known, occupants of A and B can agree about the photon's velocity C in vacuum but disagree about its left/right direction, however all are equally correct. On a later occasion an investigator may choose to walk the path of the long-gone photon; we do not need his opinion about right or left because the only path he follows is "straight ahead". Let's not complicate this with gravitational lensing or "conscious" photons. Philvoids (talk) 14:16, 23 February 2024 (UTC)