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December 5

Birds with white cheeks

Silver-eared Mesia
White-cheeked Starling
Great Tit
White-cheeked Bushtit
White-cheeked Bullfinch
White-cheeked Bulbul

What is the evolutionary advantage - or purpose - of white "cheeks" on these disparate birds? Andy Mabbett (Pigsonthewing); Talk to Andy; Andy's edits 14:54, 5 December 2024 (UTC)[reply]

In great tits, the immaculateness of the black border of white cheek patches predicted social status and reproductive success, but there was no clear evidence that it played a role in mate choice (Ferns and Hinsley 2004).

Bird Coloration, Volume 2 (p. 186)

Alansplodge (talk) 15:47, 5 December 2024 (UTC)[reply]

Here's recent a review article about what's known about the genetics of bird color patterning. We know a lot less about this topic than about the genetics of patterning in insect wings. It strikes me that all birds follow that same general pattern scheme, with only the colors varying. So in a bird that is all one color, the scheme is there, but not apparent. As for the face, there are many selection pressures that could be occurring–or that might have occurred in the past–to be tested. First, if the pattern is found only in males, there's a good chance it is sexually selected (some trait is getting sexually selected for, but the face color might just be genetically or developmentally tied to it and just along for the ride). In some species, fights between males drive selection, and drawing one's opponents to peck somewhere other than the eyes would be strongly selected for. If female choice is strong, then costly-to-maintain signals are selected for. But there is also selection for confusing predators (such as about the size and position of the eyes), and for confusing prey. Finally, the feathers near the beak get a lot more wear and tear, so need to get replaced more often. Skipping adding color might make this process faster and/or cheaper. All this is guesswork on my part so make of it what you will. Abductive (reasoning) 19:09, 5 December 2024 (UTC)[reply]

Time dilation

I can't seem to get a straight answer: How many parts per trillion between Earth's most time travelly places+where are they? (1 answer for all points a "stationary" non-"antigraviting" (i.e. helicopter/airship) human could be that exist now (i.e. Mammoth Cave/the Chunnel/2 WTC's temporary roof but not the much higher place the permanent roof's planned to be or 10ft below the deepest ice dig a human could put their body. Humans could theoretically go 10ft lower but not as is), 1 answer for if under liquids also doesn't count Mariana Trench=sea level)

Some ppl say everywhere on an equipotential surface has the same speed of time from the 2 dilations canceling out. So Everest+Mariana should be extremest? Or the Kidd Creek Mine if under liquids doesn't count. I haven't been able to reproduce cancellation with the formulae or calculators though. Some gravitational dilation calculators want distance to center which is NOT geopotential (Chimborazo's furthest, Arctic seabed closest, or North Pole if has to touch air), some want g-force???. It's not g-force unless that calculator only works for the surfaces of spheres. Earth's gravitational dilation's strongest at the base of the gravity well where you'd be weightless. Google AI dumbass can be made to say both ellipsoid+geoid for the equal dilation surfaces. Some human who might know says it's the geoid. Some probably different human I don't remember says it's only equipotential on one of rotating vs inertial reference frame. How the hell can it depend on reference frame? Clocks can't both be later than each other when they reunite (very slowly to infintesimalize kinematic dilation from the trip). Some clock pair has to be most disparate when they reunite. Maybe it can still depend in some way without violating this logic? Presumably Cayambe's the place with the most kinematic time dilation? Furthest point of Earth's surface from the axis. Presumably axis points avoid more kinematic time dilation than any other points of the planet? Sagittarian Milky Way (talk) 00:20, 6 December 2024 (UTC)[reply]

Although the Earth can be considered a rotating sphere, I think the effect of its rotation on gravitational time dilation is small. Using the formula at Gravitational time dilation § Outside a non-rotating sphere, I compute that the fractional difference is about 1.1 × 10⁻¹⁶ per metre height difference (above sea level). The fractional difference of time dilation by the velocity difference between the poles and the equator is about 1.2 × 10⁻¹², so this will beat gravitational time dilation. --Lambiam 02:41, 6 December 2024 (UTC)[reply]

How is Rainbow considered as application ?

How is Rainbow considered as application ? Source

I believe Rainbow is just a Rainbow, not a something to use. HarryOrange (talk) 22:42, 5 December 2024 (UTC)[reply]

The Okapi Framework has an app named "Rainbow", which we describe by, "Rainbow — a toolbox to launch a large variety of localization tasks." (Other than this I know nothing about Okapi and its app.) --Lambiam 01:48, 6 December 2024 (UTC)[reply]

The link to the article about rainbows has been in the "applications" section from the start, in this edit, where the applications listed were Rainbow, Cosmic microwave radiation, Laser, and Laser fusion. The first two of those are phenomena, not technologies, so it's certainly unclear how to apply equations to them - with what end in mind? Subsequently Radio wave, Gravitational lens, and Black-body radiation joined the list. Although radio waves are phenomena there are many technological things we might seek to do with them, and in the course of trying to make things work we might need numbers that come from an equation. In other cases the application might simply be to obtain numbers, to study a phenomenon like radiation. But I agree, I can't imagine in what way we could even investigate a rainbow with these equations, and so I don't understand how it's an "application". I think it might be a reference to this Feynman lecture. Near the bottom is a discussion of rainbows:

“While I’m on this subject I want to talk about whether it will ever be possible to imagine beauty that we can’t see. It is an interesting question. When we look at a rainbow, it looks beautiful to us. Everybody says, “Ooh, a rainbow.” (You see how scientific I am. I am afraid to say something is beautiful unless I have an experimental way of defining it.) But how would we describe a rainbow if we were blind? We are blind when we measure the infrared reflection coefficient of sodium chloride, or ...”

Then

“On the other hand, even if we cannot see beauty in particular measured results, we can already claim to see a certain beauty in the equations which describe general physical laws. For example, in the wave equation (20.9), there’s something nice about the regularity of the appearance of the x, the y, the z, and the t. And this nice symmetry in appearance of the x, y, z, and t suggests to the mind still a greater beauty which has to do with the four dimensions, the possibility that space has four-dimensional symmetry, the possibility of analyzing that and the developments of the special theory of relativity. So there is plenty of intellectual beauty associated with the equations.”

So, OK. But it's tenuous, and would be better removed or explained. Card Zero (talk) 05:15, 6 December 2024 (UTC)[reply]

The disambiguation page for Rainbow treats the various uses of the word equitably without over indulgence in any isolated usage such as the artistic to the unfair extent of shunning the physical reality that the electromagnetic wave understanding of light is the physicist's most applicable tool and that for this its equations are fundamental. Philvoids (talk) 11:47, 6 December 2024 (UTC)[reply]

OK? But this question is about Electromagnetic_wave_equation#Applications (which is easily missed, since it's hidden under the word "source"). Should that really list "rainbow" as an "application"? Card Zero (talk) 12:37, 6 December 2024 (UTC)[reply]

I agree not, and others in the 'Applications' list are also inappropriate ('black hole'?). Perhaps a further list of 'Phenomenon' (or similar) should be created? {The poster formerly known as 87.81.230.195} 94.1.211.243 (talk) 13:20, 6 December 2024 (UTC)[reply]

That's Black-body radiation, but yeah. Card Zero (talk) 15:03, 6 December 2024 (UTC)[reply]

That stuff was added on Feb 9, 2006,[1] by a user who's no longer active. But if their email is available, someone could try sending them a note. ←Baseball Bugs ^{What's up, Doc?} carrots→ 17:42, 6 December 2024 (UTC)[reply]