Wikipedia:Reference desk/Archives/Science/2020 February 21

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February 21

Bug ID

Body silhouette of a fashionable lady's pointer fingernail, same size, tick style head, brownish gray color scheme, brown blood, banded antennae, 6 legs, white leg side, pointed arch shaped butt, northeast us and maybe elsewhere. Sagittarian Milky Way (talk) 00:33, 21 February 2020 (UTC)

If you don't have a pic you can either look through mugshots or take the easy way out. EllenCT (talk) 02:45, 21 February 2020 (UTC)

Scientific guidelines for diet

I'm following this diet it's a scientific guideline and was wondering if I could have some assistance or help with information on how to avoid processed food and knowing the difference between packaged food and processed. I used to think everything that was packaged was bad that's not true. It's the ingredients the stuff that's in them which is basically high fat, sugar, salt, food preservatives and food additives. How do you know when you go to supermarket and pick up food or food item that it is high in fat, sugar, salt, food preservatives and food additives and should be avoided. — Preceding unsigned comment added by 2001:8003:7427:6B00:D016:393:53B6:6FEC (talk) 02:18, 21 February 2020 (UTC)

So, processed food is simply anything that has been cooked, baked, ground, mixed, or otherwise modified from the state it was in when it was harvested, collected, butchered, or otherwise first obtained from its natural state, other than having been washed, shucked, peeled, juiced, pasteurized, dried, pressed or packaged. Does that help? This is from memory, but hopefully it's enough to tell you what they wanted you to know. EllenCT (talk) 02:51, 21 February 2020 (UTC)

I want to know when I go to supermarket and look at food or food item. The information of ingredients on back nutrition information how do you know when food is high fat, sugar, salt, food preservatives and food additives and how to avoid it as that is what the guideline suggests. — Preceding unsigned comment added by 110.151.68.194 (talk) 03:50, 21 February 2020 (UTC)

You need to get a sense of how many calories from fat and carbohydrates is high, by looking at a lot of them and comparing the proportions. It's a little easier for sodium because anything above 5% the max RDA per serving is going to be high, but even then a food with 6% sodium/serving with no added salt may be considered low compared to, say, nuts with added salt bringing them to 5%. It's a little bit of an an art you can't perform without sampling the flavors, too. EllenCT (talk) 05:30, 21 February 2020 (UTC)

Read the Nutrition Facts labels. It is not only a matter of the amount of fat, but also the kind of fat. Some fat is essential to staying healthy, but it is best to drastically limit the consumption of saturated fat and trans fat. Assuming a person who consumes 1.5 kilograms (3.3 lb) per day, the Reference Daily Intake for sodium of 2300 mg per day translates to about 0.15% by weight, which is 150 mg per 100 g (say 45 mg per oz) of consumed food. This is an average value, not a ceiling. See also Wikipedia:Reference desk/Archives/Miscellaneous/2020 January 25#Convenience food.  --Lambiam 09:47, 21 February 2020 (UTC)

Probably the same OP as this one. ←Baseball Bugs ^{What's up, Doc?} carrots→ 10:11, 21 February 2020 (UTC)

Cite medical advice, don't give it directly.
The following discussion has been closed. Please do not modify it.
People should also realize that the "scientific" recommendations, except for trans fats are still in dispute. The recommendations assumed above were an omnipresent orthodoxy during the end of the last century. But I would say that the critics of it are a slowly growing minority and are correct. Demonization of salt, (saturated) fats, cholesterol etc is based on entrenched but imho appallingly bad research, that frequently assumes the truth of these deficient hypotheses and contorts evidence to fit them. Fats should not necessarily, or usually, be avoided as unhealthy and a healthy and sometimes near mandatory diet can be high - 70+% of calories from fat. Saturated fats are if anything healthy for the heart and healthy in general, better than polyunsaturated. If anything, people consume too little salt/sodium, especially in hot climates and in light of warming climates. Salt is absolutely essential; the low salt craze is the most immediately perilous recommendation, all based on a small purported effect on blood pressure whose very existence is dubious and variable. On the other hand the dietary orthodoxy greatly downplayed the danger of sugar (and other carbohydrates, especially in excess, especially in a low fat diet) - appallingly so for diabetics, but also for those with metabolic syndrome etc. An interesting and indisputable facet is the rewriting and falsification of history implicit in dietary orthodoxy. Novel dietary ingredients like refined sugar and polyunsaturated vegetable oils are treated as if people had been consuming them forever, while saturated fats and salt which had been consumed throughout (pre)history, often in higher amounts than today (esp for salt) are falsely claimed to be newcomers.John Z (talk) 08:44, 22 February 2020 (UTC) @John Z: that is quite a lot of direct medical advice, which is not allowed here, but quite a bit more disturbingly is contrary to the MEDRS sources in our articles such as Salt and cardiovascular disease. What are the sources in support of your assertions? EllenCT (talk) 00:09, 23 February 2020 (UTC) A simple rule of thumb is that if you are doing this right, then the volume of food you should be consuming should be large. The calorie density of fat is huge and that of refined carbs such as sugar is a bit less but this extremely large compared to what you can get from unrefined foods. Eating unrefined foods means eating a few kg of food per day, containing about 100 grams of fiber a day or even more. Indigenous populations who eat this way are almost totally free of heart disease. They have low levels of atherosclerosis, while people who eat the high fat, low volume Western-style diet have high levels of atherosclerosis. While about 25% of the Western population will end up dying from a heart attack or a stroke, almost 100% of people aged 40 or more have atherosclerosis at levels that are unusually high compared to the indigenous people who eat 100 grams of fiber a day. The Western medical philosophy is to accept that people are going to eat a high fat, low fiber diet and to try to prevent people from eating a diet that's even worse than the standard Western diet. The goal is then to try to coach people into eating a small amount of vegetables every day, to try to increase their fiber intake toward 40 grams a day instead of the 15 grams a day average. While such efforts can have a significant impact, e.g. the Mediterranean diet lowers cardiovascular mortality by 30%, this is far from eliminating the risk altogether. Thing is that eating a few kg worth of food every day to get to your, say, 2500 Kcal from unrefined low fat foods can require a few years of gradual adaptation of your diet. Just like most other healthy lifestyle habits it's a matter of "use it or lose it", and once you've lost it, you need to spend a great deal of effort to regain it. There is no way you can start to run an hour a day if you're a couch potato. Similarly, there is no way you can start to eat a truly healthy diet containing 100 grams of fiber a day starting tomorrow, if you're used to getting just 15 grams of fiber a day. You'll get severe stomach problems if you try to do that. Count Iblis (talk) 18:36, 22 February 2020 (UTC) @Count Iblis: again with the direct medical advice, sheesh! I know you know better than to do that here. If you're so sure, link to the MEDRS sources that say it; that's far more convincing and not a blatant flouting of the RD rules. EllenCT (talk) 00:15, 23 February 2020 (UTC)

Glass moon

If the moon was made entirely of glass, what would it look like? Would it be transparent enough that the sun would be visible through it during eclipses?

More generally, what would the "geophysics" of a glass planet be like, e.g. would there be an equivalent of tectonic plates, volcanoes, etc? 188.74.64.13 (talk) 09:14, 21 February 2020 (UTC)

Most natural glass is quite dark, and much is black. Don't expect that Sun could shine through. Even for very pure artificial glass used in optic fibres, you will be lucky to get much light through 100km. Over the aeons you can expect that it will crystallise. Meteoroids would still smash up the surface and put white powder everywhere. It would form material similar to the crust. What would happen would depend on how the glass got to be there. If it fell into place it would be hot and molten to start with. Graeme Bartlett (talk) 09:39, 21 February 2020 (UTC)

The lowest attenuation coefficient for optical fiber listed on this page of the Fiber Optic Association is 0.2 dB/km. The diameter of the Moon is about 3,476.28 km. If we drill a hole through the centre and pull a topnotch-quality optical fibre cable through – a lot cheaper than reproducing the Moon entirely in high-quality optical glass – the attenuation will be 3476.28 × 0.2 dB = 695.256 dB, or, as a fraction, 0.1^69.5256 = 0.2981×10⁻⁶⁹. The total number of photons output by the Sun in a second is less than 2×10⁴⁵. If we could somehow Death Star-wise focus all of that output on the far-side entrance of the Moon-piercing cable – but without instantly blowing up the Moon – we should expect to have to wait more than 7 petayears before even one photon gets through to the other end. But the solar system will be gone by then.  --Lambiam 10:51, 21 February 2020 (UTC)

To refine the question a little bit - what happens to an enormous ball of quartz (glass) when it's subjected to extraordinary pressure due to its own gravitation because it is so huge that it is the size of an entire moon?

Well, the thing is - we really don't know: planet-sized objects have a lot of mass, and therefore the materials in the inside are under a lot of pressure - and we probably can't come anywhere close to those levels in laboratories. But what we do know is that quartz (which I'm using as sort of a spherical cow model of common every-day window glass) will undergo a series of phase transitions; the physical properties like melting-point will change; and the phase-change also affects its optical properties (index of refraction; imperfections relating to polarization and birefringence, and so on).

Quoting Shen, Bassett, and Chou (1993), "Even though this transition has been studied extensively, there remains considerable disagreement..." among experts who have tried to create such high-pressure conditions in the laboratory. And their equipment doesn't even attempt to simulate the heat and pressure conditions at even the marginally deep interior of a large moon-sized mass! I think we can truthfully say that the best scientific minds do not really have the information to make precise predictions about the optical properties of such a massive mass of glass.

Tackling this from another angle - how could such a huge ball of silicon and oxygen form, in the first place - and in this ratio, and in this specific chemical configuration, and in an undifferentiated state? Would it, could it, remain chemically intact over the billions of years that planets tend to last? How could the ordinary forces of gravity not cause it to do something different - something more normal - something more like what we actually see in every planet that we have ever seen, studied, or theoretically-modeled? Is there any plausible method to explain why it would form a glass, instead of forming the much more common bulk silicate (silicon/oxygen) materials that we normally find in chondrites - those clumps of mostly-non-metallic matter that float around in solar systems like ours? After all, even though there is silicon and oxygen in great abundance in our universe, the most common types of rocks that float around in space near us seem to indicate that they combine in a different, non-glassy way - in the form of silicate minerals.

Nimur (talk) 16:55, 21 February 2020 (UTC)

Sure, we don't know the detailed optical characteristics of a bit of glass in the interior, but as Lambiam points out, we do know that no measurable amount of light is going to get through the bulk of the Moon optically (as opposed to thermally). I wouldn't be surprised if there were some interesting visible effects on the limbs of the Moon; these could probably be simulated if anyone wanted to put in the effort, and we wouldn't have to speculate much at all about the properties of the glass, because only fairly shallow levels would contribute. --Trovatore (talk) 07:52, 22 February 2020 (UTC)

Since we're discussing a purely hypothetical question, I suggest you hypothesize that God exists and created it that way. --69.159.8.46 (talk) 20:14, 21 February 2020 (UTC)

Yeah, my question was inspired by thought experiments like a mole of moles and Earth turning into blueberries: given this bizarre and probably impossible situation, what would happen according to our understanding of physics? Thanks for the replies so far! 188.74.64.13 (talk) 20:52, 21 February 2020 (UTC)

You did not specify what you mean by glass? Definitions vary but generally glass is a mixture of oxides which may or may be not transparent. However this is exactly the composition of the Earth's crust and mantle. So in a way the Earth is already made of glass. Ruslik_Zero 07:51, 22 February 2020 (UTC)

In the broad sense of the word, a glass is more a phase of matter than any particular chemical composition. Its defining feature is disorder, combined with a solid-like tendency to hold its shape. See glass transition for more information. A spinglass is a bit more abstract, but still a "glass" in the broadest sense. --Trovatore (talk) 09:12, 22 February 2020 (UTC)

Everyday "glass" is just silicon dioxide—"sand"—formed so it's transparent. In a realistic scenario, once you gather moon-sized quantities of anything, the "anything" self-gravitates and collapses into a sphere. This is how all stars, planets, etc. form. Said gravitational collapse converts the gravitational potential energy of the matter into heat (see gravitational compression). For something moon-sized, this is enough to melt most materials, so now you have a molten ball of silicon dioxide. Gradually, it radiates heat into space and freezes from the outside in. Again, this is exactly what happened to the Earth and Moon. To get transparent glass you have to cool the material in a controlled fashion. The whole crust doesn't cool at once, so instead you get a quartz crust. Also, the Moon's core is much like Earth's: a molten outer core and a solid but very hot inner core. If the crust were somehow totally transparent, the core would glow from incandescence, just as lava does. Cool related fact: Jupiter actually radiates more energy than it receives from the Sun, though this is mostly in infrared. (Its glow in our night sky is reflected sunlight.)

There would be no plate tectonics because plate tectonics requires water to lubricate the crust. In the absence of water, you get a single-plate lithosphere. See Earth's internal heat budget for related discussion. So, there would be volcanoes. As others have noted, silicon dioxide is the most common chemical in Earth's crust, so things don't behave all that differently from Earth, apart from the lack of water and atmosphere. Venus is worth comparing, as it's often considered "Earth's twin", except that it lost all its water from a runaway greenhouse effect. The thing to realize is our intuition is equipped to get us through everyday life. You were probably thinking of a ball of glass, but really big! But things at astronomical scales behave very differently: gravity becomes the main force shaping things, and the energies involved are way larger. --47.146.63.87 (talk) 11:42, 22 February 2020 (UTC)

thank you for this response! I was wondering if the planet could end up with a glowing core shining through a translucent crust. 188.74.64.13 (talk) 12:45, 22 February 2020 (UTC)

Per Lambiam's argument, basically not, unless it's hot enough that the glowing layer is quite close to the surface. --Trovatore (talk) 21:13, 22 February 2020 (UTC)

We also have an article called red heat which is about the visible red glow of a hot object; ... but in the context of infrared astronomy, every object in the universe is glowing hot. Some objects are exactly the right temperature to glow red - or to emit some portion of their glow in the visible-light spectrum; others are too cold or too hot, and more of the glow gets emitted at different wavelengths. The exact color - or more precisely, the exact spectrum of emitted wavelengths of light - will depend on the temperature of the object - that's blackbody radiation, and it's very well-understood. And of course, many objects are "imperfect" black-body emitters - they have material properties that modulate, filter, or augment the spectrum of energy that they emit. Astronomers are also really familiar with the weird physics of a photosphere: an outer layer that dominates the emitted energy that can be observed by an outside viewer. The opaqueness or transparency of an object's outer surface can mean that the blackbody "glow" from its inside parts doesn't necessarily make it all the way to the outside. All this relates right back to the differentiation of the object into layers, under its own self-gravitation. Nimur (talk) 18:18, 24 February 2020 (UTC)