Wikipedia:Reference desk/Archives/Science/2022 April 26

Welcome to the Wikipedia Science Reference Desk Archives
The page you are currently viewing is a transcluded archive page. While you can leave answers for any questions shown below, please ask new questions on one of the current reference desk pages.

April 26

Is there a symbol for the "age" of something (e.g. age of the Universe, age of the Earth etc.)?

Hi everyone!

I was searching for scientific articles on the ages of certain things because I am a boring person with boring interests, such as the Earth and the oldest human fossil that we currently know of. However, I noticed that across these articles, there was no symbol for the age of the object in question. For example, the Planck 2018 results and this paper from Nature just give the ages of the Universe and some zircon crystals in Jack Hills, respectively, as "Age".

So far, I haven't been able to find any "official" source (e.g. IUPAC Gold Book, IUPAP Red Book) that gives an explicit symbol for the age of an object. Does anyone know if there is a symbol for this quantity, and, if so, the source (preferably from a well-known scientific body such as the IUPAC or IAU)?

Thanks :) — MeasureWell (talk) 02:44, 26 April 2022 (UTC)

The abbreviation "BP" (years Before Present) is sometimes used in archaeology or geology to indicate a number of years before the introduction of radiocarbon dating, nominally 1 January 1950. Philvoids (talk) 05:07, 26 April 2022 (UTC)

There are no symbols for height, weight or temperature either. Very few concepts that can easily be expressed as a word have a dedicated symbol. The diameter symbol ⌀ and cartographic symbols owe their existence to the use on drawings and maps.  --Lambiam 07:22, 26 April 2022 (UTC)

@Lambiam: Right, I was a bit unclear with the question, sorry about that. Let me clarify myself here: to take your example, according to the IUPAC Green Book and the IUPAP Red Book, the symbols for height, weight, and temperature are $h$, $G$ ($W$ and $P$ are also listed in brackets), and $T$, respectively. My question is this: is there an analogous symbol for the age of something (e.g. the Universe)? Thanks for the relatively quick response, and I hope this clears things up a bit. — MeasureWell (talk) 07:38, 26 April 2022 (UTC)

I see the present age of the universe most often represented by $t_{0}$ (e.g. here in Eq. 5.63). But that is at best an informal convention, and obviously $t_{0}$ can represent other things in different contexts. --Wrongfilter (talk) 08:13, 26 April 2022 (UTC)

@Wrongfilter: I do recall seeing that in the Review of Particle Physics ("Astrophysical Constants and Parameters") as well, actually, so I agree with you there. Still, my question (which is, admittedly, very difficult to answer) somewhat remains: is there an "officially recommended" symbol for this, or for the age of something in general? (If there is, I'm quite sure both of us would agree that it could do with being significantly easier to find ;) )

Thanks for the reply anyway – if worst goes to worst, I suppose that $t$ itself could work as a symbol. (I'm not planning to publish an article in a journal or anything, so its fine.)

long live $t_{\mathrm {E} }$ as the new symbol for the age of the Earth — MeasureWell (talk) 08:31, 26 April 2022 (UTC)

There is a unit: annum multiplied to megaannum or gigaannum with symbols Ma and Ga. Could also be yra Graeme Bartlett (talk) 07:24, 26 April 2022 (UTC)

Does eating snow dehydrate us?

Regarding an emergency with a person lost in the woods: I assume it might not be the best choice, since one is also trying to fight hypothermia, but would eating snow dehydrate us? The only plausible explanation to the common advice not to eat snow since it dehydrates the body is that using calories would make us also release water (maybe through breathing more heavily) --Bumptump (talk) 22:23, 26 April 2022 (UTC)

The main thing I've heard is not to eat yellow snow. A quick web search about dehydration from eating snow finds lots of hits with conflicting info, so I'm going to stay away from answering that one. But, if you have the means and fuel to melt the snow, getting water that way should be fine. 2601:648:8202:350:0:0:0:4671 (talk) 02:13, 27 April 2022 (UTC)

This is probably a confusion with Seawater#Human_consumption. Our article drinking says that In cold and frozen environments, some animals like hares, tree squirrels, and bighorn sheep resort to consuming snow and icicles. I don't know how those animals avoid freezing themselves in the effort to stay hydrated: calories and fur apparently suffice, but maybe they also need less water than humans - some animals can reduce water use (I forget how). In principle if a human is making a net gain of water by using calories to melt it (and has a backpack full of pemmican) then getting water from ice and snow ought to be viable, but you'd have to keep pausing to warm up, and keep eating small amounts of snow all day while remaining thirsty, and ignore the temptation to eat it faster, which sounds really annoying.  Card Zero  (talk) 02:41, 27 April 2022 (UTC)

"Burning" fat releases H₂O (about 1 mol per 150 kCal), which thereby becomes available to the body, so using calories hydrates us.  --Lambiam 05:34, 27 April 2022 (UTC)

Insignificantly so. A mole of water is 18 grams. 150 kCal is about the amount of excess calories you'd burn running about 2.5 km (1.5ish miles) or so [1], and you sweat far much more than 18 grams of water in that time period. --Jayron32 10:52, 27 April 2022 (UTC)

But it debunks the supposition for "the only plausible explanation" that using calories (not for running but to melt ingested ice) dehydrates the body.  --Lambiam 20:57, 27 April 2022 (UTC)

Then don't run. If the weather is such that snow lies on the ground and you're not overdressed, you won't sweat significantly if you just stick to walking speed. Burning carbohydrates in a human body releases about half a litre of water per day with normal work. That may not be enough to survive, but it's not insignificant. PiusImpavidus (talk) 10:08, 28 April 2022 (UTC)

Still no. Even if you didn't sweat a drop, "you'd lose about 20ml of water per hour at below freezing temperatures, just by breathing. --Jayron32 15:24, 28 April 2022 (UTC)

Does burning fat to maintain body temperature increase the water content of exhaled breath? If not, this seems irrelevant to the issue at hand.  --Lambiam 07:54, 29 April 2022 (UTC)

Water is water. I don't see how consuming water could cause "dehydration", although too much snow and ice could indeed risk hypothermia. --←Baseball Bugs ^{What's up, Doc?} carrots→ 11:36, 27 April 2022 (UTC)

Melting 1 gramme of snow from freezing point and heating it to body temperature takes about 490J of energy. This energy comes from burning 0.17mmol of glucose, which takes 1.0mmol of oxygen. To absorb that oxygen from the air you have to breath about 20mmol of air, into which will evaporate about 1.0mmol of water vapour, weighing 18mg. So the extra breathing resulting from eating 1 gramme of snow will cost you only 18 milligrams of water. But you should eat it slowly, or you'll cool the blood running to your brain too much.

Or even better, burning 0.17mmol of glucose also releases 1.0mmol of water, compensating evaporation from the lungs. Burning glucose releases water and carbon dioxide in equal amounts (in mol) and the breath we exhale also has equal amounts of water vapour and carbon dioxide, so burning glucose doesn't affect the amount of water in the body as long as it doesn't cause sweating. PiusImpavidus (talk) 10:51, 28 April 2022 (UTC)

I had a look for a scientific paper on the subject, but only found:

• Is Snow a sufficient Source of Water for Horses kept Outdoors in Winter? which says: " in cold winter weather, horses being fed grass silage and adjusted to eat snow, can manage for several days with snow substituting liquid water without their physiology and welfare being challenged".

Alansplodge (talk) 18:08, 28 April 2022 (UTC)

Could the problem with snow be that it is basically distilled water, so very low in minerals? --195.62.160.60 (talk) 13:07, 29 April 2022 (UTC)

So is rainwater, but that doesn't make it dangerous. As long as you eat some minerals from some other source, the lack of minerals in the water is no problem. PiusImpavidus (talk) 10:07, 30 April 2022 (UTC)