Wikipedia:Reference desk/Archives/Science/2019 August 4

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August 4

Why isn't zero viscosity liquid helium a free lunch?

If you just put a stopper in a test tube of it before it climbs that high it will raise its center of gravity all by itself, if you stir it in a sealed container it will move forever like perpetual motion. If you were an alien with this on your planet you can do these things without having to spend energy to refrigerate it. Sagittarian Milky Way (talk) 12:50, 4 August 2019 (UTC)

You should write for a science fiction magazine. ←Baseball Bugs ^{What's up, Doc?} carrots→ 13:39, 4 August 2019 (UTC)

Superfluid helium-4 is our article. The effect of flowing up the sides of the test tube is just another form of a siphon, which, in the standard version, doesn't actually result in permanent movement of fluid, but only until it reaches the same level outside the tube as inside. Now, it may appear that you are "creating energy" during the phase where helium rises up the side, but, counter-intuitively, that is actually a lower energy state than when it's all at the bottom. For comparison, a spinning top (initially horizontal) that "stands up" is also moving to a lower energy state, even though the center of gravity is higher.

To examine this further, let's consider actually designing a way to collect energy from such a device, and see how it would fail. Let's start with a test tube precisely balanced about a horizontal shaft through the center, on which it can rotate. Make the test tube have an angled top so it goes higher on one side than the other. Put some of our "magic fluid" in the bottom, and put a cork in it. The fluid will rise up the sides, making it now top-heavy, so the test tube will flip over. You could extract a minute amount of energy from the shaft as it turns. Now, you may have been thinking that the fluid would then fall to the new "bottom", and then crawl up the sides again, to reverse the process and generate more energy. But no, there's still the same thin film on the sides from before, and no more will crawl up the sides. Well, how about that one-time energy source ? Can't we just repeat that process a billion times to get a sizable amount of energy ? No, because it will work out that it takes more energy to do the setup than you get out of it.

A modified approach might be to raise the temperature to where the superfluidity is lost, and the helium all drops to the bottom, then lower the temperature until it regains superfluidity, and climbs up the sides and flips the test tube over again. Unfortunately, the inefficiency in changing the temp will result in more energy cost than the gain (we could even figure out the theoretical limit on the efficiency based on "not being able to get a free lunch", although this wouldn't tell us the specific reasons). SinisterLefty (talk) 16:16, 4 August 2019 (UTC)

Shorter version: superfluid helium crawling up the walls does gain gravitational energy, but that's at the expense of surface tension energy - un-sticking it from the walls would cost more than you can extract from its weight. Tigraan^{Click here to contact me} 08:35, 7 August 2019 (UTC)

Yes, gravitational potential energy. SinisterLefty (talk) 15:04, 8 August 2019 (UTC)

Killing mosquitos

I heard a story on NPR Weekend Edition saying that mosquitos are considered useless and an effort is under way to find a way to make them extinct so they will not spread disease. Where would this go on Wikipedia, if anywhere?— Vchimpanzee • talk • contributions • 17:45, 4 August 2019 (UTC)

Mosquito eradication is currently a redirect to Mosquito_control#Proposals_to_eradicate_mosquitoes, but if it became more than a proposal, then an article under that name would make sense. However, if deaths from malaria decrease in an area already at the carrying capacity for humans, you can predict more wars over scarce resources and deaths from famine and other diseases, so it may not be the benefit to humanity one might expect. SinisterLefty (talk) 18:14, 4 August 2019 (UTC)

A (fairly macabre) discussion about population control in third-world countries has zero relevance to the question asked. TigraanClick here to contact me 08:32, 7 August 2019 (UTC)

The number of death is just always equal to the number of birth, no mater what. Carrying capacity doesn't apply to humans, we just kill everything else between and food if need be, and currently we basically make food out of fuel and ship it all over the world, and anyway. Gem fr (talk) 20:49, 4 August 2019 (UTC) Who do you know that eats petroleum? ←Baseball Bugs What's up, Doc? carrots→ 21:05, 4 August 2019 (UTC) Gem refers to using petroleum to farm areas that wouldn't be farmable naturally, by using petroleum-based fertilizers, burning petroleum to pump water there, using petroleum-based pesticides, and using petroleum to run tractors, combines, etc. SinisterLefty (talk) 23:01, 4 August 2019 (UTC) this. Gem fr (talk) 09:48, 5 August 2019 (UTC) In many parts of Africa, where the malaria risk is highest, they are at the carrying capacity now, and frequently do have famines. SinisterLefty (talk) 23:01, 4 August 2019 (UTC) Famines occurs because of political strife and war and broken logistics impeding the flow of humans and food, not because exceeding carrying capacity. Most humans live in cities because we can flow food from all over the world to those massively over carrying capacity place. Only a handful of nation are net exporting food (America, Australia, a few more) while most of the world depend on them. Gem fr (talk) 09:48, 5 August 2019 (UTC) Importing food requires money, and thus those living in extreme poverty must rely on subsistence agriculture, which very much depends on the carrying capacity of the area. There is a nexus with war, in that an existing famine can be made worse by war, either unintentionally or through intentional starvation of enemies, but there are also famines unrelated to war. And, as I had noted, wars are often started over competition for scarce resources caused by overpopulation. In short, any program to wipe out a disease should be accompanied by a birth control campaign, to avoid such nasty side effects. SinisterLefty (talk) 10:44, 5 August 2019 (UTC) That sounds like an argument for eugenics. ←Baseball Bugs What's up, Doc? carrots→ 13:45, 6 August 2019 (UTC) If so, then all birth control is eugenics. The goal is just to keep the population at a sustainable level. SinisterLefty (talk) 19:13, 6 August 2019 (UTC) It's only eugenics if it's forced upon you. A better goal would be to improve the lives of the populace, rather than taking the "there's no hope" attitude. ←Baseball Bugs What's up, Doc? carrots→ 19:23, 6 August 2019 (UTC) Eliminating mosquito-borne diseases and providing free birth control would improve their lives, but instantly making the area as rich as Europe and the US is unrealiastic. SinisterLefty (talk) 20:18, 6 August 2019 (UTC) If at first you don't spell right, try, try again. ←Baseball Bugs What's up, Doc? carrots→ 20:37, 6 August 2019 (UTC) If you think you can, you can; if you think you can't - you're right. ←Baseball Bugs What's up, Doc? carrots→ 20:23, 6 August 2019 (UTC) Well, you could, but it would cost several trillion dollars. Let's see, an additional 10% income tax on everyone in the developed world would do it. Think that idea will go over with the voters ? SinisterLefty (talk) 20:58, 6 August 2019 (UTC) How much do we spend on killing machines right now? ←Baseball Bugs What's up, Doc? carrots→ 12:48, 7 August 2019 (UTC)

Also, there is no serious effort to make mosquitoes "extinct" (the effort required there would be superhuman), nor is it true that they are useless. I don't know what passes for journalism on NPR these days, but the person who said that was either engaging in hyperbole, was joking, or was an idiot. Or, maybe you misheard. Matt Deres (talk) 23:08, 4 August 2019 (UTC)

Matt, our article says that there are a few mosquito species which some scientists have proposed making extinct. It would only be some 1% of the species, though. See https://www.sciencenews.org/article/mosquito-extermination-top-science-stories-2018-yir. Combining this genetic attack with more conventional methods may be the most effective approach. SinisterLefty (talk) 02:04, 5 August 2019 (UTC)

Aren't mosquitoes part of the food chain? ←Baseball Bugs ^{What's up, Doc?} carrots→ 00:12, 5 August 2019 (UTC)

Yes, but they would be replaced by others. Most likely other species of mosquitos would fill that niche. SinisterLefty (talk) 02:04, 5 August 2019 (UTC)

A History Of The Mosquito, 'Our Deadliest Predator' (Audio & Transcript; NPR Weekend Edition Sunday; NPR's Lulu Garcia-Navarro speaks to author Timothy C. Winegard about his new book about the mosquito.) -- ToE 00:24, 5 August 2019 (UTC)

"Predator" seems wrong. "Parasite" would be the right word.SinisterLefty (talk) 02:06, 5 August 2019 (UTC)

While the phrasing seems odd to most laymen, it is generally considered correct in biology. As the mosquito does not "live on or in" its victim, it is not a true parasite. It simply wanders by and takes a bite out of you. --Khajidha (talk) 17:41, 5 August 2019 (UTC)

Blackflies take a bite out of you, while mosquitoes inject disease-infected blood thinner and then suck out blood. And doesn't a predator have to kill and eat the prey, as our article says on the first line ? SinisterLefty (talk) 18:40, 5 August 2019 (UTC)

Okay, my phrasing of "take a bite out of you" was a little loose. Mosquitoes best fit under the term "micropredator", which our articles cover as a sub-type under parasitism, but I've usually encountered as a sub-type of predation. --Khajidha (talk) 20:00, 5 August 2019 (UTC)

Humans are no good either "We argue that the Anthropocene will more likely resemble the End-Permian and End-Cretaceous catastrophes, rather than the PETM." Count Iblis (talk) 03:47, 5 August 2019 (UTC)

Health measures during the construction of the Panama Canal is a relevant article, since both mosquito-borne malaria and yellow fever were eventually eliminated, and they lacked our modern tools. So, eliminating malaria in Africa may well be possible, either by eliminating the mosquitoes, or by reducing their numbers dramatically. SinisterLefty (talk) 11:27, 5 August 2019 (UTC)

Draining swamps and wetlands is likely to get a lot more pushback today then it did then, although it's happening anyway mostly for other reasons. Nil Einne (talk) 15:16, 5 August 2019 (UTC)

Not so much in the developing world, where swamps and the endemic diseases associated with them are not nearly as popular as to environmentalists in a nice comfortable city. In other words, it's a NIMBY issue. They could argue that "If you like swamps so much, why don't you return Florida entirely to a natural swamp-filled state." SinisterLefty (talk) 16:14, 5 August 2019 (UTC)

BTW, our article could probably make it clearer that many current proposals involve using Gene drive techniques. The portion on knockouts isn't particularly clear. I'm also not sure if the see also link to Extinction#Proposed is that useful as the info seems to be the same as in the mosquito article and frankly it makes more sense that it will have the same or more info. If anything, the extinction article should link to the mosquito article as the primary article. (Yes I know technically I should fix it or mention the talk page, but I can't be bothered fixing it myself at this time and suspect a comment on the the article talk page will just be ignored but people here seem interested. If further discussion is needed I do suggest it's on the article talk page.) Nil Einne (talk) 15:32, 5 August 2019 (UTC)

Looking to the future, there could be campaigns to eliminate other human parasites, so the extinction article may be the best place for the overview, with links to specific proposals or projects in other articles. SinisterLefty (talk) 16:19, 5 August 2019 (UTC)