Wikipedia:Reference desk/Archives/Science/2017 June 3

= June 3 =

7-9 hours of sleep
It is usually recommended that a human needs 7-9 hours of sleep. Does this mean 7-9 hours of continuous sleep or sleep whenever one finds the time? Maybe a human begins sleep at 10:00 pm on the ground floor and wakes up at 1:00 am (but just half-awake) and ascends the stairs to the second floor to continue sleeping until 6:00 am because the ground floor is naturally cooler than the upper floor. Or maybe the person sleeps for five hours at night continuously, but in the afternoon, the person falls asleep for about two to three hours. What counts as healthy sleep? 50.4.236.254 (talk) 05:12, 3 June 2017 (UTC)
 * I think you can sleep when you want without any problems. Ruslik_ Zero 10:37, 3 June 2017 (UTC)
 * Basically, anything which leaves you not feeling tired when you wake up counts as healthy sleep. That will vary greatly from person to person. Wymspen (talk) 11:17, 3 June 2017 (UTC)
 * See the main article Sleep. A person's desire and ability to fall asleep is influenced both by the length of time since the person woke from an adequate sleep and by internal Circadian rhythms, which cause harmful psychological and functional difficulties when disordered. See Sleep deprivation. Blooteuth (talk) 11:32, 3 June 2017 (UTC)


 * There are clear indications of segmented sleep throughout history. See siesta, second sleep if they're not in that. Wnt (talk) 12:44, 3 June 2017 (UTC)
 * Also polyphasic sleep may be of interest. SemanticMantis (talk) 15:45, 3 June 2017 (UTC)


 * See here: "Though the San, Tsimane, and Hadza often average less than seven hours of sleep, they seem to be getting enough sleep. They seldom nap, and they don’t have trouble dozing off. The San and Tsimane languages have no word for insomnia, and when researchers tried to explain it to them, “they still don’t seem to quite understand,” Siegel says." Count Iblis (talk) 19:04, 3 June 2017 (UTC)
 * I'd want to see that in a detailed peer reviewed format. The study was done via electronic devices ... I don't know how reliable they are nor what hijinks might have amused the participants. Wnt (talk) 18:41, 7 June 2017 (UTC)

Not chewing food
Chewing food is an important step in the digestive process. If a hypothetical "average person" did not chew any of their food and instead cut it into small pieces and swallowed them whole, what would be the likely effect on their digestive system?

Would it take longer for the body to digest the food? Would the body actually manage to digest all the food fully?

My understanding is that simple sugars and carbohydrates like bread would probably be fully digested, but other foods might not be. What foods would be the most difficult for the body to digest if they were not chewed before being swallowed? Links to research papers on the subject would be great.

Thanks for your time and help. — Preceding unsigned comment added by 182.253.44.86 (talk) 07:56, 3 June 2017 (UTC)
 * See Mastication. A study found that unchewed meat and vegetables were not digested, while tallow, cheese, fish, eggs, and grains did not need to be chewed. . Blooteuth (talk) 11:35, 3 June 2017 (UTC)


 * The reason for chewing (beyond avoiding choking) is to break the food into smaller portions, thus increasing the surface area and hence chemical reaction rate. Thus, the more finely food is chewed, the more quickly it will be digested.  However, digesting food quickly is not always the goal.  In the case of sugars, for example, it's best to absorb them slowly, to avoid a blood sugar spike, followed by an insulin spike and blood sugar crash.  Consuming the sugar with lots of fiber helps to slow digestion.  For example, eating an orange versus drinking orange juice.  Other foods are already slow to digest, such as fats, so there is no need to slow the process further. StuRat (talk) 17:18, 3 June 2017 (UTC)

Sump pump versus expandable hose
I noticed that the same sump pump which produces a torrent of water when used with a traditional hard-walled garden hose only produces a dribble when used with an expandable hose with end nozzles of the same diameter. Is this a known problem ? If so, what's the cause, increased back pressure from the hose to the pump, impeding it's efficiency ? StuRat (talk) 17:58, 3 June 2017 (UTC)


 * Standard US water pressure is 45 to 55 psi. Sump pumps typically put out less that 10 psi. The expandable hose needs a certain pressure to expand it. --Guy Macon (talk) 19:14, 3 June 2017 (UTC)


 * Thanks. Any idea how much pressure they need and how much a sump pump provides ? StuRat (talk) 14:58, 5 June 2017 (UTC)
 * Its likely build as Centrifugal pump and does not generate much pressure at all. Its not build for pressure but to pump up everything that gets near its vortex disc, including mud, branches, leafes etc. Pumps that generate (more) pressure would choke, block, jam or brake when feed with all that stuff a sump pump is meant to take. If you want pressure, get another kind of pump. --Kharon (talk) 01:24, 6 June 2017 (UTC)

Dancing Black Holes
I open up the Wikipedia science desk today hoping to see something about the two black holes that just merged. Instead people are preoccupied with denying the climate change and stuffing beans in their noses, it seems. I first became aware of the event when I opened the WSJ yesterday, the link is just a subscription page with the first paragraph of the article. There is however a statement there that puzzles me. When the black holes merged "...they joined in a violent embrace. In an explosive third of a second, they released the combined energy of two stars--more energy in that instant than from all light from all the galaxies in the Universe, the scientists said." Does it mean that the gravitational energy released was larger than the all radiation emitted by all stars in the Universe? Also which Universe? Visible Universe or the "whole" universe? Does the WSJ statement imply that the universe is limited in size? The event is also discussed in Astronomy Magazine and in Physical Review one can find the original article. here is the abstract

I have questions.

So far three mergers have been detected, all conveniently very far away, however the black holes are suspected to litter nearby universe. There is a giant black hole in the center of our Galaxy and some mergers must have occurred in the not so distant past. How come we do not register nearby collisions?

It is probable that in the past something like this happened very close to the Solar System. The "fabric of space" had been violently ripped, stretched and compressed. How did it affect out Mother Earth? Perhaps 500 million years ago?

What if an even like this happens not far away in the future. After all the black holes that merged were not that large. There are stars much larger still. How would it affect the civilization if it happens in the next hundred years, for instance?

Thanks, --AboutFace 22 (talk) 19:34, 3 June 2017 (UTC)
 * I'm going to shamelessly glom on to one small part of your question. When articles talk about the "universe" in this sort of way, they almost always mean (or at least almost always should mean) the observable universe.
 * WSJ is a fine paper but its science writers are probably not actually scientists, so who knows whether the writer thought the entire universe was intended. But in any case the universe is not known to be finite, and may well have infinitely many galaxies, in which case obviously the statement would not be true with regard to the whole universe. --Trovatore (talk) 19:44, 3 June 2017 (UTC)
 * To address a different part of the question, I'm curious why you think it's "probable" that it has happened "very close to the Solar System". Have you made an actual calculation?  --Trovatore (talk) 20:26, 3 June 2017 (UTC)


 * And regarding some other parts: this blog from a LIGO scientist says that a nearby (in cosmic terms) black hole collision event would rip you apart in an entertaining fashion. Our binary black hole article discusses the situations which lead to these mergers; the section on the final parsec problem explains that we don't yet know why the mergers are able to take place, so estimating how common they are is not yet possible. HenryFlower 21:01, 3 June 2017 (UTC)


 * To give a back of the envelope kind of estimate, we've seen 3 events at distances up to ~900 Mpc in about 16 months. There are roughly 600 billion galaxies in the universe, of which ~20 million are within ~900 Mpc.  This suggests we expect roughly 1 similar merger event per galaxy per 10 million years.  Not sure how close one has to be to the event to register it locally, but I suspect that only a small fraction of mergers in our galaxy would be close enough to disrupt the Earth.  Dragons flight (talk) 21:44, 3 June 2017 (UTC)


 * It's possible as as pointed out here that these massive black holes whose mergers are now detected, constitute most of the dark matter. Then as pointed out in the article, in dense regions the rate of mergers could be as high as 700 per cubic gigaparsec per year. At that rate the expected distance to the nearest such event in a 5 billion year period would be about 200,000 lightyears. Count Iblis (talk) 21:23, 3 June 2017 (UTC)


 * Just in case it's not obvious, if you look at 2 regions of space, both centered on Earth but one 1000 times the diameter of the other, the larger will have a volume of 10003, or a billion times as much, and thus, if we assume equal distributions of black holes, black hole mergers will happen a billion times more often in the larger region. So, the geometry implies that nearby black hole mergers (in the smaller region) would indeed be relatively rare. StuRat (talk) 21:46, 3 June 2017 (UTC)


 * When you say "just merged" I assume you mean "just [recently] detected", as the actual event took place about 3 billion years ago, right? ←Baseball Bugs What's up, Doc? carrots→ 22:42, 3 June 2017 (UTC)


 * Just merging is forbidden by the laws of physics. However it is common in astronomy to say things like the event happened in 2015 even if it was astronomical BC. Sagittarian Milky Way (talk) 22:59, 3 June 2017 (UTC)


 * i.e. GRB 080916C (Gamma Ray Burst, 2008 09/16, 3rd burst of the day) Actual day: 12 billion BC. Sagittarian Milky Way (talk) 23:06, 3 June 2017 (UTC)

For us it happened yesterday, or actually on Feb 3, 2017 I think. That's when the event was detected.--AboutFace 22 (talk) 00:31, 4 June 2017 (UTC)


 * Simultaneity is variable in special relativity. The event entered our light cone at that date, which is one valid definition for the phrase 'when it happened'.  In the frame of reference of the arriving gravity wave, I think it was emitted and detected at the same moment. Wnt (talk) 20:08, 6 June 2017 (UTC)

X-ray image
What exactly is that halved circle with arrows supposed to be?--Erdic (talk) 23:12, 3 June 2017 (UTC)
 * A cursor.-- Jayron 32 01:50, 4 June 2017 (UTC)


 * Specifically, that is the brightness/contrast cursor. When it is on, you adjust the brightness and contrast with the control (a mouse or wheel). On the machine I use, moving up increases contrast. Moving down decreases contrast. Moving right increases brightness. Moving left decreases brightness. 209.149.113.5 (talk) 12:58, 5 June 2017 (UTC)


 * Thank you both very much!--Erdic (talk) 23:00, 5 June 2017 (UTC)