Wikipedia:Reference desk/Archives/Science/2015 April 19

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April 19

Effect of varying dark matter density on the Solar System

Probably not the Milky Way, but still...

There are now lots of deductions and cute images that dark matter concentration can vary on a galactic scale. The Milky Way is said to actually be warped by dark matter effects from the Magellanic Clouds. I remember reading claims that the Milky Way had absorbed a satellite galaxy more recently than the initial mergers 10 billion years ago [1] but I don't know if they hold up, but any such collision could have created changes in dark matter density.

So my question is: assuming dark matter is homogeneous on the scale of the Solar System, what effects would changes in its density have on the Solar System? For example, would planets change their orbits to any measurable degree? Especially, would the Sun's brightness vary during its 240-million year orbit of the galaxy, due to the extra mass pulling it together more?

On that note I should also ask whether it's possible for the Sun to capture sterile neutrinos - can they collide with nuclei in the Sun and occasionally end up moving too slowly to escape its gravity? Wnt (talk) 11:42, 19 April 2015 (UTC)

Dark matter will be captured by the solar system. Even if it only interacts gravitationally, n-body scattering processes will cause some of it to be captured. If it interacts via the weak force or any other process, then more will be captured. This article [2] discusses work estimating the dark matter density in the solar system at 16,000 times background, which would total roughly 1/50000 of an Earth mass. That amount of dark matter would not be sufficient to have significant observable consequences. For scale, that is roughly the same amount of mass that the sun blows into space via the solar wind every 2000 years. In other words, it would be largely negligible compared to other dynamical processes. Dragons flight (talk) 16:29, 19 April 2015 (UTC)

This is a good reference (original) but I feel like it's oddly limited. After all, the Solar System started out as a giant molecular cloud forming a protostar and protoplanetary disk; the latter looks sort of a little galaxy-like, so might it not contain some dark matter? (I suppose there are likely good Doppler readings to limit how much pretty stingily, though) I would think that if it is possible for dark matter particles to exist, and to move slowly enough to interact in a three-body way with planets, they might also get caught up in a collapsing dust cloud? Also, besides any potential weak force, our article on sterile neutrinos says that they can have Yukawa interactions with ordinary leptons. It's a pity I don't understand a syllable of the article about Yukawa interactions... may have to go back and review my alphabet if I look at it again. If they do interact, I don't know how fast thermal energy from hitting something deep in the sun would send them flying. So I'm still a bit unsure what the answer is. The most meaningful answer in the ppaer is that dark matter should show up in precession of orbits that isn't observed. This inevitably leaves open the possibility that there's just enough dark matter to make orbits precess if the density gets greater at some point, or just enough that we failed to detect it by random chance, but that's a pretty weak broth to base any interesting speculations on. Wnt (talk) 19:22, 19 April 2015 (UTC)

I don't understand your complaint about the paper. The early solar system would indeed have accrued dark matter, but probably at a similar rate to the later solar system, and the formation of the solar system was only a small fraction of its history, so the contribution would be correspondingly small.

Yukawa couplings are three-way couplings between two fermion fields and the Higgs field (or any spin-0 field, but the Higgs field in this case). At ordinary energies you can ignore the Higgs field and think of it as a direct coupling between the two fermion fields—in this case, between left-handed ordinary neutrinos and right-handed sterile neutrinos and between right-handed ordinary antineutrinos and left-handed sterile antineutrinos. This is the only (nongravitational) direct coupling between sterile neutrinos and anything else. Ordinary neutrinos already barely interact with baryonic matter (nucleons and electrons) and sterile neutrinos would interact (nongravitationally) even less, because they're one more degree of separation away from baryonic matter. -- BenRG (talk) 08:46, 20 April 2015 (UTC)

I think the only effect that dark matter could have had in what usually is described by "conventional physics" is in the early universe when the first stars formed. As pointed out in this review article you could have had stars powered by WIMP annihilation. Count Iblis (talk) 16:56, 20 April 2015 (UTC)

Interesting. This article suggests that less than 0.1% the mass of a star can power it without fusion; so even a mass of dark particles less than that of Ceres might do something to the Sun? The self-annihilation would make it less than that, though. In this model I would think there could be 240-million-year variations in climate because of it. But... the premise is that there are WIMPs constantly annihilating themselves and producing energy all around us, so why don't we see them? Is this paper seriously possible, or just one of the weird things you find on Arxiv? Wnt (talk) 23:50, 20 April 2015 (UTC)

For a typical WIMP capture rate at the sun of 10²⁵ particles / s and a per particle mass of say 250 Gev [3], we get a mass flux of 4.5 kg / s. At a quasi equilibrium, roughly the same number of particles would be converted to other forms of matter/energy via annihilation, giving an energy flux of 4×10¹⁷ W, which is roughly 1 part in 100 million of the solar luminosity. It would appear that the energy flux from dark matter annihilation would have to be roughly a million times higher than that before it became significant for terrestrial effects. Incidentally, people do look for evidence of dark matter annihilation in the sun (generally looking for an excess of GeV to Tev energy neutrinos), but so far people have only set an upper bound on the rates. Dragons flight (talk) 02:23, 21 April 2015 (UTC)

Note that the article points out that: "Our Sun is 24,000 light years away from the center of our Galaxy { too far away to be powered

by DM annihilation, though experimenters are searching for the products (particularly neutrinos) of the annihilation of the small amounts of DM captured by the Sun. DM heating can also dramatically a�ect stars at the galactic center, where DM densities can be orders of magnitudes larger then found locally." Count Iblis (talk) 15:01, 21 April 2015 (UTC)

Why is Tonsillectomy so common in the United States?

It seems to me like a completely unnecessary procedure for a problem that will eventually go away in time. Isn't the removal of a perfectly functioning organ generally speaking, a bad idea unless absolutely necessary? They don't do tonsillectomies in other countries with such high frequency and people in the rest of the world are doing perfectly fine without it. So why so prevalent in the United States? ScienceApe (talk) 13:29, 19 April 2015 (UTC)

?Cash cow. Richard Avery (talk) 13:54, 19 April 2015 (UTC)

The criteria in the UK [4] (where such procedures are paid for by the NHS) and the US [5] are pretty similar, so the proportion of people that have the operation should be about the same - I don't know if they are. Of course, in less wealthy countries you may just have to suffer. However, it has been suggested that not enough tonsillectomies are now performed in the UK[6] - the situation in the US is more complicated [7]. Of course, if you read the last link you will see that tonsillectomies are performed for reasons other than tonsililitis. It does also say there that "During the briefing, the President suggested that physicians might be influenced to perform tonsillectomy surgeries based on reimbursement rates, in a situation where medical management might be equally efficacious". Richerman (talk) 14:24, 19 April 2015 (UTC)

• I have had upper respiratory issues since childhood, and three occasions on which they could have taken my tonsils out during a related operation, but the attitude was, "We don't do that any more unless absolutely necessary." (My mother--who was always the one to take me to the doctor--never argued the point, as her best friend had died in high school during a routine tonsillectomy.) I talked to my doctor a couple of years ago about a snoring problem not related to sleep apnea, and she looked at my tonsils and said I should have had them removed decades ago, and my problem would not go away until I had them out. μηδείς (talk) 17:01, 19 April 2015 (UTC)

• This seems to be part of a broader problem with American medicine of over-treating and over-medicating patients, when "eat right and exercise" should be prescribed far more often. In many cases of sore throats (and possible prostate cancer), the best course of action is often to "wait and watch", depending on the individual case, of course. If they get worse, then do something, while if they don't worsen, or even get better on their own, then no treatment is indicated. But American medicine doesn't like this approach. They want to cover themselves from lawsuits, if things do go bad, and bill for more services, in any case (this especially applies to patients with the best insurance). StuRat (talk) 18:05, 19 April 2015 (UTC)

In my case it was a policy of undertreatment that was regardless of the fact that I have always been fully insured. My problem at this point is that I would need a good year's worth of worthless studies (like a sleep apnea test, which is apparently a form of short time torture meant to induce you to torture yourself with a pump for the rest of your life) before I'd get the necessary referrals for what should have been done 30 years ago. I tend to think the premise that it is so common in the US has actually been false for decades, but it is hard to demonstrate a negative. μηδείς (talk) 01:20, 20 April 2015 (UTC)

This is getting a bit off topic, but it's all well and good to prescribe "eat right and exercise", but the fact is that the overwhelming majority of patients won't actually do it. If the choice is between prescribing some treatment that the patient will readily comply with and has a good chance of fixing their problem, and prescribing diet and exercise which you know the patient is very unlikely to do, the doctor has an obligation to recommend the treatment with a better prognosis. 202.155.85.18 (talk) 01:58, 20 April 2015 (UTC)

The problem here is that most medications and many surgeries don't actual fix the problem, unlike a good diet and exercise, all they do is "treat" it. For example, insulin shots don't cure diabetes, they just keep it from killing you quite as quickly, while eating right and exercising can prevent adult onset diabetes, and may be able to cure it, in the early stages, as well. Doctors should make that clear: "Either you eat right and exercise to permanently fix this problem, or we can give you a bunch of costly treatments, that, at best, will delay your death and cause a range of nasty side-effects". Presented this way, many more people would make the right choice. StuRat (talk) 04:52, 20 April 2015 (UTC)

I'd like to know what sort of diet and exercise treats diseased tonsils. μηδείς (talk) 21:54, 21 April 2015 (UTC)

I was talking about the general problem, not tonsils specifically. However, eating right and exercising might help tonsils, and certainly won't hurt. Specifically, on diet, I wonder if acidic or basic foods can damage the tonsils, allowing microbes in. StuRat (talk) 22:18, 21 April 2015 (UTC)

Death rates for children in the U.S. in general correlate inversely to the rate of tonsillectomies (i.e. it's economic and those that get care, get tonsillectomies and live). Diet and excercise are not issues for children under 5 unless also economic. It's rather ignorant to proclaim that the U.S. over prescribes or has too many surgeries. It's like antibiotics. All things being equal, it's generally not clear whether a sore throat is bacterial or viral so no matter what, antibiotics are prescribed because it isn't bacterial, it doesn't hurt and if it is, it cures it. All skin infections are treated as MRSA now because, of course, if it isn't MRSA the treatment still works and if it is MRSA, a lesser treatment makes it worse. There isn't a single person in the U.S. that doesn't know diet and exercise is healthier. The choice is never whether to give that advice, the choice is whether to treat the condition as it presents itself. The conditions are largely the result of being a wealthy nation. Poor nations don't have obesity issues. --DHeyward (talk) 06:18, 22 April 2015 (UTC)

One should be cautious with the "[if] it isn't bacteraial, [antibiotics] doesn't hurt" stuff. During the weeks and months after taking antibiotics, patients are several times more likely to present with an unrelated antibiotic resistant infection (e.g. [8]). If you wipe out the normal bacterial population, whatever is left will proliferate and sometimes a previously non-symptomatic bacteria suddenly becomes an acute infection as a result of clearing all the other bacteria out of its way. That's not to say that aggressive use of antibiotics isn't sometimes warranted, but it isn't necessarily harmless. Dragons flight (talk) 07:23, 22 April 2015 (UTC)

And perhaps even more important in the long run, overtreatment with antibiotics increases the risk of antibiotic resistance in bacteria. See Antimicrobial resistance#Prevention. Sjö (talk) 07:48, 22 April 2015 (UTC)

Are antibiotics really routineliny prescribed for sore throats in the US? Are we talking about everyone or just people with possibly weak immune systems or other risk factors? If you're talking about everyone, as the comment seems to imply, it's the kind of thing common in Malaysia but I would have hoped a place like the US had moved beyond that. It's probably more common than many experts would like in NZ, but definitely routine administration of antibiotics is only recommend in certain cases in NZ [9] and that's despite (but I think most experts agree not the cause of) there being an above average risk of rheumatic fever. Nil Einne (talk) 15:27, 22 April 2015 (UTC)

Most good doctors won't prescribe antibiotics for a sore throat unless there's clear spotting or a positive culture, see Streptococcal pharyngitis for images. But it is true that some doctors will prescribe on the "in case" theory as well as as a placebo to mollify an insistent patient, enough so that the above worries are well founded. μηδείς (talk) 18:26, 23 April 2015 (UTC)

hydraulic mechanism

hello, in my washing machine, there's a special mechanism that controls the running-in of conditioner. there is a reservoir into which you pour the conditioner. somewhere towards the end of the washing cycle the machine pours water on it, the level of the mixture rises and the whole reservoir (!) is drained into the main tank where the drum is, through the protruding round thing with the sleeve on it. there are no floats, valves, levers or electromagnetic actuators of any sort. I wanted to look it up to see how it works (I don't understand why the whole thing is drained when the level rises to cover the opening of the protruding thing) but I don't know what what to search for. I drew it for a better illustration. What is this mechanism (or the principle behind it) called and do we have an article on it? Thanks in advance! Asmrulz (talk) 17:49, 19 April 2015 (UTC)

It's a siphon. Here's a detailed description of how it works with the fabric softener. --Modocc (talk) 18:03, 19 April 2015 (UTC)

great, thanks! Asmrulz (talk) 18:30, 19 April 2015 (UTC)

I really dislike that setup:

1) There's always some gunk left in the bottom of the tray to dry and harden, eventually blocking the siphon.

2) Air bubbles could also break the siphon.

3) Pulling the tray out and pushing it in tends to cause spills. This is a minor problem with fabric softener but a major risk with bleach, which often uses a similar tray.

My top-loader washing machine has a cup on the top of the agitator for fabric softener. Agitation doesn't cause it to come out, but the spin cycle does. Much simpler and more reliable. StuRat (talk) 18:43, 19 April 2015 (UTC)

Possible to observe the motion of the planets as a motionless observer?

Barycenter of the Solar system. Large yellow circle is the Sun (see response below - note this is "motionless" but not accelerationless!).

Reading some of the posts above made me ponder something. Is there a point in space where it is possible to remain motionless with respect to the solar system but still be within the solar system? In which we could actually observe the orbits of the planets at their natural rate, though we would still be moving with respect to the galaxy. Or for that matter, is there a point in space where we can be absolutely still, not be orbiting anything, and be able to observe the movement of galaxies or even clusters of galaxies (let's say, in an accelerated time frame so we can actually see movement at that scale, though the article on the Milky Way states that its "Speed relative to CMB rest frame" is 552 ±6 km/s which makes me think that even at that scale my eye would be able to observe something moving that fast, but maybe I'm getting way out of my league here and am totally misunderstanding aspects of special relativity)? I think the article on Inertial frame of reference relates to what I'm getting at, but maybe some of you can point me to some other articles that discuss this? Thanks.

Lagrange points are locations where the forces cancel out. If there were only two bodies in the solar system, then a point on a line between them (their barycenter) would be such a point. With multiple objects it gets much more complicated.

In our solar system, I would guess that the L1 Lagrange point between the Sun and Mercury would be the most stable, as other large bodies are far away. However, that close to the Sun (although far closer to Mercury), the solar wind, coronal mass ejections, etc. might also tend to have effects. So, I'd still expect some station keeping would be required. Specifically, you'd stay on that line between the Sun and Mercury (or perhaps orbit about it), but would tend to fall towards one or the other, without the occasional thruster blast. StuRat (talk) 19:28, 19 April 2015 (UTC)

Objects located at the solar system's Lagrange points also orbit the sun and, in addition, these move along with the solar system relative to the CMB rest frame however, thus these points don't work although these are perhaps better than other places since less power would be needed to counter perturbations. In any case, wherever the ship is located, it would need to use its engines to counter solar winds and the sun's gravity to maintain a zero relative velocity to the CMB rest frame [or to the Solar system's barycenter, per Writ's answerS below]. Another costly problem is that the required speed for the craft of 370 km/s relative to the Sun is an order of magnitude greater than Mercury's or Earth's orbital speeds. From the List of vehicle speed records the fastest spacecraft relative to the Sun was Helios 2 with a speed of 70.22 km/s which is too slow, thus just getting the correct speed will require an even greater gravity assist maneuver. --Modocc (talk) 22:16, 19 April 2015 (UTC) -Modocc (talk) 20:34, 19 April 2015 (UTC)

No. Within the solar system, if you are not orbiting the sun, then you are falling into it! For observing galaxies, almost any point in space well away from gravitational influences will suffice, but it will take a long time to get there, and you will need to observe for a long time to get good results. I assume that you are eternal. Dbfirs 19:56, 19 April 2015 (UTC)

If you mean a point that a ship would be constantly at rest without being perturbed at all then no, as Dbfirs points out above, and the galaxy does perturb us everywhere we can possibly go within our lifetimes. It's not really a question of finding a point in space though, but a question of establishing the required velocity and maintaining it, which is possible. In other words, a ship with active engines would need to counter the continuous gravitational perturbations and the solar wind affecting it in order to remain stationary relative to the CMB rest frame. [Sorry, but I initially ignored the first question you posed, but Writ answered it appropriately]. -Modocc (talk) 20:34, 19 April 2015 (UTC)

See Sun. The barycenter of the Solar system - where I think you could stay nicely "at rest" - tends to take a refreshing dip in superheated plasma every now and then. But for a while, you could have a stable position there ... I think. Don't forget the sunscreen! :) Oh, and I'm skeptical an engine is strictly necessary to counter solar wind. I'd think that, since it is made of charged particles, with sufficient cleverness you could have some kind of magnetic field setup that deflects them slightly, then returns them to their original vector, preventing any propulsive force. I don't think the dipole magnet of the Earth does quite that though, nor do I know how to do it. :) Wnt (talk) 22:48, 19 April 2015 (UTC)

Yes, the Solar system's barycenter answers the OP's first question (I did overlook it, so I added it to my answers). Solar sails would help counter the pull of gravity (so one does not require cleverness :-). It obviously doesn't answer the last question though since the Solar System's barycenter is in orbit about the galaxy and is definitely not stationary with respect to the CMB rest frame. --Modocc (talk) 23:34, 19 April 2015 (UTC)

You asked about "natural rates" of the orbits too. So I'll add that the relativistic "natural rates" are proper time and proper length which are Lorenz invariant as opposed to coordinate time and length contractions which are not quite as natural but are considered real nevertheless. --Modocc (talk) 00:20, 20 April 2015 (UTC)

• I was quite surprised, last year, to read that the barycenter of the solar system is for the most part outside the limb, not to mention the nucleus of the sun. But is it true that as Modocc says above that the barycenter of the solar system does not orbit that of the galaxy? That seems counter intuitive, since we are not fleeing the galaxy or falling into its core. My understanding (without looking it up) is we've been in the outer limb for more than a galactic revolution. μηδείς (talk) 01:51, 20 April 2015 (UTC)

Please quote me where I say it does not, because if I did it was a misprint. ;( I may have been unclear and/or inaccurate above in some of what I've written (so I'm still editing it too). In fact, I have said the exact opposite of this for above I wrote "...since the Solar System's barycenter is in orbit about the galaxy...". --Modocc (talk) 01:56, 20 April 2015 (UTC)

Lord, you're right, you certainly did not say that, and I have stricken it. I begin to suspect I may have recently suffered a mini-stroke during a coughing fit. I suppose I should simply say I understand from the popular press that the solar system orbits the galaxy but does so with an north-and=south oscillation in relation to the galactic plain, that has been suggested as a cause of our extinction events. μηδείς (talk) 02:19, 20 April 2015 (UTC)

No medical advice, but seek it if you must. And perhaps we will put a stop to the Holocene extinction even. :-) -Modocc (talk) 04:15, 20 April 2015 (UTC)

Ummm, actually I commented too hastily - the barycenter is a point "at rest" relative to the solar system as a whole, where the planets' motion can be observed, but it's not a point of zero gravity, so it fails the OP's other criterion After all, there's not zero G next to the sun, nor are those loops a usual orbit. The best way to illustrate this is that if you picture moving the Moon away from the Earth, the barycenter of the system goes further and further away from Earth; but the gravity near Earth is affected less and less by the Moon. Spheres pull like their mass is concentrated at the barycenter, but (so far as I know...) nothing else does. Nonethless... the need for the object to match velocity with the barycenter's complicated trajectory in order to "truly be at rest" observing the planetary motions shows just how difficult it would be to construct such an orbit anywhere. Wnt (talk) 11:08, 20 April 2015 (UTC)

Yes. Likewise, when the Earth accretes mass the two distinct balancing acts go in different directions since the Moon-Earth mass center moves towards the Earth but the Moon-Earth L1 Lagrange point (which balances their gravitation as well a third body's centrifugal force but I'm ignoring that for this purpose) moves further away since the Earth has greater influence (its still mostly harmless though). -Modocc (talk) 17:01, 20 April 2015 (UTC)

Although the Solar system's barycenter and Sun's barycenter differ substantially, their respective velocities are not very different and over time average to be the same anyway since they are bound together, so instead of orbits about the Sun, imagine a solar sail providing the drag needed to deorbit, but keeping one's distance, and then floating indefinitely in a fixed stationary position relative to the Sun with the sail providing the necessary lift (I've looked for a supporting reference for this scenario, but I'm empty-handed at this point so it is a bit too handwavy for my liking). It would be called a Statite. See Dyson bubble for the concept of employing them around a star and the technical hurdles of making a sail that is light enough. -Modocc (talk) 19:10, 20 April 2015 (UTC)

The solar sail might also be useful for station-keeping, for a ship at the L1 Lagrange point between the Sun and Mercury. That is, if the ship drifts too close to the Sun, the solar sail could be deployed to push it back towards the Lagrange point. But you'd need to be careful not to go past the point, as the solar sail has no reverse gear. StuRat (talk) 22:24, 21 April 2015 (UTC)

Another option for being relatively still with respect to the solar system is to be very far out, where the orbital speed is tiny. Only minimal station keeping would be needed to stop the ship completely and still not fall into the Sun from there. StuRat (talk) 22:24, 21 April 2015 (UTC)

Can drowning cause bleeding?

Is there anybody who bleeds when he drowns? The reason I’m asking is because there’s an old first‐person shooter that I play where the protagonist’s face bleeds when he does, but maybe that’s just video games being video games again. --66.190.99.112 (talk) 19:45, 19 April 2015 (UTC)

Not drowning itself, no, but there could be related incidents. For example, falling a great distance into the water might cause both bleeding and drowning. Or, being held deep under water might cause your lungs to implode from the pressure, and also cause drowning. Or you could be shot/injured then fall into the water and drown. StuRat (talk) 19:49, 19 April 2015 (UTC)

You can sharpen water or steam with a high-pressure jet as is usually used to cut stone countertops... can you sharpen an apparently stationary pool of water by filling it with some kind of solitons? Wnt (talk) 22:52, 19 April 2015 (UTC)

I'm reasonably sure that the water pressure would just force the air out of your mouth and nose, rather than implode your lungs. It would however break your ear drums and cause bleeding from the ears. 202.155.85.18 (talk) 04:35, 20 April 2015 (UTC)

How your body would react would depend on the speed of the pressure change. StuRat (talk) 04:39, 20 April 2015 (UTC)

Please see Dry drowning. One of my sons experienced a panic attack in a swimming pool after being buzzed by a bee, at about ten years of age. He had a bee phobia as a child. His larynx spasmed, and he had a severe pressure gradient in his lungs. He inhaled no water, but very rapidly, bloody foam started gushing from his mouth and nose. He was taken by ambulance to a small local hospital where the medical staff were overwhelmed, and then by helicopter to a regional hospital where he recovered within a few days. Cullen³²⁸ Let's discuss it 05:06, 20 April 2015 (UTC)

See also Pulmonary edema which is sometimes caused by dry drowning. That says: "The overwhelming symptom of pulmonary edema is difficulty breathing, but may also include coughing up blood (classically seen as pink, frothy sputum) . . ." Cullen³²⁸ Let's discuss it 05:11, 20 April 2015 (UTC)

How does dry drowning differ from asphyxia ? StuRat (talk) 06:00, 20 April 2015 (UTC)

The one is a subcategory of the other. --Jayron32 13:45, 20 April 2015 (UTC)

Out of curiosity, what is this game? ScienceApe (talk) 01:29, 22 April 2015 (UTC)

Quake I. --Romanophile (talk) 13:27, 22 April 2015 (UTC)