Wikipedia:Reference desk/Archives/Science/2018 April 13

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April 13

Why does it take so long to determine the cause of death?

I was looking at Dolores O'Riordan's article and the coroner's office still hasn't published its report as to the cause of death. It's been almost three months. Why does it take so long to determine the cause of death? Is the reason scientific? Do certain tests take that long? Thanks. Basemetal 02:38, 13 April 2018 (UTC)

The toxicological report typically delays things the longest. The individual tests don't generally take that long, but there may be many tests desired, the coroner may decide on new tests after he receives the results of previous tests, he may want to have the tests repeated at a different facility, or he may want to consult with another pathologist about the results. On top of all of this, many testing centers have a constant backlog before they can handle new requests. [1][2] Someguy1221 (talk) 03:00, 13 April 2018 (UTC)

These sources [3] [4] note that there was little chance the coroner would have publicly released any further findings before April 3rd no matter when they received them. However they may have released these to the family, who would have been free to publicly release it themselves. Of course April 3rd has come and gone. A quick search finds this [5] [6] that the hearing was removed from the schedule with no reason given and no new hearing date scheduled. You may be interested in the sources [7] [8] for an overview of how things work in the UKEngland and Wales. Nil Einne (talk) 10:36, 13 April 2018 (UTC) 13:14, 13 April 2018 (UTC)

<WP:OR warning> I sleep with someone who works in the industry, and can confirm that, unless there is an emergency "rush" situation that pushes a forensics case to the front of the line (this usually requires a legal judge's order), cases are worked in the order received, and a backlog of 2-3 months is standard, and longer is not unusual. The test itself can be completed in a day or two, easily. The problem is there are probably many other cases in line before that one. --Jayron32 12:27, 13 April 2018 (UTC)

Actually on second thought, although the site doesn't seem to mention the info is specific to England and Wales that I can see, considering the situation in Scotland is a little different (Coroner) the info possibly only applies to England and Wales. It may also apply to Northern Ireland, but I'm not so sure. The Manchester site info is obviously specific to there, but I don't see any reason to think they're an outlier in terms of time frames. I've modified my answer accordingly Nil Einne (talk) 13:14, 13 April 2018 (UTC)

Thanks. Basemetal 14:50, 13 April 2018 (UTC)

Is dark matter segregated to the outskirts of galaxies? If so, why?

I was reading article Dark matter. Two facts about the hypothesized dark matter concept puzzled me: (1) that it accounts for more than 80% of the mass of the observable universe and (2) that it seems to be mostly confined to the outer edges of galaxies. (This sort of makes sense to an ignoramus like me, after all if it was distributed the same as visible matter, it would be all around us and the laws of gravity as applied to everyday objects here on earth would already have had to take it into account) But is that correct? Have I understood things correctly or not? Basemetal 15:01, 13 April 2018 (UTC)

The problem with Dark matter is mostly a linguistic problem rather than anything else. Here's a list of things that we know we know about the phenomenon that we have unfortunately named Dark matter. 1) The force of gravity we know to be acting on large-scale objects in the universe like galaxies is about 80% stronger than is only about 20% of what we can account for using existing models. 2) there is no #2. "Dark matter" is the collective name for all of the mechanisms that have been proposed to account for that. Here is a pretty good explanation from NdGT, which is concise and explains the problem. These aren't really "facts about the hypothesized dark matter" that you listed, instead it would be better to think about them as "hypothesized facts about dark matter". That is, proposals for what it might be. The might there is pretty well untested, however, as yet. This is a longer explanation from him as well, where he eliminates what we know it isn't, and why we know it isn't those things. --Jayron32 15:10, 13 April 2018 (UTC)

If the estimate is 80% dark matter and 20% observable matter then wouldn't it because the gravity is 5 times stronger (meaning 400% stronger) than expected from the observable matter? PrimeHunter (talk) 16:19, 13 April 2018 (UTC)

Yes, you are correct. I have ammended my original statement to be more precise in my language. About 20% of the gravity has known causes. About 80% cannot be accounted for. --Jayron32 16:31, 13 April 2018 (UTC)

Sigh. This (or the videos) still don't answer my question. It seems to be saying my question is not worded properly. That I should not be talking of "dark matter" as a thing or something. Lots of people do that, so maybe someone will humor me and just answer my question. Note that article Dark matter also sometimes phrases things as if dark matter was a "thing" (e.g. "The arms of spiral galaxies rotate around the galactic centre. The luminous mass density of a spiral galaxy decreases as one goes from the centre to the outskirts. If luminous mass were all the matter, then we can model the galaxy as a point mass in the centre and test masses orbiting around it, similar to the solar system. From Kepler's Second Law, it is expected that the rotation velocities will decrease with distance from the centre, similar to the Solar System. This is not observed. Instead, the galaxy rotation curve remains flat as distant from the centre as the data is available. If Kepler's laws are correct, then the obvious way to resolve this discrepancy is to conclude that the mass distribution in spiral galaxies is not similar to that of the Solar System. In particular, there is a lot of non-luminous matter (dark matter) in the outskirts of the galaxy."). Again, my question is this: When you read that the estimate is 80% dark matter and 20% observable matter it does not mean that the earth, the solar system, etc. are composed to 80% of dark matter, correct? Because the laws of gravity work well enough "down here", correct? They don't need to be fixed "down here", correct? Therefore if something needs to be fixed it is only at the scale of a galaxy, correct? So if "dark matter" is just a way to fix the missing 400% 80% of gravity, it is only needed "out there", not "down here", correct? So, somehow you want it "out there" and not "down here", correct? Whew. Thanks for any clarification. Basemetal 17:52, 13 April 2018 (UTC)

Yes, the effect is diffuse enough to be inconsequential on human-sized scales, and is only evident on galaxy-sized scales. Which is to say the effect is the same, but its detectability is small enough to be calculable, but not measurable, i.e. insignificant. Lots of astrophysical concepts are like that, i.e. metric expansion of space. The deal with "dark matter" is that the forces holding galaxies together at the rate at which they rotate can't explain why they don't blow apart: if you take a galaxy-sized object, start it spinning at galaxy-spinning rates, and apply the requisite amount of attractive force that galaxy has based on its observable mass, the math says the galaxy would fly apart. So there is some other force holding the galaxy together. The cause of that force is what we have called "dark matter". Of course, if "dark matter" works "out there", it also works "down here" in the same way that quantum mechanics works on all scales; its just that the math produces the same results as the simplified theory, so we can ignore it on our scales (that is to say, if you add dark matter physics to earth-based physics problems, you can perhaps calculate a negligible change in expected motions, but not on a scale that any measuring device known to man could detect). --Jayron32 18:06, 13 April 2018 (UTC)

Yes I understand why it is needed. But why is the effect inconsequential on human (or even solar-system size) scale? Simply invoking scale doesn't seem to explain things adequately. At galaxy scale it is a huge effect. It is 80% of gravity. If it is 80% of gravity at the scale of a galaxy, then why isn't it 80% of gravity at the scale of the solar system. These are percentages remember. Scale has nothing to do here. Why are the percentages different at the scale of a galaxy from the scale of the solar system? (You're probably right that "lots of astrophysical concepts are like that", but that's not really an explanation, that's just like saying, well, yes, though). Basemetal 18:44, 13 April 2018 (UTC)

It's because gravity is quite a weak and long-range force, and because dark matter seemingly has no other interaction (magnetic, electrostatic, chemical, etc.) with either "ordinary" matter or with itself. Consequently, while ordinary matter readily concentrates itself into dense stars and planets (etc.) to which we can be quite close, dark matter seems to be spread out fairly evenly through the whole volume of a galaxy (which is mostly otherwise "empty space") in a diffuse cloud which extends even beyond the detectable limits of the ordinary matter. {The poster formerly known as 87.81.l230.195} 2.218.14.51 (talk) 19:13, 13 April 2018 (UTC)

I see. So you're saying the density of dark matter across the galaxy is uniform but the ratio of dark matter to visible matter is lower in the solar system (say) than in the galaxy as a whole because visible matter tends to concentrate into clumps such as stars, planets, etc. while dark matter does not, so in those areas where solar systems are the ratio of dark matter to visible matter is lower than in the galaxy as a whole whose volume is made mostly of empty space (except for all that dark matter, that is). Is that what you're saying? Did I get this right? Now the Solar System has a total mass of 1.0014 Solar masses while the Milky Way has a total mass of 0.8 to 1.5×10¹² Solar masses. How do I calculate the total mass of dark matter in the Milky Way and in the Solar System. Article Milky Way gives something called "Dark matter density at Sun's position". Why do they need to specify "at Sun's position" if the density of dark matter is uniform? And what units is it in? Thanks. Basemetal 20:53, 13 April 2018 (UTC)

((edit conflict) Just noting the question above me was a little different when I actually wrote this post) Since dark matter does not aggregate with itself or baryonic matter due to the lack of electromagnetic interactions (which means, no binding, no scattering, no friction, passing straight through objects) it does not collect around a star. The dark matter dominates the galaxy but it is diffuse. Light matter is not so diffuse - like baryonic matter itself, there are little clumps with extreme density, and then a whole lot of nothing. That is, you have (relatively) tiny stars with immense mass, and then lightyears of mostly-empty space. The earth and the sun are incredibly dense compared to most of of space, and relatively close together to boot, so their relative motion is dominated by their own mass. Overall, dark matter tugs on the sun and the earth stronger than either tugs on the other with what should be a significant force, but since most of it is far away, the earth and the sun experience virtually the same tug. Think about the earth and the moon, and imagine the sun was completely dark, but we could somehow still see the moon. Could you tell the earth-moon system is orbiting the sun, simply from the motion of the moon about the earth? It would be extremely difficult, since the motion of the moon relative to the earth is caused almost entirely by the mass that is nearest to it - the earth. Local effects dominate local measurements. However, if you were to somehow be able to see all the other planets, you would notice something funny. The planets are far from each other, and rotate about their approximate mutual center of mass, but they are moving far too quickly. Anyway, dark matter is not even hypothesized to be segregated to the edges of the galaxy - it's commonly believed to be more concentrated in the center like everything else (see dark matter halo). But since there's basically no friction to slow it down and draw it in, it would hypothetically maintain a much broader distribution as galaxies formed, resulting in the ration of dark-matter/light-matter to get larger and larger as you move out from the center of a galaxy. Someguy1221 (talk) 21:05, 13 April 2018 (UTC)

To your question of calculations, you could take the formulas at the article I linked, and plug in values for a given model to find out the density in the solar system, and then from there calculate say the total mass in a sphere centered on the sun with the radius of the earth's orbit, which by the shell theorem will allow you to calculate how much of the Earth's orbital speed is caused by dark matter. It will probably be many orders of magnitude smaller than the sun's contribution, or at least one would hope. Someguy1221 (talk) 21:08, 13 April 2018 (UTC)

That calculation is done here. --catslash (talk) 21:17, 13 April 2018 (UTC)

See Dark matter halo. The density of dark matter goes down with distance from the center of the galaxy - but slower than for normal matter so it spreads out further. And there doesn't seem to be concentrated clumps of dark matter, though it probably has some structure it is of a much fuzzier kind. +um sorry I see Someguy1221 says this all above. Dmcq (talk) 21:43, 13 April 2018 (UTC)

Yes the calculations were pretty much already done in Dark matter halo and in Catslash's link. For the Milky Way visible matter is about 9 x 10¹⁰ solar masses and dark matter is between 6 x 10¹¹ and 3 x 10¹² solar masses. So let's say the ratio of dark matter to visible matter is of an order of magnitude between 10 and 10² (at least according to those figures; the text of the article says 95% of the mass of the Galaxy is believed to be dark matter; compare that with 80% for the whole of the observable universe). As to the Solar System: Catslash's link gives 2.3 x 10¹² kg of dark matter within the earth orbit (that's not the whole of the Solar System but ok) while the mass of the Sun is about 2.0 x 10³⁰ kg (this can be assumed to be the whole of the mass in that orbit as a first approximation, as the mass of all the planets, etc. accounts for only about 0.0014 solar mass). So the ratio of dark matter to visible matter in the Solar System is of an order of magnitude of about 10^-18. Clearly minute. Now I get it. Thanks everybody. Basemetal 23:54, 13 April 2018 (UTC)

Hmmmm... that 10¹⁸ ratio is impressive. However, Planet Nine at aphelion is at 1200 AU, so there the ratio should be 10⁸. Moreover ... the ratio would appear to be hypothetical, as dark matter hasn't been observed. The Sun does exert gravity, and so it seems at least conceivable that the Sun and other stars might have a little more dark matter in their neighborhood, a few orders of magnitude maybe?, than the surrounding empty space. (Hmmm, then again I suppose there are double stars with predictable masses and orbital periods that argue to the contrary, though I haven't looked into it) I wonder if some of the difficulty in finding the planet might possibly result from not taking a possible dark matter contribution to its orbit into account? Wnt (talk) 02:40, 15 April 2018 (UTC)

Youhave to have some sort of interaction like friction to get a gas to condense around a massive body, otherwise the molecules would just go out again in orbits at least as far as however far away they start. And there is a big halo because the dark matter doesn't seem to interact much with anything, it certainly isn't condensing at the scale of individual star systems. Gravity in itself can cause clumping but not at that scale so swiftly (by that I mean since the big bang). In fact I'm surprised it has clumped so much even at the scale of galaxies. Dmcq (talk) 10:46, 15 April 2018 (UTC)

Chemistry Question

Is there any chemical reaction if you combine povidone-iodine, salt and water together?--User777123 (talk) 21:31, 13 April 2018 (UTC)

At least in veterinary care, adding povidone-iodine to salt water is used for wound cleansing:[9] —2606:A000:4C0C:E200:0:0:0:3 (talk) 05:40, 14 April 2018 (UTC)

There might be some ion exchange between the iodide of the povidone-iodine complex and the chloride in salt, but other than that, no. 2601:646:8E01:7E0B:0:0:0:9A39 (talk) 01:17, 15 April 2018 (UTC)