Wikipedia:Reference desk/Archives/Science/2015 August 3

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

August 3

Locating the geographic poles of the Earth

How explorers, especially the early expeditions, located the poles of the Earth? You have seen those photos of people, flagpoles, tents etc. at North Pole and South Pole; how did they know that they where at the right place? --Sivullinen (talk) 01:48, 3 August 2015 (UTC)

Robert Peary#Controversy actually has some interesting discussion of how reaching a pole was supposed to be "proven" at the time; also if you follow references from that article, you can learn more. --Jayron32 02:02, 3 August 2015 (UTC)

Assuming you mean the axis of spin of the earth, then a theodolite or sextant and the stars would do it. When the stars directly overhead are motionless you are at the pole.Greglocock (talk) 02:06, 3 August 2015 (UTC)

Since the explorers were traveling in the perpetual daylight of summer, they used observations of the sun rather than the stars. You can read about Amundsen's procedure in the article Polheim. He used a sextant because his theodolite was broken, and took pains to "box" the South Pole so that at lest one of his expedition members would definitely have passed very close to the geographic pole. Scott's party seems to have used a theodolite, shown here in use [1]. Although Scott found Amundsen's tent and letter at the South Pole, of course he wanted to make his own observations rather than trusting that Amundsen got it right. The principle is that when you're exactly at the Pole, the sun goes around in a day at almost constant elevation. If you're a little away from the Pole, the sun will appear to dip a little in one direction and rise a little in the opposite direction. --Amble (talk) 02:47, 3 August 2015 (UTC)

Of course, there's also the problem that the actual poles themselves move around. That is, the exact axis of rotation of the Earth does not intersect the solid Earth at the same point all the time. See Polar motion, Chandler wobble, etc. --Jayron32 02:50, 3 August 2015 (UTC)

That's true, but those effects are too small to be relevant to Heroic Age explorers planting flags. --Amble (talk) 03:50, 3 August 2015 (UTC)

It might be dificult to say the exact spot but relatively easy to know when it was crossed. Miles in either direction, as long as it was crossed, would be good enough to claim being there. --DHeyward (talk) 05:46, 3 August 2015 (UTC)

Robert Falcon Scott and Amundsen must have both used the same highly accurate method, since Scott found Amundsen's marker flag planted five weeks earlier in the middle of a vast continent. Alansplodge (talk) 16:38, 4 August 2015 (UTC)

The method of looking at sun or stars to determine when you're at the pole gives you one definition of the pole. Using a compass reveals when you're at the magnetic pole. At the magnetic pole, a compass held on it's side will point straight up and down. Some polar explorers used compasses specifically designed to make this measurement. The magnetic poles also move over time - so this is also an inexact process.

SteveBaker (talk) 17:27, 3 August 2015 (UTC)

Magnetic poles are located thousands of kilometers away from the geographic poles and are not very relevant to the question. --Sivullinen (talk) 20:26, 3 August 2015 (UTC)

You didn't specify which kind of pole you were talking about in the question - so my response was entirely relevant right up to the time you said it wasn't! :-) SteveBaker (talk) 01:04, 4 August 2015 (UTC)

Except he did specify, in the original heading. --Amble (talk) 02:00, 4 August 2015 (UTC)

What's inside the hip?

A relative just dislocated his replaced-three-months-ago hip joint and had to have surgery this evening to put it back in place, and I was in the waiting room to hear the surgeon discuss the results after they were done. One of his reasons for saying that all had gone well was that he'd barely had to cut anything: he just made an incision in the skin and took away a little soft tissue, but everything else required no cutting. What's the hip region made of, and how can one get to the bone without cutting anything significant? I assumed that the surgeon would have to cut some muscles in order to get access to the hip joint, but that's obviously not the case. Beyond the hip article, I don't know where to look; I found articles such as Capsule of hip joint, but my knowledge is so weak that I don't even understand what the capsule of hip joint is, for example. Nyttend (talk) 02:23, 3 August 2015 (UTC)

Arthroscopy was invented almost 100 years ago, and has been industry standard for 30+ years. Many (perhaps even most) surgeries nowadays require much smaller incisions than the non-surgeon would imagine they would. --Jayron32 02:47, 3 August 2015 (UTC)

I'm confused. The relative had his leg badly out of joint, and the arthroscopy article seems to suggest (unless I misunderstand) that it's for looking around and making minor repairs, not for moving major bones that are badly out of joint. Nyttend (talk) 02:59, 3 August 2015 (UTC)

Unconfuse yourself. --Jayron32 03:02, 3 August 2015 (UTC)

You posted that while I was looking through the Hip arthroscopy article. Is this kind of stuff already in the article, or could it be added? I'm not sure where it would belong. But thanks for finding the AAOS article; it's nice and unambiguous, and quite helpful. Nyttend (talk) 03:04, 3 August 2015 (UTC)

I'm no doctor, but I believe muscles are never cut in surgery unless absolutely necessary. Muscle cuts and tears are very painful, take a long time to heal, and impair use of the muscle during healing. If you need to get access to things under muscle, you just spread the muscles apart and keep them there with retractors and other fun tools. Skeletal muscles are divided into, well, different muscles. They're discrete bundles of muscle fibers, wrapped in fascia. Part of learning to be a surgeon involves memorizing all of them and their locations. You don't have one continuous sheet of muscle under your skin. For certain surgeries, such as abdominal surgeries, they actually paralyze you with neuromuscular-blocking drugs to stop your muscles from contracting during the procedure so they will stay put. This requires mechanical ventilation, as it paralyzes the diaphragm. --108.38.204.15 (talk) 03:05, 3 August 2015 (UTC)

I would think that anything that physically must be torn in order for the hip joint to be pulled apart and moved to where it is must already have been torn in the accident, so in theory, provided the muscles can be relaxed, any debris cleared and the joint manipulated with enough control, it should be able to fit back along the same path it came out through. Wnt (talk) 03:36, 3 August 2015 (UTC)

Impossibility fallacy

By my bad luck or by some other cause, I have many times seen and heard people dismissing ideas or designs on the basis that "if this could be done this would have been done already", or "this has not been done, therefore this can not be done". What is the name of this fallacy? I have read our list of fallacies but I haven't found a close enough match. Did I miss it? What's the proper name of this fallacy? Thanks in advance, Dr Dima (talk) 04:52, 3 August 2015 (UTC)

Max Beerbohm came close to this when he said: Anything that is worth doing has been done frequently. Things hitherto undone should be given, I suspect, a wide berth. -- Jack of Oz ^{[pleasantries]} 05:56, 3 August 2015 (UTC)

It's perfectly rational to have less confidence in a claimed discovery if it's something that would likely have been discovered earlier if it were true. -- BenRG (talk) 06:17, 3 August 2015 (UTC)

(It's also rational to put less trust in someone's claims on learning that they're a politician, even though that's called "argumentum ad hominem", and to be more trusting of a physicist's claims about physics than a non-physicist's, even though that's called "appeal to authority". So it is still possible that the hasn't-been-done-before argument appears on lists of fallacies under some name, since they are bogus anyway. Someone should come up with a nice Latin name for the belief that it's wrong to pursue a line of argument that appears on these lists.) -- BenRG (talk) 07:18, 3 August 2015 (UTC)

We do have it. Faulty generalization is the term. It is most likely true of a sample that most inventions fail uniqueness. Yet we know the population has invention. That the sample doesn't reflect the population is a truism in statistics. Or perhaps more understandably, the population of all things exceeds the sample of known inventions. It is a "faulty generalization" to claim all things is bound by all known things. --DHeyward (talk) 06:53, 3 August 2015 (UTC)

Is there actually anyone who believes that claims of new discoveries are false because nothing remains to be discovered? I think "an extraordinary claim requires extraordinary proof" is closer to what people mean when they say "this has not been done, therefore this can not be done". If you produce the unicorn you claim to have caught and it passes all their tests, then they'll believe you, but not before. This saying doesn't appear on lists of fallacies, but that's fine because it isn't a fallacy. -- BenRG (talk) 07:18, 3 August 2015 (UTC)

Agree, but if people mean it literally, then it is a logical fallacy. Supdiop (Talk🔹Contribs) 08:13, 3 August 2015 (UTC)

• It is not always a fallacy, because the reasoning can be valid if certain extra premises are added. When it is a fallacy, formally it is the fallacy of the undistributed middle. Looie496 (talk) 12:47, 3 August 2015 (UTC)

• Yes, if it is something seemingly obvious, then you would expect that somebody would have tried it before. For example, if you could pour saltwater into a normal car engine and get it to run, somebody would have figured that out by now. On the other hand, there might be some new technology which could find a way to extract energy from saltwater (I'm not saying there is, just that we can't discount the possibility because it hasn't been done before). StuRat (talk) 16:17, 3 August 2015 (UTC)

And there is: osmotic power. Of course it wouldn't be useful for powering a vehicle, since the energy density is really low, and it requires expensive and fragile equipment. --108.38.204.15 (talk) 22:30, 3 August 2015 (UTC)

This is really a matter of probability and perhaps of Occam's razor. Without additional information of some kind, if you are unsure of whether something could be done, and it hasn't - the odds are much higher that it can't be done than that it can. It's not certain though - so this is a statement that should be modified by the word "probably"..."If this were possible, it would probably have been done already". Occam's razor might also apply here - that's another tool of inexactitude that never the less proves useful. StuRat's example of running a car on water is a great example of that. It hasn't been done - and the laws of physics strongly suggest that it can't ever be done *BUT* there may be laws of physics of which we're currently unaware that might make it possible. Occam's razor says that the simplest explanations are the best - and it's certainly simpler to assume that water-fuelled cars are impossible (because physics forbids them) than it is to assume that they'll eventually be possible (because we'll discover new laws of physics to make it so).

SteveBaker (talk) 17:21, 3 August 2015 (UTC)

• See also cui bono. If something does happen, it should be obvious that people benefit. There also the point that psychics never make a killing on the stock market, and that Miss Cleo didn't predict her own demise. That doesn't mean that people don't discover new useful things, like evolution, the germ theory of disease, or mechanical flight, although understanding such things had been declared impossible, or outside the realm of science. We even know how to turn lead into gold. μηδείς (talk) 21:07, 3 August 2015 (UTC)

I think some people are having difficulty understanding what a fallacy is. A fallacy isn't at all necessarily FALSE. A logical fallacy is a form of a non sequitur, the conclusion does not logically follow from the premise. "Lots of people think the world is round, therefore the world is round", this is a logically fallacious argument, even though the premise AND the conclusion are both true. An argument can't be logically fallacious some times and not at other times, it either is or isn't. "The preeminent expert on geology says the world is round, therefore the world is round". This might indeed even be an extremely good reason to believe that the world is round, but it's still a fallacious argument. Vespine (talk) 23:28, 3 August 2015 (UTC)

That's an Argument from authority, fallacious because the preeminent expert can still be wrong. However, it makes sense as an inductive argument: "The preeminent expert on geology says the world is round, therefore the world is probably round". Nyttend (talk) 17:58, 4 August 2015 (UTC)

That's exactly the point I was making :) One of the 1st replies was It's perfectly rational to have less confidence in a claimed discovery . Just like it's perfectly rational to "believe" the world expert on something, but that has nothing to do with logical fallacies. Come to think of it, I think rational is actually the wrong word here, I think it should have been reasaonable. It's perfectly reasonable to have less confidence, it's not perfectly rational. Vespine (talk) 22:52, 4 August 2015 (UTC)

This is something of a variation on the old saw "Absence of evidence is not evidence of absence", which is touched on as a sort of informal fallacy in argument from ignorance. That said, some other comments above have gotten to the edges of the problem (which is at least partly semantic). Eliezer Yudkowsky covers it well here in his blog. Essentially, while absence of evidence is not conclusive proof of absence, the absence of evidence is at least weak evidence of absence. TenOfAllTrades(talk) 03:22, 5 August 2015 (UTC)

Why do illness symptoms vary so much

Why is it that the same infection can cause different symptoms in different people or even different symptoms on the same person if they get it more than once? For example, a stomach bug can cause vomiting in some people, diarrhoea in others, both in some, and neither in a few. Why? — Preceding unsigned comment added by 94.14.228.44 (talk) 09:49, 3 August 2015 (UTC)

Symptoms are results, sometimes suffer. It is a good job done to find the cause. Other diseases for example multiple sclerosis is also known as "the disease of the thousand faces" due the variety of symptoms. --Hans Haase (有问题吗) 12:37, 3 August 2015 (UTC)

Probably the biggest factor is where the microbes develop. For example, some microbes can survive in the digestive tract, if you consume food containing them, or in the lungs, if you inhale them. For example, per plague (disease): "The symptoms of plague depend on the concentrated areas of infection in each person: bubonic plague in lymph nodes, septicemic plague in blood vessels, pneumonic plague in lungs, and so on". StuRat (talk) 15:57, 3 August 2015 (UTC)

Immune response and tolerance can vary greatly from person to person. For example, there are people that are naturally tolerant to even the latest strains of Hospital acquired MRSA while others will develop infections that cause death. It keeps the oral-fecal transmission route alive as there are still living carriers. Montezuma's revenge is another one demonstrating that regional flora are different and the populations have adapted to them. There are very few "bugs" (virus or bacteria) that kill everyone and it seems the reactions are also across the spectrum (from severe to mild to none). This recent article describes how a carrier with no symptoms, likely contaminated an endoscope with a very nasty bacteria that survives the cleaning procedure. Unfortunate for the next patients but they don't know exactly who brought it in and likely simply lived with it, unknowing. It also makes tracing difficult. Also, a person might react differently to even very minor changes in the bacteria or virus. It also varies with age and health so an infection at 20 isn't the same as an infection at 80. Another way to look at it is, prior to anti-biotics and immunizations, we still survived (albeit with poor outcomes likely in at-risk people). Polio, for example, is tolerated except for a percentage where it causes death or paralysis. We have a spectrum of outcomes for virtually every bug and that appears to be built into our natural variation. --DHeyward (talk) 19:13, 3 August 2015 (UTC)

See the Asymptomatic carrier article; Typhoid Mary was a prominent example of one. Nyttend (talk) 15:11, 4 August 2015 (UTC)

Head tattoo

What are the effects of a permanent and a temporary tattoo on scalp (especially the top part)? Can hair grow normally on it afterwards ? — Preceding unsigned comment added by 103.15.60.58 (talk) 10:44, 3 August 2015 (UTC)

Hair can grow normally over a tattoo. Causes interesting surprises when kids go into boot camp and get their head shaved. 209.149.113.45 (talk) 11:53, 3 August 2015 (UTC)

Hair regrown over a scalp tattoo has occasionally figured in supposedly historical stories as a means to send confidential messages (though I can't remember any specific instances). The device was also used in the W. E. Johns novel Biggles Buries the Hatchet, whereby an old acquaintance in a Soviet gulag alerts Biggles to his incarceration by a cryptic message and map tattooed on to the scalp of a fellow prisoner (illiterate, non-Anglophone and possibly mute – it's been a while since I read it) due for release. {The poster formerly known as 87.81.230.195} 212.95.237.92 (talk) 13:28, 3 August 2015 (UTC)

The tattoo method is mentioned in Steganography#Physical, with a link to Histiaeus, who was said by Herodotus to have used it. AndrewWTaylor (talk) 15:34, 3 August 2015 (UTC)

Funny that the obvious need to dispose of the slave afterwards isn't listed as an obvious drawback, but I guess they were pretty cheap for people of that station... Wnt (talk) 15:44, 4 August 2015 (UTC)

DNA lipofection complexes in suspension called an "emulsion"?

If DNA in solution is mixed with a lipofection reagent, in the resulting suspension correctly called an emulsion? --192.41.131.251 (talk) 12:46, 3 August 2015 (UTC)

This seems like a largely semantic question; someone might insist on a difference between a microemulsion and a "true" emulsion, for example. Nonetheless, if you are mixing phases in some fairly routine physical way (e.g. sonication), I'm thinking that ought to count as a true emulsion, no matter how complicated the structure that a manufacturer might potentially be striving to achieve with it using some well-chosen composition. The problem is, that's more an opinion than an answer, I'm afraid. It doesn't seem like an uncommon description, though. Wnt (talk) 15:38, 4 August 2015 (UTC)

Density of solids at extreme pressures

Can someone point me to a graph or equation that describes what happens to the density of solids at extreme pressures? (The density of a solid is pretty constant at normal pressures but what about cases like the density of iron at the pressure of the center of the Earth?) RJFJR (talk) 20:53, 3 August 2015 (UTC)

The Center for Rock Abuse is probably the preeminent experimental rock-crushing laboratory in the United States; they reside in the Petroleum Engineering department at Colorado School of Mines. Here's a list of their research publications. If you're interested in more observational science, Earthquake and Volcano Deformation is a good book on solid mechanics as it pertains to the massive stresses, strains, and pressures of geological processes.

If what you really seek is details about iron in the center of the earth, the models are much more diverse and a lot harder to validate empirically: you can find lots of references in our article on the inner core. Almost everything we know about this region is deduced from teleseismic soundings of earthquakes: the density can be inferred by estimating the speed of sound at which earthquake P-waves propagate.

Nimur (talk) 21:24, 3 August 2015 (UTC)