Wikipedia:Reference desk/Archives/Science/2015 May 21

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May 21

Urethral fuzz -- what's it called?

What is the scientific name for that bluish-greyish-greenish, fuzzy stuff that sometimes gets stuck in the urethral opening? 24.130.24.40 (talk) 03:31, 21 May 2015 (UTC)

Lint. ―Mandruss ☎ 03:52, 21 May 2015 (UTC)

Albino animal article request

What do albino polar bears look like? I know an albino animal is white, so what is an albino polar bear, I would assume it is still white, but just to make sure, I'm asking for an article about it.63.131.166.45 (talk) 13:25, 21 May 2015 (UTC)Nikalys Edward Earl McKean

The Polar_bear would still be white in appearance but it would not have a black skin. The lack of melanin due to albinism would cause the skin to be pale. "The hollow guard hairs of a polar bear coat were once thought to act as fiber-optic tubes to conduct light to its black skin, where it could be absorbed; however, this theory was disproved by recent studies." So I guess that means it won't freeze to death. 41.13.220.101 (talk) 13:45, 21 May 2015 (UTC)

See also this link, which was the very first I found when doing a Google search for "Albino Polar Bear". --Jayron32 13:47, 21 May 2015 (UTC)

Interesting. "A(sic) albino polar bear would have white skin and so have trouble keeping in heat." I'm having trouble understanding why it would be so. I thought their body fat was the insulator - could the colour of the skin have an effect and why? 41.13.220.101 (talk) 13:58, 21 May 2015 (UTC)

Sounds like this is still based on the solar heating theory, that part of the sunlight ends up absorbed by the black skin that would be reflected away with white skin. The above comments say this was disproven, but, if so, why do they have black skin ? There is some cost to producing melanin, after all, and if it is of no value I'd expect there to be evolutionary pressure to not have black skin.

As for the fat being the insulator, that's true and important to keep the body core temperature up, but it's also important to keep the skin from freezing. StuRat (talk) 14:32, 21 May 2015 (UTC)

Getting back to the original question of appearance, I had a crack at editing Albinism in biology a while ago. It actually gets complicated what the definition of albinism is in animals other than mammals (and plants) but for the polar bear it is quite easy. It would have white skin and pink eyes. I think polar bears normally have a black nose and black claws - so these would be white. Regarding the black skin and thermoregulation. I thought the black skin helped absorb heat and the hollow hairs prevented (reduced) the skin re-radiating to the environment.DrChrissy ^(talk) 15:38, 21 May 2015 (UTC)

The noses and paw pads would be expected to be pink. The pink color comes from blood in capillaries in the skin. When no pigment is present, the red of the blood shows through. StuRat (talk) 02:55, 22 May 2015 (UTC)

Microbiology - pathogen classification

We learned about a classification of pathogenic bacteria based on some curves, which shows the damage made in function of the strengtH of the immun system's response to them.(So for example, there was a class for bacteria which mainly causes harm through the immune response to them)

I don't really know the english name for this classification (maybe sg. like damage curves?) and I can't find any info neither in Wikipedia nor with Google... where can I find more information about this? — Preceding unsigned comment added by 193.6.50.28 (talk) 16:37, 21 May 2015 (UTC)

Does this help. --Jayron32 17:42, 21 May 2015 (UTC)

Biology/Anthropology - The development of gold in humans

This is a question that I can't find any information on. So if you are a biology buff I would appreciate you liberating me of my ignorance. So here it goes. All humans have small ammounts of gold in their body. So far as I know since gold is a good conductor of electricity the gold helps with transmitting electrical signals to the brain/body. So where does the gold come from that is in humans? I would imagine that the gold is created/formed during the early stages of human development? (fetus/infant) I wouldn't think that the gold is taken from the mother's body nor would I think that nuclear fussion is occuring. So have scientists discovered how this happens? Some type of chemical (psysiological?) process? If so does that mean that you could take biological materials x, y, and z and make gold?Agent of the nine (talk) 17:56, 21 May 2015 (UTC)

According to Composition of the human body, the human body is 140 parts per billion gold. That's a ridiculously small amount. It also has no physiological use. The gold is there because it exists on earth, and there are non-zero numbers of just about every atom on earth at just about any location on earth. Being non-zero is not the same as being significant or meaningful, however. --Jayron32 18:10, 21 May 2015 (UTC)

Wow how interesting! I swore that my highschool biology teacher said that the gold is helpful for neurotransmitters. That makes a lot of sense though. I knew that for example there is lead in chocolate but you will die of eating too much chocolate before you die of lead poisoning. There's polonium 210 in every fruit and veggie that anyone has ever eaten. We could even talk about the nonsensical claims by anti-vaxxers. "There's mercury, and metals and stuff in vaccines!". LOL quantity of "x" is always a more important factor in determining how 'x' will change an environment rather than "x" itself. I saw a scientific poster that said the amount of uranium in the average human body is "ten multiplied by three to the negative eight percent power". I have no idea how to solve that equation but in my mind the most logical answer is "one atom".Agent of the nine (talk) 18:42, 21 May 2015 (UTC)

See Dietary element. There are between 20-29 elements which have physiological uses in the human body (depending on how loosely one defines "use") Gold is not among them. I have no idea where your teacher got the notion that gold was used by neurotransmitters; while gold is an excellent electrical conductor, that is only in actual metallic gold. Any gold in your body will be in the form of gold ions, most likely, and then also it is so dilute and so spread out (an occasional atom here or there) as to be useless in transmitting electrical signals. Plus, neurotransmitters do not operate on electricity anyways. They are chemical agents, and as such, a subclass of compounds we call hormones. --Jayron32 18:51, 21 May 2015 (UTC)

Also, there are a LOT more than one atom of uranium in your body. The article I cite above gives a figure of 1.3 parts per billion for uranium (one billion is 10⁹. There are roughly 7 x 10²⁷ atoms in your body, roughly 10,000 or so moles worth, which means that there are roughly 5.3 x 10¹⁸ atoms of uranium in the average human, or 5.3 billion billion, or 5300000000000000000 atoms of uranium in you right now, give or take. That's a few more than one. Note, however, this is not a statement that there is a significant amount of uranium. It's meaninglessly insignificant. It's just a reminder that atoms are REALLY REALLY REALLY small. Like, way smaller than you probably think they are. --Jayron32 18:59, 21 May 2015 (UTC)

Gold_salts can be used as a treatment for various medical conditions, and gold nanoparticles are being researched as a drug delivery vector [1]. We wouldn't want to use humans or most animals to get gold, but there has been some interest in using some plants to get gold [2]. SemanticMantis (talk) 19:31, 21 May 2015 (UTC)

wow... so if you took a one inch by one inch square of human skin (just the epidermis for the sake of argument) how many atoms comprise that chunk of skin? one trillion? there are so many.. That means a histamine is soooooo tiny. (only 17 atoms smallest physiological compound in human body?) Hey so you know how atoms vibrate? Well I was thinking about the 4 stages of matter (solid, liquid, gas, plasma?) well the atoms in a solid "touch" each other very often because they are so close together. In a gas the atoms "touch" each other less often because they are farther apart. Well what if you made a material where the atoms "didn't vibrate" they always "touched" each other? Would that material be "super dense" or "almost indestructable"?. I'm basing this on the American military tank known as the Abrams tank. The metal on the tank is subjected to uranium which causes the atoms to "touch" more often. This makes the metal even stronger. What if the atoms are so close they can't vibrate?Agent of the nine (talk) 19:40, 21 May 2015 (UTC)

WAY more than a trillion. Try this on for size. Avogadro's number is defined as the number of carbon atoms in 12 grams of pure carbon 12. Roughly speaking, the lead of a new #2 pencil will contain about 1 grams of carbon, give or take. Inside that pencil lead then should be roughly 5 x 10²² atoms of carbon. Let's compare that to other large numbers:

1000000 one million
7000000000 seven billion, the number of people on earth
100000000000000 100 trillion, roughly the global money supply in dollars
50000000000000000000000 the number of carbon atoms in a gram of carbon

To get only 1 trillion atoms in a sample of your pencil lead, you'd need to slice it up into 50,000,000,000 pieces. That's 50 billion pieces. That's pretty tiny. Again, these numbers are so large because atoms are fantastically small. --Jayron32 20:15, 21 May 2015 (UTC)

To answer your other questions: You cannot back atoms so close they cannot vibrate; the only way to get them to stop vibrating is to remove all the heat, to bring them down to absolute zero. Also, in a solid and a liquid, the atoms are essentially always in contact with each other; they are called the "condensed" phases for that reason. The density of a substance depends on a number of factors, the three most important are a) the mass of the individual atoms (atomic mass) b) the volume of the individual atoms (related to the atomic radius) and c) the crystal structure of the solid; the exact type of unit cell determines how closely packed the atoms can get. Metals get their strength not only for their density, but also from the way the atoms all hold together. See metallic bonding. --Jayron32 20:20, 21 May 2015 (UTC)

It is also fruitless to think about atoms "touching" each other. Atoms are mostly empty space, and this concept is really important. There is no "edge" of an atom: there is simply a gradual decrease in the strength of any interaction that continues decreasing towards zero as you get farther and farther from the "center" of the atom (i.e. that poorly-defined location where the interaction is strongest). An atom is always interacting with everything at all distances - but at very close distances, the interaction is strong and occurs rapidly; at very far distances, the interaction is very slow and requires time to propagate.

The most important interaction for interatomic forces is the coulomb interaction, but all fundamental interactions play some role in the behavior of atoms (and groups of atoms).

Nimur (talk) 20:59, 21 May 2015 (UTC)

That's also strictly true, but a bit pedantic. Atoms don't have edges, but they do have edge-like behavior; in the sense that we can define a spherical region of space around the nucleus where the atom's interaction has very "edgelike" behavior. A classic example is this well-known graph; the minimum of that graph is as good of a definition of an 'edge' as any. It's why we can define things like atomic radius and ionic radius and the like. Just because it doesn't behave impenetrably, and just because it isn't a little ball bearing doesn't mean it doesn't have a meaningful edge. --Jayron32 21:10, 21 May 2015 (UTC)

Well, I dislike your choice of the word "edge." I much prefer "characteristic radius" or "scale length" or something along that line of terminology, because this word-choice wouldn't imply anything about the behavior one could expect at that radius. But this is beside the point; you are correct that we can choose to define the "edge" where ever it is convenient. Nimur (talk) 22:28, 21 May 2015 (UTC)

SO nimur your telling me that an atom in my eye is somehow interacting with a particle a trillion miles away. you said "an atom is always interacting with everything at all distances". How do you know that? Agent of the nine (talk) 21:08, 21 May 2015 (UTC)

No, that's true too. However, you have to define "non-zero" and "significant". There's a real, calculatable gravitational attraction between a speck of dust here on earth and one floating at the other end of the Milky Way galaxy, in the sense that yes, I can plug numbers in the equation and get a number out and write that number down. That's a real value, and I also have no reason to suspect it isn't a scrupulously true value. That doesn't mean it's a useful value for predicting behavior on time scales I care about. It's like the gold in your body again. It's real, it's honestly there, and it's also honestly not useful for understanding anything about how your body works, because it isn't significant. --Jayron32 21:13, 21 May 2015 (UTC)

Yes. And this is why we use simplified models of behaviors. For example, when we want to study molecular interactions, we can use Lewis diagrams. These tell us how simple atomic structures will form. The model won't work for complicated atoms; the Lewis model is not even consistent with a first-principles application of the Coulomb force law; but it works and it helps us to construct useful ideas that accurately describe some situations.

If you wanted to solve all of molecular dynamics by computing gravity and nuclear interactions and quantum-mechanically-correct electron dynamics, you wouldn't be able to write solvable equations for even the simplest molecules like water. These mathematical models may be more detailed, but they are not always helpful, and for most things we care about, these formulations surely are not tractable. Nimur (talk) 22:25, 21 May 2015 (UTC)

"Truth is much too complicated to allow anything but approximations." per John von Neumann Short Brigade Harvester Boris (talk) 02:24, 22 May 2015 (UTC)

I should note that the mercury in vaccines is discussed at thimerosal and thiomersal controversy. (the difference has something to do with lawyers playing at anagrams) However you put it, thimerosal is deadly enough that nothing can grow in vaccine containing it ... but that little bit of liquid is a lot less than the volume of the human body. The therapeutic ratio is presumably something huge, but worrying about it isn't mystically stupid, unlike most of the autism-vaccine paid science controversy.

In general, whether the gold in the human body is "significant" isn't a matter of quantity but how you measure it. A significant difference has to do with standard deviation of your testing, and more complex matters of statistics, all of which boil down in the end to certain underlying assumptions you make about what is notable/publishable. If you can't tell how much gold is in your body the amount is insignificant, and generally this is true. But suppose somebody makes a drone that shoots a certain terahertz frequency that can detect gold ions, and programs it to kill anybody with 10x the signal, and some spy spikes Osama bin Laden's whiskey bottle with trace amounts of gold before he passes it around at a meeting. Suddenly it would be significant. Since you never know what can be invented or discovered, you never really know what is significant, only what is significant to you. Wnt (talk) 23:57, 21 May 2015 (UTC)

Well, the first rule of writing fiction, as you've done here, is it's your fictional world. You decide what magic happens in it. If we're going to discuss actual scientific principles with actual science, we should avoid making shit up. --Jayron32 00:28, 22 May 2015 (UTC)

I'd prefer to call it a "hypothetical", or if in a pretentious mood, a "thought experiment". Wnt (talk) 12:12, 22 May 2015 (UTC)

argon

i've heard that 'argon' is in the air we breathe.we inhale it,but then it is totally exhaled,floating around until another may inhale it,then exhale it.so the story i heard goes that we could theorecticly be inhaling argon that socrates,plato,lincoln,etc.,had once breathed.68.98.10.160 (talk) 23:45, 21 May 2015 (UTC)

Approximately one percent of the air is argon. Since it is a so-called noble gas, it is indeed exhaled without being used. It is true that one may be inhaling an argon atom that has been breathed by anyone in history. Is there a question? Robert McClenon (talk) 23:55, 21 May 2015 (UTC)

Actually, there's some question of how thoroughly it is mixed - alas, I certainly don't know the answer. The Holy Grail of this type of question is the consideration of the fate of the blood and, um, 'water' shed by Jesus during the Crucifixion. If you simply take Avogadro's number (6.022E23) and divide by 1.4E24 cubic ml of water on Earth [3] and divide by the MW of water (18), on average there should be 1 molecule of water in 42 milliliters of water now, from any given ml of water in history. (I think ... there may be multiple errors in that because I rushed) Assuming many mls of blood were shed, you could say that any one of us is therefore the Holy Grail. However, a well sunk into the Oglala Aquifer (hmmm, I'm not sure now) or the Great Man-Made River might not get any of that, or at least not much. But then, what about water that went deep in ocean currents? And so forth. I suspect the figure doesn't really change much, because we're talking orders of magnitude and additive effects negate large order of magnitude differences - for example all the water in Antarctica doesn't reduce the amount of water in circulation by enough to make it all that much less dilution than otherwise. But modeling the spread of the "Holy Grails" around the world would be kind of a cute hydrological simulation. Wnt (talk) 00:16, 22 May 2015 (UTC)

That's an interesting thought experiment, but water isn't argon (which is what this question is about). Short Brigade Harvester Boris (talk) 00:24, 22 May 2015 (UTC)

Yes, but air would be pretty well mixed around in a few years. But anyway there would be no difference between argon atoms exhaled by someone famous, and any other collection of argon atoms in the air. Graeme Bartlett (talk) 02:52, 22 May 2015 (UTC)

But the usual way of illustrating this meme is the problem of Caesar's last breath, which involves air; argon is simply a percentage of air (about .93%), so the problems are pretty much interchangable if you include a factor for the percentage of inhaled gas that argon makes up. Fermi (or someone else the Internet has made into Fermi) gave the problem as "How many of the molecules you breathe in in one breath come from the dying breath of Julius Caesar?" Perfect diffusion is usally assumed to simplify the problem. The answer is roughly one molecule in each of your breaths comes from Caesar's dying breath, but if you Google "Caesar's dying breath problem" you can look at the specifics. (This is an example.) Obviously the identity of the person doing the initial breathing isn't relevant, and so you could with equal justification say on average, each of your breaths includes about one molecule from each of the dying breaths of Caesar, Socrates, Plato, Lincoln, and Adolf Hitler. - Nunh-huh 03:03, 22 May 2015 (UTC)

This question has come up before, e.g. here. As I said then, the question of whether an atom you inhale is the same as an atom someone else exhaled is actually meaningless in a quantum world, because of particle indistinguishability. -- BenRG (talk) 03:28, 22 May 2015 (UTC)

The question is neither actually meaningless nor mathematically meaningless. The fact that identical atoms are indistinguishable doesn't mean they don't have reality or identity. It just means we can't tag them or trace them under normal, unprepared circumstances. Hence any figure for historical purposes would have to be an estimate. But it's precisely this fact that scientists take into account when the use rare radioactive isotopes to trace the absorption and routes of various chemicals in biological systems. isotopic labeling and radioactive tracing are the exceptions that prove your rule. μηδείς (talk) 16:42, 22 May 2015 (UTC)

No, they are not an exception, because radioactive isotopes are, by definition, different atoms. If I have one atom of uranium-235, and another of uranium-238, I can distinguish them because they are different. The fact that we call them both "uranium" is somewhat arbitrary from a physical point of view; there are good reasons to do so, but that's a human construct, not a physical one. They are different atoms because they contain non-identical arrangements of their subatomic particles. This is also true of comparing a neutral atom to an ion of the same element (where the number of electrons are different) or comparing atoms with the same numbers of subatomic particles, but where their arrangment is different, see for example Nuclear isomers. However, when you have really honest-to-god truly identical atoms (like two identical atoms of U-235, of the same Nuclear isomer, of the same charge) they are literally indistinguishable, and BenRG's point stands. --Jayron32 16:49, 22 May 2015 (UTC)

BenRG (as far as I understand) is saying that because we cannot differentiate the Argon atoms the claim is actually meaningless. But our not being able to identify them individually is irrelevant to whether some of the argon atoms I am breathing now actually were or were not breathed by Julius Caesar. The methods I mentioned above take into account that we can't normally distinguish common naturally occurring isotopes, so they use rare isotopes in controlled conditions for such tests. While under normal circumstances, no specific atom of one isotope can be named Bob and then identified later as Bob, they still can assume statistically that some very high percentage of those isotopic tracers was introduced in the controlled conditions of the test. μηδείς (talk) 21:11, 22 May 2015 (UTC)

I think you're missing that there isn't any classical probabilistic interpretation of quantum statistics. An example of classical particle statistics is that if you calculate a 5% chance of A going to X and B going to Y and a 20% chance of A going to Y and B going to X, and you find A&B at X&Y but can't tell which is which, you can bet that A was at X at 20:5 odds and expect to break even. An example of quantum statistics is that you calculate a 1/6 + i/2 amplitude of A going to X and B going to Y, and a 1/3 - i/2 amplitude of A going to Y and B going to X, and they are quantum-indistinguishable particles, and you find them at X and Y. The probability of finding them there is |(1/6 + i/2) + (1/3 - i/2)|² = 25%, as in the classical case, but unlike the classical case you can't say after the fact that they took one of the trajectories but you don't know which; the classical probabilities associated with either trajectory by itself would have been 10/36 and 13/36, which don't add to the probability of the thing that actually happened.

If A and B are distinguishable in principle (e.g. they're different isotopes of argon) then the quantum prediction is that they'll follow classical statistics, i.e. that there's a 23/36 chance you'll find them at X&Y, after which you can bet at 13:10 odds that A was at X and expect to break even (after checking whether A was at X to settle the bet, which you can do in that case). But as soon as you have two indistinguishable tracer atoms, one in Caesar's last breath and one not, and one in your latest breath and one not, you can't assign a probability to its being the same one. -- BenRG (talk) 18:53, 23 May 2015 (UTC)

The last sentence of yours is essential to the apparent disagreement. If there was a finite amount of argon in existence during Caesar's era, and Argon is relatively stable (Argon 40, the most common type in the atmosphere is), and one can calculate how much argon existed, was destroyed by fission, decayed, was sequestered, and was produced by fission, or fell from the sky in the meantime, then one can calculate a probability. Not actually identify certain atoms named Frank and Sue, but estimate a population. Since the decay and production by decay of argon isotopes is known, measurable, and predictable, one can most certainly come up with a good statistical estimate. Unless you are denying any statistical estimate is possible at all, you are not disagreeing with me. μηδείς (talk) 01:49, 24 May 2015 (UTC)