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February 5

Yellow rain

In December 2012 Sri Lankan towns such as Mineragala and Southern provinces experienced Red rain and towns of Polonnaruwa and Kantale experienced Yellow rain. But the article about yellow rain totally differs from this rain. So natural yellow rain should be also included here. Sri Lanka based researches reveal that this colouration of monsoon rains was due to remains of meteorites. So what is the difference between natural and artificial ones? Source:

• [1]
• [2]
• Rupavahini broadcasting (government's official broadcasting channel)

--G.Kiruthikan (talk) 07:06, 5 February 2013 (UTC)

I fixed the dead links above. Sean.hoyland - talk 07:38, 5 February 2013 (UTC)

Both the red rain and the natural form of yellow rain are actually varieties of blood rain, which is caused by large quantities of dust and pollen in the air (the meteor hypothesis, BTW, has been disproved). "Artificial" yellow rain, however (I put it in quotes because its very existence is unproven) is a hypothetical Soviet chemical weapon allegedly used against South Vietnam by the Vietcong in 1975, which may be composed of various mycotoxins, mustard gas, etc. FWiW 24.23.196.85 (talk) 08:53, 5 February 2013 (UTC)

Law of excluded middle, null hypothesis, and disproof of god

Ok so let's say that the statement "god doesn't exist" is the null hypothesis and "god exists" is the alternative hypothesis. So the null hypothesis can not be proven and is the default position, that directly implies that the claim "god doesn't exist" can not be proven. Let's define god as the being that is described in The Book of Genesis. Since this being has been described as creating humans, that is a demonstrable claim that can be falsified. Evolution has falsified creationism, and therefore the god described in The Book of Genesis has been disproven. According to the Law of excluded middle, two contradictory propositions (i.e. where one proposition is the negation of the other) one must be true. Since the alternative hypothesis has been disproven, it stands to reason that the null hypothesis must be true according to the Law of excluded middle. So my question is, can something be true, without it being proven (using this logic)? ScienceApe (talk) 02:00, 5 February 2013 (UTC)

This is the reference desk. Can you rephrase that as a specific request for research help, rather than a long invitation to debate? μηδείς (talk) 02:13, 5 February 2013 (UTC)

A statement can be assumed true, and thus require no proof. This is the essence of the method by which most religious persons justify their convictions. 72.128.82.131 (talk) 02:38, 5 February 2013 (UTC)

Your argument utilizes the strawman argument and is not a proof; and "using this logic" [sic] one can prove anything. ~:74.60.29.141 (talk) 02:44, 5 February 2013 (UTC):~

Or disprove anything. No believer has ever come up with any evidence that would convince a scientist there is a god, and no scientist has ever been able to cause a believer to doubt there is a god. Then there are scientists who teach evolution but privately are strong believers in the God who created the universe ab initio. Work that out. -- Jack of Oz ^[Talk] 02:53, 5 February 2013 (UTC)

Not to mention that God and evolution are not mutually-exclusive. [I didn't mention that] ~:74.60.29.141 (talk) 03:48, 5 February 2013 (UTC):~

The flaw here is in this line: "Since this being has been described as creating humans, that is a demonstrable claim that can be falsified."...Sadly, that is not the case. God is described as being "omniscient" and "omnipotent" - and that's a major problem for any disproof of his existence. If this is true, then he can do absolutely anything. For example: He could create humans (per Genesis), then completely falsify all of the evidence (planting fake fossils, adding appropriate junk DNA, etc) to make it look to scientists like we evolved from pond-slime...or he could warp the minds of scientists who investigate evolution to make them believe it to be true and to ignore contradictory evidence. Heck, it might be that not one single person in the world believes in evolution but God decided to warp your mind to make you think that it's widely accepted as true. Maybe he allowed evolution to do the work and then faked the creation of the book of Genesis. An omnipotent being has literally no limits...that's why the non-existence of God is unfalsifiable - even by complicated arguments like yours. Of course my claim that there are omnipotent, green, piano-playing aardvarks living on the dark side of the moon is also unfalsifiable - and so are an infinite number of other possibilities. The "God hypothesis" therefore has a statistically infinitesimal (but not zero) probability of being true...so rational beings may ignore that possibility. SteveBaker (talk) 16:17, 5 February 2013 (UTC)

Your final sentence does not logically follow. The premise that there are is an infinite number of possible omnipotent beings does not lead to the conclusion that the probability for each of those possibilities is infinitesimally small, because that requires the unstated (and unproven) assumption that each of those possibilities is equally probable. - Lindert (talk) 16:36, 5 February 2013 (UTC)

Yeah - that's true to a degree - but since these are unfalsifiable hypotheses and none of them (including the "God hypothesis") has any solid evidence to prove them, our best guess has to be that they are equally probable. SteveBaker (talk) 20:41, 5 February 2013 (UTC)

The trick here is that you are defining "god" very narrowly here, as being not merely the god of Genesis but a particular interpretation of that god which is one whose work must leave evidence demonstrably contradictory to evolution. So your proof of "god not existing" is equally narrow. You have not, for example, disproved that there could be a God who created the world as in Genesis, but who subsequently covered up his prior work by some miraculous means to leave only evidence of the natural history implied by our current laws of physics; or who did the creation in a parallel universe and copied and refined it in this one; or who did the work in some sort of Platonic realm of archetypes; etc. Wnt (talk) 05:12, 5 February 2013 (UTC)

I am not personally very interested in not the god-vs-no-god debate - at least, not at face value. I feel that this debate has been rehashed by many intelligent people, and many many more unintelligent people, for many centuries, and in many languages. What I am interested in is the Kolmogorov complexity of their debate, and more importantly, the marginal contribution to that complexity of any new individual's argument. I fear that we are reaching a plateau, where the complexity no longer increases, because the exact same arguments for each side are made, over and over and over again, by people who have chosen not to invest the time to read the earlier parts of the "thread." Now, it's a heck of a lot of effort to expect every Tom, Dick, and Harry to start off with Plato and Thomas Aquinas and Sartre; but by golly, if somebody's interested in the subject, then they really ought to invest the time to read all the prior arguments so that we can make forward progress in the discussion, instead of repeating the same string-literal arguments, without adding to the complexity. (And yes, I posit that in five centuries of English, and five decades of digital texts, somebody has written almost exactly the same string of text as your brilliant idea to prove, or disprove, anything). If only there were a free repository of great classic literature, and short encyclopedic summaries to help guide the interested reader through the denser parts of the prose... I bet each person could expend a little effort to ramp up on "prior art," and there would be much less repetition of the elementary tenets of formal logic, theology, and the general theory of human knowledge. And more to the point, we could then process this digital corpus to estimate the Kolmogorov complexity of the god-vs-no-god debate, giving us an upper-bound of the importance of it, as measured in bits-of-entropy. We could then compare that to the bits of entropy in other observed phenomena. Nimur (talk) 05:28, 5 February 2013 (UTC)

While what you say is valid in many arenas, basic-level questions should be welcome here - we don't tell people to read Schroedinger when they ask about quantum teleportation, for example. Also there may be an argument that in modern society, our unspoken assumptions about God have changed so dramatically that the same arguments may not lead to the same conclusions, because our generalizations may not accurately reflect our actual feelings and the range of potential philosophy under which we might evaluate them. Wnt (talk) 15:24, 6 February 2013 (UTC)

This is not a place for religious debates. Why don't we just hat the whole thing? 24.23.196.85 (talk) 05:39, 5 February 2013 (UTC)

Malala, the girl who survived the Taliban's assassination attempt, today called her survival a gift from God. And there's not a soul on earth who can prove her wrong. ←Baseball Bugs ^{What's up, Doc?} carrots→ 05:47, 5 February 2013 (UTC)

Being nearly assassinated and surviving? I think I'll pass on gifts from God then thank you very much. Dmcq (talk) 10:30, 5 February 2013 (UTC)

The assassination attempt was a "gift" from evil people. If you would prefer not to survive an assassination attempt, that's up to you. ←Baseball Bugs ^{What's up, Doc?} carrots→ 14:46, 5 February 2013 (UTC)

That's the old argument from The God Delusion - why did Our Lady of Fatima not guide the bullet another 20cm that way? Or, more generally, why is there evil in the world? If you assign all evil in the world to "evil people", and all good to god, what stops me from doing the same with communism, or Thor, or the Beach Boys? --Stephan Schulz (talk) 21:47, 5 February 2013 (UTC)

Right, the assassination attempt was by humans because it was evil, whereas the recovery was by God because it was good. Teams of dedicated doctors, sophisticated medical devices, and generous donors obviously had nothing to do with it. Apparently, a 14 year old girl with zero scientific training and minimal scientific knowledge is now the world's sole scientific authority. --140.180.247.198 (talk) 15:51, 5 February 2013 (UTC)

more for us165.212.189.187 (talk) 13:58, 5 February 2013 (UTC)

I would guess the Taleban think they follow God's teaching and British surgeons are in general misguided infidels even, dare I mention it?, atheists and evil has triumphed for the moment in this case by saving her life. Dmcq (talk) 17:10, 5 February 2013 (UTC)

As (it seems to me) usual in these debates, it all hinges on each individual's definition of "God"; and (it seems to me) any such concrete definition can be disproved, the more concrete and specific the easier to disprove. In this case, God defined as the God of the first portion of Genesis. This doesn't lead to any ending, however, if one's definition of God includes transcendence over concrete definition by the human intellect. See Neti neti and Apophatic theology. Gzuckier (talk) 18:09, 5 February 2013 (UTC)

(I have un-hatted this discussion. While some responses have gone off the rails, the question is a valid one and there have been several valid answers.) SteveBaker (talk) 14:14, 6 February 2013 (UTC)

feeling "surreal" or like the world is a fabrication or a simulation

Is this a known symptom of psychosis? This is not a medical question, I just wonder if there are lots of people in society with undiagnosed schizotypal disorders, thanks. 71.207.151.227 (talk) 11:44, 5 February 2013 (UTC)

This is not about the philosophical belief, more like the emotional feeling that people have, i.e. it is a very visceral feeling. 71.207.151.227 (talk) 11:44, 5 February 2013 (UTC)

see Derealization, the reference desk cannot provide a medical opinion or speculation ---- _nonsense ferret 13:00, 5 February 2013 (UTC)

And yes it stands to reason that there are lots of people in society with undiagnosed mental illness. The NIMH found that half of all cases of mental illness begin by age 14, and that " there are long delays — sometimes decades — between first onset of symptoms and when people seek and receive treatment". --TammyMoet (talk) 13:04, 5 February 2013 (UTC)

Why do questions like this make me feel like wikipedia is a potentially endlessly recursive computer platform? μηδείς (talk) 20:44, 5 February 2013 (UTC)

Ask somebody to kick you in the shins, and then get back to us about whether it seemed "real" or not. ←Baseball Bugs ^{What's up, Doc?} carrots→ 23:28, 5 February 2013 (UTC)

Whenever I suggest that people accuse me of being cruel! μηδείς (talk) 23:32, 5 February 2013 (UTC)

I might call it the Three Stooges Experiment. If it's real, it hurts. If not, it doesn't. ←Baseball Bugs ^{What's up, Doc?} carrots→ 04:40, 6 February 2013 (UTC)

Zycosoil

Please help me by telling me what is the generic name for Zycosoil — Preceding unsigned comment added by 188.245.230.38 (talk) 12:35, 5 February 2013 (UTC)

A Google search shows it is a waterproofing agent. --PlanetEditor (talk) 12:57, 5 February 2013 (UTC)

I need to know what is the generic name for Zycosoil that is manufactured in India.

188.245.230.38 (talk) 13:13, 5 February 2013 (UTC)

It seems to be a fairly unusual product and I'm not sure that there is an agreed generic term for it. It is used to protect soil from water erosion so it could be called a 'soil protective' or an 'erosion preventer', You might find this link useful as it has a video demonstrating the action of Zycosoil. This may be a Language Desk question. Richard Avery (talk) 14:32, 5 February 2013 (UTC)

• Organosilicon compound — See also: [3]   ~:74.60.29.141 (talk) 17:05, 5 February 2013 (UTC):~

Chelating?

Has chelating have any other practicle purposes other than medical? Would the removal of rust be called this . . . or has it another name? — Preceding unsigned comment added by Cousin Bruce (talk • contribs) 13:34, 5 February 2013 (UTC)

Our article suggests it has other uses than medical Zzubnik (talk) 13:46, 5 February 2013 (UTC)

One application they missed is hydrometallurgy: for example, chelating agents can be used to extract boron from seawater, or plutonium from a nitric acid solution of spent nuclear fuel (among many other things)... 24.23.196.85 (talk) 05:22, 6 February 2013 (UTC)

Does chemical analysis count as practical? See Complexometric titration. 202.155.85.18 (talk) 08:13, 8 February 2013 (UTC)

Sure it does! 24.23.196.85 (talk) 03:35, 9 February 2013 (UTC)

Vacuum of space

does the vacuum of space exert a negative energy on objects in an outward and perpendicular direction to the surface of the objects?165.212.189.187 (talk) 14:06, 5 February 2013 (UTC)

That's sort of a backwards way to look at it. Any object in space, let's say a human who forget his space suit, has some internal pressure (blood pressure is one form of this). On Earth this is countered by atmospheric pressure. Without this, in space, there is an unbalanced outward pressure which causes the person to swell up. StuRat (talk) 14:23, 5 February 2013 (UTC)

Wikipedia says negative energy is "A plot device in fiction" Zzubnik (talk) 14:24, 5 February 2013 (UTC)

OK a positive energy from the negative mass density of space. so the vacuum of space is not exerting outward pressure on the earth? that only applies to objects with inertial outward pressure, (which the earth does not have)?165.212.189.187 (talk) 14:31, 5 February 2013 (UTC)

"Things" have internal pressure. Vacuum of space does not exert a force at this scale. Zzubnik (talk) 14:39, 5 February 2013 (UTC)

So the gravity of earth prevents its internal pressure from exploding like the human without the suit?165.212.189.187 (talk) 15:26, 5 February 2013 (UTC)

Yes, gravity holds it all together. There's also the effect of the solar wind, which tends to blow off lighter elements at the top of the atmosphere, explaining why there is so little free hydrogen and helium in the air, despite those being the most common elements in the universe. BTW, a human in space doesn't explode, he just swells up. StuRat (talk) 15:48, 5 February 2013 (UTC)

Also, the use of the word "Energy" in the question is completely incorrect. Force would've been a much better choice. Energy doesn't have a direction in space and cannot point outward or be perpendicular. Neither does pressure. Dauto (talk) 16:14, 5 February 2013 (UTC)

Thanks for clarifying. Why doesnt gravity hold the human together the same way?165.212.189.187 (talk) 16:52, 5 February 2013 (UTC)

Gravity doesn't by itself help with holding humans together; a man on the moon experiences gravity, but because the lunar atmosphere is practically nonexistent, he'd swell up as if he were in a vacuum. Launch him back into space inside a spaceship, and he'll be safe because of the air inside the spaceship, even though he's experiencing no gravity. It's simply that Earth's gravity holds the atmosphere that prevents us from swelling up. Humans have their own gravity, simply because all matter does, but we're far far too tiny for that gravity to have any practical effect. Nyttend (talk) 17:23, 5 February 2013 (UTC)

But that doesn't explain why the human will swell and the earth doesn't. Also if the swell is an action in the outward direction then what is responsible for stopping the swell. ...object in motion will stay in motion, no?165.212.189.187 (talk) 19:00, 5 February 2013 (UTC)

The same thing which keeps a balloon from exploding when you inflate it. The membranes are strong enough to withhold a certain amount of pressure, but too much pressure would, indeed, cause both to explode. StuRat (talk) 20:00, 5 February 2013 (UTC)

Gravitational forces are proportional to the mass of the object producing it. A person's gravity is simply to week to hold an atmosphere. Dauto (talk) 01:56, 6 February 2013 (UTC)

We should also state that there are other forces which can cause small clumps of matter to stick together in space. There can be chemical bonds, for example. StuRat (talk) 16:50, 6 February 2013 (UTC)

Intermezzo (zolpidem tartrate)

In the past, medications avoided English words as their names, presumably so the pharmaceutical company could protect the trademark copyright more easily. So, why does this med have an English name ? Has something changed ? StuRat (talk) 15:09, 5 February 2013 (UTC)

Hmmm, is that more English than Allegra? Wnt (talk) 15:37, 5 February 2013 (UTC)

I don't speak Italian, yet know what "intermezzo" means. So, to me, that means it has now become an English word, like "pizza". StuRat (talk) 15:51, 5 February 2013 (UTC)

If they thought that avoiding English words as drug names helps to protect trademarks (note: not the same thing as copyrights - there are no one-word copyrighted works) then they don't understand trademark law. Apple (the computer), Genesis (the band) and Mercury (the car) have no trouble protecting their trademarks. Mostly the name choices reflect style. You can look at the drug names "Dr. Bateman's Pectoral Drops" and "Lipitor" and figure out roughly when they were introduced. --Guy Macon (talk) 18:54, 5 February 2013 (UTC)

Who are "they"? The medications? --Trovatore (talk) 03:13, 6 February 2013 (UTC)

Yes. --Guy Macon (talk) 11:25, 6 February 2013 (UTC)

microbiology

Principles of pregenancy test — Preceding unsigned comment added by 93.186.23.89 (talk) 15:21, 5 February 2013 (UTC)

Information about different types of pregnancy tests and the principles by which they operate can be found in the Wikipedia article pregnancy test. TenOfAllTrades(talk) 15:29, 5 February 2013 (UTC)

Live double-headed eagles

Has a live double-headed eagle (or the body of a dead one) ever been recorded, as far as Reference Deskers know? I know that conjoined twins have been found in multiple non-human mammalian species, and I'm pretty sure that I've read about them in other chordates (amphibians, perhaps?), so I don't imagine that it would be completely impossible for the same phenomenon to appear in birds. Google gave exactly eight results, and they were either "I'll buy you a live double-headed eagle for your birthday!" or lists in which "live" happened to be right before "double" etc. Nyttend (talk) 17:18, 5 February 2013 (UTC)

Gah. I'm sure I saw an exhibit of a double-headed eagle at the Odditorium in Blackpool when I was a child. However, I don't think you can search the "Believe It Or Not" website to try and find it. Maybe someone more computer savvy than I can find it. Anyway, thanks for getting me to a site I'd been meaning to find for some time. I may be some time! --TammyMoet (talk) 18:26, 5 February 2013 (UTC)

A huge number of those kinds of things are faked by clever taxidermists. I don't think "having seen one" really tells us much either way here. SteveBaker (talk) 20:32, 5 February 2013 (UTC)

There are a number of images of two headed birds on the internet which may or may not be genuine. This one looks kosher though. Richerman (talk) 20:45, 5 February 2013 (UTC)

Double-headed eagle is a very well known symbol in European heraldry. It's been on the coats of arms of numerous countries, and is currently on the national flags of Albania, Serbia and Montenegro. Countries tend not to have mythical animals in their symbology, so I'm assuming it had some real basis. -- Jack of Oz ^[Talk] 22:00, 5 February 2013 (UTC)

Unicorns, dragons and phoenixes have all been used in European heraldry. I take it the OP is referencing double-headed snakes? CS Miller (talk) 22:32, 5 February 2013 (UTC)

Huh? I'm looking for members of the family Accipitridae (I suppose I'd accept non-eagles from that family) with two heads, in part because I'd already looked at the article Jack links, and I observed that it doesn't discuss the existence or nonexistence of individual members of this family that appeared to have two heads. Snakes hadn't even come to mind; I can't remember ever hearing of a two-headed snake. Nyttend (talk) 23:00, 5 February 2013 (UTC)

See polycephaly and here. I remember reading or hearing that two-headed carnivores usually attack each other, which would explain the lack of such birds. μηδείς (talk) 23:40, 5 February 2013 (UTC)

This more concise link works equally well, as far as I can tell. —Tamfang (talk) 01:16, 28 October 2013 (UTC)

Two headed carnivores usually attack each other? - you can't be serious! Richerman (talk) 00:40, 6 February 2013 (UTC)

I certainly can be serious that I remember hearing, I think it was about turtles, that they would bite each other. If I had a reference (probably one of those 10 most craziest critters shows) I'd give it but it's not the sort of thing I keep files on, sorry. Lol. μηδείς (talk) 01:05, 6 February 2013 (UTC)

Hmmm - my fault for editing when I've been to the pub I suppose. However, a lot of people believe nonsense like that - you should make it clear with that sort of comment that it's a joke. Richerman (talk) 06:37, 6 February 2013 (UTC)

No, it wasn't a joke. The heads supposedly peck at each other. Did you think I meant various two-headed carnivores seek out other two-headed carnivores to battle? μηδείς (talk) 17:57, 6 February 2013 (UTC)

No, I thought that "it would explain the lack of such birds" meant that the two heads always fight to the death, which sounds rather like something from an ancient Greek myth. Richerman (talk) 18:49, 6 February 2013 (UTC)

That only happens in WWE. μηδείς (talk) 03:49, 7 February 2013 (UTC)

I've heard that such reptiles go hungry because each head tries to keep the other from eating. But among turtles, at least, I wouldn't have thought the necks flexible enough for the heads to fight directly. —Tamfang (talk) 01:16, 28 October 2013 (UTC)

Tangentially, the mythological beast Carebearus, which has three heads and three bodies, and the magical ability to be in three different places at the same time. Gzuckier (talk) 14:41, 7 February 2013 (UTC)

Black sky at night

Given that there are "billions and billions" of stars and that light (obviously) travels at the speed of light, why do we see so much "black" in the night sky rather than filled with starlight? Thank you. Rdhartwell (talk) 21:04, 5 February 2013 (UTC)

Black#Why the night sky and space are black - Olbers′ Paradox --Guy Macon (talk) 21:12, 5 February 2013 (UTC)

More to the point, Olbers' paradox. --Jayron32 21:25, 5 February 2013 (UTC)

The universe is finite and expanding, which explains why it is not infinitely bright in all directions, but it does glow in all directions, see cosmic background radiation. μηδείς (talk) 23:42, 5 February 2013 (UTC)

The universe is not in fact known to be finite. See shape of the universe. (The observable universe is finite, but that's different.) --Trovatore (talk) 03:04, 6 February 2013 (UTC)

Yes, and neither is the Flying Spaghetti Monster not known to exist. There's no evidence its infinite, nor even any coherent way of formulating claims about an infinite universe. μηδείς (talk) 17:51, 6 February 2013 (UTC)

Medeis, that's just completely wrong. There are definitely coherent ways of formulating claims about an infinite universe. In Riemannian geometry, it's no more difficult to talk about an infinite universe than a finite one.

As for evidence: The simplest models having nonpositive curvature are infinite, and there definitely is evidence of nonpositive curvature. Whether that evidence is compelling or not at the current time, I can't speak to, as I'm not really up to date on that. But evidence certainly exists.

Now, there are models with nonpositive curvature that live on a compact manifold (that is, finite universe), but they're weird. They're things like a solid dodecahedron with opposite faces identified. Why the universe should have that topology would be more in need of explanation than why it should be infinite. --Trovatore (talk) 21:09, 6 February 2013 (UTC)

I am quite aware there are models which use infinity as a factor. None of them has a real or concrete interpretation. If the universe is "infinite", then however big it actually is, it is even bigger than it actually is. Among other things that means atoms have no size or charge in relation to the universe. That's fine if you want to play such linguistic games, but there's no evidence for it. μηδείς (talk) 00:27, 7 February 2013 (UTC)

You're not making any sense, Medeis. However big it actually is, it's even bigger than that??? What's that even supposed to mean? If the size of an atom is not as large as any finite submultiple of the size of the universe, then why is that bad? Mathematics is perfectly capable of handling infinities as first-class objects, and it is perfectly plausible that the universe could be an example of such. As for evidence, I already addressed that, and you haven't responded to my specific points. --Trovatore (talk) 01:21, 7 February 2013 (UTC)

Medeis is definitely wrong here. In standard cosmology, the universe is qualitatively different if its total energy density is above, equal to, or below a critical threshold. If it's above the threshold, the universe has positive curvature, and must be finite. If it's at the threshold, the universe has 0 curvature and is flat--that is, its geometry is very nearly Euclidean--which implies an infinite universe If it's larger, the universe has negative curvature and must be infinite. This model holds as long as we assume that the universe is nearly uniform at large scales (the cosmological principle). It is indeed nearly uniform within our observable universe, but whether it's uniform elsewhere is not a testable question. As for how an infinite universe can expand, imagine the set of natural numbers: 1, 2, 3, 4... This set is infinite. Now multiply every element by 2, and you can 2, 4, 6, 8... The set has expanded by a factor of 2, and is still trivial to describe. As another example, imagine a large sheet of rubber that's being stretched in all directions. The distance between any two points on the sheet will increase with time, and even if the sheet were infinite, the expansion would still be perfectly well-defined.

Trovatore is not correct in saying there's evidence of nonpositive curvature. Our best value for the curvature is 0, to within 0.4% (see shape of the universe). The fact that the universe is so remarkably flat, along with a few other problems, inspired inflation theory, which current cosmological experiments are trying to test for. --140.180.247.198 (talk) 03:30, 7 February 2013 (UTC)

My understanding is that there are some surveys that come up with a positive number and others with a negative number, isn't that so? In that case, there is evidence of nonpositive curvature (namely the studies that show the negative number). I never asserted that it was the current best hypothesis that the curvature is nonpositive; I don't need to assert that, because Medeis was claiming there was no evidence the universe is infinite, which is not so. --Trovatore (talk) 03:38, 7 February 2013 (UTC)

Oh, and by the way, zero is nonpositive :-) --Trovatore (talk) 03:48, 7 February 2013 (UTC)

The best available measurements indicate the curvature is 0, to within a small margin of error. That means there's roughly 50% chance of the actual curvature being positive, and 50% of it being negative. Whether you call that "50% evidence that the curvature is negative" or "100% evidence that we don't yet know" is a matter of semantics. --140.180.247.198 (talk) 04:42, 7 February 2013 (UTC)

Yes, but semantics are important, especially in this sort of case. There's a big difference between "there's no evidence that proposition A is true" and "the evidence that proposition A is true, and that it's false, is roughly balanced". --Trovatore (talk) 04:46, 7 February 2013 (UTC)

I agree with Medeis. Surely an infinite universe can be ruled out on account of it's finite age. If as evidence indicates it began 13+ billion years ago in a "big bang" there has not been enough time, even with inflation, for it to have achieved infinite size. An infinite universe is only compatible with "steady state", or at least either infinite age or infinite expansion rate. Desiderata9 (talk) 02:34, 10 February 2013 (UTC)

No, that is not correct. See below. --Trovatore (talk) 02:11, 29 August 2014 (UTC)

Yeah - Olbers' paradox is the answer here. It goes something like this:

• The light from a distant object attenuates as the square of the distance between us...a star at distance 2X is four times dimmer than a star at distance X.
• The number of stars (galaxies, whatever) within a distance X is (on average) four times smaller than the number at distance 2X.

So this growth in the number of stars over distance is exactly compensated for by the reduction in light over that distance...but...

• The amount of dust and gasses attenuating that light is (on average) proportional to the distance to the star ('X') - and therefore the amount of light they absorb is also proportional to X. So the further you get away from here - the less light there is (in total) coming from the stars at that range.

That sounds like it solves the problem...but sadly, no. Things are more complicated than that...

• Those intervening dust and gas clouds are heated by the incoming light - and will eventually heat up and glow - emitting the same amount of energy that they absorb. So, again, we should have an infinitely bright sky.

The resolution of this problem relates to redshift. The universe is expanding - so the frequency of light from distant objects has longer and longer wavelengths - so visible light is converted into microwaves and longer wavelengths. The "cosmic background radiation" is where that light ends up - and the sky is indeed filled with that radiation (although, interestingly, it's kinda patchy).

Stars that are sufficiently far away are retreating from us at faster than the speed of light (because of the expansion of the universe) - so their light can never catch up with us anyway.

SteveBaker (talk) 14:10, 6 February 2013 (UTC)

Steve, you were just fine until your last sentence. Light just doesn't work that way. Even if it was possible for anything to travel faster than light (it isn't in our current understanding of the universe), if you had a flashlight moving away from you at twice the speed of light, it's radiation would still reach you, because the speed of light in a uniform medium is constant. Of course, as you mentioned, it would be very redshifted so your eyes couldn't see it, but it would still be moving at the speed of light. Another example: the light from the headlamp of a speeding train isn't moving any faster than the light from your computer screen, or any other light traveling through air on Earth. —Rutebega (talk) 03:48, 7 February 2013 (UTC)

You're thinking in special-relativistic terms. Light that originates from beyond the horizon of the observable universe, from our point of view, will indeed never reach us. In any local inertial frame containing those photons, sure, they're moving at c, but it doesn't matter because such an inertial frame cannot be extended out to our position. --Trovatore (talk) 04:13, 7 February 2013 (UTC)

First, it's not true that things with a recession velocity larger than c are invisible. The recession velocity of the CMBR is about 3c and we can see it. Second, dust does absorb starlight in the real world. Only in a steady-state universe would it have to be in equilibrium with the starlight (although arguably everything would have to be in equilibrium - I'm not sure how steady-state cosmologies solved that problem).

The size of the observable universe increases with time. If not for the accelerating expansion, light from arbitrarily far away would eventually reach us. In the accelerating universe there is a genuine horizon beyond which nothing is ever visible. However it's far from certain that that model is correct; the universe could still recollapse. -- BenRG (talk) 05:01, 7 February 2013 (UTC)

OK, fair enough. There seem to be two roughly complementary notions that, at least naively, could be called "the observable universe", and I'm probably using the wrong one (i.e. the one not standardly called by that name). --Trovatore (talk) 06:14, 7 February 2013 (UTC)

Surely an infinite universe can be ruled out on account of it's finite age. If as evidence indicates it began 13+ billion years ago in a "big bang" there has not been enough time, even with inflation, for it to have achieved infinite size. An infinite universe is only compatible with "steady state", or at least either infinite age or infinite expansion rate. Desiderata9 (talk) 02:34, 10 February 2013 (UTC)

Just saw this -- normally one doesn't edit archived posts, especially from a year and a half ago, but I think it's a little bit important not to leave this as the last word.

In fact, that doesn't follow at all. An infinite universe is quite compatible with the Big Bang. If it is infinite, then it has "always" been infinite, where "always" means "at any positive time after the Big Bang" (as measured in comoving coordinates.

The reason that this is counterintuitive is that you want to extrapolate back to the actual moment of the Big Bang, where the time after the Big Bang was literally equal to zero. But that's not a useful thing to do. When you read what cosmologists write, they talk about 1 second after the Big Bang, or 10^-10 seconds, or 10^-35 seconds, but never ever ever zero seconds. The way to think of it is, that time simply does not exist. The Big Bang theory is correct, for any positive time after the Big Bang. But it simply gives us no description at all of the exact moment of the Big Bang. --Trovatore (talk) 02:11, 29 August 2014 (UTC)

Economic growth , what curve?

We are constantly told that economic growth is brilliant for us (I think it's to do with GDP?)

However what kind of growth are they implying? Linear? Exponential? Does it head towards a limiting value?

(edit) Also if it IS Exponential won't that be completely unsustainable and almost a joke that economic growth is even talked about as a fact?

Ap-uk (talk) 21:35, 5 February 2013 (UTC)AP

If you get "X" number of economists to answer this question, you're likely to get "X+1" different answers. If economists knew what drove the world economy towards a positive outcome with any certainty, we'd have been there yesterday. --Jayron32 21:37, 5 February 2013 (UTC)

Even if the answer gores someone's ox? —Tamfang (talk) 01:18, 28 October 2013 (UTC)

(from op) If it is exponential and say 3% growth I see a problem with sustaining it now as the Wikipedia article sites 1830 as a start date [[4]] . At 3% we would get doubling every 23 years and it's the old wheat on a chessboard problem [[5]] as we now are getting onto the second row where the next 23years growth must equal the sum of all that has gone before in order to grow.

Except it's not a problem, because 1) nobody's saying exponential growth can continue forever, and 2) due to inflation, you have to distinguish between growth in real and nominal terms. If the inflation rate is 2%, that means all money in the country will be worth 2% less next year. Even if the economy produces exactly the same amount of goods and services next year, its nominal growth rate will still be 2%, even though real growth is 0%. --140.180.247.198 (talk) 23:52, 5 February 2013 (UTC)

Can exponential economic growth (which of course refers to real GDP) continue forever? The answer is unknown, but here are some considerations. Malthusianism was the idea that population grew exponentially while food supply grew just arithmetically, so soon there would be mass starvation that would prevent the population from continuing to grow exponentially. The reason that was wrong (at least up to and including the present) is that it ignored technological change -- the amount of food that we know how to get out of a given amount of land itself grows exponentially. This reality of technological progress applies more generally to our ability to produce the variety of things that go into GDP -- this ability has grown exponentially. The question is whether that can be sustained even in a world with finite resources. The answer to resources running out has so far been to figure out different ways of sustaining and exponentially increasing production by shifting away from the declining resources and into currently plentiful resources. A key example right now has to do with energy: the petroleum is going to run out at some point (though predicting when is enormously difficult), but we are in the process of learning how to use solar, hydrogen fusion, etc.

The question of whether resource constraints will ultimately put a cap on world-wide output is up in the air. But never assume that human ingenuity is going to run out -- it has given us a trend of long-term exponential growth so far, and so far the optimists have been right. Duoduoduo (talk) 15:49, 6 February 2013 (UTC)

An interesting question... I won't pretend I have an answer. I wonder, for example, if there is some kind of "social entropy" that increases over time, so that the GDP can increase despite no real increase in resources. (i.e. Year 1 you own cows, the next year you own cows and iron on the same land with the same resources ... eventually you add shares in a radio station, copyright on a song, a set of collectible trading cards, a digital telephone, a paint-spattered canvas that art appraisers say is worth something, some Bitcoins, an audience of 30,000 following your blog, etc. Yet it's the same land and you still eat the same amount) Wnt (talk) 19:57, 6 February 2013 (UTC)

All of this is assuming humans stay on Earth. Remember that for all practical purposes, the universe has infinite resources, and starlight is a source of infinite energy. --140.180.247.198 (talk) 00:26, 7 February 2013 (UTC)

Burnt stew

I have a 32 quart stainless steel stock pot in which I made some stew from chicken, potatoes, onions, green beans, baby carrots, corn, dried beans, etc. I filled it almost to the top, and boiled it vigorously over an open flame. I left it uncovered, since this prevents boiling over and I don't mind the heat and humidity in winter. Everything went well the first day, and the pot was still half full by night (maybe 1/4 boiled off and 1/4th was eaten). So, I covered it and left it to cool. Early the next morning, it was still warm, and I turned the flame back on. Then I detected a burning smell. So, since the pot was still half full, something must have adhered to the bottom and started to burn. Is there any way to prevent this, other than constant stirring ? Would it have helped if I oiled the pot before using it ? Should I have left the dried beans out ? StuRat (talk) 23:17, 5 February 2013 (UTC)

How does leaving it uncovered keep it from boiling over? ←Baseball Bugs ^{What's up, Doc?} carrots→ 23:22, 5 February 2013 (UTC)

Covering a pot retains the heat that would otherwise be lost as the water vapor leaves the pot, allowing heat to build to a point where it boils over, right after knocking the lid askew. Leaving it uncovered prevents this (of course, an uncovered pot still can boil over, but this requires a significantly higher flame). StuRat (talk) 23:32, 5 February 2013 (UTC)

Put a saucepan nearly full of water on a burner of your stove, turn on the heat, watch it boil, and tell me that it doesn't boil over. ←Baseball Bugs ^{What's up, Doc?} carrots→ 03:30, 6 February 2013 (UTC)

As I said above, there is some level of flame which will cause even an uncovered pot to boil over. It being filled near to the top makes this worse. But, an uncovered pot has a wider range of thermal equilibrium, where more flame leads to more heat being lost from the top, thus keeping the temperature in check.

Incidentally, I have another stock pot, filled with water near the top, which is heated on low flame, uncovered, as a way to add humidity to the house. It has never boiled over (or boiled at all), but likely would have had I covered it. StuRat (talk) 16:41, 6 February 2013 (UTC)

My guess is that after you removed the heat and left it overnight, the ingredients compacted on the bottom and more and more as time went on, with the moisture at the layer touching the bottom of the pot reducing. In the morning when you turned the flame back on you were essentially heating rather dry ingredients which promptly burned. If you had given the pot one thorough stir (as opposed to constant stirring) before turning the flame I think you might have avoided the problem.--Fuhghettaboutit (talk) 23:42, 5 February 2013 (UTC)

Yes, one stir on reheating was all that was necessary. μηδείς (talk) 23:44, 5 February 2013 (UTC)

OK, I'll try that tomorrow. StuRat (talk) 00:15, 6 February 2013 (UTC)

I can confirm the phenomenon that leaving a pot uncovered prevents it boiling over. I always thought this was due to the pressure-cooker effect where higher pressure leads to higher temperature thus faster boiling. (Rhetorically) where do you live? That stew really sounds nice from here!

Detroit. I'll leave a bowl on the porch for you. :-) StuRat (talk) 16:43, 6 February 2013 (UTC)

There is another possible effect of leaving the lid off that would prevent boiling over: reducing the lifetime of bubbles. This is very easy to observe when boiling pasta; with the lid on, the water vapor is retained, keeping the humidity high. The bubbles formed when a protein solution is boiled last longer in a high humidity environment. When you take the lid off, the local (absolute) humidity drops to nearly the same as the room, the bubbles pop much sooner and the foamy layer shrinks. --Wcoole (talk) 22:12, 6 February 2013 (UTC)

Yes, a question of the partial pressure of the water vapor. μηδείς (talk) 00:20, 7 February 2013 (UTC)

Agreed. When you take the lid off a boiling pot of pasta full of foam, the foam collapses immediately. StuRat (talk) 00:23, 7 February 2013 (UTC)

UPDATE: When I fired it up again, I stirred it, and there did again seem to be food adhered to the bottom of the pot. I'm not quite sure why this happens, but it seems to happen every night. I also used a lower flame, and nothing burnt. StuRat (talk) 03:31, 9 February 2013 (UTC)

February 6

Law of excluded middle, null hypothesis redux

I have to ask this question again because it wasn't answered and was actually side tracked by a discussion I didn't intend. Long story short, can something be true, without it being proven? ScienceApe (talk) 01:34, 6 February 2013 (UTC)

How would you prove that it hurt if I kicked you? Can you prove that existence exists without referring to anything which exists? There are axioms, and perceptions, neither of which can be proven true, but both of which are assumed veridical. The law of the excluded middle is also axiomatic--it is the basis for any proof, but cannot itself be proven without assuming its own truth. μηδείς (talk) 01:43, 6 February 2013 (UTC)

(ec) :If you believe in philosophical realism, you pretty much have to believe that the answer is yes. --Trovatore (talk) 01:44, 6 February 2013 (UTC)

You might also look at foundationalism and coherentism, both of which are true. Whereas skepticism is a self-refuting idea. μηδείς (talk) 01:48, 6 February 2013 (UTC)

Additional concepts to consider: [David] Hume's Law (a.k.a.: Is–ought problem derived from: Fact–value distinction. For an in-depth exploration of proof vs. truth as it relates to logical constructs and string theory, (etc.) - look into Gödel's In/Completeness theorem. ~Eric _the Read 74.60.29.141 (talk) 02:01, 6 February 2013 (UTC)

Should we treat Hume's theory as true? μηδείς (talk) 02:07, 6 February 2013 (UTC)

Maybe you ought to. ~E:74.60.29.141 (talk) 02:35, 6 February 2013 (UTC)

:) ---- _nonsense ferret 03:03, 6 February 2013 (UTC)

(edit conflict)    I believe the bottom line of this discussion will depend on the definition of "truth", and the answer will be "yes/no". Can truth apply to itself? 74.60.29.141 (talk) 03:14, 6 February 2013 (UTC)

Define "prove". ←Baseball Bugs ^{What's up, Doc?} carrots→ 03:28, 6 February 2013 (UTC)

The question is nonsense as are the "answers". If there's no such thing as truth, it isn't true there's no such thing as truth. If there's no such thing as proof, there's no proof there's no such thing as proof. This thread is ready to destroy itself. μηδείς (talk) 03:35, 6 February 2013 (UTC)

Such is the nature of Existence theorem: An existence theorem may be called pure if the proof given of it doesn't also indicate a construction of whatever kind of object the existence of which is asserted. (see also: Existential instantiation) ^>poof!< _{74.60.29.141 (talk) 03:48, 6 February 2013 (UTC)}

If you say "I'm thinking of ___", and if you're really thinking of that, it's true, but there's no way to prove it. Quite obviously the answer is yes. Nyttend (talk) 04:05, 6 February 2013 (UTC)

Unfortunately, that's not a very defensible example, because once the question is asked, you are thinking of   "thinking of ____" - and you can immediately see the problem of recursive self-reference. -Thus the answer is both "yes" and "no" simultaneously. 74.60.29.141 (talk) 04:26, 6 February 2013 (UTC)

Very well to be pedantic about it; what about "I was thinking about __ two minutes ago", or what if you're in out in the woods by yourself (no cameras around) and see a leaf fall; you can't prove that you saw it fall, but it still fell. Nyttend (talk) 04:35, 6 February 2013 (UTC)

By the definition of "that which conforms to reality", it would indeed be true that the leaf fell (assuming that it actually did, which it didn't, since you just made-up that example).  ;) ~:74.60.29.141 (talk) 05:06, 6 February 2013 (UTC):~

I said that the hypothetical you is claiming to have seen it fall; since I live in the woods by myself, I'm frequently able to see things happen, and it's easy to prove that they happened, but impossible to prove that I was watching when they happened. It's simply common sense, just like denying the paradoxical nature of the first two of Zeno's paradoxes that we list; we need not make an answer more complicated that the one given (according to the paradoxes article) by Diogenes the Cynic. Nyttend (talk) 05:26, 6 February 2013 (UTC)

(edit conflict) ~ If you define truth on a case-by-case basis such that there are an infinite number of definitions and an infinite number of proofs (e.g.: the leaf proved to you that it fell) - then the answer is "yes". ~:74.60.29.141 (talk) 05:31, 6 February 2013 (UTC):~

• "All I know is that I don't know nothing" --Jayron32 06:00, 6 February 2013 (UTC)

(edit conflict) ←again ~:74.60.29.141 (talk) 06:07, 6 February 2013 (UTC):~   ~ Before I wrap my brain around a cup of hot chocolate with peppermint schnaps and head off to the realm of dreams where nothing and everything is true...

"Believe those who are seeking the truth. Doubt those who find it." ~André Gide^[6]

Now that one I like. It's going into my list of quotes and anti-quotes. -- Jack of Oz ^[Talk] 06:51, 6 February 2013 (UTC)

Suppose we constrain the question to only axiom-based formal logic systems, such as mathematics, where "truth" and "prove" can be concretely defined using the structure of the system. Then according to Godel's incompleteness theorem, it is generally the case that one can write true statements using the logic of the system that nonetheless can never be proven to be true using the axioms and methods provided by the logic system. In this sense, in most logical systems (including mathematics) there exists statements which are true or false, and yet can not be proven to be true or false. The truth of such statements is essentially unknowable. So, if you model your worldview after formal logic, then it is generally the case that there will be things that are true (or false) and yet which can never be proven to be true or false. I think this comes as close to answering the original question as possible without going off and fretting about poorly defined subjective philosophies. Dragons flight (talk) 06:17, 6 February 2013 (UTC)

The incompleteness theorems certainly make it more difficult to sustain the notion of truth-equals-provability in mathematics specifically. There are those who make the effort; intuitionists, for example, identify truth with provability, but they do so by disidentifying provability with provability in any specific formal system.

I would be cautious, though, about generalizing that observation to more quotidian sorts of truth and provability. The Goedel theorems are specific to a particular sort of proof, namely proof in first-order logic from a computably enumerable collection of axioms strong enough to interpret Robinson arithmetic there are extensions to other sorts of deductive system, but that would take us rather far afield. So while I agree that a statement doesn't have to be proved in order to be true, I don't think the Goedel theorems are the best argument to make in non-mathematical situations. --Trovatore (talk) 08:43, 6 February 2013 (UTC)

There are problems like the Halting problem which says that you cannot (in general) produce a procedure that will reliably prove whether a particular computer program will or will not eventually finish running. Whether a particular program will eventually halt is a simply boolean fact - it's true or false - but no algorithm that a Turing machine (a computer, in other words) can execute will tell us which it is. This is similar to Godel's incompleteness theorem - where there are theorems in mathematics that mathematical thinking can neither prove nor disprove.

Now...the critical question is whether a computational engine that's (logically) more sophisticated than a Turing machine could (perhaps) solve the halting problem - or whether some form of logical thinking that's outside the realms of the mathematics that Godel's theorem addresses could resolve the truth or falsehood of all mathematical theorems. As far as we know, there are no such ways of thinking. It appears that human brains are turing machines - and the "Church-Turing" theorem says that all turing engines are logically equivalent. So we're doomed to being unable to resolve the halting problem - and (in all likelyhood) unable to escape Godel's incompleteness trap.

Is it possible that some higher realms of logic/computation might exist? Maybe - but Godel and the Turing engine argument says that humans can never possibly find or comprehend it.

So the answer to ScienceApe's original question is "Yes!"

SteveBaker (talk) 13:49, 6 February 2013 (UTC)

I guess the opposite is true too, some things can be proved and yet not be true, or at least lots of people think they have proved them but I of course know they are untrue. ;-) Dmcq (talk) 14:41, 6 February 2013 (UTC)

That's just a matter of error though. The thing can obviously be untrue even though there is an erroneous proof out there that (incorrectly) said it was true. But for a correct proof with all of the i's dotted and t's crossed, then there obviously can't be something that's proven to be true that really isn't because that belies the very definition of the word "proof" - meaning "absolute certainty". SteveBaker (talk) 17:56, 6 February 2013 (UTC)

You can certainly have a valid proof of a false statement, if you start with false axioms. (And yes, axioms can certainly be false. For example the axiom of determinacy is false, though useful.)

The halting problem has a somewhat different set of issues from the Goedel theorems (which I discussed above; did you read it?) as a reason to accept that truth is different from provability. What the undecidability of the halting problem says is that there is no fixed algorithm that can correctly decide the halting or non-halting of all Turing machines. It doesn't say assert, for any specific Turing machine, that there is no way of knowing whether it halts. --Trovatore (talk) 20:09, 6 February 2013 (UTC)

Touch one part of your body, feel it elsewhere

I was going through the Allochiria article and it made me wonder if this is similar to touching one part of your body and then feeling it elsewhere. I've seen this discussed elsewhere, like on this forum. Ok, so two questions: is there an actual word for that phenomenon (touch/scratch/whatever one area of the body and feel it elsewhere)? There is a reverse phenomenon that someone mentions at the bottom of that forum, which is, you feel an itch in one area, but scratching it doesn't relieve it because the itch is actually elsewhere.

Okay, second question is, is this the same thing used in the children's trick where Person A closes their eyes and holds their arm out. Person B slowly tickles their arm from the wrist up toward the elbow (the inside bendy part — cubital fossa). Person A is supposed to point out when Person B's reached the center of their elbow, but Person B won't have... sort of like an "optical illusion" for touch. Hopefully that makes sense. Reflectionsinglass (talk) 05:53, 6 February 2013 (UTC)

I'm not sure if there's a term for general touch, but there is a concept known as Referred pain which is very similar to your first question. --Jayron32 05:59, 6 February 2013 (UTC)

Somewhat related is when somebody has a phantom limb. That is, they still feel pain or itchiness or other sensations coming from a limb which is no longer present. The nerves continue to fire even though they no longer extend all the way to their original locations. StuRat (talk) 06:01, 6 February 2013 (UTC)

Hmmm... I would add to the examples a sore gum by the second molar that creates a pain along the rim of the ear, and an unpleasant sensation from the navel that can affect the tip of the penis. These match the Straight Dope examples in terms of target, but seem outside or at least poorly specified by the classic dermatomes --- I wonder if someone has totted up enough anecdotes to tell whether there are certain specific regions of the brain that "attract stray nerves" or something...? Wnt (talk) 15:17, 6 February 2013 (UTC)

Only slightly related but I've noticed that occasionally, based on factors I can't figure out, the actual and perceived place a mosquito pierces my skin are not quite the same place. They can be several centimetres apart. No idea what is going on there but it struck me that it would be a useful risk reduction technique for a mosquito to have evolved. Sean.hoyland - talk 17:26, 6 February 2013 (UTC)

I think that's just due to having few nerves in those areas (as opposed to fingertips, your tongue, etc.). With larger objects, which trigger multiple nerves, it's not a problem. However, a small object that triggers a single nerve could be anywhere in the area that nerve covers. StuRat (talk) 17:37, 6 February 2013 (UTC)

The problem there is that I've only observed it for mosquitoes. None of the many other small biting and stinging insects, some of which are tiny, seem to produce the same effect, although admittedly they don't have the precision of the mosquito. Sean.hoyland - talk 18:06, 6 February 2013 (UTC)

There's an experiment where you close your eyes, and have a friend poke you with either one or two pins, and you tell them if it's one or two. They try at different locations and with different distances between the two. It turns out that the distance at which you can't tell two pins from one is much greater in areas like the arms, where there are fewer nerve endings. StuRat (talk) 21:10, 6 February 2013 (UTC)

• ghost limb. μηδείς (talk) 21:06, 6 February 2013 (UTC)
  • A Henny Youngman classic: "Guy goes to a doctor. Says, 'Everywhere I touch it hurts!' Doctor says, 'Your finger's broken!'" ←Baseball Bugs ^{What's up, Doc?} carrots→ 22:48, 6 February 2013 (UTC)

Thanks all for the replies! I'm not thinking of phantom/ghost limbs for sure. My own experience with this (hopefully without turning this into a medical issue) is that if I tickle the inside of my right elbow, the back of the inside of my right tongue tickles like you wouldn't believe (have to trill my tongue forever to get it to itch). I have other examples too. Someone once told me that's how acupuncture works (and incidentally that's mentioned in the forum I linked to above). That article doesn't go into it, unfortunately (because it's unknown?). Jayron32's "referred pain" may be the closest relevant answer so far: and its "the mechanism of referred pain is unknown" quote leaves me to think that may be the same thing here. I'll keep checking back for any other replies! Reflectionsinglass (talk) 09:08, 7 February 2013 (UTC)

single slit - interference in a slit

If you hold your index finger and ring finger close together and look through the little slit between them at some light, you see dark lines parallel, you can see dark lines parallel to the sides of your fingers. Undoubtedly this has something to do with the wave nature of light, interfering with itself. But this is a single slit - not a double slit. Why do you see the dark lines? Bubba73 ^{You talkin' to me?} 06:19, 6 February 2013 (UTC)

Diffraction#Single-slit diffraction. --Jayron32 06:20, 6 February 2013 (UTC)

I'm skeptical that diffraction comes into play here -- but I don't really understand the description of the phenomenon. Where are those dark lines? Looie496 (talk) 06:36, 6 February 2013 (UTC)

I agree; diffraction/interference is not a very plausible explanation, as the patterns would be on the order of thousands of wavelengths, and the light source is neither spatially nor chromatically coherent. But so then what *is* the explanation? I'm curious too. --Trovatore (talk) 06:51, 6 February 2013 (UTC)

It sounds like you are describing the Black drop effect.

Here is a paper with a far better picture of it our article has: http://metaresearch.org/home/viewpoint/blackdrop.asp

Here is a video demonstrating it with fingers: http://www.youtube.com/watch?v=wylnvUor4Z0

Here is another paper on it: http://www.rasc.ca/sites/default/files/DuvalBlackDrop.pdf

Here is a 1922 paper that shows the parallel lines that you describe (figures 14 through 18): http://www.bo.astro.it/~biblio/Horn/Blackdrop.htm

If you look at the above links and the links in Black drop effect, you will not only see an explanation, you will see several mutually contradictory explanations! Who could ask for more?

--Guy Macon (talk) 07:32, 6 February 2013 (UTC)

Nicely sourced explanation, @Guy Macon. Related question: how many Wikipedia editors monocularly occluded their own vision today reproducing this two-fingered effect? — Preceding unsigned comment added by Senra (talk • contribs) 14:35, 6 February 2013 (UTC)

Also interesting; do the same thing against a dark background with a bright light illuminating your fingers. --Guy Macon (talk) 18:56, 6 February 2013 (UTC)

I estimate that the width of the slit between my fingers is less than 0.001 meter and there are several of the lines visible. So I estimate that the lines are about 10^-4 meters apart - on the order of 200 times the wavelength of visible light. I'm not sire about the Black Drop explanation since it connects things and these lines are discrete. Bubba73 ^{You talkin' to me?} 18:18, 6 February 2013 (UTC)

Did you look at figures 14 through 18 of the 1922 paper? --Guy Macon (talk) 18:56, 6 February 2013 (UTC)

Yes, I did, but there is only one line in there whereas there multiple lines (ten or so) in the finger slit. In the figures it looks like that line is in the process of making the black drop. I can see the black drop effect in the finger slip, and these lines don't seem to have anything to do with it. Bubba73 ^{You talkin' to me?}

More like 20 or so lines. Bubba73 ^{You talkin' to me?} 02:34, 7 February 2013 (UTC)

Let me describe what I see: When I hold two fingers in parallel, try to make the slit as thin as possible, and look at a lamp shade (bright but not blinding), I see many fine parallel dark lines in the opening, parallel to the slit. As I move the fingers apart, the lines seem to get thinner until they fade away. As I move my fingers closer together, the lines get thicker, until at some point there is no transparent lines between them and the block the light. Because my fingers are not perfectly straight, some part of the slit gets blocked first in what looks to me exactly like the black drop effect. When I do the same with the tips of my thumb and index finger I see one "line" that looks like the figures in the 1922 paper.

All of the above are through the top of my bifocal glasses, meaning that the fingers are out of focus. When I look through the lower lenses, the many-lines effect vanishes and I can get the fingers much closer before I see a classic black drop with no lines. If I move my fingers far enough away that the lower lenses can't focus, I think I see lines, but it s hard to make out -- I need longer arms.

It looks like an interference pattern to me. Given the fact that I am using a "camera" made out of jelly, I'm surprised that it works as well as it does. --Guy Macon (talk) 03:31, 7 February 2013 (UTC)

I agree with your description (including the thumb and index finger) and it is the same with different types of indoor lighting. If it is interference, what causes it - perhaps reflections off both of the two fingers? The black drop article says that the effect is due to the atmosphere and optics, but that doesn't seem to be what is going on here. Bubba73 ^{You talkin' to me?} 04:55, 7 February 2013 (UTC)

My best guess is that I am seeing a combination of black drop effect, which isn't very well understood, and an interference pattern. My theory about the interference pattern is that the slightly out-of-focus fingers have a region where the blurry edges of the fingers overlap, thus allowing an interference pattern. A good experiment for investigating this would be to use a high-quality digital camera to take a picture of the finger slit, with the fingers in sharp focus and out of focus. --Guy Macon (talk) 06:08, 7 February 2013 (UTC)

It might take some work to photograph it. When I hold my hand at arm's length, the fingers are in focus but I can still see some lines. Bubba73 ^{You talkin' to me?} 06:13, 7 February 2013 (UTC)

POM application for ethanol

Is POM compatible to 30% ethanol mixed Fuels. — Preceding unsigned comment added by 115.254.23.116 (talk) 07:10, 6 February 2013 (UTC)

What's POM? 24.23.196.85 (talk) 07:13, 6 February 2013 (UTC)

http://www.broadlandmemories.co.uk/blog/wp-content/uploads/2010/10/pomadvert_1949.jpg --Guy Macon (talk) 07:39, 6 February 2013 (UTC)

From POM and a quick search, I'm guessing Polyoxymethylene [7] Nil Einne (talk) 07:51, 6 February 2013 (UTC)

In that case, it should be compatible with ethanol at any concentration. 24.23.196.85 (talk) 08:54, 6 February 2013 (UTC)

pKa-value in the medicine substance articles?

Hi,

what do you think about putting systematically pKa-values in the articles of medicine substances?

For example into the table that contains all the basic information (formula, mol. mass...)

194.100.75.169 (talk) 12:58, 6 February 2013 (UTC)

This is an article editing question that should be proposed somewhere else - you might start with the talk page of the specific compound that you have in mind, and the WP:navigational template that it uses. Of course, many medical compounds are acids and have pKa values, but there could be other components of the pill (inert excipients); they may not be pure chemicals. If they are pure chemicals, likely the article has a Template:Chembox or the like that can be filled in. Wnt (talk) 14:59, 6 February 2013 (UTC)

It should be noted that every compound with a hydrogen has a putative pKa value... --Jayron32 17:00, 6 February 2013 (UTC)

Hmmm, what's the pKa of lithium hydride? :) Wnt (talk) 19:50, 6 February 2013 (UTC)

Fair enough, but only because there are no known "lithides" to compare to. There are known examples of other Alkalides, so one could calculate the putative pKa of any other alkali-hydride compound. That doesn't mean that lithium hydride doesn't have a pKa, if lithides were known we could get numbers to calculate the putative pKa from that; the methods exist to do so, we just lack the numbers yet. The other alkalides have only been known for 40 years or so. --Jayron32 20:03, 6 February 2013 (UTC)

Ab initio prediction of pKa is reasonable for some types of structures. There's less data about alkalides to use for validation, but LiH is such a simple molecule that one could do quite advanced calculations for it in reasonable time. DMacks (talk) 20:12, 6 February 2013 (UTC)

Tests on a newborn baby

When a baby is born (in the United States), I assume that the hospital staff does a battery of tests on the baby to assess his health. Do they test if the baby is blind and/or deaf? (I assume that they do.) If so, how exactly would they test for those conditions in a newborn? Thanks. Joseph A. Spadaro (talk) 20:17, 6 February 2013 (UTC)

We have a fairly detailed article about the various newborn screening tests, which includes a section on hearing but does not appear to mention vision. DMacks (talk)

For blindness, I expect that such a test is sufficiently elementary that it doesn't necessarily rate a mention -- specifically, does the baby react to bright light? Contrast this with the hearing screening described above, or any of the other disorders noted, which require specialized procedures and equipment. — Lomn 20:34, 6 February 2013 (UTC)

Newborns can't focus, so sight tests would be unhelpful. A search on sight in newborns here gets you to the article on the disgusting, perverse, and evil movie, human centipede. But not to sight in newborns. μηδείς (talk) 21:05, 6 February 2013 (UTC)

"Newborns can't focus, so sight tests would be unhelpful" -- the former does not imply the latter. Response to stimulus is a basic means of testing that does not necessarily require comprehension or cooperation on the part of the patient. Now, that said, any sort of infant vision screening will necessarily have limitations, as the results aren't much more detailed than "nothing" or "something" until the child is old enough to provide more detailed feedback. — Lomn 21:28, 6 February 2013 (UTC)

In the UK, "Newborn babies are usually screened for any potential hearing problems using two quick and painless tests. They are the: Automated Otoacoustic Emissions test (AOE), and Automated Auditory Brainstem Response test (AABR)." The AOE test consists of "A tiny earpiece is placed in the baby's ear and quiet clicking sounds will be played through it. If the baby's ear is working normally, reaction sounds (echoes) should be produced in the cochlea. A computer is used to record and analyse the reaction sounds." In the AABR test; "three small sensors will be placed on the baby's head and neck. Soft headphones will be put over the baby’s ears and quiet clicking sounds will be played through them. A computer will then be used to analyse how well the baby’s ears respond to the sound."

A newborn baby's eyes are "checked for any obvious physical defects, including squints (where the eyes look in different directions), cloudiness (a possible sign of childhood cataracts) and redness." There are other tests including; "The pupil reflex test" (shining a light in the eyes to see if the pupil constricts), "The red reflex test" (using an ophthalmoscope to look for a red reflection from the retina, a lack of which could be an indication of a cataract) and "Attention to visual objects" (whether a newborn baby pays attention to visual objects). See National Health Service: Hearing and vision tests for children - How they are performed. I suspect that there is similar screening in other developed countries. Alansplodge (talk)

There is no routine screening for vision other than the discharging doctor assessing eye contact, which is an imperfect method. If eye contact is obviously poor, eyes are visibly abnormal, or moving abnormally (nystagmus)the child is likely to be referred to a pediatric ophthalmologist to examine the optic nerve. Many congenital defects of vision are only detected as parents begin to realize the eye contact is poor in the first months of life. One of the reasons vision screening is not done routinely is that there are no conditions which are treatable at birth but not at a few months of age, so there is little benefit from detection at 2 days as opposed to 2 months. Does this cover your concerns? alteripse (talk) 22:41, 6 February 2013 (UTC)

Yes, once again, babies don't track or focus at birth, and they may react to light even if they are blind, but it is good to know that doctors slaving for the civilized national health get credit for performing non-diagnostic tests on newborns. Good for them. μηδείς (talk) 23:01, 6 February 2013 (UTC)

It's not non-diagnostic, and pupillary response has nothing to do with the ability to focus the eyes. Blindness caused by damage to the optic nerve will result in no change in the pupil upon exposure to light, so confirming pupillary response in newborns at least rules out some (most?) types of blindness. I don't know much about the signs of nystagmus mentioned above, but I seriously doubt they would be in common use if they were not effective in establising vision problems. Evanh2008 ^{(talk|contribs)} 23:29, 6 February 2013 (UTC)

Medeis stated that "babies don't track or focus at birth." In fact, my own newborn was given the Brazelton test series at the hospital (US) shortly after birth, and was quite able to track a face. Edison (talk) 16:59, 8 February 2013 (UTC)

Off-topic material
The following discussion has been closed. Please do not modify it.
Yes, certain types of absolute blindness, not all, that can't be treated, and will be discovered by the time of the first pediatrician's visit, can be discovered at extra expense at birth. I don't think that was denied. μηδείς (talk) 00:19, 7 February 2013 (UTC) The "at extra expense" part is silly, but other than that, it's a reasonable summary. — Lomn 01:45, 7 February 2013 (UTC) You have obviously never seen an $80 charge for a tylenol on a hospital bill (I have). These things even get accounted for by the NH, although you may not see them. :) μηδείς (talk) 01:49, 7 February 2013 (UTC) I can promise you it wasnt the doctor who put the $80 Tylenol charge on your bill. alteripse (talk) 02:23, 7 February 2013 (UTC) By NH I assume you mean the British NHS. We hear a lot about the problems and deficiencies of the NHS, but if it gives you itemised bills such that you know what drugs and services you got, that's pretty good. The equivalent in Australia, Medicare, has some disadvantages. After a hospital stay and operation, you get a cacophony of invoices continuing for months afterwood. Each invoice is a standardised form, listing the date of service (which may be a survical procedure, hospital bed charge, anesthetic drug, or whatever), provider's name, the provider's Medicare registered ID number, the Medicare registered service code number, and the price. There is no text description of the service, just code numbers. In principle, you pay on the invoice and get a reciept that looks identical except it has the word "Paid" on it. You take the reciept to Medicare or your private insurere, as appropriate, and they give you a percentage (usually around 70 to 80%) back as cash. In practice, it is automated to varing degrees, depending on the service provider and what consents you have signed. Money just comes and goes from you bank account, if you agree to it. Just as you think it's been a few weeks, it's settled now, a bit more of your money suddenly dissappears. When my wife was operated on for intestinal cancer, I got an invoice a week or so later from the hospital, with several codes listed (bed use code, theater use code, bandages and materials used, etc) totalling a few $K. No problem - it was expected. Also got an invoice from the surgeon (around several $100's) and the anesthetist. No problem - they were expected as well. Then an invoice from another doctor we had never heard of. Checked up - he was another surgeon assisting - should have expected that I suppose. Then, over the next month or two, several invoices from more names we had never heard of. I checked their names in the phone book - turns out some were thousands of kilometres away in other States. I phoned our medical insurer about it - they said "don't worry about it - if the codes are valid, and of course they will be, we'll pay you." I decided to check up on it all anyway. It turns out they were all pathologists. When the surgeon (and his assistant) cut cancerous bits out of patients, they send the bits off to labs for analysis and reports, so they know a) whether or not they got it all, and b) what the consequences are if they haven't. Some lab tests are highly specialised, and not done in all cities. So the bits of you get frozen, specially packaged up, and airfreighted to a lab that does whatever is wanted. I'm impressed that it all works so well and seemlessly, but the potential for rip-offs is significant. Wickwack 124.178.141.64 (talk) 03:07, 7 February 2013 (UTC) I brought it up because when I was hospitalized for major abdominal surgery, I ended up (luckfully) getting a case of the shingles so minor I literally thought it was a bugbite. I ended up being placed in isolation, but the only treatment I was given was acetominophen, for which pills I was charged $80+. I could have got them on the street for about $2.95. My private employer's private insurance paid for it, and several hundred thousand dollars in other charges which I didn't necessarily audit line by line. μηδείς (talk) 03:46, 7 February 2013 (UTC) Why (broadly) was there charges to the extent of "several hundred thousand dollars"? We hear that the USA is the most expensive in terms of medical costs. However, my wife's operation (in Australia) for intestinal cancer was as complex as any, state of the art, and took the surgical team about 6 hours. Her entire time in hospital was about 8 days (she was off work for several weeks). The total cost for that, 3 months chemotherapy, and some radiotherapy was, as invoiced, about $28,000. That is not the full story though. All drugs prescibed, which were current standard for USA and other advanced countries, were subsidised by the government. We found out one of the drugs, for which 6 doses were required, cost ex-factory $2,500 per dose! We paid about $5 for each dose. All up, after Medicare and private insurance payouts, we were out of pocket about $2400 - we cannot complain about that. Wickwack 120.145.203.87 (talk) 06:40, 7 February 2013 (UTC) Not defending the present US system, but one aspect is that hospitals, unlike any other private business, are not allowed to turn people away because they cannot pay. That money has to come from somewhere, and that somewhere is charging more to those who do pay. In addition, medical insurance companies, unlike any other private business, get to decide how much they are willing to pay after the service has been devivered. Add a thick layer of government regulations and you get things like $2,500 per-dose drugs. --Guy Macon (talk) 06:55, 7 February 2013 (UTC) In the National Health Service we don't get itemised bills or any sort of bill at all. You get admitted to hospital, get treated and then sent home again without any mention of money. There's a fixed fee of £7.65 for prescription drugs (free for children, pensioners, disabled, unemployed etc), but drugs used in hospital are free. Sometimes there's a wait for an appointment, but urgent stuff usually gets sorted out straight away. Of course there are problems, but by and large you get top class medical attention for nothing - until you see what the tax man has taken out of your pay of course. Although health service reform is a regular political battle, nobody would get elected if they suggested abolishing it. You can "go private" if you want to, but relatively few do. Alansplodge (talk) 12:58, 7 February 2013 (UTC) Top class medical attention? Not what I've heard and read. The Australian rough equivalent, Medicare, was introduced by a Labor Government in the 1980's. At the time there was tremendous controversy, with the medical industry and lots of other folk predicting bad things would happen, based on the British experience. Most of those bad predictions have come true. Correct me if I'm wrong, but just as with Australian Medicare, in Britain if you are not privately insured, you don't get to chose your doctor, nor your surgeon, nor anesthetist, nor the hospital. While there are some brilliant world renouned doctors in the NHS, I should expect most are none to good - public service everywhere makes for merely ordinary performance. Certainly in Australia, govt provided hopsitals and doctors are very second rate. I know from experience that checking out and choosing specialists can make a big difference to the standard of care. Some well known examples of second rate British NHS efforts: Medresco one-size-fits-all hearing aids (my uncle had one - totally useless); substandard breast cancer treatment with restoration unfunded; substandard dental care. On comparison between govt funded care and private insurance funded care: A friend had, as far as I can tell, the same sort of intestinal cancer as my wife. The friend had no private insurance. She got her wound infected in the hospital. No one told her she should get post operative physiotherapy, nothing about what exercises she should do. Her chemo wasn't monitored properly, so her immune system collapsed and she got very sick. She's been a mess ever since - had to give up work. My wife, covered by private insurance, had one of the top surgeons in our city. No infection, chemo & radio went well. Physio and everything else laid on automatically. She was back at work after a few weeks and has been as right as rain ever since. In Australia, almost half the population is privately insured, compared with less than 8% in Britain. The main fundamental reason for the difference is probably cultural. English folk tend to do what is expected of them and no more; they think in terms of rights and entitlement. In contrast, Australians tend to have more initiative, and think in terms of "you get what you pay for". Personally, when I need a doctor, I want him to think I am his customer - I don't want him to think that a remote government beaurocrat is his customer, which would be the case if it's not me that is paying him. If he doesn't do a good job, just as for any retail purchase of a defective product or service, I won't pay. If the govt pays the doctor directly and you are not involved in that, it matters not a whit to either of them whether you got good service or not. Wickwack 58.169.232.124 (talk) 15:43, 7 February 2013 (UTC) I agree that the NHS provision for things like hearing aids and dentistry leave something to be desired. However, making judgements of the British system by your experience of free healthcare in Australia is not justified in my opinion. My experience of a close friend who had cancer was quite different to the one you describe, and she was given choice about which facility she wanted to be treated at although we can't pick and choose individuals. She had a healthcare professional assigned to her and during regular visits, discussed the options for each stage of treatment. Alansplodge (talk) 18:30, 7 February 2013 (UTC) Not sure about for-profit hospitals in the US, but not for profit hospitals aren't in very good financial shape in general, for reasons such as you point out (estimated that bills unpaid by patient, insurance, or government end up adding $1400 to each hospital bill which is paid) so the reason they charge ridiculous prices for cheap drugs is, because they can. Unlike outpatient pharmaceutical bills, hospital-administered drugs aren't itemized on the bills so the insurance companies (who are in a position to negotiate prices) or the individual patients (who aren't) don't get any surveillance. Of course, if they ever do get managed, like the bump in the wall to wall carpet, the cost will just have to get shifted somewhere else. Gzuckier (talk) 14:51, 7 February 2013 (UTC)

We can't forget the bilirubin test, which results in babies occasionally named Billy Rueben. StuRat (talk) 07:03, 7 February 2013 (UTC)

In that case, presumably test would be positive. Gzuckier (talk) 14:51, 7 February 2013 (UTC)

February 7

New Horizons photos of Pluto

The most recent photograph of Pluto taken by New Horizons that I've been able to find is this one, from September 2006. Since the probe is now at a little over 5 AU from the dwarf planet, I'm wondering why I've not been able to find more recent pictures. New Horizons took many photographs of Jupiter and its moons during a flyby in 2006, so it seems that they would have also planned to photograph Pluto and Charon during the approach, and not just during flyby in 2015. I've not done the math to calculate what kind of angular diameter Pluto would have from New Horizons' current location, but I have to imagine that any image taken from the probe right now would provide better detail than the embarrasingly-blurry Hubble composite (though I admittedly know little about the technical specs of the cameras on board). Evanh2008 ^{(talk|contribs)} 00:08, 7 February 2013 (UTC)

Here's a photo of Pluto, taken by LORRI, released from January 24, 2008. There's no need to remain in the dark: the science payload description contains detailed descriptions of each camera on board. Right now, the spacecraft is in the interplanetary cruise phase, so it isn't actively taking photos very often. It's pretty easy to know what the photos would look like: LORRI, the highest-spatial-resolution camera, has a 20.8 cm aperture, so you can trivially compute the farthest distance before Pluto will resolve to anything more than a single pixel. (About 500 million miles from Pluto, which is ... still a little ways to go). Space is very big! Nimur (talk) 00:20, 7 February 2013 (UTC)

Using a camera entails risks of damage, so taking lots of low-res pics is a bad risk-versus-reward option. They might take a pic occasionally, just to ensure that the camera is still working, but that's it, 'til they get closer. StuRat (talk) 00:27, 7 February 2013 (UTC)

A single pixel? According to my research (which consists of watching detective shows on network TV), you can expand a single pixel into a high-resolution picture. Just tell the technician "enhance!"... (Note to the humor impaired: no, I am not being serious) --Guy Macon (talk) 06:14, 7 February 2013 (UTC)

One of the most impressive enhancements can be seen in Blade Runner :) Reflectionsinglass (talk) 09:11, 7 February 2013 (UTC)

The ones that annoy me the most are when the technician sitting at the keyboard apparently doesn't think of enhancing the picture until the non-technical guy looking over his shoulder says "Can you enhance that?"..."Oh! Yes! I can! I'm glad you suggested that!"...Star Trek is frequently guilty of this one. SteveBaker (talk) 14:10, 7 February 2013 (UTC)

And, in the audio field, you had to love the original Star Trek episode where they detected the presence of an extra person on the ship by turning the ship's microphones way up and listening for heartbeats. I was worried that Spock would fart and permanently deafen them all. StuRat (talk) 16:31, 7 February 2013 (UTC)

Did you notice that, while their pulses were at all sorts of phases with respect to each other, the whole damm lot of them had the exact same clock-steady pulse rate? It doesn't happen that way in practice. In any group of healthy people, you get rest pulse rates anywhere from below 60 to as much as 75 or even more. Surely someone in the ship actually getting some physical exercise would have a varied rate? And some people past about age 40 or so may have the odd ectopic beat now and then. Wickwack 58.167.247.139 (talk) 00:35, 8 February 2013 (UTC)

Ack. That's why I don't like most Star Trek episodes. Their 23rd century is so clean and shiny that their Schroedinger's cat is 100% alive and even their Black Holes are actually only an unusually dark shade of gray.

And Spock doesn't fart. He simply holds it back till it comes out the other end as pseudoscience. - ¡Ouch! (^{hurt me} / _{more pain}) 17:17, 9 February 2013 (UTC)

http://tvtropes.org/pmwiki/pmwiki.php/Main/EnhanceButton --Guy Macon (talk) 17:28, 7 February 2013 (UTC)

Don't forget that, while with only a single frame or still picture, you can't enhance beyond what the pixels provide, in a video you can, to a limitted extent. If the subject, sized so that it/he/she covers only a few tens of pixels in any one frame, and it/he/she moves in a straight line a fraction of a pixel per frame (or a non-integer multiple of the pixel pitch), it can be enhanced. By means of computer software that moves it back at the same rate, in effect the number of pixels is increased, as edges in the subject cross from one pixel to another in a sort of picket fence effect. The improvement is not dramatic however - those movie simulated enhancements remain impossible. Two factors limit how good it is: 1) it cannot overcome optical blurring, and 2) the subject does not restrict their movements to convenient precise speed straight lines. Wickwack 58.167.247.139 (talk) 00:08, 8 February 2013 (UTC)

Thanks for the replies, everyone! And especially Nimur and StuRat! Evanh2008 ^{(talk|contribs)} 14:30, 8 February 2013 (UTC)

Resolved

biology

Assume there exists a 13 year old girl, capable of reproduction but still in the process of developing secondary sex characteristics, and she got pregnant. Will the girl continue developing? When will she continue developing? If she still lacks underarm hair, will her body produce such hair even if she got pregnant? — Preceding unsigned comment added by 49.145.4.37 (talk) 09:27, 7 February 2013 (UTC)

Have you seen any 40 or 50 year old women that appear to have stopped developing secondary sex characteristics at the age of 13? --Guy Macon (talk) 18:39, 7 February 2013 (UTC)

How is your posting even remotely responsive to the question? Or was it just intended as humor?75.34.25.6 (talk) 19:54, 7 February 2013 (UTC)

The post did answer the question. The more direct answer is, pregnancy does not halt puberty. thx1138 (talk) 20:27, 7 February 2013 (UTC)

Think. The end of puberty is commonly considered to be reproductive capability and achievement of maximal height. It is not "final attainment of secondary sex charateristics" because things like androgenic hair changes continue throughout life. Breasts increase size and change shape with both pregnancy and obesity. So yes, it is possible for a girl to be ovulating while she still has an inch of growth left, but both of those things are dependent on estrogen and are unlikely to be discordant. Pregnancy results in a further jump in estrogen levels and would bring growth to a close faster. alteripse (talk) 23:50, 7 February 2013 (UTC)

• The above opinions are interesting. But do we have any biologists or farmers here who might be able to refer to scientific sources that actually discuss whether pregnancy causes growth or stunting in immature animals? μηδείς (talk) 04:36, 8 February 2013 (UTC)

The question was about girls, not animals, so I gave an answer about girls, not animals. Puberty is different enough in humans that even primates are not necessarily going to help with this, let alone farm animals. The following facts are not "opinions" and are actual data gathered on American girls about 50 yrs ago. Average bone age at menarche: 12y6m Average remaining growth at menarche: 2" if no pregnancy occurs. Many, not all, girls will ovulate within the first months after menarche. Some even do it once before menarche. Here are some citations on what happens to growth when pregnancy occurs before growth is complete. http://www.ncbi.nlm.nih.gov/pubmed/8262493 http://ajcn.nutrition.org/content/60/2/183.long Look for a farmer or biologist if you like, but there is no type of person more professionally qualified to answer this question than a pediatric endocrinologist. alteripse (talk) 22:23, 8 February 2013 (UTC)

Interesting source, but the specific fact I was asking about was the difference in final height between girls who do and do not have a pregnancy while still growing. That paper was largely about fetal weight, and did not seem to compare the two populations--unless I missed it. You say 2" inches is expected after menarche with no pregnancy--doo you have the figure for how many inches are expected after menarche if there is a pregnancy? μηδείς (talk) 01:47, 9 February 2013 (UTC)

No, because it will depend on how much remaining growth when she gets pregnant. I know of a pregnancy that occurred even without menarche (i.e, the first ovulation was fertilized) in an 11 yr old mildly precocious girl who had about 3" of remaining growth by bone age prediction at the beginning of the pregnancy. The recent reports of the 9 yr old Mexican girl and of course Lina Medina are examples of more than 2" of remaining growth potential at the time of pregnancy, but i have seen no data for them on height at impregnation and height eventually attained. For obvious reasons, pregnancies in girls with significant amounts of remaining growth are rare and usually terminated, so it is typically difficult to find good data. The closer to average timing the girl's puberty is, the more likely that bone age and menarche will be concordant, and the likely height loss less than an inch. It is in a girl whose puberty is precocious that there may be more chance of losing height growth, but these are less likely to carry to delivery, and the average doctor's office height measurement is only accurate to the nearest inch in many cases, making it difficult to detect changes of growth potential unless by chance there had already been an endocrine evaluation. The camden paper discussed nutritional limitation of fetal growth and confirmed that at least some height growth continued in the girls, though measured stature was compromised by the lordosis of pregnancy so they were assessing growth by knemometry. They did not try to assess the difference between bone-age-based height prediction at diagnosis of pregnancy and eventual attained height well after delivery, which is not exact but would be the best way to answer your question. The reason we can assume that there would be at least a little height loss from estrogenic acceleration of bone maturation is that pregnancy estrogen levels are comparable to those used to accelerate bone maturation and attenuate adult height in girls thought to be too tall or in the Ashley treatment. The more common situation in which this issue comes up is when oral contraceptives are being considered in a girl who has not finished growing; potential height loss is one of the factors weighed. alteripse (talk) 02:15, 9 February 2013 (UTC)

Thanks for the detailed answer, I had assumed some stunting would be the likely case, but figured paradoxically there might be a growth spurt. The effect of oral contraceptives makes sense. μηδείς (talk) 02:26, 9 February 2013 (UTC)

Unseen effects on water when going down a drain

What causes water to swirl when going down a drain? Does it rotate in one direction in the northern hemisphere and the other direction in the southern? Question from Sir Lar Feb. 7,2013 Payson Az. 85541 — Preceding unsigned comment added by Sir Lar (talk • contribs) 10:29, 7 February 2013 (UTC)

There's a nice discussion of this here: Coriolis effect#Draining in bathtubs and toilets. Basically, unless conditions are very carefully controlled, the effect of any initial movement of the water or irregularities in the container will predominate over the Coriolis effect, which is what would cause the rotation to be the opposite direction in each hemisphere. Equisetum (talk | contributions) 11:44, 7 February 2013 (UTC)

The business of clockwise versus anticlockwise sink/bathtub swirl in the northern and southern hemispheres is a complete and utter myth. It's quite amazing to me that so many people believe this when the most trivial of experiment will demonstrate that it's clearly not true - just watch your bathtub and sinks for a few days - you won't see any consistency whatever in which way they swirl. The magnitude of the coriolis effect is vastly too small to produce this effect. Even the slightest motion of the water or irregularity in the shape of the container or the drain will easily overwhelm it. Coriolis only has an effect for things that move LONG distances in the north/south direction - things on the scale of ocean currents, hurricanes.

The interesting part of this question (and I don't immediately see an answer) is why water swirls as it goes down the drain at all.

SteveBaker (talk) 14:04, 7 February 2013 (UTC)

had one of those deeply mystical latenight college discussions on related topics once. our final decision was that spirals and/or helices are the normal state, straight lines and circles are the singular variations on the general theme. Consider; with repeating subunits, whether physical or force, there is always an angle between the new vector and the previous, which can be projected onto a vector parallel with the original, and a vector in a plane perpendicular; i.e. a forward motion, and a rotation. if the former is 0, it's a circle. if the latter is zero, it's a straight line. otherwise, a helix. thus the helical config of proteins, DNA, etc., is just an intrinisic feature of repeating subunits, not anything specificall evolved. in this case, you could sort of imagine a centripetal force, as in this case due to the "perpendicular plane" being a bowl, sort of reminiscent of Einstein's rubber sheet space topology, it's a spiral in/down, really a shallow helix/spiral combo. Gzuckier (talk) 15:09, 7 February 2013 (UTC)

I'd say spiral water flow down a drain is a result of both an unbalanced downward force and an unbalanced inward force. The downward force is easy enough to visualize, as the open drain leaves an unsupported column of water above it, which then falls down the drain. This then leaves a gap in the water, and water pressure then pushes the water in from the sides, providing the inward force. In reality, they don't happen in distinct steps like that, and the water is moving downward as it moves inward, so you never quite replace all the water, at least if the distance from the drain to the surface is small, leaving an indentation in the surface of the water, possibly extending all the way down to the drain. As for which way it chooses to rotate, I agree that any minor asymmetry can start it going one way or the other. StuRat (talk) 16:25, 7 February 2013 (UTC)

I kinda suspect some kind of conservation of angular momentum thing going on here. The huge body of water has a certain angular momentum just due to random motion in the container - but as it heads down the drain, the flow is straightened out. The conservation law might therefore imply that the angular momentum ends up being concentrated in a smaller and smaller mass of water - so the rotation rate has to go faster and faster as the container empties. That's a guess - but it might explain why the swirl goes faster and faster as the water flows away. SteveBaker (talk) 17:25, 7 February 2013 (UTC)

No need to speculate: this is a standard homework problem in any fluid-mechanics class. Here's a nice website from MIT: Conservation of Angular Momentum (in the context of an aerospace fluid mechanics class). If you refactor this as part of a flow equation, you can easily see that angular momentum effects an equivalent pressure that "pushes" the water away from the center of a vortex. This is analogous to effective gravitational potential. You can refactor the law of conservation of momentum so that in the equation, it looks like it's creating a net force, or a net pressure, or effectively creating an energy barrier, to keep the water from flowing in to the center of the vortex, in contraposition to gravity (which wants to make the water fall into a lower position, in the vortex). (This pressure is the ensemble effect of the "fictitious" centrifugal force on each fluid molecule). That's how you can sustain a "vertical edge" to the water. Nimur (talk) 01:14, 8 February 2013 (UTC)

Yes, any large body of gas or liquid will have some small random net spin (the chance of it not is astronomical) and hence, due to conservation of angular momentum spin faster as it contracts. μηδείς (talk) 19:02, 7 February 2013 (UTC)

Could Cyclic cellular automaton explain the inevitable evolution of spiral movement?--Digrpat (talk) 22:48, 7 February 2013 (UTC)

It's not really necessary to go beyond the mere fact that any mass of randomly moving particles is going to have some sort of net spin. The only way it wouldn't would be if every particle's motion miraculously happened to cancel out. Either there will be a small amount of particles on the right moving faster toward the drain, or on the left, and voila, a vortex starts spinning. μηδείς (talk) 01:35, 8 February 2013 (UTC)

Right - so (naively) if (say) 60 liters of water in an idealized 2 meter diameter cylindrical bathtub is rotating at a leisurely one revolution per minute (almost too slow to notice) then when it's drained down to the last liter, it'll be spinning at one revolution per second - and as the last 1/10th liter disappears, ten revolutions per second. But real-world bathtubs have a smaller cross-sectional area at the bottom - so when the water is spinning around in a 10cm circle centered on the drain-hole, it'll be zipping around at 100 revolutions per second! Obviously this is a very naive estimation because friction, viscosity and the irregular shape of a typical bathtub would change all of that - and also, the entire body of water isn't rotating at the same speed and some residual angular momentum surely resides in the water as it heads down the drain. But you can easily see how that rotation can go from negligable to dizzying as the water drains out. This also explains why the speed of the swirl is so much lower in a handbasin than in a bathtub.

Hmmmm....now I want to watch a swimming pool drain out! SteveBaker (talk) 17:39, 8 February 2013 (UTC)

Should I get the shingles shot?

This question has been removed. Per the reference desk guidelines, the reference desk is not an appropriate place to request medical, legal or other professional advice, including any kind of medical diagnosis, prognosis, or treatment recommendations. For such advice, please see a qualified professional. If you don't believe this is such a request, please explain what you meant to ask, either here or on the Reference Desk's talk page.

This question has been removed. Per the reference desk guidelines, the reference desk is not an appropriate place to request medical, legal or other professional advice, including any kind of medical diagnosis or prognosis, or treatment recommendations. For such advice, please see a qualified professional. If you don't believe this is such a request, please explain what you meant to ask, either here or on the Reference Desk's talk page. --~~~~

--Jayron32 00:03, 8 February 2013 (UTC)

Reventazón River vs. Reventado River in Costa Rica

First of all, feel free to move this to the Miscellaneous desk if geography isn't science-y enough. So, my question. There's the Reventazón River in Costa Rica. This river is not covered in Library of Congress Subject Headings, but LCSH does have a "Reventado River (Cartago, Costa Rica)." I suspect these both refer to the same river. I looked up Lake Cachí in Google Maps, and it's within Cartago Province. So it doesn't seem likely that two rivers with such similar names would be in the same province. Our List of rivers of Costa Rica doesn't mention a Reventado, nor does its equivalent in Spanish Wikipedia. I suspect the LCSH term is an older name for the river, but I'm trying to confirm this. I'm waiting to hear back from the Library of Congress about this, but I'm impatient. --BDD (talk) 21:59, 7 February 2013 (UTC)

Michigan has eight Pine Rivers and seven Black Rivers. Name similarity is a poor standard. Rmhermen (talk) 23:13, 7 February 2013 (UTC)

February 8

Camera quality as a function of weight

When taking a photo using a DSLR camera , is there a difference between a heavy camera and a light camera if the photo is taken handheld and all other factors being the same? — Preceding unsigned comment added by 149.135.147.66 (talk) 02:02, 8 February 2013 (UTC)

I'm no expert, but in film SLRs, heavier is generally better because of all of the film mechanism needing to get it in the correct place, etc. In a DSLR a heavier camera might be better to damp out some of the jiggling when it is hand held. Bubba73 ^{You talkin' to me?} 04:01, 8 February 2013 (UTC)

Maybe in a certain range, but there's also a point where things become so heavy we lose the ability to hold them steady. StuRat (talk) 04:23, 8 February 2013 (UTC)

This is where tripods or monopods come in. ←Baseball Bugs ^{What's up, Doc?} carrots→ 04:32, 8 February 2013 (UTC)

But the OP specifically said handheld which I would take to mean without using a tripod or monopod or other supporting device. They also said 'all other factors being the same' which is a big unclear but I take to mean that they're excluding the heavier camera possibly having a better lens, CCD and whatever else. Nil Einne (talk) 06:02, 8 February 2013 (UTC)

Plenty of sports photographers use monopods on their hand-helds, to help them steady the camera, especially on zoom-in shots. ←Baseball Bugs ^{What's up, Doc?} carrots→ 14:00, 8 February 2013 (UTC)

But how much does it help when the problem is the camera is too heavy? Nil Einne (talk) 14:42, 8 February 2013 (UTC)

The monopod (and hence the surface it's resting on) absorbs much of the weight of the camera, hence it's easier to keep steady. ←Baseball Bugs ^{What's up, Doc?} carrots→ 22:20, 8 February 2013 (UTC)

The pictures that I take my fixed lens compact film camera, are much crisper than those I take with the compact digital. With the film camera, I look through the view finder and the camera sits against my face, which helps to hold it still. With the digital, I have to hold it at arms length to see the viewing screen and it is very difficult to hold the camera still. The pictures that I take with the film SLRs are the crispest of all, as the cameras have size and you can get a proper grip. With small cameras, I have to hold them in my finger tips, otherwise part of the lens, or sensor, or view finder is obscured. I don't have a DSLR but I imagine the same it true. --TrogWoolley (talk) 09:30, 8 February 2013 (UTC)

Anti-cancer molecule TRAIL

TRAIL was recently in the news concerning a new approach to fight cancer. I have a few questions about it:

• Which cells produce TRAIL, and under what circumstances?
• Does TRAIL act on the receptors of the cell that produced it, or on some other cell?
• Is TRAIL a transmembrane protein, or is it released into the extracellular fluid? (Our article states that it has "characteristics of a transmembrane protein".)

If the answer to any of these questions is "not currently known", that would be helpful too. Thanks, AxelBoldt (talk) 04:11, 8 February 2013 (UTC)

The NCBI is a reliable source and has a page about TRAIL. TRAIL is expressed in most tissues, in various forms, but appears to cause apoptosis of transformed and tumor cells more than others. As a cytokine, it is secreted. Like TNF, it causes inflammation. -- Scray (talk) 04:23, 8 February 2013 (UTC)

MTBE

Now that MTBE has been mostly phased out as a gasoline additive, are there any large-scale uses for it left? 24.23.196.85 (talk) 06:38, 8 February 2013 (UTC)

As an additive to petrol or gasoline? That's what the article says.... So does this press release [8] Nil Einne (talk) 06:52, 8 February 2013 (UTC)

I thought that "petrol" is in fact the British word for gasoline? 24.23.196.85 (talk) 07:19, 8 February 2013 (UTC)

It is. That's why I said 'or' rather then 'and'. MTBE is evidently still used to some extent in a few countries like India [9], Singapore [10] and Malaysia [11] where the word petrol would be preferred. It's also used in some countries where the word gasoline might be preferred (well I'm not sure of this). I originally just used the word petrol, but decided to add gasoline to avoid confusion and argument. Nil Einne (talk) 07:41, 8 February 2013 (UTC)

MTBE is still used in Mali. There is a phase-out plan[12] but the old refineries are still running. Let me pull up my cheatsheet just in case anyone here is thinking of taking a vacation in Timbuktu...

Fuel of any type: Carburant.

Gasoline/petrol: L'essence or Essence

A sentence with Sélectionnez and carburant means "choose your fuel" Usually there is an octane number but you may see ordinaire or super.

A sentence with Validez and carburant means "confirm" (press "Val" to confirm.)

Unleaded: Essence sans plomb

Leaded: Essence au plomb

Diesel: Gazole or Gasoil

Liquid petroleum gas (LPG): GPL or Gépel

Heating oil: Fioul or sometimes Fuel

Crude Oil (and, I think, paraffin): pétrole

The last two come into play when you ask for petrol or fuel; they will say that they don't have any. Ask for gasoline and you may get essence or you may get gasoil.

Note: these are probably bad French.

BTW, there is an interesting story about how gasoline came to be called that: http://blog.oxforddictionaries.com/2012/04/the-origin-of-gasoline/ --Guy Macon (talk) 10:09, 8 February 2013 (UTC)

Are we talking about the same thing? The link you supplied is referring to Tetraethyllead which MTBE partially replaced. If they still haven't phased out Tetraethyllead in Mali, I'm not sure whether there are any concrete plans for phasing out MTBE (although the link you supplies is rather old). In any case, MTBE is still widely used in China. As I mentioned it is apparently used in India, Malaysia and even I think Singapore (I'm not 100% sure since the results get confused by level of discussion of production and blending in Singapore but Singapore is apparently a major importer). These are places (including China) which phased out tetraethyllead at least 13 years ago. It's also used in quite a few other Asian (including Arab) countries. I'm not sure if there is a clear phase out plan in any of these but as per the sources its use is apparently decreasing in some cases although because of price pressures not environmental or health concerns (apparently in China this includes a consumption tax [13]). However the sources suggest while production may not be increasing in worldwide terms (or at least not that much), it's not decreasing either. See also [14]. Either way all the evidence suggests MTBE is still widely used as a gasoline/petrol/whatever additive. P.S. Our article suggest TEL was phased out in Africa in 2006 although Algeria remains a holdout and there are a bunch of Asian countries and one arguably European country (Georgia) who are still using TEL. I suspect there are more who have some leaded petrol but don't really know. Nil Einne (talk) 12:36, 8 February 2013 (UTC)

You are right. I confused the two. (Note to self: next time, smoke crack after editing Wikipedia...) --Guy Macon (talk) 19:32, 8 February 2013 (UTC)

Wait a minute, how can Georgia be an "arguably European country" when in fact it's part of the USA? 24.23.196.85 (talk) 22:57, 8 February 2013 (UTC)

Jupiter and the Romans

The ancient Romans gave Jupiter its name after their main god. Did they know that it was the biggest planet in the solar system, or is it just a coincidence? It's certainly not the brightest object, or even the brightests planet visible in the northern skies, so it's not immediately clear to me why they assigned it such importance unless they knew it was so large. 202.155.85.18 (talk) 07:47, 8 February 2013 (UTC)

It is usually the brightest planet in the night sky. (Venus is seen only before sunrise or after sunset.) Ruslik_Zero 09:08, 8 February 2013 (UTC)

I was taught at school that they believed that these objects in the heavens (asters) actually were gods, like the Sun, which is the most obvious godly thing. Many certainly must have thought that Jupiter-the-God and Jupiter-the-aster were the same thing or that one was a representation of the other, but wikipedia does not explain that relation very well, for example our article Jupiter (mythology) doesn't mention the words astronomy or astrology at all. As to why it became so important in the mythology is not related to its actual size (which they could not calculate very accurately), but to the stories in the myth. --Lgriot (talk) 09:21, 8 February 2013 (UTC)

No, there's no way they could have known. No planet is big enough to show a disk to the naked eye, so they couldn't have measured any planet's angular diameter.* They also couldn't have measured distance because the only way was by parallax, but even the parallax of Mars at closest approach is less than 1 arcminute from opposite sides of the Earth.

Not only is Jupiter usually the brightest planet, it's also brighter than every star. Venus is not always visible, even in the morning or evening; it's often hidden in the glare of the Sun, although the Romans would have known this instead of thinking it disappeared.

*Actually, there is one easy way to measure angular diameter. Hold your head absolutely still, and watch as a planet disappears behind a building due to Earth's rotation. A star would disappear instantly because its angular diameter is tiny, whereas planets take a few seconds. The longer it takes, the larger the planet's angular diameter. If you're patient enough, you can also use the Moon instead of a building (see lunar occultation). --140.180.247.198 (talk) 10:37, 8 February 2013 (UTC)

That will fail for a number of reasons, including atmospheric blurring, but most importantly the fact that it is nowhere near possible to hold your head still enough. Looie496 (talk) 16:49, 8 February 2013 (UTC)

You've obviously not seen A Clockwork Orange. μηδείς (talk) 17:33, 8 February 2013 (UTC)

Interesting... I feel like there must be a way. In theory, if you have a thin piece of wood with slits of gradually increasing width through it, you should be able to move your head, looking at the images through the piece of wood, until they stop getting brighter. I have no idea if the ancients did this (or, more likely, some much more clever version) Wnt (talk) 19:04, 8 February 2013 (UTC)

I don't understand the Clockwork Orange reference, but atmospheric blurring is nowhere near enough to make a star look like a planet. On a normal night, astronomical seeing produces a disk around 1 arcsecond across, whereas planets are tens of arcseconds across. As for holding your head still, you can use a sufficiently distant object--a few hundred meters is more than enough if you can hold still to within 1 cm--or you can use a vice to clamp your head. --140.180.247.198 (talk) 19:37, 8 February 2013 (UTC)

The "vice to the head" thing was the Clockwork Orange reference. The protagonist's head being held in a vice-like apparatus and being forced to watch images is one of the iconic scenes from the movie (if not from the book). See the image at A_Clockwork_Orange_(film)#Psychology. -- 205.175.124.30 (talk) 19:48, 8 February 2013 (UTC)

"It's a sin!" μηδείς (talk) 01:22, 9 February 2013 (UTC)

About isotopes

Do heavier isotopes of a same element always have

1. heavier elements
2. heavier compounds

than those of lighter isotopes?--Inspector (talk) 12:23, 8 February 2013 (UTC)

What do you mean by "heavier elements"? The answer is yes for that part, if I understand you correctly. By volume, they are heavier in their elemental state. The compounds would be heavier, unless they combine with lighter isotopes of other elements. Otherwise, yes, the compounds would be heavier, since (as I understand it) the properties of isotopes are more or less the same, other than molar mass and stability. IBE (talk) 13:33, 8 February 2013 (UTC)

We have a whole article about isotopes, covering the differences and similarities. DMacks (talk) 16:36, 8 February 2013 (UTC)

Forms of energy

Check whether the following two points are right or wrong.
1. Sound energy is a form of energy, but sound is a mechanical wave (not energy). Light is neither energy nor a form of energy, but it is an electromagnetic radiation. Radiant energy is the energy of electromagnetic waves. Heat is not a form of energy, but heat itself is energy.
2. Energy of waves or radiations is directly proportional to frequency and inversely proportional to wavelength.
I don't know whatever I have written is right or wrong. Kindly correct the wrong statements. Sunny Singh (DAV) (talk) 12:43, 8 February 2013 (UTC)

Sound, light and heat are all forms of energy. You could probably do a bit of reading first, and post a couple of references to articles which didn't quite answer your questions. IBE (talk) 13:35, 8 February 2013 (UTC)

Not sure about this usage of "forms of energy". Energy is an attribute of certain physical phenomena and systems. Saying "sound, light and heat are all forms of energy" is like saying "my blue shirt, my red tie and my brown shoes are all forms of colour". Gandalf61 (talk) 13:47, 8 February 2013 (UTC)

The easiest way to think of energy is "the ability to cause a change". The important things about this ability is that it is a) quantifiable and b) conserved. That means that you can measure it, and that it doesn't go away, nor is it created (though it can become unusable, see entropy and second law of thermodynamics). The various "forms of energy" are the (somewhat arbitrary) way in which we organize or categorize the various kinds of changes. Like all categorization schemes, these aren't rigidly defined categories which are inherent in the system itself, but are human-created distinctions which allow us to extract more understanding about the system. So, we can talk about energy in terms of "kinetic" and "potential" forms (that is, broadly speaking, energy which is currently causing a change, and energy which is "stored up", waiting to cause a change at a future time); or we can talk about it in terms of the types of changes that occur (mechanical energy, chemical energy, light energy, heat energy, etc.) None of these definitions have bright line boundaries; they're all a little fuzzy around the edge, depending on the specific model you are using. It's important also, to note that energy is not a kind of stuff you can hold in a bottle. It's a way to quantify changes. The way in which energy, time, and matter work together is the basic definition of the science of physics: physics describes how every kind of change occurs through mathematical models. Wave energy is just energy which occurs in a repetitive pattern. Some waves are obvious (sound waves, ocean waves). There are some phenomena which can be modeled as either wave energy (oscillations of a field rather than oscillations of collections of particles) or as particles-in-motion; the fact that these phenomena could be modeled both ways is called wave-particle duality. Energy is a really complex concept, so I hope this sort of explanation is helpful. The iconoclastic physicist Richard Feynman, easily one of the most intelligent and articulate physicists of the last hundred years readily admitted that even he couldn't adequately understand nor define what energy really is. I hope that helps some. --Jayron32 14:26, 8 February 2013 (UTC)

We end up always defining something by its properties. Defining something by what it does (like energy is the "the ability to cause a change") seems to me to be the standard way of defining things. You define 'brown' by the wavelength that is reflected by a brown object. "Function" is "something that takes one value and outputs another. Knife is something that cuts, and can be hand-held. OsmanRF34 (talk) 15:47, 8 February 2013 (UTC)

What's the difference between "form of energy" and "energy"? If it's energy (like sound, light), it has to be in some form. If it's not a form of energy (like length) it cannot be energy. OsmanRF34 (talk) 14:23, 8 February 2013 (UTC)

Article heat starts with this "heat is energy transferred from one body to another by thermal interactions". This made me think that heat is energy but not a form of energy. Jayron you wrote heat energy, but this answer says writing heat energy is bad english. This is where the confusion starts. Make it clear. Sunny Singh (DAV) (talk) 17:02, 8 February 2013 (UTC)

Meh. Heat energy, thermal energy. Whatever. The language is a bit fuzzy in this regard; it depends entirely on which text book you're reading that day. Also, your sentence " heat is energy but not a form of energy" is actually logically silly: a form of something is merely an example or category of it. You can't simultaneously be something, and then not be the same thing. Heat (or thermal energy, if you prefer) is merely the energy of molecular motion. Some texts will draw the distinction between heat and thermal energy insofar as heat is the transfer or movement of that thermal energy. In that way, heat is to thermal energy as work is to mechanical energy. One very common expression of energy is the equation ΔE = q + w; that is ΔE (the total energy changes or transfers in a system) is equal to the sum of q (the heat) and w (the work). So heat just means "how thermal energy moves around" in the same way that work means "how objects move around"; and one way to think of energy changes in systems is to think of such changes as either heat or work or some combination thereof. --Jayron32 17:37, 8 February 2013 (UTC)

So, this means saying heat or heat energy; light or light energy; sound or sound energy, all are same. Sunny Singh (DAV) (talk) 05:14, 9 February 2013 (UTC)

.

Upon reading Sunny Singh's question here and last time (Nov 14 2012), and the answers, I think that folk have not percieved Sunny Singh's fundamental problem, though this time people have come close to one part of it. Sunny Singh has two areas of difficulty: a) he's not too good on the English language, and b) he doesn't have a clear idea of what energy is. To a certain extent we have to guess what Sunny wants of us, and what he needs of us, because his English is somewhat cryptic. It would be helpfull if Sunny responds to this posting and lets us know if I and the other posters are on track or off track.

First, some points on English: It is indeed poor English to say "heat energy", "light energy" and "sound energy", though you will find those phrases in lay writing and occaisonally even in professional text books. The reason why it is poor English is the same as it is poor English to write "cat animal", "goat animal", "snake animal" - becaue they ARE all animals - each phrase is much like writing "animal animal". The only difference is, everybody knows cats, goats, and snakes are all forms of animals, but those of us without a good science education may not know that heat, light, and sound are all forms of energy. Got the idea? Just as we write "cat" when we mean cat, and not "cat animal", we write "light" when we mean light.

Before answering the specific questions you posted, Sunny Singh, let's try and make what energy IS, very clear. OsmanRF gave you a key. Energy is that which can do something or change something. Energy is something that can be accumulated or converted - energy mathematically is the product of power and time (or if you like, intensity x time). For example: an electric lamp rated at 50 watts, when operated for 10 seconds, consumes 500 joules of electricity (another form of energy) and converts it into light and heat, both emitted to a total extent of 500 joules. Another example: A loudspeaker is fed from a stereo amplifier playing a pure tone at 10 watts for 1 minute. That loudspeaker has consumed 600 joules of electricity (from the amplifer) and converted it into a total of 600 joules of heat and sound. If the loudspeaker was 100% efficient, it would emit 600 joules of sound, and no heat. Get the idea? Energy is somthing that, over time, gets converted from one form to another.

Now, we can look at your posted questions, Sunny. As I said, your English is cryptic, so I've altered them a bit here and there to mean what I think you meant to say. Let us know if I guessed wrong on what you meant.

1a Sound is a form of energy - correct.

1b Sound is a mechanical wave, and a mechanical wave is not energy - This statement is wrong because a mechanical wave is a form of energy, because a transducer, such as a microphone, can convert it over time into another form (electricity).

1c Light is not energy - this statement is obviously wrong

1d Light is electromagnetic radiation - Yes it is, and electromagnetic radiation is another form of energy - by suitable means light can be converted over time into another form of energy - e.g., into heat by means of a black object.

1e Heat is not energy but heat itself is energy - This statement is wrong because heat is a form of energy - it can be converted into another form of energy (light, sound, etc).

2. The energy in waves or radiation is directly proportional to frequency and inversly proportional to wavelength. - This statement is completely wrong. I'm guessing Sunny included it because he was confused by reading physics texts while not having a clear understanding of energy first. For any sort of wave or radiation (i.e., mechanical waves such as sound, or electromagnetic radiation such as radio waves), the wave has magnitude, or intensity, measured in watts. Remember, energy is magnitude multiplied by time. Frequency and wavelength has NOTHING to do with it. If 2 watts of sound is coming out of a loudspeaker, then that loudspeaker is emitting 2 joules per second of energy, regardless of frequency. Confusion for lay people can come when discussing electromagnetic energy, which is a combination of electric and magnetic fields. Physicists don't realy know what electric and magnetic fields are. But we have long learnt that for many purposes the mathematics of waves gives the right answers, and for other purposes the mathematics of particles (photons) gives the right answers. As the theory of electromagnetic radiation is a dual of waves and photons, we can combine the two and say things like "photons are emitted at a frequency of x hertz". The higher the frequency the more energy in each photon. Note that saying "photons are emitted at 20 megahetz" (1 megahertz means 1 milion cycles per second) DOES NOT mean 20 million photons emitted per second. The higher the frequency, the fewer photons needed. The greater the power, the more photons are needed. Each photon is a packet of energy. The amount of energy in each packet is proportional to the frequency of the equivalent wave.

Wickwack 124.178.169.170 (talk) 10:04, 9 February 2013 (UTC)

Energy is an attribute of physical phenomena and systems. A thrown ball has various attributes, including height/altitude, velocity, kinetic energy and potential energy. We can say "the ball has energy" but it is incorrect to say "the ball is energy" or "the ball is a form of energy". This would be like saying "the ball is velocity". Similarly, a sound wave or an electromagnetic wave has a frequency, a wavelength, an amplitude and an energy level (or, more generally, it has a spectrum of these attributes). We can say "a wave has energy" but it is incorrect to say "a wave 'is energy" and also incorrect to say "a wave is a form of energy". Gandalf61 (talk) 11:57, 9 February 2013 (UTC)

No, that isn't right. You are correct in saying that it is wrong to say a ball is energy. It is clumsy to say that a ball of mass m at some height z is a packet of potential energy. But the analogy does not stretch to waves. A fundamental propery of waves/radiation is magnitude/intensity. The energy of a wave is merely the product of magnitude and time as I said. Any two and you can calculate the third. Thus the three things, magnitude, time, and energy, are not independent attributes. Wavelength can be calculated from frequency and velocity of propagation (which is determined by the medium) - so these are not independent of each other, either. However, frequency/wavelength/velocity IS independent of magnitude, energy and time. When a wave passes from one lossless medium to another, neither magnitude nor frequency is changed. Thus, if we want to boil waves/radiation down to the simplest set of fundamentals, there are two fundamentals: magnitude and frequency (not counting direction of propagation and polarisation). These two attributes completely describe the wave. These two attributes, along with identifying what sort of radiation it is, completely describe the radiation. So, it is perfectly ok to use the energy describing words "light", "sound" etc to mean energy in the respective energy form. There is no need nor sense in saying things like "the energy in the wave." One does not say "the radio transmission has an energy of 200 joules per second" (this is much the same as why it is bad English to say "sound energy", "light energy" etc); we can just say "the radio transmission IS 200 joules per second." (More normally we would say "a 200 Watt transmission"). It is entirely correct to say "sound is a form of energy", "a wave is a form of energy", etc. Wickwack 60.230.225.90 (talk) 13:23, 9 February 2013 (UTC)

Most of that is nonsense. Obviously a wave is not completely described by its magnitude and frequency alone. A wave has many other attributes, some of which you mention and then randomly discard. And you seem to be forgetting that most waves do not even have a single frequency. No-one says "the radio transmission IS 200 joules per second" or "the radio transmission is 200 Watts". The phrase "a 200 Watt transmission" is obviously short for "a transmission that has a power of 200 Watts". Saying "sound is a form of energy" makes as little sense as saying "my shirt is a form of colour" or "a car is a form of momentum". Sound energy is a form of energy, but the sound wave itself is neither energy nor a form of energy - see our article on forms of energy. Gandalf61 (talk) 15:57, 9 February 2013 (UTC)

Iranian and Iraqis anti-aircraft air defense

How does the present Iranian anti-aircraft air defense compares to the Iraqi anti-aircraft air defense at the beginning of the 2nd Gulf war? OsmanRF34 (talk) 14:14, 8 February 2013 (UTC)

I couldn't find any direct comparison, but this article is rather scathing of Iran's air-defence capabilities; "Iran has even more problems with its land-based surface-to-air missiles. Its only modern systems are short-range man-portable systems and some 30 short-range Russian TOR-Ms suitable only for point defense. Its other systems are 30 short-range Rapier fire units and 15 Tigercats of uncertain operational status. Its longer-range systems include roughly (154) U.S. IHawks, (45) Russian SA-2s, (10) SA-5s and a limited number of CSA-1 Chinese versions of the SA-2. All are obsolete."

Iraq in 1991 had spent a large amount of money on the best system that the Soviets (and the French to an extent) were willing to supply them with. By 2003, they only had whatever hadn't been destroyed in 1991. Although US Air Force general John W Rosa told journalists: "The Iraqi air defence system is one of the toughest, most complex systems that we see in the world... It's very capable. They're constantly working to improve it, and they have been.", Andrew Brookes, an air specialist at the International Institute for Strategic Studies in London said "It's rubbish".[15] Alansplodge (talk) 17:13, 8 February 2013 (UTC)

Kite with extremely long string

If someone had a kite with a very, very long string attached, how high could the kite reach before some physical process prevented it getting any higher? --Dweller (talk) 14:41, 8 February 2013 (UTC)

The current record may be 13,600 feet [16] but I don't think any physical process limits it to that low. "Go fly a kite" and try to better the record yourself? In the U.S. you will need FAA clearance though. Rmhermen (talk) 15:25, 8 February 2013 (UTC)

At such altitudes, does it still work like a kite? bamse (talk) 16:58, 8 February 2013 (UTC)

Yes, but at some altitude there won't be enough air to create enough lift (airfoil effect) to overcome the weight of the string. 74.60.29.141 (talk) 17:05, 8 February 2013 (UTC)

The limit has to be the weight of the kite and the weight of the string versus the amount of lift it can generate. As the kite gets higher, the string gets longer - and therefore heavier. You might think that this means that you need a larger kite to lift the weight - but that increased area also increases the forces on the string because the drag force on the kite is proportional to the area. So a larger kite needs a stronger (and therefore heavier) string...and a bigger kite to lift that additional weight...and so forth.

The difficulty is that if you double the area of the kite, you double the amount of lift (and drag) that it has. You also double its weight and you have twice the tensile strength needed in the string - which demands a string with twice the cross-sectional area - which has twice the weight per unit length. Hence, making a kite larger doesn't increase the height it can fly at.

To solve that, you're going to need to consider varying the thickness of the string along its length. Near the kite, the string has to be strong enough to support it's entire weight - plus the drag forces on the kite. But close to the ground, it only has to be strong enough to counteract the drag force. So you could save weight by using a thicker cable up near the kite and less thick close to the ground...but there must be a limit to how much that helps.

Ultimately, you're going to start to find that the lessening of the density of the atmosphere would reduce the amount of lift that the kite can get...but it would also reduce the drag on it, allowing for a larger kite without needed a heavier string.

Arguably, the Space elevator idea is the ultimate kite-like thing - it would not be kept up there by the wind, but by the centrifugal force as the earth rotates. Issues of tether strength and the variation in thickness over altitude are a big question for that kind of structure.

SteveBaker (talk) 17:09, 8 February 2013 (UTC)

[(edit conflict)] ~ However, there are aerodynamic effects on the string itself that can provide lift, as per ballooning spiders -which is still not well understood.   I haven't checked this out yet, but you might want to read:  Aerodynamics of Kites.     74.60.29.141 (talk) 17:17, 8 February 2013 (UTC)

In a place with air flowing quickly upward, like the a stationary warm-core storm, there should be enough lift on the string to overcome it's weight. StuRat (talk) 18:41, 8 February 2013 (UTC)

Gliders, hang gliders and paragliders are like kites without string. A very lucky paragilder reached 32,600 feet due to cloud suck and lived to tell the tale. World altitude record for hang gliding is 38,800 feet, although this was a balloon launch not an ascent from ground level. World altitude record for gliding is 50,699 feet. Gandalf61 (talk) 17:22, 8 February 2013 (UTC)

The problem with gliders and such is that once they are high enough to get above the beneficial "slope lift" effects - they are entirely reliant on upwelling air to get their altitude. Significantly, once they are high enough, the effect of the wind is zero - the speed of the glider relative to the air is all that matters.

A kite, on the other hand, is tethered to the ground - so it can use the speed of the wind to gain altitude. It's speed relative to the air is whatever the wind speed is. But it's ability to make use of upwelling air is limited for the exact same reason...if it doesn't happen to be in an upward current, there is nothing that can easily be done to fix that. So, in principle, a kite can do better than a glider...especially if there is abundant wind and an updraft that happens to be where the kite is situated...but eventually, the weight of the string outweighs that advantage. SteveBaker (talk) 20:03, 8 February 2013 (UTC)

So, any idea of a reasonable maximum altitude? --Dweller (talk) 20:06, 9 February 2013 (UTC)

That depends on the string's strength-to-weight ratio more than anything else. 24.23.196.85 (talk) 20:14, 9 February 2013 (UTC)

For two kites then, one with typical commercial strength-to-weight ratio, and one superduper one designed by NASA engineers in their spare time. --Dweller (talk) 20:17, 9 February 2013 (UTC)

What material should I use for the string in each of the two cases? 24.23.196.85 (talk) 20:19, 9 February 2013 (UTC)

Just ran some calcs for your second case (the "superduper one designed by NASA engineers in their spare time"): with a string made of Kevlar (assuming that the string has a constant diameter, and that I didn't screw up anywhere in my calcs, which I might well have), the ballpark figure for the theoretical "highest height" would be over 80,000 feet! Yes, you read it right -- assuming my calcs are correct, you can literally "send it soaring up through the stratosphere, up where the air is clear"! Of course, you'd first have to get permission from the FAA, because this would be a major aviation hazard... 24.23.196.85 (talk) 21:04, 9 February 2013 (UTC)

Symbol of mass number

The symbol of atomic number is Z and the reason for this is beautifully mentioned in the article. The symbol of mass number is A. What is the reason behind using A as the symbol for mass number ? Show your knowledge (talk) 18:08, 8 February 2013 (UTC)

From google I get the drift that it stands for "Atomic mass number". ←Baseball Bugs ^{What's up, Doc?} carrots→ 22:15, 8 February 2013 (UTC)

Why don't the electrons fall into the nucleus?

Electrons are negatively charged and nucleus is positively charged, we also know, unlike charges attract each other. Why don't electrons come and stick to the nucleus of the atom ? Want to be Einstein (talk) 18:17, 8 February 2013 (UTC)

They are in orbit. Just as the Earth would fall into the Sun, due to gravity, but doesn't, because of it's momentum, the same is true of electrons. There is nothing to slow them down, so they just keep on going. When a stray electron "gets lucky" and slams into a nucleus, bad things happen, like it hitting a proton and fusing into a neutron. However, the vast amount of empty space between the electrons and nucleus, compared with the size of electrons, makes such collisions extremely rare, a bit less so where the electrons are moving faster, like inside giant stars. StuRat (talk) 18:55, 8 February 2013 (UTC)

I remember two things that I have read somewhere on Wikipedia but I am not able to find them: First, electrons don't orbit the nucleus unlike planets around sun. Electrons have random motion instead of well-defined circular motion. Second, the reason StuRat mentioned is not the correct answer to my question. Want to be Einstein (talk) 19:13, 8 February 2013 (UTC)

Here you get into the classical model versus quantum mechanics. I gave you the classical model. Look at Jayron's answer below for more of the quantum mechanics model. StuRat (talk) 19:24, 8 February 2013 (UTC)

Actually, your classic model doesn't work for the following reason: An electron is charged whereas the Earth is essentially neutral. Electrical charges emit radiation when the accelerate (under classical physics). See Larmor formula. An orbit is an acceleration (all turns are accelerations); so an electrically charged particle should be radiating energy constantly as it turns its orbit around the nucleus, this loss of energy should cause the electron to spiral into the nucleus. The reason the earth doesn't do this around the sun is that the earth is electrically neutral, and so does not radiate when it is accelerated, and so can maintain a steady-state orbit. The fact that an electron has an electrical charge means that if it really was a particle in an orbit, it would either need a constant resupply of energy or it would spiral into the nucleus. The fact that this doesn't happen may be one of the key impetuses for developing quantum mechanics to explain how the atom was able to maintain a steady state despite this. --Jayron32 19:34, 8 February 2013 (UTC)

Does a single electron radiate energy when it turns, as when deflected in a CRT screen ? Also, the quantum mechanics explanation seems to come down to "we don't why, just accept it", as you put it below, so that's not really any better, just more complicated. StuRat (talk) 19:38, 8 February 2013 (UTC)

I think that is the principle behind a syncotron. 202.158.103.42 (talk) 14:28, 9 February 2013 (UTC)

Yes, electrons radiate energy when they are accelerated; when the electron fired in a cathode ray tube hits the phosphor, it will do so with slightly less energy than it would be predicted if the electron weren't charged. That's a principle which has been known since almost before people even knew that electrons existed. The Larmor principle and the first description of the electron date to the same year (1897). However, the better way to understand the principle is radio. Radio waves (photons, or light energy) is generated fluctuating electrical current. The source of the radio waves is the energy given off by variations in electrical current; you speed up and slow down electrons, and they shed radiation as a result. By controlling how you vary the current, you control how the radio waves are varied, and you can transmit information that way. That works exactly because accelerating electrons give off radiation. If the electron in an atom were in orbit, it would be under a constant acceleration, and would be similarly radiating. That it isn't is why we can safely say that the electron isn't actually orbiting. --Jayron32 19:48, 8 February 2013 (UTC)

Oh, and the "just accept it" thing isn't an admonishment to claim that QM can't be understood; it's that the implications of QM cannot be visualized. The problem is that people want to have a picture, some analogue they could create with shapes and objects they are familiar working with. You simply cannot visualize an atom like this; the problems with accepting QM principles is that you have to abandon the need to have a visual model which can represent them. So, I'm not saying "just accept it" to mean "humans cannot understand this", I'm saying "just accept it" to say "there's nothing in the way that classical objects work that can be a good analogue of this". Since, as humans, our entire sensory experience is with classical objects, there is literally no convenient way to describe a picture which correctly displays QM principles. So you have to accept what the calculations and laws tell you without having a picture to go along with them. --Jayron32 19:54, 8 February 2013 (UTC)

So how does QM explain the underlying reason why a cloud with no moving parts has momentum ? Does it come down to anything more than "that's what we observe" ? StuRat (talk) 20:02, 8 February 2013 (UTC)

That's the point. Concepts like "clouds", "moving", and "parts" are defined classically. When you say it's better to picture an electron as a "cloud", that's still depending on drawing an analogue to a classical object, and atomic level physics simply doesn't have those analogues. Electrons aren't balls, and they aren't clouds. The cloud visualization is better (because it captures the idea of nonlocalizability) but it has its own major fault in that such a steady state cloud cannot also have momentum, at least if your depending on what your experience tells you a cloud is. Quantum scale physics has all of these problems in meshing with human experience. The entire concept of wave-particle duality is a completely different sort of problem, but it's of the same ilk. A wave is a type of movement. A particle is a thing. So how can a thing be a type of movement also? One particularly bad explanation of wave-particle duality is that light, for example, chooses which set of properties it has based on the application. That's wrong headed. Light behaves the exact same way all the time in all situations. We can construct situations where modeling light as a particle works better, and we can also construct situations where modeling light as a wave works better; but neither model really captures what light is. There is nothing your senses experience that allow you to be able to visualize what light is. The best we can do is fudge together some classical concepts like "waves" and "particles": it's a shortcoming of human perception that's the problem. What we observe is a set of properties: the ways in which atoms interact with each other, the ways in which molecules form and behave, the ways in which electrons around a nucleus absorb and emit energy, etc. We run experiments and get data from those experiments. If we try to match that data with the predictions made by the equations of classical physics, it just doesn't work. That's what quantum physics does for us: it gives us a new set of equations that correctly match the experimental data of how electrons work and also correctly match the experimental data for everything else as well. As I mention below, the reason we keep the old equations around for the non-atomic stuff is that they're more convenient to work with, not because the quantum equations don't also work. --Jayron32 20:18, 8 February 2013 (UTC)

But don't you see a problem with just saying "that's the way it behave because that's what the equations say" ? This comes up in string theory, where we can come up with any of several set of equations, all of which match observations to the same degree. So, which is right ? Are we just guessing here ? StuRat (talk) 21:17, 8 February 2013 (UTC)

You're starting to edge up against a complete misunderstanding of what science is, Stu. Science doesn't tell us what is right, science tells us what works. The fact that there are multiple solutions that produce the same result is why things like string theory are open areas of research and exploration in science. We don't know the answers to the unanswered questions in physics, and a big part of that comes down to working out which of any of a number of competing theories (if any of them so far proposed) is more useful in explaining the current inadequacies in our existing models. "All models are wrong, some are useful" is an important aphorism here in understanding this. We're not trying to decide absolute rightness, we're trying to come up with more and more accurate models; but no model will ever be complete. The ones we have now are fantastically useful and accurate, much more so than Newtonian physics we used to work with (and still do work with where Newtonian physics agrees with the better, but more complex and esoteric, models). As simply as I can say it is this: the more modern theories (like QM and GR) which have gained broad acceptance are better than classical physics because the explain more phenomena in better detail, and match observed data more accurately than classical physics does. There are areas of open exploration in science (like the String Theory you keep bringing up) which are attempt to add another layer of accuracy and precision to our understanding, but which are not yet fully fleshed out nor fully accepted, because of the problems of the "several sets of equations which all match observations to the same degree". It is not a simple issue, there's thousands of physicists right now that are exploring those avenues and trying to resolve those problems you note. Most of them will go down dead ends, but perhaps someone working now will be able to add some positive confirmation to something like string theory, or another unifying theory, or maybe come up with something else. Unlike things like quantum mechanics and general relativity, these other ideas are just too new and too untested to produce anything like universal acceptance. One thing that is for certain, however, is that the new models will still need to agree with observable data at all scales and for all phenomena; if they don't they're not very useful. If they do, but don't add to the corpus of explained phenomena, then they're also not very useful. Useful new models are only those which match everything we already know AND which help to explain something we can't already explain. --Jayron32 22:35, 8 February 2013 (UTC)

When QM was new, it didn't predict everything, like the behavior of gravity, which was better explained by the older GR. Yet QRQM was generally accepted, because it explained other things better. StuRat (talk) 22:58, 8 February 2013 (UTC)

Assuming you mean GR in your last sentence, YES. --Jayron32 23:26, 8 February 2013 (UTC)

Nope, I meant QM. StuRat (talk) 00:07, 9 February 2013 (UTC)

Then the answer is still YES. --Jayron32 00:17, 9 February 2013 (UTC)

Agreed, thus refuting your statement that "Useful new models are only those which match everything we already know AND which help to explain something we can't already explain". StuRat (talk) 00:21, 9 February 2013 (UTC)

No, both Quantum Mechanics and General Relativity match everything we already know from classical physics (that is, neither of them contradicts the experimental results that classical mechanics also matches), but both theories also correctly predict things that classical physics gets wrong. That's why they are useful: They expand upon and replace simpler theories, and get more correct than the simpler theories do. If, for example, Quantum mechanics only gave us the exact same results as classical physics, and didn't give us better explanations for the things classical mechanics got wrong, it wouldn't be useful. If quantum mechanics could better explain some things that classical mechanics got wrong, but it was also wrong where classical mechanics was correct, it ALSO wouldn't be useful. That they agree in areas where observation confirms that classical mechanics was correct, and that quantum mechanics ALSO adds entire new explanations for physical phenomena that classical mechanics gets wrong (like the aformentioned problem of the electron that started this thread) is why QM is a generally accepted theory. It agrees with all of the observations classical mechanics agreed with, and adds a whole new set of observations that classical mechanics couldn't correctly predict. You can replace the words "quantum mechanics" with "general relativity" and the same statements hold true. --Jayron32 00:31, 9 February 2013 (UTC)

I wasn't talking about classical mechanics here. I was refuting your statement that "Useful new models are only those which match everything we already know AND which help to explain something we can't already explain" by giving the example where QM was a useful new model, despite not matching everything we already knew (from GR). Also, a model which explains nothing new, but is simpler, may also be useful. This comes up in reverse with string theories which want to add more and more dimensions, with little benefit. StuRat (talk) 00:21, 9 February 2013 (UTC)

The fact that GR and QM don't play well together is already well established and not in dispute. I already cited it as one of the great unanswered questions in physics. So, you're not adding anything surprising to the physics canon by noting that. --Jayron32 00:49, 9 February 2013 (UTC)

And I'm not trying to do that, am I ? I just used it to refute your statement, as I've said twice now. StuRat (talk) 06:43, 9 February 2013 (UTC)

The answer you gave is like explaining that the Earth is flat and stars are holes in a black cloth - that would be the "classical model". Your answer has been known to be incorrect for almost a century. 88.112.41.6 (talk) 19:39, 8 February 2013 (UTC)

It's not that simple. Quantum mechanics seems to work better on a small scale, and the classical mechanics approximation of relativity or relativity itself are better on a large scale. How to mesh them together is a problem that still confounds us. Things like electrons are right at the cusp of the two models, sometimes behaving like a probability cloud, and sometimes like a particle. So, relativity (and the classical mechanics approximation of relativity) isn't strictly right or wrong, and the same is true of quantum mechanics. StuRat (talk) 19:44, 8 February 2013 (UTC)

Your explanation is known to be incorrect. It violates basic laws of physics (conservation of energy and momentum). You may want to consider if your frequent contributions to the reference desk would be more valuable if you could recognize and admit when you give a wrong answer. This is not the first time I see you doing this. 88.112.41.6 (talk) 19:50, 8 February 2013 (UTC)

Actually, Stu, we do understand perfectly well how QM and classical mechanics mesh. QM laws reduce just fine to classical laws in the limits of measurements; they scale perfectly. There is no magical moment when an object stops obeying quantum rules and starts obeying classical rules; there's a continuum where the difference between the predictions made by classical physics and quantum physics decreases as the scales increase. That is, as size scales become larger, the quantum laws predict the exact same properties as the classical laws do. The entire universe can be accurately modeled entirely using quantum mechanics. We keep classical physics around because the math of quantum systems is a bitch, and if we can get the same results with the easier math, then why not? But it simply isn't true at all that quantum mechanics doesn't work on large scales. Only the converse is true: Classical physics doesn't work on small scales, but quantum physics works on all scales. That's why it's a better overall theory. --Jayron32 20:00, 8 February 2013 (UTC)

I don't agree that QM works on all scales. Here's a source which backs me up: [17]. And the opening sentence in our article says "Quantum mechanics (QM – also known as quantum physics, or quantum theory) is a branch of physics dealing with physical phenomena at microscopic scales, where the action is on the order of the Planck constant". Now, string theory attempts to unify both classical mechanics and QM, but it has it's own problems, such as having many variants, all of which are untestable. StuRat (talk) 20:06, 8 February 2013 (UTC)

And now, rather than admitting to being wrong, you go into obfuscation mode. The original question was why don't electrons go into the nucleus. Nothing to do with "scales". You gave the exact anti-answer - a known incorrect answer that was thrown out the window exactly because it was discovered that it leads to electrons going into the nucleus, making all atoms in the universe disappear in a fraction of a second. Your habit of doing this is unfortunate given the volume of text you write on the reference desk. 88.112.41.6 (talk) 20:24, 8 February 2013 (UTC)

Put up or shut up. I've provided links supporting my point. If you disagree, let's see your proof, not personal attacks. StuRat (talk) 20:29, 8 February 2013 (UTC)

Holy shit, that's your source? Don't mind if I don't believe a word of what's written on some hand-made website. I've not applied the Crackpot index to it, but my sense tells me it'd be ridiculous. Seriously Stu, if you're going to make a claim like that, you're going to need a better source. The same Wikipedia article on quantum mechanics you cite also states "Predictions of quantum mechanics have been verified experimentally to an extremely high degree of accuracy. According to the correspondence principle between classical and quantum mechanics, all objects obey the laws of quantum mechanics, and classical mechanics is just an approximation for large systems of objects (or a statistical quantum mechanics of a large collection of particles). The laws of classical mechanics thus follow from the laws of quantum mechanics as a statistical average at the limit of large systems or large quantum numbers.[35] However, chaotic systems do not have good quantum numbers, and quantum chaos studies the relationship between classical and quantum descriptions in these systems." (bold mine) I mean really Stu, if you're going to make silly claims like this, don't quote a source (the Wikipedia article) that directly contradicts you. Seriously, read the entire article next time. You might actually learn something new. --Jayron32 20:27, 8 February 2013 (UTC)

What's that opening line saying about Plank distances, then ? Also, out Theory of everything article says it's "... a theory that would unify or explain through a single model the theories of all fundamental interactions and of all particles of nature: general relativity for gravitation, and the standard model of elementary particle physics — which includes quantum mechanics — for electromagnetism, the two nuclear interactions, and the known elementary particles". So, if you're claiming that QM already does that, then why do we need a ToE ? StuRat (talk) 20:32, 8 February 2013 (UTC)

Planck distances are the distances when the classical model stops working, which is why we need the quantum model to work there. It has nothing to do with the upper limit for quantum models. The quantum models work on all scales. Also, QM doesn't do everything. QM doesn't have a good explanation for gravity, which is why we need a theory of everything. Gravity is very well modeled by general relativity in the sense that general relativity makes mathematical predictions about gravity that are borne out by experimental data, and which classical explanations of gravity do not. The other fundemental forces are well modeled by quantum mechanics: that is QM makes predictions about how forces like the nuclear forces and electromagnetic forces behave, and those predictions are borne out in the experimental data. The problem is that we have two post-classical theories, each of which very accurately matches experimental data in their own domains (and each does a better job in those domains than classical physics does) which appear to be incompatible with each other. --Jayron32 20:47, 8 February 2013 (UTC)

It sounds like the lede to our QM article needs changing, then, since it really doesn't say that now. Also, since gravity is critical to understanding macroscopic behavior, if QM doesn't explain it, then QM does have an upper size limit, be that the Plank length or something else. StuRat (talk) 21:22, 8 February 2013 (UTC)

Furthermore, Sting theory isn't trying to marry classical mechanics and quantum mechanics. It's trying to marry general relativity and quantum mechanics. GR and QM are two different non-classical theories that operate in different domains (GR models gravity, while QM models other forces) --Jayron32 20:31, 8 February 2013 (UTC)

OK, I was a bit sloppy in equating GR with classical mechanics, but they do rather go together, as GR does work with large objects, like stars and planets, and not-so-much with wave probability functions from QM. I like to think of GR as tweaking classical mechanics, while QM tosses it out the window entirely. StuRat (talk) 20:39, 8 February 2013 (UTC)

It's a far cry from a mere "tweak" of classical gravity; it also throws classical gravity out the window. Classical gravity has two problems 1) it propagates instantaneously instead of at the speed of light and 2) classical gravity is a real force, whereas in GR gravity is a pseudoforce akin to centrifugal force. That is, General Relativity says that gravity isn't a force at all; it's a geometric warping of space time that gives the observer the 'illusion' of a force. This idea that spacetime can be warped isn't a mere tweak, its the central aspect of GR and is completely and totally out of the realm of classic physics. --Jayron32 20:53, 8 February 2013 (UTC)

I call it a tweak since it seems mostly to just be another way to visualize gravity. The results are similar, whether you think of space-time as warped or explain orbits with classical mechanics. The speed of light considerations are where more of a difference is observed between the two. StuRat (talk) 21:10, 8 February 2013 (UTC)

If by "tweak" and "just another way to visualize" you mean "a complete and total rewrite of every aspect of our understanding of how the universe works on the most fundamental levels" then you may be closer to the truth. Seriously Stu, I say this out of love, because I don't want to see you embarrass yourself further along this line of thinking, but you're like a walking, talking personification of the Dunning–Kruger effect. You started with a completely incorrect premise, and rather than concede that you continue to make statements which, bafflingly, are progressively wronger and wronger. GR is not another way to visualize gravity. GR is a fundamentally different way to understand the entirety of physics and motion and kinetics and dynamics and velocity and acceleration and time and space. It has it's own mathematics, it's own geometry, there's absolutely nothing that Newton would look at and say "Yup, that's basically what I said". The results as far as gravity is concerned are not "similar", excepting in the classical limit. At an approximation, the kinds of behaviors that GR predicts about how, say, an apple will move as it descends towards the ground are identical to what classical physics says; this is analogous to the way in which quantum mechanics and classical mechanics converge to the same mathematical results when you get to large objects. However, that doesn't mean that the kinds of differences between the predictions of GR and classical mechanics makes are just minor tweaks. Classical gravity is way off and doesn't correctly model lots of behaviors correctly at all; things like black holes and gravitational time dilation and Frame-dragging and the Geodetic effect which classical gravity gets wrong in the exact same way that classical mechanics gets the atom wrong. There's just no intellectually honest way to say that General Relativity was merely a change of perspective or a tweak to classical gravity: it's a fundamentally different way to look at the universe, and it makes different predictions that match experimental results in ways that classical gravity just does not. --Jayron32 22:16, 8 February 2013 (UTC)

Look at my example, of planetary orbits. How does GR predict different orbits from classical mechanics ? Newton would definitely say "that's just another way to look at it", not, "I was wrong". It's only when you get far from our everyday experiences that GR predictions are far removed from those of Newton. StuRat (talk) 22:52, 8 February 2013 (UTC)

Well yes, in general, but even with this GR predicts the correct orbit of Mercury but Newtonian physics does not.--Gilderien Chat|List of good deeds 23:23, 8 February 2013 (UTC)

Newton gets the orbits of planets wrong by incorrectly predicting the way that they precess. The observed apsidal precession of the planets does not in accurately match the behavior predicted by simple classical mechanics (Newton and Keppler and all that jazz), you need general relativity to predict it correctly. It's wrong for all planets, but noticably so for Mercury; the incorrect predictions about Mercury's orbit are large enough that they were noted before Einstein was even born. No one could explain it until General Relativity created a model that fit perfectly. If you used a GPS in the past week, if it were not for General Relativity, said GPS would have been off by miles in telling you what your position is: based on classical understanding of gravity, your position cannot be accurately calculated using GPS, because classical gravity has no means to calculate Gravitational time dilation which must be taken into account given the distance the GPS sattelite is from the surface of the earth. Newtonian gravity can't explain Gravitational lensing, something astronomers work with every day. Also, no one said Newton was wrong. As I said above, science isn't looking for 'right'. Science is looking for 'useful'. Newton's theories are still, to this day, very useful: most of the stuff you do on a daily basis that may require basic physics calculations, such as the speed your car moves, or the trajectory of a thrown object, or any number of other common calculations, are perfectly well predicted by Newton's theories. Where they fall short, the more complete General Relativity steps in to help expand the corpus of applications, for example the two shortcomings I noted above. Now, General Relativity also predicts the same things about the speed of your car and the flight of a thrown object that classical physics does. It's just silly to do all that math to get the same answer in those sorts of applications. --Jayron32 23:25, 8 February 2013 (UTC)

I'd still call all that "tweaking". For an example of "a complete and total rewrite of every aspect of our understanding of how the universe works on the most fundamental levels", I'd go with the ancient Greek model of the "elements" being earth, air, fire, water, and ether, each corresponding with a perfect solid, versus our current understanding of the elements. StuRat (talk) 00:13, 9 February 2013 (UTC)

Apples and oranges. There's no fundamental way you can call the Platonic elements "science". However, the differences that General Relativity wrought on our total understanding of physics is akin to the difference between Dalton's atomic theory and the modern Atomic orbital model of the atom. That is, what Dalton said the atom looked like and what modern Quantum mechanics thinks the atom looks like is roughly akin to the difference between what Newton said the physical universe worked like and what GR says of the same. --Jayron32 00:23, 9 February 2013 (UTC)

(edit conflict) Damn good question. Since the structure of the atom was first elucidated by Rutherford in his gold foil experiment, that was a major, central controversy with his nuclear model of the atom. They should crash into the nucleus under the principles of classical physics, and there's nothing in classical physics which adequately explains why they don't. Indeed, that problem is one of the keystones which brought classical physics (as a means to describe atomic-level phenomena) down and led to the development of more advanced, modern understandings of the physics. Now, the first thing you need to do is to take the image of the little electron orbiting the nucleus like the earth does the Sun and put it in the same part of your mind that you keep Santa Clause and the Easter Bunny: it's a nice little story we tell kids, but its a total fiction. An electron is not a little ball. Trying to describe an atom as you would describe any other object is always problematic, but if you must create a picture in your mind, it is better to think of an electron as a cloud instead of a point. The cloud exists over a volume of space described by a wave function which describes both the shape and density of that cloud over space. Now, that cloud is imbued with certain properties that must be conserved; that is no change to that cloud can eliminate said properties. The electron cloud has, for example, momentum. Now, this momentum exists spread out over the whole cloud, and cannot be localized to any one point in the cloud (I know, this makes no sense when you try to picture it, but it doesn't need to make sense to be true. This is one of those things you have to be able to accept without a visual representation). Any changes to the cloud, such as its size, must conserve this momentum. If the cloud were entirely compressed into the nucleus, then this momentum would be localized into a single point. The fact that this kind of localization of momentum is impossible is enshrined in the uncertainty principle, which is a cornerstone theorem of modern physics. So the reason that the electron never crashes into the nucleus is that, if it did that, its momentum would be localized in one location, and the uncertainty principle says that you can't localize momentum in that way. The uncertainty principle says any particle cannot simultaneously have a precisely defined location and momentum; since all electrons have a precisely defined momentum, they can NEVER have a precisely defined location. So electrons cannot "crash" into the nucleus.

Another way to think of it is this: there is a force holding the electron to the nucleus in the same way that there is a force holding a magnet to, say, your refrigerator. Now, there is not any loss of energy as the magnet holds fast to the refrigerator. The magnet has potential energy, but so long as the magnet does no work, then it will remain stuck to the refrigerator forever without losing any of that potential energy. Work only happens when a force moves something; forces that don't move objects don't expend any work, and no energy is "used up". In almost the exact same way, the electron is "held fast" to the nucleus by the electrostatic force, but no energy is lost because the electron does no work in remaining there. Here's where the classical explanation and modern explanation diverge: if you're picturing the electron as a little ball, there's no way for it to remain in motion under such a force and do no work at all. Such a ball should spiral into the nucleus, shedding potential energy the whole way in. If, however, you think of the electron as a steady-state cloud it just remains in the same state forever, and does no work. Now, the mindfuck here is that you need to accept that this steady state cloud still has momentum without actually having any localized parts which are in motion. There's no convenient way to make that work except to say "just accept it". --Jayron32 19:00, 8 February 2013 (UTC)

Well technically in hydrogen it sort of does - the 1s electron is in an orbital which is a sphere shape and superimposed over the proton, which is also technically a sphere of probability. So under some observations, it will appear to be "inside" the nucleus.--Gilderien Chat|List of good deeds 20:20, 8 February 2013 (UTC)

And keep in mind that the electron has half a spin all by itself, in addition to the full spin of orbiting around the nucleus. So the final result is either a spin and a half if aligned, or half a spin if opposed and no other result can ever be measured. Hcobb (talk) 20:23, 8 February 2013 (UTC)

As is multiply explained above and in the linked articles, "spin of orbiting around the nucleus" is a load of completely disproven nonsense, no? DMacks (talk) 22:06, 8 February 2013 (UTC)

Well as I read it, the "cloud" does have momentum and this would thus be either in one direction or another (as a non-zero vector quantity must be) and so these effects will be observed.--Gilderien Chat|List of good deeds 23:35, 8 February 2013 (UTC)

(arbitrary break) Why is "Why don't electrons fall into the nucleus?" the single most asked science ref desk question ever?

self explanatory... μηδείς (talk) 20:43, 8 February 2013 (UTC)

Well, two things 1) It isn't (the search you gave gives LOTS of threads that mention the words "electron" and "nucleus" without addressing this specific problem) and 2) If it is a commonly asked question, that's because of what I explained above: things like atoms, electrons, light, nuclei, etc. etc. don't have analogues to what you can sense and experience in the world. There is literally no shape, object, behavior, or concept about how you experience the world with your five senses which correctly and accurately models quantum behavior. That is, the predictions you would make about an electron if you say "an electron is like FOO", where FOO is literally anything you have ever experienced, always breaks down. Some representations work in some situations, which is why we use them in some explanations, but no such representation works all that well. So, you need to rely solely on two things A) the data from experiments and measurements and B) the predictions of the equations of quantum mechanics. As long as A = B, it's a highly useful theory. The fact that it's also not a theory that lends itself to easy visualization doesn't invalidate it; but it does make it very hard for people to wrap their heads around, since we all learn by analogy; we try to connect something we're learning to something we already know. QM resists that sort of analogy, which is why it is so confusing, and why people have a hard time wrapping their heads around it. --Jayron32 21:11, 8 February 2013 (UTC)

I wasn't challenging any prior answers, just pointing out the same question was asked about a month ago and several other times I remember. A search on "fall into the nucleus" gets you lots of prior answers, only a few of which are links to Dr Who episodes. μηδείς (talk) 02:53, 9 February 2013 (UTC)

I wanted to comment on a few things, but didn't want to insert my comments into the above mess. So I'm putting all of them here.

First, why the heck are we debating whether quantum mechanics works for classical systems? It does, period, end of story. In fact, we have an article about this: correspondence principle, which gives plenty of examples. In any undergrad QM class, you get to prove ad nauseum how your quantum result for various problems reduces to the classical result in the limit of high energies and large sizes. If it doesn't, then you did something wrong, and have to redo the problem. QM is incompatible with general relativity because the former cannot describe strong gravitational fields, not because it can't describe large sizes. It's quite easy to describe weak gravitational fields in QM: just introduce a classical 1/r gravitational potential. Strong gravitational fields usually arise at very small scales, like the singularity of a black hole or the very early universe, not at large scales like that of the solar system.

Second, in the classical model where the electron orbits a positive nucleus, the electron would radiate energy and crash into the nucleus. As Jayron noted, this fact is expressed in the Larmor formula. This, again, is indisputable. Bohr model#Origins describes the historical significance of this (although strangely, Rutherford model doesn't):

"Rutherford naturally considered a planetary-model atom, the Rutherford model of 1911 – electrons orbiting a solar nucleus – however, said planetary-model atom has a technical difficulty. The laws of classical mechanics (i.e. the Larmor formula), predict that the electron will release electromagnetic radiation while orbiting a nucleus. Because the electron would lose energy, it would gradually spiral inwards, collapsing into the nucleus. This atom model is disastrous, because it predicts that all atoms are unstable."

Third, here's an alternative answer to the OP's question, which is equivalent to Jayron's in the sense that both use the same underlying theory. In quantum mechanics, the electron is represented as a wavefunction. The physical significance of the wavefunction is that if you try to measure the electron's position, the square of the wavefunction at any point is equal to the probability of finding the electron at that point. Schrodinger's equation tells you what the wavefunction can possibly look like. So, why is it not possible for the wavefunction to be extremely densely concentrated around the nucleus? Because such a wavefunction doesn't satisfy Schrodinger's equation. You can see every function that does satisfy the equation; they're called atomic orbitals. Note, however, that the squared wavefunction is only a probability distribution, and even very close to the nucleus, it doesn't fall to 0. You might ask, if this is the case, why electrons don't sometimes fall into the nucleus. The answer is that they do, and this process is called electron capture.

Finally, contrary to what Jayron said, electron clouds have no momentum. This is because atomic orbitals are stationary states, and the expected value of the momentum operator is always 0 in any stationary state. The expected value of the momentum squared, however, is non-zero, so electrons have non-zero kinetic energy. --140.180.247.198 (talk) 00:35, 9 February 2013 (UTC)

Thanks for correcting me on the momentum/kinetic energy thing. I confused the terms above in my initial explanation. However I am still pretty confident in the uncertainty principle implications of having an electron located in the nucleus. I did some more digging just now to check up on the other aspects of my explanation, and found this explanation from the University of Illinois physics department, which may be helpful towards answering the initial question. --Jayron32 00:47, 9 February 2013 (UTC)

Well, I am not a expert of Quantum Mechanics and the above discussion is completely based on Quantum Mechanics. I have thought a answer to my question but I think that is wrong. "Suppose, an electron gets attracted to the nucleus, it falls towards the nucleus, coming to a lower orbit and then to other lower orbits between the electrons's own orbit and the nucleus. We know, for an electron to come to a lower orbit, it would have to emit photon. The attraction of nucleus for an electron is not so strong that it will make an electron to emit photon. Therefore, the electron doesn't come to a lower orbit. This is why electrons don't fall in the nucleus". Am I right or wrong? Want to be Einstein (talk) 03:46, 9 February 2013 (UTC)

See my answer in this old thread. GilderienJayron32 made some similar points earlier in this thread. -- BenRG (talk) 06:02, 9 February 2013 (UTC)

How to freeze water in 5 seconds?

Watch this video I know there is a way to freeze water in 5 seconds. But I do not know how to do it. After watching the linked video please tell me a way by which I can also make water freeze very quickly. Polar Bear25 (talk) 19:57, 8 February 2013 (UTC)

Well, there are four factors on how to freeze water quickly, in general (although this seems to be a case of supercooling, see answer below):

1) Have it as close to freezing temperature as possible, before you start.

2) Expose it to extreme cold.

3) Make the water particles as small as possible.

4) Lower the pressure.

So, if you spray a fine mist of high-pressure, near-freezing water through liquid nitrogen, while lowering the temperature, you should be able to freeze it considerably quicker than 5 seconds. StuRat (talk) 20:09, 8 February 2013 (UTC)

(ec) It's called supercooling. It's a trick in which purified water is cooled down very carefully below freezing point so that it gets no 'opportunity' to crystallize. If the water is disturbed, it then suddenly starts to form ice crystals. When you see the water freezing, its temperature does not actually decrease, but it increases because energy is released by the formation of strong bonds in the crystal. - Lindert (talk) 20:14, 8 February 2013 (UTC)

How can I do this as the person in the video did ? Polar Bear25 (talk) 03:57, 9 February 2013 (UTC)

There are plenty of videos on the web, e.g. this one. For best results use distilled or spring water, and leave in freezer for about three hours.--Shantavira|^{feed me} 10:18, 9 February 2013 (UTC)

Note that spring water is not suitable because it is very far from pure. See Spring_water#Water_content. 202.158.103.42 (talk) 14:47, 9 February 2013 (UTC)

You are on the right path. Placing bottle in freezer water, but how will I freeze it. Polar Bear25 (talk) 11:09, 9 February 2013 (UTC)

Space between atoms

In the article atomic spacing it says that the distance between atoms varies from a few angstroms in solids to "as large as a meter" in "outer space". Yet I asked a similar question before here and was told that the distance between the inner electron and the nucleus could technically be infinite. The wording in the article also implies that if the distance between 2 or more atoms can be measured then the distance between the electron cloud and the nucleus can also be measured. Is there a rule for determining the distance between the inner electron cloud and the nucleus of an atom?165.212.189.187 (talk) 20:38, 8 February 2013 (UTC)

"The cloud" is just a large space where the electron "probably or usually" is. All we can actually say is how likely it is for the electron to be a certain distance away, or else to say "the electron is unlikely to be [somewhere]" for some essentially arbitrary meaning of "unlikely" (there's not literally an "inner edge" of the cloud the way your question suggests). DMacks (talk) 21:13, 8 February 2013 (UTC)

There is no such thing as an "infinite" distance. But they might mean that there is no limit to how far the distance could be, which is not quite the same thing mathematically. ←Baseball Bugs ^{What's up, Doc?} carrots→ 22:10, 8 February 2013 (UTC)

To put it in context, it's overwhelmingly likely that the electrons are closer to the nucleus than the nucleus of the next atom along - but there is a vanishingly small chance that the electron could be over on the other side of the universe. There is no particular paradox to this. The "distance between atoms" is likely to be measured from nucleus to nucleus. SteveBaker (talk) 00:08, 9 February 2013 (UTC)

Is "the" electron in a hydrogen atom really any random electron in existence and not necessarily the same over time?GeeBIGS (talk) 02:48, 9 February 2013 (UTC)

Why isn't empty space listed as a critical component of an atom? Since without it you can't have an atomGeeBIGS (talk) 02:54, 9 February 2013 (UTC)

Space would be a "component" of everything that exists, so it's kind of "understood". ←Baseball Bugs ^{What's up, Doc?} carrots→ 06:17, 9 February 2013 (UTC)

It's not a component of an electron. Quarks could also be a component of everything that exists,right? but you don't just take them for granted or as you call it understood, what's the difference?GeeBIGS (talk) 07:08, 9 February 2013 (UTC)

DVI and VGA cable

Using a DVI cable instead of a VGA cable makes any difference in quality, performance or anything?

…using the same monitor(this monitor)

thanksIskánder Vigoa Pérez (talk) 22:52, 8 February 2013 (UTC)

The Computer Ref Desk might be a better place to post this Q. StuRat (talk) 23:02, 8 February 2013 (UTC)

VGA is analog, DVI is digital. If you use VGA the monitor will convert it to digital internally, so it can't look any better than DVI. Whether it will look worse depends on the quality of the analog-to-digital converter (and how picky you are). I've seen wide variation in this, and I can't tell you anything about that particular monitor. As far as performance goes, it won't have any effect on frame rate. There could be a tiny difference in the lag time between the video card emitting the signal and the monitor displaying it, but I don't know which interface it would favor. -- BenRG (talk) 05:45, 9 February 2013 (UTC)

Use DVI if you can. If the source can produce high definition video it may only do that for DVI or the image may be slightly degraded comparatively even if it does send it over a VGA cable. Dmcq (talk) 11:56, 9 February 2013 (UTC)

Amount of heat input required to cut stainless steel plates

The first row of the table in this section seems highly counter-intuitive. If I'm reading it correctly, it seems to state that as plate thickness increases you actually need less laser power to cut through it. I've check the referenced source[18] and it is not a typo. Is this actually true? I'm having a hard time believing it despite the authoritative source. Is there an explanation for this? Dncsky (talk) 23:47, 8 February 2013 (UTC)

That does seem a little odd at first sight. I actually own a laser cutter (a 120Watt lasersaur)...and although I don't use it to cut metal - I think I may have some insight here.

I know that when cutting acrylic plastic with my laser cutter, the slot that the laser cuts acts like a waveguide - keeping the beam tightly in focus rather than spreading out. That means that you don't need much (if any) additional laser power to cut thick acrylic than thin...within reason.

When cutting wood and metal, it's common to blast a "cutting gas" into the slot where the laser is cutting - for cutting wood, you can use nitrogen to exclude oxygen from the cut and thereby prevent scorching. Or you if you're a cheapskate like me you can just blast air into the slot instead! A lot of people who are cutting metal use pure oxygen as their cutting gas. The gasses inside the cut become insanely hot and this "gas assist" lasering process pushes that hot gas into the path of the laser so that the material is pre-heated by the time the laser reaches it.

When you're cutting a thick, non-combustible material, the gas assist works much more effectively than for thin materials - and for shiney materials, the "waveguide" effect keeps the laser well focussed throughout the thickness - which is another big win. With metals, a consequence of that is that you need a heck of a lot of laser power to make that first hole (the "pierce") - but after that, you can dial it way back for the actual cutting. I'd be surprised if you could cut steel at all with a 250 watt laser without pre-heating it enough to get that first pierce hole and allow the waveguide and hot gas channelling to start working for you.

But here is the key: The business of delivering laser power onto the target is as much a matter of speed as power. My laser (which I predominantly use for cutting plywood) can cut effectively at a speed of 2,000 mm/sec only if the laser is operating at 100% full power. But you can also cut the same thickness of plywood at 50% power if you drop the feed rate to around 800 mm/sec. In effect, you're holding the laser in one place for longer so that the total energy delivered to the material is about the same. Balancing speed versus power is important for some materials that are liable to burn or melt or buckle when they get too hot.

So I suspect that although the laser power can be much smaller for thicker materials, the feed rate is probably a heck of a lot slower too.

In fact, that's backed up beautifully by our article - which shows 1,000 inches per minute as the feed rate for the thinnest steel and just 18 inches per minute for the thick stuff! In terms of Watt-seconds per linear inch of material cut (now that's a weird unit!), then using the data from the table, for the very thin steel, it's taking 1,000 Watts for 60 seconds (60,000Ws) to cut 1,000 inches of thin steel. That's 60Ws per inch of cutting. For the thickest steel, you need 250 Watts for a 60 seconds (15,000Ws) to cut for just 18" - which is 833Ws per inch. In other words, you need about 13 times as much laser energy (measured in Watt-seconds) to cut a 1" long slot in 0.25" steel than you do to cut the same slot in 0.02" steel...which (un-amazingly) is the same amount of energy per square inch of material removed - no matter the thickness.

The table is really saying that for very thick material, you can cut MUCH more slowly - and if you do that, you can get away with less laser energy. Doubtless you could cut 0.02" steel with a 250 Watt laser if you went slowly enough...and 0.25" steel would cut more quickly with a 1,000 Watt laser. But going so slowly with a thin sheet of material might produce other problems such as buckling and undesired melting away from the edge of the cut-line. So probably you have to use a lot of power to cut it quickly and thereby avoid those kinds of problem. Thicker material is unlikely to buckle - so you can take your time and use a smaller laser.

SteveBaker (talk) 00:42, 9 February 2013 (UTC)

Perfect answer. Thanks a lot!Dncsky (talk) 01:27, 9 February 2013 (UTC)

It looks like your cutting gas has a couple of uses. The Wood/nitrogen case is clearly to stop combustion, but the steel/oxygen case turns the laser cutter into a Oxyfuel cutting torch. One of those can cut steel up to 2 feet (0.66 meters) thick because the steel itself works as a fuel. --Guy Macon (talk) 03:53, 9 February 2013 (UTC)

Yes, I believe so. When I was considering using Nitrogen as a cutting gas on my lowly 120 Watt beast, I wanted to work out how long a $100 cylinder of the stuff would last me (answer: Not long enough!) - and I got into an online discussion with a guy who was actually talking about cutting thick steel. He came up with numbers that implied to me that he was using a gas stream at close to the speed of sound - blasting down through the same hole that the laser beam emerges from - so it's a properly coaxial affair. Clearly that amount of pressure with pure oxygen and with all the heat that several kilowatts of laser energy adds will indeed produce something very similar to an oxyfuel system.

I soon realised that he and I were talking about entirely different systems! My machine produces a perfectly useful "air-assist" for cutting 3mm plywood using nothing more than a $77, 0.7 cubic feet per minute airbrush compressor - feeding a coaxial air stream through a 5mm hole...not much more than a gentle breeze! But even that relatively modest gas jet produces a dramatically better cutting speed than the laser alone (and incidentally blows smoke and debris away from the horribly expensive gold coated zinc-selenium lens). So there is quite a bit of subtlety to how these systems work.

Even on my lasersaur, the means by which the laser cuts varies from material to material. When cutting wood with an air jet, it combusts the material, producing smoke, water vapor, carbon dioxide, some kind of yellowish tar-like substance that coats my machine and has to be cleaned off regularly. It leaves behind a very smooth, but somewhat charred, edge. However, if you do use nitrogen to prevent combustion, the wood just "goes away" without producing smoke and the edge of the material is very clean. When cutting acrylic plastic, the laser produces some kind of chemical change that's not just combustion - and the result is a perfectly clean cut with shiny, smooth, clear edges. With some other plastics, it simply melts the material without any chemical change whatever. SteveBaker (talk) 16:32, 9 February 2013 (UTC)

Wait: A feed rate of "2,000 mm/s"? Wow! What a nice laser you have there. Caristan, C L (2004) Laser Cutting Guide for Manufacturing. SME. p. 23 suggests a 2 kW CO₂ (pulse mode) laser cuts 1 mm stainless steel sheet at closer to 133 mm/s (8 m/min) --Senra (talk) 20:54, 9 February 2013 (UTC)

February 9

Organs Questions

I've got three questions about organs and whatnot?

• 1. If someone old dies and then an organ/body part of his/hers gets put into another body, does this organ/body part still function based on its actual age or does being put in a new body makes it function as if it were of a younger age?
• 2. What is the age limit for donating blood, bone marrow, and various organs? Can a 100 year old's donated organ(s) or blood work successfully/well in another person's body?
• 3. Does any country maintain a list of the blood types and organ donation status of all or most of its population? I'm tempted to think No and that it would be considered a violation of privacy to do something like this, but I am still interested in finding this out for sure.

Thank you very much. Futurist110 (talk) 00:24, 9 February 2013 (UTC)

1. Yes to the former, age is not a state of mind, it is a biological fact, you can't rejuvenate organs in that way. Plasmic Physics (talk) 00:33, 9 February 2013 (UTC)

Thank you very much. Here's another question--do the various human organs age and decline in the same way that humans do? For instance, a healthy human who takes care of himself/herself would probably reach age 85 or 90, but afterwards it becomes a very uphill climb, with very few people who reach age 90 reaching age 100 and very few people who reach age 100 reaching age 110. Do most human organs (if put in a functioning body) also stop functioning when they (meaning the organs) are 85-110 years old? Futurist110 (talk) 00:42, 9 February 2013 (UTC)

I'm not an expert in this this field, but I would say yes, which is why younger transplants are prefered - they have a longer useful lifetime. Plasmic Physics (talk) 00:51, 9 February 2013 (UTC)

Thank you. I'm interested in this because I saw this article from 2008 about a 123-year-old living cornea (here is that article--http://www.reuters.com/article/2008/10/23/us-norway-eye-idUSTRE49M6BL20081023). Futurist110 (talk) 01:38, 9 February 2013 (UTC)

That's believable, because I know for certain that different organs age at a different rate. Take a car for example, the tires get worn out faster than the transmission (usually). Plasmic Physics (talk) 01:47, 9 February 2013 (UTC)

But this contradicts your previous statement of appearing to agree with me that human organs probably age as fast as human themselves do. That said, theoretically it might be possible for a human male to reach age 123, but this hasn't happened before since by that point it would be extremely rare for all of a human male's organs to still be working/alive. Futurist110 (talk) 02:10, 9 February 2013 (UTC)

In the UK the age limit for blood donation used to be 70, but they scrapped that (ref), and it's now based on the donor's health. Crucially, certain medications for chronic conditions (medications that are very commonly taken by people as they age) disqualify people as donors, so in practice the number of donors older than 70 is pretty low. -- Finlay McWalterჷTalk 00:38, 9 February 2013 (UTC)

So in the U.K. someone aged 100 or above but in good health can (sometimes) donate his/her blood? What about organ donations and bone marrow donations? Futurist110 (talk) 00:42, 9 February 2013 (UTC)

83 year old kidney donor. 146.90.50.59 (talk) 01:49, 9 February 2013 (UTC)

Thank you. Futurist110 (talk) 02:10, 9 February 2013 (UTC)

As I thought I had remembered, and it's confirmed in Red blood cell, blood is constantly being created and recycled, so it might be that any donation age limits are concerns about the general well-being of the donor, rather than any concerns about "old" blood. ←Baseball Bugs ^{What's up, Doc?} carrots→ 06:13, 9 February 2013 (UTC)

Particle-wave duality

In an atom, it is said that the electron has a probability of being located at a position. Is that technically, or heuristically, correct - is the electron truely whizzing about the atom in a random way, or is it everywhere around the atom at once? I just find it hard to imagine that the electron retains its particle identity. I consider an unbound electron to be like an icy small solar system body, and a bound electron to be like the same SSSB vaporised and converted to the atmosphere of a planet. So, does the probability indicate how often the electron is expected to be encountered at that location, or how much of the electron is to be encountered at that location? Plasmic Physics (talk) 00:30, 9 February 2013 (UTC)

It's dangerous to think in those "normal" terms. It's not particularly meaningful to ask where the electron "is" or how much of it is where - because it's really only a probability field - and it (in a sense) "teleports" between locations within the probability cloud. For example, there is an effect called "Quantum tunnelling" (which is what makes the flash memory in your phone/tablet/memory-stick work - so we know it's true!). In very simple terms, the flash memory cell has a barrier between two locations that (classically) the electron cannot cross - but it can teleport between those two locations if properly coerced because there is always a finite probability of it being on the other side of the uncrossable barrier! So this is a very real effect - large, real-world things like telephones rely utterly on this weird quantum behavior. But it's quite hard to reconcile with day to day life...and that's the core problem with understanding quantum theory. At those levels of existence, things are very, very weird - and trying to get your head around a physical understanding of it is impossible. The only real way to get a handle on it is via the math. SteveBaker (talk) 01:02, 9 February 2013 (UTC)

So, a bound electron has a precise location that changes with time? I know about quantum teleportation, I just never reconcilled it with the behaviour of bound electrons. They never discussed electron motion within atoms in the lectures. Plasmic Physics (talk) 01:42, 9 February 2013 (UTC)

Quick aside — what's being discussed is quantum tunneling, not quantum teleportation, which I think is some information-theoretic abstraction rather than an electron actually showing up in a different place.

I figured. Plasmic Physics (talk) 03:48, 9 February 2013 (UTC)

Whether an electron has a precise location is a subtle question that gets into interpretations of quantum mechanics. I think most physicists generally prefer to avoid the question altogether ("shut up and calculate" says the shade of Feynman) and leave it to the philosophers. --Trovatore (talk) 03:22, 9 February 2013 (UTC)

Is there a way of testing either alternative? Plasmic Physics (talk) 03:48, 9 February 2013 (UTC)

There are more than two alternatives. As far as I know, no experiments have been devised that would distinguish among any of them. Strict positivists probably consider it a meaningless question for that reason, but for people with a more realistic view this is hard to swallow. But it's hard to get realism to play nice with QM under any conditions. --Trovatore (talk) 04:03, 9 February 2013 (UTC)

I should say, though, that your notion of a sort of "electron vapor", spread out over space, is not really one of the alternatives. Or at least I don't think it is. The electron itself is very tiny — as far as anyone knows, pointlike. The probability distribution tells you how likely it is that the electron will be found at a given location, but it is not the electron itself. --Trovatore (talk) 05:12, 9 February 2013 (UTC)

The picture of the electron in a hydrogen atom as a stationary wave and the picture of it as a particle randomly moving around are about equally valid. They can't be tested against each other—they're just two different ways of looking at the same physics.

Quantum mechanics actually has two different classical limits. If you take ħ → 0 while keeping the E in E=hf constant (so that f → ∞) you get the classical particle limit: each particle still carries energy E, but the infinite wavelength means you can never observe any wave interference behavior. If you take ħ → 0 while keeping the f in E=hf constant (so that E → 0) you get the classical wave limit: there are infinitely many particles each carrying infinitesimal energy that smoothly cover everything so you never see shot noise. Quite a lot of behavior that's often described as "purely quantum" is really behavior that vanishes in the particle limit but survives in the wave limit. Tunneling is one example of that: in the classical context it's called Evanescent-wave coupling. Of course there are other things that vanish in the wave limit but survive in the particle limit, like shot noise. Quantum mechanics sort of sits halfway between these two types of classical theories, so it's helpful to keep both pictures in mind. -- BenRG (talk) 05:15, 9 February 2013 (UTC)

I'm worried that this answer sounds overly compatible with the "electron vapor" idea. A stationary wave is not the same as a spread-out electron, any more than a radio wave is a spread-out photon. --Trovatore (talk) 05:26, 9 February 2013 (UTC)

A radio wave containing one quantum of energy is a spread out photon. A radio wave containing many times that much energy is a bunch of spread out photons. Photons are not localized in a coherent wave.

I'm not sure exactly what you mean by the electron vapor idea but I think there's nothing especially wrong with that idea. Feynman famously said that the single most informative statement about the world is "all things are made of atoms — little particles that move around in perpetual motion, attracting each other when they are a little distance apart, but repelling upon being squeezed into one another". That's a picture of atoms as somewhat sticky, somewhat rubbery balls. Sure they're quantum objects but that doesn't mean these aren't useful classical analogues for various aspects of their behavior. -- BenRG (talk) 06:56, 9 February 2013 (UTC)

Well, no, come on, I know you're a physicist and I'm not, but a radio wave is not a spread-out photon. A radio wave is electric and magnetic fields. An electron "wave" is an area of probability density. It's not a particle spread out. That's a cheap way of restoring realism that doesn't work.

You can restore realism with the many-worlds interpretation, by letting the real thing be the entire collection of worlds rather than just ours. Maybe you can restore it by the transactional interpretation; I've never understood it well enough to be sure. But not with the image of a "spread-out particle". It's just the wrong image; it doesn't lead to intuitions that correspond with theory or experiment. --Trovatore (talk) 09:12, 9 February 2013 (UTC)

I'm not a physicist, I just studied it in college. First, as I mentioned in another thread, the Standard Model is a quantized classical field theory. The wave nature of the electromagnetic and electron fields (the latter has no good name) is already there at the classical level. Quantization adds particle-like behavior, but the wavelike behavior doesn't disappear. You can and should think of a photon as the dimmest possible electromagnetic field. It's a misleading name for it, but it's too late to change that. If you want to talk about the pointlike behavior of light (i.e., shot noise), it would probably be better to talk about the "darkenon", which is one quantum of energy transferred from the electromagnetic field to a single silver halide crystal. (I just made that word up.)

Quantization is always the same. You probably wouldn't say that phonons are points and the bulk vibration of the crystal is just an indication of the probability of finding one in a particular place, but it's just as true for them as it is for electrons or photons. Or quantum vortices, which don't seem to have a commonly used name ending in -on but are particles nonetheless. -- BenRG (talk) 18:32, 9 February 2013 (UTC)

A radio wave totally is just a spread-out photon (or, more commonly, for normal amplitudes, it is a superposition of many photons). It's rarely useful to analyze this way; and we rarely have a wave at RF frequencies whose amplitude is so low as to be a single quantum emission; but this is still definitionally true and is easier to build a single RF photon emitter, in practice, than a single-photon-emitter at optical frequencies. Any electromagnetic wave can be viewed as a wave or as a particle. Considering a macroscopic wavelength as a "particle" can be very instructive in developing intuition about wave-particle duality. BenRG's comments about phonons are spot-on. Nimur (talk) 20:51, 9 February 2013 (UTC)

I disagree. It's a bad guide to intuition. It avoids confronting the failure of local realism. It sounds as though there's all this real "stuff" that's spread out over space, and that just isn't true. Also it completely clouds (ha!) the issue when you try to extend it to non-pointlike particles, like the proton — the learner can be forgiven for saying, wait a minute, here you're telling me about the proton "radius" (as distinct from the electron radius of, presumably, zero), but at the same time you have a picture of the proton as spread out over space, are these the same thing or not?

Particles are ipso facto localized, but the place they're localized to is, depending on interpretation, uncertain, different in different "worlds", or something else. --Trovatore (talk) 21:00, 9 February 2013 (UTC)

Well, I mean, the world is as real as it ever was, and failing to acknowledge that seems like an error to me. Of course there's stuff out there; it's what we've been trying to understand with all this physics nonsense. Saying that we've discovered by studying it that it isn't real, aside from being philosophically silly, doesn't tell you anything. It's wakalixes. What Feynman said about atoms does tell you things. The stickiness of macroscopic objects derives from the stickiness of atoms. Solids tend not to be sticky because they have rough surfaces and there's very little atom-to-atom contact when you press them together. Liquids stick to solids because they flow into the gaps. Gas molecules don't stick to each other because they're moving too fast, but if they slow down enough they do stick together, and that's why gases liquefy when you cool them down. And so on. Atoms are solid objects. Macroscopic solids are made of atoms and derive their solidity from the solidity of atoms (which is due to the Pauli exclusion principle). It's ridiculous to deny all of this or to imply that there's some kind of connection to many-worlds or what have you. We've actually learned some things about the everyday world in the last hundred years.

It's true that protons have an intrinsic (interaction) radius and also are spread out and that those things are independent. Saying that you shouldn't tell people about that because it's confusing isn't a very good argument. Mathematically the interaction radius shows up in the interaction part of the Lagrangian as a coupling of field values at different points in space. The photon-electron interaction in QED is a product of field values separately at each space(time) point, integrated over all the points, and that's the sense in which they are pointlike. A free field/particle is not pointlike in any way. That's why I said above that it's probably better to treat the interactions as pointlike rather than the particles themselves.

In many ways Standard Model particles/fields behave like classical particles. But saying that the particle picture is more fundamental, and the wave picture secondary, is completely wrong. -- BenRG (talk) 22:17, 9 February 2013 (UTC)

Wait a minute, I didn't say there wasn't real stuff out there. I said a delocalized pointlike particle is not "real stuff spread out". I stand by that. A point particle is a point, no matter how spread out its probability density function is. --Trovatore (talk) 22:27, 9 February 2013 (UTC)

Okay, look. What you seem to be saying is that fundamental particles don't occupy space—which means that the term "occupying space" is useless, since nothing does it—but that they do something, presumably involving the Pauli exclusion principle, that creates the impression of occupying space. I suggest calling that thing that they do "occupying space". I don't see what other meaning the term can have.

As far as I can tell, you haven't explained why you think the particles are just points even in the face of all the arguments to the contrary that I've presented. If it's because you think the wave function is a probability density, I think you're forgetting that it's a probability distribution over classical field configurations, not classical particle coordinates, since the Standard Model is a quantized field theory. If it's because of Feynman diagrams, I'll explain the reasons why Feynman diagrams are unlikely to be fundamental. -- BenRG (talk) 00:04, 10 February 2013 (UTC)

'Electron vapour' is exactly the name I would give it - a bound electron completely evaporates, from a particle into a vapour, surrounding the nucleus where the cloud density is equal to the 'probability'. Plasmic Physics (talk) 09:18, 9 February 2013 (UTC)

But that's exactly the wrong image. If you use that image, your intuition will lead you to incorrect conclusions. The electron has (as far as anyone knows) zero volume — it's just a point. That's true whether it's bound or free.

The "cloud" is a quantum superposition of places the electron might be. But each of those places is just a point (again, as far as anyone knows). --Trovatore (talk) 09:24, 9 February 2013 (UTC)

Yes, that's wrong—the electron's nature doesn't change just because it's part of an atom. If it's a cloud in that situation, it's a cloud the rest of the time too. If it's a point particle the rest of the time, it's a point particle when part of an atom. -- BenRG (talk) 18:32, 9 February 2013 (UTC)

There are several mistakes here. You're forgetting the solid-illusion, nothing is truely solid, especially electrons. Electrons consists of various fields that are concentrated in a very small space without definite boundaries. The 'radius' which comes in at a maximum of 10^-22 m, is completely arbitrary, and was chosen to represent a distance from the centre of the fields to where the electric field decayed sufficiently. Ergo, the electron itself is a tiny version of the 'electron vapour'. The only difference between the bound and unbound electron would be the diffusivity gradient and shape depending on which orbital was occupied.

P.S. From the article, 'point particle' is just a heuristic to describe the relative dimensions of a partcile. Plasmic Physics (talk) 19:36, 9 February 2013 (UTC)

Covering bare floorboards

Okay, so basically today I put the wrong kind of soap in the dishwasher (liquid instead of powder :( ) and apparently the dishwasher didn't like that. I found this out as an hour after I started the load, I got up to check it, and found the kitchen floor F**KING FLOODED IN LATHER AND SUDS! Needless to say, i put away the dishes and cleaned up the mess, and the kitchen floor was so clean afterwards I could see my reflection in it. It was then I decided that as long as I was working around the bottom of the dishwasher, I might as well nail down the curled up linoleum around the edges of the floor. So I got out a box of 1&1/4" nails and a hammer and started pounding away.
However, some portions of the floor around the dishwasher and sink were so curled, distorted, and cracked that I couldn't nail them down, I had to cut off and throw away the ends before doing so. This led to a small, but long area of bare floorboard under the sink and dishwasher. This is a problem because:

• The floor is particle board, so can cause splinters in the feet if stepped on wrong.
• In addition to the water damage that the floor has doubtless suffered through the years already, it is now completely bare and any liquid spilled on the floor in that area could damage it.

So anyway, my problem is I can't decide which substance would be best for a sort of footstop under the counter. What I want to do is take one of those inclined thresholds like the sort under a front door to a house and nail it down there. I need a footstop which can prevent water damage and accidental kicking of the baseboards, hold the linoleum down indefinitely without cracking it, and last for up to five years.
My options are:

• Metal
• Rubber
• Plastic
• Treated Wood
• More linoleum flooring
• Tile

So, which would be best? (PS I filed this under science because I thought this was an engineering topic) --Free Wales Now! what did I screw up?  00:56, 9 February 2013 (UTC)

Free Wales now? Is Jimbo in jail? Oh, wait... :)

Will a high dam sill[19][20][21] do what you want to do? They come in long versions for use with garage doors. --Guy Macon (talk) 02:30, 9 February 2013 (UTC)

A bare margin with some sort of sill is not going to do you well if you have another flood. You're probably better of with a new floor that sits flush against the counter although I am sure you don't want to hear that. I won't laugh at your situation having gone through it myself and had a friend go through it last month. μηδείς (talk) 02:49, 9 February 2013 (UTC)

Thank you, that high dam sill thing does sound exactly what i'm looking for. Since my dishwasher seems to have flooded from under the door rather than the baseplate, needing a new floor shouldn't be a problem. Pretty much all I needed was a durable "ramp" to allow water to drain out onto the rest of the floor and off the baseboards while looking decent. Heading to Home Depot tomorrow... --Free Wales Now! what did I screw up?  03:41, 9 February 2013 (UTC)

It is altogether possible that some hose behind will develop a small leak at some time and what you are doing would hide the damage and make a pool to soak into the floor. Just fix the floor properly and cover the edge between the wall and the floor behind to stop any small leak into the crack. Dmcq (talk) 11:38, 9 February 2013 (UTC)

Note that the Refdesk does not give advice, accepts no liability if black mold spreads throughout your house causing serious and permanent illness that can be palliated only by expensive visits with a mind-body therapist, and we are not licensed interior designers[22] and therefore are not allowed to give interior design advice in Florida. Except in residences. Or is it Virginia now? Heck, it's a racket every bit as legitimate as the "medical advice" thing they're always on about here. Wnt (talk) 17:35, 9 February 2013 (UTC)

why was rutherford model of an atom discarded ?

Rutherford model was discarded because according to that model electrons will radiate energy as they move around the nucleus. In Bohr model, electrons revolve around the nucleus without radiating any energy. How is this possible ? The case (radiating energy), which was applicable for Rutherford model, was not applicable for Bohr model, why. --Concepts of Physics (talk) 03:05, 9 February 2013 (UTC)

For convenience, see Rutherford model and Bohr model. Basically, the Bohr model was just more specific than the Rutherford model. Rather than predicting the electrons existed in a cloud, possibly orbiting the nucleus, Bohr predicted very specific orbits. His model never explained how stably orbiting electrons fail to radiate energy, which was part of why physicists knew there was still a deficit in their understanding of the electron. Someguy1221 (talk) 03:18, 9 February 2013 (UTC)

An easy way to think of the historical chronology of these models is this:

1. Thomson: "atoms are not indivisible, but are made up of negative subatomic particles in complicated orbits, all within a diffuse positive field"
2. Rutherford: "actually, atoms are a dense positive nucleus around which tiny negatively subatomic electrons orbit in a classical way, but I don't know why they don't lose energy"
3. Bohr: "ah, they don't lose energy because they're quantum, not classical, and in fact the way they gain/lose energy has to do with discrete stable states. But I don't know why that is other than to say that the quantum world is strange."
4. De Broglie: "ah, the reason they are distinct stable states is because there are only so many stable wave functions, and the electrons are basically waves"

It's not so much that Rutherford was "discarded" so much as "built-upon." Ditto with Bohr's, which wasn't the last step there either. (Nor was de Broglie's, of course.) Obviously I'm simplifying the technical stuff here but such is how it goes with simplifications! --Mr.98 (talk) 18:05, 9 February 2013 (UTC)

In fact, the "plum pudding" model works pretty well for many applications in classical mechanics. You only need to worry about the breakdown of this model when you perform experiments with resolution better than the scale length of the atom. That means you're sending down photons of particular wavelengths (so you need the mechanics of Compton scattering; or you're analyzing emission spectra of atoms with high resolution. If you apply classical theory to the plum pudding model, and your scale length is always sufficiently larger than the atom, you will never find any conundrums! In formulations of quantum mechanics, this is an important and often-underemphasized empirical fact. Mathematically, this corresponds to a boundary condition, or a limit case, of any equation proposed to describe a quantum mechanical system: when extrapolated to large numbers, or large sizes, the formulation must remain consistent with what we observe! It is my opinion that most of the "conundrums" people encounter when they try to study quantum mechanics would be straightforwardly resolved if people would review the mathematical conceptual leap in the limit formulation of these problems. Nimur (talk) 20:01, 9 February 2013 (UTC)

Why is the GAU-8 effective?

Why is the GAU-8 Avenger effective at destroying tanks when its caliber is only 30 mm and modern MBTs are designed to reliably withstand hits from 120 mm guns? Whoop whoop pull up ^{Bitching Betty | Averted crashes} 05:30, 9 February 2013 (UTC)

Diameter is not a determinant for destructiveness against armor; note that sabot anti-tank rounds have a "shoe" (fr. sabot) that separates from the round to release a kinetic energy projectile which is smaller than the diameter of the barrel from which it is fired.   From the article:   For reasons why a smaller diameter projectile can be desirable, see external ballistics and terminal ballistics.   ~E:74.60.29.141 (talk) 06:02, 9 February 2013 (UTC)

It probably wouldn't be sufficiently effective against a modern MBT. This 1980 report about an attack by A-10s on Korean War era M47 Pattons says the 140 hits, only 17 penetrated the Patton's armour. A Patton has 100mm of steel armour; the later M1 Abrams variants have advanced reactive Chobham composite armour which give a protection equivalent to 600-1000mm of steel armour. That's why the A-10 carried higher performance weapons like AGM-65 Maverick as well, specifically for hard targets that the GAU-8 wouldn't kill. The GAU-8 is still useful against a wide variety of battlefield targets like AFVs, APCs, trucks, tankers, jeeps, artillery pieces, tractors, and self-propelled guns, and against unfortified structures. -- Finlay McWalterჷTalk 16:33, 9 February 2013 (UTC)

That said, it's not totally useless against an MBT; given the GAU's weight of fire, it's quite possible it would be able to detrack an MBT, rendering it ineffective and vulnerable. -- Finlay McWalterჷTalk 16:36, 9 February 2013 (UTC)

The M829's KE penetrator is only 20 mm in diameter. However the A-10's cannon is ineffective at killing modern MBTs. It can handle out of date T-62s and the likes, but not a post-1980 MBT. It can several damage them, destroying their tracks, vision equipment, even weapons and engine (weakly armored grille). A machine gun can be completely destroyed by a hit and I don't think a crew would risk firing a big gun that has been damaged by an autocannon, the shell might explode before leaving the barrel. All of this is repeairable though, for an assured detruction it must used its missiles. You must remember though that MBTs are only a small percentage of the vehicles in an army. Lightly armoured and soft skinned vehicles are the bulk, and the cannon can effectively destroy these without wasting a missile.--Whichwayto (talk) 17:11, 9 February 2013 (UTC)

For a kinetic kill system like a DU anti-armour round, the crucial factor is the projectile's kinetic energy. If I'm doing the maths right, the KE (at the muzzle) for a GAU-8 round is about 0.2 MJ; for an M829A3 from an Abrams its about 12 MJ. -- Finlay McWalterჷTalk 17:27, 9 February 2013 (UTC)

Actually, in the case of the Hog's GAU-8, the most crucial factor is hitting the top armor rather than the frontal armor -- a tank's armor is weakest on top. 24.23.196.85 (talk) 20:22, 9 February 2013 (UTC)

ineffective at killing modern MBTs is incompatible with what follows that claim. A blind, motionless, gunless MTB might as well be dead. It's certainly a mission-kill, and it's an easy target for infantry with any kind of anti-armour. --Stephan Schulz (talk) 21:18, 9 February 2013 (UTC)

do we know what Mars sounds like?

did Curiosity or any other mars probe have a few grams to spare out of their multiton payload on a microphone, so we could hear what Mars sounds like? 178.48.114.143 (talk) 06:46, 9 February 2013 (UTC)

One noise emanating from this phenomenon sounded something like "Illudium Q-36 Explosive Space Modulator." ←Baseball Bugs ^{What's up, Doc?} carrots→ 07:01, 9 February 2013 (UTC)

http://www.youtube.com/watch?v=DJ3A4XOWSFE

http://curiositywatch.com/sounds-from-mars-why-curiosity-has-no-microphone/

Considering the rover is two tons, the mic would have added precisely two grams and a single analog input, and was not mission-critical, would not need to be pointed anywhere and can literally be in any crevice, does not need to even be automatically collected or read or affect any other mission requirements, can break or fail to function without consequences, yet if it happened to still work, would bring huge outsider interest in mars, I hope you will agree that I am simply smarter than NASA. That video, until the rickroll, was absolutely FASCINATING. I was like, wow, wow, wow. Two grams. Fuck you, stilted engineers. You didn't even try! 178.48.114.143 (talk) 09:01, 9 February 2013 (UTC)

I'm sorry to disappoint your hope, but I don't agree. I suspect that the predominant sounds would be those of the motion of the rover. Are those of interest? I'd be surprised if a Mars microphone picked up any interesting sounds. (dinosaurs? little green men chatting? ) Dbfirs 09:30, 9 February 2013 (UTC)

It's impossible to predict what scientific discoveries will be made in advance, or else they wouldn't be discoveries. For example, the LHC was predicted to discover the Higgs boson, a particle that's been part of the Standard Model for decades, and that nobody seriously doubted the existence of. If that's all it discovers, the LHC is a huge waste of money, but physicists are hoping for something unexpected that will revolutionize physics. What will that be? Well, if anybody knew, it wouldn't be a discovery. --140.180.247.198 (talk) 17:41, 9 February 2013 (UTC)

Mars... I can't believe I'm back on Mars. Three times before, this place almost killed me. I swore I'd never give it another chance to finish the job. Humns got no business being here. No business at all. — Michael Garibaldi. How different is that from Saigon...shit? --Trovatore (talk) 09:36, 9 February 2013 (UTC)

Yes, the sounds of the motion of the rover would have been very interesting. Out of curiosity, why do you think we wouldn't have heard wind, as in the video? Or explosions in the distance from volcanos nearby, which the rover cannot see visually? Acoustics is so so cheap. If nothing else, the sound of the gravel/sand/whatever under the rover's feet... This article says it is "probably still volcanically active today": http://en.wikipedia.org/wiki/Volcanology_of_Mars - so, out of curiosity, if the rover happened land within earshot of a volcano, you don't think having a mic onboard would be something anyone would be interested in hearing? No mic is simply irresponsible. It's not like I'm asking you to include speakers, so we can blast some music and hear its echoes if we are near a wall. I'm asking for a two gram mic. There is no excuse. Aren't there dust storms, too? You don't want to know what they sound like? No imagination around here. 178.48.114.143 (talk) 10:14, 9 February 2013 (UTC)

“Curiouser and curiouser!” Cried Alice: I find usage of the cliché out of curiosity curious interesting in a thread discussing NASA's Curiosity rover --Senra (talk) 22:14, 9 February 2013 (UTC)

If we prorate the ENTIRE budget of $2.5 billion just into the 2000 pound payload - which is a huge overstatement, imagine if a scenario where the actual final payload is just 100 grams. Making it 101 grams by adding a gram to what we consider, wouldn't have cost a further marginal $25 million or increased the budget by a full percentage point! Most of the budget is in developing the rover, delivery system, etc. So this is a huge, huge, huge, huge, HUGE overestimation. Still, by this HUGE overestimation, another 2 grams added to the payload would have increased the size of the payload by 1/500000th, or the prorated budget from $2.5 billion by another $5,000. A handful of people, hell, a single individual, would have gladly paid that amount to hear Mars. If the only place a single recording ever appeared was youtube, the advertising revenue would be more than $5,000 from it. Think about it!!! There is just no excuse, except ignorance and lack of creativity. 178.48.114.143 (talk) 10:30, 9 February 2013 (UTC)

"ignorance and lack of creativity", eh? And yet ironically they're the ones driving a robot on Mars and you're the one wasting your time ranting on an internet forum which isn't actually a forum at all.Dncsky (talk) 13:36, 9 February 2013 (UTC)

I wouldn't be so quick to discount the OP's opinions, though some of them could have been expressed in a more rational fashion. I, for one, wouldn't mind listening to dust storm or similar event taking place on Mars (imagine all the relaxation CDs off-brand record labels could sell in five-and-dime shops!), and I'm certain the cost would have been neglibible compared to the other components of the rover. Let's also not forget that technical know-how does not necessarily correlate with creativity or a propensity for brilliant ideas (for example, this is a product that smart people allow to exist). Evanh2008 ^{(talk|contribs)} 13:58, 9 February 2013 (UTC)

This question has been asked before, here. Here's one of the responses:

"Plenty of people have pushed for including a microphone on a Mars mission, most notably the Planetary Society, whose microphone actually flew on the failed Mars Polar Lander. The Phoenix lander also included a microphone, but only because its descent imager (MARDI) happened to have a microphone on its circuit board. MARDI was turned off because it had a risk of interfering with IMU measurements during landing, which could have been fatal to the spacecraft. According to an interview I heard with a Planetary Society member (Emily Lakdawalla), the Society lobbied to have their microphone included on Curiosity, but it was rejected because the rover was already complex enough (she didn't elaborate on this, and I haven't been able to find a more detailed explanation). Personally I think that's a strange reason, because a microphone is one of the smallest and simplest electronic devices possible (just look at your cellphone to see how small it could be). Having one would be great for PR, and NASA only gets funding if the public is excited and inspired by its missions."

Here's an answer from the Curiosity team themselves: [23]. The second part is interesting:

"Here's a little more info on the Phoenix microphone. It was essentially a hitch-hiker. It was built into another instrument taken off the shelf for the the lander, but it was never intended for the mission. There was no science team or budget connected to it. Since it was not intended for use it was never tested before launch and never entered into the power budget for the lander. Only after Phoenix successfully completed it's mission, 5 months after landing in the polar region, was the mission somewhat willing to test it. They couldn't do it earlier because they couldn't risk the prime goals of the mission if anything went wrong. The project manager was fairly certain it wouldn't work and was against trying it because he didn't want to raise expectations. His mind changed when we got a tweet to the @MarsPhoenix account from a man who said he was blind and how much he wished he could hear Mars because he couldn't see the pictures. A couple days later, they sent the signal to Phoenix to turn it on but we got.. well.. nothing. Empty files. If we had received anything, it would have been released. The team figured the mic was frozen solid and decided to give it a second try by leaving it on longer to warm up. Unfortunately, the Phoenix mission lost its last bit of power (as expected) before it got the second instruction." --140.180.247.198 (talk) 17:41, 9 February 2013 (UTC)

Let's rephrase the answer another way. Spaceship engineers are not stupid. They know what their instruments measure. Now, let's review this carefully, because it is not clear whether the OP knows what a microphone measures.

"Sound, obviously!" says the enthusiastic OP! "I want to record sounds! Put a microphone on the spaceship!"

Now, as the reference desk regulars who follow Science know, we've had a recent spate of questions asking about minimum densities that sound can propagate in. And, as we have repeatedly answered, there is no well-defined answer to that question. So, "is there sound on the Moon? Is there sound on Mars?" While our knee-jerk response is "of course not, these places are nearly total vacuums, and sound cannot propagate!" ... if we stop to really really carefully answer the question, we find that we must refine this to say, "...well, actually, the amplitude of acoustic waves in very-very-sparse atomspheres are very tiny, and the frequencies are very low."

This brings us back to my first point: spaceship engineers are very smart. So while you think "a microphone measures sound" and cuss out the engineers, let me defend their line of reasoning. A microphone doesn't measure sound at all. Most modern "2-gram" microphones are piezoelectric crystal attached to high gain differential amplifiers, and then digitally sampled. They measure a voltage, proportional to the mechanical stress on a piezoelectric crystal. When a sound is audible to a human, that sound corresponds to a pressure wave propagating in air, which will exert a mechanical stress on a collector plate and deform the piezo, inducing a voltage. That voltage will be amplified and sampled.

We can calculate exactly what voltage will be produced for any given deflection.

We know the density of the Mars atmosphere, and we know its pressure, and we know how much force a molecule can exert on a piezoacoustic coupling... and we know the electronic noise floor of the finest differential amplifier circuit this side of the Jovian moons... and we know the realistic sampling rate and quantization error for digitizers, because we studied elementary digital design theory... and the net result is: the signal will be all zeros.

If we know (from other experiments, and from application of the laws of fundamental physics, that it is not physically possible to measure signal, given the sparse atmosphere of Mars, we don't waste time putting a microphone on the spaceship.

Instead, we go back to basics: what are we trying to measure? Vibrations? Particle flux? We have instruments on Mars Science Laboratory to do that. MEDLI, RAD, and others.

So, the real point here is, the OP is making an unreasonable demand to place an instrument known not to work on a billion-dollar spacecraft. When the OP finances, engineers, and executes his/her own billion dollar spacecraft, they may place any instrument they like onboard ...and if that is your objective, start by reading my post on engineering tradeoffs in spaceship design, with links to a complete lecture-series... : but until then, accept at face-value this simple fact: somebody very smart thought about your idea and dismissed it for very good reasons, long before you even knew they were planning a Mars rover. Nimur (talk) 20:25, 9 February 2013 (UTC)

OMG, did you read anything that other people wrote before harping, falsely, about how it's impossible to record sound on Mars? NASA's Mars Polar Lander had a microphone, by design, for the purpose of recording sound. Phoenix carried a microphone by "accident", and though it heard nothing, the team thought that was because it got frozen and gave it a second try. The Planetary Society has built a Mars microphone for inclusion on a spacecraft, and it flew on the Polar Lander. Your claim that it's physically impossible to hear sound on Mars is simply wrong. --140.180.247.198 (talk) 00:40, 10 February 2013 (UTC)

Why is my charger emitting high pitched sound?

I think it has something to do with the transformer, but I don't know why. — Preceding unsigned comment added by Inspector (talk • contribs) 07:04, 9 February 2013 (UTC)

It uses a Switched-mode power supply, and is probably a "cheapy" ~15 kHz - which is within normal human hearing range. ~E:74.60.29.141 (talk) 07:33, 9 February 2013 (UTC)

And I am guessing that the person who asked the question is either under 40 years old (if male) or under 60 years old (if female). Otherwise he/she would not be able to hear it. --Guy Macon (talk) 11:19, 9 February 2013 (UTC)

I guess the sound frequency is much lower. There is still one other strange thing when I studied further: when I connect it to my cell phone, the continuous buzzing stopped and changed to intermittent buzzing like heartbeat buzzing in the hospital.--Inspector (talk) 11:45, 9 February 2013 (UTC)

As far as I know this is an indication that it's either broken or or does not conform to the usual specifications required in industrialised countries (conformance is often claimed fraudulently). And that it's an incendiary risk. If it's expensive to replace, the device you are charging is not very valuable, and there is no reason to trust that a new charger will be better, then I personally would just continue to use it but would be careful never to keep it plugged in when I leave the house. Also, I would always think of it first when there are any problems with radio or tv reception, wlan etc. Hans Adler 11:52, 9 February 2013 (UTC)

Hans, I wouldn't go that far... it sounds like you're spreading a little FUD about a common, harmless annoyance. It's far more likely that the power-supply is functioning correctly, but its designers did not go through the painstaking analysis to guarantee that it never emits audible noise under any condition. If the device has a marking from UL - Underwriters Laboratory - or from the FCC, then its safety and emissions have been tested and verified, even if it makes an annoying noise. Outside the U.S., other agencies and industry groups are responsible for similar testing. This should not be construed to mean that any UL-tested product is always safe under any condition - you need to apply common sense and be aware of defects and damage. But, I am not aware of any requirement that audible noise in a switching power supply must be suppressed, and I don't understand why you think audible noise has any correlation to fire-hazard. Audible noise might be caused by any number of conditions, and most are not hazardous. In many scenarios, noise might indicate that the power supply is not operating at peak efficiency or that it's exerting unnecessary mechanical stress on some component, reducing its usable lifetime. But ... risk of fire? Surely if audible noise indicated fire-hazard, then every speaker cabinet would be a fire hazard during normal use? Nimur (talk) 19:46, 9 February 2013 (UTC)

A high-pitched buzzing noise might indicate sparking, but this is improbable. More likely this is the result of some transistor-induced harmonics causing the transformer core to intermittently vibrate and emit audible noise. 24.23.196.85 (talk) 20:27, 9 February 2013 (UTC)

I think Hans Adler is suggested that any device which emits noise must be a poorly made device which fails to comply with proper safety standards as present in most developed countries and any such markings suggesting otherwise are fraudulent so that the device must be a fire risk; not that noise itself indicates a fire risk. I agree this is going way too far. It may be slightly more likely a improperly designed or made power supply which violates safety standards makes audible noise, but there are a large number of perfectly safe devices which comply with whatever local standards which also make noise. And there will be plenty of unsafe devices which don't have noise.Nil Einne (talk) 21:18, 9 February 2013 (UTC)

Modern chargers are almost certainly switched-mode power supplies (SMPS). Our own article suggests such supplies emit acoustic noise (almost a tautology?) suggesting that such noise is "[u]sually inaudible to most humans, unless they ... are malfunctioning, ...". I think that means unless the SMPS is malfunctioning, not the human. Also "[t]he operating frequency of an unloaded SMPS is sometimes in the audible human range, and may sound subjectively quite loud for people who have hyperacusis in the relevant frequency range". QED? --Senra (talk) 21:55, 9 February 2013 (UTC)

Sincere apologies to 74.60.29.141 (talk · contribs) who mentioned SMPS above. Didn't see that. Sorry. --Senra (talk) 22:02, 9 February 2013 (UTC)

I don't think I am alarmist, just a bit careful after I have read several reports like this one. Hans Adler 22:20, 9 February 2013 (UTC)

I have a bit of experience in this area, having designed everything from components for NASA manned space flight to toys for Mattel. Warnings are good, but they have to be accurate. Otherwise you are chicken little or the boy who cried wolf. The fact of the matter is that there is no known correlation between SPS acoustic noise and safety. You are warning people about the wrong things. --Guy Macon (talk) 23:26, 9 February 2013 (UTC)

It could be a phasor on overload, so toss it down the nearest disposal chute right away ! :-) StuRat (talk) 23:29, 9 February 2013 (UTC)

i think i've heard that Leptin inhibits Gerlin. is that true?

thanks. 79.179.134.180 (talk) 16:32, 9 February 2013 (UTC)

If you only think you've heard something, it is unlikely to be true. Anyway, what is gerlin? Is it like trollin?--Shantavira|^{feed me} 16:35, 9 February 2013 (UTC)

• They are somewhat antagonistic, but it's not simple - our articles (note spelling) cover this pretty well: leptin and ghrelin. -- Scray (talk) 16:55, 9 February 2013 (UTC)

In a quick scan of our articles I didn't see any discussion of that question. There is some evidence that leptin inhibits ghrelin, for example PMID 15867335, but the data seem to be limited. Looie496 (talk) 16:59, 9 February 2013 (UTC)

in simple words

how do i culculate my bmi index?, please give me a verbal explanation. thanks 79.179.134.180 (talk) 16:32, 9 February 2013 (UTC)

Please see Body mass index or http://simple.wikipedia.org/wiki/Body_mass_index --Shantavira|^{feed me} 16:38, 9 February 2013 (UTC)

Or go to http://nhlbisupport.com/bmi/ and the US Department of Health will calculate it for you. --Guy Macon (talk) 16:46, 9 February 2013 (UTC)

Measure your height (in meters) and your weight (in kilograms), and plug them into this formula:

$\mathrm {BMI} ={\frac {\text{weight}}{\left({\text{height}}\right)^{2}}}$.

That's all there is to it. Looie496 (talk) 16:48, 9 February 2013 (UTC)

Graphite

I think I have found a new way of synthesising graphite. In order to be certain that it is graphite, I need to know whether the route of production is a possibility.

Crystallisation of graphite from solution. I added organic material to 38% sulfuric acid, and boiled until the material was fully carbonised. The resulting product was a highly acidic, opaque, black sol (colloid)(?). Upon, cooling and standing for several hours, large, insoluble, opaque, black crystals have formed. I could send photos of the mystery crystals. Plasmic Physics (talk) 22:28, 9 February 2013 (UTC)

I suggest you try writing on paper with it, then using an eraser on it. If it acts just like graphite in both respects, it probably is graphite (lead behaves similarly, but I can't see how you could have produced lead without having put lead in). Of course, graphite is quite cheap, so you probably aren't going to make it any cheaper than the current methods. StuRat (talk) 22:31, 9 February 2013 (UTC)

It quite possibly is graphite. Adding oleum to sugar will produce a ball of carbon, that is larger that the reactants you started with. CS Miller (talk) 22:58, 9 February 2013 (UTC)

(edit conflict) The black stuff you made is the product of the dehydration reaction between the sulfuric acid and the organic material (a typical reaction for sulfuric acid, I should add), and as such, is essentially pure carbon. However, I should caution you that it might still contain free acid, which would tend to damage the paper. 24.23.196.85 (talk) 23:01, 9 February 2013 (UTC)

I'll wash it several times in water. Plasmic Physics (talk) 23:14, 9 February 2013 (UTC)

Considering that the sulfuric acid predominantly acts as a catalyst, and the reactant is essentially free, I fail to see how it would not be cheaper? Plasmic Physics (talk) 23:14, 9 February 2013 (UTC)

Well, the energy needed to boil it until carbonized isn't free. StuRat (talk) 23:31, 9 February 2013 (UTC)

Put it in perspective with the cost of mining, or generating thousands of degree temperatures for synthesis. Plasmic Physics (talk) 00:00, 10 February 2013 (UTC)

Should we ask the name of your unfortunate victim which you describe merely as "organic material" ? :-) StuRat (talk) 23:34, 9 February 2013 (UTC)

Don't ask, Stu. We do not out people here (unless it is public knowledge anyway) --Senra (talk) 23:52, 9 February 2013 (UTC)

I call him Cooking Oil. Plasmic Physics (talk) 00:00, 10 February 2013 (UTC)

Is your organic material free? (don't forget transportation costs!) Is the energy used to boil the acid free? Is the amortized cost of the equipment free? Is the hazardous waste disposal that your washing step requires free? Labor? Renting a building? Remember, you are competing with people who are digging graphite out of the ground in China. --Guy Macon (talk) 23:39, 9 February 2013 (UTC)

According to the charcoal article, creating charcoal by the dehydration of sugar by sulfuric acid will produce the purest charcoal. CS Miller (talk) 23:45, 9 February 2013 (UTC)

Pond scum should work, 'organic material' is a pretty wide menu. As for waste desposal, such a plant could be adjacent to a sulfuric acid plant/phosphate fertilizer pant. The hardous waste could be recyled thus. Plasmic Physics (talk) 00:00, 10 February 2013 (UTC)