Wikipedia:Reference desk/Archives/Science/2009 July 21

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July 21

Why don't birds ever get rabies?

Question as topic. Is it the case that their immune systems have no problem destroying the virus as soon as it is detected? --Kurt Shaped Box (talk) 02:42, 21 July 2009 (UTC)

I doubt it. A lot of viruses are very specific as to what kind of cells they can infect. If I recall correctly, the rabies virus can infect only mammalian nerve cells.

Think of it as, you can't run a Windows virus on a Linux box (usually, anyway). --Trovatore (talk) 03:04, 21 July 2009 (UTC)

Technical answer: The best MEDLINE hit I found (Seganti et al. "Susceptibility of mammalian, avian, fish, and mosquito cell lines to rabies virus infection." Acta Virologica 1990 Apr; Vol. 34 (2), pp. 155-63.) says the rabies virus can bind to bird cells (an early step in infection), but subsequent "events following virus adsorption" inside the cell nix the infection. "Events following virus adsorption" glosses over a ton of stuff. - Draeco (talk) 03:41, 21 July 2009 (UTC)

Birds can definitely develop rabies infection, although they are not nearly as susceptible as mammals. This paper: [1] is very interesting. It is also rather surprising. I cannot possibly imagine why 5 out of 125 starlings tested had positive rabies titres... I mean it would be mind-boggling to imagine that 4% (or more) of starlings in the wild were at some point bitten by a rabid predator and survived. Returning to the question of bird susceptibility to rabies virus, chick embryo cells are used to make some types of rabies vaccine, and, if I remember right, duck embryo cells are or have been used at some point, too; so they are definitely susceptible at least at that developmental stage. --Dr Dima (talk) 06:29, 21 July 2009 (UTC)

Interesting, thanks. It would seem that the paper you found actually supports my immune system suggestion too. --Kurt Shaped Box (talk) 08:12, 21 July 2009 (UTC)

“ The refractoriness of birds to infection with rabies virus has been attributed to a rapidly developing, active immune system that includes antibody bound to cells of the central nervous system as well as serum antibody. ”

As for why Starlings might test positive for rabies - well, it has been known for them to scavenge a bit too. I don't know how well the virus survives in carrion though. --Kurt Shaped Box (talk) 08:12, 21 July 2009 (UTC)

Hmm, I've seen them go through garbage, but I've never seen them feed on carrion. Do they do that? That can explain the positive titres alright. Or it may have been bad or misread titres :) . Anyways, to your question on how well (or how long) the virus survives after the death of the host - it depends. In some cases the virus is no longer detectable at the time of death (immune system eliminated it, but the damage has been done); in others it is present and persists for quite some time. If it is hot outside, rabies virus will persist for hours or days AFAIK. However, if it is freezing, it may persist for much longer. Rabies virus survives freezing. --Dr Dima (talk) 17:13, 21 July 2009 (UTC)

FWIW, I've (very) occasionally seen Starlings pecking at roadkilled <whatever> and the odd pigeon carcass. Not to any great extent, mind - but I suppose that if it's there, split open, available and they're hungry... --Kurt Shaped Box (talk) 23:03, 21 July 2009 (UTC)

OK, that may explain the positive titres. --Dr Dima (talk) 23:55, 21 July 2009 (UTC)

Wow, no shortage of original research today on the Science RefDesk! --Scray (talk) 01:07, 22 July 2009 (UTC)

Is Attachment Resistance Disorder the same as Reactive Attachment Disorder?

Someone recently told me a friend had "attachment resistance disorder," but a Google search turned up nothing. Would this be another way to say RAD, as above, or some other general attachment disorder?209.244.30.221 (talk) 09:24, 21 July 2009 (UTC)

Yeah, it sure looks like the person who used the term "attachment resistance disorder" just misspoke. It's impossible to know for sure from the information given, but "reactive attachment disorder" does seem like a good guess as to what the person meant to say. Red Act (talk) 14:39, 21 July 2009 (UTC)

Thanks; it makes sense. I was thikning, too, my friend may have have made a logical leap; whatever one of those substitutions is called. They may have thought, "It's attachment and something beginning with 'R'...oh, as children people with attachment disorder resist attachment, so i bet it's 'resistance.'" (The person referred to was an adult, but it's still a logical step.)209.244.30.221 (talk) 11:57, 22 July 2009 (UTC)

It's more likely that he pasted on the "disorder". Attachment resistance turns up a few ghits regarding childhood trauma [2], [3]. It might be some specialized or localized sub-definition. --- 71.236.26.74 (talk) 04:01, 23 July 2009 (UTC)

Flash memory and chargeable devices

In case of flash memory, I undertood that a charge is trapped during the write data status, and then a relatively high voltage has to be applied in reverse polarity in case of erasing (in order to release this trapped charge). I was wondering how much charge in coulombs can be trapped in a 1 GB flash memory in maximum, and if it were possible to trap large amounts of charge to utilize later as a battery (i.e. battery flash technology)?--Email4mobile (talk) 12:21, 21 July 2009 (UTC)

You just basically want a capacitor; there's no value in using something as fancy as flash memory for this. Looie496 (talk) 16:48, 21 July 2009 (UTC)

True. The total gate capacitance of a flash memory is tiny. As an example, a 3-volt 4 Mbit NOR flash chip from 2006 had a gate charge of 10^3 to 10^5 electrons [4]. That gives a maximum charge of 64 nC, or a capacitance of 21 nF. Scaling that up to 1 Gbit and ignoring the likely drop in the charge per gate, that still gives only 5.5 uF, which wouldn't power your iPod for very long. --Heron (talk) 18:12, 21 July 2009 (UTC)

Thank you very much for clarifying this information to me :).--Email4mobile (talk) 18:44, 21 July 2009 (UTC)

Two identical piece of tachyon stuff hitting each other

If you have one piece stuff traveling at half the speed of light in one direction and another identical piece of stuff traveling at the same speed in the other direction. When they smash into each other, they can stick together and come to a standstill (aka velocity of zero).

But what happens when one piece of tachyon stuff traveling at twice the speed of light, hits an identical tachyon piece of stuff traveling at the same speed but in the other direction. Do they stick together and come to a standstill? 122.107.207.98 (talk) 12:54, 21 July 2009 (UTC)

How can a tachyon exceed the speed of light? Googlemeister (talk) 13:10, 21 July 2009 (UTC)

Read Tachyon. I'm no expert, but its given that they can't travel at subluminal speeds. Rkr1991 (talk) 13:16, 21 July 2009 (UTC)

Well, given that they are hypothetical, I don't think this has a useful answer. But one question comes to mind: Would they even interact? Maybe they just fly straight through each other... --Stephan Schulz (talk) 13:26, 21 July 2009 (UTC)

Tachyons don't exist - hence there is no answer to this question. Even if they did exist, we'd not have done any science on them so we wouldn't be able to answer the question anyway. It's like asking whether the tooth fairy gives Santa's reindeer a quarter whenever they lose a tooth. SteveBaker (talk) 13:33, 21 July 2009 (UTC)

(rolls eyes) Lord, if theoretical physicists acted like the fellows on the Ref Desk do ("we can't possibly consider what would happen, even in hypothetical situations!"), we'd never get anywhere. I don't know the answer to this, but I'm sure there are theories on interactions between tachyons and other particles, including tachyons. Google "tachyon-tachkyon interaction" and you get some hits. Obviously they are speculative but lord, that's how theoretical science starts out—try to figure out what might happen, then see if there's any way to distinguish between the many possibilities. That being said, treating tachyons like baseballs is probably not correct (and baseballs don't usually just stop with a velocity of zero; they scatter). My weak, weak, weak understanding of special relativity makes me wonder whether or not you could have strictly simultaneous collisions with objects traveling at superluminal speeds (surely that runs into some sort of causality violation, no?). --98.217.14.211 (talk) 15:29, 21 July 2009 (UTC)

But that's precisely WHY ref desk replies are not like that. We're not here to generate new theories. Our job is to answer questions with known facts. The FACT is that as far as current knowledge and respectable theory goes - tachyons do not exist - nor is there any reason for them to need to exist in order to explain any real-world phenomenon - and if they did exist, then according to everything we DO know, their speed would have to be infinite and their mass and size would be a complex number - that's nonsensical even by the standards of Quantum theory! The theory that they MIGHT exist is unfalsifiable - and therefore no more worthy of consideration than Russel's teapot. Occam's razor says "Ignore this theory unless/until there is some evidence." Therefore, neither you nor anyone else can say with any authority whatever what would happen if two of them collided. So why answer the question when neither you nor anyone else have any clue whatever what the answer might be? The best service we can give to our OP is to say that these "Tachyon" things don't exist. SteveBaker (talk) 20:50, 21 July 2009 (UTC)

Positrons couldn't exist (until they were discovered, of course) because it was obvious that they could not exist because there is no way for positive protons to lose mass nor for electrons to change sign. What I'm saying is: even hypothetical things have a right of their own until the theory (any theory) predicting them has been proved wrong by evidence, not only by deficiency of current theories. If the article is not totally wrong, we do not know if tachyons exist or not. 93.132.129.137 (talk) 22:57, 21 July 2009 (UTC)

So, you're saying that the tooth fairy does give the quarter to Santa's reindeer? Tempshill (talk) 17:44, 21 July 2009 (UTC)

As I have explained before, my wife is in fact, the actual Tooth Fairy - so I asked her. She said that if she had to pay out for animals, the sharks would bankrupt her in no time. Plus the rules clearly state that teeth must be placed under a pillow. SteveBaker (talk) 20:41, 21 July 2009 (UTC)

You should know that there is not only one tooth fairy. Others probably have different contracts. 93.132.129.137 (talk) 23:14, 21 July 2009 (UTC)

Within the framework of special relativity, the answer to the question is no. A tachyon must be a fundamental particle. It cannot be a composite particle, because all known binding forces propagate only at the speed of light and hence the tachyon would literally outrun the forces trying to hold it together. Colliding fundamental particles do not stick together; they either scatter or annihilate. My guess is that the latter would be more likely for colliding tachyons, but I don't really know. Dragons flight (talk) 01:29, 22 July 2009 (UTC)

Except that there might exist a kind of force we don't know about yet that propagates faster than the speed of light. That shows that there really isn't a point in taking about such things as steve correctly pointed out. Read about positronium for an example of how two colliding fundamental particles might stick together. Dauto (talk) 05:19, 22 July 2009 (UTC)

You can't form positronium in a high energy collision. Dragons flight (talk) 09:24, 22 July 2009 (UTC)

The collision doesn't have to be high energy and even if it is, the excess energy can be shed as photons. Dauto (talk) 14:36, 22 July 2009 (UTC)

Conservation of energy-momentum applies to tachyons, as does the relation E² − |p|² = m² (where m is the rest mass). For a tachyon, by definition, m² < 0, so |p| > |E|, but for two tachyons the momenta can cancel out while the energies add, as in your example, so a bound system of two (or more) tachyons might behave like a tardyon with ordinary mass. As for large bound systems of tachyons that move faster than light ("tachyon stuff"), it's not clear to me whether they could exist. It would depend on how causality works in this universe with tachyons.

It's worth mentioning that "tachyon" doesn't really mean "faster than light" in modern physics, it means "m² < 0", and it's not clear that that actually has anything to do with faster than light motion. See this Physics FAQ page. And there's a phenomenon called tachyon condensation whereby tachyonic fields end up behaving like normal massive/massless fields anyway. This is supposed to have happened to the Higgs field in the Standard Model. -- BenRG (talk) 11:57, 22 July 2009 (UTC)

Common House Plants

Which common house plant is very sensitive to over-watering? I would think cactuses are the least? --Reticuli88 (talk) 15:04, 21 July 2009 (UTC)

Least? My understanding is that cactuses are the most sensitive to over-watering. Looie496 (talk) 16:41, 21 July 2009 (UTC)

Cacti will rot if they get too much water. Googlemeister (talk) 18:06, 21 July 2009 (UTC)

Most house-plants are sensitive to overwatering. Cacti are quite sensitive, as Looie and Meister have already pointed out. Some orchids will deteriorate and eventually die (if not treated promptly) after as little as one or two overwatering incidents; I have lost a couple of orchids this way, too. On the other end of the spectrum, Pinguicula can tolerate overwatering well, and Aglaonema will tolerate being overwatered once in a while. --Dr Dima (talk) 19:39, 21 July 2009 (UTC)

Medical/Scientific Term for Non-Aging

Is there a medical/scientific term for someone who definitely does not look their age? Reason is, I went to see my grandfather up in Northern Canada for the first time a while ago and no one pointed him out to me at first. Then this man approached me looking like in his late 50's. He had white hair but smooth skin, barely any wrinkles, he had all his hair and all his teeth. He smiled (with his very yellow teeth; he smoked Malboro Reds) and said he was my grandfather. My jaw dropped and realized that he was pushing ninety. Then I realized I have his genes because I am always mistakened for a much younger age, so is my sister. Is there a term for this? --Reticuli88 (talk) 15:11, 21 July 2009 (UTC)

Youthful, or neotenic if you prefer sesquipedalian pretentiousness. alteripse (talk) 15:14, 21 July 2009 (UTC)

"Sesquipedalian"? Ironically, "neotenic", having only 4 syllables, is not sesquipedalian, but the last 2 words of your response are. <:-p --Scray (talk) 01:04, 22 July 2009 (UTC)

hyposenescence? It's not in the dictionary, but it seems like a perfectly cromulent neologism to me. Some jerk on the Internet (talk) 17:49, 21 July 2009 (UTC)

ageria, perhaps? Another neologism, but it seems reasonable to me. --Scray (talk) 00:59, 22 July 2009 (UTC)

The formulaic expression when noting this in medical records is "appears younger than his/her stated age". So, no, no medicalese is involved. Sorry! - Nunh-huh 09:43, 22 July 2009 (UTC)

And just for the record, Reticuli88: No need to rub it in. You, too, can be hit by a bus tomorrow ;-) --Stephan Schulz (talk) 15:21, 22 July 2009 (UTC)

All in all, age appearance is nothing more than a cultural attribute. Some identifiers of age in one culture are not identifiers of age in another. In the United States, there are many different ethnicities, races, and cultures. So, it is possible to have rather odd situations such as Brad Pitt (b. 1963) being considered to young for Julia Roberts (b. 1967) in "The Mexican". -- kainaw™ 15:36, 22 July 2009 (UTC)

Gravity dependence

Hi!! I would like to know if gravity was dependent on mass or volume? I believe it is directly proportional to mass and inversely proportional to volume. Please help me out. Thanks!!--Lightfreak (talk) 18:31, 21 July 2009 (UTC)

Using Newton's law of universal gravitation (a useful everyday abstraction), the strength of a gravitational field is directly proportional to product of the masses of the two objects and inversely proportional to the square of distance between them. Volume is irrelevant, except as it often provides a minimum bound for distance. — Lomn 18:40, 21 July 2009 (UTC)

What Lomn said, except that in cases where you might know the density and volume but not the mass you can calculate mass from the other two. Not a bad way to estimate how much a planet weighs actually if you can get a good estimate of the density of the whole. Googlemeister (talk) 20:23, 21 July 2009 (UTC)

The physical property you’re thinking of, which is directly proportional to mass and inversely proportional to volume, is density. As Lomn points out, density isn’t what’s important for gravity, just mass (at least for Newtonian gravity). Red Act (talk) 20:21, 21 July 2009 (UTC)

Certainly, the force due to gravity depends on mass, not volume - but you also have to realise that the gravitational force of (say) our sun - and that of a black hole that's the same mass as our sun does (in a sense) depend on their volume since you can only get to within 700,000km of the sun without crashing into it's surface - where you can get as close as you like to a black hole because it has zero size (or if you prefer - you can get to within 3km of it because that's where it's event horizon is). The point being that both the sun and the black hole have the same mass - so if you are (say) a million kilometers away from the center of each - the force due to their gravities would be the same too. The black hole only has this crazy amount of gravity because it's small size lets you get very close to it's center. SteveBaker (talk) 20:37, 21 July 2009 (UTC)

You mean ITS CENTER. Steve remember IT'S an encyclopedia with ITS standard of correct grammar [5]. Cuddlyable3 (talk) 22:16, 21 July 2009 (UTC)

Good point. To refer to Newton's law again, it depends both on mass and distance. EverGreg (talk) 08:05, 22 July 2009 (UTC)

Actually, thinking about it, depending on how you define what it means for gravity to be proportional to something, saying that gravity is proportional to density can be viewed as not being far off. In general relativity, the Einstein tensor is proportional to the stress-energy tensor, which is essentially a relativistic generalization of density. So if you look at things from the right perspective (the weak field, low speed limit as expressed by the Einstein field equations), the OP can be viewed as being arbitrarily close to being correct. Red Act (talk) 10:01, 22 July 2009 (UTC)

True - but I think it's important that we straighten out our OP's confusion rather than deepening it. The clearest possible answer is the first one we gave. The mass matters - the volume does not. Period. SteveBaker (talk) 15:05, 22 July 2009 (UTC)

When the questioner supposes "inversely proportional to volume." it makes me wonder if he wasn't thinking of buoyancy. The apparent weight of a helium balloon is proportional to its weight and inversely proportional to its volume due to the effect of buoyancy in addition to gravity. APL (talk) 17:52, 22 July 2009 (UTC)

What kind of intelligence do mathematics require?

My best friend has always been intelectually gifted. I do not know his exact IQ, but I do know that professional, psychologist-supervised tests have shown that, whereas his memory and spatial intelligence are more or less average, his logical abilities are in the 99.999th percentile. He really excels in all fields of knowledge except one: he is quite bad at mathematics and never quite manages to grasp mathematical concepts and formulae, even if he tries hard.

I am wondering why he is so bad with mathematics if his logic is so good - I thought mathematical reasoning was closely tied to logic. Moreover, he is very good at other fields requiring logic. What explaination can you give me for this "paradox"? --81.38.156.193 (talk) 19:42, 21 July 2009 (UTC)

Do you honestly expect random users on the Internet to diagnose your friend? Learning is not simple. It is complicated. Perhaps your friend simply is not interested in math. My brother claims to have every learning disability and brain defect ever discovered to cover up the fact that he simply doesn't want to read (when forced, he reads just fine, but complains about it). -- kainaw™ 19:49, 21 July 2009 (UTC)

Sorry, I'm not buying the premise. There is no formal test, as far as I know, that distinguishes logical abilities from spatial intelligence and mathematics. Do you mean verbal abilities, perhaps? Looie496 (talk) 19:52, 21 July 2009 (UTC)

This does seem a little screwy. Logic IS mathematics (it's both how mathematics is done - and a sub-field of math in it's own right). Hence your friend is not bad at "mathematics" - he's bad at some branch or branches of mathematics...perhaps he is poor at arithmetic or calculus but great at logic and geometry maybe. Until people are exposed to higher mathematics - it's easy to go away with the impression that arithmetic IS mathematics because almost every educational system on the planet teaches arithmetic before (for example) Algebray. Having a relatively poor memory would be a handicap for arithmetic - where a lot of what gets you fast and accurate is having little "lookup-tables" memorized - the multiplication tables for example. Similarly, calculus requires you to memorize a pile of standard derivatives and integrals and such. Applied mathematics (ballistics, rigid body motion, etc) also demands that you memorize a whole bunch of equations. But logic requires little memorization - and neither does geometry (well, to a point). It might also matter whether one has a 'visual' memory or a 'verbal' one. But most of mathematics is easier if you can memorize the results achieved by others rather than starting with a 'logic' proof from scratch every time. But I'm confused. If his memory is only 'average' - how does he excel at (for example) geography and history - which are almost entirely memorization exercises? How does he do well at physics - when so much of it is mathematics? I doubt very much that these "tests" are really what your friend believes them to be. SteveBaker (talk) 20:27, 21 July 2009 (UTC)

Well, I am sorry, Looie 496, but I saw the psychologist's report and he put it quite clearly:

• memory: 101
• logical abilities: 172
• spatial coordination: 96 (all on a scale on which 100 is average, <85 is deficient and >137 is intelectually gifted).

My friend has been trying hard to learn maths for his degree, so it's not that he's trying to cover up for failure. As far as I can tell, he is genuinely trying to improve in maths (I'm quite good in maths myself and I'm giving him extra lessons, in which he works hard). Finally, I am not asking anyone ("random users on the Internet") to diagnose my friend - I'm just asking if logic abilities and maths are really intrinsically related.

@ Steve Baker: thanks very much for your answer, I find it very interesting. As for history and geography: he does indeed seem to memorise things very easily, and he always remembers the important facts and figures. He's also capable of memorising a huge amount of information in very little time. In fact, I always thought he had a gifted memory as well, until he showed me the test results to be average, so I really don't know what to say about that. As for physics: he is very, very good at understanding the concepts of physics (knowing why things happen in physics) but he is lousy at doing the practical part - good God, he's not even capable of calculating a derivative! But I guess this will remain an enigma. --81.38.156.193 (talk) 20:37, 21 July 2009 (UTC)

The rather standard Stanford-Binet Intelligence Scales separately test “fluid reasoning”, “quantitative reasoning”, “visual-spatial processing”, and “working memory”. I could see a psychologist paraphrasing those categories a little if the psychologist typed up a letter regarding the result. It seems plausible to me that someone who scores extremely high at fluid reasoning might score only average at quantitative reasoning. People who are geniuses at one thing are quite commonly only average or even “retarded” at other things. Like a lot of people with Asperger syndrome, for example.

I think the 99.999 probably just means that no questions were missed in that section, and shouldn’t be interpreted to literally mean 99.999. Standard intelligence tests like Stanford-Binet can’t distinguish between very high intelligence levels very well. Red Act (talk) 21:02, 21 July 2009 (UTC)

Yeah - I flat out don't believe the 99.999% thing - those tests aren't remotely sensitive at the very top end because there just aren't enough people in the general population who are smart enough to pass the tests at that level. Also, there is a phenomena that Mensa have noticed which is that super-intelligent people who are asked the usual "Which of these four diagrams is the odd one out?" kind of question can find obscure reasons why any one of them might be considered wrong and have to resort to trying to guess which of those reasons was in the mind of the person who created the test. There is a very real sense in which the super-intelligent are smarter than the people creating the tests.

But this case seems strange to me. We're told that the test says that memory is strictly average - yet our OP is struck by how the person is exceptionally good at 'rote-learning' subjects like history. We're told that the person has a high score on logic - yet the one topic that truly exemplifies logical thinking is mathematics - and this person is allegedly useless at math. Seems to me that the results of the test are just crap - they bear no resemblance to reality! SteveBaker (talk) 01:32, 22 July 2009 (UTC)

Yeah, I think it probably wasn’t really “logical ability” that that score was measuring, but “fluid reasoning” as Stanford-Binet calls it, a.k.a. fluid intelligence. The two tests that a psychologist would be most likely to give are Stanford-Binet and Wechsler, and the intelligence categories given above match up well with the categories in Stanford-Binet, and don’t match up well at all with Wechsler. I think the psychologist just paraphrased “fluid reasoning” as “logical ability” when giving the results, because there is a relationship between fluid reasoning and logical ability, and a lot more people would understand the phrase “logical ability” than the phrase “fluid reasoning”. And it’d be really easy to score well on a fluid reasoning test but not get good grades in math. A test of fluid reasoning very intentionally avoids relying on previous knowledge of a topic, so it’s very much a “shallow” test of “innate” intelligence, if you will. Math is very different in that regard – math is very deep, with each math course relying on an understanding of the material presented in the last. If you miss out on a good understanding in one course for any reason, that can really mess you up at all the higher levels.

However, even if it really was logical ability that was being measured, one possible way that a person might have extremely good logical ability but be bad at math is if the person has dyslexia. You can be great at thinking logically with dyslexia, but a big part of math is symbolic manipulation, and all that symbolic manipulation could be quite a problem if you have dyslexia. I’m not trying to make a diagnosis here, I’m just using the possibility of dyslexia as an example. Because, as I said, I think it probably wasn’t actually “logical ability” that was being measured. Red Act (talk) 03:01, 22 July 2009 (UTC)

Someone who was great at rote memorization and at logic would have done great in calculus, differential equations, and matrix algebra, some difficult math courses I had to take. If they had trouble with details, or tended to reverse digits, somewhat like a dyslexic, they would have come up with incorrect answers and gotten low scores. Inability to do detail work under time pressure or "exam phobia" could have crippling results. There are many component abilities necessary to do well in college math(s). I tended to approach the study of math in a verbal and logical way and it often ended badly. It is necessary, after all, to come up with the correct symbolic or numeric answer to the exam question. Reasoning and logic count for little. Edison (talk) 04:34, 22 July 2009 (UTC)

I think your friend may have dyscalculia, which is the maths equivalent of dyslexia. I'm in much the same position: apparently I have an IQ that puts me in the top 1% of the population, and my verbal skills are excellent, but my arithmetic skills are hopeless and always have been. I didn't get diagnosed with this condition until I was 38 and training to teach adults with dyslexia. I am fascinated by maths, especially the more complex stuff, but as I can't add/subtract/multiply/divide, I fail exams unless I can use a calculator. If he can get this diagnosis, he may be able to get special support from his university. --88.108.188.105 (talk) 15:46, 22 July 2009 (UTC)

I'm going to say this again for clarity: Arithmetic is NOT all of mathematics - it's not even 1% of mathematics...it's a very small branch of the subject - and not one that's studied much any more because we know how to do it now. Just because you can't remember how to do long-division or perhaps you have dyscalculia tells you zilch about how good you'd be at the other 99% of mathematics. I imagine that there are an awful lot of top notch mathematicians who do almost no arithmetic at all during the course of their daily work...and when they do - I bet they use a calculator. If you pick up a typical mathematics journal - you'll be hard-pressed to find any arithmetic in it at all. Mathematicians don't calculate 1234/5678 - they write x/y and leave it to the engineers and scientists to crunch the actual numbers. Math is about proving theorems. Using some existing theorem to figure out whether the load on this girder will break it or not is for engineers...not mathematicians. The problem is that far too many potential mathematical geniuses are put off of doing real, serious math because the for about the first five years of school, they only get taught arithmetic. Now, if you failed to get to grips with algebra - that would be a much more serious thing. SteveBaker (talk) 01:38, 23 July 2009 (UTC)

Indeed, some mathematicians have been noted for their incompetence at arithmetic. See 57 (number)#In mathematics, for example. Algebraist 01:48, 23 July 2009 (UTC)

There was a time when college math for science and engineering (calculus, differential equations, matrix algebra, stability calculations, Laplace transforms) might require 100 steps of pencil and paper conjuring to obtain the answer. If a + was substituted for a - at any intermediate step, or any other minor calculation error occurred, the answer was wrong and minor deductions to no credit might result, depending on the grader. An example of this was multiple conversions from polar to rectangular coordinates just to solve one problem. One engineering professor said "You make small error, bridge fall down, plane crash, everyone killed! Zero points!" (He was not a native speaker of English). In actual engineering practice, canned programs are commonly used and the requirement is to correctly model the system, and to select the correct analytical method. Computers carry out all the grunt work. In old files from the 1930's and 1940's I have seen analyses carried out by hand, or at most with a Marchant rotary calculator, doing numerical analysis such as Fourier analysis of an oscillogram the neutral current in a transformer, to determine the harmonics, by erecting perpendiculars every 1/8 inch and crunching the numbers. Similar dreary matrix solutions or statistical analyses were done decades ago, with the emphasis on anal. Perhaps mathematical pedagogy relies less today on pencil and paper solutions of relatively simple systems. Edison (talk) 01:48, 23 July 2009 (UTC)

Infinite amount of mass in the universe?

If the universe is infinite, does it also contain an infinite amount of mass? Does it contain an infinite number of objects such as stars and planets? If yes, where does all that mass keep coming from? Is it even possible that new objects just keep on coming on no matter how far you travel? And if no, then where do the objects stop? And wouldn't they then be contained inside a finite subsection of space, making it effectively the centre of the universe? JIP | Talk 20:45, 21 July 2009 (UTC)

If the universe is infinite, then yes, it would probably contain an infinite amount of mass. We do have some evidence from WMAP that the universe is not infinite, though. It's most likely finite, but unbounded, just like the surface of a balloon. Which point on the surface of the balloon is the center of that surface? --Stephan Schulz (talk) 20:50, 21 July 2009 (UTC)

So the size, and amount of mass, of the universe is finite, but it does not have any centre or boundaries? JIP | Talk 20:55, 21 July 2009 (UTC)

Yes, that's our current best guess (for limited values of "current" - I only follow this in PopSci sources). --Stephan Schulz (talk) 21:07, 21 July 2009 (UTC)

It looks like we need Stephen Hawking. Is Stephen Hawking in the house? Bus stop (talk) 21:12, 21 July 2009 (UTC)

There are always a few with a minority opinion, of course. You might be interested in the shape of the universe article. Red Act (talk) 21:19, 21 July 2009 (UTC)

Sorry for barging in with a [probably quite lame] question, but if the universe is like a balloon, what is on the other side of the balloon's surface? --Leptictidium (mt) 21:52, 21 July 2009 (UTC)

There isn’t another side. The balloon analogy is inexact. To make the analogy fit better, you’re supposed to think of the balloon as being a 2-D manifold, with no thickness in a third dimension. Red Act (talk) 23:20, 21 July 2009 (UTC)

Another way to think about it is that you could head off in your super-fast space ship away from earth IN ANY DIRECTION, keep going in a straight line - and then arrive back to exactly the place you started. The universe would then be finite - yet have no edges. However, since the universe appears to be bigger than the visible universe - and it's expanding fast - we could never actually take that trip because we can't ever travel faster than light and so we can't overtake the expansion of the universe. SteveBaker (talk) 23:56, 21 July 2009 (UTC)

I don't think there's any evidence from WMAP that the universe is spatially finite. The evidence is that the spatial curvature is roughly zero with some error margin, so it could be slightly positive or slightly negative. There's not a whole lot you can conclude from that. Even if the curvature was narrowed down to the positive side of zero, you can't conclude that the whole universe is a sphere with the radius implied by the local curvature; it might just be local fluctuation (where "local" means 10–100 billion light years or more). Also, even if the spatial curvature is positive and constant, you can't circumnavigate space if ΛCDM is correct (which it might not be). According to ΛCDM you can never reach anything that's farther than a present-day distance of around 16 billion light years, because of the runaway expansion, and the universe is certainly larger than that. -- BenRG (talk) 13:17, 22 July 2009 (UTC)

The surface of a balloon is bounded (as a metric space): no point is more than πr from any other. Is there some other meaning of boundedness that applies here? --Taejo|대조 11:30, 25 July 2009 (UTC)

I'm not sure that an assumption that an infinite universe means infinite mass, actually. Or infinite planets. One could imagine an almost-infinite emptiness with pockets of mass. A lot of mass, sure, but far from infinite. Anyway, as far as we can tell, it isn't infinite (nothing is, in such a case). Infinity is a tricky concept to apply to the real world. --98.217.14.211 (talk) 23:43, 21 July 2009 (UTC)

If the universe is infinite, does it also contain an infinite amount of mass? - Almost certainly, yes.

Does it contain an infinite number of objects such as stars and planets? - Again, almost certainly.

If yes, where does all that mass keep coming from? - It would all have been contained in singularity at the start of the big bang.

Is it even possible that new objects just keep on coming on no matter how far you travel? - If the universe is infinite, yes.

...but all of these things are only true if the universe is infinite...it may well not be. SteveBaker (talk) 23:56, 21 July 2009 (UTC)

… and “it may well not be” is a major understatement. Very few active researchers nowadays are considering the possibility that the universe might be infinite in size, or contain an infinite mass. That idea pretty much died out in the late 60’s, after the discovery of the cosmic microwave background radiation in 1965 cemented the big bang theory as the mainstream viewpoint in physical cosmology. There was some brief interest in exploring alternative cosmologies again in the late 70’s and mid 90’s, when certain observations cast some doubt on the big bang theory briefly. But in each of those cases, minor tweaks to standard cosmology resolved the issues within a few years.

The statement above that an infinite sized universe with infinite mass would have arisen from a big bang is highly problematic. Infinite size and infinite mass only make sense with something like the steady state theory of cosmology. If there was a big bang, then the universe must have a finite age (the amount of time since the big bang), and hence must have a finite size (or it would have had to expand infinitely fast). And if the universe has a finite size, then it must contain a finite mass. Infinite mass in a finite volume would be inconsistent with general relativity, since a black hole with infinite mass would have to have an infinitely large radius. As long as the big bang theory is correct, which very few serious cosmologists doubt any more, the universe has a finite size, and a finite mass. Red Act (talk) 12:34, 22 July 2009 (UTC)

No, that's wrong. Well, the argument is, the claim that the universe is likely finite is not. The big bang is not a simple spatial explosion, i.e. the stuff "over there" was not here and moved away, it was always "over there", and the space in between "here" and "there" expanded - see metric expansion of space. The universe exploded "everywhere simultaneously". Imagine that useful balloon suddenly being expanded from a singular point - at one moment the surface is zero, but as soon as the balloon has a non-zero diameter, all of the universe is there - it just keeps getting diluted as the balloon is inflated. This can just as well work with an infinite balloon - with a tiny bit of extra imagination ;-). --Stephan Schulz (talk) 12:50, 22 July 2009 (UTC)

The big bang is just an explosion, but it's consistent with a spatially infinite universe because it's somewhat arbitrary what you decide to call "space" (as opposed to spacetime). The Milne universe is a simple example of this. It's a special case of big bang cosmology. The universe is contained in the future light cone of the origin of Minkowski spacetime. But the cosmological time is different from the Minkowski time: it's defined to be $\tau ={\sqrt {t^{2}-x^{2}}}$, where t and x are the usual Minkowski coordinates. A surface of constant τ—that is, the cosmologist's "space"—is infinite in size and negatively curved, even though the whole universe is within the future light cone of the big bang event (the Minkowski origin) and Minkowski spacetime is flat. This doesn't accurately describe the real world, but the same basic principle applies. If the universe expands forever (i.e., if it's infinite in the time direction) then it might as well be spatially infinite also, it doesn't really matter. -- BenRG (talk) 13:17, 22 July 2009 (UTC)

Interesting. I can see your point. My mistake. Red Act (talk) 14:39, 22 July 2009 (UTC)

I agree with the poster above stevebaker for the first two answers stevebaker gave - ie it doesn't follow that an infinite universe contains infinite mass/planets - eg if the distibution is e^{-x^2} (or many other common equations) the mass/objects in an infinite universe would still be finite. In fact if you assume a 'bigbang' with mass being produced with a statistical distribution of speeds (eg p(v)=e^-fn(x) (fn(x)is x or something else), after infinite time (by when the universe is infinitely big) there still will be only finite mass83.100.250.79 (talk) 10:30, 22 July 2009 (UTC)

As I pointed out above, if there was a big bang, then the universe is finite. No matter how long you wait after the big bang, you will never reach an age of “infinity”. Red Act (talk) 12:38, 22 July 2009 (UTC)

Red Act, read BenRG's explanation above. There are Bigbang-like models with infinite spacial extent. Dauto (talk) 14:22, 22 July 2009 (UTC)

ART (Active Release Techniques)

I would like to know more about this massage/chiropractic technique that seems to be emerging recently. I did note there was a limited mention of it on Wikipedia as a sub-heading under different chiropractic techniques. Where did it originate? What principles make it effective? Any other applicable info?

208.125.237.242 (talk) 20:56, 21 July 2009 (UTC)

Is this something derived from massage parlors of the more prostitutional type, like "Full Release Massage," or does it "release" frozen joints? Edison (talk) 04:29, 22 July 2009 (UTC)

It is designed to release frozen joints by breaking up adhesions. From what I know so far, it seems it is a newer concept/method in the world of sports massage. It seems to be popular with runners (per "Running Times" article). From that article I gathered it involved targeting the problem sinew and locking onto it while manipulating the rest of the limb in a manner that simulates normal movement. Any input/clarifications/additions etc? 208.125.237.242 (talk) 14:28, 22 July 2009 (UTC)

If you use Google Book advanced search, you can find discussion of "active Release Therapy" such as [6] and [7]. Medical doctors may send patients with adhesions or frozen shoulder to physical therapists who also have manipulative techniques to release the adhesions. We cannot give any medical (or chiropractic) advice. Edison (talk) 18:22, 29 July 2009 (UTC)

Does this budgie have a disease?

Sorry, but questions calling for a medical or veterinary diagnosis are not allowed here. --Anon, 21:22 UTC, July 21, 2009.

Here's why — please consult a veterinarian. Tempshill (talk) 21:37, 21 July 2009 (UTC)

I wasn't asking for advice nor would have acted on the discussions here. I was also interesting in starting a Wikipedia article on this disease if it were one.-- penubag  (talk) 21:40, 21 July 2009 (UTC)

How can you start an article on a disease you haven't diagnosed? Nil Einne (talk) 19:08, 23 July 2009 (UTC)

Neomogroside

Does anyone know the chemical formula for Neomogroside? Also, put the source you got it from (I've started writing a Wikipedia article). Dogposter (talk) 21:36, 21 July 2009 (UTC)

Not a small molecule it seems. All I found was http://www.jipb.net/earticle_read.asp?id=11284 with a name (but not IUPAC), and http://www.lookchem.com/cas-189/189307-15-1.html with a CAS number and half a name. Doing a chemical search on the CAS gave no hits - too new to have been indexed.  Ronhjones  ^(Talk) 21:46, 21 July 2009 (UTC)

I suspected it might have been large. So it's a protein? Dogposter (talk) 21:50, 21 July 2009 (UTC)

No. It sounds like it's a glycoside. The listing on the CAS site linked above gives the following: "â-D-Glucopyranoside,(3â,9â,10R,11R,24R)-11,- 25-dihydroxy-9-methyl-19-norlanost-5-ene- 3,24-diyl bis[O-â-D-glucopyranosyl-(1f2)- O-[â-D-glucopyranosyl-(1f6)]-". So, there's at least a chance of deducing a chemical structure. However, are you sure this meets notability criteria? It is mentioned in the Siraitia_grosvenorii article as one of the compounds identified in that fruit, but does it have any independent importance that merits an article of its own? --- Medical geneticist (talk) 22:30, 21 July 2009 (UTC)

It was requested for Wikiproject Chemicals. It was on the subpage of requested articles and removed when I made it. Dogposter (talk) 22:41, 21 July 2009 (UTC)

But anyone can edit that list - it doesn't mean it's notable. SteveBaker (talk) 23:32, 21 July 2009 (UTC)

Blind

What do blind people "see"? 121.220.109.214 (talk) 22:02, 21 July 2009 (UTC)

Close your eyes. 90.208.66.95 (talk) 22:11, 21 July 2009 (UTC)

When you close your eyes, you still see small bits of light. Blind people don't even see that. Dogposter (talk) 22:14, 21 July 2009 (UTC)

I think that it's probably impossible to know for sure unless you happen to go blind and comprehend what it's like for yourself. It's a bit like asking what blind people's dreams are like - they can tell you, but you can't 'experience' it. --Kurt Shaped Box (talk) 22:55, 21 July 2009 (UTC)

There are different kinds of blindness. It's my understanding that it can range from people who see a blurry image all the way to people who lack the brain hardware needed to handle vision in any way. So, I guess the answer is anything from "They can almost see" to "They don't even see black." depending on who you're talking about. APL (talk) 23:04, 21 July 2009 (UTC)

It's a complex question. People blind from birth -- and I mean completely blind, as in lacking eyes -- usually don't describe any visual experience at all. People who became blind at some point after birth usually continue to have visual experiences of some sort, for example visual dreams. And then there is the interesting phenomenon of blindsight. Note that the majority of people who are legally blind are not fully blind, they just don't have vision to a useful degree. Looie496 (talk) 23:36, 21 July 2009 (UTC)

I suspect that totally blind people, or people whose eyeballs have been removed, still see a splotchy background of random neural activity in the low level brain centers which normally process vision, much as sighted people do when sleeping in a very dark room. This sensation might not be processed or analyzed, and they might deny "seeing" it. Similarly, I hear a constant slight noise even in a totally quiet room. The human sensory system is not noiseless. Edison (talk) 04:25, 22 July 2009 (UTC)

The sensory system is also good at detecting and supprssing noise. People who are blind from birth never have any non-noise input from the vision centers of the brain, so during the first year or so of life, the brain learns to suppress the signals from those areas. --67.185.15.77 (talk) 07:33, 22 July 2009 (UTC)

For people who aren't blind from birth, consider Eigengrau. 90.208.66.95 (talk) 11:11, 22 July 2009 (UTC)

But my doubt is Do persons who are blind right from birth ever dream at all??? —Preceding unsigned comment added by Gd iitm (talk • contribs) 17:25, 22 July 2009 (UTC)

They dream, but their dreams are non-visual. See : Cecil Adams What Are the Dreams of the Blind Like. APL (talk) 19:42, 22 July 2009 (UTC)

Try this [8] exhibition/experience/show (?) It is very interesting and can be frightening or disturbing to some visitors. I know you can find it in Atlanta, GA in the US and in Hamburg, Germany (I think that was the first one they did.) See if someone is hosting it in a city near you or contact the organizers to learn about hosting an event yourself. Must not see :-) P.S of course we have a page: Dialogue in the Dark--71.236.26.74 (talk) 23:52, 22 July 2009 (UTC)

African plate motion

I'm wondering is how old is each website. The newer ones is more accurate than the old ones. I'm not certain if Africa is just moving east or north. Our article said Africa is moving northeast. Is it east-northeast or is it north-east north. All my books is update at diff years. Source will not be helpful if is outdate. I'm not certain of the source Dragon flight gave me is update enough. They have plentys of black arrows. The thing is when plates move the shape of land deforms, and they change shape. Some plate motionss will depend on what part of plate.--69.228.145.50 (talk) 03:12, 21 July 2009 (UTC)

I'm not entirely sure, but it is being pulled apart on the East African Rift. Dogposter (talk) 00:02, 22 July 2009 (UTC)

The other thing that bothers me (and which may explain the confusion) is which part of the earth is considered stationary? If (for example) two adjacent plates have an increasingly large gap between them - how do you know whether plate 'A' is moving North or plate 'B' is moving South or both? Because the axis of rotation and the magnetic poles shift around on these kinds of geological timescales - who's to say what is the reference point for these various motions? SteveBaker (talk) 01:11, 22 July 2009 (UTC)

How about the sun? Noodle snacks (talk) 01:28, 22 July 2009 (UTC)

Er - what do you mean? SteveBaker (talk) 01:44, 22 July 2009 (UTC)

I would think the axis of rotation would be the natural reference. Not sure what you mean when you say it shifts around -- with respect to what? Looie496 (talk) 02:16, 22 July 2009 (UTC)

The axis of rotation also drifts so that's not good enough. Dauto (talk) 04:38, 22 July 2009 (UTC)

Steve, you would be right if all we had was information about the relative motion between the tectonic plates. There is also available information about the relative motion between the plates and the matle beneath taken for instance from hotspot trails.Dauto (talk) 04:38, 22 July 2009 (UTC)

Ah - cunning! So it's assumed that the hotspots in the mantle are the reference from which all of these positions are measured? Don't those also move around? It all seems rather arbitary to me...but perhaps if one source for these motions is referring to (say) the spin axis of the Earth as North/South and another is using the hotspot reference points - then that could easily explain all sorts of discrepancies in data from different sources. SteveBaker (talk) 14:56, 22 July 2009 (UTC)

The hotspots are believed to be attached to the mantle which is believed not to move. Dauto (talk) 21:06, 22 July 2009 (UTC)

Historically that is true, though modern wisdom is leaning towards the conclusion that they also move some, though not very quickly compared to plates. Dragons flight (talk) 21:11, 22 July 2009 (UTC)

If all else fails, you are usually pretty safe assuming distant stars are stationary. --Tango (talk) 00:31, 24 July 2009 (UTC)