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March 18

More quantum physics...

I need to know, in depth, all aspects of the behavior of electrons in crystaline structures (more specifically, quantum dots). If there is an article on this, please let me know. Thanks! Zrs 12 (talk) 03:01, 18 March 2008 (UTC)

Quantum dot seems like a good place to start. DMacks (talk) 04:07, 18 March 2008 (UTC)

Read it. I need to know in depth. I'm having to do a project over these things and apparently electrons act differently in them than in single atoms. (That probably sounds like I'm being short or rude, but I don't mean it like that). Zrs 12 (talk) 04:41, 18 March 2008 (UTC)

No problemo...wasn't clear from your question what if anything you already knew/had read:) By spacially constraining the electrons, the energy levels are changed, so the spectra of a quantum dot that are based on electronic transitions are different than for free atoms/molecules. Quantum well has some detail. What level and sort of project are we talking about here? "In depth" and "all aspects" sound either contradictory or unlimited in scope without knowing what kind of project and what academic level. The refs cited in quantum dot, quantum well, and potential well are good ones. DMacks (talk) 05:12, 18 March 2008 (UTC)

Thanks for your help. Well, I am in 9th grade. However, I have been reading alot about the subject and am beginning to grasp some of the more in depth concepts such as the mathematical concepts in some areas of quantum physics. This is also a project to be in the state science fair, so it probably must be done at a higher that 9th grade level to have any chance. By the way, the specific information I seek about the electrons in quantum dots is; Why are the electrons confined to bands rather than descrete energy levels where they can have partial quanta of energy (right?). And, how do the electrons behave. They bounce back and forth, but between what? Where? Are they confined to a specific area? How and why are the energy levels changed by spatial restriction? To how big an area does the Pauli exculsion principle apply? To a single atom? A molecule? What do the matrices of objects such as $|\psi \rangle$ represent?Bra-ket notation Is it correct to say that, for the photoelectric effect to take place $E_{g}\leq {hf}$ in which E_g is the energy of the bandgap, h is Planck's constant, and f is the frequency of the light?

Once again, thanks very much for your help. Zrs 12 (talk) 05:45, 18 March 2008 (UTC)

As the Pauli Exclusion Principle article states, it says that no two fermions may occupy the same quantum state simultaneously, fermions are a type of elementary particle, described by The Standard Model. I recommend purchasing the book Hacking Matter at the local bookstore, about quantum dot, wells, and artificial atoms. I suggest taking up your discussion at Physicsforums's physics section— they will be very helpful to you.[1] Mac Davis (talk) 10:49, 19 March 2008 (UTC)

Infrared raman spectroscopy

Infrared rays having best penetration in skin and flesh, why can't be utilized for in-vivo non-invasive probing? Can't these rays yield good signature of bones? Neel shah556 (talk) 04:00, 18 March 2008 (UTC)

Infrared is strongly absorbed by many of the components in skin and flesh. Water, lipids, proteins etc. Infrared therefore does not have good penetration of skin and flesh. X-rays on the other hand are not absorbed (much) by flesh and therefore penetrate the skin and flesh to the bones, thus x-rays are used to look at bones in-vivo, not infrared.--Shniken1 (talk) 12:40, 18 March 2008 (UTC)

global warming

Will rise in sea level be even across the world? Or will the rise be more in regions near to arctic and antarctic and less in regions near equator? —Preceding unsigned comment added by 59.92.113.83 (talk) 06:46, 18 March 2008 (UTC)

Sea level changes are not uniform, but it's not as simple as greater rises at higher latitudes; contributing factors are tides, density due to salinity, expansion and contraction due to heat, flows around landmasses, etcetera. Most models show that the greatest rise will be seen in the arctic (due to increased runoffs causing a drop in salinity) and the lowest rise will be seen in the antarctic. FiggyBee (talk) 07:34, 18 March 2008 (UTC)

Dumb question then - why wouldn't the higher sea level water flow down to the lower level until the levels are equal? Franamax (talk) 08:12, 18 March 2008 (UTC)

It does, but not fast enough to overcome all the other factors (which are all ongoing processes, rather than one-off starting conditions). FiggyBee (talk) 08:19, 18 March 2008 (UTC)

Thanks! I knew it was a dumb question. :) Flow varies with square-root of water head, right? It's just hard to imagine that the Arctic Ocean could fill up with water faster than it could empty out. I forgot the factor of time. Franamax (talk) 08:39, 18 March 2008 (UTC)

I agree with you Franamax. While some difference seems inevitable I have a hard time imagining a significant difference. Are we talking about fractions of an inch here ? StuRat (talk) 14:24, 18 March 2008 (UTC)

From Sea level : "Mean sea level does not remain constant over the surface of the entire earth. For instance, mean sea level at the Pacific end of the Panama Canal stands 20 cm higher than at the Atlantic end." 72.10.110.107 (talk) 15:22, 18 March 2008 (UTC)

The earth's spin alone accounts for the height of the Pacific being slightly elevated relative to the Atlantic, as I understand it, and that difference is more pronounced towards the Pacific's West end. Any of us who have spent time on bodies as small as the Great Lakes know that water level can seem to rise or fall significantly due to changes in wind direction. And, for that matter, the Great Lakes do have a flow -- a molecule of water at the West end of Lake Superior takes 15,000 years to reach the Atlantic. So water, as it were, doesn't settle and "even out" quite so quickly as we might suppose.Vance.mcpherson (talk) 15:41, 18 March 2008 (UTC)

But, of course, the Great Lakes are far more restricted in their flow to the ocean than the oceans are to each other. If the oceans were only connected via narrow channels, it would be easier to understand a difference in elevations. The tides will also cause some areas to have far higher elevations than others at any given time. However, none of this explains why the relative elevations would significantly change when more water is added to the system via global warming. StuRat (talk) 22:15, 18 March 2008 (UTC)

The Arctic Ocean may be the exception though, it only has two outlets, and some pretty big rivers flowing in, Mackenzie, Ob-Irtysh, Yenisey (I think). Plus thermal expansion as the ocean warms up, so it's plausible. I would be interested to see the models though. Rising sea levels are certainly already a problem in the Arctic. Most interesting... Franamax (talk) 01:28, 19 March 2008 (UTC)

A rise in sea level is not necessarily even around the world. As discussed above, mean sea level (MSL) involves complex measurement and it is attempted to accurately determine an MSL using the geoid as a level reference surface. A rise in sea level, however, would expand the geoid and mean sea level. Isostatic changes will also do this. Mac Davis (talk) 10:42, 19 March 2008 (UTC)

Hi. Well, I read in a book that a recent satellite measurement of the world's oceans that the mean sea level excluding waves and other anomalies in a given area was actually greatly affected by the sea bottom elevation: the surface water was generally lower near a trench and higher near an undersea mountain range. Also, a shift in sea currents could affect the amount of heat in a given area and thus the sea level. Erosion will also cause the now-undersea landforms to erode, allowing sea levels farther inland. Given the right (or should I say wrong) type of rock, the sea can either flow into the groundwater and flood a nearby low basin or create waves that enter the basin. For now, many regions in the arctic are still experiencing the shoreline recede, as the rising of the land since the last ice age is currently faster than the sea level rise, at least until the Greenland and Antarctic ice sheets start collapsing. Also, if you try to use the flood maps at flood.firetree.net, they are largely innacurate (see their disclaimer). Constant flooding in an area may also allow sea levels to creep up. If there is a river, the sea can easily flood farther inland bacause of the eroded lowlands formed by the river. Hope this helps. Thanks. ~AH1^(TCU) 21:11, 19 March 2008 (UTC)

  I belive that the sea level will not be even around the world but I do not know the answer to your second question.  But i promise I will try to find out.
                                SilverLeaf209.226.138.43 (talk) 18:22, 23 March 2008 (UTC)

MSM expiry

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. --~~~~

TenOfAllTrades(talk) 12:55, 18 March 2008 (UTC)

You should ask a pharmacist and your doctor about this. They know much more than we do. Franamax (talk) 08:00, 18 March 2008 (UTC)

Doctors and pharmacists are Wikipedia editors as well.

This is not about pharmacy or medicine. The question is: Is MSM oxidized or reduced in household storage (or does it decompose)? [household chemistry]

MSM is not pharmacy; It is a mineral (sulfur) nutrient, much like calcium or magnesium. But the question is not so much about nutrition as it is about msm decomposition in household storage. Please leave this for discussion. —Preceding unsigned comment added by Zaqry (talk • contribs) 19:42, 18 March 2008 (UTC)

Is MSM oxidized or reduced in household storage (or does it decompose)? —Preceding unsigned comment added by Zaqry (talk • contribs) 22:39, 18 March 2008 (UTC)

Does MSM decompose in household storage and how (oxidation or reduction reaction for example)? —Preceding unsigned comment added by Zaqry (talk • contribs) 18:00, 19 March 2008 (UTC)

Radio transmitter power

A 50,000-watt radio station is transmitting at full power.

a) Is there at least 50KVA (50KVA plus the heat coming out of the building) running through the power lines into the station at all times?

b) Does it matter whether anyone is talking over the radio?

c) Is the answer different whether it's AM or FM, or VHF or UHF television?

Thanks for the help! Franamax (talk) 08:08, 18 March 2008 (UTC)

My understanding is

a) Yes for FM. See c

b) No for FM, but for AM it will increase and decrease as someone talks. There is a variation of AM known as Single-sideband modulation (SSB) that only uses power when there is some sound.

c) For FM and AM yes. For TV, I am not sure but I think that US digital TV uses ATSC Standards a type of SSB. I would imagine that in video there are no "silent" pauses like in audio, so the power load will be more constant. European digital TV uses Orthogonal frequency-division multiplexing, which I am unsure about. Analogue TV uses FM, and will therefore have constant power. -- Q Chris (talk) 10:02, 18 March 2008 (UTC)

For frequency modulation, phase modulation, and ordinary analog amplitude modulation (of 100% or less modulation depth), the average power of the carrier wave remains constant so the power inflow to the building will always be at least 50 KW. For single-sideband modulation, there's no transmitted power when no one is talking so the average power of the carrier wave varies with the average volume of the modulating signal. Analog TV uses vestigial sideband modulation (a hybrid of AM and SSB) for the video and frequency modulation for the audio.

Atlant (talk) 12:04, 19 March 2008 (UTC)

Atomic Radio clocks in Bulgaria

I live in Bulgaria. How do I find out whether an atomic radio clock will work in Bulgaria? Do I have to obtain one from a specific provider? —Preceding unsigned comment added by ENiklaus (talk • contribs) 12:06, 18 March 2008 (UTC)

Bulgaria seems to be at the edge of the region where the German DCF77 signal can be received. According to the PTB, the range is 2000 km (unfortunately that's probably not very helpful, but maybe interesting). Icek (talk) 12:54, 18 March 2008 (UTC)

(edit conflict)

There are long-wave time transmissions from Switzerland and Germany which might reach Bulgaria (depending on mountains etc.) They broadcast on slightly different frequencies, so, yes, you do need to purchase the correct receiver, and there is no guarantee that it will work where you live. I have found that the UK transmission can be picked up in some parts of buildings, but not in other parts. Mountains and steel frames cause reception problems. See Radio clock for more details, but the price of radio clocks is now quite low, so if they are not available for sale in your area, then it is probably because there is not a good radio signal. A world-wide time transmission can be picked up by a GPS clock (built into most GPS units) but you need to be either outdoors or near to a large window to pick up the satellite signals. dbfirs 13:08, 18 March 2008 (UTC)

Genetic probabilities

In a problem I'm trying to solve, there are 2 alleles, A and a. a is a defective allele, so the genotype aa induces disease. Both parents are carriers: Aa.
1) What is the probability that all three children are of normal phenotype? The way I see it, the chance of the normal phenotype in one child is 3/4, the result of a simple Aa x Aa Punnett square, so (3/4)³ = 27/64.
2) What is the probability that one or more of the children have the disease? Shouldn't it be 1/4 + 1/4 + 1/4 = 3/4? But 27/64 + 3/4 ≠ 1 ... help! Thanks, anon. —Preceding unsigned comment added by 70.23.85.120 (talk) 16:48, 18 March 2008 (UTC)

You can only add probabilities when they are probabilities of mutually exclusive (i.e. incompatible) events. Child A has the disease with probability 1/4, same for B, but the probability that A or B or both have the disease is not 1/4 + 1/4 because you are double-counting the case where both A and B have it, which has probability 1/16. So the probability for two children would be 7/16, which equals 1 - 9/16 that you could compute from the probability that both were normal. With three children it is easier to start with the probability that all three are normal, and you have that already. --Anonymous, 16:58 UTC, March 18, 2008.

As an exercise to help understand the probabilities you might want to list every possible combo. Each child has 4 possible combos (AA, Aa, aA, or aa). While Aa and aA both mean they are carriers of this recessive disorder, it's probably easier to list them separately as equal probability than combine them together. So, that gives you 4^3 or 64 possible combos. List them out and record how many children have the disease or are carriers for each combo. StuRat (talk) 22:05, 18 March 2008 (UTC)

Thanks so much :-), anon. —Preceding unsigned comment added by 141.155.38.85 (talk) 17:17, 19 March 2008 (UTC)

300,000 Elephants in Chad?

In the article excepted below [and in many secondary & tertiary sources] the assertion is made that “--the Chad population was over 300,000 animals as recently as 1970 and has been reduced to approximately 10,000 as of 2006.” I have looked carefully at the publications of the African Elephant Specialist Group of the IUCN for confirmation of these figures [latest report 2007]. The IUCN folks report no data on Chad elephants before 1985. They report “no evidence” for 1981 and no figures before that time. Where did this 300,000 figure originate and who started it?

2006 Zakouma elephant slaughter refers to a series of poaching massacres of African elephants in the vicinity of Zakouma National Park in southeastern Chad. These killings have been documented in aerial surveys conducted from May through August 2006 and total at least 100 animals.[1] This region has a four decade history of illegal killing of this species; in fact, the Chad population was over 300,000 animals as recently as 1970 and has been reduced to approximately 10,000 as of 2006. The African elephant nominally has Chadian governmental protection, but the implementation practices of the government (backed with certain EU help) have been insufficient to stem the slaughter by poachers.[1] The species African Bush Elephant (Loxodonta africana) occurs in several countries of Eastern Africa. —Preceding unsigned comment added by Lynmil (talk • contribs) 19:45, 18 March 2008 (UTC)

The first reference for 2006 Zakouma elephant slaughter is where that figure comes from, but trying to track that number further back was not very successful. It is amazing how many sites quote that "300,000 in 1970" figure and how frustrating it was to try tracking the source. I was unable to find anything approaching an original source, but I think I may have a good idea on how that figure was calculated. I think it may have been a backward calculation based on the Manovo-Gounda St. Floris National Park (Central African Republic) (N 475) report or some report like it. In that report, which is not specific to Chad but could reasonably be extended in principle to all surrounding areas, they report that the region had lost 95% of its elephants. It wasn't really clear to me what time frame they were referencing. Ninety-five percent loss since when? They were probably calculating the loss since poaching became a serious problem (starting around 1970 ???). Using that figure, you simply multiply the elephant population, at the time of the report, by twenty to find the starting population. Of course, to know that an area had suffered a 95% loss means UNESCO already had to know the starting population by some other means. Althought I don't doubt the figure at all, I would like to see the original source for that 300,000 quote. SWAdair | Talk 10:26, 22 March 2008 (UTC)

The IUCN report titled African Elephants and Rhinos: Status Survey and Conservation Report (1990) gave a 1987 estimate of between 200-400,000 elephants for Central Africa including Cameroon, Central Afr. Rep, Chad, Congo, Equat. Guinea, Gabon and Zaire [Now Dem Rep. of Congo]. Nearly half (195,000) of these animals were estimated for Zaire.

The IUCN 2007 African Elephant Status Report: An update from the African Elephant Database gives the Probable number of elephants in Central Africa as 48,936, with the Probable number from Dem Rep of Congo as only 7,955 animals. Thus Zaire (Dem Rep Congo) HAS lost 95% of the estimated elephant population from 1987 to 2007. The upper estimate for Central Africa in 1990 was 375,800. The upper estimate for 2007 is 48,936; thus an estimated loss of about 76%.

I agree with “SWAdair” that someone probably extrapolated from Central Africa data to Chad, but the loss of almost 300,000 savanna elephants from Chad could not have gone unnoticed. The figure is fictitious. Lynmil (talk) 19:38, 24 March 2008 (UTC)

Paramagnetic metal that do not become magnetized.

The question is what are metals called that are paramagnetic,but do not become magnetized (they are attracted by magnets, but when removed from magnetic infuences, are not magnetic)?

What metals are these? How do I reference the subject on WikiPedia?

Thank You, My Email address (removed for your protection)—Preceding unsigned comment added by 151.202.62.236 (talk) 19:55, 18 March 2008 (UTC)

"soft magnets", see magnet also remanence and follow the links in the 'see also' section.

The remanence of a material is the extent to which the material retains the magnetic field - you are obviously asking for 'low remanence'. Please ask for furhter info.87.102.47.176 (talk) 20:15, 18 March 2008 (UTC)

You may want to have a look at [[2]] for a little fun. I saw a nifty powerpoint by a fellow from University of Victoria on paramagnetism some six years ago, and I'll be damned if I know how to find him. If memory serves, and the link I provide confirms, paramagnetism isn't so much about what metal is paramagnetic as what you did to the metal, i.e. what else is it bonded to. Gets into the realm of organic chemistry.Vance.mcpherson (talk) 20:15, 19 March 2008 (UTC)

What is cyclooctatetraene?

What is cyclooctatetraene? 66.81.43.129 (talk) 21:59, 18 March 2008 (UTC)

Take a look at our article, Cyclooctatetraene. It appears to have a lot of info. -- Flyguy649 ^talk 22:02, 18 March 2008 (UTC)

March 19

Insanity...

Is the capability to display behavior patterns indicative of insanity in any way proof that the insane entity had a mind of its own to lose in the first place?

Just musing to myself about those neglected, stir-crazy, obsessive-compulsive, self-mutilating parrots at this late hour... --Kurt Shaped Box (talk) 02:42, 19 March 2008 (UTC)

While it certainly is possible for any creature with a brain to suffer a brain malfunction, I'd expect that complex minds are more likely to have complex malfunctions. So, strange obsessive-compulsive behavior may indeed be a sign of a fairly complex mind. A simpler mind would likely suffer from a more basic malfunction, like walking in circles instead of straight. I suggest you get the parrot in question a companion (or at least a cuttlebone to cuddle with). :-) StuRat (talk) 05:45, 19 March 2008 (UTC)

Biology: What are these caterpillars doing?

What are the caterpillars doing in this video? - Pureblade | ^Θ 04:46, 19 March 2008 (UTC)

I would speculate that they are exhibiting a defensive behaviour by co-ordinated action to give the impression of a larger creature. They may also be releasing body hairs containing a very powerful irritant. It is entirely possible that they sense the presence of the video operator and are reacting appropriately. I have experienced a similar effect with pine processional moths in Spain, when I blew on them gently they all jerked simultaneously. This seems to me to be an analogous behaviour. What is slightly odd, if these are pine processional moths, is that they are out feeding in the daylight. Of course they could be a related species demonstrating similar behaviour. Richard Avery (talk) 08:32, 19 March 2008 (UTC)

To me it looks like a sped-up version of the Macarena. Clearly somebody should tell these little buggers that it isn't cool anymore, if it every was. --Captain Ref Desk (talk) 19:49, 20 March 2008 (UTC)

But more honestly: I think they are Sawfly larvae. As to how they know to do this, this article is rather evocative. --Captain Ref Desk (talk) 19:49, 20 March 2008 (UTC)

Science in my gloves

We have to wear latex gloves in the cleanroom that I work in. Under these gloves we can wear a nylon glove liner. It's just a loose fitting liner so the glove isn't directly on your skin. I've noticed that sometimes as the night goes on, stains will develop inside my glove on the liner. The stains are blue like a bit of ink has found its way into the glove but the liners are white and stitched with white thread. There isn't any obvious source for the blue color. Some of the liners can be yellowed, almost as if they have been sitting in the sun, so I tried one of those to see if maybe the blue was due to a reaction between my sweat and whatever was yellowing the liners. I've only tested this once so far but the yellowed liner produced the blue stains while a whiter liner on my other hand did not. So what could be producing the blue color? Dismas|^(talk) 08:16, 19 March 2008 (UTC)

an off-the-wall guess.... povidone/iodine (from gloves or handwashing) + starch --> blue stain. - Nunh-huh 08:53, 19 March 2008 (UTC)

I guess I should have mentioned this but we are required to wash our hands using this white foamy soap before putting the gloves on. Dismas|^(talk) 09:01, 19 March 2008 (UTC)

Hi. This may be unrelated to your question, but usually in winter sometimes I wear normal gloves on the inside and waterproof ones on the outside. If the outside of my gloves get wet, sometimes the inside will too, and I often find disgusting colour marks on my hands afterwards. Talk about a green thumb, eh? Hope this helps. Thanks. ~AH1^(TCU) 21:20, 19 March 2008 (UTC)

Two questions

What proportion of the scientific community believes the earth to be less than 100,000 years old and approximatly how accurate is carbon dating?--193.120.116.177 (talk) 11:02, 19 March 2008 (UTC)

And how old does the pope beleive the earth to be?--193.120.116.177 (talk) 11:18, 19 March 2008 (UTC)

Age of the Earth might help.

Zain Ebrahim (talk) 11:25, 19 March 2008 (UTC)

The Roman Catholic church does not have any theological issues with the earth being 4-6 billion years old. See Evolution and the Roman Catholic Church for related information. Specifically note what Cardinal Ratzinger (now Pope Benedict) said in a report: "According to the widely accepted scientific account, the universe erupted 15 billion years ago in an explosion called the 'Big Bang' and has been expanding and cooling ever since. Later there gradually emerged the conditions necessary for the formation of atoms, still later the condensation of galaxies and stars, and about 10 billion years later the formation of planets. In our own solar system and on earth (formed about 4.5 billion years ago), the conditions have been favorable to the emergence of life." -- 14:38, 19 March 2008 (UTC) —Preceding unsigned comment added by 128.104.112.85 (talk)

Do you have a reference for this?Zain Ebrahim (talk) 14:43, 19 March 2008 (UTC)

Found one: [3]. Zain Ebrahim (talk) 14:47, 19 March 2008 (UTC)

Carbon_dating#Calibration regarding the accuracy of carbon dating and radiometric_dating#Limitation_of_techniques for accuracy in dating the age of the earth. Lanfear's Bane | t 11:37, 19 March 2008 (UTC)

Carbon dating is just one kind of radiometric dating. It isn't used for determining the age of the Earth—it is only useful for dating things in smaller time periods than that. Uranium-lead dating is more common for things as old as the Earth.

As for how much of the scientific community believing the earth is less than 100,000 years old, practically none—a tiny number, insignificant when compared to the number of all scientists, and of those small number I imagine even smaller of them are active participants in a field of scientific inquiry that actually informs such assessments, or in what are considered to be real scientific institutions (not the Institute of Creation Research, for example).

There are quite a number of people outside the scientific community who believe that, but there is simply no compelling scientific evidence that the Earth is so "young" and much compelling evidence against the idea. I don't think it's an overstatement to say that the only people who believe the Earth is less than 100,000 years old are people who have a predisposition towards wanting to believe that on account of their religious beliefs.

As for the Pope, I am not aware of the current Pope's point of view vis a vis the age of the Earth. However perhaps you are referencing the work of the long-since-deceased Archbishop Ussher, who calculated that the Earth was only around 2,000 years old. --Captain Ref Desk (talk) 19:32, 19 March 2008 (UTC)

To be slightly more accurate than 'insignificant', Institute for Creation Research claims around 500 scientists (by which I think they mean those with a PhD in a scientific subject) that subscribe to their views. I'm not sure how many scientists there are in the US, but my guess is that this is substantially less than 1%. Interestingly it probably means that only a tiny fraction of scientists who are also Christians believe that the earth is less than 100,000 years old. DJ Clayworth (talk) 17:46, 19 March 2008 (UTC)

And it's the sort of number that gets smaller when you take their list and weed out all of those who 1. have degrees from non-accredited universities, and 2. are actively publishing or doing research in subjects related to things like the age of the Earth. I'm betting you'd cut the number down by quite a lot if you just took out the number of engineers—no offense made to engineers, but they seem to always predominate in the "people who think they really understand science deeply but actually have a fairly superficial working knowledge, and as such often overestimate their own competency in subjects they have not really studied seriously" category. --Captain Ref Desk (talk) 19:32, 19 March 2008 (UTC)

The precise stand of the Vatican on the Big Bang, Creation vs. Evolution, etc., can be found here: [[4]], at the Holy See's website; scroll down to paragraph 62. Other Christian denominations are not nearly so centralized, but in general the Anglican Communion has distanced itself from the notion of a 10,000 year old earth. In fact, in the West, the remaining "literalists" are largely Protestant denominations, many of whom have no fantastic claim to antiquity themselves. Vance.mcpherson (talk) 20:38, 19 March 2008 (UTC)

How do you poison a dress?

(I'm not sure whether I should post this at the Humanities-desk or here, but I figure since it has to do with medicine than history, Science would be most appropriate)

I saw the movie Elizabeth (the one with Cate Blanchett) a while ago, and something struck me: there is a subplot in it about an attempted assassination of Elizabeth using a dress that had been poisoned, so that when she would put it on, she would die (the attempt failed, obviously). That seems to me to be a not uncommon motif in literature, poisoning a dress. The most obvious other example is Medea killing Creon and Glauce by poisoning a dress.

Is this possible? I mean, can you make a dress that otherwise looks (and smells) normal, but when you touch it or wear it, it will poison you? Supposing you could, could you do it in the 16th century? I mean, if you just dunk it in a vat of arsenic-contaminated water (or something), wouldn't it be all discolored and also smell pretty foul? And is this just part of mythology, or has there ever been an attempt of using this method of assassination? --Oskar 14:45, 19 March 2008 (UTC)

It would be possible, but it seems to be firmly in the territory of soap opera and mythology. - Nunh-huh 15:43, 19 March 2008 (UTC)

So say you were a 16th century cardinal who didn't like all this Church of England nonsense, how would you do it? --Oskar 17:38, 19 March 2008 (UTC)

Get out of town? - Nunh-huh 17:49, 19 March 2008 (UTC)

Maybe it was soaked in cyanide with a nice almond scent. -- MacAddct  1984 ^{(talk • contribs)} 16:14, 19 March 2008 (UTC)

Well, the CIA considered giving Fidel Castro a poisoned wet suit, so why not? --Sean 17:11, 19 March 2008 (UTC)

Coupla drops of dimethyl mercury would do it (but long-drawn-out, not quick-convulse&die), but not sure anyone in the 1500s would be able to handle that stuff. Heck, even today it is hard to handle safely. DMacks (talk) 19:14, 19 March 2008 (UTC)

Pyrrole might be a good candidate, as it is a permeator. See [[5]]. Have no idea how they'd get the stuff in Elizabethan times, though, the synthesis of it is complex ([[6]]).Vance.mcpherson (talk) 20:50, 19 March 2008 (UTC)

Lots of things permeate skin, but need something that is reliably toxic in a dose small enough to be delivered that way. The MSDS you cite lists an acute LD₅₀ of 98 mg/kg (mouse, orally), so even if that's the right ballpark for (human, dermal), we're talking several dozen mL to absorb. In smaller doses, it's not that toxic (see note on pyrrole about its use in cigarettes). DMacks (talk) 21:00, 19 March 2008 (UTC)

I like the idea of having small poison-tipped spikes somewhere inside the dress. Mac Davis (talk) 01:47, 20 March 2008 (UTC)

How about soaking the dress in nicotine ? It's absorbed through the skin and can cause death if enough is absorbed transdermally. Tobacco farmers must wear gloves when harvesting tobacco leaves, especially after a dew or rain, as concentrated nicotine in the rain drops will pass through the skin on the hands and can cause death. StuRat (talk) 04:17, 20 March 2008 (UTC)

Of course it works. Just ask Hercules. shoy 16:42, 20 March 2008 (UTC)

I think the trick is social engineering. Even if the soaking is visible and can be smelt, you could convince the target that it's a "refreshing" or "wellness" shirt or something. – b_jonas 17:21, 20 March 2008 (UTC)

Here's how I would do it. Get some venom from a Golden Poison Frog. The batrachotoxin from the frog is so lethal that only 100 micrograms (equivalent to 2 grains of ordinary table salt) will kill a 150-pound person. Skin contact with this stuff may be sufficient, but I would mix it with dimethyl sulfoxide (available from drug stores or nutrition stores), a chemical that can be used to carry other substances through the skin. Apply drops of this to parts of the dress that would be touching the skin, shortly before the dress is worn. The wearer may taste garlic just prior to dropping dead. ~Amatulić (talk) 17:40, 25 March 2008 (UTC)

hey

wats is the common and scientific name for sponges,flat worms, earthworms, bugs, frogs, jellyfish, round worms, clams, and starfish —Preceding unsigned comment added by 165.29.165.253 (talk) 15:14, 19 March 2008 (UTC)

Well, you just listed their common names. Scientific names will depend of each species of the animal you want; out of those groups there are probably millions(?) of different species. The only group they all fall under is the kingdom "Animalia". -- MacAddct  1984 ^{(talk • contribs)} 15:27, 19 March 2008 (UTC)

Simple enough eg type 'sponge' into the search box gives the sponge page which tells that they are all of the phylum 'Porifera'. You can do the same for the rest. type 'insects' for 'bugs'.83.100.183.180 (talk) 15:50, 19 March 2008 (UTC)

Well the whole collection together could be animals! or cold blooded animals Graeme Bartlett (talk) 05:13, 20 March 2008 (UTC)

Invertebrates? Sandman30s (talk) 07:55, 20 March 2008 (UTC)

...apart from the frog, of course. Gandalf61 (talk) 10:50, 20 March 2008 (UTC)

And invertebrates is a fairly silly name based on exclusion rather than inclusion, i.e., defined as animals without a backbone. Proper nomenclature is never based on exclusion it's just a vertebrate (human) bias. --jjron (talk) 14:10, 21 March 2008 (UTC)

Tantalum hafnium carbide

We don't have any reference in the article Tantalum hafnium carbide, the substance with the highest melting point known (?). Where is the publication on the 4488 K melting point? Thanks in advance. Icek (talk) 15:55, 19 March 2008 (UTC)

This Britannica article is a very reliable source. --Bowlhover (talk) 16:00, 19 March 2008 (UTC)

Thank you, but does anyone know where to find the original publication? Icek (talk) 16:12, 19 March 2008 (UTC)

Google told me that the phrase "The alloy tantalum hafnium carbide. (Ta. 4. HfC. 5. ), with a melting point of 42158C,. is one of the most refractory substances" appears in "11 Hafnium" of doi:10.1002/9783527619634.ch32, but I don't have access to the actual text from here. A publication like that is probably well-footnoted to primary and/or reputable secondary sources. DMacks (talk) 19:12, 19 March 2008 (UTC)

New car smell

I just found out today that the new car smell is toxic and carcinogenic. So what should we do to avoid it? Would opening the windows help? --Lazar Taxon (talk) 17:26, 19 March 2008 (UTC)

Do you have a reference for this? It would surprise me (at least, in the US, with all our emphasis on car safety) that manufacturers would sell a toxic product. But, assuming you do want to avoid it.. the easiest way would seem to be, don't get a new car. Letting it air out sure seems like it wouldn't hurt either. Friday (talk) 17:36, 19 March 2008 (UTC)

I think it's more about the regulatory bodies not allowing a product to be sold that's clearly and undeniably toxic. If a company can plausibly deny a product's harmfulness (see Crisco, Dupont), that's good enough for the feds. Vranak (talk) 20:04, 19 March 2008 (UTC)

Found a couple sources: From a few years ago, saying it might be toxic, and more recently saying it's not toxic. This is what I get for not checking the wiki first- we have a decent article on this at New car smell. Friday (talk) 17:40, 19 March 2008 (UTC)

This sounds similar to the more serious problem of "new house smell". Carpets, paint, furniture, etc., all outgas fumes, some of which are toxic if they build up beyond a given concentration. This is more of a problem in recent constructions because they are designed to be more airtight. You'd think they would start to offer a service to air rugs and furniture out before they are installed, so as to allow the toxic fumes to exit. StuRat (talk) 04:10, 20 March 2008 (UTC)

New Solar Chip

I found an interesting article and forgot to bookmark it. Now I cannot find it again.

I was looking at a new type of photovoltaic device that converts sunlight directly to electricity using a photochemical nano-gate composed of niobium [columbium], gold and silver, interchangeably, on one side of the gate. There was a separate and different word to describe this type of PV cell in its own page, and I cannot remember the word.

I have tried every combination of "solar power energy photovoltaic [columbium niobium] gold silver" that I can think of in your search engine, and in Google's search engine with wiki as the first word, and I can not find the article again.

Please help me find that page again.

The above was posted to the Help Desk recently and responses have not been helpful. Does anyone have any info on the above described chip, now undergoing testing, that was described on a Wikipedia page? External links welcomed.

was it a gratzel cell? 131.111.100.44 (talk) 18:05, 19 March 2008 (UTC)

Gravity

I was just reading an article on howstuffworks.com and i though came to me, if all the gravity on earth magically disappeared, would everything float up, surely it would just stay put, coz there wouldn't be a force acting on it?Vagery (talk) 19:20, 19 March 2008 (UTC)

Not exactly. Objects would slowly move away from the Earth and slightly east as the Earth rotated away from them. Drawing a picture of the rotating Earth and the object on it may help. It isn't that the object accelerates up, it's that the Earth underneath accelerates away from the object. anonymous6494 19:27, 19 March 2008 (UTC)

Thats what i thought would happen... just checking, thnx alot manVagery (talk) 19:29, 19 March 2008 (UTC)

Um, a person at the equator is traveling with the Earth's rotation, at a rate of 40,000km (earth's circumference) per 24 hours (length of one rotation), or, if my quick math is right, about 360m/s. Initially, said person will appear to stay put, but will in reality start moving 360m/s in a straight line, as will the ground under his feet. It wouldn't take long for things to start spreading out at that speed. Naturally, the velocity will be lower for people not on the equator, but you can do the math for that yourself, multiplying that velocity by a trig function that gives you 1 for the equator and 0 for the poles. -SandyJax (talk) 19:58, 19 March 2008 (UTC)

Would the entire Earth fly apart? The plates of the crust aren't firmly stuck together, so there'd be nothing holding them down, right? And then the layers underneath are mostly solid only because of pressure, so once the layers above are gone, they'd become fluid again and spin off? Or would they cool down fast enough to remain solid? --Allen (talk) 20:38, 19 March 2008 (UTC)

If gravity disappeared only in a sphere equal to the size of Earth, then everything within that sphere would move in the same direction relative to the distant stars that it was moving at the instant that gravity disappeared, so yes, it would all fly apart pretty quickly. There would be no more reason to rotate and everything would move in straight (geodesic) lines instead. Electromagnetic forces would still keep stuff stuck together, i.e. rocks would still be rocks and magma would quickly solidify into rocks, all those rocks would continue in a straight line. That's how I see it anyway. Franamax (talk) 21:14, 19 March 2008 (UTC)

Clarify this, I didn't mean "instead" - everything is already moving along the geodesic, it just so happens that the Earth's mass shapes the local space-time continuum so that the "shortest path" is to spin around in a circle (the shortest path is actually to the centre, but that pesky ground keeps us from getting there). Removing gravity from the sphere around Earth means that the geodesic path is now determined by all the rest of the gravity in the universe, space-time is no longer warped right here, all the marbles will roll down other slopes. That's probably not clarifying anything! Franamax (talk) 22:19, 19 March 2008 (UTC)

Battleships in space

Years ago I read somewhere that steel retrieved from pre-1945 battleships was an essential component of satellites. The reason given was that all the steel smelted since 1945 (or shortly thereafter) was contaminated with radioactive elements from nuclear explosions to sufficient degree that it would affect the satellite instrumentation.

I'm not sure whether this was only for the Pioneer/Voyager probes and I'm not sure whether it was just one particular battleship, but I know I read it once and I've never been able to find a reference since. Can anyone help me out? Franamax (talk) 20:58, 19 March 2008 (UTC)

Operation Deadlight 83.100.183.180 (talk) 21:15, 19 March 2008 (UTC)

Wow, that was fast! Thank you Wikipedia, and thank you all the anonymous editors who help to build it, especially you 83.100. I believe it was the scuttled ships at Scapa Flow that I had read about. Next question: what radiation detectors is this steel used in? All of them? Where can I read up on this some more? And does anyone have a specific reference to satellites? I'm trying to build a killer trivia question here, or maybe even a Wikipedia article. Thanks. Franamax (talk) 21:38, 19 March 2008 (UTC)

Very old lead is also used. —Preceding unsigned comment added by 58.84.80.184 (talk) 21:59, 19 March 2008 (UTC)

I had heard that metal from ship wrecks was being used as casing for supercomputers because all metal was slightly radioactive just due to normal cosmic radiation that was only blocked by the deep seas, especially since some of the elements involved have half-lives of several decades. I think it's needed in supercomputers because they have trillions of bits of memory that make the slim chance that a high-speed particle will inadvertently flip one. Satellites have no protection from the atmosphere, so probably all of their delicate instruments/computer parts need this sort of protection. Quantumelfmage (talk) 20:21, 23 March 2008 (UTC)

Wow, sorry to hijack the question, but am I understanding this correctly? All steel produced since Hiroshima/Nagasaki is tainted with radioactive elements? The Operation Deadlight article isn't very clear, and I'm having a hard time believing it's true. What mechanism causes iron mined on, say, the other side of Japan to become contaminated? Thanks, Icthyos (talk) 11:03, 20 March 2008 (UTC)

I would guess (but have not been able to verify) that it is the oxygen blown through during the conversion process (see Linz-Donawitz process and Bessemer process) that has atmospheric contamination, not the ore. -- Q Chris (talk) 12:41, 20 March 2008 (UTC)

Yes, it is the air used smelting the iron and oxygen used in making the steel that introduces atmospheric contamination. Old steel can be hot-reworked so that no new air is incorporated. Incidentally, people born since 1945 can have their age determined (plus-minus a few years) by the radioactivity of their teeth. Franamax (talk) 17:12, 20 March 2008 (UTC)

It isn't just Hiroshima and Nagasaki—it's the other ~600 or so atmospheric tests as well that took place from 1946-1980 by various nations in the world. It'd be interesting to total up the cumulative megatonnage from the years of atmospheric testing, but it is well over 100MT. It would be wonderful if someone had data for background radiation levels over the 20th century, I'm sure it would be an interesting graph. --Captain Ref Desk (talk) 19:33, 20 March 2008 (UTC)

Nature Vol.437 p.433 15Sep05 Age written in teeth by nuclear tests Spalding et al has an interesting graph of atmospheric carbon-14 levels. I have a Nature subscription, see if you have access to the article here. There is some info on copyright licensing here which I don't understand, but I doubt it would be released under GFDL. The C14 ratio is stable until 1955 (when above-ground testing really got going), rises quickly to +20% by 1960, dipsy-doodles 'til '62, then skyrockets to +85% by 1965, exponential decay thereafter. We're down to approx. +8% now. Other radiation levels would likely look similar as it is diffusion out of the atmosphere that predominates over radioactive decay. Of course, a lot of the radioactive elements would still be in organic materials, water, teeth, etc. Franamax (talk) 20:00, 20 March 2008 (UTC)

PS There are little notches at 1972 and 1980 where further tests had been conducted. Franamax (talk) 20:04, 20 March 2008 (UTC)

That's not bad. Not quite as ideal as having the direct background radiation data, but still not bad. I looked at the supplementary data to see where their data source for the background C¹⁴ levels were from and found a few useful references... will see if there's data I can make a new graph out of. Supposedly all the data from that issue should be at this site but the site is current down. :-( --Captain Ref Desk (talk) 01:19, 21 March 2008 (UTC)

Actually, now that I look at it, I've seen these graphs before. We have one not too dissimilar even though it's only from the Southern Hemisphere. The data sets above are much more complete (judging from the articles in Radiocarbon) so maybe we can make a more exciting one in the near future. --Captain Ref Desk (talk) 01:24, 21 March 2008 (UTC)

Nice find on the Commons image! According to Greenpeace, 711 atmos or water tests, 438 Mt total atmos test yield, 4200 kg Pu atmospheric discharge(!!) - Greenpeace of course being a neutral source :) (though there's no reason to think they wouldn't be reliable on this).

I couldn't get at the Radiocarbon journal data, unless Jimbo wants to buy us those issues. I agree that total release of radionuclides and overall radio-persistence would be interesting. Now include decay products, organic persistence, half-lives - add in contaminated steel, dating of teeth, and one more persistent effect we could identify - we've got ourselves a new Wikipedia article: Persistent effects of atmospheric nuclear detonations. What's your diagnosis Doctor Strangelove? Franamax (talk) 02:01, 21 March 2008 (UTC)

Wiki Myth Busters...

So when you pull the ol' snap your friend in the butt with a towel prank, the snapping noise is caused by the end of the towel breaking the sound barrier. True or false? Beekone (talk) 21:09, 19 March 2008 (UTC)

Why wouldn't the snapping noise just come from part of the towel moving quickly? Mac Davis (talk) 21:50, 19 March 2008 (UTC)

According to Whipcracking, at least some whips create a cracking noise by breaking the sound barrier. Whether the towel works that way I don't know; it seems a lot shorter than most of the whips shown as being crackable in the article. --Allen (talk) 21:57, 19 March 2008 (UTC)

Straight Dope talks about it: http://www.straightdope.com/mailbag/mtowelsnap.html DMacks (talk) 22:05, 19 March 2008 (UTC)

Seems highly unlikely to me. You can 'snap' a towel (wet or dry) pretty slowly and still get a pleasing noise. The towel changing direction is large enough to compress a sufficient amount of air to create a fairly flat noise. And any ol' Joe can do it pretty much first time every time. The tip, or any other part of the towel, doesn't have to moving anywhere near the speed of sound for this to occur. This is different to cracking a whip where a long whip allows a small tip to achieve a very high speed, greater than the speed of sound, resulting in the loud crack, and it's rather more difficult for people to do without some practice. Move a whip slowly and it won't crack at all. Personally I'd say 'Busted', or at least 'Implausible'. --jjron (talk) 14:03, 21 March 2008 (UTC)

according to this site http://www.sciam.com/article.cfm?id=true-cause-of-whips-crack even classic whip crack is not caused by breaking sound barrier. Even though the speed of sound is surpassed --Urwald (talk) 18:22, 11 May 2008 (UTC)

medical terminology, not sure of spelling or existence

I was told to go to "fae" under frequent asked question. I'm trying to find out about physcadose. Possibly something to do with the liver. Is there such a word? I'm not sure of the spelling, can you help me?71.91.46.235 (talk) 22:20, 19 March 2008 (UTC)

Definitely not a word as you've written it, and no similar sounding word pops to mind. Where did you hear this word? - Nunh-huh 23:37, 19 March 2008 (UTC)

It's a bit of a stretch, but sarcoidosis? -- MacAddct  1984 ^{(talk • contribs)} 01:43, 20 March 2008 (UTC)

Turtle identification

I recently took photos (here is one of them) of a turtle on our pond that seems to be a Chicken Turtle (thanks to Joelr31 for pointing me in the right direction). I wanted to use a cropped version of the previously linked image in the chicken turtle article, but first I'd like to confirm the identification here. After looking at a bunch of pictures on the web, I'm not perfectly sure it is, in fact, a chicken turtle. As for geographic info, I live in upstate South Carolina, USA. I don't really have ideas of what else it could be, but some of the coloration/shell ridges of this turtle don't quite seem like the species, although there's probably room for variation. Are there any other species it could possibly be, or is it pretty obvious that it's a chicken turtle? Just wanted to make sure of this to hopefully prevent some misinformation here on Wikipedia. :) --JamieS93 23:41, 19 March 2008 (UTC)

Well, it could easily be the more common Painted Turtle, or something else entirely. The red coloration doesn't appear to be standard for a Chicken Turtle, and while his/her neck is long, it isn't as long as some pictures identified as chicken turtles. Personally I'd be hesitant, but I don't know a thing about turtles.--Captain Ref Desk (talk) 20:15, 21 March 2008 (UTC)

March 20

Capacitor-Batteries

Can capacitors be controlled to discharge at a near constant voltage using some electrical circuitry apparatus? In other words, I'm asking if a capacitor can be used as a battery, and how a circuit could be/is constructed to do this.

Thanks, 74.173.90.59 (talk) 00:28, 20 March 2008 (UTC) Sam

I think a capacitor that works like a battery is a battery. See battery capacity and discharging -- MacAddct  1984 ^{(talk • contribs)} 02:01, 20 March 2008 (UTC)

Ultracapacitors with carbon nanotubes covering plate surfaces to increase surface area may in the future replace common dry-cell batteries. Mac Davis (talk) 03:16, 20 March 2008 (UTC)

I think you two are totally missing the point of this question. The voltage of a battery falls off slowly as the remaining charge decreases, until the end when it falls off sharply; e.g. it could have half a charge but still 90% of the original voltage. The voltage of a capacitor, on the other hand, always falls off linearly with the remaining charge, because the energy is stored in the form of an electric field produced by separated charges. Sam here is asking whether it's possible to modify the charge-voltage relationship of a capacitor to seem more like that of a battery by using an electric circuit. I don't know the answer; I just wanted to clarify what the question is. —Keenan Pepper 05:02, 20 March 2008 (UTC)

You can use a DC-DC converter. It can take a non fixed voltage and convert it to a fixed output voltage. There will be a lower limit where the input will fail to be enough to drive the circuit. These can also be found in cameras and LED torches to extend the life of the battery. Graeme Bartlett (talk) 05:10, 20 March 2008 (UTC)

Tuberculosis

Just got back from the doctor who told me something that has left me in a bit of shock. In America where there are ample medications to treat TB vaccines are not given as in some parts of Europe, Asia and Africa where the reverse is the case. The reason is that once a person is immunized against TB they develop antibodies, the problem being that the test for TB is based on whether or not a person has the antibodies. In America people are not immunized so they can serve as indicators of an epidemic. Does this mean that in America as far as the government or health care system is concerned the it is better that the population serve as human Guinea pigs than to be immunized against a disease despite the fact that almost no one in America would be immunized against TB in the event of a major catastrophe like nuclear war, followed by bombardment with biological weapons? —Preceding unsigned comment added by 71.100.10.177 (talk • contribs)

According to the CDC, the "BCG vaccination is not generally recommended in the United States because of the low risk of infection with M. tuberculosis, the variable effectiveness of the BCG vaccine against pulmonary TB, and the vaccine’s interference with the ability to determine tuberculin reactivity."[7] table of contents. -- MacAddct  1984 ^{(talk • contribs)} 03:18, 20 March 2008 (UTC)

That would certainly confirm my doctor's comments and my fear regarding a situation where in the absence of vaccination contraction of the disease by a major portion of the US population would be too late to prevent. —Preceding unsigned comment added by 71.100.10.177 (talk • contribs)

I think basically the CDC has decided (and weighed the +/-) that the vaccine in adults is nowhere near effective enough and would just rather have doctors know if someone is infected or not. Otherwise we'd all have to get chest X-rays every year. Also there were only 646 reported deaths from TB in the US in 2005 out of 14,200+ people infected. I think a smallpox outbreak is something more more disconcerting. [8] -- MacAddct  1984 ^{(talk • contribs)} 05:13, 20 March 2008 (UTC)

Just to correct a statement by the original questioner, it's not a question of antibodies. Someone who has received BCG vaccine, or been exposed to tuberculosis, develops cellular immunity, which (rather than humoral immunity) is the mechanism responsible for positive PPD reactions. As to the other point, TB doesn't spread quickly enough to be an effective biological weapon. - Nunh-huh 06:37, 20 March 2008 (UTC)

Thanks for the clarification. However, in a situation unlike in Japan where there were intact resources surrounding the two bombings that would not be the case following a nuclear exchange today after which one might expect a combination of biological weapons meant both to kill and to exhaust resources. In other words TB might not be an effective killer but it might be one heck of a resources user along with a mired of similar lack luster bio weapons. America has been caught with its pants down before.

What can I say. The experts differ with your assessment. In a situation where healthcare resources are strained or absent, problems arising from sanitation, such as cholera and dysentery, and other diseases, they feel, are more likely to cause immediate problems than TB. The downside of BCG vaccine (ineffectiveness, and rendering tuberculin tests far less useful) are felt to outweigh the advantages (some level of immunity in part of the population). - Nunh-huh 08:37, 20 March 2008 (UTC)

United States civil defense has always been very weak. It tends to remind the voters how nasty these sorts of weapons are. --Sean 14:12, 20 March 2008 (UTC)

Worrying about whether TB would be a problem in the wake of a nuclear exchange seems, to me, to be akin to worrying about how the problem of racial prejudice would be affected after an impact event. Yes, we can dream up all sorts of mad scientist situations but if there isn't a good reason to believe them plausible (or the most effective way for anyone to get what they want) it's not worth the resources to worry about them, much less act upon those resources. There are far more effective agents for use as biological weapons than TB; if we are talking about an enemy that can start nuclear war (and would?), I'm sure they could do far worse. --Captain Ref Desk (talk) 16:57, 20 March 2008 (UTC)

LOL... You remind me of one of the reference desk librarians at our local library who likes to give her opinion whenever we consult her to find reference material and studies, such as a list of biological weapons following a nuclear attack in the order of significance of their expected impact. Alas, whenever we want reference material and studies we have learned to ask a different librarian.

Foxes in the UK

Isn't it strange that you can find foxes in Glasgow and London but not in Newcastle?Mr.K. (talk) 03:26, 20 March 2008 (UTC)

It would be strange. Do you have any references to this? -- Q Chris (talk) 12:20, 20 March 2008 (UTC)

Not more than personal opinion. Mr.K. (talk) 17:38, 20 March 2008 (UTC)

Mange perhaps? Some years ago I remember the foxes in Bristol almost died out from mange. I think outbreaks of mange remain localised.--80.176.225.249 (talk) 18:51, 20 March 2008 (UTC)

Maybe the upper class prefer to hunt in Newcastle? Nil Einne (talk) 12:06, 21 March 2008 (UTC)

sound transducer

how can i make a sound transducer by myself in home?actually i want to make a switch which can be turned on by the sound of clapping .

have a look at [9] or other links from a search for "clapper switch circuit", with which i found the given url. sorry no-one answered your simple request earlier. 153.1.253.5 (talk) 13:40, 20 March 2008 (UTC)

Quantum Mechanics: Orthogonality of Dirac Delta Function

The functions $u(x)$ and $v(x)$ are said to be orthogonal on interval $(\alpha _{1},\beta _{1})$ if their inner product is zero

$\int _{\alpha _{1}}^{\beta _{1}}u(x)v(x)\,dx=0$ (1)

For complex-valued functions or kets $f(x)=|f\rangle$ and $g(x)=|g\rangle$, they are said to be orthogonal on interval $(\alpha _{2},\beta _{2})$ when

$\langle f|g\rangle =\int _{\alpha _{2}}^{\beta _{2}}f^{*}(x)g(x)\,dx=0$ (2)

To continue my last discusstion, Quantum Mechanics: Entangled Wave Function, my question is how to prove the orthogonality of the Dirac delta function $\delta (x)$ mathematically? Or some related resource? Thanks! - Justin545 (talk) 08:53, 20 March 2008 (UTC)

This is really a maths question, but the way to prove it is to look at the definition. The dirac delta function is zero at all the places except for the argument. If you multiply this zero value by another dirac delta you, will get a zero, unless the arguments are the same, when it will be greater than zero. $\delta (t-x)\delta (t-y)=0$ if x not equal y. Graeme Bartlett. Another way to look at the dirac delta is that it is a sampling function, when you integrate its product with another function, it samples the other function at the argument to the dirac delta. (talk) 11:14, 20 March 2008 (UTC)

VHF/FM Radio Frequencies

The current commercial FM waveband is 88-108 MHz. However, I am trying to discover exactly when this spread came about.

I have a number of radio receivers, the dials on each differing significantly. One, an American set, covers 90-108Mhz. Two others, both British, cover 88-101 and 88-104 Mhz respectively. I have, however, been unable to ascertain when the full spectrum (88-108) came into use. Can anybody help?

Samilong (talk) 10:29, 20 March 2008 (UTC)samilong

Take a look at FM band, it does not answer your question, but shows even more alternatives. Graeme Bartlett (talk) 11:49, 20 March 2008 (UTC)

FM broadcasting in the USA looks like it covers more of the specifics, though it doesn't date the extension of the range from 106 MHz to 108 MHz. — Lomn 12:53, 20 March 2008 (UTC)

spin and (hyper)complex numbers -- why is the quanta of angular momentum 1/2

What is the connection between the intrinsic spin of quote-unquote elementary particles and the imaginary operator(s) defining complex numbers (and their further generalisations)? Intuitively, it seems they ought to be reasonably closely related, but this does not appear to be reflected in the "popular" literature. (One supposes that this intuitive sense could be ellaborated upon, if really necessary, but does not feel that it ought, as the connection is expected to be known, if not superficially evident.) 153.1.253.5 (talk) 13:53, 20 March 2008 (UTC)

I don't think there is any intrinsic connection.

One reason why spins are often defined as 1/2 or -1/2 is that the spin difference between the two states is one . 1. A nice simple number and ideal for quantisation. Quantisation means allowing a property to have only integer multiples of a value. Eg if energy can be 10,20,30,etc (and not 22.3, 35, or 44) Joules then that energy is said to be quantised. Quantisation can also refer to methods that treat non-quantised properties as being quantised for the purposes of simplicity (eg when contructing a model or theory)

Spin is assumed to be intrinsically quatised; why that is so is another question.83.100.183.180 (talk) 18:17, 20 March 2008 (UTC)

The reason imaginary operators/complex numbers were not used is simply that they were not needed to describe the situation. Negative number possess sufficient weirdness to do the job. Have a look at Quaternion for a 4d consistent system, (IMHO) Its only a matter of time before this is used to describe a physical processes. You might find this interesting from a quantum point of view Spin-statistics theorem. GameKeeper (talk) 21:34, 20 March 2008 (UTC)

Quaternions are used to represent rotations in 3D and 4D space - see Quaternions and spatial rotation. Indeed, part of William Rowan Hamilton's reasoning that lead to his discovery of quaternions was a search for a higher dimensional analogue of the way on which 2D rotations can be represented as multiplication by complex numbers with unit magnitude. Gandalf61 (talk) 10:46, 21 March 2008 (UTC)

Tapdancing gulls

We haven't had a gull themed question in a while so here goes. Some local species of gull tap their feet onto the ground. My guess is it's either some strange courtship ritual or perhaps a method to draw insects out of the ground (I only see them do this on grassy fields). What do you guys think? PvT (talk) 14:11, 20 March 2008 (UTC)

It makes worms come up. This answer says the sound annoys the worms, although I've heard other explanations that have it that the worms think the sound is rainfall and come up for a drinky. -- Finlay McWalter | Talk 14:18, 20 March 2008 (UTC)

I thought worms got all the moisture that they need from the ground and the only reason they come above ground when it rains is so that they don't drown. Dismas|^(talk) 15:06, 20 March 2008 (UTC)

Does it look a bit like they're doing an Irish jig? if so, yes - they're trying to get the worms to come to the surface. There's a good video of several different gulls 'rain dancing' here. I've often wondered how it is that the gulls know exactly where they need to 'dance' in order to bring up a worm. There definitely seems to be an element of skill to it - they'll wander back and forth with their heads cocked, trying to find just the right spot. Are gulls' ears sensitive enough to hear the worms moving beneath the surface? Maybe they're just looking for fresh worm casts (I personally wouldn't put it beyond a gull's intelligence to know what a worm cast is...)? --Kurt Shaped Box (talk) 18:46, 20 March 2008 (UTC)

I'd expect that any decent soil (as opposed to sand, clay, or rock) would contain worms, since they are common enough that I don't see a need to search for individual worms. I now have the urge to sneak up on a sleeping gull and glue on a pair of tap shoes, to make the dance even more entertaining. StuRat (talk) 19:12, 20 March 2008 (UTC)

If you think watching gulls do it is entertaining, try watching flamingos. Daniel (‽) 20:33, 20 March 2008 (UTC)

It's even funnier to see a young gull (it's always the recently-fledged ones I've seen doing it) determinedly dancing for worms on concrete or tarmac. I even saw one doing it on a flat rooftop once. Not *quite* as funny as seeing a woodpecker attempting to drill a steel lamppost - but still... ;) --Kurt Shaped Box (talk) 21:15, 20 March 2008 (UTC)

Thanks for the answer guys. I'm wondering though. How do gulls learn this behaviour? Is it instinctive? Is the dance itself instinctive? Obviously they don't know by themselves that their trick won't work on solid surfaces, there's some trial and error involved. This would be an interesting research project. Sure beats finding out how far penguins can poop...PvT (talk) 11:09, 21 March 2008 (UTC)

I doubt if it's 100% instinctive. At best it's probably like kittens, which know to scratch the ground after they urinate or defecate, but need to be shown by mom to put that action to good use to bury what they've produced (so as to hide their scent). StuRat (talk) 21:19, 22 March 2008 (UTC)

Ever see a gull soaking a piece of bread, a biscuit, a crisp or similar in water (swishing it back and forth) in order to soften it up before swallowing? That's never stuck me as a behaviour that has any business being hard-wired. --Kurt Shaped Box (talk) 13:14, 23 March 2008 (UTC)

What the gulls are doing is something like (or actually is) worm charming and it's likely passed on down the generations carefully from gull to gull so that this skill won't die out. Julia Rossi (talk) 11:52, 21 March 2008 (UTC)

That other famous gull hunting skill, namely cracking open bivalves and crustaceans by flying up and dropping them onto a hard surface is (IIRC - no source to hand, sorry) learned by young gulls from observing their parents/older members of the flock then perfected through trial and error. I'd imagine that it's a similar thing with the worm-charming. Gulls have a long childhood/adolescence - going from meek, timid, dopey and needy to the precise opposite of all those things in four years or so. They learn and grow as individuals. --Kurt Shaped Box (talk) 20:38, 21 March 2008 (UTC)

Hallucinations making everything appear very big or very small

I'm vagually sure I remember reading about this phenomenon (see subject line) a while ago, but I can't find any references to it now. Is this a recognized type of hallucination? Is there a word for it? How common is it? --86.135.178.19 (talk) 20:40, 20 March 2008 (UTC)

Micropsia or macropsia, depending. - Nunh-huh 01:35, 21 March 2008 (UTC)

Radioactive decay

How half-life work on individual atoms? If I have 8 atoms of substance X, which has a half life of 5s, then after 5s, I obviously have 4 atoms of X, plus whatever it decayed into and some radiation, right? So what if I have 1 atom of X? Is there a 50% chance that it will decay after 5s? If so, is that true for each atom in my 8 atom sample, i.e. that after 5s, there is a remote possibility that all of the atoms will have decayed, or that none of them will have? I'm very confused. 72.155.207.33 (talk) 22:31, 20 March 2008 (UTC)

Half-life, especially as it relates to radioactive decay describes a statistical probability for a "large" sample. The two articles I linked have more information about what "really " happens, especially for small collections of decaying particles. DMacks (talk) 22:54, 20 March 2008 (UTC)

To answer the specific example, your last statement is correct. With x atoms after one half-life, the most likely number of atoms remaining is x/2, though any number from 0 to x is possible. Additionally, in virtually all cases, x/2 is not probable -- that is, the odds are usually better than 50/50 that there are not x/2 atoms remaining. The various probabilities can be expressed via the combination function. — Lomn 23:51, 20 March 2008 (UTC)

So what determines what amount decays? 72.155.207.33 (talk) 04:52, 21 March 2008 (UTC)

Pure chance, as far as we understand it. Every atom has a 50% chance of decaying within one half life. That means that the probability for k out of n atoms decaying within one half life is ${\tbinom {n}{k}}\cdot 0.5^{n}$. If you are unfamiliar with this mathematical notation, see Binomial coefficient. The expectancy is n/2, the standard deviation is $0.5\cdot {\sqrt {n}}$. With 8 atoms, the standard deviation is thus about 1.4. The individual probabilities are:

0 atoms will decay: 1/256

1: 8/256

2: 28/256

3: 56/256

4: 70/256

5: 56/256

6: 28/256

7: 8/256

8: 1/256

Icek (talk) 06:45, 21 March 2008 (UTC)

Note also that for radioactive decay, you are in the "spooky" "God ... play[s] dice with the universe" world of quantum mechanics, where you pretty much have to leave your intuition at the door. (In actuality, with one radioactive atom you can have the situation where it is both decayed and not decayed simultaneously. Just ask Schrödinger's cat.) -- 128.104.112.85 (talk) 00:49, 22 March 2008 (UTC)

Wow, that's weird! Thank's for the link. Is this actual science, or is it an If a tree falls in a forest and no one is there to hear it sort of philosophical thing? 72.155.207.33 (talk) 01:01, 22 March 2008 (UTC)

That quantum mechanics is generally not as simple as "if no one hears the tree falling" can be seen by Bell's theorem for entangled particles. Icek (talk) 07:08, 22 March 2008 (UTC)

scientific name

what is the scientific name for fucking the shit out of someone excuse my french (yes i mean sexually)

Coitus (wiktionary) is a commonly-accepted term. — Lomn 23:52, 20 March 2008 (UTC)

Anal sex might fit the questioner's term more closely. Edison (talk) 23:55, 20 March 2008 (UTC)

There is no scientific term for unusually hard sex, if that's what you're asking. Mac Davis (talk) 00:10, 21 March 2008 (UTC)

But hey, let's make one up! How about Coitus maximus? (Someone who knows Latin could probably do better)--Captain Ref Desk (talk) 01:07, 21 March 2008 (UTC)

How about Spanish instead ? "cópula hasta muerte". StuRat (talk) 02:05, 21 March 2008 (UTC)

"Coger hasta que no haya mierde en el cuerpo" (only in latin america)

Where do I nominate questions for "best of the ref desks"? HYENASTE 16:31, 24 March 2008 (UTC)

March 21

Free falling human body

Let's say that a person is very high up in a building (the 100th floor, 200th floor, whatever). And he falls / jumps / is pushed out of the window and falls to the ground. (No parachute, no nothing.) I have heard that the human body would be dead before it hits the ground. Is that possibly true? In other words, would you die while in mid-air (and of what, exactly?) or does the impact at the ground kill you? When people were falling / jumping from the Twin Towers on 9/11, I remember people saying that they would have been dead before hitting the ground. Shock? Heart attack? Pressure/force of gravity? So, what's the deal with all this? Thanks. (Joseph A. Spadaro (talk) 07:12, 21 March 2008 (UTC))

This idea is a myth, based on poor scientific knowledge and limited reasoning powers, possibly propagated to help the victims' relatives deal with the loss more comfortably. There are many instances of people falling from great heights, for example from flying planes, and surviving.[10] There is also a worldwide sport of deliberate freefalling from planes at high altitude, the participants seem to be able to survive this experience with renewed vigour and an urge to repeat the process. Like the old saying goes 'It ain't the fall that kills ya, it's the stop at the end that does it'Richard Avery (talk) 08:24, 21 March 2008 (UTC)

BTW, according to this [11] (not the best source but I'm sure someone here could calculate it, heck I probably could but I'm lazy) terminal velocity will usually be achieved from a 96 floor jump. Anything higher is therefore irrelevant except it takes you longer to hit the ground. Indeed the terminal velocity article raises another important point. The people who jump off high buildings probably don't even go anywhere nearly as fast as free fall divers since free fall skydivers optimise their body position and clothing to reduce air friction i.e. increase their terminal velocity. People jumping off buildings don't, they may not even have the time to do so that well. Nil Einne (talk) 12:01, 21 March 2008 (UTC)

...free fall skydivers optimise their body position and clothing to reduce air friction i.e. increase their terminal velocity.

Are you sure about that? I thought the standard skydiving position (back arched, pelvis thrust forward) was designed to keep you facing down instead of up at the sky. If you wanted to fall faster, I think you would do it by either curling into a ball and falling buttocks-first, or maybe pointing your arms above your head and falling hands-first. The pelvis-first position doesn't seem particularly optimized for speed. —Keenan Pepper 15:48, 21 March 2008 (UTC)

Like Einstein's Brain, they saved Kittinger's Testicles.

Indeed. This fascinating source says that terminal velocity in normal skydiving position is about 125 mph, but adopting a "balled up" position increases this to about 200 mph. The free fall speed record without special equipment is 321 mph, and Joseph Kittinger reached speeds of over 600 mph in his record-breaking parachute descent in Project Excelsior. Gandalf61 (talk) 16:53, 21 March 2008 (UTC)

A person with a weak heart can, of course, have a heart attack while in suspense about the immediately outcome of hitting the ground. Gravitational acceleration is unlikely to kill because it must be less than one g, half the force delivered on some roller coasters. As for air pressure, at terminal velocity, the force applied by the air is equal to the force applied by gravity; that's why the velocity remains constant. An adult human weighs approximately 75 kg and has a cross-section of about 30 cm x 170 cm, so that's 15 g/cm^2 of pressure. Decidedly not a lot. A person diving head-down would experience 330 g/cm^2 of air pressure, with the reasonable assumption that the head's cross-section is 15 cm x 15 cm and the unreasonable assumption that all air resistance is provided by the head. 330 g/cm^2 is a lot, yes, but I don't think it's enough to kill.

Note that g is a measure of mass, not force or weight, so expressing pressure as g/cm^2 is technically incorrect. I did it to make visualizing the pressures easier. --Bowlhover (talk) 18:16, 21 March 2008 (UTC)

So, basically ... you are alive up until the very moment of impact? And what exactly causes the death at that point? Thanks. (Joseph A. Spadaro (talk) 05:25, 22 March 2008 (UTC))

The Project Excelsior article notes that the reason for Kittinger's high-altitude test jumps was that Air Force scientists were worried that after an ejection at high altitude, a pilot might go into a rapidly rotating fall, at speeds of up to 200 rpm, which could be fatal (I guess they observed this with test dummies) I don't konw if that is a real concern for a person, but that is one potential way in which a person might die before he or she hit the ground. --Bmk (talk) 07:34, 22 March 2008 (UTC)

Bmk - I am confused by your post. What is the potential way? Someone rotating very rapidly at 200+ rpm would (might) die from the rapid rotation itself, you're saying? Thanks. (Joseph A. Spadaro (talk) 21:14, 22 March 2008 (UTC))

Joseph, are you serious? You can take your choice depending on which part of the body hits the ground first. Perhaps a crushed skull with subsequent brain trauma? ruptured heart and major blood vessels? Broken neck and severing of spinal cord? Landing feet first can thrust the femurs up into the chest cavity with consequent damage to the cardiovascular system. I'm sure there are several other serious trauma scenarios that ultimately cause death. Richard Avery (talk) 07:34, 22 March 2008 (UTC)

Yes, I'm quite serious. Why are you suggesting otherwise? Perhaps the question may be worded better. I will assume that the doctor would write _____ on the death certificate. Blunt force trauma? Or what? And is there really any way at all for a doctor to know what killed the person, or would that be impossible to tell ... (i.e., in the resulting carnage, it would be possible / impossible to know which body part actually caused the death?) ...? Thanks. (Joseph A. Spadaro (talk) 21:18, 22 March 2008 (UTC))

For a penny, I once read that throughing a penny off the Empire State Building, it will reach its maximum speed already by falling 500 feet. By the way, Jet Li in a movie once jumped off a building several stories. It looked 5 or 6 stories. He probably jumped the safest and best way possibe. For 1 thing, he didn't fall standing vertically, but horizontally. 2ndly, he was swinging his arms, like in a specific pattern, probably to fight wind resistance. 3rd, he was breathing hardly, probably to fight against wind. And then, he landed on a soft mat. Truly amazing, I thought. Neal (talk) 20:49, 22 March 2008 (UTC).

amplifier

why amplifier have high input resistanceNippun makkar (talk) 07:34, 21 March 2008 (UTC)

Well, the full answer is that they do not always have a high input impedance. Those that do are designed that way so that the input voltage is not dropped by the input resistance of the amplifier. For instance, if the input impedance was equal to the impedance of the source voltage then the voltage at the amplifier input terminals would be exactly half the sources unloaded voltage. But surprisingly, this might be desirable in some cases. To avoid signal reflection at the input, the amplifier input impedance needs to match the source as closely as possible. In RF applications, amplifiers are often designed in the common base configuration as this results in an input impedance close to the 50Ω characteristic impedance commonly used for RF transmission lines. It can also be desirable to have an input impedance of less than infinity for noise reduction reasons. For the kind of audio frequency amps you are probably referring to, where high input and low output impedances are required, then common emitter is the configuration to use for signal level amps or some kind of push-pull arrangement for power stages. SpinningSpark 09:55, 21 March 2008 (UTC)

Specific Heat Capacity

In an experiment to find the specific heat capacity of a metal, it is found that 5200 J is needed to raise the temperature of a 2 kg block by 20 oC. How to find the specific heat capacity?

Have you looked at our specific heat article. From that you will see that specific heat is measured in joules per kg per $^{o}C$. Do you see how to calculate it now? SpinningSpark 09:35, 21 March 2008 (UTC)

Heat capacity is Joules per kgram per degree C.

So you need to work out how many joules to raise a block of 1kg the temperaure 1 degree C

eg if it take 100 J to raise the block 3C then in takes 100/3 J to raise it one.

Can you take it from there. (ask again if you get stuck)87.102.16.238 (talk) 12:02, 21 March 2008 (UTC)

Modeling Friction

Friction is usually modeled by a constant multiplied by a normal force. This is the model used in the friction article, and the one they taught me in high-school physics. It is quite clearly wrong. We all know there's a reason drag racers have big wheels, but with that model of friction it makes no difference. In my robotics class, we once made "robots" go up a slope. They held better when more weight was added. It should be the same. Is it just too complex to make a better model? — DanielLC 16:50, 21 March 2008 (UTC)

Well, for drag racers, the large rear wheels aren't to add weight but to increase surface area and give enough thickness to allow some of the rubber to melt, increasing friction further. This is why you see other auto racers weaving back in forth to melt their tires. -- MacAddct  1984 ^{(talk • contribs)} 17:06, 21 March 2008 (UTC)

There's some discussion of the less-than-ideal nature of friction and the ideas taught in school here. I would suspect that there are so many variables, an overall model is too complex for most uses, but you could probably create a good, useful model for any particular recurrent situation. So you could probably create a useful model for your robots, assuming you don't vary much between trials, but that model probably wouldn't hold for other situations. But I am not a friction expert :) Skittle (talk) 17:14, 21 March 2008 (UTC)

To give credit where it is due to WP, our coefficient of friction article does say that the COF is a system property, rather than a property of the pure materials. As Skittle says, once you have set up your system and chosen the right value of μ, then the simple linear equation is a reasonably good approximation. If you start adding weights and deforming your tyres or creating adhesion, then the equation will cease to apply. That doesn't make it "wrong". --Heron (talk) 10:29, 22 March 2008 (UTC)

universe

is there an end to the universe? either way how do you know. — Preceding unsigned comment added by 72.155.39.82 (talk • contribs)

Current theory says yes, and it is ever expanding. See observable universe -- MacAddct  1984 ^{(talk • contribs)} 17:14, 21 March 2008 (UTC)

Another answer would be to say, no, there is no end to the universe, but it is "closed" - if you and a buddy head off in exactly opposite directions, you'll eventually meet up again. From Nature journal: "If the Universe is closed, and has a small enough diameter, we may be able to see right round it because photons can traverse the whole Universe" and "The WMAP data ... suggest that we might indeed live in such a small closed universe". Of course, I'm not all that good at reading this stuff :) Franamax (talk) 20:54, 21 March 2008 (UTC)

Boomerang returns in space. Make 'splain that one now!

There have been some posts floating about socialbookmarksville relating to a japanese cosmologist's demonstration that a boomerang returns in space. Unfortunately, however, the articles have all been rather sparse on content, and one is at a loss to find any discussion on the matter. The obvious question that arises is: what's goin' on there, then? From my admittedly limited memory, all explanations of boomerang dynamics have involved recount to aerodynamics of the 'leading edge is moving faster through the atmosphere, and so generates more lift' ilk. Having always been rather dubious of the canonical explanations of "wot makes dem aerofoils werk" (planes fly upside down you know, if WWI movies have taught me anything), ones interest is perked as to what possible mechanisms might be put forward for this interesting result. Chards of regards, 83.102.28.140 (talk) 18:30, 21 March 2008 (UTC)

I see no reason why a boomerang would work in space. Boomerangs work by use of an airfoil and lift both of which wouldn't work in a vacuum. Otherwise our spaceships could take off and fly around with wings. -- MacAddct  1984 ^{(talk • contribs)} 18:42, 21 March 2008 (UTC)

Japanese astronaut Takao Doi did not throw the boomerang in space as such. He threw it inside the pressurised International Space Station and thus had all the benefits of aerodynamics to assist its flight. SpinningSpark 18:48, 21 March 2008 (UTC)

Ah, that makes more sense. No gravity, but there is an atmosphere. -- MacAddct  1984 ^{(talk • contribs)} 18:53, 21 March 2008 (UTC)

I would question the wisdom, though, of deploying a hunting weapon on board a spaceship. SpinningSpark 19:48, 21 March 2008 (UTC)

Most commercially available boomerangs aren't useful as hunting weapons. Making them reliably aerodynamic, so they come back, destroys their ability to deal any significant amount of damage. Hunting boomerangs I've seen usually have one end blunted and weighted, making them fly straight and hit hard. A proper throw can make them curve through the air, which probably led to experimentation in design and the more modern-looking boomerang. -- Kesh (talk) 00:32, 22 March 2008 (UTC)

Thinking about it, what would be the point in the first place of having a throwing weapon that returns to the user - if it's only going to be used for hunting animals (I suppose that such a device might have its uses on the battlefield)? If you throw and miss, your prey has more than likely seen your attempt and decided to bolt - whilst you stand there waiting for the thing to come back. It would make far more sense to carry a few 'one way' boomerangs and whang them one after the other in the path of your quarry's flight in rapid succession. --Kurt Shaped Box (talk) 00:52, 22 March 2008 (UTC)

There were two reasons why this was important, both stemming from weapons being expensive (in terms of time invested in making them) back when they were hand-made. Thus, you might not have very many, so didn't want to lose or damage them by having them land who-knows-where. Also, it would take quite a bit of time to track down thrown weapons even if they could be retrieved intact. This is time that could be better spent hunting. StuRat (talk) 03:33, 22 March 2008 (UTC)

Wouldn't the stray hydrogen atoms in the vacuum of space *eventually* have an effect on the boomerang's flight? --Kurt Shaped Box (talk) 20:59, 21 March 2008 (UTC)

I would expect stray rocks and the gravity of large objects to have an effect first. -- kainaw™ 21:11, 21 March 2008 (UTC)

Darn, boring old reality strikes again. 83.102.28.140 (talk) 03:34, 22 March 2008 (UTC) (OP)

No reason to let boring reality get in the way of answering an interesting question. This gives the vacuum pressure of space as 10 pPa. That is a factor 10¹⁶ lower than earth sea-level. Lets say a typical boomerang throw on earth is aimed at a target a distance of 50 feet away and the boomerang travels in a circular path. Distance travelled by the boomerang to return is 300 feet (pi is 3 in my universe). The same throw in space will have 10¹⁶ less "lift" in the direction of curve and consequently the circumference of the curved path is 3 x 10¹⁸ feet or 10¹⁸ metres (there are 3 feet to the metre in my universe). If you threw the boomerang at a velocity of 20 m/s it will return to you in about 88 million years if you manage to miss all the kangaroos and other significant objects in the universe. SpinningSpark 09:47, 22 March 2008 (UTC)

More of an unrelated history answer but..as stated above most boomerangs were the non returning kind that would be used for hunting (mainly) kangaroos and wallabies. The returning kind would be thrown over a flock of birds on a body of water, with the intent (I think) of getting the birds to get scared and fly over the ground where other boomerangs can be thrown at them.--Shniken1 (talk) 12:20, 22 March 2008 (UTC)

Metric expansion of space

Probably a FAQ but couldn't find what I am looking for!

The metric expansion of space over time is clearly not equivalent to applying an enlargement transformation to all the objects in the universe by a certain scale factor. For example, it doesn't "stretch" the solar system, or pull galaxies apart, or on a smaller scale, tear apart the atoms in molecules (a context where the primary force is not gravitational). However, the distance between distant galaxies does increase.

The intuitive explanation of why in the examples I gave where the distance does not actually increase, is that they were being held together by forces that prevented separation. Distant galaxies are not bound in the same way. Is this intuitive explanation reasonable? Or is it a mistake to view changes to the metric as in some way analogous to the application of a force? IBangMyHead (talk) 19:20, 21 March 2008 (UTC)

On a small scale, whatever the metric of the universe as a whole, space is Euclidean to all intents and purposes. Atoms remain the same size despite the expanding space. Things made out of atoms, like trucks for instance, also remain the same size. Distances between galaxies however are increasing. Think of pieces of broken ice moving apart on an expanding ocean. The ocean is expanding, the distance between the pieces of ice is increasing, but nothing much happens to each individual iceberg. SpinningSpark 19:41, 21 March 2008 (UTC)

Yes - but my question is why clusters of matter that make up the icebergs (stay pretty coherent) behave in a different way to the clusters of icebergs (which spread out). A criticism of the "rubber sheet" analogy is that if you did paint a little picture of the solar system on the sheet as you stretched it, the planets would spread out (and indeed, the planets themselves would enlarge!).

Is it because at a local level, the effects of metric expansion are effectively impossible to observe (the icebergs do expand, but it's harder to observe any change in the icebergs compared to the distances between distant icebergs which clearly grow) or is it because forces that hold the icebergs together counteract the inflationary pressure? IBangMyHead (talk) 19:48, 21 March 2008 (UTC)

User:BenRG is usually good for these kinds of question but he does not seem to have been active on the Reference Desk for a few days. SpinningSpark 19:53, 21 March 2008 (UTC)

As I understand it, it has to do with the different distances on which the forces operate most effectively. Gravity is very weak on small scales compared to electromagnetic forces. Metric expansion of space is only going to be very noticeable on massive scales; on smaller scales, the more locally powerful forces are going to reign supreme. The structure of atoms themselves are regulated by nuclear force, which metric expansion of space couldn't affect even if it wanted to, and the structural integrity of molecules is going to preserved by the electromagetic force. Does that explain things? Different forces are powerful on different scales, and that's why something that can move entire galaxies is not going to affect things within those galaxies. --Captain Ref Desk (talk) 20:04, 21 March 2008 (UTC)

1. If the answer is to do with the big bang 'throwing out matter spherically' then one would expect a universe that has the galaxies concentrated at the edge.

2. Another answer could be that the theory is simply inconsistent.

3. Another answer would be that everything should be explanding equally but the forces between 'bonded' matter (ie the icebergs) stops them doing so (as you say). ie/eg gravity affects the expansion - regions with more gravity expand less. ie the gravity forces between galaxys is very weak.

3a. Think in terms of weak springs and strong springs holding everything together - the strong springs are under tension but do not expand much eg molecules/icebergs. The weak springs are under tension but stretch lots - hence galaxies are far apart - In this case it helps if you assume that the expansion of space is accelerating.87.102.16.238 (talk) 20:14, 21 March 2008 (UTC)

3a (sub) You don't need to throw away standard euclidean space in 3a. This model works using simple concepts such as spring constant - which can be directly related to electromagnetic and gravitational forces. The only requirement for success is that the lengths are increasing and the rate of increase is increasing eg the metric is accelerating as it increases in length eg L=lenght dL/dt>0 AND d²L/dt²>0. I can't emphasise this enough!

[edit conflict] You may be right, Captain, based on this, but if so I don't understand why, because metric expansion isn't a force. (Is it?) And excellent question, IBangMyHead. --Allen (talk) 20:21, 21 March 2008 (UTC)

Yes - metric expansion can cause a force - see above comment 3a, 3a(sub) - that would go some way to explaining things - no idea if that is really true.87.102.16.238 (talk) 20:23, 21 March 2008 (UTC)

It looks like the simplest explanation for this phenonama would be that all things in the universe experience an additional force (additional to the ones you know eg gravity,electro ) that is universally repulsive. Only strongly bonded things can resist this force. What is the name if this force?87.102.16.238 (talk) 20:43, 21 March 2008 (UTC)

There's no reason to think it's not a force just because nobody else has stated it is or isn't - it acts like a force therefor it is a _____.87.102.16.238 (talk) 20:45, 21 March 2008 (UTC)

Here is some perfectly relevant discussion from Argonne National Lab, inspired by our own article. Apparently even (non-cosmologist) physicists can be confused by this question. --Allen (talk) 21:14, 21 March 2008 (UTC)

And Michael Pierce seems to agree with you, 87, although he doesn't name the force resulting from expansion. --Allen (talk) 21:20, 21 March 2008 (UTC)

It's interesting that both my question and the one raised on the Argonne Lab page were inspired by the same Wikipedia article, and by the comparison of the "raisin" and "rubber" models in particular. Captain Ref Desk's point that "The structure of atoms themselves are regulated by nuclear force, which metric expansion of space couldn't affect even if it wanted to, and the structural integrity of molecules is going to preserved by the electromagetic force" is one that I had alluded to in my question - one of the things that had caused me to ask the question was that I had in fact considered this, and on thinking about it, it seemed that the internal structure of a basic molecules could be computed (e.g. internal distances for a stable molecule) so any separation caused by inflationary pressure would end up being reversed by the internal forces anyway (and in practice the "spring" would not expand and then contract - merely resist) but this seemed to suggest the idea itself that there is an internal "reactive force" counteracting an "inflationary force" - the fact that distant galaxies have no equivalent possibility for a "reactive force" could then explain why they were affected by the inflation. But as I couldn't find anything written about this force - or at least analogy to a force - I came to the refdesk. In particular I'm not sure just how sound the analogy (or literal truth of inflationary "forcehood") is, and what consequences it has. For example, if you view it as a force, does it mean that the "springs" of atomic bonds are somehow in (very slightly) more "tension" as a result? And if it is a force, then does this have any energy implications (not all forces have an energy associated with them, but some obviously do)?

One thing that was maybe too subtle for both me and Captain Ref Desk is the comment in the Argonne link that "If everything (and I mean everything) were changing with time, such that the universe, the yard-stick, and the relative force strengths (the coupling strength) were all changing in the same way and proportionally, then there would be no way to measure such a change" which is rather insightful. You obviously can't make the universe twice as big in any meaningful way by getting ISO to define "1 new metre = 2 old metres" because, for example, formulae for gravitational attraction would simply change from F_old = GMm/r² (r measured in "old metres") to F_new = GMm/R² (R measured in "new metres" so R = 2r; the two forces would actually have different but convertible units) and there would be no observable difference. (Mental note: when metric conversion finally happens, switching from yards to metres will not increase the size of the universe by around 10% and my waist will not be 10% larger...) When we say "the metric changes" we obviously don't mean it in this naive way. Stretching my intuitive understanding a little bit, is a reason that we might look at inflationary pressure as a force, that the formulae for e.g. inverse square attraction/repulsion somehow don't change their distances, but the distances themselves should change - and if the distance doesn't change, it is apparently because a reactive force has constrained it from doing so? 87.113.64.15 (talk) 22:11, 21 March 2008 (UTC)

Note to 87.113 - by the time the USA finally switches to the metric system, I pretty much guarantee that your waist -will- be 10% larger :) Franamax (talk) 00:55, 22 March 2008 (UTC)

There is nothing pushing the galaxies apart (ignoring for the moment the cosmological constant, about which more later). The galaxies are moving apart because of inertia. They were moving apart in the past, and nothing has stopped them—gravity has only slowed them down a bit, and the other forces don't operate between galaxies at all. The galaxies have been moving apart since they formed, because they condensed from matter that was moving apart, and they acquired the average velocity of that matter. But they did condense; that means that local gravitation overcame the initial separating velocities, just like the gravity between the earth and an upward-thrown ball overcomes their initial separation velocity. Once the initial separation has stopped, that's that. There's nothing trying to make the ball fly away from the earth again, it just happened to be flying away to begin with in the unexplained initial conditions of the problem.

Aside from making galaxies and clusters condense out of the primordial Hubble flow, gravity also makes the Hubble expansion as a whole slow down. Absent a cosmological constant, the recession speed of a typical pair of galaxies can only decrease with time. But the more they recede from each other the weaker the attraction between them becomes. If the matter density of the universe is high enough (above the critical density), then the attraction wins out and the universe recollapses (i.e. the ball falls back to earth). If it's not high enough then the galaxies disperse too fast for gravity to pull them back together (i.e. the ball exceeded the escape velocity). In the latter case the recession velocities approach a limiting value and the galaxies simply recede linearly away from each other forever, with essentially no further gravitational interaction since they're so far apart.

Okay, now add a cosmological constant to this. Probably the best way to think of the cosmological constant is as a correction to the gravitational force. Along with an attraction proportional to m/r², you also have a repulsion proportional to r. At small separations the attaction wins out; at larger separations the attraction decreases and the repulsion increases until eventually there's a crossover point and the repulsion dominates. With regard to the overall motion of the universe the situation is not much different from before; there's still a critical density below which the attraction wins and above which it doesn't, except that now if the attraction doesn't win, the far future motion is exponential instead of linear (because the solution to the differential equation $r''\propto r$ is exponential). But again this only affects large clusters of matter which are still moving in the aggregate with the Hubble flow. For things which have condensed out of the Hubble flow, like our galaxy, the short-range attractive force dominates to such an extent that you can't even detect the repulsive term with the most delicate experiments. About the only visible consequence of the runaway separation is that you lose sight of other galaxies (and the CMBR). This eventually happens even without the cosmological constant, but it takes a lot longer. Other than that, life continues as normal until heat death (sorry, I know it's a downer). One caveat is that it's not clear yet whether the dark energy actually behaves like a cosmological constant. If it doesn't, there are other scenarios like the big rip. -- BenRG (talk) 00:19, 22 March 2008 (UTC)

Excellent answer, BenRG; thank you. But it leaves me confused about where "metric expansion" fits into the picture. I had the impression that for most of the 20th century, metric expansion was accepted based on Hubble's observations, but that the cosmological constant was rejected until the 1990s. So metric expansion != cosmological constant, therefore your first two paragraphs must be dealing with metric expansion. But you make it sound like a simple matter of galaxies flying apart in a Newtonian sort of way, whereas metric expansion is supposed to be spookier than that, as in space itself expanding... whoa! Is there a straightforward way to relieve some of my confusion? (I'm mindful that if one keeps asking physics people seemingly logical cosmological questions, one will eventually be told, "Sorry, beyond this point there's no substitute for learning the math.") --Allen (talk) 01:14, 22 March 2008 (UTC)

I think some confusion here arises from thinking of space and time as a static stage on which objects such as galaxies are placed. In general relativity, space-time is shaped by matter and energy, so it is not a static backdrop. Most distributions of matter and energy give rise to very complex space-time configurations. However, if we assume a particularly simple case in which the distribution of matter and energy is both homogeneous and isotropic, the equations of general relativity can be solved, resulting in the Friedmann equations. These say that the metric or scale of space (as determined by a yardstick based on the wavelength of light) is changing over time in a way that is determined by just three numbers - the average density of matter and energy; the average curvature of space and a cosmological constant. Depending on the values of these parameters, the space-time metric may expand forever, or may go through an initial expansion followed by a subsequent collapse.

The assumptions of homogeneity and isotropy on which the Friedmann equations are based are only correct on very large scales. Within our solar system, and even within a single galaxy, the distribution of matter is far from homogeneous, and the Friedmann equations do not apply. However, if we observe distant galaxies then we reach a scale at which the universe is approximately homogeneous and isotropic. Light from these galaxies is red-shifted by an amount that is proportional to their distance - this observational law is called Hubble's law. This redshift is a result of the metric expansion predicted by the Friedmann equations. We don't observe this metric expansion when looking at nearer objects (i.e. anything in our solar system or our galaxy or nearby galaxies) because the Friedmann equations do not apply at smaller scales.

We can measure the constant of proportionality between red-shift and distance, which is called the Hubble parameter. We can estimate the average density of matter and energy in the universe. And the age of the universe means that the average curvature of space must be very close to 0. These facts are all consistent with a version of the Friedmann equations in which the metric is expanding, but the cosmological constant is 0. So, yes, the expansion of the space-time metric can happen even without a cosmological constant, and cosmologists originally left the cosmological constant out of their models because there was no good reason to complicate matters by including it. However, by observing distant galaxies very carefully we can tell how the Hubble parameter has changed over time, and recent observations show that the expansion of the metric is actually accelerating. This is not consistent with a cosmological constant of 0. So the most-favoured current model of the large-scale evolution of the universe, the Lambda-CDM model, has a non-zero value for the cosmological constant. Gandalf61 (talk) 13:07, 23 March 2008 (UTC)

The expansion is just galaxies flying apart. But it's not entirely wrong to say that space is expanding, because in the case of perfect isotropy and homogeneity the matter pretty much is the spacetime. Normally there are extra degrees of freedom in the geometry beyond the ones which depend directly on the local distribution of matter. They describe what's normally thought of as the gravitational field (which extends into the empty space surrounding the gravitating matter), and gravitational waves (which can propagate through vacuum). But the extra degrees of freedom always violate homogeneity and isotropy, so when matter is homogeneous and isotropic spacetime can't "do" anything independent of the matter in it. You can read the local shape of spacetime straight off of the local stress-energy tensor. Technically the Weyl curvature is zero.

Here's the 1+1 dimensional case (or its Euclidean version, anyway). The Gaussian curvature of a location in spacetime equals the mass-energy density there. So take a little piece of two-dimensional space with positive Gaussian curvature. Homogeneity implies that the matter density is the same a little way to the side, so attach another piece of space with the same shape next to the one you already have so that they fit together smoothly. Keep doing this (sideways), and the overall shape will inevitably curl into a circle, in the same way as the surfaces in this thread. Now extend this upward (into the future) and, if you like, downward as well. You might think that you'll end up with a sphere, and you would if not for the fact that the mass-energy density doesn't remain constant. If you draw a bunch of lines perpendicular to the circle of symmetry, representing the paths of individual particles, the paths will converge (increasing the density) if the circle gets smaller and diverge if it gets larger. Overall the matter density, hence the curvature, will be inversely proportional to the radius of the circle of symmetry. (With three spatial dimensions it's inversely proportional to the cube of the radius.) Note that the circle itself and its radius are physically meaningless—just an artifact of the embedding—but they happen to be a convenient way to see the overall density. The physical reason for the change of density is the local convergence or divergence of the lines.

The completely general form of this kind of geometry is a sort of extruded circle whose radius is a function of time (only). I can parametrize this with a coordinate t measured vertically along the surface (not in the embedding space) and an angular coordinate θ, and the distance between points on the surface is then ${\sqrt {dt^{2}+[r(t)d\theta ]^{2}}}$ in the Euclidean case, or ${\sqrt {dt^{2}-[r(t)d\theta ]^{2}}}$ in the Lorentzian case. That's the FLRW metric. It's simply the most general possible geometry with this kind of symmetry.

So there's clearly a sense in which "space is expanding": the lines are diverging and (therefore, necessarily) the circle is getting larger. But at the same time it's a strange thing to say, because space isn't a substance that changes over time. The space at a later time is different space, and there's nothing that inherently relates it to space at an earlier time. What does persist with time is the matter, and the real physical content of the expansion is the divergence of the matter lines.

This may not sound much like inertia, but it's exactly the same thing. Locally the surface is roughly flat and diverging lines are just objects moving away from each other. Our lines of "constant time" were chosen on the basis of the global symmetry. Whenever we have objects locally moving away from each other we have a local Hubble-like expansion with a geometry that's locally FLRW-like, and we can choose a local cosmological time (generally not aligned with the global one) that respects the symmetry of that local expansion.

This also may not sound much like Newtonian physics, but again it's almost exactly the same thing. You can, though I don't know the details, rephrase Newtonian gravity in the same kind of geometric language. What I do know how to do is quantitatively derive the Friedmann equations from a Newtonian big bang model, so let me do that. (This is going to be a long post.)

Suppose we have infinitely many particles with uniformly distributed velocities in a Newtonian universe. At time t = 0 they're all at the origin, but an instant later they're uniformly distributed through all of space. In the absence of gravity they'll separate linearly forever. What's the effect of gravity? Well, consider a spherical region of matter centered at x₀ with radius r. Its total mass is ${\tfrac {4}{3}}\pi r^{3}\rho$, where ρ is the mass density of the particles (at a given time), and so it causes a gravitational acceleration of $Gm/r^{2}=G({\tfrac {4}{3}}\pi r^{3}\rho )/r^{2}={\tfrac {4}{3}}\pi G\rho r$ on a particle at the edge of the sphere. The rest of the matter in the universe has no effect at all, because it can be considered as a collection of concentric spherical shells around our sphere, and a uniformly dense spherical shell of matter has no gravitational field inside. (If this argument sounds a bit dubious, note that you can get the same answer with less handwaving by solving the gravitational Poisson equation.) So for a particle at x the vector acceleration is ${\tfrac {4}{3}}\pi G\rho (\mathbf {x} _{0}-\mathbf {x} )$. But there's a serious problem here: x₀ was arbitrary, so we've just derived a force of arbitrary magnitude pointing in an arbitrary direction. This has led people sometimes to claim that Newtonian gravity doesn't work for unbounded distributions of matter. But those people are wrong, because there's a hidden gauge freedom in Newtonian gravity. A constant gravitational field accelerates everything in exactly the same way, and when everything accelerates in the same way you can't tell that anything is accelerating at all. So you can add an arbitrarily time-varying spatially constant vector field to any gravitational field without changing any of the physical predictions of the theory. And all of our solutions differed by a spatially constant vector field, namely ${\tfrac {4}{3}}\pi G\rho (\mathbf {x} _{0}-\mathbf {x} _{0}')$. So they are all really the same solution. Gravity just makes the particles attract each other with a relative acceleration proportional to distance, without any particular center. Since it doesn't matter where the center is, I'm going to take $\mathbf {x} _{0}=0$.

We can add a cosmological constant to this. The cosmological constant adds a term to the gravitational acceleration that's proportional to distance, changing it to $-Gm/r^{2}+(\Lambda /3)r$, where I've arbitrarily (but with malice aforethought) chosen a proportionality constant of Λ/3. For our distribution of matter this gives an acceleration of ${\tfrac {1}{3}}(\Lambda -4\pi G\rho )\mathbf {x}$, where I've picked the origin for the Lambda term to be 0 (I can do this for the same reason as before). So the equation of motion of a particle at distance r from the origin is

$r''={\tfrac {1}{3}}(\Lambda -4\pi G\rho )r$

or with a bit of rearrangement

$3\left({\frac {r''}{r}}\right)=\Lambda -4\pi G\rho$,

which you might recognize as the $c\rightarrow \infty$ or $p\rightarrow 0$ limit of the second Friedmann equation.

Now, ρ changes with time, and not independently: it's inversely proportional to r³, where r is the distance between any two particles moving with the overall flow. So let's substitute ρ = k/r³ in the equation of motion:

$r''={\tfrac {1}{3}}(\Lambda r-4\pi Gk/r^{2})$

multiply by 2r':

$2r'r''={\tfrac {1}{3}}(2\Lambda rr'-8\pi Gkr'/r^{2})$

integrate:

$r'^{2}={\tfrac {1}{3}}(\Lambda r^{2}+8\pi Gk/r)+{\text{const}}$

divide by r²:

$\left({\frac {r'}{r}}\right)^{2}={\frac {\Lambda +8\pi G\rho }{3}}+{\frac {\text{const}}{r^{2}}}$

and that's the first Friedmann equation. I don't actually know the significance of the curvature term showing up as a constant of integration; I've been assuming no curvature.

Notice, incidentally, how this gauge freedom in the gravitational field gets us general covariance. In the absence of gravity, Galilean relativity says that we can treat any uniformly moving object as our standard of "rest at the origin". With gravity we can extend this from uniform motion to arbitrary motion. We get rid of the second and higher time derivatives by adding a uniform gravitational field proportional to the second derivative, and then eliminate the first and zeroth derivatives with a Galilean transformation and a translation. I believe there's another gauge freedom which can be used to relativize rotation as well. In fact all of this works better in Newtonian gravity than in general relativity, where all kinds of problems crop up that have no Newtonian analogue. The twin paradox shows the failure (in a certain sense) of Einstein's general principle of relativity in a Lorentzian world. In a Newtonian world, of course, the twins are always the same age when they rejoin, and there's a true equivalence of all paths.

We can also introduce perturbations. Because like attracts like, gravitation is inherently unstable; it tends to magnify small variations in the density instead of smoothing them out like electromagnetism does. So we get clumping. The clumping is probably happening everywhere, but since we can choose the origin to be anywhere, let's look at clumping around the origin. We can still use the concentric-shell argument to ignore most of the matter in the universe; it no longer applies exactly but it becomes more and more accurate as the shell size increases. The Λ term is negligible since it's proportional to distance from the origin, so the clumped matter pretty much follows the usual rules of Newtonian gravity as though it were alone in the universe. You get stars, galaxies, planetary orbits, and so on, but the aggregate motion is still roughly zero—that is, still roughly with the Hubble flow. There's nothing to give it a significant velocity in one direction or another. This applies to all of the clumps everywhere in the universe. The characteristic clumping scale will increase with time, but the Hubble flow and overall homogeneity will always persist at larger scales.

There's one important feature of general relativity which doesn't show up in the Newtonian case: the local light cones. The fact that light moves locally at c with respect to the local Hubble flow is a nice realization of Mach's principle. This has no analogue in Newtonian gravity as far as I know.

It's also worth looking at a special relativistic big bang. Again say we have an infinite collection of particles at the origin with evenly distributed velocities, but now they're evenly distributed over the hyperbolic space of SR velocities. In the 1+1 dimensional case, this means evenly distributed rapidities. After a time t has elapsed the particles form a sphere of radius ct, with the density approaching infinity near the edge. This is a lot like what many people imagine big bang cosmology to be. But t is not a very nice time coordinate, because it doesn't respect the inherent symmetry of this setup. A better time coordinate is based on the proper time of each particle, that is, $\tau ={\sqrt {t^{2}-\mathbf {x} ^{2}/c^{2}}}$. This is the cosmological time. The locus of points at a particular τ is a spacelike surface which is hyperbolic and filled with particles at a uniform density out to infinity. The particles have time-invariant recession speeds which obey Hubble's law at any given time (with a time-varying Hubble constant). This is, in fact, the ρ = 0 case of the FLRW cosmology—just a coordinate reparametrization of Minkowski space. This is why space is hyperbolic for low densities (below the critical density).

The Euclidean version of the special relativistic cosmology is polar coordinates, with τ being the radius. If your whole universe has spherical symmetry then global polar coordinates make sense. If you locally have some uniformly diverging lines then local polar coordinates make sense (which probably won't coincide with the global coordinates, though they might). Add gravity and you get global/local curvature, giving a global/local FLRW shape, which makes it sensible to use "longitude" and "latitude" lines (FLRW coordinates), which are the curved-space versions of the polar coordinates. -- BenRG (talk) 18:59, 23 March 2008 (UTC)

"He's got balls..."

Is there any real correlation between human testicle size and the propensity for bravery and courage? --81.77.147.21 (talk) 22:27, 21 March 2008 (UTC)

The verifiability and falsifiability of a claim would be in question. Mac Davis (talk) 00:28, 22 March 2008 (UTC)

It's fairly well established that high testosterone levels cause aggressive and risk-taking behavior. However, the link between testicle size and high testosterone level is less certain. In the case of athletes taking steroids, for example, they often have high testosterone levels and small testicles. StuRat (talk) 03:01, 22 March 2008 (UTC)

For what it's worth, our article on testosterone claims that it's low levels that cause aggression. --Milkbreath (talk) 03:23, 22 March 2008 (UTC)

The IP who inserted that information (without references) in October has a string of vandalism warnings around the same time and was then blocked. I would suggest that can safely be put down to vandalism and 82.42.171.4's other edits should be reviewed at as well. SpinningSpark 08:49, 22 March 2008 (UTC)

Of course there is - but only in men. silly.87.102.16.238 (talk) 11:41, 22 March 2008 (UTC)

dimethyl sulfone decomposition

Does dimethyl-sulfone (MSM) decompose in household storage, or is it stable? Would it be an oxidation or reduction reaction?

If you keep it in the bottle it should be fine. It should stay that way for years. Mac Davis (talk) 23:56, 21 March 2008 (UTC)

Are you asking again with different words? We don't offer advice on how things work inside your body. Even if it's not a medical compound, really, ask a pharmacist. Franamax (talk) 00:39, 22 March 2008 (UTC)

It is kept in the bottle in a cupboard and opened daily, with a bit spooned out. The spoon is always clean and dry, but the powder balls up a little due to attracting moisture in the air. Someone reported the same "balling up", but they also said that dimethyl-sulfone does not decompose significantly over time.

The question is straightforward and not about physiological application. I am sure the WP community has thousands of participants of any given background, but anyone knowledgeable about the stability and/or reactivity of dimethyl-sulfone at room temperature can address my question. Thank you.

dimethyl sulfone should keep for a long time when stored correctly eg in the dark, stopper on. Just how long I don't have the answer. But it is in general stable (like sugar etc)87.102.16.238 (talk) 11:50, 22 March 2008 (UTC)

Yeah make sure it is in the dark. Double bonds never like UV light.--Shniken1 (talk) 12:10, 22 March 2008 (UTC)

March 22

Automatic crossbow

Has there ever been such a device as a fully automatic crossbow? If not, is there any technical reason why not? --Kurt Shaped Box (talk) 01:14, 22 March 2008 (UTC)

Well we have an article repeating crossbow. Also take a look at Zhuge Liang#Legacy the ancient chinese supposed inventor of these.

Also this thread [12] describes unmanned automatic crossbows mounted on chariots driven by the turning chariot wheels and flung at the enemy by setting fire to the horses tails. No idea how reliable this source is, but it conjures up a wonderful picture. SpinningSpark 01:36, 22 March 2008 (UTC)

I'll test this next time I go by a stable, assuming I can find a used chariot. But what happens when the horses turn around and come running back? Maybe that's why this method of warfare didn't catch on? :) Franamax (talk) 12:27, 22 March 2008 (UTC)

Just be thankful that you weren't fighting alongside war pigs (if they ever existed). --Kurt Shaped Box (talk) 13:17, 22 March 2008 (UTC)

Why would they come running back? If someone set your arse on fire would you go back there? SpinningSpark 13:29, 22 March 2008 (UTC)

If I was on fire, I probably wouldn't be paying that much attention to where I was running. --Kurt Shaped Box (talk) 13:37, 22 March 2008 (UTC)

(e/c) Ahh, war pigs, I always wondered what Black Sabbath was going on about! SS, why would the horses keep running in a straight line? If your butt's on fire, do you keep track of directions? (Don't try this at home kids) What I was thinking of though is that they might run back towards some of the unburnt horses they were just hanging around with, horses tend to do that. And they would have kept at least one horse for the general to ride afterwards, right? Who wants to ride a smelly burnt horse? :) Franamax (talk) 13:45, 22 March 2008 (UTC)

water heater is making a whining sound

I live in a two story house. Our water heater is making a whining sound that can be heard all through the house. I'm afraid that a pipe or the water heater is going to blow and cause a terrible problem. Do you know what could be making the whining sound that has never been heard in our house before? What can we do about it?

Gas? Fueloil? Electric? Immersion? A little more detail would help. --BozMo talk 06:55, 22 March 2008 (UTC)

It sounds like you need a plumber to not only examine the water heater, butt crack this problem wide open before a serious leak occurs. StuRat (talk) 11:41, 22 March 2008 (UTC)

Googling on "water heater" whining provides many useful links. I have heard that they can make noises when there is a layer of deposits in the bottom in which water can become superheated and be forced through the deposits. It is possible that the pressure relief valve is starting to leak. I would warn you that the water heater is nothing to mess around with; when things go wrong they can go wrong big. Here is a video from Mythbusters that proves that. --Milkbreath (talk) 13:35, 22 March 2008 (UTC)

I'd amend that to "the water heater is nothing to mess around with if you don't know what you're doing". In my opinion that Mythbusters video is (like much popular entertainment) somewhat alarmist. The fact that you never hear about water heaters exploding like that in real life is good proof that, virtually all of the time, the designed-in safety mechanisms work as they're supposed to. I'm not saying it never happens, but anyone who tampers with or disables a safety device such as a T&P valve displays criminal negligence and stupidity. —Steve Summit (talk) 14:05, 22 March 2008 (UTC)

Addendum: Never? Well, hardly ever. Yikes. —scs 14:10, 22 March 2008 (UTC)

Yes, the Mythbusters are not a reliable primary source as a rule, but I watched that one, and we're seeing the true consequences of defeating the safety devices, turning the thermostat up, and then simply turning the thing on and waiting. No extra explosives or other heroic measures were used for dramatic effect. Both they and I were astonished at the violence of the event. Apparently, such explosions were commonplace before the introduction of the safety valve. --Milkbreath (talk) 14:41, 22 March 2008 (UTC)

Right. But the nice thing is, today, simultaneous failures of both the thermostat and the safety valve are exceedingly rare. I'd wager that all such failures are due to capping off of the safety valve (as in the referenced Seattle P-I article, presumably because the valve was leaking). —Steve Summit (talk) 15:16, 22 March 2008 (UTC)

Best Food

If a human had to survive on just water and one other substance, what would that substance be ? —Preceding unsigned comment added by 80.5.206.57 (talk • contribs) 15:19, 22 March 2008

In order to survive as long as possible, I think it would be sodium chloride. Without it he would die pretty soon from water poisoning. Icek (talk) 15:31, 22 March 2008 (UTC)

Does cornish pasty count as a substance? Or how about earth (soil) - with earth and water you could grow your own food..87.102.16.238 (talk) 16:22, 22 March 2008 (UTC)

Guinness? Heh, I know it's probably an urban legend - but has anyone else heard it said that you can supposedly get all/most of your nutritional needs from five pints of Guinness per day? --Kurt Shaped Box (talk) 19:24, 22 March 2008 (UTC)

Much as I am always in favour of beer theories, I would go with milk, being as it is designed to do just that - provide you with all the nutrients you need to survive. SpinningSpark 21:29, 22 March 2008 (UTC)

I think a "substance" is something with a definite chemical composition, which is not true for milk, beer and the like. Icek (talk) 11:18, 23 March 2008 (UTC)

I'd go with oxygen. — DanielLC 16:30, 23 March 2008 (UTC)

Garlic for treatment of wounds

Hello, there is hearsay about usage of garlic for the treatment of wounds up to the time of WWI. For the respective WP articles, I'd need at least one account that it was official treatment. Google was no use, neither the Project Gutenberg full text search.

Do you know of a passage in a book (even fiction) where garlic was used on a wound, or its usage was recommended by an official about 100 years ago? --85.179.13.254 (talk) 17:10, 22 March 2008 (UTC)

would this help http://news.bbc.co.uk/2/hi/health/3344325.stm

Also try searching for 'allicin' if you haven't already87.102.16.238 (talk) 17:47, 22 March 2008 (UTC)

http://www.bulkherbstore.com/GM

In his book, Advanced Treatise in Herbology, Dr. Edward Shook had this to say about the valuable antibiotic properties of garlic: "The use of garlic in the 1st World War (WW1) as an antiseptic was most sensational. In 1916, the British government asked for tons of the bulbs, offering one shilling a pound for as much as could be produced. A great quantity of it was used for the control of suppuration in wounds. The raw juice was expressed, diluted with water, and put on swabs of sterilized sphagnum moss which was applied to the wounds. Where this treatment was given, it has been proved that there has never been one single case of sepsis or septic results. Consequently, the lives of tens of thousands have been saved by this one miraculous herb."

does that help87.102.16.238 (talk) 17:51, 22 March 2008 (UTC)

Can you give me the page number of that passage, please? I would like to read it myself, and see if Dr. Shook has references for that opinion. Many thanks!

To the other poster: the antimicrobial activity of garlic compounds is well established, thanks. The question is specifically about official former usage. --85.179.15.63 (talk) 07:37, 23 March 2008 (UTC)

Sorry I haven't got the page number87.102.16.238 (talk) 10:43, 23 March 2008 (UTC)

How were you able to produce that passage, then? --85.179.24.245 (talk) 15:29, 24 March 2008 (UTC)

Genetic mutation resulting in deformities of the offspring

1. In sexual reproduction, i.e., fertilization of egg by sperm, does mutation of the egg or sperm producing organs, say by means of radiation, always result in the failure of the organs to produce viable egg or sperm, i.e., egg or sperm that can result in a fertilized egg? In other words, are deformities in an offspring due to mutated egg or sperm producing organs?
2. If mutated egg or sperm producing organs are not responsible for deformities in an offspring then is mutation of the egg or sperm, say by irradiation, after they are produced and prior to fertilization responsible for deformities in the offspring?
3. If deformities do not result from mutated egg or sperm occurring after they are produced, say by irradiation, then are deformities in the offspring the result of a faulty union of egg and sperm?
4. If faulty union of egg and sperm are not responsible for deformities in the offspring then is the genetic mechanism by which deformities occur in the offspring the result of mutation of the fertilized egg after it is fertilized, by say irradiation of the fertilized egg? 71.100.1.14 (talk) 17:18, 22 March 2008 (UTC)

1. Mutation is a process involving alteration of the genetic code. Now, mutation affecting the reproductive organs can lead to effects in the sperm/egg's DNA or their body, both of which can lead to offspring deformities. Now, your other question is backwards, and it's a fact that there are also deformities caused by other processes than mutation, e.g., folate deficiency of the mother, to name one.

2. Radiation can affect sperm as in my answer 1, or it can damage sperm's DNA directly. All radiation damages are highly dependent on the radiation dosage and the time when the mutation happens (like in the midst of cell dupication or such), and even then, the body has means to neutralize a good deal of such damage, provided it's healthy (no alcohol, no smoking).

4. Yes, also eggs' DNA can be damaged after eggs were produced (all human eggs are produced beforehand, anyway. That's why mothers are advised not to have children after 40 for mutation and other damage risk reasons, like Down's syndrome). -- 85.179.13.254 (talk) 17:37, 22 March 2008 (UTC)

So are you saying that a mutation in the parent before egg or sperm production or mutation in the egg or sperm after production but before fertilization or mutation after fertilization can result in a deformity or difference in an offspring? 71.100.1.14 (talk) 18:18, 22 March 2008 (UTC)

Yes, definitely. It wouldn't happen often, normally, as said, because of the body's defenses. The risk, however, is not exactly zero.

BTW, coincidentally, folate deficiency affects even males and their sperm, according to this fresh news article. --85.179.15.63 (talk) 07:32, 23 March 2008 (UTC)

Children's medicine 100 years ago.

In books such as The house at Pooh Corner or Peter Pan, children (specifically Roo and Peter respectively) are described as drinking medicine or tonic each day "to make them grow up strong". What was in these concoctions, would they have been prescribed by a doctor, an apothecary or made up at home? Zeimusu | Talk page 17:22, 22 March 2008 (UTC)

Mostly patent medicines, which really thrived in the early 20th century when both of those books were written, before any meaningful drug and advertising regulation was done. (Even today, under the guise of "natural" cures all sorts of hogwash is sold with fantastical claims, e.g. Airborne (dietary supplement). Let we think they were so stupid then, let us look at ourselves and our own propensity for such things!) --Captain Ref Desk (talk) 19:03, 22 March 2008 (UTC)

On the other hand, some of those concoctions might have helped, by providing vitamins and minerals which might otherwise be deficient in the child's diet. Cod liver oil is one such example. StuRat (talk) 21:13, 22 March 2008 (UTC)

The Smallest?

Is there a limit to how small a particle can be? Is there a point where a particle no longer MOVES to a point, but GOES to a point because it is so small that you can't be half way there?--Xtothe3rd (talk) 18:05, 22 March 2008 (UTC)

String theory is based on the idea that there is a minimum (1-dimensional) particle size, rather than zero-dimensional point particles. It isn't clear whether string theory is really going to work out physically and mathematically but yeah, that's the basic question it asks. More generally, though, there is Planck length, the smallest distance at which our physical theories make any sense. At a point much larger than that, though, the uncertainty principle keeps us from knowing whether a given particle is in a specific space or not. --Captain Ref Desk (talk) 18:53, 22 March 2008 (UTC)

However, the gravitational singularity of a black hole is a mathematical point. That is, it's infinitely small with no volume (but a definite mass). StuRat (talk) 21:07, 22 March 2008 (UTC)

Resolution of the naked eye

With my naked eye on an overcast day I can tell whether someone on a covered porch 500 feet away is wearing a black hat with a 3/4 inch white pendant or patch. How can I translate this to the resolution capability of my naked eye and compare it with a standard resolution capability for the human eye? 71.100.1.14 (talk) 18:53, 22 March 2008 (UTC)

The standard resolution capability is about one minute of arc (1/60 of a degree) which equals 0.0003 radians. For small angles, the angle in radians can be calculated by dividing the length of the object or separation of objects (perpendicular to the line of sight) by the distance. Now, if you see just one white patch on a black background that does not mean that your resolution is actually (width of the patch)/distance. What you would need is 2 white patches on a black background, and then determine the largest distance at which you can still see that it's 2 patches and not 1.

You can only conclude anything about the resolution capability of your eye from your experiment if the background around the hat was bright, and you could clearly see a pattern (e. g. along a horizontal line) of bright background - black hat - white patch - black hat - bright background. Then your resolution capability is at least ((width of the hat)/2)/distance.

If you are interested in the general calculation of the resolution of optical instruments (including eyes), you could start at Airy disc. Icek (talk) 19:22, 22 March 2008 (UTC)

To verify then at standard resolution capability for reflected ambient light then should I be able to see with a bright background a white patch on a 3.6 inch black object 500 feet away?

The Airy disc article seems to suggest that the reason I can see stars at night in the sky is due to the intensity of the light being emitted by the star attenuated by background and the distance, i.e., I can not see them when the background light is bright and I would not be able to see them at night at that distance if they were only reflecting ambient light like the moon.

Regarding the verification of standard resolution capability: Yes, but two white patches on a larger black background and a friend placing randomly one or two of the patches onto the background without you knowing whether it's one or two patches would be better.

Regarding the Airy disc, yes, the intensity of the light lets you see objects that are far smaller than your resolution limit.

Interestingly, one could even go beyond the Airy limit if one used a monochromatic filter and light detecting elements far smaller than the Airy resolution limit. Then you could calculate the distribution of brightness from the diffraction pattern. But of course that is assuming that your optical instrument is nearly perfect with no stray light etc. Icek (talk) 11:59, 23 March 2008 (UTC)

hummm... is it possible that this is how in part the Hubble telescope is constructed? 71.100.1.14 (talk) 18:33, 23 March 2008 (UTC)

No. Remember that the Airy disc is an idealized model. For telescopes below the atmosphere, atmospheric turbulence causes distortions of the image (see Astronomical seeing), preventing us from reaching the Airy limit (the images can nowadays improved by adaptive optics, but currently only for long-wavelength light). The resolution of the Hubble Space Telescope is about 1/20 of a second of arc - about what you get with the Airy formula for a 2.4 m mirror at visible wavelengths. Icek (talk) 19:25, 23 March 2008 (UTC)

speed of an ant

I've clocked a frightened ant at 1 foot in 3.1 seconds and faster. This give me .32 feet per second or 116 feet per hour or .02 miles per hour. Where can I find a list of speeds for other insects? 71.100.1.14 (talk) 19:09, 22 March 2008 (UTC)

Since ants vary dramatically in size, I'd expect them to also vary dramatically in speed. This will also be true for many other insects. So, a chart listing the speed of "ants", "centipedes", "beetles", "flies", etc., would be meaningless. You'd need to list the individual species of each. StuRat (talk) 21:04, 22 March 2008 (UTC)

Okay, I have no problem with that. Even though there are vast differences in speed for even the same species (humans) there is statistics which can provide a maximum, a mean and a standard deviation. 71.100.1.14 (talk) 08:26, 23 March 2008 (UTC)

There are several sources on the internet that list the speed of various animals. A published list is in Natural History Magazine, March 1974, The American Museum of Natural History; and James G. Doherty, general curator, The Wildlife Conservation Society. That list is reproduced here. A compendium that compares the collates reported in various sources for the speeds of a range of animals is points 730-745 here. IBangMyHead (talk) 12:18, 23 March 2008 (UTC)

71.100.1.14, your last two speed figures are a factor of 10 too low. We wouldn't want the ref desk to be sued by someone who was outrun by an ant. --Heron (talk) 13:16, 23 March 2008 (UTC)

These figures are based on 1 foot in 3 seconds. I originally named then "Darters" but they are an invasive species which I have forgotten the name of now. They may be moving along at 1 inch per second or less foraging and then when frightened dart off at 3 to 4 inches per second - too fast to follow with them a finger to give them a good smash. 71.100.1.14 (talk) 71.100.1.65 (talk) 08:37, 24 March 2008 (UTC)

As Stu said, it really depends on the species. Of the large Old World ants, Cataglyphis ants run pretty damn fast, easily over 10 cm/s, maybe as much as 20 cm/s. Messor and Camponotus are slower, several cm/s is probably the limit. Smaller ants are around 1 cm/s or less. However, these are just my non-scientific observations, so you should definitely NOT use them as a reference. As for other insects - please be more specific, then we (the Ref Desk) will probably be able to help. Cheers, --Dr Dima (talk) 15:26, 23 March 2008 (UTC)

The fabric of space

Did Einstine say that his math would not work unless space was actualy something. In other words, space could not simply be an empty void that matter exists in but an actual physical thing. e.g. "fabrick of space and time" I read somewhere that he called it ether.

You may be interested in general relativity and spacetime. — Matt Eason ^{(Talk • Contribs)} 20:40, 22 March 2008 (UTC)

For Einstein, space and time are bound together inextricably—you cannot reasonably talk about one without talking about the other (you cannot measure space without time, you cannot measure time without space, and you cannot talk about what you cannot measure—a few of Einstein's fundamental axiomatic realizations), and the composition of space affects the way in which time is perceived (and thus, because of relativity, the way time operates itself, as there is no time outside of space). So instead of space and time we have "spacetime".

It is not the same thing as the luminiferous aether, which was an earlier theory that Einstein rejected.

To elaborate a bit: it is not so much that empty space is not "empty" (that is, devoid of matter), it is that the idea of "space" itself is a geometrical construct, and it is more flexible than one might normally assume. The presence of any mass at all, for example, deforms spacetime, and the result is the effect that we call "gravity". We slide along this deformation in spacetime without even realizing it, towards the center of large masses, in this case, the planet Earth, along the path of least resistance.

Hopefully that will clarify things a little bit—I've oversimplified things a bit but I don't think I've committed any major errors. --Captain Ref Desk (talk) 20:40, 22 March 2008 (UTC)

Where is the centre of the universe?

If the universe is continually expanding outward in every direction, then where is the point from which it is expanding? That must be where the big bang occurred? But where is it, say, in relation to our earth? Are we nearer to the centre of the universe or the "edge" of it? As you will have guessed, I am not a science person. Kaiwhakahaere (talk) 20:34, 22 March 2008 (UTC)

Without knowing the shape of the universe, it is not possible to define a center. And further, there are possible shapes to the universe for which there is no geometric center. Also, there is no position in space "where the big bang occurred." The big bang occurred everywhere. To explain how that might be possible, think of the expansion of the universe. When we look at distant galaxies, we notice that the speed at which the galaxy is receding is directly proportional to its distance from us (Hubble's law), and this seems consistent in every direction. That is, almost everything is moving away from us, and we seem to be at the center of it all. However, this observation would be true no matter which galaxy we were in. It would subsequently be true that if we were to run time backwards, we would see everything rushing towards us and the density of matter/energy would increase towards infinity as we approached the big bang, and this observation would be the case no matter which galaxy we were in! Thus, each galaxy can equally claim that is the central point of expansion, and thus it is probably untrue that an actual "center of the universe" exists anywhere, and it is certainly untrue that the big bang occurred at one point. Someguy1221 (talk) 21:08, 22 March 2008 (UTC)

You must be the universe's fastest typist! Or our locations are actually coming together rather than moving apart! Only 34 seconds after I hit my save page button you posted a reply. And a great reply it was too. Tks. Kaiwhakahaere (talk) 21:15, 22 March 2008 (UTC)

I suspect this was a prepared answer, which took me longer than 34 seconds to read. 71.100.1.14 (talk) 08:32, 23 March 2008 (UTC)

It was 34 minutes, not seconds. -- BenRG (talk) 19:42, 23 March 2008 (UTC)

The big bang is more like a balloon being blown up than an explosion. The big bang happened everywhere - it was an expansion of the distances between things. So if everything in the universe were on the surface of a balloon while it was expanding very quickly, that would sort of be like the big bang. Quantumelfmage (talk) 05:49, 24 March 2008 (UTC)

Leap from a burning building

A question I posted above (Wikipedia:Reference desk/Science#Free falling human body) prompted this follow-up thought. If your house / apartment building is on fire, and you have to jump out the window ... what are some rules of thumb you should observe? In other words, what's the "best" way to jump out? And is there any relevance to what story up you are in the house / apartment building? Or is that essentially irrelevant? In other words, if I was very high up (on the 10th or 20th or 100th floor), would / should my jumping strategy be different than if I was not so high up (on the second or third floor)? Also, what are some considerations a person should factor into making a good decision to "should I jump or should I not?" Ultimately, if you were the Chief of the Fire Department and had to write a "how to manual" for people who find their homes on fire, what would be the best advice in these scenarios described? Thanks. (Joseph A. Spadaro (talk) 21:28, 22 March 2008 (UTC))

From a second floor window, you can break your fall with a "parachute roll" without any serious injury if you are properly trained. A paratrooper friend I used to know used to do this regularly as a party trick after we had been drinking (warning: don't try this at home). I have also read (sorry, forgot where) of a base jumper whose chute failed after jumping off a building at a great height. He managed to keep his fall under terminal velocity by grabbing the ledge on every floor as he went down. The fall is too fast to be able to actually hold on but it slowed him down enough to survive. Multiple fractures in both arms from hitting the ledges and broken legs on landing but he did survive (don't try this at home either). And now you mention it, I do have a "how to" book on surviving worst case scenarios - I'll see if I can find it. SpinningSpark 21:47, 22 March 2008 (UTC)

Thanks for the reply. It would be helpful to know what the term "parachute roll" means ...? Thanks. (Joseph A. Spadaro (talk) 22:15, 22 March 2008 (UTC))

Well, if the building really had been on fire the book would have been completely useless as it took too long to find - note to publisher: you need to embed an emergency siren in the spine so it can be located quickly. So anyway, it lists several falling scenarios, the closest to your question is "How To Jump From A Building Into A Dumpster" (dumpster = skip in UK). They recommend tucking in your head and bringing your legs around so that you are laying on your back. They say the reason for this is that the body tends to be thrown into a V on landing. If you land on your stomach this will break your back. Also, try not to leap outwards as this will carry you away from your aiming point. I would also repeat - don't try this at home - there's a lot that can go wrong with this one. If you miss the dumpster, you hit concrete. If you nearly miss the dumpster you might hit your head or your back on the edge - worse than hitting the concrete. If the dumpster is full of building rubble (what else would be in it? they are only full of empty cardboard boxes in the movies) then you may as well have aimed for the concrete. SpinningSpark 22:25, 22 March 2008 (UTC)

Parachute Roll. I don't think this is used very much anymore, but in the days when parachutes were a lot less controllable it was necessary to break you fall to avoid broken ankles. Basically, it is bending at the knees to absorb some of the shock as your feet touch down and at the same time falling to one side and turning that motion into a roll as your body hits the ground to dissipate even more of your kinetic energy. Practice from standing on the ground at first and then steadily increasing heights. SpinningSpark 22:35, 22 March 2008 (UTC)

One important thing to do from the 2nd or 3rd story is to hang from the ledge first, to lower your distance to the ground as much as possible, before you jump. Also aim for something relatively soft, like dirt or a bush or an awning. StuRat (talk) 06:32, 23 March 2008 (UTC)

Non-pop popcorn

After a nice meal i decided to have some popcorn with my beer and meaningless wikipedia-surfing. I poured the corn into the kettle and went back to my computer, waiting for the first pop. however, no pop occurred, and instead i smelt fire and when I turned around I saw thick smoke from the kettle. The corn had simply started burning instead of popping like usual - ruining the kettle in the process... I was thinking afterwards that I had put to small an amount of oil in the kettle, but after reading the popcorn article it seems that they should pop at a certain temperature, oiled or not. the next batch of popcorn (from the same bag) went fine. this is a slightly odd question, but has anyone got an idea why this might have occurred?

Did you adjust the temperature? Maybe the first lot was too high. Julia Rossi (talk) 03:10, 23 March 2008 (UTC)

Also, wikipedia surfing is never meaningless. Your knowledge increases, your eyesight deteriorates. Live long and prosper. --Dr Dima (talk) 15:54, 23 March 2008 (UTC)

How the brain processes visuals

I believe that this is a Science question ... or, rather, questions. (Question 1) When we look at a drawing of, say, Charlie Brown (or any cartoon) ... that picture in no way looks like a real human being 8-year-old boy. So, what "tricks" our brain when we see these animations to "accept" that they are people? That question was hard to word, but I hope someone catches my drift. (Question 2) We look at drawings, pictures, paintings, and visuals all the time. What exactly "distinguishes" these normal visuals from what we call "optical illusions"? In other words, in a given optical illusion, it might say: "Do you see a man or a mouse?". Some people can see the man, some the mouse, and some both. Why is that? And what exactly makes that visual different for our brain to process than when we look at a "normal" (unambiguous) visual (like my high school yearbook photo or the Iwo Jima photo)? Thanks. (Joseph A. Spadaro (talk) 22:24, 22 March 2008 (UTC))

While a cartoon face doesn't look anything like a particular human face, it is very close to looking like the Prototype Theory or average face. At a low level, we might analyze Charlie Brown's nose as a half-circle, but there is a top-down mechanism in the brain that makes us recognize it as a nose because it is in the context of a face. Each of Charlie's features do not have enough detail on their own to assert themselves as facial features, but in the context of a prototypical face and prototypical features, we can place them. So at a fine-grain, low level, high detail level, Charlie Brown's face does not look like a face, but at a high level, wholistic, gestaltic level, it does look like a face, and top-down mechanisms make us accept it as a face.

In an optical illusion like the one you described, there are neural mechanisms that force us to settle on one interpretation of an ambiguous image (usually because it is the best interpretation). But the illusionary image is constructed so that neither interpretation is clearly better, so our perception switches back and forth. So the parts of your brain are getting confused and reporting inconsistent output to the part of your brain which isn't sure whether to call it a mouse or a man. So we call it an illusion. Quantumelfmage (talk) 05:43, 24 March 2008 (UTC)

Makes sense. Then, as a corollary question ... how come sometimes I cannot "see" the alternative image until someone directly points it out exactly to me? And how come sometimes I can never "see" the alternative picture, even when someone directly points it out exatly to me? Thanks. (Joseph A. Spadaro (talk) 05:53, 24 March 2008 (UTC))

I believe that we see things as other things due to our ability to handle symbolic logic. That is, to define one thing as representing another. This is important in human communication. The cartoon may only be recognized because, in our past, we have used pictures drawn in dirt with a stick to represent people, and those who could understand had a survival advantage. I doubt if a dog could recognize a cartoon as representing a person or dog, as they lack the ability to use symbolic logic. StuRat (talk) 06:07, 23 March 2008 (UTC)

Unfortunately, we do not have much of an article for associative memory, and it's a shame. I will write one if I have time this week. For the time being, a really lousy short explanation. Objects (visual objects in particular, but any sensory or conceptual objects in general) that we encounter in real life are often incomplete, poorly resolved, or somewhat different from their "standard" form. Yet, we recognize them very reliably. The underlying neural circuitry is usually called an "associative memory" network. The network has many "familiar" or "memorized" states corresponding to familiar objects or notions; these are called attractors. Any incomplete or inaccurate input to such a network (an observed object) brings the network into an attractor state which is usually rather similar to the observed object; this is recognition. Human face, or human shape, are some of the most important visual objects in the evolutionary sense, so we tend to see human shapes even in some definitely inanimate or non-human objects (see Pareidolia). So recognizing a manga or comics character, even super deformed, is really not surprising at all. And, besides, there is also a "symbolic logic" aspect which Stu mentioned: basically, we all drew pretty schematic pictures in kindergarden, at least at first; yet they were quite easy to decipher, in most cases :) . Hope this helps. --Dr Dima (talk) 15:12, 23 March 2008 (UTC)

Thanks for Question 1 (Charlie Brown). And (Question 2): We look at drawings, pictures, paintings, and visuals all the time. What exactly "distinguishes" these normal visuals from what we call "optical illusions"? In other words, in a given optical illusion, it might say: "Do you see a man or a mouse?". Some people can see the man, some the mouse, and some both. Why is that? And what exactly makes that visual different for our brain to process than when we look at a "normal" (unambiguous) visual (like my high school yearbook photo or the Iwo Jima photo)? Thanks. (Joseph A. Spadaro (talk) 20:10, 23 March 2008 (UTC))

Could physicians work as epidemiologists?

Dear Wikipedians:

My dad graduated from a non-American medical school with a MD in public health. Instead of treating patients, he works in a non-American CDC like organization doing body check-ups for primary/secondary school students and does preventive medicine propaganda in the community and also writes out a few research papers per year on the statistics of the prevalence of various diseases in the community, results of the student body checkups, etc.

I am wondering if this qualifies my dad as an epidemiologist? And is it reasonable for physicians to work as epidemiologists?

Thanks.

76.68.9.59 (talk) 22:26, 22 March 2008 (UTC)

I could be wrong, but I don't think you need to be licsenced to work as an epidemiologist. I think that it is like many occupations, if you DO it then you ARE it. (By the way, this belief has gotten me into some arguments. I believe, for example, if you studied chemistry, but don't do chemistry, you are not a chemist). ike9898 (talk) 01:48, 23 March 2008 (UTC)

There's nothing that necessarily disqualifies a physician as working as an epidemiologist, but usually epidemiologists have very rigorous training in statistics and experiment methodology, which may or may not be part of the general med school/public health education. --Captain Ref Desk (talk) 22:49, 23 March 2008 (UTC)

There are masters and Ph.D programs for epidemiology. An allopatric medical degree is not required. Wisdom89 _{(T / ^C)} 06:24, 24 March 2008 (UTC)

March 23

Trying to recall something I read years ago

Dear Wikipedians:

I need your help in discerning a passage that I read years ago but one which I couldn't find anymore. It is related to the role technology plays in medicine.

What I can remember of the passage are as follows (italics means specific details that I can no longer remember, bold means key texts that I knew definitely appeared in the passage that I read):

“ Take the disease disease name (tuberculosis?) for example, in the 1950s there were great debates about the construction of hospitals that are specifically geared to the treatment of patients with the disease, there are back-and-forth arguments in leading medical journals about the quarantine measures, treatment processes, people couldn't even seem to agree on the a treatment process, and the case study of a girl's name, girl is an African-American.

But then the wonder-tech-gizmo-drug (an antibiotic?) was discovered. And it proved to be so effective in treating disease name, that talks of building hospitals also soon died down.

”

Thanks.

76.68.9.59 (talk) 00:16, 23 March 2008 (UTC)

Well, just judging from the dates (1950s), the fears of the epidemics and the importance of the drug, my guess would be that the disease is polio, and that the wonder drug was the Salk vaccine. But this is a wild-guess—lots of antibiotics and vaccines were developed in the 1950s to treat all sorts of things, though the Salk/polio case is one of the most famous. No clue about the case study. --Captain Ref Desk (talk) 04:54, 23 March 2008 (UTC)

But the circumstances seem to fit TB much better. Sanitoriums were actually constructed when the only treatment for the disease was isolation and bedrest; the first antitubercular drug, streptomycin, was discovered in 1943, with the discovery first published in 1947. The discovery was followed by that of para-aminosalicylic acid, and by isoniazid (the wonder drug) in 1952. It became evident that bedrest wasn't important, and sanitarium construction stopped, and existing sanitaria were "repurposed". But I don't know what case study you might be talking about. You may be interest in this article on the history of tuberculosis. - Nunh-huh 11:36, 23 March 2008 (UTC)

The only other institutions I can think of that were "shut-down" as a result of improved medical treatment were "insane asylums", but this was in the 1970s and later. - Nunh-huh 11:47, 23 March 2008 (UTC)

"Insane asylums" became "psychiatric institutions" in the 1940s. Deinstitutionalization was already in play long before the first anti-psychotics were developed, though (which was in the 1950s as well—see thorazine). It's not so much that state care of the mentally ill went away so much as it decentralized. (The dismantling of the American mental health system by Reagan actually had its roots much earlier, as people for decades felt that centralized state institutions were prone to abuse and waste that local, county or community based care was not.) --Captain Ref Desk (talk) 19:56, 23 March 2008 (UTC)

As highlighted by the above discussion, given the importance of the date range in trying to answer this, how sure are you of it? For example, if it could have been like the 1930s that would be different from if it could have been in the 1970s. The example that I can think of that best fits your text to me is leprosy. Leper colonies were of cause not uncommon in the past and I would presume there they are something often debated by the medical community once it was established. As discussed in both the linked articles, it appears to me they are generally no longer considered medically necessary by most of the medical establishment because of both the widespread availability of effective treatments and the fact that leprosy is not nearly as contagious as people believe/d. The dates on this don't really agree with your 1950s, treatments were available in the early 1940s but they weren't that effective and it was only in 1982 that an effective (multidrug) treatment was developed which combined with the acceptance that leprous was not that communicable lead to the decline of leper colonies. Leper colonies weren't of course specific hospitals but segregated communities which is another area where this doesn't fit your memory. Also the case study seems a bit iffy since it doesn't seem that the US led the way in leprosy research. Actually um ignore my example, the more I think of it, the more it doesn't fit, since you're fairly sure of the last sentence but leper colonies aren't hospitals and already existed and had for a long time, it doesn't really fit... I believe HIV was a major scare as well with suggestions for quarantine (Cuba at least put this into practice IIRC but are now consider a shining star in the fight against HIV) but that was even latter and it hasn't been beaten, it's just well understood enough that people know quarantine serves little purpose Nil Einne (talk) 17:23, 23 March 2008 (UTC)

Thank you all for your response. I can now remember it as being TB + Streptomycin. Thank you sooooooooooo much! 76.65.14.58 (talk) 23:06, 23 March 2008 (UTC)

Long-term effects of 0 g

The ISS, that beautiful star in the sky, is coming down in a few short years. Hardly completed as of yet, it will be scrubbed before 2020. I would ask for some imagination from all you readers. Some horrible tragedy inflicts the Earth below. Just for a moment, let us pretend the ISS will maintain its position as a star in our sky for many decades to come, constantly replenished, that our species will continue to inhabit the night's sky. Here's what I would like to know: If I were a crew member on the station (I am a 31 y.o. healthy male), what would happen to me if I were forced to spend a continued twenty or thirty years aboard? Could I survive? Sappysap (talk) 01:02, 23 March 2008 (UTC)

Quick answer, no one really knows the long term effects of extreme long term weightlessness since it has never been done before. However given the importance of understanding this, a lot of studies and theorising has gone on which I'm sure you could find. Human adaptation to space and weightlessness are good starting points. BTW, if something happened to earth, the people on the ISS would I'm pretty sure be screwed. It is not designed and probably isn't capable of independently supporting a human population in the long term amongst other things, they need food from earth. Also, if it's design lifespan is 10+ years, it could probably be extended by say 300-500% but I suspect no longer and even then, probably only with the support of earth. And given the tiny number of people on the ITN, presuming there are even 2 fertile people of the opposite sex on the ISS at the time something happens to earth, the human species will likely be screwed due to the inbreeding depression from the extreme inbreeding that would occur. (Not to mention the ISS would have a very limited population maximum even if it were completely self sufficient so the human species couldn't exactly 'thrive' there) Nil Einne (talk) 02:39, 23 March 2008 (UTC)

Additionally, the ISS would deorbit by itself within maybe 5 years due to air resistance. Icek (talk) 14:20, 23 March 2008 (UTC)

I should mentioned though that some of the studies/theorising may not quite cover what you are suggesting. Most commonly people analyse this from a 'trip to Mars' kind of POV or perhaps colonies on other planets like Mars or the moon (or others). These are not microgravity environments and even if the hope is for the colonies to be capable of being independent (which often doesn't mean an expectation of reproduction in the colonies in the short term), in general no one expects the colonies to be cut off from earth. And people tend to look at fairly long term, but not permanent existance in microgravity (since for all the reasons already explained and more even if we do want a colony capable of surviving without earth, we wouldn't build it in space). What all this means is that most studies consider it important that the people are capable of re-adjusting to life on earth which is one of the biggest problems with people adapted to microgravity environments (or even a lesser gravity environment) but if I understood your question correctly, this doesn't matter for your case. Nil Einne (talk) 16:49, 23 March 2008 (UTC)

WHAT??? The ISS is about to deorbit? Wouldn't that mean that it will impact the Earth like an asteroid? Isn't there anything to prevent this? Or will a shuttle retrieve the astronauts and allow the ISS to deploy safely? Or is there something I misunderstood? Thanks. ~AH1^(TCU) 18:13, 23 March 2008 (UTC)

At the height of the ISS - currently approximately 340 km - typical objects deorbit within a few years (that also depends on the ratio of mass/(area perpendicular to velocity vector) of the object), at 600 km (about the height of the Hubble Space Telescope) it's maybe a few decades. Go to Heavens-Above and click on "Height of the ISS" - there you can see that the height constantly decreases, only to be increased by a boost (which consumes fuel of which there is not much on the ISS) every month or so. The ISS will impact the Earth, but slower than an asteroid would, with only about 8 km/s. They will steer it to an uninhabited region like the southern Pacific, as they did with Mir. Icek (talk) 19:18, 23 March 2008 (UTC)

Hi. Wow. The ISS is the most expensive object ever built by mankind. Well at least it's likely to break up in midair. Thanks. ~AH1^(TCU) 00:15, 24 March 2008 (UTC)

Can we get a citation for the "scrubbed before 2020" part? Our ISS article doesn't mention anything about abandonment. —Steve Summit (talk) 00:22, 24 March 2008 (UTC)

"Jumping" of blood vessels around the eye

Hi. What's the medical term for the pulsating of the blood vessel right below the eye (in the eyebag for those with one)? Thanks. Imagine Reason (talk) 01:09, 23 March 2008 (UTC)

Blepharospasm -- — Preceding unsigned comment added by 79.76.201.53 (talk • contribs)

I don't mean the eyelid. It's more of the nerve or blood vessel under the eye (like at the bottom of the eye socket). Imagine Reason (talk) 02:03, 23 March 2008 (UTC)

Read the article fully. -- — Preceding unsigned comment added by 79.76.201.53 (talk • contribs)

Why should he read it thoroughly? Blepharospasm is unrelated to pulsating blood vessels, and accordingly, the article contains no mention of blood vessels, arteries, veins, or capillaries. Mark this one "unanswered". - Nunh-huh 11:28, 23 March 2008 (UTC)

Blood vessels dont pulsate like that and if they did you would not be able to feel it unless there were nerves in the vicinity. Its obvious you havent read the article Blepharospasm either!

I quote from the symptoms para;

Uncontrollable tics or twitches of the eye muscles and surrounding facial area. Some sufferers have twitching symptoms that radiate into the nose, face and sometimes, the neck area. Mark this one as answered by me!

OK, we'll count you as one satisfied answerer. Of some question.- Nunh-huh 14:46, 24 March 2008 (UTC)

can someone identify this flower for me?

It's a picture of a white flower with a grassy three-sided stem that grows from some tiny bulbs from underneath the grass every spring. The flowers are wrapped in a onion peal like matter before the petals spout out. the flowers smell like onions. Several flowers spout from one little area. This is in Richmond, California in Contra Costa County, California in the United States.Carritotito (talk) 02:22, 23 March 2008 (UTC)

Breaks easily when pulled? Probably onion weed[13]? Aka Asphodelus fistulosus. Our article doesn't have the same variety in the pic. Julia Rossi (talk) 03:05, 23 March 2008 (UTC)

I know Asphodelus fistulosus fairly well, and this is definitely not what you have. Asphodel has its flowers in an open panicle (spike-like), whereas all the true onions (genus Allium) have their flowers in an umbel (all flowers arise from the same point at the top of the stem). Your photo shows an umbel. If it smells like onion, it probably is an onion; there are many species of Allium native to California, plus a few noxious introduced species. The Jepson Manual (1993) lists 47 species native to California and four introduced.--Eriastrum (talk) 15:47, 23 March 2008 (UTC)

Science+nutrition

What vitamin and/or nutrient does alcohol deplete from the human body?

Calcium uptake is most severely diminished with alcohol abuse, for example. In general, as you destroy your bowel's ability to take up nutrients, all those taken up after the stomach are affected more or less. Of course, the lungs an the brain, too. --85.179.15.63 (talk) 07:29, 23 March 2008 (UTC)

B Vitamin deficiency – but I can't figure where to show you except in the article Korsakoff's syndrome – an extreme example that doesn't seem to explain how this happens Julia Rossi (talk) 08:17, 23 March 2008 (UTC)

There are two proposed mechanisms of thiamine deficiency in alcoholics: [1] diminished intestinal absorption of thiamine caused by alcohol, and/or [2] destruction of thiamine by acetaldehyde. There are many other nutritional implications of alcoholism as well. Alcohol inhibits fat absorption, and thus interferes with absorption of vitamins A, D, & E. VItamin C & K are often deficient, which together with impaired hepatic function and impaired hepatic synthesis of clotting factors helps to explain the tendency towards severe bleeding in alcoholics. The B vitamin deficiency, particularly thiamine, leads to not only Wernicke-Korsakoff syndrome, but to other less severe neurological disorders. And there are implications on minerals, as well... though alcohol doesn't affect absorption directly, alcoholism decreases calcium absorption due to fat malabsorption, decreased magnesium levels due to decreased intake, increased urinary excretion, vomiting and diarrhea, iron deficiency related to gastrointestinal bleeding, and zinc deficiencies due to malabsorption or losses related to deficiencies of other minerals. The magnesium deficiency, which is very common in alcoholics, can in itself cause calcium deficiency. - Nunh-huh 11:23, 23 March 2008 (UTC)

Calcium Chloride re Dehumidifier

Is it possible to reuse the calcium chloride that has absorbed moisture from the air by heating the calcium chloride to release the water. Or is this possibly a dangerous experiment.

Yes - put in oven at more than 100C. This is safe, do not eat, do not inhale and dust from dried CaCl2.87.102.16.238 (talk) 14:00, 23 March 2008 (UTC)

There is one product I have seen in stores which apparently contains this chemical, and which has an indicator which changes color when the chemical has absorbed all the water it is designed to. Then you plug it into an electric outlet and a built in heating element dries it out for re-use. Edison (talk) 17:59, 23 March 2008 (UTC)

Black Hole Question

If a black holes "gravity feild" has settled into static equillibrium how do black holes merge and thier gravity merge along with it? Do the fields remain static and just reinforce eachother? I'm confused.11341134a (talk) 16:50, 23 March 2008 (UTC)

I don't think a black hole can be in perfectly static equilibrium because of Hawking radiation. But even disregarding that, saying that a thing is in "static equilibrium" usually means assuming no outside influences (like being hit by a black hole). --Allen (talk) 20:54, 23 March 2008 (UTC)

A system of objects interacting only through gravitational forces can never exist in a stable static equilibrium (except in the trivial cases of there being only one object, or every object occupies the same position and has equal velocity). Someguy1221 (talk) 03:39, 24 March 2008 (UTC)

The Cat's Brain Compared to a Human's Brain

Do you know of some such website that will let me compare a cat's brain to a human's brain? --209.226.138.43 (talk) 17:56, 23 March 2008 (UTC)

Not really, but our articles on cat intelligence and human brain might help. --Allen (talk) 18:18, 23 March 2008 (UTC)

Why The Sky Is Blue?

I heard from a friend that the sky is blue because of the colour being reflected off all the water in the world.Can somebody verify that? (and no I am not doing a science project,I just really want to know) -- 209.226.138.43 (talk) 18:12, 23 March 2008 (UTC)SilverLeaf

No. See Diffuse sky radiation. --Allen (talk) 18:15, 23 March 2008 (UTC)

Hi. By the way, I'm not sure, but I think part of the reason why water (usually) appears blue is because it reflects the blue sky (either that or there is oxygen in water which scatters light). Thanks. ~AH1^(TCU) 18:18, 23 March 2008 (UTC)

Here's something from the Library of Congress about why the ocean is blue. --Allen (talk) 18:25, 23 March 2008 (UTC)

We actually have an article on the Color of water. Someguy1221 (talk) 04:52, 24 March 2008 (UTC)

Actually, pure water absorption spectrum shows an increased absorption at 600 nm and longer wavelengths (just google "liquid water visible absorption spectrum" - there are plenty of references, but some require subscription for the respective scientific journals). Simply speaking, pure water absorbs red light stronger than yellow, green, blue, and violet light. Thus, white light passing through water loses its red component, and looks "anti-red", that is, blue to the human eye. Actually, violet light is also absorbed a bit stronger, so greenish-blue may be a more accurate description. This is for pure water; any dissolved or suspended impurities may change the perceived water color further. --Dr Dima (talk) 18:38, 23 March 2008 (UTC)

Think about this: if you shine a white light (like a flashlight) on a body of water at night, it still looks blue, right? But there isn't enough intervening air to filter out the red wavelengths in the light, so it must appear blue because the water is absorbing those wavelengths. « Aaron Rotenberg « Talk « 04:49, 24 March 2008 (UTC)

FingerPrints

Why are there no 2 fingerprints alike? SilverLeaf209.226.138.43 (talk) 18:29, 23 March 2008 (UTC)

See Fingerprint#Friction Ridges. --Dr Dima (talk) 18:42, 23 March 2008 (UTC)

Also, try this Google search for more information about stochastic pattern formation and fingerprints. By the way, when editing Wikipedia, try not to start a line with spaces; it has odd formatting effects. Also, you can search for articles by typing words into the "search" box to the upper left of any page. --Allen (talk) 18:48, 23 March 2008 (UTC)

The thing I also wonder about is how permanent are fingerprints really? Some years ago I had a skin ailment that affected my fingertips (among other areas). For a time, several of my fingertips had a very smooth, taut appearance with no discernable ridges. Later, when things healed, the ridges returned, but I've always wondered with the ridges that returned actually had the same pattern as before or whether the ridges were regenerated in a different pattern than previously. Since I don't have any record of my previous fingerprints, I have no way of knowing. So how persistent are fingerprint patterns relative to diseases and physical disturbances that might temporary remove the outward manifestation of ridges? Dragons flight (talk) 19:10, 23 March 2008 (UTC)

This Google search turns up some sources like this one suggesting that they do grow back the same after physical disturbances, unless there is too much scar tissue. But I haven't looked closely enough to see if there's info on diseases, or on what mechanism preserves the original pattern. --Allen (talk) 19:31, 23 March 2008 (UTC)

Does water "go off"?

When I buy water in a bottle from the mall it has an expiration date, but I can't see why if its kept in sealed bottle you can't drink it in 100 years time. Does it go gor something?

Here is a response to a person asking the same question: http://www.madsci.org/posts/archives/aug2000/966882443.Ch.r.html

Basically, the substances that makes up the container will also leach into the water, creating unpleasant tastes. --Bowlhover (talk) 19:35, 23 March 2008 (UTC)

See Bill Nye the Science Guy Nothing444 20:00, 23 March 2008 (UTC)

Why? SpinningSpark 20:16, 23 March 2008 (UTC)

Because it's too expensive to use substances for the bottle that don't solve into the water. --85.179.24.245 (talk) 15:35, 24 March 2008 (UTC)

I guess unless it's sterile water in a sterile container, in time bugs will grow. Julia Rossi (talk) 00:31, 24 March 2008 (UTC)

I don't agree. They would need something to eat in order to grow. StuRat (talk) 02:50, 24 March 2008 (UTC)

I can't pin down the study right now but slime mould is commonly found in bottled water beyond a certain age. I suppose trace nutrients are all they need. Franamax (talk) 02:57, 24 March 2008 (UTC)

This[14] and the article anaerobic bacteria is starting to make tap water look very good. Julia Rossi (talk) 03:19, 24 March 2008 (UTC)

Stagnant does not mean 'closed in a bottle', stagnant means just 'standing'. --85.179.24.245 (talk) 15:37, 24 March 2008 (UTC)

To grow stuff in water, you need – at a minimum – a source of energy and a source of carbon. (Strictly speaking a number of trace minerals are also necessary, but to a limited extent those can be scavenged from the original source of contamination, and many are present at some concentration in the water anyway.) A sealed bottle of water contains no carbon source; there's no raw material for new bugs, so no growth occurs. (If the cap is loose, atmospheric carbon dioxide will provide carbon.) Energy can be drawn from chemical sources (sugars, proteins, or other water contaminants) but these are rare in bottled water. The usual energy source is light, which will drive photosynthesis. Since abiogenesis is unlikely in a water bottle, we also need some initial source of contamination: fungal or algal spores or the like. Most bottled water bottles (when new) are pretty sterile, they shouldn't contain any stuff that will grow.

The picture changes when you look at people who reuse and refill their bottles. biofilms tend to build up in these containers, and they are supplied with ample fresh air and light over time. (That may be what Franamax was thinking of in his comments above).

I would guess that the concern with long-stored bottled water is due to taste or leached chemical contaminants as noted above; unopened factory-packaged bottles should contain no biological contaminants, and – unless the water were badly tainted – those organisms would be too starved to grow even if they were present. TenOfAllTrades(talk) 15:58, 24 March 2008 (UTC)

Water bottles are made of plastic. Isn't that a source of carbon? — DanielLC 16:30, 24 March 2008 (UTC)

I was thinking along the lines of this and the discussion just above the figure. Note they're referring to mineral water which is a little different than regular bottled water. I'm not sure if I was referring only to the NRDC study, I recalled something more specifically along the lines of 30% of bottles with slime mold (which is a particularly resilient animal) after 6 months, but I can't find the specific ref. Cool and dark storage would be important in avoiding contamination of any kind, whether it's chemical leaching or biologic growth. Franamax (talk) 16:37, 24 March 2008 (UTC)

Snake venom - quick question

In general, is a poisonous snake's venom effective against another snake of the same species? --Kurt Shaped Box (talk) 21:07, 23 March 2008 (UTC)

Snake_venom#Among_snakes might be of some use. bibliomaniac15 Midway upon life's journey... 21:53, 23 March 2008 (UTC)

My understand is "usually, yes." Even snakes that eat other snakes are not often immune to snake venom, it's just the difference between digesting venom and having it injected intravenously. But I'm no herpetologist. That particular article section sure has a lot of "citation needed" marks. --Captain Ref Desk (talk) 22:47, 23 March 2008 (UTC)

Eggs?

What are the brown things?

Can anyone identify the brown things in the picture? They were found recently on the lights left outside for a few months near Houston, TX. anonymous6494 22:49, 23 March 2008 (UTC)

They look like aphid eggs to me. —Steve Summit (talk) 00:17, 24 March 2008 (UTC)

Aphids are viviparous, they look a bit like eggs of a lepidoptera of some description. Compare with these. [15] Richard Avery (talk) 08:42, 24 March 2008 (UTC)

Bronner's liquid soap turns white when cold

Why? —Tamfang (talk) 23:59, 23 March 2008 (UTC)

It's just a guess, but oils often do that when they solidify. StuRat (talk) 02:47, 24 March 2008 (UTC)

I was about to guess the same thing. And our article on E. H. Bronner mentions that Dr. Bronner's is castile soap, containing vegetable oils. And many vegetable oils turn white when they're cold, due to partial solidification, as StuRat said. —Steve Summit (talk) 05:16, 24 March 2008 (UTC)

March 24

Mean tropical year

Is the "mean tropical year" the average of the four tropical years measured respectively starting at the vernal equinox, summer solstice, autumnal equinox and winter solstice, or is it based on a mathematical "continuous" averaging taken over all possible tropical years through the four seasons? I have seen it described in both ways -- does anyone have a definitive answer? 86.134.46.159 (talk) 01:02, 24 March 2008 (UTC) (BTW... I should mention that the Wikipedia article Tropical year contradicts itself in this respect. In one place it says one thing and in another place it says another.)

how do i become taller?

ow i'm over 20 and my height is 5'4" so i want to more tall than before so how can i do? besides go living in asia 141.149.55.113 (talk)

(moved from WT:RD) :D\=< (talk) 04:45, 24 March 2008 (UTC)

There's nothing you can do.. try wearing shoe inserts or buy shoes with thick soles. There is distraction osteogenesis, but it's stupid and, well, absolutely insane. :D\=< (talk) 04:49, 24 March 2008 (UTC)

Aren't you the same person who asked the same question back in January? Do reread the answers at that link. Also read the "Cosmetic lengthening of limbs" section in the distraction osteogenesis article Froth referenced. —Steve Summit (talk) 05:07, 24 March 2008 (UTC)

I'm over 20 and my height is 5'4" so what's the problem? Why would you want to be taller? I think that I'm the perfect height, don't you? Are you saying that I should want to be shorter or taller? Why the hell would I want to be what I'm not? I also don't write poetry - should I worry about that and want to be a poet? Look 141..., you're asking a question like "I am white and I want to be black" or some other such other bullshit. You can and should develop the things that you are good at and not concern yourself with those things over which you have no control. And, asking the likes of us to address the things over which you have no control is really stupid. --hydnjo talk 05:56, 24 March 2008 (UTC)

No use berating the guy for asking a question. Perhaps he thought there might be an easy way to increase his height. (Certainly several completely bogus 'herbal' products are advertised.) Perhaps he has some legitimate and practical reason for wanting to be taller. (Just because we can't think of one off the top of our heads, doesn't mean it can't be true.) Most of all perhaps the guy was just curious. There's nothing at all wrong with that. The point is that it's crazy to rant at someone based not on what they said, but based on your opinions of what you suppose their motives for saying it might be. 72.10.110.107 (talk) 13:50, 24 March 2008 (UTC)

You know, this question was once asked the Cecil Adams on The Straight Dope. He gave some good answers; I'd recommend reading it. Neal (talk) 16:26, 24 March 2008 (UTC).

Bamboo

I would like to know the kinds of bamboos. Please!

Is there somthing within the Bamboo article that you don't understand? --hydnjo talk 05:59, 24 March 2008 (UTC)

I mean kinds of bamboos! Names of them!I searched in Bamboo but I didn't see that! so....!

The bamboo article says bamboo's in the subfamily Bambusoideae, which has a list of a bunch of kinds of bamboos. It looks like it lists them all, but may be not(?) -Haikon 06:23, 24 March 2008 (UTC)

) thanks u so much! To u all!

How come so many invasive species come from Japan?

...to the United States and Europe? May be "so many" is an exaggeration. I can only think of two, those ladybugs and kudzu, but if you think of Japan as a group of Pacific islands, two is a lot. I mean you probably couldn't import an invasive species from New Zealand or Hawaii if you tried. And given some of the peculiar animals native to Japan, it would seem like that ecosystem would be more on the receiving end of pest invasion.

Anyway, I'm trying to find general rules or theories regarding invasive and non-native species to answer this question, and I'm not coming up with much. (Except a "Baker's rule", and I haven't even found that really, not stated by Baker him/herself anyway.) A lot of isolated ecosystems have been screwed up because of non-native species, and in each case it's understood pretty clearly how and why, but I can't find an explanation of how any why this would happen in general, not just in a given case. Anything at all like an answer or points in the right direction would be greatly appreciated. -Haikon 06:44, 24 March 2008 (UTC)

Your first statement appears to be slightly flawed. New Zealand plants are a problem in other countries, e.g. [16], [17]. It is of course true that exotic plants are more of a problem in NZ then NZ plants in other ecosystems, but then nothing you've said suggests that this is any different from Japan except that the Japanese invasive species are more widespread, but then again, the Japanese ecosystem was always a lot less isolated then NZ or Haiwaii (meaning it was a lot less different). BTW, from what I can tell it is inaccurate to call the Harmonia axyridis a Japanese invasive species. It may be native to Japan but from what I can tell it is also native to other countries. It appears even more clear cut with the kudzu. All these two examples really tell you is that the Japanese ecosystem was not that isolated. You could just as well say any species which is native to Bali or some other small island and invasive comes from a tiny island even if in reality it is native to a lot of places. To answer your second question, in general a species will become invasive if it is able to better fill a niche then any of the existing native species. Countries with highly isolated ecosystems such as New Zealand tend to have a lot of niches which can be more effectively filled by something from somewhere in the very wide world out there. Consider New Zealand for example where the lack of large ground based predators meant that most native animals particularly birds obviously were adapted to such a situation leaving it ripe for invasion by ground based predators. Obviously for very diverse, non-isolated ecosystems like Europe, Asia or whatever, it is unlikely that there will be many niches left unfulfilled or that there will be a whole lot of invasive species coming from the small number of isolated ecosystem which are able to better fill a niche. Nil Einne (talk) 09:16, 24 March 2008 (UTC)

Big bang expansion thing

Okay, space is expanding so from my head it appears my head is the center of expansion. Got it. But am I to understand that at the atomic level space is not expanding? Electrons are not getting further away from the nucleus and the space between atoms and molecules is the same density and the distance between them is the same but what about the distance between planetary orbits? Is that expanding as well? If so by how much in a billion years? 71.100.1.65 (talk) 10:11, 24 March 2008 (UTC)

Short answer is no, space is not expanding at the atomic level because the dominant force that determines the interactions betweens atoms is the electromagnetic force, not gravity. Space is not expanding at the scale of planetary orbits either because the simplifying assumptions on which the Friedmann equations are based are only physically correct on scales of millions of light years or more. For the long answer see this question and its answers on March 21 above, and our metric expansion of space article. Gandalf61 (talk) 13:07, 24 March 2008 (UTC)

Wow, we've got a lot of questions on this lately! --Captain Ref Desk (talk) 14:30, 24 March 2008 (UTC)

Forgive me for asking a homework question, but how many different hormones are there in the human body?

Discovered at least -- I've searched this all over, and it seems a particularly pointless question to ask (given that we also have to detail every petty step in various signal transduction pathways), but alas, I can't seem to find a source that lists *every* single human hormone, or at least one that tells me that this is every single human hormone discovered so far (and numbers them). John Riemann Soong (talk) 14:33, 24 March 2008 (UTC)

There are hundreds, are you sure this isn't specific to a certain syllabus? --Mark PEA (talk) 16:13, 24 March 2008 (UTC)

Movie science: what can or can't you tell about a torpedo from its sound?

In the movie The Hunt for Red October, there's a scene in which a sonar operator reports that an incoming torpedo "went active the moment it was launched" and that the torpedo has acquired its target. Is it real science, or is it just artistic license taken by the moviemakers, that a sonar operator is able to tell if a torpedo is armed and has a lock on its target just by listening to its sound? --71.162.242.38 (talk) 16:25, 24 March 2008 (UTC)

I asked myself the same question. A torpedo can be sent out running slow and quiet so that its target might not know it's there until it's too late. Subs maneuver slowly when they aren't going anywhere in a hurry, so the torpedo doesn't need to go very fast to get over near its target. A wire-guided torpedo will be steered by the attacking sub to get it near its target, at which point it will told to turn on its own sonar and home on that, what the movie called going "active", I guess. Faster torpedo propellor speed means higher pitch and louder. (If the torpedo hasn't hit anything after a certain amount of time has passed, and the wire isn't connected any more, it will conduct a search pattern automatically, at which time the attacking sub had better have gotten its butt out of the area.) I would guess that the search sonar and the final homing sonar would differ in some audible way, so that you'd be able to tell when it had "acquired" its target by merely listening. As for whether the torpedo is "armed", I think we're supposed to imagine that Jonsey knows a hell of a lot more about this whole business than we ever will and that some combination of indicators and knowledge of the workings of Russian torpedos clues him in, so just sit back and enjoy the show. --Milkbreath (talk) 16:48, 24 March 2008 (UTC)

arsenic weight per gallon

I am desining an arsenic treatment plant for a small town in CO and I was crious to know how much a gallon of arsenic would weigh?

Thank You,

Michael miklroy04@yahoo.com

The article on Arsenic_contamination_of_groundwater might provide a good place to start. It looks as if most arsenic is in the form of dissolved arsenic salts, and therefore the weight of material to be removed may be dominated by the substance used to remove the arsenic, not by the arsenic itself. JohnAspinall (talk) 16:53, 24 March 2008 (UTC)