Wikipedia:Reference desk/Archives/Science/2007 September 24

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1 September 24

[edit] September 24

[edit] solubility of sugar in water

I need to know what effects temperature has on the amount of sugar that dissolves in water.EG: Will more sugar dissolve if the water is hotter? —Preceding unsigned comment added by Latelearner (talk • contribs) 01:29, 24 September 2007 (UTC)

Yes, more will dissolve in hotter water. Now someone please provide an equation. Edison 02:54, 24 September 2007 (UTC)

It sounds like you're doing homework. Perhaps the article solution will be useful? --Mdwyer 03:35, 24 September 2007 (UTC)

I found a table. [1]. Someguy1221 03:38, 24 September 2007 (UTC)

What's interesting about a sugar-in-water supersaturated solution is that when it cools, the sugar doesn't precipitate out. Rather, it forms a syrup.

Mrdeath5493 04:35, 24 September 2007 (UTC)

Melting point depression perhaps?83.100.254.150 06:48, 24 September 2007 (UTC)

Though if you're trying to do it, you can make sugar crystals at home by providing a crystal seed or a suitable surface. Also, as a side note - the table Someguy posted gives values for glucose, not sucrose... Nimur 04:47, 24 September 2007 (UTC)

It's all sugar ;-) Someguy1221 04:51, 24 September 2007 (UTC)

Yes, and this is why coffee and tea are often served too hot to drink, so that sugar can be easily dissolved in it. If you've tried adding sugar to iced tea, you know it doesn't dissolve all that easily. StuRat 15:59, 24 September 2007 (UTC)

[edit] Body Mass Index Calculation

"BMI ... calculated by multiplying one's weight in kg twice, then dividing it by one's height in cm" Is this a valid way to calculate BMI? —Preceding unsigned comment added by 66.238.233.150 (talk) 03:22, 24 September 2007 (UTC)

You could just read our article on Body mass index. --Mdwyer 03:36, 24 September 2007 (UTC)

SI units
$\mathrm{BMI} = \frac{\mathit{weight} \ \mathrm{(kg)}}{\mathit{height}^2 (\mathrm{m^2})}$

BMI = W/(H^2)

Let H = 100 h (conversion from metre to centimetres)

BMI = W/(H^2) = W/((100 h)^2) = (1/10000) * W/(h^2)

So we have Weight (W) in kilograms

So we have Height (h) in centimetres —Preceding unsigned comment added by 202.168.50.40 (talk) 04:47, 24 September 2007 (UTC)

202.168.50.40 04:45, 24 September 2007 (UTC)

Thanks for the reply. But my question is if there is alternative ways for reckoning it, say in Japan. The part I quoted is from a book on Japan. Is that incorrect? 71.195.106.60 04:52, 24 September 2007 (UTC)

Our own article suggests the calculation (also its definition) is universal. Someguy1221 05:17, 24 September 2007 (UTC)

From the quotation it seems as if the book has gotten which term should be squared the wrong way around. And yes, it should be the same everywhere, although the significance of a certain BMI does differ between ethnic groups. Recurring dreams 08:39, 24 September 2007 (UTC)

I do seem to recall an alternative that more accurately tried to measure body fat percentage, I think by measuring a person's weight in air and then in water and applying a formula to the two weights. Does this sound familiar to anyone ? Then there was also the less accurate "pinch an inch" method, where calipers were used to measure to amount of fat at the waist. StuRat 15:54, 24 September 2007 (UTC)

[edit] Pair of electrons .

Why do electrons in an atom makes pair ; while they repeal each other . Do free electrons also make pair ? Is there any wikipedia article about that ? —Preceding unsigned comment added by Shamiul (talk • contribs) 05:27, 24 September 2007 (UTC)

Pauli's exclusion principle, atomic orbital...Free electrons (truly free, not bound to anything positive) will just repel eachother. Someguy1221 05:47, 24 September 2007 (UTC)

Yes Pauli's exculsion principle is the relevant one here. Basically every electron wants to be at the lowest energy level, but identical electrons (with the same quantum numbers are excluded. Electrons have two spin quantum numbers which allow them to form into pairs. On free electrons, the only example I can think of is Cooper pairs in superconductivity. Cyta 10:31, 24 September 2007 (UTC)

Cooper paired electrons aren't truly free though. Someguy1221 20:59, 24 September 2007 (UTC)

...and here I thought the Pauley Exclusion Principle applied to keeping Jane Pauley off The Today Show. :-) StuRat 15:46, 24 September 2007 (UTC)

[edit] particle spin .

As far as i know particle spin refers to the revolving characteristics of an particle about an axis(same as the world spin about it's own axis). My question is : how the spin of particle is defined by number ? as we see the spin of electron and proton is half . why this is half ? please clear my confusion by assuming the world as a fundamental particle . what will be the spin of the world if we assume the world as a fundamental particle ? photon spin is 1 . what does that mean ? does photon also revolve about an axis ?

We have a detailed explanation of particle spin from various different points of view in our article on spin (physics). In general, attempts to interpret quantum spin by assigning classical physical attributes to elementary particles seem to lead to confusion and contradictions. Simplest approach seems to be treat elementary particles as point objects that have an attribute that happens to behave like classical angular momentum, except that it is quantised. Gandalf61 10:20, 24 September 2007 (UTC)

[edit] Color and octaves

The human visible spectrum entails about one octave - 380 to 770 nm. Furthermore, the color wheel depends on the upper and lower wavelengths looking the same and seamlessly blending into each other. It's interesting that visual frequencies one octave apart are perceived as similar. What's the physics behind this visual perception? Do other animals also perceive an octave of visual spectrum? —Preceding unsigned comment added by 76.27.209.182 (talk) 06:57, 24 September 2007 (UTC)

Unfortunately the lower frequencies DON't look the same as the upper frequencies - lower = red, upper = blue/violet - the way the colour wheel works is by belending red into blue via purple - it's only real on paper - the upper and lower frequencies DON't look similar - though it would (as you say) be interesting if they did83.100.254.150 07:14, 24 September 2007 (UTC)

I think the upper and lower frequencies look the same, at least to me, and first noticed when looking at a prism in sunlight. Afterwards, it occurred to me that the color wheel was continuous. —Preceding unsigned comment added by 76.27.209.182 (talk) 07:27, 24 September 2007 (UTC)

Your impression is mistaken. Your color wheel contains non-spectral colors, i.e. colors whose perception cannot be induced by any single-frequency light. The colors between red and violet on the color wheel are produced by mixing different proportions of red and violet lights. These colors are non-spectral and don't have a frequency to speak of. (See also chromaticity diagram, and the comment about the horseshoe-shaped spectral locus in particular). --71.175.68.224 10:14, 24 September 2007 (UTC)

I expect it to look like this (from Prism (optics))

What I can see is red at the top and blue at the bottom - which look different to me - however your perception may be different - if it is - please say more...87.102.21.91 11:53, 24 September 2007 (UTC)

Yes, my perception might differ - or it might just be limitations of the computer screen. The next time you see a real rainbow or prism, not printed or on a monitor, look closely and see if the far end of violet starts to look like the other end of red. It does for me. Not so on the computer monitor, though.

(from farther above) Your impression is mistaken. Great, you seem awfully sure of yourself ;) 76.27.209.182 14:46, 24 September 2007 (UTC)

OK - I strongly recommend you take a colour-blindness test. I am an expert in this field - and I can absolutely, 100% assure you that you are quite utterly mistaken - either because you have a very rare red/blue colour-blindness (I don't believe that) or because you are quite simply WRONG. Your eyes only have at most three sets of colour receptors (unless you are female and with about a one in 50 million chance you come from a second generation of colour-blind grandfathers who are colour-blind in two different ways - in which case you MIGHT be a tetrachromat - and have an extra green receptor...but you still won't see violet in both ends of a spectrum). The prism sorts colours in order of frequency. Low frequency light (red) is down one end and high frequency (blue) light is at the opposite end. There is no single frequency of light that looks 'violet' so there IS NO VIOLET IN THE SPECTRUM. Blue and red light look utterly different - so there is no possible way for one end of the spectrum produced by a prism to look even remotely similar. This is a myth that comes from Victorian times when it was believed that there was a hue/saturation colour model (which fits our perceptions) in reality - which would have required violet light. Hence the old children's ROY G BIV mnemonic for the colours in a rainbow (Red, Orange, Yellow, Green, Blue, Indigo, Violet)...well, there ain't no indigo or violet. SteveBaker 14:47, 25 September 2007 (UTC)

Yes, if someone says "I think A looks like B", you can certainly say "I don't think A looks like B", but you can't say "No, you don't think A looks like B", that's just silly. Many people think deep red and violet look similar, and I am one. This question is about perception, or what people think they see, not about the physics of the color wavelengths. Some people's brains seem to be wired to see those two colors as similar, so now the question is why this occurs. StuRat 15:30, 24 September 2007 (UTC)

Yes - the far end of violet - eg blue, indigo then violet - I see the indigo as just very blue and the violet seems pinky/blue to me - but not really the same as the purple in the colour wheel between red/blue. (And yes computer screens can't display violet properly)

There should be a separate question about the perception of the violet as we don't (as I understand it) have violet receptors - so why it appears reddish (+blue) is a mystery - I will ask a question below about it.

As for your original 'octave' or frequency doubling question - it is interesting - but I don't think the effect is similar to hearing (of notes).. maybe you should ask specifically for more details about why the eye responds to a range of frequencies..83.100.254.136 22:09, 24 September 2007 (UTC)

I have always assumed it's because the red photoreceptor has a significant response to very short wavelengths: although its sensitivity peaks at long wavelengths, it doesn't fall off very fast, and might even have a little "bump" at the other end of the spectrum. The photoreceptor response diagrams in Wikipedia seem to vary in how clearly they show such an effect, but here's one: Image:Cone-response.svg. I'm not sure what happens below 400 nm where the red, green, and rod curves stop. As you move from long to short wavelength, you get a larger and larger response of blue cones relative to red and green, until you pass the peak absorbance of blue cones. Then blue falls off, so the red and green signals are proportionally larger. The response of red cones may rise in absolute magnitude too, if there's a little "bump" as I seem to remember seeing on other diagrams. This would explain why very short wavelengths start to look reddish. --Reuben 23:35, 24 September 2007 (UTC)

Yes, that diagram shows the effect nicely. Thanks. StuRat 02:19, 25 September 2007 (UTC)

I've worked with the USAF night vision labs folks who actually measure this stuff scientifically - there is definitely no 'bump' in the red response. The 'spectrum' ends with a fading off of our blue receptor into dark blue (which is sometimes called 'indigo') - there is no 'pinkish' blue. "Ultra-violet" is a misnomer - it ought to be called "Ultra-blue" - but we are stuck with this ancient word.

Now let's be VERY careful here. If you are looking at natural rainbows...formed by raindrops in the sky...there is something else going on. Check out this photo of a "supernumerary" rainbow: Image:Supernumerary rainbow 03 contrast.jpg - here you have a number of overlapping rainbows such that the red of one of the inner bows overlaps the blue of an outer bow - producing 'magenta' (aka violet/purple) by a mixture of the blue from the outer rainbow and the red from one of the inner ones. Yes - in this circumstance, you can see violet in a natural rainbow - but that's not telling you much about the nature of vision and light - it's telling you something very complicated about raindrops and light scattering. So let's forget looking at natural rainbows...they are NOT pure spectra. Put some sunlight into a triangular glass prism - and you'll soon be convinced that there is no violet there. There simply cannot be given the way our eyes work. SteveBaker 14:47, 25 September 2007 (UTC)

Take a look at http://www.handprint.com/HP/WCL/IMG/conesens1.gif from http://www.handprint.com/HP/WCL/color1.html - note the red sensitivty starts to increase again in the far blue - could this be why some people are claiming to see purpley colours beyond indigo?87.102.10.190 15:52, 25 September 2007 (UTC)

Did you actually read the article? The bit where it shows those curves and says The photoisomerization curves should describe color vision if each type of cone contains only one kind of photopigment and if the intensity of the photoreceptor response is proportional to the quantity of photoisomerized pigment. In fact, these curves do not correspond to human color matching responses, especially for the L cones. - it then goes on to present another set of curves without the 'bump' in red - which are how we actually respond. SteveBaker 18:24, 25 September 2007 (UTC)

Yes but how were the 'human color matching responses' obtained - typically eg see Color_vision#Mathematics_of_color_perception "..In order to calibrate human perceptual space, scientists allowed human subjects to try to match any physical color by turning dials to create specific combinations of intensities (IR, IG, IB) for the R, G, and B lights, resp., until a match was found..." (assuming the same method was used in the above.)- in the link it is clear than using that data (the curves you refer to) - once past the blue peak response - the blue falls off more rapidly than the red - therefor and increase in red:blue perceptual ratio.(possibly). What do you think?87.102.10.190 19:51, 25 September 2007 (UTC)

ie in the 'ultrablue' or 'violet region' human subjects were adding an increase amount of red in comparison to blue to make the colours look the same87.102.10.190 19:53, 25 September 2007 (UTC)

EVEN WORSE this site states that

Based on the above details, the CIE (1931) Photopic Luminosity Function is a symmetrical curve fitted to an ensemble of data sets describing the Spectral Response Function of the Human Eye to radiation of inadequately controlled intensity and color temperature[[2]]

- which could mean that the rgb data discussed shouldn't even apply to indigo/violet as the commonly response curves were obtained with light "using incandescent light sources with color temperatures in the 2000-3000 Kelvin range"...87.102.10.190 20:21, 25 September 2007 (UTC)

I asked this question half a year ago (plus some more) and got some rather different types of answers. DirkvdM 16:50, 25 September 2007 (UTC)

That's one and a half years ago. Now I know what to get you for Xmas (a calendar). :-) StuRat 01:20, 26 September 2007 (UTC)

Or a pair of glasses. Or a new brain. But not for bloody christmas please. I'd prefer to get it at the birthday of the real Santa. DirkvdM 18:00, 26 September 2007 (UTC)

[edit] Two (make that Three) Quantum Physics Questions

Why are there no spin-1/2 baryons composed of three identical quarks (no nucleon corresponding to Δ++)?
Why are chargeless photons sufficient to explain the electromagnetic force between charged particles, while the strong force requires particles, themselves color-charged, to transfer force between colored particles?
Why must the quarks bound in a hadron constantly change colors?

Thanks. Ratzd'mishukribo 07:20, 24 September 2007 (UTC)

I could be totally wrong here, but isn't the first one the Roper resonance? —Keenan Pepper 19:27, 24 September 2007 (UTC)

These are quite subtle questions! I looked up answers to #1 in several places, and couldn't find anything that was totally satisfactory. It seems that antisymmetrizing the quark wave functions, assuming the orbital parts are all s=0, requires the color part to be fully antisymmetric and spin + flavor to be fully symmetric. I have not been able to convince myself that this forbids a spin-1/2 uuu or ddd nucleon without radial excitations, so there must be some constraints that I'm missing. Self-interacting gauge bosons are a consequence of the gauge group SU(3) being nonabelian, while U(1) is abelian. When you have a nonabelian gauge group, there are extra terms in the Lagrangian that don't cancel out and are equivalent to interactions between the bosons. That's #2. As for #3, the strong force that keeps hadrons together is outside the realm of perturbation theory. That means you can't assume that each quark has a well-defined color at any given time, and emits and absorbs gluons at discrete intervals. The coupling is strong, so this kind of simple picture breaks down. --Reuben 20:48, 25 September 2007 (UTC)

Update: I finally saw the light on #1. To start with, to get spin 1/2 you need the Clebsch-Gordan coefficients to come out right. That means you need two quarks in a spin-singlet, and the third off by itself. The quarks in the singlet state are antisymmetric under exchange. In a way somewhat similar to spin sums, you can't just add up r-g-b and get something that's color neutral overall. You need the color part of the wave function to be a color singlet, which means it has to be totally antisymmetric by itself. The flavor part of the wave function can't be antisymmetric at all because all three quarks are the same flavor. The orbital part is the same, all s=0 because we don't want an excited state. Therefore, the wave function has to break down into a tensor product of four completely independent parts: flavor and orbit fully symmetric, color fully antisymmetric, and spin at least partly antisymmetric. Whatever you try to do with the rest of the spin state, you can never make the whole thing antisymmetric at once. So it's verboten! Thanks for the interesting question. It was good to think that through again. --Reuben 00:42, 26 September 2007 (UTC)

As for the Roper resonance, it's a radially excited state, so the s=0 assumption above is out the window. It could then be spin-1/2 and uuu or ddd. However, the literature suggests it's something rather more complicated, with an internal structure that might be nucleon + meson. --Reuben 00:44, 26 September 2007 (UTC)

Thank you!

(Now that I know the answer, I can start working on what it means…) Ratzd'mishukribo 05:47, 26 September 2007 (UTC)

[edit] Jelly Shots

If I used vodka instead of water when making jelly would the jelly still set? --124.254.77.148 07:52, 24 September 2007 (UTC)

Vodka has a lower freezing point than water due to the alchohol content. This means it can be hard to get the jelly to set properly, especially if you use pure vodka - you'll often get a pretty 'runny' jelly. It would be easier to get to set if you diluted the vodka considerably with water. (And bonus health warning: be very careful when taking 'jelly shots', as it is easy to rapidly consume large quantities of alchohol, which can have serious health consequences, including potential brain damage or death). --jjron 09:05, 24 September 2007 (UTC)

I'm pretty sure freezing point has nothing to do with with the setting of gelatin. ike9898 17:45, 24 September 2007 (UTC)

You might want to look at the Jell-o and Gelatin articles. "Jelly" UK = "Jell-O" USA. It seems like gelatin needs some water to form a gel, but I haven't found anything yet that says what the ideal water/alcohol ratio would be. --Mdwyer 21:37, 24 September 2007 (UTC)

The guys at this site performed an extensive set of experiments to determine the maximum attainable level of alcohol that could be added to a Jell-o shot and still have it gel. TenOfAllTrades(talk) 18:40, 25 September 2007 (UTC)

Wow, we even have a Jello shot article section! DMacks 18:54, 25 September 2007 (UTC)

When making jello shots do not add more than 12oz of vodka to the mix. If you do it will be soft and running although this can be desireable as a mix too weak will result in jello shots that won't come out of the shot glass :(. SO, replace 12oz (12 shots) of the water with your drink of choice and get mixing! I've made them all the way up to 20oz but at that point its just a slimy goo that doestn't resemble jelly at all. Finding your optimal mix is half the fun. (Note: Do not add the 12oz to the original recipe, REPLACE 12 oz of water with 12oz of booze.) —Preceding unsigned comment added by 60.242.173.55 (talk) 08:01, 27 September 2007 (UTC)

[edit] Black women's buttocks

Hello, wanted to ask if there's an evolutionary explanation for black women's uniquely fat buttocks. Thanks, 87.68.194.108 09:26, 24 September 2007 (UTC)

May be a common genetic trait for some black women concentrated in certain geographic areas but women and men from White, Hispanic and other races likewise have equally large buttocks though perhaps not as concentrated in one particular geographic location. On the other hand all races seem to have members with buttocks which meet or surpass the designation of a "perfect 10." Clem 10:04, 24 September 2007 (UTC)

You may want to read our article on Steatopygia. Dismas|^(talk) 10:27, 24 September 2007 (UTC)

Interesting, thanx. 87.68.194.108

I can offer some speculation. The main purpose of fat on the buttocks (as opposed to elsewhere on the body) is to provide padding when seated. It would stand to reason, then, that those populations which had to sit on harder surfaces, like stone, would need more padding than those which had softer surfaces on which to sit, like sand or dirt. Since cavemen used to live in caves, this feature would have been positively selected, especially for women, who would tend to stay in the cave watching children, etc., while the men went hunting. Those with little buttocks fat would have risked sores, infection, and possible death. After humans moved out of caves, softer seating surfaces became available, so this feature was no longer positively selected. I imagine a more even distribution of fat has other advantages, such as providing better thermal insulation. Thus, I'd expect this trait to have largely disappeared, especially in colder climates. StuRat 15:20, 24 September 2007 (UTC)

Erm, let me get this straight, are you arguing that men selectively chose to breed with women who would have a more comfortable seat back at the ol' homestead? Does that mean that at some point in geological time men actually considered women's needs when it came to sex? --Dweller 15:27, 24 September 2007 (UTC)

No, I never mentioned sexual selection at all. StuRat 16:12, 24 September 2007 (UTC)

I'm tempted to plaster StuRat's post with the {{fact}} template (^{[citation needed]}), demanding citations for his claims... Nimur 15:34, 24 September 2007 (UTC)

That would mean my statement was speculation, would it not ? I sure wish I'd said that myself :-) StuRat 16:12, 24 September 2007 (UTC)

Goodness me, StuRat, you have excelled this time. Not every phenomona can be explained the simpistic natural section as extolled in popular science. Dawkins et al have a lot to answer for. Rockpocket 20:33, 24 September 2007 (UTC)

Is Dweller suggesting that humans are rocks? -- JackofOz 15:37, 24 September 2007 (UTC)

The "caveman" is an inaccurate stereotype. Early humans, such as the Cro-Magnon, mostly lived in huts and used caves for rituals. We know this because caves in which cave paintings have been found do not show signs of ongoing habitation. Gandalf61 15:39, 24 September 2007 (UTC)

There certainly was a time before which humans (or pre-humans) lived in huts. Where did they live then ? StuRat 16:12, 24 September 2007 (UTC)

The same places non-human primates do now: on the bare ground, in "nests", up on branches, etc. We're not well adapted to life in a cave. Matt Deres 16:31, 24 September 2007 (UTC)

There would have been millions of years between when our ancestors moved out of the trees and when they learned to build huts. I have to think they had some form of shelter in that time, such as caves. StuRat 22:55, 24 September 2007 (UTC)

I'm not entirely certain StuRat was being serious. Mind you, I'll let him speak for himself. StuRat? --Dweller 15:43, 24 September 2007 (UTC)

I am serious. StuRat 16:12, 24 September 2007 (UTC)

Lol. That's definitely my cue to log off for a while. Meanwhile, public thanks to Jack for making me smile at the end of a trying day. --Dweller 16:14, 24 September 2007 (UTC)

Belatedly, noblesse oblige. -- JackofOz 03:46, 26 September 2007 (UTC)

The idea to sit on something soft instead of something hard seems pretty obvious- even animals do this. I don't see why this would relate to what kind of house you live in. Friday (talk) 16:25, 24 September 2007 (UTC)

I have a vague recollection of a study a few years back that found that on the average black women had a greater degree of lordosis than white women. Gzuckier 17:32, 24 September 2007 (UTC)

It's the Khoikhoi, and not Africans as a whole, that as a group have the most pronounced posteriors. --M @r ē ino 19:49, 24 September 2007 (UTC)

Yes I have to agree with other posters that User:StuRat is completely off 'beam' this time.

The purpose of a large pair of buttocks is purely to store energy in the form of fat. See Hottentot —Preceding unsigned comment added by 88.109.211.7 (talk) 22:20, 24 September 2007 (UTC)

Butt then why would the fat need to be all in one place, instead of evenly distributed ? StuRat 22:55, 24 September 2007 (UTC)

I know its a bit of a bummer, butt thats the way it is 8-) —Preceding unsigned comment added by 88.109.211.7 (talk) 00:32, 25 September 2007 (UTC)

I think I saw somewhere that one idea about the advantage of storing all the fat in the buttocks is that it allows the rest of the body to maximise the surface area - volume ratio to maximise heat loss, which is important in hot climates like in Africa. So by keeping your fat all in one part of the abdomen, you can make the rest of your body skinny, and thus you can radiate your heat more efficiently than if you had your fat distributed evenly. Maelin (Talk | Contribs) 08:39, 30 September 2007 (UTC)

[edit] ancient cultures and dinosaur bones

What did ancient cultures have to say about dinosaur bones? Clem 09:58, 24 September 2007 (UTC)

The first recorded dinosaur fossil that I know of is in 1819 (by William Buckland). Previous to that, any large bone would most likely be attributed to some sort of mystical creature: A giant, a dragon, a griffon, a god, or a demon - just to name a few. -- kainaw ™ 12:30, 24 September 2007 (UTC)

Do you have references for these "dragon" bones, etc.? Clem 14:21, 24 September 2007 (UTC)

Well, if there were systematic record of them, they probably would have been identified as actual animals instead of mythical creatures. The widely accepted first documented study happened in 1819, as mentioned by Kainaw. Nimur 15:10, 24 September 2007 (UTC)

So then all of history, whether correct in its conclusion or assumption of whatever the subject might be prior to 1819 is bunk? Don't think so. In fact by providing such an answer I am beginning to think that whatever might be comming from this desk is more likely bunk instead. Clem 19:45, 24 September 2007 (UTC)

That all of history is incorrect is a ridiculous extension of the above statement. There's no need to be hostile to those that volunteer time to answer your wildly broad and vague question. Here's a link to a site that touches on the origins of dragon myths. There are countless young earth creationist sites that claim that leviathans and behemoths are dinosaurs, and others that rebut those claims. Here's a story about modern, though uneducated, Chinese villagers eating "dragon" bones. — Scientizzle 20:06, 24 September 2007 (UTC)

Everyone is entitled (and encouraged) to verify all the information provided on this reference desk. We have an entire encyclopedia, and many of our articles are carefully cross-referenced to reputable external sources. Wikipedia cannot simultaneously summarize concisely and expound in great depth. Nimur 03:10, 25 September 2007 (UTC)

Yes we've been eating fossils from pre-historic sites until some guy came along and said they are fossils. According to this site, it can calm your mind from agitation, cure dizziness, insomnia and diarrhoea and even premature ejaculation. --antilived^{T | C | G} 23:30, 24 September 2007 (UTC)

The books of Adrienne Mayor might be of interest. Review by Norman MacLeod. --JWSchmidt 02:21, 25 September 2007 (UTC)

I once heard in a tv documentary that in China dinosaur bones were considered to be dragon bones. DirkvdM 16:54, 25 September 2007 (UTC)

[edit] CATEGORY OF DISTRIBUTION / LINE AMPLIFIERS

kindly let me know that Catv distribution amplifiers/Catv Line Ampliiers can be categorised as a Intermeidate Frequency Amplifiers in terms of CATV(community antenna Television Network) used by Local Cable operator. (SEE WEB PAGE OF M/s.HANGZHOU PREVAIL OPTOELECTRONIC EQUIPMENT CO LTD, (prevail-catv.en.alibaba.com) ITEM NAME; (1) BI DIRECTIONAL TRANSMISSION TRUNK AMPLIFIER (2)BI DIRECTIONAL DISTRIBUTION AMPLIFIERS, (3) 1310N.M CATV AMPLIFERS.

waiting for your most positvie responce. —Preceding unsigned comment added by 116.71.55.121 (talk) 10:08, 24 September 2007 (UTC)

I would not call any of these intermediate frequency amplifiers. The trunk and distribution amplifiers would be categorised as wideband RF amplifiers as they handle a broad range of frequencies. The 1310nm is an infrared wavelength used on optical fibres. The RF is modulated onto the infrared frequency, and the signal can be carried over many kilometers without the loss and frequency distortion that a coax would cause. The intermediate frequency occurs in the televison when the signal is down converted.

Another place that you may see an IF in CATV, is when a satellite DTV broadcast is received the LNB converts the Ku band or C band signal to an L band ranging from 950MHz up to around 1950MHz. Graeme Bartlett 12:37, 24 September 2007 (UTC)

[edit] Sunset/sunrise on the equator

Does the sun set and rise at the same time every day day, year round, on the equator? If so, what time? I would have assumed the answer is yes, but the equator article doesn't say anything about it. 220.235.135.146 10:45, 24 September 2007 (UTC)

The sunrise article does, in the fourth paragraph. The times vary throughout the year because of the tilt of the earth. I'm glad you asked this question, because you got me poking around, and I found this [3]. I had just seen one of these again recently and vaguely wondered what it was called. The Wikipedia article on analemma explains all. --Milkbreath 11:13, 24 September 2007 (UTC)

And here I just thought that meant that Emma was anal-retentive. :-) StuRat 15:07, 24 September 2007 (UTC)

[edit] Yellow LEDs -- trivia

Red,green, orange and more recently blue led's are common - but where are all the yellow leds - for instance on consumer electronics - is there a reason why they are not used - or maybe I've just missed them.?87.102.21.91 12:19, 24 September 2007 (UTC)

Amber-colored LEDs are common. They are yellow enough. You may be mistaking them for being orange. -- kainaw ™ 12:25, 24 September 2007 (UTC)

I've seen amber ones - but they were 'amber' which to my eyes is orangey - how about a truly yellow LED?87.102.21.91 12:37, 24 September 2007 (UTC)

It must be a "style" thing; true yellow LEDs have existed for years and are as inexpensive and electrically efficient as any other color. Lately, "Chernobyl blue" has been the rage, even though blue LEDs are still substantially more expensive than the other visible colors.

Atlant 14:33, 24 September 2007 (UTC)

LEDs do not produce white light (even "white" ones are really just light blue), and as a result, you can't just stick a piece of coloured plastic over the top and make a coloured light - you need instead to dope the LED with trace amounts of various elements. Some of these are more expensive than others (red is much cheaper than blue, for example), so there tends to be bias towards these, but, as Atlant mentions, fashion plays a role too (red LEDs seem kind of 80s today, and red is quite a negative colour and is therefore generally reserved for standby or error states of electronics). In addition, gallium(III) phosphide, one of the commonest LED materials, isn't quite yellow, but more of a yellow-green; as a result, you may perceive this colour as being very green. A cursory glance around my room reveals yellow LEDs in my HDD light, printer standby light, speaker power light and router/firewall Blinkenlights. Laïka 18:20, 24 September 2007 (UTC)

I'll expand a bit on my "fashion" answer. In the beginning, when visible-light LEDs came in any color you wanted as long as it was red, red LEDs were used for everything. But as additional colors began to be available (especially that sickly yellowish-green), LED colors, at least in technical gear, began to be a bit more standardized with sickly-yellowish-green being used for indications that things were "OK" ("power on", etc.) and red LEDs meaning error or fault conditions. Yellow and amber LEDs often are used for "activity" or slightly "off-normal" normal conditions ("high speed", whatever).

Nowadays, true green is replacing sickly-yellowish-green. As this occurs, maybe you'll see more use of real yellow (since it will be more-easily distinguishable from sickly-yellowish-green). And blue, although it's usually a bad choice for both economic and ergonomic reasons (it interacts pretty poorly with human vision, especially as a display backlight), will probably remain popular until supplanted by some new and exciting color like violet or magenta (perhaps via a UV LED plus a phosphor), but those colors may not be perceived as studly enough to become universally-popular. RGB LEDs are also getting popular and inexpensive enough to see common usage. This may also lead to more color choices, perhaps even common user choice of color.

Atlant 18:49, 24 September 2007 (UTC)

The trend is already shifting. My MINI Cooper car has LED 'mood lighting' which I believe comprises a red/green LED and a blue one in the same housing. You can adjust the colour continuously from red through amber to green then through various magentas and pinks through to blue. It's very cute. The I noticed that my son's new Philips MP3 player has the same thing - a completely adjustable back-light colour. So I think we are already seeing a shift from the oh-so-trendy 'chernobyl blue' (I love that name!) to totally adjustable LED colours for backlights and such. SteveBaker 14:58, 25 September 2007 (UTC)

With regard to Chernobyl blue, I can't claim the term. It goes back at least as far as this User Friendly comic. But the term resonates well enough with enough people that I use it often. I especially like the complainer on the page who states "It's not CHERNOBYL blue, it's CERENKOV blue. Way to miss the point, there!

Atlant 15:52, 25 September 2007 (UTC)

Thanks a lot - i swear I've never seen a yellow one.. maybe I'm a bit colour blind83.100.254.136 21:58, 24 September 2007 (UTC)

I got a lot of yellow ones. They are used in optical rotary encoders I believe becasue of their wavelength being shorter than red —Preceding unsigned comment added by 88.109.211.7 (talk) 22:25, 24 September 2007 (UTC)

585 to 600 nm [4] to be precise —Preceding unsigned comment added by 88.109.211.7 (talk) 22:29, 24 September 2007 (UTC)

We discovered that my son (aged 15 at the time) was colour blind because he was unable to distinguish the amber colour of his Wii games console's LED in 'sleep' mode from the red it shows when it's turned off. Subtle yellow/orange colour confusion is symptomatic of the mildest and commonest form of colourblindness. Since this is a medical issue and we aren't allowed to offer medical advice - you might want to consider taking a colourblindness test. SteveBaker 14:58, 25 September 2007 (UTC)

I'm ok on the red ones, so it's probably alright - I remember a colour blot test some time ago - technically not colour blind though not as good clour vision as some.. I must be just buying the wrong consumer electronics!87.102.10.190 15:04, 25 September 2007 (UTC)

[edit] LEDs again

The V-I curve for a diode. Nimur 15:13, 24 September 2007 (UTC)

The voltage drop across a led is pretty much it's bandgap.. and V/R = I and light intensity is propotional to current. and the device will have a constant R?

1.So does this mean that the light intensity from an LED is instrinsically fixed. (and if so some previous posts I made were very wrong - but no one seemed to notice..)

2.Or is there a way to change the light intensity from a LED

3.If (2 = No) then does this make OLED TV's a total non-starter?87.102.21.91 12:37, 24 September 2007 (UTC)

The current through the LED is usually determined by the external circuitry (such as a ballast resistor or LED-driver integrated circuit). A few LEDs contain within the plastic package a chip resistor so they draw their rated current when operated on a fixed voltage. A very few LEDs contain a constant-current device so they draw their rated current over a wide range of operating voltages.

Atlant 14:36, 24 September 2007 (UTC)

The LED is a diode, so it is not correct to say it has a "constant R" - that would imply a linear Ohm's law applies. In fact, the current-voltage relationship is very well studied, and is often approximated as a simple exponential (I = Io * exp(V / Vth)). See the graph posted. R is not constant for nonlinear devices. Nimur 15:13, 24 September 2007 (UTC)

I meant once it's gone past the switching threshold - there R is constant? and the voltage drop across the boundary is constant? so the actual current accross the boundary is constant - and hence light intensity is constant? (or not) (excluding temp effects)83.100.254.136 22:15, 24 September 2007 (UTC)

No. Once the diode enters conduction, its voltage stays quite constant even as the current varies over a very wide range. So one might also say that the diode's resistance drops as the current increases (although not as precipitously as a true negative resistance device; the diode's VI curve always slopes upwards, at least slightly).

Atlant 00:45, 25 September 2007 (UTC)

Q number 2: My observation has been that more current through an LED produces greater brightness, at least until it overheats and burns out. Edison 04:27, 25 September 2007 (UTC)

You definitely can also dim a LED. --antilived^{T | C | G} 11:19, 25 September 2007 (UTC)

OK thanks for all your replies//87.102.10.190 15:00, 25 September 2007 (UTC)

[edit] bonobos and humans

Among the 3 species: human, bonobo, and common chimp. Can any combination of two of them mate and produce a hybrid offspring?--Sonjaaa 13:27, 24 September 2007 (UTC)

Our article on hybrids does not mention any primate hybrids and there are not many Google hits. On the other hand, some very strange hybrids do occur - see the Toast of Botswana. The proposed human/chimpanzee cross in this news story would be a chimera rather than a hybrid. DNA evidence suggests that bonobos and common chimpanzees became separate species less than 1 million years ago. As species, they are quite close - certainly closer to one another than either species is to humans - so they are probably the most likely candidate species for producing a hybrid. Gandalf61 14:32, 24 September 2007 (UTC)

Human/chimp or human/bonobo hybrids are most likely impossible (different number of chromosomes). Bonobo-chimp hybrids probably can occur (but not in nature as their ranges never overlap). As late as the forties, bonobos and chimps were often housed together in zoos, whether or not any hybrids were born, I'm not sure. --Cody Pope 18:25, 24 September 2007 (UTC)

Actually, chromosome number is not necessarily a barrier to viable hybrids. Donkeys and horses have different numbers of chromosomes (62 an 64 respectively), but produce mules. -- Flyguy649 ^talk _contribs 18:29, 24 September 2007 (UTC)

You may be interested in the Humanzee article. -- 20:48, 24 September 2007 (UTC) —Preceding unsigned comment added by 72.33.121.200 (talk)

[edit] What is the name of this plant?

Mystery shrub

This unusual leaf grows on a shrub that is very common in the Philadelphia area. What is the name of the shrub?

-- Dominus 13:52, 24 September 2007 (UTC)

I suspect it's a Red Mulberry, which sometimes has deeply lobed leaves. -- JSBillings 15:29, 24 September 2007 (UTC)

Thanks. -- Dominus 14:06, 25 September 2007 (UTC)

[edit] Peripheral nervous system: autonomic and somatic nervous system

I found this picture on the internet: http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/N/NervousSystem.gif

Is this picture really correct? Does the somatic nervous system really only control muscles that influence the "external environment"? I mean, if I pick up a mug, it both influences my internal environment (in my arm) and the external environment.
And what about when I hold my breath without pulling in my stomach (so it is not visible for the external environment that I'm holding my breath)? I would suppose that motor neurons from the somatic nervous system are activated for this control of my internal environment. Am I right? Lova Falk 14:27, 24 September 2007 (UTC)

I think you're taking "internal" and "external" too literally. By "internal environment", they mean things not directly under your mental control, like digestion, heart rate, blushing, etc., and the fact that you can hear your stomach growling and feel your pulse and see your face turn red doesn't change that. --Sean 15:13, 24 September 2007 (UTC)

I like to be very precise. :) What about consciously holding my breath? Am I right in supposing that this is under control of the somatic system, or is it part of the autonomic system?? Lova Falk 15:34, 24 September 2007 (UTC)

Breathing is an odd bird. See control of respiration. --Sean 15:52, 24 September 2007 (UTC)

I read that page and it said: "Ventilation is normally autonomic, with only limited voluntary override, but an exception to this is Ondine's curse, where autonomic control is lost."

This is still not a clear, no-misunderstanding-possible answer to my question: Is holding my breath controlled by the somatic nervous system or by the autonomic nervous system? Lova Falk 16:08, 24 September 2007 (UTC)

It's both. The intention and voluntary choice to hold your breath leads to your somatic nervous system overriding your autonomic nervous system, however, when you faint and fall over for lack of oxygen, your autonomic nervous system takes back over (unless you've successfully suffocated yourself, and then you're dead). There is a similar situation with winking. (except for the dying part) -- JSBillings 17:34, 24 September 2007 (UTC)

Thank you! That explains it all. Lova Falk 19:08, 24 September 2007 (UTC)

[edit] Dorsal root

As I wrote in my previous contribution, I like to be exact. :)

I found this picture on the internet. http://universe-review.ca/I10-13-spinalcord.jpg

I wonder if the arrow to the dorsal root is quite right. It seems to me it should be pointing to the orange-coloured "bulb" to the right of the spine. Is that correct? Lova Falk 15:55, 24 September 2007 (UTC)

No, the arrow is correct, if a little unclear. The bulb is the dorsal root ganglion. Here it is in a picture, a model, and in the flesh. --Sean 18:45, 24 September 2007 (UTC)

Thank you so much! Lova Falk 19:09, 24 September 2007 (UTC)

[edit] Seduction techniques

What's the best way for a guy in his early 20s to seduce a really sexy 45 year old blonde woman? Any tips? —Preceding unsigned comment added by 81.76.16.155 (talk) 15:59, 24 September 2007 (UTC)

Do it in a novel, perhaps a bodice ripper.

Atlant 17:16, 24 September 2007 (UTC)

Um, this is the science desk. Still, Welcome to Wikipedia. You can easily look up this topic yourself. Please see seduction. For future questions, try using the search box at the top left of the screen. It's much quicker, and you will probably find a clearer answer. If you still don't understand, add a further question below by clicking the "edit" button to the right of your question title. .--Mrs Wibble-Wobble 17:27, 24 September 2007 (UTC)

I think traditionally it happens the other way round, "Are you trying to seduce me, Mrs Robinson?". Cyta 08:30, 25 September 2007 (UTC)

Go ahead, talk, and be bold! --Click me! write to me 08:05, 27 September 2007 (UTC)

| All the advice and older women you could ask for. Beekone 18:54, 28 September 2007 (UTC)

[edit] Vogels minimum medium

What is vogels minimum medium? Is their a recipie I can follow to make it? Or can I buy it somewhere?

Thank you 128.113.36.239 18:28, 24 September 2007 (UTC)

Google tells me you want 'Vogel, H. J., 1956 A convenient growth medium. Microbiol. Genet. Bull. 13: 42–46'. Haven't found it free online yet. Algebraist 18:37, 24 September 2007 (UTC)

[5], page 2 at the top, I believe. -- Flyguy649 ^talk _contribs 18:50, 24 September 2007 (UTC)

Great! I got the PDF, now as I am not ascoiated with a lab, can someone reccomend a site online where I can buy the ingredients called for? I googled lab supply stores but they dont seem to carry these 'basic' chemicals.

Na3 citrate.2H2O 125 g KH2 PO4 250 g NH4NO3 100 g MgSO4.7 H2O 10 g CaCl2. 2H2O (dissolved) 5 g trace element solution 5 ml biotin stock solution 2.5 ml

Thanks again, —Preceding unsigned comment added by 128.113.36.239 (talk) 19:37, 24 September 2007 (UTC)

Sigma could provide you with these. Rockpocket 20:20, 24 September 2007 (UTC)

[edit] RTG shields

Can anyone explain what the heavy shield-looking things on the left side of this picture are for? Thanks. --Sean 18:55, 24 September 2007 (UTC)

Shields?

Same reason the secretary has a sound-absorbing cubicle partition:) Looks like this generator/shielding experiment is being run in part of a much larger room. Those things are at-least-potentially spewing radiation, so good to separate them from unrelated projects by distance or shielding (to keep from irradiating other things, and to keep other sources of radiation from interfering with measurements). DMacks 19:54, 24 September 2007 (UTC)

For some types of radiation, plastic shielding is used. For example, see 32P#Isotopes. --JWSchmidt 21:24, 24 September 2007 (UTC)

Considering she's standing right next to them, the amount of radiation must not be that high. No gamma radiation, at least. Note that you can see a similar shield behind the first RTG. The plastic is still pretty thick. --Mdwyer 21:51, 24 September 2007 (UTC)

Is whatever the shields are for on? — Daniel 23:02, 24 September 2007 (UTC)

~~They're probably just passive blocks, not "red alert—shields up!" kind of force-field shields:) DMacks 02:00, 25 September 2007 (UTC)~~ Whoops, probably meant to be read as the "whatever" being the RTG not the shield itself. DMacks 04:06, 25 September 2007 (UTC)

Well, I don't really know what the shields are for. An RTG is always "on", in that it's just a big chunk of plutonium that is naturally physically hot. It does not work through fission like a nuclear reactor does, but through natural alpha decay. It only puts off alpha particles, which are not dangerous unless you breathe in a chunk of an alpha emitter. No radiation at all should be getting through the casing of the RTG, which is why I'm nonplused about the presence of those shields. Alpha radiation can only make it through a few inches of air, so even if these devices were assembled here, I don't see what they're for. Maybe I'll email NASA. --Sean 14:06, 25 September 2007 (UTC)

[edit] Isaac Newton and Galileo

You have Sir Isaac Newtons birthday listed as 1643, yet other sources have it listed as 1642 same year Galileo died. Which is correct?

Walter Sept 24, 2007 —Preceding unsigned comment added by Wjchristense (talk • contribs) 19:04, 24 September 2007 (UTC)

Isaac Newton was born in England, still on the Julian calendar, on Christmas Day, 1642. If this is converted to a Gregorian calendar date, it would be 4 January 1642/3. Galileo died in Italy, which had already adopted the Gregorian calendar, on 8 January 1642. The events were 361 days apart.

When someone says that Galileo died, and Newton was born, in the same year, they are misleading you. The events only occur in the "same" year if you use one dating system for one, and the other dating system for the other. The dates have been "massaged" in order to create a "good story" where none exists. see [6] - Nunh-huh 19:16, 24 September 2007 (UTC)

Or they are speaking of a length of time rather than of a calendar year. —Tamfang 23:55, 24 September 2007 (UTC)

But they're not. - Nunh-huh 02:34, 25 September 2007 (UTC)

[edit] Tail vein versus orbital plexus

Why take blood from the orbital plexus of a mouse and not the tail vein? My lecturer (uncertain) suggested it may be easier but I don't see how that could be the case. --Seans Potato Business 19:35, 24 September 2007 (UTC)

This paper compares the techniques. Apparently it can be up to 15 times faster to do it at the eye than at the tail, and that the blood chemistry can be affected by withdrawal site. --Sean 19:49, 24 September 2007 (UTC)

[edit] What's going to happen where

Is there a map that shows geographical positions close enough to sea level to be effected by the rise of Earth's water? There's a lot of talk about America's historical landmarks along the coasts being swamped or flooded away, but what about Europe? What about Asia? What about inland places already close to sea level? Is there a place ot find a more impactful example of historical loss other than Jamestown? Beekone 20:16, 24 September 2007 (UTC)

A good starting point would be a Topographic map of the area of intestest. DMacks 20:36, 24 September 2007 (UTC)

Let's just say I wouldn't buy any property on Tuvalo. StuRat 22:42, 24 September 2007 (UTC)

You're in luck: a commment on a recent post in "Strange Maps" linked to a website that does exactly what you ask, though it only goes up to 14 meters rise. —Tamfang 23:54, 24 September 2007 (UTC)

Note that that on that map, the Netherlands is already flooded with a mere 1 m rise in sea-levels, but that is not realistic. We are used to fighting off the sea and we have the (financial) means to do so (to a point). Bangladesh is not so lucky and that is also a very densely populated country. Tuvalu and similar islands get all the attention, probably because they appear to be ideal holiday resorts. But the population is tiny compared to Bangladesh. Money-distribution may also make a big difference within the same country - Miami is bound to get more protection than New Orleans. DirkvdM 17:13, 25 September 2007 (UTC)

The Netherlands took a very long time to build all of their pumping infrastructure - also, they weren't defending the land against the sea - they were making new land from the sea bed. It's a different matter to say "Hey we're short of land - if I invest a bazillion dollars to make dikes and pump the ocean out, I can make a fortune!"...versus..."I think there is a one in ten chance of New Orleans being flooded - please Mr President can we have a bazillion dollars to fix the problem before we're flooded out?" SteveBaker 18:07, 25 September 2007 (UTC)

Your last point makes some sense (if I ignore the figures :) ), but the first bit is rather wrong (although understandably - I used to think it was like that too). In the beginning there was a swamp. A swamp is almost land, so with a little effort you can make it land. But then you have to keep on pumping out the water and the land becomes more compact, so it sinks, so you have start pumping harder. 'We' have been at that for about a thousand years now, and the land is still sinking. And now the water is rising as well. Not just the sea - rainfall is likely to get more erratic, so we can get heavier downpours in Europe, and a fair bit of that water will come our way, through the Rhine and the Meuse. We're likely to get squeezed in between two walls of water, so to say. DirkvdM 18:16, 26 September 2007 (UTC)

[edit] Are there any foods that make you happier?

Although some foods such as walnuts contain high amounts of for example serotonin, it is as far as I know unikely that it would be able to pass through the gut wall and then also the body/brain barrier.

Are there any foods that could actually make you feel happier? Thanks 62.253.45.36 20:17, 24 September 2007 (UTC)

Chocolate, perhaps? Also, St. John's Wort is a natural antidepressant, but I don't think it's actually used as food. —Ilmari Karonen (talk) 20:31, 24 September 2007 (UTC)

It's much easier to simply make use of the placebo effect of foods that you already enjoy, regardless of their chemical content. --M @r ē ino 21:12, 24 September 2007 (UTC)

Alcohol makes me happy. --Sean 21:54, 24 September 2007 (UTC)

Alcohol is a stimulant in small quantities - but a depressant in larger amounts...beware! SteveBaker 18:10, 25 September 2007 (UTC)

Anything that tastes good, although under certain circumstances (such as extreme hunger) even that isn't necessary. — Daniel 22:58, 24 September 2007 (UTC)

Sugar? Aaadddaaammm 02:30, 25 September 2007 (UTC)

You are all science experts, yet none of you has mentioned fat - eating it is said to put you in a better mood, avoiding it makes people depressed apparantly. This is consistent with my experiences. 80.0.121.52 19:37, 25 September 2007 (UTC)

Ummm sources? So chucking down a bottle of olive oil will do better than a bottle of beer (and give you a nasty diarrhoea)? --antilived^{T | C | G} 00:15, 27 September 2007 (UTC)

I think eating after a good exercise will help your mood. ^{Cite your sources!} --Click me! write to me 08:02, 27 September 2007 (UTC)

[edit] Evolution of singing

How or why did singing evolve? Thanks 80.2.197.120 20:37, 24 September 2007 (UTC)

What do you mean? Do you mean "evolve" in the sense of "progress over time" (as in, how is modern singing different from ancient singing), or do you mean "evolve" in the sense of "appear and expand in population due to natural selection"? If you mean the latter, do you mean in humans or in all animals? --M @r ē ino 21:09, 24 September 2007 (UTC)

Darwin speculates on this quite a bit in Descent of Man, if you want his point of view:

The capacity and love for singing or music, though not a sexual character in man, must not here be passed over. Although the sounds emitted by animals of all kinds serve many purposes, a strong case can be made out, that the vocal organs were primarily used and perfected in relation to the propagation of the species. Insects and some few spiders are the lowest animals which voluntarily produce any sound; and this is generally effected by the aid of beautifully constructed stridulating organs, which are often confined to the males. The sounds thus produced consist, I believe in all cases, of the same note, repeated rhythmically; and this is sometimes pleasing even to the ears of man. The chief and, in some cases, exclusive purpose appears to be either to call or charm the opposite sex.

He goes on to note that most male mammals use their voices to find and impress mates, and that humans aren't really terribly remarkable in this respect. That is, he sees it as the result of sexual selection. I doubt you'll find a much more concrete (less speculative) answer than that. --24.147.86.187 05:09, 25 September 2007 (UTC)

The analogy with songbirds is perhaps a better one because they use a variety of pitches. Whale songs are probably even closer. SteveBaker 18:03, 25 September 2007 (UTC)

Well, there's this just in..... Males with deeper voices apparently have more children. - Nunh-huh 17:20, 25 September 2007 (UTC)

Yeah - but that may be purely a secondary effect. Bigger people have deeper voices - and bigger males are stronger and therefore more likely to do well at hunting and fighting - which makes them more attractive mates. The fact that they have deeper voices may be an entirely secondary effect. SteveBaker 18:03, 25 September 2007 (UTC)

Yeah, so? Women who find deep voices sexy may have more children because they're thus indirectly attracted to mighty hunters. And that effect, in turn, may be exploited by men whose voices are deeper than they "ought" to be. —Tamfang 08:38, 30 September 2007 (UTC)

[edit] Activated Carbon

How does carbon adsorption work —Preceding unsigned comment added by Dfilion31 (talk • contribs) 21:05, 24 September 2007 (UTC)

We have a pretty detailed article about Activated carbon. DMacks 21:11, 24 September 2007 (UTC)

[edit] Causes of global warming

Over the last 300 years our population has increased 10 times. Over 5 billion more people. This means that at the moment 6 billion people are continuously radiating an average of 37°C. Next to that we are all cooking with stoves and riding cars that produce heat. I never read about this and wonder if anyone knows if these can also be accounted as large contributers to global warming. Thanks BillHicksRulez 21:42, 24 September 2007 (UTC)

yes, a less populated world, with less cars, less central heating, less factorys, less transportation etc wouldn't have a global warming problem. Apparently some people are unwilling to accept this a like to suggest that somewho switching from petrol to hydrogen or something else will solve the problem. Really we need more plants and to make less heat.83.100.254.136 21:49, 24 September 2007 (UTC)

No, the heat radiated from people and their activities is totally insignificant to global warming. If more heat is generated on Earth, more heat will just radiate into space to equal everything out. This is true unless the atmosphere changes by the addition of greenhouse gases which hold the heat in. StuRat 22:44, 24 September 2007 (UTC))

If humans did not exist, the energy that we metabolize would be consumed and radiated by other animals. —Tamfang 23:50, 24 September 2007 (UTC)

I doubt other animals (or biomass for that matter) would produce an equal amount of bodyheat. BillHicksRulez 00:40, 25 September 2007 (UTC)

Why do you doubt that? The energy input would be the same. I almost couldn't not produce equal heat. If I don't eat my sandwich, and instead let it rot, it will release a measurable amount of heat. (This is why compost heaps get so hot.) APL 01:34, 25 September 2007 (UTC)

Remember that any heat released from the human body in burning its own fuel is merely a very delayed way of re-radiating what came to Earth in the form of sunlight. Someguy1221 02:47, 25 September 2007 (UTC)

Indeed - we would have to make much food from fossil fuels. But even then - do the math: (6.7 billion people) * (100 W average heat generation/person) / (4 * pi * (6.37*10⁶ m for Earth's diameter)²) = 0.0013 W/m². That's negligible compared to the radiative forcing of e. g. carbon dioxide of about 1.5 W/m². Icek 04:00, 25 September 2007 (UTC)

So we might conclude with: Because of the increase of people we might be speeding up the process of converting potential energy into (amongst others) heat, but that this has hardly any effect on rising the global temperature? BillHicksRulez 09:19, 25 September 2007 (UTC)

Are we still talking about food? It's pretty simple. X amount of solar energy falls on the earth per unit time. A more or less constant fraction of that is captured by plants into carbon. All that carbon goes back to carbon dioxide and releases that energy, or we would be gradually buried under a continually growing pile of old vegetation. Since that did not happen when there were fewer people it is clear that humans are not contributing to the net release of biologically captured energy, other than the (relatively slow in terms of total energy balance of the earth) conversion of the great forests of Europe, North America, and now South America into CO2. Gzuckier 18:16, 25 September 2007 (UTC)

Note that this 'continually growing pile of old vegetation' is eventually going to be what we call "coal". Piles of old vegetation acts to lock away carbon dioxide...not such a terrible thing! SteveBaker 03:50, 26 September 2007 (UTC)

The main cause of global warming is the liberation of carbon dioxide from carbon compounds on earth. For example, lots of fossil fuel under the earth dug out and oxidized to free up the CO2. Human body heat and car's engine heat is totally irrelevant (relative to damage due to CO2 release).

Many many many many many millions of years ago, the earth also have a lot of CO2 in its atmosphere. At that time, you can go for a winter swim at the north pole because it's nice and very warm. 210.49.155.132 13:31, 25 September 2007 (UTC)

What about energy production that doesn't produce co2 - what if we used the same amount of energy but it was all made by nuclear/wind - would that energy (as it's thermal by products) have an effect?87.102.10.190 14:58, 25 September 2007 (UTC)

Here's the bottom line. The sun chucks a truly IMMENSE amount of energy at the earth. All of the energy from human bodies and electric heaters and cars and nuclear reactors and gigantic forest fires and volcanoes and everything else is utterly negligable compared to even 1% of the heat that the sun pushes towards the earth - so we don't have to worry about the heat that we are adding. However, if you stick a bunch of CO2 or Methane or some other 'greenhouse gas' into the atmosphere (as we have been doing) so that just a few percent extra heat from the sun gets absorbed - then you just made a massive difference to the energy the planet is absorbing because that's LOT of energy - and a few percent of a LOT of energy is still a heck of a lot of energy! So don't sweat the little stuff - we have to cut down CO2 emissions - compared to that, everything else is negligable.

Well, actually - that's a slight oversimplification. We know that white things reflect sunlight away and stay cooler than dark things...as the nice white icecaps/snow/glaciers melt and are replaced with dark rock or ocean - that'll also cause us to absorb more sunlight. Sadly, as we heat the earth up using CO2 emissions, we're raising the temperature - which is causing more snow and ice to melt - which is causing YET MORE sunlight to be absorbed (which is melting more snow & ice...). There comes a point of no return when no more snow or ice can exist at sea level and the earth gets locked into a permenantly warmer climate - and even removing the CO2 from the atmosphere won't bring it back into balance again. We really don't want to go there because that's beyond being fixable.

SteveBaker 16:09, 25 September 2007 (UTC)

I don't buy that the Earth's climate is that unstable that no moderating force could ever bring us back. For example, hotter temps would mean more water would evaporate, meaning more cloud cover. An Earth completely covered with fluffy, white clouds would then reflect more sunlight and cool off. After all, when the Earth formed, the atmosphere was full of greenhouse gases and very hot, yet it somehow managed to cool down. That said, the point at which these moderating effects kick in could be long after some truly disastrous consequences for us, so we should avoid "doing the experiment". StuRat 00:49, 26 September 2007 (UTC)

Excellent that's been bothering me for literally years - so the amount of heat we make truly is insignificant (Solar Power "The total solar energy available to the earth is approximately 3850 zettajoules (ZJ) per year Worldwide energy consumption was 0.471 ZJ in 2004."

So hydrogen cars truly are the answer - great - perhaps there is hope for the planet>87.102.10.190 17:43, 25 September 2007 (UTC)

No, no, no! Hydrogen cars are not the answer. Hydrogen is a storage technology - like a battery or a clockwork motor. Something has to make the hydrogen...probably by electrolysis of water...which requires electricity...which has to be generated from...?? If you make the electricity (to make the hydrogen for your car) by burning coal, oil or natural gas - then you are actually doing WORSE that putting the oil straight into your car because all of that messing around with electricity and hydrogen was an inefficient process. If you promise to make the electricity from nuclear, wind, solar or tidal power - then hydrogen is one possible way to store the energy...but batteries might make just as much sense. SteveBaker 17:57, 25 September 2007 (UTC)

Personally I agree that hydrogen is way overhyped. However it's not quite as simple as ou syggested. Remember the internal combustion engine is an incredibly inefficient way of getting energy from oil. Power stations or hydrogen plants could in theory be much more efficient. You also open up the way for carbon capture technologies to be used (which I also believe is overhyped and largely used by those who want to ignore the problem as a cop-out). A hydrogen car is obviously not going to be 100% efficient at using hydrogen but perhaps it can be significantly better then the internal combustion engine. It is possible (no idea how likely) the overall efficiency will end up being greater then using an internal combustion engine with a hybrid car. Of course I find it hard to believe the costs associated with switching to hydrogen are ever likely to be less then the gains if we're generating the hydrogen with fossil fuels. Chargable electric cars etc seem like a better idea to me. But it is important to appreciate the complexity of these consideration Nil Einne 16:02, 28 September 2007 (UTC)

Also, heating up the planet may release large quantities of methane, which is a much stronger (although shorter-lasting) greenhouse gas. See Methane#Sudden release from methane clathrates (and the section below that). One theory says that the largest mass extinction may have resulted from the atmosphere (and then the oceans) heating up just 5 C (about what we can expect in the next few hundred years), resulting in the release of methane, which heated up the atmosphere another 5 C, for a total of 10 C, which killed about 90% of life on Earth. Add to that that that probably happened over thousands of years while this is likely to happen over hundereds of years. Gee, what might the result be? Let's try and find out, so by all means keep taking your car to work, where the airconditioning works at full throttle and when you come home have a nice long steaming hot shower and all that. DirkvdM 17:29, 25 September 2007 (UTC)

Well, Dirk, you are a true environmentalist. Rather than risk the environmental impact of driving a car to work each day, you quit your job. :-) StuRat 00:40, 26 September 2007 (UTC)

What do you take me for? I am a Dutchman, so I go to work on my bicycle. DirkvdM 18:19, 26 September 2007 (UTC)

Work ? I thought you were allergic to that. :-) StuRat 17:05, 27 September 2007 (UTC)

What do you think I call working on Wikipedia. Hmmm, not hard to guess because I already used the word. :) I just don't get paid for it. I work out now for two days per week. Still no pay - it's a so-called 'participation place', in other words they forced work on me. No problem, it's at a Surinam radio station, where I am redesigning the website. (The design at the top is mine, for one.) Relaxed folk and I even got to sit at the manager's chair from day one - he prefers to sit in the studio. And I can come and go whatever hours I like, as long as it totals to the right amount of hours. That's what the Dutch consider working hard. And we're known for our efficiency - we've got a higher productivity per hour than the US, for example. I suspect a connection. Satisfied workers work harder. It just doesn't feel like hard work. DirkvdM 18:49, 27 September 2007 (UTC)

Yes - I'd forgotten about that. Also, methane is a MUCH nastier greenhouse gas than CO2...which is why we should be worried about the effects of cow-farts!! Truly!! SteveBaker 17:57, 25 September 2007 (UTC)

Actually cow farts aren't the problem. It's the burps. Believe me, I'm a Kiwi (people) Nil Einne 16:02, 28 September 2007 (UTC)

This is the kind of thing high school physics class should and usually doesn't teach you to experiment on by yourself. For instance: when you're standing on a crowded downtown street on a hot cloudless summer day, do you feel any heat radiated to you by your fellow humans? Passing cars? Nearby buildings? Or does it all seem to be coming from the sun? Or on a cold winter day; do you feel any heat coming from these sources, or does any heat you may capture seem to be coming from the sun? Now, take into account that the density of all these warm objects over the entire globe is quite a bit lower than this downtown scene, post industrial revolution or not. (There was a guy a while back who insisted that the major source of heat was not the sun, but in fact the internal heat of the earth. I can only assume he never walked barefoot out of doors). Gzuckier 18:09, 25 September 2007 (UTC)

I strongly agree with you - I would call this 'critical thinking skills' - and they simply aren't taught. The inability of a typical person to do these simple thought experiments never ceases to amaze me. I understand why we don't need to teach everyone a full science course - but basic experimental technique and critical thinking are essentials for modern life. SteveBaker 22:21, 25 September 2007 (UTC)

I agree too, nice logical reasoning. Now all that is left is find a solution to the existing problem. Or do you think it's possible impact is overrated? BillHicksRulez 22:53, 25 September 2007 (UTC)

I don't think the more popular accounts in the press are overrating the problems. Scientists are being very cautious about their predictions. Things like the feedback effects of melting ice on albedo and increasing temperature on frozen deep-ocean methane deposits mean that although this effect is only slowly increasing temperature now, someday it's going to flip rather suddenly.

I think we have a chance to stop it happening - but not the way we're treating the problem right now. Politicians are looking at the cost to the economy to fix the problem now and recoiling. Sadly, the cost to fix it in 10, 20 or 30 years will be VASTLY larger - and once we hit that magic 'tipping point' - we won't be able to fix it at all. To fix it we need the worst CO2 emission offenders to take drastic action - that's the Americans...and in the process, find the technologies and provide the leadership to get the rest of the world to follow.

In the very short term - we have to get ethanol production going - but not inefficiently from corn - there are better plants to choose and we URGENTLY need to find them - that should be a major research activity that starts today. We need laws that impose not-to-be-exceeded emissions caps for every process that emits CO2 or other greenhouse gasses. We need a law that says that within 5 years, it's illegal to sell a car that does worse than 40mpg - and in 10 years, it's got to be illegal to drive one that does worse than 60mpg for more than (say) 100 miles per month. There need to be similar laws about new factories, new houses...everything. We need to build new nuclear power stations. We need to exploit wind power. We need an obsolescence plan to phase out coal and natural gas as fuel sources - FOR SURE we need to stop these dangerous idiots who talk about "clean coal" as the future of power in the USA. This is going to cost money - and there is a risk that it's going to mean that we're all worse off and we have higher taxes and more expensive vehicles. For what it's worth, I think the high-tech solutions to these problems could be sold to the world - which could save US industry - so actually, it's probably not as bad for the economy as one might think.

The alternative is that the planet dies - I think it's a small price to pay. (And for the record, I already drive a 42mpg car - the average US car gets about 18mpg - and I know that my home energy bills are about half those of my neighbours - so we know the technology exists, these are NOT unreasonable goals. It really wasn't that big a deal to take those steps - and it makes my personal "CO2 footprint" about half that of a typical American.

We need to act like this problem is going to be a major difficulty for our children and quite possibly kill our grandchildren - because it very well might. SteveBaker 03:46, 26 September 2007 (UTC)

But I really like my car and my air conditioner. Someguy1221 05:11, 26 September 2007 (UTC)

Me too - my car has an air conditioner, six airbags, will go 140mph and does 0-60 in about 6.5 seconds...and manages 40 miles per US gallon. But I really like my planet too. SteveBaker 14:02, 26 September 2007 (UTC)

I agree we have to try our best to force our combined governements to put this high on their agendas. On another site a heard a remarkeble possible solution. Placing a movable giant reflector-screen insuch a position between earth and sun so it will cast a shadow over earth at specific times and places. BillHicksRulez 09:09, 26 September 2007 (UTC)

There are various 'desperation measures' like that which we could consider - another is to spray some kind of reflective dust into the air. After the 9/11 disaster in the USA, all aircraft were grounded for a few days and some enterprising researcher decided to gather temperature data for those days and discovered that they were noticably warmer throughout North America because the contrails from aircraft flying at high altitude were not being formed and that these very white trails normally reflect heat back out into space, it might be possible to spray white stuff into the upper atmosphere to increase the earth's albedo - but finding 'stuff' that'll work well (contrails are made of water vapour - and that's another greenhouse gas - so we don't want to use that 'for real').

But these things are technologically monstorously difficult. Consider a mirror big enough to block (say) 1% of the sun's rays. It would have to be about the same area as 1% of the earth's disk. You can't put something that big in orbit because the drag from even the most tenuous atmosphere would shred it. So you'd need to put it out at the L₁ lagrange point - but then it can't be a circle or a square because that would cut out the suns rays selectively on some band of the earth's latitude and not others - which would create a cool band - which in turn would do wild and crazy things to the ocean currents and our weather patterns - so it needs to be shaped maybe like a long, skinny ellipse 6300 kilometers long and about 60km wide. Something that large could have it's center of gravity at the L₁ point - but the ends would feel strong gravitational forces from the sun - so this thing can't just kinda float there. Worse still, the photon pressure on the thing would continually push it towards the earth. You're going to need rocket motors on the thing continually correcting for these things - and those have to be fuelled somehow - so you can't just stick it up there and forget about it. Even worse than that, if it's not a 100% efficient mirror (and it won't be), it's going to absorb energy from the sun and will gradually heat up. So it has to radiate heat off it's back-side somehow or it'll heat up and melt. So now we need a 99.9% reflective material that probably has to have a black coating on the back side. Super-thin aluminium foil with black paint on the back - calculate the weight of a third of a million square kilometers of aluminium and paint - now add a support structure strong enough to allow rocket motors to push on it to keep it in position. Just consider the launch costs to L₁ of a structure that is literally the size of the planet! Trust me, getting everyone switched over to 40mpg cars is much easier. SteveBaker 14:02, 26 September 2007 (UTC)

One simple way (so the opposite of 'technologically monstrously difficult') to reflect the Sun's rays might be to spread out bubbles of polystyrene in the ocean. Oceans have a very low albedo and I assume polystyrene has a high albedo. Spreading it out in Arctic oceans may bring the ice back, after which nature can take over again. Of course, there is an environmental issue, but probably nowhere near as large as with nuclear fission. DirkvdM 08:16, 27 September 2007 (UTC)

Until you find out your polystyrene bubbles are killing out the plankton so making the problem worse :-P I'm not saying this will happen, I guess there probably isn't that much in the Arctic ocean. But history is littered with ideas which may have seemed smart at the time until people realised the consequences (and sometimes the ideas didn't work at all anyway). Let's bring in mustelids to control the rabbits. Ooops that didn't work now not only do we have rabbits but we have mustelids too. Back to the topic, another idea I heard of recently is to fertilise the ocean. Some people have already began testing the idea although it's very controversial not surprisingly. There was an article in New Scientist about it a few weeks ago Nil Einne 16:11, 28 September 2007 (UTC)

Yeah, I heard of something like that too - putting iron in the ocean, which plankton or something feeds off, which absorbs the CO2, and then when it dies sinks to the ocean floor. But that is creating an entirely new situation, which may lead to the unexpected side-effects you mentioned. My idea with the polystyrene was to replace something that was previously already there, namely the ice. That disappearing has a positive feedback effect because the albedo of ice is very high, whilst that of an ocean is very low. Of course, the fact that the replacement has different other properties than the ice may still have side-effects. Such as fish eating the bubbles. But ultimately, by your reasoning, we shouldn't be putting greenhouse gases in the atmosphere in the first place. Of course, the best solution would be to stop doing that, but we need other solutions as well. Actually, we shouldn't be allowed to do anything at all, because all our actions have an effect. It's a matter of comparing the expected positive and negative effects and the potential negative effects of clomate change are so huge that we're allowed to take some risks. DirkvdM 09:56, 29 September 2007 (UTC)

One suggestion that appeals to me is to detune jet engines by some tiny fraction so that they put more soot into the stratosphere (where stuff stays for a long time because there's little convection. —Tamfang 08:42, 30 September 2007 (UTC)

And what do you think about the rise of temperature on the other planets of our solarsystem? Is it possible that we are looking in the wrong area, and that it is result of some natural cause? Btw, I appreciate the time you spent on answering the questions. BillHicksRulez 23:30, 26 September 2007 (UTC)

Of course that is possible, just about anything is possible - if you walk into a wall, there is a chance you will walk through it. Seriously. The chance is just near-infinitely small. And that's what we should look at. What are the chances? I like to compare this with when you see a couple having a serious fight and the next day you see one of them with a black eye. They say they ran into a door. Could be. Do you believe it? What are the chances? Same here. Scientists have been saying for decades that we are spewing out greenhouse gases, which are likely to noticeably warm up the planet. And now exactly that is happening, and at an incredible speed. Coincidence? Could be. Do you buy that? What are the chances? The other aspect of risk-assessment is the possible effects (effect x chance = risk). There's a real possibility that worldwide disaster will strike, dwarfing world wars in death toll. Are we going to take that chance?

The big irony is that fighting global warming is presented as something that costs money. But the opposite is true. The higher costs later are already mentioned, but what I mean is that lower energy consumption means lower cost. Steve, what do you mean by 'more expensive vehicles'? Do you mean higher production cost because of new technology? If that is the road taken, then in the long run they will still be cheaper because of the lower energy consumption. But even with existing technology we can go a long way. Just put smaller engines in the cars. Simple. For normal everyday usage the existing engines are usually waaaaay too heavy (and I'm not even talking SUVs here). DirkvdM 08:16, 27 September 2007 (UTC)

[edit] If a missile silo was bombed...

If a nuclear missile silo was bombed or submarine depth-charged with enough force, and the missile had a modern safety design and was not armed, could the blast potentially set off the nuke -- at full or partial force? Would it help if the bomb or depth charge was also nuclear? Neon Merlin 21:49, 24 September 2007 (UTC)

In general, nuclear bombs are pretty difficult to set off. If it was easy, everyone'd be doing it. An explosion in a silo or submarine could cause radiactive material to be ejected -- practically the definition of a dirty bomb -- but the odds of actually reaching criticality is pretty slim. That is, you might see an explosion of either the fissile material or the conventional explosives surrounding the pit, but the timing wouldn't be right to trigger an atomic explosion. --Mdwyer 21:55, 24 September 2007 (UTC)

And not only are they hard from a timing point of view, but every modern nuke has some form of safeguard to keep it from possibly going critical accidentally. Even those without the most sophisticated of safeguards (W80s don't have fire resistant pits, for example) would at worst spread radioactive material around, but would not detonate in a full nuclear explosion. --24.147.86.187 23:23, 24 September 2007 (UTC)

Given that the full yield of a nuclear bomb generally requires it to explode in a very controlled manner (one of the major difficulties in building the first few), I doubt this would be achieved through outside destruction. Someguy1221 00:10, 25 September 2007 (UTC)

Now, just saying is all, if we were talking about very crude nuclear weapons of the Little Boy type, and they were armed, then yes, but you'd be really, really, really, really stupid to have something like that lying around and armed, since the safety features are pretty much non-existant. You're practically asking for it to blow up in that case (which is fine if you're about to drop it out of a plane—which is the only time it should be armed)—but that's about it.--24.147.86.187 00:58, 25 September 2007 (UTC)

Read our (truly sobering) list of military nuclear accidents. Nuclear weapons have been involved in fires and explosions, jettisoned in mid-air (both deliberately and accidentally), in plane crashes and in at least one mid-air collision. In one incident an explosion of rocket fuel in a Titan II missile silo blew the 740-ton silo door 200 feet into the air and threw the missle warhead over 100 feet from the silo [7]. Although many of these incidents created radioactive contanimation, none resulted in a nuclear explosion. Gandalf61 09:23, 25 September 2007 (UTC)

The deal is that when you build your bomb, you have to keep the radioactive core separated into pieces that are each less than the critical mass of whatever substance you are building it out of is. In order to set it off, you have to bring those pieces together into one big lump. Now, you might think it's enough to take (say) two 7 kilogram hemispheres of plutonium (plutonium-241's critical mass is around 12 kg) - and push them together using (for example) a big spring to make a 14kg sphere. What would happen if you did that would be that in the fraction of a second before they got close enough to make a single 14 kg explosive lump, they would start to exchange neutrons and to get very hot - then they'd distort - maybe melt and generally not get into close enough contact to make an actual explosion. The guys who designed the very first atom bombs on the Manhatten project called this a 'fizzle' - and what you get is a very messy radioactive waste problem - and perhaps a very small explosion - but nothing very impressive. Something like this happened to the North Korean nuclear test - they did get an explosion but it was pathetic. What the early Manhatten project bomb designers did was to force the sub-critical-mass pieces of the core together using high explosives inside a heavy steel sphere which contained the conventional explosion long enough to slam the pieces or uranium together with enough force so that it happened too fast for them to melt or distort or whatever. An alternative idea that they tried (but didn't use) was to fire one cylindrical piece of uranium into a tube made of out more uranium using a small cannon. Almost all of the work that was done in the early research was to figure out how to smash the bits of the core together fast enough and precisely enough to make it go off. The bigger the yield of the bomb, the more sub-critical bits you need to slam together - and the harder it is to do that accurately.

Anyway - the consequence of that is that if you merely set off an explosion somewhere near to a nuclear weapon, you aren't going to be slamming the pieces of the core together quickly enough or accurately enough - so you'd get a nasty radioactive mess that would pollute horribly and be very hard to clean up - but which wouldn't cause a nuclear explosion. Far from being sensitive, dangerous devices like conventional explosives, nuclear weapons are really hard to set off and the slightest error causes a nasty mess, but no kaboom.

SteveBaker 15:31, 25 September 2007 (UTC)

Hi Steve—not wanted to contradict but your explanation of nuclear weapon design is off in a few places. You can fire one piece of uranium into another and have that work—that's how the Little Boy bomb used over Hiroshima worked. And the other type of design, the one which works with Plutonium, is not a matter of smashing two subcritical pieces together into a critical lump, but to take a subcritical sphere and compress it using explosive lenses, doubling the density and thus making it critical. And it is incorrect that increasing the yield is just due to having more subcritical bits to slam together—usually it is done by increasing the efficiency of the explosion (adding better neutron reflectors, better compression, injecting tritium into the core so it will generate more neutrons, etc.). See nuclear weapon design.

As I noted—it would be easy to accidentally set off the Little Boy device. It was crude, it was basically shooting one piece of U-235 into another, and if it were armed (both pieces of U-235 in the gun device along with the explosives) then a fire could very easily result in a nuclear explosion. But as I also noted, 1. that was an exceptionally unsafe design and quickly replaced, and 2. no fool would arm one of those until you were about to drop it on a city. --24.147.86.187 14:04, 26 September 2007 (UTC)

No. It's damn hard to create a nuclear explosion, when you want to. Thus the Manhattan project. You have to compress the radioactive material to reach a high density; when it starts getting hot and entering the early stages of what would be an explosion, that makes it pretty hard to compress. Any kind of external explosion isn't likely to compress the radioactive material. What you will end up doing is scattering the radioactive material all over. Gzuckier 18:18, 25 September 2007 (UTC)

Here's a little animation I found on here illustrating how the compression works. Imagine if only half of those explosives blew at the same time, or even just one of them didn't detonate right. You'd spurt the plutonium out of the center, rather than compress it. To actually have those explosions result in an implosion, you need the shock waves to line up just so. --24.147.86.187 14:04, 26 September 2007 (UTC)

[edit] violet

with reference to Wikipedia:Reference_desk/Science#Color_and_octaves a question about violet - ie why does it appear pink/purple (ie red+blue) - I can understand the blue but why activate the red sensors (and not green)? Has someone got a graph of eye sensor sensitivity in this violet/low uv region. OR is something else going on?83.100.254.136 22:12, 24 September 2007 (UTC)

Violet (or 'magenta' or 'purple') is not a single frequency of light - it's a true mixture of red and blue light. If you shine a violet/magenta/purple light though a prism, you get some red light and some blue light and no green light. This colour is unique in that regard. Yellow and Cyan can either be mixtures or they can be pure single-frequencies - but the colours around magenta (commonly named violet or purple) are always mixtures. SteveBaker 14:25, 25 September 2007 (UTC)

Erm 'steve' did you read my question - big clue - the heading violet q.v. I was not asking about purple at all (though it relates a bit.. The colour I was refering to is the just visible frequencies higher than indigo..87.102.10.190 14:55, 25 September 2007 (UTC)

The names of colours are vague and messy - there is no scientific definition of 'violet', 'purple', etc. So there is no point in arguing about the word you used and the word I used. Let's talk frequencies.

Frequencies higher than blue are 'ultra-violet' and our eyes don't react to them. There is no single frequency that's higher than blue that appears 'pink/purple'.

As I said in the previous discussion, people are fooled into thinking there is by looking at rainbows which are more complex than a single spectrum. You don't see any red/blue mixture when you look at white light split up by a simple triangular glass prism - you see blue, then darker and darker blue, then nothing.

You simply don't have a sensor in your eye that could detect a different frequency that's higher than blue - this is a demonstrable biological fact. If you were to look at a graph of frequency response for the blue sensor in your eyes, you'd see a roughly gaussian curve centered on some frequency of blue light (let's call this frequency 'F'). So light at frequency F is the most intense blue. At frequencies above F, the sensitivity of your eye rolls off. So light with frequencies above F, you don't see a new 'colour'. You just percieve it as blue - but with less and less sensitivity (darker blue if you like). You can't tell the difference between a dim light at frequency F and a brighter light at frequencies a little over F. Hence there is no different pure frequency of violet out there...it's a myth, made worse by the poor choice of name for UV-light: 'ultra-violet' (which we should probably call 'ultra-blue').

To get the colour we call violet, you have to mix together a little red light into your blue. These two frequencies together produce the impression of violet. However, this colour doesn't show up in a spectrum of colours. The myth probably came about because of supernumerary rainbows where the red from one very, very feint rainbow overlapped the more intense blue of another. Rainbows are complicated.

SteveBaker 15:51, 25 September 2007 (UTC)

Ok I get that - what about the first artificial image at Visible spectrum - would you say it is fairly accurate and out of curiousity - does the far left look at all purple/violet (not pure blue) to you? (and is it right or wrong?)87.102.10.190 16:50, 25 September 2007 (UTC)

The image at the top is the one you are talking about - the image beneath is what I got by taking that first image and removing the blue and green components from it. As you can see - there is some red over to the left. So the 'violet' you see in that image is most definitely a mixture of red and blue light (that's the only way to get violet after all). You might argue (and you should!) that this is just a computer image and that the computer screen can't display your hypothetical 'pure' violet light because it can only display red, green and blue - but your eyes can only see red, green and blue - so how would you ever know? So yes - I believe that image is wrong. I'll discuss that with the authors of the Visible spectrum page with a view to correcting it. SteveBaker 17:20, 25 September 2007 (UTC)

Messing around with DVD's as diffraction gratings on overcast days isn't really helping me.. What I really need is a 410nm monochromatic light source .. any suggestions? - then at least I'd know how I perceive 'violet'. Thanks for your help anyway.87.102.10.190 17:39, 25 September 2007 (UTC)

DVD's suffer the exact same problems as natural rainbows - you are seeing multiple, overlapping spectra - so the red of one overlaps the blue of another - producing magenta ('violet'). A simple glass prism is by far the best tool for the job. Use a cut-glass wine-glass or something - just make sure that you get just one spectrum - not lots of them running into each other. SteveBaker 17:46, 25 September 2007 (UTC)

The key for both prisms and diffraction gratings ("DVDs") is the slit. If you use a narrow slit (or a point-source of light), you'll get a single spectrum. If you use a wide slit (or a non-point source light), you'll get overlap of the multiple spectra. But a diffraction grating is just as useful as a prism for creating a visible spectrum.

Atlant 11:49, 26 September 2007 (UTC)

Yep - although for the purpose of this experiment, you don't need a perfect single spectrum - you just need an image that doesn't have the blue part of one spectrum to overlapping the red part of the others - and a slit that thin is not hard to arrange - using the sun is plenty good enough. SteveBaker 13:25, 26 September 2007 (UTC)

FYI: Here is a real spectrum (of the sun as it happens) - no sign of violet there - but again, this is a computer image so you can argue (and, again, you should) that it's not valid for that reason. However, it does prove my point that the image on Visible spectrum isn't a valid computer representation of a spectrum. SteveBaker 17:50, 25 September 2007 (UTC)

Looking around the web - I notice that sometimes ccd captured images show purpling even in the very blue region eg here http://ioannis.virtualcomposer2000.com/spectroscope/amici.html#colorphotos (see fluorescent light sources) - I assume this is due to a high intensity line saturating the blue and causing the red sensors to come on a bit (the filters therefor in the camera are not perfect)..

However this oddity I can't explain http://www.physics.umd.edu/lecdem/services/demos/demosn2/n2-03.htm - if it's a 'wet' photograph it's possible that the red sensitive part is affected by near uv, I really don't know the history of that image.

If anyone can explain the violet oddities on the first site I mentioned I would appreciate it.87.102.10.190 19:04, 25 September 2007 (UTC)

The red pigments on color film, and the red sensors in digital cameras, usually also respond to violet light. This is to mimic a similar perceptual effect in the human eye. However, the actual spectral response curves tend to vary quite a lot, which is why different photographs will show the violet end of the spectrum differently, and why none of them can be relied on for accurate colorimetry. (In particular, many digital cameras will in fact see quite a bit further into the ultraviolet then the human eye, and can often be made to register infrared by removing a filter as well.) That said, one should be easily able to verify that the human eye does perceive far violet as reddish by, for example, looking at a black light. —Ilmari Karonen (talk) 21:25, 25 September 2007 (UTC)

Looking into a black light is actually not a very good idea - your iris doesn't respond to UV energy so you can't shut out a 'bright' UV light and that means that you can damage your retina. Perhaps for that reason, the lens in your eye attenuates UV fairly sharply - people who have had their lenses removed as a result of cataract surgery can see further into the UV than 'normal' people...but from what I hear, it mostly just adds a little more sensitivity up in the near UV - it's not that you see 'new colours'. Making cameras and photographic emulsions exactly mimic the human eye's RGB behavior is tough -and none of them can correctly cover the enture gamut of the IEC chromaticity diagram and compromises are always needed. All kinds of sneaky tricks are used - and I don't think you can use those as any kind of proof of how the human eye responds. SteveBaker 22:13, 25 September 2007 (UTC)

That's not the point. The point is, if you see an ultraviolet light that's on, it looks the same color as blue light mixed with red light. Unless blue light somehow blocks the signals of the red receptors, that means your red receptors are detecting as much ultraviolet light as the would red. I think this can be explained as ultraviolet light having approximately twice the frequency as red light, and the receptors resonating at that frequency. — Daniel 23:25, 26 September 2007 (UTC)

[edit] Quantum Suicide

In quantum suicide, in order to perform the experiment, you have to put your life at risk. But why? Why can't you just flip a coin instead? It's been argued that flipping a coin is not a quantum event. However you could design a "quantum coin" so why the need to put one's life at risk? 202.168.50.40 23:02, 24 September 2007 (UTC)

The point of quantum suicide is that the observer needs to be the one who has negligable probability of surviving the experiment. If he consistently observes himself to survive, he himself has convincing proof of the Many-worlds interpretation. Outside observers will not be able to distinguish between luck and Many-worlds-ish survival, however, as even if Many-worlds is correct, they are no more likely to observe a survival event with either interpretation. Since a quantum coin that explodes when it lands tails can't comprehend its own existence, it can't be used as the subject. Someguy1221 23:17, 24 September 2007 (UTC)

As an "observer" the chance of you getting 666 heads in a row in a "quantum coin flip" experiment is also negligible. Why risk your life? Why not argue "Why is my father Bill Gates?". Statistically the chances that your father being Bill Gates must be infinitely small, therefore if your father is Bill Gates then the Many-worlds-interpretation must be true! 202.168.50.40 23:39, 24 September 2007 (UTC)

If you flip a coin, quantum or not, you have a one-in-2⁶⁶⁶ chance of observing 666 heads. If, however, you can commit to shooting yourself whenever you get tails, the only possible outcome you can observe afterwards is that you indeed got all heads: if you didn't, you'd be dead, and unable to observe anything. The things is, if the many-worlds interpretation is false, or if you did the experiment in some way that wasn't subject to quantum uncertainty (which may or may not be possible, in the sense required here), then you'd almost certainly be dead. But under the many-worlds interpretation, the experiment would result in the "multiverse" containing (at least) 2⁶⁶⁶ copies of you, of which only one is alive and thus capable of observing the outcome.

The argument is then that, assuming that your prior belief was that the many-worlds hypothesis was true with probability p, you could then apply Bayes' rule to get a posterior probability of 2⁶⁶⁶p / (2⁶⁶⁶p+1-p), which, unless p was negligible to begin with, ought to be close to 1. However, I'm not actually convinced that this this is valid Bayesian reasoning: while it's true that the probability of (at least one copy of) you being alive after the experiment is different under the various interpretations (1 for many-worlds vs. 1 / 2⁶⁶⁶ for Copenhagen), the probability of you observing that you're alive is always 1. Thus, the observation that you're alive shouldn't affect anything, since there's no way you could observe anything else. —Ilmari Karonen (talk) 00:29, 25 September 2007 (UTC)

The problem with that is that you can't be born over and over and over. This is why physicists always repeat their experiments many times to produce statistical data. Quantum suicide only applies if the observer is the subject of the experiment. If the observer is merely observing the experiment, the results he observes will distribute statistically, regardless of the proper interpretation of QM. However, it is impossible for an observer to observe his own non-existence. If Many-worlds is correct, the observer-subject of a quantum suicide experiment has a 100% chance of observing his own survival, in complete contradiction to the copenhagen interpretation, which would have him observe his own survival only sometimes, and observe nothing for other times (as the dead cannot observe, so far as we can discern). But like I said, while outside observers can witness this contradiction, their chance of witnessing it is the same no matter the proper interpretation of QM. Someguy1221 00:08, 25 September 2007 (UTC)

The problem is that if the many-worlds hypothesis is true - the when you flip your coin, there end up being (at least) two versions of the universe - in one there is you looking at a 'head' in another there is you looking at a 'tail'. In a 'single-world' version of the experiment, you are looking at either a 'head' or a 'tail'. You can't tell from that experiment whether 'many-worlds' is true or not. However, if you take a gun and put it to your head and pull the trigger, you have:

In many-worlds, a universe in which you are dead and one universe in which (amazingly) a passing gust of wind flipped the safety on the gun and prevented the gun from firing. You aren't alive in one of them - so if you are still aware of events, you are in the one where the flook happened.
In single-world, almost certainly, you are dead - but just maybe (very unlikely) a passing gust of wind saved you.

Now, if you know you are now alive, you are either amazingly lucky - or you are in that one universe of the multiverse where you survived. OK - so flip off the safety and do it again...do it 100,000 times. If every single one of those 100,000 times, something amazing happens and you survive then the probability that this is a many-worlds universe is almost 100%. Of course if you're wrong, you're dead.

However, the argument goes that if you did this experiment - and survived - you would have pretty much proved many-worlds (but only in that one version of the universe in which you survived). You can't do that with coin-tossing because you survive in all of the universes - including all of the ones where some not-surprising version of the event occurs. SteveBaker 14:16, 25 September 2007 (UTC)

Actually, there is no need for a series of suicide attempts. Life itself is risky, and increasingly so as you get older. If 'many-worlds' is true then whenever you might have died from that fall downstairs, heart attack, multiple organ failure etc. there is a universe in which you survive - so you are effectively immortal. After blowing out the candles on your millionth birthday you might begin to suspect that 'many-worlds' was probably true. (This version of the thought experiment is called quantum immortality, and is mentioned briefly in our quantum suicide article). Gandalf61 14:37, 25 September 2007 (UTC)

Yep - that's true - but playing a few dozen rounds of Russian roulette is a faster (if more dangerous) way to find out. Personally, I plan on performing your experiment - I don't like mine as much. SteveBaker 13:21, 26 September 2007 (UTC)

The problem with that (waiting for a natural death) is the question of when the relevant quantum event happened to make the parallel world in which you go on living. In the original experiment, the quantum event triggers the death/non-death. The wait-and-see method has nothing exceptional to draw your attention to the fact that you're immortal, and gives you an infinitesimal chance of being the you who lives forever. The quantum-russian-roulette ensures you experience being the immortal you, by the simple expedient of killing off all the myriad yous who aren't the right one.

-- 203.22.236.14 13:56, 27 September 2007 (UTC)

The interesting part of that is that if you believe in the many-worlds model, then in a lot of parallel universes, this has been tested and conclusively proven. There is someone out there in one of those universes who has figured this out and is making a fortune by challenging people to kill him. Of course in the majority of universes he dies at the 23rd attempt or the 400,000th attempt - only a few of them have him surviving every one of the attempts. However, even on the ones where he dies, the fact that he survived a million tries is taken as conclusive proof of the multiverse. We happen to be in one of the relatively rare/unfortunate universes where the experiment has either never been done or nobody noticed the results! SteveBaker 23:30, 27 September 2007 (UTC)

I believe the closing thoughts of a multiverse-believing quantum mechanic would make an excellent addition to the reverie-in-the-final-milliseconds genre of fiction, as in An Occurrence at Owl Creek Bridge, Tobias Wolff's Bullet in the Brain, Jacob's Ladder, etc. --Sean 15:33, 25 September 2007 (UTC)

[edit] Quantum Collapse

And another thing which simply does not make sense to me. Every single atom is in a quantum state of superposition. So how on earth could a quantum collapse occurs? Don't give me the observer answer because observers are made up of atoms too! 202.168.50.40 23:11, 24 September 2007 (UTC)

As the article states, there are many interpretations of this, but the one I find most credible is that the appearance of a wavefunction collapse is simply a result of quantum decoherence. Essentially, an observer, and everything they interact with, becomes irreversibly entangled with the system being observer, such that, instead of the observer being in one state and the system being observer in a superposition, they both end up in a superposition of states where the observer, in each state, observes the system as being in a specific corresponding state.

Thus, let's say I have an electron in a superposition of two states, either spin-up or spin-down. Once I observe it, I'm now also in a superposition of two states: one where I see the electron as being spin-up, and another where I see it as being spin-down. As it turns out, assuming that this is all there is to it automatically gives rise to something very similar to Everett's many-worlds interpretation. —Ilmari Karonen (talk) 01:04, 25 September 2007 (UTC)

Murray Gell-Mann discusses this in his book, "The quark and the jaguar". Gell-Mann is in complete sympathy with the person at 202.168.50.40: Gell-Mann feels that the universe works just fine without "observers". Gell-Mann does not like the "many worlds" interpretation. Gell-Mann prefers to speak in terms of "histories" and probabilities of alternative histories. Various physical processes (such as particle interactions with physical systems that function as particle detectors) result in decoherence independent of there being a human observer involved. When a detected particle causes a physical change in a particle detector, that physical interaction reduces the probabilities of most alternative histories (alternative paths of the detected particle) to zero and leaves one history with probability of 1. Gell-Mann calls this "pruning branches" in the tree of alternative histories, describes such "pruning" as resulting from non-remarkable physical events and contrasts it with other views of "collapse of the wave function" that are "often presented as if it were a mysterious phenomenon". Gell-Mann has an entire chapter called "Quantum mechanics and flapdoodle" in which he tries to explain why many of the purported "mysterious phenomena" of quantum mechanics are mis-interpretations of quantum mechanics. Gell-Mann does not claim that all the answers are in, but he describes clear objections to many of today's popular interpretations of quantum mechanics. --JWSchmidt 04:01, 25 September 2007 (UTC)