Wikipedia:Reference desk/Archives/Science/2009 January 16

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January 16

Saving money by freezing water

Every couple months, I buy raw chicken for my dogs for their daily meals. As time goes by, the freezer empties. To save money on electricity, I've started adding plastic bottles of water to the freezer to make up for the space that opens up as the dogs eat. I'd like to reuse these bottles, they're empty juice bottles, so how much should I fill them to keep the ice from breaking the plastic open as the water expands upon freezing? I thought about squeezing the bottle slightly before putting the cap on, thinking that the ice formation would push the sides out as far as it needed. Is this a good strategy? Thanks, Dismas|^(talk) 01:29, 16 January 2009 (UTC)

Why are you filling the bottles with water at all ? Air has a much lower thermal capacity, meaning it will take far less energy for the freezer to bring air-filled bottles down to freezer temps than water-filled bottles. As for how full, you'd need it less than 90% full of water to prevent overflowing, if the water flows evenly and no expansion or contraction of the bottle is allowed. Unfortunately, neither assumption is valid. For example, ice might very well form across the surface of the water, preventing it from expanding upwards (depending on the bottle geometry), and split the bottle open, even if only half full. StuRat (talk) 02:27, 16 January 2009 (UTC)

Why do you need bottles at all? I'm really not getting this... what's wrong with leaving your freezer half empty? --Tango (talk) 02:37, 16 January 2009 (UTC)

Yeah, since water takes more energy to cool than air does, why add room temperature water to the freezer at all? It seems that that would be a waste of energy and resources... --Jayron32.talk.contribs 02:46, 16 January 2009 (UTC)

The problem with a half-empty freezer is that whenever you open it warm air enters, and has to be cooled, wasting energy. As StuRat points out, this can be averted by filling the space with empty bottles or such. Algebraist 02:49, 16 January 2009 (UTC)

I strongly suspect that the energy required to cool the air is far, far less than the energy needed to cool and freeze the water occupying the equivalent space, by orders of magnitude. Unless you need jugs of frozen water, do not place jugs of water in the freezer to occupy the space previously occupied by frozen food. If you open the freezer "daily" just leave the space empty until you buy more dog food.How many times would one have to cool air from room temp (20 Celsius?) to freezer temp (fifteen below zero Celsius?) to make up for the energy required to cool water from over the same range? Look at the specific heat of air versus the specific heat of water as well as the heat of fusion of water. Water appears to have about 1000 times the density of air and a specific heat of 4.1813 kiloJoules per kilogram per degree Celsius, about 4 times the specific heat of air (1.0035 kilojoules per degree celsius per kilogram). Once it freezes, it has about twice the specific heat of air of the same mass, 2.050 kiloJoules per kilogram per degree Celsius). In addition, for the phase change from water to ice, add 333 kiloJoules per kilogram. It looks like the freezer would have to be opened an unrealistic number of times to make the freezing of water of the equivalent volume more economical than cooling the warm air which entered. (But, then, I am not a chemist). Edison (talk) 03:49, 16 January 2009 (UTC)

Ah, that makes sense. Yes, air-filled bottles could save some energy, water-filled bottles most likely won't (and certainly not as much as air-filled ones). --Tango (talk) 04:01, 16 January 2009 (UTC)

Except for Edison's answer, which went over my head, it sounds like the rest of you are saying that I should just put in empty bottles. I was filling them with water because I thought that the ice blocks would keep the condenser from having to run as often to maintain the temperature. That they would aid in keeping everything cold for longer than the same volume of air. Dismas|^(talk) 04:35, 16 January 2009 (UTC)

Yes, that's what we're saying. While water-filled bottles will store more coldness (don't look at me like that!), which would help maintain the temperature, that effect is outweighed by the energy required to freeze the water in the first place. --Tango (talk) 04:43, 16 January 2009 (UTC)

Thanks for dumbing it down for me. Neither of my degrees are in engineering or anything of the sort. Dismas|^(talk) 04:54, 16 January 2009 (UTC)

I wasn't intentionally dumbing it down, I was thinking about it in terms of storing coldness myself, so that's how I wrote it. (Yes, I cancel dx's too, so sue me!) --Tango (talk) 05:06, 16 January 2009 (UTC)

Please contact my lawyer immediately - he'd like to discuss what date you could make it into court! (Thermodynamics - it's not just a good idea - it's the LAW!)

There are two effects going on here:

1. Preventing volumes of cold air from spilling out and being replaced by warm air when you open the freezer door. Cold air is denser than warm air - so if you have a "chest" freezer - there is little problem - but for freezer's with doors that hinge open at the front, all of the cold air will "fall" out of the bottom in just a few seconds. To stop that, it's only necessary to prevent the air in the unused parts of the freezer compartment from moving - and a few three liter coke bottles will do that just fine.
2. The idea of 'thermal inertial' - that something like water/ice would slow down the rate of change of temperature. That's a more dubious thing. Certainly, if the thermal inertia is high then when you open the door, the temperature won't fall by so much before you shut it again. That SOUNDS good - except that the high thermal inertia ensures that having fallen a bit - it takes so much longer for the freezer to get back to the right temperature again. So from a point of view of saving energy - there isn't any benefit to using high-thermal inertia materials inside those bottles. It's only use is to prevent the temperature from rising to the point where the food might spoil - but for that, you'd need to leave the door open for a considerable amount of time even without anything like bottles of water in there.

So the conclusion is that any kind of system for stopping the air in the empty parts of the freezer from moving when you open the door is probably about as good as any other. Balloons, empty cardboard boxes, coke bottles, dead aarvarks...it doesn't matter. But if you have a "chest freezer" it's hardly worth bothering with since the cold air will pretty much stay put. So if you're going to do this - you might as well use bottles full of air because (a) the initial cost of chilling them is much less and (b) there is no chance of them rupturing. SteveBaker (talk) 15:36, 16 January 2009 (UTC)

Dead aardvarks are mostly water. Dessicated aardvarks, on the other hand, ... Saintrain (talk) 18:22, 17 January 2009 (UTC)

Cecil Adams covers this question here. --Sean 13:50, 16 January 2009 (UTC)

There is one advantage to having lots of frozen water in the freezer, it will keep the food frozen longer in the event of a power failure. You can also use freezer gel packs that will hold even more "coolth", but then again, those cost money and you can't drink the melting water on a hot day in summer. StuRat (talk) 15:24, 16 January 2009 (UTC)

How about freezing the bottles outdoors when it's cold out? Since your user page indicates that you live in Vermont, I recommend doing it today! That will give you the benefits mentioned above, without the energy cost. -- Coneslayer (talk) 15:57, 16 January 2009 (UTC)

That's an excellent idea. Even better, fill those bottles with cold maple syrup. :-) StuRat (talk) 06:57, 17 January 2009 (UTC)

I do something similar with large leftover items I want to freeze, like a ham or turkey. I have an enclosed, but unheated, porch, so I put food out there to cool down before I put it in the freezer. Of course, if I just left those items outside, I would find dogs and racoons fighting over them in my yard. StuRat (talk) 14:00, 22 January 2009 (UTC)

An additional point about not freezing water; when the frozen bottles are removed to make space for food, the energy used to freeze the water just melts away :-) Saintrain (talk) 18:22, 17 January 2009 (UTC)

Stone use

Is the British unit of weight the stone used for anything other than human body weight, commonly or otherwise? --Milkbreath (talk) 01:41, 16 January 2009 (UTC)

The only other usage I have ever encountered was by me, expressing the mass of meat in my family's Christmas dinner in stones and pounds to emphasize its size. Algebraist 01:48, 16 January 2009 (UTC)

I believe it is (or at least was) used for the weight of horses, as well. StuRat (talk) 02:21, 16 January 2009 (UTC)

Back in the 1950's it was used for weighing coal for domestic delivery. But generally, no - it's going the way of the Dodo. SteveBaker (talk) 03:06, 16 January 2009 (UTC)

I remember it being used by people buying potatoes (usually as "half a stone"), but I haven't heard that for many years. AndrewWTaylor (talk) 10:13, 16 January 2009 (UTC)

I suspect it's not even used for bodymass any more, except perhaps colloquially. I'd be very surprised if you went to a doctor's surgery or hospital and they measured your mass in anything other than Kilogrammes. Alun (talk) 13:14, 16 January 2009 (UTC)

I met Brits a few years ago who could readily state their weight in stone,(like "I weigh 12 and a half stone") but had to do mental calculations to come up with the pound or kg equivalent. When did Brit scales for home or medical use switch from "stone" to pounds or kilograms, if ever? "Stone" still shows up in Brit press along with pounds and kg for the weight of fish [1] adults [2] and babies [3] . Stone still shows up in "ideal weight" charts [4]. Edison (talk) 14:57, 16 January 2009 (UTC)

That switch has yet to occur. Every Briton I know states their weight in stones, or in stones and pounds. Scales for weighing oneself normally have a scale of stones and pounds and a scale of kilograms. Algebraist 15:01, 16 January 2009 (UTC)

Hi! <wave> It's me! The Brit who has no clue how much a 'stone' is and only knows his weight in kilo's (but who can do a rough conversion into pounds if required). :-) SteveBaker (talk) 15:21, 16 January 2009 (UTC)

Sounds like Brits vary considerably in how they note their weight. Edison (talk) 18:02, 16 January 2009 (UTC)

Steve, you live in Texas now. You don't count as a Brit. ;-) Axl ¤ [Talk] 18:18, 16 January 2009 (UTC)

Well, he certainly doesn't count as a Texan if he thinks about his weight in kilos. Dragons flight (talk) 18:28, 16 January 2009 (UTC)

I'm a Brit (that actually lives in Britain) that measures his weight in stone (well, when he weighs himself at all...). Doctors certainly use kilograms, but I don't think anyone else does (those that do, we exile to the other side of the pond ;)). --Tango (talk) 23:39, 16 January 2009 (UTC)

Don't send them to the US, as we measure our weight in pounds, except for doctors, again, always using those silly kilograms. StuRat (talk) 23:34, 18 January 2009 (UTC)

When you guys eventually get with the program and start using kilograms and kilometres (oh, alright, kilometers if you must), you'll all wonder "Why didn't we make this very sensible change two centuries ago?". -- JackofOz (talk) 04:16, 19 January 2009 (UTC)

Kilograms are too big, so you must resort to fractions or decimals to give your daily weight. StuRat (talk) 15:27, 19 January 2009 (UTC)

I'm a Englishman who lives in England, measures his weight in kilograms, but knows others who still use stones and pounds. None use pounds on their own. I also measure my height in metres but know others who quote feet and inches. I buy my bottled English beer in half-litre quantities but it's always a pint (or several) in the pub. Milk from the supermarket comes in 3.4 litre plastic containers, but from the corner shop in 1 litre packs. I fill my VW up with 55 litres of diesel and get 45 miles for every gallon. It is one of the nicer things about living here that we are able to mix everything up this way and yet still know what we want to know at the end of it. Bazza (talk) 15:02, 19 January 2009 (UTC)

Question about waves

Hi - I was at the lake yesterday afternoon - a shallow, broad artificial lake; it was a bit blowy, and I saw two types of waves - a low chop moving across the water, and other, more sinuous waves that were neither rising or falling, but remaining in place. From the article on waves, these aren't standing waves, as I understand them, because according to the animation they rise and fall, albeit in the same spot - whereas these crests remained fixed and unmoving. Is there a name for this phenomenon?

Thanks Adambrowne666 (talk) 01:44, 16 January 2009 (UTC)

In rivers you often get a bulge in the water right after it passes over a rock, so perhaps something similar is happening here. StuRat (talk) 02:19, 16 January 2009 (UTC)

Thanks for the answer, but it didn't look like that, because the crests were regularly spaced, and the water wasn't flowing - there was no movement, only apparent movement, an effect of the ripples blowing across the surface. Adambrowne666 (talk)

Could there have been a shape at the bottom of the artificial lake that resembles the shape of the waves above ? And how can you tell there was no motion of the water ? It seems to me that the chopiness would tend to disguise this. I'd dip the end of a stick in and see if you get a wake. StuRat (talk) 15:05, 16 January 2009 (UTC)

It's possible the water was moving - but is it likely in a shallow artificial lake with no inlets? - maybe, I dunno - the ducks etc were bobbing in the same spot, so it seemed not to be moving. You may be right - though I was thinking of something along the lines of the wind setting up waves that were reflected back from the shore causing interference patterns on the surface; is that possible too? - I'm totally guessing here... If it was that, would they be defined as standing waves? Adambrowne666 (talk) 11:16, 18 January 2009 (UTC)

The wind could blow the surface water one way, and it might need to flow the other way underneath, to maintain equilibrium. With wind waves being reflected back from the edge, you could get standing waves, but they would go up and down at any given point, not "stay up", as you noted earlier. StuRat (talk) 23:30, 18 January 2009 (UTC)

Yeah, makes sense - well, maybe it was flowing - next time I see it, I'm definitely going to check - my curiosity's piqued - thanks for the answers, Stu.

You're welcome. I'm curious, too, so be sure to let me know what you find out. StuRat (talk) 22:18, 19 January 2009 (UTC)

solid objects behavior under stress

we all know that any materials in solid state will respond by change in its dimension (strain)when be subjected to aforce . but will there be any change between the volume before and after applying of the force? —Preceding unsigned comment added by Mjaafreh2008 (talk • contribs) 02:39, 16 January 2009 (UTC)

We probably shouldn't be answering your homework questions, but you may want to read the articles titled Compressibility and Condensed matter physics, which contain information for you to answer the question yourself. As an alternate idea, your teacher may have issued you a text book, if our articles are more detailed than you need to answer your question, the information may likely be found there, or possibly in the lecture notes from class when you learned this. --Jayron32.talk.contribs 02:44, 16 January 2009 (UTC)

How about we assume good faith, huh? While that's certainly the kind of question that may be set for homework (although I wouldn't set it if I were the teacher, since it just tests if you were awake in class and doesn't touch on any actual understanding), it's also the kind of question that a naturally curious person may come up with by themselves. If it was homework, at least the OP went to the effort of writing it in their own words. --Tango (talk) 02:48, 16 January 2009 (UTC)

Yeah - I don't think this is in any way obviously a homework question. Certainly any material could be compressed into neutron-star-material ("neutronium") and even black-hole-material - so the answer is yes - for absolutely all normal or abnormal matter. But what about for 'ordinary' kinds of forces? Well, consider diamond - it's formed by applying huge compression forces to 'normal' carbon. The density of diamond is about 150% that of graphite - certainly that is an example of a material which can be compressed to a smaller volume...and which will remain at that volume when you withdraw the pressure. SteveBaker (talk) 03:04, 16 January 2009 (UTC)

You can try this yourself and observe the result. First, squeeze a dry sponge or a stuffed animal. Does the volume change? Now, fill a ballon or a plastic milk jug with water, with no air. squeeze it: Does the volume change? If you cannot tell by direct observation, do this experiment under water in a tub and observe the displacement. Now, explain any differences. Note: when I do this, I can dramatically reduce the volume of the stuffed animal, but I cannot reduce the volume of the water balloon. -Arch dude (talk) 22:25, 18 January 2009 (UTC)

Bogus answer based on bogus experiment: The stuffed animal is mostly air. When you compress it - you (probably) aren't compressing the solid material at all - you are either compressing or (more likely) expelling the air. The issue of whether the solid material that makes up the individual fibres is compressible is the question at issue here - and your experiment doesn't show that. SteveBaker (talk) 01:25, 19 January 2009 (UTC)

fibrinogen

a friend of mine is having a fibrinogen count that is below the reference level. the blood test report states that the fibrinogen level is 120mg/dl while the reference range is 175-350mg/dl. what will be the effect of such a shortage?what is the function of fibrinogen? i am not able to understand the wikipedia article. —Preceding unsigned comment added by 117.193.225.118 (talk) 08:38, 16 January 2009 (UTC)

The Fibrin article certainly could be made more reader-friendly. Basically, fibrinogen is a major building block for blood clots. Under conditions that trigger clot formation, a fibrin polymer can be created. This protein mesh forms the backbone of a clot. Circulating fibrinogen (an inactive form) is the principal source of fibrin, is converted to it's functional state when it is cleaved by the clotting enzyme thrombin. Information about any possible medical implications for your friend would represent medical advice, which should not come from the RefDesk. --Scray (talk) 13:05, 16 January 2009 (UTC)

Of itself, a slightly low fibrinogen level doesn't have any clinical significance. However the clotting abnormality disseminated intravascular coagulation can cause a low fibrinogen level. Axl ¤ [Talk] 18:23, 16 January 2009 (UTC)

Tests are always interpreted within a clinical situation. The fibrinogen level was presumably ordered for a specific purpose: to assess abnormal bleeding or abnormal blood tests like PT/PTT; to assess the progression of liver disease which might interfere with protein synthesis, or to assess the risk of developing cardiovascular disease. A low fibrinogen level would have different significance depending on the clinical setting in which it was ordered, so really your friend has to discuss this with his physician. - Nunh-huh 18:31, 16 January 2009 (UTC)

More likely the fibrinogen level was a default test in the coagulation screen. If the PT and APTT are normal, the fibrinogen level isn't very helpful. Axl ¤ [Talk] 07:48, 17 January 2009 (UTC)

In the context of the OP, this is beginning to look a lot like medical advice. --Scray (talk) 18:44, 17 January 2009 (UTC)

fifth dimension

what is the fifth dimension? light is said to be the vibration of the fifth dimension in the book "HYPERSPACE" by michio kaku. but in the same book, it is said that the universe was earlier made up of 10 dimensions and six broke off. ours is the remaining four. also, the remaining six dimensions have shrunk to the size of the fraction of the size of a proton. so how doesit fill our universe so that light would travel? —Preceding unsigned comment added by 117.193.225.118 (talk) 08:49, 16 January 2009 (UTC)

This sounds like fiction, not science - which fits the source you cite. We do have science-based articles on the fourth and fifth dimensions that might interest you. --Scray (talk) 12:54, 16 January 2009 (UTC)

A book called Hyperspace is unlikely to be a reliable source. Light is not a vibration of the fifth dimension, but rather an electromagnetic phenomenon that can be adequately if unsatisfyingly described in the usual 3 (special) plus 1 (time) dimensions. In science fiction, the fifth dimension is often assumed to be an extra spatial dimension that allows for faster-than-light travel via some handwaving pseudophysics, and hyperspace is the medium that allows this. In string theory, a fairly advanced and controversial area of higher nonsensetheoretical physics, more-dimensional are models considered, and they often have the property that many of the extra dimensions are somehow compacted so that we only perceive the normal ones. See String_theory#Extra_dimensions, and take an aspirin or two in advance ;-). --Stephan Schulz (talk) 13:08, 16 January 2009 (UTC)

According to the article Hyperspace (book) it is a real science book. And Michio Kaku is an expert in string theory, apparently. So I don't think the reliability of the source can be in doubt. I don't know anything about theoretical physics though. Alun (talk) 13:21, 16 January 2009 (UTC)

Thanks for pointing that out. I agree that the person who wrote the book sounds reliable, but I retain the impression that it sounds like (well-informed) speculation. --Scray (talk) 13:27, 16 January 2009 (UTC)

Ha, it just occurred to me, upon reading what you wrote that all scientific theories are well-informed speculation!! Alun (talk) 13:47, 16 January 2009 (UTC)

Why are the spatial dimensions special? Zain Ebrahim (talk) 13:28, 16 January 2009 (UTC)

For me, I can travel more easily to the kitchen than to yesterday... --Stephan Schulz ([[User talk:

A fifth dimension wouldn't fill any particular place in the universe - it would be everywhere but curled up. The usual comparison is to a telephone line, far away it looks like a line but close by for an ant it is two dimensional with one dimension curled up an circular. A string can just go straight along the line or wind around it an these two paths would be different so one can get different effects. In our three spatial dimensions there could be another tiny dimension curled up everywhere just like the curve round the wire is all along it. An alternative is tha there could be an extra huge dimension but we can't look in that direction, for instance if our universe is like a layer of an onion and light only travels along a layer of the onion, the fifth dimension would be between layers. I'm sure this is the sort of Michio Kaku would be writing anyway, perhaps you could be more specific? Dmcq (talk) 13:53, 16 January 2009 (UTC)

Michio Kaku is considered a joke by his fellow physicists and I would recommend ignoring anything he says. In this case, though, when he talks about light as a vibration in a fifth dimension he's probably talking about Kaluza-Klein theory, and when he talk about six extra dimensions he's talking about Calabi-Yau compactification in string theory. The six extra dimensions in string theory have, as far as I know, nothing to do with the one extra dimension of Kaluza and Klein's theory. There's no standard "fifth dimension" that everyone agrees on. -- BenRG (talk) 14:21, 16 January 2009 (UTC)

I have personally seen and heard the Fifth Dimension. Edison (talk) 14:47, 16 January 2009 (UTC)

Michio Kaku is the 'physicist' who is trotted out on every Science Channel and Discovery Channel show to say impressive, dramatic, surprising (and often VERY wrong) sciencey things on every subject under the sun. If you watch any of those shows - check out the photo (at right) and I'm sure you'll recognise him. He was once a leading string theorists - but I certainly would take anything he wrote in the last 5 to 10 years or so with a huge pinch of salt. His latest book is about "the technologies of invisibility, teleportation, precognition, star ships, antimatter engines, time travel and more"...which is a measure of how much he's "sold out" to the media business. He clearly hasn't been a hard-working grass-roots scientist for many years because he must be spending close to 100% of his time with film crews, in makeup tents and writing trash about precognition and teleportation with the flimsiest of scientific pretext. I find this very sad. SteveBaker (talk) 15:18, 16 January 2009 (UTC)

You know, as much as love the Science Channel and the Discovery Channel (and the History Channel too), I am distressed by all the shows on Nostradamus, the Bermuda Triangle, Roswell, etc.. Now I find out that the guy on the legitimate science shows on astronomy and physics isn't exactly reliable either? Ugh. Where's a lay scientist supposed to turn? A Quest For Knowledge (talk) 16:28, 16 January 2009 (UTC)

From my experience, most popular scien-tists (as in scientists heavily active in the popular science field not as in scientists who are popular) tend to be somewhat disconnected from real science Nil Einne (talk) 18:33, 16 January 2009 (UTC)

How about Carl Sagan? A Quest For Knowledge (talk) 19:03, 16 January 2009 (UTC)

I said most, not all Nil Einne (talk) 19:08, 16 January 2009 (UTC)

The Wikipedia Ref Desk, of course! --Tango (talk) 23:45, 16 January 2009 (UTC)

Hey, I know that book (his latest Steve mentioned, not the one under discussion here). It's riddled with factual errors. Algebraist 18:36, 16 January 2009 (UTC)

Branes? ~AH1^(TCU) 23:08, 16 January 2009 (UTC)

unified theory

have scientists arrived at an equation that can explain all the laws and features of nature? what is the equation? —Preceding unsigned comment added by 117.193.225.118 (talk) 08:50, 16 January 2009 (UTC)

Not yet. Algebraist 12:43, 16 January 2009 (UTC)

No; see Grand unification theory for the most famous attempt. Even there, it's a long way from understanding particle physics to understanding why blue-footed boobies behave the way they do. Nature isn't just big; it's everything! --Sean 13:57, 16 January 2009 (UTC)

... but it is known that 42 is the answer to life, the universe and everything. 98.220.251.111 (talk) 14:03, 16 January 2009 (UTC)

We haven't - but what we do know is that there are hard limits to what we CAN explain. We have several sources of fundamental unknowability to contend with: The Heisenberg uncertainty principle and associated quantum weirdness limits what we can know at the nano-scale. Chaos theory and Catastrophy theory limits what we can predict - even at the macro-scale. Hawking radiation has been argued as a source of cosmic-scale randomness. Godel's theorem limits what we can prove mathematically. The Halting problem (and it's greater consequences) limit what we can compute with software. So I guess what we DO know is that even if we do find "the equation of everything" - it's not going to help us to understand or predict everything. We do not have a mechanical universe (how is that a red link?!?) - and Einstein notwithstanding: "God" does indeed play dice...or possibly roulette...in fact it often seems that it's the only game (s)he knows! SteveBaker (talk) 15:04, 16 January 2009 (UTC)

What do economists know, really?

With the economy seeming to fall into a quagmire, I can't help but wonder why more economists didn't see this coming? (I suspect some did, at various points along the way, but all along the way down there has also been no shortage of people to suggest things will get better soon.)

I'm generally interested in analysis of the accuracy of forward looking economic predictions. Presumably someone tries to figure out how accurate analysts have been, right? I'm not sure what the right data sets to look at are though. Any ideas? Dragons flight (talk) 08:52, 16 January 2009 (UTC)

Economics is a science in flux. Rules change. Sometimes this is the point. For example FDIC was created in 1933 to prevent future runs on the bank, no one knew what it a run on the bank would look like with this new insurance in place. Could one still happen? No one knew because there wasn't any data for something that had never been tried before.

A lot of economists study cause and effect rather than getting good at predictions. To draw another example, suppose I asked an economist why people speed less on the freeway in a recession. They would tell you that it could be because people can't afford a ticket or that they are trying to get better gas mileage. If I ask them why they speed MORE they will say because they can't afford to be late for work or they are burning off frustration. But if I ask whether people speed more or less in a recession they would have no idea unless they went out and collected data. So they are not effective at predicting something they haven't seen. Once they have data on this though, they'll be able to predict it for a while in the future unless traffic laws change significantly, in which case they could make predictions based on old predictions but ultimately they just have to collect more data.

These mortgage backed securities are like new traffic laws. No one really knew what would happen if they started bottoming out. Sure there were some that viewed it overly optimistically, and some that viewed it overly pessimistically (turns out these ones were right).

Now that being said there are some incredibly bright economists out there that probably see true most of the time. The problem is that firms don't necessarily have the incentive to listen to these economists. Seems stupid? Its not. Companies are rewarded for taking risks. Companies are also rewarded for making short term (one-quarter) quick profits that can be put into their prediction for their next quarterly release. Unlike Japanese firms which always keep long term in mind and take very few risks, American firms jump boldly into new cash making endeavors. This generally gives American firms better growth but sucks in times like these.

In fact often companies do things that are not in their own interest. The Game Theory that is created by open markets sometimes make Prisoner's dilemmas. For example when the banks stopped leading to each other, it sucked for all of them. They would've been better off if they had all kept lending, but individually they all thought, "Well it'd be great if everyone BUT me kept lending, so that I don't have to expose myself to that risk." This creates a scenario of no lending for the Nash equilibrium.

As far as predicting stock prices or market movements anyone who doesn't have insider information is no better at predicting than a monkey throwing at a dart board. Shows like Mad Money actually predict stock movement at slightly worse than random rates. Managed Mutual funds (meaning having an active "expert" playing the market buying/selling everyday to try and maximize profits) have historically done worse than indexed funds (just a list of stocks that never changes or infrequently change) in just about any economic climate. No one can predict the market.

Anyway probably a bit wordy there, hopefully you got something interesting out of it. Anythingapplied (talk) 09:23, 16 January 2009 (UTC)

to say frankly, the world economy is controlled by the gulf countries. they provide the world with nearly 80% of crude oil and so, they can control the price of petroleum by increasing or decreasing production. a decrease in production will cause an increase in petrol prices. this increase already is causing turmoils in India. the government did not increase the petrol price significantly when oil prices rose to $140 a barrel. this results in accumulated loss for all companies. But when the price fell to $40, the gov. will not reduce the price since there was no increase. the stock market situation is similar to that of the uncertainty principle at the quantum level. you cant just find for sure anything. u can just find the probability. the same applies for weather reports and stock markets. Harnithish (talk) 09:41, 16 January 2009 (UTC)

Unfortunately in the short term doing stupid things can seem right so the more silly politicians and economists get the limelight. It annoys me at work too that people who plan properly, bring in a profit and don't have a crisis get little reward compared to people who are always rushing around patching up the trouble they've caused. But on the original question I can't answer better than the old joke of what's the difference between an exam in philosophy and in economics? ---- One asks a different question every year and expects the same answer, and the other asks the same question every year and expects a different answer. Dmcq (talk) 10:32, 16 January 2009 (UTC)

Economics isn't really a science. We should stop calling it that. You can't do experiments with economies - not proper, controlled double-blind experiments. If you could then the major opposing camps (The Marxians and the Keynsians) would long ago have figured out which of those two theories was "correct" and we wouldn't have one bunch of highly paid, trained, professional economists claiming that lowering taxes on the rich would cause them to invest more money and cause a 'trickle-down' effect from which everyone benefits - while another group of equally highly paid, respected economists claim that we should raise taxes on the rich so we can lower them for the poor and have those consumers spend more and thereby raise the economy from the bottom up. We literally don't know the answer to something as fundamental as that. Sure, we can change some policy and a year later it SEEMS like things either got better or they got worse - but without a "control group" you have no clue whether it was what you did that caused that - or some other factor like the weather or the discovery of a new source of energy or a terrorist flying a plane into a building.

The scariest thing about economists is their propensity for having graphs with no numbers on their axes! Ask them about their most well-known theory: 'Supply and demand' and 100% of the time, they'll trot out this pretty graph with one curve swooping down dramatically from one side and another curve swooping down from the other - and right there at the point of intersection there will be a big red arrow. OK - so this tells us that supply and demand should be equal and the price of the goods will change until that happens - fair enough. So, you ask - what are the numbers? At what price should we sell this item? Surely we can look at the curves and read off the answer? No? Well, at least we have the equations for price-versus-supply and price-versus-demand curves then? Well, sadly, no. Because economists have no clue how (mathematically - numerically) supply and demand change as a function of price because THERE ARE NO NUMBERS ON THE FREAKING AXES!! Proper scientific theories have to produce PREDICTIONS that can be tested. So, nobody was prepared to sign off on Einstein's theories of relativity until some poor sap had hauled a bunch of telescopes through the middle of a war zone and later out into the back of beyond and measured how a star is displaced during a solar eclipse! Where is the seminal experimental evidence for those supply and demand curves?

So what use is this wonderful 'supply and demand' theory? All it tells you is the most blindingly obvious thing - that if something gets cheaper, more people will buy it (and vice-versa) and if it gets more costly, more people will want to make it. Yeah - great job guys! If I'm a manufacturer and I make widgets in small quantities for discerning customers - so the supply is short and the prices are high...should I invest in another factory and sell twice as many widgets (albeit at a modestly reduced price) or will the price drop so steeply when I do that that I will drive the price down so far that I'll actually make less profit than I do now? Maybe instead, I should cut back on production and let the price rise? I should be able to toss the numbers into a spreadsheet using the equations provided in the Economics 101 "big book of equations" and PREDICT (within the limits of experimental error) whether I should open the new factory or not. In truth - nobody knows - ask N economists and you'll get 2x(N-1) answers! This is one of their most fundamental principles - and certainly the one they teach first in Economics 101 - and we don't have even the basic math to tell us how it works. This stuff isn't just a lack of scientific rigor - it's an actual practical matter for which there is no known answer...just look at the way governments work to try to artificially limit supply (eg by buying agricultural 'setasides' where they pay people NOT to increase the supply) - or the way that they try to increase supply by offering subsidies. These are direct tinkerings with that supply/demand curve - but in the absence of any science - there are these huge debates about whether to institute these kinds of practices. If it were a science, you'd plug the numbers into your spreadsheet - people would look at your numbers and everyone would nod sagely and "do the right thing".

That's not to say that economists are a waste of space (let's reserve that for the philosophers!) - but what they are doing isn't science - and they shouldn't call it that. Obviously there are very good reasons why they can't do these kinds of experiments - which is an excellent excuse for the state of economic theory...but we should please just not call it 'science'.

SteveBaker (talk) 14:50, 16 January 2009 (UTC)

I would rate philosophers above economists. Mistakes by economists are disastrous; mistakes by philosophers merely ridiculous. Matt Deres (talk) 16:44, 16 January 2009 (UTC)

A problem which virtually precludes the success of economics is that economists publish their findings, and the economic actors have access to these publications. They then try to gain an advantage from the insight and change their behaviour and therefore the economy which is being studied by the economists. There may not be that many people who actually read the papers of economists, but a few smart individuals should be enough (if they run successful businesses then others will be interested in their business models and copy it). In general, economists are not smarter than economic actors. Icek (talk) 22:57, 16 January 2009 (UTC)

Evidence

Apparently I hit a nerve. However, the verbose responses given above largely missed the point of the question. Rather than offering opinions about how good/terrible economics is at making predicitons, I would like to see actual evidence of what comes from those predictions. User:Anythingapplied alluded to what could be good evidence saying: "Shows like Mad Money actually predict stock movement at slightly worse than random rates. Managed Mutual funds (meaning having an active 'expert' playing the market buying/selling everyday to try and maximize profits) have historically done worse than indexed funds", but didn't give any references to back up his assertions.

In response to SteveBaker's assertion that economics is not "science" and shouldn't be treated as such, well that's what I would like to investigate. So what if there is only one economy? That doesn't preclude making predictions and verifying whether the results are statistically better than random guessing. By analogy, cosmologists have only one universe and climatologists have only one planet, and yet neither field should be accused of being incapable of scientific analysis. Some economists, such as stock analysts and money managers, are routinely making predictions about the future of the economy. Either they turn out to be right or wrong, but that's what I would like to know. Before we condemn all economists, I'd like to see some data about their actual performance. Dragons flight (talk) 16:32, 17 January 2009 (UTC)

You miss the point of my post. What makes something a science or not has nothing to do with how often it's right. It's to do with methodology. Science has a long and (mostly) successful history of applying "The Scientific Method" - where you have some idea for a theory - you test it with an experiment - the experiment either confirms your theory or rejects it. Economics doesn't (and indeed, cannot) work like that. Furthermore, it wraps itself in the trappings of science - graphs and charts - but misses out on the aspects of measurement and testing. So it may be 100% successful or worse than chance - it doesn't matter - it's not science because it doesn't apply scientific methodology. So if your goal is to claim (as I do) that economics is not a science - then you don't need evidence of how economic predictions turn out. You merely have to ask how economists make those predictions...and they'll readily admit that they can't do proper experiments because that's in the nature of their field.

Cosmologists certainly do perform experiments - a good example is that they hypothesised that the big bang was the origin of the universe. They reasoned that if that really happened then the cosmic microwave background radiation should have a certain set of properties. Finally, they launched a spacecraft with microwave detectors and they measured that radiation experimentally. The result fitted their prediction and debunked the older theories - so now we have a new cosmological finding and we regard the Big Bang as "A True Theory".

I agree that climatologists can't experiment on the entire planet - but they can take results and equations from other fields of science and apply those to the systems they study. Weather (not climate) prediction (for example) is a notoriously inaccurate field of study. We all know that weather forecasts are unreliable. But they DO use scientific principles - they have a computer with a 'model' of the atmosphere which includes things like the gas laws and the laws of thermodynamics - and they run that data against current data. They test that model (which is a kind of 'theory') against historical weather data - and that is a kind of experiment. When the model fails, they figure out why - and hopefully fix it...that is (in a sense) their scientific "law". It's not perfect and the results aren't particularly reliable because of Chaos theory...but they know why it doesn't work - and they know the accuracy of their forecasts falls of as a function of time. When the next hurricane heads towards Florida - they will predict it's track and various teams of meteorologists will largely agree on the results. Hence it's a scientific method. Economists rarely agree - if they were following a set of laws that had been scientifically derived and proved by experiment - they wouldn't disagree so violently. Stock market prediction is also unreliable - but it's not done with a scientific model - it's just statistics and the best gut feel that various stock market 'experts' can come up with.

Cosmology and climatology can build on the results of physics and chemistry. Economists have nasty unfathomables like the behavior of humans under stress, the weather, the random-seeming discovery of new raw material deposits, massive fraud in ENRON, one guy becoming President rather than another as a result of 'dangling chads' - they simply can't build their results on the back of other scientific results - and they can't come up with scientific laws of their own. It's not their FAULT that it's not a science - but none-the-less, it's not.

But none of that changes whether they are right or wrong when making predictions. Weather forcasting has a TON of science thrown at it - but Chaos theory dooms us to forecasts that are no better than chance beyond a week or so - and short term forcasts that do better than chance - but not much better than following the rule "Today's weather will be the same as yesterday"...which is remarkably effective! Some economic theories work really rather well in practice (certainly better than weather forecasting) - but they aren't based on science.

SteveBaker (talk) 18:36, 17 January 2009 (UTC)

Actually, you miss my point. I don't care what you think of their methodology. I don't care whether what they do qualifies as science. I want to see evidence evaluating their reliability.

Look at this way. Athletics is not generally considered a science. On any given day, an athlete may have a good performance or a poor one. Nonetheless, what they are capable of doing is often interesting and great athletes are consistent enough to build legendary careers.

Maybe economists indulge in superstition and fantasy, but regardless, I am still interested in whether there exist economists who are right often enough that they are able have useful insights about the future of our economy. I consider all this discussion about whether the methodology is scientific to be largely irrelevant to the question of whether economics, as a field of human endeavor, can be empirically demonstrated to be useful. Dragons flight (talk) 06:38, 20 January 2009 (UTC)

Dragons flight, there are some very successfull investors like George Soros, but I don't know their methods ;-)

I strongly disagree with SteveBaker's reasoning. Cosmologists certainly don't perform experiments! A hypothesis is not an experiment. Economists hypothesise as well, and the hypotheses can be falsified.

As I already said, the largest problem is not the inherent complexity but the lack of separation between the theory and the economic actors who shall be described by the theory.

-Icek (talk) 11:48, 23 January 2009 (UTC)

Using frogs to keep milk cold

My father told me once that when he was young (around year 1920) they used a frog to keep milk cold. They put the frog into the milk container and by having the frog there, the milk would stay cold. I wonder if this possibly could be true? --Kr-val (talk) 09:26, 16 January 2009 (UTC)

Short answer: No. Longer answer: once people found out there's a frog in the milk, my guess is that they would leave it alone, and it would stay colder because it's not being handled. I don't think that's the intended effect, though. --Scray (talk) 10:07, 16 January 2009 (UTC)

The closest thing I have heard to this mistaken lore is my dad saying they would put a jug of milk in the spring to cool it. Frogs do spring sometimes. Wasn't there a Three Stooges episode where one of them put a frog in the beer they were trying to make, saying the recipe included "hops?" Edison (talk) 14:44, 16 January 2009 (UTC)

Your dad's story is corroborated by this NY Times article from 1854. Presumably it was not unusual to find a frog in your spring-cooled milk, and some people mistakenly guessed that it was the frog that was doing the cooling. --Heron (talk) 14:35, 17 January 2009 (UTC)

moment of inertia

I looked all over for a logical defintion for moment of inertia .

i dont need a mathmatical defintion , i need atext answer without numbers...thank you...? —Preceding unsigned comment added by Mjaafreh2008 (talk • contribs) 09:39, 16 January 2009 (UTC)

Google has a special function for bringing up definitions. Search by writing "define:moment of inertia" [5] The article Moment of inertia may also help, but I guess you've read it already. EverGreg (talk) 10:32, 16 January 2009 (UTC)

It is the resistance to turning you might notice when starting a wheel rotating. It' bigger for heavier wheels. I'm sorry but maths is the language of science. One can put words in instead of the symbols but it would still be maths. Dmcq (talk) 10:44, 16 January 2009 (UTC)

It's not necessarily true that heavier wheels have a higher moment of inertia. It depends on how the weight is distributed...a point on which I elaborate in my explanation below. SteveBaker (talk) 13:48, 16 January 2009 (UTC)

The canonical 'gut feel' thing is the ice-skater spinning on tip-toe. As she starts off, her arms are outstretched - when she pulls them in she immediately spins much faster. The amount of angular momentum she has stays the same even though she's spinning faster - and that's because she changed her moment of inertia by becoming more "compact". So I guess the loosest definition would be 'state of compactness'.

Hence (to pick a practical example that I was discussing with fellow car club members a few days ago): if you have 10" radius wheels on your car with 3" deep tyres (tires) mounted - for a total radius of 13" - and you decide to switch them out for sexier 12" wheels with 1" 'skinny' tyres - you are putting more heavy metal out towards the edge of the wheel and removing some the lighter weight rubber. So even though your new wheel/tyre combo may not weigh any more than the old ones - and even though you didn't change the overall circumpherence - you may be shocked to discover that it added half a second to your 0-60 time! That's because the moment of inertia of the wheel got bigger - the denser parts moved outwards - it became less "compact". This increased moment of inertia requires more torque to accelerate them up to speed - which in turn makes your car's acceleration (and braking) noticably worse....although it does LOOK pretty cool!

SteveBaker (talk) 13:46, 16 January 2009 (UTC)

Informally you can think of moment of inertia as a measure of rotational inertia, i.e. the tendency of an object to maintain its state of rotational motion. To accelerate a stationary (non-rotating) object to a given speed of rotation, you need to give it a certain amount of angular impulse. Say you applied a torque (turning force) $\tau$ for duration $t$. You can get the same result by using half the turning force (i.e. $\tau /2$) but you have to apply it for twice as long (i.e. $2t$). Or you can use double the turning force ($2\tau$) and apply it for half as long ($t/2$). There are many ways you can accelerate the object to the same speed of rotation, but the product of (turning force)×(time) remains the same. So the product of (turning force)×(time) provides a measure of the amount of “effort” expended in changing the rotational speed of an object. You can understand an object of large moment of inertia as one whose speed of rotation cannot be changed easily — you have to either apply a large turning force, or apply a turning force for a long time, or do both, to change its rotational speed. --98.114.146.183 (talk) 18:40, 17 January 2009 (UTC)

Which part of "I don't need a mathematical definition" didn't you understand?! SteveBaker (talk) 01:20, 19 January 2009 (UTC)

Blood spurts

To kill one of my chickens for dinner, I hang it upside down, hold its head, and make deep cuts (down to the bone) on both sides of its neck, just below the skull. I know I've done it right when I see rhythmic spurts of blood shoot out. In the butchering books I've read, they say this method cuts the jugular vein, which I happily accepted due to the phrase "go for the jugular", but it occurs to me that usually arteries, not veins, should do more spurting. The cuts are so deep that I'm certainly also cutting the carotid artery. Which vessel is likely to be the important one that drains the blood out? Thanks. --Sean 14:08, 16 January 2009 (UTC)

A tree stump and a sharp hatchet also gets the job done, severing all arteries and vessels, although the chicken is likely to run around flapping its wings for a minute or less. Your method seems to offer the possibility of greater suffering for the animal if done hesitantly or incompletely, but might drain the blood more completely. Edison (talk) 14:40, 16 January 2009 (UTC)

I've done it both ways, and much prefer the way I described. I always use an exquisitely sharp knife, and I've noticed in other contexts that being cut by a very sharp blade is not particularly painful. Wacking heads off is much more likely to go awry, in my experience. --Sean 15:11, 16 January 2009 (UTC)

I realize that this still does not answer your question, but by taking a thin blade and poking it through the chickens beak (as if it were being swallowed) angled up towards the brain is the way I've done it in the past. What I was told is that if you stick the knife into the brain, it's instant death for the bird and the least painful. Then you can cut the throat and have the blood run out like you have been doing. You'll still get the death rattle effect, so watch out for blood splashing about. Dismas|^(talk) 16:35, 16 January 2009 (UTC)

I do indeed do that, but I didn't want to cloud the discussion further. --Sean 18:07, 16 January 2009 (UTC)

I argue that it would be extremely painful to have a knife thrust through the roof of the mouth into the brain. Ever had sinus surgery or dental surgery? Edison (talk) 19:46, 16 January 2009 (UTC)

According to a report by Compassion in World Farming Trust, [6] " the time taken by a chicken to die varies enormously, depending on which blood vessels in the neck are cut... Research, however, shows that of all the neck cutting methods, the severing of both carotid arteries (these are the major blood supply to the brain) is the quickest method of inducing death (Gregory & Wotton, 1986). Cutting both carotid arteries (and both jugular veins) is vital if a rapid bleed out and quick death are to be achieved. Failure to cut both carotids can add two minutes to the time taken to reach brain failure (MRI, 1984)" Rockpocket 19:28, 17 January 2009 (UTC)

Thanks for the informative reply. Carotids, then! --Sean 13:23, 19 January 2009 (UTC)

Short tongue and snipping

Medical advice question removed.

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

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

Milkbreath, StuRat (talk) 16:39, 16 January 2009 (UTC)

My tongue is very short and from the looks of it, it seems there is a sort of attachment that is preventing it from stretching out too far from my mouth. I don't know what it's called but I know that some children have this snipped in order to help with speech. However, my adult friend also had the same problem, and when he went to get his tongue pierced, the tattoo shop gladly snipped it for him. He said there was a lot of blood but now he has healed and he can stick his tongue far out. What is this surgery called and are there any health benefits for adults to have this "snipped"?--Emyn ned (talk) 14:19, 16 January 2009 (UTC)

---

It sounds as though you are talking about a frenulum. Children with ankyloglossia have a frenulum that is too short and causes problems with speech (sometimes called being "tongue tied"). The procedure you are referring to is a lingual frenectomy but the reference desk is not meant for giving medical advice. The tongue is highly vascularized and is known to bleed profusely; if the person at the tattoo shop who "snipped" your friend's frenulum also "snipped" one of those juicy arteries, that would explain the bleeding. Please ask your doctor about it. --- Medical geneticist (talk) 14:35, 16 January 2009 (UTC)

I, personally, am not asking for medical advice. I am asking what are the benefits, if any, for adult lingual frenectomy? --Emyn ned (talk) 14:46, 16 January 2009 (UTC)

you mean besides the obvious one, right? —Preceding unsigned comment added by 82.124.85.178 (talk) 15:10, 16 January 2009 (UTC)

Please let me ask a few questions of Emyn ned. You're not personally asking for medical advice? How are you asking for it, then? Whose tongue are we talking about here, yours that you described in detail in your question, or no? Are we supposed to believe that it is mere coincidence that you suffer from the very medical condition whose surgical remedy you are only asking impersonally about? Are you considering having that surgery, and would what you discover here on the Wikipedia reference desk help you decide whether to have it or not? --Milkbreath (talk) 17:19, 16 January 2009 (UTC)

Ok, pretend I asked "what is the medical benefit of adults having their stomach stapled?" And pretend I didn't mentioned anything about having a obesity issue. Would you then be able to provide me with this info? I am looking for the general medical benefits of adults have such surgery, not for me. I tried searching the internet for any reputable sites stating the need for such. --Emyn ned (talk) 18:50, 16 January 2009 (UTC)

Thanks for the reply. Yes, such a question would be kosher. Nobody's trying to hurt anybody here. The rules here are for everybody's protection. You can read all about it here. Will you please answer my other questions, and, if you don't mind my asking, what prompted you to ask this question? --Milkbreath (talk) 19:07, 16 January 2009 (UTC)

Curiosity. Why else would anyone ask any question. I am asking what are the benefits, if any, for adult lingual frenectomy? Is this a normal procedure or is it done just for children? If it is done on adults, what would some of the reasons why MD would recommend this for an adult? Next time I ask a question, I'll be sure to remove any personal experiences. --Emyn ned (talk) 19:51, 16 January 2009 (UTC)

How many possible genetic variations or combinations from one couple ?

If you have a couple and each time they have a child it's a single, not a twin or triplet etc, how many children could they theortically have before they start haveing children with the same DNA as those already born ?

Sorry if this has been asked some where else

Scotius (talk) 15:33, 16 January 2009 (UTC)

The probability of this happening is so small that it would essentially never happen in the reproductive lifetime of a couple. I don't have time to crunch the math, but I doubt that such a thing is likely to have happened in the history of humanity (surely someone will challenge this!). Each time an egg or sperm is made, the chromosomes are shuffled and randomly segregated. Nearly infinite combinations are possible. See meiosis. --- Medical geneticist (talk) 15:41, 16 January 2009 (UTC)

According to Human genome, there are about 20,000-25,000 different genes (assuming we're only interested in the actual protein-coding ones). That means the probability of two siblings having the same genes from the same parent (assuming perfect Chromosomal crossover, which isn't quite the case, and taking the 20,000 figure) is $\left({\frac {1}{2}}\right)^{2\cdot 20000}\approx 10^{-12041}$, so that would require an infeasible number of children to get the probability up to anything that isn't essentially zero. The fact that the crossover isn't perfect may increase the chances, and if you don't distinguish between different copies of the same gene it will increase the probability quite a lot (a large portion of the genome is the same in everyone, I believe), but it will still be far below anything that could happen in one lifetime. Random mutations will decrease the probability even more, as well. --Tango (talk) 15:52, 16 January 2009 (UTC)

Strictly speaking you are overcounting. In a substantial number of cases, a parent will have the same alleles on both chromosomes so it doesn't matter which one the child receives. Also, a single genotype might be arrived at in more than one way from the parents. Removing redundancies will move your stupendously improbable number to a slightly larger, stupendously improbable number. Doesn't change the conclusion, though. Dragons flight (talk) 18:39, 16 January 2009 (UTC)

Also, both parents may in many cases have the same genes. Hence, to make a calculation possible, the similarity of the parents' genes would need to be known (I suppose inbreeding would increase the chance although I still suppose it's negligible). If a more general answer is expected, distributions are instead needed. —Preceding unsigned comment added by TERdON (talk • contribs) 02:15, 18 January 2009 (UTC)

I have read somewhere that each time a sperm or egg is made the process used, meiosis, means that there will ever be two sperm or two egg with the same DNA. I just liked to know, for knowing sake. I read somewhere that a human shares something 90 odd percent of their DNA with most (non related) humans. I'm not sure if I am remembering right or getting mixed up with that one with chimps, but I'm sure it's a high percentage thats shared. —Preceding unsigned comment added by Scotius (talk • contribs) 16:01, 16 January 2009 (UTC) Scotius (talk) 15:54, 16 January 2009 (UTC)

What do you mean by "the same DNA"? It's a confusing way to express it. DNA is just a molecule. Do you mean something more like like genetically identical? Really the question depends upon the probability of recombination at the same regions and segregation to the same gamete. Tyhen you need this to happen in both parents and for these two specific gametes to come together twice. So it'a w ahole series of improbable events, it's not just about producing identical gametes twice.

On the other hand, people produce genetically identical siblings all the time. They are called identical twins. Alun (talk) 16:08, 16 January 2009 (UTC)

All siblings share at least some of the same DNA. Sibs have a coeficient of reletedness of 0.5 don't they? So about half of their DNA is always the same. In fact the question makes no sense. The couple would only need to have two children, and those two would share (on average) as much DNA with each other as each does with either parent. If the question is "how many before they produce identical sibs", then I think the question is one of probability isn't it? I would imagine that even though recombination is not completely random, it would be close to impossible except from a theoretical point of view, depending upon how strict you want to be. I mean do you want "genomically identical" sibs, or "phenotypically identical" sibs? Most of our DNA doesn't code for any genes remember. But I think this is just a different way to express the Infinite monkey theorem. Alun (talk) 15:58, 16 January 2009 (UTC)

On average, half the DNA of siblings is the same, that's what the coefficient of relatedness tells us. We have an article, Human genetic variation, which people may want to read. Basically, two unrelated people are expected to share about 99.9% of their genes (well, actually I think that's base pairs, genes is going to be a little different). I think siblings would be expected to share about 99.95% of their base pairs. --Tango (talk) 16:14, 16 January 2009 (UTC)

Yes, it's a confusing question. The question was "how many children could they theortically have before they start haveing children with the same DNA?". My answer was two, because you only need two sibs for them to share the same DNA. Obviously they are not genetically identical, but they still share the same DNA. That's because all humans share the same DNA, as you point out about ~99.9% of SNPs are shared between all humans. Alun (talk) 16:26, 16 January 2009 (UTC)

To have two children with exactly identical DNA (every base pair is identical) would be almost impossible due to random mutations and the sheer number of pairs. However, I think that have two phenotypically identical children (exactly the same traits) that are not twins is possible, but still incredibly unlikely. There's still too much information for it to really happen. Plus I don't think current technology would be able to test either scenario (because even though it looks like they have all the same phenotypes, you'd have to check every one) so I guess we'll never know. Which raises the question 'how do we know that identical twins are really identical?' Maybe the traits we can't see are different. -Pete5x5 (talk) 19:12, 16 January 2009 (UTC)

I think the question is asking for this: the genes in a human cell are grouped into 46 chromosomes in 23 pairs. The mother's egg cells (ova) and the father's sperm cells each receive one chromosome randomly from each pair. The cells that unite to ultimately form the child represent 46 of these random two-way "choices" and therefore there are 2^46 = 70,368,744,177,664 possible combinations -- much greater than the total number of people who have ever lived.

However, this is a simplified picture! First, a mutation is always possible. Second, during meiosis when the sperm and egg cells are formed, sometimes a chromosomal crossover occurs. Say that in the mother, chromosome pair #1 includes versions A and B. Then usually her egg cells will include either A or B. But in case of a crossover, an egg cell might be formed with the first 3/8 of A and the last 5/8 of B. Since there are many points on each chromosome where a crossover or mutation might occur without the result being fatal to the child, the true answer is many, many times higher than 2^46.

--Anonymous, 21:02 UTC, January 16, 2009.

As Anonymous notes, even given the astromonical number one can calculate based on the assortment of alleles from each parents, each person has the own set of unique de novo mutations that occur in the germ line. Its not known for sure, on average, how many novel mutations each individuals has, but to keep things simple lets just say there are 10. Therefore, on top of the number above (is that 70 trillion?): what are the chances that the same 10 base pairs would be mutated in two people, out of 3 billion? My maths isn't good enough to represent that number. Rockpocket 19:07, 17 January 2009 (UTC)

Storage capacity of the human brain ?

Does the human brain have a limit on how much can be stored and how many 'operations per second' like with computers ?

Sorry if this has been asked and answered somewhere else

Scotius (talk) 15:49, 16 January 2009 (UTC)

There will be a limit, but no-one really knows what it is. Physics puts an upper bound on it (you can't store more information than there are atoms, for example), but that's about it. It's probably meaningless to talk about operations per second for the brain, it just doesn't work like that (I'm not sure how it does work, though, and I doubt anyone else is!). This has been discussed on this ref desk before - try searching in the box at the top. --Tango (talk) 15:55, 16 January 2009 (UTC)

Strictly speaking, the physical limit is more like the number of possible arrangements of the atoms, which is a much larger number than the number of atoms. Though I suspect one can make practical arguments that the real answer is no where near that large. Dragons flight (talk) 18:31, 16 January 2009 (UTC)

Okaydoke, thanks Scotius (talk) 16:04, 16 January 2009 (UTC)

There are many articles on the subject on the internet, as revealed by this Google search. However, it's up to you to sift through the crap and find a well referenced, peer-reviewed article. I'm not even sure they'll be one beyond speculation. —Cyclonenim (talk · contribs · email) 17:40, 16 January 2009 (UTC)

Sifting through the crap isn't hard, just use Google Scholar. Now you just have to find something there that actually deals with this question. Algebraist 17:58, 16 January 2009 (UTC)

The brain is not a digital computer, although in the 1960's cognitive psychologists published thousands of papers comparing it to one. The comparison might be like asking noting that both a camera and Johannes Vermeer created images based on scenes, then asking what the artist's film speed, shutter speed, lens opening and focal length were. Edison (talk) 17:56, 16 January 2009 (UTC)

The brains' capacity could certainly be estimated - but it's going to come out to be a much smaller number than we might expect. The tricky part is that when we think of computers, we have a system that stores data PRECISELY - no matter how old the data is - a movie you stored will be precise down to the pixel. With the brain, the data is simplified - reduced to it's essentials. You may remember seeing a friend over the weekend - and you MIGHT even recall what they were wearing - you certainly don't remember every exact wrinkle in the clothing at the instant the person stepped into your front door. You have the impression that you remember the event like it was a movie - but you don't. Furthermore, in a month from now, you MIGHT recall that your friend showed up - but you'll probably have no memory about what they wore. In ten years time you'll have a general feeling that your friend would occasionally show up some weekends. In fifty years you'll remember you had that friend and their name escapes you. The core memory is there - it's just getting fuzzier and less exact. With a computer, it's all or nothing. It would be possible to have a computer memorize things like people do - automatically blurring the data when more memory is needed...but one of the reasons we like computers it that very precision that we lack. Wikipedia works precisely BECAUSE it doesn't work like a brain does - and that's what makes it so helpful. SteveBaker (talk) 23:52, 16 January 2009 (UTC)

"Operations per second" depends on what you're measuring. If it's conscious math (eg. "What do you get when you multiply six by nine?"), the human brain can normally do one or two operations per second. If it's applied math (eg. catching a thrown ball), the brain is better modeled as an analog computer, which can't be measured in those terms. --Carnildo (talk) 00:57, 17 January 2009 (UTC)

It's a common myth that information theory can't be applied to analog systems - but that's really not true. Any real-world analog system has finite bandwidth and there must be limits to the size of signal it can handle - and some degree of imprecision or noise in the analog 'signal' as it passes between parts of the system. That, ultimately, necessarily limits the amount of "information" that even an utterly analog system can process or store - when you know how much that is - you can convert that number to bits and produce an entirely valid comparison between the capabilities of an analog and a digital system. It's a little tougher to crunch the math because most analog systems have worse signal precision at higher frequencies - but you can do it. Once you know how many bits that is - you can build a digital system with the same capacities and if it's done right, it'll be (theoretically) capable of the same performance. I don't know enough biology to say what that number is for the human brain - but it most certainly CAN be computed. SteveBaker (talk) 04:09, 17 January 2009 (UTC)

The number of operations per second is certainly not larger than the number of synapses (between 10¹⁴ and 10¹⁵) times the maximal firing frequency of neurons in Hz (maybe 250, see refractory period (physiology)). The memory (in bits) is certainly no larger than the upper limit for the number of synapses times the base-2 logarithm of a reasonable number of relevant synapse states (one million? I don't know). Icek (talk) 01:11, 17 January 2009 (UTC)

These parameters are pretty irrelevant to the number of "operations per second." In tests, simple reaction time is around 100 msec and choice reaction time is around 300 msec. So perhaps 10 operations per second is an upper and generous bound. Short term memory can hold 7 or fewer items. Long term memory is vast. Edison (talk) 04:56, 17 January 2009 (UTC)

Reaction time is an input-to-output process. There is no reason to think that it necessarily bears of the number of operations being performed in the brain. It is also a rather poorly defined concept. Computer processors have well-defined elementary operations. One can sensible ask how many elementary operations are required for a computer to display a sentence on a screen (hint: it is much greater than 1 even though it is a single output event). But one would have a much harder time asking how many operations the brain performs when it constructs and speaks a sentence. Given the difficulty of constructing natural language software, I strongly believe that if one did try to map the brains activity in holding a conversation onto a set of elementary computer operations, the number of operations per second would be enormous. Dragons flight (talk) 05:13, 17 January 2009 (UTC)

What complicates this is that the brain is a massively parallel machine - where most computers are not. Those 10¹⁴ synapses can (in principle) all fire or not fire in parallel. Even if they can only fire 250 times a second - that's 2.5x10¹⁶ operations per second. Compared to a typical high end PC (quad core, 3.8GHz) - which can do four things in parallel in each clock tick - you only have 1.6x10¹⁰ operations per second. So on that VERY rough estimation, the brain has an edge over a state-of-the-art machine - but only by a factor or around 10,000! There are computers (such as the 'Roadrunner' at LosAlamos) capable of over a petaflop/sec (a 'flop' is a floating point operation). So 'Roadrunner' is capable of 10¹⁵ non-trivial operations per second - so maybe 5% of a single human brain!

SteveBaker (talk) 05:36, 17 January 2009 (UTC)

This hardly seems a sensible comparison. A "floating point operation" means something like a 64x64 bit multiplication computed with an accuracy of 0.5 ulp, that is, an error of less than one part in 10¹⁵. It takes a lot of transistors to make that happen, and it would take a lot of neurons too if we could do it at all, which of course we can't, except using our ridiculously slow and linear general reasoning capabilities. The brain is massively parallel at the synapse level but pretty linear at a higher level. Microprocessors are massively parallel at the transistor level too, and with more than 10⁸ transistors switching more than 10⁹ times per second, they would seem to beat out the human brain in raw switching ability. Not that that's a sensible comparison either. Also, a minor point, but the cores in your quad-core CPU are superscalar. They don't execute one instruction per cycle. -- BenRG (talk) 12:57, 17 January 2009 (UTC)

Also keep in mind that it seems that our brains are much "better" at certain tasks than a general computer. Just like a single inexpensive embedded video chip can decode a high-def movie that would churn a microprocessor, our brains are "hard wired" to very efficiently recognize faces (our brains are phenomenally good at pattern recognition), synthesize coherent speech from general ideas, and coordinate muscles. I don't know a whole lot about brain neurology but IIRC the whole brain is an "embedded system", with every neuron dedicated to a particular task. We have sensory processing neurons that are tied to consciousness-loop-neurons which are tied to a web of linked symbol-groups of neurons. Yes, it's possible for all the amazing things that we can do to be a product of a simple but large neural network. It's also clear that it's possible for consciousness to arise from an artificial processing construct, and it's particularly self-evident that consciousness as we know it identifies closely with the associative nature of the neural net. Also just because we can't do 64 bit floating point operations in our head doesn't make us stupid; our brains aren't good at that kind of thing because we haven't needed to do that kind of thing.. and now that we do, we can abstract it out and invent a machine to do it for us! While the particular algorithms used by machines and AIs are powerful and exact, abstract and stochastic thinking is actually far more powerful in that it allows high level phenomena like creativity and innovation. While a computer may be able to draw a high-resolution photorealistic landscape out of 3D vector graphics resources and update it 150 times a second, no computer today could invent itself. Not that we could invent ourselves σ_ο .froth. (talk) 18:06, 23 January 2009 (UTC)

Perception of one colour being "brighter" / "darker" than another

I'm colour deficient / colour-blind, but to me certain colours obviously appear "brighter" to me than others, but I worry that this is not the case for other people.

Yellow for example is one of the most bright colours, but not as bright as white.

Orange is darker than Yellow but brighter than red.

Red is about as dark as blue or green.

Has this been quantified in any way? Perhaps we have an article of colours organised by perceptual brightness?

As a side-note, in some software I wrote I used these colours to show priority of jobs, and I'm hoping that the colours had as much meaning to me as they did to the users!!

Rfwoolf (talk) 17:07, 16 January 2009 (UTC)

Just before hunting for more, I do know that some colours are indeed brighter than others and yellow is the brightest, although not as bright as white. Steve is the guy to wax forth on the subject, but I'll see if I can dig up some links while you wait... 79.66.46.92 (talk) 17:10, 16 January 2009 (UTC)

Eeeeee! Check this out! Luminosity function! !! And as a little background, you might want to read the colour vision article, or at least study the second picture in it. 79.66.46.92 (talk) 17:15, 16 January 2009 (UTC)

You may want to specifically look at luminance and chromaticity articles. In brief, for the people with full color vision, under not-too-dim light conditions, there is a percept of "brightness" (luminance) and an independent "two-dimensional" percept of "color" (chromaticity: think of one dimension as red vs. green and the other one as blue vs. yellow, although that is not strictly correct). Human retina, thalamus, and visual cortex are wired in such a way that our luminance percept is dominated by the responses of long-wavelength and medium-wavelength cone receptors, but not short-wavelength cone receptors; thus blue is inherently perceived as a "darker" color than red or yellow. However, you can make a brighter blue and a darker yellow to look equally bright. if you look up any two-dimensional isoluminant color chart, all colors on the chart (blue, yellow, red, green, and everything in between, including gray) should look to a human with normal color vision as having the same luminance ("brightness"). Not so for the people lacking one or two types of cone receptors in the retina: for those people different parts of an isoluminant color chart may look as having different brightness AFAIK. Hope this helps. --Dr Dima (talk) 21:12, 16 January 2009 (UTC)

The order of brightnesses that you describe are pretty much the same for people with normal color vision. What's bothersome is that the explanations for why that is revolve around being able to see color! Yellow is a mixture of red and green - so it stimulates two sets of color receptors ("cone cells") as well as the "rod cells" that see only intensity. Red, on the other hand, stimulates only the red receptors and the rod cells. So less cells are stimulated - and red looks darker than yellow. Since the red and geen receptors are each more sensitive than the blue receptors - it makes sense that yellow looks brighter than cyan or magenta. But if your cone cells don't work - I don't understand why yellow would seem brighter. That's weird. Which of the (many) varieties of color blindness do you have? SteveBaker (talk) 23:33, 16 January 2009 (UTC)

• It is not correct that "yellow is a mixture of red and green". What you mean is that the human eye cannot distinguish yellow from a mixture of red and green, because either one stimulates the cone cells the same way. --Anonymous, 05:24 UTC, January 20/09.

Another article you may want to take a look at is Munsell color system. It's been quite a while since I've studied these matters, but I think that your (along with non-color-deficient folks') perceptions of the brightness and darkness of colors involve a combination of Munsell's "value" and "chroma." Look, for example, under "Hue," at the table of different hues ("colors") at the same value and chroma. Do they all seem pretty much equally bright to you? They do to me. Deor (talk) 02:29, 17 January 2009 (UTC)

Steve: Not sure exactly, but I've done the online and offline tests where they show a serious of images where a number can be conceived in a circle of dots - after a few images I can no longer see the numbers. On a roulette table I often confuse the green chips with the orange chips. With coloured pencils at school, light green would look yellow unless I could see yellow next to it. Brown and red were sometimes confused but that hasn't really happened for a long time.

Dr Duma: Indeed those colours do seem "equally bright" to me. Rfwoolf (talk) 01:00, 18 January 2009 (UTC)

The point is this: Most forms of color blindness (such as, for example, the kind my son has) only affect one of the color receptors - and much of the time they only weaken that receptor. The form of color blindness in which no color is seen AT ALL is quite rare. There being three color receptors, Red, Green and Blue, you might have:

• Weak red
• Weak green
• Weak blue
• No red at all
• No green at all
• No blue at all
• Weak red AND weak green
• Weak red AND weak blue

...and so on...

• No red AND No green AND No blue (ie totally color blind).

The tests you took with the circles containing colored dots are quite enough to tell you which of the MANY combinations you have. But if it turns out that (like my son) you have just one weak sensor - then your color vision may be pretty good - except that you can't pass the colorblindness test because that's specifically designed to ferret out that precise situation. What you're describing sounds like your blue sensor is working OK but that either red or green (or both) aren't working correctly. The difference between green and yellow or green and orange is the amount of red - and the difference between brown and red is the amount of green but also the amount of orange - so I'd tentatively suggest your problem is with the red sensor. But this is straying dangerously from "explaining what's going on" into the realm of "Diagnosing a medical condition" - which we're not allowed to do here on Wikipedia reference desks. Our articles on color blindness DO explain this stuff in quite a bit of detail. I strongly recommend re-doing the tests (online or with a professional) - and this time pay careful attention to the precise diagnosis. This (combined with our article) will tell you precisely which sensor or sensors are misbehaving - and that should be useful to you in the future - both in ensuring you know your limitations - but also that you can be confident where there are NO limitations. My son only found out he had a problem (he is "weak green") because he couldn't tell the color of the LED on the front of his Wii game machine which is red when the thing is turned off and orange when it's in standby. He was always leaving it in standby instead of turning it off - when I'd nagged him about this several dozen times - we figured it out. But he can actually see ALL colors differently - but the difference between red and orange (which is just a small amount of green) isn't enough for him to tell the difference. He also has trouble with shades of pale blue/greens - but that's a common matter with men in general - so no big deal there. We found that a small piece of green-tinted plastic held over the LED on the Wii was enough to enable him to tell the difference - and he sometimes uses a piece of green plastic to distinguish other colors he's not sure of. Something like that could possibly help you too.

However - in DIRECT answer to your original question, the fact that you can see differences in brightness that match what "normally sighted" people can see suggests that you ARE seeing some colors correctly - and that explains my surprise in my earlier response. SteveBaker (talk) 01:17, 19 January 2009 (UTC)

Organ barter

Donating in life a kidney to a loved one is a no-brainer for me. I suppose many other people are in the same situation. On the other hand, I won't consider donating my kidney in life to a unknown person. In the case I am not compatible with my loved one, could I perhaps exchange my kidney with other people that could donate to a family member of mine? What if, a more complex scenario exits? Like A donates to B that donates to C that donates to A? --80.58.205.37 (talk) 18:32, 16 January 2009 (UTC)

See Organ transplant#Paired-exchange. Such transactions are uncommon, but not unheard of. Dragons flight (talk) 18:44, 16 January 2009 (UTC)

(edit conflict)Sure you could, if you just agreed on it with the other people involved. Under those circumstances -- where both you and the other potential donors were willing to donate organs to a loved one, but were incompatible -- they'd probably be happy to agree to an exchange. After all, the end result is pretty much the same: they go under the knife, and their loved one gets what they need. Where's the problem? There would be nothing illegal about that; anyone can donate a kidney to anyone they like, even a complete stranger. That's certainly happened before, though it's not exactly common. (Selling organs is a different story, though -- that's illegal in most countries. Technically, this would be a trade, of course, but I doubt anyone would have a problem with that, since clearly no one is trying to profit from the exchange.)

Of course, the practicalities involved could well be overwhelming: it probably wouldn't so much be a question of willingness, but rather one of timing and circumstances. There are some organizations that might be of help in a situation like this, though. -- Captain Disdain (talk) 18:51, 16 January 2009 (UTC)

The OP's example of a kidney transplant is a good one - getting a new kidney often isn't as urgent as other transplants since people can survive for years on dialysis in many cases, so you can wait for a suitable sharing arrangement to become available. --Tango (talk) 21:21, 16 January 2009 (UTC)

Private health care in the US

Why is private health care in the US much more expensive than in other developed countries? --Mr.K. (talk) 18:48, 16 January 2009 (UTC)

maybe the fact that the United States is the greatest country on Earth (as even Noam Chomsky admits) has something to do with it... 82.124.85.178 (talk) 19:00, 16 January 2009 (UTC)

That's an extremely poor explaination Nil Einne (talk) 19:01, 16 January 2009 (UTC)

I also have an explanation involving "what the market wants", if you'd prefer it. —Preceding unsigned comment added by 82.124.85.178 (talk • contribs)

Most payers for health care in the U.S. do not pay the "list price" which appears on doctor and hospital bills. The government only pays much lower rates, and insurance companies also knock the price down to half or less in many cases. It is only the person who lacks insurance but does not qualify for the government to pay who is stuck with the full price. Edison (talk) 19:42, 16 January 2009 (UTC)

It's because the United States is the only developed country in the world that doesn't have a universal health care system. See Health care in the United States. ~AH1^(TCU) 22:57, 16 January 2009 (UTC)

... but does have heavy subsidies and other political distortions of the market. —Tamfang (talk) 07:16, 18 January 2009 (UTC)

Neither of those explainations really explain why in any satisfactory way. If you say it's because the US is the greatest country, then why does the greatest country have a much more expensive cost of health care. If you say it's because it's what the market wants, why does the market want a high cost in the US but not elsewhere? You could apply those answers to many situations and they would be equally unsatisfactory. For example, why is the US one of the only developed countries that tortures people suspect of a crime? Because it's the greatest country. Why has the US economy collapsed? Because it's what the market wants. Nil Einne (talk) 08:11, 17 January 2009 (UTC)

If people don't have to pay the full cost of their health-care, they'll tend to get more expensive care than they need. I've read that HMOs were started to combat this. — DanielLC 00:13, 17 January 2009 (UTC)

Yes, darned those people who want to get cured of their illnesses. If they only just accepted their fates, and didn't demand to actually get better, we wouldn't have to have such expensive care... --Jayron32.talk.contribs 00:34, 17 January 2009 (UTC)

It's not as if there's a certain amount of necessary health care. You can, for example, do an arbitrary number of expensive tests for diseases that the patient is arbitrarily unlikely to have. That head-ache they've been having could be cancer, and they could get a cat-scan to check. The doctor, who gets payed for medical procedures, and not for the patient's health, has every reason to try to convince them to take expensive tests, and the patient has no reason to disagree with the doctor. — DanielLC 17:07, 17 January 2009 (UTC)

There are many reasons why health care is so expensive in the US. Here are a few:

1) Doctors are paid more than most other countries. Nurses and others are too, but to a lesser extent.

2) Lack of preventative care. Frequently only emergency care is available to those without health insurance, meaning they wait until the condition is far more expensive to fix, and, in the case of infectious diseases, until after they've spread them to many others.

3) Pharmaceutical companies are able to control Congress through lobbyists to prevent imports of cheaper alternative meds.

4) Lack of central planning means that you may have two hospitals next to each other with the same equipment, while neither has some other item of equipment and people must drive many miles for that. This inefficiency costs money.

5) Administrative costs are very high, due to all the competing private and government insurance programs. Hospitals need many employees to sort out all the associated paperwork. StuRat (talk) 06:45, 17 January 2009 (UTC)

You missed one that doctors cite as a major cause: The cost of malpractice insurance. Because the US legal system is prepared to award truly crazy amounts of money for things that are simple accidents or even bad luck (neither of which are "malpractice" per-se) - doctors have a need to purchase insurance against those kinds of claims. Both doctors and hospitals have to carry this insurance on behalf of Nurses and other ancilliary staff - so nobody is left 'exposed'. That insurance is horrifyingly expensive. SteveBaker (talk) 17:37, 17 January 2009 (UTC)

why does gas burn blue?

why does gas (from a stove etc) burn blue? when something spills on it and it burns orange briefly is it because its temperature is now lower or because it's not burning the same way/as purely/etc

(already tried asking google)

82.124.85.178 (talk) 18:53, 16 January 2009 (UTC)

Incomplete oxidation leaves unused hydrocarbons, resulting in orange flame. A well-regulated gas flame should be blue. - Nunh-huh 18:58, 16 January 2009 (UTC)

yes, but WHY blue? is it because the temperature natural gas burns at is a "blue" temperature (so that if you heated a rock to the same temperature, it would glow blue-hot)? 82.124.85.178 (talk) 19:02, 16 January 2009 (UTC)

I believe this [7] (from [8]) is mostly correct Nil Einne (talk) 19:05, 16 January 2009 (UTC)

The flame color section of our article on flame also addresses this. -- Captain Disdain (talk) 19:07, 16 January 2009 (UTC)

I'm sorry, could you dumb it down for me? Is it temperature, or the biproduct of a particular chemical reaction, such as a bang might be a byproduct, or what —Preceding unsigned comment added by 82.124.85.178 (talk) 23:27, 16 January 2009 (UTC)

In simple terms, when you burn anything, along with the heat energy and other forms, you get a lot of light given off. Depending on what is burning, you get different wavelengths of light given off, which are responsible for different colours. —Cyclonenim (talk · contribs · email) 23:41, 16 January 2009 (UTC)

I think the OP knows that, the question is what causes the different colours. Is it due to different temperatures (ie. black body radiation) or different chemical reactions? I think the answer is a bit of both. --Tango (talk) 23:49, 16 January 2009 (UTC)

That's right, I'm where you put me. 82.124.85.178 (talk) 00:40, 17 January 2009 (UTC)

It's simple blackbody radiation. Incomplete combustion produces a low-temperature orange flame; complete combustion produces a high-temperature blue flame. --Carnildo (talk) 01:02, 17 January 2009 (UTC)

so if the blue flame were rising through an even hotter something (being heated further as it rose, by convection-not chemically), it would turn from blue-hot to white-hot? Conversely, if it were rising through something very cold (after burning) it would go from blue-hot to mere red (or orange)-hot? Thanks! —Preceding unsigned comment added by 82.124.85.178 (talk) 01:08, 17 January 2009 (UTC)

Isn't blue-hot is hotter than white-hot? The even hotter something would already be glowing whatever colour it is, and brighter than the flame, so you probably wouldn't see the flame. Also, not being hotter than the surrounding air, it wouldn't rise, so the flame probably couldn't even form. The other way round (the flame cooling) could work, though, I think. Usually the hot particles dissipate before they can cool down that much, but in a really cold environment the tip of the flame might end up a different colour, I'm not sure... (it would have to really cold, possibly cold enough that the oxygen would condense and the flame couldn't form). --Tango (talk) 01:16, 17 January 2009 (UTC)

I think you're not using your imagination if you think that you couldn't see the flame because it was being heated by something hotter, which would itself glow too brightly. I mean just imagine a lot of holes to see the flame through, and between you and the material a mask that only shows the holes. —Preceding unsigned comment added by 82.124.85.178 (talk) 12:59, 17 January 2009 (UTC)

Are you sure about that? Our article seems to suggest you're wrong "on the right a lean fully oxygen premixed flame produces no soot and the flame color is produced by molecular radicals, especially CH and C2 band emission." Admitedly this is butane not LPG but I would presume the same reasons likely apply. Also wouldn't blue be something like 6000K? Does a stove flame realy become that hot (n.b. the image File:Wiens law.svg is highly misleading, the colours shown don't correspond with the wavelengths, I haven't yet corrected the articles hoping someone will fix it) Nil Einne (talk) 12:13, 17 January 2009 (UTC)

I think you have point there - if you hold a piece of metal (insulated, of course) in the flame of a bunsen burner (with a blue flame), it glows red hot, not blue hot. --Tango (talk) 16:29, 17 January 2009 (UTC)

Another factor, besides flame temperature, is the spectral line phenomenon. Each atom absorbs and emits certain frequencies of light, which in turn have certain colors associated with them. This has to do with the electron shells. Any time an electron jumps between shells it absorbs or gives off a specific frequency of light, due to the energy level change. The total of all of these possible jumps gives a characteristic color for each chemical element. StuRat (talk) 06:34, 17 January 2009 (UTC)

Yes, and this property of elements is used in the flame test. --Bowlhover (talk) 03:01, 18 January 2009 (UTC)

Correct me if I'm wrong, but I don't think blackbody radiation can make something "blue hot". First it heats to where it emits red light, and it appears red, then it heats to where it emits red and green light, and it appears yellow, then it heats to where it emits red green and blue light, and it appears white. — DanielLC 21:21, 18 January 2009 (UTC)

Well, yes, but then it gets hotter than that and the peak of its radiation is somewhere at or past ultraviolet, which means that the part of its spectrum in the visible range is much higher in blue wavelengths than anything else. Hence blue giant stars. Confusing Manifestation(Say hi!) 22:18, 18 January 2009 (UTC)