Wikipedia:Reference desk/Archives/Science/2010 February 28

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February 28

The Final Theory

I have read the first chapter of the book "The final theory " by McCutheon. in this book it is said that the gravitational ideas of Ein stein are not fully true .Gravitational Force does not depend on mass. Is this idea accepted by scientists.I want to get more detail free on line.--119.154.38.4 (talk) 00:32, 28 February 2010 (UTC)

Gravitational force definitely depends on mass. Try picking up a piece of paper. Now try picking up your desk. Which was easier? I'm not familiar with the book, but either McCutheon was talking nonsense or your misunderstood. Einstein's theories are very good, but they don't accurately describe all situations (namely, the very small where quantum behaviour becomes significant). Those they do describe, they describe just fine, though. It is possible that McCutheon was saying that gravitational and inertial mass (that is, the quantity that describes how difficult something is to lift and the quantity that determines how difficult something is to accelerate horizontally, which are the same thing in mainstream science) will turn out to be different under some circumstances. That's all I can think of that might make some sense. However, having done a bit of Googling, it seems the book is actually just pseudoscience and doesn't make any sense. --Tango (talk) 02:15, 28 February 2010 (UTC)

Googling McCutheon seems to make it out that it is somewhat crackpot. At the very least, it does not accord with any currently accepted scientific thinking in the slightest, and should not be taken as being representative of what any mainstream physicists believe. I would doubt just about anything in the book, personally—it does not sound reliable. --Mr.98 (talk) 02:55, 28 February 2010 (UTC)

Mark McCutcheon (not "McCutheon") has a reputation as a bit of a nut-job. There is a mini-review of his book - and an extended "email interview" with the guy here: [1]. He doesn't seem to have written any serious scientific papers - so his claim: "The Final Theory presents an entirely new understanding of planetary orbits, energy in its various forms, and current explanatory efforts such as Quantum Mechanics, Relativity Theory, etc"...is highly likely to be random BS. Overturning our knowledge of something as well understood as planetary orbits requires a very major revision of what we know about pretty much anything - but "Extraordinary claims require extraordinary evidence" - and this guy doesn't have extraordinary evidence. Sadly, there isn't a way to prevent such people from publishing "pop.sci" books that look superficially reasonable and scientific. Anyway - there is no science there. Sadly, it's overwhelmingly likely that most, if not all, of what you read in that book is sheer nonsense. SteveBaker (talk) 04:03, 28 February 2010 (UTC)

Until we can find a final theory of everything, it may be unwise to say with certitude what is true and what is not in science, since a final theory will certainly have quite an impact on theoretical physics and could/should rewrite Newton and Einstein entirely. We can only say this is what Newton and Einstein or the Standard Theory stated, and there are many other theories out there questioning these claims.

Wikipedia should provide an overview of those theories who challenge the accepted wisdom and it is to the readers to decide and debunk if a new theory that redefines everything on such a scale as Mark McCutcheon did is valid or not. Until then it remains a contender to the final theory, and yes the book provides a major revision of all of physics and provides credible evidence with mathematical proofs and equations.

If Wikipedia acts as a censor to anything new and challenging to the actual science, we will never find a final theory, because no one will ever hear of new ideas or will quickly dismiss them as pseudo-science. An encyclopedia should provide all the actual science and all claims that interpret the same phenomena differently. Of course there are many theories out there that are obviously not worth the time, but this book of McCutcheon has been a bestseller in the science section of Amazon for many years now, it has stood the test of time and should not be dismissed so easily in ignorance of the facts or the theory. It would not be very objective, and I believe Wikipedia to be objective. Myholmes (talk) 03:50, 8 March 2010 (UTC)

There IS no "force of gravity" in general relativity; in fact, there's no "gravity" at all. The phenomenon of "gravity" in GR is a by-product of the curvature of space. General relativity is not the same as quantum mechanics, nor is GR contradicted by the fact that gravity is one of the four "fundamental forces." You don't need "gravity" at all in GR. In GR, objects are "freely falling," not motivated by "the force of gravity." 63.17.52.41 (talk) 05:07, 28 February 2010 (UTC)

Newton's law of universal gravitation says gravitational attraction depends on the masses of the objects involved, and it has been shown to be true in laboratories for over 300 years. I remember an earlier question about a notion that Earth gravity does not as believed pull us down but instead it pushes everything lighter up. I don't know if the book you started to read proposes anything like that but if so, it is flat wrong. If scientists ever accept a "final theory" they can all turn out the lights and go home.Cuddlyable3 (talk) 12:05, 1 March 2010 (UTC)

No - from what I gather from reading about this book, it is one of those "expansion theory" ideas (hmmm - we don't have an article about that particular flavor of pseudo-science - hooray!). The idea is that the earth (and everything else in the universe) is expanding at an ever accelerating rate producing the illusion of gravity. Of course this fails in some fairly disasterous ways - notably that orbits don't work if there is no gravity/space-time-curvature and that pretty soon everything is moving a lot faster than the speed of light so you have to wave bye-bye to just about everything Einstein said. Evidently much of the book is spent trying to dance around those problems. It's junk. SteveBaker (talk) 13:30, 1 March 2010 (UTC)

Cuddlyable, the OP referred to Einstein, not Newton, and specified the "force of gravity." As stated above, there is no force of gravity in general relativity, involving mass or otherwise. And, indeed, on earth we ARE "pushed up" -- by energy (think of dense objects unable to pass through each other) that interrupts, via the ground or floor, our world lines from their path to the center of the earth. But the silly book the OP refers to is irrelevant to these points. 63.17.78.104 (talk) 09:23, 2 March 2010 (UTC)

Einstein's general theory of relativity is his geometric theory of gravity. It is the current description of gravity in modern physics. It unifies special relativity and Newton's law of universal gravitation. Cuddlyable3 (talk) 23:24, 2 March 2010 (UTC)

To repeat, there is no FORCE of gravity in GR, even if GR can can be described as a "theory of gravity." You could say it's a theory of gravity that does not define gravity, in any way, as a "force." Period. 63.17.35.207 (talk) 01:40, 3 March 2010 (UTC)

Desalination in the 19th. century

How could Otokichi and other members of the crew have desalinated enough water during their 14 month voyage? If done in a still, for example, wouldnt they have run out of fuel? Solar stills had not been invented in those days. 89.243.151.239 (talk) 01:21, 28 February 2010 (UTC)

• Presumably they burned a fuel, perhaps bits of their boat, to generate the heat required. Noodle snacks (talk) 01:54, 28 February 2010 (UTC)

This version of the story does say that they burned wood from their ship. Buddy431 (talk) 04:20, 28 February 2010 (UTC)

Water for Hydrogen Fuel in Deserts

One problem with solar energy in deserts is that deserts are a long way from cities, towns, and regions with large populations. One solution to this is to use the solar energy to extract hydrogen from water and transport that hydrogen to other places where it could be used as a fuel.

But one problem with this is this. Deserts are very dry. They have very little water. So where are you going to get the water that you're going to extract the hydrogen from in a desert?

Bowei Huang 2 (talk) 03:27, 28 February 2010 (UTC)

Who has proposed using hydrogen as an energy store in deserts? As you say, it's not a very good idea. There are other ways of transferring energy - a cable would work pretty well. --Tango (talk) 03:30, 28 February 2010 (UTC)

You can make a lot of hydrogen with not much water. Trucking the water into the plant from (for example) the nearest ocean - should be cost-effective. However, you can collect solar energy pretty well from places other than deserts. The only real advantage of desert compared to (say) savanna is that the land price is cheaper and you avoid the occasional cloudy day. Compared to the cost of building the plant, the land value is not likely to be an issue - and because you're using the energy to make hydrogen, which is reasonably easy to store, you don't have a problem with loss of service on cloudy days. Compared to the difficulties of working in an actual desert (like where do your staff live when off-duty?), the occasional loss of output is likely to be a small matter. SteveBaker (talk) 03:44, 28 February 2010 (UTC)

I did the maths and, to an order of magnitude, you would need about 10 litres of water per house per day. That's quite a lot of water, but it should be doable. I'm not sure it would be better than a cable, though. --Tango (talk) 07:08, 28 February 2010 (UTC)

A cable can't transport fuel so well, and the water can presumably be recycled after combustion. Aaadddaaammm (talk) 15:05, 28 February 2010 (UTC)

These statements seem to refer to photovoltaic power. Concentrating solar power like solar towers and solar troughs require rather large amounts of water. Stirling engines avoid the steam generator stage but are not widely used yet. Rmhermen (talk) 16:16, 28 February 2010 (UTC)

[2] may be of interest. Also while photovoltaic cells for hydrogen production are a possibility I believe there's a lot of interest in other methods like High-temperature electrolysis (okay this is still partially photovoltaic), photoelectrochemical cells [3] or even direct solar thermal decomposition of water with or without a catalyst in the long term (I'm referring solely to methods involving solar power). Also look at Hydrogen economy and Hydrogen production for reference to solar and perhaps [4]. As an alternative to trucking, pumping is an obvious possibility. Nil Einne (talk) 00:45, 1 March 2010 (UTC)

Why do you need fuel, though? Just have some solar panels and an electricity cable to get the electricity where it is needed. --Tango (talk) 01:02, 1 March 2010 (UTC)

Enclosure effect

sir, kindly guide me that how tunneling effect effects a gas flow in a vertical tube.I need how is turbulence effected when tube is long and tube is short. regards SCI-hunter (talk) —Preceding undated comment added 06:10, 28 February 2010 (UTC).

The article Plug flow may help. For further study see the articles Fluid dynamics, Fluid mechanics, Navier–Stokes equations (and their many links. Fluid and gas flow is a complex subject.) The onset of turbulence is a function of the Reynolds number. Cuddlyable3 (talk) 11:43, 1 March 2010 (UTC)

Exploding Chicken?!

Why do chunks of chicken, eg in a curry etc, often explode when microwaved, yet other meats like beef don't? —Preceding unsigned comment added by 194.205.143.136 (talk) 12:42, 28 February 2010 (UTC)

Chicken is often "plumped out" with water [5] (good way to flog you expensive water...), then when you put it in the microwave, the water inside the chicken boils...  Ronhjones  ^(Talk) 00:18, 1 March 2010 (UTC)

Y Thanks :-) 194.205.143.136 (talk) 09:14, 3 March 2010 (UTC)

4 Life Together, Building People

http://www.4life.com/

I can't find this information. —Preceding unsigned comment added by 71.54.166.6 (talk) 13:03, 28 February 2010 (UTC)

What information? Do you have a science question?--Shantavira|^{feed me} 13:13, 28 February 2010 (UTC)

They appear to be a company who are selling the usual junk "dietary supplements" under some vague banner of "science". In truth, science actually suggests that you won't benefit from consuming anything that this company makes unless you are malnourished or pregnant or very old or something - and even then, you'd be better off discussing any dietary supplement you might need with your doctor and getting the very specific supplement that you need rather than taking any of these unspecific products. Worse still, 4 Life sell their product through Multi Level Marketing - which means that we have a junk product being sold by a process that is in itself a process that skirts very close to "Pyramid Selling" - which is illegal in most countries. I strongly advise you to have nothing to do with this company - no good will come from either buying or selling their product. SteveBaker (talk) 18:23, 28 February 2010 (UTC)

Wikipedia tries to avoid the least hint of defamation. SteveBaker, as a lawyer you must realize that a colorable claim of product disparagement could be made in regard to some of your statements above. Given 50 states, not to mention scores of nations, the range of standards would be broad. Perhaps most important, the objective standard ("knew or should have known," "reckless disregard," etc.) would be lower for you, in that you're a lawyer, a frequent contributor to this board, a researcher into an eclectic range of topics, a skilled user of search engines, and so on. Some of what you wrote above is a statement of fact (true or false), not opinion. "Junk product," for example. And "close to pyramid selling ... illegal" is (if untrue) libel per se! -- no special dams required! Just sayin', counsellor. 63.17.36.101 (talk) 04:45, 1 March 2010 (UTC)

Calling Steve a lawyer might enable a "colorable claim" of defamation.... IIUC Steve is a games software engineer. --Trovatore (talk) 04:55, 1 March 2010 (UTC)

OK, I must have been thinking of another poster (someone recently said "I'm a securities lawyer"). But the point is, wikipedia's policy on defamation is strict -- and the above is borderline product disparagement and slander per se. 63.17.38.96 (talk) 06:40, 1 March 2010 (UTC)

4life was cited in 2004 by the US FDA for making unsupported medical claims about the benefits/uses of several of their products. In 2006, a doctors' blog wrote about the lack of scientific support for the claimed benefits of the claimed active ingredients and examining how it its sales model fits the classic MLM. If I were in a WP:POINT mood, I could probably write referenced WP article documenting how it is a MLM for junk-science, just another useless-pills scam. DMacks (talk) 07:27, 1 March 2010 (UTC)

Exactly - it's only defamation if it's not true. Accusing me of being a lawyer though...that's practically defamation! :-) I am indeed a computer games programmer. SteveBaker (talk) 13:16, 1 March 2010 (UTC)

Sealing or contracting

we know dat after big bang universe is spreading,but due to what factor it will again sealing or contracting ???

thank you —Preceding unsigned comment added by 117.197.253.161 (talk) 14:16, 28 February 2010 (UTC)

It is not certain whether the universe will go on expanding forever (see the Metric expansion of space article) or perhaps have a Big Crunch in the future. See the Cyclic model article. (Section header added.) Comet Tuttle (talk) 15:50, 28 February 2010 (UTC)

Physical exercise vs. E=mc^2

We all(?) know(?) that when you exercise, your body fat gets converted to energy, and you get leaner and lighter. From physical exercise: Most of the energy derived from fat gets to the muscle through the bloodstream and reduces stored fat in the entire body.

Then I look at the Hiroshima nuclear explosion where 0.6 grams of matter was converted to energy.

So if I go jogging and convert 0.6 grams of my stored fat into energy that's enough to turn me into a ball of superheated plasma. And level the city in the process. Just a tiny fraction of a gram of fat is enough energy to launch me to the Moon.

What's the deal here? How does exercise really get rid of body mass? Surely any explanation centered around matter to energy conversion is mythology - some fat will really convert to energy, but we are talking, what, femtograms? 88.112.56.9 (talk) 14:17, 28 February 2010 (UTC)

You're confused. Nobody is saying that matter is being converted to energy. The fat is being converted into Water plus CO2 and its chemical energy is being released in the process. Dauto (talk) 14:35, 28 February 2010 (UTC)

(ec) Yes, you're right, you can ignore direct mass/energy conversion. But the situation is no more mysterious than that after driving your car 100 miles, it's lighter by the weight of the gasoline you burned (which of course isn't a nuclear reaction, either).

The answer is basically that you combined some of your fat, and some of the oxygen you breathed, into carbon dioxide and water, which you exhaled. (There were probably a few other waste products from the reaction which your body didn't get lighter by the until the next time you went to the bathroom.) —Steve Summit (talk) 14:37, 28 February 2010 (UTC)

I'm thinking a large part of the answer is indeed in breathing. Somehow mass-energy is expelled from the body, and I don't see how it exits as energy (as per the atom bomb argument). So it must be as matter. Sweat won't qualify, as that is water plus some minerals. It must be something that expels carbon. CO2 in breathing is the only thing I can come up with, if I assume jogging won't make one excrete more... 88.112.56.9 (talk) 15:20, 28 February 2010 (UTC)

...which makes me wonder: if I sit in front of a TV, breathing heavily (not because of what I'm watching!), is that a useful form of exercise? 88.112.56.9 (talk) 15:35, 28 February 2010 (UTC)

References: Burning body fat is a chemical reaction, the Hiroshima bombing was a nuclear reaction. Vimescarrot (talk) 14:58, 28 February 2010 (UTC)

Except that both a chemical and a nuclear reactions obey E=mc^2. Energy and matter are two manifestations of the same thing, and energy is conserved. If you burn a lump of coal, the residue will have lost mass in accordance to E=mc^2, if you account for all incoming and outgoing mass. Making a difference between the two is not physically sensical. Conservation of mass-energy is the law! 88.112.56.9 (talk) 15:16, 28 February 2010 (UTC)

Further reference: See Adenosine triphosphate, which discusses (in detail) how chemical reactions are used to release energy for use in biological activity. See also: Mitochondria. --220.101.28.25 (talk) 15:13, 28 February 2010 (UTC)

The chemical reaction does obey E=mc^2 but the amount of mass involved in chemical reactions is infinitesimally smaller than a nuclear reaction. Yes, if you converted a gram of matter into pure energy, that would be a LOT of energy. But you don't do that. You're just breaking electron bonds, making some new products that are then expelled from the body as mass, not energy. Yes, there is some energy generation involved, but a LOT LESS than in a nuclear reaction. For a nice table, see Energy_density#True_energy_densities. The energy contained in a volume of U-235 is millions of times more energy than is contained in a volume of the most energetic chemical reactions (even things that are meant to be explosively energetic, like TNT). They are basically apples and oranges. Don't use measurements about nuclear weapons to try and make sense of chemical processes... you are dealing with something that is orders of magnitude different. --Mr.98 (talk) 15:38, 28 February 2010 (UTC)

Yes, I very much agree with you: the idea that a significant amount of fat is turned into energy is bunk. The above quote from physical exercise about fat and energy is misleading at best - "stored fat" is reduced by picograms. The question remains: if I lose a few kilograms due to exercise, where does it go? 88.112.56.9 (talk) 15:48, 28 February 2010 (UTC)

Oh, and googling for "fat into energy" gives 1,670,000 hits for me - probably all BS? (Not that I doubt they are BS, I'll bet most of them really are! Sports drinks and dietary supplements...) 88.112.56.9 (talk) 15:57, 28 February 2010 (UTC)

The fat is converted into other chemicals that are then used to produce the energy needed for exercise. Cellular waste products ie. (Lactic acid, carbon dioxide & water) are left over and are either recycled or expelled from your body. --220.101.28.25 (talk) 16:15, 28 February 2010 (UTC)

Still pressing the point: loss of mass through energy conversion is negligible, I think we are converging on that. Water loss (sweat, breathing) is just dehydration, not real weight loss. We are left with CO2, mostly through breathing I guess. So we are mostly left with exercise = breathing, is that it? Can I substitute a jog by some heavy breathing? 88.112.56.9 (talk) 16:53, 28 February 2010 (UTC)

There is also a great deal of waste heat produced. You need to read the links I gave above to Adenosine triphosphate and Mitochondria to be able to follow what is happening here. --220.101.28.25 (talk) 16:44, 28 February 2010 (UTC)

Still, if I convert 1 kg of fat into waste heat, by whatever means, the energy release will be enormous. Think continent-wide destruction. Really, waste heat isn't where any significant percentage of my 1 kg slimming exercise goes. You need to appreciate mass–energy equivalence. 88.112.56.9 (talk) 16:53, 28 February 2010 (UTC)

Ignore the mass–energy equivalence because it is insignificant, as explained above. We are talking chemical energy here, and yes, if you sit in front of the TV breathing (lightly or heavily as you wish), you will lose weight (including your fat reserves) unless you eat to replenish your chemical energy. Exercise is, however, a much healthier way to lose weight than a starvation diet. Dbfirs 17:25, 28 February 2010 (UTC)

What is the process by which exercise loses mass-energy? The mass exits the body by the ________ orifice? 88.112.56.9 (talk) 17:29, 28 February 2010 (UTC)

Exhalation excretes water vapour and carbon (as carbon dioxide), so that is where much of the waste goes. The other orifices serve to get rid of the less pleasant waste products. Dbfirs 17:34, 28 February 2010 (UTC)

Yes, the 1 kg of fat got turned into 1 kg of CO₂, water, and lactic acid and a few other products, releasing a certain amount of energy in the process. Some of the energy went into the work you were doing (jogging or whatever); some of it was lost as waste heat.

Strictly speaking, the mass of the products was not 1 kg, but rather, 0.9999999996 kg. 1 kg of fat "contains" about 38 MJ of useful (chemical) energy, and when that was released, it was equivalent to e/c² = 0.0000000004 kg of mass.

The reason you can lose weight more effectively while jogging than while sitting in front of the TV is of course that you're burning fat faster while exercising (which is as we've seen not coincidentally related to the fact that you're breathing faster). —Steve Summit (talk) 17:38, 28 February 2010 (UTC)

[P.S. And if you try to breathe that fast while sitting in front of the TV, you end up hyperventilating instead of losing weight, because there isn't enough fat-burning going on to consume all of the O₂ you're taking in. —Steve Summit (talk) 17:43, 28 February 2010 (UTC)]

So we seem to gravitate towards "breathing is the source of weight loss"? Is this a belief or a studied thing? If I breathe heavily due to jogging vs. due to just deciding to breathe heavily, is there a major difference? Studied measured sourceable fact vs something your parents and gym teacher told you (no worries, they told me that too)? 88.112.56.9 (talk) 18:12, 28 February 2010 (UTC)

Re importance of 'breathing', it is "measured sourceable fact". See Aerobic_respiration#Cellular respiration --220.101.28.25 (talk) 18:33, 28 February 2010 (UTC)

As far as I know, there is indeed a big difference between jogging versus "just deciding to breathe heavily". If you are exercising, you are burning significant quantities of your body's energy reserves. That process requires oxygen, and generates CO₂. You're going to have to breathe hard to get that oxygen, and to expel that CO₂.

If, on the other hand, you breathe harder than you have to for no reason, you artificially deplete the CO₂ level in your bloodstream, as explained in our article on hyperventilation. —Steve Summit (talk) 18:59, 28 February 2010 (UTC)

"Burning" (as long as we are on the science reference desk) means chemically combining something with oxygen. If I have a fat molecule and I combine it with an O2 molecule, the whole big fatty fat molecule is still there, just affixed by an oxygen atom or two. "Burning fat" does not remove fat, it just adds oxygen to it! How does exercise cause something to combine with oxygen? And how does that cause mass (molecules) to be removed from my body? We are not talking about completely non-scientific mumbo jumbo TV ads saying "magic product so-and-so burns your fat away" (combines fat with oxygen = WTF?), we are talking about physics. 88.112.56.9 (talk) 22:49, 28 February 2010 (UTC)

I think the relevant article you want is Fatty acid metabolism or Fatty acid degradation. The fat molecules (e.g. the triglycerides) are broken down into smaller molecules which are then recirculated in the blood stream. It appears they get filtered out through the liver, which means they probably end up being expelled in urine or feces or through respiration. So that's where your mass is going, almost surely. The actual energy transfer is a complicated set of chemical transformations in the cells. It appears to require a deeper understanding of organic chemistry and cellular function than I have to really understand what is going on physically. I would chalk this up to "wow biology is in certain ways more complicated than physics" and leave it at that! --Mr.98 (talk) 18:22, 28 February 2010 (UTC)

I'm thinking wow biology is complicated is the current state of art here. Some people advocate fat+O=H2O+CO2 discharge through breathing, others promote urine/feces. Considering the power of Wikipedia reference desk I'm starting to think the answer to "why does jogging promote weight loss" is "nobody really knows, but let me list some widely accepted dogma about it..." There is a lot of commonly accepted mythology like "burning fat" -- why and how are you combining fat molecules with oxygen, exactly? And what is the result of that? 88.112.56.9 (talk) 19:03, 28 February 2010 (UTC)

Biology is complicated, but the principles are all very well understood by science, you are just having trouble understanding it. When you eat a kilogram of food your weight increases by a kilogram. That extra kilogram of weight will, if your body doesn't expect to need it any time soon, be stored as fat. If it is likely to be needed sooner, it will be stored as glycogen. Either way, when you do exercise that stored food is combined with oxygen and converted into carbon dioxide and water, which leave the body (through breathing, urination and sweating - mostly breathing, I believe). When you use up the 1kg of food you eat, you will have exhaled and excreted 1kg (minus an insignificant amount due to matter-energy conversion) of carbon dioxide and water (plus the weight of the oxygen used). If you breathe more that your body requires, you just breathe the same air in and out, which achieves nothing (the physical act of breathing requires some energy, but it is fairly small). Feces contains bits of food which you weren't able to digest, so they never played any biological role and just went straight through you. As for how the chemical reactions, work, it's rather complicated, but basically the fat will be converted into glucose (sugar), which travels through your bloodstream to your muscles, as does oxygen that you inhale. Your muscle cells contain mitochondria. The mitochondria contain lots of enzymes, which mediate various chemical reactions that eventually result in the glucose and oxygen turning into carbon dioxide and water. At various stages during that process energy is produce, which is used to turn Adenosine diphosphate into Adenosine triphosphate. That ATP then travels within the muscle cell to the myofibrils which convert the ATP back into ADP and use the energy released to contract. Is that any clearer? --Tango (talk) 19:38, 28 February 2010 (UTC)

It's really not that hard. fat+O2=H2O+CO2 is the correct explanation. Feces have nothing to do with it. Read Beta oxidation, Electron transport chain and Citric acid cycle. Dauto (talk) 19:27, 28 February 2010 (UTC)

So is the main process of exercise is that it makes you breathe harder, so you expel more CO2, so you get rid of more carbon, so you get slimmer? Any sources, any Wikipedia articles that explain it? Does voluntary non-exercise-related heavy breathing have any measurable effect? Or is there some hidden magic reason why exercise gets rid of mass (please don't go back to "exercise turns fat into energy" because the nuclear bomb argument proves that wrong :-) 88.112.56.9 (talk) 22:40, 28 February 2010 (UTC)

No, the breathing is just the way you get rid of the CO2. It is the production of CO2, by burning food, that is important. When you exercise you use more energy, which means you need to burn more food, which means you produce more CO2. It is that increased production of CO2 that leads to more breathing. Breathing without there being extra CO2 to breathe out won't make any difference. Exercise gets rid of mass because it turns food, which otherwise would stay in the body, into CO2 and water, which leave the body. It does that in order to produce energy, which is needed to do whatever it is you are doing. --Tango (talk) 23:01, 28 February 2010 (UTC)

Not that this is necessarily wrong, but I find it remarkable that turning 0.6 grams of matter into energy levels a city. While my regiment of exercise that turns 6 kg (that's 10,000 times more, or make a molten mess of a continent) into energy to feeds the CO2 production process just happens inside me. Any explanation involving matter-to-energy conversion is not automatically wrong, it's just the immense amount of gigajoules that needs to be produced and stored/absorbed somewhere! 88.112.56.9 (talk) 23:12, 28 February 2010 (UTC)

You aren't turning 6kg into energy, at all. You're turning a tiny, tiny amount into energy—breaking some electron bonds, that's it. The rest you are leaving as matter. And no, "breathing more" doesn't mean you are "converting more". The muscles do the conversion, not the breathing. Comparing it in any way to the energy released in nuclear reactions is highly misleading. --Mr.98 (talk) 00:15, 1 March 2010 (UTC)

To keep the hyperbole in check, I'll point out that at the Little Boy conversion rate of 0.6 grams of matter to around 15 kilotons of blast yield, fissioning 6kg of your buttocks would produce a blast of around 150,000 kilotons. The largest earthquake on record released around 178,000,000 kilotons of energy and didn't come anywhere close to "making a molten mess of a continent". --Sean 20:14, 2 March 2010 (UTC)

When you jog (for a significant period of time may I add, otherwise you're just burning carbohydrates) you convert fat by a four-stage process until all the fatty chains are acetyl coenzyme A units. These can then be taken to the citric acid cycle and then the electron transport chain. The whole process generates a lot of ATP, which powers the vast majority chemical reactions in our bodies, but it isn't pure energy as in nuclear reactions. Chemical reactions merely create and break bonds on the molecular level; nuclear reactions go a step further and add and remove forces on the nuclear level (i.e. the atoms themselves are affected). Regards, --—Cyclonenim | Chat  19:45, 28 February 2010 (UTC)

Water Heater

The water heater contains water and is heated to provide hot water for bathing,clean dishes,etc.Also the water heater RHEEM 40 Gallons has two pipes on the top one for hot water and the other one for cold water.The water is heated at all the times,if I open my cold water faucett at my bathroom how the water heater knows that I need cold water and no hot water,how the hot water inside the water heater tank became cold water.When I touch the two pipes on top of my water heater both are warm, explain to me please. Thanks a lot —Preceding unsigned comment added by Thecrazyarchitect (talk • contribs) 14:42, 28 February 2010 (UTC)

Title added to question --220.101.28.25 (talk) 14:54, 28 February 2010 (UTC)

The simple answer is that water from the cold water outlet does not go through the water heater. At some point the cold water supply splits, one pipe goes into the heater, then to the hot tap. The other pipe goes directly to the cold tap. —220.101.28.25 (talk) 15:26, 28 February 2010 (UTC)

Cold water flows into the heater via one pipe, is heated, and flows out the other, on its way to your hot water taps. Under normal circumstances, water will never flow the other way (because there is no pressure to push it that way).

Especially when no water is flowing, a bit of the heat from the heater will creep "upstream" along the cold water inlet pipe; that's why you noticed that both pipes seemed warm. (This is probably due more to thermal conduction along the metal of the pipe itself than along the water inside.) If you were to repeat the experiment after hot water had been flowing for a while, however, I'll bet that the inlet pipe would feel cold right up to the point where it enters the tank. —Steve Summit (talk) 17:15, 28 February 2010 (UTC)

Expanding space

Hi,

So the universe is expanding, yea? Space itself is also expanding, yea? (Stop me when I'm wrong). So then do 2 points remain the same in relation to each other? If they do - how does that work? Does A-B=C or A/B=D remain unchanged? Aaadddaaammm (talk) 15:03, 28 February 2010 (UTC)

You are going to have to beef up your question with something more meaningful than that before you get an answer that makes sense. Dauto (talk) 15:39, 28 February 2010 (UTC)

I recommend you read our Metric expansion of space article, and come back with any further questions you have. Comet Tuttle (talk) 15:44, 28 February 2010 (UTC)

One thing is clear: the catalogue of terms that men of science use to describe the universe is expanding. Vranak (talk) 16:21, 28 February 2010 (UTC)

Thanks Comet - I think I have found my faulty assumption. I thought that space was all expanding uniformly - but on the local scale gravity and electrostatic attractions counteract it. Right? In case I got this bit wrong too, I'll rephrase my initial question more coherently. If space is expanding on Earth - but you have a ruler that is not expanding. You measure the distance between 3 points, A, B and C. After some time you do this again. Does the ratio of A-B:A-C remain constant, or A/B:A/C. If the ruler is expanding, you see absolutely no difference, right? Thanks. Aaadddaaammm (talk) 17:26, 28 February 2010 (UTC)

Why would the space inside your ruler not expand? Dbfirs 17:48, 28 February 2010 (UTC)

Your question is still not clear enough mainly because you define A, B, and C as points and then treat them as numbers. You can't do that. Now we can be generous to you and interpret A-B as the distance between the points A and B in which case "A-B:A-C remain constant" is correct and A/B:A/C is meaningless. Dauto (talk) 17:54, 28 February 2010 (UTC)

Rulers (and planets and stars) don't expand as space expands because there are plenty of very strong forces holding them together. The expansion of space isn't strong enough to make them change size. However, when you look at things like clusters of galaxies that are only held together by the incredibly weak force of gravity over large distances, they are easily pulled along as space expands. SteveBaker (talk) 18:09, 28 February 2010 (UTC)

It's not that simple. Galaxies are held together only by gravity and they are not expanding either. Dauto (talk) 19:02, 28 February 2010 (UTC)

Do clusters of galaxies expand? I've tried to research it, and have failed - what distance scale do you need to reach before the Hubble flow becomes the dominant source of relative motion? Certainly, within the Local Group, Hubble flow isn't a significant factor. --Tango (talk) 20:23, 28 February 2010 (UTC)

Clusters are gravitationally bound and virialised objects, so they do no expand. In fact, they accrete matter from outside, hence they can be said to grow. Superclusters have not yet turned around, and they give roughly the scale at which Hubble flow starts to dominate for any reasonable local matter distribution (overdensity) in our Universe. --Wrongfilter (talk) 20:53, 28 February 2010 (UTC)

When you say "not yet turned around" do you mean they are expanding but at a decelerating rate and can be expected to collapse in the distance future? (As opposed to the larger scales where things are accelerating and will continue to do so.) --Tango (talk) 23:04, 28 February 2010 (UTC)

This goes under the monicker of "spherical collapse model", and its extensions to non-spherical collapse. The evolution of a region around a spherical overdensity can be described by Friedmann's equation where the mean density in the Universe has been replaced by the local density (this has been shown by E.M.Lifshitz if I remember correctly). Initially, the region expands but then, since the local density is larger than the critical density, the expansion slows down and turns around. This is called "decoupling from the Hubble flow". The region collapses and by a process called "violent relaxation" turns into a "virialised" (meaning that the virial theorem holds) object in quasi-equilibrium. It's the densest regions that collapse first in the history of the Universe - these happen to be small objects, which explains why structure grows bottom-up, in a hierarchical fashion. Clusters of galaxies have already collapsed, superclusters not yet. In a Lambda-CDM Universe, which in its entirety will not collapse, there is no guarantee that superclusters will ever collapse, that depends on how large the local density really is. --Wrongfilter (talk) 12:19, 1 March 2010 (UTC)

Phosphenes

Hi,

I have another question I've been meaning to ask for ages. When you rub yours eyes, most people see some kind of "hallucination", often like a black and white grid kind of pattern, plus spots of light. I see the grid, and small bright red and green spots, plus bigger more diffuse blue spots. My question is why do the different coloured spots look different? The graph in Cone cell looks like a good start of an explanation - it provides evidence that there is some biology behind this observation, but I'm having trouble coming up with a hypothesis. Any ideas?

Cheers,

Aaadddaaammm (talk) 15:20, 28 February 2010 (UTC)

As far as I can tell, the best research indicates that pressure phosphenes are not caused by activation of cone cells, but more likely by mechanical activation of horizontal cells -- cells in the retina that normally receive input from cone cells. My source for that is PMID 2209368, also available as a PDF; the information is at the end of the paper. I haven't been able to spot any more recent research on the basic cause of this phenomenon. Looie496 (talk) 19:34, 28 February 2010 (UTC)

Isn't phosphene a poison gas? 24.23.197.43 (talk) 03:32, 1 March 2010 (UTC)

Ha ha. That would be phosgene. Looie496 (talk) 04:04, 1 March 2010 (UTC)

... or possibly phosphine. --Trovatore (talk) 04:06, 1 March 2010 (UTC)

Strange, repetitive movements in "pseudo"-epilepsy?

The other day I went to a friend's house and noticed that their sixteen year old son sometimes made a series of strange nervous movements. He did them when he was alone (or almost, since I accidentally saw him). He touched his face with the tip of his fingers, then his chest and finally his ankles; after that he touched his face again, chest and ankles, and so on until somebody called him or he proceeded to do something else. They told me some months ago that he had something like too much electrical activity in his temporal lobe but, since he had never had a seizure, he, technically speaking, didn't have epilepsy. Despite that, and in order to prevent possible future seizures, they say he takes anti-epileptic drugs.

Other than that, he is an intelligent and healthy teenager and I didn't ask them in case they were sensitive about that or something, but it made me wonder what that could be. Google didn't help, either. So, do you know if there's a relationship between epilepsy (or that "pseudo" epilepsy that they say he has) and those repetitive movements that I saw him do? --Belchman (talk) 20:58, 28 February 2010 (UTC)

We have an article on tic disorders, and treatement of tics is covered in the artile Treatment of Tourette syndrome, but that article does not mention epilepsy. AFAIK tics are considerably different to epilepsy but might be worth noting that tics and epilepsy are extremely complex conditions, so it wouldn't surprise me if there was an overlap somewhere. Vespine (talk) 22:16, 28 February 2010 (UTC)

But as far as I'm concerned tics are involuntary and somewhat uncontrollable, he did those movements only when he was alone and could stop doing them voluntarily. However, the rhythmic nature of them was definitely similar to tics. --Belchman (talk) 23:19, 28 February 2010 (UTC)

Wikipedia has an article on Obsessive–compulsive disorder that may be characterised by repetitive behaviours aimed at reducing anxiety. The Ref. Desk cannot give a medical diagnosis. Cuddlyable3 (talk) 00:01, 1 March 2010 (UTC)

Yes, it sounds much more like OCD than Tourettes (or any other tic disorder). While we can't give diagnoses, we can help people with idle curiosity, which this seems to be (the person in question is already receiving treatment). --Tango (talk) 01:05, 1 March 2010 (UTC)

Epilepsy is a term that covers at least 40 different conditions - however, this kind of repetitive behavior doesn't seem to be listed under any of them. However, we aren't allowed to diagnose medical conditions here and this could easily be some combination of conditions with a vague or complicated diagnosis which the parents have decided to summarize as "Epilepsy". SteveBaker (talk) 02:18, 1 March 2010 (UTC)

Electricity usage

How much power does an average house use at any particular moment? What power output rating of a windmill/solar panel would it take to power an average house? Which would be more economical over a long period of time? His Royal Beastliness (talk) 21:13, 28 February 2010 (UTC)

I don't thik you'll get a sensible answer to your first question without specifying the country, and probably also whether it's urban or rural. --ColinFine (talk) 22:27, 28 February 2010 (UTC)

.. and time of year. AndrewWTaylor (talk) 22:31, 28 February 2010 (UTC)

... also, it is rare for a wind turbine or solar panel installation to cater for maximum demand in a house. They are usually used for hot water or background heating + lighting, and another power source is used for heavy demands. If you can feed excess power back into the grid (and get paid for it), then it is worth considering a large installation of many Kilowatts, otherwise it is probably only economic to generate a kilowatt or two because power will be wasted when your house demand is low. Sometimes the house demand might be only a few watts (TV on standby, bells, chargers etc). As mentioned above, there are too many variables and unknowns to give good advice. As a guide, my house uses about 10Kw at maximum demand (but rarely). Those with electrical heating will use much more at maximum. The standard supply in the UK is around 20 or 25Kw maximum to domestic premises, but more if they have electrical heating. Dbfirs 22:56, 28 February 2010 (UTC)

A rural United States house at any given time in the year is what I was thinking. His Royal Beastliness (talk) 23:00, 28 February 2010 (UTC)

What do you mean 'any'? Do you want an overall average throughout the year? As mentioned above this is a somewhat useless measure since the actual amount used will generally vary considerably so simply supplying the average is not going to power the house very well, not even close. Unless you are feeding back to the power grid or have an energy storage system, it's not going to work very well at all in fact. And you're energy storage system is likely to be rather inefficient given you're probably going to need very long term storage to store a lot in summer for use in winter (depending on location somewhat) and we still don't have anything great for storage energy in that manner particularly on a small scale. And on that note, 'rural US' isn't a particularly precise geographical description since as I'm hoping you know, the US is big (as with Brazil [6], Russia & China [7]). Things will be kind different in rural Alaska from rural Arizona or Texas I'm sure. Nil Einne (talk) 00:13, 1 March 2010 (UTC)

Off-grid houses are not rare. A number of companies specialize in selling complete packages for just this purpose. The external links section of the article should lead you to examples. Usually these homes maximize efficiency in construction and appliances and so use less power than the "average" home. Banks of batteries are the usual energy storage method with any method of seasonal storage very rare. Rmhermen (talk) 00:21, 1 March 2010 (UTC)

Electric usage per household varies by time of day, by month of the year, by where in the country, and by size of the house and appliances installed (electric heat or not, air conditioning or not). See [8]. [9] says an average U.S. home uses 10,000 kilowatthours each year, which would average 1.14 kilowatts per home at an average time. [10] says "the US average per household in 1999 was 866 kwh/month" which would equal an average of 1.18 kilowatts. At 120 volt service, this would average only 9.3 amps. Watt says the average U.S. usage is 1 kilowatt (a bit low, apparently). Now consider that 100 amp service at 240 volts is common, equalling 24 kilowatts and 200 amp service is not unusual, equaling 48 kilowatts. The "average" demand is far less than the service is capable of providing. The demand would vary widely from maximum to minimum in a typical household, by a factor of two or greater. Electric utilities love electric water heating and electric heat, which help to level the load curve during the day. Edison (talk) 00:54, 1 March 2010 (UTC)

You can determine much power a specific house uses "at any particular moment", by seeing how fast the (analog) electricity meter is spinning. The meter should indicate (eg)how many revs/kWh the disc does. Time how long the disc takes to rotate once then do the maths to calculate the average power for that duration (typically measured in seconds). Mitch Ames (talk) 04:37, 1 March 2010 (UTC)

... and if you have a modern digital meter, just time the flashes (1000 flashes = 1 KWh usually). A flash every 3 seconds would be 1.2 kilowatts, and every 12 seconds would be 300 watts. To answer your question about the comparison between wind and solar, just go outside occasionally and ask "which happens more regularly - wind or sunshine?". Where I live, the former is much more common, but there are very dull days with heavy cloud cover and no wind, so I would not be able to generate much electricity on those days.Dbfirs 08:29, 1 March 2010 (UTC)

My house has a power meter calibrated up to 10 kW. To give you a single data point: In winter the highest load I see is 5.3 kW (electric room and water heating, no air conditioning). Cuddlyable3 (talk) 11:25, 1 March 2010 (UTC)

Real Medical Heroes.

I'm looking for examples of real medical heroes, people who devoted their lives to helping others. Maybe people who made a great discovery that helped lots of people, stuff like that. I'm looking for contemporary ones, like in the last century, the more recent the better. People with actual medical backgrounds, not "mother Teresa". People like Fred Hollows and Peter MacCallum come to mind. I would like about a dozen good ones. I'm a little disheartened that it wasn't just as easy as googling "medical heroes". Thanks. Vespine (talk) 22:25, 28 February 2010 (UTC)

Albert Schweitzer --ColinFine (talk) 22:29, 28 February 2010 (UTC)

Louis Pasteur, not a medical doctor but clearly counts. Jonas Salk. Comet Tuttle (talk) 23:10, 28 February 2010 (UTC)

If we're allowing nineteenth-century candidates, no list could be complete without Ignaz Semmelweis - Joseph Lister probably should be on it as well. A couple of obvious twentieth-century candidates (apart from Salk, who's already been mentioned) are Alexander Fleming, Howard Florey, Christiaan Barnard and Peter Medawar. Although he was a physicist, Peter Mansfield, inventor of the MRI scanner, made a great contribution to medicine. List of Nobel laureates in Physiology or Medicine might be a potential source of other names. Tevildo (talk) 23:20, 28 February 2010 (UTC)

...but not this Nobel Laureate who claimed to have discovered the therapeutic value of lobotomy.Cuddlyable3 (talk) 23:50, 28 February 2010 (UTC)

Indeed. I doubt that there'll be many psychiatrists, psychologists, or psychotherapists on the list. :) Tevildo (talk) 00:16, 1 March 2010 (UTC)

Though not a medical doctor, unless I'm mistaken, Marie Curie made significant advances in radioactivity which had direct influence in how cancer is treated. Dismas|^(talk) 00:12, 1 March 2010 (UTC)

What about Barry Marshall? (I don't see him in Tevildo's extensive answer, but I may have missed him). Man drank a petri dish of bacteria to prove it would make him ill: that's courage! 86.177.121.239 (talk) 00:22, 1 March 2010 (UTC)

I second Marshall, the man was working tirelessly for a long time to convince the medical community that H. Pylori was a cause of ulcers. What's really sort of sad is that he even had to go to such lengths as to infect himself in order to convince others that their long held beliefs about ulcers needed to be updated. To be fair, we should also credit Robin Warren, who worked with Marshall in pushing for validation of this finding (but was a little more sane, I guess, in not infecting himself). Both won Nobel prizes in 2005, which in my opinion, are much deserved. Buddy431 (talk) 04:35, 1 March 2010 (UTC)

How about George Frederick Dick, who with wife Gladys Dick was inventor of the "Dick Test" for Scarlet Fever? Also there is the Schick test, invented by Béla Schick for susceptibility to Diphtheria. Edison (talk) 00:35, 1 March 2010 (UTC)

Daniel Alcides Carrión is an example of someone who gave his life to the understanding of a disease important to his people. Another, not so suicidal, was Carlos Chagas. Benjamin Carson also comes to mind as a modern-day hero for many people. The team that discovered HIV, including Luc Montagnier, had a huge effect on a lot of people. If you want someone really recent, Peter Pronovost was recognized with a MacArthur grant for his work on hospital safety - not rocket science, but demonstrably saving lives. Likewise, Paul Farmer continues to be both effective and inspirational. -- Scray (talk) 00:38, 1 March 2010 (UTC)

IMHO Florence Nightingale also deserves to be on this list. Clear skies 24.23.197.43 (talk) 03:35, 1 March 2010 (UTC)

If we have Salk, we better include Sabin as well. I like Snow a lot, though there are people who question how much of a hand he really had in stopping the 1854 Broad Street cholera outbreak. Walter Reed's pretty sweet too, although the real heros are probably Clara Maass and Jesse William Lazear, who literally gave their life in fighting yellow fever. Buddy431 (talk) 04:27, 1 March 2010 (UTC)

Norman Bethune literally died from giving treatment to others. LargeScaleForest (talk) 04:29, 1 March 2010 (UTC)

Some really good suggestions, thanks for that. If anyone else has any more, please keep the suggestions to people who at least died in the 20th century, born in the 20th century is better. And doesn't strictly have to be medical, but at least sciency, not just a hard working humanitarian, made some contribution to medicine or health. Vespine (talk) 04:32, 1 March 2010 (UTC)

Louis Slotin certainly aided the health of his co-workers. 20th century, and very sciencey. LargeScaleForest (talk) 05:04, 1 March 2010 (UTC)

There are also pioneering surgeons. Denton Cooley, Christiaan Barnard, and Norman Shumway, for example, were all active in developing heart transplantation. Buddy431 (talk) 04:46, 1 March 2010 (UTC)

Or, we could talk about people who studied human nutrition, like Ancel Keys (who invented both the K-ration and advocated for the Mediterranean diet - which didn't really gain popularity until the 1990s). Buddy431 (talk) 04:54, 1 March 2010 (UTC)

Related would be Norman Borlaug, not a medical doctor but credited with saving a billion people from dying of starvation with his now-controversial Green Revolution. Comet Tuttle (talk) 06:52, 1 March 2010 (UTC)

Random heading removed. Indenting is sufficient to separate posts.Cuddlyable3 (talk) 11:15, 1 March 2010 (UTC)

Why would you think I added it to separate posts, rather than for ease of editing as I said right there in the title? Editing long sections is tedious, especially on an iPhone, and I thought it was pretty common practice to break up long sections on talk pages with occasional breaks like this. Apart from providing a visual anchor for the reader, it provides an edit button for the editor. This means people like me don't have to take quarter of an hour to post something at the end of the section. What is the problem with doing this? Has consensus shifted away from them? 86.177.121.239 (talk) 14:40, 1 March 2010 (UTC)

I think you added the heading for exactly the reason you say. Such a heading would become a superfluous line in the automatically generated contents list. Mainspace articles should have their content structured under headings but consensus is that this Ref Desk is different. One has only to scroll down the editing window to reach the bottom. That's straightforward on a PC and I guess your difficulty is that you don't find a way to scroll on the iPhone. That problem is not specific to this question. Cuddlyable3 (talk) 18:34, 1 March 2010 (UTC)

It is common to split long sections into sub-sections for ease of editing. This section is nowhere near long enough to require that, though. If you can't edit a section this long on an iPhone, you need to find another way to edit, since an iPhone is apparently not up to the job (although other people seem to manage). --Tango (talk) 21:07, 1 March 2010 (UTC)

Virginia Apgar is credited with drastically reducing global infant mortality with her eponymous test, which is impressive. You might consider Rosalind Franklin for her contribution to the structure of DNA and her work on viral structure, but this might not be hands-on medical enough for you. Dorothy Hodgkin, the Nobel chemist who uncovered the structures of biomolecules such as vitamin B12 and insulin? Again, may not be hands-on medical enough. Christiane Nüsslein-Volhard for her work on genetics, but mostly because she used her Nobel Prize money to set up a trust to help provide childcare and cleaners, to make it easier for female scientists with children. It's the cleaners that makes me love her :) 86.177.121.239 (talk) 11:00, 1 March 2010 (UTC)

You could go back further to the 10th century to the great surgeon Abu al-Qasim al-Zahrawi -- medieval Muslim scientists are often forgotten in the West. 137.43.105.22 (talk) 18:58, 1 March 2010 (UTC)

Good point, if that were what was asked for; however, s/he stipulated contemporary examples (within the last century). -- Scray (talk) 04:08, 2 March 2010 (UTC)

If y'all wanna go that far back in time, why not include Hippocrates in this list -- after all, he was the one who literally invented science-based medicine, didn't he? 24.23.197.43 (talk) 06:07, 2 March 2010 (UTC)

Ernest Beutler, who died recently, had a remarkable life spanning the range of biomedical research. He discovered the basis of a number of diseases, did some amazing basic science, pioneered treatments and devised screens and - as if that was not enough - he developed the software that would become Reference Manager. Thereby helping millions of academics immeasurably! He was also a very nice man; I had the chance to meet him late in his life and he was utterly charming.

I also can't believe no one has suggested Fred Sanger yet, who is the only living person to have won two Nobel prizes and the only person ever to have won two Chemistry prizes. Each of his Nobel winning achievements have become such cornerstones of molecular biology, that its difficult to over-emphasize how much he influenced what we now know about the genetics and molecular biology of all disease. He is very elderly now, but was described in Science as "the most self-effacing person you could hope to meet" and has enjoyed a very dignified retirement (which is more that can be said for some of his more celebrated colleagues. Rockpocket 09:07, 2 March 2010 (UTC)

Thanks everyone, there are definitely some great examples there. In case anyone else thinks they have more to add: CONTEMPORARY is my main requirement, having at least died in the 20th century, was born in is even better. Doesn't have to be purely medical, but some sort of practical contribution to health or medicine, not just theoretical.. The pioneering surgeons are great examples. Thanks. Vespine (talk) 22:22, 2 March 2010 (UTC)

One rather surprising candidate for this list would be Charles Lindbergh the famous trans-Atlantic flyer, who also happens to have been the inventor of the heart-lung machine. Clear skies to you once again 24.23.197.43 (talk) 10:50, 3 March 2010 (UTC)

Spontaneous pair creation (quarks)

I've been reading up on quantum chromodynamics. From articles such as color confinement and hadronization, it seems that quarks can appear out of nothing, as long as they are created in quark-antiquark pairs. Doesn't this violate conservation of mass? --Yanwen (talk) 23:13, 28 February 2010 (UTC)

Mass isn't conserved. Mass+energy is (E=mc² and all that). When particle/anti-particle pairs are created it is out of energy. With quarks, you use energy to pull two quarks apart and, once that energy reaches the rest energy of the pair of particles, it turns into them. --Tango (talk) 00:41, 1 March 2010 (UTC)

Strictly, the conservation law is "Conservation of mass/energy" - but in "normal" (ie non-nuclear) processes there is no interchange between mass and energy - so each is independently conserved. However, in this kind of event, it is the sum of mass and energy that is conserved. That's how (for example) an atom bomb produces energy by losing mass. This is one of the processes that turns energy into mass. SteveBaker (talk) 01:25, 1 March 2010 (UTC)

An atom bomb doesn't do anything different to a chemical bomb in terms of matter-energy conversion. In both cases there are bonds being broken and made with the end result being a lower energy (and thus lower mass) state. The only difference is that nuclear bonds involve more energy than chemical bonds. If you want a bomb that converts matter into energy, you need a matter/anti-matter bomb. A number of elementary particles of matter at the end of a nuclear explosion is the same as before, the mass difference is just due to bonds. --Tango (talk) 02:31, 1 March 2010 (UTC)

It's a bit weirder than that. In Feynmann-style quantum electrodynamics, even energy is only conserved over long time scales. Over sufficiently short time scales, the Heisenberg uncertainty principle gives enough energy uncertainty to allow the creation of particle-antiparticle pairs. In QED the vacuum, over short time scales, becomes a constant flux of omnipresent creation-annihilation events. These events don't last long enough to observe, but they contribute to the calculations that underlie particle physics. Looie496 (talk) 03:52, 1 March 2010 (UTC)

Footnote: our vacuum energy article explains this in a lot more depth. Looie496 (talk) 03:58, 1 March 2010 (UTC)

That is a widely spread misconception (or misunderstanding). Virtual particles conserve energy and momentum. The weird thing is that they do not respect the normal energy-momentum-restmass relationship. Particle physicists describe that by saying that virtual particles are not required to be on their mass shell. Dauto (talk) 05:26, 1 March 2010 (UTC)