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July 12

derivation of the kintetic theory equation

Hello.

My question is related to the derivation of the equation pv=1/3nMwC^2. Most of the derivations I have seen assume that the average time between colisions, t, is 2l/Vx when l is the length of the cube. When assuming this, you actually assume that each molecule travel from one wall to the other wall at constant velocity without any clashes with other molecules. this is an unlikely assumption, yet those derivations do succeed. my quastion is - why? and where can i find more rigorous and accurate derivation?

I am sorry for my poor english...

Thanks in advance, 94.159.137.4 (talk) —Preceding undated comment added 06:54, 12 July 2012 (UTC)

Isn't the assumption really that the collisions with other particles are elastic? If it does elastically collide with any other particle, it transfers momentum which that particle then in turn transfers to the wall after exactly the same amount of time has expired. This results in the same net effect for the wall, so the predicted pressure is exactly the same. 203.27.72.5 (talk) 07:41, 12 July 2012 (UTC)

I thought about this interpretation, but I don't think it's true. It would be true only when moving particle collides with a static particle. Think about collision between two particles with same mass and opposite X-component velocity - They both would be stopped. 94.159.137.4 (talk) —Preceding undated comment added 09:20, 12 July 2012 (UTC)

If they stopped, the kinetic energy would be destroyed; so they can't stop as long as energy is conserved. Imagine two billiard balls colliding head on. They don't stop, they bounce back in opposite directions. 101.173.170.146 (talk) 09:34, 12 July 2012 (UTC)

Yes, you are right, my fault. Yet I would be happy to see a rigorous derivation. 94.159.137.4 (talk) —Preceding undated comment added 09:51, 12 July 2012 (UTC)

On matters of mathematical rigour, I'm the last one that should be commenting, but is the derivation at Kinetic_theory#Pressure_and_kinetic_energy adequate? 101.173.170.146 (talk) 10:56, 12 July 2012 (UTC)

No, because of reasons I wrote above. You can see this thread in physicsforums.com, which explains the problem clearly (especially on "loom91"'s notes), yet no complete answer was given. 94.159.137.4 (talk) 11:32, 12 July 2012 (UTC)

A more accurate derivation can be found in the book: "Fundamentals of Statistical and Thermal Physics", by F. Reif, secion 7.13 page 278 and further. It starts with the heuristic derivation, followed by an exact calculation. Note that in the heuristic derivation the formula you get contains the square of the average speed, while in the exact calculation, you get the correct expression containing the average of the squared velocity. Count Iblis (talk) 17:33, 12 July 2012 (UTC)

Thank you! perhaps it's good idea to write in Kinetic_theory#Pressure_and_kinetic_energy that the derivation which described in the article (and in many academic textbooks...) is not an accurate one. 94.159.137.4 (talk) 06:22, 13 July 2012 (UTC)

It's not inaccurate. Simply assume that the Volume of the box is so small that the chances of a collision between particles happening before the particle reaching the wall is negligible. Then build a larger box by stacking the smaller boxes side by side and removing the walls between the boxes (Which has no effect in the pressure). Dauto (talk) 15:47, 13 July 2012 (UTC)

Oughterlony immunodiffusion

My question concerns the interpretation of Oughterlony immunodiffusion which I think it, the content in Wikipedia, can make people misunderstand some good points. For example Ag A contains two epitopes so called X and Y while Ag B contains epitope Z, if both Ags react with the mixed Ab which contains anti-X, anti-Y and anti-Z, the result should come out without any relationship (of identity, partial identity or non identity). Is that right? I think this technique was created before immunologist really understand about antigenic determinants. It originally is for study the relationship of each class of antibody. The content in the web can make people understand that the two Ags which are not relate to one another still give a result of non-identity. — Preceding unsigned comment added by 110.164.187.222 (talk) 12:05, 12 July 2012 (UTC)

You never posted an exact title as requested at Wikipedia:New contributors' help page/questions#Interpretation of Oughterlony's technique. Is this about Ouchterlony double immunodiffusion? I'm not qualified to discuss the topic. PrimeHunter (talk) 12:10, 12 July 2012 (UTC)

As explained at Precipitin, the antigen must be multivalent - if there's just one epitope per antigen, then it will react with an antibody, but it won't form a large gel-like complex; you'll have two dead-end epitopes stuck to one monomer antibody (four to IgE, ten to IgM - see antibody. I think F(ab')2 fragments are OK, but don't try to use Fab fragments. ;) ). Antibodies and antigens will ignore those that are not matches, so if you have two unrelated multivalent antigens, each should find its own favorite antibodies and form complexes with them somewhere or other, but ignore the other antibodies. That means that you could have multiple white lines, or even white lines crossing one another. Mix in a little bit of the right fluorescent antibody (or apply it to the gel afterward) and you could mark which is which in pretty colors if you want. Wnt (talk) 13:38, 12 July 2012 (UTC)

This is a minor point, Wnt, but where you mention the 4-valency of IgE, I think you meant sIgA. -- Scray (talk) 04:25, 13 July 2012 (UTC)

Thanks for spotting that! Wnt (talk) 21:12, 13 July 2012 (UTC)

looking for a chart

from organogenesis

hi! i'm a biology student, taking a course in comparative anatomy. i am looking for a chart [or something similar], which will: show the origin of the organs [what came from the mesoderm, ectoderm, etc.], and maybe even more- like what originated in the neural crest.

thanks! — Preceding unsigned comment added by 212.76.110.252 (talk) 16:10, 12 July 2012 (UTC)

You should read the relevant articles. Also check out embryogenesis and organogenesis, whic is a stub, but which has the picture I posted. You'll probably do better with a google image search. μηδείς (talk) 16:41, 12 July 2012 (UTC)

do you have any idea which key words i should use? i am looking for something with more details- like the somits.

thanks again... — Preceding unsigned comment added by 212.76.110.252 (talk) 16:48, 12 July 2012 (UTC)

Well, to begin with, see somites... but admittedly, that's not the image you want yet... Wnt (talk) 18:07, 12 July 2012 (UTC)

You should really just fool around with searches like "organ mesoderm", etc., at google images. You will immediately get hundreds of choices to browse through, rather than one at a time from us. μηδείς (talk) 18:56, 12 July 2012 (UTC)

Lasers

Wavelengths of the visual spectrum

Is the blue-violet laser stronger than the green one ? ( We are talking about pointers )124.253.89.189 (talk) 16:52, 12 July 2012 (UTC)

According to laserpointersafety.com, a violet pointer is more dangerous than a blue one, which is in turn much more of a hazard than a green one. Clarityfiend (talk) 17:11, 12 July 2012 (UTC)

What about this one. Is it exactly blue or violet ? Last time this very vendor fooled me into buying a three AAA battery laser (green) which he claimed is powerful enough to light up a matchstick ( It doesn't, though it does produce a slight sensation of heat on skin ) — Preceding unsigned comment added by 124.253.89.189 (talk) 17:51, 12 July 2012 (UTC)

The page you linked says the exact opposite of that. They seem to be specifically talking about the danger of temporary blinding/distraction, not permanent eye damage, which is why they scale it by the eye's sensitivity to each frequency (it's most sensitive to green). And they are talking about lasers of the same power. -- BenRG (talk) 02:02, 13 July 2012 (UTC)

Clarityfiend, you are misinterpreting what that site says. Lasers with longer hazard distance are more dangerous than ones with shorter hazard distances. That said, I'm not sure on what they are basing that. The official standards for laser safety do not distinguish between violet and green light.--23.24.20.245 (talk) 16:59, 16 July 2012 (UTC)

On the colour spectrum, the higher-frequency colours have higher energy. Lower wavelengths means higher frequencies means higher energy. This is also why red is less harmful to your night vision than green. BigNate37_(T) 18:50, 12 July 2012 (UTC)

This isn't strictly true; red light does not affect your night vision as much because rod cells (responsible for low-light vision) are less responsive to higher wavelengths; the chart in that article shows they are most sensitive to blue-to-green wavelengths. -RunningOnBrains^(talk) 19:52, 12 July 2012 (UTC)

I stand corrected. BigNate37_(T) 22:21, 12 July 2012 (UTC)

Higher frequencies have higher energy per photon, not per laser beam. It's the power that matters, not the color. -- BenRG (talk) 02:02, 13 July 2012 (UTC)

If you want to get an answer that makes any practial sense, you will have to qualify what you mean by "strong". The energy of the light is highest at violet and lowest at red with everything else falling in between per the spectrum in the picture above. The power of the various laser pointers is not dependent on the colour of the laser, but rather on its design. The power output in watts may be stated on the laser pointer itself or on the packaging. If you're wanting to know which will heat something up the most (i.e. which will come closest to igniting that match head) that will be the one with the highest power output. My intuition is telling me that you're not going to find a battery powered pocket laser pointer that can acutally do that though. 203.27.72.5 (talk) 01:59, 13 July 2012 (UTC)

Timeline for noticeable adverse effects from 100% recirculated commercial airline cabin air

The post above ("Airliner cabin air") got me thinking (I don't know why, but I had just assumed that airline cabin air was recirculated, at least to a large extent, which I now realize is pretty daft).

Let's take for the sake of this example a modern Boeing 767-300 outfitted with a 2-class cabin, and a full passenger capacity of 269 people. Assuming that there is NO exchange of air, and that the 100% of the air is continually recirculated, how long would it take for enough oxygen to be depleted such that some passengers will begin to experience adverse effects from the lack of oxygen? How long would it take for the majority of the passengers to lose consciousness or even die due to the lack of oxygen? --Zerozal (talk) 17:06, 12 July 2012 (UTC)

As for how long before it becomes uncomfortable, that's just a few minutes. Between lower oxygen, higher carbon dioxide and other gases, high humidity, and high temperature, it's hard to know just what makes it "stale", though. The various factors can also affect each other, like high temp and humidity causing people to emit more body odor, making the air quality quickly worsen. StuRat (talk) 17:27, 12 July 2012 (UTC)

Talking of cabin pressure in aircraft and it's effect upon humans, is it possible to get rid of hijackers by suddenly lowering the pressure ? It will cause all humans in cabin to lose consciousness (without causing any permanent damage upon them). Later all can be revived easily by bringing pressure to normal. But by that time hijackers would be nicely bound and gagged, and their toys taken away...124.253.89.189 (talk) 18:09, 12 July 2012 (UTC)

It doesn't make much sense to me. Whatever people have to deal with the terrorist, would need a mask and oxygen tank. And the terrorists could also have a mask and oxygen tank (smuggled into the plane in the same way they smuggled the weapons). Besides that, cockpit doors are reinforced nowadays, and pilots are trained not to cave in. Any terrorist without a bomb won't cause much harm. 79.148.233.179 (talk) 18:20, 12 July 2012 (UTC)

Stu enjoys posting on this forum - pity he doesn't check his facts first.

During most of the flight, the passengers are at rest. According to http://ep.physoc.org/content/64/3/205.full.pdf the rest oxygen consumption of an average fit humnan is 0.263 Litres/min A 767-300 has a cabin volume of length ~49 m, 4.72 width, with a half-circle profile. Allowing for volume occupied by seats, luggage racks, etcx, the internal volume is approx 880 m³. 269 average humans, taking the density as roughly that of water, occipies a volume of 65 litres each, or a total of 18 m³. So the volume of air in the cabin is 880 - 18 - 862 m³. Air is 21% oxygen, and 767's pressurise to 80% of sea level value. so that's 145 m³ of oxygen. 269 passengers at 0.263 l/min gives a total oxygen consumption of 0.0708 m³/min. So the passengers consume in the order of 0.05% of the available oxygen per minute, or about 3% each hour.

Humans at rest are perfectly comfortable at an altitude of about 3,000m - at that height, the pressure is ~70% of sea level. So the comfort limit is reached after about 3 hours is the cabin is 100% recirculated.

However, its more complex than that. Each m³ of oxygen consumed is replaced by a m³ of CO₂. It happens that the mammilian breathing system automaticllay regulates, but our internal sensor does not sense oxygen, it senses CO₂. So the CO₂ breathed out will cause everyone to breath harder, without them necessarily noticing it. This will completely maintain blood oxygen at saturation level for much longer than the 3 hours calculated by oxygen consumption. This principle is used in gas fire suppression (eg Inogen) in computer and server rooms - when a fire is detected, a mixture of inert gasses and CO2 is pumped in, to force oxygen out and reduce it to about half the normal level - that causes most fires to go out. The CO₂ causes any people to just breath deeper, so they are not harmed.

It also happens that humans gradually starved of oxygen don't feel discomfort - they just get sleepier and sleepier, until they are unconscious.

The overall implication is that you needn't worry about aircraft fresh-air delivery failure. Cabin oxygen will considerably outlast the fuel. You will have landed long before it is a safety issue.

Sudenly dropping cabin presure to disable terroists is a bad idea. It can only work if you disable the automatic oxygen mask system. Humans will take some time, 10 minutes or more, to loose consciousness, but they WILL suffer all manner of medical problems from tissue rupture, getting hit be objects flying about, and cardiac arrest if they have any latent cardiac issues.

Ratbone124.178.45.153 (talk) 10:56, 13 July 2012 (UTC)

I never claimed that oxygen levels alone caused discomfort after a few minutes, I listed several factors. Also, you mentioned that people breath harder as carbon dioxide goes up. I agree, but also think this makes you feel uncomfortable, as do the temperature, humidity, odors, etc. Having been on a plane parked on the tarmac without any air circulation, I can tell you it gets uncomfortable quickly. StuRat (talk) 06:41, 14 July 2012 (UTC)

It also looks like you made a math error. 49 m length by 4.72 m width, with a half-circle profile (assuming the other half to be the luggage compartment, etc.), gives me a volume of 428 cubic meters, not 880 (LπR²/2 = (49π(4.72/2)²)/2 = 428), and this is before subtracting volume for seat, overhead bins, and, of course, people. StuRat (talk) 07:02, 14 July 2012 (UTC)

And you've also failed to take into account people with diminished lung/heart function, etc., who may become uncomfortable due to oxygen deprivation (hypoxia) far sooner than healthy individuals. There's even discussion of requiring higher air pressure in the cabin, in order to protect such people: [1]. StuRat (talk) 07:15, 14 July 2012 (UTC)

I think StuRat was still right that it would be uncomfortable after a few minutes though, no so much from the lack of oxygen, but more from the humidity and temperature building up causing it to feel stifling. I suppose there might be an unstated assumption that with no air exchange the air con is also broken though. If the passengers were aware of it, I'm sure many would feel uncomfortable instantly. 203.27.72.5 (talk) 20:19, 13 July 2012 (UTC)

Actually, if the cabin was just well air conditioned, it sounds like it would be better without outside air coming in. According to Ratbone there's no real negative side effects from the lower oxygen levels. Getting drowsy from the carbon dioxide would help you get to sleep and pass the time and it should keep annoying kids less active; kind of like a primitive hypersleep. In the event of a crash the LEL of fuel air mixtures would be higher. The pilot and crew would still need some extra oxygen from somewhere, but that seems a lot easier to do than the whole cabin. 203.27.72.5 (talk) 02:33, 14 July 2012 (UTC)

Carbon dioxide, if anything, would make you breath harder, then hyperventilate. I believe it's carbon monoxide which makes you drowsy, and, if it did, you'd be in danger of dying. Lucky for us very little CO should occur in the airplane cabin, unless there's a fire. StuRat (talk) 06:44, 14 July 2012 (UTC)

Let's look at Stu's claims in turn:-

1. Experince of plane on tarmac. This is not relavent to the OP's question, as he asked about 100% recycling of air, not complete shutdown of aircon. With no air moved past your face, you will notice distress a lot quicker even if temperature and humidity are the same. Note that some people have an irrational discomfort in enclosed places when things go wrong. I have experienced people claiming they are running out of oxygen after a 10 minutes or so in a stuck elevator - complete nonsence. I too have been stuck in a powered down airliner for about 30 minutes - air quality was not a problem, but being annoyed with the boredom and delay certainly was.

2. Math error. Yes, I forgot to divide by 2 to allow for the cargo hold not being part of the available air. This means that oxygen would be down to comfort limit in about 1 hour 20 min, not 3 hours as I said. But don't forget the raised CO2 will cause the passengers to automatically breather deeper.

3. Folk with diminished health. The experience of airlines over many years is that slow air quality change almost never causes problems. This is as you would expect, as humans have considerable lung over-capacity at rest, and CO2 drives breathing depth to maintain blood oxgen at stautation level. In other words, in stale air you breath deeper but still well below breathing capacity, and as blood oxygen is still saturated, the heart doesn't see any difference.

4. Rising humidity. I had some difficulty finding a simple definitive reference for human moisture evolution rates at rest (plenty of refrences for exercising sportspersons), but figures range from 0.01 kg/hr to 0.022 kg/hr for an averge sized human at rest at 25 C. We drink about 1 litre a day when not working, but most goes to make urine, the remainder breathed out and sweated. We can expect an aircraft with aircon working but with no fresh air induction to bring humidity down to 40% REL. Accoding to my stadard ASHRAE pschrometry chart, this means a moisture load of 0.0065 kg per kg of air, and a n air density of 0.85. This equates to 2.7 kg of moisture in the cabin space. Assume each person evolves 0.015 kg/hour, and a confort limit of 70% REL, which has a moisture load of 0.011 kg/kg. This means that the comfort limit with 269 humans will be reached in 30 minutes. But, wait, there's more: All those bodies will generate heat, as perhaps the sun shining on the hull. So teh aircon will remove this heat, and removing heat from air by means of passing it over a cold plate always means condensation. This will considerable extend the 30 minite time toi discomfort, perhaps even indefinitely.

5 Raised temperatures. Since the OP's question did not required aircon to be completely shut down, there is no reason for temperature to rise. However, an aircraft at crusining altitude is passing thru very cold air, so the issue is not critical.

6 Diference between CO and CO2. Both make you sleepy. Neither cause discomfort. Recovering from CO is a serious problem though.

Conclusion: While I made a calculation error, my opinion still stands: Stu is wrong, lack of fresh air in an airliner is not of any critical importance. Ratbone121.215.69.8 (talk) 11:34, 14 July 2012 (UTC)

1) You misread my response again. I did not say "complete shutdown of aircon", as you claim. I said there was a lack of "air circulation", not "aircon". It was actually quite a cold night, and the plane was ice cold to begin with, so no cooling was needed, at least not for the time we were on the tarmac. I've also had a similar experience in well insulated houses, where, without any air circulation, a roomful of people quickly becomes "stuffy". StuRat (talk) 20:20, 14 July 2012 (UTC)

You said "parked on a tarmac without any circulation". That implies a complete aircon shutdown. Such things happen sometimes if the aircrew decide to resolve a problem by a complete shutdown of all systems then progressively bring it all online again. You can't have aircon without air ciculation thru it. In other words, I interpreted your words in a way that made the most sense - giving you the benefit of the doubt. Do you mean that the plane's normal venting was sealed? Doesn't seem likely - not at all easy to do deliberately, and why on earth would they, and not a likely fault condition. How did you know anyway? Did the crew tell you? Sorry, Stu, you're just not believable. Ratbone58.167.227.14 (talk) 15:56, 15 July 2012 (UTC)

Now I see you've moved on to accusing me of lying. On the tarmac, they always seem to turn off the air exchange here. I assume it's to prevent exhaust gasses from taxiing planes, etc., from being sucked into the passenger compartment. Or it may just be a consequence of not running the engines, which are used to power the air exchange. Perhaps they do it differently there. With a normal take-off, you may not notice it getting stuffy inside while on the ground, but when there's a delay, it's highly noticeable. Notice that things were so bad here we needed an airplane passenger's Bill of Rights, and it still allows planes to sit on the tarmac for 4 hours before fines kick in: [2]. (4 hours without fresh air might actually kill people, so I assume they periodically fire up the engines and do an air exchange.) StuRat (talk) 18:39, 15 July 2012 (UTC)

Well, if the cap fits... Actually, I don't think you mean to lie - I think you just make initial posts without thinking or checking first, then have trouble accepting you have things wrong. You are unware of how airplanes are operated. When on the ground, without propulsion engines running, airliners are powered from Auxilary Power Units (http://en.wikipedia.org/wiki/Auxiliary_power_unit) these are small turbine-powered generators usually mounted in the tail with the exhaust clearly visible. Some manufactuers install them further forward exhausting to the side - in these cases a cover closes over the exhaust when teh APU is shut down. When at least one main engine is running, the APU is not needed and is shut down. Sometimes, if convenient, aircraft on the ground are powered from a Ground Power Unit - a generator set mounted on a trailer, or in some cases, a convertor run form the airport electricity supply (Mains electricity is either 50 Hz or 60Hz, for historical & technical reasons, aircraft use 400 Hz power, so a convertor or special genset is needed). It would be very unusual indeed for an aircrew to have an aircraft unpowered when passengers are inside, unless they are resolving a problem. I have been on lots of local and international flights. Each time the aircraft was powered down, the captain first went on the PA and told us he was shutting down to resolve a problem. Ratbone124.182.16.199 (talk) 03:53, 16 July 2012 (UTC)

You don't seem to understand some of the pressures a pilot is under, at least in the US. They often have a very narrow window for take-off, and if they miss it, they then have to wait on the tarmac until there's an opening in a packed runway schedule. They can't go back to the gate, there might be another plane using it, and, if they did, they'd never get a chance to take off when another plane misses it's window. So they sit and wait, far from any electrical outlet they can use. And, even if they could, they wouldn't want to, as they need to be ready to go at a minute's notice. At the same time, they don't want to use up too much fuel, or they will then have to go back and refuel, since they often carry the bare minimum required, to keep the plane lighter. So, they often just sit there, biding their time, with the passengers suffering. Hence the need for the Passenger's Bill of Rights, to prevent such abuses. Maybe it's better in Aussie. StuRat (talk) 07:33, 16 July 2012 (UTC)

3) You still seem to be talking about normal, healthy people when you say things like "humans have considerable lung over-capacity at rest". People with certain health problems are already right at the limit, with little over-capacity to draw on, and the link I provided shows a dramatic increase in deaths during flights, likely due to changing demographics leading to more unhealthy aging baby boomers on planes. It can be argued that such people shouldn't fly, or should have portable oxygen generators with them if they do, but people aren't always aware of their health problems until they have a crisis. StuRat (talk) 20:14, 14 July 2012 (UTC)

People that seriously sick that they would be at risk would already be under professional medical advice. You get people with latent/undetected heart disease, but as has been explained, unless lung function is crippled, they are under no risk that they don't already face anyway. Your point here has been disputed by others, as you are aware - so I'm not going to waste time on it. Incidentally, us baby boomers are fitter than the previous generation (better food and medical advice, no WW2 service), and probably far fitter than the next generation, due to their obesity and lack of outdoor activity. When I was in my teens and 20's, chaps at work in their 60's could not run to catch a bus. I'm now past that age, and I can (and do, if I'm caught in the rain) run flat out for 100's of meters. And there's nothing special about me physically. Ratbone58.167.227.14 (talk) 15:56, 15 July 2012 (UTC)

You are wrong when you state that "unless lung function is crippled, they are under no risk that they don't already face anyway". Hypoxemia is frequently caused by circulation problems alone, due to heart disease, etc., or due to anemia. And a person who doesn't exert themself or spend time at high altitudes may not even be aware they have a problem, until they take a flight. See Hypoxemia#Deficient_oxygen_in_the_inspired_air for the calculations on how blood oxygen level is reduced with altitude (one solution they propose is supplementing the low pressure air with pure oxygen, but that's risky, as oxygen tanks are a fire hazard). StuRat (talk) 18:53, 15 July 2012 (UTC)

This has been quite adequately explained (blood oxygen is held at saturation level unless under strenuous exercise or lungs are just about totally knackered) - and your opinion disputed by others, so I won't waste time here. Ratbone124.182.16.199 (talk) 03:53, 16 July 2012 (UTC)

What "others" ? I must have missed it. And they aren't "my opinions", I've provided sources. StuRat (talk) 07:38, 16 July 2012 (UTC)

4) You haven't included your sources or the details of your math, so I have no way to check your work this time. However, it looks like you admit that, without any air conditioning, humidity will become uncomfortable in 30 minutes. That seems about right. However, note that you don't always start out at the comfortable 40% relative humidity you used in your figures. If the plane just took off, it may very well have higher humidity, due to having had the doors open while loading passengers. And, if it then sat on on the tarmac full of passengers waiting for clearance, where they don't seem to run any fans or air conditioning, then moisture will have built up even further. So, you want to bring in fresh, dry air quickly, once in flight, to reduce this humidity level. StuRat (talk) 21:00, 14 July 2012 (UTC)

I included sources for basic data. In any case you could google or look it up for yourself - you would leran more then. You did not give any sources at all for your original opinions in this topic - you made nothing more than unsupported personal claims, which have been conclusively shown to be nonsense. Calculations stand on their own. I gave sufficient data for anyone with basic math ability to reproduce the humidity calcs - the O2 and CO2 calcs were given in detail.

Re the 30 minute calculation, I admitted no such thing. You did not read what I wrote. I clearly explained that the calculated times, and the 30 minute value especially, was just to establish a completely worst case solidly provable limit. It was a very conservative calculation, because it is based on a 70% RH limit taken from an aircon book (Trott & Welch) I have for people in England working in an office (not at rest) - most humans at rest will tolerate much worse than that at 25 C. You have overlooked that I pointed out that aircondioning means passing air over a cold plate, and this inherently and necessarily means that excess humidity will be condensed out - so the actual time to discomfort is in excess of 30 minutes, almost certainly well in excess of 30 minutes, and may be indefinite. Ratbone58.167.227.14 (talk) 15:56, 15 July 2012 (UTC)

Is this the chart you mean ? [3]. Google was able to correct your two spelling errors and find the "stadard" ASHRAE "pschrometry" chart. (You might "leran" something from Googling it yourself, like how to spell.) But this doesn't look like the chart you are describing. What inputs did you use ? I can't follow what you did from the scant details you gave. You've already demonstrated that you lack basic math ability, like being able to divide by 2 when appropriate, so I'm not going to just take it on faith that your calculations are correct. Show them or shut up. StuRat (talk) 19:19, 15 July 2012 (UTC)

Yes - that's the chart, but the one you posted have important scales missing. Find another with the right hand scale for moisture load in kg H2O per kg air, and the use should be obvious - find the intesection of the vertical 25 C line and the curved 30% rel humidity line, then read off on the righ hand scale: 0.0065 kg H2O per kg of air, and on the density scale, missing on the one you posted, 0.85 kg/m³. Find a metric one - its so much easier. The standard ASHRAE chart has all these things. You don't need to take my calcs on faith. They only need a primary school skill level to do. So do them yourself - be independent - go divide the H20 breathed out & sweated by the 269 humans into the water load for (say) a 30% rel humdity change read form the chart. Ratbone124.182.16.199 (talk) 03:53, 16 July 2012 (UTC)

5) You can't assume that flying through cold air significantly cools the plane interior, without any air exchange. An airplane, especially a large one, has a low surface-to-volume ratio, and they also tend to have insulation in the lining of the fuselage, as you don't want ice building up and periodically melting amongst the wires and such. Solar heating can also be significant, especially when flying above the clouds. StuRat (talk) 20:31, 14 July 2012 (UTC)

Are you trying to have it both ways, Stu? Note that if the plane does heat up, relative humdity will drop rather rapidly (see any psychrometric chart), so comfort is not as affected as much as you may expect. But it's irrelevant anyway - The OP's question is not about loss of aircon, its about zero fresh air induction. Ratbone58.167.227.14 (talk) 15:56, 15 July 2012 (UTC)

That would only be true if the total amount of moisture in the air was constant as the temp increased. Obviously, with planeload of people sweating and breathing heavily, this isn't the case. StuRat (talk) 18:26, 15 July 2012 (UTC)

You haven't grasped how cooling of air works, and cooling of people works: Cold air "holds" less H2O then warm air, as shown by the psychrometric chart. (More correctly, the vapour pressure of H2O falls sharply with temperature.) Cooling air by passing over a cold surface causes condensation, as the air on contact with the cold surface is brought to saturation. Thats why aircons have drains (and slinger rings it seems). As heat and moisture are added by the passengers, the aircon will remove both. While those folk are sweating away, and they shouldn't be sweating thatmuch, they aren't doing anything, if the temperature is increasing (which in the context of the OP's question it won't), the consequent increase in saturation vapour level will significantly oppose the increase in relative humidity. If temperature rises fast enough (and that's not very fast), relative hunidity will actually fall. You can see this on the psychrometric chart - for example plot a curve of intercepts for (say) an increase from 25 C to 30 C accompanied by a moisture load increasing from 6.5g/kg to 7.0 g/kg - you'll find this drops the humidy 5%. You will actually feel marginally cooler, as the body's ability to loose heat by sweating is dependent on relative humidity. Ratbone124.182.16.199 (talk) 03:53, 16 July 2012 (UTC)

I understand all of that perfectly well, but none of it is at all relevant to what we are discussing here, which is your statement that "if the plane does heat up, relative humdity will drop rather rapidly". If it's heating up, then the A/C isn't working, so all that about A/C is irrelevant. And, I certainly understand that relative humidity would fall if you increase temperature WHILE HOLDING TOTAL MOISTURE IN THE AIR CONSTANT, but that clearly won't be the case on an airplane full of sweaty, panting passengers. You didn't seem to read or understand my post. StuRat (talk) 07:24, 16 July 2012 (UTC)

How about actually reading what I said: I covered the two separate situations: 1) air con running, which is what's relevent to the OP's question, and 2) the totally non-relevant case of aircon shut down, where both moisture load and temperature rise (if temperature rises - depends on the environment as previously explained), since you keep insisting on discussing it. You are too focused on your own view. Did you print out the Wikipedia psychrometric chart and plot the example I gave? If you did, you would have found relative humdity actually does DROP even though the moisture load INCREASED significantly - because rel humidity is very sensitive to temperature. And its rel humidity that matters. Ratbone124.182.45.47 (talk) 12:37, 16 July 2012 (UTC)

6) High carbon dioxide does cause discomfort, in that it creates the feeling that you need to breath. If you are already breathing heavily and still feel more of a need to breath, this is quite distressing. See "Use of carbon dioxide for euthanasia" (or animals), which states "research suggests that it is highly aversive and causes distress in many animal species" [4] StuRat (talk) 20:33, 14 July 2012 (UTC)

You reference is a pamphlet from the RSPCA, who does not enjoy a reputation for scientific rigor. But, more importantly, they are talking about deliberately sudden lethal doses - quite a different thing to what we have been discussing here. Gas fire suppression (Inogen being the main one) is often used in computer rooms, server rooms, and sometimes in telephone exchanges, where water could be of worse business impact than the fire. As I stated, these work by displacing oxygen with an inert gas mix, which puts the fire out, plus added CO2 so the humans automatically breath a bit deeper. There is no WP article on it, but you can go check it out. I have, as building owner's representative, witnessed a full test discharge on a new Inogen installation. Myself and colleagues walked around within the gassed room without any discomfort at all, though, as I was expecting it, I did notice I was breathing deeper than usual - but nowhere near as much as I would jogging or other physical exercise. Ratbone58.167.227.14 (talk) 15:56, 15 July 2012 (UTC)

As you put it, these are "nothing more than unsupported personal claims". StuRat (talk) 19:26, 15 July 2012 (UTC)

So, don't trust them - go research gas fire suppression youself. Ratbone124.182.16.199 (talk) 03:53, 16 July 2012 (UTC)

So why provide it at all? Why not just seal the cabin and use that air for the duration of the flight? It would have the advantages I listed above, plus reduce costs (according to Aspro in another thread), and according to what you said, would not cause any major issues. BTW, for what it's worth I don't think anything that StuRat said was relevant to what the OP asked, since the question was "how long until adverse effects?" which was further qualified by "how long until a majority of the passengers to lose consciousness or even die" and StuRat just talk about discomfort, so calling him out several logical leaps later when he's talking about a plane that was delayed on the tarmac seems a bit pointless. 203.27.72.5 (talk) 11:43, 14 July 2012 (UTC)

I took "how long until adverse effects?" to be a separate question from "how long until a majority of the passengers to lose consciousness or even die?", and considered discomfort to be an adverse effect. Note that discomfort can also lead to real medical problems, like panic attacks, hyperventilation, etc. StuRat (talk) 20:23, 14 July 2012 (UTC)

Good qestion. I'm not competent on the design/engineering of aircraft, however I do know a thing or 2 about aiconditioning of buildings. So, a few points: (1) It is quite difficult to completely seal things. In the aircon industry, there is a rule of thumb that 5% of air fed from aircon outlets should be fresh air from outside - this implies that 5% is leaving the building somewhere, otherwise pressure would rise. Nobody makes specific provision for this - leakage thru builing fabic and doors is generally very much more than sufficient. (2) I said that lack of fresh air is not critical. That does not imply it isn't desirable, especially on a long flight. That's a matter of other sorts of body odours as Stu said. Even though I am not a expert on aircraft, I do know that they do not fully pressurise (to save a bit of money on making a strong cabin). This implies a level of venting to outside anyway. Fully sealing the cabin might impoise structural safety risks if systems fail in flight. Ratbone60.230.211.9 (talk) 13:03, 14 July 2012 (UTC)

It may be of benefit to explain better how breathing works. The body breaths in response to CO2 as I said. However it is oxygen that the tissues need. We have evolved a breating system that in controlling CO2 maintains blood oxygen at saturation level - that is each red cell holds all the oxygen until reaching capillaries, becasue the lungs are ventilated at a rate a little faster than saturation requires. This has the following implications for persons at rest:-

1. If the level of oxygen in the air is reduced, CO2 remaining constant, you will feel distressed quite readily. It is a situation that evolution has not provided for.

2. If the level of CO2 (normally only about 0.03% by vol) is raised, all other gasses remaining the same, you'll breath deeper, even though you don't need to, and you won't have any discomfort up to quite high levels of CO2.

3. If oxygen level is reduced while simulaneously replacing it with CO2, you'll automatically breath deeper and blood oxygen levels will remain at saturation level, up to extreme levels where a limit is imposed by finite lung capacity.

4. If you are working physically very hard, the situation changes. With reduced oxygen pressure, your lungs may not have sufficient capacity to maintain blood oxygen at saturation level.

Do not confuse low oxygen with high CO2. The effects are different.

Interestingly, flushing the lungs with pure oxygen can kill. With near zero CO2 the chest does not move, and blood oxygen level will then fall.

Ratbone58.170.170.23 (talk) 15:33, 14 July 2012 (UTC)

Let me add some clarifications (note that I didn't say that Ratbone is wrong and frequently posts wrong answers):

"Interestingly, flushing the lungs with pure oxygen can kill", but not at sufficiently reduced pressure. At a low enough pressure 100% oxygen is fine. It's the partial pressure of oxygen in the air which is important, and that depends both on the oxygen concentration and the overall pressure.

"With near zero CO2 the chest does not move, and blood oxygen level will then fall." If you mean zero CO₂ in the air, then that's not true, since it's carbon dioxide in the lungs which matters, and that is the sum of the CO₂ inhaled from the air and that produced by the body. StuRat (talk) 20:08, 14 July 2012 (UTC)

In this case, what I said is correct, and what Stu said is mostly correct. Note that I did not say flushing the lungs with CO2 will kill, I said it can kill. If the subject human is performing significant exercise, he/she will produce more CO2 and that will generally be sufficient to maintain the breathing reflex even with pure oxygen. In hospitals, the masks etc are designed so the patient never gets pure oxygen. However, astronauts during the "space race" got pure oxygen, as their metabolic rate during takeoff acceleration made it both safe and necessary - they had extreme pulse rates and were close to their limits. Why did I say Stu is mostly correct? Well, he is correct in that no CO2 in the surrounding air is not relavent, however I am not sure where in the body the CO2 sensor is, but I don't think it is the lungs. Presumably it's actually the blood CO2 level that is critical to stimulating breathing. Reducing oxygen partial pressure will not change CO2 partial pressure - therefore it seems that reducing oxygen partial pressure will not stimulate breathing and will only make things worse. Ratbone58.170.179.193 (talk) 14:06, 15 July 2012 (UTC)

In what circumstance is "With near zero CO2 the chest does not move, and blood oxygen level will then fall" a correct statement ? Where is this near zero carbon dioxide ? In the blood ? How do you figure oxygen levels would fall in the blood without carbon dioxide increasing ? That statement just makes no sense at all. Or, as you so rudely put it "you made nothing more than unsupported personal claims, which have been conclusively shown to be nonsense". StuRat (talk) 18:22, 15 July 2012 (UTC)

Middle Eastern climate

Why is the Middle East so hot and dry even in areas that aren't in a rain shadow? --146.7.96.200 (talk) 18:38, 12 July 2012 (UTC)

Much of North Africa and the Middle East was once covered in forests. These were killed in Neolithic times by slash-and-burn farmers, and the soils were destroyed by overfarming and overgrazing by goats. See Deforestation#Prehistory. See also Cedars of Lebanon for a tree which was once quite widespread in the Middle East. With the soils destroyed, little local surface water remained to support a local rain cycle. The eastern US, for example, is very far from the Gulf of Mexico and the Pacific where its weather often originates. But there is enough retained local surface water that evaporation that occurs in Pennsylvania can fall as rain in New Jersey. Iraq is not going to get much rain that originates as evaporation in Jordan. μηδείς (talk) 18:52, 12 July 2012 (UTC)

This effect is also reinforced by the fact that the Middle East is in the Horse latitudes, where large-scale atmospheric subsidence (sinking of air) caused by the Hadley circulation suppresses large-scale rainfall. It's a major reason why much of Australia is desert as well.-RunningOnBrains^(talk) 19:58, 12 July 2012 (UTC)

It's a bit lumpy, though. The Azore High (semipermanent) really hits Saragasso Sea-NW India hard with the desert stick. Parts of Eurasia east enough get a respite, though (the monsoon, nearby ocean, and Himalayan "lid" probably helps, though). Miami, Cuba, and Taiwan would be Saharic on the other coast. Sagittarian Milky Way (talk) 22:56, 12 July 2012 (UTC)

Large continents, at that latitude, will tend to be dry. Much of the change in the climate is just the continuation of a geological cycle, where we've been slowly coming out of an ice age. The forested version of the Middle East was only possible at the tail end of that ice age. StuRat (talk) 02:58, 13 July 2012 (UTC)

The difference between Joshua Tree National Park and the Negev, of Central Asia and the Iowa plains, or of the Dust Bowl and the current drought, is soil quality, not rainfall. Of course rainfall matters hugely. But without overgrazing and the loss of soil the greater Middle East would be retain water and be greener than it is today. The connection between goats and deforestation is widely remarked upon. See also our article on deforestation during the Roman period]. μηδείς (talk) 04:07, 13 July 2012 (UTC)

why are IAU constellations biased towards the West?

Why do they not include any Asian, Arabic, African or Native American constellations? The Arabs advanced astronomy while Europe lingered in the Dark Ages, yet none of their culture is credited in modern astronomy. The Chinese constellations are extensive, more so than the Greek ones. Why are modern astronomers so racist? 76.104.28.221 (talk) 20:00, 12 July 2012 (UTC)

It depends on who you listen to: In India, for example, a lot of people use the traditional names (as do I). At the end of the day, "A rose by any other name would smell as sweet". Lynch7 20:13, 12 July 2012 (UTC)

See Astronomical naming conventions#Names and boundaries of constellations. The short answer is probably that when the scientific community adopted a consistent naming system for constellations, it was dominated by 'the West'. Note that as currently defined, the entire sky is divided into constellations, and adding 'new' ones would involve redefining the boundaries of old ones. In scientific terms, constellations are arbitrary and meaningless anyway. Regarding the Arabic influence on more meaningful concepts within astronomy, the traces of it are prominent however in the naming of stars: See Aldebaran, Altair, Algol, Betelgeuse, Deneb, Rigel, Vega etc - or simply see List of Arabic star names for them all. When you look into the night sky, if a star has a recognised name at all, the name was most likely first given by a speaker of Arabic. As for the suggestion that modern astronomers are racist, I suggest you do a little research before making such unfounded assertions - astronomy is a science practised worldwide by people of all nationalities and ethnicities, contrary to the implications of your posting. AndyTheGrump (talk) 20:35, 12 July 2012 (UTC)

I strongly agree with Andy. The conventions themselves aren't racist; both the constellation names and the star names reflect the prior dominance of different cultures in the subject. AlexTiefling (talk) 21:31, 12 July 2012 (UTC)

Racist? I wasn't aware there was a constellation called Judeus Rapax or a star called Delta Labiorum Nigri. (Most major star names are in the Arabic language of course.) Perhaps the issue here is not respect for tradition but euphemism, neologism, political correctness and the narcissism of youth? μηδείς (talk) 22:09, 12 July 2012 (UTC)

As others have noted, the constellations are an anachronism, their status reflected by their anachronistic naming system that was set some centuries ago. Star names, where they are significant enough to have proper names, are almost all Arabic. Only the lesser stars that didn't warrant names have binomial Latin titles. Modern star catalogs use alphanumerical designations, which can't have "racist" connotations at all (assuming the use of the Latin alphabet and Arabic numerals is satisfactory). Acroterion (talk) 15:29, 13 July 2012 (UTC)

I'll also note that in modern times the naming of astronomical bodies has become much more diverse: Makemake (dwarf planet), Haumea (dwarf planet) and List of geological features on Titan provide examples. A Latin grammar and terminology has been retained, and since there haven't been any imperial Romans for some time, few have objected. Besides, they were running out of Roman and Greek deities, Shakespearean characters and the like. I'll also note that many features on the far side of the Moon have Russian names, since the Soviets sent the first probes that saw the far side. They therefore had dibs. Star Names: Their Lore and Meanings is an interesting read, as long as you don't take Allen's discussions of Chinese and Mesopotamian naming too seriously. See here [5] for a critique and more bibliographic material. Acroterion (talk) 15:39, 13 July 2012 (UTC)

The names of the constellations are simply traditional, not anachronistic. There's no difference between that and the names of the continents, the elements, or the days of the week for that matter. Renaming them would be ridiculous, and is the sort of things that happens when you get dictatorial regimes, such as with the French Revolutionary calendar. How often would they have to be renamed to keep current? With every new graduating regime, or every new graduating college class? Leave if open to unending RfC? μηδείς (talk) 22:46, 13 July 2012 (UTC)

Are anachronistic and traditional mutually exclusive? I didn't think he was suggesting that we update the names either, just that their use now is anachronistic (and a result of tradition). 203.27.72.5 (talk) 23:43, 13 July 2012 (UTC)

My choice of words could have been more clear: as others note, it's more like a tradition that's been maintained for an astronomical subject that nowadays has little meaning when you can just program coordinates into your telescope and have it find the feature on its own, rather than needing to recognize the patterns of the stars to find things in the night sky, so anachronism and tradition can certainly coexist. Acroterion (talk) 01:29, 14 July 2012 (UTC)

Constellations are useful for more than aiming a telescope though. Not everyone depends on constant GPS positioning to navigate. Rmhermen (talk) 04:46, 14 July 2012 (UTC)

archaism or even atavism might be closer to what I imagine you mean than anachronism. —Tamfang (talk) 05:24, 14 July 2012 (UTC)

By the way, List of Arabic star names has a lot of what looks like junk in the "Meaning" column. There's a page somewhere, isn't there, to ask for help from someone who knows Arabic to clean it up? —Tamfang (talk) 05:24, 14 July 2012 (UTC)

No, none of these other terms than tradition or convention has the appropriate sense. Anachronism is used for a representation of a more modern fact in an inappropriately ancient context, like painting Sodom as if it were a renaissance Dutch city. An atavism is an either morally or biologically primitive avatar in modern times, like cannibalism, a person born with a human tail; but there is nothing inherently primitive (as opposed to simply old) about greco-roman culture. They had republics, democracies, atomism, evolution, and everything else we have except electricity and nuclear physics. Archaism implies the intentional use of a dead form. But there is a constant tradition of greco-roman mythology in the West. This is not the adoption of some style that has been dead for centuries,, but the retention of a tradition that has been alive in film and literature as recent as Kevin Sorbo and Lucy Lawless. Everything in our language and culture has a past, even if it is Lady Gaga referencing Radio Gaga. The word the has a past. Should we make up a new language from scratch every year because it was used by our dead relatives, and is therefore from the last Saeculum? μηδείς (talk) 05:30, 15 July 2012 (UTC)

Dark Energy as the Quantum Error Correcting Code of the Universe

Given the Holographic principle and that information can not be removed from the Universe as a whole, the "boundary" of the Universe must be smooth and expanding. If there is always exactly enough Dark energy to maintain the Universe as a Flat space then the dark energy is acting as a Quantum Error Correcting Code to pad the history of the Universe onto its "boundary".

If this is correct, what sort of test could be made for the adjustment of dark energy to "fit around" the mass content of the Universe? Hcobb (talk) 23:15, 12 July 2012 (UTC)

I gather from the use of terms in quotation marks that you might be aware that the definitions of the words you are using might not be clear to readers. I am not sure of your hypothesis so I can't help you test it. 71.212.249.178 (talk) 01:07, 13 July 2012 (UTC)

Well one of your hypotheses is that space is flat. You can test that. See if a cube with a side ten times longer has a thousand times the volume. Graeme Bartlett (talk) 11:40, 13 July 2012 (UTC)

The dark energy has a constant density in all cosmological eras. It doesn't adjust to the distribution of other matter. The continued spatial flatness of the universe is a prediction of general relativity, independent of the exact nature of the mass/energy. We don't know anything about the boundary of the cosmos (except that, if you believe ΛCDM, its future boundary is a 3-sphere—but that's a spacelike surface that can't expand or otherwise change with time, and it's probably a bad idea to believe ΛCDM). Quantum error correcting codes have nothing to do with your question. -- BenRG (talk) 15:26, 13 July 2012 (UTC)

July 13

Gravitational potential energy

Hi, Potential energy#General formula gives a formula for the the gravitational potential energy of a system of two masses. What is the generalised formula for a system containing an arbitrary number of masses? 86.179.115.69 (talk) 02:16, 13 July 2012 (UTC)

The link you provided tells you how to do it; "Given this formula for U, the total potential energy of a system of n bodies is found by summing, for all ${\frac {n(n-1)}{2}}$ pairs of two bodies, the potential energy of the system of those two bodies." 203.27.72.5 (talk) 02:34, 13 July 2012 (UTC)

Oh thanks, I do apologise, I did not read far enough. 02:40, 13 July 2012 (UTC) — Preceding unsigned comment added by 86.179.115.69 (talk)

term meaning

what is the meaning of the term-'dextrocardia' ? — Preceding unsigned comment added by Akshay15628 (talk • contribs) 03:21, 13 July 2012 (UTC)

Dextrocardia might be somewhat relevant. StuRat (talk) 03:34, 13 July 2012 (UTC)

Testing for an Alzheimer's gene

This article says this: "The catch is that a genetic test for the protective mutation is illogical, since it's so rare, experts said. In order to determine if an individual has the gene, doctors wouldn't be able to detect it."

Can someone explain this to me? It seems self-contradictory. Dismas|^(talk) 04:13, 13 July 2012 (UTC)

It seems like they really messed up their writing. I suspect they meant to say something like this:

"The catch is that performing a genetic test for the protective mutation is a poor use of resources, since it's so rare." StuRat (talk) 04:21, 13 July 2012 (UTC)

The article is full of apparent typos that change the meaning of what's written e.g. "Genetic test for the gene would(n't?) make sense on account of its scarcity", "The mutation appears to slow the production of the beta-amyloid protein, which has long (been?) considered a cause of Alzheimer's.". 203.27.72.5 (talk) 04:30, 13 July 2012 (UTC)

I submitted a post telling them how bad this article is. I suggest anyone who agrees do the same, so they will clean up their act. StuRat (talk) 05:00, 13 July 2012 (UTC)

Great idea for scientists to email religious websites to ask them to clean up their act. Could take a while though. Meanwhile I would tend to avoid religious websites if I wanted reliable medical information.--Shantavira|^{feed me} 08:33, 13 July 2012 (UTC)

I've found that even web pages with a systemic bias (religious sites, politcal sites, sites trying to sell you something) tend not to be biased when talking about subjects not relevant to their bias. In this case, the existence of a particular testing method for a disease says nothing about the existence or non-existence of God, so they have no reason to intentionally use bad logic, let alone bad English. On the contrary, if they can provide excellent, unbiased articles on subject not related to their bias, this may give them more credibility on those subjects they care about most. So, I believe they will make an effort to improve their articles, if we point out the problems to them. StuRat (talk) 18:22, 13 July 2012 (UTC)

One situation where this sort of thing might make sense is when the condition is so rare that the false positive rate for the test exceeds the actual positive rate for the condition. I think there's a name for the statistical conundrum that results... Staecker (talk) 11:42, 13 July 2012 (UTC)

It's an example of a base rate fallacy, and more specifically it's the false positive paradox. Equisetum (talk | contributions) 17:14, 13 July 2012 (UTC)

To clarify, it is of course only a base rate fallacy if you fail to factor in the base rate (incidence of the mutation in this case) into the false positive rate of the test, if you do factor it in and conclude that the test isn't worth doing because of it that's the false positive paradox. The sentence of the article seems to me that it may have been written by someone who has had these concepts explained to them, but hasn't understood them. Equisetum (talk | contributions) 17:31, 13 July 2012 (UTC)

I think the main reason a test wouldn't make sense would be that the test could only predict the absence of Alzheimer's disease, so a positive result would not call for any different action than a negative result. The only value of a test would be to give some reassurance to 1% of the population. Looie496 (talk) 18:53, 13 July 2012 (UTC)

Thanks all! Dismas|^(talk) 07:24, 14 July 2012 (UTC)

Does gravity remove space?

Let's say there is a small universe that is finite but unbounded (a closed universe), and this universe is filled perfectly evenly with particles. Will gravity pull the particles together, effectively removing space and making the universe smaller, or will gravity tug equally in all directions, keeping the particles where they are and maintaining the universe's size? Goodbye Galaxy (talk) 15:13, 13 July 2012 (UTC)

I would say that it displaces space which is what a gravitational field is: the displacement of space by the massive object. The gravity is the force of the space "trying" to get back to its rightful place in the lattice. They will coalesce in the center unless there is something to keep the outer particles in equillibrium with the central ones, right?165.212.189.187 (talk) 15:19, 13 July 2012 (UTC)

Your question does not provide enough information. What are the initial conditions? Is that universe expanding? What's the density of matter? Dauto (talk) 15:29, 13 July 2012 (UTC)

Right. Let's say no dark energy, no cosmological constant. It begins completely static. Density is very light (no need to take other forces other than gravity into account). Goodbye Galaxy (talk) 15:35, 13 July 2012 (UTC)

Yes, space will get smaller. This is the big crunch scenario. -- BenRG (talk) 15:43, 13 July 2012 (UTC)

OK, in this scenario, what if you took a spaceship and travelled "out" away from the center before the gravity was strong enough to prevent it. Would the spaceship avoid the big crunch?165.212.189.187 (talk) 19:19, 13 July 2012 (UTC)

I wouldn't think so. I'm no physicist here, but I would think several things. 1) In such a universe, a spaceship couldn't exist. 2) If such a spaceship did exist for the sake of the question, I would thing that once the ship reached the terminal boundary, it's engines would no longer be operating within the laws of physics. In fact, once crossing the terminal boundary, it is possible the ship would disintegrate because the forces that construct matter would no longer apply. Just a guess. I would think that you are assisted to the edge by the gravitational pull of the outer matter in equal balance to the pull from the inner matter. As you approach the edge, the draw will become increasingly stronger as you put more cosmic matter behind you that at some point the draw toward the center will overcome any sort of thrust you could generate. So for example, if Earth is the center and the moon is the outer edge, there is a point between them where they will null each other out. As you approach the moon, it will assist you to fight the Earth's pull. But at some point once you pass the moon, it's gravity and Earth's gravity will work against you.--v/r - TP 19:59, 13 July 2012 (UTC)

So you are saying that black holes arent the only cosmic body that can have an escape velocity greater than the speed of light?? Like if you find yourself on the "wrong" side of a giant supercluster.165.212.189.187 (talk) 20:23, 13 July 2012 (UTC)

If you consider that the universe consists of black holes, wouldn't that make sense? Again, I am not at all even educated in this area, I'm just putting a little layman's logic toward the problem. Although, let's consider the possibility that you can escape gravity. Do the forces (gravity, electromagnetic, weak, and strong) exist outside of the universe? My guess is that if particles such as the Higgs Boson cannot escape gravity, then the forces that give matter mass and ultimately the force that holds matter together would not exist beyond the terminal barrier. So you'd essentially disintegrate. If you were to escape that terminal barrier, you'd fall apart atomically and the resultant matter would fall back inside of the terminal barrier. Infact, I'd make a guess that you'd get less than a nanometer outside of the terminal barrier before this happened. Or, you could even theorize that the terminal barrier is exactly where this effect would happen. So upon reaching the barrier is where your atoms would break apart and essentially turn back toward the universe.--v/r - TP 20:41, 13 July 2012 (UTC)

None of it works, 165. If you are assuming the Universe is finite, then it has no center to move away from. The "boundaries" of the universe that have been mentioned here are not things that can be physically crossed by people. To give an awful analogy, it would be like trying to escape the earth by moving far enough along its surface. Someguy1221 (talk) 20:53, 13 July 2012 (UTC)

The OP started by stating that the question was about a unbounded universe (That is one without a boundary) and then he asked if it is possible to scape such universe (That is to reach its boundary). Do you see the contradiction now? Dauto (talk) 21:12, 13 July 2012 (UTC)

I understood it as that space is unbounded but cosmic matter is. The OP is postulating a hypothetical universe here and asking what would exist beyond the expansion of the universe.--v/r - TP 21:15, 13 July 2012 (UTC)

165.* and TParis, I assume the original question was about a universe that's spatially a 3-sphere or some other shape with a finite area but no boundary, so there's nowhere to escape to. The traditional "closed universe" in cosmology is in that category. If instead you have a finite region of stationary noninteracting matter surrounded by an infinite vacuum, the matter will collapse to a black hole, but the surrounding vacuum won't go away, and you can escape to it if you start early enough. -- BenRG (talk) 21:24, 13 July 2012 (UTC)

thanks Ben that is what I meant68.83.98.40 (talk) 22:05, 14 July 2012 (UTC)

Btw. The head question does not match the example it's like two different qs.??68.83.98.40 (talk) 00:42, 15 July 2012 (UTC)

MTT assay in vivo

Important and Urgent

Hi everyone I need to urgently know if MTT assay can be applied to tumor (in vivo) samples. If yes, how? what's the procedure and are there any protocols for it?

Then I need to know what options and methods I have to study angiogenesis in my tumor sections (in vivo).

how about cell viability? how should I check that in in vivo samples?

I would greatly appreciate if you can help me with that ASAP.

Regards everyone Siq3939 (talk) 16:00, 13 July 2012 (UTC)

If this is genuinely important, you should not be relying on random people on the internet for it. If, on the other hand it is homework, you need to show that you have attempted to do it for yourself before anybody here will help you, other than pointing you to articles such as angiogenesis and MTT assay. --ColinFine (talk) 17:04, 13 July 2012 (UTC)

And if it is genuinely urgent, you should not post a request somewhere where nobody has an obligation to respond immediately. It may be important, but if it's on this page, it isn't urgent. ~Amatulić (talk) 17:55, 13 July 2012 (UTC)

It is unlikely that a color coded reagent can be used in vivo, but if you have surgical access to the tissue, why not biopsy and use the extracted tissue in vitro? 71.212.249.178 (talk) 05:20, 15 July 2012 (UTC)

mole as a fundamental SI unit

The seven SI base units and the interdependency of their definitions

Why is mole considered one of 7 fundamental SI units?Its just a number and no physical significance. — Preceding unsigned comment added by 49.244.157.192 (talk) 17:01, 13 July 2012 (UTC)

You're not the first to ask this. See Mole (unit)#The Mole as a unit. --ColinFine (talk) 17:07, 13 July 2012 (UTC)

While that section says that it is different from "fundamental units" like the meter and the second, that is actualy also up for debate. A case can be made that physics is fundamentally dimensionless and therefore there are no units at all that have any physical significance whatsoever. Count Iblis (talk) 17:53, 13 July 2012 (UTC)

I agree that the mole is not a particularly fundamental unit. And the candela isn't fundamental either. But as Count Iblis said above, A strong case can be made that none of the base units are fundamental. Dauto (talk) 18:43, 13 July 2012 (UTC)

Isn't it a derived unit? I thought it was defined as the number of ¹²C atoms in 12g of pure ¹²C, and as such requires gram to be defined so it can be derived. 203.27.72.5 (talk) 21:24, 13 July 2012 (UTC)

Actually, I think the mistake here is that the SI system includes any such notion as a "fundamental unit". The SI Units are divided into base units and derived units. The mole is considered a base unit. Looking at the definitions of the base units, most of them have other units in their definitions; meters has seconds, second has kelvins, ampere has kilograms, seconds and meters, kelvin has moles, moles has kilograms, and candela has seconds, meters and kilograms. The only one that doesn't need antoher unit in its definition is kilogram, which is defined by a prototype. I'm a bit confused myself now as to why they have to have two groupings, since the kilogram is the only truly base unit. 203.27.72.5 (talk) 21:39, 13 July 2012 (UTC)

I fail to see how seconds have Kelvins in its definition and how Kelvins have moles in its definition. Dauto (talk) 02:55, 14 July 2012 (UTC)

The definition of kelvins refers to "water". It then goes on to define what water is using an isotopic ratio stated in a molar fraction. Similarly, the definition of seconds refers to a caesium atom at 0K (ok, so you could just as easily say "at absolute zero", but apparently they choose not to and take the more confusing route). 203.27.72.5 (talk) 03:13, 14 July 2012 (UTC)

As you pointed out, zero Kelvin is independent of the definition of the Kelvin. Note as well that a mole fraction is independent of the definition of the mole because the unit cancels out from the definition (the same unit shows in both denominator and numerator of the fraction). Dauto (talk) 17:18, 15 July 2012 (UTC)

(ec)By that logic, a meter is a derived unit, as it's the distance traveled by light in 1/299,792,458 of a second, and as such requires the second to be defined. My understanding is that being a derived unit is not so much that the definition depends on other units, but the definition (and dimensionality) is wholly specified by other units. For example, a Watt is entirely equivalent in unit and dimensionality to kg⋅m2⋅s⁻³. However that fails for the mole and the meter, as although other units are involved in their definition, there's a physical reference involved (either carbon or light) which transforms both the size and the kind of the measurement being referenced. -- 205.175.124.30 (talk) 21:51, 13 July 2012 (UTC)

That makes sense, but I still don't see how ampere is then a base unit as I can't see how any physical reference is in that definition. Or is there a reference to the physical nature of current that I'm not seeing? 203.27.72.5 (talk) 22:19, 13 July 2012 (UTC)

For "the constant current that will produce an attractive force of 2 × 10^–7 newton per metre of length between two straight, parallel conductors of infinite length and negligible circular cross section placed one metre apart in a vacuum", the physical reference is the two conductors and the electromotive force between them. Granted, it's not all that realizable of a physical reference, but it's still something more than a pure mathematical manipulation of quantities, as you get with watts or newtons. Anyway, the emphasis is not so much on "physical reference", but rather on the transformation of kind. An ampere measures current, which is substantially different type of quantity than "newton per metre per metre" or any such rearrangement of the units in the definition. In contrast, a newton is a kg⋅m/s² - both in size and in quality. Force is intrinsically nothing more than a mass through an acceleration. - Note this is highly dependent on point of view of "kind". As mentioned above, one could argue that the theory of relativity means that space and time are really the same thing with the speed of light being a conversion factor. With that sort of outlook, the definition of the meter seems superfluous, and the meter is simply a non-decimal rescaling of the (light-)second. However, for most purposes we still draw a distinction between space and time (e.g. make a distinction between seconds and light-seconds), so view a space-unit to be distinct from a time-unit. -- 205.175.124.30 (talk) 23:57, 13 July 2012 (UTC)

Yes, physics can in fact be interpreted as not requiring units at all. But even if we decide not to do that, and keep the meter, Kelvin, etc... as the metric system does, there is still the fact, as the OP clearly stated, that a mol is just a number, not a physical quantity at all. Dauto (talk) 02:49, 14 July 2012 (UTC)

A mol is not just a number. Avagadro's number is just a number. A mol is an amount of particles. Just like a kilogram is an amount of mass, a meter is an amount of distance and a second is an amount of time. 203.27.72.5 (talk) 02:56, 14 July 2012 (UTC)

But an amount of particles is just a number as in "one particle", "two particles", "three particles", "one Avogadro's number of particles" (AKA one mole of particles). So yes, a mole of something is just another name for an Avogadro's number of something - not a physical unit. Dauto (talk) 17:22, 15 July 2012 (UTC)

Equivalently, a mole is the conversion-ratio between the molecular property under consideration (like mass, or electric charge), and the quantity of molecules in the sample. If we decided to standardize a unit of mass other than the gram, we would need to standardize a different Avogadro constant to count the number of particles in a sample of unit-mass. And if we decided on a unit of charge other than the coulomb, we would similarly need a different value for the conversion factor between the fundamental charge and the unit-charge. If you study the mole in the context of electrostatics, you'll see it pop up a lot in the mass to charge ratio experiments, where it's again used as a unit-conversion-factor between "bulk" charge and elementary charge; in fact, historically, electric charge measurement was the first context in which an accurate value for N_A was measured. If I recall, it was Michael Faraday who made this connection; and if you read his works, you'll find that he's notorious for using an abundance of strange units. I haven't the slightest idea how he metered out a "grain of water", let alone how he "acidulated" it. His other unit of choice was the Leyden jar. Five-eighths of an inch of zinc converts to about... 800,000 Leyden jars. I bring this up not only because it's humorous, ... but because a genius experimentalist like Faraday was able to extract fundamental physical properties, even when his experimental setup was quantified with totally arbitrarily-selected units. Nimur (talk) 17:50, 14 July 2012 (UTC)

A grain of water is pretty easy. See grain (unit). Grains are still used pretty extensively with small arms ammunition. 203.27.72.5 (talk) 20:44, 14 July 2012 (UTC)

The usefulness of knowledge of Higgs Boson etc.

Physicists have spent countless billions on colliders and other projects to confirm the existence of this boson and other particles and fields comprising the Standard Model. Earlier nuclear research up through the 1940's produced nuclear weapons, atomic power, and nuclear medicine. Has anything useful in everyday life come from this more recent research, as opposed to the earlier findings that atoms can yield energy by fission or fusion? A large body of findings in physics might well be expected to yield improved ways to generate, transmit, convert or store energy, improve transportation or communication, diagnose or treat disease, grow or preserve food, provide fresh water, make rayguns or spaceship drives or other sci-fi staples, defend against various menaces, transmit or store information, do faster computations, or do astronomy. So far, has it amounted to anything more than an interesting challenge and a lucrative career for a great many physicists? By comparison, look how quickly electricity and electromagnetism became useful in everyday life after 1800 when the Voltaic pile was announced, or how quickly we got x-rays and radio following on the work of Bequerel and Hertz in the late 19th century. Have futurists or scientists outlined even in the most general ways how any of this new science might lead to anything useful? How can a "Theory of Everything" be "Useful for Nothing" except prying more research funding from the world's taxpayers. Edison (talk) 22:15, 13 July 2012 (UTC)

A more comprehensive understanding of particle physics could send fusion research in new directions. It would take a few decades or longer before the conclusions are fully realized though. This isn't the first time that there's been a question like this on here. 203.27.72.5 (talk) 22:46, 13 July 2012 (UTC)

"By comparison, look how quickly electricity and electromagnetism became useful in everyday life after 1800 when the Voltaic pile was announced..." About 80-120 years? μηδείς (talk) 22:53, 13 July 2012 (UTC)

Electrical telegraphs were in use much earlier. 203.27.72.5 (talk) 23:01, 13 July 2012 (UTC)

Yes, there were useful electrical and electronic devices around before 1920. By 1811 Davy demonstrated the arc light. He and Faraday used electricity to isolate severl newly discovered elements. Water was decomposed in the first year. There were extremely powerful electromagnets, magnetic telegraphs, motors and generators within 40 years, with new and useful devices every decade. Is the "PET scan" and particle beam used in hospitals actually a result of the particle physics research program, as some articles touting the benefits of the LHC imply? Our article does not say it came from modern particle physics research. The positron was demonstrated in the 1930s and the cyclotron used to make the tagging chemical radioactive also dates to the 1930's. Other claims are that we will get all this spinoff from the tools they perfect to make the LHC work, like better magnets and computers. This is like "The Apollo Program gave us Tang," not a convincing argument, since a food lab could also give us Tang, a magnet lab could engineer magnets without a LHC, and IBM or equivalent are always working on faster computers for competitive purposes. "Getting us from 21st to 23rd century science" is one valid reason, but some sizzle would be nice. (Ways in with clearly understood particle physics could lead to a quantum computer the size of a candy bar, more powerful than a university supercomputer of today, costing less than an Ipod, or an electric car battery with a 500 mile range and a 10 minute recharge time, or the ability to beam power to a spacecraft engine.) Edison (talk) 23:31, 13 July 2012 (UTC)

Telegraphs were hardly "everyday" use, and that the arc light was demonstrated was of no use before electrification. Not that I expect higgsbosoning people will happen any time soon. μηδείς (talk) 00:17, 14 July 2012 (UTC)

Just because they weren't used by everyone everyday doesn't mean they didn't effect everyday life, like for example the newspapers getting information much faster and publishing it for you to read. 203.27.72.5 (talk) 00:28, 14 July 2012 (UTC)

Yes, which people on the frontier downloaded and read every morning while brewing their mail-order espresso. See the relevant articles, gotcha, and yeah, whatever. Fully half the US was electrified by...1925. Even the first transatlantic telegraph cable took til 1858. We can continue this debate in five decades. μηδείς (talk) 03:14, 14 July 2012 (UTC)

No Edison, there are no known real world applications yet for the Higgs boson. Particle physics has had a fundamental role for our understanding of the world including Cosmology, Astrophysics, Astronomy and such, but these areas of knowledge don't have many practical applications either. Nor has space exploration. Sad will be the day when we start questioning those areas of knowledge foe their lack of practical applications. Dauto (talk) 03:20, 14 July 2012 (UTC)

I hate to break it to you Dauto, but that day came the very first time a theoretical physicist asked for funding. If you want money to do something, you can't be surprised when someone asks why that thing is worth doing. 203.27.72.5 (talk) 03:34, 14 July 2012 (UTC)

"No applications yet" ignores the actual question,which dealt with identified possible benefits from all this expensive knowledge(aside from "There will be spinoff") with 10,000 bright scientists sucking up a billion dollars a year for the past and future many years. In the 1700's electrical experimenters noted that static electricity could create light, by causing a glow in an evacuated tube containing mercury vapor, and that the discharge of a Leyden jar could make a small wire incandescent before it melted (thus cueing the thoughtful reader to a future ability of electricity to provide fluorescent and incandescent light, respectively). Eighteenth century electrical researchers also noted that an insulated wire could carry information swiftly to a remote location, even though they only had static electricity's ability to attract or repel a pith ball at the remote end of the wire as a demonstration. Someone's curiosity about "Areas of knowledge" does not automatically justify billions of tax dollars, when they might be as justifiably spent on astronomy, space probes to other planets, archeology, genomics, oceanography, entomology, paleontology, , cognitive psychologyand myriad other areas of research with their own hungry scholars seeking funding. Just as Meitner's work led to the atom bombing of Japan, governments possibly envision exotic new weapons to be derived from a better understanding of particle physics ("Screw with us and we'll pop a black hole on you" or whatever) Surely somehow this expensive and hard-won knowledge might be envisioned as having some application in a few decades, by scientisis working in the field, by science writers, or by futurists. The areas of energy production, transmission, and storage as well as information storage and transformation, and computation seem like possibilities, with possible use in medical diagnosis and treatment, besides the whole sci-fi panoply of spaceship propulsion, deathrays. wormholes, etc. If one had asked a thoughtful researcher such as Faraday or Henry in the 1820's what a complete understanding of electromagnetism might produce, they might have forecast radios, motors, telegraphs, generators , and electric propulsion, rather than sputtering pompously and indignantly "HOW DARE YOU inquire as to the practical implications of research which I find interesting!" Edison (talk) 04:10, 14 July 2012 (UTC)

Did you ever play the real time strategy game Rise of Nations? In the game you can build various big structures called Wonders (just like in Age of Empires). The wonders all come with specific advantages. The Kremlin makes spies, the Statue of Liberty has economic advantages and the space program lets you see the entire map (i.e. spy satellites). But the supercollider costs a shit load and both fixes the price of goods at the market to a lowish level makes other research instantaneous. That makes no sense and I think it just reflects the fact that there are no tangible benefits to having one so they just made something up. 203.27.72.5 (talk) 04:35, 14 July 2012 (UTC)

Edison, as far as I can tell you created this thread as an excuse to soapbox, so I don't think you should sputter indignantly about other people getting on the soapbox and saying things you don't like. -- BenRG (talk) 06:03, 14 July 2012 (UTC)

Please assume good faith. It amazes me that no one has responded with any links to discussions of how a thorough knowledge of particle physics could lead to useful devices down the road. All I've seen is vilification and ridicule for daring to ask the question. Edison (talk) 20:28, 14 July 2012 (UTC)

Here's a link that might interest you. It's Peter Higgs saying that he can't think of any practical significance for the discovery of the particle that bears his name. Here are my favourite quotes; "It’s around for a very short time. It’s probably about a millionth of a millionth of a millionth of a millionth of a second. I don’t know how you apply that to anything useful," "It’s hard enough with particles which have longer life times for decay to make them useful. Some of the ones which have life times of only maybe a millionth of a second or so are used in medical applications," "How you could have an application of this thing which is very short lived, I have no idea." And yet at the same press release he apparently still said that the government is not "investing" enough money. 203.27.72.5 (talk) 23:56, 14 July 2012 (UTC)

Here is another link to an article from the University of Warwick's Knowledge Centre that says, "The investment in CERN has paid off tremendously, as developments in superconducting magnets in the LHC have led to medical applications, detector technologies have been applied to, for example, homeland security, and advances in computing and networking have become something that we all rely on in our daily lives." 203.27.72.5 (talk) 00:13, 15 July 2012 (UTC)

The basic fact is true that the high investments in particle physics have not made commensurate direct technological returns in the area of particle physics, either militarily or civilian.

But this spending was never intended to do so. The physicists like to pretend that the governments of the world spent on this money on particle physics because they discovered that knowledge was inherently valuable. (Robert R. Wilson justified Fermilab along these lines.) But this is not why the government funded this science. The US government in particular was interested in creating a "reserve labor force" of highly-trained technical people in this country — the idea was that if you train a million Ph.D.s in physics, then some large fraction of those people will be siphoned off into practical applications (nuclear reactor engineering, nuclear weapons development, rocketry, lasers, microchips, etc.) that actually are of interest. Funding big particle accelerators was a way to keep the big physicists happy and to get them to start training up large numbers of students. And the more scientists and engineers you have, the more likely that your nation is going to be the one who discovers the Next Big Thing. (We tend to see scientific discoveries as the random Einstein or Newton born into our generation, which isn't something you can really plan for, but the truth is that nearly all the normal, non-revolutionary progress in science and technology are done by just very smart people who, for whatever reason, decided not to become lawyers or bankers or doctors. The progress of science is better seen as a product of the size and funding of the scientific community rather than the number or quality of geniuses.)

It was not just about wonder weapons, of course, though those were the spur for the post-WWII and (especially) post-Sputnik boom in American physics. There are plenty of "mundane" physics advances in the Cold War period — transistors, microchips, lasers, etc. — which played an incredible role in the American war machine. (And have had side-effects for the civilian side as well. I recall seeing somewhere a graphic which traced how many of the technologies behind the iPod originated from labs doing government-funded research.) It's also much larger than the field of physics — the same pattern was applied to oceanography, for example, which is one of the great Cold War sciences that most people don't realize got almost all of its funding from defense sources and created a bank of knowledge primarily interested in topics that would be of interest to people who develop nuclear submarines.

This, anyway, is one thread of argument in the history of science (see, e.g. Chandra Mukerji, A Fragile Power: Scientists and the State, Princeton UP, 1990). The notion of the reserve labor force was at times quite explicit in US science planning. Non-coincidentally, the minute the Cold War ended, the US started to drastically reduce its support of fundamental physics, famously with the cancellation of the Superconducting Super Collider. But if you're asking, is there a wonder-weapon-style payoff to funding particle physics? Not really, not since the early Cold War/late-WWII. (Even the H-bomb, which might be a plausible candidate, owes its development less to funding of particle physics than it does computing.) But I think you're incorrect in assuming that was the goal. --Mr.98 (talk) 14:42, 14 July 2012 (UTC)

A very good answer. It keeps thousands of smart folks doing physics research, as opposed to selling insurance, or being parasites living in their parents' basements. Even if the Standard Model is as lacking in practical applications as a thorough history of 17th century snuff boxes or a debate over how many angels could dance on the head of a pin, some of the 10,000 physicists might have a serendipitous moment and come up with the device, theory, or discovery which saves the human race from disaster. Years ago, when I was interviewing for jobs, the word was that IBM wanted to hire every promising computer scientist or engineer

they could and put them to work on some harmless or promising project, because they might come up with something which would yield profits, but at least they wouldn't develop something good for a competitor. Edison (talk) 01:41, 15 July 2012 (UTC)

Also other spin offs that wouldn't(unlikely) to of been discovered without particle physics is proton therapy in the cure for cancer, as why would any think that firing high energy subatomic particles into the body would be better at killing cancer cells, and leaving healthy cells alone, would be better than medicines. If you know what you want to discover, you will only discover what you set out to discover. You will never get a paradigm shift.Dja1979 (talk) 16:09, 14 July 2012 (UTC)

Proton beam therapy sounds like a very useful technology for treating some cancers, proposed by Wilson in 1946, using the cyclotron, invented in the early 1930's. I can't see how it is a product of the billions spent since the early 1950s to find the various particles in the Standard Model. Spinoffs as the benefit sounds like the "NASA gave us Tang" pseudo-justification. Edison (talk) 01:26, 15 July 2012 (UTC)

Since the invention of agriculture, most people are free to do useless things. However, people engaging in these useless activities have to pretend that what they do is useful to get a share of the food they need to survive. Count Iblis (talk) 16:38, 14 July 2012 (UTC)

And sometimes critical scientific discoveries were made by people intending to do nothing of the sort. Transposons were discovered because Barbara McClintock wanted to know why corn sometimes had spotted kernels. RNA interference was independently discovered in plants and animals because researchers wanted to know, in the first case, if they could make prettier flowers; and in the second case why this one particular gene, lin-4, could function wh clamile being so darn tiny. Someguy1221 (talk) 02:22, 15 July 2012 (UTC)

"Keep this generation's Feynmans and Henrys in the lab, and they might happen upon something interesting and useful" is not at all a silly reason to do this basic research, along with moving us toward 23rd century science, Startrek, and all that. But I was hoping for something like "When we learn how gravity is modulated by the Higgs boson, it might be possible to build a shield against gravity." An article last year claimed that confirmation of the Higgs would "literally shake the very foundation of our understanding of the Universe we live in." How can that not have any implications whatsoever for our technology, near or far term? Quantum physics, by comparison, led to the Tunnel diode, a useful device which would not work per classical physics, and quantum physics is claimed to have promise for future powerful quantum computers. Michio Kaku has claimed that this research could shed light on antimatter engines, teleportation, and invisibility. Is this credible? How might it work? Edison (talk) 02:48, 15 July 2012 (UTC)

If in the past scientists had only studied matters where practical "payoffs" were noticeably likely before the study began, I suspect that a lot of useful discoveries would either not yet have been made or would have occurred much later than they did.

Some people and organizations in the world have enormous amounts of discretionary funds. (See for example our list of most expensive paintings which shows the fortunes that have been spent on some famous paintings). If you were one of those incredibly fortunate individuals or organizations with more money than you could spend on projects that seemed likely to have "payoffs", it might well make sense to invest some of that fortune into research which had no apparent payoff on the grounds that, given your enormous resources, the cost is negligible and, secondly, that although the potential for a "payoff" was miniscule, the possibility that a payoff if one occurred might be enormous. CBHA (talk) 03:08, 15 July 2012 (UTC)

PS I don't mean to suggest that spending huge amounts of money on art is unwise. CBHA (talk) 03:08, 15 July 2012 (UTC)

I will. Someguy1221 (talk) 03:31, 15 July 2012 (UTC)

Fair enough Someguy. For the record, I don't think it is "wise". I just did not want to get into a fruitless discussion of the point, the value of research with no apparent payoffs being a far more interesting topic to me.

To return to Edison's point, I suspect the initial explorations that became "quantum physics" were carried out without consideration of the value of devices such as tunnel diodes. Is that true? I may be hopelessly naive about this. CBHA (talk) 04:22, 16 July 2012 (UTC)

Deflecting photons with electricity or magnetism

Is it possible to change the path of electromagnetic radiation with either an electric firld or a magnetic field? i read that when a white laser passes through air that ionizes the atoms which then keep the white light from disintegrating into its composite rays. --Melab±1 ☎ 22:51, 13 July 2012 (UTC)

That's how the Large_Hadron_Collider works. It uses magnets to control the direction of photons.--v/r - TP 22:59, 13 July 2012 (UTC)

No it doesn't. It controls the path of charged particles though. 203.27.72.5 (talk) 23:02, 13 July 2012 (UTC)

Photons have no charge, so basically no it's not possible. But light does behave very strangely in the presence of a very powerful magnet. 203.27.72.5 (talk) 23:04, 13 July 2012 (UTC)

My bad, I've been reading "proton" as "photon" all over that article by mistake. Big "uh duh" moment for me right now.--v/r - TP 23:07, 13 July 2012 (UTC)

I found a previous question about the same thing and it gave this relevant reference. 203.27.72.5 (talk) 23:17, 13 July 2012 (UTC)

The effect arises due to virtual electrons, it causes non-linear corrections to Maxwell equations, see here. The effective electric permittivity tensor and magnetic permeability tensor and the index of refraction for a region of a constant magnetic field,are given here. Count Iblis (talk) 23:53, 13 July 2012 (UTC)

Does the bending of light produced by refraction have anything to do with electrcity? --Melab±1 ☎ 00:14, 14 July 2012 (UTC)

See Refractive_index#Microscopic_explanation. 203.27.72.5 (talk) 00:59, 14 July 2012 (UTC)

You can always desribe a bending effect by an effective refractive index. Light passing through a magnetic field in vacuum will bend slightly, as I pointed out above (because Maxwell's equations are not exact, there are nonlinear corrections), this can be described as if vacuum with a magnetic field is a medium with a refractive index. The formulas are given in the last link I gave above. Count Iblis (talk) 15:22, 14 July 2012 (UTC)

Why does the linearity of electromagnetism mean light cannot be bent by electric or magnetic fields, if electromagnetism was not linear what else could it be (more specific than non-linear), and if electromagnetism were non-linear how would electric or magnetic fields bend light? --Melab±1 ☎ 04:01, 14 July 2012 (UTC)

One effect of linearity is that you can just add two things and the result will be consistent eg f(a+b)=f(a)+f(b). This means that with the Maxwell's equations that if you have light doing one thing, and light doing something else, then it can also do both at once. So a light beam going left through a strong magnetic field going up, will still be a light beam going left and unaffected. However there are materials that you can introduce that can give non linear effects, eg Pockels effect, Kerr effect, and Magneto-optic Kerr effect. Graeme Bartlett (talk) 04:33, 14 July 2012 (UTC)

I know what linearity is but I do not understand how it relates to electricity or magnetism interacting with light. If light was non-linear what specfic terms exist that fall under the category of non-linearity? Quadratic? Sinusoidal? --Melab±1 ☎ 23:05, 14 July 2012 (UTC)

The early and mid 19th century researcher Michael Faraday, after documenting the conversion of electricity to magnetism and vice versa, sought a "unified field theory" tieing in light with magnetism. He found that a powerful magnetic field caused a rotation of the plane of polarization of light. Edison (talk) 04:52, 14 July 2012 (UTC)

Order of treatment in cancer

According to what order are the elements for treating cancer (amputate/operate, chemotherapy, radiotherapy) applied? I have the impression that it's normally in the order that I cite above, but don't have any source for that. OsmanRF34 (talk) 23:22, 13 July 2012 (UTC)

Completely depends on the individual case and type of cancer in question. Assuming we're only talking about solid tumors, the position of the cancer will strongly determine whether or not an operation has a high likelyhood of success. Radiation also has risks that are specific to different areas of the body. The brain is not readily damaged by radiation but is pretty difficult to operate on. In many cases all three are used to treat one cancer. Non-solid tumor cancers (like leukemia) are obviously totally different again. 203.27.72.5 (talk) 23:31, 13 July 2012 (UTC)

I know somebody who is currently in radiotherapy and is expecting surgery after the radiotherapy is over. They refused chemotherapy, but that would also have been before the surgery. --ColinFine (talk) 23:54, 13 July 2012 (UTC)

Chemo would normally come after the op too, to clear up any cells that the operation might have missed. 203.27.72.5 (talk) 23:59, 13 July 2012 (UTC)

The order in which chemo, radiation, surgery, and adjunct treatment is as much dependent on the limitations imposed by the ethics of medical trials as anything. For instance, the order in most breast cancer is: sugery, then chemo, then radition, and then adjuct hormone treatment for the following 5 years. When my wife got breast cancer in 1997, we read up on it - that was the order of treatment then, but leading researchers suspected that it would be better to do chemo first. The trouble is, surgery was in the early days the only option. Then in the 1920's they introduced radiotherapy. Trials showed that radiotherapy after surgery improved survival rates. Nobody was game to do trials before surgury, as this would put patients at risk. The same happened when chemo was invented in the late 1940's. Today, the norm for breast cancer is still operate-chemo-radiotherapy-hormone therapy. However, with bowel cancer, the operation is very complex and difficult, and up until the invention of TME & J-pouch techniques in teh 1990's very uncertain in outcome. So ethics of testing chemo first was acceptable - sure enough, it turns out that chemo and radiation given concurrently before operating is far batter. So, until recently, the norm for bowel cancer was chemo+radiation, then operate, then follow up chemo. There is no hormone treatment applicable for bowel cancer. With the development of TME operating technique, the chances in earley cancer of cancer cells remaining is very low, so it is normal to omit follow-up chemo. Whether or not operate first is also influenced by whether tumours can ve detected before they become metastatic (spreading to other parts of the body). Wickwack120.145.53.163 (talk) 04:57, 14 July 2012 (UTC)

July 14

Cognitive biases and predictions of the end of Moore's Law

Do any purely psychological explanations exist behind why the various forms and corrolaries of Moore's Law consistently continue for longer than experts predict, making it an exception to the usual optimistic bias of technology predictions? NeonMerlin 00:13, 14 July 2012 (UTC)

Are you asking why the experts are too pessimistic? Or are you asking whether Moore's Law is an illusion? I don't see how to make the question make sense if it doesn't mean one or the other. Looie496 (talk) 00:18, 14 July 2012 (UTC)

Judging by the word any I take it he means both. 203.27.72.5 (talk) 00:25, 14 July 2012 (UTC)

Because the serious limits don't start to become evident until 2016-2022? 71.212.249.178 (talk) 00:38, 14 July 2012 (UTC)

And the reason for that is intense competition pressure. To stay on top of the game, semiconductor companies continually make huge investment in research, so that each technical bottleneck is broken just in time to keep Moore's Law in place. The rate of Moore's Law is determined by the cost of research and time-to-market http://en.wikipedia.org/wiki/Time_to_market. Both are relatively constant, hence Moore's Law is fairly constant. The explanation is not psycological, its commercial. Ratbone124.182.22.24 (talk) 01:28, 14 July 2012 (UTC)

I think the point is that that's what they always say. The supposed end of Moore's law is always just around the corner when the "serious limits" start to kick in, yet in 50 odd years it's never actually happened. 203.27.72.5 (talk) 01:14, 14 July 2012 (UTC)

The optimistic bias in technological predictions is just a lack of imagination on our part. When asked to imagine what the world will look like in the future, we might say something like "cancer will no longer be a problem". If we're pressed as to how that will happen, it's usually the most obvious hyped up area of research today, like genetic thearpy or nano-robots or something like that. History has shown us that we will probably be blindsided by some unforseen breakthough and after that we'll think it was obvious and wonder why we didn't think of it sooner. We don't have the android technology seen in the 1979 film Alien, but in that film, the computers were all using a text based operating system and had tiny CRT monitors. It's easy to think of technology giving us stuff like interstellar travel and life-like robots, but thinking of the more subtle things that take incremental advances but improve our lives by so much requires more imagination than we have. The advances won't be the ones that we think they'll be, but they'll still be awesome, and that's reflected in genuine, objective measurements of technological advances, like with Moore's law. 203.27.72.5 (talk) 01:26, 14 July 2012 (UTC)

"in that film, the computers were all using a text based operating system and had tiny CRT monitors. " Not only that, but it made a sound each time a character appeared on the screen! And the speed was about 10-20 characters per second. Bubba73 ^{You talkin' to me?} 03:30, 14 July 2012 (UTC)

And no doubt the text was far larger than on any real screen. This is a common trope in movies and TV, as a person reading small, monochrome text on a screen, in silence, just isn't very interesting to watch. StuRat (talk) 04:32, 14 July 2012 (UTC)

And often the font on the screen would be OCR-A font, which makes no sense. Bubba73 ^{You talkin' to me?} 04:39, 14 July 2012 (UTC)

From memory StuRat, no it wasn't like that because it wasn't important that the viewer actually read the text, it was just lines of text scrolling over the screen much like an old execution of autoexec.bat on a 486 running windows 3.1. 203.27.72.5 (talk) 05:46, 14 July 2012 (UTC)

I can beat the Alien example. An original Outer Limits episode featured a future video phone, with a cord, and ... wait for it ... a rotary dial. :-) StuRat (talk) 02:15, 14 July 2012 (UTC)

Ha. That's hilarious. And realistically, how much has a video phone conversation changed our lives vs wireless telecommunications and reliable buttons? But no one is going to marvel at how much CGI went into making a futuristic button. Audiences wouldn't have even understood what was going on if they saw a movie that depicted the use of a modern mobile phone back when Outer limits was on TV.203.27.72.5 (talk) 02:24, 14 July 2012 (UTC)

I think they would have. After all, the Dick Tracy two-way wrist radio (introduced January 13, 1946, with video added in 1964) had buttons, going way back. StuRat (talk) 03:15, 14 July 2012 (UTC)

Did he get spammed by Jamba!, or MMS pictures of evidence to his client using the intergrated camera? Did it have a visible antenna? Did he lose reception in underground carparks, or have no coverage in a major metropolitan area? 203.27.72.5 (talk) 03:23, 14 July 2012 (UTC)

The D'Arsonval meter movement is rather funny: [6] (at the bottom). We still use that on car speedometers and gauges, though. The speaker also looks like something from a 1960's console TV. The screen does seem to use some type of flat screen technology, at least not a CRT. StuRat (talk) 04:02, 14 July 2012 (UTC)

Can Cannabis grow in the Colorado high country?

9000+ feet, Rocky Mountains. I was walking through an open meadow near a popular golf course and noticed Cannabis looking plants growing in bunches within a large circle of area. According to the rather confusing Cannabis article, "The leaves have a peculiar and diagnostic venation pattern that enables persons poorly familiar with the plant to distinguish a Cannabis leaf from unrelated species that have confusingly similar leaves (see illustration)"—first of all, what illustration?! Okay, next, the picture to the right of the paragraph sure looks like what I saw. What "unrelated species" are there that I may be confusing this with? If this is Cannabis, does that mean someone threw some seeds there as a joke or something? Thanks! Reflectionsinglass (talk) 02:58, 14 July 2012 (UTC)

Is this a real question or just a lead up to a Rocky Mountain High joke ? StuRat (talk) 03:17, 14 July 2012 (UTC)

In case it's meant as a serious Q, let me take a stab at it: Cannabis grows like a weed, hence the name. Not sure if it grows at that altitude, but, if so, maybe some hippie spilled some seeds out of his baggie, and that's all it took.

The illustration they meant was the one to the right. Here's the full-sized version: [7].

Doing some web searches, it does appear to grow at high altitudes, but 8750 feet is the highest point I saw listed explicitly. Here's a couple sites I found: [8], [9]. StuRat (talk) 04:11, 14 July 2012 (UTC)

Wild cannabis isn't that rare of a weed in NA, but no one cares because the weed version is worthless to smoke, just like the vast majority of plants we eat, plant breeders have dramatically improved the quality of cannabis that is cultivated. The "hippie" bit is uncalled for, please keep your stereotyping to yourself. Unique Ubiquitous (talk) 05:03, 14 July 2012 (UTC)

The wikipedia article must need a visit from the PC police too then, since it says that the movement is known for experimentation with drugs. 203.27.72.5 (talk) 05:37, 14 July 2012 (UTC)

Sure, but it does not follow that those who use or grow the drugs are hippies. It has never been the case that only hippies smoked pot, and the vast majority of pot smokers today are not hippies. I would be more worried that someone is intentionally growing them up there — which can be a dangerous thing to interact with depending on who is growing it. When you see a stand of marijuana growing, consider that that's somebodies money growing out there. --Mr.98 (talk) 15:15, 14 July 2012 (UTC)

Fair enough, but what's "NA". Namibia ? Netherlands Antilles ? StuRat (talk) 05:06, 14 July 2012 (UTC)

What's the reference to "grows like a weed, hence the name" about, Stu? The etymology has nothing to do with weeds, as far as I can see. -- ♬ Jack of Oz ♬ ^{[your turn]} 05:12, 14 July 2012 (UTC)

Do you not use the slang word "weed" in Australia, for cannabis ? StuRat (talk) 05:28, 14 July 2012 (UTC)

I'm pretty sure JoO is aware of the slang word, they're just saying the etymology of the slang word has nothing to do with cannabis growing like a weed. Whether or not this is true I can't say, I had trouble any reliable sources most appear to discuss othe things like the word marijuana or pot. Nil Einne (talk) 05:49, 14 July 2012 (UTC)

Sorry, of course I know it as "weed". I misinterpreted Stu's comment, which I read to mean that the name "cannabis" was from some presumably Latin or Greek word meaning "weed". My bad. But in checking out the etymology, I did discover it's cognate with the word "canvas". That had never occurred to me, but it makes a lot of sense. -- ♬ Jack of Oz ♬ ^{[your turn]} 06:24, 14 July 2012 (UTC)

NA = North America. What else, StuRat? OsmanRF34 (talk) 05:26, 14 July 2012 (UTC)

OK, a bit non-specific, though. I listed two possible more specific meanings. StuRat (talk) 05:28, 14 July 2012 (UTC)

Which of the three contains the region mentioned in the title of this section? —Tamfang (talk) 06:08, 14 July 2012 (UTC)

People often reply to questions on one part of the world with answers on how things work in their own part of the world. StuRat (talk) 06:30, 14 July 2012 (UTC)

In order that we may answer your questions within wwikipedia ref desk guidelines, please explain at the ref desk discussion board thread on this post why you cannot see the illustration in the article you searched to the right of the text you mentioned. Please upload an image there so we may help you identify the plant, although, do be aware that people have been shot for trespassing on someone's weed patch. Please explain there what evidence you have that someone has planted these plants as a joke so that we can evaluate it, rather than speculate and debate upon it. (Comment added by User:Medeis (μηδείς), who, by omitting their name, implies that their opinion is that of everyone here, when it is really only theirs. StuRat (talk) 05:09, 14 July 2012 (UTC))

From our article it appears that some people have described ditch weed as a separate species, though I haven't reviewed the evidence; whatever it is called, it was used fairly widely for routine purposes of landscaping and preventing erosion even during the early days of Prohibition. Apparently law enforcement still goes to great lengths to seek out and exterminate such plants, though they are suited for little but genuinely medicinal or perhaps textile use. Wnt (talk) 05:14, 14 July 2012 (UTC)

I do not believe it can grow there. Cannabis needs lots of warmth and light. OsmanRF34 (talk) 05:23, 14 July 2012 (UTC)

Light isn't a problem at elevation. If anything, they get more light, especially UV. Warmth could be a problem, though. StuRat (talk) 05:26, 14 July 2012 (UTC)

Perhaps I should have elaborated. "Ditch weed", according to our article, is Cannabis ruderalis, and is hardier than the other species. Wnt (talk) 11:10, 14 July 2012 (UTC)

How can law enforcement distinguish between wild useless cannabis and smokable cannabis? Do they look different enough? OsmanRF34 (talk) 05:33, 14 July 2012 (UTC)

I doubt if they bother, but just destroy anything that looks like it. StuRat (talk) 05:56, 14 July 2012 (UTC)

Cannabis sativa grows wild in the UK, and throughout Western Europe. According to my wild flowers book it is native and not introduced. I dare say it is a common escape from cultivation (hemp). It's said that the plants have little or no pharmacological content, not sure if that is because of the variety or because of the growing conditions. Illegal cultivators in the UK use greenhouses or artificial lighting. The UK police have no interest at all in wild hemp, as far as I know. Itsmejudith (talk) 17:08, 14 July 2012 (UTC)

Thanks to all the responses. The plant is growing on private property owned by a resort, which owns the golf course as well. So there's no fear of being shot. I also assume that a pot farm would look more like that scene in the film Without a Paddle, with lots of land dedicated to these plants than just the few bunches I found. I'll bring a plant inside and compare it to the photograph in the article. The way the sentence with the phrase "see illustration" is worded, I was looking for an illustration showing the different types of plants that can be confused with cannabis. I might post a photograph of these plants as well and post a link here. Reflectionsinglass (talk) 21:31, 14 July 2012 (UTC)

Question about Big Bang theory.

Transcluded from the Miscellaneous reference desk. 203.27.72.5 (talk) 06:05, 14 July 2012 (UTC)
the Big-Bang theory is telling that the universe was originated about 13.75 billion years ago from a tiny ball with infinite density and temperature when the ball blasted with a big bang. according to the theory the universe is expanding like a balloon. My questions are:-

1. where that 'tiny ball' was? kept over something? floating some where? or hanging over something?

2. where forom that 'tiny ball' came?

3. who had created that tiny ball?

4. how is it possible that a very 'tiny ball'had so much of matter that a universe of billion galaxies with billion stars are containing?

5. If the universe is expanding then there must be one starting point and one ending point or an edge, then what is there out of the edge?

— Preceding unsigned comment added by 117.201.102.48 (talk) 04:39, 14 July 2012 (UTC)

Wouldn't the Science Desk be a better place to ask science Q's like this ? StuRat (talk) 04:46, 14 July 2012 (UTC)

4) Since matter can have an infinite density, as in the singularity in a black hole, there's no reason the entire universe couldn't fit into a tiny point. StuRat (talk) 04:48, 14 July 2012 (UTC)

You might enjoy Ned Wright's cosmology tutorial.

There was probably never a time of infinity density and temperature; big bang cosmology doesn't require that, and it doesn't seem very likely. Cosmic inflation is the best known attempt to explain the origin of the initial very dense state, but there isn't enough evidence to be sure that it's right. It isn't necessary for the expanding region to have an edge, though it could. Other than that, the answer to the questions is "nobody knows (yet)". -- BenRG (talk) 06:31, 14 July 2012 (UTC)

Your questions make assumptions that the universe "before" the big bang and "outside" it have properties like the universe we know today. But depending on the particular theory, these assumptions may be false (which is why I have put those words in quotes). For example, one common theory about the Big Bang (famously presented by Stephen Hawking is that "before the Big Bang" is like "South of the South Pole". So our experience is that wherever we are on the planet there is something to the South of us; but if we go to the South Pole, our experience (our assumption) breaks down: there is no "South" there. In the same way, Hawking suggests, at the Big Bang there is no "before". On that theory, your questions 2 and 3 do not make sense, as they contain erroneous presumptions. --ColinFine (talk) 08:42, 14 July 2012 (UTC)

(ec) I thought the idea was that since all of space was contained within the big bang--there was no "place" outside it. So it makes no sense to ask "where" it happened. It happened "everywhere". Isn't this supposedly why the Cosmic microwave background radiation is found everywhere? And, perhaps I'm wrong, but isn't the big bang also supposed to be the origin of time itself? If so it would make no sense to ask about "before" or "what caused" it, right? Pfly (talk) 08:45, 14 July 2012 (UTC)

(5) An expansion does not imply that there will not be a contraction. In other words, the expansion may go on forever - or it may not. It may contract. It may oscillate between expansion and contraction. We simply don't know. Our universe may be a bubble in an even bigger universe - or it may not. I'm reminded of one of Haldane's quotes: "The universe is not only stranger than we imagine, it is stranger than we can imagine". We can gather information and see what that information leads us to, but to suggest that we know the answers to your questions is arrogant at this point in time. Doesn't stop us theorising, of course, and shouldn't stop you asking! --TammyMoet (talk) 08:53, 14 July 2012 (UTC)

Blood test after getting infected by HIV....

I had only oral sex with a prostitute before 3 months but now I fear that it might have infected me from HIV as I had some rashes on my genitals and perhaps she also had bleeding gums........ Now I want to clear my doubt that either I got infected or not. I heard somewhere that HIV will not show up in blood test so early after getting infected, so what is right time for blood test. — Preceding unsigned comment added by 14.140.235.82 (talk) 06:19, 14 July 2012 (UTC)

Wikipedia does not give medical advice. See a doctor, or other appropriate medical practitioner. AndyTheGrump (talk) 06:22, 14 July 2012 (UTC)

See a physician. If you can not afford a physician, is there a free clinic in your area? Furthermore, Diagnosis of HIV/AIDS#Rapid or point-of-care tests also does not constitute medical advice. 71.212.249.178 (talk) 06:33, 14 July 2012 (UTC)

The OP has not asked for medical advice regarding us diagnosing or treating his condition. He has asked how soon a positive HIV test shows up after infection. The answer is that it may take very little time or more than a year. See HIV_test#Window_period. μηδείς (talk) 05:39, 15 July 2012 (UTC)

I agree with your interpretation, but that article says more than six months is extremely rare. Diagnosis of HIV/AIDS#Window period has more detail. 71.212.249.178 (talk) 22:14, 15 July 2012 (UTC)

See a doctor as soon as possible, how long you have to wait before HIV is detectable is completely irrelavant if you are already presenting symptoms. Time is of the essence, the sooner you get yourself diagnosed and treated the better. Vespine (talk) 22:55, 15 July 2012 (UTC)

Do Sounds Played at the Same Time Add?

If you play two sounds at the same time will the resulting sound wave be the sum of the two individual ones? I'm guessing no since a sound wave that is a constant would not sound like anything and you can add two sine waves to get this. Then again, going from the graph of a sound wave to what it sounds like has always been a point of confusion for me. Thank you for any help:-) 209.252.235.206 (talk) 09:02, 14 July 2012 (UTC)

Yes, they add (the wave equation governing sounds is a linear equation). You can have cancellation of sound waves (for example when you hear a beat). —Kusma (t·c) 09:09, 14 July 2012 (UTC)

Yes, if they are exactly the same sounds, in phase with each other, and both arrive at the listener at the same time, then, as you said "the sine waves will add". However, if they are out of phase, either from being produced at slightly different times, or being at different distances from the listener, they can actually cancel each other out (see noise cancellation). Note that when they do add, twice the amplitude of sound wave does not mean it's twice as loud. See decibel. StuRat (talk) 09:13, 14 July 2012 (UTC)

Thank you very much:-) 209.252.235.206 (talk) 09:39, 14 July 2012 (UTC)

You're welcome. I will mark this Q resolved. StuRat (talk) 09:59, 14 July 2012 (UTC)

Resolved

You marked it resolved prematurely, Stu. You have repeated a common fallacy. Consider two independent sound sources (meaning each has its own arbitary waveform and phase): One sound source imparts x watts of acoustic power to the environment and the other y watts. Since energy cannot be created or destoyed, there is x+y watts of acoustic power in the environment. However, the amplitude [the amount of air displacement, or the distance a freely suspended surface (a la a microphone diapham or an eardrum) will move] is proportional to the square root of the acoustic power, just as the voltage in an electric device is proportional to the square root of the power. Two sound sources being indentical in all respects except being out of phase cannot just cancel, as this would mean energy destroyed. What happens is cancellation occurs in some directions and reinforces to double strength in others, the directions being a function of the spacing and phase of the two sources. In other words, the sound becomes directional - analogous to the common use in radio broadcasting to use two or more carefully spaced antennas to provide directional coverage. This principle is also used in concert sound reinforcement - indentical loudspeakers fed with indentical program are "stacked" to beam the sound into the audience and not waste it to the sky. Complete cancellation can only occur if the two sound sources occupy the exact same point in space - a rather theoretical concept. Ratbone121.215.69.8 (talk) 10:12, 14 July 2012 (UTC)

That's consistent with what I said, where I mentioned them both adding and cancelling, listing cancelling due to "being at different distances from the listener". Obviously the two sources wouldn't be at different distances from all possible listeners, and there the sounds don't cancel. The noise cancellation article I linked to explains the details. As for the math, I linked to the decibel article, which explains the relationships between power level, volume, etc. StuRat (talk) 10:24, 14 July 2012 (UTC)

Transcluded to Ratbone's now created talk page. 203.27.72.5 (talk) 11:09, 14 July 2012 (UTC)

BTW, since you misspelled it 3 times in your post, let me point out that it's "identical" not "indentical". StuRat (talk) 10:24, 14 July 2012 (UTC)

You should know by now, Stu, that I do lnkow how to spoll, but I am a shockinkg typist. Ratbone121.215.29.47 (talk) 12:20, 14 July 2012 (UTC)

Either there's an error in your logic or you just weren't clear on what you meant Ratbone, but where you said "Two sound sources being indentical in all respects except being out of phase cannot just cancel, as this would mean energy destroyed" it sounds like you're saying that being in phase is an intrinsic property of the two sound sources. It's not the sources, but rather the waves that are either in or out of phase, and that depends on the location i.e. they're in phase at point A, out of phase at point C, and somewhere in the middle at point B. 203.27.72.5 (talk) 10:29, 14 July 2012 (UTC)

This is probably just a comment on my english, but the wording I used is entirely standard in electronics and acoustics. Engineers talk of sources being "in phase", "out of phase" etc, without implying that waves will be the same relative phase everywhere in space, a phenomena which you have clearly appreciated. Ratbone121.215.29.47 (talk) 12:20, 14 July 2012 (UTC)

Ah, yes, well I'm not an accoustics engineer, so I wouldn't know about their standard technical jargon. Thanks for clearing that for me. 203.27.72.5 (talk) 13:06, 14 July 2012 (UTC)

"Two sound sources being indentical in all respects except being out of phase cannot just cancel, as this would mean energy destroyed": well, they'd have to be in exactly the same place, and the energy will be zero at all times since no wave is actually emitted. —Kusma (t·c) 10:33, 14 July 2012 (UTC)

Correct. Ratbone121.215.29.47 (talk) 12:20, 14 July 2012 (UTC)

Two sources producing the same sounds in phase would be indentical, 180^o out of phase, outdentical. Everything else would be inbetweenical. Clarityfiend (talk) 22:37, 14 July 2012 (UTC)

Back to the OP's question, yes, the sound wave will be the sum of the component waves at the point considered. But the perceived sound will depend on the context and history, see Helmholtz's On the Sensations of Tone as a Physiological Basis for the Theory of Music. μηδείς (talk) 05:49, 15 July 2012 (UTC)

Black Holes and Dark Energy/Matter

If I'm not mistaken, I believe that the existence of black holes was early in the 20th century without the involvement of either dark energy or dark matter. Likewise, the more recent 'proof' that black holes actually exist (based on the velocity of stars orbiting around the unseen black hole) is not dependent on dark matter or energy either.

How does the existence of dark energy and dark matter effect our understanding of black holes?Honeyman2010 (talk) 11:01, 14 July 2012 (UTC)

There is theory about objects called MACHOs that could include black holes and is meant to explain dark matter. It's essentially been disproven though. Dark matter and black holes are believed to be unrelated. 203.27.72.5 (talk) 11:06, 14 July 2012 (UTC)

Agreed; there is no close relation or connection between the three concepts. Black holes were known to be a theoretical consequence of general relativity long before any evidence of their actual existence was found, and indeed the observational evidence for black holes is still somewhat indirect and not totally conclusive. Dark matter and dark energy are names for possible mechanisms explaining puzzling astronomical observations (the galaxy rotation problem and the accelerating universe respectively), but the details of these mechanisms are not completely understood. The similarity in names, each involving black/dark, is partly coincidence and partly lack of imagination on the part of physicists/cosmologists. Gandalf61 (talk) 11:23, 14 July 2012 (UTC)

Thanks for the answers, but my confusion does not stem from the similarity of the words "black" and "dark". My question seems logical since black holes represent infinite gravity, and dark matter and dark energy are thought to comprise perhaps 80% of the matter in the universe. Surely some interaction cannot be so summarily dismissed. Also, would the recent discovery of the Higgs (a scalar) and dark energy (thought to be a scalar) not suggest the possibility of a link? And, finally, if Unification is ever realized through String Theory (perhaps pushed along now with the Higgs), or some other preocess, would that bear on my question? Thanks Honeyman2010 (talk) 12:16, 14 July 2012 (UTC)

The article on MACHOs explains why it is unlikely that dark matter has anything to do with black holes. Also, you should read the article on black holes, as you seem to have some misconceptions about them. They do not have infinite gravity. According to general relativity they contain a point called a singularity that has infinite density. Their mass is finite and they may have other characteristics that define them (see no hair theorem). 203.27.72.5 (talk) 12:44, 14 July 2012 (UTC)

Please see Talk:Dark matter#Draft table. 71.212.249.178 (talk) 21:51, 14 July 2012 (UTC)

Polyvinyl fluoride and PubChem name. A little confusion.

Hello, I looked up polyvinyl fluoride in PubChem Compound and got struck. For polymers, PubChem Compound shows only the monomers. However in this case it shows fluoroacetylene instead of fluoroethylene. (i.e; fluoroethyne instead of fluoroethene). Why? And in Pubchem Substance, it is more confusing to me. Can you help me please? Your comments are always welcome. They have got it almost right for polyvinyl chloride. (For reference you may look CAS and CHEBI:)Vanischenu m^Talk 12:34, 14 July 2012 (UTC)

I don't think the answer is too exciting. It looks like they're just plain old wrong. Should be an alkene, not an alkyne. 203.27.72.5 (talk) 13:01, 14 July 2012 (UTC)

It's quite unfortunate that this occurred at a trusted site. Thank you for your kind reply. I will mark this question as resolved then.

Resolved

Vanischenu m^Talk 19:26, 14 July 2012 (UTC)

Genetic difference between Africans

Is it true that the genetic difference between two different ethnic groups in Africa like say the Hutu and the Zulu people is comparable or even greater than the genetic difference between a given black guy and a given white guy? ScienceApe (talk) 16:07, 14 July 2012 (UTC)

I found this:

Interestingly, both autosomal and X-linked sequence data show higher DNA variation within Africans than between Africans and Eurasians, contrary to the general observation of lower within-population than between-population differences in population genetics. This finding implies that Africans differ on average more among themselves than from Eurasians. Thus, with the exception of many minor unique variants, the nucleotide diversity in Eurasians is essentially a subset of that in Africans, as suggested by the observation that both Y-linked and autosomal haplotypes found outside of Africa were often a subset of the collection of haplotypes found in Africa. Our finding is more in agreement with the out of Africa model of human evolution than with the multiregional model because it is consistent with the view that modern humans originated in Africa and that a smaller subset of this population later migrated to other parts of the world. During and after the migration some variants would have been lost and, as the separation time is still short, non-Africans have not yet acquired many high-frequency variants, though they might have derived some variants from indigenous archaic populations in Asia and Europe. For these reasons, the genetic differences between non-Africans and Africans are on average smaller than the genetic differences within Africans.
(Yu et al. (2002). "Larger Genetic Differences Within Africans Than Between Africans and Eurasians". Genetics. 161, 269-274)

Which basically means yes. I don't know specifically about Hutu or Zulu genetic differences, but the latter study includes several Bantu peoples (of which the Hutu are genetically very close to) and the Zulu people. However, it also includes the !Kung, which belong to the Khoisan-speaking peoples; and two of the African pygymy peoples, the Aka of the Mbenga group and an unspecified member of the Mbuti group. The latter peoples are the most genetically diverse of the human populations on the planet, so depending on what you mean by "African" it can be skewed one way or another. Most people tend to separate the Khoisan group and the pygmies from other African populations, which in turn are separated from the more recent ethnic Arabs in North Africa (not included in study). Also note that "Eurasians" in this case refers to European (both Western and Eastern) and Middle Eastern human populations, though the sample group for them is composed purely of Europeans.-- OBSIDIAN†SOUL 17:29, 14 July 2012 (UTC)

This should not be surprising, under the the recent African origin of modern humans theory. (It is only surprising if you are fooled into thinking that superficial differences like skin color, hair type, and eye folds are actually indicative of deep genetic differences.) Imagine Africa as a big pool of genetic diversity. Spurs are flung out of it relatively recently in human history. These spurs migrate all over the place. But they are still just spurs of some initial African population — by and large, the initial Africans stay in Africa. So there would still be more diversity there than elsewhere. See also, Founder effect: populations that leave necessarily have less genetic diversity than the place they left. Such is my quite lay understanding of it, anyway. --Mr.98 (talk) 17:36, 14 July 2012 (UTC)

On an interesting note, given the historic trends of racism. The non-African population genetically closest to African populations are Eurasians. The farthest are the dark-skinned and curly-haired Melanesian Oceanians and Australian Aborigines. Just goes to show how phenotypes can be quite misleading.-- OBSIDIAN†SOUL 17:40, 14 July 2012 (UTC)

On the example of Hutu and Zulu, both groups have origins in the Bantu expansion, so that might not be the best example to use. Of course the genetic difference between two individuals depends on the specific individuals. "A given black guy and a given white guy" is too vague to be very meaningful. Pfly (talk) 03:34, 15 July 2012 (UTC)

Name for numbers in chemical notation?

Is there an overarching, dedicated name for the numbers in chemical notation indicating quantity of atoms in a molecule. For example it would refer to the numbers, collectively as a class, in water and ozone: the 2 in H₂O, and the 3 in O₃?--108.46.98.134 (talk) 16:47, 14 July 2012 (UTC)

I just looked quickly at some of our articles on formulas. They don't seem to name them though. They are just a ratio of the moles of the elements I think. Scholars may have named them at one point. If they haven't then I move that they be called 'Canoe ratio integers'.--Canoe1967 (talk) 17:50, 14 July 2012 (UTC)

Chemical formula is one link. There are more links in the article.--Canoe1967 (talk) 18:02, 14 July 2012 (UTC)

Ha! It feels like they should have a name. I want to use it in a sentence in something I am writing but I can make do. However, I'll check back for further answers.--108.46.98.134 (talk) 18:02, 14 July 2012 (UTC)

Stoichiometric_coefficient#Stoichiometric_coefficient seems to be it. I was wrong as usual.--Canoe1967 (talk) 18:04, 14 July 2012 (UTC)

Nope. That is the big number in front to count the number of molecules in a reaction.--Canoe1967 (talk) 18:09, 14 July 2012 (UTC)

Maybe not but "stoichiometric" is a great word to know.--108.46.98.134 (talk) 18:18, 14 July 2012 (UTC)

I think the numbers (and symbols) surrounding chemical symbols are informally known as "indices" (sing. "index", of course). See this. The number specifying the number of atoms of an element seems to be rather unimaginatively known as the "right subscript" from its relative position (see Chemical symbol).

Then there's also the Greek numerical prefixes (which must be differentiated from the Latin numerical prefixes used for temporarily naming new elements), mono-, di-, tri-, tetra-, penta-, etc. (e.g. H₂O (water) is dihydrogen monoxide; O₂ (molecular oxygen) is dioxygen; O₃ (ozone) is trioxygen)

And lastly, there's the terms monatomic, diatomic, triatomic, etc. But these refer to the number of atoms in a molecule, not the number of atoms of an element in a molecule (e.g. H₂O is triatomic, so is CO₂)-- OBSIDIAN†SOUL 18:25, 14 July 2012 (UTC)

Could it safely be called the 'proportional integer suffix' type thing?--Canoe1967 (talk) 18:33, 14 July 2012 (UTC)

A single Oxygen atom is roughly more than twice the radius of a Hydrogen atom. And Hydrogen is 1/16th the relative atomic mass of Oxygen of course... so "proportional" doesn't exactly fit. :P How about just "number of atoms of an element in a molecule", heh.-- OBSIDIAN†SOUL 18:52, 14 July 2012 (UTC)

'quantitative integer suffix'? I am just trying to think of a ten dollar phrase for a 2 bit number is all.--Canoe1967 (talk) 19:00, 14 July 2012 (UTC)

What's wrong with just calling it the "subscript" ? StuRat (talk) 19:05, 14 July 2012 (UTC)

I was assuming the OP wanted a fancier term is all.--Canoe1967 (talk) 19:47, 14 July 2012 (UTC)

"atomic quantity subscripts" 71.212.249.178 (talk) 21:53, 14 July 2012 (UTC)

Even IUPAC called it just as subscripts at the very sacred Golden book, the Gold Book (online version). See empirical formula. You will be disappointed to see molecular formula.
Simply, it represents the number of an atom or a species in one molecule of the compound under consideration. This is really an amazing question! Vanischenu m^Talk 23:48, 14 July 2012 (UTC)

Our Chemical formula calls them quantity subscripts. 71.212.249.178 (talk) 02:33, 15 July 2012 (UTC)

Making graphite out of wood

How can you make it? Is that technically too difficult? What happens to wood if you just put a lot of pressure into it? OsmanRF34 (talk) 17:35, 14 July 2012 (UTC)

Can you make graphite out of wood? You can certainly make charcoal out of wood, which is another form of carbon, but isn't strictly speaking graphite. Synthetic graphite is not made from wood. --Mr.98 (talk) 17:44, 14 July 2012 (UTC)

Graphite#Uses_of_synthetic_graphite has methods. That is a sub-section of the graphite article above. I would think it is more a matter of cost than difficulty. They may use it to get purer forms as well.--Canoe1967 (talk) 17:57, 14 July 2012 (UTC)

My reading of that section led me to conclude that synthetic graphite is made of Silicon carbide, not wood. --Mr.98 (talk) 18:20, 14 July 2012 (UTC)

The natural creation section says "....a result of the reduction of sedimentary carbon compounds during metamorphism." I would assume some of that was wood. It could possibly be made from wood in a lab but would probably involve more steps?--Canoe1967 (talk) 18:43, 14 July 2012 (UTC)

Right, but doesn't that probably take like millions of years? --Mr.98 (talk) 19:36, 14 July 2012 (UTC)

Yes it would probably have to be a generation lab then?--Canoe1967 (talk) 19:50, 14 July 2012 (UTC)

Wood is a very complex substance made largely of cellulose, a sugar, when dry. Charcoal is what is made be heating wood in a reducing environment, not graphite, which is made of sheets of carbon, not amorphous carbon. μηδείς (talk) 02:19, 15 July 2012 (UTC)

When I was about 10, I was given a chemistry set (something you don't see nowadays). This led me, as it did with a lot of boys, to figure out how to make gunpowder and other sorts of explosives. I aslo had a burner that used alchohol as a fuel, burning it via a wick. I found that placing a cold plate (thin pice of metal) in the top part of the flame produced copious quantities of very pure graphite in powder form adhering to the cold plate. It works on test tubes containing water too. Keit58.169.240.198 (talk) 02:16, 15 July 2012 (UTC)

That's called soot. It's not graphite. μηδείς (talk) 02:51, 15 July 2012 (UTC)

Actually, your method (or the approximate reaction scheme behind it anyway) sounds like what these researchers are doing. 203.27.72.5 (talk) 02:50, 15 July 2012 (UTC)

Well, there you go; you could make graphite from wood by first destructively distilling it to make wood alcohol, burning it and reducing the hot CO/CO₂ with a metal. Not too efficient, but there you go. 203.27.72.5 (talk) 02:27, 15 July 2012 (UTC)

Hey wait, I didn't read that part about it working on (presumably glass) test tubes. Medeis is right. It was just soot. 203.27.72.5 (talk) 03:17, 15 July 2012 (UTC)

Yes, the black stuff on the cold plate is soot. But what is soot? In this case, almost entirely carbon with a bit of hydrocarbon. Not the same as soot from other sources such as wood. What's carbon precipitated when not heated to sublimation? Why, graphite! Keit121.221.5.163 (talk) 04:02, 15 July 2012 (UTC)

What is soot, you ask? Well, it's a mixture of hydrocarbons and amorphous carbon. Amorphous carbon is a bit of a misnomer because it's actually a mixture of graphitic and diamond-like carbon. There's no reason to think that the soot you made when you were 10 had a particularly high graphite content. Why do you think the hydrocarbon and diamond-like carbon content was low? 203.27.72.5 (talk) 04:49, 15 July 2012 (UTC)

Why did I think it had no significant hydrocarbon? - because it was a dry powder with no smell. While amorphous carbon produced by other means may have traces or significant amounts of diamond-like material, anything diamond like from this source doesn't sound very likely. Amorphous carbon is relatively quite reactive compared to graphite - the stuff I made behaved as I expected it to. Keit60.230.195.6 (talk) 13:44, 15 July 2012 (UTC)

You could just make charcoal as per above and then heat that to ~3000°C to make graphite, as is mentioned under Graphite#Electrodes. 203.27.72.5 (talk) 03:20, 15 July 2012 (UTC)

How to get graphite out of wood: Buy a bunch of pencils, split them open, and take out the graphite "leads". :-) StuRat (talk) 02:35, 15 July 2012 (UTC)

Nope - that's part graphite and part clay. Keit121.221.5.163 (talk) 04:02, 15 July 2012 (UTC)

Do algae like or even need darkness once in a while?

If algae (in my case I'm very interested in growing Spirulina) are grown in a Photobioreactor using artificial light instead of direct sunlight, it seems obvious you'd have the highest yield when the light is always on. Evolutionary, though, algae are used to having at least a few hours of "rest" during the night. If you'd supply 24/7 light, could you be halting some important processes from happening? Joepnl (talk) 21:15, 14 July 2012 (UTC)

Yes and no. Please see photosynthesis. 71.212.249.178 (talk) 21:57, 14 July 2012 (UTC)

Judging by how close to the poles algae are known to thrive, I think the assumption that in nature they wouldn't be exposed to light 24/7 is incorrect. 203.27.72.5 (talk) 22:17, 14 July 2012 (UTC)

Ok, some algae (or may be all) possibly like 24/7 light. But to be more precise: I'm only referring to algae (like Spirulina) that only survive in high temperature areas and so have had millions of years of being able to "sleep" at least 6 hours a day and possibly have developed some good or even vital use for that period.

@71.212.249.178 from that article I can't see the reason why algae would or could need darkness? Joepnl (talk) 22:49, 14 July 2012 (UTC)

I was guessing yes on "like" and no on "need" for the tropical varieties you are interested in, but μηδείς's answer below is better, especially if you judge "like" strictly by growth rate. 24/7 sunlight for tropical algae isn't likely to cause enough metabolic stress on them to make their growth rate much less than twice that of 12 hours per day sunlight. 71.212.249.178 (talk) 02:25, 15 July 2012 (UTC)

Some higher plants need a period of darkness or red light to bloom. See photoperiodicity. There are photosynthetic reactions that proceed in the dark, see dark reactions. I am unaware of any metabolic need for darkness. μηδείς (talk)

dark reactions: "Despite its name, this process occurs only when light is available." photoperiodicity is about seasons whereas growing algae is about "seasons" with a duration of perhaps 24 hours or even less. What I'm looking for is research that says "Spirulina (dietary supplement) contains a lot less beta-carotene in a 24/7 light situation, compared to Spirulina that had 20 minutes / hour darkness. Joepnl (talk) 13:18, 15 July 2012 (UTC)

Are you implying that you believe this to be true because you have come across it before, and are looking for help finding a ref you know exists? μηδείς (talk) 16:42, 15 July 2012 (UTC)

Sorry, that was a bit unclear. I was trying to give an example of what kind of conclusion might come from such research, but I don't know if it has been done or did get to a conclusion like that. I can just very well imagine that algae use daylight to gather as much energy as possible, and switch to making complicated molecules during the night. If it's always "day", they might not make that switch resulting in a worse end product. My new hobby is to grow Spirulina, using artificial light, and I obviously don't want to torture the poor cells :) Joepnl (talk) 17:37, 15 July 2012 (UTC)

What color skin did the earliest humans have?

I know of the theory stating that ancient humans migrated out of Africa, but there's something about it I don't quite understand. Would the earliest humans have had black or white skin? I'm just trying to figure out if Europeans descended from black humans, or if the black skin tone was something that evolved later in Africans to cope with the sunlight. I'm just trying to understand this better. Thank you for any and all information. InforManiac (talk) 23:18, 14 July 2012 (UTC)

Black skin would have come first, as this is important to living in Africa, or any place with bright sunlight, without getting skin cancer (clothes, hats, sunscreen, and spending most of our time indoors now serve that purpose). Europeans and (north) Asians later developed lighter skin, since, with less sunlight, skin cancer was less of a concern, and lack of UV light to synthesize vitamin D became more of an issue (vitamin D supplements now lessen this concern). StuRat (talk) 23:22, 14 July 2012 (UTC)

Thank you. That's kind of what I assumed, but I just wanted to double check. Thanks again. InforManiac (talk) 23:25, 14 July 2012 (UTC)

OK, I will mark this Q resolved. StuRat (talk) 23:27, 14 July 2012 (UTC)

Actually, the idea that skin color derived as an adaptation to protect against sunlight is an outdated but still common misconception held in increasingly low regard by researchers. Rather, like most phenotypical variation between the races, it is believed to have been (at least much more) the result of sexual selection, rather than natural selection. However, Stu is correct that the original Homo Sapiens sapiens were dark skinned. For the OP, I know of a couple of very good resources on this subject (and the general outwardly physical divergences of the races that are very accessible to even non-experts, if you're interested. Note: I've removed the resolved tag since I do not believe an accurate and full answer was given and expect further discussion to be forthcoming. Snow (talk) 00:28, 15 July 2012 (UTC)

I don't understand. Why would people in tropical climates prefer dark-skinned mates, people in temperate climates prefer medium-skinned mates, and people in arctic climates prefer light-skinned mates ? StuRat (talk) 00:58, 15 July 2012 (UTC)

They don't; it's an incremental process; people tend to prefer (but not necessarily to exclusion) mates who look like those they grew up around. This does not just apply to skin color; when you look at married couples, you find they tend to have very similar characteristics in the shape and relative size of many facial features which are counter-intuitive when you look at the overall span of human variation (things like the length of the earlobe, the width of the bridge of the nose, ect.). This and a whole ton of other well evidenced mechanisms have led a strong consensus that the differentiation of light-skinned people (and different phenotypes in general) started from random mutations (as all adaptions do, whether based in natural or sexual selection) which developed slowly thereafter. That's a cursory explanation that needs a lot more extension, I know, and I hate to bring it up and then dash out just when I got your curiosity up, but as I'm short on time and it will have to wait until later -- will comment further by tomorrow at latest, my apologies! Snow (talk) 01:16, 15 July 2012 (UTC)

That seems to just be saying that people with ancestors in hot climates having dark skin and those in cold climates having white skin is complete coincidence. That's not a very compelling argument. StuRat (talk) 02:14, 15 July 2012 (UTC)

No Snow, that's incorrect, StuRat is right. Melanin which is the pigment that produces dark skin, is well known to protect against UV radiation. ScienceApe (talk) 21:40, 15 July 2012 (UTC)

comment: The primary driving factor for dark skin was probably not skin cancer, which likely wouldn't affect you until after you had children, but the fact that UV destroys folic acid (vitamin B9) in the blood, leading to spinal bifida in pregnant women. That is, an inappropriate level of melanin in either direction leads to deformities in children.

Also, chimps have pale or at least blotchy skin. Black skin wouldn't be necessary as long as we had hair or lived in the forest, but the earliest common ancestor to humans most likely did not live in the forest, and was very likely much less hairy than modern Europeans. — kwami (talk) 23:53, 14 July 2012 (UTC)

Why would the earliest common ancestor to humans be "very likely much less hairy than modern Europeans" ? --Demiurge1000 (talk) 00:50, 15 July 2012 (UTC)

See aquatic ape hypothesis. 203.27.72.5 (talk) 01:25, 15 July 2012 (UTC)

Europeans seem to be an outlier. Looking across the most divergent genetic lineages, most have very little body hair. The other famous outlier are the Ainu, also a northern (= cold, and not the environment of our common ancestors) people. — kwami (talk) 02:49, 15 July 2012 (UTC)

The primary driving factor for dark skin was its protective properties against UV radiation which cause skin cancer and other diseases. What you're saying is true, but it seems likely that it was a combination of factors. Suffice to say, having light skin in Africa and other sunny environments confers no benefit and is harmful, thus would be selected against. Aside from our head, human hair is too fine to provide much protection from the UV light on the rest of our bodies. Human populations in Africa lived in a multitude of environments, forests, deserts, jungles. It seems fairly obvious that they had dark skin. Our non-sapiens (homo) ancestors probably had dark skin as well. ScienceApe (talk) 22:04, 15 July 2012 (UTC)

I don't think this can be answered without speculation. No harm in that, so long as what is written comes from good scientific thinking, and preferably excellent sources. Has this been studied and written about by notable, suitably qualified anthropologists or similar? We also need to moderate the original question, and suggest that black and white are not the only, diametrically opposed options. There's a lot of other shades out there. HiLo48 (talk)

Of course there a lot of other shades out there. I'm just trying to figure out, generally speaking, how humanity's skin tone started and where along the line things changed. I mean, when humanity was starting in Africa, was skin tone dark and subsequently got lighter in other areas? Or did humanity's skin start out lighter, but got darker in Africa as time progressed? I thought StuRat provided me with a good answer, and I still think his answer maybe very good. I am a little confused by the conflicting opinions though. In regards to the other shades that you mentioned, File:Homo_heidelbergensis_(10233446).jpg is one of them. I just want to get a loose understanding of what happened. InforManiac (talk) 03:47, 15 July 2012 (UTC)

As far as accessible and widely well-regarded sources go, Jared Diamond wrote extensively on this subject matter in the The Third Chimpanzee, I seem to recall. That's an excellent book, by the way, that I recommend to anyone who is looking for a primer on early human prehistory and development, especially as regards animal precursors to our uniquely human traits and our later differentiations as a species. As for more technical sources, I will add some a bit later, as well as a deeper discussion of why the "trait that evolved to protect against sunlight" hypothesis is considered dubious by contemporary researchers -- would do it now but afraid I'm just out the door! Snow (talk) 00:54, 15 July 2012 (UTC)

One bad case of sunburn in Africa would make you lion fodder. The evolution of pale skin, blond hair, and blue eyes can be attributed to sexual selection. There is a pretty universal trend for females to be paler than males. μηδείς (talk) 02:13, 15 July 2012 (UTC)

Dark skin in a sunless climate causes rickets. That's a strong selective force. Since we tan, you wouldn't get bad sunburn in Africa with pale skin, you'd just get really leathery as you age. AFAIK, the preference for pale skin is a product of hierarchical societies, and presumably would not apply to foraging populations like our common ancestors: pale skin means you spend time indoors and therefore have not had a peasant's life of outdoor labor. (Men don't want to be dark for the same reason; ditto the preference for long fingernails.) I'd like to see a study that women are actually paler than men, accounting for time spent in the sun. — kwami (talk) 02:47, 15 July 2012 (UTC)

There's Sex_differences_in_humans#Skin_and_hair and at google. μηδείς (talk) 03:00, 15 July 2012 (UTC)

No kwami, dark skin in a sunless climate does not directly cause rickets, vitamin D deficiency can lead to certain diseases involving weak bones like rickets. Having dark skin means you synthesize vitamin D from the sun at a much slower rate, but if the individual is consuming a diet rich in vitamin D, it's not a problem. But yes, there was a selective force for lighter skinned individuals in Europe and northern Asia for this reason. The preponderance for getting a sunburn or a suntan for a light skinned person depends on a number of factors. Genetics is a big factor. Some light skinned individuals simply burn more easily than others. If I were to guess, light skinned people whose ancestry traces to Mediterranean countries have better protection from the sun than say... people from Poland. ScienceApe (talk) 21:51, 15 July 2012 (UTC)

@InfoManiac: Anatomically modern humans would have started out with the dark skin typical of Africans, Dravidians, Negritos, Melanesians (New Guineans) and Australian aborigines. Whites and Orientals show different mutations in the melanin genes leading to differently pale yellow and pink skins. From Race_(human_classification): "Scientists discovered a skin-lighting mutation that partially accounts for the appearance of Light skin in humans (people who migrated out of Africa northward into what is now Europe) which they estimate occurred 20,000 to 50,000 years ago. The East Asians owe their relatively light skin to different mutations.[62]"μηδείς (talk) 04:16, 15 July 2012 (UTC)

Thank you. I was just thinking about that. About a year or so ago, I was reading a news article about an African family, and a couple of the children had a certain albino mutation. I understand that there is more than one kind of albinism in humanity. But anyway, a few children of black Africans looked as European as could be. I don't remember the eye color, but instead of the hair being white, it was light blond. InforManiac (talk) 04:29, 15 July 2012 (UTC)

What color skin did the earliest humans have? arbitrary break 1

The Washington Post article cited for that claim basically backs up what StuRat said in the beginning about the vitamin D (but just makes hints about black skin being a defense from the sun). It also mentions potential sexual selection, so maybe there's not really a consensus on that part of the issue. 203.27.72.5 (talk) 04:35, 15 July 2012 (UTC)

Nautrally brown and blond hair also occurs among Melanesians and some Australian aborigines (though the allele responsible is different to that of Europeans). And both groups as well as the now mostly extinct Ainu are among the hairiest of the human populations. Same with epicanthic folds which actually also exist natively in Scandinavian, Northern Slavic, and Celtic Europeans as well as Khoisan-speakers of Africa. Nasal bridges vary considerably as well, being predominantly low in East Asians but high in most Native Americans, despite being descendants of the latter. And neanderthals were about as phenotypically varied as modern humans in terms of hair color at least.-- OBSIDIAN†SOUL 07:20, 15 July 2012 (UTC)

I'd like to see a ref that aborigines can have naturally blonde hair. I really can't imagine that. 203.27.72.5 (talk) 07:55, 15 July 2012 (UTC)

Picture of a Vanuatu Melanesian kid at right. And here's an Indigenous Australian young man with reddish blond hair and a kid with brown hair. Plenty more pictures on the net if you want. And here's an online article by Canadian anthropologist Peter Frost which mentions it: "Why Do Europeans Have So Many Hair and Eye Colors?" (note: Frost is the most famous proponent of the sexual selection origin of modern human phenotypes mentioned by Snow earlier); and one study: Abbie & Adey (1953). "Pigmentation in a central Australian tribe with special reference to fair-headedness". American Journal of Physical Anthropology. 13, 3:339–360. -- OBSIDIAN†SOUL 12:02, 15 July 2012 (UTC)

As a (white) Australian who has thru work met a large number of aborigines, I'm very skeptical of this. Meeting a full blood aboriginal with blond hair has not happened. The photo Obsidian posted is of Rowan McNamarra, a noted Australian child actor. In the movie Sampson & Delila, he appeared with blond hair, and in all movie promotional photos and movie associated pics he has blond hair. But in other photos he appears to have black or dark brown hair. Its worth noting that the film was about folk living with no hope. It is very common for such people to be mixed race. Full bloods tend to have more pride and self-worth - it may be that the film people had his hair dyed for that reason - the film, light on dialog as the character portrayed by Rowan is severely brain damaged from gasoline sniffing, is full of visual cues and symbology probably completely lost on non-Australians, and mostly lost on Australian white audiences. The text is a very old text. In my State, Western Australia, there is a group originating from the Carnarvon area amomgst whom blond hair is very common, and their facial appearance is a little different to other aboriginal groups. It was only recently (~20 years ago as I recall) that it was proved that a Dutch ship was wrecked on the coast about 300 years before white settlement, and surviving sailors were accepted by the locals and intermarried. That's where the blond hair came from. Samson & Delila, a low budget film acted, directed, and produced almost entirely by aboriginals was an absolutely excellent film by the way. Wickwack124.178.177.175 (talk) 13:17, 15 July 2012 (UTC)

Stick my IP into a geolocate site and see why I'm so sceptical of this. I'm in the middle of nowhere in the NT, I work with the indigenous here on a daily basis and I've never seen nor heard of anything like this. I won't rule out that one individual tribe in central Australia has a blonde trait, but it must be very rare. W203.27.72.5 (talk) 22:38, 15 July 2012 (UTC)

Do click the links. Like mentioned below, take a look at the frequency map of the blond hair trait. The areas where it is near universal in occurrence is in central (eastern) Western Australia, gradually tapering off to the coasts of the state. The northern areas of Western Australia and NT are excluded (0% occurrence). Also note that it's a sexually dimorphic and paedomorphic trait, i.e. it's more prevalent among women and children and will usually darken after puberty (again like European blonds as mentioned below). Besides the only other explanations really is that either the pictures are a massive photoshop conspiracy, several scientists have somehow confused Australia with Austria, or hair bleaching has just become a massive fad among Australian Aborigines of all ages. :P -- OBSIDIAN†SOUL 23:29, 15 July 2012 (UTC)

It's a study, not anecdotes. Take that in consideration. The study records blondism in central Australian Aborigines, notably among the Warlpiri around Alice Springs (AFAIK, Rowan McNamara is Warlpiri. the movie itself was about them). As an Australian I think you already know too that hair color in Australian Aborigines darken with age, and the same is true even in Europeans where most blond-haired children grow up to be brown-haired adults. And lastly, see this map of its frequency among Australian Aborigines, and note that it's less common the nearer you are to the coast.

The Carnarvon shipwreck story is also actually quite old, not 20 years ago. Though the wrecks of Batavia, Zuytdorp, and Vergulde Draeck were indeed only found in the mid-20th century, they have long been known to have sunk there. It was already a folk explanation for the occurence of blond or light-skinned Aborigines even in the 19th century in Western Australia. While intermarriage between natives and survivors is indeed quite plausible (though AFAIK, no DNA tests have proven this yet as of 2012), that does not mean that it's the cause of blondism, as it's also present elsewhere where there are no wrecked European ships, much less shipwrecked Europeans.

The Melanesians are the closest genetically to Australian Aborigines. As mentioned, the blond hair common in some Melanesian groups has been genetically proven to be native and to be caused by a different mechanism than in European blondism.

And I'm curious, why is it so hard to accept that blond hair is not exclusive to Europeans? Claims of European admixture as a reason for European features in natives (and vice versa, e.g Scandinavian epicanthic folds, most famously Björk's) based on hearsay accounts of shipwrecks or early intermarriages lost to history is common but unless substantiated by genetic studies, most if not all of it, is bullshit. Those kinds of explanations were very prevalent in the years of scientific racism (late 19th to early 20th century, pre-Hitler). Similar shipwreck stories were also used to explain some light-haired and blue/gray-eyed Mandan of North Dakota and "Blond Eskimos" in the same time period. And their existence has been used to "prove" everything from Greenlandic Viking settlers (despite the "Blond Eskimos" actually being in western Canada) to the Mormon lost tribes simply because Europeans colonists could not accept that such traits may be present in other human populations. It has since been genetically proven in 2003 that the fair-haired Kitlinermiut individuals are not descendants of early Viking explorers of Greenland.-- OBSIDIAN†SOUL 15:44, 15 July 2012 (UTC)

Yes, I was already aware. I myself first had blond hair, according to my parents, but it was dark brown by the time of the oldest photo of myself I have - age 3. I can recall being shown an aboriginal baby by its proud parents - she had light coloured hair. They told me they fully expected it to darken.

You are quite correct - the story is old. As I recall, Carnarvon area aborigines have always told whowever would listen that they had a partly white ancestry - but nobody of academic significance listened. I don't know about modern DNA test specifically, but it was proved about 20 years ago as follows: It happens that they have an inherited blood disease extremely rare elsewhere - in fact for a long time they were the only group in teh world known to have it. The disease isn't of much consequence for most of their life, as I understand, but does shorten their life a bit. A doctor researching it became aware, or already knew, of a closely similar disease confined to the descendents of a particular africaaner family in South Africa. Blood samples were obtained from SA and it turned out the disease was identical. Dutch ship crew records were then checked and it was found that a ship called at South Africa and took on some africaaners from that same family as repalcement crew. The ship was wrecked on the Carnarvon coast. For those who are unaware, Africaaners are people resident in South Africa since the 16th century, descended from Dutch pioneers. Wickwack58.170.163.160 (talk) 16:32, 15 July 2012 (UTC)

I'm guessing you meant the occurrence of variegate porphyria (common in Afrikaners) and Ellis-van Creveld syndrome (most notably documented among the Amish who were from Holland) in Western Australian Aborigines. The conclusions of both studies were actually negative. The three (possibly four) cases of variegate porphyria documented in Aborigines (out of six documented cases overall in Australia in the span of 20 years) were the result of different mutations from the South African one. And the Ellis-van Creveld syndrome is not exclusive to the Dutch, but is common in founder populations (particularly small groups of humans with little to no contact with other populations for long periods of time). See [10] and [11] for the actual studies.-- OBSIDIAN†SOUL 17:09, 15 July 2012 (UTC)

P.S. Please don't split your posts. :P It makes it confusing to determine who wrote what. -- OBSIDIAN†SOUL 17:11, 15 July 2012 (UTC)

What parts have been split up? I don't want to mix up who wrote what. Thanks. InforManiac (talk) 19:48, 15 July 2012 (UTC)

Sorry that was meant for 120.145.151.40. Disregard it. -- OBSIDIAN†SOUL 23:29, 15 July 2012 (UTC)

H'mmm... Your references support your statements, but as I recall, they traced it to a specific SA family - the newspaper article gave the Afikaner names. It could be that it was a different disease, or it could be that the researcher who gave the conclusion I reported simply got it wrong. Wickwack120.145.151.40 (talk) 18:06, 15 July 2012 (UTC)

I think they were actually simply reporting that Western Australian Aborigines seem to share two relatively rare genetic diseases that were also prevalent in other Dutch-descended populations. And they are quite correct in that. It was that connection, after all, that prompted the latter two studies which eventually proved that it was incorrect. Kind of a false positive in other words - seemingly damning evidence at first glance, but falls apart at closer inspection. Happens a lot in scientific hypotheses actually. -- OBSIDIAN†SOUL 18:23, 15 July 2012 (UTC)

@StuRat, Arctic dwelling people, Inuit and Eskimo are not light skinned. For the most part they are slightly darker than the average European. In the spring, for obvious reasons, the face and arms, if exposed, tend to get very dark. CambridgeBayWeather (talk) 12:10, 15 July 2012 (UTC)

They look rather light-skinned to me: [12], [13], [14]. However, if darker skinned, than, say, Nordic people, that might be explained by them having relatively recently migrated from more Southern portions of Asia. StuRat (talk) 19:57, 15 July 2012 (UTC)

The source you provide is wrong, StuRat. The ancestors of the Eskaleuts are ultimately derived from the Lake Baikal area. See Michael Fortescue's Language Relations Across the Bering Strait. They traditionally got their full compliment of vitamins A and D from fish oil and raw sea-mammal liver. μηδείς (talk) 21:34, 15 July 2012 (UTC)

And where did those in the Lake Baikal region come from ? Eventually they must have had ancestors from a more southerly climate, it's just a question of if it's far enough back to have allowed for major changes in skin color since then. StuRat (talk) 21:45, 15 July 2012 (UTC)

By your 'reasoning' here, StuRat, the fact that Eskimos evolved from reptiles far enough back explains why they are green. But you seem to have inadvertently omitted your source. μηδείς (talk) 21:58, 15 July 2012 (UTC)

Actually mammals did not evolve from reptiles, they evolved from therapsids. Eskimos and Inuit don't have dark skin, I suppose they have darker skin than individuals from say, Norway. I can't tell if they have skin darker than people whose ancestry is from China though. ScienceApe (talk) 22:26, 15 July 2012 (UTC)

Saying mammals evolved from therapsids, not modern reptiles is, of course, the usual gotchalism you will find on the ref desk. But therapsids have long been characterized as reptiles, it depends on how you wish to define the term, and you are quite aware of the point being made. These are the synapsids you say are not reptiles:

Synapsida	†Caseasauria Eupelycosauria †Varanopidae †Ophiacodontidae †Edaphosauridae Sphenacodontia †Sphenacodontidae Therapsida †Biarmosuchia Eutherapsida †Dinocephalia Neotherapsida †Anomodontia Theriodontia †Gorgonopsia Eutheriodontia †Therocephalia Cynodontia † Cynognathia Probainognathia Mammaliaformes Mammalia

As for the Eskaleuts, there is no evidence whatsoever that they evolved from South Asians, if you define that as India, China, and the land between. Here is a comment from an actual source:

He had brown eyes, dark skin, thick blackish hair and type A blood.

This eskimo, who lived about 4000 years ago in Greenland, also had dry earwax, shovel-like front teeth, an increased risk of going bald and the metabolism of a person who could survive in a cold climate.

And his ancestors were, to the surprise of scientists, ancient people in east Siberia rather than neighbouring Native Americans or Inuits.

All this detailed information about the long dead man has come from a study of a small clump of his hair, preserved for thousands of years in the Arctic permafrost.

Given the name Inuk, he will go down in history as the first ancient person to have had his full DNA code, or genome, sequenced. http://au.news.yahoo.com/thewest/a/-/world/6788814/genetic-time-machine-unmasks-eskimo-dna/

μηδείς (talk) 23:11, 15 July 2012 (UTC)

July 15

CIELAB color coordinates

In the CIE Lab color space colors are represented by three parameters - lightness (L*) and a* and b* channels (the * is there to prevent confusion with the related Hunter Lab color space). L* is restricted to between 0 and 100 but the a* and b* channels, which may be positive or negative, are more complicated. Some references state they don't have a theoretically defined minimum or maximum value but note that certain combinations do not produce reaalizable colors. Others state that the minimum and maximum values depend on the color space being worked in - for instance this really gorgeous pdf explains that in the a* and b* channels are restricted to -100 to +100 if working in the CMYK space, but states that larger values can be attained in other spaces. On the other hand, this online color converter - if you inspect the javascript "under the hood" - restricts the a* and b* channels to -128 to +127. What I've not found anywhere is an explanation of how the limits on a* and b* vary, why it's exactly ±100 for the CMYK space ("by definition" is the obvious answer, but I've not seen it stated explicitly elsewhere and it isn't in the wiki article), or in general what magnitude of value is certain to be unrealizable (it's not obvious to me why that javascript only uses about ±128, but I can understand it's intuitively pointless stretching to ±500). Where could this information be found? ManyQuestionsFewAnswers (talk) 02:28, 15 July 2012 (UTC)

The article claims that its 2nd external link has "explanations" for the parameters. I think the first page of [15] may do a better job for you. You probably know that an 8-bit byte representing a signed integer has the range [-128, 127] while humans are more likely to use [-100, 100] for familiarity reasons. 71.212.249.178 (talk) 05:13, 15 July 2012 (UTC)

Thanks that's a nice link. Yes, the -100 and +100 (or -128 and +127) are obviously not completely arbitrary. But while that document has a very clear explanation of the conversion process, better than the Wiki article, I can't see an answer to my original question about what are the a* and b* co-ordinates' theoretical and practical limits (if such a distinction is meaningful!). It is clear that the human gamut extends substantially beyond a* or b* = ±100 (you can see that on this document on the diagrams from page 27 onwards) even if the CMYK space doesn't, and there are imperceptible "colors" beyond that gamut. From the diagrams it looks like b* can go above 130 and still lie in the human gamut so long as a* is approximately -30, and I can't discern where the lower boundary for b* or the boundaries for a* would lie. ManyQuestionsFewAnswers (talk) 13:35, 15 July 2012 (UTC)

There's no contradiction here. The first document says "The range of a* and b* never exceeds −100 to 100 in the cmyk color space." That doesn't mean that CMYK covers exactly that range, just that the CMYK gamut is nested in that range, as you can see in some of the images in that document. It's not considered especially important to be able to work with highly saturated colors (the colors at the edge of the human gamut). Various tools limit the gamut in various ways for various reasons—because they only care about limited-gamut output devices or because they want to store a* and b* as integers in one byte each, for example. -- BenRG (talk) 23:23, 15 July 2012 (UTC)

Yes, that all makes a lot of sense thanks, I presume the human gamut is limited by biological features that have to be measured, rather than being capable of theoretical calculation, and that explains the highly irregular shape? And yes I meant to say that the -100 to +100 was just upper and lower bounds for the a* and b* channels under CMYK, but additional restrictions apply (as you say not every pair of a* and b* values can be realized). It was the nature of the upper and lower bounds that I was particularly interested in rather the extra level of complexity about how they interact! From what you are saying, ±100 or ±127 is normally "good enough" because colors outside that range are so highly saturated that humans are not visually sensitive to them? ManyQuestionsFewAnswers (talk) 00:48, 16 July 2012 (UTC)

Blood agents

According to page 72 of A Laboratory History of Chemical Warfare Agents, blood agents like hydrogen cyanide have a similar toxic mechanism to carbon monoxide. In this previous question, StuRat and Ratbone agreed that carbon monoxide poisoning is essentially painless; it just causes drowsiness, unconsiousness and then death. Yet the wikipedia article on blood agents cites "Blood Agents" by C. J. Walsh to claim that cyanide causes "...violent convulsions and a painful death that can take several minutes." So if they both work by the same mechanism, why is one painful and the other painless? 203.27.72.5 (talk) 05:43, 15 July 2012 (UTC)

This is outside my field, but I note that carbon monoxide posioning works by cripling the function of haemoglobin in the red cells of the blood (see http://en.wikipedia.org/wiki/Carbon_monoxide_poisoning), whereas cyanide posioning works by interfering with tissue cell mitochondria, and this would immediately affect brain cells (see http://en.wikipedia.org/wiki/Hydrogen_cyanide). So the mechanisms are not similar - they are completely different. This does directly contradict what Ledgard says on pages 72, 73. So I googled. See authoritative reference: http://emedicine.medscape.com/article/832840-overview#a0104 - this agrees with Wikipedia that hydrogen cynanide stuffs up mitochondria and gives details of how it does so. It is very well known, even amongst lay people, that CO affects red cells. Ratbone121.215.146.212 (talk) 10:36, 15 July 2012 (UTC)

Outside your field, but hit the spot none the less. Thanks very much Ratbone! 203.27.72.5 (talk) 11:01, 15 July 2012 (UTC)

Resolved

Yet another Higgs question

How many percent of physicists believed, prior to the recent discovery, that the Higgs boson would not be found by the LHC? How many percent believed that it didn't exist at all? It seems to me that although testing the claims of existing theories is important in science, the Standard Model's prediction of the Higgs is kind of like me predicting that the Sun will rise tomorrow. If it doesn't rise, that will be an earth-shattering discovery, but few people seriously expect it to not rise. Is this a valid characterization of the Higgs boson, or am I way off? --140.180.5.169 (talk) 06:40, 15 July 2012 (UTC)

The Higgs is necessary if the Standard Model is correct. But we already know it's at best flawed, so there is no general theoretical requirement for the Higgs tto exist. — kwami (talk) 07:30, 15 July 2012 (UTC)

Apparently the discovery of the Higgs boson cost Stephen Hawking a $100 bet. 203.27.72.5 (talk) 07:21, 15 July 2012 (UTC)

I don't get it. The particle has not been confirmed to have the behaviour expected of the Higgs, so why has Hawking admitted defeat? — kwami (talk) 07:26, 15 July 2012 (UTC)

Because he's noble in defeat. And because he's reasonably sure that if it turns out later they've discovered some unpredicted particle and the Higgs is still at large, then he will still be able to get his money back from the other guy. 203.27.72.5 (talk) 07:43, 15 July 2012 (UTC)

It has to do with Hawking's old idea about information loss due to Hawking radiation, see here. It leads to the conclusion that you can never detect any fundamental scalar particle. Count Iblis (talk) 15:34, 15 July 2012 (UTC)

We don't really have any model of the world in which the sun doesn't rise tomorrow. There are several Higgsless models. Dauto (talk) 18:41, 15 July 2012 (UTC)

Some people do. W203.27.72.5 (talk) 22:29, 15 July 2012 (UTC)

At least some of these "Higgsless" models have a spin-0 particle that behaves like the Higgs. It's just not a fundamental particle, but some kind of composite or weird non-particle state. The article claims "All of the alternative mechanisms use strongly interacting dynamics to produce a vacuum expectation value that breaks electroweak symmetry", which (if it's true) means that they all have a field like the Higgs field. Given that, I'd think it would be hard to prevent perturbations in that field behaving like a Higgs boson, though it might be easier to make the mass of the quasi-Higgs high enough that it couldn't be found at the LHC.

As for Hawking, even if he was confident in the correctness of that paper (which I doubt) it only applies to a fundamental Higgs, so he could still lose to a composite Higgs. I think he probably bet against the Higgs because it's the more interesting outcome, and didn't really expect to win. -- BenRG (talk) 23:47, 15 July 2012 (UTC)

Preserving body part for future genetic sequencing

How do I preserve a part of myself as of today so that it can be genetically sequenced when technologies become cheaper, more available, and more reliable? Also, is it possible to sequence the skeletal remains of a person? Many thanks. 180.254.88.42 (talk) 08:00, 15 July 2012 (UTC)

The bone marrow could be sequenced, until decayed, which, depending on conditions, could be under a year or up to several thousand years. The easiest way to preserve your DNA would be to pull a hair, with the root, seal it in a sterile container, and freeze it. Be sure to label it. StuRat (talk) 08:46, 15 July 2012 (UTC)

A researcher in my lab stores stuff in an ethanol water mixture on the field and in the lab for Later DNA sequencing. Don't know the ratio though.Staticd (talk) 11:02, 15 July 2012 (UTC)

According to this page,[16] at least, collecting a sample with a buccal swab (basically rubbing the inside of your cheek with a Q-tip) is another non-invasive technique, that's generally considered preferable to collecting a hair sample. If you're willing to spend a little bit of money, there are companies that are set up to help you preserve a DNA sample. Some will do things like save your sample for you at -80° C, which will presumably make the sample last longer than in a home freezer, and some companies sell chemicals for preserving the DNA sample at room temperature. To find those companies, the link above is a good place to start, or just google "DNA sample preservation". Red Act (talk) 19:01, 15 July 2012 (UTC)

Sticky robots

My son has got a bathtub toy which consists of robot shaped parts that stick to the tiles when wet. The parts are very lightweight and made of some foamy material. I was wondering about the physics behind it. Explanations can be as technical as necessary. Thanks. bamse (talk) 08:03, 15 July 2012 (UTC)

Can you provide more details? Maybe the brand so we can google it and see what you're refering to? I'm just having a hard time imagining it looks like, not having any kids (or their toys) myself. 203.27.72.5 (talk) 08:23, 15 July 2012 (UTC)

Could it contain tiny suction cups ? They tend to work much better when wet. StuRat (talk) 08:42, 15 July 2012 (UTC)

I guess these are robot-shaped versions of the more common foam bathtub letters (sample ad). The adhesion mechanism is probably a mixture of static cling (as used in vinyl decals) and soap residue. Unfortunately our article on static cling is poor, and doesn't even attempt to explain how static cling decals work. --Heron (talk) 09:39, 15 July 2012 (UTC)

Does static cling work on wet objects ? StuRat (talk) 09:41, 15 July 2012 (UTC)

Cling wrap certainly does work with wet food products, so I guess it might. 203.27.72.5 (talk) 09:50, 15 July 2012 (UTC)

Be careful not to confuse cling wrap with static cling. Cling wrap sticks by means of adhesive additives (see madsci.org [17] and [18]), while static cling is a purely electrostatic effect. --Heron (talk) 11:17, 15 July 2012 (UTC)

Hmmm...my physics lecturer said once that cling wrap was the only example of a useful purpose of static electricity in everyday life. Looks like he was confused. 203.27.72.5 (talk) 11:24, 15 July 2012 (UTC)

• Pretty sure it's just adhesion due to the thin film of water, which is highly cohesive with itself, and also adheres to the foam (due to high surface area), as well as the tile. Water is actually a good adhesive, if the right material properties are met (high surface area, small forces). Here's the same phenomenon: put a toothpick on a surface, put three small drops of water on the toothpick, then another toothpick on top. If you are careful, you should be able to pick up the top toothpick, and the bottom one will stick to it via water adhesion. Further links on water adhesion here: [19] and here [20]. (I would not personally use "static cling" to refer to this effect, even though the adhesive/cohesive forces in water have to do with electrostatic forces on the molecular level...) SemanticMantis (talk) 15:48, 15 July 2012 (UTC)

Thanks for all the replies. Indeed these seem to be like the bathtub letter mentioned by Heron. No suction cups (unless they are microscopic), they stick both on the bathroom tiles and on the bathtub and work with plain water and soapy water. If they get dry, they fall off the wall, but can be reused if made wet. The adhesion/cohesion explanation sounds very plausible to me. bamse (talk) 19:01, 15 July 2012 (UTC)

Lightning captured in nuclear explosion photograph

I came across this popular image shown in many topics related to nuclear weapons. I have noticed there is wierd lightning on the center of the picture, connecting ground and skies, and I can't manage to find out what caused it. What is that lightning ?

http://en.wikipedia.org/wiki/File:Upshot-Knothole_GRABLE.jpg

95.105.133.125 (talk) 08:57, 15 July 2012 (UTC)

vertical smoke flares which are used to observe the shock wave --Digrpat (talk) 09:07, 15 July 2012 (UTC)

Thanks, I tought it's lighning :D — Preceding unsigned comment added by 95.105.133.125 (talk) 09:41, 15 July 2012 (UTC)

Name the Lamp - please!

Yeah, that's a ... humh ? A Gooseneck lamp !

What is the English word for this office lamp with a "swan neck" backbone (you can move it in any direction - and it stays). Grey Geezer 09:30, 15 July 2012 (UTC) — Preceding unsigned comment added by Grey Geezer (talk • contribs)

The bendy bit is called a gooseneck, so the lamp is called a gooseneck lamp. --Heron (talk) 09:34, 15 July 2012 (UTC)

I have a floor lamp like that, and just call it the "adjustable lamp". StuRat (talk) 09:35, 15 July 2012 (UTC)

I'd call it a gooseneck lamp as well. Though I'm not sure what this has to do with science. Dismas|^(talk) 09:45, 15 July 2012 (UTC)

Gooseneck - sure! Thanks! Case closed. Grey Geezer 10:39, 15 July 2012 (UTC) — Preceding unsigned comment added by Grey Geezer (talk • contribs)

follow-up question from someone else What is the most common manufacturing technique used to make a lamp like this possible? What's in the shaft? 69.243.220.115 (talk) 13:38, 15 July 2012 (UTC)

The stem of the lamp consists of a series of rings that act as little joints which allow each ring to articulate and move a small amount, say a millimeter. With lots of little joints on lots of little rings, the whole thing bends and twists. --Jayron32 19:39, 15 July 2012 (UTC)

(edit conflict) One common construction is to have a spiral of metal (or sometimes plastic) in which each winding overlaps and links (but is not rigidly attached) to the adjacent ones. The whole thing can flex because the amount of overlap can change a little at each winding. DMacks (talk) 19:40, 15 July 2012 (UTC)

Looking at mine, it seems to use rings, not a spiral. There must be some type of catch on the inside of each ring to keep it from sliding completely off the adjacent ring. StuRat (talk) 20:55, 15 July 2012 (UTC)

Mine appears to use double rings, one set on the outside, and one on the inside, like so:

 ______
 \    / 
          OUTER RING CROSS SECTION
 /____\

 /____\
 ______   INNER RING CROSS SECTION
 \    /

 ______
 \   //___\
     ______   ASSEMBLY CROSS SECTION
 /___\\   /

Or maybe the outer rings and inner rings are combined into one, like so:

 ______
 \    /____\
      ______    CROSS SECTION
 /____\    /

I do find myself wondering how they assemble such a thing, though (must involve folding down some flaps, forcing rings together, then folding the flaps back up, like in a molly bolt):

 ______
 \    /___/\ <- Fold down flaps
      ______    
 /____\   \/ <- Fold down flaps

StuRat (talk) 21:12, 15 July 2012 (UTC)

Strength training

What are the advantages and disadvantages of classic weights/resistance training with cardio vs circuit training? 176.27.222.99 (talk) 13:03, 15 July 2012 (UTC)

We can't give medical advice, and this is a perfect example why. The answer depends strictly on several separate results of a physical examination. Ask a professional trainer certified in exercise planning. 71.212.249.178 (talk) 19:41, 15 July 2012 (UTC)

Im not asking for medical advice. Im asking for a scientific answer to my question which is purely academic. Its up to the person answering to give an academic answer rather than medical advice, which cant be hard since im asking a very generic question. A question asking for medical advice would be alot more specific. 176.27.222.99 (talk) 20:16, 15 July 2012 (UTC)

This is hardly a medical advice question... although the usual caveats about checking with your doctor before starting an exercise regimen... There's a lot of discussion and debate about cardio versus strength training. Generally strength training is going to help build fast twitch muscle and from an aesthetic standpoint, create more definition and possibly (depending on a lot of things) size. Cardio will improve other aspects of your fitness.

There's a lot of dogma around exercise and nutrition and so you may hear people who are absolutist about their particular position. Ultimately you have to decide for yourself. Shadowjams (talk) 20:33, 15 July 2012 (UTC)

The downside of trying to attempt a one-size-fits-all answer here could easily be fatal for more than a few percent of the population acting on it. The questioner said nothing about their body mass index, mobility, injuries, or cardiovascular history. 71.212.249.178 (talk) 22:30, 15 July 2012 (UTC)

Alcohol absorbition from mouthwash

What amount of the alcohol in mouthwash is absorbed by the mucosal membranes etc in your mouth? Assume the mouthwash is 20% a.b.v. and that the mouthwash is swirled around your mouth for 30 seconds (or show that these are unreasonable assumptions)— Preceding unsigned comment added by Egg Centric (talk • contribs)

I'll assume this is not a medical question and not a homework question. I found no useful links at Google search. Wikipedia's info in the buccal membrane inside the mouth seems very sketchy, with only a passing reference in Oral mucosa, which is a very short and uninformative article. Someone studying dentistry or oral surgery could perform a real service by improving our coverage of the buccal membrane and oral mucosa in general. Caffeine gets readily absorbed through the oral mucosa, and sugar is also absorbed slowly. As for alcohol, all I found on the web was that drinking alcohol regularly for a long time can lead to cancer of the oral mucosa, as can using a high alcohol mouthwash, even without swallowing alcohol. Edison (talk) 17:43, 15 July 2012 (UTC)

A source found at Google books says that "small amounts of alcohol may be absorbed through the buccal mucosa" without giving a formula for calculating the precise quantitative answer to your question. Edison (talk) 17:50, 15 July 2012 (UTC)

It depends on the proportion swallowed. 71.212.249.178 (talk) 19:47, 15 July 2012 (UTC)

Is aging slowing as life expectancy increases?

Life expectancy has increased greatly over the last century. However, has aging slowed down at all? I know in the middle ages for example people were considered grown and ready for marraige at around 15 years of age. Were these 15 years olds more developed than modern 15 year olds? Has puberty and growth slowed down at all?

Has menpopause got any later? What are the reasons for this? Is people in developed countries having children later an evolutionary pressure, and how do you expect this will affect evolution of H. sapiens in the near future?--178.167.159.126 (talk) 16:51, 15 July 2012 (UTC)

This is based on hearsay, but people are apparently reaching puberty faster now than before. 109.97.146.146 (talk) 17:39, 15 July 2012 (UTC)

There is evidence that women reach menarche (age of first period) earlier by 2 - 3 months per decade. This page has some interesting cross-cultural graphs. As to why this should be, I would speculate that it is a combination of factors: improved nutrition and healthcare being a large factor, and possibly oestrogenic chemical environmental residues, whose impact is still unknown. --TammyMoet (talk) 17:55, 15 July 2012 (UTC)

(ec) Yes, puberty is getting earlier. The biggest factor causing this is apparently less starvation, as one of our starvation responses is to delay the onset of puberty. StuRat (talk) 17:56, 15 July 2012 (UTC)

One of the things about life expectancy that is a bit of a fallacy is that people used to die in their 40s and 50s, and only recently began living into their 80s and 90s. This is true to a point, that is people do live longer, a bit more than they used to, but it isn't as simple as that. Much of the increase in life expectency in modern developed nations actually comes from two situations:

a) Children living to maturity

b) Women surving childbirth

In his book A Little Commonwealth, John Putnam Demos did a detailed demographic study of Plymouth Colony. Now, this was a 17th century colony of people, mostly first generation imigrants, living in a society without modern medicine and modern nutrition and the like. What he found was that males who reached their teens lived nearly as long in the 1600s as they do today, as did women who made it to their 50s. That is, if a man could make it out of childhood, or a woman could make it to menopause, their was not a dramatic difference in lifespan 400 years ago than today. It turns out the risks to long life are mostly childhood disease and pregnancy complications. If you made it through those landmark events, you stood as good of a chance of living just as long then as now. So when you see lifespan figures from the past, understand that the numbers are skewed a lot by those issues. Seeing that, at some point in history the average lifespan was, say, 50 years old doesn't mean that lots of people died in their 40s. What it means is that lots of people died as young children and it dragged the average down a lot. Now, there is a big caveat in Demos's study and that is that the situation is very different in cities, where sanitation really lowered lifespans of people. Plymouth was a small, agrarian society where the problems of urban sanitation don't create the close proximity necessary to spread epidemic disease like black plague, cholera, typhus, and the like. If there are three things which have raised life expetency more than any other in the modern world it has probably been, in order a) vaccinations against childhood disease b) prenatal care and c) urban sanitation. Everything else has made small, incremental advances, but those are the three biggies. As far as directly answering the question regarding age of maturity at both ends of life (puberty and old age); a lot of that is cultural as much as anything else. As others have noted, for health reasons it seems people are reaching puberty earlier than before, but for nearly all of history 15 years old has been an age when a person has reached biological sexual maturity. That does not mean that a person is emotionally or culturally considered ready for adulthood, parenthood, or sexual activity. Many of those things are determined by one's culture: in one place and time, 15 year olds are considered full adults, while in other places and times the age may be younger or older. --Jayron32 18:43, 15 July 2012 (UTC)

Specifically, water treatment and sewage treatment seemed to be absolutely critical to increasing the average lifespan, by stopping the spread of water-borne diseases.

I believe many measures of life expectancy also exclude infant mortality. StuRat (talk) 20:37, 15 July 2012 (UTC)

This is certainly the argument of e.g. Ivan Illich, who felt that improvements in sanitation were a larger factor in improved human life expectancy and wellbeing than the medical profession had provided. (Not saying I agree with him, am curious why he didn't rate progress in things like vaccination so highly, but that what StuRat and Jayron say is sensible.) ManyQuestionsFewAnswers (talk) 00:38, 16 July 2012 (UTC)

There are some specific aspects of aging which now seem to happen more slowly:

1) Skin aging. Due to spending less time in the sun, wearing more clothes, using sunscreen, moisturizers, etc.

2) Dental wear (distinct from other dental problems). Food used to contain bits of sand and such, which wore down the teeth, but with modern processing, our food doesn't contain this. Also, people formerly used their teeth as general tools, for cutting materials and such, but now we use external tools (although I have to admit to occasionally biting open a blister pack/clamshell, like the one containing the scissors needed to open blister packs/clamshells :-) ). StuRat (talk) 20:46, 15 July 2012 (UTC)

I'm pretty skeptical of number 2 — do you have a source for that?

To add my own speculation on top of speculation, I think a lot of people show less "visible signs of aging" than you see in movies of people of the same age in, say, 1940 or 1950, in large part because most people now don't smoke. But I don't have a source for that (would be interested to know if someone does). --Trovatore (talk) 22:18, 15 July 2012 (UTC)

Chimmney-like thing in boats

How is called this chimmney-like thing that are found in many boats?--90.165.112.194 (talk) 18:12, 15 July 2012 (UTC)

I think it is normally called a 'ventilation cowl' - see here for some information on how they are used: http://www.generalcargoship.com/ventilation-of-cargo.html

It's called a "Dorade box", and it's for allowing air in below deck while making sure no water gets in. Dominus Vobisdu (talk) 18:27, 15 July 2012 (UTC)

How long does it take for wind turbines to pay for themselves?

The House of Lords says 1.1 years but that doesn't include profit, taxes, shipping, or salaries. Can anyone get this NREL spreadsheet to say? It has Excel macros so it's not working for me at the moment. 71.212.249.178 (talk) 19:52, 15 July 2012 (UTC)

That first link also doesn't seem to include the land purchase price, which can be significant for a large wind farm (especially if they need a buffer zone, as neighbors probably don't want massive windmills right on their fence). StuRat (talk) 20:32, 15 July 2012 (UTC)

I hope only the footprints of the turbines take land area economically, e.g. from agriculture. 71.212.249.178 (talk) 22:27, 15 July 2012 (UTC)

Your question doesn't make sense to me. Don't they pay for themselves by generating profits? W203.27.72.5 (talk) 22:19, 15 July 2012 (UTC)

Yes, but in how much time? Can you get the spreadsheet to work? I better fire up windoze. 71.212.249.178 (talk) 22:27, 15 July 2012 (UTC)

The house of lords document is not about dollar terms. Building anything requires energy, energy for melting aluminum, mining the metals, shipping parts, etc. The document tells the reader how much energy is required to build each type of plant, and how long the then built plant would have to operate to create the amount of energy required to have built it in the first place. Unique Ubiquitous (talk) 22:39, 15 July 2012 (UTC)

Hydrogen critique?

Even liquid hydrogen has less than a third the energy density of gasoline.

So, I've been really interested in hydrogen vehicles recently, and if one day in the future I can afford one, I hope to buy one (which might be a challenge living in Canada, but one step at a time). One thing I've noticed though, in the criticism section of our Wikipedia article is that critics claim that "hydrogen vehicles will emit more carbon than gasoline vehicles (in their lifetime)". How is this so? Is it because the number one way that companies produce hydrogen is through using fossil fuels? Electric cars face the same thing, except worse, considering the source of their electricity mainly comes from fossil fuels too. But wouldn't a simple solution to harnessing hydrogen be electrolysis, perhaps using solar electricity (which can even easily be done at home)? And what other problems (besides cost) could the hydrogen car face? Thanks, 64.229.5.242 (talk) 19:59, 15 July 2012 (UTC)

Storage for hydrogen is remarkably difficult. It embrittles metals in which it is stored or pressurized. There are some ceramics virtually impervious to damage from this, and systems to compensate for it, but they are fragile, heavy, and bulky and thus unsuitable for transportation. Hydrogen also has a colorless flame which is often considered a safety hazard, You may be interested in http://windfuels.com, http://airfuelsynthesis.com, page 28 here and the conclusions of this paper. 71.212.249.178 (talk) 20:24, 15 July 2012 (UTC)

As far as creating hydrogen at home using solar power, this wouldn't be practical. A huge array of solar panels would be needed, since solar cells are rather inefficient. StuRat (talk) 20:18, 15 July 2012 (UTC)

Solar is expected to be competitive with wind after 2020, depending on how well Makani Power does. 71.212.249.178 (talk) 20:24, 15 July 2012 (UTC)

One man a few years ago had an array of solar panels on his roof, and it could easily power his house. I doubt that a "large array" would be needed to split water, which only needs at least 1.23V. 64.229.5.242 (talk) 20:54, 15 July 2012 (UTC)

Voltage has nothing to do with it. You can get any voltage you want out of an arbitrarily small array of solar panels, but then the current is so low that won't generate hydrogen at a sufficient rate to do anything with it. There's also the problem of liquifing the hydrogen once you generate it. If you're burning the hydrogen as the BMW Hydrogen 7 does, you will only get something like 30% of the generated solar power back as kinetic energy in the movment of your car. If it uses hydrogen fuel cells, then it should be about the same efficency as an electric car (since you're basically just using the generated hydrogen as a battery. The solar panels themselves take huge amounts of energy to create (due to the zone refining required to get pure silicon), which is almost always sourced from fossil fuels. Electric cars that use batteries also have the advantage of storing the waste energy from braking, which even your hydrogen fuel cell car won't do. W203.27.72.5 (talk) 22:13, 15 July 2012 (UTC)

A house uses less electrical energy than a car in use, unless it has electrical A/C or electrical heating on, in which case solar panels on the roof aren't likely to get the job done. (The fact that everybody doesn't already power their houses entirely with roof solar panels is evidence enough that this isn't practical.) StuRat (talk) 21:24, 15 July 2012 (UTC)

I guess solar is already technically competitive with wind in the middle of the day peak during the summer, but not enough to make investing in solar a better idea than investing in wind for probably at least a decade. 71.212.249.178 (talk) 21:31, 15 July 2012 (UTC)

Also, any new technology could be responsible for lots of carbon emissions, if it results in us dumping our current fleet of vehicles in junkyards. We should wait until each vehicle is due for replacement, before switching to a new technology, or, where possible, modify our current vehicles now, to use more efficient technology. StuRat (talk) 20:22, 15 July 2012 (UTC)

Science disciplines

Are Biology and Chemistry subsets of Physics or are they completely different but have overlaps?176.27.222.99 (talk) 20:13, 15 July 2012 (UTC)

I'd call them separate, and biologists and chemists would likely agree, but a physicist might disagree. StuRat (talk) 20:16, 15 July 2012 (UTC)

Biology is a separate subject. Chemistry really is a branch of physics. Dauto (talk) 20:22, 15 July 2012 (UTC)

But it can be argued that biology overlaps with organic chemistry. StuRat (talk) 20:25, 15 July 2012 (UTC)

Or biochemistry. W203.27.72.5 (talk) 23:12, 15 July 2012 (UTC)

http://xkcd.com/435 71.212.249.178 (talk) 20:28, 15 July 2012 (UTC)

Yes, they overlap. The difference is that chemistry not only overlaps with physics, it is pretty much completely covered by the definition of physics (which studies the basic property of matter including its chemical properties). Dauto (talk) 20:37, 15 July 2012 (UTC)

Biology cannot be derived from the laws of physics. The genetic code is arbitrary. There is nothing in the makeup of DNA that requires that any three base pairs be physically determined to code for a certain amino acid. For example, UGG does code for tryptophan, but that is merely historical accident--there is no physical or chemical reason it had to do so. In This is Biology, Ernst Mayr gives an off-the-cuff list of two dozen concepts like ecological niche, sympatric speciation, and sexual selection which are emergent and cannot be reduced to any chemical description or physical laws. μηδείς (talk) 21:19, 15 July 2012 (UTC)

The gas cloud that collapsed to give rise to our Sun, the Earth and the othe planets also gave rise to you and me. One can, in principle, formulate any biological question in terms of only the fundamental laws of physics, as a summation over the initial conditions of that gas cloud. Count Iblis (talk) 22:52, 15 July 2012 (UTC)

• You won't have to go that far to defend the point that biology is chemistry constrained by existing living beings. You can rest assured that everything that's within a living being is explained by chemistry/physical/mathematical concepts. What else could someone expect? OsmanRF34 (talk) 23:47, 15 July 2012 (UTC)

Then do it or show where it has been done. "What can be asserted without proof can be dismissed without proof" - Hitchens. μηδείς (talk) 23:21, 15 July 2012 (UTC)

I don't know if the question is whether or not one can be derived from the other so much as whether they are considered separate sciences. When I studied chemistry, it was taught by the School of Physical and Chemical Sciences. It's since become the School of Physics, Chemistry and Technolgy, and includes IT subjects. Biology was always taught by the School of Life Sciences. W203.27.72.5 (talk) 23:12, 15 July 2012 (UTC)

Mathematical Formulation of the Standard Model

From a mathematical point of view(I am a mathematician). Looking at the description of the Standard Model (mathematical formulation), it looks quite ugly. Compared to lets say the Maxwell equations or Einstein's field equations which look mathematically aesthetic, the formulation of the standard model seems to be a huge mess. Is there a simpler formulation than in the article available or has there been any research related to simplifying the formulation (lets say by basing the theory on the fewest possible "simple" axioms)? I noticed that physicist do most calculations and derivations much more sloppy (eg. Renormalization) than it is done in mathematics (this is also mentioned in the article Yang–Mills existence and mass gap). Is there any research on a mathematical rigorous formulation of a theory (standard model or something different)? --helohe (talk) 23:57, 15 July 2012 (UTC)