Wikipedia:Reference desk/Archives/Science/2009 September 6

= September 6 =

Human race vs Human species
More and more I hear people on the radio or in books speaking of the 'human race'. I tried to ignore it but recently I read it in a lot of well-informed science fiction stories and today I heard it on a science program! that was too much. We're a species. How come we call ourselves so often a race? Where did it come from? None of the articles about race and racism I could find on Wikipedia seem to address the problem. Is it merely a slip of the meaning of the word or has it got a deeper meaning? Thank you. 190.244.183.244 (talk) 02:36, 6 September 2009 (UTC)
 * I doubt it's "more and more" &mdash; it's always been a common phrase. Probably you've just been noticing it more.
 * I see nothing wrong with the term. Certainly it has nothing to do with racism; kind of the opposite, given that "the human race" includes all "races".  But it has a harder, more martial, more mythical sound to it than species, and sometimes that's desired.  Species is a coldly scientific word, and doesn't work well when the poetic or emotional or metaphysical aspects are connotations you want to get across. --Trovatore (talk) 02:57, 6 September 2009 (UTC)
 * As Trovatore says, it doesn't have any special meaning, it's just the colloquial usage. Words in the normal vulgar lexicon are often very different from their purely scientific meaning, and that's just how it is.  Happens all the time.  My pet peeve is decimate. ~ Amory  (user • talk • contribs) 03:32, 6 September 2009 (UTC)


 * The usage is very common and not at all new. It appears in "The Time Machine, by H. G. Wells [1898]" and in "Frankenstein, by Mary Wollstonecraft (Godwin) Shelley [1818]".  And those are just the first two books that it happened to cross my mind to search. I'm certain that I could find others.
 * Besides, "Human Species" isn't quite right either. "Human" refers to a handful of species, we just happen to be the last one standing. APL (talk) 04:10, 6 September 2009 (UTC)
 * Not quite. According to our article a human is a member of the species homo sapiens (and, indeed, homo sapiens redirects to human). It is a single species, which may (in some taxonomies) have extinct subspecies such as homo sapiens idaltu. Modern humans are subspecies homo sapiens sapiens. Gandalf61 (talk) 12:19, 6 September 2009 (UTC)
 * Perhaps the usage isn't completely nailed down, but using "human" to refer to all of genus Homo is common enough that the human article starts "This article is about modern humans. For other human species, see Homo (genus)." APL (talk) 17:39, 6 September 2009 (UTC)


 * "Race" comes from a word meaning "line", which could be broadly interpreted to include "species", although it's more normally used to mean "sub-species", i.e. varieties within a species - although, technically, every "variety" within the human species is unique from the DNA perspective, except for identical siblings. Baseball Bugs What's up, Doc? carrots 09:12, 6 September 2009 (UTC)
 * Thank you, that was really interesting. OP. 190.244.183.244 (talk) 13:49, 6 September 2009 (UTC)


 * The trouble is that we're comparing one fairly vague term "race" with another vague term "species".


 * The scientific definition of 'species' is generally that two animals are of the same species if they can successfully interbreed. That would make all modern humans be a part of the same species.  However, we say that lions and tigers are different species - despite the existance of ligar and tigons.  Actually, that's a terrible example because ligars and tigons are generally infertile - but I happen to like the words "ligar" and "tigon"! Dogs and Wolves might be a better example.


 * Race (biology) has a somewhat better definition in biology (and all humans are of one race under that definition too) - but the use of the term Race (classification of human beings) in everyday speech has a different meaning. The trouble with the everyday meaning is that it takes a somewhat arbitary group of genes (the one for skin color, for example) and promotes that to higher significance than any other group you might pick.  Why classify people according to their skin color rather than (say) their lactose-tolerance or their eye color?  It doesn't make any kind of scientific sense.  What we're really trying to capture is the place where the persons ancestors originated before the mass migrations of relatively modern times has caused that to become a largely irrelevent thing.


 * So to directly answer the OP's question: Yes, we are all one species. Yes, we are all one Race (biology).  No, we aren't all one Race (classification of human beings).


 * SteveBaker (talk) 14:00, 6 September 2009 (UTC)

Future human evolution and brain complexity
What environmental conditions will be required in order for future human evolution to favour an increase in brain complexity rather than a decrease? Neon Merlin  06:19, 6 September 2009 (UTC)
 * Anything that causes intelligent people to mate more. APL (talk) 08:49, 6 September 2009 (UTC)
 * For further information on this theory, see Space Seed and Star Trek II:The Wrath of Khan. Baseball Bugs What's up, Doc? carrots 09:06, 6 September 2009 (UTC)
 * For further information on this theory, see Space Seed and Star Trek II:The Wrath of Khan. Baseball Bugs What's up, Doc? carrots 09:06, 6 September 2009 (UTC)


 * For traditional evolution to work, two things have to happen - firstly, there has to be a genetic mutation or a chance combination of genes that results in some physical change. Secondly, that change has to give the recipients of that mutation an enhanced probability of passing the gene(s) onto the next generation.  So IF there is a genetic change that makes some people smarter than others - and IF that change means that they have more children than the average person - THEN the population will tend to become smarter.  Sadly (perhaps) it's not clear that our intelligence is genetically determined...and it's far from clear that more intelligent people have more children.  Perhaps very mentally deficient people are less likely to have kids - but there is some evidence that things are heading the way of the movie Idiocracy (it's a terrible movie - no need to watch it!)...the idea being that intelligent people are too busy with their exciting jobs to raise kids - where the dumb people have nothing better to do - so they have vast families.  That would tend to produce an evolutionary pressure AGAINST rising intelligence.


 * But that's traditional evolution. Modern humans have a tendancy to break the rules.  When there is a genetic mutation that might prevent some couple from having kids - we step in with medical treatments for infertility.  If someone is too stupid to hold down a long term job - we don't allow them and their children to starve - we provide social security and food stamps and such - so they survive, despite that evolutionary pressure.


 * What I think is more relevent here is the concept of 'memetics' - the evolution of ideas. If two individuals have brains of identical make-up - but one is educated to modern standards and the other is brought up by wolves - we're going to say that the latter person is not as intelligent as the former.  Education is memetics in action.  Ideas that work are passed on by teachers to children - ideas that don't work fall by the wayside.  Ideas evolve.  Since humans are the carriers of these 'memes' - we can get more intelligent (well, depending on your definition of that tricky word) as time passes.  I believe that is the fundamental flaw in the ideas behind Idiocracy - the brains of the kids who come from large families with stupid parents aren't measurably genetically different from the single child of a Nobel award winner - so providing we have an educational system that allows the efficient passing of memes from the brain of the Nobel prize winner into the brains of the kids of stupid parents, our "intelligence" can continue to evolve despite the lack of genetic improvement.


 * SteveBaker (talk) 13:39, 6 September 2009 (UTC)


 * Efficient transfer of memes in a cognitive way, that is. The other six kinds of transmission listed in the article won't make us smarter, they'll just make more memes. 213.122.26.161 (talk) 14:12, 6 September 2009 (UTC)

APL may not have considered that much mating these days is recreational. Anything that causes intelligent people to procreate more will have the desired effect. Cuddlyable3 (talk) 13:51, 6 September 2009 (UTC)


 * Contrary to what SteveBaker says the Heritability of IQ article indicates intelligence is even more determined by genetics than height. Interesting the correlation between twins gets closer the older they are. It also lists a couple of genes which do contribute to intelligence though probably a very large number do, the number of repeats in bits which don't occur in genes also contributes though I didn't see that mentioned in the article. Dmcq (talk) 14:05, 6 September 2009 (UTC)
 * And anything I've read about it indicates rich people do tend to have more children and that correlates reasonably well with intelligence. But then so do the poor. It's the in betweeners that don't. Dmcq (talk)
 * And there are good and evil people in all economic classes. Until basic human nature can be overcome, there will be no real improvement in the human condition, regardless of "intelligence". Baseball Bugs What's up, Doc? carrots 14:13, 6 September 2009 (UTC)
 * "Practically, however, the upper bound of these correlations are given by the reliability of the test, which tends to be 0.90 to 0.95 for typical IQ tests..." how is the reliability of an IQ test tested? Is there an official prototype person with an IQ of 100, used for calibration, preserved at a constant temperature under a glass jar in Paris? 213.122.26.161 (talk) 14:22, 6 September 2009 (UTC)
 * You test a person lots of times and see how much the results vary. --Tango (talk) 14:53, 6 September 2009 (UTC)
 * Some people's results on repeated IQ tests vary a great deal, presumably because they were tested on days on which they had lot of intelligence, or an unusual lack of it. So for this method of testing the test to be a good one, it would have to be performed on a person whose intelligence was known to be constant. Even better, take a person whose intelligence varies over time by a known amount, and see if the test can pick up on the variations accurately. 213.122.26.161 (talk) 15:30, 6 September 2009 (UTC)
 * We can't have someone we know to have constant intelligence or that has a known variation in intelligence because our only measure of intelligence is the one we are testing. You have to just do the same experiment with lots of people. --Tango (talk) 17:28, 6 September 2009 (UTC)
 * Most people aren't much of a fan of the sort of things that would be required to manually affect human evolution. See eugenics. Evolution is a rather nasty business -- rapid "progress" is made only by the lack of reproduction (often death) of the great majority of individuals in a species. Most people aren't that interested in participating in that type of ethical system. Much of what we call "civilization" are safety nets so that just because you are born with poor eyesight or stubby legs or a slightly less-than-average brain, you don't have to actually die. Consider how much money we funnel to genetic diseases that affect a small minority of people—this is an act of humanity, not evolutionary fitness. There's no reason that eugenics couldn't be made to "work", but it would involve implementation on a horrific, probably impossible scale. --98.217.14.211 (talk) 14:37, 6 September 2009 (UTC)


 * Forgive me for avoiding the direct question, but I think it is important to point out whenever questions like this are asked that the minimum time it would take for any manipulation to have the tiniest noticeable effect is on the order of 1000 years. Thus, while such questions might be philosophically interesting, it's important to realize that they don't have any practical relevance. Looie496 (talk) 14:42, 6 September 2009 (UTC)


 * Well, not necessarily. It depends what you are trying to select for and what measures you are willing to take. If you're talking about one gene, and are willing to sterilize everyone else who doesn't have it, then you could do it in one generation. Again, nobody wants to do that, though. --98.217.14.211 (talk) 14:53, 6 September 2009 (UTC)


 * Where did you get that 1000 years from? If you look at dogs or cats selective breeding has made a huge difference in far far less time. Much of their breeding only started in the 19th century. Dmcq (talk) 15:22, 6 September 2009 (UTC)


 * What makes you say that? With drastic enough measures the average [something] of the human race could be changed noticeably in a single generation. To pick a horrific example, if tomorrow the all powerful eugenics king declared that white people were not allowed to reproduce, what would that do to mankind's average skin tone? APL (talk) 17:50, 6 September 2009 (UTC)


 * Well if you look at Human skin color it seems that people in Europe were probably dark coloured at the end of the last ice age and the white colour you see now mainly came about in the last 12000 years or so, a third of the change may have happened after the Egyptians stated their civilization so within the time of recorded history. And that was without any eugenics king declaring anything. Dmcq (talk) 18:10, 6 September 2009 (UTC)


 * A dog generation is about 1/10th of a human generation and usually includes multiple offsping, so dogs can probably evolve over 10 times faster than humans. And concerning the other points, it's true that you can get faster changes if you focus rigorously on one factor and select rigorously for it.  So for example, if you sterilize everybody whose brain size is below the mean, you might get a perceptible increase in brain size in a hundred years.  But for plausible interventions, it's difficult to get below 1000. Looie496 (talk) 18:26, 6 September 2009 (UTC)
 * Generation length is only one factor in evolution speed. One way to get fast evolution in humans would be to concentrate on just a small group. If you choose 100 people (50 male, 50 female - you might be tempted to have more women, but I don't think it would actually be a good idea) that are already above average in what it is you are interested in and you encourage early and plentiful reproduction you can get a generation every 20 years and remove people from the group that don't fit your requirements you could get pretty rapid selection. --Tango (talk) 18:52, 6 September 2009 (UTC)


 * The Ashkenazi intelligence article discusses the hypothesis that ashkenazi jews have greater intelligence on average than most other groups and that the difference is due to natural selection during the middle ages. Dmcq (talk) 20:22, 6 September 2009 (UTC)

Formula for subjective sound fading with distance, and adding
1) You are in a flat agricultural field (for example) with a speaker giving out, say, 60 decibels. What would be the formula for how the sound fades away the further away you stand from the source? 2) You have two speakers the both give out 60 decibels. If you put them close to each other, can you get more sound at any point than 60 decibels? What would you get? I realise I have not specified every parameter, so reasonable assumptions can be made. 78.146.76.67 (talk) 11:31, 6 September 2009 (UTC)


 * Calling sound levels "decibels" is a common error. The term 60 decibels is not a measurement unit; it just means a ratio 1,000. Possibly the OP should have posted "60 dB(SPL)" where SPL is the level reference of 20 micropascals (μPa). 0 dB(SPL) is barely audible. 1) In open air if a speaker gives 60 dB(SPL) at 1 meter one hears 60 - 10 20 log(r) dB(SPL) at other distances r meters. 1) Two such speakers broadcasting noise can give 63 dB(SPL) at 1 meter. If they broadcast a single frequency tone then the received sound is spread in a complex interference pattern with peaks of 66 dB(SPL) at 1 meter in some directions. The agricultural field is assumed not to reflect any sound. Cuddlyable3 (talk) 12:56, 6 September 2009 (UTC)
 * Thanks, can I just check I understand the formula please? Have I calculated correctly: at 10 meters away the answer would be 50 dB(SPL), at 100 metres away it would be 40 dB(SPL), and at 1000 metres away it would be 30 dB (SPL)? And at a billion (thouand million) metres away the noise would be minus 30 dB (SPL) - that cannot be right! 78.146.76.67 (talk) 13:31, 6 September 2009 (UTC)
 * Sorry. I corrected "10 log" to "20 log". At 1000 meters the speaker becomes inaudible. At greater distances the value goes negative.Cuddlyable3 (talk) 13:46, 6 September 2009 (UTC)
 * The negative thing worries me - should not the noise just get closer and closer to zero the further you are away? 78.146.76.67 (talk) 13:50, 6 September 2009 (UTC)
 * As dB is not an absolute measure, 0 dB has no particular physical meaning and is not the same as "no signal". Negative dB simply indicates that the ratio is increasingly smaller, and that your signal is increasingly less audible. &mdash; Lomn 14:07, 6 September 2009 (UTC)


 * This is a suprisingly difficult thing to answer.


 * The energy transmitted is proportional to one over the square of the distance - that's nice, simple physics. If you double the distance you are from the speaker - you get one quarter of the sound energy.  Easy!


 * However - you used the word "subjective" in your subject line and "decibels" in your question - and herein lies the tricky part.


 * The human ear doesn't report a doubling of sound energy as a doubling of percieved loudness...it depends on the duration and frequency of the sound waves as well as the amplitude. But very roughly - the sound has to have 10 times more energy behind it in order to sound twice as loud.
 * A decibel expresses the ratio of two sound levels - not some absolute number - there are many variations on the use of the term - read: Decibel (or the entire decibel article if you're brave!). Typically, audio equipment is described in terms of 'dbA' - which is ten times the log-to-base-ten of the ratio of the sound energy produced to the quietest sound a human can hear. So a difference of 10 decibels sounds like a doubling in loudness - and a 60 dbA speaker can sound like 6 doublings in volume - 2x2x2x2x2x2 - 64 times louder than the quietest sound you can hear.  A 70 dbA speaker would produce ten times as much sound energy - and sound twice as loud.
 * Incidentally - this is why listening to loud music can be so damaging to our hearing. The damage is done by the energy transmitted into our ears - but ten times the 'safe' amount of energy only sounds twice as loud.




 * Putting two speakers close together does indeed double the amount of sound energy - but a mere doubling of energy doesn't sound twice as loud to a human. There is also an ikky complication if the two speakers are playing anything like the same sound - interference.  If both speakers were playing the exact same perfect sine wave then as you walked around them, the sound would get louder and quieter because at some places the sound waves would add together and in others they'd cancel out.


 * SteveBaker (talk) 13:20, 6 September 2009 (UTC)

Thanks. You can imagine the speakers are giving out (different) traffic noise. I'd be very interested to know the formula for "adding" the noise of two different speakers which are at different distances. Also, as I wrote above, I think I must have misunderstood the formula given for the fading of noise with distance. (I'm ultimately trying to estimate the noise at particular coordinates from a non-straight road - probably best to model as several point souces of noise which correspond to individual cars on the road). 78.146.76.67 (talk) 13:46, 6 September 2009 (UTC)
 * If you do that, don't forget to take account of the fact that traffic slows down around tight corners - resulting in more vehicles tending to be there than on the straight parts - but also that the engine noise will vary with speed. If big trucks are to be considered, you'll need to consider the noise they make when engine-braking.  You probably need to calculate the sound energy emitted by each point-source - use the inverse-square-law to calculate the total energy at any given point - then convert that into dbA's using the equation in the decibel article. SteveBaker (talk) 15:17, 6 September 2009 (UTC)


 * A more or less direct quote (after poor translation) from my physics book: The total sound intensity at a specified point is the sum of the intensities caused by single sound sources. This result can be can be applied to, among other things, combining the intensities of different kinds of noise sources. It is not valid if the waves have a phase relation. It should be noted that aside fading with the squared distance and reflection/absorption by ground and other surfaces, the sound fades due to absorption by air. The correct approach to this problem depends on whether you want a safe upper limit or accuracy. --194.197.235.240 (talk) 15:22, 6 September 2009 (UTC)


 * If you're serious about this there is professional acoustic modeling software that's used by architects, but I don't know anything about it. For a point source the 1/r² law implies a 20 dB drop for each factor-of-10 increase in distance; for example 80 dBA at 1 meter becomes 60 dBA at 10 meters and 40 dBA at 100 meters. When combining multiple sources it's the energy that adds linearly, not the perceived loudness (ignoring interference, which should be safe to do in this case). If L is a dB measure of loudness then the correct formula for combining them would be $$L_{\text{total}} = 10 \log_{10} \sum_i 10^{L_i/10}$$, but in most cases you can approximate that pretty accurately by $$L_{\text{total}} \approx \mathop{\text{max}}\, L_i$$. Aside from reflection off solid surfaces, the 1/r² law can be modified by temperature gradients above the ground, which can act as a converging or diverging lens. I suppose there wouldn't be much reflection or temperature variation out in a tilled field, but I'm not sure. -- BenRG (talk) 15:30, 6 September 2009 (UTC)


 * Sound normally fades faster than the inverse square law in a field because the sound is refracted upwards. If you have a clear sky and a cold night though the air will be colder near the ground so the sound is refracted down and it fades more slowly than inverse square. Interestingly sound is not in the main 'carried' by the wind downwards, what happens is that the air in the wind travels faster further away from the ground so making sounds refract down more downwind and refract up into the sky upwind. Dmcq (talk)

Thanks for all the above, especially to BenRG for his formula for combining several sound sources. I seem to recall reading on one of the Wikipedia articles that I read a day or two ago that subjective noise decreases with 1/r and not 1/r**2. Perhaps it would be easier if I considered the sound energy for the fading-with-distance and sound-adding calculations, and then after calculating the sound-energy for the X.Y points I was interested in, I then converted this sound energy into dB(SPL). In that case would the sound energy from different sources of traffic-noise simply add? I assume they would decay 1/r**2. How do you convert sound-energy into dB(SPL) and back please? 78.146.254.202 (talk) 09:19, 7 September 2009 (UTC)


 * Sound intensity and sound intensity level are of interest. --194.197.235.240 (talk) 11:03, 7 September 2009 (UTC)


 * Traffic noise goes down as 1/r (or in fact a bit faster than that normally because of refraction). The traffic noise is along a line source. There is a considerable amount of refraction reducing the noise because the air normally gets colder with height. A tilled field in sunlight would make the problem worse because it is dark and absorbs heat. That is why sound hardly travels at all on sunny days but you can hear foghorns from many miles away at night. Dmcq (talk)

I'm very interested in traffic noise going down by 1/r rather than 1/r**2 - the former should mean that sound from further away is less attenuated, and would make a big difference to the results of calculations. Do you have any sources, preferably online, that reinforce that idea please? I'm not sure that the two articles above do. Since I've been brought up from a schoolboy to believe that things attenuate by 1/r**2, I need to have a clear explanation for 1/r rather than 1/r**2. Thanks. 89.242.115.9 (talk) 20:23, 7 September 2009 (UTC)
 * 1/r2 comes about like this: If you imagine a point source of sound (or light or heat or almost anything with waves) out in the middle of nowhere - and imagine it producing one short BEEP! of sound.  That sound radiates outwards in all directions equally so at any given moment the sound wave is the surface of a sphere that's growing at the speed of sound.  Well, the initial burst of sound energy is spread out over that entire surface - so the amount of sound energy at any given point on the surface is equal to the initial sound energy divided by the area of the sphere - which is 4 pi times the radius squared.  Hence - the sound at any point at a distance 'r' is proportional to 1/r2.   However, we've been talking about sound ENERGY - and as I explained above - the human ear isn't a very linear device.  The formula in decibel and A-weighting (which weights the results based on frequency) relates the percieved VOLUME to the incident ENERGY - and it's not a simple relationship...but I suppose if you imagined that the ear was percieving that volume was proportional to the square of the amount of energy - then volume would be proportional to 1/r - but I don't think that's true.
 * At any rate, this is a horribly complicated business. Firstly, you don't know your source data to enough precision.  Just how much noise does a vehicle make?  You have everything from a prius running in all-electric mode - up to an 18 wheeler doing engine braking - and everything in-between.  Then you have the number and mix of vehicles on your road - the effects of corners and hills changing their engine speeds and causing them to bunch up in some places and spread out in others.  You don't know the distribution of frequencies within those sounds.  Then you have the effects of refraction and reflection of the ground - and absorption of sound by the ground, trees, etc - which is different for sounds of different frequencies and different frequency components within a single sound.  When you get to the end of all of that - then you have to consider that humans don't perceive sound in a simple way - you have to turn incident energy into dBa numbers using the A-weighting approach.  There are so many unknowns in that set of variables that it's going to take a really expert person to get the error bars down to something manageable - or else you're going to have answers that have a couple of orders of magnitude of error associated with them! SteveBaker (talk) 11:25, 8 September 2009 (UTC)


 * That's assuming a steady stream of traffic. Why not try google with something like 'traffic noise attenuation with distance'? You'll get some more complex formula that do an accurate job up to a hundred meters or so - after that atmospheric conditions make a large difference. It is a popular study. Dmcq (talk) 00:30, 8 September 2009 (UTC)

Defunct Sciences
Hello. I'm looking for a list (or group) of studies which were once considered scientific but are now considered (by the vast majority) as defunct. An example I could think of is alchemy; does anyone know any others?

Many thanks in advance. Cuban Cigar (talk) 13:59, 6 September 2009 (UTC)


 * I wonder if reading lines on your palms or bumps on your head would qualify? (Now, I'm seeing Daffy Duck disguised as a swami - "No bumps? We make some!" [pulls out hammer and whacks Porky over the head a few times]). Baseball Bugs What's up, Doc? carrots 14:09, 6 September 2009 (UTC)


 * Check out the articles in Category:Pseudoscience. Some examples include Astrology and Phrenology. -- KathrynLybarger (talk) 14:15, 6 September 2009 (UTC)


 * See also List of topics characterized as pseudoscience. Not all were considered legitimate in the past, but many were. --98.217.14.211 (talk) 14:51, 6 September 2009 (UTC)


 * We can do better than that: Superseded scientific theories seems like a good place to start. Category:Obsolete scientific theories has a LOT more! Some of the entries in List of experimental errors and frauds in physics might also qualify. SteveBaker (talk) 14:57, 6 September 2009 (UTC)

Far out this is exactly what I was looking for =) Thanks all for your help.Cuban Cigar (talk) 13:02, 7 September 2009 (UTC)

list of chemicals by density?
Dear Wikipedia!

I would like to ask if there is or if it is possible to create a list of chemicals (not only chemical elements) by density? Of course, list of only those chemicals, that have an article in Wikipedia (and when the density is given in the article).

Thank you! JTimbboy (talk) 14:08, 6 September 2009 (UTC)


 * There are vastly too many known chemical compounds to list...millions of them at least. You need to narrow your criteria before there could be any chance of finding such a list.  (eg: If you wanted the 100 densest or the 100 least dense, maybe we could help). SteveBaker (talk) 15:00, 6 September 2009 (UTC)
 * Since you are restricitng your request to chemicals on Wikipedia, the answer is -- maybe. You will need to either get a Wikipedia database dump and run a program on you own computer, or write a "bot" and get permission to use it. In either case, you will process all articles that include the chembox template. You do this by going to Special:WhatLinksHere/Template:Chembox. After you get your list the first time, you can look at the "what links here" page occasionally to see if thre are any new chemicals, and update your list. As steve baker said, there are a LOT of chemicals, so if you want to place your in Wikipedia itself, you will need to use multiple subpages. -Arch dude (talk) 16:53, 6 September 2009 (UTC)


 * You can save yourself a lot of effort because density is related to the average atomic weight of a compound. For liquids and solids this produces one set of data, for gases another set of lighter densities.
 * Thus without even looking I can tell you that C6H12O6 (glucose) has a very similar density to H2O (water), C2H5OH (ethanol), diamond is higher (C). Fe2O3 (rust) is higher still, and PbO (lead oxide) is very high.
 * Other factors do affect this, particularily bond length (which is why black phosphorous (P) is not higher than graphite (c).83.100.250.79 (talk) 19:04, 6 September 2009 (UTC)
 * A bit more advanced is to use mathematical techniques to generate densities eg 83.100.250.79 (talk) 19:08, 6 September 2009 (UTC)

JTimbboy (talk) 16:57, 7 September 2009 (UTC)Thank you all for your help!

Yes, there are too many chemicals to make a list of them by density, I should have mentioned that I meant very well known chemicals.

SteveBaker, I would be very grateful if you could tell me where could I see the list of the 100 densest or the 100 least dense.JTimbboy (talk) 16:57, 7 September 2009 (UTC)
 * I didn't say I had such a list - just that we'd stand a better chance of finding some kind of list for you if you could narrow the criteria. SteveBaker (talk) 02:42, 8 September 2009 (UTC)
 * I can get you started..
 * Least dense : hydrogen, helium, methane, ammonia, neon, ethyne, ethene / nitrogen / carbon monoxide (equal), ethane, oxygen, fluorine, propyne / argon, propene, propane / carbon dioxide / nitrous oxide (equal), oxygen difluoride...
 * Most dense Osmium
 * Also see List_of_elements_by_density - the most dense elements will be a good guide to the most dense compounds.
 * I've missed out odities such as styrofoam since these are mixtures, as well as leaving out extra terrestial stuff.83.100.250.79 (talk) 17:27, 7 September 2009 (UTC)

What is the transit time for the human baby gut?
What is the transit time for the human baby gut? —Preceding unsigned comment added by 213.40.97.246 (talk) 14:35, 6 September 2009 (UTC)
 * Where does this human baby gut live and where would it like to go? And will it be traveling by bus or by train -- I'm assuming it does not yet have a license?  DRosenbach  ( Talk 01:39, 8 September 2009 (UTC)
 * Uh, hilarious.
 * Children with diarrhea have a mean whole gut transit time of 5.5-7.3 hours, and 14.1-15.5 hours during the recovery period. Another study in ill preterm babies found that those fed small amounts of milk had a WGTT of about 32 hours at 3 weeks and 21 hours at 6 weeks. Here's more about baby poo than you'd ever want to know: That study of healthy children found the transit time in under threes is about 30 hours, and in those aged 3-4 it is 36 hours. Fences  &amp;  Windows  02:38, 9 September 2009 (UTC)

LiFePo4
Sometimes when I find a site with a fairly low price for LiFePo4 the cells are not encased or does not include a charger. Where can I find encased technology of good or best quality with a charger at the lowest price? -- Taxa (talk) 16:58, 6 September 2009 (UTC)


 * I don't know the answer to your question but where did you find the cheap LiFePo cells? I'm interested in getting some myself. --antilivedT 04:25, 7 September 2009 (UTC)


 * LiFePo4? Am I to understand that it includes polonium?  If so, where did you find those cells, especially at a "fairly low price"?  Polonium is very expensive, mind you. 98.234.126.251 (talk) 06:01, 7 September 2009 (UTC)
 * Do a search on both spellings and see if you get any results that include polonium. You probably will not since Li and Fe as part of the term modify its sufficiently to make the distiction between Po4 and PO4. -- Taxa (talk) 01:01, 9 September 2009 (UTC)
 * I assume it's LiFePO4 as written with total disregard for what it actually means:) DMacks (talk) 06:08, 7 September 2009 (UTC)


 * Well, the article Lithium iron phosphate battery has a list of manufacturers at the bottom -- maybe some of them might let you order the batteries (and charger) by mail-order catalog at wholesale prices. (You know that for the very lowest prices, buying straight from the manufacturer is usually the best option when possible.)  But then again, maybe they don't do that.  The only way to find out for sure is to check the company websites. FWiW 98.234.126.251 (talk) 06:21, 7 September 2009 (UTC)

icd-9 volume 3
There are three volumes of ICD-9-CM. Is volume 3 procedures only performed in a hospital? —Preceding unsigned comment added by 70.5.85.60 (talk) 17:23, 6 September 2009 (UTC)

Electronics Project
guys I have a project on Low noise amplifier .Plz can smebdy suggest a very basic tutorial starting right from the basics with circuit diagram


 * What do you consider "basic"? I would suggest Chapter 11 in Gray & Meyer for a theoretical overview, and I think Planar Microwave Engineering has an entire chapter on LNAs.  Are you simulating this design in SPICE, building the circuit out of discrete components or designing for an ASIC, or simply studying the topic for general overview?  The design methodology for LNAs will vary dramaticallly depending on what your actual needs are - first of all, what are you amplifying?  Voltage amplifiers and current amplifiers have different topologies for best noise characteristics.  Next, what are your power, bandwidth, operating frequency?  These will also help you select a topology.  How do you define "low noise" (e.g. 80 dB, 130 dB, spurs, noise floor, intermodulation, total harmonic distortion, etc.)   You might be best served by a basic introduction to amplifiers in general (specifically electronic amplifier), and pay close attention to the relationship between different figures of merit and the noise performance.  Then, you can "zoom in" on low-noise topologies and see some tricks to get the noise figure lower.  Nimur (talk) 20:17, 6 September 2009 (UTC)


 * Here's a tutorial from National Semi, on Youtube. They're pitching their own tools, though, so you have to parse through some commercial product placement; but they have Bob Pease hosting, so it's probably worth it.  He "can't tell you how to make a low noise amplifier", but he's going to "talk about how not to make a high-noise amplifier" with his classic awesome hand-drawn notes. Nimur (talk) 20:32, 6 September 2009 (UTC)

HNO3+carbamide
In gold refining neutralizing nitric acid in aqua regia is often done with carbamide. Can you help me writing the formula of this reaction?Renaldas Kanarskas (talk) 20:36, 6 September 2009 (UTC)
 * Carbamide is urea. I believe the reaction may be precipitation of urea nitrate (which allows excess nitric acid to be filtered off as this solid)

(NH2)2C=O + HNO3 >>> [(NH2)2C+-OH] [HNO3-]
 * There is no precipitate in reaction between aqua regia and carbamide. But there is a lot of fizzing, than show us significant amount of gas produced. Renaldas Kanarskas (talk) 21:58, 6 September 2009 (UTC)
 * Sorry, I realised that as I read more about gold refining .. see below for a fizzy reaction.83.100.250.79 (talk) 22:04, 6 September 2009 (UTC)
 * See Urea nitrate (I may be wrong - there may be another reaction) —Preceding unsigned comment added by 83.100.250.79 (talk) 21:29, 6 September 2009 (UTC)
 * Actually that probably isn't right - looking at the methods for gold refining it looks like the urea is being oxidised by the nitric acid (catalysed by nitrous acid present in aqua regia). Looking... (seems this only works in dilute HNO3)
 * In concentrated acid it would be easy to assume that everything is converted to N2, CO2 and H2O , in which case an equation would be fairly easy to get. Is that what you had in mind.?83.100.250.79 (talk) 21:55, 6 September 2009 (UTC)

5 (NH2)2C=O + 6 HNO3 >>> 5 CO2 + 8 N2 + 13 H2O
 * This is a balance reaction, but I can't guarantee it is the reaction that happens.83.100.250.79 (talk) 22:02, 6 September 2009 (UTC)
 * Thank you, will try to use this! Renaldas Kanarskas (talk) 22:49, 6 September 2009 (UTC)
 * Actually, concentrated HNO3 is normally reduced to NO2 in a redox. Tim Song (talk) 01:18, 7 September 2009 (UTC)
 * according to no toxic oxides of nitrogen are produced. Still could be N2O I suppose.83.100.250.79 (talk) 16:02, 7 September 2009 (UTC)
 * Interesting. It could be that the nitric acid was not very concentrated after all (it's 1/4 of a.r.) - but N2? That's weird. IIRC only really dilute nitric acid does that.Tim Song (talk) 18:20, 8 September 2009 (UTC)
 * NO2, NO, and NO2+ / NO+ would all be likely to react with the amine group on urea

(NH2)2C=O + NO2+ >>> (NH2)C(=O)(N+H2NO2) (NH2)C(=O)(N+H2NO2-) >>>   (NH2)C(=O)(N+NO) + H20 (NH2)C(=O)(N+NO) + H20 >>> NH2)C(=O)(OH) + H+ + N2O etc
 * That's just a speculation, NO+ would make N2 by the same process, both being electrophilic attack on the NH2 ... finally subsitution of H2O at the C=0 ... giving CO(OH)2 (carbonic acid)
 * There should be a lot of NO+ / NO2+ in aqua regia.83.100.250.79 (talk) 20:52, 9 September 2009 (UTC)
 * Cl2 may also react with urea (as do hypochlorites). There are examples of nitrous acid reacting with urea, so NO+ should react as well. The real reaction will be more complicated.83.100.250.79 (talk) 21:03, 9 September 2009 (UTC)

Relativity and Existence
The star Beta Comae Berenices is about 30 light years away. I was born about 25 years ago. Does this mean from the perspective of Beta Comae Berenices I do not exist? TheFutureAwaits (talk) 22:28, 6 September 2009 (UTC)
 * You do, they just won't know it until another 5 years or so. I doubt they're watching your house. But they could be watching TV broadcasting signals. For them, Disco is still all the rage here, as far as they know. Baseball Bugs What's up, Doc? carrots 22:39, 6 September 2009 (UTC)
 * I'm not sure if that's right. If that's true then you're saying everything beyond a person's immediate influence is predetermined as it has already happened but they have yet to experience it. TheFutureAwaits (talk) 22:48, 6 September 2009 (UTC)
 * "Predetermined?" Well, let's take an example closer to home. At the ballpark, the concession stands have the game on TV. However, due to FCC concerns and such, there is a slight delay, maybe 7 seconds. So if you happen to be watching the game through an exit portal and also watching the TV, you might see the batter hit the ball somewhere. Then you turn to watch the TV, and 7 seconds later you'll see the batter hit the ball. So it's "predetermined" in the sense that what the electromagnetic waves are carrying has already happened. That's going to be the case, whether the delay is 7 seconds or 30 years. Baseball Bugs What's up, Doc? carrots 00:44, 7 September 2009 (UTC)
 * Not really...on the earth, the time would be so instantaneous that it truly is action/reaction, rather than having something happen to you then 5 minutes later you experience it. Ks0stm  (T•C) 00:00, 7 September 2009 (UTC)
 * It just depends on how you define existing yet. In the reference frame there that's stationary relative to us (and probably in the frame of the star itself) your birth is in the past even though someone there couldn't receive information of the event for another 5 years.  I don't know what you want to call that.  However there are some reference frames at that point in which your birth is still in the future (frames moving very quickly away from Earth).  Deciding in what situations you qualify as existing isn't necessarily a easy question.  For example a proponent of four dimensionalism would say that you exist regardless of where they happen to be in time and space. Rckrone (talk) 23:54, 6 September 2009 (UTC)
 * If an explosion equal to 100 trillion666 megatons happened 30 light years away now, would we even know about it, let alone exist? So maybe you don't exist there yet, but it's inevitable that you will. Like the above poster said, it depends on your point of view/philosophy and your reference frame. Sagittarian Milky Way (talk) 00:25, 7 September 2009 (UTC)
 * This is entirely a "Tree falling and no one listening debate" and it centers on the fact that people are confusing an event with information about an event. You were born 25 years ago.  Information about your birth has not yet reached Beta Comae Berenices.  That doesn't mean that according to (hypothetical) people at Beta Comae Berenices you do not exist, it just means they don't know that you exist.  There's lots of things that have happened that you have no knowlegde of.  It doesn't mean they didn't happen.  -- Jayron  32  03:57, 7 September 2009 (UTC)
 * That's it. You got it. Baseball Bugs What's up, Doc? carrots 04:04, 7 September 2009 (UTC)


 * Something to keep in mind is that there is a distinction between events that are in your light cone and events that aren't. A past event in your light cone is unambiguously in the past regardless of reference frame.  Any event outside your light can be in the past, present or future depending on your reference frame.  For example TheFutureAwaits' birth is outside the light cone of someone who is on Beta Comae Berenices right now.  If they're stationary relative to Earth, TFA's birth is 25 years in the past as it is to us here on Earth now (although they can't yet know about it).  But if that observer were to suddenly accelerate away from Earth to faster than (5/6)c, then TFA's birth would suddenly become a future event.  That's not something that can happen with the Giants game I missed last week. Rckrone (talk) 04:44, 7 September 2009 (UTC)


 * No, I think your obfuscating the reality of the situation with fancy physics; your still confusing the actual event (TFA's birth) with the receiving information about his birth, which can be played around with. By accelerating at (5/6) c, what you are doing is essentially outrunning the information, thus dilating the delay of that information reaching you to infinity (by keeping the information outside of the "light cone" forever). However, that doesn't change when the event happened, it just changes when the information arrives. Still the same tree, still the same sound, your just running away before you can hear it...-- Jayron  32  04:54, 7 September 2009 (UTC)
 * I wrote a response but Relativity of simultaneity does a better job explaining than I do. Rckrone (talk) 05:32, 7 September 2009 (UTC)
 * Yeah. You're right.  Darn that whole "Lack of a priviledged reference frame" thing.  Sometimes the tree makes a sound before it even lands... -- Jayron  32  05:46, 7 September 2009 (UTC)
 * I generally agree with your crossed-out answer more than I agree with the "relativity of simultaneity" article... -- BenRG (talk) 12:15, 7 September 2009 (UTC)
 * If the article is incorrect or confusing, we need to edit it to make it more correct and clear. Always remember that while simultaneity is not absolute, causality is always preserved.  The hypothetical observer outside the light-cone could not have been impacted by the OP's birth yet, because of causality; but they could have predicted it (assuming they had sufficient prior information) and therefore be aware of it (speculatively) before confirmation arrives.  If their predictions were wrong, they would have no way of knowing until (at least) after the light cone from the OP's birth "arrives" at their location.  Nimur (talk) 15:20, 7 September 2009 (UTC)


 * One mistake people sometimes make in these things is thinking of objects as points in spacetime. Objects are lines in spacetime. The situation is like this:

| |                X  * here-and-now BCB -> |\ | | \|               |  * birth of TheFutureAwaits |
 * The event marked X is the earliest point on BCB's worldline where your birth or subsequent events could have a causal effect. So, from the perspective of Beta Comae Berenices when? "Right now"? Meaningless. At the time the light we're now seeing from it was emitted? That's about 35 years prior to X. Same cosmological time as determined by CMB anisotropy? Around 5 years before X. I can't think of any other reasonable question to ask along these lines.


 * Forget the relativity of simultaneity. Different coordinate systems assign different coordinates to the same point. That's all there is to the relativity of simultaneity. It's not "wrong" as such, just meaningless. It's a statement about coordinate systems, and coordinate systems don't exist. -- BenRG (talk) 12:15, 7 September 2009 (UTC)
 * "Now" does have meaning in the context of a particular frame. (I would point out there's a difference between "meaningless" and "not particularly useful". I would agree that it's often not a particularly useful way to think about the relationship between two events.)  In this case I was using "now on BCB" to mean the point that's at the same time as here, according to the Earth frame.  I wasn't as clear about that as I could've been. Rckrone (talk) 17:42, 7 September 2009 (UTC)

But cause and effect travel at, at most, the speed of light. What good is existance if it doesn't make a mote of a difference to the most sensitive detector? (at least temporarily, or, if you're receeding fast enough, indefinately/forever) You can't even be aware of the existance of an event without it causing an effect (otherwise, how did you notice?) TheFutureAwaits exists, to an omniscient observer outside spacetime. But so do the 2012 Olympics (probably). I think we can agree, using the usual Plain English sense of the language, the 2012 Olympics don't exist yet. There is a very high probability that there will be a day, that they exist. That means, for now, they don't exist. That doesn't stop from people from planning or predicting events that don't exist because we're trying to make them exist, or finding out what will exist before it does. And for high likelyhood things (like Greenwich sun meridian crossings?) it's only natural to list tomorrow's and 2010's as fact, but technically they are just as much fiction as Moby Dick until they occur, in the flesh. Interestingly enough, on the last one Ockham's Razor says shut up. Sagittarian Milky Way (talk) 01:16, 8 September 2009 (UTC)
 * I think any attempt to naturally generalize plain English language, which is based on a classical picture, to the relativistic case is going to be problematic. In the classical case, events fall into only two categories: past and future (ignoring border cases), and so there are a bunch of equivalent ways we can define the concept of events that haven't happened yet.  Some of them are as events that can't affect us now, events the we can still affect, or events that are forward in time from where we are now.  In the relativistic case those three aren't equivalent (and the last one depends on your reference frame which makes it kind of problematic).  I don't think there's a natural way to resolve the ambiguity without just deciding on some new definitions. Rckrone (talk) 06:57, 8 September 2009 (UTC)

Would these tomatoes growing at a sewage works be safe to eat?
I just saw this article. Would the tomatoes be safe to eat? I understand that the sludge is eventually turned into compost which is presumably safe to grow food plants in, but what about these plants that are growing directly on the waste? Spin Dryer (talk) 23:27, 6 September 2009 (UTC)


 * What mechanism would cause them to be unsafe to eat? What about that process concerns you? -- Jayron  32  23:29, 6 September 2009 (UTC)
 * Just wondered if there could be pathogens taking up into the plant, and therefore the fruit. Spin Dryer (talk) 23:39, 6 September 2009 (UTC)


 * Food has been grown with feces as fertilizer for thousands of years. That's not a problem. Pathogens won't go through them. More worrisome are things like heavy metals that might also be in waste water. --98.217.14.211 (talk) 23:57, 6 September 2009 (UTC)


 * That's the story that was told to me by someone who worked at a sewage farm. At the place he worked, they apparently had some very large, very healthy-looking tomato plants with nice-looking fruit growing in unexpected places. The staff were told that the tomatoes were unsafe to eat (and not to even think about picking them) due to the possibility of contamination by heavy metals and other chemicals from the various cleaning products that people routinely flush/put down the sink. --Kurt Shaped Box (talk) 09:24, 7 September 2009 (UTC)


 * People don't actually flush that much nasty stuff down the sink. The main problem with heavy metals is purely 'natural': they bioaccumulate. In other words, are enriched upwards in the food chain - which we're at the top of. So our feces would normally contain many, many times more heavy metal than the corresponding amount of plant-mulch or cow dung. --Pykk (talk) 19:23, 7 September 2009 (UTC)


 * In the US, people put all kinds of stuff down the sink. Maybe not so much things like Mercury, but there are all kinds of traces of medications in the water.  Googlemeister (talk) 13:33, 8 September 2009 (UTC)


 * Untreated human waste is not considered a safe fertilizer, and contamination of vegetable fields with human sewage has been blamed for a variety of outbreaks, including cholera, norovirus, and the parasites Giardia and Ascaris (roundworms). -- Scray (talk) 01:27, 7 September 2009 (UTC)
 * I think it's important to understand (given the OPs second comment) that AFAIK the danger comes from contamination. It's difficult to grow something in sewage and ensure you don't get any of it on the stuff you are growing. Washing is not guaranteed to get it all off and you may only need a small amount and I presume it may even penetrate the surface somewhat. anyway. I expect this is particularly a problem with leafy vegetables but low hanging fruit like tomatoes will still have some risk. Nil Einne (talk) 09:08, 7 September 2009 (UTC)
 * Certainly bugs can penetrate fruit skin. My father was a ship's doctor in the Royal Navy in WW2 and had to deal with a Dysentery outbreak caused by sailors eating water melon stored by traders underwater in the then infected Sweet Water Canal. The sailors seemed to think if they washed the melon and cut the skin it was good enough to sterilise the interior. --BozMo talk 09:28, 7 September 2009 (UTC)
 * Hmm, even if true it hardly proves that the pathogens got through the unbroken rind. Enough of them might have stuck to the rind after washing, and then when the sailors cut into it, they carried them into the meat on the knife.  I don't know for sure that the pathogens can't get through, but I have to say it seems a little unlikely to me given the thickness of watermelon rind and the size of ameobae, combined with the existence of a plausible alternative explanation. --Trovatore (talk)

Identify this.
What is the large plane featured in this image? Thanks in advance, Perfect Proposal 23:28, 6 September 2009 (UTC)


 * The answer is on the image description page - "The Space Shuttle Challenger crewmember remains are being transferred from 7 hearse vehicles to a MAC C-141 transport plane". Nanonic (talk) 23:34, 6 September 2009 (UTC)


 * Concur, that is a C-141. Googlemeister (talk) 13:30, 8 September 2009 (UTC)