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

= February 16 =

Time
Why do AM and PM start at 12:00 instead of 1:00? JCI (talk) 03:50, 16 February 2009 (UTC)


 * Because they stand for "before noon" and "after noon" in Latin. See 12-hour clock. --98.217.14.211 (talk) 04:33, 16 February 2009 (UTC)


 * Can I also add that am should be thought of as starting at 0:00 (just the maths does) CipherPixel (talk) 08:54, 16 February 2009 (UTC)

When does 12 a.m. mean noon?
After reading 12-hour clock, I was quite surprised to find that the US Government Printing Office defines 12 a.m. as noon. (See this document and scroll down to section 12.9 or search for "noon".) I know that going back to the Latin, noon is neither ante- nor post- meridiem. But it seems when it is used, common modern interpretation is that 12 a.m. is midnight and 12 p.m. is noon. Is there any historic precedence for the GPO definition? Is there any other entity in this world that uses this convention? -- Tcncv (talk) 07:43, 16 February 2009 (UTC)
 * I'm more used to 24 hour time but the US GPO actually makes sense to me, since it goes 1am - 10am then 11am, it only follows that next is 12am followed by 1pm. Vespine (talk) 08:40, 16 February 2009 (UTC)
 * If you wish to communicate clearly and logically, say 12 noon and 12 midnight. Use of a.m. & p.m. after 12 is ambiguous and needs context to assist a correct interpretation.  Even those who know the modern convention often get it wrong!    D b f i r s   09:11, 16 February 2009 (UTC)
 * The problem with your definition is 12:00:00.00000000000000000000000000000000000000000000000000000000000001 p.m. is clearly intended and logically can only be 0.00000000000000000000000000000000000000000000000000000000000001 seconds after noon. If you use 12 am to mean 12 noon then you have the oddity of suddenly changing to pm with the smallest measurable time interval afterwards which IMHO makes no sense. As I've remarked before when this came up, 12 pm as noon therefore makes a lot more sense and it seems to me outside of the US there is little ambiguity or confusion. Definitely when I searched, by and large the vast majority of sites used 12 pm to mean noon and 12 am to mean midnight. Google searches are of course hardly scientificly compelling but given the evidence, I see little reason to presume there is any real common misconception. Of course, I'm not denying that strictly speaking, the terms are ambigious or just plain wrong but then again, this is hardly uncommon with a lot of the English language. After all, most of us can survive when we say 'the weight is 80kg' even though they're really talking about mass. For that matter, as I've remarked before elsewhere on wikipedia, I personally don't care if people say their timezone is -5 GMT or -5 UTC. The fact that GMT is ambigious and they probably mean UTC but could mean UT1 is no concern of mine. I don't need that level of precision. I just don't want to have to work out or remember WTF EST is. This doesn't mean of course there aren't cases when you need to be completely unambigious or that even in general, it may not make more sense be accurate and avoid unambigious terms. Simply that it isn't really IMHO that big a deal. P.S. I originally had a lot more zeroes but for the sake of the reference desk, I reduced it Nil Einne (talk) 10:40, 16 February 2009 (UTC)
 * If it's 0.0 seconds after noon, it's equally 0.0 seconds before noon. I don't see any compelling reason that it's more reasonable for AM to be a half-open interval closed on the left, than a half-open interval closed on the right.  The only correct (and only safe) approach is to say "12 noon" or "12 midnight", and we ought to insist on these terms.
 * Except of course that a general switch to 24-hour time would be even better. I made the switch long ago because I was irritated at having to get up at 7 AM (or whatever) and sleeping through it because I'd set my alarm for 7 PM. --Trovatore (talk) 10:48, 16 February 2009 (UTC)
 * I usually use 24 hour alarm clocks for that reason. However I have never really found the need to use 24 hours clocks in general usage. It's not that hard to use both, as it suits you. P.S. You haven't explained what happens at 12:00:00.00000000000000000000000000000000000000000000000000000000000001. Clearly 12:00:00.00000000000000000000000000000000000000000000000000000000000001 noon or midnight make little sense. P.P.S. Again I don't deny that a general switch to 24 hours may be better, simply that it doesn't really cause that many problems using both. Of all the confusing problems we have in the world, there are far bigger ones like the way some people insist on using customary units in everday life when most of the world has moved on Nil Einne (talk) 10:53, 16 February 2009 (UTC)
 * I missed this because of the anon intervention. Sure, epsilon after noon is PM.  Just like epsilon before noon is AM.  And noon itself is neither, just like 0 is neither negative nor positive. --Trovatore (talk) 11:56, 16 February 2009 (UTC)
 * Nil Enne has a point. It makes sense for pm to start 1 second after 11:59.59. Rather than 1 second+some arbitrary infintesimely small unit of time. The fact is the minute where the clock read 12:00.xx is in the pm, why not make the whole minute in the pm, rather than all of it except one infintesimal instant? —Preceding unsigned comment added by 129.67.37.225 (talk) 11:36, 16 February 2009 (UTC)
 * Assuming (and it's actually quite an assumption) that time is modeled by the real numbers, then the "1 second+infinitesimal" is not an option. The boundary point of AM, and the boundary point of PM, are both noon; the only question is which set noon actually belongs to, if either.
 * But there is no truly standard convention. The only safe course is not to depend on how the phrases "12 am" or "12 pm" will be understood (which means not using them at all).  These locutions should simply not appear; they should be considered incorrect. --Trovatore (talk) 11:44, 16 February 2009 (UTC)
 * I think you're overcomplicating things. I'm personally not trying to argue from a strictly mathematical sense and as I've said before, I'm not denying at 12 noon and 12 midnight may be the only tecnically correct terms. My question is from a human POV, which one is more logical and simpler? Should 12pm be 12 noon or 12 midnight? Since most people other then SB accept that 12:00:00.0000000000000000000000000001 pm (or whatever) is 0.0000000000000000000000000001 seconds after noon it makes a lot more sense for 12pm to be 12 noon. Again let me repeat the fact this may not be entirely technically accurate or that you can make a legitimate argument that it should be midnight doesn't change the fact it's a lot simpler and more logical then suddenly changing at some underdefined interval which depends on what kind of mathematics we use and perhaps what kind of precision or accuracy we count time with. Let's not forget the whole idea from a scientific viewpoint of 12 noon actually being noon is bunkum anyway in basically every location of the world given the nicities of time zones, daylight saving time and astronomical realities particularly when we start to get to such a high level of accuracy. The whole thing is completely arbitary anyway that's why people prefer the simpler notion of 12:xx pm being 12 noon/afternoon then 12:xx pm being 12 midnight if it's precisely that and not even the tiniest measurable time interval after and if it is a measurable interval after then 12 it's 12 afternoon. If you still don't accept it then good luck I guess, meanwhile most of the world gets by fine accepting 12pm as 12 noon and 12am as midnight and trying to tell them they're wrong or it doesn't make sense isn't getting anywhere since for reasons I've tried to explain, it makes a lot of sense to most people who don't get into the overtly complicated mathematics and definition side of things which for reasons I've already explained seems a bit pointless. 14:18, 18 February 2009 (UTC)


 * Nobody can ever agree on what 12am means, so just use 12 noon or 12 midnight as appropriate. There is also confusion about when "midnight on Sunday" is. Is it the end of Sunday or the beginning? This confusion is so great that it's very common to see events advertised as being at either 11:59pm or 12:01am so there isn't any doubt. --Tango (talk) 11:51, 16 February 2009 (UTC)
 * I believe I am right in saying that trains in Britain are never timetabled to depart or arrive at midnight, for this very reason. DuncanHill (talk) 14:57, 16 February 2009 (UTC)
 * I disagree, most people can agree on what 12am means. There is some confusion, but it far less common then people make out. Nil Einne (talk) 14:18, 18 February 2009 (UTC)


 * Why doesn't the whole world go onto UTC and be done with it. That will not only eliminate the a.m./p.m. ambiguity, it will eliminate time zone confusion as well. After all, the US is moving to metric measurements. While we're at it, let's eliminate the 50 -States- State governments of the US, each with its own legislature and set of laws - it's clumsy, expensive, and confusing (though it's a lawyer's paradise in disentangling inter-State affairs. - GlowWorm. —Preceding unsigned comment added by 98.17.32.201 (talk) 14:53, 16 February 2009 (UTC)

I don't believe that 12:01am is confusing - you simply have to think for a moment. The number indicates the number of hours that have elapsed ante-meridiem. Hence 12:01am and 00:01pm are simply two different expressions of the same moment. The 24 hour clock is just a system where all hours are conventionally expressed ante-meridiem. Treating 12:01am as being shortly after midnight is silly. SteveBaker (talk) 15:10, 16 February 2009 (UTC)
 * What does "number of hours that have elapsed ante meridiem" mean? "Ante meridiem" means "before noon", "hours elapsed before noon" doesn't make sense. The only way I can see to interpret it is as "hours until noon", in which case 12:01am should mean one minute before midnight, which is certainly doesn't. --Tango (talk) 17:17, 16 February 2009 (UTC)


 * The way I see it is this: We divide the daylight hours into morning and afternoon, but we don't divide the night-time hours.  There are no words for "before midnight" and "after midnight"; both before and after midnight are still parts of "night" - except that the date changes, but it's still "night" at 12:05 am.  The morning ends and the afternoon begins at noon.  The precise point of noon (if such a thing even exists; it's gone as soon as it arrives, not a second later, not a milli-micro second later, but instantenously) is probably in neither camp, but noon is when the afternoon begins.  We start books on page 1; we start months on the 1st; so if noon is when the afternoon starts, then it makes sense to consider it part of the afternoon, rather than the very end of morning.  It has intuitive sense, but may not appeal to scientists.  --  JackofOz (talk) 23:12, 16 February 2009 (UTC)
 * But the start of a book isn't the end of something else. The hour from 12 noon to 1pm is certainly part of the afternoon, just as the 1st of March is part of March (the fact that we say 1st March, not 1 March is relevant here, and there's lots of interesting stuff about how time was measured and referred to in the past, but I won't get into it), but the instant of 12 noon and the instant at the beginning of 1st March are boundary points and it's completely arbitrary to assign them to either interval. It's far better just to leave them as separate points, hence "12 noon" rather than either "12 am" or "12 pm". --Tango (talk) 14:42, 17 February 2009 (UTC)
 * It seems to me that the 24 hour clock begins at 0.000000000000001 and continues to 24.000000000000000000000. By contrast the 12 x 2 hour clock talks of 12.02 am/pm instead of 00.02. I still think of noon as 12.00pm. Kittybrewster  &#9742;  14:56, 17 February 2009 (UTC)
 * The point is though that arbitary or not, it's a lot simpler for 12 pm to be 12 noon then for it to be 12 midnight particularly since the instant is basically just that, an instant which can be as small as we measure time. The problem with books is they are not a continuum since words or letters are discrete elements which is something that doesn't exist for time. Therefore you can easily say what the end of Harry Potter 1 is and what the beginning of Harry Potter 2. I've tried to avoid getting too complicated until now but if you get into the complicated side of things, but you have to really ask what do you mean by an instant when you are talking about a continuum anyway? It seems to me we're talking about something as meaningless as 'when does life start'. Since as I mentioned, even the 'instant' we would call noon isn't even noon nearly everywhere it becomes even more meaningless. This isn't uncommon in life. So if we are going to use something so meaningless, why not choose simplicity and not complicate things with 12:XX pm being the noon/afternoon period (i.e. during the daylight hours for most places) rather then the overtly complicated 12:xx pm being the afternoon period (during the daylight hours) unless it so happens it's the exact instant (00 precisely) we call 'noon' in which case 12:xx pm is 12 midnight. P.S. This will be my last posting on the subject in this thread and I'll probably just link here if it comes up again. P.P.S. Simplicity is the primary reason why I prefer metric over customary units, the complication of having two unit systems is bad enough but the overt complexity of a a system which doesn't fit in with our decimal numerical system or for that matter makes even less sense in other areas (seriously 0 degrees being a temperature with no meaning to anything we experience in real life nor any scientific meaning and where our universal solvent on earth boils at 212 degrees?). On the other hand, I do continue to use 1KB=1024 bytes so :-P Nil Einne (talk) 14:18, 18 February 2009 (UTC)

Academia at present
How could anyone be so complacently content with how the education system is today honestly? It's become more closed than actually being uneducated, as it seems. First of all, isn't there clearly a monopoly in nations? How could you monopolize knowledge? (That, of course, depends on whether 'education' still cares about knowledge nowadays.) How could you necessitate huge fines just for these bureaucratically-sanctioned 'educators' to 'teach' you? (Which mostly means shoving their own opinions on theories and whatnot down throats.) How could it be so tense? All of this wasn't founded like this though, was it? 94.196.67.254 (talk) 12:17, 16 February 2009 (UTC)


 * What country has a state monopoly on teaching? Every country I know allows for private schools... --Tango (talk) 12:21, 16 February 2009 (UTC)


 * No... I'm talking about something deeper than that. A monopoly on knowledge itself that the education system as a whole creates that makes it seem like knowledge couldn't possibly exist outside it. —Preceding unsigned comment added by 94.196.67.254 (talk) 12:43, 16 February 2009 (UTC)
 * In that case, I don't have the faintest idea what you're talking about. Do you actually have a factual question? --Tango (talk) 13:09, 16 February 2009 (UTC)


 * Perhaps you could be more specific in your question. What for instance would I be able to see that was different if things were the way you wish they were? Dmcq (talk) 13:36, 16 February 2009 (UTC)


 * It is possible that the OP refers to fringe areas of knowledge (spiritual, esoteric, psychoceramics, etc) which are excluded from mainstream education. There are, after all, folks who think that creationism should be part of the curriculum in physics and biology.  If so, the question may be better placed at the humanities desk.  --Cookatoo.ergo.ZooM (talk) 13:40, 16 February 2009 (UTC)

The education system certainly doesn't have a monopoly on knowledge - after all, there are public libraries, Wikipedia, the Internet - all of those are sources of knowledge that lie outside of the education system. If as Cookatoo suggests you are asking why the people in control of the education system act to limit what knowledge they teach - then that also is true, simply because there is more knowledge in the world than one person could possibly ever learn - and someone has to decide what subset of all knowledge is most important for people to know. Hence (for example) we teach basic algebra in schools - but we do not teach the proof of the three color map theorem. The reason for this should be self-evident - algebra is useful to everyone (eg I know my car just travelled 300 miles on 10 gallons of gasoline - how good is my mpg this week?) - but knowing WHY the three color map theorem is true is pretty much useless for every day life - and only a very few mathematicians really need to know it. So yeah - they limit what is taught to a reasonable set of things that the average person has time to learn and will find useful later in life. SteveBaker (talk) 15:03, 16 February 2009 (UTC)
 * Perhaps the other reason we don't teach the proof of the "three color map theorem" is because it doesn't have one, seeing as it isn't true... ;) --Tango (talk) 15:16, 16 February 2009 (UTC)
 * Spoilsport! --Stephan Schulz (talk) 15:28, 16 February 2009 (UTC)
 * Duh! The "three colour map theorem" works perfectly well.  I once tried it out on the map of Down Under and had one colour left.  --Cookatoo.ergo.ZooM (talk) 16:44, 16 February 2009 (UTC)
 * D'oh! How stupid we mathematicians have been all these years... why didn't you tell us?! --Tango (talk) 17:08, 16 February 2009 (UTC)
 * Do'h indeed. Sorry - I meant four-color...not three. You see what happens when they don't teach you stuff!  I should have gone with Fermat's Last Theorem. SteveBaker (talk) 21:48, 16 February 2009 (UTC)
 * Teaching the only known proof of the four-color theorem would be like teaching the phone book — it has a huge section of tedious, mechanical checking of an enormous number of cases; thus far, AFAIK, no human has ever gone through the whole thing — it's been verified only by computer. Of course arguably the "real" proof, from the perspective of a human mathematician, is the part that reduces the problem to those machine-checkable cases, and that could possibly be taught.  I don't know whether it would be an undergrad or grad level course, as I don't know how difficult that part of it is. --Trovatore (talk) 21:56, 16 February 2009 (UTC)
 * I believe it's still way beyond the lecture-course level, in terms of size if nothing else. The five colour theorem, on the other hand, was on my undergrad course, and takes about half a lecture. Algebraist 22:02, 16 February 2009 (UTC)
 * Academia as we know it in western culture arose from the Medieval university system of Europe. The OP's assertion that academia "wasn't founded like this..." is astonishing, considering that the medieval university was intended as the exclusive mechanism for passing literacy and historical knowledge to the next era of monks, selectively excluding the masses.  As the system progressed, (a few revolutions later), academic institutions changed focus pretty significantly, and the philosophy of education changed dramatically.  "The role of religion in research universities decreased in the 19th century, and by the end of the 19th century, the German university model had spread around the world."  That is to say, students participated in four years of focused "undergraduate" curriculum with a major specialization, instead of five or seven years of religious, liturgical, and philosophy training in Greek and Latin, with the occasional mathematical theory course.  Most prestigious American universities did not switch to the "German" model until around the first World War (Academic major attributes this to Harvard in 1910, but I have heard differently).  In any case, it has been a fight uphill for centuries against the "establishment", with effort to liberalize the system.  In my experience, the more rigorous scientific disciplines suffer less from the "shoving of theories and opinions", because most of science is pretty self-evident if you know where to look for evidence.  Nimur (talk) 17:24, 16 February 2009 (UTC)
 * "most of science is pretty self-evident if you know where to look for evidence." goes into the quote-file:) DMacks (talk) 01:29, 17 February 2009 (UTC)
 * Just as an addendum, the first university in the US to really emulate a German model in terms of an undergraduate/graduate division was Johns Hopkins University. (There is more to the European model than just academic majors.) It's also of note that America was a considered largely a scientific backwater until the 1920s or so. --98.217.14.211 (talk) 01:54, 17 February 2009 (UTC)
 * Hmm, the US was a scientific backwater but at the forefront of technological (in things like engine design, flight, the work of Edison...). Sounds like the way we thought of Japan in until the 1990s.  Seems like there is a story there.--OMCV (talk) 04:16, 18 February 2009 (UTC)

I suppose the OP wanted to know why academia has a monopole of who may call himself educated (=degree's system). —Preceding unsigned comment added by 80.58.205.37 (talk) 13:02, 20 February 2009 (UTC)

quantum mechanics(a particle in box)
It is possible that a particle in a box is equaly likely to moving in either direction. Iwant a disscation on it.Supriyochowdhury (talk) 14:03, 16 February 2009 (UTC)
 * You say "either direction", does that mean you are talking about a 1D box? If the scenario is symmetric, then the solution will be. I don't know what you mean by "disscation", do you mean "dissertation"? If so, we're not going to write your dissertation for you. --Tango (talk) 14:07, 16 February 2009 (UTC)


 * I think the OP meant "discussion". A Quest For Knowledge (talk) 16:11, 16 February 2009 (UTC)


 * Try google with your question title "quantum mechanics(a particle in box)" and and one of the first entries it comes up with is the wikipedia article Particle in a box. It is worthwhile learning how to use search engines like this. Dmcq (talk) 14:14, 16 February 2009 (UTC)

It is almost certain that your particle in a box is equally likely to be moving in both directions. If not then it will be drifting in one direction and ending up at one side of the box. Graeme Bartlett (talk) 20:25, 16 February 2009 (UTC)

Terpenes
are Terpenes base or acidic and can they be turned solid? —Preceding unsigned comment added by 76.14.124.175 (talk) 16:35, 16 February 2009 (UTC)


 * It all depends on the Terpene you mean. Isoprene will neither be acidic or basic nor will it be solid at 25°C as the article states. Of course a long enough Polymer of Isoprene units will turn solid at room temperature, as will substituted Isoprenes. For all other Information see Terpenes or ask a more specific question. --91.6.7.232 (talk) 17:38, 16 February 2009 (UTC)

Vision, light pollution, and the Milky Way
Hi. Let's say someone had 20/1 vision. Now let's say that another person with 20/40 vision, after dark-adapting their eyes away from as many streetlights as possible, at a given location, at night, can see objects up to a limiting magnitude of +4.5, without wearing glasses. Now let's say that the subject with 20/1 vision looks at the sky under the same conditions, would the subject be able to see the Milky Way (the subject with 20/40 vision cannot see the Milky Way under these conditions, but is able to from a location with less glare and light pollution)? Thanks. ~ A H  1 (TCU) 16:50, 16 February 2009 (UTC)


 * I don't visual acuity is the right measure of quality of eyesight for this. Visual acuity is about how well you can resolve small things, you're talking about how well you can see dim things, they are completely different abilities. Also, does anyone actually have 20/1 vision? That would be extremely impressive. --Tango (talk) 17:07, 16 February 2009 (UTC)


 * Resolving small things is the same as resolving dim things for a camera or a telescope. Is the human eye any different?  Nimur (talk) 17:31, 16 February 2009 (UTC)
 * On second thought, probably not. The size parameter is dictated by the angular area of a single pixel; the dimness is more of a signal-noise question or quantization size per-pixel.  Nimur (talk) 17:33, 16 February 2009 (UTC)
 * Sensitivity comes from the number of rods & cones, resolution from that too, but mostly from lens shape (i. e. I have 20/30 vision because my lenses are a little deformed). It is possible that the pixelation from a finite number of rods/cones could start to blur images at 20/1 vision (certainly it would before you got to 20/0.00001, for instance).  As above, I don't think there are likely to be many people with 20/1 vision (although it may be possible - one must remember that people exist who are nine standard deviations from the mean). Wily D  18:03, 16 February 2009 (UTC)
 * According to our article on visual acuity, 20/10 or possibly 20/8 is about the limit for humans. I'm not sure visual acuity follows a bell curve (I believe there are more people with worse than 20/20 vision than there are with better - 20/400 (uncorrected, which is what we're talking about) isn't very uncommon, the equivalent in the other direction would be 20/1, which is unheard of), so the 9SD thing doesn't necessarily apply. --Tango (talk) 18:09, 16 February 2009 (UTC)


 * It should be noted that the Earth is part of the Milky Way Galaxy. Just about everywhere you look, you're looking at the Milky Way.  Now if you want to look at the rest of the Milky Way Galaxy, that's a different question.  Sorry to be anal, but it always bugs me when I hear people say things such as "I can't see the Milky Way Galaxy".  I always want to say back, "You're looking at it right now.".  Whew!  That felt good to get off my chest.  :)  A Quest For Knowledge (talk) 18:17, 16 February 2009 (UTC)
 * "Milky Way" in this context (which is the original context) refers to the disk of the galaxy, which appears from our perspective to be a band of densely packed stars going all the way around the sky. --Tango (talk) 18:38, 16 February 2009 (UTC)


 * Well, the thing is, I have relatively poor vision, and wearing glasses allows me to see more stars in the night sky. For example, just today, I was able to see Venus in glasses 1 minute before sunset, but not without glasses until about 2 mintues after sunset. Maybe visual acuity is a measure of myopia or non-myopia-ness? Or, would someone with 20/1 vision see objects 20 times "closer" than people with 20/20 vision, meaning that astronomical objects seem "closer", and thus brighter as well? I came up with this (hypopthetical) question after a friend claimed he had 20/1 vision (being able to see the entire eye testing chart as well as all the copyrights), and he also claimed that he has never looked up at the night sky (I don't know if either one is true or not). I find that a limiting magnitude of about +5.5 is sufficient to glimpse the Milky Way. Would people with a higher-than-average visual acuity be able to see down to a better limiting magnitude under identical conditions? Thanks. ~ A H  1 (TCU) 23:30, 16 February 2009 (UTC)


 * First, visual acuity is how small of an object, in terms of angular size, that you can see. So yes, myopia directly decreases visual acuity by preventing the lens from focusing correctly.  People with better vision certainly don't see objects as if they were closer; all objects appear to be of the same size to you and your friend.  If he has 20/1 vision (I doubt it; why not test him?), he can see something of a certain size, say 1 mm, from roughly 20 times the distance somebody with 20/20 vision can.  But that's just because his eyes can focus more accurately, not because of anything mysterious.
 * Second, it makes sense that you can see more stars with your glasses than without. Stars are point sources, and the better the eye focuses, the smaller the area it takes up on retina.  A small circle of confusion is good because more light is being focused on fewer rod cells, so the star needs not be as bright to be detected.  A large circle of confusion has the opposite effect.  For an extreme case, imagine finding a star using a telescope and throwing the instrument way out of focus.  You won't see a thing.
 * The Milky Way, however, is anything but a point source. Blurred vision should not be much of an impediment to seeing it because it's always "blurred" in the sense that it has no sharp edges.  Smoothening out the transition from the Milky Way to the rest of the sky by a tiny bit can't have much of an effect.  --Bowlhover (talk) 02:27, 17 February 2009 (UTC)

hydroponics
do hydroponicaly grown plants grow faster than dirt grown plants? —Preceding unsigned comment added by 76.14.124.175 (talk) 18:11, 16 February 2009 (UTC)


 * According to our article, yes. A Quest For Knowledge (talk) 18:21, 16 February 2009 (UTC)

sudden freezing
i noticed that some times that while opening abottle of water (in liquid state) after take it out from afreezer it suddenly start to freez , do this have some thing to do with pressure ,,, ? —Preceding unsigned comment added by 86.108.53.185 (talk) 18:32, 16 February 2009 (UTC)


 * Supercooling. DMacks (talk) 18:34, 16 February 2009 (UTC)


 * Supercooling is a possibility, but the more likely explanation is the one you came up with, that the water is pressurized and that it is therefore able to stay liquid at a colder temp. Releasing the pressure allows it to freeze quickly. StuRat (talk) 19:03, 16 February 2009 (UTC)


 * (edit conflict)Well, I guess supercooling can be a factor as well, but if it's a pressurized container -- say, a can of soda -- that's not the reason. Rather, that'd be the CO2 in carbonated drinks. You don't mention if the water is carbonated, 86.108.53.185, but you do mention pressure, so I'm going to assume that that it is -- and you're correct, it does have something to do with the pressure. When you open the bottle, the CO2 gas suspended in the liquid expands and the pressure between the contents of the bottle and the atmosphere outside is equalized... and when gases expand, their temperature drops. Since you've kept the bottle in the freezer, the temperature of the water is already very close to its freezing point; when you open it and release the pressure, it cools down a little bit more, and that's enough to make a difference: it freezes. You don't get a solid block of ice, of course; it's more like a bottle filled with slush, because the temperature drop isn't that dramatic... but ice is ice. -- Captain Disdain (talk) 19:15, 16 February 2009 (UTC)

Water freezing up in an ice cube tray
I've noticed something strange a couple times when I made ice cubes. Normally, when you freeze water in an ice cube tray, I would expect that the surface of the ice cubes to be (more or less) flat. However, a couple of times, towards the centers of the several of each ice cubes' surfaces, water had apparently frozen up. They sort of looked like inverted icicles. I'm using a standard ice cube tray and a plain old refrigerator. How is this possible? A Quest For Knowledge (talk) 19:00, 16 February 2009 (UTC)


 * See ice spike. StuRat (talk) 19:04, 16 February 2009 (UTC)


 * That's it! Thanks. A Quest For Knowledge (talk) 19:12, 16 February 2009 (UTC)


 * Water has many unusual and mysterious properties, some mysterious even to science. I've read that one experiment suggested water to be H1.5O! ~ A H  1 (TCU) 23:21, 16 February 2009 (UTC)


 * Do you have a source for this? That doesn't make much sense to me.. there are Non-stoichiometric_compounds but water isn't one.  Friday (talk) 17:51, 17 February 2009 (UTC)
 * See Water (molecule). DMacks (talk) 19:02, 17 February 2009 (UTC)

Percent of people infected by the "common cold" each year in US
About what percentage of people are infected with the common cold each year in the US? I'm looking for an authoritative source -- a peer-reviewed journal or NIH website, for instance, would be great. I was able to find one here that said 90%, but I also found another (can't locate it at the moment) that said 35%.

Any help would be greatly appreciated!

&mdash; Sam 72.248.152.57 (talk) 20:07, 16 February 2009 (UTC)


 * The CDC page links to a huge number of academic and medical sources. "HPIVs are ubiquitous and infect most people during childhood. The highest rates of serious HPIV illnesses occur among young children. Serologic surveys have shown that 90% to 100% of children aged 5 years and older have antibodies to HPIV- 3, and about 75% have antibodies to HPIV-1 and -2."  The difficulty is in defining the "common cold" - depending on how widely you categorize ailments as "common cold", you will get incidence estimates that vary by orders of magnitude.  Nimur (talk) 21:12, 16 February 2009 (UTC)


 * Hmmm... the 90-100% figure would appear to be the total number of children exposed to the viruses at some point in their lives, not the total number of infections per year. But thanks for the sources. If anyone sees anything else, it would also be helpful. Thanks, Sam 146.115.120.108 (talk) 23:51, 16 February 2009 (UTC)


 * As soon as I read this question, I wonder what do you mean by 'infected'? Does the person have to show symptoms, or just come in contact with the virus?  I don't know if refining the question like this will get you a better answer (maybe scientific journals all define infected the same way), but it might help (and I'm curious).  -Pete5x5 (talk) 05:59, 17 February 2009 (UTC)

Sex hormones in ham?
Does ham sold in Canadian markets naturally or artificially contain human sex hormones or any substances with similar effects on humans? Neon Merlin  21:27, 16 February 2009 (UTC)
 * I would seriously doubt it. This sounds to me like an urban myth. That said, I believe that some plastics can degrade into chemicals similar to oestrogen. That may not be true, however -It's only half-remembered.-- Neo  Nerd  21:36, 16 February 2009 (UTC)
 * NeoNerdi you're probably thinking of Bisphenol A We haven't had a question mentioning that for a while. Waiting for Benzyl butyl phthalate to take off . Use of growth hormones in pork production is prohibited in the US and Europe AFAIK.  I found this study which you might find helpful .  You might also have found  or .  Estrogens naturally occur in pigs.  We need industrialized agriculture to feed our masses.  Unfortunately that comes at the price of sometimes having undetermined health effects.  I's good to be vigilant, but the media scare waves based on some poorly represented study are rarely helping. 76.97.245.5 (talk) 23:41, 16 February 2009 (UTC)
 * Tangential to the urban myth: If male pigs are not castrated, the meat may take on a on an unpleasant odour that 40% of the human population is able to detect. This is due to skatol and androstenon, especially the latter which is a pheromone. EverGreg (talk) 19:16, 18 February 2009 (UTC)

New colours
Could there be colours waiting to be discovered / thought up by our minds / whatever? - Jarry1250 (t, c) 22:01, 16 February 2009 (UTC)
 * Just a guess, but I'm going to have to say no. Every 'colour' in the sense we think of (the visible spectrum) is dependent upon wavelength, and I'm guessing we know all the individual wavelengths which produce different shades of different colours. The only way you could alter this is by going outside the visible spectrum, and then the product wouldn't be defined as a colour, per se. —Cyclonenim (talk · contribs · email) 22:29, 16 February 2009 (UTC)
 * You also have combinations of those wavelengths to consider. --Tango (talk) 22:38, 16 February 2009 (UTC)
 * No you dont, waves superpose. —Preceding unsigned comment added by 129.67.37.225 (talk) 00:10, 18 February 2009 (UTC)
 * How is that a refutation? —Tamfang (talk) 07:29, 20 February 2009 (UTC)
 * Any combination of waves from the set of possible wavelenghts superpose to make another wave which is already in the set of possible wavelengths, so by considering all possible wavelengths all possible combinations are already considered.
 * You seem to be saying that superposition creates a new simple wave, which is not true. —Tamfang (talk) 12:34, 23 February 2009 (UTC)


 * You could make new colours be fiddling with how the human eye works, but I think that's it. Pretty much all the colours possible are shown in the CIE 1931 color space chromaticity diagram (pictured here, but it won't be displayed correctly by your monitor). It doesn't correspond to precisely how the human eye sees colours, but it's designed to be pretty close (it's meant to be the "chromatic response of the average human viewing through a 2° angle" - what "average" means in that context, I don't know). --Tango (talk) 22:38, 16 February 2009 (UTC)
 * Even among normally sighted people there's some variation in the cone responses; I believe they averaged over that. -- BenRG (talk) 01:56, 19 February 2009 (UTC)


 * (ec) Human perception of colors correspond with how our visual and neural hardware perceive wavelengths of light. It's a finite range of possible perceptions—with the "standard hardware". There are some people who apparently have non-standard visual hardware who can see more colors than the majority of us can (see tetrachromacy), and of course there are those with non-standard visual hardware who perceive less colors than the majority of us (see color blindness). Other than those possibilities, there's no way for humans to experience more colors than the standard "visual spectrum". --98.217.14.211 (talk) 22:40, 16 February 2009 (UTC)
 * (triple edit conflict!) You may want to look at tetrachromat. If tetrachromacy in humans exists, then the trichromatic colors won't cover all the colors tetrachromats can see. 152.16.144.213 (talk) 22:41, 16 February 2009 (UTC)


 * On the other hand, not all colours appear in the spectrum. Brown, for example.  We perceive this as a colour separate to anything else, even though we know it's some combination of spectral colours.  The spectrum would have infinite gradations (not all discernible to the human eye, admittedly), so theoretically there's an infinite number of ways of combining two or more spectral colours to come up with a complex colour (again, not all separately discernible to the human eye).  Have all of these possible combinations been recorded and named?  I very much doubt it.  --  JackofOz (talk) 22:54, 16 February 2009 (UTC)
 * Not named, but we do know all the colors people are capable of seeing; they're all on that diagram, except that it doesn't show different brightnesses (and ordinary display screens are incapable of showing it correctly). -- BenRG (talk) 01:56, 19 February 2009 (UTC)


 * I could imagine that evolution or genetic engineering may expand the sensitivity of human eyes, say, into the infrared spectrum.  There may be significant benefits if folks could see a warm (edible) rat in some post-acocalyptic scenario in the middle of the night.
 * There may also be significant advantages if humans could "see" ultrasound or gravity waves or whatever. It would make sense to invent terms of pseudo colours for these new sensations.  If you can visually interprete the bits and bytes generated by the graphic card of your PC you have already saved €250 for a useless monitor.  --Cookatoo.ergo.ZooM (talk) 22:57, 16 February 2009 (UTC)
 * Also, as Steve alluded to recently (though I don't recall that he brought up this specific aspect), certain wavelengths in the near UV are invisible not because the retina doesn't respond to them, but because the lens filters them out. If your natural lens is removed (e.g. for cataracts) you will be able to see this light, and as it has a different mix of responses from the three sorts of cones than any other wavelength, you may perceive a color that no one with normal eyes can see.
 * (also don't forget the hooloovoo). --Trovatore (talk) 22:58, 16 February 2009 (UTC)
 * The IR emitted by a rat is very distant IR. About 10µm, I think, compared to the limit of human vision of about 700nm, so that's more than a ten-fold increase, whereas the current range of human vision is less than a factor of two from one end to the other. So engineering human eyes to see those wavelengths would be very difficult. Other animals can do it, though, see Infrared sensing in snakes. I guess we could try and add some snake DNA to our genome... --Tango (talk) 23:08, 16 February 2009 (UTC)
 * The question also is one of language. You might be able to imagine a new color, but how do you communicate that to others?  See Minor Discworld concepts.76.97.245.5 (talk) 00:24, 17 February 2009 (UTC)
 * It's quite complicated - there are at least four ways to answer this question:
 * There are colors we can't perceive because our retina is not sensitive to them (eg InfraRed). You can see infrared using night-vision equipment - but that works by turning the IR into shades of green.  You aren't 'seeing' the colors as different (it's just plain old green) - but you can see things that you wouldn't ordinarily be able to see like that a car has recently been driven because the engine bay is hot and therefore emitting IR "light".  Without this extra 'sense' we can't tell the difference between a car with a hot engine and a car with a cold engine - they look EXACTLY the same.
 * There are colors in the near UltraViolet that we can't perceive with normal eyesight because there is a protective sun-screen over our eyes that protects the retina from sunburn. However, some people have that protective layer removed as a result of cateract surgery.  After surgery they can see light in the near ultra-violet - but it just looks blue.   However, you can see blue-ish spots and stripes on flowers - which are really ultraviolet spots and stripes that the flower has evolved to attract bees (which can see into the UV).  But just as with night-vision - it doesn't seem to be anything amazing - just shades of blue.
 * We only have three kinds of 'cone' sensors in our eyes - so we see all colors as if they were mixtures of red, green and blue. But in the real world, there are (for example) 'kinds' of yellow that are mixtures of red and green and 'kinds' of yellow that look absolutely identical to us - but which are really pure frequencies of yellow light with no trace of red or green.   If we had the eyes of certain species of freshwater shrimp - we'd have as many as twelve different cone types and the world of color would be VASTLY richer and different than we can actually see.   In that sense, there are vast ranges of color that exist physically - but we just can't tell the difference.   It's like we're all somewhat colorblind.  So there are "more" colors out there - but to see them, you've somehow got to become a shrimp...unless...
 * There are very, very few women who are 'tetrochromats' who have a fourth kind of green sensor - they see colors in a richer way than we do - and they could distinguish colors that we consider to be identical as if they were very different indeed. Just two such people have been identified as a result of genetic studies.  They have to have both parents who are colorblind in very specific ways.  But they TRULY see colors that we can't even imagine.
 * SteveBaker (talk) 01:22, 17 February 2009 (UTC)
 * It's not at all true that "we see all colors as if they were mixtures of red, green and blue"—see my response below the divider. -- BenRG (talk) 01:56, 19 February 2009 (UTC)
 * Steve: Brown is a desaturated, dark red. It is not somewhere outside the CIE diagram. Edison (talk) 01:52, 17 February 2009 (UTC)
 * Edison: There are different browns. Some are more a dark orange, or even dark yellow, than dark red.
 * Yeah - brown is nothing particularly special - it's a word we use to mean various dark shades of red/orange/yellow.
 * Speaking (typing) as a colour blind person, I see a lot more brown than normally sighted folk. I take this to mean that we tend call things brown when they don't have a 'clear' colour. Mikenorton (talk) 14:04, 17 February 2009 (UTC)
 * When you say you see more brown, what that means is you can't distinguish between brown and certain other colours (red and green?). That doesn't mean brown is any different to any other colour, it just happens to be the one you have difficulty with. Basically, you see all combinations of red and green as the same thing, brown is one of those combinations. Why you describe it as seeing lots of things as brown, rather than lots of things as red, or lots of things as green, I don't know... convention, maybe? Or is there some underlying reason? Anyone? --Tango (talk) 14:12, 17 February 2009 (UTC)
 * Not exactly, I have problems generally with any mixed colours that involve red or green, e.g. mauve looks blue to me, but all 'muddy' reds and greens look brown to me, if I can't see a distinct colour, I call it brown. Mikenorton (talk) 16:43, 17 February 2009 (UTC)
 * It sounds like your response to red and green are the same as each other and significantly reduced from normal (you can't distinguish brightness of the colours you see as the same colour). The fact that they're the same is why anything that's just made up of red and green looks the same, and the reduction from normal levels is why it looks brown (rather than yellow, say - I'm assuming you see yellow as brown, yes? Whereas someone with normal colour vision sees bright yellow and yellow and dark yellow as brown (ish)). --Tango (talk) 18:01, 17 February 2009 (UTC)
 * Just to clarify, I see pure red as red, pure green as green and indeed bright yellow as yellow. I have the most common red-green colour blindness with a reduced sensitivity to red and green. It's worth remembering that, just like everyone else, I learned to call colours by particular names, whether I actually 'see' red as other people see red is impossible to tell. Mikenorton (talk) 18:11, 17 February 2009 (UTC)
 * So it's when red and green are mixed that you can't tell how much of each there is? So essentially you can't distinguish different shades of brown - reddish-brown, greenish-brown, yellowish-brown and anything inbetween all looks the same? And you call them all brown because that's what the rest of us call them - we just use the word to describe lots of colours which to you are just one colour. If my understanding is right (scientific method: Make observations, form theory, make prediction, test prediction!) you should have difficulty distinguishing bright orange and bright yellow, is that correct? --Tango (talk) 18:20, 17 February 2009 (UTC)
 * Better finish this off now, I'm having trouble counting the colons. Yes I have problems with that pair (more with yellowish orange and yellow) and similarly yellow and yellowish green. Otherwise your description seems about right. Mikenorton (talk) 18:35, 17 February 2009 (UTC)
 * My theory stands up to empirical testing (to an acceptable margin of error), fantastic! Thanks for helping me get my head round this. --Tango (talk) 19:07, 17 February 2009 (UTC)
 * @Mikenorton: It's quite rare to have both 'weak red' and 'weak green' colorblindness - much more common is 'weak red' on it's own or 'weak green' on it's own (which is what my son has). It's overwhelmingly likely that you have either one or the other but not both...and it would be valuable for you to find out which.  What this does is to tend to make shades of orange, yellow and 'lime green' (yellowish-green) harder to distinguish - but it doesn't make it impossible.  We discovered that my son is colorblind at age 16 when he got told off for not turning off his Wii videogame console.  It has a tri-color LED that shows red, orange or green.  Orange is 'standby' and Red is 'off' - and it rapidly became obvious that he couldn't distinguish the orange from the red because they differ only by a small amount of green - and with less sensitive green receptors, he can't tell the difference.  But his handicap is very minor.  In fact, the ONLY time it shows up seems to be with tricolor LED's and the fact that he fails the standard colorblindness test.  The rest of the time, his color perception seems OK.  FWIW, we were able to help him with the Wii problem by taping a piece of green-tinted candy-wrapper over the Wii's LED.  This shut out most of the red light so that he's now able to see whether the LED is very dimly green or off altogether.  Experimenting with colored filters may well help you in similar situations. SteveBaker (talk) 14:26, 18 February 2009 (UTC)
 * (He doesn't have green receptors; see my response below the divider. -- BenRG (talk) 01:56, 19 February 2009 (UTC))


 * Steve: I thought I had read somewhere that the UV color was at least a little outside of normal experience. It certainly seems possible a priori — say, if a certain near-UV wavelength produced a larger ratio between the blue-cone response and the green-cone response than any normally visible wavelength, then you wouldn't be able to reproduce that signal by any combination of normally visible light.  (I suppose people could see it if you shined that wavelength at them at such high intensity that enough of it came through the protective layer — good luck getting that past the ethics committee!) --Trovatore (talk) 02:02, 17 February 2009 (UTC)


 * The problem is that you only have three color sensations (Red,Green,Blue) - and all color perception is mixtures of those sensations. Ultraviolet light (for people who have had cataract surgery) stimulates the blue sensor and does not stimulate either of the other two - so the sensation is no different from a rather pure blue.  My mother had cataract surgery and she wasn't aware of having seen amazing "new" colors - but rather she sees blue in places where she didn't before.  She's an avid gardener and was somewhat surprised at how formerly uniformly colored blooms now had spots or stripes or other markings.  But sadly (and predictably) no 'new' colors.  Presumably objects with large amounts of UV reflectivity would also change hue slightly - but still, she's unable to perceive 'new' colors.  That's not possible without having more color sensors - and for that to happen, you'd have to be born as a tetrachromat or a freshwater shrimp. SteveBaker (talk) 03:18, 17 February 2009 (UTC)
 * Well, you seem to have skipped over my point, though. It may be true that your mother doesn't see any new colors; I don't know.  But if it were the case that one of these wavelengths she now perceives could get a higher ratio of blue-to-green, or blue-to-red, or blue-to-(0.3*green+0.7*red), or something like that, than any normally-visible light — then she theoretically could, because no linear combination with positive coefficents of normally-visible light could get you that ratio.
 * Note that just because she hasn't seen any such colors doesn't refute the idea, because she presumably has not been exposed to pure light of such a wavelength.
 * Whether this actually happens, as I say, I don't know. But it's not as simple to refute as you're making it out to be. --Trovatore (talk) 03:40, 17 February 2009 (UTC)
 * Indeed - she should be able to distinguish things as being different colours when we see them as the same colour, that's seeing new colours. The new colours will just be new shades of blue/violet, since it's only pretty near UV so isn't that different from blue, but it's still new colours. It will be rather difficult to distinguish them, since the human eye isn't very sensitive to differences in wavelength towards the ends of our usual range, but it will distinguish them a little. --Tango (talk) 13:34, 17 February 2009 (UTC)
 * That isn't the point. Being able to distinguish things that we see as the same color is not perceiving new colors — you might be able to distinguish A and B even though a person with normal lenses couldn't, but you'd maybe see A the way you used to see C and B the way you used to see D, so there's no new color being perceived.
 * The point is that maybe, for every wavelength that you and I can see, whenever the blue cones are firing at 100%, the green cones or the red cones are also firing, say at at least 5% and least 7% (these are just made up numbers).
 * Whereas maybe when Steve's mom looks at this new light, when it fires her blue cones at 100%, it's only firing her green cones at 2% and her red ones at 8% (again, made up).
 * In that case she would have a mixture of signals from the cones that is not possible, with any light, for a person with natural lenses. --Trovatore (talk) 19:25, 17 February 2009 (UTC)
 * But if you distinguish colours by seeing them as other colours then you lose the ability to distinguish those colours, so that doesn't help - that's just seeing different colours, not new colours. Someone without the filtering lens can distinguish between, say, "blue+UV" and "blue", two colours which the typical human can't distinguish between. (Perhaps I'm using the word "colour" slightly differently to its standard definition.) --Tango (talk) 19:45, 17 February 2009 (UTC)
 * I get the feeling neither you nor Steve has read what I actually wrote. --Trovatore (talk) 20:47, 17 February 2009 (UTC)
 * I read it. That's distinguishing new colours. If it was monochromatic UV, then it would be distinguishing UV from black, if it's UV+something visible then it would be distinguishing that from just the visible part. When you see extra strips on petals, that's distinguishing the colour of the strip from the colour of the rest of the petal, which the human eye can't usually do. --Tango (talk) 21:43, 17 February 2009 (UTC)


 * I read it too - and I didn't reply immediately because I wanted to check my sources to be absolutely sure. I don't think there is a 'new' color there.  UV light starts at 400nm.  When I look at higher resolution plots similar to the diagram above I find that the red receptor doesn't function to any measureable degree at 400nm.  Green and blue are both tailing off - but green hasn't completely gone away the ratio of green and blue at 400nm is not a whole lot different than in the "indigo" blue region right next to the 400nm cutoff.  It's possible that the precise shade of blue you'd see wouldn't be identical to any 'normal' shade of blue - but the difference is right down in the noise.  I don't think there is a noticably new color there - although I'll admit that it's mathematically possible.  Most important of all - LOTS of people have had this surgery and I can find no references to anyone seeing anything stunningly novel - they mostly report seeing new patterns and that some 'normal' objects seem to have shifted color - but not one (that I could find) report anything "new". SteveBaker (talk) 22:50, 17 February 2009 (UTC)
 * Wait a minute — you're saying the red cones don't respond to 400nm light? Then why does it look purple? --Trovatore (talk) 23:28, 17 February 2009 (UTC)
 * (See my response below the divider. -- BenRG (talk) 01:56, 19 February 2009 (UTC))


 * No, what I'm talking about is actually seeing new colors (or at least, new ratios of signals from the cones, that are not possible for a person with natuarl lenses). What you were talking about, in the 13:34 17 Feb post, was only making different color distinctions, which is not the same thing. --Trovatore (talk) 21:49, 17 February 2009 (UTC)
 * Well, it's just going to look like a slightly different shade of violet (as Steve says), you're not going to notice it as being new if you're just looking at it in isolation. You'll only realise it's new when you compare it to existing shades of violet. --Tango (talk) 22:54, 17 February 2009 (UTC)
 * And how exactly do you know that? --Trovatore (talk) 22:59, 17 February 2009 (UTC)
 * Because I've looked at the graphs and can see that the green and red lines are pretty much flat by that point. --Tango (talk) 23:00, 17 February 2009 (UTC)
 * Well, those graphs are obviously wrong (or, let's say, "incomplete") because they don't show the response of the red cones to violet light. The red line should start turning upwards again towards the left edge — that's why you see violet light as "purple". --Trovatore (talk) 23:05, 17 February 2009 (UTC)


 * Yes - the graph that's attached to this thread is wrong on several levels - it does miss out the little 'bump' at the end of the red curve - but worse still, someone has 'normalised' the responses to some arbitary 0..1 scale - when in reality, our eyes are rather insensitive to blue compared to red and especially green. I have a much more accurate plot which makes this rather clearer.  The red 'bump' actually confuses matters still further because there are places where a mixture of red and blue light can produce a 'magenta' shade that produces the exact same response as true 'violet' light on the visible side of the 400nm cutoff.  There is pretty much guaranteed to be some mixture of plain old red and blue light that produces the exact same response as near-UV light does in these post-cataract-surgery people.  And as I said before - if people started to see "new" colors after surgery - surely at least a few of them would have written about it - or it would be mentioned in the literature...and it isn't - so that is really the bottom-line proof we need.  All that is ever reported is seeing 'old' colors in 'new' places. SteveBaker (talk) 14:11, 18 February 2009 (UTC)
 * (No such bump—see my response below the divider. -- BenRG (talk) 01:56, 19 February 2009 (UTC))
 * (outdent) Ah, thanks, Steve — I was getting concerned that I might have misheard the thing about the red response at the violet end. Actually I'm a little disappointed I didn't, as that would have meant there were something interestingly complicated going on.
 * Anyway, I'd be interested in seeing this more accurate plot, if you have sufficient rights to upload it, or if you can supply an external link. --Trovatore (talk) 20:52, 18 February 2009 (UTC)
 * If people are interested, after a little Google Scholaring I found this paper about an experiment from 1980 finding the response curves. Page 5 shows the (normalised) curves they found, however for some reason that doesn't seem to be explained the curves for all except the "blue" cones are truncated at 400nm, and just the blue line continues to 350nm (which the description of the methodology suggests they were all tested to). You can clearly see that the green and red lines are both increasing again towards shorter wavelengths, and that the red curve has climbed back above the green one by 400nm and will presumably continue to climb above it (I can only guess). The graph shows that the response of the red and green cones to violet light (at about 400nm) is approximately the same as that to a combination of equal parts (assuming everything works linearly, which I think it does, at least approximately) blue light (at about 470nm) and red light (at about 650nm). The blue cone's response to violet light is significantly greater than its response to blue light, however - that may be less relevant due to the greater overall sensitivity of the red and green cones (according to Steve - this paper doesn't discuss that, at least not simply). This all seems to be consistent with the idea that violet looks like a mixture of red and blue due to the "bump" (the graph only shows an increase, but there is almost surely a decrease again at some point) in the red cone's response curve (or, more accurately, due to a greater bump in the red curve than the green). --Tango (talk) 17:00, 18 February 2009 (UTC)


 * See "List_of_colors". The article describes ulfire and jale as shades of ultraviolet, but in reality (in fiction, actually) they are two more primary colors that can be seen by a race whose eyes can see well into infrared and ultraviolet (a very good sci-fi book, by the way, that). Carlos Castaneda reports an indefinable color in one, I forget which, of his hallucinatory tours-de-force; a monster guarding a path shows him its colored back. --Milkbreath (talk) 02:25, 17 February 2009 (UTC)
 * It may be possible to stimulate the cones in different ways, for example the green cone absorption spectrum overlaps the red substantially and the blue somewhat, so there is not normally a pure green cone stimulation. If a pattern of light could illuminate the retina so that only green cones were stimulated you would get some form of ultra green colour sensation. Graeme Bartlett (talk) 03:23, 17 February 2009 (UTC)
 * Or even better, infragreen. The color of the Mushroom Planet. --Trovatore (talk) 03:41, 17 February 2009 (UTC)
 * Yes, you could (theoretically) connect electrodes to the retina/optic nerve and make all kinds of weird things happen, but you couldn't do it by shining light into the eye (which is what we usually mean by "seeing"). --Tango (talk) 13:34, 17 February 2009 (UTC)
 * Another idea for ultragreen is to bleach the red and blue cones with bright deep red and violet light, and then look at green spectral colour and see what it appears like. Graeme Bartlett (talk) 20:42, 17 February 2009 (UTC)
 * This is getting ridiculous. I've just found that we have an article on precisely this concept: Imaginary color. --Tango (talk) 00:55, 21 February 2009 (UTC)