Wikipedia:Reference desk/Archives/Science/2009 February 28

= February 28 =

Using neutrinos for communication
Glass Earth, Inc. is a science fiction short story by Steven Baxter. The technology part of it hinges on an invention to speed up global communications. Instead of sending signals via surface lines wrapping the globe, or bouncing them to a satellite and back, the company has hit on a way to control how neutrinos change their status, I think in the story it's their "flavor". They use a particle accelerator to produce collisions that send a stream of neutrinos in a straight line through the center of the earth and to the antipodes. Besides the accelerator, the only installation required is the detector at the other end. By modulating the neutrino states as if they were voltages, the information is transported.

I found that a fascinating conceit. Is the science simply wrong, as in it violates a fundamental constraint of nature, or could this in principle be done pending future advances?--Goodmorningworld (talk) 03:46, 28 February 2009 (UTC)


 * Creating neutrinos is relatively easy, although I'm not certain what degree of control one could have over their states. But the problem is that the same thing that makes neutrinos able to pass straight through the Earth with negligable loss make them almost impossible to detect: They almost never interact with anything. Neutrino detectors are notoriously massive, and maybe someone else can answer whether it's even theoretically possible for them to be small. Someguy1221 (talk) 04:56, 28 February 2009 (UTC)


 * AFAIK Cherenkov radiation offers a nice way of detecting neutrinos. You need a transparent medium (e.g. water) and lots of detection devices.  You need that much of your transparent medium because it increases your chances of getting some results.  Another way is to count collision products.  The Homestake Experiment used a chlorine solution.  Again you need lots of it to catch the few reactions.  The guys at the Cowan and Reines neutrino experiment created 5×1013 neutrinos per second per square centimeter and were able to detect only 3 reactions per hour as a result.  Don't know about the "relatively easy" part when it comes to creating neutrinos for a communications device.  Neutrino oscillation sends modulating neutrino states to the realm of si-fi.  The neutrinos we observe are thought to be mixes of 2 or more states and the mix changes.  What might be possible is a digital device that sends digitally encoded messages in the amount of neutrinos you produce during a given period.  Message density would be lousy and costs almost certainly prohibitive with current means.  E.g. look how long it takes to power up the LHC or an atomic power plant.  Just sending "SOS" in morse code could easily take months.  There would also be a high error rate due to natural fluctuations.76.97.245.5 (talk) 07:22, 28 February 2009 (UTC)
 * "Relative" to detecting them, that is ;-) Someguy1221 (talk) 11:10, 28 February 2009 (UTC)
 * Yeah - it's certainly possible - in principle - to send messages through large, solid objects using some kind of modulated neutrino stream. But the bandwidth of such a link would be of the order of one bit per day - the transmitter would have to be something like a nuclear reactor that could be turned on and off - or perhaps moved from one place to another - and the receiver would be some VAST tank of dry-cleaning fluid buried deep in a mine-shaft, studded with costly electronics.  'possible' and 'practical' are not the same thing.  But I don't really see the benefits.  A set of satellites in orbit is much cheaper than the gargantuan equipment needed to modulate and detect neutrino flow - the equipment needed to send and receive such signals is small enough to be hand-held and the only real downside is that it takes maybe twice as long for the signal to get there...but compared to the delays inherent in statistical analysis of neutrino detection when just a couple of detections per hour is the maximum rate possible...there is no reason that I could imagine for wanting to use such a device. I have not read "Glass Earth Inc" and our one-line summary ("A policeman must sort through the memories of a murder to find out who the killer is, and in the process, learns more about himself then he ever knew.") is less than revealing about the purpose of this neutrino communication trick.  Why was it important to the plot?  SteveBaker (talk) 13:27, 28 February 2009 (UTC)
 * Oh! Now you're putting me on the spot… it's been years since I read the story and unfortunately I am not possessed of a photographic memory… But! The gubmint's on the case already PDF: a project to induce rock deformation processes under the San Andreas fault (p.19) is already well under way. They mention "glass earth" (p.24) and that 1 in 1013 particles (p.4) make it all the way through this ole planet… Well that explains that fearsome excavation on Magnolia Boulevard… could I interest you in some prime real estate in the Valley?--Goodmorningworld (talk) 14:55, 28 February 2009 (UTC)
 * There are many other, less exotic, subatomic particles (like, say photons) which would work much better than neutrinos for the same purposes. Imagine me talking to you on the phone, but you only hear one consonant or vowel per hour.  That's the sort of level of reliablity neutrinos provide.  I suspect that this is a case of the author picking an exotic sounding real science term and just making up a use for it.  Here in the real world, there does not seem to be any compelling reason to use neutrinos for communication; they will still be bound to the speed of light, and so would not be any better than ordinary radio (light) waves/photons, and there are many reasons why they would be WORSE.  We already have reliable photon detectors out there which have been working for us for, oh, 100 years or so.  If it ain't broke... --Jayron32. talk . contribs  13:31, 28 February 2009 (UTC)
 * The benefit is that they can get from A to B marginally quicker since going through the Earth is quicker than going round it. So, we have fantastic latency and terrible bandwidth - kind of the opposite of using satellites (although the bandwidth for neutrinos is several orders of magnitude worse than the latency for satellites). --Tango (talk) 14:41, 28 February 2009 (UTC)
 * Actually I read somewhere (coulda been in the Weekly World News, coulda been SciAm) that data sent over the wires does not in fact propagate at light speed despite them being electromagnetic waves, but only at one-tenth the speed effectively… guess them lil' photons bump into each other like billard balls and there is some friction involved!--Goodmorningworld (talk) 15:02, 28 February 2009 (UTC)


 * The whole point is that neutrinos are better than photons, albeit in some very specific ways that may not be of use in most situations. Neutrinos are essentially unstoppable and unshieldable; unlike radio or microwave photons, they're not subject to any sort of interference.  Lightning and solar storms have no effect.  You don't need to have a dish or antenna on the roof to pick them up; they'll get to you in a bunker a mile underground, so you're protected from blizzards, hurricanes, and bombs.  Open line of sight isn't required for neutrinos.
 * Using visible or infrared photons is also inferior over long distances. Either you need line of sight and clear air (for laser communications), or you need waveguides (fiber optics) and lots of repeaters to cover any substantial distance.  Long-distance optical fiber is expensive to place, and vulnerable to enemy action, political whims, power failures, ship anchors (quite common), and earthquakes:.
 * In all cases, the time of flight for neutrino communications is shorter. Consider the worst case scenario: two people want to communicate between points on roughly opposite sides of the globe (Perth, Australia and New York, USA, perhaps).  The straight-line distance (as the neutrino flies) is about twelve thousand kilometers; going around the surface circumference is about twenty thousand.  (The actual distance over the surface will be quite a bit longer, as there aren't any great-circle communications links from Perth to New York.) Communication over fiber will take longer than the distance suggests, as the speed of light is about 30% lower in optical fiber than it is in vacuum; substantial time will also be lost at relay stations where the signal is processed in and out of fibers.  Radio is even worse.  The distance from ground to geostationary satellite and back is more than seventy thousand kilometers.  For a few applications (telepresence for telesurgery, for example) reduction in latency is worth almost any price.
 * The catch, of course, is that we lack any method to generate and detect powerful, modulated beams of neutrinos in anything approaching an efficient or cost-effective way. With current technology we couldn't send more than a few bits an hour, and we'd have to use billion-dollar particle accelerators and tens-of-millions-of-dollars detectors.  For such a system to be viable, you need to make neutrino generation and detection much more efficient; call that the unobtainium problem for this science fiction concept.  To the best of my knowledge, the generation problem is not solvable any time soon, and the detection problem is virtually intractable.
 * Incidentally, the world of science fiction is chock-full of uses for neutrinos. In Larry Niven's Ringworld series, the Ringworld's foundation is made of scrith &mdash; a material that stops roughly half of all neutrinos striking it with a layer about 30 meters deep.  Greg Egan used neutrinos in Wang's Carpets as a gentle, non-invasive probe of alien life.  Dan Simmons uses modulated neutrinos for military communication in the later parts of his Hyperion series.  The assorted Star Trek spinoffs can't resist the little neutrino, and – occasionally – they do use it in a way that makes a modicum of sense.  (Their favourite particle, though, is most certainly the tachyon.  Since it hasn't been observed and its properties are poorly defined, it's much more useful to twenty-fourth century scriptwriters.)  TenOfAllTrades(talk) 15:02, 28 February 2009 (UTC)

(unindent) It's crazy to claim that the time of flight of a neutrino makes it superior to a photon. The best neutrino detectors we have can only detect one out of every...uncountably large number...of neutrino's! So sure, the photons get there pretty quickly but all but 0.000000000...lots more zeroes...0000001% of them are completely ignored by the detector! So your transmitter has to transmit the first bit of the message as a gazillion-bazillion neutrons for about 20 minutes in order to be reasonably confident that the detector will pick up one or two of them. The tiny fraction of a second of latency you save by shooting your neutrino's through the earth are completely SWAMPED by the 20 minutes you have to wait in order to detect one of them! There is no object in the universe that's sufficiently transparent to neutrino's - yet opaque to photons that's big enough to save you 20 minutes at the speed of light!

Meanwhile, we've sent a few terabits over good old transatlantic cables, satellites, or carrier pidgeons. No matter the interference - if you could use a piece of equipment the size of a neutrino transmitter/reciever pair and send a few bits per hour we could have error-correcting codes with redundant transmission and enough sheer transmission power that we'd get through ANY amount of interference. Do you SERIOUSLY believe that there are any circumstances whatever in which photons are not at least a million times better? That's just beyond crazy!

Also neutrino's are NOT immune to interference. If your transmitter happens to be between the sun and the receiver then your receiver will be totally swamped with solar neutrino's and you'll get big-time interference from that damned great neutrino source in the sky. This might not be a practical problem for one transmitter and one receiver - but as soon as you get widespread adoption of the technology, those outages and interference between transmitters (which - bear in mind - cannot by any means be directional) would soon be a problem.

This is so far beyond reasonable...I can't believe anyone would even consider a vote in favor of the idea. SteveBaker (talk) 19:24, 28 February 2009 (UTC)
 * See, I saved you the trouble of brewing a cup of coffee LOL. Actually 1 in 1013 neutrinos are detectable with current technology after their trip through Earth (a lump of rock to us, an airy wisp to them). This figure comes from the DUSEL people at Homestake that I linked to above. I admit, I was having a bit of fun with them earlier, as their PDF file looks like something cooked up by a mad scientist gunning for the Ig Nobel prize, but in fact Raymond Davis Jr., who directed the Homestake Experiment, shared the Nobel prize for it in 2002. 106 is a million, 109 a billion, so we need to send ten trillion neutrinos on their way if one of them is to register on the detector. Multiply this by another factor of thousand to get a margin of safety and we're at ten quadrillion. That's only twice as much as the investment banks wrote off last year in dollars :-) How many neutrinos can we transmit per nanosecond, and how quickly can we modulate the stream? How expensive is that and how much do we need to figure for the detector? Suddenly it's beginning to look much more like an engineering and business problem than a physics problem. Which means that Yankee ingenuity will find a way, as it always has… (Probably going to need more orders of magnitude for error correction and a "wrapper" that distinguishes your message neutrinos from other broadcasters, the Sun and cosmic sources…8-) --Goodmorningworld (talk) 19:59, 28 February 2009 (UTC)
 * Exactly, it's an engineering and business problem. That's what all the responses have said - it's theoretically possible, just overwhelmingly impractical. --Tango (talk) 20:42, 28 February 2009 (UTC)


 * Steve Baker has it 100% right here (as usual). Lets simplify it. The supposed "benefit" of nutrinos is that they can travel through the Earth. The problem is, your nutrino detector is going to be made out of the same stuff the Earth is. Like atoms and molecules and stuff like that. So you broadcast some information via nutrinos. How do you catch those nutrinos to be able to read what you have broadcast? See the problem here? --Jayron32. talk . contribs 19:50, 28 February 2009 (UTC)
 * We already have neutrino detectors, I think it's creating the neutrino stream that will be the hard part - creating enough neutrinos quickly enough for the largest imaginable detector to pick up the signal at even a few bits an hour would be next to impossible. Building a slightly smaller detector wouldn't make that big a difference. --Tango (talk) 20:42, 28 February 2009 (UTC)
 * You may be a bit too pessimistic. I, however, was much too optimistic. The MINOS experiment in Minnesota collects collision events of neutrinos fired off from Chicago.

"More than a trillion man-made neutrinos will pass through the MINOS detector each year. Because neutrinos interact so rarely, only about 1,500 of them each year will collide with atoms inside the detector."

- MINOS FAQ


 * The "trillion" sounds low, could be a dumbed-down figure to signify "very many" for the general public. The 1500 events per year arithmetically come out to a few hours per bit and perhaps give hope for still more in the future. However the 1500 per year is a statistical figure which cannot be taken as "1500 smallest units of information", the number of bits per year would be smaller and availability is capricious.


 * This is very disheartening, I had no idea that it was so hard to generate neutrinos at a handsome clip.
 * Maybe we should start thinking out of the box. Pocket supernovas, anyone?--Goodmorningworld (talk) 22:52, 28 February 2009 (UTC)


 * This confrontation on the Reference Desk a year ago is an interesting and relevant read. --Bowlhover (talk) 19:55, 28 February 2009 (UTC)
 * Hmm - yeah - this guy "SteveBaker" had the neat idea to point out that if you absolutely had a need to communicate through the solid earth, you'd do better to use high explosives and seismometers. Sure, the speed of sound is kinda slow - but still, you could probably arrange to send one bit per second.   Definitely an incentive to keep your emails short though! SteveBaker (talk) 02:03, 1 March 2009 (UTC)
 * There isn't a need to communicate through the Earth, that just happens to be the quickest way from A to B. Your method would be far worse that existing methods that go around the Earth. --Tango (talk) 11:44, 2 March 2009 (UTC)


 * There was a semi-serious proposal for this back in the 70's (see abstract here). The actual paper doesn't seem to be online, and I've never read it, but from what I heard the idea was to use neutrinos to send covert messages to Ballistic missile submarines (which would use the surrounding seawater as a detector mass) (I'm not sure how the sub was supposed to detect the interactions — a hull studded with photomultipliers doesn't seem terribly practical). The main advantage over other communications media is the difficulty of intercepting (or even detecting the existence of) the transmission. So it's not as insane as it sounds. Well, not quite, anyway.
 * Actually, I think the main point of the proposal was that Peter Kotzer thought he could get the Navy to give him some money to look into it further... -- Speaker to Lampposts (talk) 08:32, 1 March 2009 (UTC)
 * Crazy proposals are made to the Military all the time - that doesn't legitimize them at all! SteveBaker (talk) 16:37, 1 March 2009 (UTC)
 * You guys are all forgetting that unobtanium is an excellent neutrino detector. --Sean 19:52, 1 March 2009 (UTC)
 * I see another problem with this whole thing; everyone keeps saying that we need to be able to fire way more neutrinos, but what if we just had a better detector? I haven't really done the reading that everyone's been linking to, so maybe I'm suggesting something more difficult/less efficient than just firing 100 quadrillion neutrinos.  But the way I look at it, didn't people once find it impossible to detect other things, like x-rays and such effectively?  But we found an efficient way.  There's probably a way for neutrino's too.  -Pete5x5 18:56, 6 March 2009 (UTC)

Observation of a mysterious psychological phenomenon
How is it that an individual is able to detect when another is staring at him or her even when the starer seems to be beyond even the peripheral vision of the detecter? Furthermore, as the starer, I can usually sense that the other individual can detect my staring insofar as I seem to know when the detecter will return the stare imminently? Is it the case that I was mistaken in the first question and the starer is simply NOT beyond the periphery of the detecter, or is there something more to this apparent example of ESP?Lashyn (talk) 04:54, 28 February 2009 (UTC)
 * It's likely not ESP. There are several things at work here probably:
 * When someone is very close to you and staring at you, like right behind your back, there are other cues, such as the sound of them breathing or their body heat or smell, which may lie below your conscious perception, but which you clearly are able to detect. Thus, that "creepy" feeling when someone is reading over your shoulder.  You can't see them, but you "know" they are there because you can sense them with your other senses.
 * You're eyes are scanning much more than you realize. When you look at something, your eyes don't focus exclusively on that thing, but rather they spend most of the time looking at what you are concentrating on, and the rest of the time scanning your field of vision.  If you watch someone's eyes very closely, you will see they are almost never "still", but constantly shifting and moving and refocusing.  Thus, while you aren't looking at the guy staring at you, you still "see" him.  Also, our minds are atuned to making eye contact; think how disconcerting it is to talk to someone who DOESN'T make it.  Our mind automatically notices when someone is making eye contact with us, even from a great distance.  These two things make evolutionary sense, as the first thing means that we can reflexly react to a threat even if we aren't focusing on it.  The second makes sense because knowing when someone is watching you can be quite important if you need to assess his friend/foe status.  Someone looking at you should always be a "person of interest"...
 * A sort of deja vu when you realize that someone IS staring at you. When you notice someone staring at you, you reflexively assume he HAS been staring at you for a while, then you convince yourself that you noticed it earlier.  You really didn't, but like all forms of deja vu, your mind creates the memory and so it feels real.
 * Does this all sound like reasonable explanations besides ESP? --Jayron32. talk . contribs  05:20, 28 February 2009 (UTC)


 * We have an article for this: The Psychic Staring Effect, but it's not very comprehensive, probably because there doesn't seem to be a lot of convincing scientific data about the thing, despite numerous research efforts. Still, it may give you some pointers on where to look for more information. Personally, I'm extremely skeptical. -- Captain Disdain (talk) 10:16, 28 February 2009 (UTC)


 * I too am extremely skeptical. I suspect that the 'observer selection' effect is happening.  When someone sneaks up and stares at you from behind - but you DON'T notice them - you aren't creeped-out and you never know that you failed to spot them.  It's ONLY in those cases when you did eventually spot them that you (perhaps retrospectively) felt that you were 'feeling their presence'.  There is strong evidence that our conscious minds operate with a significant delay behind 'real time' events and that our subconsciousnesses 'edit' the perception of the world to make everything self-consistent after the fact.  So it could be that we see someone who WAS looking at us - this gives our conscious mind the 'creeped-out' feeling immediately - and then a second or so later, the knowledge that we just saw them hits our conscious brain.


 * But if it were somehow to be shown to be true aside from all of that - then there are even more subtle cues you could be picking up on - every object in a room reflects light onto every other object - and every object blocks ambient light from every other object. When something as large as a person moves within a reasonably close distance to you, your surroundings change in subtle ways - shadows shift as light that was reflected from the walls behind you is blocked, the color of the person's clothing alters the color of the light being reflected off of things close to you.  Similar things happen in the audio domain - ambient sounds such as the whir of the fan in your computer are attenuated by this new, large, soft object in your proximity.  This is more than enough for your visual/audio system to realise that there is something large in close proximity that you aren't otherwise aware of.  The 'creepy feeling' would be a very useful evolved response to a potential danger. "Warning - Potential sabre-toothed tiger sneaking up behind you - don't move but get ready to move!".


 * There is certainly no reason to suspect this 'psychic' crap might be true. The idea that this rather simple phenomenon could require most of physics to be rewritten when there are any number of plausible explanations is an exceedingly stupid one. SteveBaker (talk) 13:13, 28 February 2009 (UTC)
 * My psychic staring perception is absolutely awful. Maybe I'm paranoid (actually, no maybe about it), but I always think people are staring at me, and so I am very self-conscious. I quite often look around to find that people actually aren't staring at me. This whole psychic staring effect to me seems like a load of confirmation bias. --Mark PEA (talk) 14:19, 28 February 2009 (UTC)
 * As a matter of fact, I and my many fellow sufferers from Human Spontaneous Involuntary Invisibility, or HSII, are afflicted with the opposite condition. There's always people cutting in front of us in line as if we weren't there, and when we get to the counter at the Dept. of Motor Vehicles the lady gets up and puts up the Lunch Break sign because she doesn't see us.--Goodmorningworld (talk) 15:22, 28 February 2009 (UTC)
 * Heh, I get that even when I'm the only customer. Typically, it's in a cafe where you have to order at the counter.  I'm in plain view (and I have a fairly large build, so I'm hardly easy to miss), but sometimes I've stood there for a couple of minutes, just to see how long it takes before one of the up to 6 people behind the counter notices there's someone there.  And then one of them finally says "Oh, I didn't see you there.  Are you right?"  That tempts me to turn and walk out, but that would mean I've wasted my time, so I say "No, not yet" or some equally smart remark, and order what I came for.  --  JackofOz (talk) 21:50, 28 February 2009 (UTC)


 * Rupert Sheldrake's book "The Sense of Being Stared At" covers this. --TammyMoet (talk) 18:01, 28 February 2009 (UTC)
 * The Sense of Being Stared At covers the flaws of his experiments. --Mark PEA (talk) 19:18, 28 February 2009 (UTC)


 * Sheldrake follows the classic path of the failed scientist. He spent an eternity collecting degrees from various colleges - then when he finally has to do 'real' work, he works for nine years as a biochemist trying to figure out some thing or other to do some hormone in plants - then (having utterly failed to do whatever he was supposed to be doing) he claims that it's beyond the ability of biochemistry to do that!  This sounds pretty petulant to me!  Then he starts writing a bunch of populist crap about all manner of pseudo-science.  Who knows whether he really believes it or not - but he's out to parley his qualifications and supposed decade as a working scientist into some kind of credibility for his whack-job ideas and churn that into book revenues.  Then he comes out with a bunch of other scientists who supposedly back his theories.  At first sight, these look credible - take, for instance, David Bohm - an impressive ex-Manhatten project Physicist who was allegedly impressed with Sheldrakes' work...but Bohm died in 1992 -most of Sheldrake's ravings were published after 1996 - so Bohm can't possibly have seen most of the things the Sheldrake is claiming.  Worse still, when Bohm made that comment, he'd been through a couple of years of acute depression and had electroshock therapy...can we really trust this as some kind of peer review?!?  I don't think so.  This is absolutely typical of this kind of crank stuff...the deeper you look, the crappier and flakier the information becomes. SteveBaker (talk) 01:32, 1 March 2009 (UTC)

I deny the truth of this claimed effect. It has been tested repeatedly by psychologists back to Titchenor, and only chance effects were seen in many opf the experiments. It seems to be purely anecdotal. If the starer's face is visible in peripheral vision, it is very salient, draws your attention, and AHA! You've caught them. If it is out of sight and you happen to turn and catch them, it confirms the myth. But you are utterly unaware of the times when a person out of your visual field stared at you and you failed to catch them. Like other ESP experiments, it is easy to produce positive results. Edison (talk) 21:04, 28 February 2009 (UTC)


 * Certainly our eyes are EXTREMELY sensitive to subtle motion in our peripheral vision. If you live in the UK where we have 50Hz television - when you look straight at the TV, it looks fine...but if you catch it in your peripheral vision, you can see it flickering.  (Some people can see this in US 60Hz television too...but less so).  We are SO sensitive to this that even fairly subtle lighting changes in our periphery are noticeable to the point of being distracting.  I'm pretty sure that anyone who is moves up behind you (especially indoors) is going to cast a shadow or alter the ambient light levels in your periphery - and it's quite likely that you're noticing that on a subliminal level. SteveBaker (talk) 01:32, 1 March 2009 (UTC)
 * Intuition, perhaps? ~ A H  1 (TCU) 01:22, 2 March 2009 (UTC)

contradiction between lorentz transformation and length contraction
the lorentz transformation equation for x' in the coordinate system K' as seen from the other coordinate system K is $$x^' = \frac {x - vt}{\sqrt {1 -\frac{v^2}{c^2}}} $$. But this means that x' should be farther from the origin as seen from K which means that the length will increase. This is contradictory to the length contradiction in special relativity. Please explain if i am wrong--harish (talk) 09:05, 28 February 2009 (UTC)

The length of an object, say $$l'\,$$, is obtained by simultaneously measuring the position of two extremes, say point 1 and point 2 with coordinates $$x_1'\,$$ and $$x_2'\,$$ and subtracting them. So $$l'=x_1'-x_2'\,$$. The condition of simultaneously measuring both ends tells us that $$t_1'=t_2'\,$$. If now we apply the Lorentz transformation to both time and space coordinates at both extreme points, we get four equations:
 * $$x_1' = \frac {x_1 - vt_1}{\sqrt {1 -\frac{v^2}{c^2}}}$$,
 * $$x_2' = \frac {x_2 - vt_2}{\sqrt {1 -\frac{v^2}{c^2}}}$$,
 * $$t_1' = \frac {t_1 - \frac v{c^2}x_1}{\sqrt {1 -\frac{v^2}{c^2}}} $$, and
 * $$t_2' = \frac {t_2 - \frac v{c^2}x_2}{\sqrt {1 -\frac{v^2}{c^2}}} $$.

But we've seen that $$t_1'=t_2'\,$$ which allows us to obtain
 * $$\frac {t_1 - \frac v{c^2}x_1}{\sqrt {1 -\frac{v^2}{c^2}}} = \frac {t_2 - \frac v{c^2}x_2}{\sqrt {1 -\frac{v^2}{c^2}}} $$

which simplifys as
 * $$t_1 - \frac v{c^2}x_1 = t_2 - \frac v{c^2}x_2 $$

and
 * $$t_1 - t_2 = \frac v{c^2}(x_1 - x_2) $$

The expression for $$l'\,$$ then becomes
 * $$l' = x_1' - x_2' = \frac {x_1 - vt_1}{\sqrt {1 -\frac{v^2}{c^2}}} - \frac {x_2 - vt_2}{\sqrt {1 -\frac{v^2}{c^2}}} = \frac {(x_1 - x_2) - v(t_1 - t_2)}{\sqrt {1 -\frac{v^2}{c^2}}} = \frac {(x_1 - x_2) - v(\frac v{c^2}(x_1 - x_2))}{\sqrt {1 -\frac{v^2}{c^2}}} = \frac {(x_1 - x_2)(1 - \frac {v^2}{c^2})}{\sqrt {1 -\frac{v^2}{c^2}}}$$
 * $$l' = (x_1 - x_2) \sqrt{1 -\frac{v^2}{c^2}}$$

Now, assuming that the object is at rest in the coordinate system K (that's an important point), we must have $$l = x_1 - x_2\,$$ and we don't care about the simultaneity of those measurements since the object is at rest. Defining $$\gamma = \frac 1 {\sqrt{1 - \frac{v^2}{c^2}}}$$, we get
 * $$\gamma l' = l\,$$.

Conclusion: the size of the object $$l'\,$$ measured in a coordinate system K' where it is in motion is smaller then its size $$l\,$$ measured in a coordinate system K where it is at rest. Dauto (talk) 16:24, 28 February 2009 (UTC)

current even not grounded
Hello,

It seems simpler.

If one is touching a current carrying wire no matter current is A.C. or D.C. should one get a current through its body.I think it should. Consider two points on my finger touching wire they will have some potential difference and ofcourse current will flow .But ya if one was touching ground potential difference will high and got high current so but if only wire is touch P.D. will be there and so current.

Is that concept is right and if not whats wrong with that and how can be improved. —Preceding unsigned comment added by 122.163.42.205 (talk) 12:58, 28 February 2009 (UTC)


 * If the current in the wires is not enough to overcome the electrical impedance or Electrical resistance of your body, then the current will not flow to any meaningful amount. (the equations imply perfect linearity; that is ANY voltage should always produce a current in any medium; however for practical purposes, extremely high resistances will produce such small currents that they are undetectable, and therefore essentially nil).  If you have two wires with a small voltage difference between them, and hold one wire in each hand, likely no measureable current will flow.  If the voltage is high enough, then current WILL flow, which can be a dangerous thing, as there's stuff in your body that does not react kindly to having electricty pass through it.  Even if it causes no damage, it can create some uncomfortable or painful effects.  Now, as to the difference between passing through the two wires OR passing from one wire to the ground; it depends upon which voltage difference is greater.  Since the impedence between your outstretched hands and your hands and your feet is likely to be similar, the deciding factor on which path the electrons take will be whichever path will allow the electrons to lose the most energy.  If the path to the ground does this, it will take that path rather than the path to the other wire.  --Jayron32. talk . contribs  13:24, 28 February 2009 (UTC)

If you touch even one wire with one finger, even while not touching a grounded object, painful or dangerous current can flow, if the wire is at a high enough voltage like a transmission line. It might be due to capacitive current. Edison (talk) 20:48, 28 February 2009 (UTC)


 * If you're not familiar with capacitive current, I will briefly summarize it. It is possible for current to flow, even though there is no complete circuit, for some amount of time.  During this time, electric charge is stored on a capacitor (which may be your body).  This current could be sufficiently high to be harmful.  Also, remember that you can have a complete-circuit to ground if you are not totally isolated from the environment (a lot of materials act as conductors when a sufficiently high voltage is applied).  Nimur (talk) 22:41, 28 February 2009 (UTC)

Diagnosing asthma in children
Hi all the article on asthma does not say why peak expiratory flow rate tests are not used to diagnose asthma in children. I have read elsewhere that they are used in children over 5 and in another source, Clinical Medicine by Kumar and Clark, that excercise tests are mainly used to diagnose asthma in children. Please help - thanks in advance. —Preceding unsigned comment added by 139.222.241.116 (talk) 15:39, 28 February 2009 (UTC)
 * Peak expiratory flow rate measurement is strongly influenced by effort. It is difficult to get young children to exert a standard amount of effort for what they may see as a pointless exercise.  Also, asthma is "reactive" airway disease, and as a rule the lungs of a child with asthma function normally at rest (between exacerbations).  Exercise is a common trigger, but is not uniformly so.  It's a heterogeneous disease.  --Scray (talk) 17:36, 28 February 2009 (UTC)

Many thanks for the reply. But your post made me think - The PEFR test is used commonly in diagnosing asthma in adults but don't the lungs of adults who have asthma function normally at rest as well? So how is the test beneficial? —Preceding unsigned comment added by 139.222.240.115 (talk) 18:36, 28 February 2009 (UTC)
 * PEFR measurement alone cannot be used to diagnose asthma. The diagnosis is based on history (pattern of symptoms, triggers, etc) supported by testing.  Improvement in PEFR after bronchodilator treatment may be suggestive, but more formal (and much more accurate) spirometry is generally used.  In many people with true asthma, the spirometry may be normal, but a challenge test can bring out evidence of airway obstruction; common challenges include exercise, cold air, and methacholine.  PEFR can be useful in gauging response to treatment, and empowering patients (who have a chronic condition, after all) to assess the severity of exacerbations that might need escalated or more intensive treatment.  --Scray (talk) 02:46, 1 March 2009 (UTC)

Why all the various notations for wavelength and frequency?
I hate using (nu) because it looks like a v

Also, there is lamda, and f, and h

Please someone correct me if I'm wrong

(nu) = frequency

f is also frequency

lamda is λ is wavelength

h is also wavelength?

I am learning chemistry and physics at the same time, and I already asked at Yahoo answers. I am OCD, and this multi-naming is really truly frustrating me. I am fixing to start the chapters on waves, and optics (all in physics) but also am doing chemistry review and there is some alternate terminology but the reason is explained well, but I just can't understand it unless someone puts it in laymen's terms. I have tried to read the relevant wikipedia articles, and the gist is something like "chemistry uses lamda, h, and (nu) to highlight the relationship that electromagnetic radiation propogates at a constant phase speed of c = 3*10^8 m/s" whereas "physics takes a holistic approach and analyzes this stuff from looking at everyday wave phenomena like a buoy in the ocean--the waves can be imagined as the buoy oscillating up and down in simple harmonic motion, and its not a physical phenomenon but almost like a mathematical phenomenon governed by a math formula x-doubledot plus cosA(x+phi) = 0"

This my amalgamation of trying to make sense of various online sources with what my book says. My instincts were to ask this on the math refdesk, because I like the style of mathematicians' explanations on stuff like this. I received a very good answer a long time ago about the dx or dt at the end of an integral explanation, and I truly understood the explanation. I don't really understand what I wrote, but I wish to understand why use the various symbols. I really do want to know the reasoning behind keeping around both sets. I personally prefer f for frequency and don't have preference on what to use on the rest.

I am going to print out my responses, because I really need a custom explanation. I like math symbols that make sense, and delving into the science fields of chemistry and physics, they don't have the "purity" that I'm accustomed to from my endeavors in calculus.

If someone else can just write me an explanation that makes sense to me, and won't conflict with my science books, then I can finally just memorize the formulas. Until then, I'm hesitant of memorizing the wrong set of formulas. I am also a perfectionist, as evidenced by how apologetic I am for asking this simple question. Please AGF me, and help me make sense of these two seemingly incompatible reasonings for keeping around both sets of symbols. Thanks very much.

LeeJaedong (talk) 16:42, 28 February 2009 (UTC)


 * h is Planck's constant. The others are right. It doesn't really matter what you call things, you use whatever symbols aren't already being used for something else, although there are certainly symbols that are generally used for certain things - you should always specify what you mean by each symbol the first time you use it, though. f is often used for a miscellaneous function, so isn't always available for frequency. You may need to alter your handwriting slightly to distinguish all the different symbols. My handwriting changed a lot during my first year of uni - I now cross 7's and z's, I loop ells, I put ticks at the top of 1's, v's, w's and o's, etc., etc.. I write nu's with a straight line down and right, and then a curved line up and out to the right and then back in to the left, whereas v's have a straight line down and right and a straight line up and right, with a horizontal tick at the end - they are easy to distinguish (my u's look more like by v's than my nu's do - that's what the horizontal tick is for, u's don't have them). --Tango (talk) 16:57, 28 February 2009 (UTC)

I also have a pet peeve against the use of the $$\nu$$ because it looks like a v. But you must be aware that other people like using it and there's nothing you can do about it. There is no other reason for the the multiple notations beyond the fact that different people have different tastes. Get used to it. Just remember that the impostant thing is the physical concept, not the symbol used to describe it. Dauto (talk) 17:05, 28 February 2009 (UTC)


 * Just consider yourself lucky you're not learning maths too. With German fraktur and Hebrew letters as well. Plus a whole load of invented symbols. On that theme do people have to learn German to do chemistry in your neck of the woods? Anyway its all nothing compared to what the Jpanese do every day of the week Dmcq (talk) 00:15, 1 March 2009 (UTC)
 * Yeah, some of the symbols in maths are really bad. My handwriting includes 6 different p's. And I still don't know what the symbol that this book I have uses for the residue field of a local field is meant to be - I think it's either a weird I or a weird F... --Tango (talk) 00:18, 1 March 2009 (UTC)
 * Six? I think I only know 5: lowercase, uppercase, fraktur for ideals, BB for probability and script for powerset. I have recently had to learn to write Thorn, though, which more than makes up for it. Algebraist 00:38, 1 March 2009 (UTC)
 * Immediately after posting I realized I had forgotten the mysterious Weierstrass p. Algebraist 00:41, 1 March 2009 (UTC)
 * Yep, those are the 6 (although I use $$\mathbb{P}$$ for projective space, rather than probability). There is also rho, which you need to be careful to avoid making it look like a p. And you've mentioned thorn (which I've never had to use). I can't think of another letter that's as troublesome as P... --Tango (talk) 01:08, 1 March 2009 (UTC)


 * Science and math really needs to take a lesson from computer science. We've all learned that using good, clear variable names is one of the most critical things to writing clear, unambiguous code...the same applies to equations.  I would NEVER consider using 'f' for 'frequency' - even less, some impossible-to-type wierd-assed v!  I can't tell you the number of times I've looked up an equation on Wikipedia and found one or more completely undefined terms!  By all means use single-letter variables in informal doodling - but when it comes to publication - the 'hard' sciences should hold to the formal requirements of good programming style!  Properly spelled out variable/constant names - in language-independent ASCII - with proper 'declarations':

equation waveFunction (     constant  phaseSpeed : units distance time-1,      parameter frequency  : units time-1,      parameter wavelength : units distance ) {     wavelength = phaseSpeed / frequency ; }


 * SteveBaker (talk) 01:09, 1 March 2009 (UTC)
 * Do you know how long that would make most formal proofs? Mathematical notation is all about making things concise while still being unambiguous, and for the most part it succeeds. Concise notation, preferably chosen in such a way that the notation mirrors the behaviour of the object it represents (for example, $$\frac{\mathrm{d}y}{\mathrm{d}x}$$ looks like something divided by something else and it behaves like something divided by something else - this makes remembering the chain rule, say, really easy (obviously, you need to be careful to remember that "cancel the dx's" is a mnemonic, not what is actually happening)), makes doing maths easier and quicker. If we had to write out "the derivative of vertical position with respect to horizontal position" (or whatever x and y are representing), nobody would ever bother doing maths and you wouldn't have a computer to program. "Let vp be the phase speed, ν be frequency and λ wavelength, then λ=vp/ν." is perfectly clear and is much easier to use than your notation. --Tango (talk) 15:31, 1 March 2009 (UTC)


 * Yes - and that's exactly what beginning computer programmers say: "Why do I have to say 'numberOfTriangles' instead of 'nt'? They both 'work' - and 'nt' is less typing."  However, over the years and with programmers turning out millions of lines of code in their careers - we've learned (typically, the hard way) that the time consumed in entering things in shorthand forms is more than recouped in the clarity of reading it later.  The cost of a single error (even more so in math than in computer programs) is so spectacularly high that in the age of the computer and with things like editors that do automatic name completion and such - it's less effort overall to do it right - and the results are clearer and unambiguous for the next generation of readers. SteveBaker (talk) 16:32, 1 March 2009 (UTC)


 * Ok, that's not at all clear because the default font shows vee and nu identically, but it my handwriting it would be perfectly clear. --Tango (talk) 15:32, 1 March 2009 (UTC)
 * Aha! Gotcha!  My point - precisely.  You even found it necessary to say 'vee' and 'nu' in order to disambiguate it.  Look at that exact same equation in our Wavelength article:
 * "Wavelength λ is determined using the formula
 * $$\lambda = \frac{v}{f},$$
 * where v is the phase speed of the wave and f is its frequency.
 * See what I mean? SteveBaker (talk) 16:32, 1 March 2009 (UTC)
 * This (in maths, at least) is actually quite a small problem compared to the problem of different definitions. Any sensible author defines the symbols they use (where it's ambiguous), but they don't always bother telling you if rings have 1s, if lattices are bounded, if 0 is a natural number, what locally compact means today, and so on. Algebraist 16:39, 1 March 2009 (UTC)
 * No mathematician would write up maths in a font where vee and nu look the same. In the default LaTeX font, $$v\,\!$$ and $$\nu\,\!$$ look sufficiently different that there is no problem. If you aren't familiar with the default LaTeX font (which won't be the case for any experienced mathematician or scientist, but nevertheless) then you may not know if one of those symbols in isolation is one or the other, but it really doesn't matter. All that matters is that if they both appear in the same bit of maths, you can tell them apart. Not knowing how to pronounce them is a little annoying, but it's not a real problem. --Tango (talk) 16:51, 1 March 2009 (UTC)
 * There are some formal maths systems around, The Mizar system is about the most readable see Mizar Mini-tutorial but you'd have to be a massochist to do any new maths in it or explain things with it rather than just use it for formal verification. A bit like trying to use COBOL to write a compiler (yes it has been done!, see Micro Focus International). And even with Mizar people tend to use single character names for variables. Try substituting some long names into that tutorial example and see what you get :) Dmcq (talk) 16:17, 1 March 2009 (UTC)


 * I am very much a fan of Steve's variable-naming. If formal proofs took a few extra pages to print, that would be an acceptable tradeoff to make them comprehensible.  This is especially important when you are using a text as a reference rather than a class-aid.  When I pull out my physics books to check an equation I haven't used in four years, the last thing I want to do is parse through variable soup - and in this particular author's notation, is $$\nu$$ with or without the $$2\pi$$ factor included... if the equations were cleanly printed with unambiguous plaintext names, it would be much simpler.  If brevity is that important, then a single, consistent, exact mapping between variable and plaintext name should be included as an appendix.  (This is why I love my Thermodynamics book).  Nimur (talk) 16:36, 1 March 2009 (UTC)
 * We're not talking about a few extra pages. We're talking about a 20 page paper taking, maybe, 100 pages. A one blackboard proof taking five blackboards. And it's not just length, it's time - it would take five times as long to write up your papers, you would cover a fifth as much in a lecture, etc. (I'm making a guess at the factor of 5, it could well be quite a bit more, I would be very surprised if it were less.) --Tango (talk) 16:59, 1 March 2009 (UTC)
 * It's also worth entertaining the possibility that math (and other disciplines) could move to paperless presentation of proofs and other content, in which variables are unambiguously named, and the display could be made compact by wikilinking abbreviations to their definitions and units. Then maybe we would not have to worry so much about killing trees.  It's also possible that we waste "paper" (i.e. space) with redundant work made necessary by the confusion we are discussing.  --Scray (talk) 18:21, 1 March 2009 (UTC)
 * A system by which hovering over a variable gives you a tooltip with its definition could be useful. Links would be unnecessary and probably unhelpful. Many variables don't really have a definition, though (although it might be useful if hovering over it told you its domain). --Tango (talk) 20:03, 1 March 2009 (UTC)

That seems like the perfect oportunity for me to voice my rant about how much I hate WP's defaulf font. Dauto (talk) 21:16, 1 March 2009 (UTC)


 * Not sure what that rant's about, but on the business of long names can I point to Chunking (psychology) and to how much more efficient people are coding in less verbose and more high-level programming languages. Dmcq (talk) 21:26, 1 March 2009 (UTC)
 * I really don't give a damn about some psychological theory. Practical computer programmers have learned the hard way how important this is to clarity.  The temptation to brevity is always there - and good programmers resist it strongly because they know the consequences.  To pick an example out of the air - let's take a look at the very first piece of PHP code wikipedia runs when you start it up:

require_once( './includes/WebStart.php' );
 * 1) Initialise common code

require_once( "includes/Wiki.php" ); $mediaWiki = new MediaWiki;
 * 1) Initialize MediaWiki base class

wfProfileIn( 'main-misc-setup' ); OutputPage::setEncodings; # Not really used yet

$maxLag = $wgRequest->getVal( 'maxlag' ); if ( !is_null( $maxLag ) ) { if ( !$mediaWiki->checkMaxLag( $maxLag ) ) { exit; } }

$action = $wgRequest->getVal( 'action', 'view' ); $title = $wgRequest->getVal( 'title' );
 * 1) Query string fields
 * We don't write long names like 'MediaWiki', 'OutputPage' and 'maxLag' for fun! The program would have worked just as well if the code was written with 'M', 'O' and 'L', and there would have been less typing and a much more compact representation - but programmers coming fresh to the code (or even the person who wrote it coming back to it years later) would have a much harder time finding problems and fixing them.  Wikipedia has about 300,000 lines of this stuff (that's maybe 5,000 pages).  It's not a matter of a mere 20 page proof!  The extra effort to expand a mere 20 pages into a more readable form would be negligable compared to the intellectual effort required to figure out the proof in the first place.  Programmers are very practical people - we don't lift a finger if we don't have to.  We've arrived at the benefits of long variable names through the totally pragmatic process of suffering develoment hell with short variable names back in the 1960's and 70's and gradually coming to the realization that a little more typing and perhaps a doubling in the amount of stuff we carry around is more than worthwhile.   A programmer who habitually used small variables names would be unlikely to keep a job in any kind of large scale programming effort.  That's not to say that we don't seek brevity - we certainly do, where it's appropriate.  We don't write "integer", "character", "floating point" or "double precision floating point" - we say "int", "char", "float" and "double".  Most modern programming languages use every single character in the ASCII character set for something (except, perhaps '@' - for historical reasons). SteveBaker (talk) 01:35, 2 March 2009 (UTC)
 * Mathematicians have been around far long than computer programmers and have been using modern notation for hundreds of years (if memory serves, the Ancient Greeks were a little more verbose). It seems to work well for us. I rarely have any problem remembering what a variable means (it often doesn't matter - we try to keep things general as much as possible, so all you need to know is what type of object it is and we use various conventions for that, which, along with context, tend to work - it might be a little more useful in the sciences, or applied maths, to be more verbose, but it tends to work anyway).
 * Perhaps the difference is in the number of times a variable is used. In maths, a given variable will probably be written dozens if not hundreds of times in a few pages. When programming you tend not to use the same variable more than a handful of times during any given part of the code (except for things like iterators which are often given single character names). This means that when programming it is often easier to use a long name and let your code be self-documenting as much as possible, rather than using a short name and defining what it is with a comment in every subroutine. Whereas in maths, it is easier to write a sentence at the beginning of each theorem or lemma explaining precisely what "x" means and then just write "x" the next hundred times. --Tango (talk) 11:57, 2 March 2009 (UTC)


 * Then this is a perfect opportunity for me to point out that Wikipedia doesn't have a default font. Your problem is with your browser's default sanserif font (I know IE's is vile, for instance), not with WP. Algebraist 00:33, 2 March 2009 (UTC)
 * IE's default/generic CSS sans-serif font appears to usually be Arial, which is the same as Firefox 3's default CSS sans-serif font. (At least it is on my computer and other people have also mentioned it.) However IE does sometimes pick another default font (why I'm not sure and as you can't change the default CSS sans-serif font on IE unlike you can with Firefox, you're SOL if it does (well there are ways to convince it to change the default but it's not easy).   So I guess if you consider Arial vile then it is, as is Firefox. If not, then it's not unless your unlucky. IE7 does use Cleartype by default regardless of your OS settings which is annoying if you don't have an LCD monitor. Nil Einne (talk) 11:15, 2 March 2009 (UTC)

SteveBaker, your idea of replacing mathematical symbols with something more descriptive would make sense if, as you said, the extra effort at writing time payed off with extra clarity at reading time. But it doesn't. In fact, it makes it harder to read. With fully descriptive symbols any equation with more then a few terms or factors wouldn't fit the page and would require a lot of effort to parse it properly. The one letter per concept standard used allows people to (with no more then a glance) comprehend long complex equations, as long as some reasonable formatting has been performed by the author. Programs such as Latex do most of the hard work of properly formatting equations automatically. Dauto (talk) 21:39, 1 March 2009 (UTC)

Wow, thanks so much guys. I have really enjoyed reading this conversation; I have learned a lot, and feel a lot better now. Thanks a ton! LeeJaedong (talk) 01:40, 2 March 2009 (UTC)

Characteristic time scale for rotational motion.
I am interested in knowing the time scale on which a molecule rotates in free space. I have estimates for the three principal moments of inertia. I know that this time would depend on the particular J state involved, so perhaps we can assume that the molecule is in the ground rotational state. I have looked at Rotational spectroscopy and Moment of inertia but neither seem to address this issue. Thanks in advance Man It&#39;s So Loud In Here (talk) 16:55, 28 February 2009 (UTC)


 * Use the formula $$L=I\omega\,$$ and the eigenvalue relations $$L^2|l>=\hbar^2l(l+1)|l>$$. Dauto (talk) 17:38, 28 February 2009 (UTC)


 * Is this material covered in a WP article, for those who would like to understand more? --Scray (talk) 17:46, 28 February 2009 (UTC)


 * From infrared spectroscopy, you will notice that most molecular vibrations and rotations occur at infrared frequencies, while atomic vibrations and rotations often occur at optical frequencies. Larger molecules will have resonances at lower frequencies (due to larger mass), but their spectra may be dominated by functional groups, (small, tightly-coupled sub-molecule atom-groups).  Do you need help converting infrared frequency to time scales?  These should be on the order of 10x10-15 seconds, or ~ millionths of nanoseconds.  Nimur (talk) 22:46, 28 February 2009 (UTC)


 * For molecular vibrations, each [normal mode] has a characteristic frequency at which it oscillates. When more energy is put into the system the range of motion is increased but the frequency, and therefore the time period, doesn't change.  The article here on the quantum harmonic oscillator has been very helpful. I am confused about rotations though and think the page on the rigid rotor is not very helpful.  First off things are different because when you pump more energy into a rotational mode the frequency of rotation increases by some (quantized) amount. Let's say I have a molecule, and I've calculated the three principal moments of inertia and therefore have $$I$$ as a diagonal matrix. How would I go about finding the rotational frequency for the ground state? (this is not a homework question I assure you, although it sounds like a good one).  Man It&#39;s So Loud In Here (talk) 02:18, 1 March 2009 (UTC)


 * Dauto Should I take from your formula that for a rotational eigenstate with $$l$$ quanta in the $$i$$ direction the angular velocity is $$\omega_i=\frac\hbar{I_i}\sqrt{l(l+1)}$$? Then the period is just $$\frac{2\pi}{\omega}$$. Man It&#39;s So Loud In Here (talk) 02:51, 1 March 2009 (UTC)
 * Also with no characteristic frequency, is there no zero-point energy in rotations?Man It&#39;s So Loud In Here (talk) 21:15, 1 March 2009 (UTC)
 * Yes and no. A rigid rotator has no zero-point energy. In reality, vibrational and rotational terms aren't separable, so it does. But it's small enough to be neglected in most cases. --Pykk (talk) 00:21, 2 March 2009 (UTC)

Hormones and neurotransmitters
As I understand, the same chemical can be a hormone and a neurotransmitter, but when is it a hormone and when is it a neurotransmitter? Do I understand correctly that both chemicals influence other cells, but if it is produced by a nerve cell, we call it neurotransmitter, and when it is produced by any other cell, we call it a hormone? Or is there more to it? Lova Falk (talk) 17:14, 28 February 2009 (UTC)


 * A hormone is released in the bloodstream. A neurotransmitter is released into the synapse cleft. Dauto (talk) 17:25, 28 February 2009 (UTC)
 * Ah! It is as simple as this. Thank you! Lova Falk (talk) 17:37, 28 February 2009 (UTC)
 * PS Maybe not quite as simple. My textbook says: "There are axosecretory synapses, in which an axon terminal synapses with a tiny blood vessel called a capillary and secretes its transmitter directly into the blood." Do the authors of this book just express themselves in a sloppy way or are there exceptions to the rule? Lova Falk (talk) 17:49, 28 February 2009 (UTC)
 * The difference between hormone and neutransmitter is in scope of action. When the trasmitter is released in the bloodstream (using an axosecretory synapses, for instance) it may act on all the body cells that happen to have detectors for that substance (provided that enough of the transmitter was released to begin with).When the transmitter is released in a synapses cleft (acting on another neuron, for istance) the action may be restricted to just one cell at a time and will act on a much shorter timeframe. Dauto (talk) 18:49, 28 February 2009 (UTC)

soda ash clairification
Is soda ash used in swimming pool treatment the samae thing as soda ash used in well water treatment. We lost our supplier for the soda ash we used in our water system and can see there is what is called soda ash in both swimming pool sites and water sites. Thank you Marilyn  —Preceding unsigned comment added by 63.46.128.40 (talk) 18:26, 28 February 2009 (UTC)


 * Soda ash is the old-fashioned name for Sodium carbonate - and sodium-carbonate is sodium-carbonate is sodium-carbonate. So if what you have is pure soda ash with no other ingredients - and what you need is pure soda ash with no other ingredients - then it should be just fine.  Since both swimming pools and drinking water need similar properties - I (personally) would feel perfectly OK with stuffing the pool stuff into my well. SteveBaker (talk) 18:57, 28 February 2009 (UTC)


 * Difficult to know, because nonstandard nomenclature is, well... nonstandard. Do you have any old buckets which state definitively whether it's sodium carbonate? Additionally, please note that different formulations can make a lot of difference - for one easy example, it would be a horrible idea to use 80% Na2CO3 in the same amount that you would use 10%. (Not to mention that you wouldn't know what's in the remaining 20% or 90% composition.)
 * Even with a chemistry degree, I would be extremely hesitant to use something meant for one purpose for another in this manner. arimareiji (talk) 19:03, 28 February 2009 (UTC)


 * You REALLY must be careful, because like other terms such as Lime (material) or Potash, there are actually many compounds that fall under the "soda ash" label. Soda ash (unqualified) is usually used to mean sodium carbonate, but "caustic soda ash" is sodium hydroxide and there are other variations.  The problem is that, in the 19th century world, "Soda ash" meant "a melange of sodium containing compounds" while "potash" meant the same for potassium and "lime" meant the same for calcium.  These compounds could be seperated or treated to form new compounds, but the entire class is still known as "soda ash"; just different kinds of soda ash.  The convention has just hung around for 150 years or so.  As noted, what is called "soda ash" for one application may be very different than what is "soda ash" for another.  You would need to know the assay of the soda ash in the water treatment application, and obtain something which was the same stuff.  Just being called "soda ash" makes no guarantee that it will be... --Jayron32. talk . contribs  19:14, 28 February 2009 (UTC)


 * What Jayron said. One other thing which might help explain why we're advising such strong caution... drinking genuinely strongly-alkaline water is a really good way to wind up in the hospital or dead, health food gurus' claims notwithstanding. Underdoing the amount (and alkalinity) could be dangerous if it means bacteria don't get zapped, but overdoing it can easily be just as dangerous. If you ever saw a skull and crossbones on a sign in a really old Western that warned "ALKALI WATER" - well, alkalosis can kill you a lot faster than dehydration. arimareiji (talk) 19:40, 28 February 2009 (UTC)


 * This is all very interesting and all - but nobody has yet said why putting soda-ash-designed-for-swimming-pools into drinking water would be such a terrible idea. You typically ending up ingesting a fair amount of pool water - and when you add soda-ash to your well, you obviously have to take precautions to use appropriate amounts - perhaps to check pH and such. People who get their water supplies from their own wells know how to deal with the water not becoming too alkaline.  People outside of big cities live from well water throughout Texas - it's not at all an uncommon thing.  Why is this so terrifyingly different for 'pool soda ash' than 'well soda ash'? SteveBaker (talk) 00:55, 2 March 2009 (UTC)
 * You drink far more water from a well than you do a swimming pool, that makes a big difference. Swimming-pool-soda-ash might not be purified as much as drinking-water-soda-ash, since there is no need to and it save money, and those impurities will become a problem when you drink several litres of well-water. --Tango (talk) 12:00, 2 March 2009 (UTC)


 * In the water supply here the water companies uses slaked lime to achieve correct pH that stoppes pipes from being dissolved. I hope you are testing the water before drinking it! Graeme Bartlett (talk) 20:21, 1 March 2009 (UTC)

Why Are People So Stupid?
Why do people take a health class, learn about the germ theory of disease, and yet still think that going outside in the cold is what causes their illnesses. I thought we were out of the dark ages, but I guess not. Why do you think people think this? 169.229.75.128 (talk) 19:24, 28 February 2009 (UTC)


 * Because there is a correlation between low temperatures and people getting ill, and people often misunderstand the natures of causation and correlation. See Common cold for details. --Tango (talk) 19:30, 28 February 2009 (UTC)


 * That, and people have forgotten about the importance of handwashing in disease prevention. It's nasty to think about, but 1) cold weather -> runny nose 2) runny nose gets wiped by hand 3) hand touches object (i.e. door handles) 4) other hand acquires infectious mucus from object 5) repeat steps 1 and 2. arimareiji (talk) 19:44, 28 February 2009 (UTC)


 * But the cold weather doesn't CAUSE the runny nose. 169.229.75.128 (talk) 19:55, 28 February 2009 (UTC)


 * My nose and the weather outside beg to differ. ;-) But more importantly, so does wisegeek.arimareiji (talk) 20:12, 28 February 2009 (UTC)
 * I concur. We now have two anecdotes, thus data, QED. :) --Tango (talk) 20:33, 28 February 2009 (UTC)
 * Germs may be the cause of a particular disease, but dried out sinuses due to low humidity inside in the winter might lessen the bodies resistance, as could stress or other effects of extreme cold. Cold weather might increase to chances of exposure to a germ resulting in the full-blown infeection. Edison (talk) 20:45, 28 February 2009 (UTC)


 * Cold weather does too cause runny nose. When you inhale, the cold air cools the internal surfaces of you nose cavity. Then when you exale warm and humid air, the vapor condenses on these cold surfaces and the now liquid water runs down your nose, hence a runny nose. Dauto (talk) 20:48, 28 February 2009 (UTC)

The problem is that the average person in the street is continuously bombarded with false information. We're told that herbal remedies will cure medical conditions by 'boosting your immune system' (these statements have not been verified by the FDA, this food supplement is not designed to diagnose or treat any medical condition) and that you can lose (up to) 30lbs (results not typical) just by taking this pill without exercising - and eating all you want!! (results obtained along with diet and exercise). We find 'dianetics' filed in amongst 'diabetics' in book stores - we have homeopathic remedies (ie pure water) in amongst actual real treatments in pharmacies. We have adverts on TV telling you that "it's now well accepted that male enhancement really works" - and that "we couldn't say this was true if we didn't have TWO!!! US patents for our product!!!" (sadly, yes you could - and a patent proves nothing). We have 'energy drinks' in the 'health food' aisles in supermarkets and yoghurt that makes you shit at "more regular" intervals (Why is that important?). I especially liked the product that contains as it's "active ingredient" something described as "a tiny relative of the mushroom" (they mean it has fungus in it). Even fully trained doctors are prescribing antibiotics for viral diseases such as the common cold because people who've sat around for an hour with a whiny sick kid don't want to leave the office without a prescription for SOMETHING in their hands. No wonder people are confused! Who should they believe? SteveBaker (talk) 20:49, 28 February 2009 (UTC)
 * We don't need no education?  But seriously, the United States has mandatory free public education and in many places it's all-year long.  If this kind of exposure to scientific fact is not able to eliminate misinformation, I can only conclude that in some statistical sense, much of the population will never be able to distinguish fact-based reality from fiction.  Calling them "stupid" is just a pejorative label of their alternative viewpoint about reality.  Nimur (talk) 22:50, 28 February 2009 (UTC)
 * Well -- just to pick what may be one of the most obvious examples here -- if one authority tells you that the Earth is 4.5 billion years old, and another tells you that it's 6,000 years old, and you're in an environment where a lot of the people you know will insist on the latter being the truth, no matter how much that violates logic or what scientists say, it's not that surprising that a lot of people get confused about a lot of things. It's not just a question of providing people with education, because not all of that education is good or provided in the interests of expanding the recipient's knowledge and understanding. -- Captain Disdain (talk) 23:20, 28 February 2009 (UTC)
 * The average person in a US street is bombarded with the kind of information you refer to. The UK does not have such bad advertising (it doesn't have good advertising, but everything's relative), yet people here still have many of the same misconceptions. I think it's word of mouth that spreads the kind of nonsense we're talking about, not TV. --Tango (talk) 23:49, 28 February 2009 (UTC)


 * Many schools teach their pupils to be stupid - they actively discourage questioning attitudes & encourage the thoughtless acceptance of "authority". In the world of employment, again, stupidity can be advantageous - after all, pointing out one's boss's errors is unfortunately not a good carreer move in many companies. DuncanHill (talk) 23:53, 28 February 2009 (UTC)
 * And hence, we don't need no education -Pete5x5 (talk) 05:12, 2 March 2009 (UTC)
 * Schools generally teach fact learning because it is easier to test than understanding and governments want statistics they can misrepresent during elections. --Tango (talk) 00:03, 1 March 2009 (UTC)


 * Cold weather doesn't cause a cold, but it can decrease blood flow to the head, weakening the immune system in that area. For example, I find that I most often experience colds and diarrhea (AKA stomach flu, a misnomer) in the wintertime, although this isn't always the case. As for education, North America probably has quite poor mathematics curriculums in elementary school, I remember people in my class struggling with problems which, I know in some other countries, is taught, say, five years earlier. As for misconceptions, there are plenty of them. In fact, I wouldn't be surprised if most people "know" more misconceptions and myths than they do facts. For example, I know this is OR, but I've often noticed people misidentifying "power" as the most important aspect of a telescope or misidentifying Venus as an airplane.


 * It's strange, that people who don't care about nearly anything, can suddenly defend to death a misinformation what they have heard from a friend who heard form another friend who read it in a magazine. "It's absolutely true that yoga can change your bioenergy flux and cure cancer if you concentrate enough". --131.188.3.20 (talk) 13:53, 2 March 2009 (UTC)

Stone-age axe-head factory.
I recently listened to the audio book of Bill Bryson's A Short History of Nearly Everything. Near the end he speaks of a place in Africa (Rift Valley?) where there are remains of a massive stone-age axe-head factory. He describes how hundreds of people must have been employed in the production of stone tools for some time at this one location. Because I only have the audio book, I don't know how he is spelling the name of this place, but it sounds like Olega Sally, although that's not how it's spelt so I can't find out any further info on it. Can anyone give me the actual name of this place please? Thanks.91.111.64.177 (talk) 23:04, 28 February 2009 (UTC)
 * Are you sure it wasn't Olduvai Gorge? That's sort of the best known rift valley site.  --Jayron32. talk . contribs  23:30, 28 February 2009 (UTC)


 * It's Olorgesailie (no idea if that will be blue!) DuncanHill (talk) 23:42, 28 February 2009 (UTC)


 * Here's a blue link, though not one of WP's. // BL \\ (talk) 00:16, 1 March 2009 (UTC)


 * Olorgesailie is on the WikiProject Missing encyclopedic articles list of important/missing articles - so hopefully someone will fix that. SteveBaker (talk) 00:52, 1 March 2009 (UTC)
 * Not exactly my cup of tea, but I dug up what I could. Clarityfiend (talk) 06:06, 1 March 2009 (UTC)
 * Thank you! That's great!  This is the Ref Desk at it's best - feeding consumer demand back into the encyclopedia.  With a new article like that (and one so well referenced) - you should probably shoot a line to the Template_talk:Did_you_know folks - they'll put a line from the article onto Wikipedia's "Did You Know" box on the front page and within days roughly a gazillion* avid Wiki-acheologists will have edited the heck out of it and you'll have a proper article. (* five)SteveBaker (talk) 15:55, 1 March 2009 (UTC)
 * Alas, it isn't long enough (1500 words) for DYK. Too bad, because the Italian POWs would have made a nice hook. Clarityfiend (talk) 21:02, 1 March 2009 (UTC)
 * No, no, no! 1500 CHARACTERS - not words! You have over 2600. You need to get a move on though - once the article is more than 5 days old, it no longer qualifies. SteveBaker (talk) 23:23, 1 March 2009 (UTC)
 * Actually, its 1500 characters of main-body text, not counting references, infoboxes, hidden comments, categories, templates, etc. Ran the main text thru Word, and it's only 819 non-space characters.  It would need to be about twice as long to qualify.  And he has 4 more days (March 5th) to get it in under the next update.  --Jayron32. talk . contribs  01:17, 2 March 2009 (UTC)
 * Julia Rossi has gone ahead and nominated it. I've expanded it a bit, but it's still rather marginal, especially since DYK doesn't use stub articles. Well, we'll see. Clarityfiend (talk) 07:56, 2 March 2009 (UTC)
 * Another collection of stone age tools was recently found in Colorado. It consisted of 83 Clovis-style tools. I wonder if it was the stock of a stone age merchant. The find is described at http://news.yahoo.com/s/ap/20090226/ap_on_sc/ancient_tools
 * GlowWorm. —Preceding unsigned comment added by 98.17.40.185 (talk) 02:08, 1 March 2009 (UTC)

Thanks guys, good work. I'd stick a 'resolved' thingie on this if I knew how.91.111.64.177 (talk) 18:43, 1 March 2009 (UTC)
 * Easy! You just say  (things inside doubled curly braces are 'TEMPLATES')...although I generally advise against doing that because other editors may yet have more information (or, more importantly, corrections to existing responses) - and I always feel that the big RESOLVED check mark dissuades people who come along later from reading the question and it's responses so far because they suspect that the OP (that's you) won't be coming back to read more.  That's sad because very often the most interesting and perceptive answers come along later because not everyone patrols the RD every day (especially over the weekend).  But if you feel the need - go ahead and stick a  on it. SteveBaker (talk) 23:45, 1 March 2009 (UTC)
 * Isn't there a template for articles that says something like "This article brought to you by the fabulous people at the RefDesks"? DuncanHill (talk) 12:09, 2 March 2009 (UTC)


 * No, there isn't. SteveBaker (talk) 20:15, 2 March 2009 (UTC)