Wikipedia:Reference desk/Archives/Science/2009 March 9

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March 9

Exploding Cell Phones During Recharging

A friend who lives in Spain sent me an email warning about not using a cell (mobile) phone while it is recharging. I will spare you all the gory photos, but the text read:

Don't know if any of you have seen this before, but if you're prone to answering the phone whilst its plugged into the charger you might want to rethink that practice !!!

A few days ago, a person was recharging his mobile phone at home. Just at that time a call came in and he answered it with the instrument still connected to the power outlet. After a few seconds electricity flowed into the cell phone unrestrained and the young man was thrown to the ground with a heavy thud. His parents rushed to the room only to find him unconscious, with a weak heartbeat and burnt fingers. He was rushed to the nearby hospital, but was pronounced dead on arrival. Cell phones are a very useful modern invention. However, we must be aware that it can also be dangerous...

Never use the cell phone while it is hooked to the electrical outlet!

I tried a few variations on "exploding cell phones" and "dangers of recharging cell phones" in the Archives' Search box, but didn't find anything useful to me, as I had no plans to use the cell phone while pumping gas. Is this email warning reasonable; that is, is it true or possibly true? Would it make a difference if the phone was recharging in Europe at 220 V as opposed to in North America, at 125 v? Thanks for your help. // BL \\ (talk) 00:29, 9 March 2009 (UTC)

This stinks of "Urban legend" - if this were a common occurrence, you can bet there would be HUGE warning stickers all over your cellphone telling you not to do it - and they'd probably make the phone so it would refuse to take or accept calls while charging in order to discourage this terrible practice. As always, urban legends should be checked out at http://www.snopes.com - and indeed it has a page about it: [1]. The second example they quote - is your email...word for word! It concludes that this is an exceedingly rare thing - but that once in a while, cellphone batteries can explode. (They point out that the ONLY proven cases have been Nokia phones WITH COUNTERFEIT BATTERIES...they also point out that in a couple of cases, the person was merely sleeping a few feet away from the phone when it exploded...so making calls on the phone isn't the problem). But there are maybe half a dozen cases worldwide over a period of several years. It's also dangerous to eat lunch (you could choke and die - the food could have been poisoned or it could harbor deadly diseases) - it's exceedingly dangerous to drive your car - all of these things are VASTLY more likely than that you'll be killed - or even harmed - or even mildy inconvenienced - by an exploding cellphone. So the advice "Never use the cell phone while it is hooked to the electrical outlet!" is about as useful as "NEVER EAT LUNCH!" or "NEVER DRIVE YOUR CAR!!!". It's quite utterly bogus, terrible advice. By all means carry on using your phone - and if you own a Nokia and ever have cause to change the batteries - make sure you buy them from Nokia and not from some guy at your local market! Please - when you hear this crap via email - either check it out on snopes.com - or just ignore it. SteveBaker (talk) 00:38, 9 March 2009 (UTC)

Yeah, because talking on your cell phone 24/7 is a basic human need like food and transportation. A better analogy would be "not driving your car after midnight (when the drunks are driving home)". Each person is capable of weighing the odds and deciding if the risks are acceptable to him or her—if not talking on your cellphone while it's charging makes *you* feel better then by all means go ahead and ignore my hyperbolic collegue. – 74  01:14, 9 March 2009 (UTC)

Actually it has been pretty well established by risk communicators that most people are pretty bad at weighing risks for them sensibly, even if they have really good sources of information. (Ergo, Las Vegas.) The human brain is not a terribly rational organism—it gives certain perceived outcomes vast more weight than others even if the odds are astoundingly against them. (On a side note, is talking on a cell phone a basic human need like food? No, of course not. Like transportation? Yes, almost exactly...) --98.217.14.211 (talk) 01:57, 9 March 2009 (UTC)

Ha. Are automobiles a "basic human need" now?

Seriously, I regularly use my phone when it's plugged in. Not because I talk on the phone "24/7", but because I only rarely use my phone, and I don't notice when the battery runs down. ... until I need to make a call. APL (talk) 15:23, 11 March 2009 (UTC)

Automobiles? No. Steak? No. Transportation? I think a good case can be made (how many self-sufficient people do you know?). In fact, I'd list "transportation" higher than "communication" ("food" and "shelter" are obviously higher still). – 74  19:39, 11 March 2009 (UTC)

(After e/c, and I have read your amendments, Steve - I added your name as 74.137.108.115's comment has intervened, and I was not directing my remarks to him/her.) I shall forgive you for the "Duh" in the original edit summary. (Please understand that I am laughing as I type this.) I think the photos short-circuited my brain and I forgot common sense, and S.O.P, which includes checking Snopes and Mythbusters and a general look around the Net. And, given how thoroughly, albeit relatively gently, you dissected the argument presented by the OP in the immediately preceding query, I am not surprised your patience for those who may not "think before they type" is in current short supply. So, thank you, and I shall slink off to whimper quietly in the further reaches of cyberspace, but not before I email the friend the Snopes's link. // BL \\ (talk) 01:06, 9 March 2009 (UTC)

The interesting question is whether the friend who forwarded this junk to you will, in turn, forward it to all of the other people (s)he sent it to - and also back to the person who sent it to him/her? I strongly suspect not. Dramatic news of exploding cellphones travels fast - news that the world is a calmer, simpler place without all of these dread dangers...that travels much more slowly. SteveBaker (talk) 01:24, 9 March 2009 (UTC)

P.S. I don't even have a cell phone. // BL \\ (talk) 01:36, 9 March 2009 (UTC)

Just a general note on this story: whenever you see something that warns that an everyday activity that seems harmless is actually horribly dangerous and could kill you at the drop of a hat, there are generally some telltale signs of an urban legend:

• Someone dies or is horribly mutilated in a dramatic fashion.
• It's telling you that something you may do all the time is a very bad idea.
• It's too good or too bad to be true, or violates common sense -- that is to say, the results of the action are dramatically disproportionate to the action itself.
• There are no dates, names, or places included in the warning, so there's no way for you to verify the story.
• It's told as a story, with a degree of drama and a punch line or a moral at the end.
• It's reported in an e-mail that's obviously being passed around, rather than a news site, and you are encouraged to pass it on to everyone you know.

This particular story hits just about all of the above points. Not all urban legends do, of course -- and just because something is an urban legend, that doesn't necessarily mean it's not basically true. But if someone tells you something that hits, oh, let's say three of the above points, your bullshit detector should be tingling, and you probably shouldn't accept it at face value. (Which you didn't, of course, so good job there!) -- Captain Disdain (talk) 08:03, 9 March 2009 (UTC)

Hardness of diorite?

Can someone tell me the Mohs scale of mineral hardness value for diorite? (It's not in the list.) RJFJR (talk) 02:47, 9 March 2009 (UTC)

I'll guess at around 6, based on a quick look at the hardness of the components of diorite. I imagine the exact value would depend on the relative concentrations of the constitiuent minerals. Mattopaedia ^{Have a yarn} 03:36, 9 March 2009 (UTC)

Assuming that the main components are feldspar and hornblende, then around 6 would be about right. If there is a lot of biotite (hardness 2.5-3) in a particular variety, that's a different matter. Mikenorton (talk) 09:04, 9 March 2009 (UTC)

Thank you. It's weird, I was wartching something on TV and they said diorite was so hard the only thing that could cut it was diamond (they couldn't figure out how an ancient city was built), but 6 isn't that hard. They pronounced it die-or-ite and I think I looked up the right spelling. RJFJR (talk) 15:54, 9 March 2009 (UTC)

Well, assuming that they really were talking about diorite (and that is the way its pronounced in my experience), you could cut it with anything made mainly of quartz such as quartzite, obsidian or chert. Mikenorton (talk) 16:46, 9 March 2009 (UTC)

Please tell me you weren't watching that "Ancient Aliens" show on the so-called-"Discovery Channel". I caught about 10 minutes of it before my wife made me switch it off because the shouting was annoying her! That show was SO full of bullshit and misinformation - I don't know where to start. Lying about the hardness of a mineral is the very least of the crap they fed people last night. SteveBaker (talk) 18:20, 9 March 2009 (UTC)

I listened to it while doing a crossword puzzle (which shows how much attention I wasn't paying to the show). Occasionally I put my head up when they said something particularly lacking in rigor. I walked out when someone tested a 'bagdad battery' with a voltmeter under no load conditions. (Couldn't they find anyone who knew what internal resistance means?) I went and read the wikipedia article on diorite instead. RJFJR (talk) 18:49, 9 March 2009 (UTC)

Elsewhere Wikipedia refers to diorite as "extremely hard" and notes its use in ancient Egypt to work granite. http://en.wikipedia.org/wiki/Diorite

Identify an insect

Good day. Can someone identify this insect? I photographed it today, in the Anza-Borrego Desert State Park, California. It was about 1.5 to 2 inches long. Thanks. Rockpocket 03:17, 9 March 2009 (UTC)

• 
• 
• 

Looks like a soldier beetle to me. --Dr Dima (talk) 04:43, 9 March 2009 (UTC)

I think you may be correct, thank you. Next question, can anyone identify a species? Rockpocket 05:56, 9 March 2009 (UTC)

Actually, after a bit more research, I think it is the Desert blister beetle (Lytta magister). [2] Rockpocket 06:21, 9 March 2009 (UTC)

Can well be. Lytta genus is in Meloidae (blister beetles) rather than Cantharidae (soldier beetles), so I was wrong, then. My apologies. For the fans of entomological confusion, here's a semi-famous fact: Meloidae contain and secrete cantharidin, Cantharidae do not. Actually, the historic confusion between the two families is to blame for that. The "Spanish fly", Lytta versicatoria, has been known as Cantharis vesicatoria or (usually dead and dried) as cantharides. Still, my bad. --Dr Dima (talk) 07:18, 9 March 2009 (UTC)

Not at all, your answer got me looking in the right direction. Thanks again. Rockpocket 07:32, 9 March 2009 (UTC)

I made a few tweaks to your new article, Rockpocket. Now we need someone to create an article on the species' describer, George Horn, who seems notable enough. Deor (talk) 15:22, 9 March 2009 (UTC)

… which I've just done at George Henry Horn. Deor (talk) 21:51, 9 March 2009 (UTC)

Are all treatments that depend on belief placebos?

If a patient has to believe in the viability of a health treatment for it to work, is it necessarily a placebo? NeonMerlin 04:48, 9 March 2009 (UTC)

If a "treatment" requires belief for any recuperative action than it must not be bioactive. Any recuperative action it does have must therefore be by placebo effect, so yes. However, I would hazard that there is a middle ground where bioactive compounds are more effective when the patient believes it is a cure-all. In these cases you would have to define "work", before your question could be answered. Rockpocket 06:14, 9 March 2009 (UTC)

No. There's an interesting article in the New Scientist regarding placebo and the placebo effect, which among other things tells us that belief is not the main factor in the placebo effect: rather there are other factors such as being made to feel comfortable with the consulting environment and physician. [3] This article also gives the information that people who believed the morphine they were being given was going to work, experienced a greater analgesic response than those who didn't. Nobody would suggest that morphine came under the placebo category! --TammyMoet (talk) 10:06, 9 March 2009 (UTC)

There are a couple of "mind over body" techniques that basically work by the person controlling their breathing, heart rate, thought processes etc. I don't think they would be effective if people didn't think it would work. They also work differently from placebos because the individual tries to actively control bodily functions. There is unfortunately a grab bag for this kind of thing that spans from tried and established relaxation techniques to the latest and greatest loony cure-all fads. Someone learning not to turn into a quivering bag of hysterics or fainting whenever there's a thunderstorm without taking any "little pink pills" is likely to depend on that individual starting to believe that the sky isn't going to fall and hit him. That's a far cry from things like "curing infections through willpower". I'd suggest antibiotics for the latter which will work whether you hold the firm conviction that pharmaceutical companies are run by crooks or not. I was trying to find some examples for you, but anything even remotely going in that direction is likely to come under much scrutiny and as a layperson it's hard to distinguish the ones that deserve it from the "friendly fire" casualties. 76.97.245.5 (talk) 10:57, 9 March 2009 (UTC)

does atmospheric pressure include the vapor pressure of the water vapor in it?

I'm trying to do a lab with some psychrometric equations. Atmospheric pressure for the room (I believe) in which our experiments took place was measured, but I am not sure whether this is total pressure or the pressure of dry air. Does atmospheric pressure normally include the water vapor pressure? Thus in a closed system the atmospheric pressure surrounding a reservoir of water should increase with further evaporation? (This is different from saturation water vapor pressure and water vapor pressure being equal, I believe.)

Particularly I am confused by an equation I'm given for specific humidity -- the ratio of the molecular weight of water and dry air (0.622) multiplied by the water vapor pressure , divided by (total pressure - 0.378*water vapor pressure). Maybe the math is not working at 4 am in the morning, but why subtract water vapor pressure from the total pressure of the air, if I'm trying to calculate specific humidity which tries to relate the amount of water vapor to the amount of mixture? John Riemann Soong (talk) 08:16, 9 March 2009 (UTC)

Vapor pressure has a separate section (albeit brief) on use in meteorology at the bottom. 76.97.245.5 (talk) 11:02, 9 March 2009 (UTC)

The pressure measured by a barometer will include water vapor partial pressure, but that does not mean that the atmospheric pressure over a water reservoir will be any higher. Dauto (talk) 17:05, 9 March 2009 (UTC)

Wouldn't water vapor in air make the air less dense and lighter? Edison (talk) 19:30, 10 March 2009 (UTC)

Yes. Dauto (talk) 03:35, 11 March 2009 (UTC)

air sacs

What is the name of air sac which is found in human's lung? —Preceding unsigned comment added by 196.200.102.42 (talk) 09:16, 9 March 2009 (UTC)

The normal structure is an alveolus, whereas disease can result in blebs and cysts. --Scray (talk) 09:28, 9 March 2009 (UTC)

Meson number

We have baryon number, but, apparently, "meson number" is not a noted concept. Can someone shed light? —Anonymous Dissident^Talk 09:52, 9 March 2009 (UTC)

Ah, don't worry. I guess (1-1)/2 doesn't make sense, so I answer my own question. —Anonymous Dissident^Talk 10:02, 9 March 2009 (UTC)

photons

how do photons carry light? —Preceding unsigned comment added by Lightfreak (talk • contribs) 12:28, 9 March 2009 (UTC)

Photons are light. Light isn't some separate thing which they carry. Algebraist 12:31, 9 March 2009 (UTC)

light

is light an electromagnetic radiation or the theory of photons right?```` —Preceding unsigned comment added by Lightfreak (talk • contribs) 12:40, 9 March 2009 (UTC)

Your question doesn't make much sense, but I think you want Wave–particle duality. Algebraist 12:44, 9 March 2009 (UTC)

Light is an electromagnetic radiation and the photon theory is right. Dauto (talk) 16:33, 9 March 2009 (UTC)

Light is its own thing. It is not a particle, and its not a wave. It is just light. It's just doing what it always does. It is important to note that what is changing is not the light itself, its the model we use to explain light. We use the wave model to explain some behaviors of light, and we use the particle (photon) model to explain other behaviors. Light is not switching between these two forms, it doesn't change its behavior, what changes is the models we have to use to explain its behavior in terms that have analogs in the "Big World". The problem is that light has no analog in the big world, so we need to use these two models in conjunction. We treat light as a hybrid of a wave and a particle, but light itself does not change its nature, what is changing is the model we use to explain it in terms we can grasp. --Jayron32.talk.contribs 16:52, 9 March 2009 (UTC)

thanks! But could you please define light and its composition?--Lightfreak (talk) 09:23, 10 March 2009 (UTC)

Light is what comes out of the light bulb when you flick the light switch. That's just what light is. Light can be thought of as modulations in electric and magnetic fields, or as massless elementary particles, but that's not how it is defined. It isn't really composed of anything - it's just light. --Tango (talk) 11:42, 10 March 2009 (UTC)

Sure. Light (by extension all forms of electromagnetic radiation) is perterbations of the electric field inherent in the universe because of the existance of electric charge. The behavior of these perterbations are explained by Maxwell's equations. When you have an electric charge, you generate an electric field. If you disturb that field, you generate a wavefront much like throwing a stone into a clean lake. Except for two things: 1) The field is three dimensional and not two and 2) you could also look at the wave front as a little billiard ball. See, this is where the physics does not match our perceptions; light is not a substance; it does not have a composition. It is energy. It's an action, not a stuff.

Maxwell himself made the common mistake, in his A Dynamical Theory of the Electromagnetic Field, when he refered to the electric field as a "substance", expecting it to be related to the Aether which supposedly provided the medium which carried the wave. Aether, however, does not exist. Modern physics treats space itself as this medium; thus we get the rather bizarre concepts as a "mediumless wave". If light is a wave, then some "substance" must be vibrating to carry that wave (think like an ocean wave or a guitar string vibrating). However, light is not a wave, per se, but it behaves like a wave in the sense that it does some physical things that waves do, like refraction and diffraction. Also, since it a) isn't actually being carried inside a medium, and b) it can be "quantized" (i.e. it behaves like it exists in localized places and times) then it also behaves like a particle, a little billiard ball. See, particles don't need a medium to propagate in, so if we think of light that way we do not have to invent any "Aether", which we know not to exist. Plus, particles are the only way to explain behaviors like the Photoelectric effect, which would not make sense at all if light were a wave. Except that particles don't work either, since they don't diffract like waves do, and light clearly diffracts (bends around corners). So we are left with the psychologically unsatisfying result that light is not a wave, or a particle, but some thing which behaves like one or the other depending on how we look at it. We don't have any way to relate light to anything we can handle, so we can only say that we need two competing and otherwise mutually exclusive models to explain it. It sucks, but that's just the way it works. --Jayron32.talk.contribs 11:56, 10 March 2009 (UTC)

The main motive of yur answer is that light is simply an energy whose propogation is undefined. Its properties are a mix of electro magnetic, wave and particle propogation.--Lightfreak (talk) 08:44, 12 March 2009 (UTC)

light

i have some doubts in the article "light".Please help me out with it.--Lightfreak (talk) 13:04, 9 March 2009 (UTC)

You're really going to have to be more specific than that. Could you describe your doubts? -- Captain Disdain (talk) 13:27, 9 March 2009 (UTC)

thanks! I could not axactly understand which amonst all the theories was correct.If it was the particle theory then how come the first line itself states light as electro magnetic radiation.If light consists of photons then how come polarisation was observed? Hope you can help out.--Lightfreak (talk) 09:13, 10 March 2009 (UTC)

See above. Light is not a wave or a particle. It behaves in certain situations like one or the other, but it isn't either. We don't have anything in the world we can handle with our hands which works well as a model for light, so we need these two mutually exclusive models to explain light in terms we can grasp; it doesn't mean light is one or the other, it just means that we need both to be able to put light in terms that our brains can work on... --Jayron32.talk.contribs 12:12, 10 March 2009 (UTC)

It might help you to read my (long-ish) reply to the question just below this one...I think it explains the wave/particle mess a little more clearly. SteveBaker (talk) 14:23, 10 March 2009 (UTC)

The meaning of Frequency in physics

Usually c(transmission speed) = f(frequency)• w(wavelength) ;

However, if I, per second, send 3 photons(wave packets) of wavelength 1cm at the speed of light, there would be gaps between the wave packets, so the rule above above fails.

I feel insecure/unsure about this, and I have not succeeded in finding a measure covering the situation above.

Should there not be an explicit statement, that the wave packets should be immediately adjacent, for the rule above to work ?

Should there not be a special measure for the example above to work ?

83.226.97.214 (talk) 13:29, 9 March 2009 (UTC)

You need to either think about light in terms of photons, or waves, not both. Combining the two interpretations is rather tricky. If you want to think it terms of wavelengths, do everything with waves, no photons. If you want to work with photons, think in terms of energy (E=hf). --Tango (talk) 13:36, 9 March 2009 (UTC)

What would be the problem? There would be three separate "pulses" of light; each pulse would have its own frequency and wavelength (these would be dependent on the energy of the single photon, primarily due to the method you used to make those photons). If you wanted to, you could also "time-average" over a long period of time, and you would begin to see the repetitive nature of the pulses showing up as a frequency-component in your received spectrum (note that only special cases of light have a "single" frequency - most light is best described by a combination of frequencies - in your case, this would include both the individual photon frequency AND the 3-pulse-per-second pulse repetition frequency). The problem is that with only 3 photons per second, you would need to average many many time-cycles to show any meaningful "spectrum" wave-like behavior (because there is not a large amount of energy per pulse). All in all, this is a situation which is best treated exclusively with the particle model. Nimur (talk) 15:11, 9 March 2009 (UTC)

Phrased another way, "gaps" in the spatial extent of the wave packet really just means that the individual photons do not interfere with each other. If you space the photons closer together, their wave-nature will cause them to interact. The result will be a different distribution of received photons at the receiver. This distribution is slightly random, but again, on the long-term average, it will be exactly described by the interference pattern of the wave representation of the individual photons. Nimur (talk) 15:13, 9 March 2009 (UTC)

I think the OP is confusing then frequency of the photons (which is indeed related to the speed and wavelength through $v=\lambda f\,$) with the frequency of photon emission (3 photons per second in the example). Those are completely separate comcepts. The photons can have gaps, be contiguos, or overlaping. Dauto (talk) 16:07, 9 March 2009 (UTC)

Forget light - because it's complicated. Think about sound. If I hit middle-C on the piano (well - let's make that be an 'idealised' piano..a music synthesiser that's set up to produce pure sine waves) and also hit the 'G' above that at the same time and hold them down - then there are two frequencies present in the resulting waveform - one is a 261Hz sine wave - the other is a 391Hz sine wave. The 'v = f . w' equation holds for each wave independently - so the wavelength of the two notes is different. The actual wave-shape is complicated because there is constructive and destructive interference going on...but we're all very happy with the resulting math.

OK - now consider hitting just the middle-C key once per second for half a second each time - beep-beep-beep-beep...forever. You now have a 261Hz sine wave plus a 1Hz square wave. One modulates the other. This produces a vast number of harmonics and other frequencies - each with it's own wavelength and frequency - all moving at the same speed. The shape is now rather simple to look at on an oscilloscope or something - but it took a lot of frequencies to reproduce that shape. However, the mathematics are well-behaved.

Now - if you buy a brand new piano - pound the key three times - and then (very quietly) smash the piano into a million pieces so it'll never play again - then you have another wave modulating the first two which has a frequency of zero hertz(!) and an infinite wavelength (because it'll never repeat)...this gets really impossible to think about! At that point you have to stop thinking about your performance as a sum of frequencies and start thinking of the individual notes as wave-packets - like photons - and you have to use different mathematics to handle it in order to avoid the ugly infinities that pop up. Nothing really different happened - it's just that the math falls apart when the frequency hits zero.

Similar thinking helps you get through the 'wave/particle' thing. If your photons come in a steady, uniform stream then it's not a problem to think in terms of continuous frequencies of light. When they come less frequently - then you have to think of pulses of light - and when there are just three of them - the mathematics of 'waves' stops being very useful - and you're better off thinking of particles. SteveBaker (talk) 18:12, 9 March 2009 (UTC)

SteveBaker's excellent explanation misses the target by a hair. Even when dealing with individual isolated photons, it is essential to keep their wavelike nature in mind. Individual photons still behave in a wavelike manner suffering (for instance) interference, difraction, and refraction. Dauto (talk) 19:42, 9 March 2009 (UTC)

Yes, indeed - but that's true of sound too. Even if you buy that new piano, hit middle-C then destroy it so it never plays another note...you can still talk about "the frequency of the note" - even though it has some components that are mathematically tough to deal with as waves. The sound from that one note still behaves like a wave - it'll refract through slits (on the scale of sound waves, a doorway makes a pretty good slit!) - and it'll echo off of distant mountains...just like a wave. But you can also talk about "the note" as if it were a particle because it's confined in space and time. SteveBaker (talk) 14:18, 10 March 2009 (UTC)

It's not that simple. The photons are produced and detected one at a time. That's why they are considered particles. If you emit one photon and observer 'A' detects it, observer 'B' won't be able to detect it as well because there was only one photon to begin with. If you play one piano note, everybody in the room will hear it. The note isn't a particle, really. Dauto (talk) 16:01, 10 March 2009 (UTC)

Not true. See Double-slit experiment. You can set up situations where a single particle, even a particle with a measurable rest mass like an electron, can be emited one at a time and still display wave-like properties. You can actually get one photon to behave like a wave... --Jayron32.talk.contribs 16:58, 10 March 2009 (UTC)

I'm not sure if you were talking to me, but if you were, I don't know where you got the idea that I thought othewise. Dauto (talk) 17:06, 10 March 2009 (UTC)

Sorry. I misinterpreted your comment. I thought you meant that light only had wavelike properties in bulk and that single photons only had particle-like behavior, which is of course not the case. My bad. --Jayron32.talk.contribs 22:35, 10 March 2009 (UTC)

Hullo all above ! I am the originator of the query. This is to thank you for Your efforts. I am going to attempt a new round, if it may please, titled "Frequency in physics ?" / Rolf

Heparin and Bleeding Tests

Heparin acts by decreasing the activity of thrombin, the common endpoint of coagulation cascades

Why then, does it only affect pTT blood times (intrinsic pathway), and not the PT(extrinsic pathway)?

--Cacofonie (talk) 15:40, 9 March 2009 (UTC)

Actually it does affect PT. However it only has a mild and unreliable effect. Axl ¤ [Talk] 18:49, 9 March 2009 (UTC)

SNOMED-CT abbreviations

I've been looking at SNOMED. I see that it has a lot of terminology. Does it have abbreviations? For example, does it have "tab = tablet" and "hctz = hydrochlorothiazide"? -- kainaw™ 17:47, 9 March 2009 (UTC)

The use of abbreviations in medicine, though widespread, is fraught with danger through misinterpretation. Recognised systems of nomenclature and classification such as SNOMED don't use abbreviations because they detract from the clarity those systems are attempting to achieve. Mattopaedia ^{Have a yarn} 11:23, 11 March 2009 (UTC)

The point of a nomenclature with abbreviations is to remove the abbreviations in existing medical records to remove misinterpretation. If a doctor types hct by accident when he means hcl, having it automatically expand to hydrochlorothiazide instead of hydrochloride will increase the possibility that the doctor will realize his mistake. -- kainaw™ 13:25, 11 March 2009 (UTC)

Communicating meaning with distant space aliens - no pictures allowed

This discussion began at Wikipedia:Reference desk/Language. -- Wavelength (talk) 19:05, 9 March 2009 (UTC)

Imagine that the two-way communication of signals between us and some space-aliens orbiting a distant star has been established. They are blind and immobile and cannot use pictures or diagrams of any kind. There is no pre-established code or alphabet. While I can imagine that eventually the meaning of mathematical or logical symbols might eventually be established (for example tranmitting many messages such as "..+..=...." would give meaning to + and =), would it be possible to eventually build up enough meaning from a zero base so that in time they would understand what was meant by the message "Last thursday my Uncle Bill went to the supermarket"? Helen Keller springs to mind. 89.240.206.60 (talk) 02:01, 8 March 2009 (UTC)

I don't see how it's possible to go from 2+2=4 to any non-math concept. Remember, it was impossible to decipher hieroglyphics without help from the Rosetta Stone, even though they were written by human beings, and this would be n times worse (n >> 1). Clarityfiend (talk) 05:22, 8 March 2009 (UTC)

Earth has blind, immobile animals called barnacles, and some humans have done research on how to talk with animals (http://www.howtotalkwithanimals.com/), but I have never heard of anyone attempting to communicate with a terrestrial barnacle. Instead of contemplating communication with alien barnacle-like creatures, why not ponder how we humans can communicate better with each other? -- Wavelength (talk) 06:45, 8 March 2009 (UTC)

LINCOS was a whole elaborate language (developed at length in a book) based more or less around that premise (though I think there were some abstract mathematical images included)... AnonMoos (talk) 07:00, 8 March 2009 (UTC)

H. Beam Piper's much-reprinted story Omnilinual has terrans cracking the Martian language by finding a periodic table. Unfortunately, the idea in the story simply doesn't work: the English names for common elements only make sense in the context of the history of science, not modern science (eg oxygen = 'acid-maker' and hydrogen = 'water-maker]; these are Graeco-Latin rather than English, but German for example translates the roots and still perpetuates the errors), so why assume that the Martian names would be meaningful? --ColinFine (talk) 18:51, 8 March 2009 (UTC)

Maybe the aliens were using a constructed language whose intent was to make it easier for outsiders to learn.

The entries in our version of the Periodic Table have only the symbol, the atomic number, and the atomic weight. The entries in an alien version might have far more information on a particular element, making the linguists' job easier.

But it might still be difficult to recognize a "Periodic Table" when we find one. There are many ways of illustrating the periodic table, and it just got more complicated.

http://www.sciencedaily.com/releases/2010/03/100304142300.htm

"The new antinucleus, discovered at RHIC's STAR detector, is a negatively charged state of antimatter containing an antiproton, an antineutron, and an anti-Lambda particle. It is also the first antinucleus containing an anti-strange quark."

"The familiar Periodic Table arranges the elements according to their atomic number, Z, which determines the chemical properties of each element. Physicists are also concerned with the N axis, which gives the number of neutrons in the nucleus. The third axis represents strangeness, S, which is zero for all naturally occurring matter, but could be non-zero in the core of collapsed stars. Antinuclei lie at negative Z and N in the above chart, and the newly discovered antinucleus (magenta) now extends the 3-D chart into the new region of strange antimatter." 99.9.112.31 (talk) 18:31, 13 March 2010 (UTC)NotWillRiker

Is there a joke hidden in the misspelling of "Omnilingual"? —Tamfang (talk) 04:57, 10 March 2009 (UTC)

For what it's worth, I coincidentally ran into the following article today ---> Pioneer plaque ... in which NASA scientists are, in fact, trying to communicate with distant space aliens ... albeit with the use of pictures. (Joseph A. Spadaro (talk) 22:20, 8 March 2009 (UTC))

The essential bottleneck to get through may be that of naming geometric shapes, such as a triangle. A triangle could then be used to build up other shapes. The triangle could be named after being identified by its mathematical properties. If however they have no sense of the spatial, then you are stuffed. 89.243.72.122 (talk) 23:56, 8 March 2009 (UTC)

How can an organism distinguish between a random collection of perceptible stimuli and a purposeful collection of perceptible stimuli produced by intelligent design? How can it distinguish between a message and a non‑message?

-- Wavelength (talk) 02:09, 9 March 2009 (UTC)

Humans or even sheepdogs or bees seem to have no problems with doing that. And if we humans recieved a signal from a distant star in the form of the Fibonacci series or any other simple mathematical series, then that would indicate that the sender was an intelligent being. 89.242.94.128 (talk) 11:37, 9 March 2009 (UTC)

The series should not be too simple, as then we could not be sure it was not generated by some nonsentient physical process. The Fibonacci sequence in particular is a very bad example, as it is known to appear in nature without any involvement of intelligence, see Fibonacci number#Fibonacci numbers in nature. — Emil J. 13:42, 9 March 2009 (UTC)

This fellow's research into a generalization of information theory that assumes no prior common language might be of interest, for a formal take on a specific variation of the question, which he calls "Universal Semantic Communication". The general strategy is to frame it as goal-oriented communication, which allows us to conclude that we've successfully communicated something when we can achieve some goal as a result of the communication faster than we would've been able to do without it. --Delirium (talk) 02:55, 9 March 2009 (UTC)

It might be worth posting this question on the mathematics desk. I am sure that they would have ways of encoding mathematics that they would think recognisable (and going from simple operations to advanced formula). They might even have some insights in how to jump out of Mathematics. -- Q Chris (talk) 13:49, 9 March 2009 (UTC)

[The copied text ends here.]

This reminds me of the book "Contact". Axl ¤ [Talk] 19:13, 9 March 2009 (UTC)

(And actually, I believe the answer is in that very book. The aliens in the book send humanity a set of plans for building a massively complex machine. In the course of building it, our technology is pushed along towards theirs - and in the end, the machine makes it possible to communicate with them. It's left deliberately unclear whether the machine tells our hero what it's all about - or whether it physically transports her to their planet and lets them talk face-to-face. But in our case, we don't know how to do the latter - so we have to do the former. Tell them how to build a computer that can run a program we send them that will interact with them and tell them all about us. See my post below for more details about how you do that. Contact (the book, much more so than the movie) is quite the most well-thought-out alien contact story I've ever come across. If it happens - that's exactly what it'll be like. SteveBaker (talk) 22:12, 9 March 2009 (UTC)

I'll admit I haven't read the book, only the movie, but if we send the aliens plans for a massively complex and expensive machine that does nothing but show them an image of their father while making some cryptic, but ultimately meaningless remarks, then I fully expect them to eventually show up with a fleet of warships to wipe us out. (Once their economy recovers from spending their GNP on a machine that doesn't do anything.) I hope that the book's story was a lot less stupid. APL (talk) 02:11, 12 March 2009 (UTC)

Sorry to hijack the question, but I don't quite agree that mathematics can be a universal language. See my question here. --99.237.96.33 (talk) 21:11, 9 March 2009 (UTC)

Since all we can really send (at least at first) is numbers...probably binary numbers. It makes sense to start with numbers - move to arithmetic and then to algebra. But indeed - then what? What I'd hope to do would be to start to express ALGORITHMS - written in a computer programming language. That's not a big stretch from algebra and arithmetic. If you can teach them that - then you can hope that they would have the technology to automate the execution of such an algorithm...ie that they have computers. If they do - then you can progress to sending them a huge AI program that will allow them to experiment with communication at higher levels. If you're talking to a bunch of aliens who have somehow not invented computers of some kind - then we'd have to somehow encourage them by sending algorithms that are too complex to solve on paper and hope that they'd latch on to the need to automate this stuff somehow. But there is always the MASSIVE practical problem that in any likely scenario, the aliens would be perhaps 50 light years away. It would require an entire generation of humans to ask the aliens a question and get an answer back. So if we do manage to discover that they exist, I think we have to assume as little as possible about them and proceed as if they know as little as possible. So I'd send a MASSIVE message that starts with prime numbers (hopefully to get their attention), then counting, then arithmetic, algebra and algorithms - then a bunch of simple programming 'test programs' to ensure their computer works correctly - and finally as large and sophisticated a program as we can manage to divise for them to interact with - and as much data for it to work with as we can manage to send given the (likely very limited) bandwidth available. The hope would be that that within perhaps 110 years later (50 light years each way with 10 years for them to figure it all out) we'd get back a reply in the form of a massive program written in the same programming language as ours - plus as much data as they dare send. What happens next depends entirely on what they say. As I pointed out before - if what we get back is a blurry video of some complex interpretive dance plus the digital data describing the chemical odours given off by the participants...then we may be in a lot of trouble! SteveBaker (talk) 22:02, 9 March 2009 (UTC)

You want to send ALICE as our ambassador? Could work, I guess! That message really would be enormous, though. It would take several days to send, at least, and we would need to send it multiple times to be sure they got it cleanly (no fancy error correctly codes possible, just simple repetition is all we have). --Tango (talk) 22:46, 9 March 2009 (UTC)

Yeah - exactly. A digital ambassador/teacher - perhaps it could also learn and have them transmit the results it garners back to us. SteveBaker (talk) 03:38, 10 March 2009 (UTC)

In all likelihood we would not be trying to teach the aliens anything. It is overwhelmingly likely that they would be more advanced than us and our job would be to listen and try and interpret what they say. I think that also comes from Carl Sagan (Cosmos?) but can't be sure - too long since I read him. SpinningSpark 23:04, 9 March 2009 (UTC)

Yeah - but if they're much smarter than us then they may consider our best efforts to be about as annoying as a yapping dog. I think it's in our interests to share some of our best stuff with them. But opinions vary on that point. SteveBaker (talk) 03:38, 10 March 2009 (UTC)

We need to teach them some kind of system of communication, though. Whoever starts the conversation has to do that bit, regardless of the relative levels of advancement - when it takes generations for a round trip, you can't waste the first one just saying "Hello". --Tango (talk) 23:15, 9 March 2009 (UTC)

Yep - exactly. The first message really has to count - you may not live to hear the reply - but for sure you won't live to hear the answer if you need to ask a followup question after you hear what they have to say! SteveBaker (talk) 03:38, 10 March 2009 (UTC)

If pictures were allowed in this, the first question could be do you own a pair of 3D polarised glasses? SpinningSpark 23:22, 9 March 2009 (UTC)

Actually - that's PRECISELY the kind of thing you can't do. How do you know they have two eyes? How do you know that their eyes are insensistive to polarisation (as ours are) - if they are then polarised glasses might not be necessary - or they might not work. Our aliens may use some kind of radar or sonar for depth perception - and have just the one eye. So no - that would really suck as a way to talk to them. If you wanted to send them 3D images, you'd probably need to chop a 3D volume up into 'voxels' and transmit it like that...but it's not great. I have my doubts whether a 2D image would work either - if they do have a special 3D imaging organ - then perhaps they'll be completely unable to comprehend a 2D image? It's definitely a leap of faith to assume pictures will work. SteveBaker (talk) 03:38, 10 March 2009 (UTC)

Life on Earth has various systems of perception, including various types of 2D and 3D ways of viewing the world. We can expect an alien biosystem to be similar (evolution tends to find things that fit niches very well, and different niches have different best systems), so hopefully they can conceive of a 2D image even if they don't personally see the world that way. --Tango (talk) 11:55, 10 March 2009 (UTC)

If they see through the use of sonar, then it's almost certain that they don't have the concept of a 2D image. --Carnildo (talk) 00:48, 11 March 2009 (UTC)

Did you read my comment? If they use sonar, but have studied other life on their planet that uses light, then they should be able to conceive of a 2D image. We can conceive of ETIs that use sonar despite not using it ourselves, why can't they conceive of ETIs that use light? --Tango (talk) 16:57, 11 March 2009 (UTC)

We can concieve of ETIs that use sonar, sure, and ETIs that use sonar can concieve of creatures that use light, but does that mean they'll grasp all the consequences of using light? If your primary perception of the world is through reflected sound waves, it's hard to imagine that subtle variations in the surface chemistry of an object are important to the perception of the world. If your view of the world is inherently 3D, it's hard to imagine that the edge outline of an object viewed from a specific direction could be used to convey the shape of the object. --Carnildo (talk) 23:07, 11 March 2009 (UTC)

(Responding to Delirium on "Goal Orientated Communication") It's hard to see how that would be useful here. The method specifically requires interaction between the parties to succeed, the one thing thing we cannot have. My suggestion would be to first establish symbols for "yes" and "no". This could be done with the help of mathematical language. Having established a basic arithmetic, correct and incorrect equations could be stated followed by the yes/no symbols. This starts to give you a method of answering questions and is the door to real information exchange, but that's about as far as I've thought it through. SpinningSpark 23:19, 9 March 2009 (UTC)

That is of course assuming a semantic equivalence between false and no; and true and yes. It seems plausible that some meaningful semantics might not follow such a convention. For example, a large chunk of human history and culture is founded on the affirmation of patently false ideas. Nimur (talk) 23:49, 9 March 2009 (UTC)

Nonsense! We send a 'count' sequence in binary to establish that we're talking in binary and which bit is least-significant. Then we send a few dozen of the first prime numbers to kinda verify that this isn't a natural phenomenon...to provide examples of large numbers. Then we need to start with 1 @ 1 % 2 $ ... 2 @ 3 % 5 $ ... 9 @ 5 % 14 $ ... 2 & 2 % 4 $ ... 2 & 5 % 10 $ ... 10 # 5 % 2 $ ... 4 # 2 % 2 $. (I presume you figure that '@' is plus and '&' is multiply and '#' is divide - but you might not figure the point of the '$' and '%'. Then when we've done a few hundred examples, we go with 1 @ 1 % 4 ^ ... 2 @ 3 % 1 ^ ... 10 # 5 % 4 ^ ...and so forth. How long does it take to figure out that $ means TRUE and ^ means FALSE from that? I don't think that's hard at all - you can then express things like 'greater' and 'less' instead of '%' for 'equals' 1 @ 1 < 4 $ 1 @ 1 > 1 $. If you send enough examples (and you could send tens of thousands of them pretty quickly) - it would take a pretty stupid civilisation to not be able to figure it out. You can't build such a sensitive radio detector and not have a knowledge of basic arithmetic! Once you have that, you can say things like A @ B % B @ A $ ... and start introducing algebra. You'd probably want to use reverse-polish notation rather than infix in order to avoid the need to send parentheses...but that kind of thing ought to work for math, logic and (importantly) algorithms. You could send algorithms for factoring primes, calculating square roots, calculating pi...and I think any decent computer programmer could figure them out no matter how cryptic the symbology...although it might take you a while. But the degree of algorithmic sophistication it takes to describe an algorithm to factor primes is plenty good enough for describing a simple AI program. It's definitely do-able if the aliens are at least as smart as us. SteveBaker (talk) 04:00, 10 March 2009 (UTC)

How do you get across the concept of a variable? I guess you need to do it with lots of simple examples. "A:=1, A+1=2", "A:=7, A+2=9", "A:=1, B:=2, A+B=3". It really would end up being an extremely long message - it would take a lot of examples of each thing to make sure they've got it, they can't easily ask for clarification if there's one bit they just can't get their "heads" around. If you want to send multiple example programs, you're going to end up getting into the realms of years of transmission - although, if it takes 50 years for the message to get there, that might be reasonable. --Tango (talk)

The time between when a civilization is able to dabble in intra-galactic communication and its own self-destruction can be measured in nanoseconds in cosmic time scales. Think virtual particles AЯE us! ;-) -hydnjo (talk) 23:54, 9 March 2009 (UTC)

It's encouraging that so far we've been unable to find alien life in our solar system. If we did - then it would imply that life can form EXCEEDINGLY easily throughout the universe - and then the failure of SETI to find any of it would suggest that civilisations do indeed self-destruct before they are capable of interstellar communications. But so long as life seems rare - there is at least the hope that it's so rare that we shouldn't be surprised at the lack of SETI results. If we do find life on Mars - we should worry about our futures...the search is more than mere curiosity! SteveBaker (talk) 04:15, 10 March 2009 (UTC)

I read an article once that took that point of view, but I don't buy it. It's assuming that a lack of ETIs talking to us implies a lack of ETIs, which I don't think is the case. There are plenty of reasons why an ETI might not be broadcasting signals we can receive (which is basically just signals sent intentionally) - for example, they may have decided that it's not worth trying to talk to people when you have a 100+ year round trip (particularly if they have a shorter lifespan than us, and I would put the odds of that at 50%, since I have no reason to assume our lifespan is longer or shorter than the average for intelligent beings). They may be devoutly religious and reject the notion that there could be life on other planets. They may have decided to broadcast on completely different frequencies than we expect. Etc. Etc. Etc. --Tango (talk) 14:06, 10 March 2009 (UTC)

Certainly it's not a definite thing. But this is an area where we currently have zero data - we don't know how many aliens there are - what their propensity/ability to communicate is - or even how common life is at the microbial level! But the balance of probability swings dramatically if we find other life (albeit simple) on our own doorstep. At that point, the default assumption changes from "we have no idea how common life is" - to "life is probably extremely common indeed"...although that could still be an incorrect assumption. And at that point, where we'd strongly SUSPECT that life is common - we'd have to start being concerned that so little of that presumed life is able to talk to us.

As for the frequencies they might transmit on...this has been thought about rather carefully - and there are only so many ranges of frequency where communication at these distances is practical. For example - you'd want to pick a frequency that wasn't being naturally emitted in vast quantities by the star you are orbiting around - because your signal would get lost in the noise. You'd also want to avoid frequencies that would be more strongly absorbed or scattered by interstellar gasses and dust. You also need frequencies that can be produced and detected with a manageable size of antenna - and where the amount of energy required to produce the signal isn't insane. When you add up all of the constraints, the range of frequencies can be narrowed to a fairly manageable set...and that's essentially what SETI has done. SteveBaker (talk) 11:36, 11 March 2009 (UTC)

Not "able", "willing and able". Just because they aren't talking to us doesn't mean they can't. --Tango (talk) 16:55, 11 March 2009 (UTC)

First give either axioms or examples to explain 4-dimensional euclidean geometry (three dimensions of space and one of time), and use that to make videos. Unlike the kind of videos we have, which show what we see and thus only have 3 dimensions (including time) these will show things as they are and thus aren't prohibited. Even if they're blind, they live in four dimensions of space time and must adapt to understand accordingly. From there, it's just a matter of giving them enough to understand our culture well enough to know who your uncle Bill is, what a supermarket is, and when last Thursday was. — DanielLC 06:05, 10 March 2009 (UTC)

Your question, as you asked it, already would include that we had a lot in common with those aliens. The fact that we know there's another species out there means that we have received some evidence of its existence. Our idea of what is and isn't "intelligent" tends to be very closely modeled on humans. For an omnivore like humans that's useful to avoid ethical problems with eating other living things. The aliens need to be at least as "bright" as humans are. They can't be much more advanced or too different either, because they'd have to to chose the same methods to communicate (e.g. electromagnetic waves within a certain frequency band). They would also have to be a bit more advanced or it is unlikely that they'd expend the energy and other resources required to broadcast, rather than just listen (as we did with SETI). Some of the mathematical solutions even assume that their methods of describing their world evolved along the same path as ours. They should also not turn over generations (lifetime) much faster than we do. Longer would actually be preferable. If we can indeed find a species that fits the bill, it would be best to determine mutual needs and benefits and then base our attempt on that. Is there something that we have, and can spare, that they need? Before you get to communicating at a level that you are heading for with "uncle Bill" that would also require both civilizations to convince themselves that the other doesn't pose any threat. With interstellar communication and the current human population aliens would face the problem that we would change a lot from one message to the next. Political leaders, country boundaries, goals, ethics, all that only follows some general trends with lots of fluctuation. Depending on whether they're optimists or pessimists we are a species that is rather destructive to itself and it's environment or Mostly harmless with violent episodes. In the millenia it would take for communication to reach the "small talk" level it is highly unlikely that your phrase would still make sense even to the humans. For casual communication dropping a couple of individuals into the other's environment would work best. Learning the varied meaning of words and phrases of a foreign language is difficult enough even for humans who at least are of the same species and from the same planet (Your particular aliens could spend months trying to find out the significance of thursday without capital T :-) 76.97.245.5 (talk) 08:13, 10 March 2009 (UTC)

• The fact that we know there's another species out there means that we have received some evidence of its existence. - Yes, but that might (for example) be as a result of detailed spectrographic analysis of their planet's atmosphere. That's the kind of thing NASA plan to do in the wake of whatever findings we get from the Kepler Mission that just recently launched. We may not have had a message from them yet. There are several sci-fi examples (Star Trek, for example) where all of the intelligent species of the galaxy have already formed a 'club' and are communicating with each other on narrow-beam links - but they've agreed on a 'prime directive' that says that nobody talks to newly evolved species like us until we make the first move and indicate a willingness to talk. I imagine there were quite a few tribes in Africa (and certainly still some in South America) who wish the 'advanced' civilisations on this planet had been following such a policy over the past few centuries!

• The aliens need to be at least as "bright" as humans are. - Probably. But we could also envisage a situation such as in that god-awful movie Idiocracy - where they were once really smart but have been dumbed-down by their technology to the point where they don't understand it anymore. It seems unlikely - but I suppose it's possible. In that case, I suppose we end up talking to their computers not to the aliens themselves - who just see the results in cartoon-form inserted into reruns of 'The Little Mermaid'.

• They can't be much more advanced or too different either, because they'd have to to chose the same methods to communicate (e.g. electromagnetic waves within a certain frequency band). - Why? If they are super-intelligent, they might deliberately toss out their tachyon intergalactic-internet and send us slow old radio signals because they are smart enough to have analysed OUR atmosphere remotely and they see none of the side-effects of advanced tachyon technology. (Or whatever it is). It's definitely not impossible that smart aliens would dumb-down to baby-talk when they communicate with us.

• They would also have to be a bit more advanced or it is unlikely that they'd expend the energy and other resources required to broadcast, rather than just listen (as we did with SETI). - Again, that's likely to be true - but perhaps they simply have different priorities. If (for example) they know that their sun is going to explode in 1000 years and they have no way to avoid that fate - they might rev up interstellar communications technology as either a last-ditch/last-hope way of getting some super-advanced lifeforms to somehow help them out...or they might simply want to send us their equivalent of Wikipedia as a way for their species to be remembered and not have died in vain. If we (at our technology level) decided that we wanted to build a radio transmitter with the power to reach nearby stars - we could probably do it in 5 years. We simply don't have that as a priority right now.

• Some of the mathematical solutions even assume that their methods of describing their world evolved along the same path as ours. - That's a tough sell. It's hard to believe that at least basic mathematics and logic aren't universal. Sure, they may never have stumbled on Godel's theorem - or the travelling salesman problem - but I'd be really surprised if they couldn't add, subtract, multiply, divide, compare and do the basic operations of (say) a Z80 computer. If they've reached that level in mathematics - then we can talk.

• They should also not turn over generations (lifetime) much faster than we do. Longer would actually be preferable. - Why? I don't see that as a determining factor. We have generations that are too short for interstellar communications within a single generation - but it doesn't stop us having a passionate interest in doing it (consider the $600M we just spend on Kepler - who's sole purpose is to look for planets that might harbor life that we could maybe talk to...but not within the lifetimes of any of the people who designed, launched or paid for that mission).

• If we can indeed find a species that fits the bill, it would be best to determine mutual needs and benefits and then base our attempt on that. - There is no time! If we want to find out ANYTHING about them - we have to send everything we want to send in one shot...wait a hundred years...and see what they tell us in return. We can't afford to tell them all of our basic arithmetic and say "Tell us if you understood all that - and if you do, we'll send you some more!"...because we'd get old and die before they said "Yes". We have to send as much as possible in that first shot - and hope that some of it 'sticks'.

• Is there something that we have, and can spare, that they need? - Since physical contact is likely to be impossible (or at least many centuries away), the only thing we can send or get in return is information. Since information costs almost nothing to duplicate - we can "spare" all of it. Because the round-trip time is so long, we have to send it all without knowing which of it they need. But in terms of haggling over the terms of an information exchange ("We'll tell you the secret of quantum cryptography if you'll tell us how you make high density computer chips")...that's not gonna work. Firstly, lying and cheating is far too easy - secondly, enforcing a 'payment' is impossible, thirdly, haggling takes too long. All you can hope is that by sending everything you can think of - they'll be grateful enough to send us everything they can think of in return. But there are certainly no guarantees here.

• Before you get to communicating at a level that you are heading for with "uncle Bill" that would also require both civilizations to convince themselves that the other doesn't pose any threat. - being 50+ light years away - and yet not already on our doorstep 1000 years ago - is enough to convince me that they don't pose a threat. If they are smart enough to overcome that hurdle - then there is probably nothing we can tell them that they don't already know.

• With interstellar communication and the current human population aliens would face the problem that we would change a lot from one message to the next. - Yes. That's a problem. But there is no solution - we either do it or we don't. Look at our situation 100 years ago - and some of our views on equality and fairness have changed DRAMATICALLY over that period. We'll certainly change again over the next 100.

• For casual communication dropping a couple of individuals into the other's environment would work best. - but that's virtually impossible. The only thing we can send in a reasonable time-scale is information. That's PRECISELY why I advocate teaching them a simple programming language (easily done with basic math) - and then sending them an Artificial Intelligence program with as much of "us" in it as possible. Done right (and I'll admit that our AI techniques won't be up to doing that for another 50 years) - that would be exactly like sending one of us into their environment - except that we can send that artificial human mind at the speed of light instead of in a slow old rocket-ship. (Which we also won't know how to do for AT LEAST 50 years - and in fact may find to be impossible).

• Learning the varied meaning of words and phrases of a foreign language is difficult enough even for humans who at least are of the same species and from the same planet (Your particular aliens could spend months trying to find out the significance of thursday without capital T :-) - yes, but just as a human child can learn language in a couple of years just by listening and babbling back - so our AI software can first learn to speak 'human' then (when it gets to their world) - learn to speak (or flash or fart) their language. Once it knows both, it can be our ambassador to them and can advise them on what we'd like them to send us back in return.

Really - the approach of sending them a big piece of AI software is the ONLY way to make this happen - and it's quite do-able. SteveBaker (talk) 14:06, 10 March 2009 (UTC)

I recently read the serial "A New Order of Things" by Edward M. Lerner. He takes that approach in the story. AI "Trade Agents" are sent to the other worlds, when run on an appropriate computer they decrypt themselves and negotiate the trade of information between the worlds. (He discusses it briefly here.)

Of course, it helps that, in the story, the inhabited systems are Centauri, Barnards Star, etc. We should be so lucky.

(As an aside, in the story Humans are at a slight disadvantage because we have so much information freely available over the Internet. (Which, Apparently, the AI agents are given access to.) Wikipedia may be weakening our bargaining position with alien AIs. Just throwing that out there.) APL (talk) 02:04, 12 March 2009 (UTC)