Wikipedia:Reference desk/Archives/Science/2009 June 2

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June 2

What are the "tubes" on USB and similar cables?

My wife asked me about this last night. My guess is that it's some sort of inductance coil to reduce RF interference, but I realized that I don't know for sure. Now I'd like to know. Donald Hosek (talk) 01:20, 2 June 2009 (UTC)

A ferrite ring. It stops common mode signals traveling on the cable, and your guess is correct. They may be required to meet an EMI standard, or electromagnetic compatibility to stop the device beding disrupted by a strong nearby signal, such as a mobile phone. Graeme Bartlett (talk) 01:33, 2 June 2009 (UTC)

I fixed your redlink to common mode - hope you don't mind SpinningSpark 18:14, 2 June 2009 (UTC)

Thanks, the red link was a prompt for someone to write an article. I have now made a disamig page as there are two quite distinct meanings and four articles. Graeme Bartlett (talk) 06:20, 3 June 2009 (UTC)

Coughing and sneezing while unconscious

Can humans cough or sneeze while they are unconscious? -- Beland (talk) 05:05, 2 June 2009 (UTC)

It depends on the level of unconsciousness. Look at the Glasgow Coma Scale and you will see that in lighter states of unconsciousness the patient may be able to obey verbal commands. It seems possible that in this condition they would cough and sneeze. Richard Avery (talk) 07:18, 2 June 2009 (UTC)

Cough is a reflex, not requiring any cognitive input. Even in deep coma people will cough with irritation of the trachea (I've seen this many times). I don't know whether the same is true of sneezing, but I would guess that the right irritant could induce a sneeze in an unconscious person. --Scray (talk) 09:48, 2 June 2009 (UTC)

So what would be the purpose of endotracheal suction of saliva and secretions if the unconscious patient is able to cough? 86.4.190.83 (talk) 13:08, 2 June 2009 (UTC)

They may reflexively cough, but still not with enough vigor to clear their own air passages. Like blinking, there are likely both reflexive and voluntary components to coughing, and unconsciousness may hinder the clearing process without completely eliminate the cough reflex. Additionally, as Richard Avery has noted, there are different severities of unconsciousenss, and every patient is in a way unique; one patient may be able to clear his own air passages unconsciously, and another may not. --Jayron32.talk.contribs 13:31, 2 June 2009 (UTC)

Interesting. Has anyone ever seen anyone sneeze while they are unconscious? -- Beland (talk) 15:17, 2 June 2009 (UTC)

GPS in plane

Is current plane doesn't equip with GPS? Or within the black box that can survive crash? With current technology, is it possible to equip life vest with GPS? Thanks for the answer. roscoe_x (talk) 05:14, 2 June 2009 (UTC)

Many commercial aircraft are equiped with GPS: GPS_navigation_device#Commercial_Aviation. Smaller and older aircraft often do not have GPS. The GPS is not part of the black box (flight data recorder), but the data from the GPS is required to be stored on the flight data recorder (see [1] item 39). Yes, it is possible to equip lift vests with GPS. Sancho

Also it would be possible to equip each life vest with a satellite distress beacon. Of course it's not going to happen on a commercial airliner because it is not required by law and it would increase ticket prices by tens of cents. --203.22.236.14 (talk) 07:43, 2 June 2009 (UTC)

I think the op is slightly confused with how GPS works. GPS is passive. A GPS reciver doesn't transmit anything, just recives information from satalites to work out its location, meaning a life vest equipped with GPS wouldn't be much use other than to tell the wearer where they are. As far as I know you cannot be tracked via GPS. Gunrun (talk) 10:47, 2 June 2009 (UTC)

Quite so, GPS is passive (but a nearby GPS receiver could be detected due to it's internal amplification of the GPS signal). But I believe the OP's real question is "That AirFrance plane seems hard to find, couldn't it have some device to make it easy to find?" That device would be something like GPS+distress beacon and yes, it's very possible. Actually, I'm surprised that aeroplanes don't constantly upload all data that would be stored in the blackbox via the satellite phone network. --Polysylabic Pseudonym (talk) 11:03, 2 June 2009 (UTC)

From what i've found there are regulatory rules around carrying distress signals. Virtually all commercial planes must carry some - automated and manual. There are even life-rafts for planes that have them built into them. Not sure about life-jackets commercial wise but they exist. My understanding of the Air France disappearance was that the plane was flying over a part of the world that gets very limited coverage in terms of Radar / satellite and that was what has caused the difficulty of finding. 194.221.133.226 (talk) 11:12, 2 June 2009 (UTC)

Yes - as others have pointed out - you have to combine a GPS unit with some kind of a transmitter in order for someone else to find out where that unit is. However, in the case of the Air France disaster, the plane probably crashed somewhere in the mid-Atlantic - perhaps 800 miles from the nearest land. Being that far from civilisation means that there is certainly no cellphone coverage and you'd need a pretty powerful transmitter to reach anywhere useful. Just about the only practical technology would be a satellite phone. But you can't put all of that technology into something like a life vest because it's simply too expensive. There are something like 50,000 large passenger aircraft in the world - that's probably five million life vests - of which perhaps a few dozen ever get used for their intended purpose! Adding a satellite phone to each one...with a battery that's kept constantly charged - and replaced when it breaks...a phone that'll survive the worst a plane crash can do...that's an expensive thing - many hundreds of dollars each, certainly. You'd perhaps need to spend several billion dollars to add such a feature to the world's airliners...and quite frankly - it's a total waste of money because airline life vests are so very rarely used.

In the case of the Air France disaster - it appears that the aircraft was in mid-Atlantic, so it would have been flying at perhaps 30,000 feet. Whatever happened was so fast that a mayday signal couldn't be gotten out - and involved a sudden loss of cabin pressure and electricity. Basically - that means an explosion or catastrophic structural failure of some kind - and crash from 30,000 feet. Nobody is going to survive that. Having a way to find a few lifejackets floating out from the wreckage afterwards cannot possibly justify the cost.

The aircraft's own flight recorder does have various transmitters to aid in finding it later - but that assumes that the thing survived the initial disaster - and a fall from 30,000' and a good soaking in salt water afterwards. Those things are tough - but they aren't invincible. Finding the one from flight 447 in a search area of perhaps half a million square miles is going to be very hard indeed...it's probably impossible.

SteveBaker (talk) 12:27, 2 June 2009 (UTC)

Steve, an EPIRB radio beacon transmits via Satellite. Also the phones I was talking about were satellite phones which likewise have global coverage. I'm pretty sure there's global coverage. It should be fairly trivial to install at least one EPIRB in a location on an aeroplane where it will in any disaster end up separated from the wreckage and floating (radio isn't much good under hundreds of metres of water). Come to think of it, all of the black box data -- were it not automatically transmitted during flight over the satellite phone network -- could be easily stored on a small solid state memory device attached to such a beacon to make that also easy to find. --Polysylabic Pseudonym (talk) 12:47, 2 June 2009 (UTC)

"...is it possible to equip life vest with GPS?" Sure, here's one such set up. Many are carried on military and general aviation aircraft. Polysylabic Pseudonym above has linked to the two relevant articles.—eric 13:24, 2 June 2009 (UTC)

And the ugly truth of telecommunications finally comes out! Instantaneous, point-to-point radio contact is much less seamless than it appears to the untrained eye. Just because you can whip out your mobile phone and dial a long-distance number without interference from every other mobile phone on the street doesn't mean an airplane can do the same! Our radio systems, in general, are horribly short-range. While it is true that we do have some technologies for long-range transmissions, the amazing web of instantaneous digital connectivity to every other part of the world is only made possible because in most of our daily life, we are never more than one mile from the nearest cell tower, not more than 100 feet from the nearest 802.11 access point. This allows us to use high-frequency, wide-band shared channels. But these channels are not very good for long-range transmissions. Although it appears to be "point-to-point", it's a really complex set of relaying to get your off of the shared radio channel as proximally as possible. So, when you make a "wire-free" long distance call from your mobile phone to your friend in Angola, the wireless hop is not actually all that far. A series of base-stations route you to a cable (optical fiber) network, and the signal travels by wire for a very very large portion of its journey. It crosses the ocean by submarine communications cable, hits a couple more optical cable routers, and finally gets sent out to a field transmitter which is not more than a few thousand meters from the intended recipient.

An aircraft which is 3000 kilometers from the nearest base station has surprisingly few options for telecommunication, and they are not all that high-tech. On board, there is a suite of radios, ranging from VHF and UHF digital radios to very "1950s" style HF (shortwave) radios with ranges of around a few hundred kilometers. While in flight, the aircraft will often fly "convoy-style", maintaining communication to the ground by proxy over an HF channel to another aircraft a few hundred kilometers away. This radio signal is very low-bandwidth and not exactly reliable. (This has caused problems before). Unfortunately, the sort of nifty broad-band technologies we've grown very accustomed to are based on much higher frequency signals which have much shorter range. Trying to transmit a VHF radio or a 2.4 GHz microwave "mobile-phone" over a thousand kilometers is just not practical.

Maintaining a bidirectional satellite-based communication link during the entire flight would be really quite challenging, although not impossible. Therein lies the "ten extra cents per seat" which was casually described above. Now, here comes another ugly truth about satellites - they're not really global in coverage! To receive effective satellite service, a location must have one or more satellites above the horizon and in view of the transceiver. To save power and decrease launch costs, these communication satellites are NOT in a geostationary orbit - rather, they fly in constellations in predetermined orbits. These orbits do not necessarily provide full coverage for the entire planet (at least not out to "five nines" or 24-hours, 7-days-a-week). (Which telecommunication company wants to pay huge sums of money to provide fantastic satellite reception to the middle of the ocean? The number of subscribers out there is a little low). So, even satellite-based schemes might not provide a 100% uptime on the communication link.

In summary, the transoceanic airplane provides an interesting insight into our communication infrastructure. When isolated from the enormous network of ground relays, optical cables, and effective satellite coverage, the only viable solutions are pretty old-fashioned shortwave radios. Because of fundamental bandwidth limitations, these links are not suitable for an "always-on", constant monitor of the aircraft's position - imagine what would happen if every aircraft on the planet started broadcasting wideband digital updates over globally-ranged transmissions at 9 MHz - there's a shared channel, and it'd get used up pretty darn quick. (If you can't imagine, let me present an analogy - the idea is that you want every individual on a football field to yell all their conversations loud enough so that every other person can hear them, even on the other side of the field. But everyone will be yelling at the same time, and constantly hearing all the chatter from every other person - it destroys any hope for effective communication). Nimur (talk) 15:30, 2 June 2009 (UTC)

Awesome explanations! So there is no satellite that covers the crash area of AF447? If there was one, could it have located the wreck by simply looking? Without a 2-way radio communication. Satellite imagery says there are satellites that can distinguish objects on the ground at least 50 cm apart. Jay (talk) 10:03, 3 June 2009 (UTC)

No - you really don't understand the immensity of the task. They have actually found some wreckage now - just a few small parts. But the search area was immense - thousands to hundreds of thousands of square miles...they got lucky because another aircraft spotted burning wreckage on the ocean while it was still dark and that stood out fairly clearly. You don't take satellite photos at night. Suppose you take a photo (even from some super-high rez military spy satellite) with enough resolution that you can spot wreckage. 50cm resolution isn't enough - let's suppose it needs 20cm resolution to see a floating life vest that's maybe 40cm across for what it is. OK so on your (roughly) 1000x1000 resolution computer screen, you can start looking at the photos this satellite produced - right? You're looking for that life vest. But at 20cm resolution, each 1000x1000 pixel photo covers just 200x200 meters of the ocean. To look for wreckage over just one square kilometer, you'd have to carefully inspect 25 photographs looking for a TINY orange spec just a couple of pixels across that's just barely a smudge on your screen. To search 100,000 square kilometers, you have to look CAREFULLY through 2.5 million photographs of dull, boring ocean! Do have any conception about how impossible that is?!! SteveBaker (talk) 13:34, 3 June 2009 (UTC)

I didn't think of the human angle to it after the satellite had done its job. Also, I missed out that night could be a hindrance, though I did consider cloud cover. But shouldn't the task be fairly straightforward for a digital image processing software - to detect an orange, or yellow or red dot within a limited-coloured canvas of ocean? Jay (talk) 14:30, 3 June 2009 (UTC)

That's assuming you actually got a photo that shows the orange life vest. Any number of things could obscure it, or they might not be wearing a vest at all (holding onto debris, for instance). — The Hand That Feeds You:^Bite 20:14, 3 June 2009 (UTC)

"[Sarkozy] said France has asked for help from U.S. satellite equipment to locate the plane." (http://www.wral.com/news/national_world/world/story/5254928/). Would be interesting to see what the US provided. Jay (talk) 03:47, 4 June 2009 (UTC)

Commercial aircraft are equipped with ACARS, which can send low-volume data. The system uses VHF radio when in line of sight of a fixed tower (essentially when over land) SATCOM (Inmarsat) when over ocean except at high latitude, and HF when over the poles. The ACARS unit aboard the aircraft is used, among other things, to send critical maintenance information (engine performing out of specification) and takeoff and landing information. This info is gathered automatically using the datalink that connects the various computers aboard the aircraft. The datalink always has location and time infor from the aircraft navigation system, which generally uses GPS plus an inertial navigator, at least. There is nothing to prevent the ACARS from sending the aircraft's location if something bad happens, but this is has not been done because this was not one of the goals of the ACARS system. Flight 447 sent out several maintenance alerts, presumably via Inmarsat, and could easily have sent a location message if anyone had thought to add this function. This is trivially easy to see -- in retrospect. -Arch dude (talk) 18:45, 2 June 2009 (UTC)

Update: The ACARS messages do in fact contain the location information. The last flight 447 message had location information to 3 decimal places (about 100 meters.) The problem, apparently, is that this classified as "maintenance data" not "critical flight data," so it (apparently) was not conveyed to the SAR crews. I suspect that this will change in th future. -Arch dude (talk) 22:01, 2 June 2009 (UTC)

I am puzzled that it is not required for all planes to continuously send out its location, say once a minute. If something suddenly happens to a plane and communication is cut off then there is not time to only then send a message. A simple flight number and GPS location (which includes altitude) once a minute is not a lot to ask for. That's maybe 30 bytes of data per plane per minute. I'm sure the cost is negligible for hooking into something like Irridium or Globalstar - and besides you probably get great reception from 10km up. Is there any downside to this? 196.210.200.167 (talk) 19:29, 4 June 2009 (UTC) Eon

Evolution denial & genetic engineering

Do evolution denialists usually take a stand on genetic engineering? If yes, for or against? --KnightMove (talk) 09:58, 2 June 2009 (UTC)

Since almost all of them are religious fundamentalists - it's probably safe to say that most of them are against genetic engineering...although logically, they should probably conclude that it simply doesn't work and is therefore harmless...but logic isn't generally their strong point. SteveBaker (talk) 12:03, 2 June 2009 (UTC)

Actually, Steve, you'd be surprised at how some of the even Young Earthers manage to weave modern genetics into their story. The Answers in Genesis people are the best in this respect, going to great lengths to appear biologically sophisticated.) I think they would probably argue that no new species would be created by such genetic engineering, though of course you can make changes to a species (in the same way you can breed dogs to superficially look different, but they are still dogs. (I don't agree with this, but that's likely their argument.) Answers in Genesis has a LOT to say about genetics in general, about stem cells, and about cloning, but I don't see anything about genetic engineering. I'm not sure they would disagree with it if it were just being used for medical activities, but I'm just speculating. --98.217.14.211 (talk) 12:33, 2 June 2009 (UTC)

Re it's probably safe to say that most of them are against genetic engineering: I find that hard to believe considering that half of Iowa is under GM corn with no signs of the Creationists making any fuss. --Sean 13:22, 2 June 2009 (UTC)

Surely evolution and genetics are logically and conceptually independent of one another ? You could (hypothetically) have evolution without genetics or genetic inheritance without evolution. Darwin, Wallace and Huxley formulated evolution without knowing anything about genetics - indeed, Darwin proposed the entirely incorrect idea of gemmules. When Mendel discovered the laws of genetics he knew nothing of evolution. It is only the joining of the two strands of thought in the modern evolutionary synthesis that makes us think they are inextricably intertwined. Gandalf61 (talk) 15:22, 2 June 2009 (UTC)

You're perfectly right, but evolution deniers usually believe in God as the only ruler of life, which plausibly might make them disregard genetic engineering. Whether this really is the case, was my concern. --KnightMove (talk) 19:35, 2 June 2009 (UTC)

Could you have genetic inheritance without evolution? The only way I can see this working is with no copying errors and asexual reproduction. I'm no biologist though; any thoughts? (Oops, this may be derailing. Should I start a new question?) 80.41.123.51 (talk) 20:02, 2 June 2009 (UTC)

They don't deny the possibility of birth defects; some even say that (some) existing species are corrupted varieties of those that existed in Eden. —Tamfang (talk) 16:58, 4 June 2009 (UTC)

It doesn't automatically follow that individuals who dispute evolution on a religious basis are against genetic engineering. Its a little more complex than that. There are practical examples of genetic mutation and by implication, microevolution, that makes it very difficult for scientifically educated anti-evolutionists to dispute the genetic basis of phenotypic inheritance (though millions of uneducated ones do so quite vehemently). Since genetic engineering (at our current level of sophistication) really impacts at this level, is entirely possible to come up with a rationale whereby one can resolve an anti-evolution, pro-GM stance.

For example, a report issued by the National Council of Churches of Christ takes such a positive stance toward GM. The report sees us continuing God's work in genetic engineering: "Dominion carries with it a concept of custody, of stewardship, of being responsible for, of caring for all creation." They believe the Scripture "exalts the idea that men and women are coming into the full exercise of their given powers of co-creation." In other words, they see GM as a fulfillment of our "dominion over the fishes of the sea, and the fowls of the air, and the beasts." (Genesis 1:26).

However, while accepting microevolution one may still reject macroevolution and the common descent, instead believing the range of species today derive from baraminologic "kinds". They key distinction, in their minds, is the genetic "missing link" between micro- and macroevolution, which allows them to accept the former while disputing the latter. Rockpocket 01:09, 3 June 2009 (UTC)

Except that there's really no difference between micro and macro evolution. — The Hand That Feeds You:^Bite 20:19, 3 June 2009 (UTC)

Other then you can observe micro in real time. Macro has to have ancient remains to back it up. 65.121.141.34 (talk) 20:28, 3 June 2009 (UTC)

Output per man per shift

"output per man per shift" in any massproduction manufacturing industry?

Sathyavolu sar (talk) 14:36, 2 June 2009 (UTC)

This question is a double-post. A few answers were provided here. We can't answer your question any better unless you elaborate on what you mean by "output." Output can be measured a lot of ways. If you have a specific industry in mind, then it should be easy - count the number of widgets built, on average, during one shift. Different companies might have dramatically different productivity, but in a commodity industry those sorts of variations either equalize or one company goes bankrupt. The most uniform system for comparing different industries is to measure the value of the items produced, in dollars (or other currency). I would imagine that the output per man per shift is on the same order of magnitude as the wage paid to that man per shift (unless there is a severe case of worker exploitation, with the profits of the output being disproportionately allocated elsewhere). Nimur (talk) 15:38, 2 June 2009 (UTC)

Depending on the what you seek to do with the answer, output-per-worker may not be the correct measure. For example, if you want to know by how much output increases when a plant employs an additional worker, you want the marginal-worker-output, not the average-worker-output. Wikiant (talk) 15:46, 2 June 2009 (UTC)

In fact, we have an article on that, Marginal product of labor. Nimur (talk) 15:58, 2 June 2009 (UTC)

what is the name of the little crab animals that live in the sand that you see when a wave uncovers them

what is the name of the little crab animals that live in the sand that you see when a wave uncovers them. we saw them when we were at Daytona beach. thay look like tiny shells after a wave washes over them then they burrow themselves back into the sand —Preceding unsigned comment added by 72.65.6.228 (talk) 15:13, 2 June 2009 (UTC)

Emerita (genus)? Talitridae? Bus stop (talk)

Sandhoppers maybe? Check out Amphipoda, the family to which the already mentioned Talitridae belong. If you could specify a size it may be Emerita, again mentioned above, however I get the feeling that you mean something smaller. Hope this helps. 144.32.155.203 (talk) 15:56, 2 June 2009 (UTC)

Besides all of the above, you could also include the Uca genus or Fiddler crab. There are likely dozens of genera and hundreds of species of crabs that exhibit this behavior. --Jayron32.talk.contribs 03:47, 3 June 2009 (UTC)

Or better yet, the Ocypode genus, aka Ghost crab aka Sand crabs. These are often tiny (like, corn-kernel-sized) and make those tiny little holes in the sand at the beach. --Jayron32.talk.contribs 03:49, 3 June 2009 (UTC)

Judging by the location and personal experience, Emerita (genus) is definitely my pick. Sifaka ^talk 05:35, 3 June 2009 (UTC)

Missiles

Missile Technology involves which branches of engineering in actual sense????It may look naive but this doubt has been pounding me from a long time!!!! Does Mechanical Engineering play a significant role in this technology???? —Preceding unsigned comment added by 121.246.174.130 (talk) 16:52, 2 June 2009 (UTC)

Mechanical engineering, aerospace engineering, and electrical engineering are the primary contributing disciplines, with a significant amount of computer science, mathematics, chemical engineering, and other fields. It helps to break down the "missile technology" into some constituent elements, such as propulsion, structure, guidance/control, logistics, and so forth. Take a look at this FAQ from Lockheed Martin - they want "Aerospace Engineering, Business, Computer Engineering, Computer Science, Electrical Engineering, Finance, Human Resources, Math, Mechanical Engineering, Nuclear Engineering, Physics, Supply Chain Management, and Systems Engineering." It's worth noting that "missile" is an extremely broad term - an ICBM is designed and built with a host of different technologies than, say, a TOW missile. Nimur (talk) 17:03, 2 June 2009 (UTC)

A missle, like any other manufactured object, requires many disiplines to come together correctly. Mechanical Engineering plays an important role in keeping the missle in one piece while it reaches the target. On top of that, modern missles are most often computer guided, so programmers and computer engineers will need to have a role in building a missle. There are "rocket scientists" who may work on propulsion as well as the fields listed by the poster above. If you are studying to be part of the mechanical engineering field you should have no trouble finding a job anywhere that you find manufatured goods (and often beyond that). 206.131.39.6 (talk) 17:21, 2 June 2009 (UTC)

What do flu virus names mean?

For instance, H1N1 or H5N1. What is the H and the N? What are the numbers? Do these names apply only to influenza A viruses or are they given to B and C viruses as well?

-- Lesath (talk) 16:59, 2 June 2009 (UTC)

Have you seen H1N1#Nomenclature? "Influenza A virus strains are categorized according to two proteins found on the surface of the virus: hemagglutinin (H) and neuraminidase (N)." The numbers represent variations of these proteins. Nimur (talk) 17:16, 2 June 2009 (UTC)

LOL, each genotype has its own page? In any case, wouldn't a nomenclature discussion be better on a more general page or is this repeated on H5N1 too?

Nerdseeksblonde (talk) 15:38, 8 June 2009 (UTC)

Organometallic Compound

Why sodium ethoxide is not a oganomeallic compoun?Supriyochowdhury (talk) 18:11, 2 June 2009 (UTC)

For a compound to be considered organometallic, there must be a bond between a metal and a carbon atom that posses mainly covalent character. Sodium ethoxide contains a mostly ionic interaction between a sodium (Na⁺) ion and an ethoxide ion (EtO^-). I hope this helps. —Preceding unsigned comment added by 144.32.155.203 (talk) 18:19, 2 June 2009 (UTC)

Exactly. here there is a bond between sodium and oxygen, not carbon. Rkr1991 (talk) 07:56, 3 June 2009 (UTC)

Bees

Hi, i am doing a project on bees at school and i have a few questions.... I am trying to understand why bees bother collecting pollen and nectar from plants? what's motivates them? also why do they bother making honey? again what's in it for them? it seems to me like they are working all their lives, while other animals are busy just pleasing themselves? 80.47.194.97 (talk) 18:13, 2 June 2009 (UTC)

A good place to start would be on our article on the European honey bee which is quite detailed on many of these matters. It specifically talks about what bees do with pollen and nectar and honey. From that article, you can follow blue links to other articles which contain even more information. Honey is a good read as well. --Jayron32.talk.contribs 18:38, 2 June 2009 (UTC)

Briefly summarized, the bees are motivated by nectar, not pollen. However, the flowering plants benefit when bees spread pollen. You might also want to read about pollination, which also discusses the coevolution of bees and flowering plants. Nimur (talk) 18:54, 2 June 2009 (UTC)

They collect the pollen in their pollen baskets and feed it to the baby bees. Bees are built out of pollen and run on nectar (and in the case of honey bees, on honey when they can't get the nectar). 213.122.59.67 (talk) 20:17, 2 June 2009 (UTC)

I don't think it's scientifically accurate to say bees are built out of pollen. Nimur (talk) 21:37, 2 June 2009 (UTC)

Pollen is important for bees too. Pollen baskets evolved to help the bee, not the flower. As our honey bee article notes, pollen is a good source of protein for developing bees. (Nectar and thus honey are low in protein.) -- 128.104.112.106 (talk) 20:16, 2 June 2009 (UTC)

Resonance and Delocalisation

All the important properties of some covalent speices can not be explained by representing single Lewis dot structure or by showing a single structure bbased on theory of hibridisation .Again unusual stability of some covalent speices can not be explained by considaring bond energies and bond length predicted by V.B.T. after that a new thought resonance arise which can explained above property quit sucssessfully. Tell me that how it fulfill these blanck. What is the requirement of the theory of "resonance and delocalisation"?Rikichowdhury (talk) 18:36, 2 June 2009 (UTC)

Resonance is an artifact of an insufficient model. There is no "fliping" between structures or back-and-forth shuffling of electrons in real molecules. The electrons are stable and no different than in molecules whose Lewis dot diagrams do not show resonance. Resonance is a heuristic invented to fit the real behavior of molecules to the Lewis model, especially where the Lewis model cannot accurately represent the actual bonding in the molecule. Valence Bond Theory and the Lewis model cannot, for example, handle fractional bond order. Other theories, developed simultaneously to VBT, such as Molecular orbital theory do a fantastic job of handling fractional bond orders, and there is no need to introduce resonance into molecular orbital theory. However, MOT has its own shortcomings, such as its inability to deal with molecular geometry in a convenient method. Thus VBT or VSEPR theory handles geometry very well, but does not handle bond order well. MOT is complimentary because it handles bond order very well, but not geometry. Of course, real molecules are not identical to either model, and no single model can fully capture reality, but these two work well together in explaining much of molecular behavior. Delocalization is a slightly different issue; it is a real event which occurs in situations where bonding electrons are not "localized" between two atoms, but instead are shared equally among a group of atoms. Two classic examples are the "Three-center two-electron bonding" in diborane and the cyclic delocalized pi-system in aromatic hydrocarbons. --Jayron32.talk.contribs 18:48, 2 June 2009 (UTC)

Grignard Reagents

Would there be a reaction between a grignard reagent and a carboxylic acid, I have drawn a few (probably flawed) mechanisms which would suggest a ketone and water as the products, in addition to HOMgX. This just seems unlikely, it doesnt sit right as it involves OH^- as a leaving group and I felt that as a small ion it would be a poor leaving group. Am I missing some fairly basic organic chemistry?
This would be so much easier to post if I knew how to insert chemical structures in here. —Preceding unsigned comment added by 144.32.155.203 (talk) 18:43, 2 June 2009 (UTC)

The first reaction between a grignard reagent and a carboxylic acid is an acid-base reaction: the carbanion is a wickedly-strong base, removes H+ from the acid to give the carboxylate anion. Later (i.e., if there is still more grignard present), another carbanion can attack the carbonyl (just like for ketones and aldehydes). This tetrahedral (4 sigma bonds) intermediate can collapse to reform the carbonyl and eject an oxygen, but IIRC often does not for magnesium-based reagents. The reaction probably just stops at this stage. When you add water after the reaction is done, you protonate the oxygen anion, and this structure (looks something like a hemiacetal collapses to form a carbonyl. Nucleophilic reactions at carboxyl are not simple replacement of the singly-bonded piece, but rather are reactions of the carbonyl itself. That is, the loss of hydroxyl you propose is not direct. The reason that its instability isn't a problem (if it were to occur by that type of mechanism) is that you aren't just "creating unstable hydroxyl from nothing": the starting material is also an anion. You have to look at the overall reaction, and see that the result is more stable, even though it may have lots of instability. DMacks (talk) 18:59, 2 June 2009 (UTC)

If a grignard reagent gets anywhere near an active hydrogen containing compound (that is even a weak acid), then the immediate product is the corresponding alkane and water. Rkr1991 (talk) 07:54, 3 June 2009 (UTC)

Water? DMacks (talk) 08:00, 3 June 2009 (UTC)

about water quality.

sanitization process and chemicals using in water treatment plants. The concentration and duration period also want to know. —Preceding unsigned comment added by 94.97.53.246 (talk) 19:28, 2 June 2009 (UTC)

See Water purification. 78.144.244.22 (talk) 22:21, 2 June 2009 (UTC)

Cactus Question

I recently impulse purchased this cactus, which may have been poorly cared for in the past. I was just wondering what species it might be, and also what are the brown fuzzy things on it, circling the top of the plant?

Brown Spots Close: http://commons.wikimedia.org/wiki/File:CactusBrownSpots.jpg Full Cactus: http://commons.wikimedia.org/wiki/File:FullCactusWindow.jpg —Preceding unsigned comment added by Mattman723 (talk • contribs) 19:50, 2 June 2009 (UTC)

It looks like a barrel cactus to me, though I'm quite ignorant on such things. --Sean 21:17, 2 June 2009 (UTC)

Well it doesn't have notches that deep, so I doubt it. M@$+@ Ju ~ ♠ 23:18, 2 June 2009 (UTC)

Here is a cactus ID site [2]. The ring of "brown fuzzy things" may be flower buds, but possibly abhorted. Richard Avery (talk) 06:10, 3 June 2009 (UTC)

Here is a "ID request" forum on that site. It might help if you took a better picture, as the detail is in shadow in the window shot. You could also look through all the globose cacti here. --Sean 12:45, 3 June 2009 (UTC)

Does this article sound feasible at all?

This thing Does it defy the laws of physics? --71.234.104.243 (talk) 20:31, 2 June 2009 (UTC)

This invention is not new. It has been 'discovered' many times, but it violates the laws of physics and no one claiming discovery of such a machine has ever successfully demonstrated it. *Max* (talk) 21:37, 2 June 2009 (UTC).

Per Max, any perpetual motion machine of the first kind must violate the law of conservation of energy. Unique arrangements of magnets have been popular among perpetual motion aficionados for years; unsurprisingly, not one such invention has ever been successful. TenOfAllTrades(talk) 21:40, 2 June 2009 (UTC)

Here is the patent application: [3]. (Hmmm - he lives on "Asylum street" - what are the odds?) This is certainly recommended reading for enthusiastic "nut-job" spotters such as myself. (I'm DEFINITELY going to have to figure out a way for someone to pay me a dollar every time someone confuses "force" with "energy".) The Chicago Tribune article says he spins the wheel and it spins for a while and then stops...this is pretty much exactly what you'd expect any claim of a perpetual motion machine to do - so there is no surprise there. On my home Wiki, I have a "You know you are a crank when..." checklist for exactly this kind of occasions: [4]...let's see how this guy does...hmmm...so far only a rather disappointing 3 out of a possible 8 points - but I've decided to award him a bonus point for using his magnets "in cold fusion mode" - which is certainly a novel and exciting breakthrough in perpetual motion machine design. He has "neutron barrier planes" AND "atomic holes" - and it somehow involves the synergy of the entire universe as a part of it's operating mechanism - which is all really quite remarkable for a machine comprising a dozen magnets nailed onto a wheel. It's comforting to know that this wonder of mechanical genius operates equally well in clockwise AND anticlockwise rotations. But I trust that if he gets his patent, he'll be claiming that it proves that his machine works - and if he doesn't get it, he'll claim it's "big oil" putting him down...so we can look forward to plenty more fun in the future. SteveBaker (talk) 22:56, 2 June 2009 (UTC)

I think I have stumbled across a free energy system. I take TIME, and convert it to electricity. You see, I put in some TIME at another place from my home. They in turn give me a slip of paper periodically. In turn, I give this slip of paper to a a person in another building. Following the paper trail, another company sends me a slip of paper in the mail, to which I attach yet another slip of paper and mail back. As a result, I plug into the wall and get electricity! BRILLIANT! :) Arakunem^Talk 23:08, 2 June 2009 (UTC)

Does he get any extra points for "rolling stator magnetic field in the fourth dimension" (beyond the existing point for a reference to magnetism)? I think he should do. --Tango (talk) 01:01, 3 June 2009 (UTC)

Well, perhaps a half point. He might mean time (4th dimension?) in which case this is just a fancy way of saying "it's moving", for which no bonus is possible. A true crazed nut-job wouldn't be satisfied with a mere 4th dimension - it would have to be the 11th or something. To be honest, I'm bitterly disappointed that he's not yet announced that he intends to fit this to his car. Proper perpetual motion machine designers no sooner have an idea for their machine than they're out there pulling the motor out of their 1986 Acura to make way for it. But he's just getting into the role - and he's already comparing himself favorably to Edison...that's a promising start. SteveBaker (talk) 02:20, 3 June 2009 (UTC)

I just ... don't understand. The man has built a prototype. Doesn't he spin it and ... see that it does not continue spinning? Doesn't he see that his prototype is incapable of powering anything? I can understand if he is put off by complex mathematical theories or well-established scientific explanations, because those require either a certain level of comprehension or a blind trust in "smarter" scientists who DO understand. (I mean, I can write out some Maxwell equations and take a Cauchy integral and prove beyond any reasonable doubt that there is no way to have a "continuous never ending force-field" around a closed contour... but that requires knowledge of some higher math!) So my (dis)proof of the concepts in the machine might be worthless to the man. But ... he has built this machine! Can't he see that it doesn't actually work? When he tries to power it up, and it doesn't power up, you don't need any theoretical knowledge to verify that behavior. Why in the heck doesn't he accept empirical evidence? Nimur (talk) 03:24, 3 June 2009 (UTC)

And then he says it doesn't work because the magnets need to be more precision-machined and precisely aligned! That would mean... he would have to have an analytic, mathematical description of where to place the magnets and how to shape them (so that he could give the schematic to a machinist). So, he will have to measure, "by observations of the universe and reason itself," the force induced by each magnet (sort of like experimentally rederiving the Biot-Savart law?) And then he will need to calculate the fluxes and field lines and all that (sort of like, solving some Maxwell equations?) If he actually put in the proper scientific rigor into these measurements and calculations, he would rederive all of electromagnetism, and see for himself that his plan doesn't work. That's experimental physics, but he's apparently two hundred years behind on his reading, because it has been done and confirmed observationally a hundred thousand times by high school physics students. It's very frustrating to see how far these cranks can get, because most of the people who look at their work don't know enough to debunk it. Nimur (talk) 03:38, 3 June 2009 (UTC)

As my "You know you are a crank when..." page points out - 99% of cranks are not just ill educated in the sciences - but actually proud of the fact because (they generally claim) their thinking isn't restricted by the limited world-view of the people who went before them. Sadly, this neglects the solid fact that real earth-shattering advances are always made by building on the work of those who came before. Because they don't know all of this really well known science, they are doomed to repeat the mistakes of others. This failure to understand the difference between a force and energy has resulted in this guy wasting (probably) years of his life - paying a small fortune to patent lawyers and making himself look like a complete idiot to the majority of the people he's trying to impress.

It's not just knowledge though and education though. Even if he's unaware of the laws of thermodynamics - and cannot calculate all of those complicated interactions between magnetic fields (I'm quite sure I couldn't do that) - even if you know nothing of that...using the very basics of the scientific method would tell him he's going nowhere with this: He spins the wheel - it spins for a while, then gradually comes to a stop. He claims that this is just because he doesn't have the magnets quite perfectly set up and machined. But it would take him only minutes to try a 'control' experiment in the time-honored scientific tradition. First give your wheel a push of a known amount (maybe wrap a known length of string around the axle and hang a weight on the end to make it spin at a known rate) - and just measure the amount of time the machine takes to come to a stop. Then replace the magnets with bits of non-magnetic material weighing the same amount - which ought to nullify whatever effect you think you have invented. Now give the wheel the same initial push and time how long it takes to stop in that case. Do the experiment 100 times and average the results.

We all know that if he did that super-simple experiment, he'd discover that his complicated system of magnets has NO effect whatever. Not just that his magnetic motor isn't quite able to overcome friction - he'd find that the wheel would spin for exactly the same amount of time whether the things around the edge are magnets or not. At this point, a rational person would have to concede that they were wrong and go back to the drawing board. THAT is what makes someone a scientist - not the years of training and brain full of laws and equations. Although those kinds of things definitely help you to say "Hmmm - I think I'll try to invent a perpetual motion machine today...oh...but wait...those darned laws of thermodynamics again. OK then - back to making a better mousetrap." - but they aren't NECESSARY to being a scientist. SteveBaker (talk) 13:20, 3 June 2009 (UTC)

Nimur, Perpetual motion enthusiasts are convinced that if they can only "balance" out the forces that are working to slow down their machine. A non-working prototype that "isn't quite balanced" will still be taken as a proof of concept by these people, because they take it as given that they can "balance" the forces in such a way that they get free energy, in their mind the only part of the design that needs testing is everything else.

Of course, to a rational outside observer that's completely backwards. I don't need proof that you can spin some magnets around in a circle. What I need proof of is that you can "balance out" the laws of thermodynamics. APL (talk) 13:44, 3 June 2009 (UTC)

As long as his hydrocoptic marsel vanes are properly fitted to the ambifacient lunar wane shaft, I can't see why it wouldn't work. --Sean 12:56, 3 June 2009 (UTC)

vapourised alcohol after flaming sambuca?

Hi a friend of mine after having downing a shot of flaming sambuca always inverts the shot glass. He then proceeds to lift up the glass marginally (enough to get a straw under), and then inhales. He says that by doing so he is breathing in vapourised alcohol. He claims these actions help one get drunk faster. I thought wouldn't the gases in the glass just be normal gases found in air with perhaps a bit more carbon dioxide? Would there be any vapourised alcohol? Presumeably a little - but I believe alcohol (in this case just talking about ethanol, obviously) is not very well absorbed when inhaled anyway; so I think that these actions wouldn't help him get drunk more quickly. Am I right? Any thoughts on the matter would be much appreiciated! Thanks RichYPE (talk) 20:58, 2 June 2009 (UTC)

The dude wants to get drunk on Sambuca??? That should be your first clue as to how seriously to take his ideas on the subject. --Trovatore (talk) 21:03, 2 June 2009 (UTC)

Sambuca isn't good for anything else... --Tango (talk) 21:07, 2 June 2009 (UTC)

Sure it is. You put it in coffee. Or you drink it in small quantities to appreciate the taste. But drink enough of it to get drunk? What, you're out of Listerine? --Trovatore (talk) 22:36, 2 June 2009 (UTC)

...and here I should probably point out that neither I nor the Wikimedia Foundation advocates drinking Listerine.... --Trovatore (talk) 22:39, 2 June 2009 (UTC)

Inhaling alcohol vapour would probably get it into your blood pretty quickly, but I can't see why there would be more than trace amounts under the shot glass in those circumstances. --Tango (talk) 21:07, 2 June 2009 (UTC)

Vaporized ethanol can certainly get one drunk...it's used in alcohol research quite often and there are vaporizers on the market (of varying legality). It's a rapid onset of intoxication if the vapor is of sufficient quantity, and it's well absorbed. A just-consumed shot glass always has remnants of the prior contents sticking to the sides, so there would be, presumably, some modest amount of ethanol vapor in the trapped space of an inverted shotglass...but probably not much. I'd guess that the effect of the shot itself would be of a considerably greater get-ya-drunk magnitude than a a little extra vapor...consider this: if your friend had had taken a deep breath over the full (pre-lit) shot, he probably would have gotten a similar amount of ethanol vapor exposure, and trying to become inebriated that way would likely have taken a looong time. — Scientizzle 21:09, 2 June 2009 (UTC)

Back-of-the-envelope calculation: Assume a shot glass volume of 50 mL (about 1.7 ounces). Assume further an in-glass gas temperature of 25 degrees Celsius (77 Fahrenheit). If the glass were entirely filled by ethanol vapor (no air, no water vapor, no other volatiles), there would be just under a tenth of a gram of ethanol present. That works out to a little over 0.1 mL (0.004 fluid ounces) of liquid alcohol, or less than one-hundredth of a shot. Those numbers are pretty generous assumptions, too — if the gas is hotter, it will be less dense and contain less alcohol; there's also little likelihood that other gases (including air and water vapor) will not be present to dilute the alcohol. The stuff he's inhaling might have an interesting taste, but it's not going to do a damn thing for his (in)sobriety. TenOfAllTrades(talk) 21:20, 2 June 2009 (UTC)

Those are good calculations. Furthermore, obviously the absolute maximum amount of ethanol vapor that would be possible to inhale is limited by the amount of liquid left in the glass following shot consumption. Considering the poster's friend is clearly out to get hammered, it's doubtful that there'd be more than a few mL total (of a 42% EtOH fluid) left over for straw-vacuum removal. The contribution of this extra step should have minimal effects on insobriety and will likely leave your counter sticky with Sambuca. — Scientizzle 22:35, 2 June 2009 (UTC)

There's a whole lot of mythology and urban legends surrounding alcohol, like most other mild-altering substances. Since feeling drunk is very subjective, it's easy for people to believe all sorts of unreasonable things about what makes them more or less drunk. Pretty much any high schooler will tell you that, for example, drinking beer through a straw gets you drunk faster. It's complete bullshit, but it's often repeated and widely believed. Friday (talk) 21:13, 2 June 2009 (UTC)

To be honest - if you really wanted to get drunk faster (why is that a good idea?) then not setting light to the sambuca in the first place would really be the best idea! What's burning isn't really the little coffee bean in there - it's the alcohol. By burning it off, you're lowering the amount of alcohol you drink. SteveBaker (talk) 12:58, 3 June 2009 (UTC)

Here is an article about some folks trying to open an alcohol vapor bar, with mixed results. --Sean 13:00, 3 June 2009 (UTC)

wow thanks to everyone who helped! Thanks especially to tenofalltrades for the calculation. I shall inform my friend of the error of his ways! Cheers RichYPE (talk) 19:23, 3 June 2009 (UTC)

Phosphorus in Evolution

In evolution of complex organisms from small and primitive ones, how and why was the Phosphorus taken as a candidate to be a part of almost all life in such a vital form, such as in DNA, ATP, Lipid layer etc, even so when it is not available in atmosphere, only present in soil, and that too almost always in complex phosphate ion forms because of its high reactivity? We (organisms in general) are slowly running out of easily accessible phosphorus. If we really run out, what will be the course of evolution from there on? - DSachan (talk) 21:49, 2 June 2009 (UTC)

Why are we running out of phosphorus? How does it get lost (or made inaccessible)? --Tango (talk) 22:33, 2 June 2009 (UTC)

Phosphorus mentions that "In 2007, at the current rate of consumption, the supply of phosphorus was estimated to run out in 345 years." This is for industrial production of phosphorus compounds, which would presumably include fertilizer. I guess that's the question; what does that mean for everything that needs it to live? Someguy1221 (talk) 23:36, 2 June 2009 (UTC)

Actually, I read something (I think) in a recent issue of Scientific American in an editorial which claimed that the current existing phosphate mines will be tapped out in 40 years or so, and they warned of an impending "phosphorus famine". However, I am not sure if they took into account anticipated untapped phosphorus sources. --Jayron32.talk.contribs 23:59, 2 June 2009 (UTC)

Surely that is phosphorous that we are using for industrial/agricultural purposes, most phosphorous will be in some kind of cycle. Organisms die and decompose, the phosphorous gets back into the soil, gets absorbed by plants, the plant gets eaten, whatever ate the plant gets eaten, so and so on until it ends up in an organism that decomposes and it gets back into the soil. I guess it is possible it is gradually getting leached into the oceans, but that's never going to happen on a scale of 40 years. --Tango (talk) 00:54, 3 June 2009 (UTC)

Oh, the phosphorus isn't going anywhere. However, phosphorus deposits in concentrations we need to use to make all the fertilizer to grow all of the food we do now IS, and that seems to be the big problem. Phosphorus basically allows us to grow much higher calories/acre in terms of food production than would be possible without it. The question comes what will happen when all usable phosphate mines pan out. If we have no sources of phosphate fertilizer, what will happen to our farming practices. Its a genuine problem; I am not sure I trust the 40 year figure, but fertilizer phosphorus is a finite resource, and its a problem that we will likely run into some day in the future. --Jayron32.talk.contribs 03:07, 3 June 2009 (UTC)

It's an interesting question, but it isn't the one the OP asked. --Tango (talk) 13:10, 3 June 2009 (UTC)

If you have access to the journal Science, there's the classic article "Why nature chose phosphates." Westheimer, F.H. (1987) Science. 235(4793):1173-8. [5] If you don't have journal access, you'll probably be able to find a pdf copy or two floating around on the internet if you search on the article title.-- 128.104.112.106 (talk) 14:49, 3 June 2009 (UTC)

It has been suggested that life began either inside the earth or at the ocean floor, so the atmosphere may have been largely irrelevant. Also, see Abiogenesis#Polyphosphates. --JWSurf (talk) 15:02, 3 June 2009 (UTC)

overpressure wave calculation

Hi When you calculate the pressure produced by the blast wave from an explosion, when it is an overpressure shockwave, that means it is over regular atmospherice pressure. Does this mean that objects struck by the wave feel 14.7 psi (atmospheric) plus whatever psi the shockwave is ? for example if the shockwave is 3 psi, does this mean it is subjected to 17.7 psi, or would that object already be experiencing atmospheric pressure, like we do everyday, and only experience 3 psi of pressure? I ask because different sites say different things. Thank you

Robert —Preceding unsigned comment added by 79.67.192.228 (talk) 22:06, 2 June 2009 (UTC)

It's called "over"-pressure for a reason! It's the pressure over and above atmospheric pressure. So, yeah - if the air pressure today is 14.7psi and I set off a stick of dynamite that produces 3psi of overpressure - then (say) a brick wall nearby has 17.7 psi pushing on one side of it - and only 14.7 psi pushing on the other side. It might seem at first sight that a mere 3 psi was nothing much - but if you have a 10' x 6' wall in a room then that's 10x6x12x12=8640 square inches - which is 25920 pounds of force - something like 13 tons. SteveBaker (talk) 23:29, 2 June 2009 (UTC)

If you aren't familiar with pressure measurements here's some context. Weather patterns can regularly cause a 1% variation in atmospheric pressure, and really awful hurricanes can maybe cause a 3% variation (underpressure). The worst storm underpressure ever registered about a 13% under-pressure. A shockwave with 3 psi overpressure is about 20% overpressure (twice as bad as a hurricane!), and though it isn't sustained, it's localized - as Steve Baker pointed out above, it can create some pretty nasty forces on anything it hits. (Straightforward multiplication of the shockwave overpressure peak times the area gives you a good estimate, but not an exact value, of the net force on the wall - there are transient time effects and a host of complex fluid-flow issues as well). Nimur (talk) 03:47, 3 June 2009 (UTC)

global warming potential

how can a GWP value decrease if the gas is in the air for a longer amount of years.? Global warming potential thanks, -Bill —Preceding unsigned comment added by 173.30.14.113 (talk) 23:27, 2 June 2009 (UTC)

I think you've somewhat misunderstood. The amount of a gas typically decreases over the years - it's broken down in one way or another. So the amount of damage you do by putting (say) a ton of Methane into the upper atmosphere gets less and less as that gas breaks down over the years. SteveBaker (talk) 23:32, 2 June 2009 (UTC)

but why after 500 years does the total potential of methane summed over the 500 yrs equal 7.2 and over all 20 yrs it's so much higher at 72? —Preceding unsigned comment added by 173.30.14.113 (talk) 01:11, 3 June 2009 (UTC)

The GWP is how much worse that gas is than CO2, it depends on the timescale because different gasses break down or are removed from the atmosphere at different rates. The GWP of methane decreases over time, which means it must be breaking down or being removed faster than CO2. --Tango (talk) 01:20, 3 June 2009 (UTC)

Indeed. GWP compares the effect of an instantaneous release of a given GHG to an instantaneous release of the same amount of CO₂ over a given number of years. CO₂ is relatively slowly removed from the atmosphere - it's lifetime is hundreds of years (albeit its not quite so simple). Methane (CH₄)is, molecule for molecule, a stronger GHG than CO₂. But it breaks down over only a few years into CO2 and water (and the water is removed from the atmosphere nearly instantaneously). So over time, the GWP of methane approches that of CO2. One important take-home is that a naked GWP value is useless - you always need to know the time frame over which it is computed. If none is specified, often but not universally 100 years is assumed. See Global warming potential#Importance_of_time_horizon. --Stephan Schulz (talk) 09:51, 3 June 2009 (UTC)

Ultimate Fate of Mankind

Has anyone ever done a survey of what the general populace believes the ultimate future of humanity is? For example, 40% say we'll colonize the universe, 40% say we'll blow ourselves up, 20% believe some deity will end it all, something along those lines? TheFutureAwaits (talk) 23:28, 2 June 2009 (UTC)

I imagine such a survey would depend very much on when you did it (during the cold war I expect a very large proportion expected use to blow ourselves up, probably fewer do now, although maybe a few more since North Korea started making significant progress with its nuclear program), and the populace you targeted (basically, the more religious people you ask, the more people are going to give a religious response). It would be interesting to find out, though (I don't know if such surveys have been done). It's not really what we're here for, but we could hold a mini-survey of ref deskers (whose opinions are far more interesting that the general populace!). Personally, I think the two most likely ultimate fates are colonising the solar system and then getting wiped out when the sun dies (that gives us few billion years - one billion on Earth, but we could move further out, although our population may need to dramatically reduce), or colonising the galaxy (I very much doubt we'll ever leave the galaxy, the distances involved are just too vast and faster-than-light travel is just too unlikely) and getting wiped out when the galaxy runs out of stuff to make new stars out of and the old ones all die (which gives us about 100 trillion years). I know this is far longer than other animal species have generally lasted, but intelligence means we adapt to new environments without evolving physiologically (so staying the same species), other species have had to become new species in order to deal with new environments. --Tango (talk) 23:42, 2 June 2009 (UTC)

Everything must have an end, so one day humans will no longer exist. 78.151.147.255 (talk) 00:16, 3 June 2009 (UTC)

Why must everything have an end? --Tango (talk) 00:50, 3 June 2009 (UTC)

Humanity will replace itself within the next 20 years. See Technological singularity. -Arch dude (talk) 01:31, 3 June 2009 (UTC)

I'm not at all convinced. I haven't even seen a reliable quantification of human mental capacity, so how could anyone possibly make such a prediction? --Tango (talk) 01:44, 3 June 2009 (UTC)

Twenty Years? Care to ... make a wager on that? APL (talk) 13:51, 3 June 2009 (UTC)

Sheesh, you know, it would be nice if the Refdesk regulars would try to answer the OP's question while citing some sources, so the OP can do some research on his or her own, instead of spouting opinions without any citations. He didn't want our opinions; he wanted to know about everyone's opinions. OP, I found this link on Google Books that says that a 1995 Gallup poll conducted in the US said that 61% of the adults and 71% of the teenagers agreed that "the world will come to an end or be destroyed". In a separate study, a sample of 17,000 high school seniors (meaning 17 or 18 years old), "more than one-third" agreed with the statement, "Nuclear or biological annihilation will probably be the fate of all mankind within my generation." As you can probably guess, the book itself is called "The End of the World As We Know It", so it doesn't dwell on the other options that people chose; but you can presumably track down the footnotes in the book or use search engines to find these polls (and hopefully followup polls to indicate trends). Tempshill (talk) 02:23, 3 June 2009 (UTC)

According to Christianity in the United States, about 76% of the US population is Christian, and 40% of the Christians are evangelical. The bulk of these profess literal belief in the bible, and therefore believe that the rapture will occur "soon." That pretty much does it for mankind. -Arch dude (talk) 03:48, 3 June 2009 (UTC)

As always, it's going to depend on what you define as the "ultimate fate." For example, if humans don't extinguish themselves, but gradually evolve, there will be some point when we are, beyond any reasonable doubt, decisively not human (unless we genetically stagnate indefinitely). So, would that be the end of humanity? You have to precisely define all the other terms as well: "human", "civilization", "ultimate", etc... Nimur (talk) 03:53, 3 June 2009 (UTC)

Our OP isn't interested in what WE thing the end of humanity will be - but what the population in general believes. The trouble is that most of the general public are very susceptible to suggestion. If you ask "What do you think the chances of us blowing ourselves up with nuclear weapons is?" you'll get some highish number. If you ask "Will we get wiped out by a massive meteor strike like the Dinosaurs?" you'll get another high number. You can keep this up indefinitely and the probabilities will soon add up to more than 100%! But if you go and ask "Do you think humanity will get off the earth and live on other planets?" which would preclude any abrupt, disaster-type ending - then they also pick a highish number. People don't think these things through very carefully and they are terrible at understanding probabilities. So this kind of survey depends very sensitively on the questions you ask. SteveBaker (talk) 12:54, 3 June 2009 (UTC)

Steve, again, some source citations would be useful for our OP instead of just ragging on some of his possible assumptions. Tempshill (talk) 20:26, 3 June 2009 (UTC)

While I agree the way you word the question will have a big influence, as is well established in the public polling arena [6] and most people don't think much before answering, I don't think your example demonstrates that well. I can easily see someone saying yes to multiple questions of yours even with great thought because none of them specified it as what you believe is most likely. There's no reason why you can't believe all of those have a good enough chance of happening to say yes. And someone may say no or maybe even though they think one of those is the most likely fate simply because they think the chance for all is relatively low. Nil Einne (talk) 17:13, 8 June 2009 (UTC)