Wikipedia:Reference desk/Archives/Science/2007 September 7

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September 7

Creating a three dimensional display with diffraction patterns and coherent light

Why would it not be possible to create a three dimensional computer display by showing moving interference patterns on a display device and illumating with coherent light?
The relevent articles on holography may have ommitted to divulge the prohibiting principle on account of the conspiracy their techfuscation and my ignorance.
Many thanks, 86.132.15.29 00:59, 7 September 2007 (UTC)

One problem is that the screen needs resolution comparable to the wavelength of the light; for visible light that means billions of pixels per square inch. Another problem is that calculating the diffraction pattern is very expensive, especially with that many pixels. I don't think this is possible with current technology. There are other ways of making 3-D monitors -- see volumetric display. -- BenRG 10:30, 7 September 2007 (UTC)

Wouldn't that just be a hologram? Synthetic holographic displays have been demonstrated (very small volumes, very low resolution, very poor update rates, very big computers!) - I saw one at the SigGraph conference many years ago. It showed simple shapes (cubes, tetrahedra, teapots, etc) in a volume an inch or two on a side that updated a few times a second. It required a refrigerator-sized minicomputer to drive it and required some very fancy technology to filter the light. I believe this is what is being described in Hologram#Dynamic_holography. SteveBaker 13:37, 7 September 2007 (UTC)

How long ago was it? Computers have gotten a lot faster in recent years, so that something that would have required a Cray-2 in 1985 can be done on a desktop system today. --Carnildo 21:29, 7 September 2007 (UTC)

I would take a stab at forecasting that this technology will eventually become commonplace. As parallel processing increases and pixel densities improve it should become possible to have LASERs and computer power together on the same chip. At least it does not have to calculate at the speed of the light frequency. You could then cover the inside of walls with it to create a holographic chamber. Graeme Bartlett 22:15, 7 September 2007 (UTC)

Chickens

What are unsexed chickens?155.205.201.11 02:51, 7 September 2007 (UTC)

Chickens with their sexual organs removed. Capon is a type of unsexed (or desexed) male chicken. Tasty, tasty. HYENASTE 03:24, 7 September 2007 (UTC)

Wrong, see sexing. Cacycle 03:25, 7 September 2007 (UTC)

Could it not refer to either? HYENASTE 03:28, 7 September 2007 (UTC)

Not really. A desexed animal is one that's been rendered infertile. Unsexed is not a synonym of desexed. -- JackofOz 04:45, 7 September 2007 (UTC)

To get the answer here, unsexed chickens are chickens for which the sex is unknown. Baby hens and roosters look the same externally, but it is useful to know what is what! —Preceding unsigned comment added by Graeme Bartlett (talk • contribs) 07:09, 7 September 2007 (UTC)

...so that they know which fluffy little chicks to gas. :-( --Shantavira|^{feed me} 07:36, 7 September 2007 (UTC)

Luxury! --Sean 14:48, 7 September 2007 (UTC)

Also see the excellently-named article Chick sexing. --Sean 14:48, 7 September 2007 (UTC)

And its not as easy as it looks. It take a lot of experience to be a fest sexer. Mrdeath5493 18:29, 8 September 2007 (UTC)

iPod playlist randomization

Whenever I set my iPod to shuffle my entire playlsit, the first song is almost always a song I really, really like. Is this algorithm truly random, or does it favor songs that have received a high number of plays in the past? --The Fat Man Who Never Came Back 03:15, 7 September 2007 (UTC)

Without really giving you an answer, they claim the playlist is random, but I too have noticed there seems to be preference for playing regularly played, and therefore presumably favoured, songs. I wonder if it isn't a 'smart' algorithm that in fact does factor in the play count (although presumably if that was the case, over time it would become more and more biased by the ever increasing play count on those songs, unless that's factored in too). --jjron 07:22, 7 September 2007 (UTC)

I have no idea about the design of Apple software but are you sure this isn't just a case of observer bias. You tend to remember when the first song is one you really like more then when it isn't Nil Einne 11:20, 7 September 2007 (UTC)

No, I tested it several times. Believe me I have some real crap on my iPod, and it consistently chose a good song first.--The Fat Man Who Never Came Back 11:43, 7 September 2007 (UTC)

Newsweek and The Wall Street Journal weigh in. (many others available by searching ipod random function). --LarryMac | Talk 12:02, 7 September 2007 (UTC)

If you are rating your library's songs, iTunes has an "Play higher rated songs more often" check mark in the Party Shuffle mode. Are you sure that isn't selected? The iPod has a similar feature as well. Titoxd^{(?!? - cool stuff)} 18:19, 7 September 2007 (UTC)

Moon Phases

I was asked to chart the 16 phases of the moon. I have researched and only found 8. Do you know the names and have the charts to the 16 phases of the moon? 68.104.172.14 05:07, 7 September 2007 (UTC)

Lunar phase indeed lists eight. Could the request be associated with Hindu tradition? Googling for moon "16 phases" suggests Hindus count 16 phases or "kalas". The first two are called Amrita and Manada (type those into google if that's what you are looking for.) Weregerbil 06:07, 7 September 2007 (UTC)

....also called the sixteen "digits" of the moon.--Shantavira|^{feed me} 07:44, 7 September 2007 (UTC)

It's not really a scientific matter. As far as science is concerned, moon 'phases' are merely a convenience for humans - there aren't really discrete phases in reality - there is a continuously variable amount of shadow and light on the surface of the moon as viewed from the earth. The choice of 4, 8, 16 or a hundred names for various amounts of shadow is a purely linguistic matter. So the number of phases may vary from culture to culture, from language to language. Perhaps you should ask this on the language reference desk? SteveBaker 13:28, 7 September 2007 (UTC)

Elastic Behaviour in Polymers

I have a challenging question which I would like help on.

I am interested in polymer materials that increase in strain over time. For example, this material is one which is initially of 20mm in length and after it is left alone in normal conditions for say five hours its length increases to 22mm.

I have heard of anelastic materials which exhibit this sort of behaviour, but I do not know for certain. I have tried to research this behaviour online, but I have not found much useful information. It would be very helpful if someone could provide me with a list of materials that exhibit this type of behaviour (I am after specific materials e.g. Polyvinyl chloride). Thank you very much. —Preceding unsigned comment added by Total revolt (talk • contribs) 05:21, 7 September 2007 (UTC)

I would look at Hygroscopic materials - these absorb moisture from the air and thereby get larger. I don't know of a polymer that works like that - but if you are only seeking a 10% increase then maybe you could mix sodium hydroxide or calcium chloride (both strongly hygroscopic) into a regular polymer - or perhaps find a chemical varient of a polymer that would have these kinds of substances bound as side-chains? Dunno - we need a chemist. Someone here will know. SteveBaker 13:24, 7 September 2007 (UTC)

The question itself is confusing: how does the change of length relate to the idea of strain? That is, does the material become elongated while just sitting on the table, or is it under tension and gradually elongates, or...? Is it getting larger in volume (swelling lengthwise) or just stretching and narrowing (deforming like a piece of rubber)? There are lots of polymers that absorb water (polyaspartate is a good one), not sure which ones swell (and which of those swell directionally, as the question seems to imply?) vs which just "fill in spaces" in the existing matrix. DMacks 14:32, 7 September 2007 (UTC)

I am interested in a material that becomes elongated while just sitting on the table. This could be caused by initiated by compressing it beforehand or adding a certain substance to it. Ideally, the material is not getting larger in volume, just increasing in length. User:Total Revolt —Preceding unsigned comment added by Total revolt (talk • contribs) 03:28, 8 September 2007 (UTC)

Entomologist needed; weird bug in my room!

Okay, there's this weird bug hanging on my window blinds and I really want to know what it is:

• It flies.
• Its pretty big. Counting its wings folded behind it its like 2 inches long, though its body is more like 1 inch
• It has really long back legs and short front legs.
• Its green.
• I'm not sure what its doing. At first I thought it was eating some of the dirt on my window blinds (don't ask), but I think its just chilling. It keeps pulling its back legs up and rubbing them.
• I live in Northern California.

What is this bug? Atropos 05:24, 7 September 2007 (UTC)

Any chance you can get a picture of it? Someguy1221 06:05, 7 September 2007 (UTC)

A locust? — Kieff | Talk 06:15, 7 September 2007 (UTC)

It looks like a locust, but its legs are all much more thin compared to its body than any of the pics shown. Atropos 06:38, 7 September 2007 (UTC)

Acrida cinerea or any of its cousins? -- Sundar ^{\talk \contribs} 06:46, 7 September 2007 (UTC)

Sounds like another species of grasshopper other than your usual locusts. The green colouring, size, and behaviour (e.g., rubbing its legs) ring true with many grasshoppers I've seen. --jjron 07:10, 7 September 2007 (UTC)

I think it's probably a cricket, does it look like this? [[1]]Richard Avery 07:13, 7 September 2007 (UTC)

It's not a Praying mantis then? Nil Einne 10:58, 7 September 2007 (UTC)

It could be a Katydid. -- JSBillings 12:53, 7 September 2007 (UTC)

I found a weird bugger in my room once. It was my roommate. —Bromskloss 13:46, 7 September 2007 (UTC)

Well at least it wasn't mating (or buggering) Nil Einne 14:32, 7 September 2007 (UTC)

Buggers? Lanfear's Bane 15:46, 7 September 2007 (UTC)

It looks a lot like the cricket and catydid pictures, but its legs are a lot thinner and its body is only about half as long as its wings, while those all have the long portion attached to the end of the body. Also, its head looks a bit like a praying mantis. It really reminded me of a cross between a cricket (though the crickets I'm familiar with are brown) and a mantis.

Its probably just some odd species of cricket. Atropos 23:42, 7 September 2007 (UTC)

From your description I'm pretty sure that the insect was a katydid (Family Tettigoniidae). The Bush Katydid (Scudderia furcata) is very common in California--I've seen it or a similar species many times (I live in central California). Try doing a image search in google using the keyword Scudderia and see what you think. Katydids neither bite nor sting, but they can damage plants by eating the leaves. They have a clicking song.--Eriastrum 17:45, 8 September 2007 (UTC)

Thankyou! I think that's definitely what it was. All of you rule. Atropos 19:58, 8 September 2007 (UTC)

Pathogens in flower vase water??

In the UK some hospitals are prohibiting cut flowers in wards and patient rooms because there is a perceived risk from organisms that may grow in the water of the vases and if the water is spilled this could constitute an infection risk to patients - and presumably staff.

My question is - does any biologist or microbiologist out there, or indeed anyone, have any sourced information about the incidence of organisms that could cause infections in humans? We all know the water goes off and smells and maybe bacteria grow in the water but just how dangerous is it to human health. Richard Avery 07:19, 7 September 2007 (UTC)

Bear in mind from the case you mention it sounds like this isn't just water but water containing the stems of cut flowers, which are potentially good sources of nutrients and bacteria. Also in hospitals many people are somewhat immuno-compromised and are much more susceptible to infection then the average person. The hospital would be much more worried about the risks to patients then they would be to staff Nil Einne 10:56, 7 September 2007 (UTC)

I did a few searches and came up with some links but there are more. [2] [3]. From what I can tell there is definitely some concern about types and level of growth of bacteria in flower vases. But there has been no evidence for any infections linked to these sourced. However in strongly immunocompromised patients, e.g. ICU, burns units it's still recommended to remove such risks. In more normal wards I think most hospitals wouldn't be so concerned but you ideally should still treat the water with disinfectants like hypochlorite to be safe. Nil Einne 11:14, 7 September 2007 (UTC)

Remember this is a hospital - there are open wounds and people with compromised immune systems - so even the normal bacteria that's in soil (and therefore on these plants) could be a problem. It's not hard to imagine a splash of water as flowers are changed - or an accidental spill getting dirty water onto a dressing and thereby soaking into a wound. It would be nice to know whether they are banning them because of a 'perceived' risk - or because someone has done actual studies to make it an 'known' risk? If it's the former - then yeah - maybe it's an overreaction, but if it's the latter, perhaps not. There are plenty of things in soil (and therefore, eventually in the water of cut flowers) that can be harmful to humans. Amoebae grow in soil and thrive in dirty water. They can form 'cysts' (like 'spores' in plants) that let them blow around in the air as the water dries up. Our article on the amoeba lists five species that are hazardous to humans. Ever heard of amoebic dysentery? Obviously that's just one thing that might be in the soil that could do this...I'm sure there are any number of other bugs. Remember - commercial plants are probably grown in composted animal manure. Now - are those actually real problems that cause an unacceptable risk to patients? I don't know - but it wouldn't surprise me to find that the concern of the hospital is warranted. What I bet they have NOT studied is the benefit to patients of having flowers in terms of making them happier, perhaps relieving stress, reminding them of the person who gave the flowers - there is a lot going on with the 'placebo' effect where the mind drives recovery and who knows what effect flowers might have on that. SteveBaker 13:15, 7 September 2007 (UTC)

One example is Legionella bacteria that cause Legionaire's disease. Cases of infection are linked with bacteria in the ventilation system, not flower vases. However I suppose it's possible. Flyguy649 ^talk _contribs 15:56, 7 September 2007 (UTC)

OK, thanks for your comments guys, the two links make interesting reading and indeed show that some tricky bugs do grow there but the jury is out on their actual effect. It also seems that the anxiety could be overcome with the addition of hydrogen peroxide which disinfects the water and then the patients could be safely cheered up. Richard Avery 15:31, 10 September 2007 (UTC)

Identify this waterborne organism

I noticed several worms (looking like young earth worms) constantly pulsating (most of them with one end inside some tubular "mud" structure) in rain water collected in a roadside of a tree-covered campus in Bangalore. Please look at the two videos below and help identify the organism.

Commented out problematic videos SteveBaker 03:40, 10 September 2007 (UTC)

Excuse the poor resolution and glare. -- Sundar ^{\talk \contribs} 09:31, 7 September 2007 (UTC)

I couldn't view the videos, and I'm not familiar with the fauna of India, but from the still images those look like they could be redworms.

Earthworms can't tolerate being submerged in water -- they drown. I'm guessing that the "pulsating" motion you describe is the worm's feeble attempt (using musculature optimized for burrowing through soil) to swim away. (But this is pure speculation, and without having viewed the video I could be very wrong.) —Steve Summit (talk) 13:27, 8 September 2007 (UTC)

Steve, thanks for your suggestion. It doesn't look like redworms much. A lot of them are only slightly bigger than mosquito larvae and the bigger ones are about twice the size. The pulsating motion I described was seen in every individual organism (worm) and appeared to be characteristic of them (similar to mosquito larvae) rather than a "feeble attempt." They seem to be adapted for those conditions. I'll try to take a higher resolution still photograph on Monday and upload. -- Sundar ^{\talk \contribs} 15:28, 8 September 2007 (UTC)

They look like tubifex worms to me. Take a look at our article Tubifex tubifex and also do an image search on Google using the key word tubifex.--Eriastrum 17:54, 8 September 2007 (UTC)

Eriastrum, based on image search for "tubifex", I think you're right. Thanks for the information. This was happening when I saw. -- Sundar ^{\talk \contribs} 05:37, 9 September 2007 (UTC)

Can bamboo be grafted while growing?

I know trees can be grafted either within the same species, or even using parts of the same tree (crossing branches together) this is most frequently in Arborsculpture. DOes anyone know of a similar process for bamboo? Or think that it is possible?

Thanks! —Preceding unsigned comment added by 128.113.36.239 (talk) 13:21, 7 September 2007 (UTC)

I doubt it. Bamboo is a species of true grass and one of the odd things about true grasses is that they grow at the base of the plant rather than at the tops (as with - for example - most trees and shrubs). This is because grazing animals eat the tips of grasses and if that was where the growth was happening then they'd be in trouble. So it may well be that because of this, conventional grafting might not work - but finding definite information about that might be tough. SteveBaker 13:55, 7 September 2007 (UTC)

Grafting of bamboo was covered in "The Grafting of Large Monocotyledonous Plants" by Thomas J. Muzik and Carl D. La Rue in the November 28, 1952 edition of Science. If you can somehow get a copy of that article, you can see how they did it. -- kainaw™ 14:04, 7 September 2007 (UTC)

It shouldn't really be that hard. Both [4] and [5] should have it and many academic libraries should have access to it (albeit they may require you be a member although I note that Jstor says "Our license agreement with libraries allows for use of the archive by anyone present in the library, whether or not they are affiliated with that institution"). Most decent academic libraries would probably still have the paper journal too, albeit perhaps in storage (i.e. it may not be accesible to non members). You could take a look at your local public libraries and academic libraries and see if they offer what you need. Even if your local library doesn't have the journal it could potentially get it via the interloan system for a fee. Or if you're desperate you can buy it for US$10 [6] Nil Einne 14:30, 7 September 2007 (UTC)

Why do spiders hang upside down in their webs?

Why do they wait in a head-downward position? Why not head up? Or any other direction? —Preceding unsigned comment added by Dominus (talk • contribs) 13:40, 7 September 2007 (UTC)

Well, I would guess that they want to be able to get to any point on their webs really quickly - and downhill is faster than uphill. So they want to be at the top of the web - and in order to see what's going on - facing downwards makes sense. Also, they spin silk from their hind-end, so if they need to escape on a thread in the wind then attaching the line from their rear end and sailing downwards would be the fastest thing. But that's a guess - it's hard to know for sure. SteveBaker 13:49, 7 September 2007 (UTC)

Your guesses are no good. Spiders do not wait at the top of the web; they wait in the middle. -- Dominus 14:09, 7 September 2007 (UTC)

His second guess about spinning a thread fast for escape is still a possibility. Would it force more blood to the brain so they think a little sharper? This is a completely random guess on my part :p Capuchin 14:16, 7 September 2007 (UTC)

My guess is that it has to do with staring at the bright sky all day long. Not good for the eyes and all that. If I had to hang in a web all day long, I'd probably look down too. ;-P --24.147.86.187 14:25, 7 September 2007 (UTC)

I don't know if there is a well understood reason. It could be a left-over behavior from when spiders hung from a single thread, it could be related to markings on the abdomen to warn off predators, for orb-weaver spiders, it might be related to how they construct their webs. -- JSBillings 16:03, 7 September 2007 (UTC)

Since humans, as most animals do, hold their heads up, you assume that that's normal. Spiders might wonder why all the other animals are upside down. Maybe they figured out that that's because they always walk on the ground - in which case spiders also have their heads up. But in the web there is no need for that. Then again, that doesn't explain why they prefer the heads down position over others. One possibility is that other animals will, like you, consider that an abnormal position and therefore be less inclined to think that what they see is an animal. DirkvdM 08:23, 8 September 2007 (UTC)

Maybe what someone should do is invent an upside-down world wide web, then we could all hang around upside down.  :) -- JackofOz 13:47, 8 September 2007 (UTC)

You're asking for this - don't you Aussies already do that? DirkvdM 17:47, 8 September 2007 (UTC)

Certainly not. -- JackofOz 01:18, 10 September 2007 (UTC)

My guess. Their spinners are in the rear abdomen. Unlike spiderman, they cannot shoot their webs so they attach it and use their body weight as tension. This implies head down. --DHeyward 06:32, 11 September 2007 (UTC)

I was able to speak with Jonathan Coddington, a research entomologist with the Smithsonian Institution, and an expert on spiders. His answer was that the spider wants to attack in a downwards direction to get a speed and force assist from gravity. For this reason spiders construct their webs so that the lower part is most likely to catch prey, and then waid above this part, pointing downwards, for quick attack.

He said it had nothing to do with vision, and that spiders are nearly blind. -- Dominus 15:10, 11 September 2007 (UTC)

All those eyes, and still nearly blind? The spider article says "Their eyes are single lenses rather than compound eyes, ranging from simple light/dark-receptors to eyes rivaling those of a pigeon (some jumping spiders). [...] in some cave species, there are no eyes at all. Several families of hunting spiders, such as jumping spiders and wolf spiders, have fair to excellent vision.". DirkvdM 18:30, 11 September 2007 (UTC)

A theory for the origin and purpose of dark matter and energy. Could it be true?

This is a theory for the origin and purpose of dark matter and energy. I just thought of this and i'm not a physics student. I just want to know if there is a chance that this could be true or if others have already thought of it.

We basically know that our universe is expanding and it will keep expanding until all matter tears itself apart (The Big Rip) 20 billion years from now. I think the dark matter and energy around us now is a remnant of an old universe that existed before the Big Bang that created our universe. It's the remains of a previous Big Rip.

What’s the point of dark matter / energy? Dark energy drives the universe's expansion. I think dark matter slows it down. Right now there's more dark energy than dark matter in the universe - that is why it's expanding. I think that after each Big Rip, the concentration of dark matter relative to dark energy increases. This increase slows down the expansion of the next universe and gives it a longer life. This cyclical process will keep happening until the increased concentration of dark matter vs. dark energy nullifies the expansion. Then that universe should exist forever (no more Big Rips) or at least a much longer time than usual. Also, it will be more tightly packed by cosmic standards and bodies of matter will be closer together. I think dark matter and dark energy act as a balance scale for gravity and expansion. —Preceding unsigned comment added by 67.110.174.2 (talk) 15:54, 7 September 2007 (UTC)

For this theory to be scientifically sound, you will need some kind of observable evidence which backs up your prediction. For that to be effective, you will probably have to quantify your assumptions with some mathematical rigor. To be sure that you haven't overlooked some detail, you should review the entire body of established literature. This process will take some time and require a lot of peripheral understanding of physics. The typical approach is to be a physics student; this will enable you to make informed judgements about the present state of the discipline, and eventually contribute to the body of knowledge. What you have provided here is sort of vague and may even border on unfalsifiability. Good luck! Nimur 18:02, 7 September 2007 (UTC)

Unfortunately, we don't really know enough about dark energy to make any clear conclusions about what it is. Depending on the nature of dark energy and its equation of state, there may or may not be a Big Rip. We hope to catch a first glimpse of the dark energy equation of state parameter w within the next 10 years or so. As for dark matter, we expect to be able to understand it in terms of heavy particles that are simply difficult to detect because they don't have electromagnetic or strong force interactions. A lot of scientists are hoping that LHC will be able to produce particles like this.

Your idea reminds me a lot of the ekpyrotic cosmology, which is a modern form of a cyclic universe. You might also enjoy reading about the bubble universe theory / chaotic inflation. --Reuben 19:01, 7 September 2007 (UTC)

All of the cosomologies that rely on a big-bang happening more than once (with big rips or big crunches or whatever) are problematic and unfalsifiable. The problem is that when all of everything is within the singularity at the very start of the big bang, there is no information contained within it. This means that absolutely no information about the preceeding universe (if indeed there was one) can make it's way into this one. Everything that may have proceeded the big bang is irrevocably lost. Given no information about the preceeding universe, we are unable to either prove or falsify it's existance. So, yeah - it could be that the universe is cyclic - but there is nothing we can say either way about that. Feel free to believe in a cyclic universe - but you can no more prove it than you can prove that Santa Clause brought it in his sack. It's rather pointless to spend time thinking about it. SteveBaker 20:43, 7 September 2007 (UTC)

I've seen versions of string theory in which the universe expands and collapses over and over, and each time the fundamental force constants and the allowable particles change randomly. It was a way of making the existence of life not anthropic, but probabilistically inevitable. Although it still suffers from the issues Steve gave, the whole...not being able to test it thing. Someguy1221 21:22, 7 September 2007 (UTC)

The ekpyrotic model doesn't have an initial singularity, and predicts a characteristic spectrum of gravitational waves. --Reuben 21:56, 7 September 2007 (UTC)

BF Skinner

Was his mother really a crack whore as the article about him suggests? I'd never heard that. —Preceding unsigned comment added by 198.150.162.65 (talk) 19:38, 7 September 2007 (UTC)

That was vandalism, now removed. Someguy1221 19:42, 7 September 2007 (UTC)

I knew Mother Skinner, and she was a marginal whore at best. --Sean 21:43, 7 September 2007 (UTC)

Did she own the original Skinner box? Edison 00:09, 8 September 2007 (UTC)

Despite Skinner's best efforts with the old dear, he found you can lead a whore to culture, but you can't make her think. Rockpocket 00:47, 8 September 2007 (UTC)

I've reported this user to Wikipedia:Administrators' noticeboard/Punsters asking for lifelong bans from editing Wikipedia ---Sluzzelin talk 02:31, 8 September 2007 (UTC)

Its a fair cop, guv'! Rockpocket 04:21, 8 September 2007 (UTC)

How much plutonium

How much plutonium has been produced or exists on earth today? —Preceding unsigned comment added by 88.109.213.2 (talk) 22:29, 7 September 2007 (UTC)

Exact numbers will not be available, because production amounts of plutonium are considered secret by all nations that produce plutonium (knowing production numbers or even production capability gives you the tools needed to estimate a stockpile size very accurately). But maybe we can get an order-of-magnitude estimate by thinking about how many nuclear weapons are on the earth today, most of which use plutonium cores (because it is very efficient, and easier to produce than enriched uranium for a large nuclear power). According to List of states with nuclear weapons, there are about 20,000 nuclear weapons in the world at the moment. I would guess that on average they each have at least 10 kg of plutonium in them. I have no idea how much plutonium would be in the sparkplug of a Teller-Ulam design, and can find nothing which would give much of a hint in any of the related articles (or a few other sites I checked). But okay, that puts a minimum of around 200 tonnes of plutonium around today and refined for weapons purposes. It does not include plutonium produced incidentally as part of nuclear reactor operations, which is probably quite a lot, but most of it is never separated from the fission products and is just deposited as nuclear waste (at least it is in the US—I don't know if other countries do reprocessing). --24.147.86.187 22:55, 7 September 2007 (UTC)

Oh, I just checked plutonium, and it says there is an estimated "300,000 kg accumulated worldwide". So 200 tonnes as a guess was the right order of magnitude, but still about 100 tonnes short — probably because nations keep more plutonium reserves than they use in weapons themselves. Note, by the way, that the amount produced is probably almost identically to the amount used on Earth today, since it has a relatively long half life (it is a weak alpha emitter). --24.147.86.187 22:58, 7 September 2007 (UTC)

(EC) The book Plutonium and Highly Enriched Uranium 1996: World Inventories, Capabilities and Policies, by David Albright, et al., says that in 1996 there were 1160 tonnes of plutonium and 1770 tonnes of HEU in worldwide inventories (page 396). It's probably similar today. --Sean 23:11, 7 September 2007 (UTC)

How large of a cube would that be, if it were all piled together (not that I would for a microsecond consider doing that)? Edison 00:11, 8 September 2007 (UTC)

Well, it has a density of 19.816  g·cm⁻³... soooo.... umm... in any case, it is pretty dense stuff. --24.147.86.187 00:24, 8 September 2007 (UTC)

Uh, I don't think you could put it all together in a cube (critical mass might become an issue at some point along the line). --SB_Johnny | ^PA! 00:58, 8 September 2007 (UTC)

You could, but you'd have to do it very, very quickly, and then run away really, really fast. :) Anyway, I calculate that it would be a cube 8.4 meters on the side. --Sean 01:23, 8 September 2007 (UTC)

Please note that the Reference Desks cannot offer professional advice. You should consult a qualified mad scientist. Gandalf61 13:39, 8 September 2007 (UTC)

-- Yo. -- Nimur 16:46, 8 September 2007 (UTC)

Global Warming Real Estate Speculations

Much of the news on Global Warming is in the negative; Would the warming up of the planet make Russia's Tundra area prime real estate? And what about 1918 The Year Without A Summer? --i am the kwisatz haderach 23:32, 7 September 2007 (UTC)

Perhaps, if you like your real estate to have an atmosphere containing "billions of tons of methane gas". See also Effects of global warming for the environmental payoff for a nice duplex in the Siberian peat bogs. Rockpocket 00:59, 8 September 2007 (UTC)

If you want to speculate on warming, don't buy tundra. The effects of warming on tundra are not generally positive. Instead, look for land that will become seacoast due to sea level rise. Look for steep terrain that is just inland of current low-lying areas. make sure you purchase land that extends from just above the current sea level to at least a few meters above the current sea level. Your best bet is to look at very low areas, and to turn your investment over about once every ten years as the sea level rises. In South Carolina, you will be moving west at about one mile per decade, while the traditional land owners will move more slowly. -Arch dude 02:48, 8 September 2007 (UTC)

The bad thing about global warming is not that the new climate (once it has stabilised to one) is worse. It's the change itself that's the problem. Life is used to a certain climate and any change will make it less adapted, possibly resulting is mass extinction. The worst one, the Permian–Triassic extinction event, which killed about 2/3 of species on Earth, is speculated to have been caused by an initial rise in temperature of about 5 C, roughly what is expected to happen in the next few centuries. Except that it took a whole lot longer then. A few centuries is the blink of an eye in evolutionary terms. So if a similar change over (tens of) thousands of years had such a dramatic effect, what will the effect be if it happens in such a short time span? In human terms, things might not seem so bad, because we are highly adaptable and can simply shift our population centres. In theory, that is - a shift across borders would likely result in war. And then of course there's the dying of other species, because we depend on them in many ways, mostly indirectly, but also directly because the traditional agriculture will not be sufficiently adapted to the new climate (if it settles to one, that is). Again, humans can adapt, but, again, it's the transition itself that is the problem. The search for a more adapted agriculture will take some time (decades, centuries?), during which there will be less food. And if this happens worldwide, there will be no surpluses elsewhere to compensate.

To clarify, what I meant to say was that the best that can happen to a region is not a change to a 'better' climate, but no change at all. There is no such thing as a better climate. Actually, climate means predictable weather and when it changes, that means there will be less climate, however odd that may sound. And farmers are highly dependent on the predictability of the seasons. Stupid thing is, we're building up excessive luxury at the expense of the very basis of our livelihood, namely food (and water, for that matter). Our descendants will be pretty pissed off with us. DirkvdM 08:52, 8 September 2007 (UTC)

What does any of that have to do with real estate speculation? Perhaps buying coastal and lake-front properties in areas that are currently completely ice-locked would work out well. (Remember to account for changes in sea-level.) APL 04:58, 10 September 2007 (UTC)

No appreciable effects will happen in your lifetime. Better to buy bonds than to speculate on GW real estate. --DHeyward 07:54, 10 September 2007 (UTC)

There are certainly some places you don't want to buy right now. In Alaska and Siberia, the permafrost is melting, turning areas that used to be rock-hard soil into swamp. True, Florida isn't likely to vanish in your lifetime, but there are areas that will be affected, and those tend to be in the extreme north and south. --Carnildo 21:12, 10 September 2007 (UTC)

The effects on agriculture will be worldwide, and with our food patterns depending for a large part on international trade, the countries that rely on that most will suffer most. Some countries may get lucky, say if they have invested in foodcrops that don't really belong in that climate but coincidentally belong in the new climate (insofar as one can call it that), but that's extremely unlikely.

In answer to APL's question about the relevance of my remark, I guess I wasn't clear enough; climate change will have negative consequences everywhere, even if it seems that one aspect is positive. The negative sides will likely prevail, wherever you buy your land. Maybe the best bet would be New Zealand, because it is likely to suffer least, so people will start to move there. Until the Kiwis will stop the flow, in which case they might also find themselves at war. DirkvdM 06:06, 11 September 2007 (UTC)