Wikipedia:Reference desk/Archives/Science/2007 December 13

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December 13

loss of power in optical frequencies

Is there a way to work out the loss of power in a coherent beam of electromagnetic energy in near optical frequencies? My purpose is to work out an effective range for a scifi laser gun working in either IR or x-ray. --203.171.195.34 (talk) 00:48, 13 December 2007 (UTC)

The angle of divergence is very roughly equal to the wavelength divided by the initial diameter of the beam. For details see Angular resolution, Diffraction limited, Airy disc. Icek (talk) 02:32, 13 December 2007 (UTC)

The other thing that's going to have a dramatic effect on range is whether you're firing it through some medium (like air for example) - if it's being used in a vacuum then it's a different matter of course. SteveBaker (talk) 12:54, 13 December 2007 (UTC)

I was particularly thinking about it firing through air at sea level. --203.129.38.192 (talk) 16:53, 13 December 2007 (UTC) (formerly 203.171.195.34)

I thought as much. Check out the graph here: Image:Atmospheric_transmittance_infrared.gif - it shows how well the atmosphere transmits IR - and as you can see - you need to pick a frequency where the air isn't going to block it. 3.5 microns is a good wavelength. SteveBaker (talk) 05:37, 14 December 2007 (UTC)

There's also the problem that lasers aren't truly monochromatic. They transmit over a narrow band of wavelengths, and this causes the beam to become incoherent at some distance. This is largely an engineering issue, however, so for the purpose of scifi you can declare the beam to be coherent as far out as you like. Someguy1221 (talk) 05:41, 14 December 2007 (UTC)

Child pyromaniac

Is child pyromania an actual diagnosed disorder. I asked a Psychologist who is a friend of mine, and they said it was real, but didn't know if it was a diagnosed disorder. This information is for the AFD. Thanks, Malinaccier (talk) 01:33, 13 December 2007 (UTC)

It's in the DSM-IV (see here), so I'd say yes. For more see the "Encyclopedia of Mental Disorders" pyromania entry here. -- HiEv 02:38, 13 December 2007 (UTC)

Though I should have noted that it's not specific to children. -- HiEv —Preceding comment was added at 02:43, 13 December 2007 (UTC)

Rationale behind intraperitoneal injection of immune cells?

What's the rationale behind intraperitoneal injection of immune cells in lab experiments? Is it easier for them to migrate from there than from under the cutis of the skin? If so, any idea why? Do you know of any other options? The journal club presentation I give tomorrow is on a paper that used this mode of injection and it's not likely to be questioned but I'd like to be prepared just in case as well as understand for my own knowledge. --Seans Potato Business 09:10, 13 December 2007 (UTC)

i.p. injections facilitate faster absorption of the injected material as the peritoneum is highly vascularized (draining into the hepatic portal vein). Subcutaneous injections have a slower absorption. Also, i.p. is quite easy to do... — Scientizzle 16:17, 13 December 2007 (UTC)

crystallization

In the early stages of crystallization of a solution the solute molecules begin to come together from the solvent and begin to form clusters.But what is the idea behind the crystallization of water into frost we generally see on a nasty winter morning.Water is a solvent right. —Preceding unsigned comment added by 218.248.2.51 (talk) 09:43, 13 December 2007 (UTC)

Water vapor in the air is a solute. Air is the solvent. Someguy1221 (talk) 10:51, 13 December 2007 (UTC)

Do try this link ..crystallization.--Mike robert (talk) 23:03, 13 December 2007 (UTC)

Flour

Were going to play a practical joke on a friend and want to know whats safe to snort Sugar or flour etc —Preceding unsigned comment added by King Alaric (talk • contribs) 12:40, 13 December 2007 (UTC)

I'm not convinced that any of those things are safe - but I would suggest something that dissolves in water so it won't hang around stuck to nasal passages and lung linings for long. So definitely NOT flour. Salt would probably be safest...especially if you ground it down into a finer powder using a mortar and pestle first. But as I said - I'm not sure any of those things are exactly safe, you should use the smallest amount you can. SteveBaker (talk) 12:50, 13 December 2007 (UTC)

At least in the long run, flour is definitely NOT safe; it causes baker's asthma [1] (no apparent relation to SteveBaker). Confectioner's sugar often has cornstarch or other anti-caking agents added so I'd rule that out too. If "Microfine powdered sugar" is just sucrose, you'd probably survive a small amount of that, but we're verging into medical advice and if your joke goes awry, you may need legal advice too! As one data point, the powder form of Serevent asthma inhalers use lactose powder along with active Salmeterol anti-asthma drug.

Atlant (talk) 13:23, 13 December 2007 (UTC)

Mentioning sugars, how about icing sugar, which is just glucose and a lot finer than normal cane sugar? --antilived^{T | C | G} 00:32, 14 December 2007 (UTC)

• I wouldn't do this myself, but I suppose you could snort dry nasal spray powder (baking soda and salt) to alarm your friend and then later flush it out of your nose with warm water. Anytime you inhale something, though, there's a risk of nosebleeding, so you might want to mention this prank to a nurse or doctor first and get their opinion rather than doing some dumb thing that some guy on Wikipedia suggested. --M@rēino 14:52, 13 December 2007 (UTC)

• I'm surprised that no one has mentioned it, but cocaine is relatively safe to snort in low quantities. Anyway, who's ever heard of snorting flour off a hooker's ass? --Sean 21:25, 13 December 2007 (UTC)

• This begs the question: what do they use in the movies? I doubt they're snorting actual cocaine. And after searching the internet I found that this has been asked on three different versions of Yahoo Answers. The most common answers are baking soda, flour, powdered sugar, powdered milk and vitamin B powder. Both flour and sugar are reported to have nasty side effects. This page lists different substances that are supposedly used as cocaine props depending on whether it is to be shown lying around or snorted. 152.16.16.75 (talk) 01:58, 15 December 2007 (UTC)

I'm having a hard time imagining a "practical joke" involving phony cocaine that isn't a collossally bad idea carrying numerous serious risks of many different types; you might as well go whole hog and use plaster of paris. --Scheinwerfermann (talk) 15:56, 17 December 2007 (UTC)

Cooking Meat

Why is it that humans have to cook most meat to order to avoid becoming sick, while wild animals do not? —Preceding unsigned comment added by 195.188.208.251 (talk) 14:26, 13 December 2007 (UTC)

Humans can eat raw meat without getting sick. However, they risk catching various diseases and parasites that animals commonly catch, such as worms. In addition, the meat you buy from a supermarket is pretty close to carrion :) The animal will have been slaughtered some time ago, this being practical and how we like our meat, which only increases your chances of catching something. So, humans can eat raw meat without getting sick every time. Animals don't always avoid getting sick from eating raw meat. You don't want the life-expectancy of a wild animal. Skittle (talk) 15:46, 13 December 2007 (UTC)

Actually, humans don't require most meat to be cooked in order to avoid sickness. If the meat is from a freshly - slaughtered animal, and hasn't had the chance to have started to become rotten due to decomposition, AND if there are no harmful pathogenic organisms in the meat (such as bacteria or worms or such), then it really is completely fine for humans to eat raw meat. Or, rather, it is completely fine for humans who are not philosophically opposed to eating meat, that is. When people eat steaks that are cooked to be rare they are actually consuming raw uncooked meat in the middle of the steak. The reason this is considered safe enough to eat by many people is that the outside parts of the meat that are exposed to the air is where decomposition happens more quickly than in the center of the meat, which is protected from direct exposure to air.

If a piece of meat has started to "turn" and begins to smell and taste like it's undergoing decomposition, it still may be safely consumed by humans if its thoroughly cooked by being heated to a temperature of at least 170 degrees Fahrenheit (71 degrees Celsius). The heat destroys the harmful bacteria that are living on the meat. However, as the decomposition process continues, the risk factor of picking up something nasty from the decaying meat increases over time. In warmer climates this was historically (before the invention of modern refrigeration) a problem, because warmer conditions speed up the decomposition process. Just as putting a piece of meat in your refrigerator or freezer helps to prolong its shelf life, so too did keeping a piece of meat in cold storage outside of the house in northern latitudes help prolong its shelf life. As a result of this, people who lived in warmer climates tended to eat meat that was more thoroughly cooked than those in colder climates. This also led to the heavier use of hot spices to mask the flavor of turned meat in warmer places around the world.

The idea that wild animals do not get sick from consuming decaying meat is a fallacy. Animals that eat only freshly killed meat have much less chance of picking up parasites and harmful bacteria. Animals that are scavengers, however, often suffer from all kinds of parasitical infestations and problems with digestion of very rotten meat. The longer the life expectancy of a scavenging species of animal, the more likely it is that the individuals of that species will pick up parasites. Bears are a good example of this. In the wild, it is quite common to find bears whose body tissues are riddled with worm infestations. There is a theory that this is why some bears that get older become seemingly insane - due to the fact that they are in constant pain and physical turmoil from all the parasites inside their bodies. At least that was what a Native Alaskan told me once while I was growing up in Alaska. It may be just a folk tale, but there may be some truth to it, as well. At any rate, I've seen when hunters have cut open grizzly bears, and their meat is riddled with so many tiny pellets of worm cysts that it is gritty to the touch. This probably comes from the fact that grizzly bears are notorious for eating turned meat - in fact, after killing an animal, the bear won't eat it right away, but will often dig a hole in the ground, dump the carcass in the hole, urinate on it, cover it with a few scoops of dirt and leaves, and then leave it to rot for a few days. I've seen this in real life - we stumbled on such a hole with a day-old dead elk calf in it - and then promptely got out of there! The rotting process makes the dead carcass softer and easier to chew for the bear (and perhaps makes it easier for the bear's digestive system to break down the proteins). But it also provides an optimum condition for all manner of nasty parasites and bacteria to grow before the bear eats it. You can often tell when a grizzly bear is around because they smell like a walking garbage dump and cesspool combined, and so it is with little difficulty to imagine where the bears pick up all those worm infestations... Saukkomies 16:02, 13 December 2007 (UTC)

Bear in mind that even if you kill all the parasites and bacteria in the meat there is still the possibility toxins produced by said bacteria will remain as these are not usually destroyed by cooking. This is one of the reasons cooking is not always sufficient with significant 'bad' meat Nil Einne (talk) 18:56, 13 December 2007 (UTC)

True, but for these toxins to be in great enough levels to do any real harm, the meat in question would have to be in pretty sad shape. Still, from accounts of people who have had to undergo extreme measures in order to survive, it is quite surprising what the human digestive system can handle. Saukkomies 23:11, 13 December 2007 (UTC)

What's also relevant is the quality of the meat (farming). For example as a sashimi fanatic I was very keen to just walk into my local supermarkey and just buy some raw salmon and take it home with some wasabi, mayonnaise and soya sauce. But no there's a difference between sashimi grade salmon and normal commercial salmon. The commercial salmon is generally meant to be cooked, which kills all parasites. The commercial salmon is also usually farm-produced, where parasites are apparently very common and very easy to get. Sashimi-grade on the other hand is usually freerange caught, must be healthy, and the sashimi-chef is trained to look and detect any parasites. Even then, there are still problems - it's difficult to detect all parasites. Many countries (for whatever reason) now have laws that any fish that is to be sold for raw consumption has to be flash-frozen for a certain amount of hours which kills of the parasites. But critics argue that proper sashimi is never frozen and that freezing hampers the taste.

But eskimos continue to eat raw meat and blubber, and millions of people eat sushi and sashimi every day. There are things like biltong and other forms of cured meats which is raw and slow-dried. So clearly there are some cases where raw meat is okay for humans, provided the animal is free of parasites and types of bacteria (think salmonela with chicken)

What I don't know for sure is why certain animals have a much higher tolerance. My father would sometimes give meat to the dog if it has been left in the fridge too long and didn't quite smell right (it wasn't raw, but I do believe animals do have a higher tolerance) Rfwoolf (talk) 16:30, 13 December 2007 (UTC)

Animals may vey well have a higher tolerance (although bear in mind Sauk said above, just because the animal ate it doesn't mean it didn't give it parasites or cause other problems). One of the common suggestions, although I don't think this is really backed up by any evidence is that we have evolved to have a low 'tolerance' because we have been cooking food for so long so it hasn't been as important Nil Einne (talk) 18:56, 13 December 2007 (UTC)

Animals probably also have a higher tolerance for illness as well, by this I mean, when my dogs eat their own feces, grass, raw fat from whatever I'm cooking or whatever is their dish of the day, they don't come and tell me "jeez, that last meal had me up all night" or have me bring them glasses of water. They just go off and deal with it. My girlfriend is a vetinary nurse and tells me amazing recovery stories of animals on the theatre table one day, running around the next, but I think when your an animal, it doesn't pay to compain - you just get on with it. 81.144.241.244 (talk) 13:48, 18 December 2007 (UTC)

I grew up in Alaska. My father was a search and rescue helicopter pilot, and would sometimes be called out to some Bush community to air-vac someone to a hospital for an emergency. I remember at least three separate instances where there was some Alaska Native who had to be flown in an emergency situation due to some bad meat they had eaten. One of these cases was an old woman who'd left a leg of moose behind her cast iron wood stove for too long. It killed her in the end. So, sure, the Inuit eat raw meat, but that doesn't mean it can't hurt them. Saukkomies 23:17, 13 December 2007 (UTC)

• You might be further horrified to read Carbon monoxide#Role in physiology and food, which notes that the US and other countries permit meat packers to treat their meat with CO, which can keep it looking nicely fresh and red for up to a year (!), even though it's rotting away. Luckily it will still smell bad once you get the package open, though one assumes they're working on that problem as well. --Sean 21:38, 13 December 2007 (UTC)

Curing has long been used to conserve meat. Here nitrite (if nitrate is used it is reduced to nitrite by certain bacteria) protects the meat from bacteria like Clostridium botulinum as well as from discoloration. The drawback is the formation of cancerogenous nitrosamines which may have been responsible for the higher rates of stomach cancer before preservation by freezing was available to most people. Icek (talk) 13:58, 14 December 2007 (UTC)

I love this board. This a really great, helpful answer & discussion.--The Fat Man Who Never Came Back (talk) 14:04, 14 December 2007 (UTC)

Curing meat is also linked to higher rates of deliciousness. --Sean 14:42, 14 December 2007 (UTC)

Average Interstellar Distance

Over at the Wikipedia:Reference desk/Science#Aliens discussion, the Drake Equation came up, which lets you estimate how many communicating civilizations are in the Milky Way at the moment. I've been playing with the interactive version, but now I'm having trouble conceptualizing the totals that I get. Let's say I decide that there are 10, or 42, or 1,000 communicating civilizations. Assuming that they are evenly spaced throughout the galaxy (and likewise assuming that each civlization is confined to its home star, mainly to simplify the math), what is the average distance in light-years between two species? Thanks for any help! --M@rēino 15:28, 13 December 2007 (UTC)

The area of the galactic disk is about 5×10⁹ square light years. To estimate the distance between civilizations, you can divide that up between N societies and take a squart root to get a linear distance. So with 1000 communicating civilizations, the average seperation is ~2200 light years. Dragons flight (talk) 15:55, 13 December 2007 (UTC)

Just in case you start wondering about how close they'd have to be for us to detect them, here is an important fact: If you took our most powerful radio transmitter, put it on a planet orbiting Proxima Centauri (the closest known star - just 4.2 light years away) - then we would not be able to detect it with our most powerful radio telescope. So even if the alien civilisation was our immediate next-door neighbour, we probably wouldn't be able to hear their transmissions. Some people argue that as the civilisation gets more advanced technology, their radio transmitters would get more powerful and we'd be able to pick them up - however, the science of efficient communications says that the most efficient possible means of communication is indistinguishable from white noise. This means that we almost certainly couldn't detect a more advanced civilisation either. Unless the aliens somehow know we're here and are actively aiming a narrow-beam of radio waves (or perhaps a gigantic laser) at us, we stand no chance whatever of finding them. We need vastly more sensitive radio telescopes - perhaps mounted on the far side of the moon where it won't get interference from earthly transmitters. SteveBaker (talk) 05:26, 14 December 2007 (UTC)

Fortunately, such narrow beams already exist. But yes, as you said, the difficulty is knowing where to aim (as that observatory can pretty much only listen/transmit to one teeny piece of the sky at once. Someguy1221 (talk) 05:38, 14 December 2007 (UTC)

"If you took our most powerful radio transmitter, put it on a planet orbiting Proxima Centauri (the closest known star - just 4.2 light years away) - then we would not be able to detect it with our most powerful radio telescope." <-- According to this, the Arecibo message should be detectable by any civilization with an Arecibo -like detector in the Messier 13 cluster, 25,000 light years away. --JWSchmidt (talk) 05:57, 14 December 2007 (UTC)

But the beam is focused - sending at 2380 MHz with a 305 m aperture gives you roughly an angle of divergence (or rather half-angle) of a = c/(2.38*10⁹ Hz) / 305 m, and the fraction of the unit sphere which is illuminated by the beam is approximately b = a²*pi/(4*pi) = 4.26*10^-8. The distance you can reach is, compared to the distance you can reach with an omnidirectional transmitter, b^-1/2 = 5*10³ times as large (it's only a rough estimate, but to show the order of magnitude). Icek (talk) 13:44, 14 December 2007 (UTC)

Yep - but it entails their highly directional transmitter being aimed at our highly directional reciever at precisely the moment we happen to be looking. If they happen to aim at the earth and spend 8 hours transmitting the complete Encyclopedia Galactica at us (as aliens are certain to do! :-) - but they do it when Aracebo is on the opposite side of the planet - or looking at some other star - then we aren't going to know about it. These hypothetical aliens have to know that we are here and broadcast the same signal over and over again using that narrow beam transmitter for centuries at a time. They could reasonably guess we are here from studying earth's transits in front of the sun and plotting the results of our industrial growth in things like our CO2 output. But then they'd need to keep that expensive resource focussed on us from Victorian times (maybe) until we happen to look in their direction. They'd know the odds of this actually working were small - so perhaps they wouldn't bother. For this to work, we either need omnidirectional transmitters or omnidirectional recievers or two civilisations with infinite patience! Our best chance is to study more of these 'exo-planets' (orbiting other stars) and see if we can find one with evidence of civilisation in it's atmosphere - and start broadcasting and listening in it's direction 24/7 for centuries. Somehow, I can't imagine the governments of the world paying for that. SteveBaker (talk) 17:14, 14 December 2007 (UTC)

• Thanks for all the answers! Looks like I'll hold off on sending out the invitations for my "welcome, space aliens" party for a century or so. --M@rēino 16:41, 14 December 2007 (UTC)
  • But you're still inviting us too - right? SteveBaker (talk) 17:14, 14 December 2007 (UTC)

US: Pounds, ounces, and grains

Once again Wikipedia confuses me with US measurements.
I have read Pound (mass) and it fails to express what Americans use in practise for weight. I've heard of things like "he weighed 6 pounds 4 ounces". I've seen American products with liquids measured in oz. (ounces). But I've never ever heard of grains. Please tell me, do Americans actually practically use grains? If you order up something would you ask for "About 2 ounces and 50 grains?". And what about using decimals: can you order 4.32 pounds of something? Or how about 4 pounds and 12.3 ounces of something? Is that the practical implementation of the system? Thanks! Rfwoolf (talk) 15:33, 13 December 2007 (UTC)

Either pounds (including decimals) or pounds and ounces (possibly including decimals on the ounces). Grains are not widely used, except maybe in certain fields (gunpowder?). Of course, in everyday speech, you would probably say "a pound and a half of meat", not "one point five pounds of meat" nor "one pound, eight ounces of meat". -- Coneslayer (talk) 15:49, 13 December 2007 (UTC)

Keep in mind that the fluid ounce is a measure of volume, not weight (or mass), so bringing liquids into the discussion will only confuse things. I thought grain was used in the pharmaceutical industry, but the article only mentions bullets and gunpowder. --LarryMac | Talk 15:59, 13 December 2007 (UTC)

Replying to myself to mention that the grain article does mention a few other applications. Also, the Apothecaries' system (apparently obsolete) used grains. --LarryMac | Talk 16:03, 13 December 2007 (UTC)

The weight measurement term "grain" is only used in gunpowder and not other places is due to two reasons: 1) it is a very minute measurement, so its applicability is not very wide, and 2) it is archaic because it is part of the old English measurement system, so that with industries such as pharmaceuticals, chemicals, and such the more modern use of grams prevails.

Slight correction, from a frequent user of the 'American' system. Grains are used to measure the weight of the bullet, not the powder. You could of course measure the powder in grains if you wanted to, but when you see ammunition specified, the weight in grains is the weight of the actual projectile. --66.195.232.121 (talk) 16:46, 13 December 2007 (UTC)

Grains are very commonly used to measure power, also. But yes, when you buy the box of ammo that says "180 grain JHP" they're referring to the bullet weight. Friday (talk) 20:22, 13 December 2007 (UTC)

As far as using decimals, Coneslayer is correct for most of the time. However, decimals used in weight in regards to pounds or ounces is actually very prevalent in grocery stores in the U.S. This is due to the labels on food items. Canned goods often will use decimals (such as 10.5 ounces), and packaged fresh meat in the butcher section will also use decimals with pounds (so you'd find the label on a packaged pork roast say 5.35 pounds). However, in normal conversation what Coneslayer said was much more common - that people don't talk about pounds in terms of decimals, but rather in terms of fractions, or in conjunction with pounds and ounces combined. So for instance, one would say "a pound and a half", or "one pound eight ounces", which is of course the same thing as 1.5 pounds... Saukkomies 11:22, 13 December, 2007. (UTC)

You'll order a pound and a quarter of meat from the butcher, but what you'll get is 1.25 pounds of meat, because the scale he uses measures using decimals. --Carnildo (talk) 23:10, 13 December 2007 (UTC)

"Grains" were definitely used in pharmaceuticals (and not just weaponry). The standard aspirin tablet in America is the "5 grain" aspirin which is now described as a 325 mg tablet. Take a quarter of that and you get the low-dose aspirin tablet originally used for children and now used for cardiac care. And that is how that aspirin tablet came to have its weird 81 mg dosage; it's really 1.25 grains, 1/4 of a standard 5 grain pill.

Atlant (talk) 17:59, 13 December 2007 (UTC)

In the US you'll rarely hear "grains" used as a form of measure. I'd bet at least half of Americans don't even know that it's a form of measure. However, as far as "pounds" goes, Americans often mean Pound-force, instead of Pound (mass). For example, we in the US often hear phrases like, "If you weigh 120 pounds on Earth, then on the Moon you'd weigh 20 pounds." That's only true if you're talking about pounds as a force, because that is affected by gravity. -- HiEv 00:06, 15 December 2007 (UTC)

Who discovered that Armadillos have identical offspring and how did they do that?

In the article on Armadillos it says they reproduce by Polyembryony in which they typically have 4 babies per litter and they are each genetically identical, like identical twins. I am curious, who made this discovery about armadillos and how was it done? It seems like this is the kind of thing that wouldn't be possible to learn without the use of modern genetic science techniques. I really want to know who and how they discovered this characteristic in armadillos and particularly what got them looking in that direction; what made them even think of looking into that possibility?

Zescanner (talk) 15:52, 13 December 2007 (UTC)zescanner (Jeff in Arkansas)

• This isn't an answer since I am not a historian of armadillology, but this does not seem particularly weird to me. If you've ever seen a litter of puppies, you know that they can be very different individuals right from the start. Presumably anyone caring for captive armadillos (zookeepers, zoologists, etc.) would notice the striking lack of individualism in a given litter. You don't need modern biochemistry to do genetics research, as history of genetics will attest. --Sean 17:50, 13 December 2007 (UTC)

It was discovered by HH Newmann and JT Patterson, reported in a number of papers in the early 20th century, the first being "A case of normal identical quadruplets in the nine-banded armadillo, and its bearing on the problems of identical twins and sex determination" Biol. Bull. Vol. 17 No. 3. This was, obviously, before modern genetic sequencing was available, so how did they discover it? To quote the authors, they "had the good fortune to secure four embryos... from an adult female [and] found four placentae enclosed in one amnion" [2] They went on to secure further gravid females and found that is typical (though on further investigation there is actually four amnia, but all are enclosed in one chorion). I think, as with much science, the discovery was a fortuitous result of their studies into embryology, rather than asking that direct question. It was almost 90 years before the discovery was confirmed genetically (PMID 9025312). Rockpocket 18:32, 13 December 2007 (UTC)

I suppose that the fact that the four offspring are always of the same sex might have been a hint. -Arch dude (talk) 00:16, 14 December 2007 (UTC)

Sherbet and Water

what is the scientific explanation when you mix sherbet with water?195.234.48.50 (talk) 16:15, 13 December 2007 (UTC)

Melting? I'm not really sure what you're getting at—does something unusual happen that you're referring to? -- Coneslayer (talk) 17:49, 13 December 2007 (UTC)

When you add water to sherbet, the citric acid and bicarbonate of soda dissolve. When they're both dry powders, they can't really interact, but when they're both dissolved in the water they can 'get at' each other. So, the citric acid and the bicarbonate of soda react with each other to produce sodium citrate, water and carbon dioxide. The carbon dioxide (being a gas) bubbles out of it, making it fizz. Which is really the point of sherbet: originally sherbet powder was made to be mixed with water to make a fizzy sherbet drink. The carbon dioxide that bubbles out of sherbet to make it fizz is the same stuff that makes a fizzy-drink fizz. Skittle (talk) 18:08, 13 December 2007 (UTC)

Oh, I found this website that might be helpful to you :) Skittle (talk) 18:11, 13 December 2007 (UTC)

Ah, I only know about Sherbet (U.S.), which is not the same as sherbet. That clears things up. -- Coneslayer (talk) 18:21, 13 December 2007 (UTC)

No - the British "sherbet" is not at all the same thing. In the US, sherbet is synonymous with 'sorbet'. In the UK (and possibly Australia and/or NewZealand) it's a kids candy - it's most often seen as a dry white powder that can be mixed in a drink - or (more often) sucked into your mouth through a licorice 'straw' in a thing called a 'sherbet fountain' or stuck onto a lollypop and sucked off in a "sherbet dab"...actually, there are dozens of uses for this stuff in kid's confectionary. It's weird that it doesn't seem to have ever made it into the US market...although 'pixie sticks' may be similar stuff but in vivid colours. SteveBaker (talk) 05:12, 14 December 2007 (UTC)

Origin of Life

Did life begin and go completely extinct more than once on earth?--76.28.67.224 (talk) 19:43, 13 December 2007 (UTC)

There is no evidence for this. Certainly since the Ediacaran life has had a continuous presence. In the Cryogenian period life could have almost disappeared, but there was not much as we know it back then, and something probably survived - eg hydrothermal vent bacteria and blue green algae. On the Creation theology side of things God created the Universe, sea creatures and Humans, everything else was made, but at no point was all this destroyed (yet). Graeme Bartlett (talk) 20:18, 13 December 2007 (UTC)

If you accept the genetic evidence underpinning the last universal common ancestor theory then all currently existing life is related to each other and share a common heritage going back 3.5+ billion years. There is no evidence for life ever having arisen independent of the currently existing group, but we also can't exclude it. Dragons flight (talk) 20:35, 13 December 2007 (UTC)

Paul Davies has recently suggested in the magazine Scientific American that life evolved more than once independently in earths history and such life forms may still survive today even in our own bodies.[3]--Fang 23 (talk) 21:11, 13 December 2007 (UTC)

Did life begin and go completely extinct more than just once on earth?

I must have missed it (in which case nobody reads this stuff anyway)...

Do we have an article on the male equivalent for parthenogenesis ?

Help, I am an endangered species! Cookatoo.ergo.ZooM (talk) 22:05, 13 December 2007 (UTC)

I think the answer to this question is an overwhelming NO. The smaller life is, the higher its population, once the first chemicals could replicate themselves it would be nearly impossible to stop life because it would exist in the oder of billion billion billion billions. The only way to do it would have involved completaly changing the enviroment of the entire planet extremely significantly (a whole orbital change).--Dacium (talk) 00:52, 14 December 2007 (UTC)

Well, a burst of gamma radiation from a nearby supernova might do the trick in wiping out all life on a planet. -- HiEv 00:16, 15 December 2007 (UTC)

Paul Davies suggestion implies that the alternate form of life did not go extinct. For this to exist it would have to be a lifeform not recognised so far. Perhaps a mineral form or nanobe would be in this category, but as I said above there is no evidence of it. Graeme Bartlett (talk) 02:28, 14 December 2007 (UTC)

I don't think we can know this. We don't have fossil evidence going back far enough to see even the first emergence of life. If life appeared, was eradicated, then restarted from scratch, it would have to have happened LONG before we run out of fossil evidence. Actually, I rather suspect life did start more than once...but it depends on your definition of "life". Current theory says that in the early oceans (or perhaps underground), a DNA/RNA-like molecule simply happened out of nothing from random reactions of Amino acids (which we know from countless experiments can appear in early-earth conditions). So here is the question: Did the very first self-reproducing molecule (which we would define as "life") become so spectacularly successful that we are all descended from it? That seems unlikely to me. It seems to me that there must have been some false starts - a molecule that could reproduce made a few hundred copies of itself in the warm summer sun - then when the water cooled in the winter, it fell apart and "died". At that early stage, that would constitute the spontaneous creation of life - followed by it's extinction. I could EASILY imagine this happening many, many times before a molecule that was robust enough to survive an entire year - a decade, a century...would happen to emerge by pure luck. TECHNICALLY - this would fulfill the OP's conditions - life arouse - life went utterly extinct - life reappeared and evolved into us. What I find much harder to believe is the idea that life would emerge - evolve to the state of (say) 6" long fish - and THEN go extinct. That's a tougher sell. But this is all speculation. We'll never know. SteveBaker (talk) 03:39, 14 December 2007 (UTC)

On the other hand, if life did evolve to those 6" long fish, then go completely extinct, then I beleive it would have been cause by one of those armageddon-like catastrophes (you know, giant meteor, lava all over the surface of earth) so it would destroy all traces of those fish and we'd have no way to know about it. – b_jonas 10:49, 14 December 2007 (UTC)

Well, yes - but it doesn't matter - we can't see back that far anyway. Even if they had formed fossils and NOT be catastrophically erased, the oldest fossils we have are not even close to being old enough to show these hypothetical creatures...they've all been eroded away or subducted as a result of plate tectonics or whatever. SteveBaker (talk) 17:03, 14 December 2007 (UTC)

That's not entirely true. There is a large period of time between say 600 Ma and 2.5 Ga where there are still plenty of reasonable rocks and no macroscopic fossils. Maybe you could invent and destroy fish very early in Earth's history without leaving evidence, but for much of the history of the planet we can say with confidence there were no fish. Dragons flight (talk) 17:18, 14 December 2007 (UTC)

werent there small worm fossils from 1 billion years ago?--76.28.67.224 (talk) 14:18, 30 December 2007 (UTC)

Biology

what are bacterial STDs —Preceding unsigned comment added by 147.226.243.137 (talk) 20:50, 13 December 2007 (UTC)

Have you tried Sexually transmitted disease#Bacterial? -- Coneslayer (talk) 21:02, 13 December 2007 (UTC)

Black cats

What breeds of cats would black cats be? —Preceding unsigned comment added by Heegoop (talk • contribs) 21:19, 13 December 2007 (UTC)

Many breeds of domestic cat can be black. Probably the most common in the US is the domestic shorthair. ike9898 (talk) 22:24, 13 December 2007 (UTC)

Actually, our article on domestic shorthair cats says that they are not really a true breed. ike9898 (talk) 22:27, 13 December 2007 (UTC)

There is a relatively new breed called the Bombay that is all black and was developed to look like a miniature black leopard. Our article isn't very good, so check out Bombay cat on google for better information.--Eriastrum (talk) 23:09, 13 December 2007 (UTC)

• "The black cat is a feline whose fur is uniformly black. It is not a particular breed of cat and may be mixed or of a specific breed." Now there is the Bombay (cat) pure breed, which is pretty consistently black, but like most pure breeds, this is a very small proportion of the population -- the breed formation process didn't begin until the 1950s. Among the major breeds there are two big contributors to the black population, AFAIK: (1) many Bicolor cats are overwhelmingly black with small white patches, and (2) Tortoiseshell cats can be primarly black with orange/brown hairs. --M@rēino 16:54, 14 December 2007 (UTC)

Ex Vivo In Vivo?

According to our ex vivo article, ex vivo is usually in vitro. This implies that it's sometimes in vivo. Would an in vivo ex vivo experiment be taking something out and putting it a) back in or b) in another animal? --Seans Potato Business 22:52, 13 December 2007 (UTC)

Not exactly. By saying an ex vivo experiment is usually in vitro, means that sometimes you can have an ex vivo ex vitro experiment. Good examples of this are in silico and, to a lesser extent, in situ. (EhJJ) 23:35, 13 December 2007 (UTC)

I'm not sure one would say that an ex vivo experiment would also be in silico. I would say these are generally considered be mutually exclusive (either an experiment is done on dissected tissue or on a computer, but not both.) In situ experiments are a good example, though. Rockpocket 00:30, 14 December 2007 (UTC)

Symptoms and side effects

A long time ago, I was given a medicated cream to treat a fungial infection. The major symptom of the infection was dry, cracked skin, and the main side effect of the medicine was dry, cracked skin, which made the decision of when to stop treatment a bit exciting. Are there any other situations where the main symptom of the a medical problem and the main side effect of the treatment are the same? --67.185.172.158 (talk) 23:02, 13 December 2007 (UTC)

One example: a major symptom of insomnia is being tired, especially in the morning. The major side effect of taking sleeping pills is feeling tired, especially in the morning. --NorwegianBlue ^talk 23:25, 13 December 2007 (UTC)

I just recently saw someone point out that one of the side effects of aspirin can be pain and headaches.[4] -- HiEv 00:35, 15 December 2007 (UTC)

Global warming and over population

Which is a bigger problem global warming or the amazingly fasting growing population?--Sivad4991 (talk) 23:21, 13 December 2007 (UTC)

Thanks for asking the question. Overpopulation is the direct cause of the changes in climate. I find the trend now to put such great emphasis on climate, and so little emphasis on overpopulation, somewhat depressing. --NorwegianBlue ^talk 23:28, 13 December 2007 (UTC)

This article "Is Anyone Listening?" by Isaac Asimov might interest you. --NorwegianBlue ^talk 23:39, 13 December 2007 (UTC)

They're related but not exactly the same thing at all. Per capita the most populous countries produce far fewer greenhouse gases, etc., than do Western countries of less population but much higher energy consumption. See, for example, per capita carbon dioxide production; China and India don't even make it on the list, even though in terms of raw numbers they rank much higher (but still below the US). To blame all of climate change on overpopulation neglects the fact that there is not a direct correlation between population size and energy usage, it's a bit more complicated than that. If the US population suddenly jumped by 10% it would use a lot more energy than if the population of India jumped by 10%, even though in terms of raw bodies the US jump would be much smaller. --24.147.86.187 (talk) 23:43, 13 December 2007 (UTC)

They are both problems - but there isn't much doubt that global warming is the more urgent. If we don't get serious about it, global warming will become totally disasterous within a couple of generations. Population growth is currently running at 10% per 100 years - and that rate of increase is slowing down. What is encouraging is that the more developed countries have decreasing populations - and the population boom in India and China is levelling off. The massive boom is actually in Africa - which is unfortunate because that country is the most severely lacking in resources to support more people.

Supporting large populations in poorly resourced countries is something you could fix with limitless energy supplies - one hopes that what comes out of solving global warming will be better ways to produce energy cheaply and safely. If you have energy - you can build desalination plants - then you can irrigate fields - then you can use intensive agriculture - and then Africa's population can grow without consequences that are too serious. But the energy problem has to be fixed before that.

But without doubt, if the earth's population was 1% of what it is now, global warming wouldn't be a problem - we could all pollute all we wanted and the planet would hardly notice. But I think it's possible to solve global warming without having to address the population problem - so that should certainly be our priority. There are really no downsides to having a planet with 1% of the present number of humans - the problem is how to get there from here.

SteveBaker (talk) 00:08, 14 December 2007 (UTC)

Asimov wrote how he feared that the problem of going to get there from here will be solved:

“ And as the population increases, as people crowd together more closely, as people find they can only get a smaller and smaller part of a pie that does not increase as the numbers do (but decreases in many ways), there will be increasing alienation, increasing refuge in drugs, increasing crime, increasing chance of war. In short, the world will become ever more violent. Every one of these changes, which come about more or less directly because of the ever-increasing population, will serve to raise the death rate. There will be increasing starvation, and bodies weakened by undernourishment will be more prone to disease. There will be more deaths by violence. In short, the Four Horsemen of the Apocalypse (Famine, Pestilence, War, and Death) will ride the Earth.

This might seem a natural way to make overpopulation self-limiting. It will seem an automatic cure -- but what a horrible cure it will be. Surely, the alternative of a deliberate effort to lower the birthrate is far preferable. But is anyone listening? Does anyone care?

”

--NorwegianBlue ^talk 00:52, 14 December 2007 (UTC)

If that 1% were Americans then it could still easily be an issue in the long run. America only makes up 4% of the current world population and yet out-pollutes in both raw numbers and per capita every other country on the globe. --24.147.86.187 (talk) 00:23, 14 December 2007 (UTC)

(Edit conflict): I would like like to reiterate that IMO the core of the problem is overpopulation, coupled with a very uneven sharing of wealth. The CO2 that contributes to global warming is produced by human activity, and it is a problem because there are so many of us. Sure, much more CO2 is produced per capita in rich countries, which tend to have lower birth rates. In a utopian future society where developing countries had caught up in wealth, their birth rates would probably also have lowered, leading to a stabilization of world population. Their CO2 emissions, of course would have increased dramatically. And world population would stabilize at a level disastrously high, climate being but one of the victims. I read Asimov's essay "The Power of Progression", on which the article I linked to was based, as a youth, and it made a great impact on me. I fully agree that harsh measures must be taken to limit CO2 emissions. I believe that even harsher measures are necessary to control the population explosion. --NorwegianBlue ^talk 00:26, 14 December 2007 (UTC)

Sorry, but you are claiming that population and CO₂ emissions correlate and they don't, which is my point. The problem is not that there are "so many of us" but that "we have become incredibly energy dependent—some far more than others—and we derive this energy from really unpleasant sources." Population size is a variable here but not the primary one—many places with very large populations (Africa) don't have correspondingly high emissions, and many places with relatively small populations (the United States) do have high emissions. Appealing to a "utopian future society" doesn't really convince anyone of anything. I don't mind Asimov but come on, the man isn't gospel. The question of the relationship of population to crime, wealth, emissions, etc. is more complicated than anyone can just gesture at and expect to be compelling. I'm not saying that overpopulation isn't an issue—obviously it is—but claiming it is the only issue of note is hyperbole and not well thought-out, Asimov or no Asimov. Overpopulation is not the driving force of all the world's ills, sorry. The world is more complex than that. (Or put another way: If you want me to be compelled, cite some stronger reasoning/evidence than just repeating what Asimov wrote over a decade ago. People have been writing about overpopulation since the 19th century, the sky hasn't fallen in yet.) --24.147.86.187 (talk) 02:24, 14 December 2007 (UTC)

• I made no statement about correlation in the previous post, I made a statement about causality. If I were to make a statement about correlation, it would be that CO2 emissions correlate with wealth×population.
• I'm well aware that people have been writing about overpopulation since the 19th century. Whether global warming should be classified as "the sky falling in" appears to be a matter of debate. --NorwegianBlue ^talk 09:20, 14 December 2007 (UTC)

Growing population is arguably not a problem now. I believe the UN predictions are for the world population to peak at 12billion at 2050, most growth in 3rd world counteries. Many first world counteries (especially in europe) are already declining population numbers, as first world people tend to have significantly less children. What IS the problem is the polution in general. For example if everyone that were alive today used resources and poluted the way the average americian does, the resources and world would be destroyed very quickly. This is why polution is a concern, because if most of the population 'develops' to match america we will have a huge pollution problem. We already have enough population to cause this problem. Even if the world capped at 7 billion people the pollution problem from devlopment of most of the world would cause huge enviromental problems.--Dacium (talk) 00:41, 14 December 2007 (UTC)

I fully agree with the statement "Even if the world capped at 7 billion people the pollution problem from devlopment of most of the world [to match America] would cause huge enviromental problems." For the very same reason, I find little comfort in predictions of world population stabilizing at 12 billion in 2050. --NorwegianBlue ^talk 01:05, 14 December 2007 (UTC)

If overpopulation was solved thoroughly enough, it would eliminate global warming, in addition to solving the other problems associated with overpopulation. The reverse, however, is not true, in that just solving global warming alone wouldn't help with the other problems associated with overpopulation. So one could argue that overpopulation is the bigger problem, in that if you could ask a magic genie to fix just one problem, it would make more sense to ask for a (deathless, magical) large reduction in the world's population, rather than to ask for greenhouse gas concentrations to return to preindustrial levels.

Another reason that overpopulation could be viewed as the bigger problem is that it's probably harder to solve painlessly than global warming is. Global warming can probably be solved by technological means and political willpower by a small fraction of the world's population working on the problem. Overpopulation could be helped somewhat by improving access to family planning and reproductive health care and information, eliminating incentives to have larger families, public education about the consequences of continued population growth, and improving access of women to education and economic opportunities. But really substantial population reduction in a painless way would involve most people in the world choosing to have fewer than two children. It's easier to get a small fraction of the world's population to work toward a goal than it is to get most people in the world to work toward a goal. Plus, people react a lot more negatively to a suggestion that they consider choosing to have only one child, than they do to a suggestion to replace their lightbulbs and buy a more efficient car. MrRedact (talk) 03:08, 14 December 2007 (UTC)

I disagree. There is evidence (look at the UN estimates below) that populations are stabilising as countries become more affluent. You can see that aside from Asia and Africa, populations sill stabilise and even fall a little by 2150. Asia is levelling out rapidly and only Africa is really growing at alarming rates. It seems likely that - just as with Asia - Africa would self-stabilise eventually. If the UN numbers are to be believed, I think the earth's population will stabilise and then S-L-O-W-L-Y decrease without any drastic measures at all. It's certainly not an urgent panic. The effort to bring populations down would be tremendous - it would require horrible laws that would breach ethical and religious behaviors. It's virtually impossible to get a simple law passed to limit automobile gas consumption in every country around the world...you think you'd get countries to agree to pass laws to halve their birthrate?...I don't thing so! We're going to need to sort out global warming LONG before we can attack the population problem. We need to reduce emissions by 40% over 20 years. You'd have to ban ALL human reproduction for an entire generation to achieve a 40% population reduction - and then how would the smaller population of workers support all of those elderly people? It would be an utter nightmare. On the other hand, switching power stations over to wind, solar and (mostly) nuclear, requiring a very do-able 40mpg average for cars and light trucks, requiring industry to cut emissions by similar amounts...it's hard - but it's very definitely do-able. We have to focus on solving the most urgent - and the most solvable problem first. The evidence is that the population problem may well fix itself. SteveBaker (talk) 03:25, 14 December 2007 (UTC)

Woahhh there. There is something severely wrong with those numbers. Dacium said: "UN predictions are for the world population to peak at 12billion at 2050" - there is simply no way that can be true! There are about 6.6 billion of us now - for the population to DOUBLE in 43 years is virtually impossible! This table is from our "World population" and is referenced as coming from www.un.org:

World historical and predicted populations

Region	1750	1800	1850	1900	1950	1999	2050	2150
World	791	978	1,262	1,650	2,521	5,978	8,909	9,746
Africa	106	107	111	133	221	767	1,766	2,308
Asia	502	635	809	947	1,402	3,634	5,268	5,561
Europe	163	203	276	408	547	729	628	517
Latin America and the Caribbean	16	24	38	74	167	511	809	912
Northern America	2	7	26	82	172	307	392	398
Oceania	2	2	2	6	13	30	46	51

So we'll only hit 8.9 billion by 2050 - and even by 2150 we'll only be at 9.7 billion. SteveBaker (talk) 03:10, 14 December 2007 (UTC)

I fully agree that it is urgently important to develop alternative energy sources, wind, solar and nuclear, and to limit CO2 emission from industry and transportation in whatever ways possible. However, when you write "We're going to need to sort out global warming LONG before we can attack the population problem.", I'm puzzled. In my view, much of what we have been discussing in this thread is whether we should treat the symptoms or the cause of the disease. I think we should do both. However, when I read the previous statement, it translates to "First, let's treat the symptoms and ignore the cause". You also write that "The evidence is that the population problem may well fix itself". I agree, one way or another it will. However, it may do so in very unpleasant ways. Therefore, I believe it is important to increase awareness that global warming and overpopulation are tightly interrelated. --NorwegianBlue ^talk 10:06, 14 December 2007 (UTC)

This is a reference desk, remember? Not a debate forum. --Anonymous, 16:04 UTC, December 14, 2007.

(You might think that but...)

It's not a matter of 'symptoms' and 'causes'. In the end (and I'm being deliberately vague about units and definitions) we have this "thought equation":

   GlobalWarming = PopulationSize x CarbonFootprintPerPerson

If we need to reduce global warming to (say) one quarter of it's present value in the next 20 years, we can either reduce the population to a quarter of it's present value (in 20 years) - or we can reduce the carbon footprint of each person by a factor of four over the same period (or some combination of the two). The problem is that if you attempted to fix global warming by reducing population, you simply couldn't do it fast enough without going out there with machine-guns and taking out 75% of the people out there. That would have to be 75% across-the-board too, you couldn't just take out 100% of the sick and elderly and all of the prison population and 30% of the other adults and leave the children alone. If you did that, the problem would come back again 20 years later when the kids are fully grown.

Even if you somehow prevented all human reproduction for the next 20 years, something like 70% of the people who are alive today would still be living - and you'd only have reduced the population by a third or so...nowhere near enough to prevent a global warming disaster. Cutting population by humane, acceptable means would take several hundred years - and we just don't have that long.

There simply isn't a way to solve global warming by attacking this particular root cause. We have to look at the other factor on the right side of the equation (which is just as much a 'root cause' as population size). We have to cut per-person CO2 production by a factor of four. This is also exceedingly difficult - but it's certainly not impossible. With care we can halve the amount of energy each person uses - better insulate our homes, have 45mpg cars, transport more goods by rail, waste less things that could be recycled, use less packaging, eat local food instead of shipping it, find better industrial processes, build "combined heat and power" schemes in cold parts of the world...you name it. And we can also try to halve the amount of CO2 we produce in generating that energy (carbon sequestration, biomass-fuels, nuclear, wind, solar). That's all do-able...although it's not cheap and requires politicians who are not invertibrates.

But killing 75% of the population just isn't going to happen and even the most draconian birth control measures won't make a dent in the problem in a reasonable time-frame.

SteveBaker (talk) 16:38, 14 December 2007 (UTC)

Taking heed of Anonymous' reminder that this is not a debate forum, it might be appropriate to return to the OP's question: Which problem is bigger, global warming or population growth? Since the two are interrelated, as shown by SteveBaker's equation above, the question needs to be rephrased to get a meaningful answer. --NorwegianBlue ^talk 12:47, 15 December 2007 (UTC)