Wikipedia:Reference desk/Archives/Science/2007 August 29

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[edit] August 29

[edit] Chill

Hi, what is actually (ie biologically) happening when one feels a chill running through one's body, or back or whatever? Thanks —Preceding unsigned comment added by 218.250.156.40 (talk) 01:55, August 29, 2007 (UTC)

First, what causes it... This is caused by the sympathetic nervous system, which triggers the fight-or-flight response. It is normally caused by the perception of something requiring the body to prepare for a fight-or-flight response, but can also be triggered by a minor chemical imbalance. The imbalance is normally corrected immediately, but the sudden rush of endorphins and/or adrenalin can cause chills, sweats, and goose bumps.
Now, the chill... As explained, the body is in fight-or-flight mode. One of the responses is to constrict blood flow through much of the body (preparing to need a burst of oxygen-rich blood in a moment's notice). That constriction flows across the skin and is felt as a "chill". This is normally accompanied by the other responses, but can be a chill with no other responses when caused by an imbalance. -- Kainaw(what?) 02:13, 29 August 2007 (UTC)

Thanks a lot! —Preceding unsigned comment added by 218.250.157.77 (talk) 01:41, August 30, 2007 (UTC)

[edit] Hollow moon

Is it true that the moon is actually hollow? --124.254.77.148 02:33, 29 August 2007 (UTC)

See Hollow moon. There are various advocates of this theory - eg. [1]. But I doubt that most terrestrial scientists take it seriously. -- JackofOz 02:39, 29 August 2007 (UTC)
Yes, Mighty Mouse ate all that delicious green cheese. Clarityfiend 03:50, 29 August 2007 (UTC)
If the moon were hollow, then:
  1. The moon would long ago have collapsed into the hole in the middle - and we'd be looking at a solid (albeit smaller) moon.
  2. There is no known mechanism for a large hollow body to form. What we know of planetary formation would not permit that.
  3. We have measured the vibrations of the moon from the impact of discarded a lunar lander crashing into it. The resulting seismic signals show a solid moon.
  4. The moment of inertia of a hollow sphere is wildly different from a solid sphere. Careful measurement of the moon's moment of inertia clearly prove that the moon is quite solid.
  5. The mass of the moon is easily measured from it's gravity. If it were hollow, the material which the skin of the moon would have to be made of would have to be insanely dense.
This is a really obvious nonsense theory. Why do people have to keep coming up with these things? Are the mysteries that we REALLY have not interesting enough for them?
SteveBaker 15:24, 29 August 2007 (UTC)
Perhaps it's because the real mysteries take the form of "Why doesn't the zero-point energy of the vacuum cause a large cosmological constant?". You can see how "the moon is hollow!" could hog the limelight. --Sean 19:35, 29 August 2007 (UTC)

[edit] Moon's moment of inertia

So, how has the Moon's moment of inertia been determined? It's not as if we could just apply some known force and measure what happens. --Anonymous, August 29, 2007, 20:08 (UTC).

Well...that's not exactly true.
I only know that the rotational inertia of the moon has been measured because hollow moon says so. But if I was an astronomer given the task of doing this I'd note that the moon is almost exactly tidally locked to the earth (ie the same face of the moon faces the earth all the time). That means that theoretically, the length of a lunar day and a lunar month ought to be identical. Yet we know that the duration of the moon's orbit is slowly increasing. As the orbital speed changes then the moon's rotation has to change to compensate for the orbital speed change. We know the size if the force that's doing that (the gravitational forces of earth and moon) - so we could measure the rate at which the orbital speed and rotational speed are changing (which ought to be fairly easy to measure since Apollo dropped laser reflectors onto the moon). So a known force (the tidal force) is being applied and we can measure what happens. But that's speculation. I don't know how they actually did that - I'm relying on Wikipedia (Dangerous!!) SteveBaker 21:38, 29 August 2007 (UTC)
Here is how they proposed to do it in 1977. SteveBaker 21:44, 29 August 2007 (UTC)
Well... it is exactly true. The tidal force isn't something "we" apply.
Regarding the first answer, you're talking about measuring the extent by which the change in rate of rotation speed lags behind very small changes in the orbit. I find it hard to believe that enough precision would be available th atway. As to the second answer, only the abstract of that article is available online free. It apparently refers to measurements based on effects of the orbit on a lunar orbiter. But that ought to be impossible; because the gravitational fields of a hollow sphere and a solid one of the same mass are identical, it would seem that such an experiment could only detect departures from spherical symmetry, not the distribution of mass by depth. I must admit that to having no idea what is meant by "C 22 gravity harmonics", though. --Anonymous, August 29, 22:18 (UTC).
The Moon is is tidally locked, but it still oscillates with a motion called libration. This oscillation would depend, I think, on the Moon's moment of inertia. -Arch dude 23:52, 29 August 2007 (UTC)
(Update) Ah, yes. A quick google for moon libration inertia gives a lot of papers that show that libration is used to measure inertis, and that are measuring things that are several orders of magnitude more subtle than a hollw moon would be. -Arch dude 00:00, 30 August 2007 (UTC)
Aha. I was thinking of libration only in terms of the apparent motion due to the difference between the essentially constant speed of revolution and the varying speed of the moon in its orbit, but that also causes a change to the angle of the tidal force, and that causes a real motion, and there we go. Thanks! --Anon, August 30, 02:15 (UTC).
I also wondered how the moment of inertia is measured by fine observations of satellites in lunar orbits. Surely a hollow shell would be indistinguishable from a solid moon as far as Lunar Prospector is concerned! Without having done the homework, I think it must work something like this: the moon's librations depend on its mass distribution in several ways. The amount of torque depends on how asymmetric the moon is, and the angular acceleration is the torque divided by the moment of inertia. You can see the librations from Earth and make very fine measurements without leaving home. But if you don't know how much torque is causing the librations, you can't calculate the moment of inertia. So you need the satellites to tell you how lopsided the moon is, and therefore how much torque is acting on it. That probably dominates the uncertainty on moment of inertia. (Just to repeat, this is an educated guess - my university doesn't seem to have an online subscription for reading those papers either!) --Reuben 02:40, 30 August 2007 (UTC)
The moment of inertia of a hollow sphere is quite different from a solid one - even if their masses are identical. For a uniform solid sphere it's 2mr2/5 and for an infinitely thin spherical shell it would be 2mr2/3 - for something which is hollow but not infinitely thin, it's somewhere between those two limits. So there is a huge difference in the two - even with fairly poor precision one would be able to tell the difference between the two. As noted in NASA's 'moonfacts' the measured moment of inertia is about 1% less than theory would suggest for a uniformly solid sphere. (A hollow sphere would have more inertia than a uniformly solid sphere. That means that not only is it solid - but it's also denser in the center than it is at the surface. SteveBaker 04:00, 30 August 2007 (UTC)
Are you responding to my post? I don't disagree, but I don't see how that relates to the question of how satellite tracking is sensitive to moment of inertia. --Reuben 06:51, 30 August 2007 (UTC)

[edit] Vision improved?

Something really weird happend yesterday. I went to the eye doctor and he told me my vision improved and its rare but he's seen it before in people that have improved their health (I went from 205lbs (30% bodyfat) to 165lbs (about 11% body fat) but I have never heard of this, is it really possible? I didnt believe it either at first but he gave me new contacts and I see very well with them. —Preceding unsigned comment added by 76.167.145.55 (talk) 04:03, August 29, 2007 (UTC)

Note that nothing said here may be taken as medical advice. Sudden worsening of vision has sometimes been found due to a high blood sugar from adult onset Diabetes [2] , [3],[4] , and with improved blood sugar levels, the vision has sometimes improved, if the vision changes were due to the effect of high sugar causing swelling of the clear tissues in the front of the eye (as opposed to the more permanent effects on the retina). Weight loss due to diet and exercise can lead to improved blood sugar levels. In any event, congratulations on having vision improvement rather than vision detriment. Edison 17:31, 29 August 2007 (UTC)
(to Anon) My vision has improved slightly in one eye over the past number of years enough that my prescription is off in an old pair of glasses. So you aren't unique here! Flyguy649 talk contribs 21:44, 29 August 2007 (UTC)
Near-sightedness (myopia) is common in the young, and far-sightedness (presbyopia) is common in older people. Thus, it's fairly common for those who are near-sighted in their youth to see their vision improve slightly with age. This happened to my brother, he was slightly near-sighted, then his vision was perfect for maybe a month, now he is slightly far-sighted.
Another possibility is that it's just an inability to measure your vision accurately. Since they rely on the "which one is better" method, and I usually can't really tell between two adjacent settings, I might pick the worse setting of the two one time and the better setting of the two the next time, even though there was no real change. StuRat 04:18, 30 August 2007 (UTC)
In that situation, I tell the optician that I can't tell the difference. In fact, they usually phrase it as 'Which is better? 1, or 2? Or are they the same?' at my place. After all, no point in giving a potentially wrong answer to that sort of question. Skittle 14:31, 30 August 2007 (UTC)
My optometrist measures my prescription with a machine (that you look in with a picture of hot-air balloon in it) and then confirms it with the "which is better" - which is also for astigmatism correction. Flyguy649 talk contribs 13:27, 30 August 2007 (UTC)

[edit] Germans then and now

This is more of a historical-biological question. Are the physical characteristics of today's German people any different than that of their 11th century ancestors? I know some Germans that have dark hair, brown eyes, and very tan scan. I realize that not all Germans are tall with light skin and blue eyes, but I'm sure some sort of change had to take place over the course of a millennia. I guess it also depends on what area of Germany you choose and what the staple diet of the people was at that time. If they were underfed for example, they would be shorter because of a lack of protein and vital nutrients required for healthy growth. However, this is just a generalized question. --Ghostexorcist 07:25, 29 August 2007 (UTC)

((Probably an archeologist would be a good person to ask (or an anthropologist) - ie someone who studies skeletons of 15th century germans - maybe such people hang out on the humantities desk - I suggest you ask there as well..87.102.18.14 11:50, 29 August 2007 (UTC)))
I think geography is important more because of interbreeding with neighboring people. Those in northern Germany would tend to resemble Swedes, Danes, Finns, and Norwegians (blonde hair and blue eyes), while those towards the south would tend to resemble the French and Italians (dark hair and eyes). StuRat 04:08, 30 August 2007 (UTC)
I don't know much, but it's a fact that they were shorter. I'm not sure these are facts, but at least rumor has it that Frederic the Great, when recruiting his famous soldiers (the "Potsdam Giants" - in German simply "lange Kerls" = tall guys) only from people that were 1.80m (5"11') or taller, had some trouble finding enough (capable) people. Well, the population was also smaller, but still I don't think you'd have any trouble finding men of +1.80m in Germany nowadays. (No guarantee that this story is true, it's just hearsay; but the different size of people in the Middle Ages is an often talked-about fact; also see the linked article.)
What you're mentioning about dark hair, brown eyes, and tan scan, however, seems more of a genetics question. So apart from emigration of specific types and from immigration (not in extreme numbers since the 11th century... if you disregard the 20th century which has greatly changed the German population), the regional differences that you mentioned are important. Northern Germans come generally closer to the stereotype (tall, blond, blue-eyed - think of stereotypes about the Dutch or Scandinavians) than do South Germans, and I would speculate that this was even a bit more true before mobility increased dramatically in more recent decades and through WWII - though one can hardly stress enough that even in the North, the stereotype is far from being true in general. (For current numbers, this article might tell more, but it's not for free... But google tells us that "In Germany, among 6000000 school children only 31.80 percent had both blond hair and blue eyes..., while of the 75377 Jewish children 42 percent were of the ..... As the percentage of blond types among the Germans in Prussia is very high ..." - so, judging by the context, these may be figures from the 1930s). Happy googling... --Ibn Battuta 23:57, 30 August 2007 (UTC)
Comment. In my experience the germans aren't that tall..83.100.249.228 15:58, 1 September 2007 (UTC)

[edit] Biros!

Here's a stumper for you all. At work I enjoy using many different colours of biro. I have found that while the blue and black ink biros write well, the red ones don't write quite as well, and the green ones very rarely work. Why is this? Is it a different viscosity of the ink? Out of 4 green biros from 2 different batches, I have only just got 1 to write at all, and it doesnt write very well. Capuchin 09:08, 29 August 2007 (UTC)

Could it be that green is not a popular coulour, and that the biros sit around for ages on the shelf before you use it? Perhaps exceeding the shelf life. The same could apply for red. I noticed that no one steals a red pen, but the blue and black pens disappear fast. Blue and black are far more popular and would have a faster stock turnover rate. Graeme Bartlett 09:13, 29 August 2007 (UTC)
I'll snoop around and check tomorrow morning! :) Capuchin 09:56, 29 August 2007 (UTC)
I vote for Graeme Bartlett's explanation. The other point I'll note is that water-based pens (such as Biros) often write poorly on xerographic copies or printouts, owing to an overall fine coating of hydrophobic plastic toner materal on the printout. But I've never known that malfunction to be color-sensitive.
Atlant 11:39, 29 August 2007 (UTC)

This problem varies from make to make surely?87.102.18.14 11:41, 29 August 2007 (UTC)

Yes there are some good quality pens around that work. Also some workplaces have more problematic pens than others. The kind of workplace that buys 10000 biros at a time can have problem with aging biros. And the fine point pens seem to blockup more easily than the coarse tipped pens. Graeme Bartlett 14:49, 29 August 2007 (UTC)
I assume you refer to Ballpoint pen rather than the felt-tip variety. Except for the most expensive name-brand ones, they always seem to stop writing long before the ink is used up. I have tried the time-tested method of scribbling them back and forth on scrap paper while muttering (usually ineffective), using centrifugal force by whirling/flipping them like an old mercury fever thermometer (often effective) and applying heat to the tip (rarely effective but often satisfying). The centrufugal force method might be more effective if the pen were attached to a motor to allow more effective centrifuging of the ink, forcing fresh ink around the ball to flush out the dried ink, but of course there is the likelihood of the attempt producing a line of sprayed out ink on anything within range (been there, done that), and/or a pen/projectile flying loose and causing injuries or damage. This has been discussed at Answerbag.com: [5]. [6] suggests storing biros vertically with the cap on, and running the tip across an eraser to force the stuck ball to roll and to clean the dried ink off the ball. Edison 17:18, 29 August 2007 (UTC)
erm had you tried licking the tip? - re wetting the dry ink? (I'm finding it difficult to resist advertising my favoured biro brand - which of course work down to the last mm of ink)87.102.18.14 18:17, 29 August 2007 (UTC)
(US readers may not appreciate that 'Biro' is the name of a company that makes cheap ballpoint pens. They have had such a longstanding dominance of the market that many people in the UK call all ballpoint pens 'biros' no matter who makes them.) SteveBaker 21:22, 29 August 2007 (UTC)
Except there is no such 'biro' firm, which an internet search confirms, perhaps you meant...87.102.14.233 08:22, 30 August 2007 (UTC)
In other words, a genericized trademark. Titoxd(?!? - cool stuff) 06:48, 30 August 2007 (UTC)
Not a company Steve, but the inventor, László Bíró. The company you're thinking of is Bic, but is not where the name comes from. I forgot to look this morning. I will try to remember tomorrow! Capuchin 08:32, 30 August 2007 (UTC)

Could it be the reason red and green pens "are shit" is because nobody needs red and green pens. It's a sort of reverse reasoning which perhaps someone could tell me the name of..87.102.14.233 09:55, 30 August 2007 (UTC)

I'm not sure this works for "biros", but at least for regular fountain pens (which are much better for the environment anyways, if you excuse me saying so) black and blue ink are in fact different, with the black ink eventually jamming the pen (I think the culprit was soot, but may be completely wrong). I don't think it would happen in the short lifetime of a "biro", but since we're not talking about the difference between black and blue anyways - there's at least a slim chance that some other ingredient would just jam the pens faster. I lean towards the simple explication of the expiry, though. --Ibn Battuta 00:04, 31 August 2007 (UTC)

[edit] Speedy Than Light

I read somewhere that Hawkings had discovered thermal radiations thats coming from Black Holes. Black Holes are huge masses that wont even let light go away from it. So does it mean that the particles in "Hawking's Radiations" has velocity more than of light ?

Oasa 11:33, 29 August 2007 (UTC)

No, the photons are generated exterior to the event horizon from vacuum fluctuations (This is a simplified explanation, but is an intuitive way to look at it). See Hawking Radiation. Capuchin 11:43, 29 August 2007 (UTC)
If you are interested in faster than light phenomena, check out faster-than-light and the theoretical tachyon. Capuchin 11:57, 29 August 2007 (UTC)
These particles are not travelling faster than light. The black hole's event horizon does prevent things that are moving no faster than light (that is to say: "everything") from escaping. What's happening here is that there is a peculiar process happening throughout the universe where (even in a complete vacuum) a particle and it's anti-particle may spontaneously pop into existance for no particularly good reason (See Pair production). Generally, this is irrelevent because they collide and cancel each other out shortly afterwards. However, if one of those particle pairs happens to pop into existance close to the event horizon of a black hole then before they get to annihilate each other, one of the two particles may stray across the event horizon while the other does not. This prevents them from cancelling each other out. Hence, one particle (like maybe an electron) shoots off into space (which it can do without travelling faster than light since it's already outside of the event horizon) - while a negative particle (a positron perhaps) falls into the black hole. This effectively results in the black hole "emitting a particle" - whilst simultaneously losing a small amount of mass. Seen from a distance, it's just as if the black hole is emitting random particles while gradually 'evaporating'. This is explained quite well in Hawkin Radiation. It's only a theory though - it's not proven and many cosmologists are skeptical about it.
(What I don't understand is why we don't get a random mix of (say) electrons and positrons being emitted - which would still cancel out. Also, if the black hole is absorbing a random mix of particles and antiparticles - how come it 'evaporates'?)
SteveBaker 14:16, 29 August 2007 (UTC)
For the evaporation, the article explains it quite well (although oversimplified): "In order to preserve total energy, the particle which fell into the black hole must have had a negative energy (with respect to an observer far away from the black hole). By this process the black hole loses mass, and to an outside observer it would appear that the black hole has just emitted a particle.". As for the still cancelling thing, i'm not sure that there's any reason for the emitted particles to come into contact and annihilate is there? Capuchin 14:21, 29 August 2007 (UTC)
Yeah - I already read that. It says it's true - but I don't understand why. Why couldn't it be the particle with the positive energy that fell into the black hole (resulting in the hole gaining mass and Hawking radiation being negative energy)? This would allow a black hole to grow by 'devouring the vacuum'! Energy would still be conserved. Personally, I'd expect it to be entirely random whether the particle or the antiparticle that fell into the hole - resulting in (on average) no net loss or gain to the mass of the hole - and the resulting radiation would be a random mix of positive and negative particles - which would (presumably) annihilate each other almost immediately. The result of which would be: No Hawking radiation - no black hole evaporation. If those particles and antiparticles didn't annihilate each other - then Hawking radiation would be a random mix of particles and antiparticles - but the black hole would not evaporate.
So why the asymmetry between particles and antiparticles? Why does the antiparticle get swallowed by the black hole in preference to the positive particle? SteveBaker 15:15, 29 August 2007 (UTC)
There's no asymmetry between particles and antiparticles: both come out. The asymmetry is between positive-energy and negative-energy particles of all types, including both electrons and positrons. Positive-energy electrons and positrons (and everything else) tend to escape, while negative-energy ones tend to fall in. There's no connection between having a positive or negative energy, and being a particle or antiparticle. --Reuben 16:54, 29 August 2007 (UTC)
OK, so Someguy1221 made a good point (and then self-censored it!): that story about a pair of particles, one with positive and one with negative energy, is itself quite suspect as an explanation for how Hawking radiation works. In fact, it might even be totally bogus. It is the most common non-technical way of explaining Hawking radiation, and if I remember correctly, Hawking himself uses it in A brief history of time. I can't claim to understand the "real" version, but I think I know enough to answer Steve's questions.
  • The possibly-bogus explanation involves negative-energy particles going in and positive-energy particles coming out.
  • There's no particular correlation between negative/positive energy and particles/antiparticles.
  • Particles and antiparticles come out in equal numbers (it's a perfectly thermal distribution, so you can write a partition function).
  • This last point remains true even in the "real" treatment.
Here's a paper if you want the "real" version: [7]. I only skimmed part of it; it's good, but this is not light reading. --Reuben 17:49, 29 August 2007 (UTC)


Surely the positive/negative energy particle explanation is an outdated one from Dirac hole theory. They can only exist for a short time due to the Uncertainty Principle. The reason we may see more particles than antiparticles coming out is that antiparticles will annihilate with the many particles that make up the universe, giving off photons. As to why the universe has more matter than antimatter, that is another, much more difficult, question. Cyta 09:28, 30 August 2007 (UTC)
That might be a reasonable explanation for why Hawking radiation would consist almost entirely of regular particles and photons - but it doesn't explain why the black hole would gradually 'evaporate'. Ingestion of more 'negative energy' than positive seems like the only way that could happen and I don't understand why that asymmetry would exist. SteveBaker 14:13, 30 August 2007 (UTC)

Well Thanks to All of you I simply cant understand everything you told. I am just in 12th Std.Please explain to me this in that way I can understand. I understand that a particle and an anti-particle is formed (like the way in which a neutron splits into positron and an electron) at the event horizon. So why dont the black hole attract both of them before one of them escapes. One More thing: Black Holes gets destroyed(evaporated), is there any proof ? I have read about special relativity but i still cant take to my mind that why cant the newtonian and gallilean principles be applied. Once More Thank you!! Oasa 03:27, 2 September 2007 (UTC)

The black hole can attract both particles in, before either escapes. But sometimes, one of them just very luckily gets out. Remember, even if it's only a teeny itsy bitsy bit from the event horizon, it can still get away if it's going fast enough. There is no experimental proof that black holes actually evaporate, as we have not yet devised a way to monitor the very dim emissions caused by hawking radiation from the distance to the nearest black hole (I'm not sure if it's even possible at that distance). Someguy1221 03:19, 2 September 2007 (UTC)
Thanks, yet the word "Fast Enough" it must fastr than C right ? and what about Special Relativity Does the White Holes Really exist. Has anyone seen White Holes ? White Hole and Black Holes are Part of wormholes. So does it mean that All the matter that Black holes absorb is released through white holes (may be absurd)? One of my friend said that it is theorotically proved that we can travel to future ? WHat is the theory called so that i can look for it ? Oasa 03:39, 2 September 2007 (UTC)
Fast enough doesn't mean faster than C, it just means really darn close. Remember, light can still escape a black hole if it's going the right direction, right up until it hits the event horizon. So something going just a little bit slower can too. Someguy1221 03:35, 2 September 2007 (UTC)
Well to start with, you can certainly travel to the future, all you have to do is...nothing. You're traveling into the future right now! As for white holes, we have an article on that, although I can't promise any of it will make sense. But no, those have never been experimentally proven to exist either, as none have ever been found. There is large uncertainty as to wether they exist, mainly from the inability of quantum physics and relativity to describe what happens at a singularity, like that in the center of a black hole. Some physicists interpret thegeneral relativistic analysis of a black hole's singularity as suggesting that the future of a particle within a black hole always lies towards the singularity, and once it reaches that singularity, the future of the particle must lie yet somewhere else, leading to the suggestion of white holes and wormholes. But again, relativity can't actually explain what happens in a singularity with certainty, so we can only conjecture, and you can read white hol at your lesiure. Someguy1221 03:51, 2 September 2007 (UTC)
Sorry! I didnt get you . What do you mean by saying that by travelling in right direction we can escape from the black hole? The question about Relativity is that why can the general principles be applied. If a person travelling (with a velocity v) in the opposite direction to light doesnt that mean the velocity of the light is (V+C) to the observer. I reread the article but still cant make-out.Can you help me in the Future-Travel I mentioned above. Oasa 03:49, 2 September 2007 (UTC)
Ah, it seems my response to your latter question landed above you in the database lockup and subsequent edit conflict. Anywho, when I say in the right direction, I mean that if a photon is headed straight for a black hole, it's going in. If it's headed straight out, it'll leave (I'm not sure of the best angle for escaping a spinning black hole, though, might not be straight out). For those angles inbetween, depends on how close the photon is to the event horizon and how big the black hole is. As for relativistic velocity addition, I'm not sure I can give you any better explanation than that it is derivable mathematically from the assumption that light's velocity has the same measure for all observers. You might want to start a new thread on that at the bottom, and maybe someone else can offer a nicer explanation. Someguy1221 03:56, 2 September 2007 (UTC)


I meant to a distant future or a distant past. So as per you, if we head in a particular direction if we head then we will be able to escape less than the escape velocity. Is that possible in Earth too (less than 11.2 KM/s). What is the possible explanation behind it ? For Relativity I shall start a new topic. Once again Thanks .... Oasa 04:10, 2 September 2007 (UTC)
Well, no one has ever formed a convincing theory of time travel, just lots of conjecture. Read time travel for more. As for the escape velocity...I find it instructive to ask people to think in terms of extremes...For example, you state that the escape velocity from the Earth is 11.2 KM/s, now, this would be the same whether the Earth is right where it is right now, or alone in some distant part of the universe, away from all other objects. Now, imagine you are one light year from the Earth. You are still affected by its gravity to a degree, but do you think you need to reach the same velocity to get away? The answer is no. Think of it this way: You take off from the Earth's surface at escape velocity, and as you get further and further, the Earth's gravity slows you down below what you thought was escape velocity, but you're still escaping! Escape velocity only applies to a particular distance from an object. So, while the escape velocity from a black hole may mathematically be C at the event horizon, the escape velocity goes down as you get further away from it. Someguy1221 04:18, 2 September 2007 (UTC)
Thanks and a lot of thanks. Now my doubt is almost cleared,actually I meant it from earth's surface, but still I cant understand by "direction".

One More thing if we are attracted by earth, we also attract earth and hence both gets an acceleration.but the acceleration of earth is very very small because of its huge mass. My question there are so many persons,objects etc so does earth accelerate in that direction in which the vector sum of all these gets.Another thing because of the attraction of sun and earth, earth accelerates but why doesnt earth fall on sun like we do by the atraction of earth. i.e. why doesnt earth accelerate in a st.line towards sun and fall on it. instead it does on eliptical orbits.And how does the orbiting prevent the fall.

Well, I'll make one more attempt to explain "direction." Imagine you take off from Earth's surface with escape velocity. Except, you accidentally point your rocket straight at the Earth? Gonna escape? You have escape velocity. Now, yes, quite correct, the net gravitational force is the vector sum of all the little gravitational forces from everything in the observable universe (and the big gravitational force from the sun). So, as surprising as it might be, the Earth is actually accelerating more or less directly into the sun. But why doesn't it get any closer!?! Try reading centripetal acceleration, and come back if you still have more questions, always welcome! Someguy1221 04:47, 2 September 2007 (UTC)


Tanks again. I appreciate your patience. Actually I was trying to say that does the escape velocity depends upon direction. i.e. Consider A rocket projected at 30 degree and another with 90 degree. Will the velcoity they need to escape from earth differ ? I read but still cant understand "why doesn't it get any closer!?! " Oasa 05:19, 2 September 2007 (UTC)

(de-indenting for readability) Well, for normal examples, it shouldn't. As long as you're not heading into whatever you're trying to escape, you'll escape. You'll just go in an ever largening spiral instead of going straight out. I'm not sure if this is true for black holes, if maybe there is a general relativistic effect that might make it work out differently (i'm very sketchy on GR, so I wouldn't know anyway). Now, since I think we answered your original question here, I think the other two should also get new sections. But to try and answer that last one, the result of a force is to accelerate the recipient of that force. To accelerate means to change one's velocity. In the case of centripetal acceleration, since the direction of acceleration is always perpendicular to the direction of motion, this never imparts energy (and therefore, change in magnitude of velocity) onto the recipient of the force, by the work formula: W = \bold{F} \cdot \bold{D} = F D \cos\phi . In fact, this is the same deal with spinning a tennis ball attached to a string about your head; once it's up and spinning, all you're actually doing is pulling it towards yourself, but as in the previous case, it never gets close. When accelerating an object perfectly perpendicular to its direction of motion, all you succeed in doing is changing its direction of motion. As a visual aid, imagine dropping a ball onto the ground, but from 1000 miles up. It falls straight down. If you throw it a bit, it'll land some distance from where you were hovering over. As you can imagine, the faster you throw it, the further it will land. If you throw it really really fast, it'll just take off and never come back. Now, try to imagine that there might be some inbetween, where the ball is just balanced between trying to fall and trying to get away. This is where things enter orbit (it doesn't have to be perfectly balanced. If it is not perfectly balanced, the orbit will be elliptical instead of spherical, and alternate between getting closer and farther from the Earth). I am appending to this section a nice picture of this. Someguy1221 05:39, 2 September 2007 (UTC) Image:Newton Cannon.svg

Thank You all of you here ends my doubt. Truly I understood everything.Oasa 03:29, 3 September 2007 (UTC)

[edit] What effect do creatine supplements have on insulin levels?

What effect do creatine supplements have on insulin levels? Creatine affects insulin levels but I'm not sure exactly how. Up or down. Can it cause diabetes or other problems? Also what impact does this have on blood sugar level? --Gosplan 11:55, 29 August 2007 (UTC)

Creatine supplements#Safety states that there are no known problems associated with the supplements, except possibly muscle cramping. Algebraist 13:03, 29 August 2007 (UTC)
Note that if you are looking for medical advice, people on Wikipedia are not qualified to give it: Wikipedia:Medical disclaimer -- 21:34, 29 August 2007 (UTC) —Preceding unsigned comment added by 72.33.121.200 (talk)

[edit] Network subscribers in South Africa

Hey Wikis, i was wondering if any one could tell me how many subscribers are listed on the mobile networks in SA(Vodacom, Cell C,MTN,Virgin Mobile etc)I have already searched on wiki so thanks for that info....Also what would you consider to be luxury features on a cellphone and which are a basic needs. Any added info on this topic would be appreciated! Crazypinkster 12:32, 29 August 2007 (UTC)

For me, I consider these to be basic features:
1) Having a directory of names and phone numbers with the ability to both call those numbers and display those names when a call is received (a version of Caller ID).
2) Phone should display the number of minutes/days remaining before it goes dead.
3) Should save a list of missed, received, and sent calls (dates, times, and names/numbers).
4) Should hold a charge for a long time and recharge at home or with the cigarette lighter in a car.
5) Cell phone should take and store phone messages. Ideally these should be stored right in the phone, as opposed to making you call some number to get your messages, but that would only work if you had free incoming calls.
6) Good reception everywhere I need to use it.
7) No "roaming" charge.
8) Silent ring (vibrate) option.
9) No ability for the government to track you down by your cell phone (it should be anonymous).
10) Callers should have to enter a code number (which I've previously given them) after dialing the phone number, or it should ignore the call. This would prevent drunken bastards from calling me at 3 AM unless I actually know them. (Alas, my phone lacks this feature.)
Unimportant to me:
1) Games.
2) Multiple ring tones.
3) Being small enough to fit into a wallet.
4) Color screen with fancy graphics.
5) Camera (I have a real digital camera).
6) Speaker phone (nice idea, but it's going to drain those batteries too quickly).
7) Not having any buttons (the iPhone).
8) Internet access (I don't want to squint at the Internet through a 2 inch screen.)
9) Text messaging (how is getting sore fingers by typing in hieroglyphics better than talking ?).
Unfortunately, to get most of the important things, I had to accept some of the unimportant things. I have a Motorola V170 with a Tracfone plan; not perfect, but fits my needs fairly well. I live in the US and don't know if either of these is available in South Africa. StuRat 03:41, 30 August 2007 (UTC)
  • Although the two are related, there is a difference between what your cell phone is able to offer and what your cellular network is able to offer. This is what confuses me about the OP's question: Are you asking about basic/luxury needs on a cell phone with regard to the networks, or in general? For example I don't know of any cell phone that takes a voice message on the phone itself, usually voicemails / messages happen when the call diverts back to the network (because your phone is off / out of range / you didn't answer it) and then the network puts the call through to your voicemail bank, plays your customised message (if applicable) and records a message, then, according to your account's settings will notify you of a message by sending an SMS/text.


  • Another example is the storing of SMSs/texts on the phone instead of the SIM card - some phones do this, others don't, and the phone's that do will usually have a setting.


  • South Africa's networks are actually great. There is a bit of a fuss that it's "So expensive" - and yes, when comparing the costs around the world South Africa's telecoms don't fair very well; but having compared the networks in South Africa and the networks in Australia, I'd have to say South Africa's are absolutely gold. Almost none of the networks in Australia have free voicemail (compare with South Africa where they all have free voicemail). In South Africa on Cell C you can recharge your credit for as little as R5 (approx. $USD0.65), on Vodacom for R12 (approx. $USD1.80) and the credit doesn't expire for at least a month - compared with Australia where almost all minimum recharges are $AUD29.00 (approx $USD24.00) (There are some exceptions, such as a $AUD10.00 (approx $USD7.00 recharge with Optus where the credit lasts for 7 days!). As far as I know, all networks in South Africa don't charge you to check your balance, and it's always easy to do such as punching in '#101*' - compare with Australia where you get charged for this on certain networks -- and you have to call a hotline to get the information


  • Strictly speaking, originally, "basic" functions of a cellular network and cellular phone was to simply be able to make and receive calls much like you would on a landline phone - it "rings" when somebody calls it, and you can also pick it up and dial a number. Of course this evolved, and you could store contacts on it. This evolved to being able to store more information on contacts, and of course ring tones evolved. ... Flash-forward to the future, and now phones do a whole host of functions: GPS navigation, graphics, games, internet functionality, cameras (something I'm very critical of with phones), etc. I would still rate all of those as "luxuries", but as technology develops the market will become to dictate that a phone should have certain things as basic functionality - for example it would be 'bad' if a phone would only allow you to store 7-8 SMS/texts (consider the Nokia 3310 that used only store about a dozen) - now phones store hundreds of SMS/texts. There also used to be phones that were only compatable with certain 'bands' of network range, and now most phones are 'dual-band' and are more compatable with reception.


  • But to answer what network capabilities are considered "basic" and which are considered "luxury", I'd like to think that checking your balance for free should be considered basic, voicemail should be considered basic (I'll compromise and say "even if you have to pay for it"), SMSs should be considered basic, call diverts are basic, etc.<br /.


  • I hope this has been of some help
  • Rfwoolf 04:11, 30 August 2007 (UTC)
I haven't managed to find anything recent on Vodacom and Cell C or Virgin. Rfwoolf 04:30, 30 August 2007 (UTC)
I'm a bit of a minimalist when it comes to phones. The number one feature I looked for in my present phone was the shape of the charger socket! All of my previous three or four phones - along with those of my family - have failed because the weird multi-pin charger socket wore out and the phone wouldn't reliably recharge. My present phone has lasted longer than any previous phone I've owned because it has a 'conventional' Barrel connector. So - the nature of the power connector has become my #1 requirement on a new phone! SteveBaker 14:03, 30 August 2007 (UTC)

[edit] Helium Baloons

How many helium baloons would i need to take off or glide with, if i had them attached in clusters around my armpits and the back of my heel? (kinda the same pose in the cartoon where that boy flies with the snow man )(You know the one....) —Preceding unsigned comment added by 81.76.125.193 (talk) 15:17, August 29, 2007 (UTC)

42 weather ballons full Gzuckier 15:57, 29 August 2007 (UTC)


Well considering im a 16 year old weighing no more than 10 stone ( unlike the 33 year old, truck driver) it should be significantly less... also how can i avoid air fines (bearing in mind i live about 10 miles from cottesmore airport) where would i get the weather baloons, and where would i get a parachute, in england *cough* nanny state *cough*? answers appreciated ... —Preceding unsigned comment added by 78.144.55.130 (talk) 17:24, August 29, 2007 (UTC)

If you seek manned flight, I recommend the safer, slower process of becoming a certified pilot. This way, you will learn the appropriate regulations that will prevent harm to yourself and others. The process can take as little as a few weeks or months, depending on how well you progress. Remember - aviation rules are not only there for your safety, but for the safety of others. Imagine if your lawn-chair-balloon contraption interfered with a commercial aircraft flight - you would be personally responsible for endangering other people. Do not violate local laws by operating an unregulated aircraft. Nimur 17:32, 29 August 2007 (UTC)
See Cluster ballooning. It's more dangerous than you think, so you're pretty much on your own figuring out how to do it. —Keenan Pepper 17:43, 29 August 2007 (UTC)
Ah, you see, the nanny state is everywhere, not just the UK. But seriously this sounds like a bad idea. A fall from 20 feet could kill you as would a strike from a Greater Black-Backed Gull (see below)Richard Avery 17:59, 30 August 2007 (UTC)
Bear in mind if you do this in the US in particular in or near a no fly zone you might find some fighter jets heading your way. And if you're near commercial aircraft, particularly if you're wearing a rucksack or you look foreign well let's just say you may find you trip rather short and the landing far faster then you had planned (of course you may already be in pieces so you won't care) Nil Einne 22:04, 30 August 2007 (UTC)


"The movie The Red Balloon, made in France in 1956, ends with a simulated cluster balloon ride as a young boy, having lost his magical red balloon to a gang of vandals, then finds all the other balloons in Paris coming to him." Hmm........ A gang of vandals? I'm not sure what that would be like outside of Wikipedia. Juanita Hodges 17:08, 31 August 2007 (UTC)

[edit] odd question - spin inversion

If a proton, neutron, or electron is isolated in space (ie no magnetic or electric fields) then the energy of the two spin states is equal (I'm assuming the answer to this is yes)

1.Is the spin here considered to be undefined (eg a 'supposition of states' or whatever language term used to describe 'unknown until tested') or is a particles spin fixed even though the energy between states is zero.

2.If spin inversion occurs the energy change is zero, but the spin change is 1 - does this mean that a photon of energy 0 is emitted - does this count as a non event?

3.(ignore depending on Q.1) If the spin IS fixed - what rules govern spin inversion here - is there a rate of inversion, is it allowed or forbidden.87.102.18.14 15:42, 29 August 2007 (UTC)

It would be in a superposition of states, and if there is no field, then the distribution should be equal. In order to check the spin, you would need to probe the particle, which would typically require an applied magnetic field. The spin can't really invert until it has been determined in the first place (so what you describe in (2) is a "non-event"); detection of any emitted energy would mandate that the spin is first measured (i.e. an applied field). Nimur 17:28, 29 August 2007 (UTC)
You have to be careful here. A spin-1/2 system can't be in an equal superposition of all spin states; every possible state vector describes some definite spin axis (see Bloch sphere). On the other hand, a spin-1/2 system described by a density matrix can be in a spherically symmetric state, namely 1/2 times the identity matrix.
Regarding the original poster's second question, a free electron or proton can't emit a photon (or any other particle) without violating the conservation of energy-momentum. As you say, the energy of the emitted particle would have to be zero. -- BenRG 21:24, 29 August 2007 (UTC)
You think there is a spin axis?? (like a direction in space?)?87.102.14.233 08:59, 30 August 2007 (UTC)
Hm? Yes, there's a spin axis. Electron spin is described by a spinor, which points in a particular direction like a vector does. -- BenRG 21:34, 30 August 2007 (UTC)
I thought it merely had value - are you sure? I mean it's easy to quote articles.213.249.232.202 06:16, 31 August 2007 (UTC)
What I mean to say is that given that the spin can be either 'alligned' or 'opposed' to the field (since it is quantised) a concept of direction is irrelevent. It is the field itself which has a direction. Do you agree?213.249.232.202 07:21, 31 August 2007 (UTC)
It's tricky to talk about this because of the lack of a good ontology for quantum mechanics, but the following is true: Any wavefunction describing an electron spin system can be interpreted as a direction (ray) in space. If you do a Stern-Gerlach measurement along the axis of the ray, you'll find the spin to be pointing in the direction of the ray with probability 1. If you measure along a different axis, you'll find one of the two axis-aligned states with probabilities related to the angle between the measurement axis and the ray. To put it in purely operational terms, when you prepare a spin system you choose a particular spatial direction, and when you measure it you choose an axis, and the transition probabilities are a monotonic function of the angle between the two. -- BenRG 11:22, 31 August 2007 (UTC)
Though I appreciate what you are saying.. Isn't it impossible to measure the spin 'off axis' - you need a field to observe it - and there is only one field. (and the percentage of spins aligned/unaligned would depend on their thermal energy, but could be affected by light - causing low to high spin energy transitions).87.102.88.202 14:03, 31 August 2007 (UTC)
Yes, you only get one chance to measure the spin of any particular electron, and you have to choose a particular axis before you do the measurement. What I said above has to be taken as a statistical property of an ensemble of systems or as a Bayesian confidence level. And I ignored all the nasty experimental details that real physicists have to worry about. -- BenRG 23:46, 31 August 2007 (UTC)

[edit] Discouraging collared doves from my bird table?

I got a bird table for my garden a few months ago (I don't only just feed the gulls any more!). One problem though - I have way too many collared doves coming down and eating way too much birdseed. As well as being easily capable of devouring a 10lb bag of seed in two days, they also chase the other garden birds away if they approach the table. These critters look cute, sweet and innocent but they have an aggressive streak towards smaller birds - and they'll even drive the magpies and crows away. Just about the only bird that isn't phased by them are my great black-backed gulls, which have absolutely zero interest in eating seed in the first place. They're seriously worse than the starlings when it comes to being mob-handed, winged hogs.

Does anyone know of a way that I might discourage the doves from feeding in my garden? I don't want to shoot, poison or otherwise kill anything - and I don't want to stop feeding the birds. Is there such a thing as a 'dove proof' feeder I can hang on the table? --Kurt Shaped Box 17:37, 29 August 2007 (UTC)

You can certainly invent complicated feeders that birds have to hang upside down from (or something difficult like that) which would discourage birds like doves that can't do that. You could also devise something where the perch that the bird stands on to get at the food is a counter-balanced lever that closes a door and shuts off access to the food to any bird that weighs more than the counterweight - this could be used to shut out large birds and let the smaller ones have access to the food. You could make a large clear plastic cube and put the food inside - then cut holes as entrances and exits that are too small for a dove to get into. SteveBaker 19:38, 29 August 2007 (UTC)
You have black backed gulls? Why not stop feeding those FEARSOME PREDATORS, let them get hungry and angry, then let them deal with the doves for you? —Preceding unsigned comment added by 84.65.105.7 (talk) 20:32, August 29, 2007 (UTC)
No! It's worse! These are GREAT black-backed gulls. SteveBaker 00:29, 30 August 2007 (UTC)
That's quite funny - the thought of these gulls actually motivating themselves to hunt, that is. If I stopped feeding them, they'd just go and hang out near the house of the next 'gull friendly' person on the street. Or they'd rip open my rubbish bags. A lot of people on my street like the seeing the GBBGs feeding up close - just look at the general size and impressiveness of them!, so they tend to be somewhat 'pampered'. --Kurt Shaped Box 09:27, 30 August 2007 (UTC)
Is this a very roundabout seagull question? >:|      :) --frotht 22:05, 29 August 2007 (UTC)
(It has seagull in it...I think it counts.) SteveBaker 00:29, 30 August 2007 (UTC)
or you could make a protective cover out of what we call 'chicken wire' or 'wire netting' in the UK. You can buy it in several different sizes. I would think 2 inch holes would allow the little birds in and keep the bigger birds out....sorry for stating the obvious. On a slightly related ornithological note, we had no collared doves in the UK in the 50s then a few were brought over from the US for a private aviary and now we are similarly plagued with the damn things. Do they taste good? Richard Avery 17:53, 30 August 2007 (UTC)
I'm in the UK too, dude! :) While cute, the collared dove is very, very annoying. I don't mind the screeching of nesting gulls outside my bedroom window, the chattering of magpies or the warbling of an overzealous song thrush early in the morning - but that constant, repetitive 'coooo coooo cuk' from the doves goes right through me like a dripping tap. It's worst in the summer when it starts getting light at 4am - there's no way I can sleep through that racket. I figure that if they were good to eat, they'd be finding their way into pigeon pies (wot? no article???) - which they don't seem to be. --Kurt Shaped Box 18:08, 30 August 2007 (UTC)

I have had neighbors with birdfeeders or who just throw food out to feed birds. The result is noisy birds when I try to read or watch TV and lots of bird crap all over. I say don't use bird feeders. Juanita Hodges 17:10, 31 August 2007 (UTC)

You could put a roof over the feeder so birds have to duck to get to the food. A balcony over the entrance is used here in Australia to deter some birds from using nesting boxes. Polypipe Wrangler 07:47, 1 September 2007 (UTC)

[edit] The American Dental Association made a vaccine to Streptococcus mutans and then patented it and sat on the patent so ensure dentists stayed in business???

My dentist told me that in dental school a professor claimed that in the 1950s, the American Dental Association made a vaccine to Streptococcus mutans and then patented it and sat on the patent so ensure dentists stayed in business. I've asked him about it and tried to find information confirming if this was true or not. Google only finds that some people are working on a vaccine. The Streptococcus mutans article's is vague on the idea of a vaccine and it's one source on that is some website that's unviewable unless you pay them a lot of month first. Juanita Hodges 18:30, 29 August 2007 (UTC)

If they patented it in the 1950s, that patent would be expired now. The patent would have always been public and whatever it covered would have long since become unprotected as well, so anyone (drug company, private or university researcher, etc) could work on making it. That's the whole model of the generic-drugs business—patent protection is quite limited and once something is patented it soon becomes free-for-all. DMacks 18:40, 29 August 2007 (UTC)
I would add that taking out a patent on something is in no way proof that it actually works. You can patent the most outrageous concepts whether true or not. People have FAR too much respect for the patent system. It's perfectly possible that this guy did indeed patent this - but that doesn't prove that a usable vaccine has ever existed. SteveBaker 19:32, 29 August 2007 (UTC)
A shame, since otherwise I'd be getting to work in a British Rail flying saucer. GeeJo (t)⁄(c) • 19:03, 30 August 2007 (UTC)
A patent is a bargain that society makes: you tell us how to do something neat, and we'll give you a temporary monopoly on making money off of it. There is no way to sit on a patent indefinitely, since that would break the inventor's side of the deal. You can try to get an extension, but not for 50+ years. For that, you need copyright. --Sean 19:46, 29 August 2007 (UTC)
And even then, copyright is not infinite. Well, at least not yet. Titoxd(?!? - cool stuff) 19:49, 29 August 2007 (UTC)
Trademarks, on the other hand, are infinite as long as they are still being used. But we digress. And please do not take this as legal advice! --Anonymous, August 29, 20:08 (UTC).
The pitiful article, Caries vaccine, points out that researchers are still working on a vaccine against tooth decay. It would be important to point out that although decay is still a very common problem treated in dental offices, you still have gum disease, root canal issues, trauma, cancer, and replacement of teeth that dentistry would still need to address even in the event of a 100% effective vaccine. ;) And those are the first things that come to mind. There are still many other problems. Thus, I, myself, am not too worried about dentistry staying in business. - Dozenist talk 00:05, 30 August 2007 (UTC)
Along that same line, there is actually a vaccine out for dogs now for periodontitis. It covers three different Porphyromonas species (see Porphyromonas gingivalis for the human version of the bacteria). --Joelmills 02:48, 30 August 2007 (UTC)
There is this article. As I recall, the biggest hurdle was the transfer of the bacteria by sharing glasses/kissing etc. Since you'd need a prescription to get the bacteria, you'd be giving it out illegally, or some other nonsense. In any case that is a place to start. I also did a Google search for "tooth decay bacteria genetic modification", and got some hits about modified sugar cane and other things along those lines. --Cody.Pope 10:19, 30 August 2007 (UTC)

[edit] Wind data

I'm looking for any sites with quantitative data I can use to show relationships between geographic features and/or seasonal variation with changes in wind speed. Any links would be appreciated. --Sopoforic 20:21, 29 August 2007 (UTC)

Google Search turns up some geographic sites on wind erosion? Might be of help SGGH speak! 21:14, 29 August 2007 (UTC)
Yes, but those are more geographical features created by wind than wind created (or channeled) by geographic features, although they both effect each other, I suppose. StuRat 03:05, 30 August 2007 (UTC)
this pdf also seems to have soem figures SGGH speak! 21:14, 29 August 2007 (UTC)
Well, I don't know about the World, but for the Great State of California, here's a place I drive by every now and again, their site with wind reports, http://www.energy.ca.gov/wind/overview.html --Jacobi am the kwisatz haderach 21:28, 29 August 2007 (UTC)