Wikipedia:Reference desk/Archives/Science/2007 May 31

= May 31 =

Aneurysm
It's sort of a weird question. The defecation article says sometimes blood vessels burst and people die from straining too hard. So do most aneurysm deaths happen in the bathroom? I think most people with aneurysms don't know they have aneurysms. Also, do people with aneurysms have to be careful about going to the bathroom? Coolotter88 00:32, 31 May 2007 (UTC)
 * Stating the obvious, but have you tried the Aneurism article? Some of your assumptions don't sound far fetched except perhaps for the first one, the article states that most aneurisms form in the anterior cerebral artery, with systemic hypertension as a leading contributing factor to development and formation of said aneurism. Vespine 03:33, 31 May 2007 (UTC)


 * It's not quite accurate to say that straining hard will cause a dissecting aneurysm. When aneurysms do occur, they have may nothing to do with straining, there are many factors involved, including multifactorial genetics, diet, blood pressure, age, &c. It is unlikely (though not rare) that an individual will form an aneurism at some point in their life, that is, a bulging of an artery. Some individuals live a long time with no symptoms, some live long enough to die of other things. And some people, unfortunately, end up bursting those bulges. Straining (though more commonly, the sudden trauma of, say, a fall or an automobile collision), does increase the likelihood of bursting the aneurism if it already exists, but doesn't necessarily make an aneurism more likely to develop. The blood vessels more likely to be damaged during defecation are veins. Veins around the anus are particularly susceptible to the formation of bulges, and these bulges are called varices or hemorrhoids. Straining may precipitate their formation, and further straining, or passing stool, may cause these bulges to rupture. Although this can be a medical emergency, it would only rarely cause death: the blood in the toilet is usually a clear signal to get to the hospital. The other relatively common morbidity associated with bowel movements is vasovagal syncope. Bearing down to defecate can stimulate the vagus nerve, which in turn slows the heart beat, which in turn lowers blood pressure, which then causes the individual to faint; and fainting people tend to hit their heads. tucker/ rekcut 16:03, 31 May 2007 (UTC)

educational
hello my name is ujas, i had passed my 12th science with mathmetics group from GSEB (gujarat secondey education board)  this year (2006-07). i would like to know that now in which field i should have to go now? i am a littelbit confuse about it ... i want to go in aeronautic engineerng but my parents wants me to go in mechanical engineering. so please guide me what should i have to do? and if you have any other good fields in which my carrrier can be more britter then please tell me. i am waiting for reply... —Preceding unsigned comment added by Ujaszaveri1989 (talk • contribs)


 * It's your life. Listen to yourself. Take advice, but not demands. -- Phoeba WrightOBJECTION! 03:56, 31 May 2007 (UTC)


 * Also, there would be a certain amount of overlap between mechanical engineering and aeronautical engineering, so if you're willing to put the effort in you may want to enrol in one of the two degrees, but take as many courses as you can from the other field as well, so that at the end of the semester/year you can decide whether you prefer one direction over the other, and possibly transfer across to the other stream. Confusing Manifestation 04:16, 31 May 2007 (UTC)


 * It's purely about interests. What do you like to do? What do you want to do? What do you want to learn to do? Etc. These are all factors. I know many many many people who spent 3+ years getting a degree and then realize that they don't like it, and then are stuck with it because of the time and money they invested in it already. That's not the way you should go. Your school's career services or councelling center should have tests that they administer to you to help you figure out what your interests are in. If you want suggestions, we would at least need to know more about your interests and your career goal (which reminds me, I have to get something similar done...). --Wirbelwind ヴィルヴェルヴィント (talk) 04:54, 31 May 2007 (UTC)


 * Hi Ujas. I'm just about to finish a four-year Master of Aeronautical Engineering degree, so I can sympathise with your dilemma. Aeronautical engineering is largely similar to mechanical engineering (you study most of the same principles, but they're applied to specific aeronautical issues, so for example where you'd study fluid flow in a mech. eng. course, you concentrate on aerodynamics and where you'd learn about dynamics of mechanical systems in mech. eng., you study flight dynamics). Your understanding of engineering principles should be reasonably similar at the end of the course.


 * I know quite a few mechanical engineering students and, in the UK at least, there seems to be a feeling that the aeronautical course is a bit harder - there tends to be more material to cover (since you have to learn the principles of engineering and the principles of aeronautics) and some of the mathematics in aero subjects can be pretty hard. On the other hand, the attraction of aeronautical engineering for me was in large part because I was very interested in aircraft. If you share that enthusiasm, it'll give you a better context to relate to and help to keep you motivated during long nights trying to get your head around turbulent flow modelling! Don't take on an engineering course lightly - it's brain-taxing hard work, a very large amount to learn and generally doesn't leave much time for socialising. You will need to be very confident of your maths, because you'll use it every single day and probably take it well beyond "high school" level.


 * Another factor you should take into consideration is career prospects. Mechanical engineering is sometimes perceived to be more widely applicable by employers (although in my experience if you can do the aero stuff you won't struggle to tackle mechanical problems). On the other hand, entry to specific aeronautical jobs may require an aeronautical qualification. So if you definitely want to work in the aircraft industry, aeronautical engineering may be best for you, whereas if you're not sure and want to keep your options open, mech eng. might be a safer choice. India has a rapidly-growing aeronautical industry so if you're set on a career with aircraft, now may be a good time to go for it. Aeronautical jobs tend to be restricted to a smallish number of locations so you may have to be prepared to move away from home to get the job you want; mechanical engineers, on the other hand, can usually find work anywhere there's significant industry.


 * On the whole, it's your decision to make and the course that's right for you will depend on your interests and aspirations. Take your parents' advice into consideration but try to make them understand that it's going to be you doing the work and your career at the end of it, so you have to be sure you're making the right choice for yourself rather than for them. Whatever course you study, if you become a qualified engineer you will be a respected professional and your parents will have good reason to be proud of your accomplishments. I wish you the best of luck for the future. --YFB ¿  05:01, 31 May 2007 (UTC)


 * Since this is an encyclopedia, you might want to look at the articles for engineering, mechanical engineering, electrical engineering, aeronautical engineering, and perhaps liberal arts (if only just for perspective). I recommend that you study something which will teach you valuable skills and open your career prospects; I think any engineering discipline can take you in whichever direction you want to go.  Work hard, Nimur 06:06, 31 May 2007 (UTC)


 * It's important that you do your degree in a subject that you have a passion for. It's a lot of work and a large chunk out of your life - if you don't enjoy it, you won't do well in it.  If you took a degree in aeronautical engineering and found that your parents were right and that all the good jobs were in mechanical engineering - then consider this: A really good grade in an Aeronautical Engineering degree would get you a better job in the Mechanical Engineering field than a poor grade in a Mechanical Engineering degree would - and if you are doing your degree in a subject that interests you - you'll get a much better grade than in a subject that you are studying "because you have to". SteveBaker 15:08, 31 May 2007 (UTC)

liver cirrhosis
Is liver cirrhosis a communicable disease or non-communicable disease? Or is it both? I'm not sure. PLEASE HELP! I need to know fast!!


 * See Liver cirrhosis. In short, it itself is a non-communicable symptom of other diseases. Some, like alcoholic liver disease are non-communicable, but certain communicable diseases can result in liver cirrhosis, for example Hepatitis B. Rockpock  e  t  04:35, 31 May 2007 (UTC)


 * 'Depends how many people you can convince to come to the bar/pub with you! But as Rockpocket mentioned, cirhossis can be a sequela to more-normally communicable diseases.


 * Atlant 13:15, 31 May 2007 (UTC)

Mugugudhu Tree? + plant ID
Alright, I keep seeing (multi-lingual) net spam involving a "Mugugudhu Tree", someone named Sipewe Mhakeni, and the spread of AIDS in Africa. When I google "Mugugudhu" all i get is 500 copies of this same spam or paraphrases of it. So ... What is a Mugugudhu tree???

Answer: I think that this may be a reference to Hlengwe word "Mugugudo" for the Tall Firethrorn Corkwood tree. Here's the link: http://www.zimbabweflora.co.zw/speciesdata/species.php?species_id=133310

On a (semi-unrelated) topic, is Texas mountain laurel the same sort of plant as the "mountain laurel" with white flowers in North Carolina? Vultur 04:32, 31 May 2007 (UTC)


 * Likely, it's bullshit -- Phoeba WrightOBJECTION! 06:02, 31 May 2007 (UTC)

Here's the link []. this article (from this or another news source) gets copied everywhere. WARNING: extremely disturbing. Vultur 14:12, 31 May 2007 (UTC)

Dream world & dog world
Ok, as I sit here watching my german shepherd twitch while she sleeps, "chasing rabbits " as my dad used to call it. I wonder if she dan differentiate between the "dream world" and the "real world"? I don't know or I wouldn't ask. Thanks 24.226.90.6 04:43, 31 May 2007 (UTC)Rana sylvatica
 * Since we can't ask, I'm pretty sure the best anyone can do is guess. Do you know a second language? Sometimes drawing an analogy between different languages can be a good exercise in comprehension. As in it can open your eyes to the fact that the way you do something isn't necessarily the only way to do it, in fact there may be vastly different ways, ways you would have never even thought of. A dog's mind would work in vastly different ways to a humans, it would be very difficult to even imagine how they conceptualise anything, let alone a dreams. It's one of the things that makes them so mysterious and interesting, they can be so like people, but so unlike at the same time. Vespine 05:00, 31 May 2007 (UTC)
 * I imagine that there can never be an effective translation between a human language and a dog language (if one even exists). Our ability to precisely define and work with abstract ideas is probably unrepresentable in the dog's mind (and thus, their hypothetical language).  Conversely, their ability to not distinguish certain things would lead us to conceptual quandaries (for example they may have a simplistic view of "fun", "exercise", "eating", and "survival", and may never be able to fully separate such concepts as distinct entities).  We have an article on animal psychology which you may find interesting. Nimur 06:10, 31 May 2007 (UTC)


 * Looking at that article, I'm quite surprised that there's no mention of parrots in the "Disorders of animal behaviour" section. Parrots are incredibly prone to psychological problems - they get depressed very easily, self-harm and can go completely psychotic. I'd write about it myself but most of what I know is anecdotal, based on personal observation or 'stuff I read a long time ago and can't remember where'. I have heard from parrot owners (apparently, Moluccan Cockatoos often have severe problems) with birds who've been prescribed antidepressants or valium. --Kurt Shaped Box 06:28, 31 May 2007 (UTC)


 * I often see and hear my 'indoor budgie' doing the same sort of thing at night. He twitches as he sleeps and sometimes he'll flick out a wing or make tiny murmuring noises. I lie in bed and wonder if he's dreaming - and what he's dreaming about, if he *is* dreaming. --Kurt Shaped Box 06:16, 31 May 2007 (UTC)
 * He's trying to escape my sleeping pointer.

--TotoBaggins 16:42, 31 May 2007 (UTC)


 * Sometimes he does really freak out at night - fluttering around the cage, banging into things and screeching until I turn the light on. It could be a nightmare - or it could just be that he's fallen off his perch and can't see to find his way back up. --Kurt Shaped Box 16:53, 31 May 2007 (UTC)


 * It's clear from the paws twitching - the tiny little barks and the chewing motion of the jaws that our dogs are dreaming about hunting prey animals. From an evolutionary perspective, it would probably be disadvantageous for those dreams to seem too real - so my bet is that it's the same as with humans.  Dreams seem to serve a purpose in allowing the brain to rearrange and recategorize memories - and if we can't dream, we become disoriented and forgetful - so this is a critical maintenance function for the brain.  The clear fact that other higher mammals and birds dream means that it's important at a pretty fundamental level.  But in humans, dreams are only 'remembered' if the subject wakes up in the middle of one (presumably because the reorganisation is incomplete).  I think of it as being something like 'defragging' a disk on a Windows PC.  Since there is nothing to be gained by dreams seeming real after the event, they are automatically forgotten as soon as they are over - but while they are happening, they seem real - so waking up in the middle of one leaves you in that weird half-and-half state where you have to think rather carefully about what you just dreamed in order to mentally flag is as 'garbage'.  But it's not obvious whether all animals have the intellectual capacity to do that.  It can't seem too real though - if you were just dreaming about having chased down a succulent young rabbit - and right before the good part some stupid human wakes you up - then perceptually, you just magically disappeared from that field with all the really good hiding places - onto the living room carpet.  I don't imagine that the dog would find that at all 'normal' so it would be clear that what preceeded the sudden jump must be nonsense.  From an evolutionary perspective, it would be wasteful (for example) if the dog thought the dream was real and spent a large fraction of the day going back to the field looking for the dead bunny. SteveBaker 14:57, 31 May 2007 (UTC)


 * I can't remember where I recently read this (some magazine or journal), but a study was recently done on dogs. They determined that dogs tend to dream of activities they had done that day.  The theory is that this happens in order for the dog to analyze its routine and make improvements, or improve its memory, or something.  I wish I could remember where I read that, it was an interesting article.  --Joelmills 23:47, 31 May 2007 (UTC)


 * Whoops, it was rats not dogs, and the study is actually quite old. It was done at MIT and showed that after performing an activity such as running on a track, rats replay the activity during slow-wave sleep. --Joelmills 04:23, 1 June 2007 (UTC)

John Kanzius's "salt-water fuel" claims
What's the deal with http://www.youtube.com/watch?v=4kKtKSEQBeI ? I searched for keywords like "radio frequency water dissociation" and "radiolysis" but couldn't find anything like it. There was a lot of stuff about pulse radiolysis, but that uses high-energy electrons from a linac, and there was a lot of stuff about radio frequency electric glow discharge plasmas, but that only happens in rarefied gases (certainly not liquids). Does anyone know what's going on here? Is it all just a hoax? —Keenan Pepper 07:17, 31 May 2007 (UTC)


 * Imagine how much electric energy is wasted to hydrolyze and then combust that hydrogen! This video does not provide any insight into how much electricity is used to run this gigantic machine (but it's probably summed up as "a lot").  Sorry, there is no free energy; only a series of energy conversions (from electric to RF to chemical and then to heat).  Furthermore, energy is lost in each stage.  Nimur 08:14, 31 May 2007 (UTC)


 * I also object to the word-choice of the narrator in this video. The salt-water never burns.  Water is dissociated into hydrogen gas, which bubbles out and then (the hydrogen) burns.  The salt-water is never combusting at all.  Burning hydrogen is nothing new; if anything, this whole video is just an inefficient way of making hydrogen.  Nimur 08:20, 31 May 2007 (UTC)
 * Maybe it's a new incarnation of a water fuel cell? DMacks 14:26, 31 May 2007 (UTC)


 * Whatever it is, it's either (in effect) just a very inefficient electric motor - or another over-unity perpetual motion machine - so it won't work because it violates at least one of the laws of thermodynamics. If it's the former, it's irrelevent - if it's the latter, it's a hoax. SteveBaker 14:41, 31 May 2007 (UTC)

Sorry if my question was unclear: My belief in the conservation of energy and the second law is unshaken, but I'm wondering if there's a new physical phenomenon here. I wouldn't have thought it possible for radio waves to dissociate water, because a single RF photon doesn't have anywhere near enough energy to break a covalent bond. On the other hand, if the RF is somehow accelerating the salt ions... it's not free energy, but it could be something interesting. —Keenan Pepper 18:55, 31 May 2007 (UTC)

I believe the "inventor" cretated artciles on wikipedia which were deleted as spam and hoax. It appears to be a money making scam. The only difference between this and the nigerian bank accounts that have millions of dollars in your name is that the nigerian bank accounts may actually exist. --Tbeatty 06:21, 2 June 2007 (UTC)

Interstellar travel - the best man for the job is an asshole?
Back to the 'sending a man to Proxima Centauri' idea. Considering that it would be a very long, lonely journey, wouldn't it make sense to select an astronaut for the job who was basically a self-centred, misanthropic loner? If you want a man to spend decades in space by himself, then surely someone with these qualities would be the ideal candidate? --Kurt Shaped Box 07:27, 31 May 2007 (UTC)


 * But then what is the point of sending that person there? To prove that we can do it and waste a few trillion dollars? --antilivedT 07:58, 31 May 2007 (UTC)


 * You might want to compare this with the sorts of crews on long, isolated science expeditions. Of course, nothing to date compares with a journey of that magnitude.  But a nuclear submarine can be away from port for weeks, months, and hypothetically many years.  Those crews are selected primarily based on skills and training, but with some care towards psychological and social factors.  Nimur 08:07, 31 May 2007 (UTC)
 * Even something like the more secluded Antarctic stations might give more insight. I think people who go there tend to be non-assholish.  Nimur 08:10, 31 May 2007 (UTC)


 * I very much doubt such a mission would use a one-man crew. Imagine spending a zillion dollars and having the guy (or girl) die en route! You'd need a sizable crew for maintenance and repairs, and scientific research. Besides, even the most misanthropic jerk would probably go crazy after that long alone. Clarityfiend 09:13, 31 May 2007 (UTC)


 * Would there be any advantage to crewing the ship with eunuchs? --81.77.236.185 09:42, 31 May 2007 (UTC)
 * No long lines at the volunteer booth.  ◄    Zahakiel    ►   19:16, 31 May 2007 (UTC)


 * I like the approach taken by some SciFi books - ship component parts - assemble on site. You send frozen eggs and sperm and have a robot turn them into human beings at the far end - then you educate them as explorers, colonists, whatever as needed. You could easily ship a few thousand crewmembers in a tiny volume. (Yeah - OK - I'm aware of the ethical/moral issues). SteveBaker 14:35, 31 May 2007 (UTC)


 * Hmmm. If your robot is bright enough to care for, entertain and educate a thousand or more three year olds plus stop them from wrecking the spaceship by pushing toast into the fusion drive or whatever, then it is probably bright enough to go exploring on its own. Gandalf61 16:04, 31 May 2007 (UTC)
 * But robots don't have a soul. Or maybe intelligent robots do.  Or maybe humans don't... Nimur 19:53, 31 May 2007 (UTC)

By the way, is it true that Bill Gates is considering to travel to space? 84.160.225.88 22:33, 31 May 2007 (UTC)
 * Maybe - but User:Nimur says it's pointless because you've got to have a soul. :-)
 * But seriously - I believe he's one of the people who bought a ticket for the first Virgin Galactic sub-orbital flight. SteveBaker 01:51, 1 June 2007 (UTC)
 * I think 84.160 was making a joke, alluding to the question title... --mglg(talk) 02:12, 1 June 2007 (UTC)

I've taken the liberty of changing this section's title from "Intergalactic" to "Interstellar" because, for crying out loud, it ought to be obvious that the nearest star ("Proxima") is not in another galaxy. &mdash;Tamfang 03:08, 1 June 2007 (UTC)

How big a scope?
In the light of some of these space travel questions, is there a theoretical limit to the size of an orbiting telescope? Obviously it could be constructed in sections. I mean if you could build a large enough telescope, from the point of view of research there would be little need for space travel, apart from colonization and mining perhaps.--Shantavira|feed me 09:50, 31 May 2007 (UTC)


 * Interestingly, you don't even have to construct all the sections&mdash;you could construct an astronomical interferometer in space which harvests light from widely spaced mirrors to generate the resolution of a large telescope with relatively little mass. (This technique is used for radio telescopes on Earth to create effective apertures tens, hundreds, or even thousands of kilometers in diameter.)  Orbiting optical interferometers have been proposed, though as far as I know none have yet been launched.  The upper bound on the size of such an instrument comes down to solving a number of engineering issues; I'm not sure if there's a theoretical maximum limit.
 * As an aside, I'd have to dispute your suggestion that space travel would be rendered useless by such a large scope. There are all kinds of research that still would have to be done in person&mdash;you can't drill a core sample, grow alien bacteria, or explore the oceans of another world from light years away. TenOfAllTrades(talk) 15:13, 31 May 2007 (UTC)


 * Any very extended artificial object in space would be subject to tidal forces. If nothing but gravity holds the thing together Roche limit applies. Otherwise Tensile strength is (technically) the primary limiting factor. 84.160.225.88 22:25, 31 May 2007 (UTC)


 * The Hubble Space Telescope was put in orbit to minimize atmospheric distortion. Orbital telescopes with glass mirrors have obvious size limitations, and low size means poor light gathering. Since its launch astronomers have developed adaptive optics to move portions of the mirrors of large earth-based telescopes at high frequency to cancel out the atmospheric distortion. Earth-based scopes can be huge to capture more light, and do not need billion dollar high-risk space walks to replace gyros and batteries. In addition, earth-based scopes separated by several hundred meters gain additional resolving power when the images are combined. Two small scopes separated by 300 meters have much of the resolution, if not the light gathering power, of a 300 meter diameter telescope, if their images can be properly combined.  relates the latest findings using 4 of the 6 mirrors of the Center for High Angular Resolution Astronomy (CHARA) interferometric array on Mount Wilson, Calif. Using an "infrared combiner" they combined the images from 4 scopes separated by "nearly 300 yards" to achieve 100 times the sharpness of Hubble images. They obtained images of the surface of a "sun-like" star called Altair, and could image a dark band around the equator of the star caused by its rapid rotation. Researchers said they expect to be able to image exo-planets as well. Future uses of space based scopes might require robotic missions to repair and maintain them rather than "hands-on" repairs by astronauts. The advantages of freedom from atmospheric distortion and light pollution remain, and space-based scopes coule be placed at opposite portions of the earth's orbit to allow extremely broad based interferometry. Edison 13:43, 1 June 2007 (UTC)

Ethene
Hello all. I'm looking for information for these two particular questions.

1)What affects its profiablity. 2) What affects the location of the chemical process (of ethene).

This is for homework yes, but im asking for information, not answers.Cuban Cigar 10:12, 31 May 2007 (UTC)


 * Ethene is produced almost entirely by cracking large hydrocarbons - in order to produce it, you need high temps (900°C), but the flash of heat must be incredibly brief (a matter of milliseconds), followed by chilling it in liquid methane to -150°C. This is a rather expensive process, and produces huge amounts of waste heat - you may want to consider the recycling of this waste heat, and the costs of the feedstock (ethene production can use almost anything with carbon and hydrogen in it). Laïka  12:36, 31 May 2007 (UTC)

Future of Medicine
Is it likely in the future that humans will be able to regenerate a new leg, if the old one was amputated, like the starfish do? Is it likely/possible, in the far future, that we can generate gills in the human body? --Juliet 12:51, 31 May 2007 (UTC)


 * That is one of the areas of stem cell research - growing organs. It is possible that entire appendages could be grown.  However, nothing will happen in the near future due to the belief that scientists throw babies in blenders and puree them into stem cells. --Kainaw (talk) 13:03, 31 May 2007 (UTC)

Yes. both of these and more will be possible soon.

(response to anonymous post directly above) What utter rot. Something that's possible soon is an oxymoron. Don't say things are possible until it is proven possible. From what I've seen (although I must claim some ignorance), we've only been able to construct simple tissue that is some measure of similarity to the tissue we have in other organs. To do even that, we have to build our own supporting structure for the cells to convince them to become something like the cells we want them to be. The step from that to an organ, with all the necessary supporting and connective tissue and circulatory system is quite huge. Don't get your hopes up by listening to this Futurist propaganda. My apologies to you if you are suffering some ailment and hoping stem cell research is your miracle cure. I'm hoping maybe one day we may be able to patch organs with tissues created from stem cells, and I'm thinking that may be the best we can do without introducing a whole new Pandora's box of problems related to the "solution". Root4(one) 03:59, 1 June 2007 (UTC)


 * (edit conflict) You may be interested in our article on artificial urinary bladders - biologists can build new bladders using nothing more than a few cells from the patient's old one. As for gills, there probably wouldn't be much point - we have SCUBA gear, rebreathers and atmospheric diving suits, so why go to the hassle of engineering a vastly complex organ system when a tank of good old O2 does the job just as well. One big problem is that fish, being cold blooded, don't need much oxygen - humans are not, so a working set of gills for a human would be roughly the size of a small car (sea water is 7 ppm oxygen, so for every litre of oxygen (~ one minute of breathing with a fully functioning rebreather), you'd need 200 kilograms of water, which is roughly the volume of two large dustbins - factor in all the equipment and you've got one bulky breathing system, whether it's biological or mechanical). You may be interested in Artificial gills (human). Laïka  13:16, 31 May 2007 (UTC)


 * You might enjoy our Artificial organ and Tissue engineering articles.


 * Atlant 13:18, 31 May 2007 (UTC)

They are all possible now, we just don't know exactly how :] HS7 13:58, 31 May 2007 (UTC)


 * Per scientists in Rome used stem cells from the patients' own bodies to create vaginas in two women born without one. The lead scientist said it is the first step toward creating other organs. Edison 14:33, 31 May 2007 (UTC)


 * A bit less inflammatory comment on the "babies in blenders" topic: there are essentially three kinds of stem cells: adult, cord blood, and embryonic. The first is extracted from an adult. A number of therapies, some used, some upcoming, use them. One example is the artificial vagina mentioned above. Cord blood come from the umbilical cords of newly born babies. And embryonic come from embryos. Research involving the last is partially restricted in the U.S., since getting new embryonic stem cells kills the embryo. However, new embryonic stem cells can be grown from existing ones. Research involving embryonic stem cells from "approved" stem-cell lines is legal in the U.S. Research involving adult and cord-blood stem cells is pretty much unrestricted worldwide. Many researchers feel that embryonic stem cells have more potential for new therapies than other types, because of their ability to become any type of cell. However, a disadvantage is the tendency to produce cancers, with the result that there are currently no successful therapies involving embryonic stem cells (last I checked, anyway). --Tugbug 20:41, 31 May 2007 (UTC)

Clarification of table salt vs Na+
Hi! I'm new to this site & have searched for the answer to my dilemma. I have tried to explain to my sister the difference between her electrolyte labwork of Na+ (she usually has low levels due to her epilepsy medications) and regular table salt. She is convinced if she uses extra salt on all her food will increase her sodium level. Since she is also hypertensive & is on meds for that, I told her this is not the right thing to do. She cannot or will not comprehend the difference. I have asked her doctor to explain this to her, but he is not very good at relaying information in layman's terms. Can you help me in any way? Articles, personal experience, anything would be greatly apprecialted!

Every day the average adult on an industrialized diet ingests hundreds to thousands of mg of sodium. Most of the Na is in the form of salt (NaCl), but once digested, Na is Na and the source is unimportant. And every day the average adult excretes precisely the same amount of mg of Na in her urine. If we increase our salt intake we simply increase our salt excretion; if we decrease our salt intake by 90% we simply decrease our salt excretion by 90%. Shifts in dietary Na cause very minimal changes in body Na retention. This is why dietary salt restriction causes only a small blood pressure reduction even in someone with hypertension. This is why extra dietary salt does not make most healthy people hypertensive. The Na concentration in lab tests reflects both body water and body Na, and there are many kidney and hormone mechanisms to keep these in balance. Some drugs affect this balance, and can change the level at which the water or Na is maintained. Anticonvulsants like carbamazepine (Tegretol) are especially likely to do this but the effect is not a large one. However anticonvulsant hyponatremia is usually mild (e.g., serum Na of 133 instead of 137) and causes no problems, but cannot be altered much by increasing dietary Na or decreasing dietary water. I hope this is clearer. alteripse 15:43, 31 May 2007 (UTC)

Bromine
According to the following chart, the reduction of water is at -0.83 and the oxidation of water is at +1.23. The reduction of hydrogen ions is at 0 and the oxidation of hydroxide is at +0.40. When determining what kind of electrolyte to use in electrolysis, which values do you compare them to. For example, if I try to electrolysis a solution of sodium bromide, do I compare bromine's value of 1.09 to 1.23 or 0.4. I'm trying to figure out if bromine can be made via electrolysis. --Russoc4 18:24, 31 May 2007 (UTC)

Bromine will oxidise the things in the 2nd column lower down on the list. Oxygen will oxidise bromide. So if you electrolyse a solution containing bromide - it is easer to produce bromine than oxygen. You can adjust ph, concentration of NaBr, temperature, or pressure to vary the results slightly. GB 06:36, 1 June 2007 (UTC)
 * But the production of oxygen from water is higher than the production of bromine from bromide on the list. --Russoc4 17:36, 1 June 2007 (UTC)

Finding gravity
How can I find gravity if I have the maximum velocity and max horizontal displacement?


 * That's kind of a trick question, because it is impossible to find gravity using horizontal displacement. If you have the vertical displacement, you can use the formulae on this page: Uniform acceleration. --Russoc4 21:20, 31 May 2007 (UTC)
 * That's all that's given though..velocity 15m/s and horizontal displacement 70m. I have no idea how to get started.
 * That's not enough information. You would need to know at least the direction of the velocity and assume that the the starting and ending point is the same vertically, as opposed to say standing at the edge of the Grand Canyon. Clarityfiend 21:35, 31 May 2007 (UTC)
 * Well they are using a mini launcher to shoot something. Does that fit into the equation at all?
 * If they told you a launch velocity of 15 m/s and a horizontal displacement, it makes more sense to assume g = 9.8 m/s2 and ask you what angle it was launched at. Someguy1221 21:53, 31 May 2007 (UTC)
 * It's on a different planet and i need to find the gravitational acceleration
 * Projectile motion is a little more complicated, if you don't know what you're doing. You do need to know the angle of the trajectory though. Or is it shot perfectly horizonatally? --Russoc4 21:59, 31 May 2007 (UTC)
 * I would think 45 degrees since it says max horizontal displacement


 * I've seen this problem in beginning physics books. The expected solution is to realize it is a 45 degree launch (due to maximum horizontal displacement).  Therefore, the horizontal velocity is 7.5 m/s.  Of course, they treat the planet as a flat plane without air resistance.  So, it is in the air for 70m / 7.5m/s.  Now, you know the initial vertical velocity is 7.5m/s and the number of seconds it is in the air.  You can calculate the m/s2 from there. --Kainaw (talk) 22:22, 31 May 2007 (UTC)
 * Except that if the total velocity is 15 m/s at a 45° angle, the horizontal component is (15/sqrt(2))m/s, not 7.5m/s. --mglg(talk) 22:30, 31 May 2007 (UTC)


 * Correct. I divided it in half.  It is the square root of 1/2 the square of 15, or 10.5m/s. --Kainaw (talk) 22:33, 31 May 2007 (UTC)
 * Errr...is the answer 20m/s/s? Doesn't look right —Preceding unsigned comment added by 71.82.135.128 (talk • contribs)


 * How did you get 20m/s/s? Questions like this are in the very beginning level physics.  At that point, the trick is to focus on the units.  You want m/s2.  You have the initial vertical velocity (10.5m/s).  You need to divide that by ?s to get m/s2.  You have horizontal velocity in m/s and distance in m.  Divide m by m/s and you get s.  Of course, the final answer is a generalized estimate as it doesn't take into account the curvature of the planet, air resistance, spin of the planet etc... --Kainaw (talk) 22:46, 31 May 2007 (UTC)


 * The final answer then be 2.28m/s2? —Preceding unsigned comment added by 71.82.135.128 (talk • contribs)
 * If the initial horizontal velocity is 15/21/2 = 10.6 m/s, then it takes 6.6 seconds to travel 70 m. The vertical velocity undergoes a net change of 21.2 m/s, as the final vertical velocity is exactly opposite the initial (assuming the projectile lands at the same altitude it was fired from), and this also takes 6.6 seconds.  21.2/6.6 = 3.2 m/s2.  I'm sorry I didn't notice the word "maximum" in your initial question.  Someguy1221 23:45, 31 May 2007 (UTC)

Wind speed at altitude
What is the average wind speed at around 8,000 to 20,000 meters, what I mean is constant or relatively constant winds, not gusts. And, while I'm at it, what's the air pressure, including the increased or, I think, decreased pressure of moving air, in that range? Thanks, 21:47, 31 May 2007 (UTC)


 * Winds aloft forecasts for the US can be found here. Atmospheric Pressure covers the relationship between altitude and pressure in the International Standard Atmosphere. As for the moving air, are you referring to dynamic pressure? anonymous6494 03:02, 1 June 2007 (UTC)

Zooming in on planets
It is possible to track planets in other systems with reasonable accuracy. Can't telescopes zoom in on these when they are lit by the sun in its solar system, to study details and maybe even find other blue planets? 81.93.102.185 21:50, 31 May 2007 (UTC)
 * Short answer, they are too far away, and therefore, appear incredibly small and dim to our earthly telescopes. Few extrasolar planets have been directly observed for this reason. Most are discovered with indirect evidence, such as observing planets partially eclipsing their stars.--Russoc4 22:02, 31 May 2007 (UTC)
 * Can you give an example of such case? Most of the extrasolar planets that I have heard of are discovered because of gravitational wobbles.--0rrAvenger 08:25, 1 June 2007 (UTC)
 * It's not necessarily that they're too dim. Most of the planets discovered are very large, comparable with Jupiter, but orbiting very close to the parent star, so called hot Jupiters. A Jupiter-like object orbiting around a Sun-like star at around one tenth of the distance from Earth to the Sun, could appear as bright as 17th or 18th magnitude from a viewing distance of 10 parsecs. That's well within the reach of good amateur telescopes with a decent CCD camera. Even the Earth as viewed from 10 parsecs would shine in reflected light at a magnitude within reach of a telescope like Hubble. The main problem in actually viewing the planet, is that it's orbiting a brighter star. In the hot Jupiter example above, the star would be shining at around 5th magnitude at that distance, approximately 100,000 times brighter than the planet. For the Earth, an alien looking in with a telescope at the solar system would see the Sun being over a billion times brighter than the feeble light from the Earth. If the difference in brightness wasn't enough, then the apparent separation would also be very small. In the hot Jupiter example, the Sun and planet are separated by just 10 milliarcseconds as viewed from 10 parsecs away - equivalent to the diameter of a golf ball viewed from over 500 miles away. It would be very difficult for even Hubble to achieve that sort of resolution, even if the glare from the parent star could be reduced. Richard B 00:16, 1 June 2007 (UTC)


 * How big a telescope would you need to get that sort of angular resolution? --Carnildo 23:24, 1 June 2007 (UTC)


 * I also suppose that there is a limit to the zooming you can achieve using optical techniques? -- WikiCheng | Talk 05:27, 1 June 2007 (UTC)


 * Theoretically, not if you're willing to build an arbitrarily large telescope. Although I suppose at some rediculous zoom, cosmic background radiation might be brighter than the light you are trying to detect.  Anyone?  Someguy1221 05:49, 1 June 2007 (UTC)


 * 0rrAvenger: See Methods of detecting extrasolar planets. According to the exoplanet article, this detected 5 planets up to 2004, including TrES-1. Algebraist 08:55, 1 June 2007 (UTC)

Sleeping
Since it is nearly June and the weather has been growing warmer and warmer, I noticed that in the morning, I seem to have moved a lot during my sleep. Is this because I am using a lighter blanket that does not pin me down during the summer? or is it because the hot weather makes people more restless during sleep? Coolotter88 22:09, 31 May 2007 (UTC)
 * I experience more tossing and turning during hot nights. How lovely to have a freezer, where you can shove your sheets and blanket for a good hour before bedtime. :) 81.93.102.185 22:12, 31 May 2007 (UTC)

How to make a milkshake
Whenever I try to make a milkshake I end up with a solid part separated from a liquid part instead of creamy goodness and I dont know why. I put ice cream and milk in a blender too make it. What do I need to be doing. Please help. —The preceding unsigned comment was added by 71.185.132.35 (talk • contribs).
 * Blend it a little longer? Eventually, it should become a suspension (assuming, of course, the solid object you are trying to blend can be broken down by a blender) - which is the good creamy stuff.  x42bn6 Talk Mess  22:38, 31 May 2007 (UTC)


 * Most blenders don't work well - the ice cream floats and avoids mixing into the milk. I use a "drink mixer" attachment on my electric mixer. It takes a bit of practice to keep it in the mug and not all over the counter. --Kainaw (talk) 22:40, 31 May 2007 (UTC)


 * Did you remember to add the guar gum, carrageenan, disodium phosphate, and cellulose gum? --TotoBaggins 22:52, 31 May 2007 (UTC)


 * When blending, try shake it a little. "Shake it a baby" (But refrain from "twisting and shouting" unless you like lemon icecream) Rfwoolf 13:49, 1 June 2007 (UTC)


 * I have found that crushed ice is a suitable alternative to provide thick consistency. Check that your blender is powerful and sturdy enough to crush ice.  I use about 12 cubes per quart of milk, plus two bananas, plus another fruit, for a healthier fruit-based milkshake.  Nimur 17:09, 1 June 2007 (UTC)


 * You can add a thickening agent like cornstarch. Cornstarch is pretty common to use in milkshakes as you can find if you search around on google for recipies. -- Diletante 17:36, 1 June 2007 (UTC)


 * Practice making milkshakes! You don't need corn starch or anything weird in it really. My dad can make a mean (nice) milkshake with just ice cream, chocolate sauce, and milk, and without the solid part separated from a liquid part instead of creamy goodness that I always seem to get. [' Mac Δαvιs '] ❖ 02:37, 2 June 2007 (UTC)


 * Note that chocolate syrup contains weird things like corn syrup. -- 23:10, 3 June 2007 (UTC)

Consuming out of date yogurt
Would eating a refridgerated out of date yogurt (say 9 months out of date) made from pasturised milk be bad for human consumption ??. If so why ?? what harmful bacteria could be present ?? Wikinomad 22:38, 31 May 2007 (UTC)


 * Billions of years of natural selection have given you a powerful tool for detecting things that will harm you. It and its predecessor tools have helped every single one of your ancestors -- all the way back to that first bit of genetic material floating in the primordial soup -- survive to breeding age.  Use it!  --TotoBaggins 22:49, 31 May 2007 (UTC)


 * Well, if not most of them sisters and uncles would have died without successful breeding the world would have been overcrowded some billion years before now. Aflatoxin is nothing your nose warns you about. 84.160.225.88 22:57, 31 May 2007 (UTC)


 * The trouble is that those billions of years of natural selection didn't condition you to eat yogurt! (See below for a discussion of the issues of adult lactose intolerance - that means we've only been eating yogurt for at most a few thousand years) - but yogurt was unknown in many western nations until the 1960's or so - and two generations is far too few to have evolved a means for dealing with the stuff.  There is no way that most human populations can have evolved to detect bad yogurt by smell or taste...especially because it's made by bacterial fermentation of milk!  It already contains some of the byproducts of contaminated milk products - so this is bound to throw off whatever senses we have to detect a problem.  There is a reason they put that date stamp on the container...believe it! SteveBaker 01:42, 1 June 2007 (UTC)


 * I think he means that it would smell bad and things that smell bad = should not eat normally. Common examples of things that smell bad and that's how you know you shouldn't eat them are faeces and corpses. Certain compounds associated and compounds that have a chemical structure similar to those compounds are the ones that noses have decided smell good and smell bad! [' Mac Δαvιs '] ❖ 04:04, 2 June 2007 (UTC)


 * Check whether it is a use by or best before end. BBE products should be safe to eat beyond the date. Use by products are generally not safe beyond the date. --h2g2bob (talk) 10:21, 2 June 2007 (UTC)

Delta H
in the reaction 2NO2 <--> N204

the forward reaction causes a lowering of color when the temperature is reduced.

My question is: Will the delta H (a triangle with a H) be positive or negative if the temperature is reduced?

Speeding up my scope
How can I simply speed up my oscilloscope from 40MHz to 80 MHz please?
 * In general you cannot. The 'scope is either an analog scope or a digital scope. If analog, its speed is limited by a bunch of analog circuitry throughout the design all the way from the front end to the sweep. More likely, you have a digital scope. In this case, the scope is basically an analog front end followed by an ADC followed by a memory buffer followed by a computer. It is usually limited by the speed of the ADC, but there are other possibilities. Some digital scopes can run at higher speeds by reducing the resolution: check your manual. Some dual-channel scopes can run at higher speeds when using only one channel: again, check the manual. -Arch dude 23:28, 31 May 2007 (UTC)


 * You can't, but this 100MHz scope is currently going for $0.99 plus shipping on eBay. --mglg(talk) 23:28, 31 May 2007 (UTC)

My scope is 2 channels at 40 Mhz per channel. Can I somehow add the channels to get 80MhZ?


 * No, sorry.


 * Atlant 23:56, 31 May 2007 (UTC)

Schucks! OK. But I know my 40MHs is only where the response is -3dB, so can I boost up the high frequencies to get more bandwidth?


 * For an analog scope, yes, you can do this to a point. But eventually, you'll be overloading the input stages of the vertical deflection subsystem in order to get enough signal through to the deflection plates. (Our Equalization article discusses this principle.) For a digital scope, there's probably a "brick wall" filter ahead of the sampling system and you can't beat the Nyquist frequency of the sampler in any case.


 * The one truly wild thing you could do (at least in concept) is put an electronic SPDT switch between your signal-under-test and the two input channels of the scope. Then drive the switch with an 80 MHz square wave so it switches your input signal between Channel 1 and Channel 2 80 million times per second. Then overlay the two waveforms on the screen; they'll produce a replica of what you'd get from a fast 'scope. This is almost too difficult to do in the real world, but it's a fun thought experiment. It's somewhat analagous to building your own effective-time sampling oscilloscope.


 * Atlant 13:05, 1 June 2007 (UTC)

Why has lactose tolerance become universal (in western world) in only 2000 years?
During Roman times about 2000 years ago, everybody was lactose intolerant. They only drank milk as a laxative. Now, only about 100 generations later, almost everybody in the west is lactose tolerant. Why anmd how did it become universal so quickly? Surely lactose intolerance dosnt kill you? (I am lactose intolerant.) How else could it have spread through the population so quickly in evolutionary terms? Thanks.


 * Well, evolution is not just about death. It is about differential birth/death rates, and the locus of selection can vary (individuals, populations, etc.) depending on who you ascribe to. Which isn't a full answer at all — I just want to point out that the "if it doesn't kill you it doesn't have an effect on evolution" line is false, albeit popular. Just as a fanciful example, imagine that being able to share a fine brie with a lady friend increased the ability of males to get it on with greater numbers of ladies, resulting in greater numbers of babies. Nobody would necessarily die from such an outcome, but any genes which aided in seducing lady friends would become represented disproportionately in the next generation. --24.147.86.187 23:36, 31 May 2007 (UTC)
 * As far as this bit goes, it actually would be about death if all the lactose intolerant locals are beeing wiped out by lactose tolerant invaders ;-) Someguy1221 23:39, 31 May 2007 (UTC)
 * While the ancient romans may not have been very lactose tolerant, northern Europeans were. Lactose intolerance has a little demographical information on this. I notice your IP is from the UK, so you might just be seeing a distorted cross section of the west. Someguy1221 23:38, 31 May 2007 (UTC)


 * Also, our article on lactose intolerance seems to indicate that not everyone was lactose intolerant at all in Roman times. The Romans were but that is not a large number from a population standpoint (assuming you are not counting subjugated peoples as "Romans"). In fact that article seems to indicate, though it is uncited, that modern distributions of tolerance are not terribly far different than those in Roman times. --24.147.86.187 23:40, 31 May 2007 (UTC)


 * Lactose intolerance doesn't kill you, but being lactose-tolerant lets you use more food sources. You can't eat grass directly, but if you can drink milk, you can use a cow to convert grass to food. --Carnildo 23:58, 31 May 2007 (UTC)


 * All that I've read about this suggests that the trend started when humans started to use farming in a big way...long before the Romans. The theory is that if you are a farmer and there is a severe drought - your crops turn to straw - but your animals can survive better than you.  In this situation, if you can tolerate milk then you can milk your cows, goats and sheep - and you can survive until things improve.  However, if you can't then your only option is to start slaughtering your animals for the meat.  This means that even when the situation improves, you've lost most or all of your herd and you are in trouble next time around.  So there is a slight survival benefit for farmers in being tolerant of lactose - so evolution kicks in and within a surprisingly few numbers of generations, we're mostly all lactose tolerant.  The suspicion is that for the majority of westerers, these kinds of food crises don't happen so often anymore - so the evolutionary pressure to become lactose tolerant has disappeared while we still have a significant number of lactose intolerant people in the population.  In populations where farming never took off (or arrived much later), latose tolerance is a disadvantage because it may prevent children from being 'automatically' weaned from their mothers milk when their lactose intolerance naturally kicks in at age 1 to 2 years. SteveBaker 01:32, 1 June 2007 (UTC)


 * If the question was not in response to the recent press release that states "the gene that controls our ability to digest milk [as adults] was missing from Neolithic skeletons dating to between 5840 and 5000 BC. However, through exposure to milk, lactose tolerance evolved extremely rapidly, in evolutionary terms. Today, it is present in over ninety per cent of the population of northern Europe and is also found in some African and Middle Eastern populations but is missing from the majority of the adult population globally," you may want to have a look at it, or the New York Times article showing similar findings. - Nunh-huh 01:41, 1 June 2007 (UTC)


 * It's more accurate to call it "lactase persistence", as baby humans have always had the enzyme (lactase) that digests lactose. Adults did not develop it de novo, but evolved the neotenous trait of continuing to produce it in the digestive tract later in life. This is why it appeared so rapidly, whereas we still cannot eat grass because we have no history of digesting cellulose. Bendž|Ť 09:36, 1 June 2007 (UTC)

Thanks for answers. So while the Romans were (and to a certain extent still are) lactose intolerant, northern europeans were not. I note that you only need one copy of the gene to be lactose tolerant, so a 5% intolerance rate would suggest (1-p)^2=0.05 where p is the probability of having a gene, and giving p = only about 75%. I also wonder if it is possible that lactose intolerance could be caused by not eating milk or milk products for a long time due to Enzyme induction and inhibition. I stopped consuming milk or milk products for some years. On a hot day I drank a lot of milk and realised I was lactose intolerant. Now I have been drinking milk and milk products for some time and I may be getting more tolerant perhaps due to enzyme induction, or perhaps as the article suggest due to gut bacteria adjusting to it. user:80.0.125.54


 * Your maths is right, but the answer's closer to 78%. The problem is that assumptions are made. A European nation with that sort of intolerance rate may experience a high degree of Asian immigration. Intollerance allele frequency would be overestimated by the formula as it hasn't had time to spread through the population, and may never if cultural segregation is the norm (breaking another assumption). There would be a higher level of homozygosity than a natural distribution would predict, with "p" perhaps closer to 85%. You can't acquire lactose intolerance unless your small intestine has been damaged or operated on :) Bendž|Ť 12:53, 1 June 2007 (UTC)

Peanuts not good for pregnant women - why?
Why indeed?
 * Because recent studies have revealed a tentative correlation between eating peanuts during pregnancy and giving birth to children allergic to peanuts. See HERE. Anchoress 00:01, 1 June 2007 (UTC)

How small are tiniest tv cameras?
I saw something on the internet which claimed that someone had a tiny tv camera concealed in the part of a pair of spectacles that goes across the nose and connects the two lenses. Is this possible please, or was it just hype? Thanks


 * Well, the camera that I strapped on the front end of some model trains last Christmas (for the pleasure of the grandkids, of course ;-) ) is a cube about 1.5 cm on each side, including its 2.4 GHz radio transmitter and a bulky plastic case; I haven't cracked it open but I'd imagine the internal workings are about 1 cm square by 1 cm deep (with the depth established by the optics). Not quite the size you mentioned, but not far from it either.


 * Atlant 00:02, 1 June 2007 (UTC)


 * Yes - they definitely exist - I've seen them. SteveBaker 01:21, 1 June 2007 (UTC)


 * But the interesting question is whether they have seen you. &mdash;Tamfang 03:13, 1 June 2007 (UTC)

Thanks. Anyone know where I could buy one from please?


 * Google ought to be able to find these easily. I'd start with "TV-camera surveillance".


 * Atlant 12:51, 1 June 2007 (UTC)

Dark Matter "Planets"?
I read an article about a dark matter galaxy. If a bunch of dark matter could get together and act like a galaxy, could there just as easily be dark matter planets in orbit around stars? Has anyone found evidence of them? (I know that many extra-solar planets are found by their gravitational influence on their suns. Does this mean that if we found one made out of dark matter, we wouldn't realize it for quite some time anyway?) Have they been predicted to exist or not exist by anyone who knows what they're talking about? --67.110.213.253 23:42, 31 May 2007 (UTC)
 * Was there a dark matter galaxy? What are the constituents of a galaxy? [' Mac Δαvιs '] ❖ 23:50, 31 May 2007 (UTC)
 * I've never seem a claim like this before, but I think the bit about dark matter "condensing like water droplets on a spider web" is most likely just a very very bad analogy. There is no evidence for dark matter interacting through anything other than gravitational forces, and so there is no evidence it can litteraly "condense" into solid matter.  And so this "dark matter galaxy," if it exists, would simply be a very dense cloud of gas that happens to be...dark.  Someguy1221 23:53, 31 May 2007 (UTC)
 * Dark matter lists the different proposed types of dark matter, I suggest you look there for more information on what it can do. Someguy1221 23:55, 31 May 2007 (UTC)
 * Thanks for the answer, and I'll take a closer look at that section now. I admit that I kind of skipped through that bit of the article earlier. So if all it does is interact through gravity, and gravity is what makes things clump together, why wouldn't dark matter clump together? Or do you mean that it exerts gravity but is unaffected by it? --67.110.213.253 00:37, 1 June 2007 (UTC)
 * I would say gravity is what pulls things toward each other, not what clumps them together. Imagine two large asteroids, you would like to say that gravity might clump them together (assuming they hit eachother right, instead of being blasted into pieces), but imagine that they can only interact with gravity.  If they actually struck, they would simply go through eachother, and would orbit about one another forever, assuming there's nothing else nearby (and ignoring the emission of gravitational waves).  So clearly gravity alone will not clump things together.  Someguy1221 00:43, 1 June 2007 (UTC)
 * ...Crap. And dark matter planets seemed like such a cool idea, too. Anyway, I think I get it now. Thanks! --67.110.213.253 00:56, 1 June 2007 (UTC)


 * If dark matter only interacts via gravity, and does not "feel" electromagnetic forces or the strong or weak nuclear force, then I don't think it can even form atoms, let along something as big as an asteroid, planet or sun. Remember that even friction is really electromagnetic forces in disguise. With only gravitational interactions, I don't think dark matter can "clump" on anything smaller than galactic scales. However, there are several alternative and competing theories of dark matter - see self-interacting dark matter for an example that might accommodate dark matter planets. Gandalf61 14:49, 1 June 2007 (UTC)