Wikipedia:Reference desk/Archives/Science/2009 June 8

= June 8 =

Plant without soil
I have this plant in my garden which grows on a rock. It does not touch any soil which I can see and I can move the whole rock (about 1 metre wide and long) with the plant on it anywhere. The plant grows on one face of the rock, about 1 metre long and has big leaves about 30 cm long. What kind of plant is this and how does it live without soil?

Thanks in advance, 220.244.76.121 (talk) 02:40, 8 June 2009 (UTC)


 * Some species of air plant maybe?  Sp in ni ng  Spark  03:12, 8 June 2009 (UTC)


 * Plants living on a rock or rocks are called lithophytes. Lithophytic plants are way too numerous to list. Can you post a picture of the plant somewhere? That would be the best. Telling us what part of the world you are living in would also help. --Dr Dima (talk) 03:38, 8 June 2009 (UTC)


 * Having said what I said, it may actually be a good idea if we at least start a list of lithophytic plants. The problem is, there are plants like Capparis sp. or Hyoscyamus sp. that thrive in cracks of a rock or in a crevice of a stone wall, but are far more often found in regular soil; and there are plants like some species of Laelia that are almost obligate lithophytes. Should we come up with a criterion, or just bundle them and let the reader read? --Dr Dima (talk) 03:48, 8 June 2009 (UTC)


 * Even trees can grow without soil. Here is one I photographed in Scotland. Plants only need air, water, and a tiny amount of nutrient. See hydroponics.--Shantavira|feed me

Alternative earphones with remote and microphone for iPod touch
moved to WP:RD/C Nil Einne (talk) 17:01, 8 June 2009 (UTC)

Which vegetable oil is most healthy for vegetarians?
I'm looking for answers based on scientific evidence rather than something resulting from opinions formed from advertising or habitual use (eg olive oil). These two tables http://www.vaughns-1-pagers.com/food/vegetable-oils.htm http://www.annecollins.com/dietary-fat/omega-3-efa-6-chart.htm give lists of consituents of the oil, since I could not find a similar table on Wikipedia.

Canola oil is another name for rapeseed oil. I see that the amount of Omega3 in Canola oil differs considerably between the two tables - the small print in one of them says the amount listed is reduced during processing. I'm also wondering how much Omega3 there is in supermarket-bought 100% walnut oil, probably formed from hot-pressing, since neither of the labels on bottles from two different supermarkets mention it - yet I would have thought this would be a selling-point.

Fat summary: saturated fats - bad, should be avoided as far as possible. Transfats - very bad but not found in *liquid" vegetable oils. Monounsaturated - good, reduce bad cholesterol. Polyunsaturates - not so good as they reduce good cholesterol. But Omega3, which is a kind of polyunstaturated fat, is on the other hand good for you and said to be insufficient in peoples diets.

So given the above, which vegetable oil is best? Expense is not an issue. It may be that a blend of oils, determined by linear programming might be optimal. 78.149.143.187 (talk) 11:54, 8 June 2009 (UTC)
 * The question is clearly expressed, but I am not sure if the title is supposed to add an element to the mix. Is there a reason to believe that the healthiest oil for vegetarians would not also be the healthiest for omnivores? Also, the healthiest oil on strictly nutritional grounds may not be commercially available. Are you looking for something you can purchase and consume now, or a project to research? For example, argan oil and babassu oil are cultivated, and acorn oil to a lesser extent. You may care to investigate Sclerocarya birrea (S. caffra), aka the marula. BrainyBabe (talk) 12:21, 8 June 2009 (UTC)
 * We even have an article: Marula oil. BrainyBabe (talk) 12:28, 8 June 2009 (UTC)

I am looking for something available from supermarkets or health food shops. I do not know if the best oil for vegetarians would be the same as that for omnivores. Marula oil, at least, seems to have a lot of saturated fat in it. 89.242.81.255 (talk) 14:41, 8 June 2009 (UTC)


 * I don't think you can come up with a clear answer to this, since as with so many things when it comes to diet, there is still a fair amount of dispute. How can you come up with a 'best' when you aren't sure what's better? For example there is some evidence olive oil is good for you olive oil but how good and why? As the phenolic compounds (and vitamins), which may be partially the cause of olive oil's alleged healthy properties, break down significantly in 12 months the oil may be good in 2-3 months, not so good or at least no different if it's 12 months old. How significant the omega 3 to omega 6 ratio is another thing that remains unclear . Another issue particularly since you talked about unusual oils. If these are organic or other speciality products, they may lack added antioxidants etc which despite the beliefs of those who think everything should be natural could be beneficial. Also, virgin olive oil and other oils with a low smoke point may not actually be a good oil for high temperature cooking (particularly anything over 200 degrees C) such as deep frying or perhaps traditional Asian style stir frying and high temperature roasting/baking due to the low smoke point . Indeed this very high temperature cooking particularly deep frying is one area (IMHO) where the science is particularly unclear due to the complexity of what is formed, what breaks down, oxidises, etc   . Some of the beneficial compounds in olive oil may also decrease relatively rapidly for example . And oils high in polyunsaturated fatty acids are prone to oxidation   so it's possible an oil high in saturated fats may in fact be better then an oil high in PUFA for high temperature deep frying perhaps even if you only use the oil once. Remember that even if if the quantities formed are small, depending on how bad these are it could still be worse. This may be more of an issue in a restaurant etc but it does depend how often you reuse the oil (if at all), how long you deep fry for and temperatures. Home cooking is more likely to lack a temperature controlled deep fryer, filtering to remove crumbs and the deep fryer may be uncovered all of which are likely to be bad. And interesting enough, repeated heating and cooling of the oil may make things worse since the lower temperatures are apparently quite bad when it comes to oxidation . Another factor, if you are referring to deep frying or any other case where you reuse the oil because of the oxidation, formation of potential carcinogens and other issues associated with repeated use, while you've said expense is not an issue, if using a more expensive oil means you will re-use it (more?), then it's potentially better for you to use the cheaper oil but refresh your oil more often. Of course since deep frying is not particularly healthy, it may just not do it, and things may not be so complicated. But then again, a perhaps interesting issue is the answer may even depend on the person. If you have a family background with a lot cases of cancer then you potentially should be more worried about carcinogens then if you have a family background with a lot of cases of coronary heart diease. One final thing that's worth remembering is where the money is coming from for research etc. Ge
 * You may wish to try hempseed oil, which according to our article is extremely high in EFA's. However it is not suitable for high temperature frying. --TammyMoet (talk) 18:09, 8 June 2009 (UTC)

Sorry I should have added that I never fry food, except very ocasionaly vegetable stir-fry. The great majority of the oil would be eaten by drizzeling over pasta, salads, etc. And it was "BrainyBabe" who mentioned the exotic oils, not me. The choices I have in practice are between things like canola, olive, flax, or walnut oils, or combinations thereof. 78.149.238.54 (talk) 19:15, 8 June 2009 (UTC)
 * In that case, hempseed oil is the best bet. It tastes good too! --TammyMoet (talk) 08:15, 9 June 2009 (UTC)

I think your best bet is simply to vary your cooking oil. Butter, canola, olive, peanut are four common ones that spring to mind. Vranak (talk) 02:28, 11 June 2009 (UTC)

Does cooking linseed make its oil accessable?
The Omega3 oil found in linseed, also called flax seeds, is believed to be beneficial. While flax oil is available it is expensive and tastes bitter in my experience. Flaxseed is much cheaper and tastes OK. But I understand that if you eat it raw it just goes straight through you without any of the oils inside the seed being digested, due to the seed-coat protecting them. To be digested it should be ground before eating - which is inconvenient to do.

My question is, does boiling linseed for 15 or 20 minutes (by adding to pasta or rice etc) rupture the seed coat and make the oils inside available to be digested? 78.149.143.187 (talk) 12:08, 8 June 2009 (UTC)
 * Yes it ruptures the seed coat. Whether it affects the quality of the oil is another question, as something boiled is not coldpressed. One simple way of ingesting raw linseed oil is to take a spoonful of linseed and chew it for 30 seconds, then swallow with a little water. I do not find the taste bitter. No need for coffee or spice grinders, etc. BrainyBabe (talk) 12:24, 8 June 2009 (UTC)
 * How do you know it ruptures the seed-coat please? 89.242.81.255 (talk) 14:51, 8 June 2009 (UTC)
 * Because if you chew with normal vigour for 30 seconds, not bite and gulp in two seconds but masticate with your molars for half a minute, the linseed becomes a paste. Try it yourself. Spit it out and look. Poke it with your finger. Can you see any intact seeds? Some might call that original research, frowned on here, but I would call it the empirical method. "Suck it and see", as they say, or in this case, spit it and see.  This method is simple, free, requires no equipment, and does not depend on another level of processing (to gelcap form) with its own issues of stability, etc. Also, he enzymes in saliva help the process of digestion begin correctly; see that article.  BrainyBabe (talk) 18:00, 8 June 2009 (UTC)
 * Sorry, what I meant was, how do you know it ruptures the seed-coat after being boiled for 15-20 minutes? 78.149.238.54 (talk) 19:23, 8 June 2009 (UTC)
 * Ah, the problem of the unclear referent! Again, perform the experiment. Boil a handful of linseed in a pot of water. (Leave out the additional ingredients such as rice, so that you are observing a single variable.) After 20 minutes' boil, turn off the heat. Look at it. Let it cool down. Poke it with your finger. Do you see any intact seed hulls? You can perform the same experiment with a grinder (electric or manual) or a mortar and pestle, for comparative purposes. BrainyBabe (talk) 06:33, 9 June 2009 (UTC)
 * FWIW, you can also get cold-pressed lin/flaxseed oil in gelcap form. No taste at all there. --Kurt Shaped Box (talk) 12:31, 8 June 2009 (UTC)
 * What you want out of your linseed oil (most likely) are polyunsaturated fatty acids. Heating oil will turn those into ordinary fatty acids at temperatures ard.  195 F- 265 F. In addition flaxseed oil also has it's Smoke point at the upper end of that range.  Labels like "cold extracted" or "cold-pressed" make a lot of sense for your salad oil.  For cooking oil it's less useful and can even be bad.  For frying you have to keep and eye on the smoke point and Trans fat.  (P.S.: For more info see Nil's detailed post above.) 71.236.26.74 (talk) 16:52, 8 June 2009 (UTC)
 * "Heating oil will turn those into ordinary fatty acids at temperatures ard. 195 F- 265 F." That's very interesting - do you think that is the reason why the supermarket walnut oil does not mention Omega3 on the label, despite giving the % composition of other fat types, because its likely to have been obtained by hot-pressing and thus the Omega3 has been turned into a more ordinary fat?? And, by the way, I almost never fry food. 78.149.238.54 (talk) 19:29, 8 June 2009 (UTC)


 * More likely because it isn't a mandatory part of Nutrition facts labels. The second reason is that "high in omega 3" is just as efficient for marketing and they can't be sued if some curious consumer group does some testing and finds there's not as much as they thought.  Then there is the fact that omega3s are mot all that stable and do deteriorate after a while.  With walnut oil you also don't get mega market manufacturers who can shell out money for testing that isn't requited by law.  With all types of oil there's things they don't test for like Benzopyrene, Benzyl butyl phthalate or Bis(2-ethylhexyl) phthalate. Cyanide is another ref-desk favorite.  Then there's Tannin which is good or bad for you depending on how much (total) you consume and whom you ask. Buying organic or at health food stores won't make a difference there, because their products are just as likely to contain the above as the stuff off the supermarket shelf.  In short not everything is all that healthy as the media would make it seem once you start looking under the hood.  And there is such a thing as way too much information.  Use what you think tastes good and try to eat a varied and mixed diet. (If you have to be a vegetarian remember to take B12 supplement.  You won't get that from any plants and your body will run out of it at some point. 71.236.26.74 (talk) 22:34, 8 June 2009 (UTC)
 * You are confusing vegetarians with vegans. 89.240.49.146 (talk) 22:48, 8 June 2009 (UTC)


 * By heating these polyunsaturated fats, you can polymerize them and make a skin. This is how oil paint works, although that may use oxygen as well.  The branched chain fatty acid is very hard for humans to metabolise. (we need an article on these) Graeme Bartlett (talk) 22:04, 8 June 2009 (UTC)

Death by hypodermic to the heart?
My roommate and I noticed that "The Rock" was showing again yesterday. This inspired the conversation that led to me posting the following. Towards the end of the movie Nicolas Cage's character injects an antidote he desperately needs directly into his heart. One of us believes that this scene is realistic, at least in principle, believing that if the antidote had the proper effect quickly enough and if he had a high enough pain threshold, then the character should be ambulatory rather soon and functioning at nearly his normal level. The other of us believes that the process of injecting anything directly into the heart would lead to death rather quickly, given the required injury to the heart itself. I tried Googling this issue without much luck. Any thoughts, anyone? —Preceding unsigned comment added by 68.37.188.33 (talk) 15:01, 8 June 2009 (UTC)


 * Hopefully someone with more medical knowledge will reply in detail. but intracardiac injections are real. I think they're only used in extreme emergencies because of the obvious danger to the heart itself and the coronary artery. APL (talk) 15:10, 8 June 2009 (UTC)


 * Am personally skeptical that it would work like that, but its a great movie anyway. 65.121.141.34 (talk) 16:37, 8 June 2009 (UTC)
 * As APL said, intracardiac injection is real, but it is only done by professionals. Nicholas cage was not paying much attention to where he jabbed that needle, and wasn't working to hard to keep it still while it was in. It seems to me that he would have microscopically shredded the tissues in his heart, and would have died. Plus, with that quick jab, he could be injecting the antidote into the muscle instead of he blood stream, which would kill him. D rew S mith  What I've done  21:23, 8 June 2009 (UTC)


 * In old murder mysteries, people were killed by a hatpin jab to the heart. There are also medical reports of a hatpin thrust into the heart causing death. Seems much like a hypodermic jab. Edison (talk) 17:06, 9 June 2009 (UTC)


 * FYI nerve gas antidotes in autoinjectors are not injected in the heart. AFAIK they're always injected in a muscle (e.g. on the outside of the thigh). It's doesn't make for such a dramatic scene, though.Sjö (talk) 19:24, 9 June 2009 (UTC)


 * Pulp Fiction also had a scene with an intracardiac injection. Ugh!!!!  67.122.209.126 (talk) 13:28, 10 June 2009 (UTC)


 * Wikipedia's article is incorrect. Intracardiac injections are not "often used" in emergencies. Streptokinase is never given by this route. Axl  ¤  [Talk]  18:37, 10 June 2009 (UTC)
 * This letter in The Lancet describes several case series. However the technique is not recommended by any resuscitation council, nor is it widely practiced. Axl  ¤  [Talk]  18:46, 10 June 2009 (UTC)
 * I have fixed the article now. Axl  ¤  [Talk]  18:54, 10 June 2009 (UTC)
 * To address the original question, it's been about 10 years since I saw the movie so I reviewed our article. The injection of atropine might work. Nerve agent antidotes usually contain pralidoxime as well as atropine. However I am unconvinced that intracardiac injection would have any benefit over intravenous injection, particularly in someone who is conscious (and therefore has circulating blood). Axl  ¤  [Talk]  19:06, 10 June 2009 (UTC)


 * Before doctors were trained in CPR, and before electric defibrillators were common, doctors would inject adrenaline directly into the heart with a large bore needle several inches long. This was common from the 1920's to the 1960's. See this publication from thee 1920's. Note that they even mention cardiac massage(probably internal via incision) and artificial breathing. They do not claim the technique had a high success rate.  . See also . Edison (talk) 21:19, 10 June 2009 (UTC)

heat into electricity
is there something maybe like a solar panel which can convert relatively large amounts of heat say a 10000 joules possessed by its surrounding air at a 1000 kelvin within a few seconds or even a few milliseconds? --harish (talk) 15:04, 8 June 2009 (UTC)


 * In principle this is just a heat engine - you pump a working fluid through a heat exchanger so it absorbs heat and maybe undergoes a phase change as well. Then you pass the hot fluid through a turbine which extracts work from it. While driving the turbine, the fluid expands and cools, so you pump it round again. In practice, 1000K is a high working temperature - for comparison, the superheated steam in a fossil fuel power plant has a maximum temperature of about 800K. So you probably need to borrow technology from the nuclear industry which is designed for higher working temperatures - maybe advanced gas-cooled reactor or very high temperature reactor technology. If you want to increase the power of your heat engine then you increase the surface area of your heat exchanger and pump fluid through at a faster rate. Gandalf61 (talk) 15:56, 8 June 2009 (UTC)


 * There is also the thermoelectric effect, which has some similarities to the photoelectric effect, but it is even less efficient in practice. Nimur (talk) 17:00, 8 June 2009 (UTC)


 * You really need a temperature DIFFERENCE in order to extract some energy. So if all of the machine's surrounding air is at 1000K, you've got to find a way of connecting the thing to something at much lower temperature. If you can do that then using some substance that is a gas at 1000K but a liquid at the lower temperature (water might be a reasonable choice) then water is flashed into steam by your 1000K heat source - is used to drive a turbine - the outlet from which is passed through cooling coils in the cold part of the system to condense back into water and continue around to the hot side again.   A steam engine would work - so would a stirling engine...there are many possibilities...although it's hard to imagine anything that could do that within seconds.   But if the entire machine is immersed in 1000K temperatures - there is nothing you can do to extract energy because that would violate the laws of thermodynamics. SteveBaker (talk) 18:40, 8 June 2009 (UTC)
 * It depends on exactly how you interpret the question - if it is one batch of hot stuff containing 10kJ being converted at once, then a few seconds is probably unrealistic, if it is a continuous process converting 10kJ per second, that is perfectly achievable. A typical fossil fuel power plant generates far more than 10kW. --Tango (talk) 18:56, 8 June 2009 (UTC)
 * The archetypal device that does this conversion is a Stirling engine. The max possible efficiency is determined by the Carnot cycle. 207.241.239.70 (talk) 19:25, 8 June 2009 (UTC)

How far do iron ore Lake Freighters travel from Minnesota or Northern Michigan, through the Soo Locks & past
the Mackinac Bridge then south on Lake Michigan to the steel mills in Gary, Indiana? —Preceding unsigned comment added by 72.204.36.33 (talk) 15:52, 8 June 2009 (UTC)


 * You should be able to figure this out yourself, I would think, by looking at a map and using its scale. You might use our articles about Duluth, Minnesota, Soo Locks, and Gary, Indiana to get an idea of where these places are. —Bkell (talk) 00:48, 9 June 2009 (UTC)
 * Using Google Earth, I get between 850 and 900 miles from Duluth to Gary. I tried to keep a short path but actual lake freighters have to stay in separated upbound and downbound shipping lanes so the the actual mileage may vary a little depending on the direction of travel. Rmhermen (talk) 02:58, 9 June 2009 (UTC)

porcupines
Are porcupine quills coated with venom or bacteria to cause infection? The article did not seem ot mention this one way or another. 65.121.141.34 (talk) 18:57, 8 June 2009 (UTC)


 * No, they are not. They are modified hairs - nothing more.  The keratin makes them stiff.  You may be thinking of hedgehogs.  Many breeds of hedgehogs perform a ritual commonly called "anointing".  They spread various chemicals (which may contain poisons) on their quills.  Some people think that they do it increase the odds of infection in a predator.  Others think it is just for camouflage. --  k a i n a w &trade; 19:03, 8 June 2009 (UTC)
 * I read in The Book of General Ignorance that the hedgehogs specifically chew poisonous frogs and suchlike and spread the resultant juice over their spines. Vimescarrot (talk) 21:37, 8 June 2009 (UTC)
 * Page 93. It also mentions the smells of many things can cause this behaviour, including shoes, cigar butts, furniture polish, creosote, coffee, boiled fish, face cream and distilled water. The animal world is a funny thing. Vimescarrot (talk) 21:39, 8 June 2009 (UTC)
 * Distilled water has a smell? (I mean, to any creature other than Shai-Hulud?)  Tempshill (talk) 23:59, 8 June 2009 (UTC)


 * There are creatures far smaller than the mighty Sandworm that can nevertheless smell pure water quite well. Try "insect water receptors" in Google Scholar, and you will not lack the stuff to read for the evening :) --Dr Dima (talk) 01:13, 9 June 2009 (UTC)


 * I'd say The Book of General Ignorance is well titled. Richard Avery (talk) 06:56, 9 June 2009 (UTC)

While it true that porkies don't purposefully coat themselves in biological agents, they are not particularly "clean" animals. Part of thier mating ritual involves the male urinating on his partner. Yes a "natural" Golden Shower. They also "Den" for the winter and live with thier own faeces. Thier meat is parasite free and you can eat them raw (tastes awful though) but I wouldn't suggest licking one. 67.193.179.241 (talk) 10:35, 9 June 2009 (UTC) Rana sylvatica


 * Urine is not "dirty", and faeces (from a healthy animal) are not infectious (how would the porcupine survive the winter while "incubating" with it, if it were "dangerous"?). You may find this behaviour disgusting, but this does not make the animal unclean in any objective way. --TheMaster17 (talk) 12:40, 9 June 2009 (UTC)
 * Feces from healthy animal may still contain pathogens dangerous to other animals. APL (talk) 12:52, 9 June 2009 (UTC)


 * I read in The Book of General Ignorance that the hedgehogs specifically chew poisonous frogs.. Since Hedgehogs are not found in South America which is AFAIK the only place that has poison frogs: How the blazes can they chew them? (Help remedy my general ignorance:-)71.236.26.74 (talk) 18:13, 9 June 2009 (UTC)
 * They probably get them in pet stores.
 * Seriously, though. Poison Dart Frogs are not the only frogs that contain poisons. A bunch of them contain skin irritants that might be sufficient for the hedgehogs' purpose.
 * Or the book could have been completely wrong. Very possible. APL (talk) 18:34, 9 June 2009 (UTC)


 * If hedgehogs were to buy poison dart frogs in a pet store, they'd be in for a very bad surprise: captivity-bred poison dart frogs do not contain batrachotoxin! The poison dart frogs don't produce it, they get it from the beetles they eat; see the ref in batrachotoxin. On the other hand, toad posion bufotenin is probably produced by the toad itself. --Dr Dima (talk) 20:50, 9 June 2009 (UTC)


 * Thought they might have mistaken a toad for a frog. Mistaking a frog for a toad isn't that unusual, but the other way round?  Maybe the "General Ignorance" people should wait for the next edition of their own book ;-)71.236.26.74 (talk) 04:08, 10 June 2009 (UTC)


 * Poisonous frogs do not only occur in South America. Poison dart frogs are just one familly of frogs: their fame does not precude the existance of poisonous frogs on other continents, eg. Wikipedia has at least 15 articles on African poison frog species (see Mantella), so hedgehogs could indeed have population overlaps with poison frogs.YobMod 15:36, 10 June 2009 (UTC)
 * The book says toads, not frogs, although I was given to believe that there is no scientifically concrete definition distinguishing the two, so I call them all frogs. Does that help? Vimescarrot (talk) 18:07, 10 June 2009 (UTC)

Name of those polystyrene packing forms?
Hi - I need a generic name for those shaped polystyrene blocks you find in boxes of new equipment. Is there one, can anyone help?

Thanks,

Adambrowne666 (talk) 20:20, 8 June 2009 (UTC)


 * Do you mean Foam peanuts? Or do you mean Expanded polystyrene shaped blocks like the ones used to protect electronic equipment in its shipping box? --Dr Dima (talk) 20:33, 8 June 2009 (UTC)


 * The latter, please, if there is a simple name for them. Adambrowne666 (talk) 20:43, 8 June 2009 (UTC)


 * They are called "molded expanded polystyrene" or "foam shipping blocks". --Dr Dima (talk) 20:48, 8 June 2009 (UTC)


 * Foam shipping blocks - perfect! - thanks for the prompt replies, Dr Dima Adambrowne666 (talk) 20:51, 8 June 2009 (UTC)


 * "Rigid plastic foam blocks" is another term used. —Preceding unsigned comment added by 98.17.43.186 (talk) 11:33, 9 June 2009 (UTC)


 * Styrofoam Cuddlyable3 (talk) 19:57, 9 June 2009 (UTC)


 * No, not Styrofoam. That is a common mistake. Styrofoam is a patented brand of polystyrene foam, and can come in any shape (e.g. sheets or disposable coffee cups), and not necessarily as shipping blocks. In other words, not all styrofoam is molded into shipping blocks, and not all shipping blocks are made of styrofoam. --Dr Dima (talk) 20:30, 9 June 2009 (UTC)

All matter Black hole
If all of the matter in the Universe fell into a Black hole how big would the Black hole be? -- Taxa  (talk) 20:45, 8 June 2009 (UTC)


 * As big as the whole universe. --Jayron32. talk . contribs  21:02, 8 June 2009 (UTC)


 * That depends on the size and density of the universe. The entire universe is probably infinite, so that would result in an infinitely big black whole. If you mean just the observable universe, then it still depends on the density. I believe if the density were exactly equal to the critical density, then the Schwarzschild radius of the black hole would be equal to the current radius of the observable universe (the event horizon would essentially be the cosmological horizon). This isn't a coincidence and, in that situation, you could sort of think of the universe as being inside a black hole (emphasis on "sort of"). I believe current estimates put the density quite a bit lower than that, though, so the black hole would be smaller than the current observable universe. --Tango (talk) 21:09, 8 June 2009 (UTC)


 * BenRg seems to think that the statement above is not quite correct as you can see here. Dauto (talk) 02:49, 9 June 2009 (UTC)
 * I've done the maths, BenRG is correct (well, I get 390 billion light years, rather than 250 billion, but close enough). I've done some further calculations and it isn't the volume of the observable universe that corresponds to a black hole of critical density, it's the Hubble volume (which is often mistaken for the volume of the observable universe, which probably explains my mistake - either I, or whoever wrote wherever I read it, got them mixed up). (Actually, my calculations came out with it being about 10% off the Hubble volume, I'm not sure where the discrepancy came from - different sources for the various constants, probably.) --Tango (talk) 03:15, 9 June 2009 (UTC)


 * Could what we consider the universe be inside a black hole, without us being aware of it? 89.242.125.32 (talk) 10:32, 9 June 2009 (UTC)


 * If we are not aware, how should we answer your question? ;-) Scientific answer: As no theory at the moment is able to describe the central singularity of a black hole (where the mass is located), there is no way we could answer this. But you are free to speculate that these "coincidences" have a deeper meaning, it is just not proveable at the moment. --TheMaster17 (talk) 12:45, 9 June 2009 (UTC)
 * A black hole doesn't necessarily have all the mass at the centre. It takes time for the mass entering the black hole to get to the centre. General relativity tells us it will always get there in finite (proper) time, but it will spend some time not being there. If the universe was going to undergo a big crunch, that might be consistent with it being in a black hole (that isn't expected to happen, though, the expansion is measured to be accelerating, not slowing). There is a multiverse theory that involves universes in black holes, see Lee_Smolin. --Tango (talk) 16:58, 9 June 2009 (UTC)