The best answers address the question directly, and back up facts with wikilinks and links to sources. Do not edit others' comments and do not give any medical or legal advice.
CBS TV today showed a profile of the current state of North Korea. They showed the version of goosestepping employed by both the North Korean army and young girls of that country marching. In both cases, as they marched their heads moved up and down more sharply than in WW1 or WW2 films of the German army goosestepping. The NK soldiers hats almost fly off on each step. How does the standard NK goosestep differ from the Nazi 20th century German goosestep? What is the advantage of marching thus versus the march step of present day US, British,or German troops? Does goose-stepping cause the hip injuries and muscle strains that it would seem likely to cause? Do Goosesteppers actually march that way when they have to get 20 miles from Point A to Point B in a war? Edison (talk) 01:16, 12 November 2010 (UTC)[reply]
On a side note, and unrelated to the science of the question, the Wehrmacht were the normal German army during WW2, and one did not necessarily have to be a Nazi to be in the Wehrmacht. Towards the end of the war, the only requirement to be in the Wehrmacht was being alive. You are probably thinking of the Schutzstaffel, or SS. --KägeTorä - (影虎) (TALK)01:45, 12 November 2010 (UTC)[reply]
Movies from WW1 showed the Kaiser reviewing soldiers who were clearly goosestepping. There were no SS then. But they marched with less up and down snap than the North Koreans, the observation key to the original question. Do the NKs go up on tiptoe with each step while the Germans marched flat footed, or what? As for it being a ceremonial step used in review, did WW2 Germans marching from town to town march the same as Allied soldiers, and what commands were given to start them/stop them marching like geese? It would seem likely to have an attendant cost in soldiers unfit for duty due to injuries of the hip or knee. Edison (talk) 06:01, 12 November 2010 (UTC)[reply]
Yes, I know that well enough. As the article on Goose-step says, it was a Prussian invention. I was referring to you implying that the Wehrmacht were the same as the Nazis - which I see has been corrected in the original post. --KägeTorä - (影虎) (TALK)13:03, 12 November 2010 (UTC)[reply]
See the NK at 1:00 in this Youtube: [1]. They bounce more than the WW2 Germans victory march in Paris in 1940, at 0:25 and following:[2], though the SS does bounce a bit in this :[3], but still less than the NK marchers. (The Rockettes bounce even more than the NK forces, while doing a similar step (at 0:25):[4])Edison (talk) 06:27, 12 November 2010 (UTC)[reply]
Look at the way British Military marches during Trooping the Colour they would get no 20 km in that way. Both ways to march were and are 100% for ceremonial use. The GDR army was marching that way till their end in 1990. In German the whole thing is called Stech-schritt Stab-step sounding more dangerous than goose. --Stone (talk) 06:33, 12 November 2010 (UTC)[reply]
@ HiLo, well sort of [5], but the effect with the goose seems to be caused by the upper part of the leg is hidden thus giving a sort of strutting gait. This is emulated in human marching by keeping the whole leg stiff - Hmm, that's a bit obvious. Richard Avery (talk) 09:54, 12 November 2010 (UTC)[reply]
Just to say that the German Army abandoned the goosestep at the start of WWIIafter 1940. The Soviets used it following the Imperial Russian tradition (Peter the Great copied it from the Prussians). The North Koreans have taken it from the Soviets (maybe via China?[6]). The Russian Army still uses it too[7]. BTW the British Army quick march[8] is certainly a very efficient way of moving troops from A to B (hardly changed since the 18th Century according to this[9]) - the slow march[10] is purely ceremonial. Alansplodge (talk) 13:16, 12 November 2010 (UTC)[reply]
Here are real geese stepping, at 0:55 :[12]. Here is an animated Donald Duck goose-stepping, at 3:45, bobbing up and down about as much as the North Koreans: [13]. Still no answer as to why the NK folks heads snap up and down as they execute the goose step to a greater extent than any previous fascist troops, so that soldiers' hats almost fly off. Is it a faster cadence, or something different in the execution of the step? Was there ever a problem with goose-steppers kicking the butt of the soldier in front? Edison (talk) 00:55, 13 November 2010 (UTC)[reply]
Maybe. The listed info is not of high quality. The reference supplied points to a letter to the editor[15], not a study. This letter in turn references a study[16] but that study is comparing peanut oil to olive oil, it's not trying to find out if peanut oil is bad. Tree nuts do have many health benefits, but peanuts don't. I wouldn't go so far as to say ban them as unhealthy, but I would say don't try to gain any health benefits from them, and eat them like you would other so-so foods. Ariel. (talk) 04:11, 12 November 2010 (UTC)[reply]
Peanut oil does have its benefits, however. It has a very high smoke point which allows foods to be fried at a higher temperature; higher temperature frying results in higher outward pressure of water as it leaves the food, which coincidentally results in less oil getting into the food, resulting in a crisper fried product with less oil in it; thus foods fried in peanut oil can be lower fat than those fried in other oils. --Jayron3204:28, 12 November 2010 (UTC)[reply]
(edit conflict with Jayron) The Atherogenenicity of Peanut Oil has been well established for quite some time (since the 1970s, at least: [17] and [18]). It is said to produce "fibrous", rather than "fatty" lessions; I'm not sure if that makes any difference in terms of heart disease. So yes, peanut oil is worse for clogging the arteries than most other unsaturated fats. Is it worse than saturated fats? The 1971 report showed coconut oil (high in saturated fat) and peanut oil having similar effects. So no, peanuts aren't going to be as healthy as tree nuts. You should probably treat them more on par with red meat than walnuts. Few would say that beef is unhealthy in moderate amounts, but eating too much can cause heart problems. Buddy431 (talk) 04:38, 12 November 2010 (UTC)[reply]
According to the peanut article, the FDA in 2003 released a statement that "Scientific evidence suggests, but does not prove, that eating 1.5 ounces per day of most nuts, including peanuts as part of a diet low in saturated fat and cholesterol, may reduce the risk of heart disease." Of course, that was under George W. Bush, and one might suspect that America's fiduciary duty to recommend domestically grown products would have been morally superior to any potential health science data... Wnt (talk) 09:39, 12 November 2010 (UTC)[reply]
Much as I hate George W. Bush, this particular attitude is not something you can pin on him. Favoring domestic food producers with powerful lobbying groups, even at the expense of science, is a non-partisan issue in US politics - everybody does it. thx1138 (talk) 00:54, 13 November 2010 (UTC)[reply]
I have to agree that "antioxidant" is an overused buzzword in terms of health. It is a real chemical activity, yes, but biological systems don't work like beakers in a laboratory — you never really know the effect that something will have until that exact compound is tested. For comparison consider enantiomers, which always have the same basic chemical properties, but often have completely different effects in the body. Wnt (talk) 18:45, 13 November 2010 (UTC)[reply]
why is AC more dangerous than DC?
Normalising for voltage and current, etc. is it because the peak voltage of AC is higher than the average voltage? Does the body adapt less well to an alternating current and is more likely to send ion channels out of whack? John Riemann Soong (talk) 05:21, 12 November 2010 (UTC)[reply]
I thought it was because if you grabbed a live AC wire it would force your muscles rigid and you wouldn't be able to break free, whereas a DC wire would have the opposite effect - such that the consequences of shock are VERY different in severity depending on current type. 59.46.38.107 (talk) 05:25, 12 November 2010 (UTC)[reply]
Alternating current also has a frequency (50-60 Hz, depending on location) which can cause Ventricular fibrillation Higher frequency may avoid this problem, but as frequency increases, efficiency decreases, so that's a problem for transmission as well. War of Currents covers some of these differences, and it has a reference for the heart trouble issue. However, safety aside, DC power transmission has serious problems with long-distance losses. Because of this, DC power transmission systems tended to be smaller in scale (each neighborhood or sizable factory would have needed its own dedicated power plant), which has serious problems in terms of expense and feasibility.
AC power experiences much lower losses, it also reacts better to step-up and step-down transforming, so you can transmit long distances at MUCH higher voltages than you can at DC power, which only adds to the difference in efficiency. --Jayron3205:37, 12 November 2010 (UTC)[reply]
At the same voltage and current, AC and DC should have similar voltage drops at the same distance of transmission, AC is easily stepped up via transformers for more distant transmission with lower "copper losses." I do not agree with 59.46.38.107's statement that DC makes you let go of a live wire. The "war of the current" tests generally showed greater lethality for AC than for DC at a given distribution voltage. Quite a low voltage might be lethal for some people, so do not experiment at home. The real difference was that AC was carried on overhead wires at 4kv or whatever, while DC was carried at a much lower voltage, initially 110 volts or so in the US. The problem was that only dense central cities like New York or Chicago or London could support a DC central station every couple of miles, whereas with AC a power plant could send out high voltage for many more miles economically, to be stepped down to 120/240 or so by transformers wherever there was a customer or a load center.
Ironically, for very long distance transmission, DC is now popular, at 500 kilovolts or so. Of course it would be quite lethal to contact it at those high voltages. Edison (talk) 06:15, 12 November 2010 (UTC)[reply]
I also do not agree with 59.46.38.107 - it's actually the opposite of that. AC has zero crossings which enables you to let go, but DC does not, and will hold the muscles rigid. Ariel. (talk) 06:45, 12 November 2010 (UTC)[reply]
For example: [20] Quote: "Direct current (DC) is more likely to cause muscle tetanus than alternating current (AC), making DC more likely to "freeze" a victim in a shock scenario. However, AC is more likely to cause a victim's heart to fibrillate, which is a more dangerous condition for the victim after the shocking current has been halted."
However, that said you also have "Low-frequency AC produces extended muscle contraction (tetany), which may freeze the hand to the current's source, prolonging exposure. DC is most likely to cause a single convulsive contraction, which often forces the victim away from the current's source." - which doesn't contradict the above, it just says the shock will move the hand, then freeze it, instead of freezing it in the original place.
On top of all that you also have an interesting table showing that 60hz AC requires less current than DC to cause trouble. Interestingly higher frequency AC is about the same as DC.
Final conclusion: Both AC and DC have hazards, but the hazards are different. Sometimes AC wins, sometimes DC, and there is no clear "better". Ariel. (talk) 10:41, 12 November 2010 (UTC)[reply]
It seems to me that whichever kind of power people want to tell you to stay away from, they say that that kind is more dangerous. --Anonymous, 23:18 UTC, November 12, 2010.
The "zero crossings" of AC occur 120 times per second (US),(110 per second, many other countries), so inertia would prevent much movement of the hand away from the wire before the next peak caused another strong contraction. Edison (talk) 17:55, 12 November 2010 (UTC)[reply]
You mean 120 and 100, of course. --Anonymous, 23:18 UTC, November 12, 2010.
You are right if it is 50 rather than 55 cycles in the non-US world. I forget sometimes. There was also 25 cycles and several other frequencies in the past. Edison (talk) 00:44, 13 November 2010 (UTC)[reply]
I just tried out holding the probes of a multimeter hard and the lowest I could get was about 1.3 megohms, I had to get things quite wet to get down to 250 kohms, that would only pass one milliamp at 250 volts. I can see it could get to be quite appreciable if my hands were actually in water but I'm a bit surprised that just one milliamp can have such an effect as people describe from touching a wire. The body must be very sensitive to low currents. Dmcq (talk) 01:09, 14 November 2010 (UTC)[reply]
The resistance of the body can drop quite dramatically after a certain voltage is surpassed. Part of this is that the conductivity of the skin is regulated by how open the pores are, and cells have membrane potentials, and changing their membrane potentials will affect their conductivity. If you get shocked quite a bit, your skin will open up its pores due to stress, which will decrease the resistance of your skin even further. John Riemann Soong (talk) 01:29, 14 November 2010 (UTC)[reply]
Cat swallow food when upside down
Is it true that cats can't swallow food upside down, and they rely on gravity for it to fall down their throat? They "bolt" food instead of swallow it? I've heard this for ages, but I can't find a single mention of it when searching, so now I'm wondering if I was mislead. Ariel. (talk) 07:32, 12 November 2010 (UTC)[reply]
This article specifically mentions peristalsis of the feline esophagus as a normal function [22]. I would think that peristalsis indicates a 'true swallow', and does not require gravity. SemanticMantis (talk) 15:14, 12 November 2010 (UTC)[reply]
They kept saying how the cat is drinking better or smarter or something than the dog, but that video shows the dog doing the exact same "lift" a column of water and close jaws around it that the cat does! Only the dog also make a spoon of sorts with his tongue. So it seems to me that cats are not unique in this. Ariel. (talk) 20:32, 12 November 2010 (UTC)[reply]
Ptosis in traditional cultures
There's some very good news (for women and men...) in our article on the brassiere — namely, that the bra does absolutely nothing to prevent ptosis (sagging), and perhaps is even counterproductive. It should be shouted from the rooftops... But it does leave me wondering: it is not at all uncommon when looking at film from various scantily clad 'indigenous' societies, to see women who have indeed developed ptosis to a truly remarkable degree. What is the reason for that? Wnt (talk) 09:08, 12 November 2010 (UTC)[reply]
The article on Ptosis_(breasts) offers scant information beyond the obvious that the fascia, skin and suspensory ligaments generally become more lax with age. The observation about 'indigenous' ladies is spurious as a large majority of ladies demonstrate the same effect, we just don't see so many UK indigenous ladies in such a state of undress. Richard Avery (talk) 09:36, 12 November 2010 (UTC)[reply]
Pregnancy is also a factor, so women in societies where the childbearing age is relatively early are likely to have a greater degree of ptosis than women of the same age in, say, the UK. Physchim62(talk)18:57, 12 November 2010 (UTC)[reply]
I don't see how something that happens naturally like having children under the age of 18 is tragic. It is not socially encouraged in Western culture, but that is really just an invention of the last century there too. Googlemeister (talk) 20:40, 12 November 2010 (UTC)[reply]
@ Googlemeister, so how many 18 year olds are in a position to give a baby a start in life, in the UK or Canada, let alone in Niger. The invention of which you speak is called health and social development. Just because it is 'natural' doesn't make it the best option. Richard Avery (talk) 10:26, 13 November 2010 (UTC)[reply]
aDMISSION into XLRI
I didnt complete my Btech yet because I still have 3 backlogs even after completing my 4rth year. I applied for XAT 2011 because I will anyway get my final memo by end of january 2011. When should I actually apply for admission into XLRI??? Should I do it now itself or after I get my XAT score card?? My aggregate is very less at present......will it affect my admission??? After I write my supplementaries I will achieve 57% as my aggregate.......will it be okay??? —Preceding unsigned comment added by 115.109.194.75 (talk) 12:44, 12 November 2010 (UTC)[reply]
I don't think it's that hard to get the gist of what the OP is asking about. It's true without knowing the details no specific answer can be provided but on the other hand, it's also true the OP would be much better of talking a careers or some other advisor at their tertiary institution and/or the people who run the XAT/XLRI [26]Nil Einne (talk) 18:33, 13 November 2010 (UTC)[reply]
Limits of Gene Therapy?
With the advances being made in using our own skin cells and turning them into stem cells, in the future would it be possible to say for example they found the gene for diabetes and they changed some cells to not include diabetes or cancer, would you be able if they put into a person enough stem cells without those genes could it then replace all the other cells in the body from those stem cells that multiply and replace all the other cells in the body? Is that even possible or are the newly injected stem cells only limited to certain areas in the body? How does or would that work? —Preceding unsigned comment added by 71.137.241.60 (talk) 15:27, 12 November 2010 (UTC)[reply]
This is a rather complicated question because you are asking about several big "if"s.
First, it is true that scientists can reprogram stem cells to resemble a mature cell type, but it should be recognized that the resulting "re-programmed" cells are not exactly the same as if they developed according the normal developmental programs. There's a lot we don't know about possible tumorigenicity of reprogrammed cells.
Second, not all organs of the body are amenable to simply injecting a whole bunch of stem cells in and hoping that they somehow replace the normal tissue architecture. One exception is blood cells, which are produced in the bone marrow and might be particularly amenable to replacement by stem cells (that's what a bone marrow transplant is, after all). However, most tissues of the body are highly organized in terms of blood vasculature, nerve innervation, and connections between cells. Some researchers think we might be better off growing new tissues in the lab (tissue engineering) and then transplanting them the same way we might with a donated organ.
Third, diabetes and cancer are multifactorial conditions. For most common diseases, there isn't a single gene that can be removed or replaced with gene therapy "to not include diabetes or cancer". This is a much too simplistic concept of disease and in reality human diseases are much more complex. Only in very rare families do these types of conditions act as a heritable "single gene" disorder. Type 2 diabetes is really a problem with insulin resistance meaning that the peripheral tissues become insensitive to insulin, resulting in increasing requirement for insulin production by the pancreas and eventually the pancreas failing to meet the insulin demand. This is different than type 1 diabetes, where the pancreatic islet cells are typically destroyed by an autoimmune process. These two distinct forms of diabetes have different degrees of genetic contribution and would require different approaches in terms of a "stem cell replacement" strategy. Sporadic cancers (the vast majority of cancers) occur through a highly complicated multi-step process that usually entails lifelong exposure to carcinogens and chance somatic mutations. This simply is not amenable to a gene therapy treatment.
Technically, stem cell therapy need not be gene therapy. Cell types are established by a combination of epigenetic modification of genes, active feedback from existing patterns of transcription factor and other regulatory gene expression, and environmental cues. Culturing a cell type under just the right circumstances, with the right drugs, can occasionally lead to transdifferentiation without the need to change it genetically, though certainly gene therapy can be used to give cells a stronger hint about what you want them to do. In concept, it is conceivable that the right drug, perhaps a drink from a certain fountain or the fruit of a rare tree from Eden, could lead certain cells to take on stem cell identity, or stimulate the growth of existing stem cells throughout the body. Of course, such a drug may be harder to find than to imagine. Wnt (talk) 18:39, 13 November 2010 (UTC)[reply]
The first lady, Floé, is clearly a muscular athlete who uses her arms in her sport and has increased the muscles in her axilla to the point that when she opens her axilla to this extent the muscles stretch against the skin making an ouline. If you raise your own arm and feel in the axilla you will detect these muscles, here [27] is a diagram to help understand my explanation. Richard Avery (talk) 18:40, 12 November 2010 (UTC)[reply]
I think this picture is a little more clear. The muscle involved is mostly the latissimus dorsi. Most people don't flex their lats to this degree (and even fewer do so with such little fat tissue to obscure things), so it's somewhat striking. But that's not unheard of; everyone is built a little differently. Most athletes only show a single mass for their bicep, but then again some show a split muscle - they just happen to have the right balance of large muscle and trim fat to allow it to show. Matt Deres (talk) 01:29, 13 November 2010 (UTC) I did a short image search to see if I could find an example of the "split" bicep and I'll tell you this for free: internet porn isn't nearly as gross as the stuff you see in an image search for "bicep".[reply]
You know there's actually no such word as bicep, right? The singular and plural are both biceps; the bicep version is a back-formation. I wonder how your search would have gone if you'd used the more formal spelling. But after the warning I'm not going to check it out myself. --Trovatore (talk) 07:25, 14 November 2010 (UTC)[reply]
I'm not entirely convinced of this. In this image it doesn't look like her body fat is that low to be able to determine that level of striation in those muscles, given the definition (or lack thereof) seen in her other muscles - the abdominal region, clearly visible here, is a good place to look for this. And when you view the uncropped image you realise the cropped version is a little deceptive, as the muscles aren't under any particularly great tension which could otherwise help bolster that explanation. With their nature and appearance, I'm kind of suspecting stretch marks. --jjron (talk) 05:12, 14 November 2010 (UTC)[reply]
I'm not convinced it's muscle, either. It's just such a tiny area, and it's not under as much strain as other parts of her body. I suppose another possibility is that they're simply wrinkles. --Sean19:46, 15 November 2010 (UTC)[reply]
winds
Anyone know where I can find data on the speed and direction of winds in central Hampshire? Or any other climate data on the same area as well.
Looks like it's easy to get to genus, hard to get to species. In short, there are likely congeneric look-alikes within the same region. According to our page Russula,
"While it is relatively easy to identify a sample mushroom as belonging to this genus, it is a significant challenge to distinguish member species of Russula. This task often requires microscopic characteristics, and subtle subjective distinctions, such as the difference between a mild to bitter and a mild to acrid flavor."
I am intrigued by this "its quality is improved once parasitised by the ascomycete fungus Hypomyces lactifluorum, transforming it into an edible known as a lobster mushroom." Maybe the parasitic fungus (if present) can help clarify the host species, e.g. if the parasite is highly specialized to one species. SemanticMantis (talk) 19:49, 12 November 2010 (UTC)[reply]
Also, are you trying to ID a sample, or just curious? If the former, the commonness of R. brevipes will be a clue, e.g. if there are dozens of the same mushroom in a few different patches, I would have more confidence in the species ID. SemanticMantis (talk) 19:58, 12 November 2010 (UTC)[reply]
I am trying to identify this one. These were the only mushrooms in the patch, apart from some two others just out of the picture. And are there any poisonous mushrooms in the genus that can be mistaken for R. brevipes? --TheHighFinSpermWhale20:02, 12 November 2010 (UTC)[reply]
I am not an expert in mushroom ID, and I am not advising you to eat this or any mushroom. Anything can be mistaken for anything with the proper lack of experience and perception. That being said, our List_of_Russula_species contains two poisonous examples. According to their Wikipedia pages, neither has the decurrent hymenium that our article on R. breviceps indicates. Keep in mind that list may not be complete or accurate. See also [28]. Seriously, eating mushrooms without expert identification is potentially deadly. Hope this helps, and that someone with more experience chimes in. SemanticMantis (talk) 20:28, 12 November 2010 (UTC)[reply]
The effects of heat on an electrical arc
This is merely a point of empirical curiosity, which seems not to be addressed anywhere else on the web (which is, in and of itself, curious). I have observed that an electrical arc, in this case generated by a 600,000 volt stun-gun, will ignore the UN-lit end cigarette,traveling the shortest, most direct route around the outside of it, to connect to the other post on the opposite side. However, light the cigarette, and repeat the same steps, placing the now lit end of the cigarette between the two posts of the stun-gun, and now the arc will actively seek out the "cherry" and go through it to get to the opposite post. An interesting side-note, at this point, is that the arc will completely ignore the cold ashes that have already burned, seeking out the still burning cherry, altering it's path to do so. So, my question, being two-fold, is this; Why does this happen, and how? Take your time in answering. I've wondered this for roughly twenty years. I can wait a little longer. It's not for a test, or any other kind of project. I simply have a scientific curiosity. If you can't figure this out, you're in good company. I've been seeking an answer from a wide selection of people, over the years, to no avail. However, I'd like to thank you for your time, and effort, in advance. I'm eager to see if this question, "How/why does heat/fire affect an electrical arc", can finally be put to bed. 74.60.220.9 (talk) 20:00, 12 November 2010 (UTC)[reply]
Well you will be interested to know that flames conduct electricity! In my boiler there is something called a flame sensor - it works be trying to send electricity through the flame and measuring how much current goes though, when the fire is on it completes the circuit. The same thing makes a Plasma speaker work. Ariel. (talk) 20:36, 12 November 2010 (UTC)[reply]
(ec) Flame is a plasma, which unlike a gas conducts electricity. So the arc goes through the flame because that's the path of least resistance, in this case the path of least electrical resistance. The arc actually also ionizes the atmospheric gas, turning it, too, into a plasma, but the smallest length of gas that needs to be ionized by the arc involves taking a shortcut through the already-available plasma of the flame. Red Act (talk) 21:12, 12 November 2010 (UTC)[reply]
plus, an unlit cigarette is basically a wad of paper, which is a fairly decent insulator. an electrical arc will follow the path of least resistance, and since the cigarette has a small cross-section it will generally arc around it rather than through it. --Ludwigs215:47, 13 November 2010 (UTC)[reply]
When I carry a tray across a room, my arms don't do any work on the tray. I totally understand this. However, I think that my legs are doing work on the tray. My walking legs provide the horizontal force that move the tray. Is this correct or not, and if not, why not? Lova Falktalk11:10, 13 November 2010 (UTC)[reply]
1. Because the term work, like theory, means something different in physics from that in general usage. Also because arms are wimps compared with legs, for most people. Imagine Reason (talk) 13:39, 13 November 2010 (UTC)[reply]
(edit conflict) Because the muscles in your arms have to exert a force to counteract gravity. In physiological terms, this is "working" and consumes chemical energy, though no "work" is done by your arms in the physics sense. You legs are doing work in the physics sense because your centre of gravity moves up and down as you walk, but leg muscles are accustomed to this and don't tire easily. Dbfirs13:42, 13 November 2010 (UTC)[reply]
As I understand it, your arm muscles are constantly flexing to keep the tray in place. The tray moves up and down all the time, and its this that makes your arms feel tired. 92.29.122.31 (talk) 17:50, 13 November 2010 (UTC)[reply]
Folk are confusing "force" with "work".
A magnet exerts a force - it does not "do work". Your fridge magnet will stay stuck to your fridge until hell freezes over without "running down" because it doesn't need to expend energy to do it. Energy is produced or consumed when something that's exerting a force moves. So when you peel the magnet off of your fridge, it costs your muscles energy to do it. When you release the magnet from a half inch away from the fridge, it releases that energy by moving back onto the fridge - and the energy you added with your muscles is turned into heat and sound as it snaps back onto the metal. The magnet itself doesn't HAVE energy to give away - it's not like a battery or a wound-up clockwork toy.
The clockwork toy is a great analogy. If you wind up a clockwork toy car and place it on the table with your hand in front of it, you can feel it pushing against your hand. But until you move out of the way and let the car shoot across the table, it's its spring won't ever run down. It'll stay there with the spring wound up, actively pushing against your hand, until you release it - even if that takes an hour, a week or a thousand years. Once the car starts moving, it gains "kinetic energy" (the energy of motion) and gradually loses the energy in the spring.
The situation is exactly the same as with another common force...gravity. If you place a tray onto a table, the tray and the table are exerting forces on each other - the tray is being pulled downwards by gravity - and the table has interatomic forces that resist motion and press upwards onto the tray to prevent it from moving. Again - there are lots of forces being applied here - but no energy is being produced or consumed in the process because nothing is moving (technically: because nothing is accelerating). The tray will stay there, resting on the table forever without the table or the tray "running out of energy" because they are doing that. But if you exert chemical energy from your muscles to pick up the tray - you are giving it energy because you are working against the force of gravity...and when you drop it onto the floor, this energy will be released as it falls, turning into kinetic energy (motion) and then into heat and sound as it hits the floor. Cuddlyable3 (talk) 14:16, 13 November 2010 (UTC)[reply]
"Work = force x distance" is WRONG! The correct formula is "Work = force . distance" as it is the Dot product of two vector properties that yields a scalar result and not in this case the cross product.
Your arms do a small amount of positive work while accelerating the tray against inertia (applying a force), "dot" the distance where that force is applied. But you do an equal amount of negative work decelerating the tray while it continues to move in the same direction when you get to the other end of the room (the dot product is negative). (This negative work makes a lot more sense if you consider a hybrid car with regenerative braking!)
Now the reason why your legs don't get credit for holding up the tray is that a better designed tray carrier would just slide frictionlessly across the floor, holding it up the whole time without consuming energy.
But I don't give my legs credit for the vertical position of the tray, I want to give them credit for the horizontal movement of the tray. Lova Falktalk20:19, 13 November 2010 (UTC)[reply]
There is work done by your legs to carry the tray from one position to another horizontally. If the tray weighed 100 kilograms (220 lb), your legs would notice that more (they would notice if you just stood there, too, but they would notice even more if you tried to walk). WikiDao ☯ (talk)20:35, 13 November 2010 (UTC)[reply]
We do have an article on the physics of this: Work (physics), which says:
What you feel when you are just holding the tray is its Weight, or the force of gravity. If you were carrying the tray in a gravity-less environment, so that its weight was zero but its mass was still say 100 kg, you would find it more difficult to move it "horizontally" than if its mass was only 10 kg. See also Mass versus weight. WikiDao ☯ (talk)21:01, 13 November 2010 (UTC)[reply]
... and in physiological terms, your legs need to do work both to accelerate and decelerate the tray. There is no way that the kinetic energy can be recovered, so work has to be done to bring the tray to rest again, even though the total work done in physics terms is zero. The work done appears (at least partly) as heat in the muscles of the legs and to some extent in the back and shoulders. Your arm muscles would also do some work if you held the tray out in front of you, but obviously not if the tray was held by a harness round your neck. Dbfirs21:22, 13 November 2010 (UTC)[reply]
I see no reason why muscles couldn't do the equivalent of regenerative braking, converting some of your kinetic energy back into ATP. I think they don't, but it's not ruled out by the laws of physics. Likewise, you could gain energy carrying a heavy object downhill. The long and short of it is that our bodies suck at this task. We lose a lot of energy (as heat) unnecessarily. Otherwise we wouldn't get tired. -- BenRG (talk) 00:49, 14 November 2010 (UTC)[reply]
To this day it mystifies me why muscles didn't evolve with a "hold" mode that would require no energy to use; though biological uses for it would be rare you'd think there'd be some. I wonder if the myosin heads all locked down in one static pattern for some hours, that structural flaws might damage the muscle? Wnt (talk) 18:58, 13 November 2010 (UTC)[reply]
Birds lock their claws onto a perch, and some animals sleep standing up by locking their legs, but I think this is joints not muscles that achieve this effect. Dbfirs21:22, 13 November 2010 (UTC)[reply]
You expend plenty of energy moving the tray around, but that's because we're pretty inefficient at that sort of thing, and that's not the same as doing work (in the physics sense of the word). There's a lot of frictional forces involved, and all that energy ends up becoming heat. You can think of the amount of work done on the tray as how much energy you've added to it. If you carry the tray around and it ends up back where it started, you haven't actually changed the tray's situation so you haven't done any work on it (even if you expended energy). If you lift the tray up to a higher position, you have done work on it since now the tray has more potential energy than it did before. If you throw the tray, you've done work on it by giving it kinetic energy. Rckrone (talk) 04:08, 14 November 2010 (UTC)[reply]
Perhaps this is in part a biology type question? When one is carrying a tray, even though the tray is not moving up or down visibly, the actin and myosin fibres in your skeletal muscles are actually engaging and disengaging many times a second and expanding a large amount of energy to do so. As such, you arm is getting pulled down very minutely and pulling itself back up again very minutely to counteract the force of gravity and thus you ARE actually doing work by carrying a tray. Muscles such as smooth muscle work by a slightly different mechanism so this same engaging and disengaging does not happen. Thus if your arm was made of it you would THEN not be doing any work, however this type of muscle fibres reacts more slowly and your controllable muscles are not made of them. -- Sjschen (talk) 00:02, 16 November 2010 (UTC)[reply]
A firearm is effectively a single-stroke Internal combustion engine or heat engine and efficiency is described by thermodynamic cycles. None of these cycles exceed the limit defined by the Carnot cycle which states that the overall efficiency is dictated by the difference between the lower and upper operating temperatures. Most engines have energy efficiency of about 18%-20% which I expect is similar for firearms. Cuddlyable3 (talk) 13:56, 13 November 2010 (UTC)[reply]
Our article on physics of firearms claims roughly 30% efficiency for what is nominally a very efficient cartridge. It's actually not too difficult to calculate for yourself if you know the amount of gunpowder used along with the mass and muzzle velocity of the bullet. The lone external link from that article here puts the energy content of powder (including binders and additives) at about 1.3 million foot-pounds per pound of powder (about 4 kilojoules per gram); that's equal to about 190 foot-pounds or 260 joules per grain of powder. Multiply that energy density by the mass of powder in the load and that tells you how much energy goes in.
Next calculate the muzzle energy of the bullet. (That's one half of the mass of the bullet, multiplied by the square of the muzzle velocity — be careful with your units). Divide the kinetic energy of the bullet by the total energy supplied by the powder to get the energy conversion (chemical to kinetic) efficiency of the gun. Let's take a .44 Magnum with a 200-grain (13 g) bullet and 18.3 grains (1.2 g) of powder, and a nominal muzzle velocity of 1520 fps (463 m/s), based on this table. The energy in the powder is 4.8 kJ, and the kinetic energy of the bullet is 0.7 kJ, for an efficiency of just 15%. TenOfAllTrades(talk) 15:47, 13 November 2010 (UTC)[reply]
I'm not sure I understand the assumptions behind your question. I'm not familiar with any work that suggests the uncertainty principle is somehow linked to dark energy; could you provide a bit more information about where you're coming from on this? TenOfAllTrades(talk) 15:53, 13 November 2010 (UTC)[reply]
I’m guessing part of the confusion here is a matter of glancing at the ΔE and the Δt in the uncertainty principle, and thinking "oh, ΔE and Δt give units of power". However, power is ΔE divided by Δt, whereas the uncertainty principle involves a product of ΔE and Δt.
Also, although the uncertainty principle and dark energy both involve an uncertainty as to how much energy there is, the two are unrelated. The uncertainty in energy involved in the uncertainty principle is due to the wave nature of particles. The uncertainty in energy involved in dark energy is a matter of our observatories having difficulty observing the energy due to other reasons. The uncertainty in energy involved in the uncertainty principle is negligible except when dealing with very tiny amounts of energy, and very tiny amounts of time, neither of which apply when doing cosmology. Red Act (talk) 17:58, 13 November 2010 (UTC)[reply]
I think Hcobb is talking about the idea that the dark energy is vacuum zero-point energy. The problem is that the predicted zero-point energy density is much too large (by a factor of at least 10120 in certain units). So this is a case of quantum mechanics giving a huge (and wrong) answer.
There is actually no energy-time uncertainty principle in quantum mechanics. There probably should be, but there isn't, because time isn't an observable. Nevertheless, it seems hard to avoid the prediction of an enormous cosmological constant in any theory of quantum gravity. The reason (as best I understand it) is that virtual particles look locally just like real particles. You can't have gravity couple to one but not the other unless gravity somehow has nonlocal knowledge of the system. It's not good enough to say that the zero-point energy just isn't there; it is there in the mathematics, and you have to figure out a way to get rid of it. This is a major unsolved problem. -- BenRG (talk) 01:17, 14 November 2010 (UTC)[reply]
From above: "There is actually no energy-time uncertainty principle in quantum mechanics"
Hmm? How is time less an observable than position? You don't deny there's a position–momentum one?
I've always interpreted the time–energy conjugacy as one way of looking at, for example, the fact that you can't have a truly monochromatic plane wave of light unless it has always existed and always will. If you have a bounds on when a photon was emitted, it comports limits on how well you can know that photon's energy. No? --Trovatore (talk) 07:57, 14 November 2010 (UTC)[reply]
Time is not an observable#Quantum mechanics. It's treated as a parameter which is known, a priori, to arbitrary precision. Quantum mechanics doesn't give you a probability distribution over times, whose standard deviation would be the Δt in ΔEΔt. In classical wave theory there is an energy-time uncertainty relation and I suppose that can be adapted to quantum mechanics somehow, but it's not exactly analogous to the famous ΔxΔp uncertainty relation. It probably should be, but it's not. This is the famous "problem of time" in quantum gravity, or one aspect of it anyway. I only mentioned this because the original question mentioned energy-time uncertainty. It may have nothing to do with what I said about vacuum energy. The vacuum energy is related to the (more general) uncertainty principle, since you can think of the vacuum as being made of a bunch of harmonic oscillators whose ground-state energy is the vacuum energy, but it may have nothing to do with an energy-time uncertainty relation specifically. -- BenRG (talk) 05:12, 15 November 2010 (UTC)[reply]
The Double-slit experiment article would benefit from a better illustration than this diagram. But in your video the sea of waves obscures the essential explanation that at any point on the screen, the 2 separate waves from each slit meet for the first time, and their interference occurs there. It also needs to be clarified that whether their interference is constructive or destructive depends on the difference in their path lengths, which is a function of the angle. The light source is drawn larger than necessary. It's not clear why some thin ray lines are drawn from the start before the light waves appear nor why they develop into green walls. The interference pattern is static so I don't think any purpose is served by animating the gradual buildup of the waves. Cuddlyable3 (talk) 01:21, 14 November 2010 (UTC)[reply]
The size of these videos is still a huge problem - even over cable modem it stops and starts. I believe that you should shoot for this video to be viewed at the preview size you have it at now, and make the file as small as needed for this one purpose. Therefore I think you should make the slits a little larger, or a little more prominent. I suspect it may help if the slits are made two different colors, and the waves are made two different colors, so that you can see the interference more clearly... but that too would add confusions that would have to be explained.
The video as-is already has some value, but I think that a little tinkering well more than double its usefulness. I agree with most of Cuddlyable's comments except I do think that the gradual buildup of the waves is quite useful and definitely should not be taken out. Wnt (talk) 04:41, 14 November 2010 (UTC)[reply]
1. Technical improvement: I have reduced the file size to 1.1 MB. The clip has to be modified because the resolution is now very poor. I will work through the rest to see what can be done. Thank you for the response. --Cookatoo.ergo.ZooM (talk) 09:25, 14 November 2010 (UTC)[reply]
This loads and plays very well for me, at least, and at the inline resolution the image is still very clear. I would encourage you to use this as is; any further improvements might involve adding more detailed information at the end. Wnt (talk) 15:19, 14 November 2010 (UTC)[reply]
(Referring to the modified clip). Half-way through the clip at 0:22 the light source inexplicably changes to somewhere between the slits. The illumination from the source to the slits should be shown. It is wrong to show the constructive/destructive pattern forming immediately the light leaves the slits. Cuddlyable3 (talk) 15:22, 14 November 2010 (UTC)[reply]
There are two takes in the clip: Take 1 shows the 2 separate waves (one originating at each slit) and their "intersection" (= interference). At 0:21 the 2nd take commences. This take shows the "composite" (ie single) wave as it is generated by constructive / destructive interference.
As a professional ignoramus I may easily misunderstand aspects of this experiment.
I will render take 1 with the light from the slits showing as 90° sectors (+/- 45° from the axis), rather than 180° sectors. The interference will then start a bit off the slit panel. I will also tweak take 2 so that the composite wave does not start in between the two slits but further "back". Thank you for the comments and greetings from Vienna. --Cookatoo.ergo.ZooM (talk) 16:44, 14 November 2010 (UTC)[reply]
November 14
converting doi to acs-style citations
Are there any automated services that will convert doi's to ACS-style citations?
Here on Wikipedia, we have Template:doi and Template:cite doi. I believe "cite doi" will expand to a full citation - though I'm not sure how, I imagine it uses one or more web service APIs either provided by Wikipedia's tool server, or by http://dx.doi.org (the DOI resolving service). You could use the Wikipedia cite-doi tool to generate the citations, and then copy/paste (or screen-scrape, if you need the process to be automated). Note that there seems to be a few minutes of delay when using the cite-doi template while the plain-text is generated and later subst'ed by a bot. Nimur (talk) 04:12, 14 November 2010 (UTC)[reply]
Tensor of Inertia
My book says, without proof, that the tensor of inertia remains unchanged to first order for small angular displacements about the principal axes, but I don't think this is true. Don't the products of inertia gain a first-order factor? 76.68.247.201 (talk) 02:11, 14 November 2010 (UTC)[reply]
which obviously has first-order terms. What is true, though, is that the tensor of inertia viewed as a geometrical object (the ellipsoid of inertia) is symmetric around the principal axes. So, for example, the moment of inertia around an axis inclined from a principal axis doesn't vary to first order in the angle, since it's an even function of the angle. Probably that's what the book was trying to say (or did say?). -- BenRG (talk) 04:31, 14 November 2010 (UTC)[reply]
I'm sorry, but I don't follow :(. I've decided to take a few photos from my book, because I don't think it says what you're trying to say.
Here, the question asks to prove that the products of inertia are unchanged to first order...but they clearly aren't! This is important, because the authors use this result to derive Euler's equations.
As far as I can tell you're right. Either your textbook is clueless or I am. It may be me. Can anybody else take a look at this? -- BenRG (talk) 10:22, 15 November 2010 (UTC)[reply]
I concur, the book looks wrong to me. Just looking at the first page, anyway, I get that, e.g., to first order in α, Ixy=-4mα, so unless I'm missing something, problem 7.11 b appears to be asking you to show something that isn't actually true. Red Act (talk) 11:16, 15 November 2010 (UTC)[reply]
So what does that imply about Euler's equations? Is there another reason why we'd ignore the products of inertia when finding how the angular momentum changes when an object deviates from its principal axes? 76.68.247.201 (talk) 14:35, 15 November 2010 (UTC)[reply]
Looking for a talk that may have been featured on TED
I'm pretty sure that I saw this on TED talks, but either it's not there anymore, or I am remembering it wrong, but either way, I'm looking for a guy who made a speech about a program (an NGO?) that he was running on (west?) Africa helping to alleviate local desertification by introducing herds of large herbivores into fields periodically to allow their hooves to churn up the soil and their manure to fertilize. He talked about how modern agriculture usually pins overgrazing as a cause for desertification, when in fact historically large herds of herbivores would have periodically grazed small areas completely, allowing the plants to recycle and maintaining the ecosystem. Does this ring bells with anyone? I can't find the specific TED talk but I don't really need it if I could just find out the name of the guy. Thanks! 173.183.68.27 (talk) 03:25, 14 November 2010 (UTC)[reply]
Pressure waves of a certain range of frequencies within a fluid medium
The perception caused by vibrations within the ear or other analogous sense organ.
The second definition is key, if you could generate signals to the ear by means other than pressure waves, perhaps one could define that as sound. However, I suspect that under normal circumstances that's unlikely. Sound information can be transmitted via electromagnetic vibrations (that's what radio is), but the information needs to be decoded and broadcast via a speaker of some sort. --Jayron3203:33, 14 November 2010 (UTC)[reply]
Bear in mind that in the very high atmosphere or in outer space, atoms are typically charged. The solar wind is, for some reason I don't understand, a combination of electrons and protons rather than neutral hydrogen atoms. Thus any pressure wave in the medium is going to be involve variations in charge as well.
I am curious whether the various short sounds in the video represent actual changes over time in the medium, or whether they are spatially localized features that the satellite passes through on its orbit. Wnt (talk) 03:48, 14 November 2010 (UTC)[reply]
These "sounds of Jupiter" are electromagnetic signals. They are detected by an instrument (in this case, a VHF/UHF radio that flew on the Voyager probe. Those radio signals are measured at several megahertz - and they are mixed down to audible bands by a very common process known as heterodyning. Then, they are played through a speaker. So, if you could fly past Jupiter like Voyager did, and if you could survive "sticking your head out the window", you would not hear these sounds: first, they are not acoustic waves; and second, they are not in the audible frequency range. Interestingly, here on Earth, the equivalent radio-processes occur, but the relevant parameters of our planet's magnetic field are a bit different than Jupiter - so the very low frequency radio chirps here on Earth are at audible frequencies. (They are still not acoustic waves, though - so you still need a radio to hear them). Nimur (talk) 04:23, 14 November 2010 (UTC)[reply]
Also, for the advanced readers: there is such a thing as a magneto-acoustic wave - which is a unique coupling of electromagnetic (radio) wave into a pressure disturbance in a sparse plasma). However, the sounds we are hearing in this Jupiter demo-tape are not due to magneto-acoustic waves - they are actually due mostly to electron gyro frequency noise. Anyway, magneto-acoustic waves only occur in sparse plasmas, and the magnitude of the pressure-waves would be too small to be detected with an acoustic microphone - not to mention what would happen if you tried to put a human ear in that environment!) Nimur (talk) 04:26, 14 November 2010 (UTC)[reply]
This isn't my field, but the heterodyning you describe sounds like a cheap cheat, and contrary to what the video says are actual vibrations in the auditory range. I see that Voyager could detect ion acoustic waves with its instruments in the 50 Hz to 12000 Hz range.[29] I didn't look for the provenance of this YouTube recording to figure out exactly what is being measured, but I see no reason to think the video isn't right about them being, essentially, a sort of sound. Wnt (talk) 05:03, 14 November 2010 (UTC)[reply]
For further information, Magnetosphere of Jupiter is a very complete article. Yes, there is radio-emission in the VLF (audible base-band) range at Jupiter. I am pretty sure the sounds in the Youtube link are down-mixed UHF - but I may be incorrect. To find out for certain, you can compare to NASA's Jupiter Sounds archive - these recordings are each accompanied by a bit of scientific explanation. And if you're very interested, Imke de Pater (arguably the world expert on Jupiter's radio emissions, and planetary science in general) has a paper on Jupiter’s radio spectrum from 74 MHz up to 8 GHz and a website of her own on Jupiter sounds. Like a false color image, these sounds are "false-frequency" audio - the actual source data is pre-processed and output at a range that humans can hear. I would say that this process has limited scientific utility, but sure does sound cool. Nimur (talk) 05:32, 14 November 2010 (UTC)[reply]
I saw the date 1979 mentioned, which is when Voyager 2 passed Jupiter, and that article mentions a NASA "Symphonies of the Planets" 5-disk set, from which this audio should have come. It is possible to find out more about the datasets at [30] which has many records for Voyager 2 fluxgate magnetometer readings. Unfortunately, their information for the magnetometer (also linked from the Voyager 2 article) is now giving an error message. [31] describes "dual low field (LFM) and high field magnetometer (HFM) systems. The dual systems provide greater reliability and, in the case of the LFMs, permit the separation of spacecraft magnetic fields from the ambient fields. Additional reliability is achieved through electronic redundancy. The wide dynamic ranges of +/- 0.5 G for the LFMs and +/- 20 G for the HFMs, low quantization uncertainty of +/- 0.002 nT in the most sensitive +/- 8 nT LFM range, low sensor RMS noise level of 0.006 nT, and use of data compaction schemes to optimize the experiment information rate all combine to permit the study of a broad spectrum of phenomena during the mission. Objectives include the study of planetary fields at Jupiter, Saturn, Uranus and Neptune; satellites of these planets; solar wind and satellite interactions with planetary fields; and the large-scale structure and microscale characteristics of the interplanetary magnetic field. The interstellar field may also be measured." Now from the previous reference I take it that stellar winds do involve vibrations in the range of hearing, and the magnetometer is directly measuring some kind of buffeting at the spaceship itself, rather than at a distance by radio. The exact kind of wave, whether it's compression or transverse, I couldn't say from what I've read so far. Wnt (talk) 06:35, 14 November 2010 (UTC)[reply]
Just to clarify one thing: the key difference between acoustic- and magneto-acoustic wave is the mechanism of energy transfer. In the case of acoustic waves, the energy is conveyed by inter-atomic collisions. In space plasmas, the densities are far too low to sustain such aerodynamic/acoustic effects. So, energy is mediated between distant ions via ion/electromagnetic-wave interaction. Most of the time, these result in plasma oscillation. In some situations, this interaction can result in a propagating "pressure-front" in the plasma, but the pressures are still near-vacuum, so it's not quite like an ordinary sound wave in air. The question of measuring "at the spaceship" vs. "at a distance by radio" is moot - you are always measuring at the spacecraft. The question is whether the magnetometer is sensitive to ion pressure or magnetic fields - but from its name, it should be obvious that magnetometers measure magnetic field intensity (and typically, because of geometries, magnetometers are sensitive at ultra low frequency). Comparatively, an ion energy spectrometer would actually measure ion impingement; and a dipole electric field antenna would measure electric fields (because of geometries, a whip antenna will be sensitive at much higher frequencies than a similarly-sized loop magnetometer). The crucial piece of physics is that plasma-interactions describe the relationship between all three types of measurements - ion bulk motion, electric field, and magnetic field. Nimur (talk) 18:50, 15 November 2010 (UTC)[reply]
Middle-grounders on ID--What, If Any, Spokespeople Exist?
It's understood that the subject of what is called Intelligent Design Theory is dominated by those who assert their having already identified good evidence for external involvement in the origin, development, and/or internal workings of Earth and the life on it. What is the status of their claims in terms of whether they have produced even a single piece of purported evidence that has given the actual scientific community at large pause, and what is the nature of any more abstract debate that may be going on about the future prospects for finding such involvement? As the question of the heading asks, are there any substantially middle-of-the-road players who approach the topic holistically without submitting themselves to being committed to employing Occam's Razor?Julzes (talk) 03:37, 14 November 2010 (UTC)[reply]
There really aren't many. Intelligent Design isn't a particularly scientific approach towards working out the manner in which the world came to be. It starts with the premise that the Christian God created the world, assumes that to be true, then seeks to find evidence to support that. That particular approach is not very scientific, and most scientists who work in the fields ID also works in dismiss it offhand because of this. You would find many cosmologists, or evolutionary biologists, or geologists who seriously give it credence. Of course, you likely could find somebody, but the preponderance of respected scientists don't take it seriously in any way. However, please note that this doesn't mean that their aren't religious scientists, or that one must support the idea of Intelligent Design (as a specific theory) in order to be religious. I consider myself a rather devout Christian, but I have no pretense towards needing Intelligent Design in order to reconcile the current scientific understanding of the world, including evolution, the big bang, and anything else the ID people don't want to accept, with my religious view. --Jayron3203:49, 14 November 2010 (UTC)[reply]
Few middle of the road people would want to associate themselves with the strong statements of intelligent design or creationism. There are other discussions which are relevant, but not easily related to the traditional debate. For example, the weakless universe thought-experiment sought to disprove the anthropic principle by showing that a less elaborate physics could produce a world like ours. But which side is which — does the anthropic principle show that humans, by possessing an "awareness" relatable in concept to the soul or to God, have participated in the process of creation? Or does the idea that the universe contains extra complexity and wonder unneeded for us to merely exist prove the fecundity of the divine imagination?
A concept which interests me is whether the slow, cold end of the expanding universe is truly a barren dustbin of history, or whether there could be interesting "chemistry" among the remaining small particles — or new ones — when the tick of the clock is a googol of years. For example, picture two neutrinos of opposing weak isospin slowly orbiting one another in empty space. Could the weak force hold them together, despite the short range[32] of its carrier particle, if you have 10100 years to wait for the particle to slip out and cross a vast range of empty space "unnoticed". I always see the Heisenberg principle stated as an approximation, after all. Whether the weak force can apply to them or not, or if simply gravity between these tiny particles keeps them clustered, is the angular momentum of the orbit that they make quantized in terms of ? Are there discrete photons or gravitomagnetic particles that might cross between them over vast lengths of time, allowing them to interact? There is something aesthetically appealing to me that our world as we know it is still only one of the first few "moments" of the Big Bang, and that a long succession of interesting worlds of physics and chemistry of ever colder temperatures and smaller particles and larger distances still await their time. If successor regimes of physics exist that are also capable of supporting interesting life and thought, then that would pretty much blow the anthropic principle out of the water, and hint rather strongly at some clever design behind the cosmos. I wouldn't say the absence of it is a disproof, however. Wnt (talk) 04:30, 14 November 2010 (UTC)[reply]
(ec):::The term "intelligent design" has come to exclusively mean a pretty narrow subset of religious beliefs that directly contradict scientific fact; these views tend to be pretty radical, so I agree with Jayron that there isn't really a "middle ground" for intelligent design. However, the phrase "intelligent design" can also be interpreted in other, more benign ways. Isaac Newton's description of a "clockwork universe theory" could be branded "intelligent design" - but it does not stipulate certain insane ideas like young earth creationism. There is scholarly debate - mostly in the humanities and philosophy, and not in the scientific community per se, about whether the universe is deterministic or random; and whether there is a role for a deity in our scientific understanding of the world. These could be classified as a "middle ground." But I would be very reluctant to label any theory "intelligent design" because that term has come to mean a very specific set of far-flung, radical Christian-inspired ideas. Nimur (talk) 04:36, 14 November 2010 (UTC)[reply]
Not quite the subject matter I was trying to address because of how contaminating the influence of ID on 'intelligent design', I suppose. Since I can expect to run up against an edit conflict if I try to fully present what I'm after, and since new Earth creationism has been singled out already, where is old Earth creationism in the debate (particularly with latitude given to the sense of 'create')? What of so-far unknown but plausible influences? Is there any attempt to comprehensively and coherently address plausible specific holes in scientific ontology, or is it entirely each discipline to its specific purview and each scientist to his or her own expertise (which it seems might leave a gap or gaps in reasoning or evidentiary search)?Julzes (talk) 05:51, 14 November 2010 (UTC)[reply]
I cannot see how there can be a "middle ground". Either there is or there isn't an intelligent designer. Pretty binary state of affairs there. And there is no point halfway between zero and one in a binary system. HiLo48 (talk) 05:57, 14 November 2010 (UTC)[reply]
I think you misunderstand the question. The poster is asking if there is anyone doing or proposing research into detection of intelligent design who is actually acting in good faith. The answer is none that I know of. No one has yet come up with a proposal for how to detect evidence of intelligent interference in the evolution of life. thx1138 (talk) 06:02, 14 November 2010 (UTC)[reply]
There's an article specifically about old Earth creationism. Oddly, it doesn't address what to me seems like the most obvious way to reconcile religious and scientific ideas, which is to recognize that the time scale used in an author's prologue about the writing of a work is not the same as the time scale of the book itself. Just because Tolkien's works cover thousands of years in Middle-Earth doesn't mean it took thousands of years for him to write them, nor does it mean that the writing was in the same order as the plot. It is entirely reasonable in scientific terms to believe that our universe is a lovely four-dimensional sculpture with a splendid internal consistency of design, but that the author isn't finished with it yet. I would suggest that if you look very closely, some of the chisel-marks are still apparent; and it is not hard for anyone to see that there is still some sculpting to be done before perfection can be attained. But these things are primarily if not entirely visible in social terms, in the minds of men, rather than as aberrations in the fundamental rules of science; the purpose of the plan being, I would speculate, that when those who have suffered and striven have developed deep virtues and appreciation, and the cause of their suffering is scoured away as if it never were, one is left not with a meaningless paradise of opium dreams but a real paradise in which all of the joys are rooted in the free will and essence of the people. Wnt (talk) 06:12, 14 November 2010 (UTC)[reply]
The only part of your comment that relates to this discussion is your assertion that the chisel marks are still apparent. The original question was, has anyone proposed a scientific approach to looking for such chisel marks? The answer, so far, is no. thx1138 (talk) 06:25, 14 November 2010 (UTC)[reply]
It is hard to say what is relevant in such matters, and harder to decide on proof. I would say, for example, that if you look at the film of the funeral following the 16th Street Baptist Church bombing, you see people grieving, from such injustice, and yet so unified, so free from hatred, so unaccountably dignified, and with our retrospective knowledge that their firm faith was such a fundamental turning point toward the end of racial injustice, there is just some overwhelming sense that more than random chance is at work; that they were allied with the Holy Spirit. You can't test something like that with a multimeter. The real miracles aren't the achievement of a mundane end by impossible means, but the achievement of an impossible end by mundane means. Wnt (talk) 07:00, 14 November 2010 (UTC)[reply]
In my opinion, what makes the scientific description of the world so fascinating is the idea that surprisingly complex and beautiful results readily spring from such a deceivingly simple looking set of rules. As a student of math I've gotten a front row seat to examples of beauty popping out seemingly from nothing, so I know that it's possible. And yet some people try to convince me that this sort of miracle is a fantasy. They claim that such complexity could only possibly arise from a set of laws that is equally complex (i.e. some active and unpredictable God). This strikes me as a colossal failure of the imagination. I don't ever want to believe that reality is that dull. It's depressing. Rckrone (talk) 17:35, 14 November 2010 (UTC)[reply]
Alright, my opinion: There is nothing wrong with intelligent design as a belief: it's entirely unprovable, and entirely unfalsifiable. basically the question is this: do we assume that the universe (as it is) was designed to be as it is, or do we assume that the universe (as it is) is a product of deterministic/random forces. Either is a belief, and neither belief has any real basis in evidence. The problem with (the dumber) elements of ID is that they start making claims that are contrary to our understanding of the universe in order to support their particular understanding of religious texts. That's just narrow-minded. There is no contradiction between religion and science (in fact someone - I forget who - said that faith transcends and incorporates both evidence and belief), except to the extent that people believe they have to oppose one to advance the other. If you think about it, gravity is such a profound statement of belief that it is surprising that physics doesn't have priests.
So, people with faith are really nice people, eh? So are most of my friends, and a bunch of more profound non-believers you'd be hard pressed to find anywhere. And didn't Isaac Newton prove gravity with an apple? That sure didn't need any god. HiLo48 (talk) 10:06, 14 November 2010 (UTC)[reply]
There is a set of natural laws that describe the falling of an apple, by which you can link the moment when the apple to falling to a future in which it has fallen further by a specified amount. One can postulate that the same moment could be linked to a different moment in which the apple has stopped, or moved sideways, using a different set of physical laws. This is a different dimension of time, moving forward in a different direction from the same moment in spacetime. The known set of laws makes the most sense, because it is what you remember, what you observe, what the textbooks say that you read, what others you speak to have always known. But what if some other set of laws started to acquire some of the same characteristics? What if you have a choice of whether to move your subjective experience entirely in one dimension of time, or in a combination of the two? What if your action in one timeline influences your ability to take part in another? The reason why I emphasize the need of science and faith to respect one another is that while science is the tool to explore a known universe, there may still be some advantage in looking toward others. Wnt (talk) 15:06, 14 November 2010 (UTC)[reply]
LOL'ing at the idea that Newton's argument for gravity did not require belief in a God. Take a look at Isaac Newton's religious views sometime, and the role they played in the formation and expression of his theories. As far as Newton was concerned, gravity was an argument for God, the prime mover who set everything in order, and kept it that way... Newton was a very odd duck and neither atheists nor modern Christians will on the whole find much comfort in his views. --Mr.98 (talk) 19:31, 14 November 2010 (UTC)[reply]
Rupert Sheldrake's ideas fall somewhere between a religious ID position and the mainstream understanding of evolution by natural selection. To his supporters he's a respectable, educated scientist who is making some imaginative but scientific leaps; his opponents decry his work as "magic". -- Finlay McWalter ☻ Talk17:46, 15 November 2010 (UTC)[reply]
Fuzzball vs. Big Rip
The Big Rip hypothesis supposes all space could be torn apart after cosmic expansion gets off the leash. I would assume that a black hole with a mathematical point singularity at the center should be unaffected by this, since there's no one point to be ripped from another (though I suppose a few things falling in the event horizon at the last minute might discover their status is moot). But a fuzzball (string theory) describes an alternate object, the size and mass of a black hole but filled with strings, that already somehow maintains its structure within highly curved spacetime. What happens if one of these goes up against the Big Rip? Wnt (talk) 05:16, 14 November 2010 (UTC)[reply]
Considering we know nothing about about: Black holes, Cosmic Rips, fuzzballs or Dark Energy it's gonna be tough to answer your question! :) I mean all those things have theories and math, but no direct observations. (The observations of black holes could also be super massive objects, there is no direct evidence that they are singularities.) Ariel. (talk) 07:11, 14 November 2010 (UTC)[reply]
Interesting. To summarize here, they say that phantom energy (with a speed of sound squared greater than 0 and less than 1, whatever that means) will accrete into a black hole, dominating over Hawking radiation "until it reaches the Planck mass" at a time "near" the Big Rip. As what I get the impression is typical when you start combining event horizons and negamatter (well, negative energy) you end up with "traversable wormholes", or at least a possibility thereof. (but would infinite phantom energy follow you?) All hands, abandon universe! Wnt (talk) 18:54, 14 November 2010 (UTC)[reply]
This site under a disclaimer that anything it publishes need be true claims that in ancient times, human urine was used as a tooth whitening product. By modern standards of whitening efficacy the answer to the OP is "Neither." but that need not diminish any excuse for trying. Cuddlyable3 (talk) 14:50, 14 November 2010 (UTC) WARNING of explicit picture![reply]
As burping involves the expelling of air from the oesophagus it is necessary to have air in the stomach in the first place. Repeated burping will exhaust this supply. You have consciously or unknowingly developed the skill of swallowing air to be able to burp at will. This is a very useful skill if you, for some unthinkable reason, lose your larynx as aerophagia facilitates esophageal speech. Some year ago this was bravely used by the actor Jack Hawkins following a condition that required the removal of his larynx. Oddly it does not mention it in his article but I have very clear memories of hearing him being interviewed and collecting an award using this throat voice as it was called. Caesar's Daddy (talk) 16:29, 14 November 2010 (UTC)[reply]
I have this particular ...skill... as well. I don't think the air goes down to the stomach with me. I just swallow some air, restrict the lower part of my larynx for a fraction of a second, and let the air out in a constricted burst that makes a sound in my throat. It's a bit different from proper burping, as swallowed air is momentarily stored in a place that feels higher up, rather than being generated in the stomach. The belching article doesn't really properly describe it... 88.112.56.9 (talk) 18:17, 14 November 2010 (UTC)[reply]
I agree. For me, I just force air out of my mouth while it's closed (I just try) and then I feel this little bump in the higher part of my larynx, then I burp. Περσεύς|Talk to me18:20, 14 November 2010 (UTC)[reply]
Oh, and you can add my userbox {{User:Perseus, Son of Zeus/UBX/Burp on command}} to your userpage too. I am the same person as 173.49.140.141. Just logged in. Περσεύς|Talk to me18:21, 14 November 2010 (UTC)[reply]
Those who have a desire to learn how to perform esophageal speech, either for impressing (or disgusting) others or as a real way of communicating (in cases such as larynx removal due to cancer, or similar situations), can attempt the following actions which may or may not induce a belch. A)"Wiggling" the throat. Pressing the tip of the tongue forcefully against the lower front teeth should cause the larynx area to move out, causing air to displace into the esophagus. The throat muscles can then be relaxed, and the belch forced out by contracting the diaphragm muscles, or contracting and relaxing the same throat muscles again.
B), Breathing air into the stomach. This can be done by inhaling while keeping the throat muscles tight and glottis closed, so that no air can get into the lungs. If the throat is kept closed while still attempting to breathe in, the air should divert into the stomach, then the normal maneuver can be used to belch out the air.
Περσεύς|Talk to me19:26, 14 November 2010 (UTC)[reply]
I found a wiki-quote by Einstein: "It has become appallingly obvious that our technology has exceeded our humanity", but sadly it's unsourced, and googling doesn't help. It's
a fascinating quote, and I'd love to read it in context. Does anyone know where I can find it? Thanks, Idunius (talk) 15:16, 14 November 2010 (UTC)[reply]
And which of those 350,000 also-unsourced results contains the quote in context? Which of them lists where the quote is originally from? This is what the poster is obviously asking for, not more unsourced quotations. Einstein is one of these figures that people for whatever reason love to attribute quotes to, often without any evidence that he actually said what was being attributed to him. --Mr.98 (talk) 19:19, 14 November 2010 (UTC)[reply]
Er no, that's the whole quote that people keep repeating and saying that he said. I assume it was part of a longer statement about some topic or event, or from a book, or in response to a question from someone else. He probably didn't just walk up to a reporter, say it, and then walk away. I remember the lore surrounding some of his other quotes were about nuclear weapons, my WP:OR is that this sounds like it could be a similar theme. DMacks (talk) 19:43, 14 November 2010 (UTC)[reply]
As Mr. 98 says, I was hoping to learn the exact source. (Was the context political? Scientific? Is he referring to any specific event?) Is it certain that it's Einstein? I have, as I said, googled already, and I found a plethora of sites with the quote, but not a single reference except just simple statements that it's Einstein. /--Idunius (talk) 19:50, 14 November 2010 (UTC)[reply]
The OP knows that and has said so. He's asking if we can dig up the original source. (There are some days when I find the Ref Desk to be essentially useless! We've just spent six lines telling the OP what he obviously already knows if anyone had bothered to read his or her question for what it straightforwardly said. Blah.) --Mr.98 (talk) 21:24, 14 November 2010 (UTC)[reply]
I poked around quite a bit in Google Books — it's a quote that is thrown around dubiously and unsourced again and again. I doubt he actually said it, to be honest. It is probably one of these half-remembered things that has just been passed around for a decade or two. --Mr.98 (talk) 21:27, 14 November 2010 (UTC)[reply]
Same here. I also found a German translation, and searched pretty carefully for the entire quote as well as individual words (using Internet search engines as well as searching a digital library of his works). Over and over again, it's attributed to Einstein, but not to a specific writing or lecture. Would be a nice (possibly fruitless, I'll admit) research project, to thread back in the earliest uses of the quote to try and find its source. Would require a very good library. -- Scray (talk) 00:18, 15 November 2010 (UTC)[reply]
...though this probably doesn't fall into that category, truth be told. It'd be nice to know where the alleged quote came from, but it's not a real secret of the universe. --Mr.98 (talk) 00:17, 16 November 2010 (UTC)[reply]
Proton Gun
In an ancient ZX Spectrum game, The Korth Trilogy, the antagonist aliens used "proton guns" that fired a stream of protons at a target that "simply smash atoms to pieces" on their spaceships and used "proton force fields" force defence that operated on the same principle (they would shred any projectile fired through them). They used ships armed with this technology to blockade Earth, but were unable to invade as the guns couldn't be used in an atmosphere as there would be an explosion as soon as the protons hit the atmospheric molecules and the forcefields would overload when flying through the atmosphere due to the constant impact of the same molecules.
Protons are just hydrogen nuclei and they don't really have any exceptional ability to smash stuff. They do have a positive charge which lets you accelerate them with magnets, so maybe the proton gun makes some sense, but I'd better leave it to one of the engineers to explain why it's more effective to just shoot bullets. The proton force field is pretty much nonsense though. Rckrone (talk) 18:10, 14 November 2010 (UTC)[reply]
You can use a particle accelerator in space, sure; see Particle beam weapon. These were investigated quite heavily as part of the Strategic Defense Initiative. I believe that in general using protons would be problematic since they have a positive charge, and generating a negative charge is pretty easy to do. In particle beams that use hydrogen ions (protons), they usually add an electron to them before sending them out, so they are electrically neutral. Anyway, long story short, you can use these, they have some desirable properties and some less desirable ones, but they aren't too essentially different than using a laser or something like that. They have no magical atom smashing properties. In space such weapons are more desirable than on Earth, as I understand it, because the atmosphere would absorb a lot of the energy and make them far less efficient than, say, a stream of bullets. I doubt they'd "blow up" as described; it's more like your particle beam would just be very weak or require exponentially more energy for the same effect. On the other hand, for very long distances in very short timescales (essentially "instantaneous" by human standards), they could be useful, hence their research for missile defense (which would require shooting things hundreds if not thousands of miles away very quickly, for which projectiles — bullets or rockets or kinetic weapons — are ill-suited). --Mr.98 (talk) 20:04, 14 November 2010 (UTC)[reply]
Maybe in a very literal sense, but I think one can recognize that there are different properties to a stream of blocks of lead and a stream of protons. That's the distinction I'm indicating. --Mr.98 (talk) 23:04, 14 November 2010 (UTC)[reply]
Different solvents - which are functionally the same?
Knowledge of solvents would be useful to me, as I often find myself having to do difficult cleaning jobs, where it would be disastrous if the underlying thing was damaged or discoloured. For example, I have a lot of hardened drips of emulsion paint (called latex paint in the US) on the surface of gloss paint (called I think oil-based enamel paint in the US). 1) What commonly available solvents would dissolve or soften the emulsion/latex paint, but not affect the gloss/oil-based-enamel paint underneath?
Some personal research shows that nail polish remover does this. The nail polish remover I used appears to be mostly acetone and water. I've also seen a product on the internet that consists mostly of acetone, toluene, a little methanol, (according to its MSDS sheet) and probably water which claims to do this, but which is not easily available in the UK. A comment in an internet forum suggests that methylated spirits/Denatured alcohol may do the same, in other words ethanol.
There are many different solvents. 2) Is it possible to classify them into groups of similar solvents? 3) Will the ethanol in methylated spirits be functionally equivalent to the acetone and toluene, as solvents?
I have dried paint on some polyester clothing. 4) Would the above solvents dissolve the polyester if I tried to clean it with them, or soaked it in them?
There is another solvent in an expensive specialised cleaner spray that I sometimes use: ethylene glycol. 5) Is there another readily available solvent that is functionally the same as ethylene glycol, in other words dissolves the same things and even more importantly does not dissolve the same things? Thanks 92.15.7.155 (talk) 19:18, 14 November 2010 (UTC)[reply]
I don't know nearly enough to speak about what will work on paint, but to get you started, the solvents article has groups of common solvents, and rates them based on how polar they are. (A main property distinguishing toluene from water is how much the positive and negative charge on the molecule is split up; molecules with all C and H tend to be pretty non-polar, whereas water has two protons sticking out to one side) Problem: if you know acetone works, what is easier than that? If you check the charts, ethanol is not that different from acetone in some ways, but it has a terminal -OH that makes it a polar protic solvent and greatly increases its hydrogen bonding potential. Again, I don't know what this means for latex and oil paints. Wnt (talk) 19:36, 14 November 2010 (UTC)[reply]
When a wave pulse travels from a heavy string to a light string, what happens? Is its behaviour similar to when a pulse travels from a light string to a heavy string (i.e. it is partially transmitted and partially reflected), or is its behaviour different?--220.253.217.130 (talk) 20:15, 14 November 2010 (UTC)[reply]
I still don't understand why we can't fix the coastline length precisely via some software, which thoroughly outlines the upscaled coastline and then calculates it length (like tracking down via some flexible stuff and then straightening it to evaluate)? —Preceding unsigned comment added by 89.77.156.31 (talk) 21:53, 14 November 2010 (UTC)[reply]
The obvious answer is that the coastline is as long as a ship would take to sail around it. The ship is not going to make minute acrobatic curves just to stay a fixed distance from the caost... This is a better solution than a "length of the ruler" version. Just work with a real ship under real conditions. 91.183.62.45 (talk) 23:52, 14 November 2010 (UTC)[reply]
People make useful and functional measurements of coastlines all the time. The paradox does not preclude this, but instead refers to the notion of well-defined exact measurement in a model system. The apparent paradox is that the observed length depends on the scale of measurement. The method you mention could be used to take such a measurement, but this does not matter at all in terms of `solving' the paradox. SemanticMantis (talk) 00:56, 15 November 2010 (UTC)[reply]
There is no paradox here at all. There are two empirical observations, made originally by Lewis Fry Richardson and subsequently put into a wider mathematical context by Mandelbrot:
The measured length of a coastline (or any other natural border) depends on the measurement scale (informally, the "ruler length"). This appears strange at first glance, but is actually not that surprising - even the mesaured distance around a perfectly circular island would depend on whether you were sailing round it in a supertanker or a rowing boat.
The measured length of a coastline (or any other natural border) does not seem to tend to a finite limit as the measurement scale is made smaller and smaller. This is counterintuitive, and is how coastlines differ from smooth curves such as circles. We can assign a definite length to a smooth curve by finding the limit of the measured length for smaller and smaller measurement scales - in effect, the curve is "straightened" by examining it at smaller and smaller scales. Mandelbrot showed that this limiting process does not work for (most) fractals, and so he interpreted Richardson's research as evidence that coastlines and other natural objects are more closely modelled by fractals than by smooth curves. Gandalf61 (talk) 11:37, 15 November 2010 (UTC)[reply]
I still don't fully understand how this applies to real coastlines as opposed to theoretical ones you might find in a math text. Below a certain scale (A few meters) there IS no coastline, fractal or otherwise, there's just a beach. The coastline is a theoretical average of the waterlevels at various times of the day, year, and even minute. That must surely follow a curved line and not a jagged one (Whoever heard of a jagged average?).
It's often implied in these sorts of discussions that the ocean is this frozen, unmoving zone and that individual grains of sand could be definitively assigned to either the ocean or the shore. APL (talk) 22:18, 15 November 2010 (UTC)[reply]
Well, not all coastlines are gently curved sandy beaches, of course.
Suppose you've got a coastline that's jagged rock. Which jags are you going to measure, and which not?
And then there are river mouths. Where a river reaches the sea, and gets wider and wider until it forms a bay, how do you measure that? If you "walked along the shore", you could end up walking dozens (perhaps hundreds) of miles inland.
I'm not saying choices couldn't be made about how to answer each of these questions. But the whole point is that that there's clearly no one, single, obvious answer. And every different answer yields a different coastline length. —Steve Summit (talk) 00:43, 16 November 2010 (UTC)[reply]
FTL communication?
Alice and Bob are 1 ly apart. This should mean that it would take at least 1 yr for Alice to send a message to Bob. However, what if Alice has a pole that's 1 ly long, and she taps on it repeatedly to send Bob a message in binary? Why wouldn't this work? --75.33.217.61 (talk) 22:07, 14 November 2010 (UTC)[reply]
I think we get this question once a month on here? It doesn't work because the pole is not truly rigid — it's a bunch of discrete atoms connected by electron orbits and somesuch, and conveying the "tapping" (or rotating, or whatever) means each atom has to move, turning the atom next to it, at a speed around speed of sound in the material in question. It's not instantaneous. Being perfectly rigid would mean transferring the atoms at infinite speed, which obviously doesn't happen. --Mr.98 (talk) 22:31, 14 November 2010 (UTC)[reply]
November 15
prehistory of the sahara region
I've read somewhere that the Sahara around 800,000 years ago was a hot humid swamp-like area (no information on what it was like 1-2mil years ago), and I'm wonder if there are any biologists/anthropologists linking the emergence of human culture in N.Africa and the migration out of Africa by homo erectus to the later desertification of the region? I'm not necessarily suggesting it's true, but it seems obvious enough a connection that quite a few people would have proposed it. 173.183.68.27 (talk) 00:12, 15 November 2010 (UTC)[reply]
What is the proposed mechanism for anthropogenic desertification of an area the size of Europe? I just don't see it as likely in the slightest. I could see prolonged greenhouse effect and etc. contributing to or accelerating desertification in a desert that size, but causing it outright? I think it's well beyond the capability of human beings until very recently to do such a thing. --Mr.98 (talk) 00:21, 15 November 2010 (UTC)[reply]
Fire, really. It's a long shot I know, but an increased population of hominids with a lot of use for fire could have created large areas of grassland, holding much less moisture and disturbing the monsoon patterns coming in from the atlantic, leading to desertification. obviously positive feedback would be the active mechanism here, I don't think it would have been possible to burn that much forest. 173.183.68.27 (talk) 00:31, 15 November 2010 (UTC) -- I guess the main weakness if that forest fires don't create grassland, so there may be something else. 173.183.68.27 (talk) 00:34, 15 November 2010 (UTC) -- i guess Deforestation in New Zealand supports this somewhat. 173.183.68.27 (talk) 00:45, 15 November 2010 (UTC)[reply]
I don't place much credence in H erectus causing this change - Sahara#Climate_history talks about climate changes impacting the Sahara. FWIW you may be interested in reading about a technique used by Australian Aboriginals called Fire-stick farming which most likely did result in large scale changes to the landscape, flora & fauna (though not necessarily desertification). --jjron (talk) 14:43, 15 November 2010 (UTC)[reply]
Have you never wondered why there can be two completely different ecosystems present at the equator; the Sahara and the Amazon? It is obvious that climate change is what keeps the Sahara in its current state, and that not enough moisture is coming in to replenish the soils, but it is equally as true to say that if there were no trees in the Amazon, there would likely be a lot of desert there too; it is the existence of the rainforest that keeps the rainforest alive because it holds on to the moisture and influences the weather (lowering temperature and increasing precipitation) in the area. I will read up on the Aboriginal situation though, that might make for interesting evidence! Thanks. 173.183.68.27 (talk) 05:34, 16 November 2010 (UTC)[reply]
The Sahara isn't at the equator; the Congo is, and is rainforest like the Amazon. But, in any case, there are lots of instances of places at the same latitude with significantly different climates, so the supposed fact wouldn't be surprising if it was true. --Anonymous, 06:24 UTC, November 16, 2010.
The prevailing winds over the Sahara have a LONG fetch over land, with almost no source of water feeding them. That's why it is so dry. In the past, when landmasses were at slightly different locations, and winds blew from different directions, there may have been more sources of water upwind from the Sahara. As it stands now, the winds over the Sahara, which blow almost straight out of the east, have about a fifth of the earth's surface to blow over before getting to the Atlantic. Generally, you find deserts on the downwind side of continents, and forest upwind. There are also rain shadow effects. Its a complex thing, however, and this is a bit of a simplification. --Jayron3206:32, 16 November 2010 (UTC)[reply]
The position of the Sahara within the horse latitudes is significant; I've often seen a popular though rather simplistic cartoon of the winds circulating in bands through the upper atmosphere and coming down over drier areas - it must be on Wikipedia somewhere... Wnt (talk) 12:21, 16 November 2010 (UTC)[reply]
Guy who blinked a lot after beheaded
I heard a story a long time ago in school that a guy proved that the head is alive briefly after being beheaded, and he did this by stating that after he is beheaded he will blink a lot. I think he was beheaded by guillotine (not sure why), and sure enough he blinked a lot after his head came off. Is this story true? Does anyone know what I'm talking about or who this guy is supposed to be? ScienceApe (talk) 00:50, 15 November 2010 (UTC)[reply]
(edit conflict) The story is told of Antoine Lavoisier, who was indeed beheaded by guillotine. It's a widely told story, but appears to be apocryphal; see The Straight Dope column on the matter. I have yet to see any serious academic supporting the story. That's not to say that a person couldn't blink after his head's chopped off, just that there's no contemporary suggestion that Lavoisier did. even citing the same source, that's pretty impressive, 173 Buddy431 (talk) 01:01, 15 November 2010 (UTC)[reply]
I'm talking about the Lay's potato chips. They come in small bags and big bags, and I've noticed that the small bags seem to taste better than the big bags, which before I attributed to scarcity (there's less, so each chip tastes better). Obviously the solution was to perform a double-blind study ;) I set up the project as follows: my assistant put four plates on a table: 2 labelled "small" and "big" respectively, then places the same number of chips (from the correct bag) in the same arrangement on each, then shuffling the plates randomly. She then leaves with the bags. I come in, unaware of which are which, and shuffle them again. The subject then comes in and tastes chips from two of the plates, which s/he selects and guesses on a folded sheet of paper with four circles: s/he writes either s (small), b (big) or Ø (not tasted) for each circle which s/he places in a box, knowing that it is possible that both are from the same bag. My assistant then came in and recorded each selection from the slip, and I looked on the underside of the plate and recorded the correct answers. I did not see the subject's answers, nor my partner the correct answers. I repeated this about 200 times, discarding the "used" plates and chips each time. When I brought all the data together at the end I found the accuracy rate was about 79%, which to me was shocking. Now I know what happens (and got full points on my project :), my question is: what accounts for the difference? 24.92.78.167 (talk) 01:48, 15 November 2010 (UTC) PS: The plates were paper, the writing was in pencil so as not to show through, and the chips were all sour cream and onion flavor. The subject was not allowed to touch the plates except to sample the chips.[reply]
how many subjects were there? How did you explain them to rate the chips? Were they guessing which tasted better? Which they thought was crispier? or were they asked specifically to guess which bag they thought it came from? The chips are purged with nitrogen or something aren't they? Which is inert but maybe a small amount of air still remains in the bag so when the bag is bigger the amount of air is more. My dad does plant maintenance at a smallgoods factory and he says their vac equipment can be running at 85% and it's still "good enough" even tho it normally runs at 97% or something, but even at 100% it's not a perfect vacuum. I realize the nitrogen purging thing is a completely different process, but maybe similar tolerances apply. Vespine (talk) 02:57, 15 November 2010 (UTC)[reply]
(edit conflict)Cool study! Just a few ideas:
- the amount of air in the package
- there may be a significant difference in the way/time/place of packaging that accounts for the taste, though you'd have to ask Lays
Date codes as mentioned by Ariel seem the best explanation. But the explanation can simply be unattainable. Without, that is, a lot more information and a lot larger study. Maybe the potatoes vary by packing plant, and maybe one packing plant, carrying potatoes from one source, specializes in packaging large bags, or small bags. And on and on—oil—air pollution—plastic blades in one type of machine—steel blades in another type of machine. The product is uniform, but not perfectly so, and there is probably more than one factor of variability between the large bags and the small bags. Bus stop (talk) 03:14, 15 November 2010 (UTC)[reply]
Say you left a pound of deli turkey slices in a bag at room temp for 8 hours.
Most people will tell you to toss them. But I'm guessing you want other options. Were they unopened? Because they will cut down on bacteria drastically. Are they very salty? That helps too. You can freeze them, to kill many, but not all bacteria (but freezing does nothing to existing toxins - if there are any). You can also fry or bake them. I would use your built in chemical detector - sniff them. If there is any hint of bad smell toss them, but otherwise you are probably OK. Of course most people work on the better safe than sorry system, but if they smell OK, and you are not an infant or elderly, have a normal immune system, and are not taking antacid drugs (of any type, prescription or over the counter), your risk is low. As soon as you smell them, put them in the freezer (to cool them quickly) or eat them immediately. Ariel. (talk) 05:31, 15 November 2010 (UTC)[reply]
The practices of the deli where you bought the slices will also be significant. Were the slices freshly cut on a clean machine, or had they been in a display for many hours? I agree with Ariel that I personally would take the risk unless the turkey smells bad. A hundred years ago most people would have been happy to eat such meat without question. The human stomach is good at killing bacteria, but it cannot eliminate toxins, and, just occasionally, it fails to eliminate a large intake of acid-resistant bacteria, so there will always be a small risk, even with fresh meat. Dbfirs10:11, 15 November 2010 (UTC)[reply]
The machine is probably clean, as I've eaten their meat for a couple of months without a problem. The bags were unopened. I put them in the freezer and haven't taken a look since. Imagine Reason (talk) 14:50, 15 November 2010 (UTC)[reply]
Partial reflection when light travels from a fast medium to a slow medium
When light travels from a fast medium to a slow medium, you get refraction, do you also get partial reflection (as you do when the light travels from a slow medium to a fast medium)? 220.253.217.130 (talk) 06:30, 15 November 2010 (UTC)[reply]
Sure you do, else you wouldn't get an effect like this:
Notice how you can see the mountain in the lake? That's because the surface reflects light. The light moves faster in the air than it does in the water, so this is exactly the effect the OP is asking about.
Hello. Gravitational energy is not infinite. An object may fall for a long time, but eventually its gravitational potential will reach zero and then no more force will be exerted on it. If this was not the case, falling objects would be accelerated forever and gravity would be a perpetual motion machine.
Dark matter exerts a repulsive force on other matter which is accelerating the expansion of the universe. However, at some point this repulsive force must become zero to prevent it from becoming a perpetual motion machine. Where is that point? Leptictidium (mt) 07:46, 15 November 2010 (UTC)[reply]
You are thinking of Dark energy, not Dark matter. And the simplest answer to your question is "no one has any idea". Dark energy is just an idea, or more accurately it's a way trying to "patch" holes in observations vs. theory. No one has observed it (they have only calculated it), and there could be a wide variation in it's effect, and still match current observations. For example an idea called Big rip does actually suggest the force will become infinite. Ariel. (talk) 08:27, 15 November 2010 (UTC)[reply]
So sorry, "dark energy" then. But if it does become infinite, isn't that a violation of the second law of thermodynamics, since it generates a force perpetually? Leptictidium (mt) 08:49, 15 November 2010 (UTC)[reply]
The "limit" is probably the edge of the observable universe (from the reference frame of the hypothetical dark energy), but since this is all hypothetical, it would be very difficult to try to prove this. Perhaps, one day, we will realise that there is a much simpler explanation. Dbfirs09:28, 15 November 2010 (UTC)[reply]
You say "An object may fall for a long time, but eventually its gravitational potential will reach zero and then no more force will be exerted on it". This is incorrect. Gravitational potential energy is calculated by integrating the gravitational force with respect to radial displacement. This integration introduces an arbitrary constant of integration, which can be chosen to make the potential energy 0 at whatever point you like. Sometimes it is convenient to take gravitational p.e. as being 0 for some initial configuration; sometimes we take gravitational p.e. to be 0 for a hypothetical infinite separation. The configuration that we choose as a zero point for gravitational p.e. 0 is an arbitrary benchmark - it has no physical significance. Gandalf61 (talk) 10:24, 15 November 2010 (UTC)[reply]
Surely if I am falling towards the Earth, the point at which gravitational potential energy would become zero is the centre of the Earth, no? Leptictidium (mt) 10:30, 15 November 2010 (UTC)[reply]
You can choose to make the gravitational p.e. zero at the centre of the Earth if you want to. Or you can choose it to be zero at the surface of the Earth, or wherever you like. It is arbitrary. The physically meaningful quantity is the gravitational force, which is the gradient of the potential, and so is unchanged by adding or subtracting a constant from the potential. Gandalf61 (talk) 11:13, 15 November 2010 (UTC)[reply]
As (not) explained in gravitational potential energy, but implicit in the formulae given and the statement about separating all bodies to infinity, there actually is a logical zero point for gravitational energy, which is when an object is separated from all other masses by infinite distance. It is (theoretically) possible then to calculate the potential energy as a negative number that is the sum of all the negative gravitational potential energies from all masses. Though in practice distant, little-known astronomical masses tend to be neglected, and often an arbitrary zero is chosen. But I don't think anyone chooses a zero at the center of the Earth, since nothing can fall to there. Wnt (talk) 11:25, 15 November 2010 (UTC)[reply]
There is no logical reason why Leptictidium cannot choose zero of potential energy to be at the centre of the earth. It is a perfectly reasonable treatment for the gravitational potential of a single body and avoids negatives, though I agree that physicists normally take zero at infinity. Dbfirs14:00, 15 November 2010 (UTC)[reply]
Yes but it has no special meaning on a cosmological scale. Even if a object is at the centre of earth it can fall to lower gravitational potential by falling in to the centre of the sun or the galaxy. The only choice of zero point that has no negative potential energy is when all mass in the universe is collapsed in to a singularity in a black hole. I do not know if such a reference point is meaningful given all the complexities with infinity and time dilations. --Gr8xoz (talk) 15:00, 15 November 2010 (UTC)[reply]
I did say "of a single body", and I know the standard treatment is to take zero at an imaginary point somewhere on the other side of the universe, but the OP was just making a simple analogy and it made perfect sense to me. Dbfirs23:03, 15 November 2010 (UTC)[reply]
Assume for simplicity that there is a point mass M all alone in the Universe, alone, that is, except for a small test particle of mass m at infinite distance from M. m has kinetic energy K = 0 at this point, and we choose the zero of potential T = 0 at this point, too. Next, m falls towards M, hence its kinetic energy K increases. At the same time, because it falls into the potential well, its potential energy T decreases. Conservation of energy requires that the motion is such that the total energy K+T remains constant (energy restricts motion), namely K+T=0. In fact, since M is assumed to be a point mass, the kinetic energy of m increases without bound - I guess that's what you mean by "gravity would be a perpetual motion machine". But that's not true, because as K increases, T continues to decrease, also with out bound, to minus infinity. Although both K and T become infinite, their sum always remains zero. Your mistake is in looking at kinetic energy alone, whereas you have to think of total energy, then there's no problem. Of course, in reality there are no point masses (except maybe black hole singularities but those cause extra problems), and therefore you cannot get anywhere infinite kinetic energy. Dark energy is a different story again which cannot be satisfactorily treated with classical mechanics. --Wrongfilter (talk) 17:31, 15 November 2010 (UTC)[reply]
Well if the potential energy converted into kinetic energy reaches the rest mass of the falling item, I believe you will reach an event horizon. Past this barrier it will not be possible to extract any more energy. Graeme Bartlett (talk) 19:30, 15 November 2010 (UTC)[reply]
I'm not sure I know the answer to this question, but I'll try my best. First of all, at issue is not whether the dark energy is "there" in some abstract sense, but whether you can build an engine that exploits the force to produce an unbounded amount of work. I think I can rule out that possibility. In the distant future, the expansion is well approximated by de Sitter space. Any particular person can be causally influenced by only a part of the de Sitter space, and that part can be covered with static coordinates that resemble a "black hole turned inside out"—in other words, a spherical region with an event horizon at the edge. The event horizon attracts objects in the interior like a black hole would; that's how the dark energy force shows up in this model. At this point it's clear that you can attach a potential energy to every point in the spherical region to make the dark force conservative. To put it another way, there's a limit to how far you can allow two masses to be pushed apart while still extracting energy from the pushing. Beyond that point, the repulsive force itself prevents you from ever receiving any energy from the motion of the masses, because the energy is also pushed away too fast for it to get to you. That shows up in this model as one or both masses crossing the event horizon.
A slightly different question is whether the dark energy itself could somehow be harvested. The nature of the dark energy is totally unknown (it may not even be there) and there's no reason to think that it can be gathered, but even if it can, the amount you can gather would be limited by the radius of the spherical region, I think.
The nature of energy conservation in general relativity is complicated and unclear. I think your question in its most general form may actually be unsolved. -- BenRG (talk) 19:41, 15 November 2010 (UTC)[reply]
Animals suffocated in bed
I'm sure my animals aren't unique in that they like to burrow under the sheets of my bed for the warmth. (It's mostly the cats but also one of the dogs) I've often wondered though, can the animal suffocate and if it can, how will it go? Will it simply fall asleep and never wake up? Or will the, completely healthy, animal's brain realize that it's not getting enough oxygen and make the animal want to escape, meow, whimper, etc? I realize that there are unknown quantities here and those are namely the amount of fabric on top of the animal and whether there is a tunnel to fresh air left from where they burrowed. I suppose that the answer to "can it" will be yes given enough sheets and blankets, so for now let's just assume that there is a sheet, a quilt, and another blanket.
Note: I'm not seeking medical/veterinary advice. I'm just inquiring as to the physiological response of a cat or dog and the possibility of an unfortunate event. I do not plan on testing this out on any animals, unless by "test" you think I mean continuing to let my animals sleep under the covers whenever they like. All my animals are of reasonably good health considering their ages and are seen by a vet on a regular basis. Dismas|(talk)09:21, 15 November 2010 (UTC)[reply]
Humans - who are a not dissimilar animal - don't commonly suffocate if, as frequently occurs, they are covered by the bedclothes as described. Why then would cats or dogs? FWIW I have on occasion shared a bed with a cat, who indeed liked to get under the bedclothes, and no deleterious outcomes ensued. Without being able to think of any appropriate references, I would have expected that, like you or I, a cat or dog would sense whether it was in an over-stuffy situation even in sleep, and wake up and/or move to improve matters. 87.81.230.195 (talk) 09:54, 15 November 2010 (UTC)[reply]
If I cover face with all that, it becomes incredibly hot and stuffy in a short time. I've seen cats and dogs spend much more time that way. Additionally, while we're all animals of one sort or another, dogs and cats handle heat differently than we do. Dismas|(talk)10:48, 15 November 2010 (UTC)[reply]
I have never heard of an animal suffocating like that. Aso, when I was a kid, back in the days when winters were cold in the UK and when the house had a single coal fire in the living room, I remember frequently sleeping completely under the covers. The room temperature was probably a little above freezing, there would oftem be ice inside the windows in the morning. -- Q Chris (talk) 12:35, 15 November 2010 (UTC)[reply]
[35] specifically mentions blankets and duvets as a risk for infants. It also confirms what I had suspected, the risk is more their limited mobility and ability to move these objects or otherwise clear obstructions. Notably I can't find any mention of cats suffocating in sheets or whatever but do find plenty of mention of the behaviour, I myself let the cat sleep under the duvet on occasion. Nil Einne (talk) 14:43, 15 November 2010 (UTC)[reply]
(ec)87, are you using "bedclothes" to refer to sheets and blankets? I've never heard it used that way (though it sounds quaintly appropriate to me); everything else being equal, I would assume you're talking about pyjamas/nightgowns - and having animals stuck in there would probably lead to very little sleep at all... 64.235.97.146 (talk) 14:27, 15 November 2010 (UTC)[reply]
I concur. I suppose they can be thought of as clothing the bed rather than the person. The OED gives a definition from c1440 ". . . Bedclothe, or a rayment for a bed." 87.81.230.195 (talk) 21:19, 15 November 2010 (UTC)[reply]
(Partly OR) There are many references[36][37] about cat problems with breathing, such as after a frantic mouse chase, and it is distressing when this happens to one's own pet. OTOH a cat seems to deliberately to obscure airflow to its nose when sleeping e.g. by curling its tail over the nose as well as burrowing under bedclothes as the OP describes. A cat with a fur coat in a warm place can reduce its metabolic rate e.g. to take a cat nap, where it needs little oxygen. Our article Cat#Physiology notes the range of breathing rate 16-40 breaths per minute of a cat, which is wider than that of a human, typically 12-20 breaths per minute. The OP's question would be answered by an experiment on a sleeping and trusting pet that I am not prepared to do either. Cuddlyable3 (talk) 16:30, 15 November 2010 (UTC)[reply]
Hydrogen sulfide
Under what conditions does hydrogen sulfide exist in the liquid phase, simultaneously as sulfur is in the gas phase? Are there more than one molecular structure for sulfur in this phase combination, maybe diatomic surfur? What does liquified hydrogen sulfide look like? How good a solvent does it make? Compare the solubility of sodium sulfanide in liquid hydrogen sulfide, to that of sodium hydroxide in water. Does it autodissociate like water? Plasmic Physics (talk) 14:14, 15 November 2010 (UTC)[reply]
I was just reading yet another story about potential correlations between cell phone frequency EM radiation and brain tumors. I don't really want to debate the pros and cons of the argument here — I'm just referencing it for the context, and want to, for the sake of argument here, assume that the correlations are valid.
Most of these articles seem to imply that holding the phone an inch away or so negates the problem, or at least lessens it.
My science question: why would this be the case? Can an inch (or less) of air actually deflect enough of the EM radiation in question to make a difference? If so, shouldn't there be some relatively easy way to build shielding into the casing that would scatter the EM radiation away from the earpiece? --Mr.98 (talk) 17:48, 15 November 2010 (UTC)[reply]
If you want an example of this, test an induction-based recharger. I have one for my watch. If it sits on the recharger, it blinks, so I know it is recharging. If it is about 1/4" off the charger, it blinks. If it is 1" off the recharger, it doesn't blink anymore. At about 1/2", it is flaky. Sometimes it blinks, sometimes it doesn't. All that is between the electromagnetic source (the charger) and the watch (which is designed to absorb and make use of the energy) is air. -- kainaw™18:00, 15 November 2010 (UTC)[reply]
Forgot to answer the other questions... Can cell phones be shielded so they don't emit electromagnetic waves? Yes - easily. But, they won't work anymore. The main function of a cell phone is to send/receive EM energy. Can a simple device be made to keep the phone an inch away from your head? Yes. About 10 years ago, I saw a guy on TV telling you that you need to cut 1" off a toilet paper tube and tape it to your phone to keep it 1" away from your head. -- kainaw™18:03, 15 November 2010 (UTC)[reply]
Let me clarify, because I think it's not clear what I'm suggesting, or something. (Obviously I know that the phone needs to be emitting to be functional. Obviously I know you can build in some kind of physical means of keeping the phone an appropriate distance.)
Below is a crude but hopefully amusing ASCII diagram of someone holding a banana-shaped phone which is sending out microwave radiation in an approximately spherical pattern, zapping our poor fellow's brains with said EM radiation. (I have placed the phone some distance from the head, but that is just to illustrate the radiation direction. Imagine it is right next to the head.)
ooo . . .
o o . . .
0 x x 0 . . .
| u |...\\....
| P |...||....
\___/ .// .
/ \ . pO .
| | || .
Here is another similarly crude diagram where some sort of barrier has been put on the face-side of the phone which reflects the EM radiation off of it. The result is that only a small part of the overall EM sphere is reflected or scattered away from the head:
ooo . .
o o . .
0 . . 0 . .
| u | \\\....
| U | |||....
\___/ /// .
/ \ pO .
| | || .
It seems to me that this would be relatively trivial and only have a marginal effect on phone quality? (It would be, I presume, a directional effect, so the direction you were facing might change your reception.) Is this a ridiculous notion?
And while I am not a scientist, it strikes me that the induction charger might not be exactly analogous, since it involves a different part of the spectrum and different intensity? --Mr.98 (talk) 21:17, 15 November 2010 (UTC)[reply]
I know some things about science, I can confidently tell you that energy of the EMR used by cellphones do not meet the required threshold to cause you to develop cancer. It is simply a urban myth reslting from a poorly conducted experiment. Plasmic Physics (talk) 22:00, 15 November 2010 (UTC)[reply]
I'm not asking you for an assessment of the threat, as I made clear in the first paragraph of my question. I really do wish people would actually read the question before trying to answer it. This seems to be a real epidemic on here lately. --Mr.98 (talk) 23:54, 15 November 2010 (UTC)[reply]
There is no need for such a contraption as what you're proposing, is what I was trying to say. The air does not absorb the EMR, if it did, then the signal can not travel long distances. The cellphone emits a spherical wavefront, the energy of a wavefront is almost constant at any radius however, the energy is spread over a larger surface when the radius is large. This is propotional to luminous flux. Moving the cell phone away from the ear, increases the radius and consequently decreases the luminous flux. Luminous flux affects rate of possible DNA mutations per unit time. The frequency of EMR affects how DNA reacts. Plasmic Physics (talk) 00:23, 16 November 2010 (UTC)[reply]
Again, I don't really care about your off-the-cuff, undergraduate-physics assessment of the hazard. That's an issue I don't actually think you know enough to answer about. --Mr.98 (talk) 14:09, 16 November 2010 (UTC)[reply]
Why would it only have a marginal effect on quality?!? Going by your illustration, You've just completely cut out reception of all cell-towers to your left! Worse is if you make a call facing one way, and then turn to face the other way you'd lose your connection and the phone would probably not have time to make a new connection so the call would just drop.
Looking at your illustration again, perhaps you think that the waves bounce off your skull? They don't. They go straight through. Phones just wouldn't be usable otherwise. APL (talk) 22:11, 15 November 2010 (UTC)[reply]
I don't think the bounce off the skull, no. If you conceptualize the radiating frequencies as a sphere coming out of the phone, I think you'd need a wedge of about 25%-30% removed to avoid going through the human skull, based on some rough approximations on my part. Which probably would have an appreciable effect, if you are in an area with only a few cell towers. But I assume that most urban areas are pretty well saturated by towers at this point (at least where I live, it seems like every large building has one). So the worst effect would be that sometimes you'd have to turn to find a better signal? That doesn't seem like the worst outcome to me, if there is actually a long-term risk otherwise.
But if that's the case, why does adding the inch of air between your head and the phone matter? What's the inch get you? To return to one of my original questions, why would it be any safer to hold the phone an inch from your head? --Mr.98 (talk) 00:10, 16 November 2010 (UTC)[reply]
I think most mobile phones already have a directional antenna that mostly radiates away from the head, this gives best signal quality since almost no radiation passes through the head, some are reflected and the most are absorbed.
File:Cellphone head sar 1.pngCalculated specific absorbed radiation (SAR) distribution in an anatomical model of head next to a 125 mW dipole antenna. Peak SAR is 9.5 W/kg averaged over a 1 mg cube. (USAF/AFRL). Note the concentration to the surface, most of the radiation only penetrate a few cm.
I have not heard the recommendation to hold the cellphone a inch from the head. I think it is reasonable to assume that any health effect decrease faster than linearly so it is better to spread the exposure over larger area if the effect exists at all. I also think the recommendation can have to do with the near field of the phone, this can afect both reception and health effects. --Gr8xoz (talk) 02:04, 16 November 2010 (UTC)[reply]
OK, this I get. It's not the air, it's the distance from the point source, so that the amount of EM radiation is more diffusely distributed. That is useful to know and I see where I was confused about the nature of the alleged threat — thanks! --Mr.98 (talk) 15:21, 16 November 2010 (UTC)[reply]
Gr8xoz actually has a relevant point. If holding the phone 1 inch from the head improves reception then this is a good thing if you are concerned about the level of the radiation for whatever reason since this will generally be reduced (as the phone adjusts the signal strength based on the reception). This BTW is a common concern with things that allege to reduce radiation to the body, by screwing with the signal they may just make the signal stronger. Of course if by holding your phone 1 inch away your call lasts longer because you can't hear each other properly this may also negate any purported beneficial effect. Also while I'm less sure of this, I presume if you're using packet switched calling, more noise may mean more transmission may mean more radiation. Nil Einne (talk) 08:50, 16 November 2010 (UTC)[reply]
As a high school teacher where students are not supposed have phones visible in class, a common storage location used by female students is in their bra. If they can cause brain tumours, what about breast cancer? HiLo48 (talk) 18:09, 15 November 2010 (UTC)[reply]
I would not summarize the current state of medical opinion on mobile-phone effects so bluntly. There is an enormous body of research on mobile phone health effects, and it is hard to say there is a strong consensus opinion. Our article, Mobile phone radiation and health, summarizes the state of knowledge pretty thoroughly. A few things we do know for sure: the frequency that cell-phones operate at can cause radiological harm. The intensity at which cell-phones operate at might be safe. Numerous studies exist, varying in their level of certainty and scholarly merit; the results variously confirm or refute the idea that mobile phones have increased cancer (and specifically, tumor and glioma) incidence. Nimur (talk) 18:59, 15 November 2010 (UTC)[reply]
I know that we don't yet have scientific certainty on whether cell phones can cause cancer. My question was a hypothetical. Ifthey can cause brain tumours, what about breast cancer? These girls have them close to their breasts for longer periods than normal users would have them close to their heads. HiLo48 (talk) 21:12, 15 November 2010 (UTC)[reply]
Can you please cite A few things we do know for sure: the frequency that cell-phones operate at can cause radiological harm. Microwaves fall between radio waves and infrared and visible light on the electromagnetic spectrum, neither of which cause "radiological harm". I'm not saying the case is shut, but if there is an effect, it isn't great, that is for sure. Very few technologies are perfectly safe, look at cars, the amount of people that die because of cars is staggering, but it's a risk we accept because the benefit of road travel is so great, even if a few people die by mobile phone, I dare say most people would still accept the risk rather then give up their phone. That's not saying that if we do find "something" we shouldn't make phones safer if we can, but it does mean that if we can't find a link we should make one up to panic people into buying magical microwave blocking holograms for $30 that do nothing. Vespine (talk) 22:10, 15 November 2010 (UTC)[reply]
I would hardly panic: I personally think the risks of cancer due to mobile telephony are small. But here are some citations: first, the thermal effects section of our article - it is beyond dispute that microwave radiation can cause tissue heating. A Google scholar search on biological effects of microwave radiation turns up numerous books and papers. And here's an IEEE paper, Biological effects of radiofrequency/microwave radiation, that essentially summarizes 50 years of research, establishing "safe" power exposure thresholds. I'm of the impression that even at full transmit power, the radio-intensities in mobile telephones are below the threshold of "significant" risk, but I would be reluctant to call it "zero" risk. Nimur (talk) 01:00, 16 November 2010 (UTC)[reply]
See the article above or the article I posted in the topic above this one. There is still a lot of scientific uncertainty on the question. The NY Times article cites a number of cases where EM radiation in the frequencies in question did create detectable abnormalities in rats. It's unclear what the epidemiological connection is or whether we can detect one at this point. It's unclear what the long-term risk is, which makes it impossible to make a good cost-benefit decision. Nobody is suggesting that a cell phone will give you cancer tomorrow — the suggestion is that after a few decades of heavy use like we've been doing since the late 1990s, there could be a huge uptick in things. It seems to me like a reasonable thing to wonder about, and to be cautious about, given the volume of people we're talking about here. Automobiles are not a great comparison — people were willing to adopt reasonable measures (which cost time and convenience) for safety (e.g. seat belts). --Mr.98 (talk) 23:47, 15 November 2010 (UTC)[reply]
It strikes me that it would matter whether or not the phone's EM radiation was constant when the phone was in "standby" (not talking) mode, among other things. I think the short answer is "nobody is really sure." Breasts and brains are different types of tissue, for one thing, and would presumably respond differently. It's not clear that causing one kind of cancer would necessarily imply that the other kind would be caused the same way, is what I'm saying. --Mr.98 (talk) 21:22, 15 November 2010 (UTC)[reply]
In any case, phones transmit almost not at all when they're sitting there unused. However, I suppose in this day of wireless headsets, you might have a phone in your bra that was making a call. APL (talk) 22:22, 15 November 2010 (UTC)[reply]
Don't phones do some sort of connection every so often? I know someone who leaves a (GSM) mobile near their speakers/amp all the time (connected to their computer) so you do hear it connecting every so often when not doing anything (even receiving SMS or whatever). I don't know how this power level compares to when it's making a calls or internet connection but it's obviously higher then the normal baseline. It doesn't last extremely long but then again for typical teens in many countries most of their usage may be sending and receiving SMSes anyway although in some I would guess mobile internet usage is increasing. If I were the parent of a teen, I'd be more worried about them getting some sort of RSI or other problem from SMSing too much or perhaps going deaf from listening to loud music then I would breast cancer from storing their phone in their bra. Somewhat OT but some people store their phones in a pouch around their waist, while not as close this is usually fairly near the testicles for males and I know people who don't like it for that reason. Many store their mobiles in their pocket which although further isn't that far. (From a search, the heat from laptops seems to be a more common concern however.) Nil Einne (talk) 08:32, 16 November 2010 (UTC)[reply]
Bipedalism, pelvis size, and childbirth
I often come across the claim that humans evolved to have smaller pelvises because bipedalism wouldn't be practical otherwise...with the price that childbirth becomes much riskier. But this seems hard to reconcile with the obvious fact that a lot more women appear to have difficulty giving birth than have difficulty simply walking upright...so how to justify the claim that they both exert comparable amounts of evolutionary pressure (or at least did before the advent of modern medicine and medicalized childbirth?) 129.2.129.161 (talk) 18:25, 15 November 2010 (UTC)Nightvid[reply]
Bipedalism#Humans discusses speculation as to why we have evolved to be bipeds; it says there are at least 12 theories about this, so it's going to be a little difficult to pick a single answer to your question about evolutionary pressure. Interestingly we have a whole article on Human skeletal changes due to bipedalism which does not mention the pelvis. (It does mention the hip.) Comet Tuttle (talk) 19:16, 15 November 2010 (UTC)[reply]
You've missed that childbirth would not be such a problem if babies did not have such large heads. The question is, when did we start to get such large heads that this caused a problem? Most speculation I've seen places that after the rise of bipedalism. The evolutionary arms race then comes between the baby, 'wanting' to be born with as large a head as possible, and the mother, who needs to survive the process well enough to raise the child. This is speculated as the reason why human babies are born so helpless, effectively premature even at full term, so that they can continue to grow their enormous heads outside the mother, after having made it through the pelvis. 86.164.144.120 (talk) 20:22, 15 November 2010 (UTC)[reply]
Aspartame vs. Sugar on teeth
It's well accepted that Sugar damages your teeth especially in large quantities, but is Aspartame (specifically from diet sodas) as bad, the same, or worse then sugar on teeth? Are there any studies that address this? Thanks! Chris M. (talk) 19:15, 15 November 2010 (UTC)[reply]
From this link, 'The American Dental Association has noted it "welcomes the development and FDA approval of new artificial sweeteners that are shown to be safe and non-contributory to tooth decay. . . . Aspartame is an FDA-approved, safe sweetening agent and flavor enhancer that can be substituted for sugar in the diet."' That doesn't explicitly say apartame is non-contributory to tooth decay though. Franamax (talk) 20:53, 15 November 2010 (UTC)[reply]
Here is a 2001 American Dental Association review which says "Non-nutritive sweeteners found in diet soft drinks may not be directly cariogenic because tooth decay producing bacteria cannot ferment aspartame...". Here is the ADA mentioning "...non-cavity causing sweeteners such as aspartame...". Still haven't found a specific study though. Franamax (talk) 21:04, 15 November 2010 (UTC)[reply]
Think about how sugar damages teeth. Bacteria ferment it to some sort of acid, generally by oxidising the carbon backbone until a carboxylic acid group appears. How are bacteria going to ferment aspartame? It is a peptide yes but the COOH groups are esterified. John Riemann Soong (talk) 23:47, 15 November 2010 (UTC)[reply]
Not to mention that the amount of aspartame needed to get a level of sweetness is much less than an equivalent amount of sugar. There's so little aspartame in most foods that the effect on teeth is really a moot point anyway. Keep in mind, though, that something like Diet cola generally still has Phosphoric acid, which will still attack teeth. Buddy431 (talk) 03:45, 16 November 2010 (UTC)[reply]
Compared to other cars, the Nissan GTR is heavier and less powerful but still is incredibly fast. I've compared it with more powerful cars that also have AWD. I've also compared it with lighter more powerful cars. All of this combined with the low price does not make sense to me. If anyone can help, I would appreciate it. 158.135.169.37 (talk) 19:44, 15 November 2010 (UTC)[reply]
Well, obviously how a car performs in a race isn't just about power and weight, otherwise, the winner of every race could be predicted by just plugging in figures into a simple formula, which is obviously not the case. If you are interested you should probably start by reading the article Nissan Skyline GT-R, It has a lot of information about the car's performance features.Vespine (talk) 21:47, 15 November 2010 (UTC)[reply]
You haven't defined "incredibly fast", so it's hard to pin anything down. For stoplight-to-next-stoplight fast, torque will be most important, and the gear ratio will count too. For a highway car, the ratio of the highest gear will decide how fast it can go, in combination with the horsepower. For getting around a road course or rally stage, handling becomes important (steering, brakes). For oval or sprint track racing, you optimize straight-line acceleration, slowing into a corner, and accelerating out of a corner. To keep a "fast" car cheap, match the gear ratios to the torque curve of the motor so it appears fast, then minimize everything else. Take out the standard ABS, rear wiper, comfortable seats, use a smaller HVAC system, allow only 2GB of storage in the MP3 player (if you've gotten to that stage, you're pretty desperate to cut weight and cost :). Automobiles actually made for sale are a whole package, so you have to evaluate all their costs and benefits. You didn't mention fuel costs or insurance rates at all, and those can have a huge impact on just how "incredible" you think a car is once you are the one actually operating it. Franamax (talk) 07:26, 16 November 2010 (UTC)[reply]
In terms of the 'cost' part of the question, some of that comes down to expectations, 'street cred', showoff factor, market psychology, or whatever you may like to call it. In short Nissan is chiefly recognised as a manufacturer of relatively bland, low cost, mass market cars. So even if they produce a killer car like the GTR, they can't expect to get the sort of coin for it that the exclusive marques like Ferrari, Lamborghini, Porsche etc can ask. Why would anyone pay that money for a shopping trolley brand when they could be driving one of the world's exclusive cars, even if the Nissan is faster, more powerful, better optioned, more reliable, or whatever else it may be? Like it or not, you do pay for the badge. --jjron (talk) 12:30, 16 November 2010 (UTC)[reply]
Roaccutane Treatment
The following discussion is closed. Please do not modify it. Subsequent comments should be made on the appropriate discussion page. No further edits should be made to this discussion.
hi, i am using roaccutane treatment since 4 months. however, after i read in the article in this site that it makes back ache, a question crossed my mind: is it dangerous to continue with this treatment if there is a disc problem even if it is not a serious problem? because i used to have back ache before i started roaccutane. i am looking forward to get your reply even if it is medical question because it will help alot. thanks
The reply is that you have to consult your doctor. Please do not trust random strangers over the Internet with important medical questions; your health may be damaged if you follow bad medical advice, even if it's given with good intentions. Comet Tuttle (talk) 20:58, 15 November 2010 (UTC)[reply]
The discussion above is closed. Please do not modify it. Subsequent comments should be made on the appropriate discussion page. No further edits should be made to this discussion.
Conversion from Seconds to Meters
If a distance unit like a meter is used to measure length in 3-dimensions and a unit like a second is used to measure a length in time, which some indicate is the 4th dimension, is there a conversion equation that states the measurement of time in that of distance? For instance, X seconds = a * Y meters. -- Sjschen (talk) 21:58, 15 November 2010 (UTC)[reply]
I'm not entirely sure what you're asking, but it sounds like it has to do with special relativity. At velocities approaching the speed of light, a coordinate or vector of time has to be descibed in terms of space. As in, for this spatial coordinate or vector, time is such. One should be carefull when discussing dimentions, space and time maybe dimensions, but they are different kinds of dimentions. The are, up to date, twelve spatial dimentions, and two temporal dimenstions. Plasmic Physics (talk) 22:19, 15 November 2010 (UTC)[reply]
Only four are accepted in Special relativity where the "conversions" are really rotations in 4-D space-time. Different proposed theories predict different numbers of possible dimensions, but only the four of special relativity have actually been "discovered". Most of the other "predicted dimensions" are too small to measure. Dbfirs22:31, 15 November 2010 (UTC)[reply]
I'm just curious because if one can use meter to measure the the "first 3" dimensions I'm wondering if one can use the same unit to measure the "4th" dimension, given some imaginary alien that lives in these 4 dimensions just like we do our 3. It certainly would be fun (albeit nerdy) to say that the laundry will be done in some X meters instead of minutes. -- Sjschen (talk) 23:51, 15 November 2010 (UTC)[reply]
You're confusing spatial dimensions for temporal dimensions, there is a hypothetical fourth spatial dimension which is defined in terms of meters. Time is not the fourth spatial dimension, it is the first temporal dimension, it is the fourth perceptable dimension. Everything lives in these four dimentions. Plasmic Physics (talk) 01:29, 16 November 2010 (UTC)[reply]
Us earthlings do it the other way round! We define our metre to be 1⁄299,792,458 of a light-second! We do it that way simply because we can measure time far more precisely than we can measure length: so it makes sense in practical terms to define the unit of length in terms of the unit of time, rather than the other way round. But, logically speaking, there's nothing to stop me saying that it takes my washing maschine about 8 light-micrometres to do a load of laundry ;) Physchim62(talk)00:48, 16 November 2010 (UTC)[reply]
Ah yes, sorry, I gave the wrong result. 8 light-micrometres is about how long I spend each day wondering how I always seem to have clean laundry. My partner tells me that the washing machine takes about 720 light-gigametres to do a load, and has suggested I measure this value more precisely myself ;) Physchim62(talk)01:37, 16 November 2010 (UTC)[reply]
You can choose to use a system of natural units in which the speed of light is 1 by definition, in which case time can be measured in meters (not "light-meters"), just like spatial distance. Instead of thinking of "space" and "time" as two "different kinds of dimensions", it works fine (better even, when doing general relativity) to think of spacetime as being a 4-dimensional manifold in which "space" and "time" dimensions are not distinguished, except for there being a metric tensor that introduces a local directionality to spacetime. Red Act (talk) 03:39, 16 November 2010 (UTC)[reply]
The OP is asking for the distinction between tropospheric ozone and stratospheric ozone. The mechanisms for creating the two are very different, and the two sources of ozone do not mix. Stratospheric ozone is generally created from the action of ultraviolet light on oxygen in the stratosphere. This ozone in the stratosphere then absorbs more UV light, and prevents that UV light from reaching the troposphere. Within the troposphere, most of the ozone is anthropogenic (human made); it is generally created in car exhaust. Tropospheric ozone is a serious polutant, as an eye and lung irritant. There would always be trace amounts of tropospheric ozone, due to lightning, but its concentration would be much less without humans. Paradoxically, human activity also tends to decrease the availibility of stratospheric ozone. So the next effect of human life seems to be to remove ozone from the stratosphere, where it can effectively block UV radiation, to the troposphere, where it aggrivates asthma and allergies. --Jayron3204:24, 16 November 2010 (UTC)[reply]
"it is generally created in car exhaust" kind of, but actually its formed when NO2 is broken down by sunlight and reacts with oxygen. We do have a specific article on tropospheric ozone by the way. I might be wrong here, but I can't think of any natural processes that produce NO2. Whilst there would be a very very tiny amount of tropospheric ozone naturally, our actions definitely significantly increase it. Ah yes, a source, this bascially backs up what I said, but unsurprisingly confirms I was wrong, tiny amounts will be formed due to plant VOC emissions. A google scholar search for "tropospheric ozone natural" brings up papers which you might find interesting. One thing they discuss which our article neglects (been meaning to sort it out) is that tropospheric ozone damages plants as well (thankfully all that CO2 we're producing goes some way to negate the effect. SmartSE (talk) 15:20, 16 November 2010 (UTC)[reply]
Lightning also produces ozone (and this occurs in the troposphere), but the quantities are small compared to the other sources discussed above. In any case, lightning is rarely anthropogenic. Nimur (talk) 17:13, 16 November 2010 (UTC)[reply]
A Paradox?
At what point is change noticeable to the human eye? As if I where to add one granule of sand to a heap, at what point would any person recognize change? 66.229.227.191 (talk) 23:29, 15 November 2010 (UTC)[reply]
Your question is not very clear, are you asking if there is a paradox because some changes are too small to perceive with the naked eye? I don't see any paradox. Vespine (talk) 00:19, 16 November 2010 (UTC)[reply]
I guess in the title I was inplying that it is somewhat a paradox, as I was hoping to find a mathematical solution to the Sorites Paradox. But that wasn't apart of the question, I just want to know at what size does change become perceivable? 66.229.227.191 (talk) 00:25, 16 November 2010 (UTC)[reply]
It's not a mathematical solution, per se, but a question about human psychology/physiology. There probably isn't one answer in most cases, but a spectrum of likelihood where people will say it falls on one side or the other. (This is the "group consensus" mentioned in the article, which is probably the most "scientific" way to study the question, though it will aid the philosophers none.) On some issues, though, there are physiological reasons that we detect certain things as being discrete changes. Color, for example: show people a rainbow spectrum of chips with very slight differences between each color, and ask people to point to "red", and they'll all pick the same chip, more or less. This is because it correlates with the firings of the nerves in our eyes, or something like that ("red" is when one cone triggers at the maximum, and a rod at its minimum, or something like that... it's been awhile since I took psych). --Mr.98 (talk) 00:47, 16 November 2010 (UTC)[reply]
Wow, I'd never heard of the Sorites paradox until I read this question, and yet I have a paper in submission at the moment which discusses a very similar problem in metrology... It's amazing what you can learn at the WP Reference Desk! Anyway, the paper hasn't passed the reviewers yet, so let's hope they don't ask me to discuss Greek philosophy on top of everything else ;)
To translate my proposition into the language of the Sorites paradox, I say that a heap is no longer a heap if you can tell the difference on removing a single grain. A bit like saying you're rich if you don't have to worry about your bank balance! In more formal terms, "tell the difference" is related to the measurement uncertainty of whatever method you are using to measure your heap: nowadays, that doesn't just have to be human vision. So, if we define the quantity n as the "size" of the heap (by whatever method of measurement), and the quantity N as the number of grains, the heap remains a heap if the quantity 1/N can be treated as a differential dn/n under the conditions of measurement, the quantity 1/N being the fractional change in the number of grains when N changes by one grain. You can treat 1/N as a differential if the discontinuity in the measurement result when the number of grains changes by one grain is, or would be, significant compared to the uncertainty of the measurement result, discounting the contribution to the uncertainty from any correction for systematic measurement error.
The problem with the paradox is one of human perception and linguistics, not reality. We make the distinction between grains of sand and a heap, not nature. I don't consider it much of a paradox, myself. A term like "heap" has no real scientific meaning, which is why we use precise terms for masses of thing (e.g. a kilogram) for things that have to have real answers. I have heard philosophers banter on about "baldness" in the same way — when do someone become "bald"? What's the hair that does it? It's just navel gazing in my opinion. --Mr.98 (talk) 14:04, 16 November 2010 (UTC)[reply]
My solution would be to define the heap only in the limit of N to infinity (and making the grain size scale inversely with N so that the total volume remains constant in the N to infinity limit). If N is not strictly infinitely large, you only have an approximate heap that gets worse the smaller N becomes.
In statistical mechanics a similar problems arises in the theory of phase transitions. Given some amount of matter, you want to be able to say that it is in one phase or another phase (like liquid or gas). But it turns out that for finite amount of substance, phases are not defined. Obviously, if you have only a few molecules, you can't tell which phase the substance is in, so the situation is analogous here. Strictly speaking, you need to take the limit of an infinite amount of substance (the so-called thermodynamic limit). What happens mathematically, is that the partition function is an analytic function of the temperature for any finite number of particles, but in the limit of an infinite number of particles, a singularity can develop which then defines the phase transition.
The point is then that a Taylor expansion at a point in one phase won't converge into the regime of the other phase. So, an extrapolation based on accurate measurements of the properties of the system in one phase to predict the behavior in the other phase will fail. As long as accurate extrapolation gives the correct result (in the limit of infinite accuracy), you can say that the system is qualitatively the same and thus in the same phase. Strictly speaking, you need an infinite amount of particles for the distinction between phases to arise. Count Iblis (talk) 04:36, 16 November 2010 (UTC)[reply]
An actual answer to the question
In psychology, this concept is called a just-noticeable difference or JND, and has been studied very intensively as part of psychophysics. The principle result is that a JND is generally a constant proportion of the perceived magnitude of a quantity, however the size of that proportion varies according to the nature of the stimulus. This rule is known as the Weber-Fechner law. Looie496 (talk) 17:52, 16 November 2010 (UTC)[reply]
There's already an equation? So I spent all of last night trying to create an equation myself was useless... this actually happens to me quite often... they should make a rule to do more research before trying to solve something that's already been solved :/ 66.229.227.191 (talk) 20:31, 16 November 2010 (UTC)[reply]
Miscellaneous questions about work and energy
1) If work is done on a system, then W = ΔE. But how can we calculate the work done by the system on its surroundings? Intuitively, I would think the answer is -ΔE, but I can't prove it :(. When I try, I run into contradictions (two planets at rest, gravitationally attracted to each other; if one planet is considered as the system, then its energy will increase. Wext = -ΔE, then the other planet shouldn't speed up, but it does).
It depends entirely on what conventions you are using. All that matters is that changing the direction of the work switches the sign of ΔE. Under some systems, we take the perspective of the system (chemical thermodynamics takes this perspective, thus exothermic reactions have a ΔE < 0 ). Under other systems, we take the perspective of the observer (who is part of the surroundings), thus the sign convention would be opposite. However, your intuition is correct. All other things being equal, the only difference between the direction of the work is the sign of ΔE. It becomes obvious if you place two objects on a number line. If object A pushes object B in the positive direction, then object A did +ΔE, if object B pushes object A with the same force over the same distance, then object A did -ΔE. As long as you keep the perspective on "work done on/by object A" you will always get opposite signs for those two situations. The implication of the independence of work from the frame of reference is the Law of conservation of energy. If you could vary the amount of work merely by changing the frame of reference, then total energy would not be conserved. --Jayron3204:17, 16 November 2010 (UTC)[reply]
If I could change the amount of work done in an isolated system just by altering my frame of reference, that would imply that if I was in motion past an isolated system, and observed the work done in the system, that value would be different than if I was stationary relative to that system. That would imply that there were differing amounts of energy exchanged in the two situations; where would the extra energy come from or go to? --Jayron3205:00, 16 November 2010 (UTC)[reply]
In the original example, both planets gain positive kinetic energy and the system (the two planets together) loses gravitational potential energy. Dbfirs08:41, 16 November 2010 (UTC)[reply]
Is it true that wireless internet will never attain the speeds of (optical) fibre internet due to the laws of physics? We're having a debate about an National Broadband Network in Australia at the moment and I hear this statement a lot. I'm wondering if it is theoretically true. 124.149.24.85 (talk) 10:35, 16 November 2010 (UTC)[reply]
I believe that the theorietical maximum is based on the frequency of the carrier, and light has a much higher frequency than radio. However I don't think that radio or fibre are near this maximum (though I could be wrong), so possibly tomorrow's wireless will exceed the maximum speed of today's fibre -- Q Chris (talk) 11:32, 16 November 2010 (UTC)[reply]
'Speed' can be a bit of nebulous term. It's more an issue of bandwidth. The argument goes that due to the finite range of frequencies available for wireless transmission it can only handle so much bandwidth, whereas for fibre, if you're running out of bandwidth you can just lay another optical fibre cable down and increase it. Wireless is often proposed as a solution in low population density areas for two main reasons - the wide spread of the few people makes laying the cable uneconomical, and secondly with only a small number of people accessing the wireless network each can have a bigger share of the limited bandwidth and thus achieve higher speeds than would be possible in high population density areas (but not as high as they'd get with fibre). As the saying goes, never say never, but with current technology and knowledge these limits apply. --jjron (talk) 12:13, 16 November 2010 (UTC)[reply]
In order to expand on the image description, so the image can be moved to Commons,
Is anyone on the Science Reference desk able to provide a more specific species
identification?
Image is used on Fauna of Borneo if you need some indication of geographical location.
If grey squirrels had not been introduced into the UK, would red squirrels still be in such decline as they are now? In other words, have the grey squirrels merely taken up the space left by the red squirrels, or have they ousted them by direct competition or disease etc? Thanks 92.28.252.5 (talk) 13:26, 16 November 2010 (UTC)[reply]
There are various theories as to why grey squirrels have generally supplanted red squirrels - here - but the consensus does seem to be that the red squirrel has declined due to competition, rather than any other reason. Ghmyrtle (talk) 13:36, 16 November 2010 (UTC)[reply]
Seeing the space station
If I were to buy a medium range consumer available telescope and look at the international space station with it from earth, would I be able to see the station clearly and in detail? —Preceding unsigned comment added by 93.84.7.186 (talk) 14:11, 16 November 2010 (UTC)[reply]
The International Space Station's orbit never brings it lower than 278 km (173 miles) above ground. I'm not certain what is considered a typical "medium range consumer telescope" today, but I doubt it would have useful magnification much above 300 power. Even at 500 power, at the very best the station would look as though it was about 1/5 km (1/3 mile) away -- and usually farther, depending on where it was in its orbit and where on the ground you were. Not what you would call seeing it "clearly and in detail". --Anonymous, 14:31 UTC, November 16, 2010.
Starting about halfway down this page, there are several images (including some video) of the ISS transiting (passing in front of) the Sun and the Moon. Note that to observe a solar transit you need to have an appropriate telescope with suitable filters, and to get anything that would look space-station-like you need to have a big aperture telescope (several inches). Here's another solar transit, captured using a 160 mm (roughly 6-inch) telescope. Meanwhile, it is also possible to catch the ISS by itself — this image used a 100 mm – 3 inch – refractor.
However, what you aren't going to see when you look through the scope is the ISS hanging there in space. It's in low Earth orbit, moving at more than seventeen thousand miles an hour, and it's going to be rushing across the sky at about 1.25 degrees per second. It's very bright (when illuminated by the Sun) but very, very quick. Chasing it with your telescope is going to be difficult; you'll be lucky to see it slide briskly across your field of view. (The last link I provided above describes the challenge.) Ralf Vandebergh is an old hand at this stuff, however; he's coupled a video camera to his 10-inch Newtonian, and then stacks video frames together to get sharper, lower-noise images. With lots of time, effort, and practice, he's able to generate processed images that look like this or this. This remarkable frame may have captured an astronaut on a spacewalk. TenOfAllTrades(talk) 15:08, 16 November 2010 (UTC)[reply]
You can see the International Space Station with the naked eye; and you can photograph it directly, if you're careful. But it sounds like you want to produce an image of more than a bright dot. So let's clarify: a "medium range consumer scope" will probably not provide enough angular resolution, even in perfect weather and overflight-trajectory conditions, to image small details of the spacecraft. You will need a pretty good sized scope - we could say, eight-inch aperture as an absolute minimum, and a larger scope for better imaging. There are two optical "hard limits of physics" you need to worry about: angular resolution, and field of view. Our article angular resolution describes the physical limitations of angular resolution - it depends on your telescope aperture, so you can calculate a minimum observable feature size for any give down-range distance. The ISS is going to overflying me at about 750 km downrange for the next three weeks, so my eight-inch will allow me to resolve 2.0 meter features. (That's pretty darned good!) Now here's the really hard part: the other limiting factor, field of view, which depends on your telescope focal length. You can think of this as "magnification power." The more you magnify, the smaller the area of sky you can look at. So you're going to need a really accurate computer prediction of the ISS trajectory (which you can find from NASA's website or the various enthusiast tools linked above - I use kstars on Linux). And you're going to need a really carefully aligned telescope (I'm usually pretty darned sloppy, but you should find true astronomical north with a polar scope, weight down your scope with a really good tripod and mount, and very precisely position your sights on the expected overflight path. You'll have one spot of sky - you can't move your scope fast enough to track ISS. (Military-grade fast-tracking scopes that can pan the sky as fast as an orbit-track as an "exercise to the reader"). Now, you've got to wait - depending on how perfectly aligned your clock is to the ISS (in theory, both you and NASA are synchronizing to the GPS clocks). The ISS should enter your field of view exactly on schedule, and you'll have ... about two seconds, if you're lucky. So you'll want your imaging system to capture as many photos as possible (burst mode, or video mode). And you'll want to make sure your imagers are well coupled, optically, to your tube, so that you aren't losing resolution at the film or digital imager. Finally, be certain to run some numbers for your optical system, camera's shutter speed, ISO settings, and set your exposure settings properly - you won't be very happy if you return a photo of a black sky or a washed-out dot! If you're lucky, you'll have captured ten or so photographs of the ISS overflight. With a good deal of image post-processing (to first order, an image stack to denoise, and maybe a superresolution algorithm), and you should be able to produce fine-quality photographs of ISS. As I mentioned, my 2-meter feature resolving capability means I could (theoretically) produce a decent photo of the solar panels and individual modules; but I recognize the inherent challenges in this endeavor. So far I have not been able to capture ISS - but the orbit's approaching my latitude/longitude in end of November! Nimur (talk) 18:14, 16 November 2010 (UTC)[reply]
Fingerprints and obvious stuff like height, weight and various other things. Identical twins should give you a clue although given that the clone would likely be raised in a rather different environment some differences are likely to be more pronounced. (Clones and identical twins also have a relatively different genetic history.) Nil Einne (talk) 18:47, 16 November 2010 (UTC)[reply]
![[27]](http://www.google.co.uk/imgres?imgurl=http://z.about.com/d/sportsmedicine/1/0/Z/7/pit.jpg&imgrefurl=http://www.luvurfitness.com/more/foam-rollers-for-myofascial-release-and-massaging-tight-muscles&usg=__YzngRZVOLkIzfI9Ngf50CVzaKG4=&h=356&w=412&sz=59&hl=en&start=45&zoom=1&tbnid=cX5vRE9P19KHpM:&tbnh=137&tbnw=159&prev=/images%3Fq%3Darmpit%2Bmuscles%26hl%3Den%26sa%3DG%26biw%3D1024%26bih%3D591%26gbv%3D2%26tbs%3Disch:10%2C1279&itbs=1&iact=hc&vpx=127&vpy=291&dur=5151&hovh=209&hovw=242&tx=110&ty=154&ei=jondTO_bFsXHnAfxp4ndDw&oei=condTOLEMsH38AaCofX0Dg&esq=4&page=4&ndsp=15&ved=1t:429,r:5,s:45&biw=1024&bih=591){kind=link}
--Ludwigs2 07:31, 14 November 2010 (UTC)
