Wikipedia:Reference desk/Archives/Science/2010 June 18

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June 18

Angle grinder -lidl/aldi/netto

Barely a week goes by without one of the above supermarkets having an angle grinder on special offer - this confuses me as I don't consider it a household essential.. yet they still seem to sell. Question (bit of a straw poll but I hope you will humour me) - what do individuals use them for? (I mean 'household' use). Also does Walmart or whatever in the US have a similar obsession with the sale of this machine tool? Thanks.83.100.250.191 (talk) 00:03, 18 June 2010 (UTC)

I've used one to cut a long metal bolt, I also used one to trim a metal rod that was in the way of a light fixture. If you are handy, then it's a useful tool to have. And no, I have not seen any particular obsession here in the US, but that kind of thing goes in cycles. I hope they sell safety equipment with it (face shield), it can be a dangerous tool (always stay perpendicular to the rotation of the disk). Ariel. (talk) 01:44, 18 June 2010 (UTC)

I restore classic cars - angle grinders are great tools for hacking out bits of rusty sheet-metal, sawing heads off of stubbornly stuck bolts - all sorts of general metal cutting. I don't think I've ever seen one in WalMart - they might stock them, but it's just not the kind of store I'd look at when buying tools. Most of their stuff is cheap junk. SteveBaker (talk) 04:20, 18 June 2010 (UTC)

And don't forget that many men collect tools they have no use for and will never use...it's a guy thing, like women collecting shoes. StuRat (talk) 13:10, 18 June 2010 (UTC)

I find them remarkably useful for cutting bolts, rebar, plate, grinding rough metal, grinding down welds, etc. I have two, in fact, because my first one was too small for some of the work I was doing. That said, I obviously work with metals more than most people, and I wouldn't consider them a normal household implement. They're noisy and produce showers of incandescent sparks that can do bad things if they end up in your eye or in something flammable. Acroterion _(talk) 15:49, 18 June 2010 (UTC)

With the explosion of Harbor Freight and other 100% no-name import tool stores, things like this are becoming very common in the USA. Yes, you can get an angle grinder at most Wal-Mart stores (pneumatic or electric) and I wouldn't be surprised if I saw one in a rural supermarket either (if you can tell a difference between a Wal-mart and rural supermarket). What's becoming very popular is the "multi tool" (basically a vibrating dremel), the handle sits parallel to the path of vibration so you can use it for cutting, sanding, polishing, etc. As far as either of these being a "household item".... you would be surprised how many (probably bad) ideas you come up with when you have one! --144.191.148.3 (talk) 16:33, 18 June 2010 (UTC)

conservation of PH

Starting with neutral organic chemicals is it possible to turn the mixture acidic by any reaction (including bacteria etc) while keeping all reaction products in the final mixture? Ariel. (talk) 01:43, 18 June 2010 (UTC)

Probably not. Lots of compounds are highly pH sensitive. For example, amino acids can protonate or deprotonate at specific pH's. You'd need to post the specific reaction so we can check it, but the pH environment is generally very fundemental to the nature of compounds dissolved in solution. --Jayron32 01:52, 18 June 2010 (UTC)

If the solvent is ethyl acetate+water+etc then ester hydrolysis will make the solution turn acidic. A catalyst is usually needed which can be an enzyme [1] , a metal salt [2] or other things.

Is that what you meant.?83.100.250.191 (talk) 02:10, 18 June 2010 (UTC)

Or react acetic anhydride with water - the reaction products are acetic acid only.83.100.250.191 (talk) 02:19, 18 June 2010 (UTC)

Start with glucose and oxidise it to pyruvic acid. You can choose pathways where ethanol rather than CO2 is released. John Riemann Soong (talk) 15:39, 18 June 2010 (UTC)

Or even do use a CO2-producing pathway: it's soluble in water and would make the solution acidic. The extent is complete oxidation of any organic material in an enclosed container (to trap the product gases until cooled): CO2+H2O, CO2 dissolves in H2O, now you've got carbonic acid. DMacks (talk) 16:58, 19 June 2010 (UTC)

Or acyl chlorides and water. Provided you don't release so much HCl that some of it evaporates from solution of course. John Riemann Soong (talk)`

From one perspective, since the haloform reaction consumes base, it makes the solution more acidic. And the product (if you use chlorine) is chloroform and carboxylate. John Riemann Soong (talk) 17:14, 18 June 2010 (UTC)

Wine to vinegar. Physchim62 (talk) 00:39, 19 June 2010 (UTC)

Mobile phones in supermarkets

Hi. I live in the UK and I find that, almost without fail, my mobile never seems to get a signal when I am in my local supermarkets (Marks and Spencers, Sainsburys and Asda). I do not seem to get the same problem in other buildings (no matter how large) or in other shops. This has made me wonder whether there is anything about the building or contents (e.g. refrigeration units) of a supermarket that might prevent me getting a signal, or whether it might even be intentional for them to block the signal (although I can't see why). Any thoughts would be appreciated. GaryInLondon (talk) 02:40, 18 June 2010 (UTC)

There are ways to reduce or jam signals and there are businesses that do it to keep employees from using cell phones (they can only use them in the cell phone designated area). Some department stores who are worried about competitors may also jam phones and can be recognized if you start taking photographs and they ask you to stop. Ask the management. 71.100.0.224 (talk) 03:32, 18 June 2010 (UTC)

Does the building have a metal roof? Ariel. (talk) 03:46, 18 June 2010 (UTC)

Interesting; I'd like to know how widespread this practice is — in the US, radio jamming is illegal, including jamming a cell phone signal. Comet Tuttle (talk) 03:49, 18 June 2010 (UTC)

There's a difference between active jamming and natural attenuation of the signal. In the smaller traditionally-built supermarkets in rural northern England, mobile phones usually work, but I have a problem at home caused by very thick stone walls. Dbfirs 07:43, 18 June 2010 (UTC)

No problem getting a good signal in my local (large) branches of Sainsbury's and Asda, though a metal roof might well make a difference, as will the distance from the base station of course. You can find (clunky) maps of UK base stations here.--Shantavira|^{feed me} 09:11, 18 June 2010 (UTC)

I don't know about there, but supermarkets in the US are massive, with maybe a dozen aisles and fully stocked shelves between you and the outside when you're in the center, whereas the typical office building has a window within view at all times. So, the signal just has to go through more stuff. StuRat (talk) 12:59, 18 June 2010 (UTC)

I'd guess it's more to do with the distance from the base station than anything else, although a metal roof and cheap reinforced concrete construction won't help. Many UK supermarkets are built on cheap land with nothing else around but carparks, so it's hardly "hot territory" for the phone companies to ensure coverage. I can't imagine that the store is actually jamming coverage, because that costs money for no real benefit to the store. Physchim62 (talk) 01:51, 19 June 2010 (UTC)

I also don't believe that supermarkets are intentionally messing with cel-phones.

However, it's interesting as a thought experiment. I notice that many people in the supermarket call home to verify what they should buy and how much. If they weren't allowed to phone, would they buy more or less? APL (talk) 02:56, 19 June 2010 (UTC)

They'd buy less from that supermarket. 81.131.37.105 (talk) 14:19, 19 June 2010 (UTC)

As highlighted already, the Telecommunications Act prohibits interference with the EM spectrum so intentional suppression is illegal in the UK.

I'd agree with the previous points about the amount of metal in the structure interfering with the local infrastructure coverage.

ALR (talk) 19:10, 19 June 2010 (UTC)

Life on mars

Quick version: What I'd like is some old(er) sources which specifically make reference to the possibility of life on Mars, or the solar system in general, but before scientific consensus thought it was likely or possible. I specifically want to see HOW the topic is addressed. Did "science" say "it's not possible" or did they say "evidence suggests it's unlikely but more research is required". That kind of thing.

If that doesn't make enough sense, this is the "not so quick version". I'm writing an article about scientific discovery and basing it around the idea of "Life on Mars". When i was growing up, I didn't study astronomy or anything, but the impression I got from pretty much everything i ever read or heard was there was no life anywhere else in the solar system. This idea has been turned right on its head, quite recently in the scheme of things.

The point of my article is about how science constantly examines its beliefs and follows where the evidence leads. The idea that there might be life on Mars has shaken the scientific establishment but "believers" weren't persecuted and it wasn't ignored or covered up, it has been fervently pursued and is now one of the most exciting and important areas of research. I'm going to use this as contrast to the argument frequently made about science being scared of "supernatural" beliefs because they threaten the "established" beliefs of science. Vespine (talk) 05:40, 18 June 2010 (UTC)

I have to disagree with a part of what you wrote - the idea of life on Mars has not shaken up anything. Mainly because it's still just an idea - nothing has been found. (And the rock found on earth that might be from Mars doesn't count.) You'll have to wait for something to be found, and for best drama it will need to be something non-obvious, which some will say is proof of nothing, and others will say is proof, and only later will one or the other be known to be right. (That rock might turn out to be it.) It's far too early to use Mars for this. Also - it's very easy to forget about all the revolutions that turned out to be wrong, and where the establishment was right, and the "crank" was forgotten. There's a lot of selection bias going on here. Ariel. (talk) 05:59, 18 June 2010 (UTC)

The older view of course is that Mars was covered in irrigation canals and turned colors every spring as the plants sprouted. Rmhermen (talk) 06:06, 18 June 2010 (UTC)

well i disagree that "nothing" has been found. Extraterrestrial_life#Extraterrestrial_life_in_the_Solar_System several discoveries have been made, not just on Mars but several other places, which recently have made it more of a possibility. So anyway, this article makes it seem to me that the "possibility" has been considered for a long time, so where did my preconception of there being no other life in the solar system come from? I've discussed this with more then a couple of people and they all agreed with me that growing up you learned that Earth harbored the only life in the solar system.. Even watching cartoons we knew marvin the martian was a joke because there was no life on mars. Vespine (talk) 06:17, 18 June 2010 (UTC)

And? There still isn't life on Mars, nothing changed. And the link you posted says the same thing - no life (but some water). Your preconception, as you call it, is still correct as far as we know - no one has found any life. Ariel. (talk) 06:36, 18 June 2010 (UTC)

We're obviously not understanding each other. YES of course there is still no life found on Mars but now it is acknowledged as a real possibility, much more so then not too long ago. We weren't really actively looking for life on other bodies in the solar system, partly because we didn't have the technology, but partly because it seemed much less possible! Now what we've learned about extremophiles and astrobiology, it no longer seems so extremely unlikely! Not that I don't appreciate your input but if you still don't get what I'm trying to say, i don't need another reply from you telling me how wrong I am. I'm after sources specific to life in the solar system previous to say about two decades ago. Thanks.Vespine (talk) 08:58, 18 June 2010 (UTC)

Interesting - I always thought it was the reverse. After evolution, science assumed life was everywhere, including mars, and only after we got there and really looked around (i.e. now) do we no longer think there is life there. The viking missions (40 years ago) looked for life, so at least as far back as then it was thought mars had (or could have) life. And before that people looked for evidence via telescope. (And yes, we didn't understand each other. I think it's because we came from exactly opposite assumptions.) Ariel. (talk) 09:41, 18 June 2010 (UTC)

This section: Extraterrestrial life#Early_modern_period and the following one cover what you ask I think. It was pretty much assumed there was life on other planets, but when we actually got there and there was nothing, at that point the ideas started to shift the other way. Ariel. (talk) 10:00, 18 June 2010 (UTC)

Science can, and often does, entertain several conflicting theories when evidence is sparse. One sufficient evidence accumulates, we laugh at the theories that turned out to be wrong. I still like the idea (suggested long ago) that life on earth actually originated on Mars and was carried to earth by meteorites. Dbfirs 07:38, 18 June 2010 (UTC)

I disagree with the premise here. I don't think the possibility of there being life elsewhere in the solar system has changed much at all over the past 150 to 200 years - and certainly not in the last 50. But we've certainly changed where we think it might be:

• For the longest time everyone thought that Venus would be the most likely place - imagining lush swampy jungles and such like. But results from spacecraft showed Venus to be an exceptionally nasty place - and the possibility of life there was largely discounted. But recently, we've found 'extremophile' bacteria on earth, now people are starting to entertain the possibility of life on Venus once more!
• Now we're looking at icy moons far out around Jupiter and perhaps Saturn - and thinking that they are the likely places to look for life - when in the past, they'd have been considered to be completely impossible.
• The one constant through all of that was Mars - which was always considered to be a possibility for life - and is still considered a possibility today. The results we saw from the Viking survey missions of the 1970's showed much the same promise as we see today with the Mars Polar Lander with much the same tantalizing uncertainty. Our Life on Mars article has a reasonable 'history' section which explains that life on mars was stated as an explicit possibility in 1857 - and was probably thought to be a possibility by William Herschel as early as 1800.

What's really changed is that we've gone from highly speculative statements based on the appearance of the planet through a blurry telescope and horribly inaccurate estimates of surface temperatures from orbital data - to actually sending scientific instruments there and measuring things. Yes there is water on Mars - but no, there aren't any large canals flowing with water. What's also changed is our greater appreciation of how varied the conditions can be on earth and still have life flourish. I was watching a documentary the other night about how puddles of liquid CO2 exists at the bottom of some deep ocean trenches - and that there are small crabs and other animals that can live - even in close proximity to such nastiness! If that's possible - then life beneath the ice sheets of various moons of Jupiter and Saturn starts to look very much more plausible.

SteveBaker (talk) 11:40, 18 June 2010 (UTC)

That's actually some pretty good answers thanks, and some good sources. I also have recently read and watched a few things specifically about Enceladus and Europa which is what lead me to consider this question. So what I'm hearing is that probably my preconception, while growing up, that extraterrestrial life was not being expected in the solar system was a, common or not, misconception, not based on scientific consensus, but maybe just public opinion or pop culture or something. Thanks.Vespine (talk) 11:53, 18 June 2010 (UTC)

It's actually more interesting to me that the idea of life of Mars was rather quashed quite quickly in the 1960s. If you read sci fi from that era, the idea of life on Mars is presented as a not-that-far-out thing. I'm thinking of Stranger in a Strange Land, Martian Timeslip, etc. The life on Mars part of those stories are often the part that needs the least explanation. By comparison, by the late 1960s, 1970s, and so on, the idea that life would somehow actually be there seems to be quite hard to sustain, just ridiculous. Reading those stories now, and they sound quaint in their easy presumption that there could be life at all on Mars (creatures and plants and etc.), not just intelligent life. It was relatively recently that we found out that the planet was basically a dead desert, maybe with some frozen microbes hiding somewhere but that's it. --Mr.98 (talk) 13:30, 18 June 2010 (UTC)

I strongly disagree. If the scientific opinion in the late 1960's and early 1970's was that there couldn't be life on Mars, why did NASA spend a billion dollars (which would be an inflation-adjusted $5.4bn today) to send the Viking program there specifically to look for it? Those two missions launched in 1975 and must have started planning and budgeting in precisely the period you're talking about. To the contrary - scientists were rather of the opinion that they WOULD find life there - which is why the US taxpayer was convinced to spend so much. These days, comparable missions (such as the Phoenix lander and ill-fated Mars Polar Explorer) are funded on a shoe-string ($350 million). SteveBaker (talk) 14:01, 18 June 2010 (UTC)

Well, my timing might be off. But it's not too far. What I'm saying above is that in the late 1960s, it appears not to have been a big deal to assume there was life on Mars. At some point between then and, say, the 1990s, that changed. Whether that was in the mid-1970s or early-1970s or late-1970s, I don't know. --Mr.98 (talk) 16:59, 18 June 2010 (UTC)

It's possible you are talking of the time right after the Viking missions landed. When nothing was found, the idea of life on Mars become less popular. Ariel. (talk) 21:36, 18 June 2010 (UTC)

It's not even true that "nothing was found". In fact, the criteria that the designers of the mission set out for the positive detection of life by the on-board instruments were fully met - in a sense the instruments did indicate the presence of life. The flaw was in the experiment, which (it later emerged) could be fooled by non-biological processes which could plausibly be happening in Martian soil. It is most certainly NOT the case that the Viking landers proved that there was no life there - to the contrary, they produced evidence that it could be there - but sadly, due to the flaw in the tests they'd devised, the experiments didn't show that life must be there. That's not much to show for a billion dollar expenditure - but they did snap some cool photos and gather plenty of other scientific data so it wasn't a complete bust. SteveBaker (talk) 03:49, 19 June 2010 (UTC)

Again, Steve, I think we're talking past each other. I'm talking about large, multicellular life primarily, the sort of thing that excites the public imagination. There were no plants or critters. Imagining that there would be plants and critters on Mars seems to have been rather unimaginative in the 1960s. By the 1980s, nobody thinks there are any seriously there, and the question of "life" had receded into one about microbes. There's a big difference in the popular/public perception between microbes and critters. Nobody is saying Viking was a waste of money or time or anything. --Mr.98 (talk) 07:26, 20 June 2010 (UTC)

It's been a constant that there might be "life on mars", but the potential forms that life might take has constricted dramatically! As late as 1900 it would not have branded you as a crackpot to put forth a theory that the Martian canals were created by intelligent beings. APL (talk) 21:16, 18 June 2010 (UTC)

Also note that what people mean when they say "life" has changed. Early on, we were only concerned with intelligent life, or at least large animals. Some scum growing in a pond on some other planet wouldn't have been very interesting 100 years ago. Now that we could examine it's DNA, such scum would be extremely interesting, so there is far more interest in finding "any life" now than there was back then. StuRat (talk) 12:53, 18 June 2010 (UTC)

Radio Interference on a 'dead' radio.

On my journey to work in an urban environment, there is a specific spot where I get the sound of interference from my car radio speakers. It is a sort of clicking sound and is the typical sort of noise that one is used to hearing on occasions if a police car drives past, or there is known radio/electrcial activity nearby. My question arises because this happens when my car radio is TURNED OFF.

I have thought about this over several days, trying to work out how it happens and what processes are going on. But I always come up against the same problem . . . If there is no electrical current through my radio, what is generating the noise from my speakers?

I hope you can help. —Preceding unsigned comment added by 194.223.35.225 (talk) 07:12, 18 June 2010 (UTC)

Inductance? Dismas|^(talk) 07:23, 18 June 2010 (UTC)

What about the various beeps and bells your car makes? Are those piped through the speakers? Ariel. (talk) 07:23, 18 June 2010 (UTC)

Well it actually doesn't make many but I always assumed that those warning beep noises came directly from elsewhere - or how would I hear them if I had no car radio? Am I wrong? Are my speakers actually turned on while the radio itself is turned off? —Preceding unsigned comment added by 194.223.35.225 (talk) 07:28, 18 June 2010 (UTC)

It depends on the car, some have a dedicated speaker, others use the existing speakers. I think using the speakers is more common - it's easy to test, just make it beep and listen for where it comes from. Ariel. (talk) 09:43, 18 June 2010 (UTC)

On many (most?) cars speakers come standard. Radios are an option, but the speakers are difficult to install once the car has been assembled, so they get installed at the factory. APL (talk) 06:04, 19 June 2010 (UTC)

The interference is probably generated in your speaker coils by a large electromagnetic field. You could probably reproduce the effect at home by connecting a transformer to a household battery near to the car speakers. Dbfirs 07:31, 18 June 2010 (UTC)

Aaaah yes, of course: An electromagnetic field could be the energy that powers my speakers while also creating the souind. Thanks to both of you for showing me how this can happen. —Preceding unsigned comment added by 194.223.35.225 (talk) 08:00, 18 June 2010 (UTC)

You don't even need a strong electromagnetic field. Take any low-impedence speaker, grab a nine-volt battery, and hold a coin over the leads of the battery. When you generate a spark, you should hear the spark through the speaker. You have just made a basic radio. David E. Hughes performed these experiments in the 1870's, unfortunately he was basically ignored at the time, as no one saw any application for this novelty. We could easily have had broadcast radio several decades earlier had his work not been dismissed. Radio-frequency induction can occur with just about any speaker, and sometimes for unknown reasons, speakers can just start making sounds. Pay it no mind. --Jayron32 06:16, 19 June 2010 (UTC)

I was once in my kitchen with my boom box plugged in, but turned off, when it said, loudly, "How ya doin', good buddy ?". After I peeled myself off the ceiling, I realized it was just a stray CB transmission. StuRat (talk) 12:43, 18 June 2010 (UTC)

Poorly maintained CB radios are notorious for this sort of thing. (However I have to assume that modern digital units don't often have this problem.)

When I was growing up a neighbor (Briefly) had a CB that we could hear on just about everything we owned that had a speaker. Very strange. Intuitively you would think that this level of interference is impossible, but apparently it's not. APL (talk) 06:26, 19 June 2010 (UTC)

breasts full of milk

Can cats who have had their kittens taken away and have breasts full of milk die or be injured by the absence of nursing or else what happens to the milk? 71.100.0.224 (talk) 11:16, 18 June 2010 (UTC)

Very unlikely. I don't know about cats, but in humans (and cats are likely to be the same) the back-pressure eventually shuts down the milk production, and the lack of lactation does not stimulate any more milk production. It eventually gets reabsorbed. It hurts though - it can hurt a lot. See Breast engorgement which also discusses what you asked. Ariel. (talk) 11:30, 18 June 2010 (UTC)

Of course for most animals losing all their young even in a litter wouldn't generally be that uncommon an occurence. For the mother to not be able to survive this is needless to say unlikely Nil Einne (talk) 20:44, 18 June 2010 (UTC)

This newspaper in 1998 reported that El Niño weather left eight hundred dairy cows unmilked because of disrupted power, who died after becoming infected. Cuddlyable3 (talk) 21:39, 20 June 2010 (UTC)

Of course, dairy cattle are hardly a normal example of milk production in mammals (not that you said so). We actually have an article on mastitis in dairy cattle, which is apparently quite common. Matt Deres (talk) 21:47, 20 June 2010 (UTC)

I fixed your link -- it was missing a bracket. 67.170.215.166 (talk) 05:11, 21 June 2010 (UTC)

Thanks! Matt Deres (talk) 20:23, 21 June 2010 (UTC)

Why are there no Herring Gulls in Hampshire?

In my local area (Southampton, UK), seagulls are very common, it being near the coast, however, it is only the small gulls (Black-headed gulls I believe). When I go to coastal areas in other parts of the UK, there are always loads of the huge Herring Gulls...but for some reason, there do not appear to be any in Hampshire, which surprises me, as these gulls are usually common in urban areas, as they are well-fed by litter louts. We do have wheeliebins as opposed to black bags (the large gulls enjoy ripping those open) and waste in incinerated rather than going to landfill sites (another favourite haunt of gulls) now but I'm not sure that is the reason. The WP article on Herring Gulls shows they are found in every coastal area of Great Britain but I am not sure if there are other areas of the UK that don't have them.

GaryReggae (talk) 11:21, 18 June 2010 (UTC)

The lack of a local landfill and the presence of wheelie bins is certainly a possibility, IMO. Herring Gulls, as well as being longer and taller, are also far more 'substantial' birds - and need to eat a lot, for their size. Perhaps they are unable to eke out a living on discarded food items found in the streets? Has the sea been fished out where you are, as a matter of interest? If so, that's another possibility. Herring Gulls do prefer to feed their chicks on fresh fish. Strangely, the HG is actually declining as a species in the UK, despite the urban colonies in certain areas exhibiting massive yearly growth... --Kurt Shaped Box (talk) 17:13, 18 June 2010 (UTC)

Another possibility is that the Southampton herring gulls are all on the Isle of Wight! Southampton is actually quite a way from the open sea, so maybe the larger gulls have stayed closer to the open water, leaving the smaller gulls to pick up the urban food that's still available. Physchim62 (talk) 00:36, 19 June 2010 (UTC)

It is usually associated to food. There must be no fish-and-chip vans and outlets in Southampton. No fishing-trawlers. Normally along the Kent coast when getting your fish-and chips you have to watch out for the big gull awaiting his opportunity, usually perched above the van itself! MacOfJesus (talk) 21:45, 23 June 2010 (UTC)

Immunosuppression drugs -> skin like tissue paper?

About 20 years ago, my grandmother had a kidney transplant and, as a result of the immune suppression drugs that she takes, her skin is extremely delicate and very slight knocks or abrasions will remove it. Recently, while alighting from a motorcar, her ankle was caught in the seat-belt and the resulting pressure created a wound. Apparently, when her hosieries were removed at the hospital, her skin was in the mesh of her tights. I am not seeking medical advice; she is now receiving daily care from the NHS. I would like to know whether this is a known condition and whether it has a name? Is it a rare reaction to immunosuppression? --78.150.225.204 (talk) 13:51, 18 June 2010 (UTC)

Skin thinning and easy bruising are common side effects of corticosteroids (source), which are a widespread and very powerful class of immune suppressants. The medical term is skin atrophy. I personally have some nasty scars from when I was on prednisone. --Sean 14:56, 18 June 2010 (UTC)

Sodium bromide as salt substitute

Would sodium bromide be a good salt substitute? --Chemicalinterest (talk) 15:29, 18 June 2010 (UTC)

This link discusses an incident where sodium bromide was taken instead of sodium chloride (by accident). I'm not sure whether that toxicity is caused because there was too much sodium bromide, or if it's because NaBr itself is toxic. Regards, --—Cyclonenim | Chat  17:51, 18 June 2010 (UTC)

The Bromide article discusses some of the toxicity/biochemistry of this ion. DMacks (talk) 18:36, 18 June 2010 (UTC)

Salt substitutes normally replace the sodium metal cation not the chlorine halide anion. The usual substitutes are calcium, potassium or possibly magnesium, all of which are needed in human biology. This is to reduce the chance of hypernatremia, excessive sodium levels (natrium is the old name for sodium, its the source for sodium's symbol, Na). Excessive chlorine levels is hyperchloremia, which appears to be asymptomatic. As bromine is a sedative, it shouldn't be used. Selenium and iodine are toxic in more than trace amounts. The common polyatomic ions like nitrate or sulfate are also poisonous. Phosphate is probably safe. CS Miller (talk) 13:22, 19 June 2010 (UTC)

Windmill on an airplane

There was previously some discussion about whether net energy would be harvested from having a windmill on a car. Would a windmill on an airplane harvest energy in a steady wind? I imagine it could do so when the wind was gusting, due to the accelerating wind acting against the inertia of the plane. 92.15.14.87 (talk) 17:31, 18 June 2010 (UTC)

As mentioned in the other thread, the ram air turbine is a windmill that pops up if all the engines fail, and it generates emergency power so the pilot can at least have some flight instruments to read, and try to control the plane. But in ordinary flight, a windmill would create drag on the aircraft, and the aircraft's engines will have to use more energy to overcome this drag than the amount of energy the windmill can generate. This occurs regardless of whether the aircraft is flying into the wind or with the wind. It's a net loss, which is why you don't see windmills on airplanes. (Last point of clarification: The ram air turbine generates extra drag, too, but if the engines have all failed then you have much bigger things to worry about than the little windmill's extra drag.) Comet Tuttle (talk) 17:44, 18 June 2010 (UTC)

I meant steady wind and steady level flight also - no diving. What about on a glider? 92.15.14.87 (talk) 18:04, 18 June 2010 (UTC)

No net power can be harvested this way - there is no such thing as a free lunch. But if your glider needs electrical energy - then a windmill will rob you of some kinetic energy (and therefore make you lose height faster and ultimately glide less far) - but if you need electricity to power instruments or whatever, then that might be a trade-off that you're prepared to make. SteveBaker (talk) 18:39, 18 June 2010 (UTC)

A windmill on a glider will produce a less efficient glider. If you need juice for electronics, solar panels are a more elegant solution, given the big long wing surface. With the widespread introduction of large lithium-ion batteries, battery-powered electric propulsion is becoming possible, allowing self-launching and extended flight for gliders, but that's a windmill in reverse. Basically, any harvesting of energy via a windmill on any moving object will come at a cost of worse performance or higher energy consumption, all things being otherwise equal. Acroterion _(talk) 18:43, 18 June 2010 (UTC)

As mentioned in the other thread (and still true here), it's not necessarily true that adding a windmill will make your aircraft less efficient. It could add more drag than the power it produces, but it could also add less than that; it could even reduce the drag. What it can't do is give you enough power to preserve your steady-state flight without any other power source. That would be a perpetual motion machine. (In the case of a ground-based vehicle, though, even that's not true, because you can extract arbitrary amounts of energy from the motion of the air relative to the ground.) -- BenRG (talk) 19:11, 18 June 2010 (UTC)

One thing to consider that might be getting overlooked in some of the above... the speed of the wind relative to the ground is pretty unimportant. An airplane in flight is moving pretty fast through the air. So the effective wind is backwards relative to the plane, at whatever speed the plane's airspeed is at the moment. So you don't need to worry whether the wind will run out - there will always be wind, as long as the plane is moving fast enough to sustain flight. Friday (talk) 19:17, 18 June 2010 (UTC)

You can not harvest energy from a steady wind, you can only harvest it from a changing wind, or a wind that is different from something else (like the ground). See Dynamic soaring for a dramatic example. Ariel. (talk) 21:32, 18 June 2010 (UTC)

When we are flying, we have airspeed and ground speed. Whether we are flying into the wind or with the wind, we still fly at the same airspeed, and as far as the aircraft is concerned, that's all that's relevant. Therefore, assuming steady wind and steady level flight (we call that "straight and level"), the airplane will always be flying x miles per hour in relation to the air moving around it. In that respect, the airplane is already using (or fighting against) all of the wind energy available to it. If it's flying with the wind, it tracks faster along the ground (ground speed). If it's flying against the wind, it tracks slower. Adding a fan at that point would cause more drag, and slow the aircraft down (or cause it to require more power). Falconus^{p t c} 22:02, 18 June 2010 (UTC)

Some of the early biplanes like the de Havilland Tiger Moth and de Havilland Dragon Rapide had small wind driven generators to provide electrical power. MilborneOne (talk) 15:54, 19 June 2010 (UTC)

Someone mentioned drag. You would have two powers fighting against themselves. Either the plane would fall or the power received would be too weak to be significant. The energy received would be at the expense of dragging the plane. So, whatever energy would be received would be "lost". Every effort is made to reduce the drag to make the flight economical. Air has a very heavy drag effect. So the method you envisage to recover some of the energy would result in spending more!

The support teams of The Ras Taltan, a cycle race in Ireland incorpurating the Ring of Kerry, reported that the cycles strapped to their support cars had the effect of producing very low MPG in fuel consumption. MacOfJesus (talk) 21:31, 20 June 2010 (UTC)

The Komet fighter also had a ram-air turbine in the nose to provide electric power. 67.170.215.166 (talk) 05:15, 21 June 2010 (UTC)

Does abstinence cure any addiction?

Addiction of no matter what - sex, drugs, gambling. The idea behind it is that if you stay clean for a long time, your body will reset the addiction. --Quest09 (talk) 17:33, 18 June 2010 (UTC)

I'm not sure you can say abstinence cures addiction because usually people who abstain for years from, say, alcohol after becoming alcoholics can relapse on the first drink years later. If it was a cure, this wouldn't happen. Instead, it's just staying away from what weakens you. With respect to drugs, it's going to depend on the type of addiction: psychological or physical? Psychological addictions should be easier to remove by abstinence, but physical addictions often require weaning off the substance rather than a complete halt. Regards, --—Cyclonenim | Chat  17:47, 18 June 2010 (UTC)

Some would say yes, you can quit anything cold turkey if you have the willpower. Others would say no, you never truly cure an addiction unless you replace it with something else. There is probably a little truth in each, but since addiction is such a multi-faceted problem, there is no clear answer to your question. All we really know is what we have observed of the process, we don't have clear evidence of addiction at work inside the body, aside from chemical changes which are only a small part of the process. --144.191.148.3 (talk) 17:49, 18 June 2010 (UTC)

A distinction must be made between physiological dependence (Physical dependence), in which the balance of neuroactive chemicals in the brain is altered directly by the substance abuse, and behavioral addiction, in which the the balance of neuroactive chemicals in the brain has not necessarily been externally perturbed. In either case the etiology, the symptoms, the treatment, and the results vary greatly, so nothing general can be said without overgeneralizing the things grossly. --Dr Dima (talk) 18:17, 18 June 2010 (UTC)

My Google search for abstinence cure addiction found http://health.howstuffworks.com/addiction.htm/printable. I did not find there a definitive answer to your question, but I did find some interesting information.—Wavelength (talk) 02:53, 19 June 2010 (UTC)

This might be a language / definition problem. Does "cured" imply "permanently cured"? During the period of abstinence, by definition, one is not participating in the activity. This could be labeled "temporarily cured" (insofar as the person is not participating in the activity). But there is always the possibility of relapse. "Addiction" is subject to interpretation: broadly speaking, we can sub-categorize it into "physiological" and "psychological" dependence. The "cure" for addiction can be interpreted subjectively and may span these categories. For example, detoxification following a drug or alcohol addiction is typically the first step in treatment. For certain drugs, total "cold-turkey" abstinence techniques may actually be less effective than other methods (often a surrogate substance is used to help alleviate withdrawal symptoms - e.g., Opioid Replacement Therapy). Details depend on the type and circumstances of physical dependence. But "detox" is not the same as "cured" - it is obvious that relapse is a serious issue, because addiction has a significant psychological component, independent of physiological/chemical dependence. In the medical or psychological community, this problem of definition is sidestepped by using more precise terms. For example, a patient is classified based on the type of dependence, rather than simply saying that they are "addicted". This helps decide what kind of treatment is preferred. It is pretty rare (at least in the modern institution of psychology) to say that anybody is ever "cured" of a psychological issue, including addiction or substance abuse problems, because "cure" implies some kind of certainty that relapse will not happen. People who undergo treatment for addiction have various strategies to reduce the probability of relapse - again, based on the type of addiction and the circumstances, this might include total abstinence. Nimur (talk) 18:33, 19 June 2010 (UTC)

In studying the life of Saint Augustine, he stumbled on a number of positive steps towards a cure of addiction. However, the cure comes in steps. For The Alcoholics Anonymous there are twelve steps. Study C.G. Jung. All agree that there are steps towards a complete cure. Going-it-alone is a very hard road, and would not be possible for some kind of addictions, and because man is a gregarious creature the cure would needs be with others. MacOfJesus (talk) 20:51, 20 June 2010 (UTC)

'natural' alkyl halides?

Are there any natural alkyl halides produced by living organisms? Would I see ever see chlorine substituted on a random amino acid in a protein for instance? John Riemann Soong (talk) 18:11, 18 June 2010 (UTC)

I don't know any specific complex natural alkyl (sp³) halides off-hand, but maybe follow the links and refs in the "Occurrence" and "Biosynthesis" sections of our haloalkane article? DMacks (talk) 18:31, 18 June 2010 (UTC)

See also Organochloride#Natural_occurrence not much info, or Encylo..Britanica better. Not suprisingly things that live in salt water are a common source.

eg http://www.google.co.uk/search?hl=en&q=asparagopsis+taxiformis&meta= (mentioned in the britannica article) aka Limu kohu

There's a nice example of thr type of thing found here google books:Invitation to organic chemistry By A. William Johnson page 113, with both alkyl and alkenyl halide (carbon-iodide bonds are also common - but most I've seen are attached to benzene or similar)

If you want more then I recommend trying using google scholar http://scholar.google.co.uk/ (searching "natural product" + bromine/halogen , with marine/algae etc to narrow seems to work..) if you don't use scholar search returns a lot of results about metal halide lights for marine aquariums...

eg this worth reading (and lots more) turns up easily with aromatic, akenyl and alkyl halides.

Alternatively hunt down and marry a marine biochemist.. :) 87.102.32.15 (talk) 19:21, 18 June 2010 (UTC)

As for halogens in amino acids - I was going to say not likely - since most examples I know of tend to appear to be the result of electrophilic attack on double bonds eg terpene like compounds etc .. but no: [3] halogenated tyrosines found in marine animals - spongin in sponges and gorgonin in Gorgonians this time - again marine creatures.87.102.32.15 (talk) 19:49, 18 June 2010 (UTC)

For an sp3 halogenated amino acid look into "barbamide" structure- contains a trichloromethyl group that is thought to derive from a halogenated leucine [4], there are probably thousands of other examples.87.102.32.15 (talk) 21:01, 18 June 2010 (UTC)

Thyroxine is not an alkyl halide, but is a halo-organic formed naturally in the human body. Physchim62 (talk) 00:29, 19 June 2010 (UTC)

What's the selective pressure (or function) of the iodide substitutions? Is it for their EWG effect to make the molecule easier to cleave? Make the molecule exceptionally large, bulky and fat-soluble? Or? John Riemann Soong (talk) 16:27, 21 June 2010 (UTC)

Also I take it most of our iodine nutrition comes through the form of I- iodide and not elemental iodine :o -- does an enzyme oxidise iodide to some intermediate which can then grab electrons on an aromatic ring? Or does the iodide ion attack aromatic rings nucleophilically? (With the help of an enzyme, of course.) John Riemann Soong (talk) 16:29, 21 June 2010 (UTC)

As usual, you can start reading wikipedia to find leads to help answer your questions. The thyroxine article mentions some of the key enzymes, and also tells you another article to read. That article (as well as the ones about each enzyme) tell you more (with refs to scientific literature) about the chemical origin of the iodine atom and the chemistry of its reactions. What I don't see is information about "why iodine" (speculation on evolutionary pressures or hereditary tracing of the related regulatory pathways). DMacks (talk) 14:22, 22 June 2010 (UTC)

Amino acids in a vegan diet

Do vegans have any deficiency of particular amino acids in their diets, or do they have all of them? Thanks 92.15.14.87 (talk) 18:18, 18 June 2010 (UTC)

According to our article Legume: "Legumes contain relatively low quantities of the essential amino acid methionine. To compensate, some vegetarian cultures serve legumes along with grains, which are low in the essential amino acid lysine, which legumes contain. Thus a combination of legumes with grains forms a well-balanced diet for vegetarians." SteveBaker (talk) 18:29, 18 June 2010 (UTC)

Yeah, rice and beans, aside from being tasty, is likely to have the amino acids you need, all together in one meal. You can get all essential amino acids from plant material, but you have to know what you're doing. Whereas you can be an uneducated meat eater and easily get them all. Friday (talk) 18:45, 18 June 2010 (UTC)

Vegans who don't go to any special effort are most likely to be short on lysine, but as the other replies pointed out, eating legumes is a good solution. Soy protein in particular has nearly the same quality as beef protein, so vegans who eat lots of soy products don't need to worry about this. (There may be other issues with eating lots of soy, though.) Looie496 (talk) 21:37, 18 June 2010 (UTC)

While this is not something I've looked into myself very well, I saw something a few week back while researching for another answer. I can't seem to find the particular source (well one of the ones I did find may be it, but I seem to recall something that I didn't see in any of the sources I provided). But sources (some of these may be a bit biased but their citations and info seems resonable to me) like Protein combining, Vegetarian nutrition, [5], [6] [7] [8] [9] (unsure about this source, comment on tryptophan doesn't appear correct) suggest while you do want a balanced diet, it is rather hard to get insufficient essential amino acids even on a vegetarian or vegan diet provided you have sufficient calorific intake.

Even if you only eat potatoes, you could easily get essential amino acids in sufficient quantities (sources say 6-8 large potatoes), although your diet is likely to be deficient in other areas (and I find it doubtful many people in the developed world would choose such a diet not counting those who eat mostly chips of either kind of course). Rice seems a bit more iffy 7.5 cups of cooked rice seems quite a lot then again if it's the only thing your eating you may need that much to fulfill you calorific intake.

In any case, note there is no need to combine proteins in one meal to ensure sufficient protein intake or balanced protein intake, simply get enough thoroughout the day. Body builders and others who want a high protein diet obviously need to take a bit more care to ensure their protein intake isn't limited by a small intake of one essential amino acid.

But in summary although getting amino acids in sufficient quantities seems to be a common concern, from what I can tell it's not really generally that big a deal, even without great effort most vegetarians and vegans who have access to a resonable set of foods won't usually won't end up deficienct even without making much of an effort. Nil Einne (talk) 22:51, 18 June 2010 (UTC)

The things I'm familiar with vegans often being deficient in (if not careful) is not amino acids but rather iron (Anemia) as well as Vitamin B12 (Vitamin B12 deficiency). Buddy431 (talk) 01:55, 21 June 2010 (UTC)

Natural sea salt

Is natural sea salt any healthier than artificial salt? --75.25.103.109 (talk) 21:07, 18 June 2010 (UTC)

When you say artificial salt, do you mean to refer to a salt substitute? If not, I think sodium chloride is sodium chloride and it doesn't matter from whence it is derived, whether sea or flats. DRosenbach ^{(Talk | Contribs)} 21:26, 18 June 2010 (UTC)

(after ec)The term "artificial salt" is pretty meaningless. Sea salt contains sodium chloride (table salt) plus other stuff, depending where it came from. See Sea_salt#Taste_and_health. My understanding is, there is no evidence that sea salt is healthier than any other salt. Many people consume too much sodium, and eating sea salt won't change that. There is a widely held superstition that "natural" things are healthier than "artificial" things, but the people who go around believing such things usually can't explain what they even mean by those terms. A grizzly bear is very natural indeed but should not be considered safe. Friday (talk) 21:27, 18 June 2010 (UTC)

(ec2) That depends on the rest of your diet. It contains a lot more minerals other than sodium and chloride, but if you get adequate amounts of them from the other things you eat, it might not make much of a difference. Looie496 (talk) 21:28, 18 June 2010 (UTC)

(ec again!) Have you read Sea_salt#Taste_and_health? Sea salt contains some iodine which we need in our diet but standard table salt does not. As already mentioned, they are both almost entirely sodium chloride so there is little difference. 86.7.19.159 (talk) 21:30, 18 June 2010 (UTC)

You got that backwards - table salt usually has iodine added, and sea salt contains no significant iodine. Friday (talk) 21:33, 18 June 2010 (UTC)

Seaweed does, though. Kind of a lot of it if I recall correctly. No real relationship with sea salt, of course, except that you could argue that the saltiness in seaweed is sea salt, and you might expect the same type of consumer to eat it. --Trovatore (talk) 21:36, 18 June 2010 (UTC)

Iodine is not added to salt in the UK. Sea food is a source of iodine, especially seaweed. 92.15.4.168 (talk) 13:40, 19 June 2010 (UTC)

To my knowledge no one is artificially manufacturing salt. It would be a very expensive process, and salt is pretty cheap. Most table salt comes from salt mines where workers dig up giant deposits of salt from parts of the ocean that dried up eons ago. APL (talk) 21:51, 18 June 2010 (UTC)

Around here, most table salt comes from evaporation. They have big shallow ponds carved out of San Francisco Bay. The salt article doesn't seem to have a breakdown of how much is evaporated, versus mined, worldwide.

Even though it's evaporated from seawater, it's not ordinarily marketed as "sea salt". I don't know whether there are any special rules to qualify the product as "sea salt" or not. --Trovatore (talk) 23:04, 18 June 2010 (UTC)

I didn't realize that. I thought that all salt that came from evaporation was sold as "Sea Salt". I wonder what the difference is. It would be hilarious if it were just marketing. That is, the same salt, from the same source, sold as both table salt and sea salt, for different prices. APL (talk) 03:02, 19 June 2010 (UTC)

Sea salt is generally unpurified. Table salt, whether it is mined or evaporated from ocean water, goes through a purification process to be almost pure sodium chloride. So, if you take sea water, evaporate the water, and then use the leftover crystals directly, that's "sea salt". If you take that sea salt, further purify it and remove all the non-sodium chloride impurities, you have "table salt". --Jayron32 05:12, 19 June 2010 (UTC)

Assuming 'artificial salt' means refined rock salt (ie the mined type) there is difference that rock salt is very old and was laid down before man made polution, whereas sea salt has the potential to be polluted by more recent man made discharges. In practice I have no idea if this is a factor or whether there is regulation of sea salt purity.87.102.32.15 (talk) 22:55, 18 June 2010 (UTC)

So sea salt is sodium chloride with some contaminants, whereas table salt is slightly purer sodium chloride with different contaminants. Gandalf61 (talk) 09:16, 19 June 2010 (UTC)

You would be healthier adding no salt at all to your food. It's very likely that you get more than enough salt or sodium hidden in the processed foods you eat. I think the recently reduced UK target for salt consumption is 4g per day, but the true optimum is belived to be about 2.3g per day as far as I recall. I suggest you try estimating and adding up your total salt or sodium intake per day (from the nutritional information given on processed foods where available etc) - you will almost certainly have an unpleasant surprise. 92.15.4.168 (talk) 13:33, 19 June 2010 (UTC)

For a good salt substitute; try Ruthmol Salt. MacOfJesus (talk) 23:44, 19 June 2010 (UTC)

Most Salt substitute is potassium chloride. While it's true that most westerners consume much more sodium than they need, and that they could do to get more potassium, there are definite health implications involved with consuming too much potassium as well. I'd recommend having a good reason before using a salt substitute, and discus it with your doctor ahead of time. Buddy431 (talk) 01:45, 21 June 2010 (UTC)

Organic Materials

what are the molecular components from which organic materials are constructed?Sadiehyde (talk) 21:50, 18 June 2010 (UTC)

See functional group. --Chemicalinterest (talk) 21:57, 18 June 2010 (UTC)

Blossoms and leaves: coming and going

As I recall from my experience, spring blossoms on some deciduous trees appear first at the extremities and drop off last from the extremities, and spring leaves appear first at the extremities and autumn leaves drop off last from the extremities. To what extent is my memory correct? What is the scientific (possibly biochemical) reason for the blossoms and leaves behaving in those ways?—Wavelength (talk) 22:58, 18 June 2010 (UTC)

How much sunlight and shade do the extremeties see versus the interior branches? TenOfAllTrades(talk) 23:11, 18 June 2010 (UTC)

Apparently, they see more sunlight and less shade, but I do not know how much, either in absolute measurements or in relation to the amounts seen by the interior branches.—Wavelength (talk) 23:23, 18 June 2010 (UTC)

The distribution of plant hormones might have something to do with it eg Auxins I would guess that they dominate at growing tips and diffuse to the 'interior parts'. Also see Plant hormone - .. - Abscisic acid seems to be involved (in some cases) - though I'm not sure if it's causal (or the mechanism by which it is produced at growing tips..) . Maybe someone else can expand on this.87.102.32.15 (talk) 23:17, 18 June 2010 (UTC)

By the way I can't actually confirm what you remember - and there are growing tips all over the plant branches (potentially).. so .dunno. 87.102.32.15 (talk) 00:27, 19 June 2010 (UTC)

Neither do I believe that deciduous trees in general lose their blossom or leaves in this way. Richard Avery (talk) 14:16, 19 June 2010 (UTC)

As I understand it; It does depend on the weather and the soil and the altitude and of course the sunlight. The blossoms will tend to develop into fruit, or fall-off in frost early, or come off early in a storm. MacOfJesus (talk) 23:12, 19 June 2010 (UTC)

Blossoms will, after pollination will progress towards becoming fruit, and will fall-off when ripe unless weather conditions dictate otherwise. MacOfJesus (talk) 08:08, 20 June 2010 (UTC)

Plants that have their flowers in spikes such as a foxglove nearly always open from the bottom up. I think they go to seed from the bottom up too. Flower spikes that open from the top down are rare. 92.28.240.72 (talk) 10:14, 20 June 2010 (UTC)

Why is the speed of light relative to an observer constant regardless of the velocity of the source of light or of the observer?

The whole relativity thing depends on this phenomenon, so it would be interesting to know WHY this is the case.––220.253.96.217 (talk) 23:31, 18 June 2010 (UTC)

Because that explanation best fits the universe we observe. At some point, questions of "why" regarding fundamentals are philosophical rather than scientific. — Lomn 01:17, 19 June 2010 (UTC)

The two parts of this have two different answers. The reason it remains constant regardless of the velocity of the source is basically the same as the reason waves generated by a boat traveling through water remain constant regardless of the velocity of the boat. But the reason it remains constant regardless of the velocity of the observer is much deeper: it is a result of the Einstein equations for special relativity, which say that when an observer moves, the basic laws of physics only remain valid if time is rescaled, and the amount of rescaling is exactly what is needed to keep the apparent speed of light constant. Looie496 (talk) 01:28, 19 June 2010 (UTC)

Modern physics rejects Looie496's assertion that the reason the speed of light remains constant regardless of the velocity of the source is basically the same as the reason waves generated by a boat traveling through water remain constant regardless of the velocity of the boat. Looie496's presumption that there exists a medium (water) that light travels in is the old Luminiferous aether theory that has been disproven since 1887 by the Michelson–Morley experiment, Cuddlyable3 (talk) 11:27, 19 June 2010 (UTC) small tweak

Relativity does not presume that there is no such thing as space. Light as viewed in special relativity consists of oscillating electric and magnetic fields, and those fields are defined in spatial coordinates. Maxwell's equations for electromagnetic fields produce an oscillation that propagates across space according to the wave equation, which is the same equation that governs the propagation of waves across the surface of a body of water. Looie496 (talk) 17:08, 19 June 2010 (UTC)

The Wave equation to which you refer is derived by the classical mechanics of applying Hooke's law to an elastic medium, in which one finds a physically realizable value for the speed of wave propagation. Maxwell in 1865 published his equations believing in the rest frame of the luminiferous medium. They are laws of Classical electromagnetism. Maxwell was no more able than Robert Hooke to conceive the relativity of the speed of light though he knew an approximate value of c. Cuddlyable3 (talk) 23:42, 19 June 2010 (UTC)

The whole relativity thing depends on that only if you chose to follow the historical aproach (which most introductory books do) and postulate the constancy of the speed of light and get everything else from there. Alternately you could postulate, for instance, the Lorentz transformations and get everything else from there (including the constancy of the speed of light which is not a postulate on that approach). You might ask now why does the universe obey the Lorentz transformations? Well, it is a matter of space-time symmetries. The Lorentz transformations obey a set of symmetries which are generalizations of space rotations. Asking why the universe obeys Lorentz covariance (That's the technical name of the symmetry) is simmilar to asking why the universe is isotropic and homogeneous. The answer of couse is that's simply the way it is and we know that from empirical obsergations. There is no why. Dauto (talk) 03:11, 19 June 2010 (UTC)

I think it's important to distinguish "we don't know why, or even if there is a why" from "there is no why". The former would be a much more justified statement. --Trovatore (talk) 03:19, 19 June 2010 (UTC)

I think the latter is the better statement. Dauto (talk) 15:52, 19 June 2010 (UTC)

Why do you think that? Of course, it's a stronger statement, and we want to make the strongest statements we can justify. But I don't see that you have any justification for it whatsoever. --Trovatore (talk) 18:51, 19 June 2010 (UTC)

I agree with Trovatore. Lorentz invariance could easily end up having an explanation (in terms of some sort of pregeometry). -- BenRG (talk) 18:58, 19 June 2010 (UTC)

Of course there could be an explanation but ,like a three year old child, we could simply ask another 'why' question such as 'why is that pregeometry that way?'. Let's not kid ourselves, all scientific theories rely on some kind of axiom or priciple for which, within the framework of that theory, 'there is no why' is the only possible answer. Since there is no way around that, I believe that 'There is no why' is the better statement. Dauto (talk) 02:40, 20 June 2010 (UTC)

I very strongly disagree. Just because it's turtles all the way down doesn't mean you have to stop at the first turtle. Now, it would be different if you said "we're pretty sure this is the way it is, whether we know why or not", that would be a useful and practical statement. But insisting that "there is no why" reminds me of strong atheism, which I think is pretty ridiculous. --Trovatore (talk) 03:23, 20 June 2010 (UTC)

I think that "there's no why" is indeed the best answer to that kind of question. Why do you say strong atheists are ridiculous? It seems to be a point of view as viable as any of the world religions if not more. Dauto (talk) 17:05, 21 June 2010 (UTC)

Well, I think you're wrong. You have no justification for claiming there is no why. Or if you do, you haven't explained it. I think the same thing if you're claiming actively that there is no God, but I probably shouldn't have brought that up because it's not really the issue here. --Trovatore (talk) 23:15, 21 June 2010 (UTC)

While we're mincing words, "it is a result of the Einstein equations for special relativity..." This is accurate, but it is phrased in such a way that it sounds like one day Einstein just decided that he should write some equations to make the speed of light constant in all frames. The way the universe works is not a consequence of Einstein, or any other scientist's equations. The universe works the way it does - and Einstein's equations happen to explain this particular detail in a simpler and more consistent way than any other explanation. Universal principles are not a "consequence" of our mathematical effort to represent them. Instead of attributing this fact to the equations, we should say "if this fact were not true, there would be an inconsistency in the universe because of the way that electromagnetic waves work. This inconsistency was first resolved mathematically by Einstein." Nimur (talk) 18:40, 19 June 2010 (UTC)

If you're asking why we believe it: testing. If you're asking why it's true, special relativity explains it. — DanielLC 06:30, 19 June 2010 (UTC)

...And if you're asking "why it is the way it is instead of working out some other way", that answer lies at some level in either philosophy or religion. The most agnostic answer to the "big why" is probably the Anthropic principle which is a type of logical tautology. The Anthropic Principle states that the laws of the universe exist the way they do because we are observing them. To state it another way, the fact that humans exist to observe the universe is predicated on the fact that the laws of the universe cannot exist in any way other than what we are observing, because if they were different, the universe under THOSE laws could not have produced humans to observe them. Or, to put it a third way, if the universe obeyed different laws, it would not have produced an intelligent life form to ponder the universe. So the answer to "why" could just be that if it were different, it wouldn't exist in a way to allow us to observe those differences. --Jayron32 06:52, 19 June 2010 (UTC)

That's a pretty "extreme" statement of the strong anthropic principle" - as you have phrased it, Jayron, you discount the possibility of a null space within which certain physical laws could differ while still providing a universe suitable for intelligent life. Nimur (talk) 18:48, 19 June 2010 (UTC)

I agree. E.g., there is a formal description of Jayron32's brain, therefore any algorithm that aims to simulating it, defines the laws of physics of a a universe in which he lives. Count Iblis (talk) 19:16, 19 June 2010 (UTC)

Looking at the philosophical answer: Does this "big why", and what is said above "prove" the existance of God, as defined in Saint Thomas Aquinas' proofs of God's existance? Particularly so, if it is said that: the universe cannot exist in any way other than what we are observing. Also, defining how a person thinks in whatever method, could in itself be proving God's existance! If you assume that the observer observes that which is in reality, you could be proving God's existance. Neil Armstrong's statement 1969: "There is a Santa Claus"! However, there is a way around it! If you say that there is no reality outside yourself, and that the only thing I know is that "I" exist. But then, there is no light and no universe! And as for the speed of light: that is just a figment of one's imagination! MacOfJesus (talk) 20:50, 19 June 2010 (UTC)

I would start with e=mc^2 - once you have that relativity is required. The reason is that as an object gets faster it's mass goes up (since it's energy has mass), to speed it up even more requires even more energy, that additional energy makes it even heavier. Carry that to the end shows that at a speed of c the mass is infinite. That basically requires relativity. Because without it you could add speeds, for example .75c + .75c = 1.5c But we already showed that speeds above c mean infinite energy. So in a universe where mass and energy are interchangeable relativity is required. Ariel. (talk) 07:54, 20 June 2010(UTC)

Try studying Physics and Existentialism at the same time. MacOfJesus (talk) 08:05, 22 June 2010 (UTC)

To go back to the original point of the OP; Maybe it is because we observe by light, which is everywhere for the viewer so there is no start point as light is everywhere as the viewer cannot observe anything without it! MacOfJesus (talk) 11:58, 23 June 2010 (UTC)

Paper cuts vs. "normal" cuts

I've seemed to notice that paper cuts have more pain to them than your average minor cut, and a kid in my scout troop who accidentaly sliced his finger with a knife (almost bad enough for stitches) said it hurt less than some paper cuts he's gotten. What causes paper cuts to hurt worse than other "normal" cuts? Ks0stm ^(T•C•G) 23:49, 18 June 2010 (UTC)

From Paper cut: "Paper cuts can be surprisingly painful as they can stimulate a large number of skin surface pain receptors (nociceptors) in a very small area of the skin. Because the shallow cut does not bleed very much, the pain receptors are left open to the air, ensuring continued pain. This is exacerbated by irritation caused by the fibers in the paper itself, which may be coated in chemicals such as bleach. Additionally, most paper cuts occur in the fingers, which have a greater concentration of sensory receptors than the rest of the body."[10] Ariel. (talk) 00:15, 19 June 2010 (UTC)

semiconductor doping

If silicon chips are doped with arsenic, why doesn't touching them poison you? --75.25.103.109 (talk) 23:55, 18 June 2010 (UTC)

1. No one ever touches them. The part you see is a plastic cover, the silicon is inside.
2. There is a VERY tiny amount.
3. The arsenic is tightly bound in the silicon, and will not come out just because it's touched.

Ariel. (talk) 00:13, 19 June 2010 (UTC)

You don't get arsenic poison by touching a piece of arsenic elemental anyway; you get it by touching then ingesting, inhaling fumes or the volatile compounds such as arsenic trichloride, or intentional poisoning. --Chemicalinterest (talk) 10:58, 19 June 2010 (UTC)

The amounts are tiny, and by the time an electronic chip gets to you, the consumer, it is virtually impossible for any arsenic to be chemically active or in any way exposed to you. Arsenic would be tightly bound inside the semiconductor crystal lattice - see doping (semiconductor) - and the concentrations would be insignificantly small. Inside a semiconductor fab, arsenic gas may be released into an ion implantation chamber. This is usually an airtight device (hermetically sealed vacuum chamber). Arsine and Arsenic trifluoride are commonly released into the chamber. "Since these gases are all highly toxic or otherwise hazardous, additional input purging and trapping systems are needed to ensure that the all of the source gas is removed from the system before wafer loading or removal." Arsenic breaks out from these "extremely toxic" gases at high temperatures inside the ion implanting device. It then diffuses into the substrate (and is therefore deeply buried inside the silicon ("deep" can mean nearly 1 micron - but we can safely say that no arsenic will "rub off" the chip. (Microchip Manufacturing, Chp. 11 "Diffusion Sources"). Occasionally, an epitaxial layer will intentionally be doped with arsenic, but even during the processing, the gas is introduced in amounts of around 20-100 parts per million (relative to the already near-vacuum conditions inside the chamber). Again, safety devices are supposed to flush the chambers and input plumbing to ensure that the gas is totally purged before anybody is exposed to the wafers. At least one study has been published to investigate the effects of prolonged exposure to arsenic for people who work in the silicon fabs (factories) (and also, copper smelters, who are exposed to even higher concentrations because arsenic occurs naturally in copper ores). Here is Biological monitoring of arsenic exposure of gallium arsenide- and inorganic arsenic-exposed workers, (1989). It was found that these workers had "far higher" concentrations of arsenic than a control-group, but it seems that there was no conclusive evidence that even this elevated level of arsenic was unsafe. Nimur (talk) 19:08, 19 June 2010 (UTC)

I used to work in a wafer fab where we used arsine both for doping the semiconductor and for making passivating glass layers (ASG - arseno-slicate glass). Arsine smells of onions, and when a local farmer harvested his onion crop, we evacuated the clean room in double quick time... We also had one of the marketing guys ask the almost exact question above - "hey, if you've got arsenic on top of the chips, isn't that dangerous?" - to which I gave the somewhat innacurate answer "only if you eat a lot of them". --Phil Holmes (talk) 10:53, 20 June 2010 (UTC)

It's possible that an impurity was added to the arsine to make it easy to smell. I don't actually know if these gas compounds have an intrinsic smell. On the other hand, if a safety-odorant additive or impurity would interfere with the gas during silicon ion implantation, it might not be added... This guideline from the CDC says that "Arsine is a flammable and highly toxic gas with a garlic-like or fishy odor that does not provide adequate warning of hazardous levels." Nimur (talk) 17:24, 20 June 2010 (UTC)

I'd like to know if there is way to extract the arsenic to use as a poison without access to complex lab equipment. TheGoodLocust (talk) 22:32, 21 June 2010 (UTC)

And why do you want to know this -- are you planning to poison someone? In that case, I must warn you that today's forensic labs can detect arsenic unfailingly, and that attempted murder gets you a 20-to-life sentence. But if you're just looking for realistic ways to do it (for a detective novel or something), then subliming elemental arsenic (simply by heating) will separate it out from all the other microchip components. Keep in mind, though, that you're very likely to poison yourself in the process. 67.170.215.166 (talk) 02:17, 22 June 2010 (UTC)

Would I poison myself by inhaling it? How much circuit board would I need to poison people in a small room? What I mean to say is, could a person dump some in a fire and have it kill those in the room over a period of time? And no, I'm not planning on poisoning anyone. My dad actually got in trouble back in the 30's for reading a book on poisons! TheGoodLocust (talk) 03:44, 22 June 2010 (UTC)

You have to be much more concerned about Fluxide for solder in joining metals. If you are looking for a "useful" poison, poisonus plants are much more lethal. Also beware of the heavy metals getting into the system. Aluminium sauspans that are cleaned too well, is a no,no. MacOfJesus (talk) 23:35, 23 June 2010 (UTC)

Oh, I'm well aware of more useful poisons (have quite a few in my backyard actually) and could easily go into the forest to find some really deadly mushrooms that look like edible ones - it might be funnny to actually combine a poison with an ayahuasca analogue now that I think about it. I was just curious from a "Macguyver" perspective if I could throw some chips in a fire and poison a room full of people. I guess it might just be easier to mix some bleach and ammonia though. TheGoodLocust (talk) 04:00, 24 June 2010 (UTC)