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August 4

# of days Medicare pays in rehab

My friend was told Medicare would pay only up to 20 days in rehab. Is this new? It used to be 30 days.```` — Preceding unsigned comment added by 71.232.189.242 (talk) 01:14, 4 August 2013 (UTC)

I believe that is true, and then it pays 80% out to 100 days. But I may be wrong. Bubba73 ^{You talkin' to me?} 01:43, 4 August 2013 (UTC)

It's probably worth pointing out that there is more than one country in the world with a health scheme called Medicare. And, not surprisingly, they're not all the same. HiLo48 (talk) 02:27, 4 August 2013 (UTC)

Yes, but it is unlikely that someone from Massachusetts would be interested in any program from outside the U.S. --Jayron32 03:08, 4 August 2013 (UTC)

North America (USA & Canada) plus Australia, at least use 'Medicare'. (National Health Service(NHS) in England) --220 of ^Borg 06:52, 4 August 2013 (UTC)

Missed Medicare Resources in Hong Kong. --220 of ^Borg 07:23, 4 August 2013 (UTC)

In Canada it is only called medicare in New Brunswick. TFD (talk) 07:31, 4 August 2013 (UTC)

Bee-eater pic

In this picture of a European bee-eater, what's that butterfly it's holding in its beak? 24.23.196.85 (talk) 05:55, 4 August 2013 (UTC)

Looks like Vanessa cardui. What you see are mostly the undersides of the left fore- and hind-wing. --Dr Dima (talk) 01:49, 5 August 2013 (UTC)

Thanks! I prob'ly should've known this -- it's one of the most common lepidopterians in the world (better known as the Painted Lady). BTW, does anyone know whether it's toxic like the Monarch? I've checked the article, and it says nothing about that. (It does say in the Bee-eater article that the bird avoids certain toxic insects, but doesn't say which ones -- only that it (obviously) doesn't avoid bees, which are also quite toxic.) 24.23.196.85 (talk) 05:31, 5 August 2013 (UTC)

No definitive reference found either way, but in 45 years of active interest in lepidoptery, I've never seen it suggested that this or related species in Great Britain are significantly poisonous to birds. {The poster formerly known as 87.81.230.195} 212.95.237.92 (talk) 14:10, 5 August 2013 (UTC)

...and the mere existence of that photo strongly suggests that these birds don't avoid them! SteveBaker (talk) 15:28, 5 August 2013 (UTC)

Presuming, of course, this bird isn't suicidal, stupid or visually impaired. From the frequency other species crash into my clearly dirty windows, I'd say "seems to suggest". InedibleHulk (talk) 09:36, 6 August 2013 (UTC)

It could also be that the Bee-Eater is immune to certain toxins found in certain butterfly species (the article says it's immune to bee and wasp venom, so it could also be immune to butterfly toxins). If so, it's not the only species to have this kind of immunity -- the Black-headed Grosbeak, for example, can even eat the highly toxic Monarch butterfly without harm to itself! 24.23.196.85 (talk) 01:23, 7 August 2013 (UTC)

posthumous fatherhood from culled sperm

Is it possibe to make a dead man father children through Testicular sperm extraction? Pass a Method talk 12:34, 4 August 2013 (UTC)

That process requires live sperm, so it will be progressively less successful as the sperm die following the death of the man. The time from death until there are no viable sperm will depend on many conditions, including the condition of the testicles at the time of death. This search for direct answers was unrevealing. -- Scray (talk) 13:22, 4 August 2013 (UTC)

Was the sperm extracted before or after death? A dead man can have previously donated sperm the normal way, and had it properly frozen. The thawed sperm can then be used to posthumously conceive a child. --Jayron32 01:54, 5 August 2013 (UTC)

Would a man who froze to death and stayed that way be a candidate? InedibleHulk (talk) 09:38, 6 August 2013 (UTC)

I suspect it would depend on how he got that way. Generally sperm banks freeze the stuff really quickly in liquid nitrogen or something. A very slow freezing might somehow damage the material - or freezing to the wrong temperature might be an issue. I'm not 100% sure about that - but it's certainly a potential problem. SteveBaker (talk) 16:39, 6 August 2013 (UTC)

Is it possible to study human language development

Is it possible to study human language development by filming a human from birth to death and recording down all visual and audio signal that a human has come across in their lifetime. This capability must surely be possible with the budget of a large country like USA. The source of data will be useful for scientists for hundreds of years to come to analyse the psychological development of a human. So why was this not initiated? Surely the scientist around the world can easily obtain funding to perform the experiment. It cannot be because of privacy because the data(film) will never be released to the general public. 220.239.51.150 (talk) 15:38, 4 August 2013 (UTC)

Sure it's possible, it just isn't very practical (not to mention that it raises a plethora of ethical questions). Anyway, the ref desk really isn't the place to speculate on such things... 70.112.97.77 (talk) 16:18, 4 August 2013 (UTC)

Bear in mind that a year of film takes a year to watch. Looie496 (talk) 16:28, 4 August 2013 (UTC)

Almost certainly the technology exist to make it technically possible. (I even recall a science fiction story where everything and everyone was recorded 100% of the time.) But, as IP 70. says, it raises ethical questions. Would any parent consent to a child being filmed 24/7 from birth? Humans tend to find privacy pretty important Sounds a bit like The Truman Show --220 of ^Borg 16:54, 4 August 2013 (UTC)

The technology to record that much stuff is too recent to have been used to record an entire human lifetime...so no, it can't possibly have happened. It has, however, been done for shorter periods quite recently. For example, this excellent TED talk discusses recording all of the activity in an entire house as a child goes from birth to being able to talk. He tracked every single time his child made a noise when water was involved and got a beautiful series of audio snippets that showed how the child went from having no speech to being able to say the word "WATER" perfectly. SteveBaker (talk) 21:45, 4 August 2013 (UTC)

Classic link there from Steve, but it should be noted that it's the researcher's own child, so he has a lot more leeway. Raising a child so you can keep a camera on it for its whole life, so you can use it to extract data, sounds more like the subject of a Jodi Picoult novel than a real research experiment. If you did it at a university, you would have to go through an ethics committee, and they would be likely to block it, I would assume. Privacy is absolutely an issue, because at least the researchers would need to have access to the data, and they do not enjoy unfettered access to anyone's private world. They are not the CIA, after all, nor even anything close. The child, upon reaching almost any age, would have the right to withdraw consent, and that would simply make it pointless. Also it would have to be followed through by different researchers. I would say any research like this is a long way off. IBE (talk) 13:32, 5 August 2013 (UTC)

How would that help much in studying language development? Every parent in the world has a good idea of what their child hears, from the moment of birth to early childhood. That knowledge doesn't give them any insight on how the brain is structured, how sound is processed, the role of nature vs. nurture, whether a universal grammar exists, whether a critical period exists for language acquisition, etc. A better experiment would be to deprive a child of any language and see if they can still a language after childhood. This "forbidden experiment" has been done before, and the answer seems to be no: see Genie (feral child) and Victor of Aveyron. --Bowlhover (talk) 08:11, 5 August 2013 (UTC)

I think there is something to be gained by careful observation over time - and being able to go back and note carefully how speech transitions from one phase of development to the next would be valuable. For example, my son started off saying single words - then went to beautifully, grammatically correct phrases - then seemed to take a step backwards and start saying grammatically incorrect phrases before eventually correcting those errors and becoming fluent. The reason for this is that the first grammatically correct phrases were being memorized in one chunk - like they were a single word. Only later did he start trying to form new phrases - and having to actually master grammar. This tells us all sorts of interesting things - but having noticed that change, I was unable to go back and see how it started. There is no doubt in my mind that having a record of everything the child ever said would be useful in understanding the stages of development. But as Been Emotional said - it's an ethical nightmare to do that. Sure, researchers would love to have all of the episodes of The Truman Show on DVD - but that's not going to happen. SteveBaker (talk) 14:17, 5 August 2013 (UTC)

It occurs to me that we should mention Lifelogging.

This is the idea that people might voluntarily record everything that happens to them (to at least some degree). Some of those people attempt to record everything they hear and see (including their own voices) - and often other data like body temperature, heart rate, blood pressure and so forth. I suppose that if they chose to make that vast pile of recordings available towards the ends of their lives, it might tell researchers quite a bit. The problem, again, is that this is a relatively new idea - and the technology to store all of that data and to capture it using a portable device is still non-trivial. Certainly it's becoming possible though. The Google Glass headset can record sound and video and stream it continually via your cellphone to some kind of "cloud" storage system. I'm not sure the battery life of headset and phone are yet good enough to record everything on a 24/7 basis without recharging issues...and there might be times when cellphone access was patchy or unavailable - but with spare batteries and an acceptance that some data might be lost - this is becoming plausible. Another issue is that this is something that's really only being done by adults - so it'll miss that person's childhood language development - having a child wear something like this from birth is clearly unreasonable. SteveBaker (talk) 15:26, 5 August 2013 (UTC)

Do boron exists in asteroids?

I want to make a science fiction story that is based on polywell reactors for space energy, and so because it uses aneutronic fusion its fuel is hydrogen and boron. There is a lot of hydrogen in space, from ice electrolysis, but I never find any reference to boron in space either in asteroids or other planets 140.0.229.26 (talk) 15:55, 4 August 2013 (UTC)

See this paper for a review of the data on boron abundance in meteorites -- the best source of evidence. The answer seems to be yes, but not in very high concentrations. Looie496 (talk) 16:25, 4 August 2013 (UTC)

Where does the element boron come from? A few physicists from University of Illinois have already fact-checked and veried some of the claims in our boron article. Like those professional physicists, I (as a non-practicing physicist) have not ever heard much talk about stellar nucleosynthesis of boron. (Compare, say, hydrogen-burning, lithium burning, nucleosynthesis production of sodium, or iron... these were all homework problems in one astronomy-related class or other, and the details stick in my mind!) But I remember no discussions about boron! This is apparently because boron isn't commonly made by stellar nucleosynthesis - at least not by the major reactions. Boron is made by a more esoteric process, spallation of lithium by high-energy cosmic rays. As such, it's going to be much more rare everywhere in the universe: on earth, in asteroids, in stars. Nimur (talk) 17:07, 4 August 2013 (UTC)

Are you sure you're not thinking of Beryllium? 202.155.85.18 (talk) 01:17, 5 August 2013 (UTC)

I frequently think about beryllium, but in the instance above, my thoughts, discussion, and the source I linked to were related to boron. Some of that discussion also applies to beryllium - which is commonly produced by cosmic ray spallation, because (like boron) production of beryllium by stellar fusion requires a very low-probability reaction. I found this website from the folks across the bay: "how did the various chemical elements of the periodic table form?" Nimur (talk) 03:07, 5 August 2013 (UTC)

I have nothing to add here. I just really like the phrase "I frequently think about beryllium". You should get that on a T-shirt, or in Latin on your coat of arms. APL (talk) 11:27, 5 August 2013 (UTC)

"Soleo cogitare beryllium" - sounds pretty good! SteveBaker (talk) 20:18, 8 August 2013 (UTC)

I'm getting a mental picture for your story: A team of 20 mules, in spacesuits of course, hauling one of those asteroids away. ←Baseball Bugs ^{What's up, Doc?} carrots→ 22:55, 4 August 2013 (UTC)

Seems good enough. It seems that the story will be like a huge evil company controlling all boron mines on earth and the researchers found out about boron on space so they are trying to escape from that evil company monopoly, ohh wait seawater have a lot of boron.... Is there any way to extract boron out of seawater? 140.0.229.26 (talk) 00:42, 5 August 2013 (UTC)

Yes, but it seems the reason for it is to make safe drinking water, not to get the stuff.[1][2] Clarityfiend (talk) 00:56, 5 August 2013 (UTC)

As a matter of fact, it's also possible to extract pure boric acid from seawater by means of liquid-liquid extraction with ethohexadiol (formula C₃H₇CH(OH)CH(C₂H₅)CH₂OH) or similar chelating agents; however, for economic reasons this is normally done with concentrated salt-lake brines rather than seawater. 24.23.196.85 (talk) 01:31, 6 August 2013 (UTC)

Fooling Archimedes?

The other day I got into a debate with a friend concerning the Archimedes Principle. I raised the point that in some circumstances a carefully constructed object could be devised to fool the test - the interior of the object could simply be a combination of materials of different densities that balance out to the target density; for example, a hollow (ie: air filled) gold plated cube with just the right amount of lead applied to the interior walls. It makes perfect sense to me, but my friend seems to think that I'm horribly mistaken. Can someone here help settle the debate? 70.112.97.77 (talk) 16:05, 4 August 2013 (UTC)

Gold (19.30 g·cm⁻³) is denser than lead (11.34 g·cm⁻³). AndyTheGrump (talk) 16:09, 4 August 2013 (UTC)

To expand: the problem given Archimedes was to determine if a solid object was made of gold. Lead is much less dense than gold. You would need something denser than gold as well as lead to make something with the same density as gold. What you are saying would be right in other circumstances but the thief would have had to use something like osmium or platinum with the lead, which they didn't have at the time and are extremely expensive. Dmcq (talk) 16:13, 4 August 2013 (UTC)

Sorry, yes, I really should have consulted the periodic table before posting! Okay, so assuming that some denser material were available then it would be possible. Thanks! 70.112.97.77 (talk) 16:27, 4 August 2013 (UTC)

Sure, fooling the Archimedes test that way does indeed work. With some simple assumptions like the cavity is located so it does not change the object's center of mass.

In the particular case of fake gold bars, type tungsten gold bar or fake gold bar into your favorite web search engine. Tungsten is so slightly lighter than gold that simple tests have a hard time detecting it. For fake gold you'll need a metal that is both heavier and cheaper than gold (the periodic table leaves you little choice there), and can't easily be told apart from gold (electric conductivity, behavior in electromagnetic fields (see metal detector), doesn't give off radiation, etc). And someone will quickly figure out how to detect cavities inside a gold bar if those start appearing on the market - tap it, if it rings like a bell, well, uh oh... 88.112.41.6 (talk) 20:29, 4 August 2013 (UTC)

Above was mentioned center of mass... but a proper fake should also preserve the moment of inertia! Two objects with the same center of mass, but different moments of inertia, behave very differently. Just by swinging a hollow metal sphere around a little bit, or rolling it around... we could measure a difference, even if its average density and center of mass were perfectly matched to another solid sphere of the same outer dimension. I'd wager a gold brick that most people could even "feel" the difference, without rigorously measuring it.

We could enumerate other physical properties we might test: any imperfection in mimicking the correct thermal capacity or thermal conductivity won't make it past a few really "low-tech" tests. Nimur (talk) 22:30, 4 August 2013 (UTC)

The density of tungsten is very similar to that of gold and the bar sounds about the same, an easy way to find if a bar contains tungsten is to use a strong magnet, gold is diamagnetic, it repels a magnet, whereas tungsten is paramagnetic and so is attracted. See [3] Dmcq (talk) 23:28, 4 August 2013 (UTC)

I don't think "Archimedes' Principle" is the phrase you're looking for. That describes a property of buoyancy, not the "Eureka" moment where he realized that an object displaces a volume of fluid equal to its own volume. (And then used that to calculate an objects density, thus proving it was made from gold.)

Perhaps that's the "horrible mistake" your friend believes you've made. I don't believe that you could construct an object that would defeat the Archimedes' Principal. APL (talk) 11:24, 5 August 2013 (UTC)

It wouldn't have been possible at the time of Archimedes to make something with the density of gold out of other materials but it is quite easy to do nowadays. That's what another contributor was saying above about searching for tungsten gold bar, people have been swindled using imitation gold bars. Dmcq (talk) 11:51, 5 August 2013 (UTC)

And of course Achemedes could have been fooled too if the object in question was hollow. His approach would say "This is not gold" - even though it might well be. SteveBaker (talk) 15:14, 5 August 2013 (UTC)

That wasn't Archimedes' task - he was trying to see if the king was being cheated. A hollow space would be just as damning as an admixture. (Though I have a feeling that in such situations, the real answer is, come up with a great experiment and describe it to further your reputation, then tell the king whatever result he wants to hear!) Wnt (talk) 18:21, 5 August 2013 (UTC) oops, that was stupid, nevermind - he'd have weighed the crown and if it were all gold, that shouldn't be punished Wnt (talk) 19:45, 5 August 2013 (UTC)

Dmcq, yes. But my point was that constructing such an object would not defeat the "Archimedes' Principle", it would defeat the gold-test that Archimedes invented while taking a bath. They're not the same.

Archimedes is famous for more than one thing. APL (talk) 22:19, 5 August 2013 (UTC)

What kind of insect is this?

Orthoptera on a basil leaf.

What kind of insect (an orthoptera, I suppose) could this be? It was found in Southern Germany, on a basil leaf. Thanks. --Edcolins (talk) 19:13, 4 August 2013 (UTC)

It must be a female speckled bush-cricket. Could somebody confirm? --Edcolins (talk) 20:01, 4 August 2013 (UTC)

Yes, speckled bush cricket, female from the ovipositor curving up at the back. Richard Avery (talk) 06:29, 5 August 2013 (UTC)

Thank you! --Edcolins (talk) 19:29, 5 August 2013 (UTC)

Resolved

August 5

CNC milling?

I've been running one of these 3D printers for a while now, making and selling various items, particularly decorative figurines and keyrings, and I'm wondering about trying this milling thing, opens up opportunities for all sorts of different materials. Thing is, I'm not too sure on what sort of machine I'd want, wondering at what the limits would be on these 4-axis machines, whether they would be able to carve the shapes I'd want or not. then again, would that not involve attaching the item to the machine in some way, leaving a clear mark on it? I realise I don't actually know how these machines work at all, would it be possible just to upload a 3D model file into one and leave it to do all the work, or are things more complicated with these?

213.104.128.16 (talk) 11:23, 5 August 2013 (UTC)

As far as leaving a mark where it's attached, yes, you would typically have some finishing work to do after it come off the machine, to grind/sand it down and polish it. StuRat (talk) 12:55, 5 August 2013 (UTC)

(I also have a 3D printer - and also a couple of laser cutters - and I'm about to get into 3D milling machines too - so I've done quite a bit of research into them).

There are basically two kinds of CNC milling machines - 3 DOF and 5/6 DOF. "DOF" means "degrees of freedom" and describes the number of ways in which the cutting head can move.

• A 3 DOF machine can move in three axes just like your 3D printer can - but it can't create undercuts because it's removing material from above, not building it up from below.
• A 5 DOF or 6 DOF machine can also tilt either the milling head or the workpiece (or sometimes both) to reach underneath overhangs...it can make some things that even 3D printers can't make...but even a 6 DOF machine can't make some things that a 3D printer can make because the cutting head is kinda large and can't make it into some small spaces. A 5/6 DOF machine is basically a robot arm holding an electric drill with a milling bit.

So to do most of what you can do with a 3D printer really requires a 5 DOF or 6 DOF milling machine...the snag is that those things cost an absolute fortune! Many tens or possibly hundreds of thousands of dollars. 3 DOF machines are vastly cheaper - and there are designs out there to let you make them for about the same cost as a 3D printer.

The term "4 axis" is a bit confusing. Sometimes it refers to a 3 DOF machine with the fourth axis being the rotation of the milling bit itself (which is cheating!)...rarely it means that this is a 4 DOF machine - which would be able to rotate the workpiece around one axis (like a lathe maybe) with a 3 DOF machine doing the cutting. That wouldn't get you much further than a straight 3 DOF machine. Almost certainly, if this is something costing under $10,000 dollars then "4 axis" really means "3 DOF".

To attach the workpiece to the machine generally involves clamping small pieces to the platform - which might not leave a mark - but does result in you having a block of material at the base of your object that can't be milled and may have to be sawed off by hand. For large sheet materials, some CNC machines have a vacuum table that holds the part in place. Those only work well for relatively large parts. Yet a third alternative is if you can drill a hole inside the base of the workpiece and thread a bolt into it. You can then clamp the bolt, do the milling, then unscrew the bolt at the end.

In terms of working with these machines - they are very much like a 3D printer - you can upload a 3D model and (with appropriate software to plan the tool paths) just set the machine running.

To mentally visualize what a 3 DOF CNC machine can do, imagine you had a small electric drill mounted in your 3D printer in place of the hot-end extruder. Now imagine you lower the Z table all the way to the bottom (or raise the head all the way to the top - depending on how your 3D printer works) - then put a solid block of plastic into the machine. Now, this hypothetical 3D printer could cut away material, one layer at a time by moving the head back and forth over the parts of the plastic that you don't want anymore - then raising the workpiece (or lowering the head) a fraction of an inch and doing it again. The process is kinda like 3D printing in reverse.

If you have a website someplace with pictures of the things you sell, I could quickly tell you which of them a 3 DOF machine could make.

SteveBaker (talk) 14:07, 5 August 2013 (UTC)

You could try one of the milling services on the web, just like there are 3D printing services. That would give you a good feel for what you can get done and the prices are fairly reasonable. Have you tried sintered metal 3D printing? Dmcq (talk) 15:26, 5 August 2013 (UTC)

If you want a number of the same you could try casting in metal. and of course if they can be made from sheet metal there's all sorts of other options. Dmcq (talk) 15:35, 5 August 2013 (UTC)

3D printers that can do sintered metal aren't cheap - they rely on high powered lasers, plasma arcs or something similarly expensive and dangerous to sinter the metal - and that's a very difficult problem for a cheap design. My two 100 watt (made-on-the-cheap) lasersaurs cost $8,000 each in parts alone - and 100 watts of laser power is nowhere near enough to do metal sintering. So unless you're making a LOT of money doing this, you'll be stuck with paying someone else to make the parts on a machine you'll never be able to afford!

I know of one guy who made a cheap(ish) laser-sintering 3D printer - but his machine sinters wax laced with carbon...hardly metal...but you could use his wax objects in a lost-wax casting process.

But if you're thinking about making molds and casting objects in metal then another approach is to make a two-part 3D-printed mold and use that to cast metal objects. Obviously you have to have relatively low melting point metals and do your printing with the highest melting point plastic your printer can manage...sadly ABS and PLA (which are the two plastics that most 3D printers use) both melt at around 220C - which is unfortunate because metals like tin and lead melt at temperatures at least that high - so the mold would melt and be useless. But there are a few metal mixtures that melt at much lower temperatures - yet at high enough temperature to be useful for things like jewellery and key-fobs - sadly, some of those are toxic, so you have to be careful. Field's metal might be a good choice - it melts at 62C - Woods_metal#Related_alloys gives a list that includes all of the low-melting-point metals that I know of.

Another option is to make the object itself in plastic, then make a synthetic rubber mold from it and cast using that.

If you're interested in materials other than plastic - but would like to stick with 3D printing, this stuff should be of interest. It's made from wood-pulp and formed into a filament with a binder that most 3D printers can melt. Printed objects look and feel like wood (although without any grain). Some people are investigating using 3D printers with two heads - one loaded with light colored wood filament and the other with a darker version of the same material - and actually printing fake grain into the objects they make.

Fun stuff! SteveBaker (talk) 16:04, 5 August 2013 (UTC)

I was thinking of them sending off to a service doing sintered metal like for a milling service, sorry I should have made that clear. I'd have thought buying any machines would need to be carefully justified compared to sending off to a service which specializes in doing the work. Dmcq (talk) 20:22, 5 August 2013 (UTC)

Yes, I agree that using a service that can print in difficult materials is a good option - but from the point of view of someone who is attempting to manufacture things for profit, using a service like that will sharply limit how much money you can make - they definitely aren't cheap. For the laser-cut stuff that we do, it would be about 20 times more expensive to have the product made by a service than making it ourselves. We could possibly use them for making prototypes - but unless a LARGE fraction of the final selling price is reflecting your design expertise, it's not a viable option. SteveBaker (talk) 16:35, 6 August 2013 (UTC)

Sounds good that wood material. Someone told me once they were going to use a wood effect paint and I thought they were joking - and they went ahead and got a nice wood effect with it! By the way for that wood material they can make it darker or lighter by using a higher or lower temperature when they melt it. Dmcq (talk) 20:38, 5 August 2013 (UTC)

Oooh! That's a really good idea. (Am ordering wood filament for my machine now!)...do you happen to know what temperature range is needed to produce a substantial change in color? SteveBaker (talk) 16:35, 6 August 2013 (UTC)

It says on the page you pointed to, you can range between 180°C and 245°C, [4] shows it is quite effective. Dmcq (talk) 17:45, 6 August 2013 (UTC)

Poison ivy for apes

Take a typical member of each great ape species and expose all of them to poison ivy. The human will get urushiol-induced contact dermatitis, but what about the others; are we the only species allergic to it, or will other apes also have problems? Neither article that I linked says anything about other species; I know that the plant doesn't cause problems for ruminants, but I know nothing about non-human primates. Nyttend (talk) 14:36, 5 August 2013 (UTC)

Having furry bodies helps them a lot. In order to get problems with poison ivy, it has to rub against your skin. A thick layer of fur makes that rather difficult - so I would expect that other great apes would have much less problems with the stuff than we "naked apes" do. The chemical involved (Urushiol) provokes an immune response that ultimately causes the symptoms. This article says "Deer and other animals can eat poison oak leaves without any apparent ill effect. Birds nest and find shelter in the plant. Only primates (humans, apes, chimpanzees, etc.) seem to have a reaction to poison oak." - so I guess you have an answer. SteveBaker (talk) 15:13, 5 August 2013 (UTC)

Drawback or limitation of modern synthetic theory of evolution or neo-Darwinism

What are some Drawback or limitation of modern synthetic theory of evolution or neo-Darwinism?

AmRit GhiMire 'Ranjit' (talk) 14:48, 5 August 2013 (UTC)

So, to be clear, you're talking about Modern evolutionary synthesis (which is also called "neo-Darwinism" and which is the way that evolution is understood in the last 50 years) - which (according to our article) "is still, to a large extent, the current paradigm in evolutionary biology."

The most obvious unresolved issue for me is abiogenesis. How did the first self-replicating molecule come about? Once such a thing existed, evolution became inevitable...but getting from "inert" chemistry to that is something of a leap. There are plenty of possible explanations - most of them plausible - but we don't know exactly which of them is true.

Our article Objections to evolution covers a huge array of objections that have been raised - but few, if any, are thought to be problematic by the vast percentage of scientists in the field - they are generally trivially easy to debunk using easily obtained evidence.

Evolution is one of the most solidly well-understood and verifiable theories in science - there really aren't "drawbacks" or "limitations" in the theory.

SteveBaker (talk) 15:06, 5 August 2013 (UTC)

I have to agree, there aren't really any drawbacks. There are disputes over the interpretation of such things as kin selection and selfish genes, but these are actually metaphysical disagreements--no one disputes the facts. Evolutionary psychology is ideologically controversial, but it's quite far removed from the modern synthesis itself. μηδείς (talk) 17:15, 5 August 2013 (UTC)

At least at the molecular level, the occasional impact of "Hopeful Monsters" shouldn't be dismissed entirely - things really do get abruptly reverse transcribed, recombined etc. to form dramatically new gene structures. Also, the theory doesn't really address the issue of heritable epigenetic change - the mechanisms making that possible are the products of evolution, but it means that the reaction norms of any given genotype are far more complex than previously imagined. Wnt (talk) 18:26, 5 August 2013 (UTC)

Who was Dr Price?

As a side issue to a question on the Language Desk, I found that the triple expansion engine (as used in the Titanic) seems to have been a British invention. According to History of British Shipping by Adam Kirkaldy, "Then Dr Price invented the triple expansion engine, effecting further economies in the consumption of fuel" (p.131). One was apparently fitted to SS Aberdeen (1881). Does anybody know anything about the ingenious Dr Price? His full name would be a start. Our Compound engine#History has a Spanish destroyer as the first in 1886, although it was built on Clydebank. Alansplodge (talk) 15:51, 5 August 2013 (UTC)

An article in The Quarterly Journal of Economics, "Substitution and Complementarity in Endogenous Innovation" (August 1993), discusses the rise of steam ships and cites:

• Harley, Charles K., "The Shift from Sailing Ships to Steamships, 1850-1890: A Study in Technological Change and its Diffusion," in Donald N. McCloskey, ed., Essays on a Mature Economy: Britain after 1840 (Princeton, NJ: Princeton University Press, 1971).
• Rosenberg, Nathan, Perspectives on Technology (Cambridge: Cambridge University Press, 1976). Ch. 11

I don't know whether either of these would mention Dr. Price, but they're the closest I come to any useful-seeming information so far. --some jerk on the Internet (talk) 21:00, 5 August 2013 (UTC)

I found many texts over the decades which parroted the line "hen Dr Price invented the triple expansion engine.." without any details. But the actual designer of the first successful triple expansion engine, used on the Aberdeen (1881) for high speed London-Capetown-Melbourne runs was "Doctor" Alexander Carnegie Kirk, See [http://books.google.com/books?id=m8TsygLyfSMC&pg=PA694&lpg=PA694&dq=the+aberdeen+1881+napiers&source=bl&ots=fXgwCpa8Kn&sig=A2yIROVbkJhIu-cUFElFlKDg-D4&hl=en&sa=X&ei=428AUqvXGurAyAHLloDAAQ&ved=0CFAQ6AEwBg#v=onepage&q=the%20aberdeen%201881%20napiers&f=false Biographical Dictionary of the History of Technology (2013) - Page 694. Maybe Price was one of his associates. Edison (talk) 03:52, 6 August 2013 (UTC)

Thank you both. I intend to put an entry on Timeline of steam power if nothing else. We already have an article, Alexander C. Kirk, which mentions the Aberdeen and her engines; how I didn't find it myself remains a mystery. One can imagine a muffled cry from the Aberdeen's engine room voice tube; "She cannae tak' much more Kirk!" ;-) Alansplodge (talk) 16:34, 6 August 2013 (UTC)

Epilepsy: is there a limit to how often seizures can be photoinduced?

The way I understand it, flashing lights, even TV episodes, can induce epilepsy - occasionally even first seizures in children who haven't previously experienced them. Yet epileptic seizures are typically followed by a postictal state where no seizure can be induced. What I'm wondering is, does the photoinduction actually increase the overall tendency to have seizures on a consistent basis, and if so how much, or does it just affect the timing of seizures? In other words, is there a sort of "fuel for epilepsy" that gets consumed during seizures, and the lights merely provide a "spark"? (I'm picturing a hopefully thought experiment where an epileptic al-Qaeda member is locked in subbasement 25 under Diego Garcia, in a cell with a stunning light show going day and night... by what factor are his seizures increased over the long haul?) Wnt (talk) 18:38, 5 August 2013 (UTC)

Yes, there is a sort of "fuel for epilepsy". Electrical activity in the brain depends on ion concentration differences between the interior and exterior of brain cells, and those differences run down during a seizure. Afterward they are slowly reestablished by ion pumps. And yes, seizures can increase the probability of future seizures, by means of a phenomenon known as kindling. That doesn't always happen, but it can. Seizures can be triggered in anybody by electrically stimulating the brain -- that's what happens in ECT -- but light will only trigger seizures in people whose brains are particularly vulnerable. I don't know whether there is evidence that experiencing light-induced seizures increases the probability of future seizures. Looie496 (talk) 19:04, 5 August 2013 (UTC)

Very good point about the kindling model! I suppose the question actually breaks down into two separate conditions: (a) whether photoinduction can be used (perhaps together with isoniazid, thiosemicarbazide, harman, pentylenetetrazole, 3-mercaptopropionic acid, and/or strychnine) to help induce first seizures in non-epileptics and perhaps even to "kindle" long term epilepsy, and (b) what its effect is on those who already have longstanding epilepsy. I was only thinking about the latter above, but of course, depending on the person either might be relevant. Wnt (talk) 19:27, 5 August 2013 (UTC)

Human decontamination

Hello everyone,

I was wondering what cleansing agents were used for human radioactive decontamination? Do they contain more tensioactive agents than normal soaps, or special chelating agents like EDTA to help remove metallic radionuclides? Or perhaps do they contain some abrasive agents (as suggests the term Abrasivstoff in Dekontafix) to help remove the dead layer of skin and along with it any surface contamination? Regards, 141.30.214.203 (talk) 19:15, 5 August 2013 (UTC)

While we didn't go into too much details during my basic training two decades ago, the mantra seemed to be lots of soap and lots of water. Granted, we were mostly taught about chemical decontamination - but no mention was made that nuclear decontamination would be done differently. WegianWarrior (talk) 19:24, 5 August 2013 (UTC)

A quick search turns up [5] which seems to prefer dermabrasives (I actually didn't read much of this, but it looks useful). Wnt (talk) 19:31, 5 August 2013 (UTC)

Thank you for this paper; it looks like many solutions exist depending on the nature of the contaminant: EDTA for ⁹⁹Tc^m, soft abrasives, foams, detergents, etc. Always a pleasure to read the Ref Desk. Regards, 141.30.214.203 (talk) 19:49, 5 August 2013 (UTC)

Deep space travelers beware

What are some of the little known dangers of deep space travel? Are we attempting to solve them now or is that on the back-burner as we focus on inter-planetary travel closer to Earth?— Preceding unsigned comment added by 65.64.111.126 (talk) 19:21, 5 August 2013 (UTC)

Health threat from cosmic rays, IRWolfie- (talk) 19:53, 5 August 2013 (UTC)

Also the deterioration of the human body in low gravity, and the inherent dangers of travelling in an inhospitable vacuum vast distances from any help or hope of rescue or resupply, while completely dependent on high-technology devices for survival. -- The Anome (talk) 19:56, 5 August 2013 (UTC)

See also Effect of spaceflight on the human body and Space medicine. Dominus Vobisdu (talk) 19:58, 5 August 2013 (UTC)

And this is just for interplanetary travel. Deep space, in the sense of interstellar travel, also has the disadvantage that it is currently impossible -- and may well forever be impossible -- to traverse these distances in a human lifetime, or much vaster timescales in the case of intergalactic travel. Even travelling to the Oort Cloud, just a single light-year away in our immediate solar neighborhood, would present a major challenge.

Other than the creation of faster than light travel or teleportation, possible hacks that conform to current physical knowledge which have been suggested to sort this out include generation ships, sleeper ships, "nearly as fast as light" ships which would exploit relativistic time dilation, and the use of von Neumann probes or starwisps to carry and re-create human life from stored information or biological material over the course of thousands, or millions, of years.

Each of these may or may not be possible, and would in each case carry risks of their own. Unless something drastic happens to the human race in the next thousand years, I would expect someone's going to try at least one of these in that time. -- The Anome (talk)

Oh, and also don't forget the psychological effects of long-term isolation of tiny groups of people. -- The Anome (talk) 20:23, 5 August 2013 (UTC)

Ah, yes. The dreaded SPACE MADNESS! "I have had this ice cream bar since I was a child. People always trying to take it from me. Why won't they leave me ALONE!!!!" (Now I've got a hankering for some chocolate covered raisins. Popping out to the store... be right back!) Dominus Vobisdu (talk) 20:32, 5 August 2013 (UTC)

Yep. Space Madness (see here for TVTropes' take on this), a.k.a. the Pain of Space in "Scanners Live in Vain". -- The Anome (talk) 20:52, 5 August 2013 (UTC)

You asked for little-known problems, but most people responded with well-known problems. Here's some that might be a problem from years in space:

1) Nutrition. We may not know about every vitamin and mineral humans need. It's possible there's something vital that we run out of after years without eating real food.

2) Exposure to chemicals. Materials in the ship might give off fumes as they age, which are not filtered out, causing long-term exposure hazards. The same is true of packaging leaching chemicals into the water and food.

3) Instead of isolation, people might have problems being stuck with the same group of people for years. For example, who is having sex with whom could cause some serious tensions.

4) Lack of elderly care facilities. In a multi-generational ship, what do you do with people too old to care for themselves, especially those with dementia ?

5) Too small of a gene pool. In a multi-generational ship, inbreeding will eventually be a problem unless, say, millions of frozen sperm and eggs are shipped with them to be used for reproduction.

6) Freezer burn. If food, sperm, eggs, or even people are frozen, then slight changes in temperature, over time, can cause degradation. StuRat (talk) 21:26, 5 August 2013 (UTC)

Solution for (4) and maybe (1) too: Soylent Green. Clarityfiend (talk) 22:35, 5 August 2013 (UTC)

There may be social problems with a multi-generational ship, too.

In books this is always represented as a total breakdown of civilization and people forgetting that they're on a ship, but it wouldn't have to be that drastic. What if the people who arrive at the destination know full well they're on a ship, but don't want to abandon their home by going down to the planet? (Imagine giving up your home and roughing it on an unknown world because your great-great-great-grandfather agreed to be a pioneer!)

That's just one example. Just about any kind of social breakdown we have here on Earth would be worse if it happened on a generational ship. APL (talk) 08:51, 6 August 2013 (UTC)

Genuine inquiry here: I remember one novel detailing exactly the first scenario you describe above; who else touched upon it? Snow (talk) 09:11, 6 August 2013 (UTC)

Have a skim through this. I can think of a couple offhand that also fit the scenario (Brian Aldiss' Non-Stop, David Lake's Walkers on the Sky, but it's a popular trope, and I'm not at home where I can reflect further and skim my collection (I'm at work and really should be doing some :-) ). {The poster formerly known as 87.81.230.195} 212.95.237.92 (talk) 13:01, 6 August 2013 (UTC)

Larry Niven's short story "The Long Way Home" is a variation of it. Clarityfiend (talk) 00:29, 7 August 2013 (UTC)

A risk I would worry about would be being passed by later, more advanced ships. This has been explored by a number of sci-fi writers, so maybe it's not all that "unknown", but it would sure suck to go through all that trouble only to get to the other planet and have people already there who tell you "Oh yea, We invented the Warp Drive about a week after you left." APL (talk) 08:51, 6 August 2013 (UTC)

Are you sure that's really the worst case scenario? Mightn't it be worse to hear that they invented it last week? Snow (talk) 09:50, 6 August 2013 (UTC)

One of the earlier treatments would be A. E. van Vogt's "Far Centaurus". Clarityfiend (talk) 00:31, 7 August 2013 (UTC)

Dust. No, seriously, very much a problem and one of my favourite examples of how poorly understood the rigors of space-travel are and how inadequately the complexities are treated in popular media and amongst amateur enthusiasts. There's a lot of matter out there and when you're traveling at the kinds of velocities that we would almost certainly be looking at for exploration beyond the solar system, it only takes a very, very small amount of it to annihilate a craft of any realistic proportions upon collision. As to your second question, much thought has been given to how we might tackle the herculean task of interstellar travel, with most of the better-regarded proposals originating from the middle of the last century and having been debated (with regard to which is most feasible) by engineers and scientists from a wide-array of disciplines ever since. However, as regards actual practical efforts (or indeed even efforts to generate general support for such a venture), your assumption is quite correct; the priority in terms of research an expenditure has been overwhelmingly on "local" space travel (and indeed, extremely local), and there's increasingly less support for even these efforts in terms of both public support in leading industrial nations and financial support from the governments of same. <tangent of questionable appropriateness regarding question> You know, every time I've ever heard the query "If you could have a conversation with anyone, living or dead, who would it be?", one of the names that always comes to the top in my mind is Carl Sagan, but at this point I don't think I could look him in the eye, we've all collectively dropped the ball so poorly as regards vision for the future of our species outside of Earth. </tangent> Snow (talk) 09:00, 6 August 2013 (UTC)

If you are a telephone sanitizer, the risks are well know, just not to you. See: [[6]]. Dominus Vobisdu (talk) 09:13, 6 August 2013 (UTC)

Which brings up the next little-known danger: forgetting where your towel is. - ¡Ouch! (^{hurt me} / _{more pain}) 09:36, 7 August 2013 (UTC)

There are also a possibly infinite number of unknown unknowns in Parts Unknown (might help to read the transcript in the description, but only maybe). InedibleHulk (talk) 09:51, 6 August 2013 (UTC)

On a generational ship, would there not also be a risk of a population explosion and therefore using up the resources too soon? 184.147.136.32 (talk) 11:20, 6 August 2013 (UTC)

Don't forget to pack all the microorganisms for your gut flora etc. 20.137.2.50 (talk) 12:57, 6 August 2013 (UTC)

Carl Sagan has pointed out that on the Earth you can find enough Deuterium to move the Earth itself all the way to Saturn's orbit. This can be done to deal with the Sun's gradual increase in brightness. Count Iblis (talk) 13:00, 6 August 2013 (UTC)

I fail to see what that has to do with the question which was asked. IRWolfie- (talk) 23:51, 6 August 2013 (UTC)

The implication (as I read it) was that the Earth itself could be a vessel capable of significant space travel, which affects some of e.g. StuRat's points. ManyQuestionsFewAnswers (talk) 22:04, 7 August 2013 (UTC)

The earth is already engaged in significant space travel. I suspect if it was forced out of its orbit, there could be catastrophic consequences for its inhabitants. So let's hope no one tries it anytime soon. ←Baseball Bugs ^{What's up, Doc?} carrots→ 02:02, 8 August 2013 (UTC)

August 6

Which human ancestors invented fire?

In the course of evolutionary history ,Which human ancestors invented fire?

AmRit GhiMire 'Ranjit' (talk) 00:26, 6 August 2013 (UTC)

Probably Homo erectus: see Control of fire by early humans. AndyTheGrump (talk) 00:30, 6 August 2013 (UTC)

And that would be "discovered how to use fire", not "invented". StuRat (talk) 00:39, 6 August 2013 (UTC)

Roasting, stewing, frying, and baking of food with fire could be considered "inventions," since at the time they were new and useful processes, resulting from happy accidents, or from observation and experimentation. Edison (talk) 14:47, 6 August 2013 (UTC)

There is also a distinction between those who used fire that they found in their environment (from forest fires, lightning, volcanoes, whatever) and those who created the means to make it from scratch. The latter would definitely be an "invention"...and I think that this is what we should probably be discussing here. SteveBaker (talk) 16:25, 6 August 2013 (UTC)

Type of solid

What is the term for a covalent network solid that melts by ionising? For example, -ABABA- → AB⁺ + ABA^-. Plasmic Physics (talk) 04:48, 6 August 2013 (UTC)

Generally, covalent network solids (like diamond, silicon, Bakelite, etc.) melt WITHOUT ionizing. Can you give an example of a covalent solid that ionizes as it melts? 24.23.196.85 (talk) 04:56, 6 August 2013 (UTC)

I'm certain that some of the hyperfluorinated metals exhibits this sort of behavior, though I can't seem to find a good example at the moment. Plasmic Physics (talk) 05:03, 6 August 2013 (UTC)

Metal fluorides are ionic solids, not covalent. 24.23.196.85 (talk) 05:42, 6 August 2013 (UTC)

Not generally, that is an over-simplification taught in secondary schools, just like "the conjugate of a weak base, is a strong acid" which is not strictly true either. See aluminium fluoride for an example of a covalent metal fluoride. Plasmic Physics (talk) 05:51, 6 August 2013 (UTC)

Correct, but AlF₃ breaks up into neutral molecules upon melting, not into ions. 24.23.196.85 (talk) 07:44, 6 August 2013 (UTC)

Indeed. However, I did not give it as an example of the substance in question, but only of a non-ionic metal fluoride. Plasmic Physics (talk) 08:36, 6 August 2013 (UTC)

Do any of the transition metal hexafluorides qualify? And ReF₇? Double sharp (talk) 07:45, 7 August 2013 (UTC)

None of the ones list on WP, or rhenium heptafluoride are covalent networks. Plasmic Physics (talk) 08:04, 7 August 2013 (UTC)

Struck out my question above Brain was not retrieving information properly – oops! Double sharp (talk) 08:43, 7 August 2013 (UTC)

Some sort of homoassociation of the parts? DMacks (talk) 05:56, 6 August 2013 (UTC)

Perhaps. Would it be a two step process, whereby the solid breaks into individual monomeric molecules, followed by their homoassociation? Plasmic Physics (talk) 07:05, 6 August 2013 (UTC)

It will be the other way around -- the solid will first break into neutral molecules, which may then self-ionize (but only to a small extent). 24.23.196.85 (talk) 01:41, 7 August 2013 (UTC)

No offense, but I'm certain that that is the same order as what I used. Plasmic Physics (talk) 02:18, 7 August 2013 (UTC)

Is solid oxonium hydroxide stable under pressure, or does it require an applied electric field? I wonder how the density would be different from ice. Plasmic Physics (talk) 07:14, 6 August 2013 (UTC)

Do you mean hydronium hydroxide (also known as dihydrogen monoxide)? If so, it is stable under pressure, but experiences melting point depression and requires supercooling to remain in solid form (it will melt under pressure otherwise). As for the density, it's the same as that of ice -- for obvious reasons! 24.23.196.85 (talk) 01:32, 7 August 2013 (UTC)

No, I'm not using a pseudonym (yes, pseudo-, not syno-) for molecular water. I'm talking about a legitimate salt of composed of discrete ions. Plasmic Physics (talk) 02:18, 7 August 2013 (UTC)

I ask because I know that an equilibrium shift can occur as a consequence of a change in pressure, I also know that this is only applicable to gases, as solids and liquids are incompressible. However, I also know that that last bit is only true for relatively small changes in pressure. Solids and liquids can actually compress under MPa pressures and higher. So, I wondered if MPa or greater pressures, could indeed shift the K_w away from water. Plasmic Physics (talk) 02:27, 7 August 2013 (UTC)

If you're looking for a solid composed entirely of H₃O⁺ and OH^- ions, you won't find it anywhere -- such a solid cannot exist because of energy considerations. Only in a plasma can water be completely ionized! 24.23.196.85 (talk) 04:11, 7 August 2013 (UTC)

I care to know what these energy considerations are - Gibbs, entropy, enthalpy, etc. (FYI I thought that the water decomposes into the elements before becoming a gas plasma.) Plasmic Physics (talk) 04:18, 7 August 2013 (UTC)

American plague

European diseases killed many native americans, why did not american diseases kill the europeans? — Preceding unsigned comment added by 128.214.48.186 (talk) 09:59, 6 August 2013 (UTC)

The Straight Dope tacked this thoroughly. 184.147.136.32 (talk) 11:28, 6 August 2013 (UTC)

This was discussed a couple of weeks ago - see Wikipedia:Reference desk/Archives/Science/2013 July 13#Natives. Clarityfiend (talk) 13:16, 6 August 2013 (UTC)

European diseases may not be the whole story. Count Iblis (talk) 13:49, 6 August 2013 (UTC)

In the Jamestown colony, most of the settlers died their first year. Lack of food was a cause, but they also died from malaria, dysentery and "fevers." The local germs may have been strains they had not encountered back in Britain. The river water may have been nasty, but so were many rivers in England. The local natives were likely not only living in healthier locations, but probably had more natural resistance to the local pathogens. Edison (talk) 14:39, 6 August 2013 (UTC)

Jared Diamond wrote perhaps the definitive work on this exact subject (at least as far as material that is accessible to a wide audience), if you're looking to understand the subject in detail. I recommend the book in any event as a must-read, but here's the long and the short of it - animal domestication. Most infectious diseases pass into the human population for the first time as a result of zoonosis and as Eurasians had been living in close proximity with their domesticated species for many thousands of years by the point of time in question, they had built a healthy collection of diseases, but also had steadily built immunities to the same, limiting their virulence. Native Americans, by comparison, had only a handful of domesticated species (only a very small portion of all species on the planet possess a social nature and other features which make them good candidates for steady and lasting domestication through the methods that are available to a non-technologically advanced people), which were not very well dispersed geographically and as such had not developed nearly as extensive a collection of diseases/immunities. Unfortunately for these peoples, they also lacked the immunities necessary to protect them against the diseases brought with Europeans, and even the pathogens that had relatively mild effects on their Eurasian hosts of this era could in some cases prove deadly to their new American hosts, to say nothing of a disease like small pox, which spread well in advance of the Europeans themselves. Snow (talk) 00:27, 7 August 2013 (UTC)

Another factor was that indigenous Americans, having had little experience with deadly epidemics, did not have cultural coping techniques like quarantine. They learned, to be sure, and survival rates went up when practices like quarantine were enforced. But at first the natural reaction was exactly the kind of thing that exacerbates epidemics. This is beside the point of why did not "american diseases kill the europeans?" Folks like Jared Diamond have tackled that quite well. Pfly (talk) 10:37, 8 August 2013 (UTC)

DNA questions

1. How many codons are there in a base pair?
2. What is the size in megabytes of the human genome?

--Czech is Cyrillized (talk) 23:46, 6 August 2013 (UTC)

One codon equals three base pairs, so there is 1/3 of a codon per base pair. Estimates of the number of base pairs in the human genome vary a bit due to technical reasons, but the most recent value I've seen is around 6.3 billion (in women, with two X chromosomes rather than an X and a Y). Since each base pair contains two bits of information, that yields slightly under 1.6 GB of information. Looie496 (talk) 00:11, 7 August 2013 (UTC)

You can download each chromosome (or those for any of 50 or 60 other species) here. If you grab the "GBK" file, you can unzip it and watch a sea of A's, G's, C's and T's scroll by. I was able to download the full set within a minute or so...and with compression - the whole thing fits comfortably onto a double-sided CD-ROM. You don't even need a DVD, let alone a BluRay disk. It's kinda humbling actually.  :-) SteveBaker (talk) 02:36, 7 August 2013 (UTC)

Because of this compactness I've always thought of the human genome as a good demonstration of the power of procedural generation (yes, I realise that the analogy isn't exact). Equisetum (talk | contributions) 19:12, 8 August 2013 (UTC)

August 7

Creating a Faraday cage without matter.

Greetings!

I've been studying the concept of Faraday cages and how they contain energies from certain frequencies of the electromagnetic spectrum. I have a question, though, as to how this relates to the properties of visible light apropos human sight. To wit, certain materials—such as the acrylic used to make a woman's swimsuit—remain impermeable to wavelengths longer than 400 nanometers, even when wet. (Otherwise, why would she even wear it?)

I clearly understand the concept as it relates to matter. Nevertheless, I cannot help but wonder: Could one achieve a similar effect with energy, or some other immaterial substance? Namely, is there any method known to science that can create an immaterial, two-dimensional barrier though which Gamma Rays, X-Rays, and Ultra Violet can pass, but not Visible Light (or, for that matter, Infrared, Microwaves, or Radio)?

If so, how would somebody go about doing so, and what would the risks and implications (if any) would such a device entail? Thank you.Pine (talk) 03:47, 7 August 2013 (UTC)

Gravity perhaps? I'm visualizing an array of microsized blackholes in a vacuum. If the curvature of space-time can that be calibrated, it should allow only certain frequencies to pass. As for how to create such a device, I have no answer. Plasmic Physics (talk) 03:58, 7 August 2013 (UTC)

Pine, you seem confused about a couple of things. A faraday cage works by surrounding the protected area with electrical conduction paths (typically either wire mesh or conductive sheets). It works by forcing the electric field within to be such that no voltage can be measured or defined between any point on a object within, and any point on the inside of the shield. For any frequency not zero, subject to some practical limitations, faraday shields cancel out any external magnetic field because such fields will cause a circulating current in the faraday cage, which will set up another magnetic field equal and opposite.

Things that are not transparent, such as swimsuit cloth, are NOT faraday cages. Such things work by attentuation - as the electromagnetic waves (light) penetrate into the material, the interact with the material molecules and are converted to heat. Another example of attenuation is the absorption of light in pure water. The greater the distance into the water, the dimmer the light gets. This has nothing to do with faraday cage operation - pure water does not conduct electricity.

All manner of substances are available that attenuate visible, light, xrays etc. For xrays metals are commonly used. Lead is very effective. In medical xray rooms, good thick concrete walls are used to protect the operators.

What do you mean by "immaterial"? If you mean blocking radiation by use of more radiation, it cannot work, as energy can neither be created nor destroyed - only converted from one form to another - as in the converstion of light or radio waves into heat. Such conversion requires the use of physical matter. Faraday cages are by definition made of matter, which supplies the electrically conductive paths. If you mean "force fields" a la Star Trek, that's just science fiction nonsense.

1.122.160.132 (talk) 04:18, 7 August 2013 (UTC)

I noticed those confusions as well, however, I ignored the bulk of the query and only focused on the question actual at the very end. With regards to 'immaterial', I think that the OP is referring to 'not of matter'. Plasmic Physics (talk) 04:23, 7 August 2013 (UTC)

You're right, I am confused.

Somebody told me that the protective mesh on the door of a microwave oven acts as a Faraday cage allowing visible light (400 nm to 700 nm) to pass through, but not the microwaves themselves (12 cm, or so). i.e. One can see his food being cooked, without himself being cooked in the process.

Yes, by 'immaterial,' I mean something not of matter that would produce a similar effect, but would also block out the visible spectrum.

Does this violate the laws of thermodynamics? Or can it theoretically happen? Pine (talk) 04:35, 7 August 2013 (UTC)

No, nor really. If you take my above gravitational solution into account, you can deflect or absorb the unwanted frequencies. When microsized blackholes evaporate, they release only x-rays and γ-rays. Plasmic Physics (talk) 05:22, 7 August 2013 (UTC)

While one could argue about semantics, it is correct to say that the mesh in the door of a microwave oven acts as a sort of faraday shield in reverse, working with the magnetically doped door seal (positioned within just the right dimensioned metal parts) and the inner metal surface of the oven to keep the microwaves safely inside. (A true faraday shield is an enclosing electrically conductive surface that keeps outside energy getting inside.) The mesh is a good electrical conductor, and the microwaves set up circulating currents in it, causing the microwave enegery impinging on the mesh to be reflected back into the oven. The key to understanding this is that the microwave energy is reflected back in, not converted into heat as it passes through.

To eliminate radiated energy from a given region without the use of matter to do the conversion or reflection is not possible. It would indeed violate an important thermodynamic principle: As I said above, energy can neither be created nor destroyed, but only converted from one form to another - the so called First Law of Thermodynamics.

1.122.207.51 (talk) 06:05, 7 August 2013 (UTC)

Blackholes do not destroy energy, so no it does not. Plasmic Physics (talk) 07:21, 7 August 2013 (UTC)

KDKA's weakened radio signal

When my father was a child, he says KDKA (AM) was audible throughout the Eastern United States at night. The article Greg Brown (broadcaster) agrees it was audible ~175 miles away. Finally, I can confirm it too: as recently as 2004, I picked it up clearly in South Carolina.

But it is no more! Even in different parts of Central Pennsylvania, I can no longer hear it. Not even a small flicker even fades in. And it can't hold a candle up to the easily audible WBZ (AM) and KYW (AM).

What happened? I can't find anything written about a signal reduction. Magog the Ogre (t • c) 04:53, 7 August 2013 (UTC)

All three staions have similar frequency and power output, so in general, coverage should be about the same. What is your location now? Perhaps you are closer to WBZ than you are to KDKA.

In general though, AM distance reception is not what it was in earlier decades. The technology of modern solid state receivers with synthesised or digital tuning results in poor intermodulation performance - this results is weak signals being overiden by what appears to be white noise. Transistor radios made up to the 1980's and tuning with variable capacitors can be a lot better in this regard. Well designed tube radios better again. As well as that, with the increased use of electrical appliances of all kinds, there is more noise to drown weak signals out nowadays.

Local geology can affect reception. AM travels well over water and can be affected by monazite etc. HV powerlines also affect it.

Lastly, an anecdote: I once worked in a similar 50 kW AM "clear channel" station. Over a few years, more and more complaints arrived from distant (300 to 700 km) listeners that our signal was dropping. Eventually we realised that some villain was sneaking in to the unattended transmitter site and bit by bit digging up the copper earth mat and stealing it (a buried mesh of thick copper wire extending over several acres. As well as causing power loss in the ground, it altered the intended direction of radiation.

1.122.207.51 (talk) 06:23, 7 August 2013 (UTC)

I am in central Pennsylvania. I travel within parts of central Pennsylvania. Magog the Ogre (t • c) 05:05, 8 August 2013 (UTC)

Interesting. KDKA transmits from Alison Park, at the extreme western end of Pennsylvania. KYW transmitts from Lafayette Hill, at the extreme eastern end. WBZ transmitts from Hull in Mssachusets, much futher from you than either KDKA or KYW. However KYW has a directional antenna. I was unable to find out on the web the preferred direction, but westerly would seem likely. So all three should be equally good or equally bad for you. Perhaps you could email the station engineers for their view. If you use the form provided under "Contact" in KDKA's website, be sure to put in the first line "For Station Engineer" - you'll get a good answer then, and not one from some PR or sales person.1.122.190.3 (talk) 09:14, 8 August 2013 (UTC)

In the United States, we can get such information from the FCC, including their extensive collection of online databases. For example, you can use the online AM Broadcast Station database to find data and diagrams, including antenna radiation pattern for the KYW licensee (and even a graphical plot plus detailed information about both antenna masts). Nimur (talk) 17:15, 8 August 2013 (UTC)

Which shows that WBZ's antenna directionality is aligned so as to somewhat reduce signal strength at Magog's location. Oh well. However these FCC files are apparently calculated radiation fields. Local geography and HV power lines can significantly affect signal strength as I said before. Usually radio station management and sales staff regard fringe coverage as unreliable and therefore a nuisance (they can't charge advertisors full rates for it), however the station engineer will have a good handle on what the real (not calculated) coverage is. 1.122.175.140 (talk) 01:00, 9 August 2013 (UTC)

Melting and boiling points of the heavy alkali metals

Caesium has melting point 28.44 °C; francium has melting point ~27 °C; ununennium is predicted (see the article's infobox) to have a melting point of 22–24 °C. Why are they so close to each other? (The lighter alkali metals have a more normal trend.) Can anyone offer a (relativistic) explanation?

The boiling points also behave similarly: Cs 671 °C, Fr predicted to be 677 °C(!), Uue predicted to be 655–669 °C.

(A lessened effect seems to occur in group 2; Ubn may at the high extreme have a melting point higher than Ba and Ra (why?), but everything else conforms to normal periodic trends.)

Standard Double sharp disclaimer: Please give sources if possible, because I want to include this into an article (in this case, alkali metal). Double sharp (talk) 07:43, 7 August 2013 (UTC)

The 1978 Bonchev full-text (cited as the source for the data in the ununennium infobox) is available here (note Table 1 and figures 6 and 7). The properties of Cs and Fr are quite similar to each other, and the predicted properties of Uue are extrapolated based on a variety of parameters derived from empirical data, which are periodic. They are not based on first principles/relativistic considerations. -- Scray (talk) 22:29, 7 August 2013 (UTC)

Interesting. And yet Fricke (1971) [7], which is relativistic (I think), also gives a melting point of 0–30 °C and a boiling point of 630 °C for Uue. The lower value of 0 °C is all right, but is there any mechanism that would give the higher value of 30 °C? Double sharp (talk) 11:38, 8 August 2013 (UTC)

Note that the francium value is certainly theoretical rather than empirical, because a macroscopic amount of francium has never been collected in one place, and if you did, it would give off so much heat from radioactive decay that it would essentially instantly explode, with the radiation killing anyone nearby. So even the meaning of a melting point for francium is a bit obscure. I suppose it means something like "if by pure chance, one chance in $10^{10^{\textrm {largevalue}}}$, it so happened that not too many francium atoms in your sample decayed in the interval of observation, but the laws of probability worked otherwise as expected except for that, this is the melting point you'd see". --Trovatore (talk) 21:38, 8 August 2013 (UTC)

Why has no one ever tried to deposit a francium vapour onto a cooled surface to form a nanolayer, which is then slowly heated to test francium's melting point. Plasmic Physics (talk) 23:54, 8 August 2013 (UTC)

Well, I can't tell you for sure why (or even that) no one has ever tried that. But I can tell you that the largest amount of francium that our article mentions being collected in one place is 300,000 atoms, which works out to about 10^−16 grams. If you think you can measure the melting point of that, even in a monolayer, go ahead and write a grant proposal. How much can you learn about the melting point of a 3D material from a monolayer, which is effectively 2D? Doesn't strike me as the same thing. --Trovatore (talk) 00:16, 9 August 2013 (UTC)

OK. FYI: nano- and mono- are not the same thing, a nanolayer can consist of any number of layers with a cumulative thickness of less than a micron. Plasmic Physics (talk) 00:20, 9 August 2013 (UTC)

I think you're vastly underestimating the difficulty of assembling and manipulating a macroscopic quantity of francium—even a microscopic macroscopic quantity. The largest quantity ever collected has been about 300,000 atoms, and that only in the vapor phase. If you made a solid cube out of it, it would be less than 70 atoms on a side–and it would be vigorously heated by more than 2000 radioactive decay events every second. And even if you were able to measure a melting point using such a small quantity of material, it wouldn't be 'correct' anyway. Melting points are depressed sometimes by very significant amounts when you deal with very small particles; see melting-point depression. Essentially, the unusual or quirky behavior of the atoms at the surface or edges dominate the 'bulk' material behavior that you're trying to measure, resulting in a very sensitively size-dependent melting temperature. TenOfAllTrades(talk) 00:21, 9 August 2013 (UTC)

That is why I suggested a nanolayer and not a nanodot. Is it not possible to use the depressed melting point data to improve current estimates of the bulk melting point? Plasmic Physics (talk) 00:44, 9 August 2013 (UTC)

Relative motion..

A driver was sent to traffic court for speeding. The evidence against the driver was that a policeman observed the driver's car alongside a second car at a certain moment, and the policeman had already clocked the second car as going faster than the speed limit. The driver argued, "The second car was passing me. I was not speeding." The judge ruled against driver because, in the judge's words, "If two car were side by side, you were both speeding." In this case, how to argue the case in term of physics in the favour of accused driver?

AmRit GhiMire 'Ranjit' (talk) 14:15, 7 August 2013 (UTC)

This sounds like a homework question aimed at testing your understanding of concepts and the articulation thereof, and unwarranted deductions based on flawed interpretation of wording. On the other hand, my experience of the legal system makes this kind of abuse of logic (often deliberate on the part of the practitioners manipulating the outcome, being protected by the shear weightiness of the process of fighting it) pretty standard in the application of "justice". — Quondum 14:24, 7 August 2013 (UTC)

As stated, the judges' decision is clearly wrong. You could be parked, stationary with another car passing you at the instant the policeman observed you. Your statement of the story is that the policeman observed the action "at a certain moment"...ie, over a period of zero elapsed time. Since the measurement of speed requires knowing the distance travelled over time, (even if it's distance travelled relative to another car) - having a zero-time snapshot tells you nothing whatever. If that were literally true then he has no clue how fast you were moving.

But if this is what the claim hinges on then it's a ridiculously fabricated situation - nobody could see an event like this in a literal instant.

In reality - a policeman doesn't get an instant, zero-millisecond snapshot picture of the event. He'd easily be able to tell whether the two cars were or were not going at the same speed from a one or two second glance...and if we trust his testimony then both drivers were indeed speeding and the judge made the right call. If we don't trust the police officer's testimony then all bets are off and we have no way to know whether the accused was speeding or not.

The only other possible inference (and one that this contrived story may be trying to elicit from you) is that the two cars might have been driving around a tight bend in the road - with the accused driver on the inside of the curve and the speeding car on the outside. Both cars could then remain side-by-side with the car on the outside of the curve traversing a longer distance than the one on the inside. Thus the outside car could be exceeding the speed limit while the inside car was not.

But that's one hell of a stretch. In any practical situation, the difference in speed would have to be tiny - probably less than the threshold of error that the police would allow for in using a speed gun. I don't buy it - if that's it, then in any practical situation, the driver is guilty as hell!

SteveBaker (talk) 16:58, 7 August 2013 (UTC)

If I were the driver's lawyer, I would argue that the policeman's account of the relative speed of the two cars is not reliable, because his attention was focused on the first car. I would also look for anything in the law that required a radar speed record, and if there were such, I would argue that, even if the policeman's account is reliable, it is not codified in the law that the policeman is allowed to make inferences (even valid ones) from the speed of one car and its relative speed to another car. That's not really an answer to a science question, but it might be an answer to the original question in some other context. --Trovatore (talk) 21:50, 8 August 2013 (UTC)

Why no industrial scale production of human breast milk using transgenetic cows?

More than 25 years ago I thought that by now we would be living in a World where genetic modification of animals would have led to many applications. While you could expect that some predictions would turn out too difficult to realize, (e.g. genetically engineered pigs to grow human organs has faced problems due to retrovirusses), it's rather strange that almost nothing has changed in the food industry. So, what is preventing us to make progress with genetic modification of animals? Count Iblis (talk) 19:42, 7 August 2013 (UTC)

How do you propose getting human milk from a cow? ←Baseball Bugs ^{What's up, Doc?} carrots→ 21:04, 7 August 2013 (UTC)

It's difficult enough convincing the population that tiny modifications in the genes of cereals are safe to eat, so can you imagine the reaction of mothers asked to feed their babies milk from cows with human udders? Research is continuing, but slowly. Dbfirs 21:18, 7 August 2013 (UTC)

It's not so much the udder, it's human nutrients in human milk which are alleged to be better for baby than cow's milk is, provided the mother is producing adequate and good milk, which not every woman can. So it would require engineering cows to alter the chemistry of their milk to simulate human milk. Given that some of the benefit of human milk is alleged to be the ingestion of antibodies which the mother has in her system, it would be a very tall order to make a cow produce that. They would be better off focusing on what the negatives are with cows' milk, and trying to fix that. ←Baseball Bugs ^{What's up, Doc?} carrots→ 01:58, 8 August 2013 (UTC)

I believe (sorry, can't track down references right now) that I have also read about research showing that the mother's milk changes composition over time as the baby's needs change, and can react to things such as an infant's illness or stress as well. Obviously those are benefits an artificial milk will never produce, but I suppose it would still be a big step up from formula - many mothers pump and freeze milk because their schedules (or their baby) don't allow for a regular nursing schedule. But like Dbfirs points out, it will likely be a very long time till people accept cows with human genes. Human insulin is produced on a large scale by genetically modified bacteria, but our article on Humulin doesn't really make it clear if there are definitely human genes added to the bacteria. 209.131.76.183 (talk) 11:36, 8 August 2013 (UTC)

Researchers have worked on exactly this project, as of 2011. www.cbsnews.com/8301-504763_162-20071923-10391704.html I have limited internet access at work so I cannot provide more links, but googling 'cow human gene' and similar terms will be productive. 198.190.231.15 (talk) 13:42, 8 August 2013 (UTC)

• Our article on genetically modified organisms contains the following paragraph:

In 2011, Chinese scientists generated dairy cows genetically engineered with genes for human beings to produce milk that would be the same as human breast milk.[56] This could potentially benefit mothers who cannot produce breast milk but want their children to have breast milk rather than formula. Aside from milk production, the researchers claim these transgenic cows to be identical to regular cows.[57] Two months later scientists from Argentina presented Rosita, a transgenic cow incorporating two human genes, to produce milk with similar properties as human breast milk.[58] In 2012, researchers from New Zealand also developed a genetically engineered cow that produced allergy-free milk.

So clearly people are working on that sort of thing, but all the progress has been very recent. Looie496 (talk) 14:08, 8 August 2013 (UTC)

Note that these advances involve changing to human style lysozyme and lactoferrin and removing beta-lactoglobulin. They make the milk "more human-like" but by no means human. Basic parameters like the overall fat content are different. It is no easy task to change everything, hard even to tell if you've missed something. Also, I worry about putting human-style immune functions (the lysozyme and lactoferrin) into an otherwise bovine context - you might get infections that don't bother the cow, but adapt to defeat the human antibacterial measures, and do bother the humans. But that is IMHO. Wnt (talk) 15:02, 8 August 2013 (UTC)

Most abundant organic polymers

According to the respective articles, the #1 abundant organic polymer is cellulose and #2 is lignin (which apparently employs 30% of non-fossil organic carbon). Is there a longer list available (say, a top 10), particularly one with estimates for the global mass and the % of non-fossil organic carbon employed? List of most abundant organic polymers would be an interesting article... ManyQuestionsFewAnswers (talk) 22:27, 7 August 2013 (UTC)

There are chitin (fungi, protostomes) and keratin (vertebrates). You seem to be aiming for long-chain structural polymers. μηδείς (talk) 23:43, 7 August 2013 (UTC)

I suspect keratin is nowhere near as abundant given that vertebrates form a relatively small % of biomass, but I could be wrong. My not particularly well-informed guess would be that several hemicelluloses would be higher on the list. There are other polysaccharides (e.g. pectin), as well as polypeptides (presumably the most abundant being RuBisCO) and nucleic acids, which I suspect would rank lower. But I'd love to see some hard data. ManyQuestionsFewAnswers (talk) 01:27, 8 August 2013 (UTC)

August 8

Water-soluble material ?

Is there a water-soluble material which is not soluble in a solution of sodium hypochlorite (chlorine bleach) dissolved in methanol (alcohol) ? It can be only slightly water soluble, but can't be at all soluble in alcohol or bleach. If so, what is it/are they ? If not, why not ?

Also, mixing chlorine bleach with ammonia is dangerous, as it produces chlorine gas. Is there any such danger from mixing it with ethanol, or any other dangers ? StuRat (talk) 06:39, 8 August 2013 (UTC)

Well chlorine + ethanol produces chloroform, heat and then chlorine gas once hot, so don't do this. Ammonia and chlorine can make chloramine or hydrazine, neither a good idea. I don't think that methanol and bleach are a good combo either! Graeme Bartlett (talk) 11:16, 8 August 2013 (UTC)

I see. Can bleach be safely diluted in anything else besides water ? StuRat (talk) 16:23, 8 August 2013 (UTC)

What's your goal here? Might be many possible solutions to "what you're trying to accomplish" other than as you've phrased it, and also your application may limit the solutions (ha!) that might answer your general question. DMacks (talk) 17:20, 8 August 2013 (UTC)

Cancer

Is cancer partly genetic as some families don't have many cancer sufferers compared to others? — Preceding unsigned comment added by Clover345 (talk • contribs) 09:35, 8 August 2013 (UTC)

Definitely, and many of the genes responsible have been identified, such as the BRCA mutation. Diet, exercise and environmental exposure to carcinogens are other major factors which affect cancer rates. StuRat (talk) 10:27, 8 August 2013 (UTC)

Do you have any source about exercise as a carcinogen factor? 79.156.170.130 (talk) 12:27, 8 August 2013 (UTC)

It is lack of exercise that is the factor: see Cancer#Diet and exercise. AndyTheGrump (talk) 12:34, 8 August 2013 (UTC)

LOL, yes, I would have thought that was obvious, but have appended to my original response to make it clear. StuRat (talk) 16:19, 8 August 2013 (UTC)

structure of element 171

See Fricke [8] (relativistic). It's probably a solid at STP, right? Seeing as I have so far failed to find any reliable sources on the possible structure, can someone give their predictions here (with thoroughly citable reasoning? – especially polyatomic vs. diatomic.) Thanks. Double sharp (talk) 11:40, 8 August 2013 (UTC)

The social structure of ants, bees etc. and the evolutionary explanation to their sexual reproduction

Colonies of ants, bees etc. have a single individual (the queen) that procreates. Is there a name to this social structure? I guess it would be related (but not identical) to eusociality.

Also, these organisms have sexual reproduction, but I can't think of any evolutionary justification to it. As far as I understand the Red Queen hypothesis doesn't apply because the queen and the male that impregnates her are siblings. What's the explanation?

Thanks, 84.109.248.221 (talk) 11:57, 8 August 2013 (UTC)

See kin selection and evolution of eusociality. Also, you might find "Darwin's special difficulty: the evolution of “neuter insects” and current theory" interesting. Sean.hoyland - talk 12:05, 8 August 2013 (UTC)

When only a single queen is present, the colony is called monogynous, and when many fertile queens are present, the colony is polygynous. These habits do not clearly break along the pre-social to eusocial continuum, and some species have colonies of both types. Note that a queen is not usually inseminated by a sibling male. Many species (e.g. honeybees, fire ants, etc) have massive nuptial flights, where all the drones and virgin queens go out at once to play. The evolution of eusociality is an ongoing topic of research, but it is commonly agreed that Haplodiploidy has plaid a role in the social insects. However, haplodiploidy is not a necessary condition, as there are eusocial, monogynous mammals (naked mole rats), and haplodiploid solitary wasps. The classic text on all things social insect is The Insect Societies, by E. O. Wilson, [9], and I highly recommend it to any interested parties. SemanticMantis (talk) 13:30, 8 August 2013 (UTC)

Are all flames produced by fire?

Can flames be produced through any other source? Like when an atomic bomb goes off and you see the fireball, are those flames being produced through simple heating of the atmosphere via the nuclear products or is something actually burning (redox) that produces those flames? ScienceApe (talk) 15:16, 8 August 2013 (UTC)

Air can be heated to incandescence without a chemical combustion reaction. If you accept the definition of flame provided in the leader to our article, though, the word "flame" refers to that type of incandescent air related to fire (that is, ordinary chemical combustion). So, this is really just a question of how you want to use the word.

As far as I know, Atomic Fireballs are flavored with cinnamon, and have neither flame nor fire. Nimur (talk) 15:58, 8 August 2013 (UTC)

Incandescence by definition involves the emission of visible light. Heating air to incandescence? I don't think so. To emit light, a substance must be an effective black body radiator for light. All the gasses in air, Nitrogen, oxygen, argon, etc) are fully transparent. Flames from burning hydrocarbons emit visible light mostly because they contain carbon, which is one of the best black body radiators (not transparent) known. The fireball following atomic bomb detonation contains all manner of compounds from the earth thrown up by the blast, some set alight, some just heated enought to emit as black bodies without combustion. The explosion itself emits visible light directly. You can heat the gasses of air hot enough to ionise them (well above black body incandescence temperature), which will produce light, but then you no longer have air. It's a bit like saying let's heat water to incandescence. You won't have water any more longer before you get hot enough for ionisation. It will split into H2 and O2 longer before, and further into monoatomic hydrogen and oxygen at lower theperatures. And ionisation always involves emision at specific wavelengths, unlike black body radiation, which is essentially random noise (all wavelengths). 1.122.236.146 (talk) 16:20, 8 August 2013 (UTC)

1.122.236.146_(Geolocate), you're seriously suggesting that atmospheric air can not incandesce when heated, because it's transparent at room temperature? Although that's an interesting piece of thought-experiment science-fiction, it's totally false. Air - including nitrogen - incandesces when heated, and emits visible light whenever its temperature is high enough. You might want to re-read black-body radiation and incandescence. Nimur (talk) 16:30, 8 August 2013 (UTC)

Yeah - and if you doubt it - I guarantee that you've seen it with your own eyes. The air glows during a lightning strike. There are no other substances introduced into the path of the lightning bolt - so it must be the air that's glowing. Indeed the air forms a plasma with a core temperature around 50,000 K, causing it to glow with a blue-white color.

The problem with our OP's question is that the terms "Fire" and "Flame" are inextricably entangled and confused - and not very well defined in scientific terms. Is the sun "on fire"? Are there "flames" coming out of the surface? What about molten steel? Are electrical sparks a kind of flame?

Our dictionaries fail us at these times - so answering a question that's a bout mere words in a scientific manner is kinda silly. Put it this way - there are certainly ways in which gaseous and finely divided airborne particulate substances can be made to glow brightly in the absence of any vigorous oxidation processes. If the former is "flame" and the latter "fire" - then yes. SteveBaker (talk) 20:08, 8 August 2013 (UTC)

You can get flames by burning various substances in chlorine gas, so an oxygen atmosphere is not necessary. μηδείς (talk) 22:00, 8 August 2013 (UTC)

mathematical proof to evolution

Should it be possible, in principle, to proof mathematically that mechanisms like natural selection, sexual selection etc, combined with mutation rate like the rate found in nature, can create the diversity and complexity of life as we see it? did researches tried to construct such proofs? thanks, 94.159.164.161 (talk) 19:27, 8 August 2013 (UTC)

Evolution is certainly a "self-evident" logical consequence of systems that

1. Replicate themselves on the basis of a design embedded as a part of themselves.
2. Compete for limited resources of some kind - without which they cannot replicate.
3. Have occasional errors in the replication process.

If those three conditions are satisfied, then there is no way that evolution cannot occur because:

1. The errors will result in some differences in the design of some individuals relative to their parents.
2. The competition for resources will result in the numbers of accidentally improved designs increasing.
3. Result in a gradual improvement in the design.

Turning that into the language of mathematics ought not to be difficult.

Life (as we know it) uses DNA as the "embedded design", has to compete for nutrition and possibly other things, and DNA is subject to random mutations and transcription errors. Hence life evolves. QED.

Very minimal computer-based systems (See: Artificial life) bearing just those three basic characteristics have been shown to evolve every bit as strongly as "real" living things and Genetic algorithms are routinely used by software engineers to solve certain sorts of programming problems using an "evolutionary" approach.

SteveBaker (talk) 19:51, 8 August 2013 (UTC)

See "Fine-tuned Universe".—Wavelength (talk) 20:11, 8 August 2013 (UTC)

No, don't see Fine-tuned Universe since it has nothing to do with the question.

See Evolutionary dynamics and Evolutionary game theory instead.

Dauto (talk) 20:32, 8 August 2013 (UTC)

• There isn't really any need for a mathematical proof. To people who understand genetics, it is completely obvious that evolution will occur if enough time is allowed. The problem is that people who have doubts about evolution hardly ever have any knowledge of genetics, so it isn't obvious to them. Looie496 (talk) 21:16, 8 August 2013 (UTC)

You may be right in this case, because you'd only be proving things about a model anyway, not about the real world of biology. But, in general, "obviousness" is no reason not to prove things mathematically. For instance, certain "obvious" facts are actually wrong, and other "obvious" results are very rather difficult to prove, e.g. the Jordan curve theorem. In that case, the value of the proof is not only that it gives us certainty of the result, but the methods developed for that proof are also useful to prove other, less obvious things. SemanticMantis (talk) 21:24, 8 August 2013 (UTC)

• No. The premise is a corollary of reductionism, that everything (and its' explanations) reduces to the laws of physics expressed in a few equations and the original state of the universe. But There are loads of concepts which in no way can be reduced to the laws of physics: in This is Biology, Ernst Mayr gives an off-the-cuff list of two dozen concepts like ecological niche, sympatric speciation, and sexual selection which are emergent and cannot be reduced to any chemical description or physical laws. See [[10]]. To even pretend that one could, from bare premises, predict a pouched mammal that eats only Eucalyptus leaves or the existence of such organisms as Vampyroteuthis is intellectual hubris. μηδείς (talk) 21:54, 8 August 2013 (UTC)

But if you have some emergent phenomena then these are (to some degree) independent of the underlying model, then it is possible (in principle) to predict these phenomena. The issue is simply that a higher level description in terms of the emergent phenomena captures the relevant dynamics of the system. So, if a lion is chasing a wildebeest, the dynamics of this system is appropriately described at the level of these animals. You could describe everything in terms of atoms, but to make the lion and wildebeest visible, you have to integrate out the lower level dynamics, and then invoke the definition of the higher level concepts in terms of the lower level description. For some systems one can actually perform such calculations within some appropriate approximation, such methods are known as "renormalization group methods".

These methods have been particularly successful in explaining the thermodynamic propreties of substances near the critical point where phase transitions happen. These thermodynamic properties do not exist at the level of atoms (they are emergent phenomena), yet one can explain them starting form a model about the atoms and their interactions. It was always believed to be impossible to do so (because the thermodynanic properties only become well defined in a regime that is infinitely far removed from the scale that your model applies to, so it seems that it would require an infinite computational effort to compute them), until Wilson showed in the early 1970s that one can in fact quite easily compute the quantites of interest.

So, I would not give up on the idea of deriving biological behavior that is to some degree universal from the underlying laws of physics. Count Iblis (talk) 23:37, 8 August 2013 (UTC)

The whole purpose of the concept of emergence is precisely to deal with higher level phenomena which are not able to be described or hence predicted from lower level phenomena. I strongly recommend reading Mayr, who formulated the biological species concept (another phenomenon which is based on the interactions of populations and cannot be predicted from physics or chemistry) and who as the "Dean of biology" was the voice of 20th century consensus. Mayr criticised S J Gould, but far less than he did reductionists like Richard Dawkins. Gould's emphasis on radical biological contingency reveals another concept that argues against such physiochemical prediction. Read Gould's description of the lone German Shepard dog which over a period of six weeks almost sent the Kiwi bird into extinction. Bully for Brontosaurus PDF'. That's hardly something that can be explained or described in terms of masses and velocities of C, H, N, O, Mg, & P. μηδείς (talk) 00:56, 9 August 2013 (UTC)

Stages

Is this sentence scientifically correct? "First we are gametes, then zygotes, then embryos, and then fetuses." Pass a Method talk 00:24, 9 August 2013 (UTC)