Wikipedia:Reference desk/Archives/Science/2009 January 9

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January 9

Do we know if egg-laying is painful for birds?

Is laying an egg be as painful for the hen bird as childbirth is for human women? I'm just guessing that no-one has researched this in any great depth - but the thought crossed my mind when seeing these videos on YouTube. It certainly doesn't look as though it's fun for her - put it that way. Anyone have any info? --Kurt Shaped Box (talk) 00:11, 9 January 2009 (UTC)

I believe the main reason for the amount of pain human women have during childbirth is that the process works the same way as in other mammals, but with the pelvis rotated 90 degrees (to enable us to walk upright), so it doesn't quite work as "planned". Also, the large size of a human's brain (and therefore head) at birth relative to their pelvis in adulthood (compared to other mammals) is going to cause problems. So, I would expect (without evidence to the contrary) that egg-laying is as painful as childbirth in a typical mammal, which is significantly less than in humans. Someone else may well have evidence to the contrary, of course. (Also, quantifying pain is extremely difficult just within humans, trying to do so meaningfully between different classes is going to be next to impossible.) --Tango (talk) 00:25, 9 January 2009 (UTC)

Yeah, I suppose. Birds (or at least the species I'm familiar with) seem to have an incredible tolerance to pain - or at least they're better at keeping a stiff upper lip than we are. I've seen gulls trying to walk on two badly broken legs without crying out, or even losing their composure. A budgie of mine that caught a toenail in the wire of its aviary and ripped it off trying to escape squeaked in pain exactly once when it happened, then afterwards *seemed* completely unconcerned. Though I'd guess that their biochemistries would be screaming out if we were to examine samples of their blood... --Kurt Shaped Box (talk) 01:29, 9 January 2009 (UTC)

Well, eggs are a lot more, er, "vagodynamic" than babies, for one, and presumably if a woman were to give birth every second day or so like chickens lay eggs, it would get significantly less painful. My impression from watching my hens is that the process is more along the lines of taking a satisfying shit. --Sean 01:33, 9 January 2009 (UTC)

Speaking as a guy with no kids (so I might be completely and utterly wrong) - but it's the contractions (not the 'passage' of the infant itself) that are the main cause of pain in childbirth, aren't they? --Kurt Shaped Box (talk) 01:38, 9 January 2009 (UTC)

The crowning is apparently one of the most painful parts. --Tango (talk) 02:20, 9 January 2009 (UTC)

Also, while the same situation applies to me as KSB I suspect one of the reasons the contractions are painful is because of what happens during them Nil Einne (talk) 09:36, 9 January 2009 (UTC)

What happens during a contraction? Isn't the contraction what is happening? The muscles around the cervix contract, dilating it. --Tango (talk) 12:47, 9 January 2009 (UTC)

I'm pretty sure that what women refer to as a 'contraction' refers solely to a contraction of the womb. The cervix thing is called something else (is effacement the correct word, or does that just refer to the end result of the process?). --Kurt Shaped Box (talk) 03:24, 10 January 2009 (UTC)

According to Cervical dilation, contractions of the womb cause the cervix to dilate. It seems I was slightly incorrect to say "the muscles around the cervix", it's the muscles around the uterus (which is connected to the cervix). --Tango (talk) 19:25, 10 January 2009 (UTC)

A chicken egg seems larger than the mother's skull, whatever that's worth in comparing human childbirth pain with egg-laying pain. The chicken should be laying a quail egg for it to be comparable. But, then, maybe a hen has a larger pelvis relative to the egg than a human mother does relative to the baby's skull. Edison (talk) 05:22, 9 January 2009 (UTC)

Shouldn't you be comparing it to the body size rather then skull size? Part of the reason is because the chicken has a rather small head compared to its body compared to humans. Nil Einne (talk) 09:38, 9 January 2009 (UTC)

Indeed, the reason I mentioned heads above is because with human babies the head is the largest part. That's not the case with chickens. --Tango (talk) 12:47, 9 January 2009 (UTC)

O.K., I agree it is a meaningless comparison. Edison (talk) 17:12, 9 January 2009 (UTC)

Another data point for my "it's not particularly painful" opinion is that childbirth is usually injurious -- and commonly fatal (absent medical care) -- to the mother, while egg laying almost never is. --Sean 11:56, 9 January 2009 (UTC)

Our maternal death article states that 'The historical level of maternal deaths is probably around 1 in 100 births'. Now I've started this, I'd be quite interested in seeing the figures relating to how many 'attempted layings' result in egg binding (which nearly always results in a nasty, slow, lingering death without human intervention) in hen birds of various species. I do however suspect that this data does not exist (or only exists for domestic chickens - which lay far more eggs than they would naturally anyway). --Kurt Shaped Box (talk) 03:38, 10 January 2009 (UTC)

A good layer can put out 200 eggs per year, so at the human death rate that would mean the average hen only lasts for six months of laying, which is certainly not the case. --Sean 18:35, 11 January 2009 (UTC)

Using the definitions of pain from the article, "an unpleasant sensory and emotional experience associated with actual or potential tissue damage, or described in terms of such damage" or "Pain is whatever the experiencing person says it is, existing whenever he says it does" then we cannot know if the bird doesn't talk. We should define our terms before answering. Icek (talk) 11:59, 9 January 2009 (UTC)

It's also notable (according to many mothers that I've spoken to) that the memory of the pain goes away amazingly quickly - after a matter of days, I believe - leaving a strange memory of it being a rather easy, even enjoyable, process...overlaid with a rational knowledge that it simply cannot have been so. This mental 'censorship' of the event is clearly of evolutionary benefit - if women remembered in full lurid detail what they had to go through the last time they gave birth - they'd be much less likely to go and do it again! SteveBaker (talk) 19:43, 9 January 2009 (UTC)

(Oh - and I'd like to personally thank Sean for coining the word "vagodynamic"...I can see it having widespread use in the manufacture of certain sex aids and porn movies. The science of vagodynamics holds all manner of interesting prospects for the future! :-) SteveBaker (talk) 19:43, 9 January 2009 (UTC)

For childbirth pain (from watching it and also having it described to me later), the crowning is far more painful than the contractions. Contractions are painful for however long they are occurring, and then everything is fine as if nothing happened, although they do become almost constant near the end, which is part of the whole pain experience. But the stretching during the actual birth is much worse. Afterwards, as Steve said, the memory of being in pain is still vivid, but not the exact sensation of it; I can remember the most physically painful thing I've ever experienced and I can still cringe from the memory of how it felt, but apparently that doesn't happen with childbirth pain. Adam Bishop (talk) 13:44, 13 January 2009 (UTC)

The pelvis shape in women hasn't evolved as quickly as the human (and baby) head size has increased. Posture has changed from quadrupedal to bipedal. In particular, women with android or anthropoid pelvis shape have a tighter birth canal, leading to increased pain during delivery (and increased risk to the mother and infant). Axl ¤ [Talk] 18:18, 13 January 2009 (UTC)

If our universe is an open one, is not that a a paradox?

Assuming that the bing bang theory is true, it would have sense to think that the matter is eternal going on from big bang to big crunch (not a big crunch exactly)over and over again, but if the universe is an open one.. wich is the origin of the "extremely dense and hot state point" that gave origin to the big bang expansion? --Starlingmaximilian (talk) 01:10, 9 January 2009 (UTC) Thanks and sorry for the poor english. —Preceding unsigned comment added by Starlingmaximilian (talk • contribs) 01:10, 9 January 2009 (UTC)

That's an excellent question, and not one we have a clear answer too. There are some theories involving multiverses, or you can go with "God did it", or probably one of numerous other ideas I can't think of. There is no widely accepted answer among the scientific community though (it's difficult to even work out what the question means, "what happened before the big bang" makes no sense since time started at the big bang, so it can't have a cause in the usual sense). --Tango (talk) 02:25, 9 January 2009 (UTC)

It's certainly a question that doesn't have an answer just now. It's possible that we'll never be able to answer it because when all of existance is contained in a literal singularity - then all information from "before" the singularity has been erased. If no information whatever passed between what came before - through the Big Bang - and on to us, how could we ever work out what came before? The "Big Crunch" hypothesis was a rather elegant and satisfying one - but sadly, it doesn't appear to be true. One kinda comforting thing is that the answer doesn't matter. For the same reason that we can't find out what happened before, there can be no influence from that time on present or future times - so the knowledge is purely a matter of satisfying curiosity - it wouldn't lead to further insights - useful inventions - or anything of that sort. SteveBaker (talk) 05:11, 9 January 2009 (UTC)

Perhaps all previous universes were closed, and this was the first big bang with enough oomph to be open. Last call, drink up, heat death awaits! --Sean 12:01, 9 January 2009 (UTC)

It seems to me that the oscillating universe model is just as bad in this respect, as we have no explanation of what created the universe, either way. (Or, if an OU is assumed to always have existed, why exactly that would be and how is that any better than saying that God always existed and then created everything ?) StuRat (talk) 17:10, 9 January 2009 (UTC)

The thinking about the oscillating universe (at least prior to the information BenRG explains below) was that if the big crunch singularity DID look exactly like the big bang singularity - then because they are both zero sized dots containing all of everything - then when the big bang goes off - the results are 100% identical each time. So the last time around, there was a SteveBaker sitting at a computer typing this exact answer into a web site called Wikipedia - and making the same spilling mistooks too. If every universe is IDENTICAL to every other universe - then that is 100% equivalent to saying that time is looped - and then we have no beginning and no end - a circle of time that simply exists. Sadly, things like the randomness inherent in quantum theory - and the stuff that BenRG explains below - means that this cannot and would not work out like that. Big Crunch was simplistically very elegant - but it's not true - so we're having to look for another answer. SteveBaker (talk) 19:34, 9 January 2009 (UTC)

The oscillating universe model is unworkable because a big crunch is not a time reversal of a big bang. Entropy continues to increase when the universe contracts, and matter becomes increasingly clumped, in contrast to the big bang where matter is extremely uniform. The big crunch singularity doesn't look like a big bang singularity and you can't really graft them together.

Also, there was no big bang. The so-called "big bang" model that's used to describe the present-day structure of the universe has a singularity about 13.7 billion years ago. But the model is not valid in the vicinity of the singularity, so that part of the model isn't used; instead it's cut off at a finite distance from the singularity and grafted on to some other model (like inflation). The big bang model still works well to describe the present-day universe and cosmologists still quote "time since the big bang" since it's a convenient way to identify events in that model. But those times aren't measured from any physically meaningful origin point, since the big bang singularity that would be the origin of the measurement was removed from the model. If you go back 10⁻³⁰ seconds from "10⁻³⁰ seconds after the big bang" you might end up in the middle of the inflationary epoch, or in some totally unknown pre-inflationary state, or past the beginning of the universe, depending on the details of the pre-big-bang physics. The age of the universe also depends on the pre-big-bang physics, and could be anywhere from 13.7 billion years to infinite. -- BenRG (talk) 18:55, 9 January 2009 (UTC)

Roger Penrose currently has a non-complete but interesting proposition called conformal cyclic cosmology which does not require the previous universe to collapse for a new one to 'big bang'. [1]

Strength of intermolecular forces

I know that dipole-dipole attractions hold solids and liquids together for polar molecules, and that london dispersion forces hold the solids and liquids for nonpolar molecules.

However, given several molecules (their formulas), I was asked to determine which had the "strongest intermolecular attraction"

For example, between (A) H2NCH2CH3CH3NH2 and (B) CH3CH3CH3NH2, I thought that (B) would have the strongest intermolecular attraction since the molecule is polar, whereas (A) is symmetrical and thus doesn't have a dipole moment. However, my teacher said that (A) has two sites, one on each end, where opposite partial charges between the molecules can attract each other, so (A) has stronger intermolecular forces. I am very confused: how can (A) have stronger intermolecular forces when the molecule does not display a dipole moment and thus has no dipole-dipole attraction. I thought we had to look at the polarity of molecules as a whole, not the polarity of individual bonding regions. Can someone please explain? —Preceding unsigned comment added by 68.111.75.89 (talk) 04:11, 9 January 2009 (UTC)

Intermolecular attraction is often local, especially for polar/ionic effects: "an amine group" is able to hydrogen bond, regardless of whatever else may be happening anywhere else in the molecule. Also, (A) doesn't actually look like you think it does...writing the way you did reinforces a very incorrect fiction for the overall molecular geometry. DMacks (talk) 05:17, 9 January 2009 (UTC)

Also, molecule A, being a rather long chain alkane, will have free range of motion around each C-C bond, and will assume whatever conformation will be the most stable. Get a simple molecular model kit and build it; you can easily make a "V" shaped conformation with the amine groups at the tips and a CH2 at the point. With that conformation, one can easily see (even ignoring H-bonding effects) that one can make a conformation which is quite polar; the question then becomes whether the energy of the intermolecular forces in THAT particular conformation can overcome the energy difference between that conformation and, say, the somewhat more stable "straight chain" conformation. Of course, none of that matters much because the H-bonding effects from the 2 amine groups overwhelms any other forces. However, my explanation could possibly work for a molecules where, say, the H's are replaced by say CH3 groups or something like that.

The questions about intermolecular forces are not as simple as often made out in a high school chemistry class, as there are often factors that, for simple reasons of time constraint, cannot be taught. There's lots of factors happening here, and one needs to consider all of them... --Jayron32.talk.contribs 13:06, 9 January 2009 (UTC)

Lightning

Hi, here are some questions my son has been asking me and I would be interested in hearing some thoughts. I'm not sure if I've answered him correctly...
1. If lightning follows the path of least resistence, why does it strike the highest point? Surely it should bypass a pole for example and go through the air and hit the ground?
2. When lightning strikes the ocean, how far does it spread? Does it kill fish on the surface only?
3. Somewhere I've read that a single lightning strike can power New York for a year. Why can't scientists capture lightning and harness its power? What are the challenges faced in doing this? (this one got me thinking too)
thanks, Sandman30s (talk) 11:39, 9 January 2009 (UTC)

1) Because the electrical resistance of the pole is enormously less than that of the air. Algebraist 12:26, 9 January 2009 (UTC)

3) Your source was wrong. The amount of electricity New York uses in a year is rather more than the amount of energy released by a hydrogen bomb, let alone a lightning bolt. Algebraist 12:31, 9 January 2009 (UTC)

(ec)Lightning follows the path of least resistance, yes. But air has a much higher electrical resistance than the pole in question. I don't know anything about the ocean question, but the energy will dissipate very quickly in the water. And the meme about the single lightning strike powering New York for a year is simply wrong. A lightning's power is in the terawatts, but it's lifetime is very short. The energy is impressive, but not that big. I may have dropped a zero here or there, but I come to about 500kWh for one lightning strike - theoretically enough to cover the electricity used by maybe 1000 average flats for one hour, not 10 million for a year. The problem is reliably capturing that energy and releasing it in a controlled manner. --Stephan Schulz (talk) 12:47, 9 January 2009 (UTC)

Our article on Resistivity has info to help quantify the first question. Resistivity is the measure of how much a substance resists the flow of electricity; i.e. low resistivity = high conductance. Air, being made of gasses, has large gaps between individual molecules, meaning that in order to conduct electricity, one has to force electrons to jump across a HUGE gap. At standard earth conditions, a good approximation is that most gases are 1/1000 as dense as solids or liquids; so all other things being equal, gases should be 1000x more resistive to electricity than solids. Of course, there is a huge variability in the resistivity of solids, largely due to how strongly those solid materials "hold on" to their electrons; however for nearly all but the most exotic materials, air is almost ALWAYS more resistive. So electricity will only stay in the air for the shortest distance possible... As far as number 3 goes; the difference between harnessing the electricity in a lightning bolt and generating it in a power plant is something akin to harnessing the power of a nuclear bomb and using nuclear fuel in a nuclear power plant... It may be possible to a point to do so, but there are so many more practical means of generating electricity. --Jayron32.talk.contribs 12:59, 9 January 2009 (UTC)

I wouldn't say that the density of the material is the most important factor in electrical conductivity, but rather whether the material has free electrons. Metals tend to have this, so conduct electricity well. You can get electricity to flow long distances through a vacuum or some very thin gases, such as those in fluorescent and neon signs. StuRat (talk) 17:02, 9 January 2009 (UTC)

Number 2 was asked here a while back, only about a lake instead of the ocean. Same difference. Here is the answer from that question. --Milkbreath (talk) 13:07, 9 January 2009 (UTC)

Algebraist and Stephan are correct about question (3). Here is an estimate from "All About Lightning" (ISBN 048625237X) by Martin A Uman: it would take 100,000 lighting-conducting towers in a moderately lightning-hit area to produce as much power (100 MW) as one small power station. --Heron (talk) 20:18, 9 January 2009 (UTC)

Thank you all for the answers. A link within that lake strike link above says "A single lightning stroke can deliver a billion electron volts and 100,000 amps" - can someone compare this to a power plant (to end up with a megawatt figure) and let me know how you did the calculation? (sorry I should've paid attention in grade 11) and BTW that New York figure was from a children's encyclopedia but he can't remember which one, although he could have been wrong - perhaps it's for a day rather than a year. Sandman30s (talk) 20:35, 9 January 2009 (UTC)

An electron volt is a unit of energy - namely the amount of energy that one electron gains if it is accelerated through a potential difference of one Volt. This is a very small unit, roughly 1.6E−19 Joule. A billion (US style) is 1E9, which makes one billion electron volts 1.6E-10 Joule, or approximately nothing. A billion (European style) is 1E12, which makes a billion electron volts 1.6E-7 Joule - again, roughly nothing. I suspect the linked article is not a reliable source. 100,000 amps is not a unit of energy, but a current, and the energy depends on the potential difference again. I estimated around 500 kWh above, based on numbers from Lightning. That is 1800MJ, or the output of a 100MW power station over 18 seconds. --Stephan Schulz (talk) 21:13, 9 January 2009 (UTC)

My answer to #1: The high electric field initiates a leader from pointy objects. This leader ionizes the air up to the charged cloud. Only then does the return stroke occur. Surely this must be covered in our article on Lightning? Hmm article seems to say that leaders are initiated from the cloud. But Ive seen a pic of a leader emanating upward from a tree before the main strike.--GreenSpigot (talk) 21:40, 9 January 2009 (UTC)

My answer to #2: This is the 3D version of the 2D problem of cows getting killed due to the surface electric field in the region of a strike. Cow have rather a large 'wheelbase' so can pick up more volts than say humans for a given field strength in the ground surface. What is the maximum electric field strength that fish can stand? Maybe some one has modelled this scenario?--GreenSpigot (talk) 21:57, 9 January 2009 (UTC)

My answer to #3: What is the duration of the average strike? Work out volts x amps x time (gives you energy) and you'll see why. --GreenSpigot (talk) 22:00, 9 January 2009 (UTC)

3) I hope little Johnny is in graduate school, because the matter of electrical power is frightfully complicated. First, Stephan Schulz is right, of course; that website is bogus. But we can take average figures from our article "Lightning" and get a ballpark figure, bearing in mind that no two lightning bolts are the same, and they vary greatly.

First we need to get the terminology straight, because it is not straight right out of the box. When we talk about lighting up New York, we're talking about power. Sort of. What the electric company calls "power" is really what everybody else calls "energy". A watt is a unit of power, but power companies actually sell kilowatt-hours, each one a thousand watts used for an hour. It's like having ten 100-watt lamps on for one hour. A kilowatt-hour can be expressed any way you like, but one good way is in joules of energy, a joule being one watt-second (you're starting to get comfortable with the concept, aren't you?). One kilowatt-hour is 3.6 megajoules, or 3.6 million joules.

You want to calculate the power (energy) in a lightning bolt given only volts and current. Our article says, "...approximately one gigavolt (one thousand million volts) for a 300 m (1000 ft) lightning bolt" and "With an electric current of 100 kA..."(100,000 amps). (They call it a "thousand million" because the Brits and the Americans call that different things sometimes, but let's call it a "billion" here.) The formula for electrical power is P=EI, that is, power equals electromotive force (i.e., volts) times current (I forget why it's "I". Mostly because "C" means about 15 other things already, I think.). This is really power, and the answer is in watts. If we apply this to our lightning, we get one billion times one hundred thousand, so by adding exponents of ten we get 10 to the 9+5, or 10 to the 15th power, which we can call 100 terawatts or 100 times ten to the 12th. So far so good, but we need to calculate the energy, what the "power" companies admittedly aptly call "power", you remember. Our theoretical lightning bolt lasts for something like 300 milliseconds, or 0.30 seconds. We're shooting for joules (watt-seconds), so we simply multiply, getting 30 terajoules, or 30 million megajoules. As I'm sure you recall, a kilowatt-hour is 3.6 million joules, so 30 million million must be divided by 3.6 million, giving us 8,333,333 kilowatt-hours. That's a whole lot of energy.

I found a website that claims that New York City uses some 12 million megawatt-hours a year, which, to match our units, is 12,000 million kilowatt-hours. Divide that by the energy in a lightning bolt, and we get 1440. That means that our lightning bolt can power NYC for 1/1440 of a year, which is 1/1440 times 365 days, or about a quarter of a day: 6 hours. That's a lot of energy.

Too much, I think. I don't like that billion-volt figure. Sure, it takes a billion volts to ionize 1,000 feet of air, but once the current starts, the voltage is going to go way down. I've heard figures of some tens of millions of volts, call it 50 million, which sounds more reasonable. So, we can divide our answer by one billion divided by 50 million, which is 20, so 8,333,333 divided by 20 is about 417,000 kilowatt-hours. And six hours divided by 20 is 18 minutes. --Milkbreath (talk) 00:28, 10 January 2009 (UTC)

Unfortunately, the high voltage and the high current do not exist at the same time ( the voltage at ground level is (by definition) approx zero). Ever heard of Source impedance? and the impedance of an arc--GreenSpigot (talk) 01:09, 10 January 2009 (UTC)

(edit conflict)As for #3, not only is it difficult to store the energy from a lightning strike, but one time I asked that same question, and it turns out that lightning is Direct current, and the type we use is alternating current. So unless you can somehow store all that energy in a giant capacitator to ensure a constant supply, add a gigantic reverse-AC/DC adapter, transport the electricity in wires, and step down the voltage for safe use in homes, I would think that energy from lightning would be too difficult to manage. ~AH1^(TCU) 01:12, 10 January 2009 (UTC)

Milkbreath, the 300 miliseconds you assume is much to long. It's ok for a full lightning strike, but an individual discharge only takes about 0.4 milliseconds. A strike consists of several bolts, and the breaks in between are about 99% of the total time. So by that you are off by a factor of 100. --Stephan Schulz (talk) 01:17, 10 January 2009 (UTC)

Yeah, it did seem long, but I couldn't find a figure in the article, so I went with the caption on the picture at "Lightning#Discharge". So if we divide by 100, it's still a lot of energy, but it will only run the Big Apple for 10 seconds, which is the sort of range I expected when I started this. --Milkbreath (talk) 01:29, 10 January 2009 (UTC)

CO2 in a fish tank for plants

I keep fish in a tropical aquarium and I'm trying to encourage better plant growth. It has been suggested that I introduce a CO2 injection system to up the amount of CO2 in the water. Could I just add some fizzy bottled water every now and then? Wouldn't this add more CO2? Would there be any risks to the fish? Thanks.91.111.119.120 (talk) 12:51, 9 January 2009 (UTC)

Adding carbonated water might boost the CO2 -- I'm not sure what the injection system would actually inject (basically, whether it'd be acidic or not). As for risks to the fish, it seems likely. I strongly suspect that ingredients apart from water and CO2 are in whatever bottled water you have -- even chlorinated or fluoridated water would present hazards, and treatments like those might not be required listing on the side of the bottle. — Lomn 13:50, 9 January 2009 (UTC)

Fizzy bottled water is probably a bad idea as this will be (I believe) more acidic than your usual tapwater, upsetting the pH of your aquarium. Not to mention the hardness of some fizzy drinks. When it comes to plant growth, have you tried other remedies first? This includes fertilizer for the plants (which go well with most fish but some snails and shrimps are sensitive to it) and changing the fluorescent light to one optimized for plant-growth. The choice of plants also matter of course. EverGreg (talk) 14:06, 9 January 2009 (UTC)

Soda water is acidic, but there's no way around that — adding CO₂ to water makes it acidic regardless of the source. If that's the only problem (I don't know this), you can easily offset the acid by adding something alkaline to the tank also. Drops meant to alter the pH of an aquarium are available at any supply store. --Tardis (talk) 16:23, 9 January 2009 (UTC)

If you're already aerating the water for the fishes' sake then CO2 won't be a limiting factor. Have you considered the benefits your aquatic plants would receive from improved illumination? Upping the light supply with grow lamps will dramatically boost plant vitality.--Digrpat (talk) 18:45, 9 January 2009 (UTC)

Consider LED grow lamps if temperature is an issue. APL (talk) 20:31, 9 January 2009 (UTC)

This site might help. - [2] - see particularly the DIY yeast reactor. (This is what they have to say on other plant related issues - [3]). The more costly issue than introducing CO₂ into the water is going to be the fact that you'll have to monitor the chemical composition of the water more closely and frequently. Don't know about DIY test kits. _Lisa4edit76.97.245.5 (talk) 08:20, 10 January 2009 (UTC)

Many types of soda water have quinine in them, and although I don't know what effect it will have on fish I can't see it being good. -Pete5x5 (talk) 08:14, 11 January 2009 (UTC)

Your fish won't get malaria. Axl ¤ [Talk] 19:18, 13 January 2009 (UTC)

How is it that all life on Earth descended from a common ancestor and not multiple ancestors?

One thing that has always wondered about as far as evolution goes is the concept that all life on Earth descends from a common ancestor. It seems to me that if life was created in primordial soup, it would have done so multiple times. That is to say, if one pool of primordial soup produced life, so would a second pool of primordial soup, a third pool, a fourth, etc.. Also, it seem to me that life could have formed more than once within the same pool of primordial soup. Therefore, there should be multiple ancestors and multiple lines of descent, not a single common one. How is this possible? Does this mean that one line of life wiped out all the other ones? Or is the spontaneous generation of life so unlikely that it only occurred once on Earth? (If that latter, is this a possible explanation for the Fermi Paradox?) I'm aware that we have articles on evolution, abiogenesis and common descent but other than a single sentence in the common descent article, "The theory of a common ancestor between all organisms is one of the principles of evolution, although for single cell organisms and viruses, single phylogeny is disputed" I don't see anything that specifically addresses my question (but maybe I missed it). 216.239.234.196 (talk) 14:25, 9 January 2009 (UTC)

There are two point here. The first is that, given enough resources, life grows exponentially. Hence, without competition, once the first life has been established, it will spread very quickly (on an evolutionary time scale). The second point is that once one kind of life has been established, the very existence of this may inhibit the formation of an independent strain, as the existing life forms are much better at consuming precursor molecules and structures than potential proto-life strains. Thus, even if it takes an average of only a million years or so for primordeal life to develop, the chances of two independent strains are very low. Thirdly, as we now know, there has been and still is a horizontal exchange of DNA, e.g. via viruses. Thus, the tree of life really is a complex graph, and only the major gene flow follows the tree structure. --Stephan Schulz (talk) 14:39, 9 January 2009 (UTC)

I don't think anyone is saying life couldn't have evolved more than once here on earth. However there is no evidence of more than one line, the form that gave rise to our current DNA and RNA. For all I know there could be some other form of life on earth not reproducing that way but I very much doubt it. It may be there was more than one form of life and the current form was just far better and the other form just died out, just look how many good viable species go extinct nowadays - there's a lot of competition. It is all speculation though without any evidence and I wouldn't hold my breath waiting for some evidence to come along. Dmcq (talk) 14:54, 9 January 2009 (UTC)

In addition to the points above, I also would say that the spontaneous generation of life may be so unlikely, that not only did it only occur once on Earth, it may not have occurred on many other Earth-like planets where it could have. We may be the only planet in the universe, or even among many parallel universes, where it did occur. One piece of evidence that it may be more common than this is that life seemed to evolve shortly (on geological time-scales) after the Earth cooled, which would seem to indicate that life occurs as soon as conditions exist which allow it. StuRat (talk) 16:49, 9 January 2009 (UTC)

According to this scientific American article some microscopic life forms that may have evolved from a different common ancestor than the ancestor of Archaea, Eubacteria and Eukaryotes may still exist today.--Apollonius 1236 (talk) 00:24, 10 January 2009 (UTC)

To be very careful about that article - it doesn't anywhere say that there is any evidence for this. It says that there are a lot of people LOOKING for that evidence - and that it could hypothetically be true - but it goes on to say that every single time someone THINKS they've found such a thing, it's only ever turned out to be a weird-but-still-related-to-us kind of a creature. SteveBaker (talk) 14:12, 10 January 2009 (UTC)

It's not conclusive that there was only ever one start for life on Earth - it's possible that our ancestor was simply able to out-evolve the competition and eliminate them in the (L-O-N-G) period before we have good fossil records. However, from all we know - this does nicely support the possible extreme coincidence required to get that first life-form started. The "abiogenesis event" (the moment when something that wasn't alive became alive) is a hard thing for science to explain - and if we had conclusive evidence that it happened many times then there would be a severe problem - because explaining how it came about from 'chemistry' alone is tough. But the fact that it probably happened only once gives us an elegant 'get-out-clause'. If the event happened only once in billions of years and over billions and billions of gallons of ocean water (or tens of thousands of volcanic vents or whatever) - then the probability of that event MUST be vanishingly small. That not only allows us to hypothesise quite amazingly unlikely events - but it actually means that a more causal explanation would have to be wrong! We are therefore required to imaging such incredibly unlikely things as the completely accidental arrival of just the right amino-acids in one place and in just the right order to make a self-replicating molecule form from a bunch of random interactions. That's a spectacularly unlikely thing. But if it only had to happen once in all of time and within all of the oceans on all of the planets in all of the galaxies in an enormous universe (or possibly, even a multiverse) - then any event that's possible will have happened somewhere at some time. That makes life appearing somewhere in the universe an almost certainty! By the 'anthropic principle' - we are (by definition) the product of that one event. This changes the science dramatically. If there had been multiple abiogenesis events - we'd be in deep trouble with the religious nuts. SteveBaker (talk) 19:22, 9 January 2009 (UTC)

I'm not sure I understand your last point. Are you saying: We'd be in trouble with religious people because if abiogenesis is common and therefore science should be able to explain it but can't? If so, it just means that science can't explain it yet. We're all just passing through history. 216.239.234.196 (talk) 20:22, 9 January 2009 (UTC)

Yes - pretty much. They'd be able to say "See how Godsome intelligent designer is creating all of these new creatures - and your evolutionary theory can't explain them because they are all clearly totally unrelated"...or something like that. However, if there has only been one such abiogenesis event EVER - in the entire history of the universe perhaps (think 'Panspermia' or the Anthropic principle) - then it only has to be possible for a molecule to come about that way and a really LOW probability of such an event is merely confirmation of it's viability as an explanation. Anyway - it's no big deal - just an observation - we may yet find the true cause of that event. SteveBaker (talk) 05:16, 10 January 2009 (UTC)

I think its important to note that there is a difference between "all extant life on earth" having evolved from a common ancestor, and "all life on earth" having evolved from a common ancestor. When the beginnings of life were brewing in the primordial soup, there may well have been lots of different pre-RNA forms that stored, transmitted, and duplicated "genetic" information. These could have evolved independently. If you wish to define these as "alive" then all living things may not have evolved from a common ancestor. There could even have been other forms of "life" that evolved from the iron-sulfur world or any other mechanism that we are unaware of. Some of these would be doomed to failure, restricted by the limits of their own basic chemistry. These could have bounced around for many millions of years "surviving" in the unique environment at that time. But we do know that only one chemistry had the right combination to develop to the point in prehistory where that we could detect it. And all the others must perished, as the environment changed and no longer became optimal for the genesis of life. This isn't such a huge stretch of the imagination, because we know that also happened to whole lineages of DNA based life.

We don't know whether this happened, or if it did, how long or how advanced different types of life could have co-existed. There is no evidence for it, but not evidence against it either. We just don't know (yet). Rockpocket 05:31, 11 January 2009 (UTC)

Orders of magnitude for force...?

Hi. Why isn't there an orders of magnitude table for force? (Like there are for pressure, mass, etc. etc.) It'd be nice to have one, no? Kreachure (talk) 16:30, 9 January 2009 (UTC)

Sure, but this isn't the place to request a new article. This is: Requested_Article#Topic_areas_in_applied_arts_and_sciences. You might also leave your request on the talk page for orders of magnitude . StuRat (talk) 16:37, 9 January 2009 (UTC)

Well okay then, I just thought there was a particular reason for there not being one. Sorry... Kreachure (talk) 16:52, 9 January 2009 (UTC)

I LOVE those order-of-magnitude pages - please, get proactive and make one. It's so useful when answering a question here to be able to say "...and that's as heavy as an aardvark!" or "...and that's as fast as a rifle bullet!". Good catch! SteveBaker (talk) 19:08, 9 January 2009 (UTC)

If you're mentioning aardvarks because you're trying to memorize the dictionary, I see you've made very little progress. --Bowlhover (talk) 21:15, 9 January 2009 (UTC)

Ah - but how do you know which end I started reading from? Ha! The force exerted by a falling Zygolophodon would be harder to figure out because they are extinct...although I think I could definitely guarantee at least a couple more orders of magnitude than the animal at the other end of the dictionary! SteveBaker (talk) 02:33, 10 January 2009 (UTC)

So do I, so I made one: Orders of magnitude (force). --Heron (talk) 20:08, 9 January 2009 (UTC)

How else would we know how many football fields long anything was? hydnjo talk 20:25, 9 January 2009 (UTC)

Thank you, Heron. That's more like the kind of reply I was hoping to get. Can I say I just love Wikipedians sometimes? :) Kreachure (talk) 20:56, 9 January 2009 (UTC)

This thread inspired me to take a look at Orders of magnitude (pressure). I'm not the most mathematical guy, but I notice that the entry for the atmospheric pressure on Pluto has "10⁻³ Pa" in the "Magnitude" column and "0.5 Pa" in the "Pressure" column. That doesn't seem right; is "10⁻³" perhaps an error for "10⁻¹" (or, less likely, "0.5" an error for "0.005")? Deor (talk) 23:18, 9 January 2009 (UTC)

@Deor: "I'm not the most mathematical guy," ...But when she smoothed her curves she nearly broke my spline... [sincere apologies to The Kinks] --Scray (talk) 23:40, 9 January 2009 (UTC)

Yes, Scray, I too was thinking of the Kinks when I typed that. Deor (talk) 01:48, 10 January 2009 (UTC)

Yes, it's one of my fav songs. We need more songs with punchlines like that. StuRat (talk) 06:29, 12 January 2009 (UTC)

I think the table is correct, Deor. The "10^-3" section is supposed to include all values from 1 mPa up to 0.999 Pa. I agree that it looks odd, but it will look less odd if someone can find examples for the 1 mPa and 10 mPa orders of magnitude. --Heron (talk) 13:46, 11 January 2009 (UTC)

Cnidocysts stronger than a bullet??

Hi (again). After I found sources for the cnidocyte article claim that a cnidocyst accelerates to over 5,000,000g, I noticed that the cited source also says that despite its small mass, it's able to produce over 7GPa of pressure, "which is in the range of that generated by some bullets". According to orders of magnitude (pressure), the weapon discharge of a bullet is of 400MPa. I would like to know if all this makes sense. Even if it doesn't, I would like to know how a cnidocyst actually matches up to a bullet. Would it be able to puncture (on the microscopic level) a flak jacket significantly, for example? Thanks in advance, Kreachure (talk) 16:50, 9 January 2009 (UTC)

The deal is that the forces involved are proportional to the mass as well as the accelleration (F=Ma - Newton's law). While the accelleration is high - the mass is TINY (much lower than a bullet) - so the force exerted on the cnidocyte is very small indeed - much MUCH less than a bullet. That's why we make bullets out of lead (or depleted uranium) - because they are HEAVY. If you make a bullet out of foam polystyrene...you know what would happen. Similarly, although the cnidocyte might well survive the impact with the flak jacket - it couldn't deliver anywhere close to enough energy to make a hole in it. SteveBaker (talk) 19:06, 9 January 2009 (UTC)

But then how is it able to exert so much pressure? Is it wrong? Because the most conservative estimates I can find are along the lines of 10^7 Pascals, and the pressure a bullet exerts would be around 10^6 Pascals. My guess is that the microscopic area of effect is what makes the number jump so high, but the pressure is indeed there at the tip of that microscopic harpoon, no two ways about it. So, could you say that at the microscopic level, a cnidocyte is indeed as powerful as, or even more powerful, than a bullet? Kreachure (talk) 21:31, 9 January 2009 (UTC)

I suppose you could, but it raises what is in my opinion a more relevant question: have you stated anything of meaning? I'd stick to "x exerts more pressure than y" and not attempt to make any claims such as "more powerful" in such ludicrous cases of apples-to-oranges. — Lomn 22:22, 9 January 2009 (UTC)

Okay, forget the word powerful if you want. My question would be if the cnidocyst does indeed exert more pressure at the microscopic level than a bullet, enough to puncture an armor-like material. I've heard that it's able to puncture through the shells of some sea creatures, so that's pretty impressive considering it's just a microscopic needle... Kreachure (talk) 22:33, 9 January 2009 (UTC)

The pressure is high because pressure is force divided by area. The area is TINY - so even though the force is also pretty small - the area is much smaller. So, yeah - the pressure is high...but the force didn't change. Breaking things is about ENERGY - not pressure. Because the mass is so small, there is a microscopic amount of momentum - hence no damage when the cnidocyst (I love typing that word!) hits the body-armor. SteveBaker (talk) 02:21, 10 January 2009 (UTC)

Hmm... well, I guess that makes sense. Thank you. Kreachure (talk) 13:53, 10 January 2009 (UTC)

Protein Engineering

Does anyone have a good classification system for the following methods used to engineer proteins, enzymes in particular: direct evolution (1), rational design (2), site-directed mutagenesis (3), computational protein design algorithms (4), random mutagenesis (5), DNA shuffling (6), RACHITT (7), StEP (8), SCOPE (9), SISDC (10).

I think it's best divided into (1) and (2) and that (1) is sub-divided into (5)-(10) and that (2) is sub-divided into (3) and (4). Is this a good classification or does someone have a better one? 90.221.241.97 (talk) 19:57, 9 January 2009 (UTC)

Don't ignore the part about folding. It will make your classifications more extensive, but more useful. Two proteins that come up identical after processes (1) or (2) can be entirely different animals if they are folded differently. There are a couple of searchable databases around for proteins. Check the archives. We've had a couple of questions from user Seans potato business. 76.97.245.5 (talk) 21:14, 9 January 2009 (UTC)