Wikipedia:Reference desk/Archives/Science/2010 May 12

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May 12

Nernst equation for reaction 2A+ + B ----> B2+ + A2

Take maybe, Ag+ and Zn(0) ...

How do you use the Nernst equation when the donor species and the receiving species give and receive a different amount of electrons? I've tried looking up examples online, but the websites are being obnoxious and giving nice examples like Cu(II) and Zn(II). I'm trying to figure out how you would figure out the reaction quotients (for the ln Q) term when say, Ag+ is oxidising Cu(0) to Cu(II), or Cr(VI) oxidises Fe(II) to Fe(III) and becomes Cr(III) in the process.

Do you set up separate Nernst equations for each half-cell, or write a Nernst equation for the whole reaction? Sometimes they seem to give different results (because of where z gets applied). John Riemann Soong (talk) 00:48, 12 May 2010 (UTC)

You balance the equation, and then use the appropriate cooeficients in the equilibrium value in the Nernst equation. So, for example, say I have silver ions being reduced and copper being oxidized to copper(II). I would write:

2Ag⁺_(aq) + Cu_(s) → 2Ag_(s) + Cu²⁺_(aq).

In this case, n=2, and

K = [Cu²⁺_(aq)] ⁄ [Ag⁺_(aq)]².

I hope that helps; be feel free to ask if you're still confused. Buddy431 (talk) 05:41, 12 May 2010 (UTC)

Controlled criticality accident?

Back a few weeks ago I went on a tour of the TRIGA Mark II nuclear reactor at Kansas State University, they said something about they could do controlled supercriticality or something of the sort, and they had a picture of a nearly-blinding burst of either Cherenkov radiation or some other bright blue-white light, similar to this except extremely bright. How does this (what I'm assuming is a) controlled criticality accident work? Ks0stm ^(T•C•G) 02:55, 12 May 2010 (UTC)

If it is controlled and intentional, than it is not an accident. 174.58.105.234 (talk) 04:29, 12 May 2010 (UTC)

That's not exactly what I was asking... Ks0stm ^(T•C•G) 04:30, 12 May 2010 (UTC)

Like you guessed it's Cherenkov radiation. All they do is remove some of the moderators. The reactor then starts "running", and the Cherenkov radiation happens automatically. It's not really a criticality accident - it's just the normal operation of the reactor. With the moderators you can dial the reactor up and down. A criticality accident and the normal running of a reactor are just different levels of the same thing. Prompt critical is a good article about the difference between the various levels of criticality. Ariel. (talk) 09:29, 12 May 2010 (UTC)

Just noting that you are confusing the control rods with the moderator. They are not the same thing. Control rods control the reaction rate. Moderators change the properties of the neutrons (e.g. slow down fast neutrons, because slow neutrons work better with certain types of reactor fuels). You don't remove the moderator while a reactor is running—it's just part of the reactor core. You can remove control rods (to increase the reaction rate). --Mr.98 (talk) 13:45, 12 May 2010 (UTC)

A nuclear reactor has to go critical to work. Graeme Bartlett (talk) 10:49, 12 May 2010 (UTC)

It's called "pulsing". It's a neat thing you can do with TRIGAs specifically:

The prototype TRIGA (Training, Research, Isotopes, General Atomics) nuclear reactor was commissioned on General Atomics' then new site on May 3, 1958. Known as the TRIGA Mark I reactor, it was originally licensed to operate at a power level of 10 kilowatts, but was soon upgraded to 250 kilowatts. This little reactor, because of its inherently safe features, could also be rapidly "pulsed" to power levels of over 1000 megawatts after which (and without any outside intervention) it would return, in a few thousandths of a second, to a safe low power as a result of the effect of the ubiquitous warm neutrons. This original TRIGA, designated as a nuclear historic landmark because it pioneered the use of unique, inherently safe capabilities in nuclear reactors, operated successfully until 1997, when it was permanently shut down because of its age. The pulsing feature of UZrH fueled reactors, first demonstrated in this prototype TRIGA at General Atomics, are standard among many TRIGA reactors, and special designs of pulsed TRIGA's in use today routinely achieve power levels of 22,000 MW to test the safety of fuels for nuclear power reactors.[1]

Basically you can pull out all of the control rods, it will get supercritical, but because of the way a TRIGA is set up, it will quickly and automatically stop the reaction. (The reason it works is that TRIGA fuel is made so that the hotter it gets, the worse it is at sustaining nuclear reactions. So it basically won't be able to melt down—the more it reacts, the more it automatically starts to correct itself. It's a good thing for a research reactor though it wouldn't work for a power reactor.) Google "TRIGA pulse" and you'll find a lot of pages on it (though most are fairly technical). There are a number of YouTube videos of TRIGAs doing this, including one of the reactor which you toured. --Mr.98 (talk) 13:34, 12 May 2010 (UTC)

There are a number of videos of such pulses on Youtube. --Sean 13:53, 12 May 2010 (UTC)

Awesome, thanks Mr.98 and Sean, that's what I was looking for. That seems to be what they were describing on the tour, and that video of the pulse actually is the KSU reactor. Thanks! Ks0stm ^(T•C•G) 00:39, 13 May 2010 (UTC)

See also void coefficientJabberwalkee (talk) 16:38, 16 May 2010 (UTC)

Bomb bays

How many, if any, internal bomb bays do the F-15 Eagle, F-15E Strike Eagle, F-16 Fighting FalconF/A-18 Hornet, and F/A-18E/F Super Hornet have? --The High Fin Sperm Whale 04:58, 12 May 2010 (UTC)

All of the articles list only the number and configuration of Hardpoints on the aircraft, leading me to believe that none of them have internal bays. Beach drifter (talk) 05:08, 12 May 2010 (UTC)

Al four designs date before the stealth time and at that time a multi role jet was designed that way. Stealth design makes internal bays for bombs and rockets necessary to reduce radar reflections.--Stone (talk) 05:23, 12 May 2010 (UTC)

Interesting question, but I agree with Beach drifter & Stone. I believe that only bombers of that 'vintage' carried weapons(bombs) internally. The fighters would have internal cannon/guns. FYI the F-105 Thunderchief had hardpoints and an internal bomb bay. See Specifications(Armament)
* Bomb bay has something to say about the issue,"Notable exceptions are the F-101, F-102 and F-106 interceptor aircraft, all of which had bomb bays" Where they carried their missiles. It seems they had NO external hardpoints. I thought some of the fighters you mentioned could carry weapons 'semi-recessed' into the fuselage, but can't find any mention on Wikipedia.--220.101.28.25 (talk) 08:20, 12 May 2010 (UTC)

The F-102 and F-106 each had two hardpoints (one under each wing) for drop tanks, but carried all their missiles inside the fuselage. The F-101 had a missile bay in the fuselage, but could also carry missiles (notably the oversized Genie missile) semi-recessed under the fuselage. FWiW 67.170.215.166 (talk) 02:14, 13 May 2010 (UTC)

Interesting 67.170.215.166. Perhaps the articles need slight updates? I specifically searched them for "hardpoints", with no result. Need WP:RS too of course. --220.101.28.25 (talk) 00:28, 14 May 2010 (UTC)

I'll do that tomorrow if I have time. Clear skies to you 67.170.215.166 (talk) 04:22, 14 May 2010 (UTC)

Another polite IP! How nice! Happy Editing! --220.101.28.25 (talk) 05:02, 14 May 2010 (UTC)

Done, check it out if you want. 67.170.215.166 (talk) 07:33, 15 May 2010 (UTC)

I can confirm that neither F15, F16 or F18 have internal bomb bays (I've built flight simulators for all three!). You see them on stealthy planes like the F117 and F22 because the weapons themselves are not stealthy and you'd spot the aircraft on radar if it had them mounted externally. SteveBaker (talk) 15:00, 12 May 2010 (UTC)

External weapons

How do having missiles and bombs carried externally on a stealth aircraft compromise its stealth? How does the radar pick them up? Thanks.--116.71.46.255 (talk) 15:11, 12 May 2010 (UTC)

Radar works by sending out radio waves and seeing what bounces back. When the signal is returned it indicates there's an object in that direction. A stealth aircraft minimize the ability of radar to detect it by being shaped in such a way that most of the radio waves that hit it get reflected off in a different direction than they came from, which means they'll never return to the radar antenna. If you stick objects on the outside, they mess up that shape. The radar will hit these external objects and reflect back to the antenna and make the plane's presence apparent. See also Stealth_aircraft#Detection. Rckrone (talk) 16:45, 12 May 2010 (UTC)

The other important factor is that stealth aircraft are often coated with materials that absorb radar. These coatings are incredibly expensive, so the military doesn't apply them to bombs and missiles. --Carnildo (talk) 01:44, 13 May 2010 (UTC)

Working principle of a corner reflector

All the above. Also, the fins mounted on the missiles very likely make very good reflectors as they are usually at a 90° angle forming, at least, a partial corner reflector. (see also Retroreflector) These very effectively reflect radar directly back to the transmitter. This is likely to be one reason why the tail fins on stealthy aircaft are seemingly never at 90° to the fuselage. Also why some, ie the B2 Spirit bomber have no tail fins. See also Stealth technology/ Radar cross-section (RCS) reductions --220.101.28.25 (talk) 00:50, 14 May 2010 (UTC)

Vulcans, Romulans and Remans

In the Star Trek universe, these three races are all related. Vulcans are the original race with those who would become Romulans leaving the planet (about 5000 years ago) to find their own planet somewhere "out there." Eventually, they do. Surprizingly, we are also introduced to Remans (who live on the sister planet to the Romulans). What does not make sense to me is the significant differences in the appearances of the three races. Given that it is only 5000 years from when the Romulans left Vulcan to the "present" day Trek universe (and an even shorter time for the Reman off shoot), is this enough time to effect the changes we see (especially with the Romulans and Remans)? If I left Earth, travelled to another planet that could sustain me, would my decendents look that much different than those who remained on Earth? —Preceding unsigned comment added by 99.250.117.26 (talk) 05:14, 12 May 2010 (UTC)

I think the underlying question then should be - how much can the external characteristics of a population of humans change in 5,000 years? - I think that's a very interesting question, and I look forward to reading the properly sourced responses! 218.25.32.210 (talk) 06:03, 12 May 2010 (UTC)

It's quite easy to change appearance in a few dozen generations with a breeding programme, as we do with breeds of dog! Dbfirs 07:57, 12 May 2010 (UTC)

QI claims that dogs are unique in that respect - domestic cats don't have anywhere near the variation that dogs do. So they say. 212.219.39.146 (talk) 09:50, 12 May 2010 (UTC)

It is believed that dogs do not originate entirely from a single species, i.e. certain closely related dog-like species from different parts of the world were mixed-in after they became domesticated, which may account for some of the extra variations. Another example of huge changes in physical appearance is of course, the domestic pigeon, a favourite of Darwin. 210.254.117.185 (talk) 10:18, 12 May 2010 (UTC)

Last I heard dogs were domesticated exactly once, and from wolves. That being determined by genetic analysis. --203.202.43.54 (talk) 07:57, 14 May 2010 (UTC)

Remember this is a work of fiction, anything is possible. However there could be a mutation that makes part of the gene expression very variable, or part of the genome very mutable. So radical changes are possible within a species or over a few generations. Graeme Bartlett (talk) 10:48, 12 May 2010 (UTC)

How different are Vulcans and Romulans anyway? They don't appear to be that different in looks, from what I remember just a slightly thicker eye area. Humans vary in eye fold shape too, but are still the same species. Ariel. (talk) 11:06, 12 May 2010 (UTC)

Also see founder effect. 131.111.185.68 (talk) 11:15, 12 May 2010 (UTC)

Have you seen the differences between the Klingons in the original series compared to those in the next generation? That was like 50-100 years difference, so perhaps alien species are really good at changing their appearances in short time scales in the star trek universe. Googlemeister (talk) 13:35, 12 May 2010 (UTC)

Ahem! "We do not discuss this with outsiders!" --Stephan Schulz (talk) 15:26, 12 May 2010 (UTC)

(edit conflict) That was due to a failed genetic experiment, not evolution. Vimescarrot (talk) 15:32, 12 May 2010 (UTC)

First of all, I agree that since Trek is science fiction, they use a certain amount of "literary license" in the story line. Also, the difference in the appearance between a Vulcan and a Romulan is is significantly less than between either of them and Remans. Even here on Earth, the variations between the various races is fairly negligble and, if I understand a National Geographic special I recently watched, took place over many thougsands of years (i.e. 100,000 +). So, I guess I am wondering just how much change one could expect given the relatively short timespan between the people leaving Vulcan and finding Romulus and Remus . . . so as someone earlier stated in rephrasing the question: how much can the external characteristics of a population of humans change in 5,000 years? —Preceding unsigned comment added by 69.77.185.91 (talk) 13:57, 12 May 2010 (UTC)

I think the Founder effect, as linked to above, is the most likely explanation for the descendants of colonists being significantly different from the parent population. The Memory Alpha article on Remus [2] says that the Remens may be descendants of Romulans, but could also be a separate species. The latter certainly seems more likely. --Tango (talk) 14:21, 12 May 2010 (UTC)

5000 years is typically more than 150 generations. A lot can change in that time. Out of Africa is only ~10 times farther back. The Americas have only been populated for ~15000 years. --Stephan Schulz (talk) 15:37, 12 May 2010 (UTC)

To add to the confusion of the origin of the Remans, there are several novels that outline their Vulcan/Romulan origins (i.e. some Romulans betrayed other Romulans who were living on Remus at the time, marooned them there and made slaves of them.)Somehow, the harsh conditions resulted in an appearance significantly different from their Romulan/Vulcan origins - I guess this is what happens when literary liciense goes too far . . . —Preceding unsigned comment added by 69.77.185.91 (talk) 14:46, 12 May 2010 (UTC)

I don't think the Romulans are really that different than the Vulcans physically. (Different skin-tones, slightly different eyebrows and facial structure)

More interesting is the mental differences. Vulcan minds have a hard time coping if they don't adopt a strictly logical way of thinking from a very young age, but on the plus side they get some nifty telepathic abilities.APL (talk) 02:11, 14 May 2010 (UTC)

Jumping

If I want to jump up into the air at 5.4 m/s relative to the ground after one second, do I have to apply an acceleration of 5.4 m/s² (just the Delta-v) or an acceleration of 15.2 m/s² (Delta-v plus defeating 1 g of Earth gravity)? --213.229.148.222 (talk) 08:34, 12 May 2010 (UTC)

If you start at rest (relative to the Earth) and accelerate at a constant rate (relative to the Earth) and after one second your velocity (relative to the Earth) is 5.4 m/s then, by definition, your rate of acceleration (relative to the Earth) is 5.4 m/s². But the constant force required to produce this acceleration is m(g + 5.4) N. Gandalf61 (talk) 08:56, 12 May 2010 (UTC)

It is more likely that your acceleration will be impulse-like, because you can only apply a meaningful force while your feet are in contact with the ground. Because you are not a point-particle, you can continue to change your momentum even in mid-air, but for simplification, consider that effect "negligible." So, if you want to jump off the ground with an initial velocity of 5.4 m/s (which would be pretty darned fast for a human jump), you would undergo an "instantaneous" acceleration (rather, a very abrupt acceleration lasting a few milliseconds or tens of milliseconds), as your legs and knees and feet execute the momentum transfer. It seems reasonable that this acceleration might be as high as 2 or 5 g - in other words, 20 or 50 m/s², but would only last a brief instant. Then, you would have no additional acceleration other than the constant acceleration of gravity, and your jump would slow and you would follow a parabola trajectory until you land on the ground. Since you wanted to have a velocity of 5.4 m/s after one second, you need a much higher initial velocity - we can calculate what that might be using basic physics, but it's safe to say "impossible for a human to jump that fast." Nimur (talk) 10:14, 12 May 2010 (UTC)

The relevant equation is: v = u + a.t where v is your velocity, a is your acceleration, t is the time and u is your initial velocity. There are two 'phases' to your motion and we have to resolve them separately. The first phase is when you start pushing off the ground with some acceleration - the second is when your feet leave the ground and you are in free-fall. However, since gravity slows you down during this second phase, the fastest you'll ever be moving upwards is the instant your feet leave the ground. So that means we know some of the numbers in this equation: v must be 5.4ms^-1, u is zero, but 'a' and 't' are unknowns. Since we have an equation with two unknowns, there must be an infinite number of possible solutions. A very short but very fast acceleration or a more prolonged but gentler one would do. So we need more information...and we have that...the length of your legs. So we can use another equation: d = u.t + 1/2 a.t² (d is 'distance travelled' - the other things are the same as in the previous equation). We know 'd' (the difference in your body height when squatted and when fully extended at the point your feet leave the ground), u is still zero, and we still don't know 'a' and 't'. But now we have two equations with two unknowns and we can solve for that.

When you do that, you get: a = v²/2d. How long are your legs? If we guess ~1 meter then the acceleration is something like 14.6 ms^-2...that's about 1.5g.

The tricky part of your question is about the nature of acceleration versus gravity. Your acceleration is whatever it is - gravity is a force, and your net acceleration is determined by F=m.a (F is the total force, m is your mass, a is the acceleration). To get the desired acceleration (by solving the previous pair of equations) you need to divide the force applied by your leg muscles MINUS the force due to gravity - and divide by your mass.

Of course this is all an approximation - I'm assuming that the force applied by your muscles is the same throughout the jump - which it won't be - and the calculation should really be done separately for your body, your upper and lower legs and your feet because (for example) your feet don't start to accelerate until the very last part of the jump...but in terms of figuring out whether this is even possible, the simplified version of the math is probably good enough.

SteveBaker (talk) 14:53, 12 May 2010 (UTC)

Oh - poop - I forgot that you said "after 1 second" - that makes things more complicated...v=ut + at², we know that u is zero, t is 1 and v is 5.4 so a is 5.4ms^-1 - which is much less acceleration than before - but because d = u.t + 1/2 at², you'd have to be accelerating to the desired speed over a distance of 2.7 meters - which you can't do because your legs aren't that long! So now you'll have to leave the ground at a higher speed - before the 1 second time limit is up and allow gravity to slow you down so that you hit that precise speed at the desired time. SteveBaker (talk) 20:53, 12 May 2010 (UTC)

Experiments in making LCDs

I've been reading about ways of making various display technologies at home, and I came across this video: http://www.tricklife.com/view.php?id=1049 which claims to be instructions on how to make an LCD using a battery, a magnet, water, and sugar. Unfortunately the video is corrupted or something, and it only plays the first 30 seconds. Is anyone familiar with this method? I'm a bit suspicious since I see no polarizing material. Are there any other methods for making something similar? I'd be happy with a single "pixel"-like thing which demonstrates the principle. Internet searches were no help, but maybe my google-fu is weak. —Preceding unsigned comment added by 69.196.132.120 (talk) 08:58, 12 May 2010 (UTC)

Modern LCDs are made using an electroactive polymer that has the property of changing its optical polarization when voltage is applied. Such molecules are not commonplace, though there are many with at least a weak effect. I think it is impractical to make any of these using "kitchen chemistry" - certainly, you need more than just sugar and a battery. For example, MBBA is one such molecule with the electrooptical properties that would make an LCD display possible. 4-Cyano-4'-pentylbiphenyl is a bit more modern, and here is how to make it - but again, hardly something you can do with sugar and a battery. Cholesteryl oleyl carbonate is a biological / organic liquid crystal, but I don't think that it can be made with kitchen ingredients either (our article says it can be found in some hair dyes). I also do not believe that it can be used as the active element in an LCD screen - I think it is more useful during the processing stages. Nimur (talk) 10:19, 12 May 2010 (UTC)

As an aside - an awful lot of those YouTube (and other) "science videos" where someone purports to do something quite amazing with common kitchen chemistry are faked. This is really, really annoying - if there were one category of Internet nastiness that I could wave away with a magic wand...that would be it! SteveBaker (talk) 14:28, 12 May 2010 (UTC)

Thanks for your answers. I eventually found this question on instructables which refers to this video in which Tim Hunkin (hosting The Secret Life of Machines) uses some liquid crystal he got from a lab/manufacturer. I think I'm going to see how well it works to extract the liquid from some displays I have (the black+grey displays in calculators, watches, etc). Failing that, I'll see if anyone will send me some. 75.119.253.30 (talk) 17:30, 12 May 2010 (UTC)

colorblind cuttlefish and camouflage

Since cuttlefish are supposedly colorblind, how are they able to change their own color to match their surroundings? 210.254.117.185 (talk) 10:13, 12 May 2010 (UTC)

There is no requirement that an animal can perceive every aspect of its own actions; for example, humans have a capability to emit odors that they can not smell, and regularly emit infrared radiation that they can not see. The extent to which the cuttlefish is aware of its own colorful pattern may be limited. The color-change reflex is controlled to some extent by the chromatophores themselves, and not by a central "perceptive" nervous system response. Nimur (talk) 10:25, 12 May 2010 (UTC)

So the chromatophore's themselves have some sort of color-sensitive receptor?? 210.254.117.185 (talk) 13:01, 12 May 2010 (UTC)

. You say, "the color-change reflex is controlled to some extent by the chromatophores themselves, and not by a central "perceptive" nervous system response", but the article you linked says "it has been demonstrated that the background adaptation process is vision dependent (it appears the animal needs to be able to see the environment to adapt to it)". --Sean 15:00, 12 May 2010 (UTC)

Would you believe I asked this same exact question on here two years ago? #Cuttlefish_wants_to_cuddle. --Mr.98 (talk) 13:39, 12 May 2010 (UTC)

Cool, that's helpful. Thanks for fishing that out (lol). I'm reminded of the fact that many colorblind people can tell the difference between colors, but are simply unable to name them. Apparently because color is processed multiple times in the brain, and we are only conscious of it once, though there are residual effects of being able to see color below consciousness. I wonder if cuttlefish as well may be aware of color on a different level, though I guess that depends on how they were determined to be "colorblind" in the first place, i.e. if they have the hardware or not. 210.254.117.185 (talk) 14:03, 12 May 2010 (UTC)

I don't think your perception of colorblindness is correct. There are many varieties of colorblindness - relating to the four kinds of receptors we have in our eyes (Red, Green, Blue and "Brightness"). Colorblindness entails one or more of those kinds of receptor being either weak or non-existant. In cases where red, green and blue sensors are all missing - then the person can only see brightnesses - just like looking at an old black-and-white movie on TV. In those cases, it's not a question of being unable to "name" the colors - those people live in a world entirely devoid of color. In other cases (like my son - who has a 'weak green' detector), the person is able to see and name almost all of the colors - except for those that are distinguished by subtle differences in the color range of the defective sensor. My son can easily see and name green, red, yellow and orange - as well as cyan, blue and magenta. BUT (and this is how we found out he was colorblind) can't tell the difference between the very pure red of the LED on a Nintendo Wii that's turned off - and the orange when it's in standby. The difference is evidently a really subtle change in the amount of green light - and his weak green sensor simply can't tell him which is which. He manages perfectly well in 99% of the cases where color perception is important...but does have the annoying habit of leaving his Wii in standby mode instead of turning it off!

So there are many possible kinds of colorblindness - of different degrees of rareness and impediment. But I don't think any of them are cases where the person can distinguish the colors but not name them. For that to be the case, we'd be talking about some kind of brain problem - not colorblindness. SteveBaker (talk) 14:24, 12 May 2010 (UTC)

Some types of colorblindness are caused by brain problems -- the term used is "central colorblindness" or more formally cerebral achromatopsia. The inability to name colors is called color anomia; it may or may not go together with inability to distinguish colors. As you say, though, a person with color anomia but not color agnosia would not usually be considered colorblind. Looie496 (talk) 15:56, 12 May 2010 (UTC)

Yes, I was referring to something like color anomia, not true colorblindness like SteveBaker's son seems to experience with some types of green. So basically it's possible that the colorfish could be color "unaware", though their body reacts to color at a lower level of conciousness (or maybe I should call it "nervousness"), where the cuttlefish doesn't need to be aware of the differences. But, I have to disagree partly with the fact that color agnosiacs are not considered colorblind, because surely there are many inflicted with central colorblindness that simply assume their are physically colorblind, and are never tested properly for their "brain problems". Note: most of what I've read concerning such conditions comes from the writings of Ramachandran, who also describes a condition in which the patient believes they are blind, and can't pass any vision tests, but yet is able to put keys in slots and open doors when ordered to do so, due to their "central blindness". 219.102.220.188 (talk) 00:48, 13 May 2010 (UTC)

survival instinct

Why does the survival instinct exist? What made inanimate matter in the primordial soup want to survive? —Preceding unsigned comment added by Yourmindisthesceneofthecrime (talk • contribs) 13:32, 12 May 2010

If they sunk back into the ooze then we wouldn't be here asking questions and postulating hypotheses. The question is the answer. Vranak (talk) 13:48, 12 May 2010 (UTC)

In a random genetic mix - those that didn't have the "want to survive" genes didn't survive - and those that did have the "want to survive" genes survived. Hence every living thing from that point onward had the "want to survive" genes. If for some reason (mutation, perhaps) a new kind of lifeform appeared that had a defective or missing "want to survive" gene - it would rapidly die out. Hence, evolution favors the present situation.

The precise abiogenesis step that took us from "inanimate matter" to "living thing" is not well understood yet (although there are some excellent hypotheses out there). However, it seems likely that a self-reproducing molecule simply formed from random chemical reactions in the early Earth. That molecule (being able to reproduce) was too simple to "want" anything - but it did reproduce. Since there would be random errors in the copying process, things like "genes" would soon appear - and the molecules that were better able to reproduce would succeed and the molecules that did a terrible job would cease to be around in large numbers. Now you have molecules that are progressively better and better at surviving...it's a bit of a stretch to say that they "want" to survive...but then: Does a bacterium "want" to survive - or is it merely "able" to survive?

SteveBaker (talk) 14:11, 12 May 2010 (UTC)

The Selfish Gene by Richard Dawkins is a great book for discussion of questions like this. Looie496 (talk) 16:34, 12 May 2010 (UTC)

Evolution

I was looking at the plants in my garden today, and I thought why is there so many different types of plants, different shapes, trees grass ferns weeds etc. Plants should evolve to best suite the environment yes? So why don't they all look the same? --ame —Preceding unsigned comment added by NettleSpors (talk • contribs) 13:42, 12 May 2010 (UTC)

I have three answers:

Firstly: Gardens are very artificial things. Go out into a nearby forest and look at the natural setup. Now you find that the plants are much less varied. The reason for that is that people have gone out to far distant habitats all around the world - looking for striking and unusual plants to sell to people who plant gardens. Those plants are not at all well-adapted to the environment where they now find themselves - which is why you have to weed (to shut out more effective - but ugly - plants from competing with yours), water, feed, trim and prune...it's also why you have plants that die without producing offspring and have to be replanted.

Secondly: Evolution is a complicated process. Just as animals can evolve different lifestyles within a single habitat (there are herbivores that exploit plants and carnivores that exploit the herbivores) - so plants may evolve to make a living by being tall and getting high enough to grab the maximum sunlight, or to cope with less sunlight and live on the forest floor. There are many possible 'niches' within a given habitat - and there are a whole lot of different strategies that can server to perpetuate a species. Each niche produces a different-looking plant.

Thirdly: Evolution is a complicated process!! If one plant was used to living in dry grasslands and another had adapted to living in a swamp - and something in the landscape changes to make the whole area become a moist forest - then both kinds of plant have to evolve to living in that new situation. However, they will end up looking different because evolution can only work with what it's got. The dry grassland plant may lose it's adaptation to need less water - and gain the ability to work with less light - but it can still be a "grass-like" plant. The wetland plant evolves the other way - gaining the ability to work with less water. The resulting plants may well be dramatically different - yet equally able to survive. Do that enough times - and you have a wild variety of shapes and forms.

SteveBaker (talk) 14:02, 12 May 2010 (UTC)

Not sure about "Go out into a nearby forest and look at the natural setup. Now you find that the plants are much less varied." What about rainforests? They're are far more diverse than any garden I've ever seen! We should have an article on the maintenance of biodiversity as that is effectively what you are asking - why isn't there an optimum species for each environment and why are there still so many species? It's a hotly debated topic in plant ecology _{(useless article!!)}. There are a couple: unified neutral theory of biodiversity _{(a pretty horrible article though)} and Intermediate Disturbance Hypothesis. This might be of interest (I think the link is free). Broadly speaking I agree with Steve's point that evolution is very complicated - we can't ever really hope to understand it and it doesn't work in a controlled, linear, deliberate or obvious manner! There is a suggestion that species create more species since each one creates new ecological niches for other species (a bit of a circular argument however). That's the basis of this paper which suggests that the diversification of angiosperms (flowering plants) allowed ferns to diversify. Another driver of this may be the Janzen-Connell effect - basically plants may be less likely to survive near their parents due to increased risk of disease and herbivory and because they will use resources (light and nutrients) similarly and this creates space for more species to establish. It's also worth noting that the environment is constantly changing, if one optimum species evolved it would soon go extinct once the environment changed. Even within a species, individuals differ in their ability to withstand a drought and this applies even more so between species (can't find any free papers about this). In an extreme drought (or fire - because some species are adapted for it whereas others are not) some individuals die whereas others survive. All in all this keeps plenty of plants alive, they're more resistant to mass extinctions than animals too as they will happily sit out poor conditions as seeds or spores. Make any sense? 131.111.30.24 (talk) 15:04, 12 May 2010 (UTC)

Niche differentiation is worth a read too and this (and the paper) suggests that we are making the conditions for one species to dominate. Also linked to Steve's first point, moving all those plants around for gardens means they can escape and become invasive species. Some people use the term Homogenocene (as in homogenous) for what may occur in the future (or is happening now) if our actions continue to cause a mass extinction and the world is populated by far fewer species. 131.111.30.24 (talk) 15:27, 12 May 2010 (UTC)

Darwin called it the principle of diversion. In Origin of Species he wrote "We know that it has been experimentally shown that a plot of land will yield a greater weight, if cropped with several species of grasses, than with two or three." This perfectly illustrates the reason why life would tend to diversify rather then homogenize. Vespine (talk) 22:12, 12 May 2010 (UTC)

Funny you should say that, I've got a whole lecture in front of me written to answer whether Darwin was right regarding that exact quotation. It's basically very hard to conduct a good experiment to test it as there are so many uncontrollable variables. Some experiments have found an effect but as the species richness increases the probability of having highly productive species increases, therefore making it more likely that the more diverse systems are more productive. A study at the Cedar Creek Ecosystem Science Reserve found that more diverse plots are more resistant to drought (in terms of the percentage biomass lost) and that they regained their biomass more quickly. But the plots were differentially fertilised, when nitrogen is added, diversity decreases and it also affects root allocation since the plants need fewer roots to acquire equal nitrogen, consequently they are more susceptible to drought as they can't access water! A reanalysis showed that in actual fact, biomass and species richness did not correlate at all. An observational study of Swedish islands found that some ecosystem processes actually decrease with increased diversity. What does this all mean? Things are a lot more complicated than we tend to realise! _{Shout if you want some links to papers}

Vespine you say "This perfectly illustrates the reason why life would tend to diversify rather then homogenize" but what does a single species gain from being in a more productive ecosystem? I'd argue the opposite since herbivory is more likely to occur there. Your point sounds slightly Gaian, as attractive and reasonable a hypothesis that it is, I can't seem to think of a mechanism by which it could work. 86.7.19.159 (talk) 22:50, 12 May 2010 (UTC) (same as 131)

I'm struggling to understand what you are actually trying to say. "Things are a lot more complicated than we tend to realize!" I completely agree, I tend to include that as a unspoken disclaimer in a discussion regarding just about anything really. Of course there must still be a balance. I don't think saying that "increased biodiversity in some places decreases some eco processes" is contrary to anything I said at all. I don't doubt there would be a point where an ecosystem is more or less optimally diversified; obviously having a million species in a square yard of soil isn't going to be optimal.. The question as I read it was why is there 20 species of grass instead of 2. The question "why is there 20 species instead of 40" would lead to a different answer. Secondly, I think this is committing a logical fallacy but humor me for a second: Extrapolate what would happen if there was a "perfect" form and every living thing was striving to evolve to it, in my opinion the flaw in that premise is patently obvious, but that's essentially what the question is asking.. As for "but what does a single species gain from being in a more productive ecosystem?" I think the question it self is absurd, by very definition "more productive" means there is some benefit, if there was nothing to gain it would not be "more productive". Vespine (talk) 00:15, 13 May 2010 (UTC)

By "Things are a lot more complicated" I guess I was meaning that there is never one simple explanation for anything, and this is particularly true in ecology. Whilst at first appearance, increased biodiversity would appear to always be a good thing, when you start to look at it more closely it gets more complicated. You're right that it's obvious why there is no optimum form for everywhere but at the same time we don't have one single way of explaining why there is so much diversity in tropical forests. I stand by the fact that a single plant species doesn't gain from being present in a more productive ecosystem and that there is no inherently good thing about a productive ecosystem. It is beneficial for a single species to be productive as they can produce more seed, but I don't see why it would be better for all the species (please correct me if I am wrong!). Ecosystems could be far more productive than they are, see Miscanthus giganteus as an example, but for whatever reason they aren't. It's worth mentioning intercropping and push-pull technology as situations where a more diverse system in agriculture is more productive than a monoculture. In these situations the species complement each other and I imagine that this also occurs in nature to some degree. 131.111.30.21 (talk) 09:19, 13 May 2010 (UTC)

Going back to the OP, we should also have mentioned that the plants in your garden have been bred selectively to look different by us and this is responsible for the amazing forms you see. 131.111.30.21 (talk) 09:19, 13 May 2010 (UTC)

It's called interspecies dependency. Tigers aren't tigers without a few boars around. Vranak (talk) 02:49, 13 May 2010 (UTC)

Nose hair

How come men's nasal hair starts to grow out of the nose around age 40-45? I understand why puberty causes changes in hair growth, but is there some related hormonal trigger that men experience in their 40s that makes nose hair grow long? Citefixer1965 (talk) 15:24, 12 May 2010 (UTC)

Don't forget ear hair. Deor (talk) 15:29, 12 May 2010 (UTC)

This Straight Dope article addresses both. I've searched for more information myself - it sounds like we don't know! Don't forget eyebrows either! Maybe someone with medical knowledge can explain, my guess would be that it'll be due to changing hormonal balance (testosterone maybe). 131.111.30.24 (talk) 15:43, 12 May 2010 (UTC)

The Neoteny theory proposes that we are a primate foetus that has become sexually mature. As we age more traits similar to a juvenile chimpanzee appear. Like increased hairiness and larger ears. --Digrpat (talk) 17:37, 12 May 2010 (UTC)

Most hair follicles in the body have androgen receptors of various sensitivities. The most sensitive area of skin to respond to even early and mild rise of testosterone is the pubic area, which is why that is usually the first place that hormonal hair grows at puberty. Second is the axillae, which is often the second place that androgenic hair grows at puberty. In other words one can rank all the areas of the human body where the hair thickness changes in response to androgens. There are several dimensions to hormonal hair growth: androgen receptor sensitivity and density, androgen levels, and duration of androgen levels. In addition to the hormonal effects, the obviousness of the hair depends on the density of hair follicles per square cm of skin, and on the darkness of the hair and paleness of the skin. So areas like nostrils and ears will respond to androgens with hair growth, but only after prolonged elevation of androgens (i.e., later in life). We arbitrarily consider puberty to end with reproductive fertility and achievement of adult height but our bodies continue to change in response to various hormones throughout our lives. alteripse (talk) 02:13, 13 May 2010 (UTC)

Volume of air in lungs

Why is the volume of air that we breathe in slightly larger than the volume of air we breathe out? —Preceding unsigned comment added by 138.16.32.88 (talk) 17:11, 12 May 2010 (UTC)

Seems dubious to me. Why do you believe that is true? Looie496 (talk) 17:19, 12 May 2010 (UTC)

CO₂, O₂ and N₂ gases aren't going to be kept in your body so the volume of gas going in should be identical to the volume leaving. More CO₂ than O₂ will leave your body, though, because O₂ is converted to CO₂ in respiration. Regards, --—Cyclonenim | Chat  17:22, 12 May 2010 (UTC)

The O₂ we take in and CO₂ we let out don't necessarily have to be in balance. It depends on the ratio of carbon and oxygen in what's being broken down. For carbohydrates they should be roughly balanced, but breaking down fats would take a lot more outside oxygen per carbon I think, which would make the volume being breathed in larger. On the other hand, your out going breath probably has more water vapor in it unless it's really humid out, which would work the other way. I don't have any idea what the magnitudes of either of these effects would be. Rckrone (talk) 17:47, 12 May 2010 (UTC)

That's correct, it's called the respiratory ratio. This is one of the few free sources I can find. For pure carbs it is 1 as they have the formula CH2O but for fats with almost no O it is 0.7. We burn about half and half normally so ours is 0.85. Since exhaled air is only about 4% CO₂ this variation can't make a great deal of difference to the volume of air. 86.7.19.159 (talk) 19:28, 12 May 2010 (UTC)

PV=NRT, so if the air being breathed out is warmed by its trip through the respiratory passages and lungs, its volume will be larger exhaled, even if the same number of molecules are present. The amount of water vapor in exhaled air is likely larger than in inhaled, meaning N is also likely to be larger. Edison (talk) 18:23, 12 May 2010 (UTC)

But CO2 is not an ideal gas. Googlemeister (talk) 14:28, 13 May 2010 (UTC)

But N and T are larger. And are the inspired gases themselves "ideal?"How does carbon dioxide depart from ideal gas characteristics? Surely not by being immune to temperature changes with respect to its volume. When a balloon is filled with carbon dioxide and cooled in liquid nitrogen, its volume decreases dramatically before it solidifies. Edison (talk) 18:51, 13 May 2010 (UTC)

To Googlemeister: The real gases behave like ideal gases for any non-extreme temperature and pressure conditions. At anything humans can survive in, for any standard component of air, a real gas will not deviate enough from that of an ideal gas to make any substantial difference in the numbers. --Jayron32 20:42, 13 May 2010 (UTC)

I assume it takes more energy to breathe in than to breathe out (relaxation of muscles?), so the extra effort required might give the impression of being "larger". 219.102.220.188 (talk) 05:01, 13 May 2010 (UTC)

From Pulmonary surfactant#Compliance:

"Measurements of lung volume obtained during the controlled inflation/deflation of a normal lung show that the volumes obtained during deflation exceed those during inflation, at a given pressure. This difference in inflation and deflation volumes at a given pressure is called hysteresis and is due to the air-water surface tension that occurs at the beginning of inflation."

See the article for the rest of the details. Ariel. (talk) 22:21, 13 May 2010 (UTC)

Dark energy & dark matter

what relationship does dark energy and dark matter have with each other? —Preceding unsigned comment added by 165.212.189.187 (talk) 17:25, 12 May 2010 (UTC)

we infer their existence from the study of astronomy. —Preceding unsigned comment added by 122.169.152.60 (talk) 18:12, 12 May 2010 (UTC)

Oh, I understand. —Preceding unsigned comment added by 165.212.189.187 (talk) 18:13, 12 May 2010 (UTC) what relationship does dark energy and dark matter have with each other? —Preceding unsigned comment added by 165.212.189.187 (talk) 18:14, 12 May 2010 (UTC)

First, have you read our articles on dark energy and dark matter? We're not really sure what they are, as we can't directly observe them (that's the "dark" in the name), and proposed indirect observations aren't universally recognized as being valid. Our article on the Lambda-CDM model of cosmology lays out in short form what physical effects are believed to be the result of dark matter and dark energy. As for the relationship between the two, though, the first response is a fairly good one. We infer the existence of both, and as we don't really know what either of them truly are, we can't compare them much further. — Lomn 19:15, 12 May 2010 (UTC)

(edit conflict) :There is probably very little relationship between them (less than between ordinary energy and ordinary matter). Dark matter was so-called because we can't see it. Dark energy was so-called because "dark" came to mean "mysterious", not because it has any connection with dark matter. Then Dark flow was named for the same reason. It is still possible that none of them really exist, but we will need a very clever "theory of everything" to explain the effects without them. Dbfirs 19:18, 12 May 2010 (UTC)

... so does E still = MC², when the M is the mass of dark matter? Can we hope for a dark matter atomic bomb in future wars? Adambrowne666 (talk) 21:48, 12 May 2010 (UTC)

If it really is mass matter, then yes, E still = mc². But that doesn't tell you how to actually perform that conversion, and for something as elusive and non-interacting as dark matter may be, that may not be possible. -- Finlay McWalter • Talk 22:08, 12 May 2010 (UTC)

E=mc² is always applicable. Dauto (talk) 22:30, 12 May 2010 (UTC)

But it doesn't mean you can make atom bombs out of everything. Technically if you converted the mass of your foot into pure energy it would blow a city all to hell. The thing is, you can't make that conversion directly, generally speaking. Nuclear fission and fusion are something of the exception as they allow you to actually convert a significant (but still small) amount of mass into energy in a useful and deliberate way. --Mr.98 (talk) 22:37, 12 May 2010 (UTC)

Agreed. The dark matter bomb idea is complete nonsense. Dauto (talk) 22:44, 12 May 2010 (UTC)

That's what makes it a good idea. Adambrowne666 (talk) 23:43, 12 May 2010 (UTC)

Being nonsense makes it a good idea? Are you talking about reallity or science fiction? Dauto (talk) 23:56, 12 May 2010 (UTC)

I'm more interested in why we should be "hoping" for more powerful weapons of mass destruction in the next war... --Tango (talk) 01:00, 13 May 2010 (UTC)

Yeah, sorry - wasn't being clear - I just like silly ideas, and yes, I'm talking science fiction. When I wrote it, I was being playful, but of course that doesn't necesserily come across in this context. Adambrowne666 (talk) 01:00, 13 May 2010 (UTC) - and hope was used playfully too - but maybe we should hope for it - I'm imagining a WIMP bomb that sends out a huge burst of completely undetectable energy that not only leaves buildings intact, like the neutron bomb, but also has completely no effect on any life forms.

Is dark matter out there or in here?

The dark matter article is very good, but I still wonder where the stuff is. Is it out there in space - the connective tissue of the large-scale structure of the universe - or is it all-pervading? Is there some here in my room, or do I have to go farther afield to not see it?

Thanks Adambrowne666 (talk) 21:44, 12 May 2010 (UTC)

It's very possibly everywhere, or distributed with some structure. We don't know what it is (and to be honest we don't really know that it exists), and we can't (well, maybe) detect it. If dark matter exists, and if it consists of WIMPs, then there might very well be bunches of it drifting ineffectually through you right now; there are, after all, heaps of other particles that really do exist travelling through you, to similarly little effect. -- Finlay McWalter • Talk 21:55, 12 May 2010 (UTC)

The best candidate we have for dark matter are weakly interacting massive particles (WIMPs) in which case gazillions of them went through your body during the time it took you to read this post. Dauto (talk) 22:27, 12 May 2010 (UTC)

Gazillions? No. The "M" in WIMP is for massive. If the WIMP scale is somewhere in the range 1 - 1000 GeV, as often assumed, then the universal density is of order 1 per m³. Similarly, because they are massive, they would be relatively slow moving (on astronomical scales anyway). The density should increase in deep gravity wells, like galaxies and star systems, but the number passing through any person in any instant would still be relatively small. Dragons flight (talk) 01:43, 13 May 2010 (UTC)

Actually the local dark matter density is close to $\rho \sim 0.3GeV/cm^{3}\,$ and with a tipical speed of $v\sim 270km/s\,$ we get a flux of $\phi \sim {\frac {100GeV}{m_{NEUTRALINO}}}\times 10^{5}cm^{-2}s^{-1}$ which can easily put the number of neutralinos passing through a human in the range of 100 million per second. Dauto (talk) 02:55, 13 May 2010 (UTC)

"Massive" in physics doesn't mean "very big", it just means "has mass". There is no requirement for them to be moving slowly, apart from being slower than the speed of light. --Tango (talk) 10:22, 13 May 2010 (UTC)

No, "massive" in WIMPS actually does mean very big. The term was chosen to contrast WIMPS with neutrinos and other forms of light dark matter that had low mass per particle. Similarly, if you assume dark matter (whatever its form) was non-gravitationally decoupled from the rest of matter in the early instants after the Big Bang, then its mean temperature in the modern universe would be the same order of magnitude as the cosmic microwave background and the cosmic neutrino background. For a massive particle, that implies a velocity much less than the speed of light (hence "slow"), while neutrinos and other forms of light dark matter would still have speeds approaching the speed of light. My mistake above was not appreciating that being in a galaxy raises both the average density and the average speed of the WIMPS by many orders of magnitude, so that the flux in our galaxy is about 10⁹ times the flux in intergalactic space. Dragons flight (talk) 19:37, 13 May 2010 (UTC)

Thanks both of you for v prompt and useful answers Adambrowne666 (talk) 01:08, 13 May 2010 (UTC)

And if the dark matter is neutrinos with mass then the number passing through a human may be about a trillion times more. Graeme Bartlett (talk) 09:14, 13 May 2010 (UTC)

So, a trillion gazillion. Comet Tuttle (talk) 16:53, 13 May 2010 (UTC)