Wikipedia:Reference desk/Archives/Science/2008 August 27

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August 27

Springs and simple harmonic motion

Okay, here's the thing. Physicists model the motion of a block attached to a spring using a sinusiodal function, or simple harmonic motion. I'm fine with this, but why can't the motion of the block be worked out from Newtonian mechanics? I've tried to do it, and haven't gotten very far, but it should be feasible. Normally I wouldn't have a problem, but then my teacher showed that, if our guess of the motion of a spring was correct, the angular frequency ω must equal sqrt(k/m), and used this to show that the amplitude of the initial compression doesn't affect the the period. But isn't this bad physics? After all, it could be that our guess of the motion of the block on the spring was wrong. If I'm not explaining myself well, just let me know. Thanks! —Preceding unsigned comment added by 65.92.231.82 (talk) 00:55, 27 August 2008 (UTC)

It is done through Newtonian mechanics - you set up the differential equation, $m{\ddot {x}}=mg-kx$ which comes from Newton's Second Law of Motion. You can then make the substitution $X=x-mg/k$ and substitute that in to get an equation of simple harmonic motion. Confusing Manifestation(Say hi!) 01:28, 27 August 2008 (UTC)

Can you give more details. I'm trying it now, but the d^2 never disappears, and the cosines never apprears. —Preceding unsigned comment added by 65.92.231.82 (talk) 02:27, 27 August 2008 (UTC)

The key equation of SHM is ${\ddot {x}}=-ax$ (which you'll have after the substitution suggested by ConMan - the a will be replaced by an appropriate constant of proportionality involving ks and ms), that is acceleration is proportional to displacement and in the opposite direction. You then simply observe that the sine (or cosine - which one you use depends on boundary conditions) function fits that equation, so you can use it as a solution. Just assume that $x=A\sin(\omega t)$ (this is called an "ansatz"), substitute it in and solve for the constants, then you have your answer. --Tango (talk) 02:40, 27 August 2008 (UTC)

Is this (using an ansatz) the only way of getting the equation? —Preceding unsigned comment added by 65.92.231.82 (talk) 02:55, 27 August 2008 (UTC)

It's the only way I know of. It's certainly the easiest. --Tango (talk) 03:40, 27 August 2008 (UTC)

SEPARATION....OF....VARIABLES. GAHHH. This is the VERY FIRST TECHNIQUE THEY TEACH YOU FOR SOLVING DIFFERENTIAL EQUATIONS. YOU LEARN IT DURING YOUR FIRST SEMESTER OF INTRODUCTORY CALCULUS. AND THEN YOU GO OFF AND GET ADVANCED DEGREES IN ENGINEERING OR APPLIED MATHEMATICS AND LEARN FOURIER TRANSFORMS AND LAPLACE TRANSFORMS AND NUMERIC SOLUTIONS AND FIFTY NINE VARIATIONS ON HOW TO SOLVE DIFFERENTIAL EQUATIONS ... AND YOU FORGET SEPARATION OF VARIABLES. Nimur (talk) 21:36, 27 August 2008 (UTC)

Firstly, calm down! There is no need to shout. Secondly, it's been a while since I learned how to separate variables and I'm probably just being blind, but how do you separate a 2nd derivative? What am I missing (unless you mean to use ConMan's substitution first, in which there really wasn't a need to shout since he'd already said it)? --Tango (talk) 21:56, 27 August 2008 (UTC)

It's possible to do using the substitution ${\ddot {x}}={\dot {x}}{\frac {d{\dot {x}}}{dx}}$ and a bunch of rearranging (and fiddling around with a plus-or-minus sign), but I agree the ansatz is much neater. More generally, you could use an exponential ansatz, as long as you're prepared to work with complex numbers (and know the relationship between the exponential and trigonometric functions). Confusing Manifestation(Say hi!) 05:10, 27 August 2008 (UTC)

There is a very good underlying question here. We know that $x=A\sin(\omega t)$ or, more generally, $x=A\sin(\omega t)+B\cos(\omega t)$ gives a family of solutions to the equation of motion - but how do we know that this covers the whole solution space ? How do we know that there isn't some set of initial conditions that will result in an entirely different solution with very different behaviour ? Well, in this particular case we know that the differential equation is linear, which allows us to use the superposition principle to create a two dimensional family of solutions which we are sure covers the whole solution space. But if the equation of motion is non-linear (if, for example, we exceeded the spring's proportional limit) then it becomes much more difficult to know that we have a complete family of solutions (or even to find any exact solutions in the first place). This is why physicists and engineers will always attempt to linearise a problem if they possibly can.Gandalf61 (talk) 10:19, 27 August 2008 (UTC)

Is it obvious (I know it's true) that linearity immediately implies a 2d solution space? I might be being unusually stupid, but I don't see it. Algebraist 22:04, 27 August 2008 (UTC)

It's not obvious to me, but that's not saying a lot - I avoid differential equations when I can help it! --Tango (talk) 22:17, 27 August 2008 (UTC)

So do I, and (since I also like a big hefty result) I would prove this with the Picard-Lindelöf theorem, but that isn't obvious and doesn't require linearity. Algebraist 22:20, 27 August 2008 (UTC)

Obviously we only have a 2 dimensional solution space if we have a 2^nd order linear d.e., not for all linear d.e.s. For the general case, if f(x) is a solution of a n^th order linear d.e. then the n^th derivative and above are expressible as a linear combination of f and its first n-1 derivatives. So if f is well-behaved enough to have a Taylor series expansion, doesn't it follow that the values of the first n coefficients in the Taylor series uniquely determine the rest of the coefficients, and hence uniquely determine f, and so we have an n dimensional solution space ? Gandalf61 (talk) 16:11, 28 August 2008 (UTC)

I think the sinusoidal representation is the simplest solution to understand. All motions can be broken down into sine and cosine waves by Fourier analysis any way. Its just that in a linear spring mass system, there are no harmonics above the fundamental. —Preceding unsigned comment added by LargoRhythm (talk • contribs) 21:44, 27 August 2008 (UTC)

Yawning

I was yawning earlier today, twice, while other people were yawning. It made me wonder, why is yawning contagious? —Preceding unsigned comment added by Earthan Philosopher (talk • contribs) 03:18, 27 August 2008 (UTC)

See Yawn#Contagiousness, in short - no-one knows. Nanonic (talk) 03:24, 27 August 2008 (UTC)

The cited article actually agrees with original research and common experience: yawning is highly contagious. Edison2 (talk) 03:57, 27 August 2008 (UTC)

Yep - I'm pretty sure we know it's contageous. I believe there was a Science Friday piece on NPR that talked about this. What that show said was that yawning is nothing to directly do with tiredness - it's body-language that means something like "We all need to stop what we're doing and do something else now"...which could include going to bed. The reason it's contagious is because other people are subconsciously agreeing that there needs to be a change of group activity. SteveBaker (talk) 04:31, 27 August 2008 (UTC)

Okay I wrote out a response but lost it since it was blocked. Anyway I'm rather surprised about the article, it mentions yawning in non-human animals but mostly seems to treat these as seperate issues. To me that doesn't make much sense, I see no reason to presume humans are special here, whatever reasons for yawning hold for us likely hold for at least some other animals particularly those close related to us [1]. There are quite a lot of theories of why animals yawn [2], one of them is to show off their teeth. This would also explain why yawning is contagious, if another animal is showing off it's teeth you'd want to as well. Incidentally I came across this [3] paper of a Biology 103 student "We cannot be certain that humans have evolved from monkeys" do people really right that sort of thing in Biology papers? Nil Einne (talk) 08:03, 27 August 2008 (UTC)

I was under the impression that we can be certain that humans aren't descended from monkeys, but humans and monkeys are both descended from some proto-simian. Algebraist 10:45, 27 August 2008 (UTC)

I don't know much about the details of yawning, but the picture in that article could make a great lolcat. the wub "?!" 12:09, 27 August 2008 (UTC)

(Humans are a member of the Ape family - apes are not monkeys) Well, we aren't descended from any living species of ape. All apes are descended from a common antecedent - but that antecedent must in turn have been an animal that you would describe as an ape. That in turn must have descended from some kind of a simian (a "monkey") - but, again, probably not any living species. So the correct statement is: "Humans are descended from an animal that would be classified as an ape. Humans are not descended from any living species of ape." - I don't quite know why people fixate on "monkey" - the closest classification is "ape" and there are plenty of earlier species we descended via - so we're also descended from small furry mammals, fish-like things...bacteria. SteveBaker (talk) 13:38, 27 August 2008 (UTC)

I think the problem is most people don't understand that apes are usually not considered monkeys, particularly historically when the monkey thing first arose nor do they understand that monkeys (and apes) nowadays are not in fact the same as the ancesteral 'monkeys' (and apes) we all evolved from we so from their POV we are descended from historic modern day monkeys and we get silly questions like why did monkeys stop evolving (what?). (Of course it gets worse when they think humans are the end all of evolution and so ask why monkeys don't evolve into humans but that's another issue.) I'm still rather surprised the student thought it wise to demonstrate that ignorance in a biology paper but anyway... Nil Einne (talk) 20:04, 27 August 2008 (UTC)

I was told that we yawn because our brain lacksz oxygen. Philosophia X Known(Philosophia X Known) 15:06, 27 August 2008 (UTC)--Earthan Philosopher

No - that would simply cause a slightly increased rate of respiration. Lack of oxygen in the brain is, however the cause of ridiculously large fonts in signatures. SteveBaker (talk) 03:54, 28 August 2008 (UTC)

Its psychological. Just take a look at this word.

Y-A-W-N and again Y-A-W-N and again Y-A-W-N

Now dont you feel like yawning? (I do --- and did it) —Preceding unsigned comment added by 79.76.200.98 (talk) 01:54, 29 August 2008 (UTC)

man without a face

hi, on channel 7 last night there was a story about a man (or kid?) with a strange growth on his face. Does anyone know if we have an article on this, and what is the condition called? 203.35.135.133 (talk) 07:38, 27 August 2008 (UTC)

I didn't see that report - but some possibilities are Proteus syndrome, von Recklinghausen's disease, Elephantiasis, Neurofibromatosis. SteveBaker (talk) 13:29, 27 August 2008 (UTC)

The program might have been aboutJoseph Merrick.

Wanderer57 (talk) 13:33, 27 August 2008 (UTC)

(That's what I was thinking - and that's where I got the list of diseases from!) SteveBaker (talk) 14:58, 27 August 2008 (UTC)

It might also be McCune-Albright syndrome or polyostotic fibrous dysplasia as shown on television recently in some countries with the case of Marlie Casseus, a young Haitian girl who had an 18 pound "growth" removed from her face. Nanonic (talk) 15:06, 27 August 2008 (UTC)

And strangely enough, being Wikipedia, we do have a fair few articles on people known for little more than having an odd tumour. Jose Mestre was featured on a Discovery Channel program called The Man with No Face in which he underwent surgery to have an enormous abnormal growth removed from his face.[4] Nanonic (talk) 15:12, 27 August 2008 (UTC)

Which was on the TV series My Shocking Story which is being shown on the Seven Network in Australia, so that's probably the person the original poster was talking about. Also see Mark Tatum who had to have his face effectively removed because of mucormycosis. Graham87 16:00, 27 August 2008 (UTC)

Cat Eyes

Do cats have a second set of eyelids under their regular ones? A little while ago I was petting my cat, and his eyes opened a bit, and there was skin covering them, which opened when I woke him up. Black Carrot (talk) 08:05, 27 August 2008 (UTC)

Sounds like the nictitating membrane. Algebraist 08:20, 27 August 2008 (UTC)

It's worth noting that if you can still see the membrane on your cat, you should take it to see a veterinarian. It's usually a sign of illness in cats. —Cyclonenim (talk · contribs) 11:29, 27 August 2008 (UTC)

Agree, this sounds like an unusual appearance and you should consult a veterinarian. Otolemur crassicaudatus (talk) 15:58, 27 August 2008 (UTC)

I think that's a bit hasty. It only happened once, and it fits the conditions mentioned in the article - he was asleep, and his eyelids slid open a bit. Thanks for the reference. Black Carrot (talk) 03:27, 28 August 2008 (UTC)

Can tapirs pick things up with their nose?

I asked this on the miscellaneous reference desk a while ago but no-one really knew - basically, can they use their nose anything like how an elephant uses his trunk? Can they pick up food and pop it into their mouths? Can they hold objects with their noses? Bradley10 (talk) 09:24, 27 August 2008 (UTC)

This National Geographic video shows them using their noses at least to assist in getting food into their mouths. Fribbler (talk) 11:35, 27 August 2008 (UTC)

Jurassic Park question

Is what they did in Jurassic Park possible if we did have any dinosaur blood? I know that the mosquito/amber technique wouldn't actually work, but could you, say, clone a dodo from the taxidermy dodos they have in Tring? Or could they make some new Yahzee River Dolphins? Bradley10 (talk) 09:27, 27 August 2008 (UTC)

DNA doesn't last forever - I don't think the mosquito/amber trick does work. While the shape and tissues of the mosquito are still there - the actual chemical composition of the DNA in the blood in it's stomach is completely wrecked. This is acknowledged in Jurassic Park too - they claim that they had to carefully reassemble the DNA - and fill in the missing bits with Frog DNA (this actually turns out to be the reason for the downfall of the park - most people miss that point in all of the action!)

A Dodo is much more do-able - the last viable DNA is only 350 or so years old, so perhaps it could be made to work. The Yangtze River dolphin is even easier because the DNA may still actually exist in the last few animals.

But using this technique to bring a species back is problematic. To get a viable breeding colony requires a sufficiently diverse gene pool. It's not enough to have one male and one female because all of their offspring would share genes from the same set of two archetypes - and the resulting in-breeding would soon produce all sorts of major health problems. Opinions vary on the minumum number of individuals needed - I heard the number 50 at one time - but a lot depends on how genetically diverse those 50 individuals are - and on how closely scientists could control their subsequent breeding to maximize diversity over the succeeding generations. We probably don't have DNA from 50 Dodo's - and we might not have it from 50 River Dolphins either.

With Jurassic Park, there are even bigger problems - the plants that the herbivores ate are probably all extinct - or perhaps have evolved chemical defenses that the dinosaurs would not be able to counteract (this too comes up in the movie - but very briefly). The idea that the T-Rex can survive on a diet of goat and lawyer is ridiculous - they'd need contemporary animals, which in a real Jurassic Park would be worth vastly too much money to feed them to carnivores. There might also be issues with them surviving modern diseases - but it's also possible that their great antiquity would mean that modern diseases were not able to infect them. It's hard to say. Worst of all - the amount of oxygen in our atmosphere is much less than it was in Jurassic times - the odds are good that these gigantic creatures wouldn't have sufficient lung capacity to survive at all in the modern world.

Another issue (which is carefully skirted in Jurassic Park - but which would affect the Dodo and River Dolphin too) is that having the DNA isn't enough. You also need to turn that DNA into a fertilised egg cell and implant it into the womb of a suitable donor species. In the case of a Yangtze River dolphin - you might be able to implant the egg into a Ganges River dolphin (or one of the other handful of river dolphin species) - but those are also under pressure. You probably can't use one of the more common oceanic dolphins as a surrogate because they live in salt water and river dolphins don't. Same problem with the Dodo - can you find a sufficiently close surrogate mother bird who can lay an egg containing the right nutrients, of sufficient size to contain the chick of a 50 pound bird? The nearest living relatives of the Dodo are pigeons...so no hope there. Perhaps some other large, flightless bird would be able to form a large enough egg - but there is no guarantee that it would have the right shell thickness with the right amount of oxygen transport and the right nutritional stuff.

With dinosaurs, you're in deep problems there. There are no relatives of the dinosaurs left to act as surrogates. This is quietly swept under the carpet in Jurassic Park.

There are some strong candidates for "bringing back" - I think the Mammoth is the most likely. Modern elephants are probably "close enough" to birth a mammoth calf - and we have freeze-dried meat with (perhaps) viable DNA from a significant number of individuals to make a breeding herd. Mammoths lived in sufficiently recent history that diet and such like wouldn't be a major issue.

It's an interesting matter - I think we'll see some of this kind of thing happening...but almost certainly not with Dinoasaurs.

SteveBaker (talk) 13:16, 27 August 2008 (UTC)

This is intriguing. Thank you.

I'm curious about your point that a T. rex could not survive on a delicious diet of modern goats and lawyers. Based on no knowledge of the matter at all, my impression was that an ancient carnivore such as a dinosaur could live on modern reptiles or mammals. What dietary requirements might be missing? Presumably the fat and protein in modern animals would provide the necessary energy supply and amino acids for growth (or am I wrong on that point as well?) Wanderer57 (talk) 13:59, 27 August 2008 (UTC)

No doubt the proteins and amino acids are there - but who knows what else too? Perhaps there are missing 'trace elements'? Look at modern animals: A lion can't live if fed only dog food (believe it or not - I know someone who tried that!)...and lions and dogs those are both modern carnivores. Chocolate is poisonous to dogs. Who knows what wierd stuff a dinosaur needs in it's diet? Who knows what stuff in modern foods would be poisonous to it?

Let's do a thought experiment. Consider even a human - cloned into an alien society a few million years in the future when humans and all of the apes and monkeys are long-extinct and giant super-intelligent cockroaches are now running the place. They find a mosquito trapped in amber with human blood in it's gut...they do the Jurassic Park thing and make a baby...so what happens?

The baby is brought into the world from an artificial placenta in an utterly sterile environment to avoid infection. They roach scientists have carefully researched all of the foods humans ate and they've even cloned tomatoes, corn, cows, etc. They somehow reproduce all of the nutrients present in human milk and make sure the baby gets all of that good stuff. But the scientists rapidly discover that the kid's blood won't clot. They have no clue why. They've double-checked the diet - cloned all the right foods - but eventually it dies. Well, maybe there was a cloning problem - maybe the DNA they got was from a haemophiliac. But no. They try this a dozen times with a dozen different clones from different DNA sources - always the exact same problem. They are totally at a loss.

What happened? Well, they cloned the human - but they didn't clone any "gut flora" - the 300 different species of bacteria that are specialised to live in the intestines of humans. A baby naturally gets those from it's mother - through all sorts of mechanisms. But a clone grown in a sterile lab a million years from now wouldn't pick them up. Our gut flora provide us with vitamin K2 - which is needed for blood clotting. No gut flora (or the wrong kind of gut flora or something that's poisoning the gut flora) - no K2 - the clone dies.

How would those future alien scientists figure that out with no living humans or human-descendants to study? Even if they do figure it out - perhaps no suitable bacteria exist in their future world that could substitute for the ones we get naturally. If there are 300 species of them living in our gut - then they would need an ungodly amount of research to figure out which ones they need to clone (and where the heck they'd get the DNA from is anyone's guess) in order to "fix" the poor clone's vitamin K2 deficiency.

We have no clue what subtle things like that we'd have to provide to a baby dinosaur...it's very likely we'd miss a whole bunch of things - even if we DID clone all of the right food plants and such. The problems of raising a creature from the Jurassic would be overwhelming...not just that some species of berry in the park happens to be poisonous - as chocolate is to a dog.

SteveBaker (talk) 14:53, 27 August 2008 (UTC)

Also, what would happen if the aliens used DNA from one of the uneaten lawyers? They'd get their butts sued off for negligent cloning over the blood clotting issue. Litigious Park! Franamax (talk) 18:21, 27 August 2008 (UTC)

The only (partly) serious attempt I know of to clone an extinct animal is that of the Thylacine which survived until the 1930s. You may want to read the article for some of the challenges faced, and this is with an animal relatively recently extinct Nil Einne (talk) 19:45, 27 August 2008 (UTC)

P.S. Just remembered after reading SB's post there has ben some talking regarding the Woolly mammoth too and this is mentioned in the article although I don't think there is a specific effort yet Nil Einne (talk) 19:51, 27 August 2008 (UTC)

Is there any animal which lacks self-preservation instinct?

So that's the question: does any animal which lacks survival instinct, and survives just "by chance"? Maybe sea sponges? Leptictidium (mt) 11:31, 27 August 2008 (UTC)

Sea sponges don't have a nervous system - they certainly don't have a brain - so they lack pretty much ALL instinct. So you've certainly answered your own question there. In general, there are lots of animals that don't have brains - or whose brains are far to primitive - so we could probably form a long list that would meet your criterion. But you're probably thinking of higher animals - so let's look in that direction a bit. I'm not sure what you mean by "survival instinct". Survival isn't a single ability - it's a HUGE range of abilities - and "instinct" implies something we're born with - not learned behavior. Humans lack the instinctive ability to eat the right things and exercise properly - that certainly affects our ability to survive in SOME circumstances - yet even newborn babies have the instinct to hold on tightly to your fingers if you try to lift them up by their hands. So to find an animal that lacks some survival instincts is easy - probably all animals have some gaps - but to find one that has no instincts for surviving any set of circumstances probably does require finding one with almost no brain at all. SteveBaker (talk) 12:49, 27 August 2008 (UTC)

Thank you. Leptictidium (mt) 12:52, 27 August 2008 (UTC)

Your body doesn't crave certain food when it is missing essential nutrients? I most certainly do have instincts for nutrition and exercise. It is only through years of practice that we manage to suppress those instincts. Plasticup ^T/C 13:52, 27 August 2008 (UTC)

The problem is that we evolved in a time when certain high-energy foods (animal fats for example) were in exceedingly short supply. We have the "instincts" to eat large quantities of those foods whenever they are available - but they were so rare and hard to obtain without taking a lot of exercise - that it was impossible to overeat on a routine basis. Therefore we never evolved a mechanism to stop us from eating them when we start to get fat. In a world where you needed to put on a few pounds in the summer in order to survive a long, hard winter - having an instinct to NOT stuff our faces with egg, bacon and cheese McMuffins would have been pretty fatal - so it would be evolved away in no time flat. Worse still - it's pretty clear that we've evolved to crave foods that have high nutritional content - so we not only lack an instinct NOT to over eat - but we also HAVE an instinct to shovel down as much fatty food as we can find! Now we know (intellectually) how bad this instinct is - we can use our big-brain intellects to fight against it...but (for some people at least) it's tough.

It's a similar deal with exercise - we didn't need to evolve a mechanism for craving "pointless" exercise because we got plenty of exercise doing our daily food hunting and the issue of "Death by under-exercise" simply never needed a "survival instinct". Now we no longer do that by necessity - we pretty much lack any instinctive desire to leap on a treadmill a couple of times a week. SteveBaker (talk) 14:13, 27 August 2008 (UTC)

Glaucoma / abd pain

While reading Cope's "Early Diagnosis of the Acute Abdomen", a trusted reference on the surgical abdomen, I came across the following statement: ...the observer must remember that certain extra-abdominal conditions may cause deceptive pain within the abdomen; thus...even acute glaucoma may temporarily mislead the practitioner. Can anyone explain how glaucoma could possible be misinterpreted as an acute abdomen? Tuckerekcut (talk) 16:38, 27 August 2008 (UTC)

The short answer is referred pain—conditions which cause pain in one of the body to present as pain elsewhere. The mechanism of pain referral is not well-characterized, but our article addresses some possibilities. This article notes that referred pain in the abdomen can be caused by acute angle-closre glaucoma, and is symptomatic of a loss of blood supply to the eyeball. TenOfAllTrades(talk) 17:48, 27 August 2008 (UTC)

For anyone else interested in a more complete answer (though your short answer is appreciated Ten), this [5] has a well thought out mechanism. In short, Noxious stimulation of trigeminal nerve afferents activates the paratrigeminal nuclei in the medulla with secondary stimulation of the vagus nerve. Tuckerekcut (talk) 18:23, 27 August 2008 (UTC)

Wow, and I thought computer-speak was nonsensical =P --mboverload@ 04:36, 28 August 2008 (UTC)

What happens when blood goes into tissue?

 Done

I know, I know, I know - no medical advice!!! So use some discretion here - but I can't seem to find anything on google..

A moment after I had some blood taken for tests, I noticed a large bulge near the site. Apparently the blood had (at some point) flown into tissue.

Any information I can have on this? Does blood typically get absorbed? How does it get absorbed?

Thanks Rfwoolf (talk) 18:18, 27 August 2008 (UTC)

Why ask if you know we can't answer? It could be a bruise, or it could be something entirely different. If you are seriously concerned about it, please seek the advice of a physician. --Russoc4 (talk) 18:25, 27 August 2008 (UTC)

On the contrary you can answer general medical questions so long as it isn't tantamount to medical advice. My question is: What happens when blood is injected (leaked) into tissue? Does it get absorbed? In what way would it get absorbed? Rfwoolf (talk) 18:29, 27 August 2008 (UTC)

The lesion you describe is known as a hematoma. The entrapped blood will slowly degrade by several mechanisms. Some blood cells will be broken down by natural and mechanically accelerated hemolysis. Macrophages and similar cells may consume and degrade some constituents. Some white blood cells are capable of migrating back to the intravascular space. The plasma will likely diffuse through the tissue and migrate in and out of spaces based on osmotic forces. Some cellular debris may stay in the hematoma site for a long time. Tuckerekcut (talk) 18:35, 27 August 2008 (UTC)

Thank-you! Hopefully this question will be indexed by google and your answer will be helpful to others will similar questions. Rfwoolf (talk) 18:48, 27 August 2008 (UTC)

Evolution and the "no new information" argument

I really just don't understand this one. What do creationists even mean when they say "no new information is ever created through mutations/evolution"? Do they mean more genetic code isn't being added? (gene duplication) Or are they ignoring the fact that ACC and CAC, while the same base amino acids, code for completely different proteins? -- MacAddct  1984 ^{(talk • contribs)} 19:09, 27 August 2008 (UTC)

I've never heard this one before (I don't spend much time listening to creationists), so can you give us a link to somewhere the argument is presented? Algebraist 19:13, 27 August 2008 (UTC)

I'm currently at work and sites such as Answers in Genesis [6] and Dr. Dino [7] are blocked because of its content "religion" (har har). Talk.origins has a brief description, but it's not very informative. I'll provide more links later, if no one expands upon it. -- MacAddct  1984 ^{(talk • contribs)} 19:26, 27 August 2008 (UTC)

My understanding is most creationists claim mutations are always deleterious and/or there is no evidence/it is impossible to form new, more complicated, structures from mutation. Nil Einne (talk) 19:32, 27 August 2008 (UTC)

See [8] for example (does [9]) work? A mutation, being a random change in highly specified information contained in the nucleic acid base sequence, could almost never do anything but scramble the information; that is, reduce the information. Now sometimes such a loss of information results in a new trait—for example, purple or red flowers where there were only blue ones before (yes I know how dumb that is and how they're missing duplications etc but that's not the point) Nil Einne (talk) 19:36, 27 August 2008 (UTC)

Thanks Nil and Macaddct. Algebraist 19:39, 27 August 2008 (UTC)

Yeah, that's exactly the kind of argument that I often seen getting used. (Thanks for the cached link). -- MacAddct  1984 ^{(talk • contribs)} 19:59, 27 August 2008 (UTC)

(edit conflict x5) Sounds like a misunderstanding/misapplication of the Second law of thermodynamics. Although entropy increases overall in a universe sense, biological/living systems can organize/reorganize. --mboverload@ 19:38, 27 August 2008 (UTC)

Indeed you may also want to see Specified complexity for further understanding of their flawed thinking Nil Einne (talk) 19:40, 27 August 2008 (UTC)

[EC]The attempted argument is a bastardization of information theory. Objections to evolution#Evolution cannot create information discusses it, but here's the gist: in order to justify a necessisary "intelligent designer", some folks have decided to make the nonscientific (and clearly false claim) that only a intelligent agent can add information into a system because natural systems can, allegedly, only lose information. This natural-systems-can-only-lose-information paradigm stems from a mischaracterization of thermodynamics and incorrect assumptions about the nature of genetic mutation. The Specified complexity arguments of William Dembski are commonly cited (outlined in his "Law of conservation of information"). — Scientizzle 19:47, 27 August 2008 (UTC)

Oh okay, that's pretty much what I suspected. Thanks for the links. (I was trying to find it listed in criticisms of evolution article maybe I'll redirect it) As always, just blatant and willful ignorance of facts. -- MacAddct  1984 ^{(talk • contribs)} 19:59, 27 August 2008 (UTC)

Various experiments have shown to everyone's satisfaction that species do change over time, so the Creationists have been backed into saying those changes are going "downhill" by losing genetic information:

The rare ‘beneficial’ mutations to which evolutionists cling all appear to be like wingless animals, blind cave animals, and many examples of antibiotic resistance. They are downhill changes, losses of information which, though they may give a survival advantage, are headed in precisely the wrong direction for evolution. (source)

This rebuttal to the recent successes of the critters in the E. coli long-term evolution experiment concludes with "it is only possible to obtain truth about the past if we start with the only source of absolute truth in the present—the inerrant Word of God". So there you are. --Sean 19:55, 27 August 2008 (UTC)

So they aren't trying to convince him to hand over his "data" then unlike some other creationists? Nil Einne (talk) 20:07, 27 August 2008 (UTC)

A side note (and hopefully not to stray too far off-topic), Arguments creationists should not use is a beautiful example of back-peddling and apologetics. -- MacAddct  1984 ^{(talk • contribs)} 19:59, 27 August 2008 (UTC)

Oh, I don't know. It's actually much more honest than most Creationist groups in the respect that they recognize that some arguments which are incredibly common that Creationists have been using forever are wrong to the point of making the Creationists look stupid or dishonest (e.g. the Darwin eye misquote, which is always a useful way to spot totally ignorant Creationists). --98.217.8.46 (talk) 21:26, 27 August 2008 (UTC)

Creationists either don't understand - or refuse to acknowledge - the most basic science on this. The things they say are (without exception) ridiculously easy to demolish - but the people they are aiming these bogus arguments at are desperate to believe whatever crap is hurled in order that they can continue to cling to horribly outmoded beliefs. So there is guaranteed to be a breakdown in communication.

Here is the truth:

Evolutionary change comes about through at least THREE mechanisms:

1. Sexual reproduction - where two sets of similar (but not identical) genes are shuffled together.
2. Viral gene insertion where some virus comes along and inserts its DNA into that of the host species.
3. Mutation - where either a transcription error in the DNA or a zap from radiation or some nasty chemical agent in the environment (a carcinogen, for example) causes the insertion, deletion or corruption of a part of the genetic code - resulting in a brand new gene popping up.

Mutation is a genuine source of completely new genes - they come from absolutely nowhere in the environment - it's a truly random change.

The other two mechanisms are indeed nothing more than a reshuffling of existing genes. But even that can result in totally new "features" in the resulting organism because the consequences of two old, well-established proteins meeting in the same animal for the first time in history can easily result in some bizarre - but useful - side-effect.

So - sure, new 'features' can arise that have never been seen before - there is no problem with some limited pool of information being the only source of genetic material...that's obviously not true. Creationists who claim this are simply sticking their fingers in their ears and singing "La, la-la, la-laaaa. I can't hear you!" because they've been told this plenty of times and clearly enough.

The reason the entropy argument is bogus is because entropy only increases in closed systems - and it's a statistical increase - not an absolute cast-iron increase. So within a group of animals stuck in a "closed system" (on an island or something), the arrival of new mutations results in a very few, rare improvements that survive into the future and a much larger number of disasterously 'damaged' creatures that don't survive long enough to pass on their genes to the next generation. The total entropy of the island does exactly what the laws of physics predict - it increases.

Life on earth is evolving and improving - but at the cost of increasing the chaos on the planet at a much higher rate than would occur if there was no life (or life without evolution).

We can simulate this in a computer relatively easily. When we do this, we can actually measure the entropy of the system and watch it increase as predicted by physics while the synthetic "animals" befome more and more well-suited to their artificial environment.

SteveBaker (talk) 03:40, 28 August 2008 (UTC)

I have seen the computer models before but it was awhile ago. Is this mostly university stuff or are there public resources on it? It would be most excellent if I could get a simplified version to just watch =P --mboverload@ 04:33, 28 August 2008 (UTC)

Artificial life and Evolutionary algorithm are the articles you need. I'd be surprised if there were no decent public-domain evolutionary demonstrations. However, it would be rash to assume there was anything to watch - firstly, even computer-based evolution can take a LONG time to develop anything interesting - and secondly, the systems involved are not necessarily graphical things you can watch. However, there are a few programs out there that run over a few days and produce brief graphical output - I have no idea whether any are in the public domain.

Some of these are pretty amusing - and they are rarely what you either want or expect. One guy built a system where each creature was made up of a set of cuboids hinged together with simulated "muscles" operated by an elementary neural network "brain". The size and shape of the cuboids, the positioning of the muscles and the connections within the brain were all determined by a set of "genes" that could be passed on from one critter to another with cross-breeding and mutation for variation. His first attempt was to try to evolve something that could walk - so he'd set up a bunch of randomly generated synthetic creatures and he'd have his software watch them move. Initially, some of them just 'twitched' - that nudged them SLOWLY in some direction. The one that moved furthest over some period of simulated time would go on to provide the genes that would be mutated to form the next generation. He ran the program for days and found from the readout that the winning creature could move amazingly fast - much faster than he expected. Viewing the "design" of the winning creature revealed that it had just one cuboid - no muscles and no brain whatever. It was very tall and very narrow and beat all the other creatures merely by falling over! Its center of gravity moved by half its height in just a few simulated seconds - so it met the criteria of moving the furthest in the allowed time - and it simply evolved to get taller and taller and narrower and narrower. Later, he fixed that problem by changing the fitness criteria - and found that his creatures would evolve to exploit bugs in his code - he fixed bugs and then found that many of his creatures merely consisted of two blocks, one muscle and a very simple brain. They simply vibrated at high frequencies and mysteriously slid across the ground - it turned out that they had evolved to exploit matematical roundoff error as a source of energy.

You might consider these as 'failures' - but in truth they are elegant demonstrations that creatures (even synthetic ones) will evolve to fit perfectly into their environment. If their environment inadvertently provides 'free energy' from roundoff errors - then for them, that's as important as sunlight is to plants out here in the real world. Making synthetic creatures evolve to look and behave like real creatures turns out to be virtually impossible. SteveBaker (talk) 06:08, 28 August 2008 (UTC)

Thanks Steve! I guess the "models" I saw were just an "envisioning" of possible evolution =( --mboverload@ 06:11, 28 August 2008 (UTC)

See List of digital organism simulators

Also : "it turned out that they had evolved to exploit mathematical roundoff error as a source of energy." It would be a great line in a science fiction short story. APL (talk) 16:20, 28 August 2008 (UTC)

It would have made a much better (albeit much geekier) ending to The Matrix. SteveBaker (talk) 19:50, 28 August 2008 (UTC)

YouTube user cdk007 has some excellent videos of computer programs he wrote that show how mutations and natural selection take place. -- MacAddct  1984 ^{(talk • contribs)} 14:02, 28 August 2008 (UTC)

The evolution of intelligence

It seems odd to me that at least three, probably four, groups of animals have developed highly complex and intelligent brains independently (corvids, parrots, cetaceans, and primates), during the Cenozoic era, while no known fossil from the Mesozoic has an encephalization quotient (EQ) much above that of an ostrich (the highest are troodontids). (I say "possibly four" because there were parrots in the Cretaceous, but I'm not sure about their intelligence.)

Is there any speculation as to why this is? (Is the Mesozoic fossil record poor enough that we could have missed an entire taxon as significant as, say, parrots or corvids?) —Preceding unsigned comment added by Vultur (talk • contribs) 23:33, 27 August 2008 (UTC)

One of the principles of evolution, articulated by Stephen Jay Gould among others, is that in any sufficiently large evolving population even a purely random exploration of all possible niches will lead to increasing diversity as one moves away from ancestral forms and tries new paths of life. Applied to the EQ in particular, this implies that since animals started with no brains (0 EQ), then even randomly directly evolution will lead to an expanding diversity of EQs. As a result, both the average and top performing EQ across any taxonomic group is likely to improve over time. If you look at the work of Jerison, for example, he generally concludes that the average EQ of birds and mammals has been increasing essentially since the inception of these groups, but that this random exploration of the "intelligence" space proceeds very slowly (perhaps max EQ doubles every 25 million years or so). If the average intelligence of birds and mammals has been improving gradually for a very long time, it is not too surprising that the intelligence of the brightest birds and mammals is also at or near a historical maximum today.

There is also a view that reptiles and fish, which still have low EQ even today, may be unable to evolve a high EQ due to the metabolic requirements of a large brain. In other words, high intelligence may be only possible in warm blooded organisms. However, if you believe that at least some dinosaurs were warm-bloodied then that still doesn't explain why 180 million years wasn't long enough for dinosaurs to develop interstellar travel. So ultimately I dont have a good answer for you. Dragons flight (talk) 07:03, 28 August 2008 (UTC)

I don't mean to contend with Gould here but that sounds awfully teleological. --98.217.8.46 (talk) 14:33, 28 August 2008 (UTC)

Teleology would assume there is a plan or purpose beyond the evolution. Gould's point, somewhat oversimplified, is that given enough time random evolution will try nearly all possible stratagies for survival. Hence starting at any fixed taxa, the diversity of approachs is likely to increase across the range of species that are its descendants. That some descendants happen to become brainy requires only a sufficiently large pool of randomly evolving species and an assumption that increasing brain power is both physically possible and not so deleterious as to cause a species extinction. Dragons flight (talk) 18:49, 28 August 2008 (UTC)

A useful analogy is a simple random walk on the Euclidean plane. The expected position of the random walker (i.e. (expected x, expected y)) remains at the starting point no matter how long the walk has been going on, but the expected distance from the starting point increases with time (I think it goes as the square root of the number of steps). The reason is that x and y coordinates are equally likely to go up or down, but distance starts out at zero and can only go up. Evolution is also a kind of random walk, and any metric which starts at zero and can be positive and can't be negative will increase with time for the same reason. It won't increase forever—since there are also downward pressures which have no analogue in the simple random walk—but it will increase for a while from zero to some stable nonzero average. -- BenRG (talk) 19:33, 28 August 2008 (UTC)

Thank you. Perhaps the question was a bit poorly worded; I get that intelligence tends to increase over time [though I'm not sure it's a pure random walk; has any clade ever *reduced* its brain/body ratio over time? I'm sure one has, but I can't think of any.] I was wondering because we've only had 65 million years since the last big "reset" mass extinction, and the dinosaurs/pterosaurs/freaky mesozoic weirdnesses had much more. —Preceding unsigned comment added by Vultur (talk • contribs) 00:14, 29 August 2008 (UTC)

Objects rotating in space

I contend that it is impossible for an object to be rotating in more than one axis simultaneously without a continual force acting upon it, but there are others that disagree with me. Picture a pencil spinning along its axis, nudged so that it also spins end over end. Doesn't the gyroscope effect prevent an object that is rotating on one axis from also rotating on another axis such that after it has rotated 180° it is then rotating in the opposite direction on the original axis of rotation? Surely this periodic reversal of rotation (in an absolute, external observer sense) requires continuous application of force? How can I more clearly elucidate my point, or am I mistaken? — PhilHibbs | talk 23:38, 27 August 2008 (UTC)

Any two rotations in 3D space around any two axes (that intersect - presumably at the object's centre of mass) combine to make a single rotation around a single axis, see Euler's rotation theorem. This means that if you try to make something rotate simultaneously around two axes you'll actually find that it's rotating about one, different, axis. --Tango (talk) 23:56, 27 August 2008 (UTC)

And that rotation can't change without external force, by the conservation of angular momentum. Algebraist 23:57, 27 August 2008 (UTC)

This is actually not true, see below. -- BenRG (talk) 23:25, 28 August 2008 (UTC)

I don't see how what you've said below contradicts what I've said. I've just quoted a mathematical theorem, I'm pretty sure it's right, Euler knew his stuff! --Tango (talk) 20:15, 29 August 2008 (UTC)

Certainly you can combine any number of rotations in to a single rotation about some other axis. Whether you can change the rotation without an external force is a little tricky. The classic example of the spinning ice-skater who - with arms outstretched - can change the SPEED of her rotation by pulling her arms inwards. That's a change in speed - but not of the axis of rotation. However if she pulls in just one arm, she'll start spinning around an axis that DOESN'T run through her head and her feet. But she's still spinning about the same axis from a point of view of conservation of rotational momentum because her head/body moved one way as the arm moved the other way - the axis of rotation for the entire system is still vertical with respect to the ice - but from the perspective of the skater, it changed.

This principle is important for spacecraft. Using thrusters to change your axis of rotation consumes reaction mass - rocket fuel - which is valuable stuff...but instead you can have a big flywheel inside and use solar power to spin it up and to keep it spinning against friction. When the spacecraft needs to rotate, it applies forces to the flywheel - the flywheel spins one way - the remainder of the spacecraft rotates the other way in order to conserve rotational momentum. The spacecraft APPEARS to rotate without any external force being applied - where in physical terms, it's total rotational momentum didn't change. This mechanism is how the Hubble Space telescope turns to point where it needs to point without ever running out of fuel.

Gyroscopes are not magical - they use the same principles. When you see a kid's toy gyro spinning on a table - you do indeed see it "precessing" (it's axis of rotation changes) - but that's because there IS an external force - friction with the table (or whatever mounting points it uses) and gravity.

SteveBaker (talk) 03:06, 28 August 2008 (UTC)

I don't know, I still find gyroscopes kind of freaky. Confusing Manifestation(Say hi!) 03:59, 28 August 2008 (UTC)

An ice skater in outer space can change her axis of rotation by redistributing her weight, see below. -- BenRG (talk) 23:25, 28 August 2008 (UTC)

An ice skater in outer space? How can you skate in zero-g? — PhilHibbs | talk 07:59, 29 August 2008 (UTC)

I'll bet you could skate around the inside of a cylinder. Starting and stopping would be problematic though. APL (talk) 20:28, 29 August 2008 (UTC)

OK here's a follow-up. What does torque-free precession mean in this context? It looks to me like it's referring purely to the precession of an axis of symmetry, not the precession of an axis of rotation. — PhilHibbs | talk 13:28, 28 August 2008 (UTC)

Angular velocity (ω) can change without a torque. Angular momentum (L) is constant in the absence of torque, but L is not a scalar times ω, it's Iω where I (the moment of inertia) is a symmetric 3×3 tensor. Any real symmetric matrix is orthogonally diagonalizable, so you can think of the tensor as three orthogonal axes (the principal axes) with a scalar moment of inertia associated with each one. You can convert between L and ω by individually scaling their components along the three principal axes (thus L and ω do not generally point in the same direction). The trick is that as the object rotates, its principal axes rotate with it. If L is aligned with a principal axis (say x) then it doesn't matter; L = I_xω and that doesn't change as the y and z axes rotate into each other. If L is not aligned with a principal axis (or any combination of axes with the same scalar moment of inertia) then the angular velocity, hence the physical axis and speed of rotation, changes with time even though there's no torque. If the object is not solid then the moment of inertia may change in more complicated ways; objects tend to deform such that one of their principal axes aligns with L. -- BenRG (talk) 14:46, 28 August 2008 (UTC)

Thanks, I almost understood that! (need to re-read it and mull over it a little more). 4179 Toutatis appears to be behaving oddly, though. What's going on there? — PhilHibbs | talk 16:50, 28 August 2008 (UTC)

That's what free rotation looks like when L isn't aligned with a principal axis. See Poinsot's construction, which is summarized by the delightful phrase "the polhode rolls without slipping on the herpolhode lying in the invariable plane". The angular velocity is tracing out a herpolhode. The angular momentum, if it were plotted on the frame, would point toward the lower left. To directly answer your question, an isolated pencil in outer space can't spin around its long axis while also spinning end over end (tracing out a disc), but it can spin around its long axis while also tracing out a double cone, sort of like that asteroid is doing. -- BenRG (talk) 23:25, 28 August 2008 (UTC)

If Spaceman Biff sets his #2 yellow pencil spinning around it longitudinal axis, then he flips it to make it rotate around an axis perpendicular to the initial axis of rotation, it will precess. Edison2 (talk) 05:14, 29 August 2008 (UTC)

I've heard that claimed, but I'm not convinced that it is true. — PhilHibbs | talk 07:59, 29 August 2008 (UTC)

You can try the effects of rotations yourself using Orbiter_(sim). The physics model is very elaborate. It takes some time to get a grasp of the controls, but it is really worth the effort. —Preceding unsigned comment added by 84.187.95.86 (talk) 20:34, 29 August 2008 (UTC)