rewtedesco

Not knowing for sure if the source is reliable: Is it a hoax? is it half true? Or is there someone who speculates in commodities and likes to raise the prize? Or all of the above?

The would like to bring this back to the core of the discussion. There's a drastically largely raising concentration in the atmosphere as it hasn't been in any of the previous records from plants and ice probes. Higher C02 levels result in a higher likelihood of photons in the near infrared range to be absorbed in the atmosphere. These photons, if they leave the atmosphere carry energy, away from the earth. Increasing the absorption rate for these parts of the spectrum in the atmosphere reduces the rate of energy transport in a spectral bands where the CO2 is absorbing. At the same time the input from the sun remains pretty much unchanged, so does geothermic activity for the whole of the planet. The temperature at the surface depends on the long term radiation balance between incoming radiation from the sun and outgoing radiation which has a different spectral distribution than the incoming radiation. For the earth it's a lot more infra red and near infra red radiation sent out than what comes in, while there is a lot more visible light and UV coming than what goes out in those spectral ranges, mainly by reflection. But the total sum of energy in the incoming radiation averaged over a rotation of the earth or a longer period is balanced by the total energy of all outgoing radiation. There is no other type of balancing of energy flows between the earth and outer space other than the radiation balance. After all, we're not sending star ships out carrying hot water and dumping it somewhere, and we're not picking icecubes from comets, like you can see in a funny science fiction animation in "Futurama". Radiation balance which is a completely dynamic equilibrium can exist and will establish itself under any condition. The theoretical effective average black body radiation temperature of the entire planet earth plus atmosphere has to be equal to what we would find from computing the temperature of a black body that emits as much energy as the earth receives. This temperature is substantially below the actual surface temperature of the planet, by about 33 degrees. The atmosphere keeps us warmer than the computed temperature because it reduces the rate at which radiation energy can be transported. If there were only a change of CO2 concentration and no other effects the temperature has to raise. Since the raising CO2 concentration reduces this rate of energy transport to maintain radiation balance (by means of the increased absorption of photons by CO2 molecules), the temperature within the atmosphere and the surface raises. It has to raise to a point that a larger number of infrared photons are emitted until the incoming energy of radiation equals the outgoing radiation energy. We are actually lucky that the black body radiation increases (in the idealization) with the 4th power of temperature. Otherwise, with a lower power law, the temperature would have to raise more drastically. But that was all just considering CO2 alone. Then there's water and the change of water vapour in the atmosphere affects the radiation balance as well by changing the absorption spectrum of air. The diminished water vapour in the atmosphere described in the naturenews article partially counteracts the effects of CO2. This is good but it's not really good enough, because it doesn't completely compensate for the increase of the effects of CO2 and other green house gasses, and since effect isn't quite understood, it can't be excluded that it reverts itself sooner or later. This effect of counter trends and feedbacks that end up reducing the effects of CO2 are often used by the "skeptics" to claim victory. It is often said that the planet can easily deal with all this and we should stop worrying. It's true that simple laws of physics will make sure that the planet 'deals' with it. The problem is only that we may not like how that process plays out for us. The planet remains close to the radiation balance under any circumstances (as long as the sun doesn't decide to do something funny and it really doesn't look like that at all. All kinds of things can happen that we haven't yet heard of. It's even plausible that there is an increase in photosynthesis if there's more heat and more CO2. But it's also plausible that this increases the absorption of light in the oceans, making the ocean surface even faster warmer, which also is seen as a consequence of reduction of snow cover on land and ice on the oceans. Hopefully we find other effects that automatically counteract the effects of green house gasses, but I'm not holding my breath. Of course, I am confident that the planet will survive whatever dumb policies may be developed in reaction to the circumstances. Whatever happens, melting glaciers, more storms here, new deserts there, torrential rains, or simply the pretty possibility of growing wine in Greenland. It's all a matter of gradual and sometimes drastic changes in the complex dynamics of the atmosphere due to small changes of some important parameters, in particular temperature. And its more than that: It includes widely unknown and hard to predict changes in the biosphere, from plant growth to urban development. I don't subscribe to the "mother earth idea", but the truth is that on a very basic level of physics one can't dismiss the idea that our own brains are part of that biosphere. And btw, a raise of temperature has a lot of effects on human brains directly, that's were simple physics, physiology and psychology play nicely together, see the heated debate about the consequences and the silly question "who did it" (I'm just pulling you leg, or am I?) The bottom line is that many "skeptics" say that all this is so terribly complicated and therefore unproven with enough confidence, and that there is no way to figure out with reasonable accuracy how the small changes of thermodynamic variables will influence the climate. But then they say that since we can't demonstrate with complete certainty that it wasn't "our fault", we should just simply stop worrying about it. I think its complete capitulation, more like what the folks from the Easter Islands may have done in their last years, while spending their last resources on building monstrous stone figures. That certainly didn't help, and all the recent amassing of "piety" in America looks also kind of silly. Is even a small level of raise of CO2 levels, which is actually just a trace gas in the atmosphere responsible for such large changes that a few 1000 additional molecules in a cubic cm make a difference? I had my doubts about that too but then one can easily find the scientific and experimental evidence for that. For example, the description in http://climatephysic...opic/3057255/1/ explains it quite well. I'm citing here a whole paragraph of that: " The method of calculation is as follows. The atmosphere is treated as a column of gas, with a longwave input at one end (the surface), and short wave input at the other (the Sun). Using the known absorption spectra of gases in the atmosphere, the calculation proceeds line by line through the spectrum to calculate how much radiation is transmitted and absorbed and emitted all along the atmospheric column. The end result is a profile of radiative heating and radiation flux, with a power spectrum of longwave emission at the top, and another for backradiation and solar transmission at the bottom. The calculation is repeated for different gas concentrations, and different conditions. With higher concentrations, the backradiation increases and the emission at the top drops. The forcing, by definition, corresponds to the change in longwave emission at the tropopause." It may not be immediately intuitive, but there is nothing too mysterious about it. It's similar to a change of apparent color and transparency of a gas or of a fluid by dissolving small amounts of substances that change how well light of a certain frequency range goes through, is absorbed or transformed to other frequencies by absorption and emission. Only it's infra-red instead of visible light, and the cited description is more accurate. And I just realize that I could have just thrown this reference in here instead of writing this long diatribe. Just read that source. It's well explained. Is human activity the reason for CO2 levels rising? I don't see how it could not be: If we burn up most of the fossil energy resources in two hundred years which formed over millions of years, I would bet that's much like a huge monstrous forest fire raging on a large part of the planet. It's bloody unlikely that photosynthesis in the biosphere has picked up speed sufficiently to compensate for the increase of CO2. Without putting any blame here, it's a simple question. Can you prove that humans didn't do it, and can you prove that inaction is the best we can do now? Actually that are really two questions. Even if humans didn't "do it", it is pretty darn clear how we can reduce green house gas production, and how it can be turned into a great benefit for the slumping economy. That would be an appropriate reaction of the biosphere to regulate itself automatically, wouldn't it? So if there is something like "Mother Earth" or Gaya, it's us. We better step up to the plate.

Oh I agree that I will need a second opinion and find another orthodontist. I am concerned that my ideas may be total baloney, and I absolutely don't want to mess up my little boy's teeth (wait, didn't he already measure taller than me?). There is the little problem though that orthodontists usually also run a business, and are usually highly specialized to be efficient. The one I visited with my kid is definitely specialized in terms of what types of braces they use. So it's a little bit like asking a Honda only dealer to sell me a Ford or Toyota after they have tried so hard to convince me that Honda is the only real car and only consider their trade-ins for other models. So I want to figure out what possibilities actually exist and then find an orthodontist who can do it. I'm hoping a little bit that a more impartial specialist comes across this thread. For example, someone who teaches this stuff at a dental school. Regarding the 'dreamed up' teeth-pressing-apart device: You're right that without any additional measures one can't simply press the teeth apart without taking their rotational degrees of freedom into account. The device would have to be stuck on and between both teeth, and in addition the rotation needs to constrained by further stabilising it using the next teeth. So it would be a device that is attached to four teeth with the gap in the centre. The two molar teeth behind the gap and the first premolar and the canine in front of the gap would all be in connection with the device (or may be I should call it a partial brace). So it wouldn't be quite as "local" as it may appear from my description in the original post above. I could find that typically one can move a tooth at about a rate of 1mm per month. The amount of additional space needed is about 6 mm. The gap at the closest distance is about 3.5 mm wide, and the new tooth will need about 8-10 mm, judging from the completely emerged symmetric tooth. I know that this business is technically complicated but I'm not convinced it's rocket science. Any ways, I shall check out some books on orthodontics. I may actually really learn something.

I'm using Mathematica under Ubuntu (linux) most recent version 10.04 - It works without a problem (I haven't tried it on other operating systems, but I think there isn't anything different). Regarding question 2: Play with mathematica as soon as you can get your hands on it, and use the gazillions of demos on their site to learn more about using it properly.

It is interesting (not positive and not negative, but interesting) to know that I'm not the only one often confused about Entropy. It also doesn't help to capitalize the word. I think it has been one of the more confusing topics while studying physics and I'm still not out of the woods. But I actually do believe, now more than before, that entropy has indeed physical reality. And it has at least as much physical reality as energy has. Why is it then so confusing? I believe it has to do with the fact that entropy was originally introduced in the age of steam engines. Usually one is first exposed to entropy in the context of some kind of physical system going through the Carnot cycle. After that, one either learns a lot more on thermodynamics in physical chemistry, and one may be soon completely comfortable to compute all these different thermodynamic quantities, Gibbs energy, Helmholz free energy, Entalphy and all that. In my case, however, the orientation was a little different. The course on chemistry for physics students was offered on a far away campus and started at 8:15 am, and, as the comedian Lewis Black said on stage about a course he flunked on economics, it's not so easy to learn anything so early in the morning with one bloodshot eye. . It so happened that the students who got up late but may have had long discussions till late at night (first about the universe, then perhaps about nature and beauty - and finally the real geeks, drunk from the topic and the beer - about the beauty of women - who had all left the place early enough to get away from them .... ), these physics students (including myself) were then again confronted with the by then already forgotten topic of entropy when we got to statistical mechanics, almost all of which I've forgotten now. By then one had already sufficiently adjusted to more abstract formal systems, for example in QM, and it was simply OK that the entropy there was introduced based on the relation between energy states and probability in multi-state systems. And so this appeared much easier to comprehend than all the stuff that came from Carnot diagrams, because we didn't know then exactly why something that was discovered and explained in the context of steam engines would have any relevance for such things as the black body radiation and even in cosmology. In particular for modern biology, entropy becomes extremely important. One needs to know about it in neurology in particular for the understanding of biological systems for learning, but also directly related to machine learning, Bayesian modelling, because there are plenty of bridges between biology, statistical mechanics and computer science. This topic is interesting for me because I also want to fill all the gaps I have and want to be able to get some of this nice feeling that comes with "getting it". But for now I'm pretty stupid about all this. I'll try any ways, bare with me. One of the best short and to the point explanation of entropy I found in the first 12 pages of Feynman's book Statistical Mechanics, A set of lectures, 1972, Benjamin Inc. This is how Feynman does this: He puts together one statement as if it was simply true (it is actually) namely stating that "The key principle of statistical mechanics is as follows: If a system in equilibrium can be in one of N states, then the probability of having energy E_n is (1/Q) exp(-En/kT), where k is Boltzmann's constant. The first important thing here is that infamous normalization with Z, which is the partition function. Feynman used the symbol Q instead of Z, but Z is somehow more appealing to me: Helmholtz has defined the same thing as Z, namely German "Zustandssumme", which may be vaguely translated as state sum. This general formula with the exponential function can also be derived (somehow, forget the details) by combinatorics arguments and by taking the limit for a system were the number of states N is very large (Stirling's formula is used there). There is one sentence written by Feynman here that lights an LED in my head, even though it sounds somehow tautological: "Because two states of the same energy are equally probable, the probability of a state having energy E is a function only of the energy; P=P(E)". Think about it: No matter how the energy is related to other physical quantities, or defined to be related to other physical observables, the probability of the system being in a particular state depends only on that energy itself. Next one has to understand (or somehow accept) that if there is a probability function somehow defined or invented, one can make predictions (or more to the point, write down equations) about the expectation values of all kinds of quantities. So that's where Feynman writes down immediately the second equation in the book: The expectation of a physical observable that is associated with a quantum-mechanical operator A can be written as the normalized sum over all states of the inner products, namely as (1/Z) \sum_n <n| A | n> exp(-E_n/kT) whereby quantum mechanical states are written as |n>. It doesn't seem to matter if one understands the operator A as an operator on a Hilbert space or as some finite or infinite matrix and replaces <n|A|n> by x^tA x (where x is now some vector valued state), or if one replaces the sum by some (approximate or exact) integral over the state space. How does this lead to entropy: All you have to do is try to compute the expectation of the energy itself. That could be something like this: <E> = (1/Z) \sum_n E_n exp(-E_n/kT) The assumption is that Z is known for this. But then one may notice that if you write something like x exp(x a) it looks like the differential of exp(-x a) with respect to a, or in this case, like the differentiation with respect to (1/kT). This differentiation can be pulled in front of the sum and the interesting relation comes out: <E> = k T^2 d (ln(Z))/dT which contains the derivative of the logarithm of the partition function with respect to temperature. So there is already the logarithm here, not surprising: if the exponential function is in the game, the logarithm is just around the corner. Now put yourself in the shoes of Helmholtz who may have convinced himself that the Boltzmann equation is correct, namely that the energy of some state in which a system is and the probability of being in that state are directly related as p = (1/Z) exp(-E/kT). But perhaps Helmholtz didn't care about the probability and wanted the energy back. That would be E = - kT ln(p) - kT ln(Z) Cool, says Helmholtz and tries to compute the expectation <.> value of the energy, always assuming that somehow Z is known and equal to its expectation value. <E> = -kT <ln(p)> - kT ln(Z) So there is now this weird thing in there with the expectation of the logarithm of the probability. It certainly didn't really go that way but imagine that Helmholtz simply didn't care much about this weird thing and uses the symbol S as S = -k <ln(p)> and rewrite the above as <E> = TS - kT ln(Z) Then he rewrite this one more time because that thing kT ln(Z) makes about as much sense on first view as the entropy S, namely as follows: A = -kT ln(Z) = <E> -TS or F = U-TS (in Feynman's book) This has the symbol A for Arbeit (German for work, namely physical work, steam engines and such, perhaps early attempts at cars) Actually it was A = "useful work", while TS goes through the chimney. Now it's called free energy F, same thing as free work A, in the sense of free to use or useful work. I have no idea if this is how it was actually worked out by Helmholtz but it is kind of interesting to know who enormously general these relations are. In many cases, it is possible to compute the partition function directly from a formal model. That gives the free energy. And if it is also possible to formally compute <E>, then it's no problem to compute the entropy explicitly. Sometimes, and in machine learning where this stuff is also useful, there is no way though to compute the partition function. But there is usually some cute way to compute the entropy: You just bang your learning model in shape so that it becomes possible, which usually means to explicitly define an energy function in such a way that Z can be formally computed, or approximated. In Feynman's book on page 12 then already this whole schebang is used to compute the black body radiation. And that is another reason I looked into these things: One has to know about the origin of the formula for black body radiation and why it goes with a 4th power of T because this has recently been quite useful in the context of trying to debunk the so called deniers of human caused global warming. A recent new argument is to claim that there is no way to compute objectively the theoretical black body radiation from the earth and then to account for the difference that the atmosphere makes. Some deniers try to tell that now that the average surface temperature is not well defined, and hence the arguments for claiming that the earth surface temperature is raising is void. Even though there are a bunch of trained physicists who, imo went astray, are behind that, I think it's total b.s. But I won't get into this now and I'm not gonna start a flame here trying to torture "doubters". There are others who have done this with much more elegance. Almost forgot why on earth I felt the need to write all this stuff down. And now I'm running out of steam (darn entropy) - That big question is ringing in my head, and I hope to find simple explanations: What does this mean: "Life exports entropy" (sounds very deep, doesn't it, but is it?) I think in simple terms it means: Live needs to use energy while reducing entropy locally, but can only do that by increasing the entropy of the entire system which includes life itself and the environment. The export of entropy goes out through dumping all kinds of things, or by the smoke stack. Instead of life call it biosphere, a little less general than life. The question is then, how does life find a trick that results in the local reduction of entropy, that is, going to a less likely states? How does this work on the small scale of a cell, and how on the scale of a complex larger biological system? It's an important question to answer correctly and in detail, because this may be a new wonder weapon against creationists who always come up with the at best lazy idea that the new information comes from something not explainable by known laws of physics. I mean, even if I or others can't make it clear right away, and even if some pius fool may find a bible story, or a wondrous verse in the Koran or in the Torah, or even a Buddhist sutra that seems to mention entropy, count on this: I am absolutely going to stay in the physics department. But I would like to see not just a hand waving explanation for this, rather one that really starts from statistical mechanics, no less. (I'm learning it , i'm gettin there....)

Not sure if anyone will read this on a science forum, but there is simply no other forum where one could ask a question on orthodontics without being presented with the standard answer: as many braces as you can possibly fit in your mouth and pay for. My 15 year old son has a tooth with delayed eruption. This is the second premolar right (number 12). The root is completely developed and the tooth is just below the gum line but is hindered by the two neighboring teeth which are beginning to migrate to fill that gap. We went to an orthodontist for consultation, after this was pointed out by a dentist. A dental model was made and a bunch of complete x-rays to see the exact conditions. I expected that next would be a simple design of a small device similar to a retainer that would be inserted to slowly bring the two neighbour teeth sufficiently apart so there was enough space for the new tooth. I asked the orthodontist how likely it would be that that tooth would actually succeed to erupt assuming proper treatment. The answer was quite vague. I didn't expect a sure answer, but expected a somewhat more reassuring answer and got the impression that there wasn't much of a chance at all. The orthodontist proposed a complete brace system that would cover all teeth, both lower and upper teeth, starting with the upper teeth. The argument for that was that the upper teeth needed to provide a little more space for the lower teeth to go further apart, and so first the upper teeth would have to be equipped with braces to create later even enough space for braces on the lower teeth. If all that should fail, the specialist explained that there there was another additional treatment possible, namely wrapping a sling around the none erupted tooth to slowly pull it up. I was not exactly convinced and explained to the orthodontist that I actually had expected a more local treatment rather then an entire braces system that involves the entire mouth, which would certainly not to my son's liking. Another circumstance is the relatively high total cost of the proposed treatment, which would be about $5-6000 just for the braces, plus a hard to predict additional cost for an alternative treatment, namely a small orthodontic surgery, and additional lab costs, should the braces alone not help. This is not small cash for me but I would be happy to pay this if there was just a little more likelihood of success, and the confidence that the method proposed by the orthodontist is indeed the only possible treatment. Other than for this one delayed tooth, my son has no other health problems and no other problems with his teeth, no other misalignments, and he also takes well care of his teeth, no cavities. No one would expect him to have to wear braces because everything else in his mouth is fine, straight teeth without deformation and without overcrowding except for this one place. Another consideration is my speculation on possible genetic factors here: I had a very similar condition. In my mid-thirties I lost the lower right canine (number 10), and it turned out that it was still my last baby tooth. The second tooth had never erupted, and much later I found out that it is embedded horizontally in my mandible below the incisors. This is mainly why I'm suspicious if my son's tooth will ever erupt, with or without braces. Nevertheless, I think some kind of treatment should be tried. So I proposed that there should be a simple device with a small spring load inserted between the two neighbour teeth which exerts a small force on them, pushing them apart. It would have to be carefully monitored to see if the orientation of the device has to be adjusted to avoid "derailing" of these neighbours. Even though the orthodontist began to entertain this idea and considered asking a lab if they could provide such a device, his final decision was to not take on something like that. He stated frankly and with honesty that it would be unusual given this common practice and he would not be sure if he could take the risk of providing a care that may result in other problems he could not foresee, and possibly be blamed for it. I understand this concern completely, but still didn't give up the idea. I believe (and hope) the orthodontist didn't think that I'm a complete cook. However, in the friendly discussion we disagreed over something that he considered as completely in the assertive, almost fundamental, for the entire business of making braces for teens and adults. The central argument was that without the complete support of an overall braces system, there was no control over what would happen to the teeth. And I said there is no need for complete control. I argued that complete control over how all teeth adjust would only be necessary if the system was pretty much out of balance already, which is very unlikely in the case of my son's teeth. I don't understand how a natural proper arrangement of the growing teeth would be possible if there weren't plenty of self regulating biomechanical and physiological processes going on already. The orthodontist's central argument appears to me too close to a an idea that almost everyone needs braces, which of course he wouldn't say and didn't say. Hence my question. What is the state of the art really? Does a method like I tried to outline actually exist? It could be even a simple retainer device that is only used overnight. In this case my son would simply insert with a gentle pressure a special device that is held in place by the two neighbouring teeth and exerts a small pressure of, say, 0.3 N (one ounce) on the two teeth, pressing them apart. This device would have to be, of course, tailored to the specific case. If I look at the dental model which I kept for the time being I believe to have a very clear intuition of how this device would be oriented and how it exerts forces (including a small extension by a very small brace that may be necessary to also keep the canine tooth in check to not be pressed out as an unwanted side effect). Should I be so utterly wrong in my intuition?