A science question

I think you might have misunderstood what I was saying. I didn't mention the word "heat". I wasn't equating temperature to heat. I was abandoning the term "heat" altogether in an attempt to avoid confusion between its lay and formal definitions, and instead used the term temperature. Nope, and this is why I didn't want to get into formal definitions. According to Hyperphysics on Temperature, "Temperature is not directly proportional to internal energy since temperature measures only the kinetic energy part of the internal energy, so two objects with the same temperature do not in general have the same internal energy."To see why this is true you can read Hyperphysics on Internal Energy.A little knowledge is a dangerous thing. I find it wonderful that you're willing and able to examine and understand this stuff, just get used to making lots of wrong turns along the way. I make mistakes all the time, and I often find that I have misconceptions buried deep in areas that I thought I understood. If you enjoy learning for learning's sake then this is great for both of us, and Sylas deserves a lot of the credit. If you only wanted to know whether the earth is getting hotter or colder then this might be frustrating. I think you're reading more into this than I was saying. As Sylas has correctly pointed out, heat is not the kinetic energy of molecules. I was agreeing, and at the same time stating that the requirements of a consistent framework for thermodynamics require that heat not be viewed in this way.About the rest of the paragraph, along with snippets from here and there: What a "Through the Looking Glass" world we have now entered! Things were so much simpler and more understandable when heat could just be considered the kinetic energy of molecules. Now that we're so much more knowledgable we can confidently make statements like, "The object is heated but gains no heat."Sorry for the sarcasm, but we started out just trying to figure out whether the Earth gains or loses heat, and this whole heat digression, while extremely educational, isn't necessary.Light is not heat. Within a thermodynamic context light can be the means of conveyance of heat flow, but light is not heat.Consider an analogy. If I carry a glowing hot ingot from my fireplace to the anvil in my workshop, there has been heat flow between these two points. I was the means of conveyance of that heat, but I am not heat.What actually happens with infrared radiation is that some of the internal energy of a molecule is converted to a photon (EMR) which travels through space and strikes another molecule, adding its energy to that molecule's internal energy. Heat has flowed from one point to another by means of infrared radiation, which is just a frequency band of EMR, but infrared radiation is not heat. It is EMR.Another way to understand that EMR is not heat is to consider microwave radiation. Probably the microwave frequencies in your kitchen microwave are different from those used in microwave communication links, but I'm sure they're close enough that what I say here is accurate. A microwave photon strikes food in your kitchen microwave and adds to the food's internal energy, leading one to perhaps conclude that microwaves are heat. But a microwave photon from a microwave transmission strikes a receiving dish and is reflected to the central antennae where it excites electrons and causes microcurrents, not heat. So now microwaves are not heat. Then a storm blows a tree down into the path between the microwave transmitter and receiver, and the microwaves no longer reach the receiver but are aborbed by the tree and add (slightly) to the tree's internal energy. So now microwaves are heat again.But microwaves are not heat. Light is not heat. Infrared radiation is not heat. EMR is not heat. It's photons. According to Hyperphysics on Heat Radiation, "Radiation is heat transfer by the emission of electromagnetic waves which carry energy away from the emitting object."I long for a simpler time! --Percy

Is anyone else a little confused as to how Hyperphysics defines Heat and Heat Transfer. They define Heat as "energy in transit from higher temperatures to lower temperatures" and Heat Transer as "Transfer of heat from higher temperatures to lower temperatures."Equating the "heat" term, Heat Transfer becomes "the transfer of (energy in transit from higher temperatures to lower temperatures) from higher temperatures to lower temperatures." That seems nonsensical. Instead of "Heat Transfer" shouldn't it be "Energy Transfer?"Also, I'm a little confused as to why EM radiation isn't heat, considering it is "energy in transfer."Is it because that energy isn't necessarily travelling from a higher temperature to a lower temperature? In other words, "heat" is the transfer of energy between two bodies of different temperatures, and the transfer is contingent on there being two bodies of different temperatures, whereas the energy in transit due to radiation is the result of the temperature of one body, and doesn't necessarily go from a higher temperature to a lower temperature.

I am leaving this thread for others at present; but I want to endorse the above. I'm not really as insistent on rigidly precise formal usage as it appears looking back on this thread; mainly I was standing by a comment that one thing TheLiteralist got right was a distinction between heat and kinetic energy of molecules.For thermodynamics, I'm just a novice who borrowed a couple of text books. One thing you guys might like to try is a few simplified calculated examples. Consider a planet with a homogenous surface, bathed in solar radiation from all directions (ignore night and day, winter and summer) put in some numbers for things like specific heat of the surface material, the albedo, the amount of absortion in the atmosphere at visible and at infrared wavelengths, and so on. See if you can get a simple model that allows a temperature for the surface to be calculated. This may clarify some of what is actually happening.Cheers -- Sylas

Percy,Instead of avoiding the term heat...how about I relent (since there's more I don't know than know about the subject); I will know what you mean when you say something has heat--that's the way I've said it all my life anyway. All my "precision" was quite unjustified (but it was a little fun). I'm glad that many of my misconceptions were corrected, though (thanks all).We now return you to your regularly scheduled thread...and simpler times! --TheLit

Hi JustinC,Without getting into too much detail, I'll just say I don't feel entirely comfortable with the definitions of heat and related terms at HyperPhysics. My guess is that it's not because they're wrong, but because my background isn't sufficiently deep for me to make the proper interpretations of definitions and descriptions. Language is not a very precise means of communicating something as mathematical as heat. I have a feeling that after one plays with the equations and some example problems for a while that the proper concepts and their interrelationships become embedded in one's mind, and then the language descriptions make perfect sense. But when all you do is attempt to learn something by reading instead of by doing then you're left trying to make Talmudic distinctions between word definitions, and language just isn't that precise.Sylas's suggestion to improve our understanding by tackling an actual problem is a good one, but it's not for everyone. Some people understand things quickly, and this is approach is best for that type of person. Some people like me are slower on the uptake, and this approach can take some considerable time, so while I would like to do this, I won't be. Some people just aren't science and math people and are never going to reach the point where they can make sense of the math. And some people, while curious, aren't *that* curious - they just wanted to have an interesting discussion.From a lay perspective, the biggest single problem I see with the definition of heat at HyperPhysics is one you already noted: that heat is energy in transit. But thermodynamics says that heat can only flow from a hotter body to a colder body, and there is definitely energy in transit from the colder body to the hotter body, just not as much as in the reverse direction. Perhaps by heat they really only mean the net of all energy in transit, and that's why in one of my posts I said perhaps they're actually looking at the problem at a process level, i.e., at a higher level of abstraction. At the level of solving thermodynamic problems perhaps they do not care as much about the means of heat flow, though one might then ask why they're so careful to define the three different ways of conveying heat.Whatever the right answer, I feel very uncomfortable with a definition of heat that means sometimes light is heat and sometimes it isn't. Light is always photons or electromagnetic waves (wave/particle duality), and its nature is unchanged whether or not it becomes heat at its destination.--Percy

Hi TheLit,You were originally wondering how we know the earth as a whole is cooling. We know this because the temperature gradient within the earth goes from cool on the outside to hot on the inside. If the earth were getting hotter then the reverse would be true, with the outside being hotter than the inside.We could confirm that the earth is cooling through a rather complex mathematical exercise, assuming that sufficiently accurate data is available, but this would to tough even for scientists who specialize in the field. Suffice to say that scientific work on this area *has* been done (several people have posted links), and if any contradiction with expectations had been found it would be well publicized, especially in Creationist circles. People who enjoy proving things to themselves should not be discouraged from attempting this exercise, but it certainly isn't for everyone.Surprisingly, I was able to type this post without using the word "heat".--Percy

I addressed this before and got no answer. Let me try again. I do not understand how the above is true.The earth is not a solid block or trapped within walls. It is a mobile system with a rather open/flexible outer boundary.Just because it is hotter on the inside than the outside, does not necessarily mean that it is cooling, only that the greatest amount of energy is coming from internal rather than external sources, or (well I'll get to the other in a sec)...There are internal sources of energy (gravity and radioactivity) which raise the temperature of the internal parts of the planet. This energy is moved through various mechanisms towards the surface, but it does not always reach the surface and definitely not evenly. A hard crust acts much like the crust on the top of a pot of cooking soup, trapping the heat below.At the surface energy is being reflected from external sources, as well as being absorbed and emitted. I don't think we have a budget figured out yet but that we are not totally hot, or hotter than the inner core, at the surface does not seem to me to prove we are losing heat either. We did lose much of our atmosphere earlier, and now that we have heavier atmospheric particles they do not escape as much but still can and certainly do act to redistribute energy through currents.It seems to me the only thing we can know is that there is some reason for the surface being cooler, whether it is that the planet's atmosphere is losing energy to space, or that mechanisms of trapping and distributing energy have kept the hottest parts toward the center does not seem so certain.But I am certainly open to correction on this one.It might be interesting to look at other planets or planetary bodies to make comparisons. Venus for example certainly is an energy trap, yet it still has a solid surface, and perhaps a much hotter interior core.This message has been edited by holmes, 03-10-2005 11:54 AM

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holmes
"...what a fool believes he sees, no wise man has the power to reason away.."(D. Bros)"...don't believe I'm taken in by stories I have heard, I just read the Daily News and swear by every word.."(Steely Dan)

I guess there are really two questions:

1. Is the earth a net radiator or net receiver of heat?
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2. Is the earth growing hotter or colder?

Regarding the first question, does the earth radiate more heat than it receives, the answer is an unequivocal yes. Once we know the direction of the gradient, the thermodynamic laws are all we need to conclude whether the earth is a net radiator of heat. Heat can only flow from hot to cold. Considering only the solid Earth as our system, if the interior is hotter than the exterior, then heat is flowing from the interior to the exterior. No other conclusion is possible. Heat can't flow in the other directionOur atmospheric buffer between the Earth's surface and outer space may give the appearance of introducing complexity, but not really. If the heat from the interior of the earth were not being radiated out into space, either directly or first to the atmosphere and then out into space, then the atmosphere would simply get hotter and hotter. But it doesn't. This brings us to my second question, is the Earth itself growing hotter or colder? After all, the Earth could be radiating more heat than it receives from the sun, but its internal heat engine could be generating more heat than is radiated, and we could be getting hotter.There are a couple arguments against this possibility. One is the dominant theories of the origin of the solar system, which hold that the planets were much hotter shortly after their original formation. If the earth cooled from an original molten state but is no longer cooling, then what occurred to reverse the trend? One possibility is that perhaps the Earth has reached thermodynamic equilibrium and so is now radiating as much heat as it generates, which means the Earth is not cooling but is merely standing pat with regard to temperature. Growing hotter wouldn't be a possibility unless the heat engine increases its output over time.Another argument against the possibility that we're getting hotter is that I think we have measurements indicating that the solid inner core is slowly expanding, which could only happen if the earth were cooling.One potential source of confusion is that the temperature gradient does run in the opposite direction near the surface in many parts of the world. For instance, I know that the temperature of the earth 330 feet beneath my house is 52^oF because that is the temperature of the water my water pump brings up from the ground. In the winter the surface temperature is often colder than 52^oF, and in the summer it is often warmer. But these are mere boundary condition variations. The net must be that the earth is a net radiator of heat into space, because the temperature gradient of the other 4000 miles beneath the surface permits nothing else.--Percy

Actually, the greatest amount of energy by far for the Earth is coming from external sources, not internal ones, by a factor of about 300,000 or more.That energy radiates out into space again, rather than percolating down in towards the centre. We know this, because the temperature gradient really does mean that there is a flow of heat from the centre out to the surface. This contributes its tiny fraction to the net energy flux, the vast majority of which ends up radiated into space as infrared radiation. The net energy flux, for Earth, or Venus, or any other planet, is effectively zero. The surface temperature is governed by the way in which that energy flux is absorbed and transformed and passed on. For example, a thick atmosphere (a bit like a blanket) does not actually provide any additional energy; it just slows the transmission of energy, especially if it is opaque to infrared light. The amount actual radiated energy is going to balance the input insolation; but the less efficient transmission means a warmer surface is required to drive the balancing infrared emissions. The temperature is basically driven to the point where the energy flux is able to balance the books and bring the output infrared radiation to match the input insolation (plus the tiny little bit of extra energy from internal processes).When you say we don't have the energy budget worked out; what this really means that that we don't have nailed down all the various transport mechanisms by which energy transfers. That the end result balances inputs and outputs over time, however, is given. If there was any excess input, or excess output, this would drive a temperature change until they balance again; a nice example of a feedback loop.To get an idea of the complexity of all the processes that are involved in a full description, see this Lecture online at California State University.Cheers — Sylas

Great link - thanks! An aside: I loved his unique contribution to the technical jargon: "vanishingly dinky"!--Percy

I want to thank you and percy for both sticking with me on this topic, as if I am wrong it is definitely a deficiency which I need to overcome.That said, I am still not convinced. But maybe we are slightly talking past each other. The problem I had was with Percy's comment that the fact that the atmosphere has a lower temperature than internal lithospheric regions proves that the earth is cooling.I do not understand how that fact necessarily proves the theory, given that what we are discussing is temperature of large scale masses of vastly different chemical constitution and physical environment. I apologize as what I wrote was not exactly what I meant. When I said "only that the greatest amount of energy is coming from internal rather than external sources", I really meant "only that there is greater production of thermal energy at the core due to internal physical processes, than there is production of thermal energy in the atmosphere due to external (off earth) sources."Hopefully the difference is obvious with this clarification.I have tried to emphasize what I was getting at by pointing out that we have a physical boundary between the two systems (mantle/core and hydro-atmosphere). Thus energy and temperatures located in one system do not have any inherent effect on the other (at least not large scale).An analogy I used was a cooking pot of soup or baked beans with a skin that has developed and a heat lamp on it, another analogy could be a pizza with a nice layer of cheese with a heat lamp above it and a grill below. In both cases one can use the heat lamp to remove cooling, yet the internal areas may be much hotter than the externals. Anyone having bit through a warm layer of cheese to find the unbelievably scalding layer of sauce below has an idea what I am getting at. A heat lamp would not necessarily produce an effect where the cheese must be at a hotter temperature.I do get that external heat is not percolating down to the center. This I can understand but it does not derive from the fact that the core is hotter than the atmosphere. That is where I was having problems. The core seems irrelevant to this question.I would add though that rise in temperature change is not necessarily the only result. Atmospheres can store energy and transport it via different mechanisms which do not necessarily require absolute temperature change.I thought your link did a good job of explaining mechanisms atmospheres have for handling energy, beyond purely temperature rises.To conclude let me repeat again, I am not trying to argue we don't have a system which is cooling or stable, I am only having problems regarding what comparisons of core and atmospheric temps have to do with proving theories about the earth as a whole cooling.

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holmes
"...what a fool believes he sees, no wise man has the power to reason away.."(D. Bros)"...don't believe I'm taken in by stories I have heard, I just read the Daily News and swear by every word.."(Steely Dan)

If you're saying that there cannot be heat flow between the mantle/core and atmosphere, then I don't think this is correct. You go on to say: The rate at which cheese conducts heat may be less than tomato sauce, I don't know, but it is not 0. There is no perfect insulator of conductive heat except a vacuum. If you pack a container of boiling water inside a sphere of styrofoam a mile thick, the water will still gradually cool by heat conduction through the styrofoam to the outside environment for as long as it is warmer than the outside environment.Thus, what you said in Message 127 about "A hard crust acts much like the crust on the top of a pot of cooking soup, trapping the heat below" isn't the way heat works. The hard crust conducts heat just like everything else made of matter. Some materials are better insulators of heat than others (the absence of all material is the best insulator of conductive heat, a vacuum again), but all materials conduct heat.Engineers designing the Hoover Dam calculated that the temperature of the concrete would rise 40 degrees while curing, and that the entire structure would take 125 years to cool naturally. Because the stresses that would develop during uneven cooling would crack the concrete, they laced the structure with 1" water pipes during construction through which they ran river water and later refrigerated water, and they monitored the exiting water temperature so as to know the proper temperature of water to send in so they could achieve even cooling as the cells of the structure were completed. Hmmm, didn't mean to get into that much irrelevant detail, but the point is that even very large structures made of materials you might think would impede heat flow conduct heat, even if slowly. And while I'm not going to bother to look up figures, my guess is that rock and concrete are pretty fair conductors of heat.Nature abhors a temperature gradient and will do its best to smooth it out - this is the 2nd law of thermodynamics. If you have a temperature gradient then there must be a heat flow, and there is no material in the universe that can stop it. On average, all the solar energy received from the sun is radiated back out into space. If it weren't then the atmospheric temperature would be increasing over time. And the temperature gradient within the earth requires that the earth itself is radiating some additional heat off into space, either directly into space or indirectly by conduction through the atmosphere, otherwise once again the atmospheric temperature would be increasing over time.--Percy

Almost. I am not saying that there cannot be heat flow, but the nature of the flow (as well as other physical realties) could be such that higher temperatures are found within the planet rather than in the surrounding atmosphere, and thus where the hottest temps are does not suggest if the entire system is cooling. Hey now, you should know I already understand this concept. Interestingly enough styrofoam cups are often used in chemistry experiments on thermodynamics because of their insular properties. They do not have to be perfect in order to trap the greatest heat (or temperatures) within, even over a very long period of time. While this is correct, it still does not add up to all portions of the earth necessarily having the exact same temperature at this time. Further, it does not indicate at all that the atmosphere should be hotter than the core.One aspect where the earth differs from a piece of sytrofoam is that it has distinct layers of material, sublayers within those layers (based on further physical differences), and some form of movement within the layers which means energy is removed in some other fashion than simple temperature increase.Let us say at the core was a simple cigarette lighter. Even if it stayed lit for 4.5 billion years and there was no energy loss from the earth system, would we have to see the atmosphere be the same temperature as the core... or hotter? I think you will agree it would probably not.The important factors are not just temperature and time, but amount of internal energy (which we see is different than temperature), the total amount of matter, its various phases and mechanisms for heat distribution within those phases.Just because the amount of energy (as well as temperature of core material) is substantially more than a lighter, I am not sure I can say that it must all have been distributed evenly by now. Much could be trapped within the molten cycles of the core and mantle, expansion of material causing the loss of much of the energy it has to impart before it hits the crust.And even when it reaches the crust, how much will be tranferred and trapped within the next layer for a portion of time?As far as whether the atmosphere is relatively insulated from core temps I note the following from Sylas's citation: Now I realize that the trivial reference could be because solar energy could be so much more than the energy being produced at the core, but I am not sure if that is so. That there is more reaching the atmosphere from solar than core is true, but that does not mean it is greater in toto for the earth system as a whole.I might also mention that we can see thermal layering within the hydrosphere and atmosphere. Despite billions of years the oceans of water and air contain different thermal layers and are not of one temperature... they have not evened out, and it does not appear to simply be a product of the earth cooling.For example the atmosphere is made up of several layers which go back and forth in temperature. While the troposphere does decrease in temperature, the next does not, the following one does, and the one after that increases. Here is a link to Wikipedia's page on the atmosphere. It has a pretty good breakdown of layer and temperature properties. The outside (or top) is not necessarily the coldest layer.It is also interesting to note the history section regarding the formation of earth's atmosphere and that this is considered our third one so far. Is this our final one? How much of the crust formation and so formation of the 2nd and 3rd atmospheres were a result of internal cooling rather than cooling to the outside? With the crust formed, why can temps not be regulated and trapped much as in the atmosphere?I hope this is not annoying to you or Sylas. I am sincere in not seeing the connection between simple temperature variance between core and atmosphere as indicative of anything. I can see saying there is evidence of cooling to the outside based on the fact that our atmosphere is not totally gone, or that it should be higher than it is in general... just not because it would be as hot as or hotter than the core.

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holmes
"...what a fool believes he sees, no wise man has the power to reason away.."(D. Bros)"...don't believe I'm taken in by stories I have heard, I just read the Daily News and swear by every word.."(Steely Dan)

Edited for style. --PercyI think I've already made the points I can think of. Most of the details you mentioned don't seem directly relevant to whether the earth radiates more heat into space than it accepts. I can point out a few things that don't like quite right to me, so in case it helps I'll address just those points. No one thinks the atmosphere should be hotter than the core, and I can't think of anything I or Sylas said that would make you think we were arguing for that. If you can find the place where we said something that led to this misimpression then maybe I can clarify. Heat cannot be trapped. Short of a vacuum insulating layer, a temperature gradient is *always* indicative of conductive heat flow. If this indicates that you believe the heat flow is causing the different layers of the earth to change temperature, then I don't think this is correct. At the undetailed level appropriate to this issue, there is a temperature gradient from the hot core to the cool lithosphere. Heat flows along the gradient, but the temperature of the layers doesn't change.--PercyThis message has been edited by Percy, 03-12-2005 19:23 AM

The energy budget on the surface of the Earth and in the atmosphere is very complicated. The link I gave previously can be summarized in this diagram: Temperature gradients within the atmosphere are quite complicated. The flow of heat by convention and conduction can move both up and down, and at the same time there is a flux of radiation passing through the atmosphere. But heat flow by conduction always goes along the gradient.Within the Earth the matter is simpler. There is no radiation; and the temperature gradient sufficies as a formal thermodynamic proof that heart is flowing outwards to the surface; not inwards from the surface. The source of this heat is radioactive decay.Cheers -- SylasThis message has been edited by Admin, 03-13-2005 08:31 AM