tisdag 6 juli 2010

From Hot to Cold as Smoothing

In previous posts on backradiation comparing radiation to heat conduction/diffusion, the 2nd Law of Thermodynamics enters in the discussion as stating that without forcing heat flows from hot to cold, but not from cold to hot.

Another way of stating this principle is to say that diffusion acts to decrease differences by local averaging or smoothing, like softening an image in Photoshop. This is a stable process as shown by e.g. the Swedish tax system.

On the other hand, the reverse process of heat flowing from cold to hot increases differences as in sharpening an image in Photoshop. This is an unstable process, which is shown by the impossibility of restoring a smoothed image in Photoshop by sharpening.

The reason heat cannot by itself flow from cold to hot is thus that this process is unstable and thus impossible to observe and thus unphysical. Similarly backradiation is unstable and unphysical.

This connects to my treatise of why time has a forward direction:
which I hope you will have some time to look at. The central idea is that travel backward in time is unstable and thus unphysical. Instability is unphysical because it requires infinite precision which cannot be realized. When you smooth a picture in Photoshop, irreversibly small details are lost by blurring, and blurring is necessary because the precision is finite.

For a more mathematical presentation of the same idea as a version of the 2nd Law of Thermodynamics based on finite precision computation, see the upcoming book
In short: You have to throw old newspapers and clear the disc from old scientific reports, in order to not get drowned in useless information. Getting rid of information is the most basic instinct of life. Metabolism is destruction of information. Metabolism is necessary for the anabolism of growth.

16 kommentarer:

  1. Are you aware of the Hubble telescope, its failed main lens, and the mathematical sharpening that took place to enhance blurry images? You can sharpen images, although usually not perfectly. (There will be zeros in the point spread function).

    As for the arrow of time. Computation is only possible if you already have an arrow of time, thus you can't use it to explain that arrow.

  2. The idea that the atmosphere only radiates energy away from the earth is absurd. The fact that it also radiates towards the earth in no way contravenes the laws of thermodynamics.

    I asked you a couple of times before how many papers and textbooks related to atmospheric physics you had read. You refused to answer. I cannot help but conclude that you lack the necessary knowledge to form sensible opinions on this subject.

  3. Well, well, I have written several books on turbulent fluid/thermodynamics and since climate is turbulent fluid/thermodynamics, I believe I have something to say. I don't form opinions but seek to understand. And the blogosphere is free.

  4. Climate physics is rather more than that. Your view that "backradiation is unphysical" is, I'm afraid, absurd, and I've shown you why it is wrong. I showed you a paper presenting measurements of radiation from the night sky on a clear night. You didn't offer any useful response to that.

    Strange indeed to claim that you don't form opinions. What else is there but opinions on your blog?

  5. The fact that you can take infrared photos of a cold night sky with a sensitive camera, does not mean that the cold night sky is warming the photographer. Or is it? Of course I seek to form opinions, opinions based on mathematics and science. This is my job.

  6. You have claimed that the atmosphere physically cannot radiate towards the Earth. It comes as no surprise to me that when that claim is shown to be quite false, you change your claim.

    Consider a body. If it absorbs electromagnetic radiation, will it a) get warmer, b) get colder, or c) remain at the same temperature?

  7. Depends om its temp and the surrounding temp incl radiation.

  8. Incorrect. The answer is (a).

  9. No, because if it absorbs it also emits radiation, and the net flow depends
    on the surrounding medium.

  10. Indeed, if it absorbs, it also emits. It emits because it has been raised to a higher temperature. This is basic physics, demonstrate by innumerable experiments.

    Please clarify your current position: if I have understood correctly, you no longer deny that the atmosphere emits radiation towards the Earth, or indeed that the Earth can absorb that radiation; you just don't believe that absorbing EM radiation will change its temperature at all. Is that correct?

  11. No: I say that radiation energy, like heat energy, by itself transfers only
    from hot to cold.

  12. So, you believe all of the following:

    1. The atmosphere emits radiation, some of it towards the Earth
    2. The Earth absorbs some of that radiation
    3. The Earth is warmer as a result
    4. The net flow of energy is from the hotter Earth to the cooler atmosphere.

    At some point you seemed to think that 4 was incompatible with some or all of 1, 2 and 3. It is not.

  13. What is the net result of your investigation? That an Earth with atmosphere is warmer than without?

  14. Some comments:

    1. There is no net flow of heat from the the earth surface to the "colder atmosphere" if you take into account the incoming sunlight. Then one could of course argue that this is not relevant, but climatologists are cunningly ambiguous about that point. For example: Ray Pierrehumbert comments on the increase of temperature high up in the stratosphere something as follows: "This is not a violation of the 2nd law of thermodynamics since the earth is in the atmosphere of the sun". I interpret that as he considers the incoming sunlight as a relevant heat flow. The mystery is then to explain why the earth surface has a higher temperature than the upper atmosphere without there being any net heat flow to or from any part of the system. Conclusions?

    2. By adding more mass to the atmosphere and thereby thickening it you are indeed likely to change the living conditions on the earth surface since the pressure and density increases. And as I have commented on before there are different ways of excerting pressure. One is to shine light, another is to bounce.

  15. Roger,
    I found this online greenhouse effect calculator to assist in your investigations: