söndag 23 oktober 2011

Do Living Physicists Support DLR/Backradiation?

The inventor of the idea of DLR/backradiation supporting CO2 alarmism: Pierre Provost, 1791.

In Section 5.2 of Mathematical Physics of Blackbody Radiation I recall the following statement from Planck's The Theory of Heat Radiation:
  • We shall assume that the radiation in one direction is completely independent of the radiation in a different direction, even opposite.
  • But the empirical principal law that the emission of any volume-element depends entirely on what takes places inside of this element holds true in all cases (Prevost's principle). A body A at $100^{\circ} C$ emits toward a body B at $0^{\circ} C$ exactly the same amount of radiation as toward an equally large and similarly situated body B' at $1000^{\circ} C$. The fact that the body A is cooled by B and heated by B' is due entirely to the fact that B is weaker, B' stronger emitter than A.
This statement can be seen as the origin of the idea underlying CMB and DLR that the radiation from a blackbody is independent of the temperature the environment or background. Planck refers as support to Prevost's exchange principle from 1791:
  • Absolute equilibrium of free heat is the state of this fluid in a portion of space which receives as much of it as it lets escape. Relative equilibrium of free heat is the state of this fluid in two portions of space which receive from each other equal quantities of heat, and which moreover are in absolute equilibrium, or experience precisely equal changes.
  • The heat of several portions of space at the same temperature, and next to one another, is at the same time in the two species of equilibrium.
Mathematical Physics of Blackbody Radiation I give a new analysis of blackbody radiation challenging the idea of Provost/Plank of two-way radiative exchange of heat between two bodies with the hotter winning the game of net heat transfer as a stronger emitter.

So what is true physics:
  1. Is radiative heat transfer one-way from hot to cold, as my analysis suggests?
  2. Is radiative heat transfer two-way with the hotter being the stronger, as Provost claimed in 1791?
Does it matter? I say yes, because the stability properties can be vastly different in one-way and two-way transfer. It can be the difference between a harmless climate sensitivity of 0.3 C and and alarming of 3 C.

To empirically distinguish between 1. and 2. is difficult since only net heat transfer is directly observable. To refer to two-way transfer as an empirical principal law, as Planck does, is questionable.

The question is open. It would be interesting to see new independent support of 2. from active physicists living today. One can argue that the 2nd law of thermodynamics supports 1. but not 2. The 2nd law was unknown to Provost.

A scientist putting forward a certain statement as true often refers to some other scientist as being the responsible, typically the scientist who first gave the evidence of the truth. If that
first scientist is dead and cannot answer questions, which is often the case (as in Planck's reference to Provost), a scientific controversy may arise from different interpretations of what the now dead scientist actually meant or did. Therefore science should be carried by living scientists who carry the responsibility and are willing to answer questions.

In the present case there is a confusion between
  • radiation as electromagnetic wave,
  • radiation as heat transfer,
which makes the debate confusing, but there seems to be no living physicist willing to answer the questions and carry the responsibility.

18 kommentarer:

  1. Hi Claes!

    I am trying to understand your arguments considering non background radiation, but I haven't succeded so far.

    I will suggest a simple test situation. Take to boxes, cages, of similar conveniant size, strong enough (steel and glass) to endure beeing evaporated of air. Let's hang a metal ball in a wool thread from the top inside each case. Let evrything have living room temperature. Then we evacuate the air in both cages, so there will be no "temperature" inside unless the inner walls and the ball, and no conduction beetween the balls and the surroundings. Then vi put cage A inside a freezer where the walls and the air has a temperature of -20C, and let cage B stay outside in the living room temperature.

    Let's check them up the next day with the following hypothesis:

    H0: The two balls will have the same temperature.

    H1: One of the balls (cage B will be my guess) will be considerably colder.

    Which one will be your favorit, and why?

  2. A will be cooler. What is this exp supposed to test?

  3. Thank's for your answer, A will be my guess too (wrongly written in my first post).

    But you have only adressed the first half of my question. The other half is WHY. I think A will be colder because it recieves less heat radiation from the surroundings, (the only way to exchange energy in this case) but enough to never get colder than -20C. So both balls will be in equilibrium with the surroundings due to the radiation from the surroundings, i.e. "back radiation" is real physics.

    Or, have I missed something of the traditional explanation or of your interpretattion?

  4. So, if I understand it right, the question is does body A at temperature T_A radiate independently of body B at temperature T_B?

    Why isn't this a testable configuration?

    If one sets up an experiment where body A sees body B , but one screens body B so that the detector only sees body A, shouldn't this be able to test the hypothesis that body A radiates independently of body B by conducting the test with and without body B present?


  5. (continuation of my previous comment)

    Thinking about it, an even better experiment would be the same setting. And then to introduce first a body B with temperature T_B >> T_A. And then repeat the experiment with T_B << T_A.


  6. Claes,
    Is the silvering in the thermos flask not supporting 2? Not sure how efficient silvering works but if through reflection body B may look as warm as body A is this not supporting the idea that radiation goes in all directions equally? Body B looks warmer as it reflects incoming radiation and not due to changes in temperature difference between A and B

  7. I do not see the beauty of this exp. A is radiating to a background of lower temp
    and thus cools off, while B keeps it's temp. Where is the beef?

  8. Why not let the surroundings be body B and screen the detector so it only sees radiation from body A?

  9. Well, lets alter the situation a bit. While A is still put into the freezer, B is put outside the room where the surrounding temperature is at 0C. Then they both will have to cool, and after sufficient time they both will enter 0C. (And A will still reach -20). Will the rate of temperature change be the same for both balls, or do you think, as I do, that the rate between 20C and 0C will be higher for ball A, A will reach 0C sooner. My explaination for this will be that B during the process will absorb more heat radiation from the surroundings than A. Do you have an other opinion?

    I think this example has enough beauty to deserve an answer based upon physics rather than sighing over the estetichs. The point is I am really trying to understand your point of view here, and I am trying to clarify the situation with some basic question.

  10. B will not absorb more heat than A, just radiate away less because the background of B is warmer than that of A. Elementary heat transfer according to True-SB. No reason to refer to any False-SB.

  11. I'm looking at your Computational Blackbody Radiation-document and are trying to understand you arguments for arriving at the Plank's law and there is one thing I really need your explanation and justification for.

    In section 7.1, p. 181 (PDF p. 17) you write "viewing physics as a form of analog computation with finite precision.

    First of all, can you elaborate exactly what you mean with physics in this context?

    And secondly what is your experimental/theoretical arguments that this is the right view?


  12. One more question, are you working with c=1 units?


  13. It is natural to view physical processes as cause-effect systems or input-output
    mechanism and the procedure from input to output can be viewed as a form of (analog) computation. Finite precision computation can be seen as a small dissipative diffusion (averaging-smoothing) effect causing damping or cut-off of
    high frequencies which is seen in blackbody radition.

  14. Claes wrotez
    Finite precision computation can be seen as a small dissipative diffusion (averaging-smoothing) effect causing damping or cut-off of high frequencies which is seen in blackbody radition.

    But this then looks like an ad-hoc justification to get the right spectra.

    Is there any ab initio justification for taking this view?


  15. Thank's Claes for a straight forward answer. It's a bit hard to imagine that a body not will radiate against a warmer body. Your thoughts are challenging. I'll reread some of your post on the topic, and continue to follow your blog.


  16. IceskaterFinland says, Radiation emitted from materials results in cooling where the radiation is emitted.

    You can easily show that a warm cooling objects surface rises in temperature when the cooling rate is reduced by the presence of an introduced midrange temperature object or if you allow the hotter object to increase the temperature of the nearby cold object.

    No laws of thermodynamics are broken by this

    The backradiation is part of a cooling process.

    The second law of thermodynamics applies to the impossibility of constructing heat engines that use cooling to do work. Obviously no work is being done since both objects are cooling when viewed in terms of their total heat content.

  17. Read my new post