onsdag 28 juli 2010

The Wise and the Fools of Backradiation

Roy Spencer feels an urge to make a follow-up to his "controversial post on the effect of infrared "backradiation", the existence some dispute" by suggesting a "simple and inexpensive Experiment to Investigate Infrared Sky Radiation Effect on Temperature Changes". 

This is simply the standard blackbody in the form of a box (cavity) with a hole absorbing and emitting radiation to the surrounding. The air in the box is initially at 300 K and the surrounding is kept at 290 K. Spencer asks for the temperature in the box after some time. 

The answer is of course 290 K. But this is not because of any form of "backradiation", but because the cavity reads the temperature of the surrounding from its spectrum, and then decides to cool or warm depending on its own temperature. As illustrated in the model studied in Computational Blackbody Radiation, now updated with a section giving evidence that backradition is non-physical.

The key feature of this model is that the form of a blackbody spectrum is determined by 
the temperature which sets the cut-off according to Wien's Displacement Law. The result is
that a warmer body can heat a colder body, because the colder body can absorb high-frequency radiation and grind it to heat. But a warmer body cannot get heated by absorbing low-frequency radiation from a colder body, because the required high frequency input is missing and cannot be created out of nothing.

Two blackbodies of equal temperature do not exchange heat energy, because the reason to do so is lacking (according to Leibniz' Principle of Sufficient Reason).

We may compare to the following familiar situation:
  • One wise can teach many fools something of interest, because the fools cannot avoid absorbing the message because they are without defense. Even if the message is not understood in detail, it will have an effect as elevation of general knowledge/temperature. Education is meaningful, to some degree in some sense.
  • Fools, even many,  cannot teach a wise anything of interest, because the wise will simply not listen, because of an inability to absorb trivialities: We know that intelligent FRSs proudly claim that they cannot learn anything from the blogosphere.
  • In successful education, the student may over time become as knowledgeable as the teacher, but not more...as the student learns the teacher gets less and less to teach...

3 kommentarer:

  1. I have lately wondered if there is perhaps something Freudian over Spencers repeted attempts to convince the general public about the reality of the Greenhouse Effect. It should be admitted that he posesses some insight into the subtleties of the atmospheric problem that so far has not passed onto the minds of a majority of both skeptics and alarmists. It is true that at the moment there is no fully developed alternative theory that explains and quantifies the fall in the readings of thermometers as we go higher in altitude, despite that fact that the problem as attracted attention since the middle of the 19th century, if not before. However, I cannot help but to read some tacit message between the lines: "Now I've given you all the clues, please physicists, bring this to an end, I'm to involved to do it myself". If this is the case Roy, then you have my sympathies ;)

  2. Could I suggest another experiment for those in cold climates where there is lots of snow. Body temperature is about 37C +/- about 2C. Measure the outside temperature, the air humidity, the wind velocity (for wind chill calculation) and your body temperature, build an igloo, get inside and measure the temperature, the air humidity, and your body temperature regularly. Firstly, you will feel a lot better being out of the wind. Then you should see the temperature of the air increase due to natural convection from your body surface. The air temperature and the igloo internal wall temperature will never reach your body temperature. Your body temperature will not increase beyond your normal temperature. As the body starts to run out of fuel (assuming no food intake) the air temperature will start to fall. How long can you last? I have read upto 5 days. (There was an Australian who lasted 10 days in a cave on MT. Everest but he was eating chocolate. If you have sufficient data which can be replicated and find something interesting (such as heat transfer from the packed snow walls to the body -smile) then you maybe able to publish it at least in those journals(??) that accept papers from alarmists.

  3. 一棵樹除非在春天開了花,否則難望在秋天結果。..................................................