The concept of "backradiation", the fundamental postulate of CO2 alarmism, goes back to Prevost's Theory of Exchange (1791) retold in Maxwell's Theory of Heat (1871) as follows:
(p 240-241)
- ...this character of the transfer of heat, that it passes from hotter to colder bodies, is true the same whether it is by radiation or conduction that the transfer takes place.
- ...a cold body has no power of acting at a hot body at distance so as to cause it to emit radiations,
- nor has a hot body any power to stop the radiation of a cold body.
- ...it follows that if two bodies have the same temperature, the radiation emitted by the first and absorbed by the second, is equal in amount to the radiation emitted by the second and absorbed by the first during the same time.
- The higher the temperature of a body, the greater the radiation is found to be, so that when the temperatures of bodies are unequal, the hotter body will emit more radiation than they receive from colder bodies, and therefore on the whole, heat will be lost by hotter bodies and gained by colder until thermal equilibrium is attained.
Prevost's theory of exchange from 1791, postulating "backradiation" from cold to hot, was thus picked up first by Maxwell, then by Planck and was then found to be the perfect argument for CO2 alarmism.
Let us scrutinize the logic of Maxwell motivation of two-way transfer expressed in points 2. and 3. above:
- Since a cold body cannot cause a hot body to emit more, a hot body cannot stop a cold body to emit.
Is this a valid scientific argument? Let's make a parallel:
- Since a fool cannot make a wise wiser, a wise cannot stop a fool telling nonsense.
This is the logic of the populism of the web, and so it may carry some truth.
But the following question present themselves:
- Does a similar populism govern physics? Is Maxwell's logic correct?
- Is Maxwell's argument itself populistic rather than scientific?
- Is Maxwell's reference to the authority of Prevost a valid scientific argument?
I have my answers, but I leave the questions open. It would certainly be very illuminating to listen to what a living physicist would say today. Is Prevost's Theory of Exchange still valid, and if so is there any evidence beyond that presented by Maxwell?
Inlägg
"3...nor has a hot body any power to stop the radiation of a cold body."
SvaraRaderaIf it had, the result would be that two bodies with equal temps would seize to radiate towards each other. Anyone believing that?
Two bodies with different temps may have some part of their radiation spectrums overlapping. And if some frequencies are emitted, they are also possible to be absorbed, even if they are coming from a colder body. Something strange with that?
SvaraRaderaRemember that E-M-waves are force fields acting on charged particles even if these are vibrating more or less.
It is necessary to make a distinction between on one hand radiation = electromagnetic wave and on the other hand radiative heating = increase of internal energy of material body. This is not done in the present discussion and the result is confusion which fosters alarm.
SvaraRaderaBut how can a (black)body distinguish between energy with the same frequency coming from two bodies, one warmer but with overlapping spectrum of the colder. The receiving body has a temp in between. Absorption in one case and reflexion in the other! There is no logic in that.
SvaraRaderaYes, there is because the cut-off is one-sided high frequency cut-off, discriminating like a semi-conductor.
SvaraRaderaBut I am talking about frequencies in resp spectra that all three bodies have in common, frequencies that all bodies emit and thus also can absorb. These frequencies exist and, I repeatt, how can the middle temp body treat them differently. There is no information in the EM-wave about the origin.
SvaraRaderaI don't see the problem: For frequencies below cut-off of all bodies there is no heating effect.
SvaraRaderaHow does the cut-off conform to the absorption spectra of water?
SvaraRaderahttp://www.britannica.com/EBchecked/media/1369/The-absorption-coefficient-for-liquid-water-as-a-function-of
The spectrum of liquid water shows a quite sharp drop to zero between 1000 nm and 100 nm including the visible spectrum and part of the ultraviolet.
SvaraRaderaBut it is highly absorbent in the infrared and has another cut-off in the longer waves.
SvaraRaderaIt's also not temperature dependent.
"I don't see the problem: For frequencies below cut-off of all bodies there is no heating effect."
SvaraRaderaOk,the bodies emit and absorb radiation with frequencies within their spectra. Above cutoff the radiation is just absorbed and transformed to radiation within the spectrum.
But this means that radiation from the atmosphere(back-radiation) exists even if it is not heating earth directly. So Maxwell is right in stating:"3...nor has a hot body any power to stop the radiation of a cold body."
No, the point is that radiation above cut-off is absorbed and stored as heat instead of being re-emitted.
SvaraRaderaMy claim was: Maxwell is right in his claim 3)
SvaraRaderaAt equlibrium the heat energy is transformed to radiative energy, otherwise the body will heat up. Example: Radiation from sun transforms into IR from earth.
You are missing the point and the logic: The Sun makes the Earth radiate, so it is meaningless to say the Sun does not prevent the Earth from radiating.
SvaraRaderaAt equilibrium the earth radiates the same energy (for a short time) whether or not the sun is there, acc to what Maxwell states in 3)
SvaraRaderaAnd his statement 2) is so evident, the sun radiates the same energy whether or not the earth is there.
The Sun and the Earth form an interacting system and it is meaningless to speculate about what would happen if the Sun was not there.
SvaraRadera"It is necessary to make a distinction between on one hand radiation = electromagnetic wave and on the other hand radiative heating..."
SvaraRaderaThere are not different types of EM-waves(radiation)! This has been discussed many times. Radiative heating is performed by quite ordinary EM waves. The EM energy can be transformed into different types of energies.
Hav you seen the comments at the end here Claes?
SvaraRaderahttp://claesjohnsonmathscience.wordpress.com/2012/03/12/interaction-light-matter-trivial-and-nontrivial/
Yes, I have commented.
SvaraRadera"Claes JohnsonMar 12, 2012 01:29 AM
SvaraRaderaIt is necessary to make a distinction between on one hand radiation = electromagnetic wave and on the other hand radiative heating = increase of internal energy of material body. This is not done in the present discussion and the result is confusion which fosters alarm."
exactly! and you are right about the frequency and cut offs as being the reason why a warm body may not be radiatively heated bu a cooler body, this is to do with quantum interaction of radiation with electron orbitals. If the incoming radiation is of too low a frequency, it cannot excite the electon to a higher quantum level and therefore cannot heat the body. It is the excitation of electrons that is the means by which radiation is converted into kinetic heat. Radiation into vibration. EM vibration into physical vibration.