On 09/08/2015 18:24, Alastair McDonald wrote:
"Metman2012" wrote in message


The term cold radiation really only applies to the radiation when it arrives
at a body. If it has originated from a cooler body then it is cold radiation
and the other body will cool. If it has originated from a warmer body then
it is hot radiation and the other body will warm.



The temperature of a body depends on the net (a word of one syllable)
radiation it absorbs and emits. There is only one source for the
emissions, the body itself, but there can be lots of sources of the
radiation it is absorbing. Obviously it is the sum of the radiation from
all those sources that will determine how the temperature of the body
itself changes. And its final temperature will be reached when that sum
equals the radiation it emits as a blackbody.

Does that make sense?

Cheers, Alastair.



The second paragraph does make sense, but I notice that no mention is
made of hot or cold radiation.

But your first paragraph is less clear (partly because I have to reread
it to see what's cooling what). My understanding is that a body will
cool by itself unless it is subject to heating from another body hotter
than itself. So without the sun, the earth would be considerably cooler.
The sun itself is cooling, or at least it would be if there were no
processes maintaining it's heat. However the fuel for these will
eventually run out and it will cool of its own accord without any
nearby cool bodies making a ha'p'orth of difference.

If you have two bodies, one hotter than the other and they are touching,
then heat flows from the warmer to the cooler until they are the same
temperature. The cooler body doesn't reduce the temperature of the
warmer body. I believe this is because of increasing entropy. My
(limited) understanding of entropy is that everything is cooling and
that eventually (next week?) we will have the heat death of the
universe. Everything will be cool (pretty cold).

I suspect that we might be in a war about semantics in this thread but I
don't think it's worth arguing over as nobody will be changing their
position on it (unless it gets very hot, or cold).