On Friday, 7 August 2015 21:20:02 UTC+1, Alan LeHun wrote:

Alastair says...
Do hot bodies emit radiation? YES! Let's call that hot radiation.

Why not just call it radiation?

Do cold bodies emit radiation? YES! Let's call that cold radiation.

Why not just call it radiation

If a cold body absorbs hot radiation, will it warm or cool? Of course it will warm.

If a body receives more radiation than it emits, it will warm.

If a hot body absorbs cold radiation, will it warm or cool? Of course it will cool. Do you agree?


If a body emits more radiation than it receives, it will cool.

Exactly, if the radiation a body receives is from a cooler body, then the first body will cool. So it is possible to cool a body with radiation, and it only makes sense to call it cold radiation.

It is not defying the Second Law of Thermodynamics, because the first body will warm the second until both are at the same temperature. But it is difficult to experience or demonstrate because both bodies are surrounded by the ambient radiation. You need strict experimental conditions, such as those used by Pictet to see it happening.

Sorry if this is an angry reply. I am in the middle of responding to Dawlish.

Cheers, Alastair.