Wuwei
Gold Member
- Apr 18, 2015
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I agree with everything you say.Equilibrium will be reached when both temperatures are the same.
I have to agree with IanC on this.
In Ian's "what-if physics" (I'm going to steal that) example (all radiation in, none out, as he maintains part time) I see an otherwise closed system into which you continuously pump energy, and that should heat up beyond all limits. At least, common sense would dictate that. In that scenario, the term "equilibrium" makes no sense. And no, in a "real physics" situation, equilibrium is reached when the emission from the object equals the absorbed radiative flux (subject to the inverse square law), and thus the object's equilibrium temperature is way below the sun's, practically and also theoretically. Thank physics for that, for otherwise we'd all be cooked.
Otherwise, I've by now reached the conclusion that Ian's example isn't as enlightening as it seemed initially (even if we could work out the contradictions), as it (as I think you suggested) doesn't really shed a light on the Greenhouse Effect.
I am happy to realize that on the "real" physics side Ian, you and I agree that back radiation is huge, even exceeds the sun's flux absorbed by the earth: 340.3 vs 240,3 W/m². That is the main reason why the earth is at an average temperature far higher than the -18°C it would reach without the GHE. Let the denialings gnaw on that.
But I have a problem with the idea of a system of all radiation in, none out. There is a classical optical reciprocity theorem that says that the path of a light beam from point A through the system to point B is the same that a beam would follow from from B to A.
If we want to drop that requirement, we would need to invent a one-way optical valve. I think this would be the EM version of Maxwell's Demon for particles which highly frowned upon.