Well, you know physics trumps what you, or anyone else believes, every time. And yes you can "prove it", in a lab. After all, the absorption coefficients of the H^- ion are actually measured in laboratories (i.e., Andersen, et al., 1997 and references thereto). Those absorption coefficents are consistent with those which are calculated from first principles, also known as physics (i.e., Kuan, Jiang & Chun, 1999). And all of the observed & calculated absorption coefficients, applied to radiative transfer models of the solar photosphere, are consistent with observations of the sun (i.e., John, 1988, John, 1989 and John, 1991). This is a direct application of laboratory data to stellar atmospheres, which clearly shows that H^- opacity is responsible for the solar continuum emission. The fact that we cannot build a 400 kilometer replica of the solar photosphere is not something to hide behind.

Indeed so, but neither density nor distance is the key to understanding absorption in a plsama, or in a neutral gas. Absorption is the key, and a strong absorption coefficient will trump both density and distance. All you have to do is look at the radiative transfer equation, where dI/ds (I is the spectral intensity and s is path length or distance) is set equal to emission minus absorption minus scattering. A strong absorption coefficient will be effective over a short distance. You don't find density explicitly in the equation anywhere, beause it is included in the absorption coefficient. So a small absorption can produce dramatic results over a long distance (which increases the path length) or in a dense environment (which increases the mass absorption coefficient). And a large absorption coefficient does not need much of either path length or density to get the job done.

This means that you can't make absolute statements like "I dont believe that distance creates a blackbody spectrum in a thin plasma" and expect to get away with it. In all cases, plasma or not, you need to know the specifics of the situation first. Distance without any question or doubt at all, certainly will produce a blackbody (or near blackbody) spectrum, in a thin plasma, or a thin neutral gas, if the absorption coefficient is strong enough. The depth of the solar photosphere is roughly 400 km, and decades of both laboratory data & physical theory clearly show that in the solar photosphere, the H^- absorption coefficient is strong enough to do exactly that (i.e, John, 1989).

Actually, yes it is. The global average surface temperature of Earth is 288 K (about 59 F), whereas its effective radiative temperature is 255 K (about -1 F). The radiative temperature is cooler than the surface kinetic temperature because an outside observer is looking at the cooler outer atmosphere, and therefore sees a cooler temperature. You will find this explained in any book on atmospheric physics, i.e., The Physics of Atmospheres by John Houghton, or Dennis Hartmann's book Global Physical Climatology.

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The point of philosophy is to start with something so simple as not to seem worth stating, and to end with something so paradoxical that no one will believe it. -- Bertrand Russell