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[michaelsuede]

I watched this lecture and read over this paper by Prof. Pierre-Marie Robitaille, Ohio State University, on Kirchhoff’s Law of Thermal Emission.

 

The claim is made that When Kirchhoff and Planck were conducting their blackbody experiments, they would take a box and line it with soot, then place elements in the box and monitor the spectra of those objects.  In this blackbody box, the observed spectra of the elements always transformed to that of a blackbody.

 

Then they took a near perfectly reflecting box lined with silver and put elements in it.  In that case, the spectra of those elements would NOT change to that of a blackbody.  It was only after adding back in a small amount of carbon (a near perfect absorber) did the spectra transform to that of a blackbody.

 

Planck writes, “It is therefore possible to change a perfectly arbitrary radiation, which exists at the start of an evacuated cavity with perfectly reflecting walls under consideration, by the introduction of a minute particle of carbon.”  Based on Kirchhoff’s and his own findings, Planck derived Planck’s Law of Thermal Emission.

 

Prof. Robitaille states that, as a result, Planck came to see the graphite particle as a catalyst, when in fact, it was acting as a perfect absorber.  It was the same as if the experimentalists had lined all the walls of the box with graphite.  Kirchhoff and Planck should have considered the perfectly reflecting case as a separate valid case, yet they did not.  This serious error resulted in Kirchhoff and Planck believing that their equations could be applied universally.  Consequently, Planckian radiation is dependent on the nature of the radiating object.

 

He's authored several other papers on this subject:

 

An Analysis of Universality in Blackbody Radiation

Kirchhoff’s Law of Thermal Emission: 150 Years

On the Equation which Governs Cavity Radiation

Further Insight Relative to Cavity Radiation: A Thought Experiment Refuting Kirchhoff’s Law

Blackbody Radiation and the Loss of Universality: Implications for Planck’s Formulation and Boltzman’s Constant

 

I'm not a chemical engineer, so I'm curious what professional engineers think about this.