Quantum_ Einstein, Bohr and the Great Debate About the Nature of Reality - Manjit Kumar [11]
Lummer and Pringsheim reported their results at a meeting of the German Physical Society held in Berlin on 3 February 1899.36 Lummer told the assembled physicists, among them Planck, that their findings confirmed Wien's displacement law. However, the situation regarding the distribution law was unclear. Although the data was in broad agreement with Wien's theoretical predictions, there were some discrepancies in the infrared region of the spectrum.37 In all likelihood these were due to experimental errors, but it was an issue, they argued, that could be settled only once 'other experiments spread over a greater range of wavelengths and over a greater interval of temperature can be arranged'.38
Within three months Friedrich Paschen announced that his measurements, though conducted at a lower temperature than those of Lummer and Pringsheim, were in complete harmony with the predictions of Wien's distribution law. Planck breathed a sigh of relief and read out Paschen's paper at a session of the Prussian Academy of Sciences. Such a law appealed deeply to him. For Planck the theoretical quest for the spectral energy distribution of blackbody radiation was nothing less than the search for the absolute, and 'since I had always regarded the search for the absolute as the loftiest goal of all scientific activity, I eagerly set to work'.39
Soon after Wien published his distribution law, in 1896, Planck set about trying to place the law on rock-solid foundations by deriving it from first principles. Three years later, in May 1899, he thought he had succeeded by using the power and authority of the second law of thermodynamics. Others agreed and started calling Wien's law by a new name, Wien-Planck, despite the claims and counter-claims of the experimentalists. Planck remained confident enough to assert that 'the limits of validity of this law, in case there are any at all, coincide with those of the second fundamental law of the theory of heat'.40 He advocated further testing of the distribution law as a matter of urgency, since for him it would be a simultaneous examination of the second law. He got his wish.
At the beginning of November 1899, after spending nine months extending the range of their measurements as they eliminated possible sources of experimental error, Lummer and Pringsheim reported that they had found 'discrepancies of a systematic nature between theory and experiment'.41 Although in perfect agreement for short wavelengths, they discovered that Wien's law consistently overestimated the intensity of radiation at long wavelengths. However, within weeks Paschen contradicted Lummer and Pringsheim. He presented another set of new data and claimed that the distribution law 'appears to be a rigorously valid law of nature'.42
With most of the leading experts living and working in Berlin, the meetings of the German Physical Society held in the capital became the main forum for discussions concerning blackbody radiation and the status of Wien's law. It was the subject that again dominated the proceedings of the society at its fortnightly meeting on 2 February 1900 when Lummer and Pringsheim disclosed their latest measurements. They had found systematic discrepancies between their measurements and the predictions of Wien's law in the infrared region that could not be the result of experimental error.
This breakdown of Wien's law led to a scramble to find a replacement. But these makeshift alternatives proved unsatisfactory, prompting calls for further testing at even longer wavelengths to unequivocally establish the extent of any failure of Wien's law. It did, after all, agree with the available data covering the shorter wavelengths, and all other experiments bar those of Lummer-Pringsheim had found in its favour.
As Planck was only too well aware, any theory is at the mercy of hard experimental facts, but he strongly believed that 'a conflict between observation