Black-Body Theory and the Quantum Discontinuity, 1894-1912 by Thomas S. Kuhn

Black-Body Theory and the Quantum Discontinuity, 1894-1912 Reviews

• 
  Erik

  I am not crazy about Kuhn as a philosopher, but as an historian of science he is unmatched here. The Planck Black Body Law is an historical mess, and is rarely taught the way it was discovered. It was NOT developed as a response to the "ultraviolet catastrophe," which it predates. E=nhv wasn't even part of the original deduction which started instead from the entropy of an oscillator as a function of its energy and the size of the chunk e (epsilon). Planck got e=hv from Wien's law almost as a slight of hand after he knew the expression for the oscillator's entropy. And then of course it took an Einstein to convince the physics community that the radiation is quantized as well as the energy levels of the oscillators. How he did that, as explained by Kuhn, was via his "box in the box" thought experiment. At first I hated this story because it wasn't the way I learned it, now I love it because the story is so rich and real to me.
• 
  Ari

  The first part is very technical, with equations, and a bit of a struggle for me. But it was interesting seeing what physics was like c. 1900.
  The second part picks up the pace a bit and looks at the adoption and influence of the early quantum theory.
  
  Kuhn's claim -- which I hadn't heard before but am now decently convinced of -- is that the folk history of quantum mechanics is wrong. In one of those surprisingly common ironies, Planck came up with the (correct) blackbody formula for all the wrong reasons. Around 1900, he was interested in defining the entropy of radiation fields, and slavishly copied Boltzmann's derivation for ideal gasses. And he found that by leaving a finite size for the elements in the analysis, he got a formula that matched observation and seemed to make sense. He didn't understand this -- and neither did anybody else -- to be a break with classical physics.
  
  I had vaguely thought Planck was trying to solve the Ultraviolet Catastrophe and fixed it by introducing energy quanta. In fact, nobody had actually noticed the ultraviolet catastrophe in classical physics until AFTER Planck had published his [correct] law and [incorrect] classical derivation of it. It took until 1905-1908 before physicists noticed that Planck's derivation was wrong, that classical physics led inevitably to the wrong answer, and that Planck's law could be saved by introducing energy quanta.
  
  Planck himself ones commented that "science advances one funeral at a time." This episode is a counterexample. Nobody understood the need for energy quantization until 1905. By 1915, it was widely accepted by fairly senior people (Planck, Lorentz, etc).
• 
  Alex

  UGA: Philosophy of Science
• 
  Ahmed

  nice