Reluctant revolutionary


  Niels Bohr (1885-1962) and Max Planck in Copenhagen, 1930.
  Neither Max Planck nor his contemporaries immediately recognized the full import of the hypothesis that energy was quantized-some physicists even thought that they could dismiss the term h as a mathematical fiction. How deep the contradiction was to the former physics only became clear with the developments of the next few years. Almost five years had passed when the young Albert Einstein ventured to take the next step with his light quantum hypothesis. Eventually, a whole decade later, the quantum hypothesis was accepted by the scientific public at large. In 1911 quantum theory moved to the forefront of physical research. Gradually, physicists realized that the quantity h had a significance beyond the radiation problem, providing the key to understanding atomic processes. h became a constitutive component of modern physics particularly through the atomic theory of the Danish physicist Niels Bohr, and in the mid-1920s quantum mechanics eventually provided an interpretation of h and the Planck relation e = h n. Planck did not contribute significantly toward the development of his quantum hypothesis into quantum physics. This became the task of a younger generation of physicists. Nevertheless he participated in the discussion about the basic physical and epistemological issues and as a sympathetic critic offered his input to the developing field.

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  "In introducing the quantum of action h into the theory, one must go about it as conservatively as possible, that is, only those changes are to be made to the theory that have been found to be absolutely necessary."
Max Planck, 1910

The 1st Solvay conference in the fall of 1911, a "summit conference" of leading physicists of the time, provided the breakthrough for Planck's quantum hypothesis. Thereafter, quantum theory moved into the focus of contemporary physical research.