Science by Conversation
Quantum theory was not an overnight success. Its reception during the first decade of its history was hesitant, and its practitioners were scarce. By 1910, the Planck postulates were more or less recognized, but they had been applied mostly to problems concerning radiation and the solid state, and hardly at all in the realm of atoms and molecules. There had been no movement toward the formulation of a general quantum physics.
In the summer of 1913, there appeared in the Philosophical Magazine the first of a series of papers that began to turn the tide. The author was Niels Bohr, a twenty-eight-year-old Danish physicist with a rare personality. Bohr's theory described the behavior of atoms, particularly hydrogen atoms, with a carefully concocted mixture of the Planck postulates and the classical mechanics of Kepler and Newton. Bohr applied the theory, with spectacular success, to the beautiful spectral patterns emitted by hydrogen gas when it is excited electrically. (The physical apparatus is similar to that used in neon lighting.) This was, to the physicists of the time, an incredible achievement. Spectroscopists, the experimentalists who study the regularities of light wavelengths (spectra) emitted by atoms and molecules, had done their work so long without benefit of a theory that they had despaired of ever finding one. Bohr's papers brought new hope for spectroscopy, and for quantum theory as well.
To some extent, Bohr's role in this was good fortune. Quantum theory loomed large enough in 1913 that its value to atomic physics could not have been missed much longer. Even so, Bohr's task was no simple exercise. It took skill and intuitive sense in large measure to devise a workable mixture of classical and quantum physics. Einstein remarked that he had had similar ideas, “but had no pluck to develop them.” To Einstein, Bohr's sensitive application of the “insecure and contradictory foundation” supplied by quantum theory to atomic problems was a marvel, “the highest form of musicality in the sphere of thought.”
Bohr did more than create theoretical masterpieces. He also built, almost