Quantum_ Einstein, Bohr and the Great Debate About the Nature of Reality - Manjit Kumar [57]
Bohr's trilogy was published virtually unchanged in the Philosophical Magazine as 'On the Constitution of Atoms and Molecules'. The first, dated 5 April 1913, appeared in July. The second and third parts, published in September and November, were a presentation of ideas concerning the possible arrangements of electrons inside atoms that would preoccupy Bohr for the next decade as he used the quantum atom to explain the periodic table and the chemical properties of the elements.
Bohr had built his atom using a heady cocktail of classical and quantum physics. In the process he had violated tenets of accepted physics by proposing that: electrons inside atoms can occupy only certain orbits, the stationary states; electrons cannot radiate energy while in those orbits; an atom can be in only one of a series of discrete energy states, the lowest being the 'ground state'; electrons can 'somehow' jump from a stationary state of high energy to a stationary state of low energy and the difference in energy between the two is emitted in a quantum of energy. Yet his model correctly predicted various properties of the hydrogen atom such as its radius, and it provided a physical explanation for the production of spectral lines. The quantum atom, Rutherford said later, was 'a triumph of mind over matter' and until Bohr unveiled it, he believed that 'it would require centuries' to solve the mystery of the spectral lines.36
A true measure of Bohr's achievement was the initial reactions to the quantum atom. It was discussed publicly for the first time on 12 September 1913 at the 83rd annual meeting of the British Association for the Advancement of Science (BAAS), held that year in Birmingham. With Bohr in the audience, it received a muted and mixed reception. J.J. Thomson, Rutherford, Rayleigh and Jeans were all there, while the distinguished foreign contingent included Lorentz and Curie. 'Men over seventy should not be hasty in expressing opinions on new theories', was Rayleigh's diplomatic response when pressed for his opinion about Bohr's atom. In private, however, Rayleigh did not believe 'that Nature behaved in that way' and admitted that he had 'difficulty in accepting it as a picture of what actually takes place'.37 Thomson objected to Bohr's quantisation of the atom as totally unnecessary. James Jeans begged to differ. He pointed out in a report to the packed hall that the only justification that Bohr's model required was 'the very weighty one of success'.38
In Europe, the quantum atom was greeted with disbelief. 'This is all nonsense! Maxwell's equations are valid under all circumstances', said Max von Laue during one heated discussion. 'An electron in a circular orbit must emit radiation.'39 While Paul Ehrenfest confessed to Lorentz that Bohr's atom 'has driven me to despair'.40 'If this is the way to reach the goal,' he continued, 'I must give up doing physics.'41 In Göttingen, Bohr's brother Harald reported that there was great interest in his work, but that his assumptions were deemed too 'bold' and 'fantastic'.42
One early triumph for Bohr's theory clinched the support of some, including Einstein. Bohr predicted that a series of lines found in the spectrum of light from the sun that had been attributed to hydrogen actually belonged to ionised helium, helium with one of its two electrons removed. This interpretation of the so-called 'Pickering-Fowler lines' was at odds with that of its discoverers. Who was right? The issue was settled by one of Rutherford's team in Manchester after a detailed study of the spectral lines instigated at the behest of Bohr.