Quantum_ Einstein, Bohr and the Great Debate About the Nature of Reality - Manjit Kumar [3]
When Einstein and Bohr first met in Berlin in 1920, each found an intellectual sparring partner who would, without bitterness or rancour, push and prod the other into refining and sharpening his thinking about the quantum. It is through them and some of those gathered at Solvay 1927 that we capture the pioneering years of quantum physics. 'It was a heroic time', recalled the American physicist Robert Oppenheimer, who was a student in the 1920s.10 'It was a period of patient work in the labo-ratory, of crucial experiments and daring action, of many false starts and many untenable conjectures. It was a time of earnest correspondence and hurried conferences, of debate, criticism and brilliant mathematical improvisation. For those who participated it was a time of creation.' But for Oppenheimer, the father of the atom bomb: 'There was terror as well as exaltation in their new insight.'
Without the quantum, the world we live in would be very different. Yet for most of the twentieth century, physicists accepted that quantum mechanics denied the existence of a reality beyond what was measured in their experiments. It was a state of affairs that led the American Nobel Prize-winning physicist Murray Gell-Mann to describe quantum mechanics as 'that mysterious, confusing discipline which none of us really understands but which we know how to use'.11 And use it we have. Quantum mechanics drives and shapes the modern world by making possible everything from computers to washing machines, from mobile phones to nuclear weapons.
The story of the quantum begins at the end of the nineteenth century when, despite the recent discoveries of the electron, X-rays, and radioactivity, and the ongoing dispute about whether or not atoms existed, many physicists were confident that nothing major was left to uncover. 'The more important fundamental laws and facts of physical science have all been discovered, and these are now so firmly established that the possibility of their ever being supplanted in consequence of new discoveries is exceedingly remote', said the American physicist Albert Michelson in 1899. 'Our future discoveries,' he argued, 'must be looked for in the sixth place of decimals.'12 Many shared Michelson's view of a physics of decimal places, believing that any unsolved problems represented little challenge to established physics and would sooner or later yield to time-honoured theories and principles.
James Clerk Maxwell, the nineteenth century's greatest theoretical physicist, had warned as early as 1871 against such complacency: 'This characteristic of modern experiments – that they consist principally of measurements – is so prominent, that the opinion seems to have got abroad that in a few years all the great physical constants will have been approximately estimated, and that the only occupation which will be left to men of science will be to carry on these measurements to another place of decimals.'13 Maxwell pointed out that the real reward for the 'labour of careful measurement' was not greater accuracy but the 'discovery of new fields of research' and 'the development of new scientific ideas'.14 The discovery of the quantum was the result of just such a 'labour of careful measurement'.
In the 1890s some of Germany's leading physicists were obsessively pursuing a problem that had long vexed them: what was the relationship between the temperature, the range of colours, and the intensity of light emitted by a hot iron poker? It seemed a trivial problem compared to the mystery of X-rays and radioactivity that had physicists rushing to their laboratories and reaching for their notebooks. But for a nation forged only in 1871, the quest for the solution to the hot iron poker, or what became known as 'the blackbody problem', was intimately bound up with the need to give the German lighting industry a competitive edge against its British and American competitors. But try as they might, Germany's finest physicists could not solve it. In 1896