Quantum_ Einstein, Bohr and the Great Debate About the Nature of Reality - Manjit Kumar [134]
On Wednesday, 26 October, the proponents of the two rival versions of quantum mechanics addressed the conference. During the morning session, Heisenberg and Born gave a joint report. It was divided into four broad sections: the mathematical formalism; the physical interpretation; the uncertainty principle; and the applications of quantum mechanics.
The presentation, like the writing of the report, was a double act. Born, the senior man, delivered the introduction and sections I and II before handing over to Heisenberg. 'Quantum mechanics,' they began, 'is based on the intuition that the essential difference between atomic physics and classical physics is the occurrence of discontinuities.'14 Then came the metaphorical tipping of their hats to colleagues sitting only feet away as they pointed out that quantum mechanics was essentially 'a direct continuation of the quantum theory founded by Planck, Einstein, and Bohr'.15
After an exposition of matrix mechanics, the Dirac-Jordan transformation theory, and the probability interpretation, they turned to the uncertainty principle and the 'actual meaning of Planck's constant h'.16 It was nothing less, they maintained, than the 'universal measure of the indeterminacy that enters the laws of nature through the dualism of waves and corpuscles'. In effect, if there were no wave-particle duality of matter and radiation there would be no Planck's constant and no quantum mechanics. In conclusion, they made the provocative statement that 'we consider quantum mechanics to be a closed theory, whose fundamental physical and mathematical assumptions are no longer susceptible of any modification'.17
Closure implied that no future developments would ever alter any of the fundamental features of the theory. Any such claim to the completeness and finality of quantum mechanics was something that Einstein could not accept. For him quantum mechanics was indeed an impressive achievement but not yet the real thing. Refusing to take the bait, Einstein took no part in the discussion that followed the report. Nor did any one else raise objections, as only Born, Dirac, Lorentz and Bohr spoke.
Paul Ehrenfest, sensing Einstein's disbelief at the boldness of the Born-Heisenberg assertion that quantum mechanics was a closed theory, scribbled a note and passed it to him: 'Don't laugh! There is a special section in purgatory for professors of quantum theory, where they will be obliged to listen to lectures on classical physics ten hours every day.'18 'I laugh only at their naiveté', Einstein replied. 'Who knows who would have the [last] laugh in a few years?'
After lunch it was Schrödinger who took centre stage as he delivered his report in English on wave mechanics. 'Under this name at present two theories are being carried on, which are indeed closely related but not identical', he said.19 There was really only one theory, but it was effectively split in two. One part concerned waves in ordinary, everyday three-dimensional space, while the other required a highly abstract multi-dimensional space. The problem, Schrödinger explained, was that for anything other than a moving electron this was a wave that existed in a space with more than three dimensions. Whereas the single electron of the hydrogen atom could be accommodated in a three-dimensional space, helium with two electrons needed six dimensions. Nevertheless, Schrödinger argued that this multi-dimensional space, known as configuration space, was only a mathematical tool and ultimately whatever was being described, be it many electrons colliding or orbiting the nucleus of an atom, the process took place in space and time. 'In truth, however, a complete unification of the two conceptions has not yet been achieved',