Quantum_ Einstein, Bohr and the Great Debate About the Nature of Reality - Manjit Kumar [155]
Einstein might have moved from Berlin to Princeton, but physics was moving on without him. He knew as much, but felt he had earned the right to pursue the physics that interested him. When he arrived at the institute in October 1933, Einstein was shown to his new office and asked what equipment he needed. 'A desk or table, a chair, paper and pencils', he replied.6 'Oh yes, and a large wastebasket, so I can throw away all my mistakes.' And there were plenty, but Einstein was never disheartened as he sought his holy grail – a unified field theory.
Just as Maxwell had unified electricity, magnetism and light into a single all-encompassing theoretical structure in the nineteenth century, Einstein hoped to unify electromagnetism and general relativity. For him such a unification was the next step, as logical as it was inevitable. It was in 1925 that he undertook the first of his many attempts at constructing such a theory that ended up in the wastebasket. After the discovery of quantum mechanics, Einstein believed that a unified field theory would yield this new physics as a by-product.
In the years following Solvay 1930, there was little direct contact between Bohr and Einstein. A valuable channel of communication ceased with Paul Ehrenfest's suicide in September 1933. In a moving tribute, Einstein wrote of his friend's inner struggle to understand quantum mechanics and 'the increasing difficulty of adaptation to new thoughts which always confronts the man past fifty. I do not know how many readers of these lines will be capable of fully grasping that tragedy.'7
There were many who read Einstein's words and mistook them as a lament at his own plight. Now in his mid-fifties, he knew he was regarded as a relic from a bygone age, refusing, or unable, to live with quantum mechanics. But he also knew what separated him and Schrödinger from most of their colleagues: 'Almost all the other fellows do not look from the facts to the theory but from the theory to the facts; they cannot extricate themselves from a once accepted conceptual net, but only flop about in it in a grotesque way.'8
In spite of these mutual misgivings, there were always young physicists eager to work with Einstein. One was Nathan Rosen, a 25-year-old New Yorker who arrived from MIT in 1934 to serve as his assistant. A few months before Rosen, the 39-year-old Russian-born Boris Podolsky had joined the institute. He had first met Einstein at Caltech in 1931 and they had collaborated on a paper. Einstein had an idea for another paper. It would mark a new phase in his debate with Bohr, as it unleashed a fresh assault on the Copenhagen interpretation.
At Solvay 1927 and 1930, Einstein attempted to circumvent the uncertainty principle to show that quantum mechanics was inconsistent and therefore incomplete. Bohr, aided by Heisenberg and Pauli, had successfully dismantled each thought experiment and defended the Copenhagen interpretation. Afterwards, Einstein accepted that although quantum mechanics was logically consistent it was not the definitive theory that Bohr claimed. Einstein knew he needed a new strategy to demonstrate that quantum mechanics is incomplete, that it does not fully capture physical reality. To this end he developed his most enduring thought experiment.
For several weeks early in 1935, Einstein met Podolsky and Rosen in his office to thrash out his idea. Podolsky was assigned the task of writing the resulting paper, while Rosen did most of the necessary mathematical calculations. Einstein, as Rosen recalled later, 'contributed the general point of view and its implications'.9 Only four pages long, the