by Manjit Kumar
Heisenberg had long wanted to be Sommerfeld’s successor at Munich. In 1935 Stark called Heisenberg the ‘spirit of Einstein’s spirit’ and launched a concerted campaign against him and theoretical physics. It culminated on 15 July 1937 with the publication of an article in the SS journal, Das Schwarze Korps, in which Heisenberg was branded a ‘white Jew’. He spent the next year trying to remove the slur that, if it stuck, would place him in real danger of being isolated and dismissed. He turned to Heinrich Himmler, head of the SS, who happened to be a family acquaintance. Himmler exonerated Heisenberg, but blocked his appointment as Sommerfeld’s successor. There was also a proviso that in future he should ‘clearly separate for your audiences, in the acknowledgement of scientific research results, the personal and political characteristics of the researcher’.36 Heisenberg duly obliged in separating the scientist from the science. There would be no more mention by him of Einstein’s name in public.
The Göttingen physicists James Franck and Max Born were exempt as war veterans from the ‘Aryan clause’. But neither man chose to exercise his right, believing that to do so was tantamount to collusion with the Nazis. Franck was condemned by no fewer than 42 of his colleagues when he submitted his letter of resignation, for fuelling anti-German propaganda by stating that ‘we Germans of Jewish descent are being treated as aliens and enemies of the Fatherland’.37 Born, who had no intention of resigning, discovered his name on a list of suspended civil servants published in the local newspaper. ‘All I had built up in Göttingen, during twelve years hard work, was shattered’, he wrote later.38 ‘It seemed to me like the end of the world.’ He shuddered at the thought of ‘standing in front of students who, for whatever reason, have thrown me out, or living among colleagues who were able to live with this so easily’.39
Suspended but not yet sacked, Born had never felt particularly Jewish, he confessed to Einstein. But now he was ‘extremely conscious of it, not only because we are considered to be so, but because oppression and injustice provoke me to anger and resistance’.40 Born hoped to settle in England, ‘for the English seem to be accepting the refugees most nobly and generously’.41 His wish was granted when he was offered a three-year lectureship at Cambridge University. Believing that he might be depriving a deserving English physicist, Born accepted only after being reassured that the post had been created especially for him. He was one of the lucky few whose contributions to physics were internationally recognised, unlike the ‘young ones’ for whom Einstein said his ‘heart aches’.42 But even scientists of Born’s calibre had to endure periods of deep uncertainty about their future. After his time in Cambridge was up, Born spent six months in Bangalore, India and was seriously considering a post in Moscow, when in 1936 he was offered the chair of natural philosophy at the University of Edinburgh.
Heisenberg had tried to convince Born that he was safe, since ‘only the very least are affected by the law – you and Franck certainly not’. He hoped, like others, that things would eventually settle down and ‘the political revolution could take place without any damage to Göttingen physics’.43 But the damage was already done. It had taken the Nazis a matter of weeks to transform Göttingen, the cradle of quantum mechanics, from a great university to a second-rate institution. The Nazi minister of education asked David Hilbert, the most fêted mathematician in Göttingen, whether it was true ‘that your Institute suffered so much from the departure of the Jews and their friends?’ ‘Suffered? No, it didn’t suffer, Herr Minister’, replied Hilbert. ‘It just doesn’t exist any more.’44
As news spread of what was happening in Germany, scientists and their professional bodies quickly swung into action to help colleagues fleeing Nazi oppression with money and jobs. Aid organisations supported by gifts and donations from individuals and private foundations were set up. In England, the Academic Assistance Council, with Rutherford as its president, was established in May 1933 as a ‘clearing house’ that found temporary posts and offered help for refugee scientists, artists, and writers. Many initially escaped to Switzerland, Holland or France and stayed only a short while before travelling on to Britain and the United States.
In Copenhagen, Bohr’s institute became a staging post for many physicists. In December 1931, the Danish Academy of Sciences and Letters had chosen Bohr as the next occupant of the Aeresbolig, ‘The House of Honour’, a mansion built by the founder of the Carlsberg breweries. His new status as Denmark’s leading citizen meant he enjoyed even more influence at home and abroad, which he exercised to help others. In 1933 he and his brother Harald helped set up ‘The Danish Committee for Support of Intellectual Workers in Exile’. Through colleagues and former students, Bohr was able to get new posts established or have vacancies filled by refugees. It was Bohr who got James Franck to Copenhagen on a three-year visiting professorship in April 1934. After a year or so, Franck moved on to a tenured position in the United States, which, along with Sweden, was the final destination of many who arrived in Denmark. One man who did not have to worry about a job was Einstein.
In early September, as fears for his safety in Belgium grew, Einstein left for England. For the next month he kept a low profile, staying in a cottage on the Norfolk coast. Soon the tranquillity by the seaside was shattered when he learnt that Paul Ehrenfest, in a fit of despair while estranged from his wife, had committed suicide. It happened during a visit to an Amsterdam hospital to see his sixteen-year-old son Vassily, who suffered from Down’s syndrome. Einstein was shocked at the news that Ehrenfest had also shot Vassily. Remarkably, the boy survived but was blinded in one eye.
Although deeply upset at Ehrenfest’s suicide, Einstein’s thoughts soon turned to the speech he had agreed to give at a fundraising rally highlighting the plight of refugees. The meeting, chaired by Rutherford, took place on 3 October at the Royal Albert Hall. A public eager to get a glimpse of the great man meant that there was not even standing room on the night. Einstein succeeded in addressing the audience of 10,000 in his heavily accented English without once mentioning Germany by name, at the request of the organisers. For the Refugee Assistance Council believed that ‘the issue raised at the moment is not a Jewish one alone; many who have suffered or are threatened had no Jewish connection’.45 Four days later, on the evening 7 October, Einstein left for America. Due to spend the next five months at the Institute for Advanced Study, he never returned to Europe.
As he was being driven from New York to Princeton, Einstein was handed a letter from Abraham Flexner. The institute’s director was asking him not to attend any public events and to exercise discretion for own his safety. The reason Flexner gave was the danger posed to Einstein by the ‘bands of irresponsible Nazis’ to be found in America.46 Yet his real concern was the damage that Einstein’s public statements might inflict on the reputation of his fledgling institute, and therefore on the donations it relied on. Within a matter of weeks, Einstein found Flexner’s restrictions and increasing interference suffocating. Once he even gave his new address as ‘Concentration camp, Princeton’.47
Einstein wrote to the trustees of the institute to complain of Flexner’s behaviour, and asked them to guarantee him ‘security for undisturbed and dignified work, in such a way that there is no interference at every step of a kind that no self-respecting person can tolerate’.48 If they could not, then he would have to ‘discuss with you ways and means of severing my relations with your Institute in a dignified manner’.49 Einstein gained the right to do as he pleased, but at a price. He would never have any real influence in the running of the institute. When he backed Schrödinger for a post at the institute, it effectively ruled the Austrian out of the running.
Schrödinger did not have to leave Berlin, but did so as a matter of principle. He had been in exile at Magdalen College, Oxford University less than a week when, on 9 November 1933, he received some unexpected news. The president of the college, George Gordon, informed Schrödinger that The Times had called to say that he would be among the winners of the Nobel Prize that yea
r. ‘I think you may believe it. The Times do not say a thing unless they really know’, said Gordon proudly.50 ‘As for me, I was truly astonished, for I thought you had the prize.’
Schrödinger and Dirac were each awarded a half share of the 1933 Nobel Prize, with the deferred prize of 1932 going to Heisenberg alone. Dirac’s first reaction was to refuse it because he did not want the publicity. He accepted after Rutherford convinced him that refusing it would generate even greater publicity. While Dirac toyed with the idea of rejecting the prize, Born was deeply hurt at being ignored by the Swedish Academy.
‘I have a bad conscience regarding Schrödinger, Dirac, and Born’, Heisenberg wrote to Bohr.51 ‘Schrödinger and Dirac both deserved an entire prize at least as much as I do, and I would have gladly shared with Born, since we have worked together.’ Earlier he replied to a letter of congratulations from Born: ‘The fact that I am to receive the Nobel Prize alone, for work done in Göttingen in collaboration – you, Jordan and I – this fact depresses me and I hardly know what to write to you.’52 ‘That Heisenberg’s matrices bear his name is not altogether justified, as in those days he actually had no idea what a matrix was’, Born complained to Einstein two decades later.53 ‘It was he who reaped all the rewards of our work together, such as the Nobel Prize and that sort of thing.’ He admitted that ‘for the last twenty years I have not been able to rid myself of a certain sense of injustice’. Born was finally awarded the Nobel in 1954 for ‘his fundamental work in quantum mechanics and especially for his statistical interpretation of the wave function’.
After the difficult start, by the end of November 1933 Princeton was beginning to appeal to Einstein. ‘Princeton is a wonderful little spot, a quaint and ceremonious village of puny demigods on stilts’, he wrote to Queen Elizabeth of Belgium. ‘Yet, by ignoring certain special conventions, I have been able to create for myself an atmosphere conducive to study and free from distractions.’54 In April 1934 Einstein made public that he would be staying in Princeton indefinitely. The ‘bird of passage’ had found a place to nest for the rest of his life.
Einstein had always been an outsider, even in physics, beginning with his days in the Patent Office. Yet he had led the way for so long and so often. He hoped to do so again as he came up with a new challenge for Bohr and the Copenhagen interpretation.
Chapter 13
QUANTUM REALITY
‘Princeton is a madhouse’ and ‘Einstein is completely cuckoo’, wrote Robert Oppenheimer.1 It was January 1935 and America’s leading home-grown theoretical physicist was 31. Twelve years later, after directing the building of the atomic bomb, he would return to the Institute for Advanced Study to take charge of the ‘madhouse’ and its ‘solipsistic luminaries shining in separate and helpless desolation’.2 Einstein accepted that his critical attitude towards quantum mechanics ensured that ‘here in Princeton I am considered an old fool’.3
It was a sentiment widely shared by the younger generation of physicists who, having been weaned on the theory, agreed with Paul Dirac’s assessment that quantum mechanics explained ‘most of physics and all of chemistry’.4 That a few old men were fighting about the meaning of the theory was, for them, neither here nor there, given its enormous practical success. By the end of the 1920s, as one problem after another in atomic physics was solved, attention shifted from the atom to the nucleus. During the early 1930s, the discovery of the neutron by James Chadwick in Cambridge, and the work of Enrico Fermi and his team in Rome on the reactions induced by the impact of neutrons on nuclei, opened up the new frontier of nuclear physics.5 In 1932 John Cockcroft and Ernest Walton, Chadwick’s colleagues in Rutherford’s Cavendish Laboratory, constructed the first particle accelerator and used it to split an atom by breaking apart its nucleus.
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 Einstein-Podolsky-Rosen paper, or the EPR paper as it became known, was completed and mailed by the end of March. ‘Can quantum Mechanical Description of Physical Reality Be Considered Complete?’, with its missing ‘the’, was published on 15 May in the American journal Physical Review.10 The EPR answer to the question posed was a defiant ‘No!’. Even before it appeared in print, Einstein’s name ensured that the EPR paper generated the kind of publicity nobody wanted.
On Saturday, 4 May 1935, the New York Times carried an article on page eleven under the attention-grabbing headline ‘Einstein Attacks quantum Theory’: ‘Professor Einstein will attack science’s important theory of quantum mechanics, a theory of which he was a sort of grandfather. He concluded that while it is “correct” it is not “complete”.’ Three days later, the New York Times carried a statement from a clearly disgruntled Einstein. Alt
hough no stranger to talking to the press, he pointed out that: ‘It is my invariable practice to discuss scientific matters only in the appropriate forum and I deprecate advance publication of any announcement in regard to such matters in the secular press.’11
In the published paper, Einstein, Podolsky and Rosen started by differentiating between reality as it is and the physicist’s understanding of it: ‘Any serious consideration of a physical theory must take into account the distinction between the objective reality, which is independent of any theory, and the physical concepts with which the theory operates. These concepts are intended to correspond with the objective reality, and by means of these concepts we picture this reality to ourselves.’12 In gauging the success of any particular physical theory, EPR argued that two questions had to be answered with an unequivocal ‘Yes’: Is the theory correct? Is the description given by the theory complete?
‘The correctness of the theory is judged by the degree of agreement between the conclusions of the theory and human experience’, said EPR. It was a statement that every physicist would accept when ‘experience’ in physics takes the form of experiment and measurement. To date there had been no conflict between the experiments performed in the laboratory and the theoretical predictions of quantum mechanics. It appeared to be a correct theory. Yet for Einstein it was not enough for a theory to be correct, in agreement with experiments; it also had to be complete.
Whatever the meaning of the term ‘complete’, EPR imposed a necessary condition for the completeness of a physical theory: ‘every element of the physical reality must have a counterpart in the physical theory.’13 This completeness criterion required EPR to define a so-called ‘element of reality’ if they were to carry through their argument.
