Einstein: His Life and Universe

Einstein also became a supporter of racial tolerance. When Marian Anderson, the black contralto, came to Princeton for a concert in 1937, the Nassau Inn refused her a room. So Einstein invited her to stay at his house on Mercer Street, in what was a deeply personal as well as a publicly symbolic gesture. Two years later, when she was barred from performing in Washington’s Constitution Hall, she gave what became a historic free concert on the steps of the Lincoln Memorial. Whenever she returned to Princeton, she stayed with Einstein, her last visit coming just two months before he died.⁶³

One problem with Einstein’s willingness to sign on to various and sundry movements, appeals, and honorary chairmanships was that, as before, it opened him to charges that he was a dupe for those that were fronts for communists or other subversives. This purported sin was compounded, in the eyes of those who were suspicious about his loyalty, when he declined to sign on to some crusades that attacked Stalin or the Soviets.

For example, when his friend Isaac Don Levine, whose anticommunist writings Einstein had previously endorsed, asked him to sign a petition in 1934 condemning Stalin’s murder of political prisoners, this time Einstein balked. “I, too, regret immensely that the Russian political leaders let themselves be carried away,” Einstein wrote. “In spite of this, I cannot associate myself with your action. It will have no impact in Russia. The Russians have proved that their only aim is really the improvement of the lot of the Russian people.”⁶⁴

It was a gauzy view of the Russians and of Stalin’s murderous regime, one that history would prove wrong. Einstein was so intent on fighting the Nazis, and so annoyed that Levine had shifted so radically from left to right, that he reacted strongly against those who would equate the Russian purges with the Nazi holocaust.

An even larger set of trials in Moscow began in 1936, involving supporters of the exiled Leon Trotsky, and again Einstein rebuffed some of his former friends from the left who had now swung to become ardently anticommunist. The philosopher Sidney Hook, a recovering Marxist, wrote Einstein, asking him to speak out in favor of the creation of an international public commission to assure that Trotsky and his supporters would get a fair hearing rather than merely a show trial. “There is no doubt that every accused person should be given an opportunity to establish his innocence,” Einstein replied. “This certainly holds true for Trotsky.” But how should this be accomplished? Einstein suggested it would best be done privately, without a public commission.⁶⁵

In a very long letter, Hook tried to rebut each of Einstein’s concerns, but Einstein lost interest in arguing with Hook and did not respond. So Hook phoned him in Princeton. He reached Helen Dukas, and somehow was able to make it through her defensive shield to set up an appointment.

Einstein received Hook cordially, brought him up to his study lair, smoked his pipe, and spoke in English. After listening to Hook again make his case, Einstein expressed sympathy but said he thought the whole enterprise was unlikely to succeed. “From my point of view,” he proclaimed, “both Stalin and Trotsky are political gangsters.” Hook later said that even though he disagreed with Einstein, “I could appreciate his reasons,” especially because Einstein emphasized that he was “aware of what communists were capable of doing.”

Wearing an old sweatshirt and no socks, Einstein walked Hook back to the train station. Along the way, he explained his anger at the Germans. They had raided his house in Caputh searching for communist weapons, he said, and found only a bread knife to confiscate. One remark he made turned out to be very prescient. “If and when war comes,” he said, “Hitler will realize the harm he has done Germany by driving out the Jewish scientists.”⁶⁶

CHAPTER TWENTY

QUANTUM ENTANGLEMENT

1935

“Spooky Action at a Distance”

The thought experiments that Einstein had lobbed like grenades into the temple of quantum mechanics had done little damage to the edifice. In fact, they helped test it and permit a better understanding of its implications. But Einstein remained a resister, and he continued to conjure up new ways to show that the uncertainties inherent in the interpretations formulated by Niels Bohr, Werner Heisenberg, Max Born, and others meant that something was missing in their explanation of “reality.”

Just before he left Europe in 1933, Einstein attended a lecture by Leon Rosenfeld, a Belgian physicist with a philosophical bent. When it was over, Einstein rose from the audience to ask a question. “Suppose two particles are set in motion towards each other with the same, very large, momentum, and they interact with each other for a very short time when they pass at known positions,” he posited. When the particles have bounced far apart, an observer measures the momentum of one of them. “Then, from the conditions of the experiment, he will obviously be able to deduce the momentum of the other particle,” Einstein said. “If, however, he chooses to measure the position of the first particle, he will be able to tell where the other particle is.”

Because the two particles were far apart, Einstein was able to assert, or at least to assume, that “all physical interaction has ceased between them.” So his challenge to the Copenhagen interpreters of quantum mechanics, posed as a question to Rosenfeld, was simple: “How can the final state of the second particle be influenced by a measurement performed on the first?”¹

Over the years, Einstein had increasingly come to embrace the concept of realism, the belief that there is, as he put it, “a real factual situation” that exists “independent of our observations.”² This belief was one aspect of his discomfort with Heisenberg’s uncertainty principle and other tenets of quantum mechanics that assert that observations determine realities. With his question to Rosenfeld, Einstein was deploying another concept: locality.* In other words, if two particles are spatially distant from each other, anything that happens to one is independent from what happens to the other, and no signal or force or influence can move between them faster than the speed of light.

Observing or poking one particle, Einstein posited, could not instantaneously jostle or jangle another one far away. The only way an action on one system can affect a distant one is if some wave or signal or information traveled between them—a process that would have to obey the speed limit of light. That was even true of gravity. If the sun suddenly disappeared, it would not affect the earth’s orbit for about eight minutes, the amount of time it would take the change in the gravitational field to ripple to the earth at the speed of light.

As Einstein said, “There is one supposition we should, in my opinion, absolutely hold fast: the real factual situation of the system S₂ is independent of what is done with the system S₁, which is spatially separated from the former.”³ It was so intuitive that it seemed obvious. But as Einstein noted, it was a “supposition.” It had never been proven.

To Einstein, realism and localism were related underpinnings of physics. As he declared to his friend Max Born, coining a memorable phrase, “Physics should represent a reality in time and space, free from spooky action at a distance.”⁴

Once he had settled in Princeton, Einstein began to refine this thought experiment. His sidekick, Walther Mayer, less loyal to Einstein than Einstein was to him, had drifted away from the front lines of fighting quantum mechanics, so Einstein enlisted the help of Nathan Rosen, a 26-year-old new fellow at the Institute, and Boris Podolsky, a 49- year-old physicist Einstein had met at Caltech who had since moved to the Institute.

The resulting four-page paper, published in May 1935 and known by the initials of its authors as the EPR paper, was the most important paper Einstein would write after moving to America. “Can the Quantum-Mechanical Description of Physical Reality Be Regarded as Complete?” they asked in their title.