An Interview with Einstein

Two weeks before Einstein died he was visited by a historian of science. They sat in Einstein's study and discussed some of his illustrious predecessors in the evolution of physics

by I. Bernard Cohen

On a Sunday morning in April, two weeks before the death of Albert Einstein, I sat and talked with him about the history of scientific thought and great men in the physics of the past.

I had arrived at the Einstein home, a small frame house with green shutters, at 10 o'clock in the morning and was greeted by Helen Dukas, Einstein's secretary and housekeeper. She conducted me to a cheerful room on the second floor at the back of the house. This was Einstein's study. It was lined on two walls with books from floor to ceiling and contained a large low table laden with pads of paper, pencils, trinkets, books and a collection of well-worn pipes. There was a phonograph and records. Dominating the room was a large window with a pleasant green view. On the remaining wall were portraits of the two founders of the electromagnetic theory – Michael Faraday and James Clerk Maxwell.

After a few moments Einstein entered the room and Miss Dukas introduced us. He greeted me with a warm smile, went into the adjacent bedroom and returned with his pipe filled with tobacco. He wore an open shirt, a blue sweat shirt, gray flannel trousers and leather slippers. There was a touch of chill in the air, and he tucked a blanket around his feet. His face was contemplatively tragic and deeply lined, and yet his sparkling eyes made him seem ageless. His eyes watered almost continually; even in moments of laughter he would wipe away a tear with the back of his hand. He spoke softly and clearly; his command of English was remarkable, though marked by a German accent. The contrast between his soft speech and his ringing laughter was enormous. He enjoyed making jokes; every time he made a point that he liked, or heard something that appealed to him, he would burst into booming laughter that echoed from the walls.

We sat side by side at the table, facing the window and the view. He appreciated that it was difficult for me to begin a conversation with him; after a few moments he turned to me as if answering my unasked questions, and said: "There are so many unsolved problems in physics. There is so much that we do not know; our theories are far from adequate." Our talk veered at once to the problem of how often in the history of science great questions seem to be resolved, only to reappear in new form. Einstein expressed the view that perhaps this was a characteristic of physics, and suggested that some of the fundamental problems might always be with us.

Einstein remarked that when he was a young man the philosophy of science was considered a luxury, and most scientists paid no attention to it. He assumed that the situation was much the same with respect to the history of science. The two subjects must be similar, he said, because both deal with scientific thought. He wanted to know about my training in science and in history, and how I had become interested in Newton. I told him that one of the aspects of my research was the origin of scientific concepts and the relation between experiment and the creation of theory; what had always impressed me about Newton was his dual genius – in pure mathematics and mathematical physics and in experimental science. Einstein said that he had always admired Newton. As he explained this, I remembered those striking words in his autobiographical statement following a critique of Newtonian concepts – "Newton, forgive me."

Einstein was particularly interested in the various aspects of Newton's personality and we discussed Newton's controversy with Hooke in the matter of priority in the inverse-square law of gravitation. Hooke wanted only "some mention" in the preface to Newton's Principia, a little acknowledgment of his efforts, but Newton refused to make the gesture. Newton wrote to Halley, who was supervising the publication of the great Principia, that he would not give Hooke any credit; he would rather suppress the crowning glory of the treatise, the third and final "book" dealing with the system of the world. Einstein said: "That, alas, is vanity. You find it in so many scientists. You know, it has always hurt me to think that Galilei did not acknowledge the work of Kepler."

We then spoke of Newton's controversy with Leibniz over the invention of the calculus, and how Newton had attempted to prove that his German contemporary was a plagiarist. There was set up a supposed international committee of inquiry, composed of Englishmen and two foreigners; today we know that Newton anonymously directed the committee's activities. Einstein said that he was shocked by such conduct. He did not appear too much impressed when I asserted that it was the nature of the age to have violent controversies, that the standards of scientific behavior had changed greatly since Newton's day. Einstein felt that whatever the temper of the time there is a quality of human dignity that should enable a man to rise above the passions of his age.

Then we talked about Franklin, whose conduct as a scientist I had always admired, especially because he had not entered into such controversy. Franklin was proud that he had never written a <70> polemic in defense of his experiments or his ideas. He believed that experiments can be tested only in the laboratory, and that concepts and theories must make their own way by proving their validity. Einstein only partly agreed. It was well to avoid personal fights, he said, but it was also important for a man to stand up for his own ideas. He should not simply let them go by default, as if he did not really believe in them.

Einstein, who knew of my interest in Franklin, wanted to know more about him: Had he done more in science than invent the lightning rod? Had he really done anything of importance? I replied that in my opinion the greatest thing to come out of Franklin's research was the principle of the conservation of charge. Yes, said Einstein, that was a great contribution. Then he thought to himself for a moment or two and, with a smile, asked me how Franklin could have proved it. Of course, I conceded, Franklin was only able to adduce some experimental examples of equal positive and negative electrification, and to show the applicability of the principle in explaining a variety of phenomena. Einstein shook his head once or twice, and admitted that until then he had not appreciated that Franklin deserved a place of honor in the history of physics.

The subject of controversies over scientific work led Einstein to take up the subject of unorthodox ideas. He mentioned a fairly recent and controversial book, of which he had found the non-scientific part – dealing with comparative mythology and folklore – interesting. "You know," he said to me, "it is not a bad book. No, it really isn't a bad book. The only trouble with it is, it is crazy." This was followed by a loud burst of laughter. He then went on to explain what he meant by this distinction. The author had thought he was basing some of his ideas upon modern science, but found the scientists did not agree with him at all. In order to defend his idea of what he conceived modern science to be, so as to maintain his theories, he had to turn around and attack the scientists. I replied that the historian often encountered this problem: Can a scientist's contemporaries tell whether he is a crank or a genius when the only evident fact is his unorthodoxy? A radical like Kepler, for example, challenged accepted ideas; it must have been difficult for his contemporaries to tell whether he was a genius or a crank. "There is no objective test," replied Einstein.

Einstein was sorry that scientists in the U. S. had protested to publishers about the publication of such a book. He thought that bringing pressure to bear on a publisher to suppress a book was an evil thing to do. Such a book really could not do any harm, and was therefore not really bad. Left to itself, it would have its moment, public interest would die away and that would be the end of it. The author of such a book might be "crazy" but not "bad," just as the book was not "bad." Einstein expressed himself on this point with great passion.

Much of the time we spent together was devoted to the history of science, a subject that had long been of interest to Einstein. He had written many articles about Newton, prefaces to historical works and also biographical sketches of his contemporaries and the great men of science of the past. Thinking aloud about the nature of the historian's job, he compared history to science. Certainly, he said, history is less objective than science. For example, he explained, if two men were to study the same subject in history, each would stress the particular part of the subject which interested him or appealed to him the most. As Einstein saw it, there is an inner or intuitional history and an external or documentary history. The latter is more objective, but the former is more interesting. The use of intuition is dangerous but necessary in all kinds of historical work, especially when the attempt is made to reconstruct the thought processes of someone who is no longer alive. This kind of history, Einstein felt, is very illuminating despite its riskiness. <71> It is important to know, he went on, what Newton thought and why he did certain things. We agreed that the challenge of such a problem should be the major motivation of a good scientific historian. For instance, how and why had Newton developed his concept of the aether? Despite the success of Newton's gravitation theory, he was not satisfied by the concept of the gravitational force. Einstein believed that what Newton most strongly objected to was the idea of a force being able to transmit itself through empty space. Newton hoped by means of an aether to reduce action at a distance to a force of contact. Here is a statement of great interest about Newton's process of thought, Einstein declared, but the question arises as to whether – or perhaps to what extent – one can document such intuition. Einstein said most emphatically that he thought the worst person to document any ideas about how discoveries are made is the discoverer. Many people, he went on, had asked him how he had come to think of this or how he had come to think of that. He had always found himself a very poor source of information concerning the genesis of his own ideas. Einstein believed that the historian is likely to have a better insight into the thought processes of a scientist than the scientist himself.

Einstein's interest in Newton had always been centered on his ideas, which are to be found in every textbook of physics. He had never made a systematic examination of all Newton's writings, in the manner of a thorough historian of science, but of course he had an appreciation of Newtonian science that could come only from a scientific peer of Newton. Yet Einstein was keenly interested in the results of scholarship in the history of science, such as the development of some of Newton's fundamental opinions in his successive revisions of his major works, the Opticks and the Principia. In our correspondence on this subject, the question had arisen as to whether there was any sense in which Einstein might have "revived" a Newtonian concept of light in his paper on photons in 1905. Had he ever read Newton's writings on light before that year? He told me: "As far as I can remember I had not studied, or at least not studied profoundly, the original before I had to write the little foreword for the Opticks. The reason is, of course, that everything that Newton ever wrote is alive in the later works in physical science." Furthermore, "younger people are very little historically minded." Einstein's main concern had been his own scientific work; he had known of Newton primarily as the author of many of the fundamental concepts in classical physics. But he had encountered Newton's "utterances of a philosophical character"; these were cited again and again.

In 1905 Einstein knew that Newton had espoused a corpuscular theory of light, a fact which he must have found in Drude's famous book on light, but he had evidently not known until many decades later about Newton's attempts to blend a corpuscular and wave theory. Einstein knew of my interest in the Opticks, especially in the influence of this book on the later course of experimental physics. When I remarked on the greatness of Newton's intuition about the study of light being the key to exact knowledge of the corpuscles of matter, Einstein misunderstood what I had said. He replied that we must not take too seriously the historical accident that Newton's corpuscular view of light with wave aspects sounds something like modern statements. I explained what I had meant: Newton had attempted to infer from what we call interference or diffraction phenomena the size of the corpuscles of matter. These intuitions might be very profound, Einstein agreed, but not necessarily fruitful. For example, he said, Newton's thoughts on this subject did not lead anywhere; he could not prove his point nor derive precise information about the structure of matter.

Einstein was actually more interested in the Principia and in Newton's views on hypotheses. He greatly esteemed the Opticks, but primarily for the analysis of color and the magnificent experiments. Of this book he had written that "it alone can afford us the enjoyment of a look at the personal activity of this unique man." Looking back over all of Newton's ideas, Einstein said, he thought that Newton's greatest achievement was his recognition of the role of privileged systems. He repeated this statement several times and with great emphasis. This is rather puzzling, I thought to myself, because today we believe that there are no privileged systems, only inertial systems; there is no privileged frame – not even our solar system – which we can say is privileged in the sense of being fixed in space, or having special physical properties not possible in other systems. Due to Einstein's own work we no longer believe (as Newton did) in concepts of absolute space and absolute time, nor in a privileged system at rest or in motion with respect to absolute space. Newton's solution appeared to Einstein ingenious and necessary in his day. I was reminded of Einstein's statement: "Newton, . . . you found the only way which, in your age, was just about possible for a man of highest thought and creative power."

I remarked that Newton's genius was displayed in his adopting as a "hypothesis" in the Principia the statement about the "center of the system of the world" being fixed, immobile in space; that a lesser man than Newton might have thought he could prove such an assertion, either by mathematics or by experiment. Einstein replied that Newton probably did not fool himself. He was apt to know what could be proved and what could not; this was a sign of his genius.

Einstein then said that the biographical aspects of scientists had always interested him as much as their ideas. He liked to learn the lives of the men who had created the great theories and performed the major experiments, what kind of men they were, how they worked and how they treated their fellow men. Reverting to an earlier topic of our conversation, Einstein observed how many scientists seemed to have suffered from vanity. He pointed out that vanity may appear in many different forms. Often a man would say that he had no vanity, but this too was a kind of vanity because he took such special pride in the fact. "It is like childishness," he said. Then he turned to me and his booming laugh <72> filled the room. "Many of us are childish; some of us more childish than others. But if a man knows that he is childish, then that knowledge can be a mitigating factor."

The conversation then turned to Newton's life and his private speculations: his investigations of theology. I mentioned to Einstein that Newton had essayed a linguistic analysis of theology, in an attempt to find the corruptions that had been introduced into Christianity. Newton was not an orthodox Trinitarian. He believed his own views were hidden away in Scripture, but that the revealed documents had been corrupted by later writers who had introduced new concepts and even new words. So Newton sought by linguistic analysis to find the truth. Einstein remarked that for him this was a "weakness" in Newton. He did not see why Newton, finding his own ideas and the orthodox ones at variance, did not simply reject the established views and assert his own. For instance, if Newton could not agree with the accepted interpretations of Scripture, why did he believe that Scripture must nevertheless be true? Was it only because the common point of view was that fundamental truths are contained in the Bible? It did not seem to Einstein that in theology Newton showed the same great quality of mind as in physics. Einstein apparently had little feeling for the way in which a man's mind is imprisoned by his culture and the character of his thoughts are molded by his intellectual environment. I did not press the point, but I was struck by the fact that in physics Einstein could see Newton as a man of the 17th century, but that in the other realms of thought and action he viewed each man as a timeless, freely acting individual to be judged as if he were a contemporary of ours.

Einstein seemed particularly impressed by the fact that Newton had not been entirely satisfied with his theological writings, and had sealed them all up in a box. This seemed to indicate to Einstein that Newton was aware of the imperfect quality of his theological conclusions and would not present to public view any writings that did not measure up to his own high standards. Since Newton obviously did not wish to publish his speculations on theology, Einstein asserted with some passion that he personally hoped no one else would publish them. Einstein said a man has a right to privacy, even after his death. He praised the Royal Society for having resisted all pressure to edit and print writings of Newton which their author had not wanted to publish. He believed that Newton's correspondence could justly be published, because a letter written and sent was intended to be read, but he added that even in correspondence there might be some personal things which should not be published.

Then he spoke briefly about two great physicists whom he had known well: Max Planck and H. A. Lorentz. Einstein told me how he had come to know Lorentz in Leiden through Paul Ehrenfest. He remarked that he had admired and loved Lorentz perhaps more than anyone else he had ever known, and not only as a scientist. Lorentz had been active in the movement for "international cooperation," and had always been interested in the welfare of his fellow men. He had worked on many technical problems for his own country, an activity which was not generally known. This was part of Lorentz' character, Einstein explained, a kind of nobility which made him work for the well-being of others, preferably in anonymity. Einstein also expressed great affection for Max Planck. Planck was a religious man, he said, and always sought to reintroduce the absolutes – even on the basis of relativity theory. I asked Einstein whether Planck had ever fully accepted the "theory of photons," or whether he had continued to restrict his interest to the absorption or emission of light without regard to its transmission. Einstein stared at me for a moment or two in silence. Then he smiled and said: "No, not a theory. Not a theory of photons," and again his deep laughter enveloped us both – and the question was never answered. I remembered that Einstein's 1905 paper, for which (nominally) he had been awarded the Nobel prize, did not contain the word "theory" in the title, but referred instead to considerations from a "heuristic viewpoint."

There are fashions in science, Einstein said. When he had studied physics as a young man, one of the major questions being discussed was: Do molecules exist? He remembered how important scientists, men like Wilhelm Ostwald and Ernst Mach, had been explicit in stating that they did not really believe in atoms and molecules. One of the greatest differences between physics then and now, Einstein observed, was that today nobody bothers to ask this particular question any more. Although Einstein did not agree with the radical position adopted by Mach, he told me he admired Mach's writings, which had had a great influence on him. He had visited Mach, he said, in 1913, and had raised a question in order to test him. He asked Mach what his position would be if it proved possible to predict a property of a gas by assuming the existence of atoms – some property that could not be predicted without the assumption of atoms and yet one that could be observed. Einstein said he had always believed that the invention of scientific concepts and the building of theories upon them was one of the great creative properties of the human mind. His own view was thus opposed to Mach's, be- <73> cause Mach assumed that the laws of science were only an economical way of describing a large collection of facts. Could Mach accept the hypothesis of atoms under the circumstances Einstein had stated, even if it meant very complicated computations? Einstein told me how delighted he was when Mach replied affirmatively. If an atomic hypothesis would make it possible to connect by logic some observable properties which would remain unconnected without this hypothesis, then, Mach said, he would have to accept it. Under these circumstances it would be "economical" to assume that atoms may exist because then one could derive relations between observations. Einstein had been satisfied; indeed more than a little pleased. With a serious expression on his face, he told me the story all over again to be sure that I understood it fully. Wholly apart from the philosophical victory over what Einstein had conceived Mach's philosophy to have been, he had been gratified because Mach admitted that there might, after all, be some use to the atomistic philosophy to which Einstein had been so strongly committed.

Einstein said that at the beginning of the century only a few scientists had been philosophically minded, but today physicists are almost all philosophers, although "they are apt to be bad philosophers." He pointed as an example to logical positivism, which he felt was a kind of philosophy that came out of physics.

Now it was time to leave. I was horrified to realize it was a quarter to 12. Knowing that Einstein tired easily, I had meant to stay only half an hour. Yet every time I had gotten up to depart he had said, "No, no, don't go yet. You have come to see me about your work and there is still more to talk about." Yet at last I was taking my leave. Miss Dukas joined us as we walked toward the front of the house. As I neared the stairs, I turned to thank Einstein, missed a step and almost fell. When I had recovered my balance, Einstein smiled and said, "You must be careful here, the geometry is complicated. You see," he continued, "negotiating stairs is not really a physical problem, but a problem in applied geometry." He chuckled and then laughed out loud. I started down the stairs and Einstein began to walk down the corridor toward the study. Suddenly he turned and called: "Wait. Wait. I must show you my birthday present."

As I returned to the study Miss Dukas explained to me that Eric Rogers, who teaches physics at Princeton, had made a gadget for Einstein as a present for his 76th birthday, and that Professor Einstein had been delighted with it. Back in the study, I saw Einstein take from the corner of the room what looked like a curtain rod five feet tall, at the top of which was a plastic sphere about four inches in diameter. Coming up from the rod into the sphere was a small plastic tube about two inches long, terminating in the center of the sphere. Out of this tube there came a string with a little ball at the end. "You see," said Einstein, "this is designed as a model to illustrate the equivalence principle. The little ball is attached to a string, which goes into the little tube in the center and is attached to a spring. The spring pulls on the ball, but it cannot pull the ball up and into the little tube because the spring is not strong enough to overcome the gravitational force which pulls down on the ball." A big grin spread across his face and his eyes twinkled with delight as he said: "And now the equivalence principle." Grasping the gadget in the middle of the long brass curtain rod, he thrust it upward until the sphere touched the ceiling. "Now I will let it drop," he said, "and according to the equivalence principle there will be no gravitational force. So the spring will now be strong enough to bring the little ball into the plastic tube." With that he suddenly let the gadget fall freely and vertically, guiding it with his hand, until the bottom reached the floor. The plastic sphere at the top was now at eye level. Sure enough, the ball nestled in the tube.

With the demonstration of the birthday present our meeting was at an end. As I walked out to the street, I thought to myself that of course I had known that Einstein was a great man and a great scientist, but I had had no idea of the warmth of his friendly personality, his kindness and his rich sense of humour.

There had been, during that visit, no sense of the imminence of death. Einstein's mind was alert, his wit was keen and he had seemed very gay. On the Saturday following my visit, a week before Einstein was taken to the hospital, a Princeton friend of long standing and intimacy went with Einstein to the hospital to see Einstein's daughter, who was ill with sciatica. This friend writes that after he and Einstein left the hospital that Saturday, "we went for a long walk. Strange to say, we talked about our attitudes toward death. I mentioned a quotation from James Frazer in which he said that fear of death was the basis of primitive religion, and that to me death was both a fact and a mystery. Einstein added, 'And also a relief.'"

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