Authors: Philipp Frank
From the very beginning it had been the idea of the founders that it should somehow have a cloistered character. As Flexner once expressed it: “It should be a haven where scholars and scientists may regard the world and its phenomena as their laboratory without being carried off in the maelstrom of the immediate.” This seclusion of the institute was increased in 1940 when it moved away from Fine Hall and the Princeton campus to its own building, situated a few miles outside of the town of Princeton.
Flexner first set out to look for the great masters who were to form the basis of his institute. He traveled through America and Europe looking for men of such rank who were available. In the course of these journeys he came to Pasadena in the winter of 1932. There he discussed the matter with R. A. Millikan, the famous physicist, who said to him: “You know that Einstein is a guest here at present. Why don’t you tell him about your plan and hear his opinion?” At first Flexner was rather hesitant about discussing such questions concerning teaching and administration with a man who had already become a legend. He was afraid to approach Einstein because he was “a too much lionized man.” Millikan told him, however, that Einstein was a man who was interested in all projects for improving the training of young scholars and who liked everything that was new and bold. “I will tell him about you immediately. Look him up at the Athenaeum.” This is the faculty club of the California Institute of Technology, situated in the midst of a beautiful palm garden, where foreign scholars stayed as guests.
Flexner described this visit as follows:
“I drove over to the Athenaeum where he and Mrs. Einstein were staying and met him for the first time. I was fascinated by his noble bearing, his simply charming manner and his genuine humility. We
walked up and down the corridor of the Athenaeum for upwards of an hour, I explaining, he questioning. Shortly after twelve, Mrs. Einstein appeared to remind him that he had a luncheon engagement. ‘Very well,’ he said in his kindly way, ‘we have time for that. Let us talk a little longer.’ ”
At this time Flexner did not yet consider Einstein himself for this institute. He wanted only to hear his opinion about the plan. They agreed to meet again early the next summer at Oxford, where Einstein was to lecture.
As they had planned, Einstein actually met Flexner on the beautiful lawn of the quadrangle of Christ Church College at Oxford, where Einstein was staying. Flexner describes the meeting:
“It happened to be a superbly beautiful day and we walked up and down, coming to closer and closer grips with the problem. As it dawned on me during our conversation that perhaps he might be interested in attaching himself to an institute of the proposed kind, before we parted I said to him: ‘Professor Einstein, I would not presume to offer you a post in this new Institute, but if on reflection you decide that it would afford you the opportunity which you value you would be welcome on your own terms.’ ”
They agreed that during the summer Flexner would come to Berlin to continue the talks. It was the summer of Papen’s interim government in Germany, the summer when the German Republic was already dead and led only a ghostly existence. Einstein saw the future with complete clarity and had decided to keep the road to America open for himself.
When Flexner came to Berlin, Einstein was already living in his country home at Caputh near Potsdam. It was the same summer and the same house of which I have already spoken in
Chapter X
. Flexner arrived at Einstein’s country house on a Saturday at three in the afternoon. He describes his visit as follows:
“It was a cold day. I was still wearing my winter clothes and heavy overcoat. Arriving at Einstein’s country home, beautiful and commodious, I found him seated on the veranda wearing summer flannels. He asked me to sit down. I asked whether I might wear my overcoat. ‘Oh yes,’ he replied. ‘Aren’t you chilly?’ I asked, surveying his costume. ‘No,’ he replied, ‘my dress is according to the season, not according to the weather, it is summer.’
“We sat then on the veranda and talked until evening, when Einstein
invited me to stay to supper. After supper we talked until almost eleven. By that time it was perfectly clear that Einstein and his wife were prepared to come to America. I told him to name his own terms and he promised me to write to me within a few days.”
As was his custom, Einstein, wearing a sweater and no hat, accompanied his visitor through the rain to the bus station. The last thing he said on bidding Flexner farewell was: “I am full of enthusiasm about it.”
Einstein soon communicated the conditions under which he would take the new position in a letter to Flexner, who found them much too modest for such an institute and for a man like Einstein. He requested that the negotiations be left to himself and to Mrs. Einstein. The contract was concluded at this time. Einstein pointed out that he was obliged to spend the winter of 1932–3 in Pasadena and could not go to Princeton until the fall of 1933. At that time he still had intentions of spending a part of every year in Berlin, for he preferred not to be unfaithful to his friends in the world of physics there. But he was very much aware of coming events. When the Nazi revolution took place early in 1933, the way had already been prepared for his emigration to America, and in the winter of 1933 Einstein entered upon his new position at the Institute for Advanced Study, which Flexner had founded at Princeton. Now there was naturally no further mention of spending a part of the year in Berlin. Einstein moved to Princeton to become a permanent resident and citizen of the United States. There were still, however, a number of stages through which he had to pass in order to achieve this goal. He had entered the country only as a visitor and for the present had no legal right to remain here permanently, to say nothing of becoming a citizen.
The institute that Einstein joined was in some respects similar to the Kaiser Wilhelm Institute to which he had belonged in Berlin. Thus he once again occupied a position that in a certain respect had always appeared distasteful to him. As I have already mentioned, he always regarded it as an uncomfortable situation for anyone to be paid only for his research work. One does not always have really valuable ideas, so that there is a temptation to publish papers of no special value. Thus
the scientist is subject to a painful coercion. But when one is a teacher with a moderate load one has every day the consoling feeling of having done a job that is useful to the society. In such a situation it is satisfying to carry on research for one’s own pleasure during the leisure hours, without compulsion.
On the other hand, however, a man of creative ideas like Einstein chafed under the daily routine of teaching. He found the idea of teaching very noble, but when he was actually offered a position where he would be able to devote himself entirely to research, he was unable to refuse it. At the new Institute he was able to guide talented students who had already acquired the doctorate in carrying on their researches. In consequence, however, his contact with students was restricted to a very small group. Einstein often vacillated between a feeling of satisfaction at being spared any routine work and a certain feeling of loneliness due to his isolation from the great mass of students.
This divided attitude was quite in accord with his divided attitude toward contact with his fellow men in general, which has already been mentioned repeatedly. This division, which has played a large part in his entire life, manifested itself also in his attitude to his environment in Princeton. It would have been simple enough for him to give lectures or to organize a seminar, which many of the students might have attended. Einstein, however, felt that it would not be fair for him, a man with an international reputation, to enter into a contest with the professors of the university, some of whom were still quite young. They could with some justification regard it as “unfair competition.” At any rate Einstein very punctiliously avoided any such competition for students. It is possible, however, that he exaggerated in his mind the touchiness and ambition of his colleagues, since many would gladly have taken advantage of the presence of such an outstanding scientist in Princeton to learn from him themselves. As things were, his presence there has not been utilized so much as it might have been. No one, perhaps not even Einstein himself, can say to what degree this situation is due to his consideration for others and his aversion toward more intimate contact with people.
By and large, at Princeton Einstein took up his researches where he had left off in Berlin; this is true both of the problems themselves and of the way in which he dealt with them. It was always very characteristic of him to be independent of his environment. Just as at the time of our meeting in Berlin twenty-five years before it had been a matter of indifference to
him whether he was working at his problems in his study or on a bridge in Potsdam, so now it made no difference to him that he had moved his office from the western suburb of Berlin to the distinguished American university town of Princeton beyond the ocean.
Three groups of problems occupied Einstein during this period. In the first place there was the desire to develop his special and general relativity theories of 1905, 1912, and 1916 into an ever more logically connected structure. In one important point Einstein succeeded in making a great advance at Princeton. It will be recalled that Einstein regarded the gravitational field as a geometrical property of space, which can be called in a word the “curvature.” This curvature is determined by the presence of matter in space and can be computed from the distribution of matter. If the curvature of space, or, in other words, the gravitational field, is known, then one also knows how a body that is present in this space will move. This is given by the “equations of motion,” which can be stated briefly as follows: A body moves in such a manner that the representation of the path in a four-dimensional space-time continuum is a geodesic (shortest) line. This would be entirely satisfactory if one assumed that matter and force field were two completely different entities. But one is driven closer and closer to the conception that the mass of a particle is actually nothing but a field of force that is very strong at this point. Consequently “motion of mass” is nothing but a change of the force field in space. The laws for this change are the “field equations” — that is, the laws that determine the force field. But if the motion of the body is already determined by the field equations, then there is no more room for special laws of motion. One cannot make a supplementary assumption, in addition to the field equations, that masses move along geodesic lines. Instead these equations of motion must already be contained in the field equations.
C. Lanczos, Einstein’s co-worker in Berlin, had sketched the idea of deriving the laws of motion mathematically from the field equations. His derivation, however, did not appear satisfactory to Einstein, and in Princeton he succeeded in showing in a completely convincing way that only the field laws need be known in order to be able to derive the laws of motion from them. This is regarded as a confirmation of the idea that matter is nothing but a concentration of the field at certain points.
I have already mentioned that Einstein liked to have the assistance of young physicists or mathematicians, especially when he
dealt with involved mathematical computations. From Berlin he had brought with him the Viennese mathematician Walter Mayer, who soon obtained an independent position at the Institute of Advanced Study and no longer collaborated with Einstein. During the first few years of Einstein’s residence a very talented Polish physicist, Leopold Infeld, came to Princeton, where he remained several years and with whom Einstein worked out the aforementioned proof of the “unity of field and matter.”
Einstein liked to discuss with Infeld all kinds of problems, including the fundamental problems of physics and their development. These conversations gave rise to the book by Einstein and Infeld,
Evolution of Physics
, which has achieved a wide circulation. It is certainly one of the best presentations of the fundamental ideas of physics for the public at large.
Infeld wrote also an autobiography entitled
Quest: The Making of a Scientist
. This book contains much about Einstein’s life at Princeton as seen by a keen observer and competent collaborator.
A second group of problems with which Einstein was intensely occupied at this time is the criticism of the development of the quantum theory, which has been described in Ch. IX. Einstein felt impelled to show by concrete examples that the quantum theory, in the “Copenhagen” form in which it had been formulated by Niels Bohr, did not describe a “physical reality,” such as a field, but only the interaction of the field with a measuring instrument. A paper that Einstein published together with N. Rosen and B. Podolsky, two young physicists, was particularly important in this discussion. This paper shows by a simple example that the way in which the quantum theory describes the physical condition in a certain spatial area cannot be called a complete description of physical reality in this area.
This work stimulated Niels Bohr to formulate more clearly than he had previously done his standpoint on the question of physical reality. Bohr now rejected definitely all the “mystical” interpretations to which his theory had been subjected. Among these was the conception that the “real state” in a spatial area is “destroyed” by observation, and similar ideas. He now stated clearly that the quantum theory did not describe any property of a field, but an interaction between field and measuring instrument. It is plain that one could not decide between the conceptions of Einstein and Bohr by general logical considerations, since they were not opposed assertions, but rather opposed proposals.
Einstein proposed to retain tentatively a kind of description of the physical state in an area of space which was not too far from the way in which the language of daily life describes reality. This means that he proposed to describe the physical state in an area in such a manner that the description itself need not state with which measuring instrument it was obtained. Einstein has been well aware that it would not be absurd to abandon this kind of description where the laws of physics are formulated in terms of a “field”; but he would abandon it only if it became necessary beyond any doubt.