Disturbed by my overall reception at the seminar, I returned home, and with the rashness of youth, I wrote a letter by hand to Albert Einstein, describing the negative reaction of the audience towards his goal of unifying gravity and electromagnetism in one geometrical scheme. I also included the two manuscripts that I had written on his unified field theory. “. . . I have today held a talk on my work with regard to your theory at the Niels Bohr Institute, Copenhagen,” I wrote, “and there found only complete misunderstanding. In fact, it appeared that the main purpose was to undermine my personal confidence as to my ability. I would be eternally indebted if you could find time to read my work, and should you find yourself satisfied with my interpretation, mathematical ability, and conceptions, that you return same to me with your opinion . . . I found the Personel [sic] at the Bohr Institute completely without the fundamental knowledge necessary for the understanding of your Theory of Generalized Gravitation, and need I state how great a disappointment this was to me.
“Moreover,” I continued helpfully, “I found the attitude of the persons concerned contrary to all aesthetic feeling and conceptions, and I feel that you should become aware of what is really going in the opposite camp.”
I posted the letter, along with my two manuscripts, one of which pointed out a potential problem in his unified field theory, to Einstein at the Institute for Advanced Study at Princeton University, New Jersey. My manuscripts were titled “Theory of Quantized Unified Fields” and “On Unified Field Theory and the Equations of Motion.”
The year was 1953. I never expected a response. It had been a valuable learning experience for me just to write the papers and to give the seminar. Why would I anticipate that Einstein would have time, great physicist that he was, to read and respond to my letter and manuscripts? Perhaps he would be offended that an unknown, unschooled young man in Copenhagen dared to criticize his published theory.
Three weeks later, an airmail letter with U. S. stamps arrived for me at my parents’ apartment. The return address was Einstein’s home at 112 Mercer Street, Princeton, New Jersey. Even then, in my excitement, I reflected on the fact that Einstein did not use the Institute for Advanced Study as his official address. I tore open the envelope and found that Einstein had written back to me in his own handwriting! He had also included a reprint of the appendix to his latest edition of The Meaning of Relativity, which I had not yet read. The book I had borrowed from the university library was an earlier edition.
But unfortunately, Einstein’s handwritten letter was in German, and my German from two years of study in two different Danish schools was not up to the task of understanding it.
I immediately thought of my barber, Hans Busch, who was of German extraction. I rushed down the street on that warm June afternoon and burst into Hans’s shop shouting, “I just received a letter from Albert Einstein in America! It’s written in German. Can you please help me translate it?”
It was midmorning, a busy time in the small shop, and the men sitting and waiting for their haircuts stared at me in astonishment. The barber looked at me, his scissors clipping at a customer’s hair, and said, “Just a minute, John. I need to finish with this gentleman.”
I curbed my impatience and sat down to wait, feeling exhilarated. Finally, Hans Busch’s elderly client rose from the barber chair, brushing stray hairs off his jacket, and paid for his haircut. He joined the other customers seated around me to watch the show.
“All right, John,” Hans said, wiping his hands on his apron and turning to me. “What’s this you have here?”
I pulled the letter out of my pocket and handed it over. It was written on two sides of a piece of stationery. Hans perused it quickly and stopped at the end, peering at it intently. “Well, indeed, this letter has Albert Einstein’s signature!” The other customers stood up and gathered round to stare at the signature too. The barber said, “What have you been up to, John?” and he smiled. I gave him, and our audience, a brief summary of how I had spent my spare time during the past year, the talk I’d given at the Niels Bohr Institute, and why I had written a letter to Einstein.
Hans proceeded to translate the letter into Danish orally, despite some difficulties with the technical terms in German, while we all stood listening attentively. According to the translation, Einstein made constructive comments and criticisms on my manuscripts, and attempted to answer my criticisms of his mathematical formulation. He also had some things to say about my audience at the institute.
“‘I can understand very well that your work has not found a favourable reception in Bohr’s circle,’” Hans translated. “‘For every individual and every study circle has to retain its own way of thinking, if he does not want to get lost in the maze of possibilities. However, nobody is sure of having taken the right road, me the least.’” *
Einstein went on to make some profound comments about physics as it was at that time. Later, I was able to obtain an English translation of the letter, and had more time to contemplate Einstein’s ideas. Indeed, his comments still have significance for many of the endeavours of physicists today:
I do not believe that one achieves one’s objectives by first setting up a classical theory and then quantizing it. Although this, of course, has been successful in the interpretation of classical mechanics and in the interpretation of quantum facts by modifying this theory according to the principles of statistics. But I believe that in the attempts to carry over this method to field theories, one encounters ever increasing complications and the necessity to increase the number of independent assumptions monstrously. For generally covariant field theories* this will be even worse.
I even think that the mechanics based on the quantum theory cannot provide a useful starting point for a more profound theory, despite its significant successes, because I can see by looking at it that it has accepted the understanding of the “quantum jumps” in an “illegal” fashion by raising probability to a reality and in doing so giving up the reality of the quantum states (in the old sense). Thus one wants to explain why an apparent arbitrarily small perturbation can change the energy of an atomistic system by a finite amount [Einstein’s italics].
I understood from Einstein’s words that he believed that the old quantum physics that he had been involved with, in the early days of the birth of quantum mechanics, represented a complete description of reality, whereas the later quantum mechanics and quantum field theory, which were accepted in the 1950s, were based purely on probability theory and statistics, and did not constitute a complete and real description of nature.
Einstein continued:
In view of this state of affairs I see myself urged to consider the logical simplicity as the sole guide using general relativity. This leads me to the attempt (but not to the conviction) to seek the future in a field theory (in the old sense) (generalization of the theory of the gravitational field). The point of view that one is not allowed to construct the Lagrangian function from logically independent terms appears essential to me. I send you my latest research from which you can see what I mean by that.
I was overwhelmed by the amount of obviously pertinent information one of the world’s greatest physicists had imparted to me, and I understood the significance of Einstein’s comments for the future of physics. It is clear from his comments on quantum mechanics and the way it was applied at the time that he had not wavered in his opposition to Bohr’s interpretation. The famous discourses on the meaning of quantum mechanics between Bohr and Einstein, initiated at the 1927 Solvay conference and pursued over several years, had not persuaded Einstein to join the herd of physicists who were convinced that the probabilistic interpretation of quantum mechanics was here to stay.
Einstein went on in his letter to make an important statement about singularities