8 INTRODUCTORYin Princeton on March 19,1949, on the occasion of Einstein's seventieth birthday.
Most of us were in our seats when Einstein entered the hall. Again there was this
brief hush before we stood to greet him.
Nor do I believe that such reactions were typical only of those who were much
younger than he. There were a few occasions when Pauli and I were both with
him. Pauli, not known for an excess of awe, was just slightly different in Einstein's
company. One could perceive his sense of reverence. Bohr, too, was affected in a
similar way, differences in scientific outlook notwithstanding.
Whenever I met Einstein, our conversations might range far and wide but
invariably the discussion would turn to physics. Such discussions would touch only
occasionally on matters of past history. We talked mainly about the present and
the future. When relativity was the issue, he would often talk of his efforts to
unify gravitation and electromagnetism and of his hopes for the next steps. His
faith rarely wavered in the path he had chosen. Only once did he express a res-
ervation to me when he said, in essence, 'I am not sure that differential geometry
is the framework for further progress, but, if it is, then I believe I am on the right
track.' (This remark must have been made some time during his last few years.)
The main topic of discussion, however, was quantum physics. Einstein never
ceased to ponder the meaning of the quantum theory. Time and time again, the
argument would turn to quantum mechanics and its interpretation. He was
explicit in his opinion that the most commonly held views on this subject could not
be the last word, but he also had more subtle ways of expressing his dissent. For
example, he would never refer to a wave function as die Wellenfunktion but would
always use mathematical terminology: die Psifunktion. I was never able to arouse
much interest in him about the new particles which appeared on the scene in the
late 1940s and especially in the early 1950s. It was apparent that he felt that the
time was not ripe to worry about such things and that these particles would even-
tually appear as solutions to the equations of a unified theory. In some sense, he
may well prove to be right.
The most interesting thing I learned from these conversations was how Einstein
thought and, to some extent, who he was. Since I never became his co-worker, the
discussions were not confined to any particular problem. Yet we talked physics,
often touching on topics of a technical nature. We did not talk much about statis-
tical physics, an area to which he had contributed so much but which no longer
was the center of his interests. If the special and the general theory of relativity
came up only occasionally, that was because at that time the main issues appeared
to have been settled. Recall that the renewed surge of interest in general relativity
began just after his death. However, I do remember him talking about Lorentz,
the one father figure in his life; once we also talked about Poincare. If we argued
so often about the quantum theory, that was more his choice than mine. It had
not taken long before I grasped the essence of the Einstein-Bohr dialogue: com-
plementarity versus objective reality. It became clear to me from listening to them
both that the advent of quantum mechanics in 1925 represented a far greater