EINSTEIN'S RESPONSE TO THE NEW DYNAMICS 449
Not that from then on he desisted from criticizing quantum mechanics. He had
recognized it to be part of the truth, but was and forever remained deeply con-
vinced that it was not the whole truth. From 1931 on, the issue for him was no
longer the consistency of quantum mechanics but rather its completeness.
During the last twenty-five years of life, Einstein maintained that quantum
mechanics was incomplete. He no longer believed that quantum mechanics was
wrong but did believe that the common view of the physics community was wrong
in ascribing to the postulates of quantum mechanics a degree of finality that he
held to be naive and unjustified. The content and shape of his dissent will grad-
ually unfold in what follows.
In November 1931 Einstein gave a colloquium in Berlin 'on the uncertainty
relation' [El6]. The report of this talk does not state that Einstein objected to
Heisenberg's relations. Rather it conveys a sense of his discomfort about the free-
dom of choice to measure precisely either the color of a light ray or its time of
arrival. My friend Gasimir has written to me about a colloquium Einstein gave
in Leiden, with Ehrenfest in the chair [Cl] (this must have been in November
1930). In his talk, Einstein discussed several aspects of the clock-in-the-box exper-
iments. In the subsequent discussion, it was mentioned that no conflict with quan-
tum mechanics existed. Einstein reacted to this statement as follows: 'Ich weiss es,
widerspruchsfrei ist die Sache schon, aber sie enthalt meines Erachtens doch eine
gewisse Harte' (I know, this business is free of contradictions, yet in my view it
contains a certain unreasonableness).
By 1933 Einstein had stated explicitly his conviction that quantum mechanics
does not contain logical contradictions. In his Spencer lecture, he said of the
Schroedinger wave functions: 'These functions are supposed to determine in a
mathematical way only the probabilities of encountering those objects in a partic-
ular place or in a particular state of motion, if we make a measurement. This
conception is logically unexceptionable and has led to important successes' [El7].
It was in 1935 that Einstein stated his own desiderata for the first time in a
precise form. This is the criterion of objective reality, to which he subscribed for
the rest of his life. By 1935 Einstein was settled in Princeton. At this point, I
interrupt the account of the quantum theory in order to describe what happened
to Einstein and his family from 1932 to 1945.25b. Einstein at Princeton
Einstein settled permanently in the United States in October 1933. His thoughts
of leaving Germany had begun to take shape two years earlier, however. In
December 1931, he wrote in his travel diary: 'Today, I made my decision essen-
tially to give up my Berlin position' [E18]. He was on board ship at that time, en
route to his first stay in Pasadena. It was an atmosphere conducive to reflecting
on the recent happenings in Germany. A year earlier, the National Socialists had