464 THE QUANTUM THEORYimagination appear so necessary and so natural that he is apt to treat them not as
the creations of his thoughts but as given realities' [E4]. His insistence on objective
reality is a perfect example of such a mental process.
Finally, I should like to reiterate my own view that Einstein's technical objec-
tions to quantum mechanics are unfounded, but that I do not know whether either
quantum mechanics or general relativity is complete, or whether their desired syn-
thesis can be consummated simply by welding together their respective sets of
postulates.26c. Uberkausalitat
In 1923 Einstein published an article entitled 'Does field theory offer possibilities
for the solution of the quantum problem?' [E20]. It begins with a reminder of the
successes achieved in electrodynamics and general relativity theory in regard to a
causal description: events are causally determined by differential equations com-
bined with initial conditions on a spacelike surface. However, Einstein continued,
this method cannot be applied to quantum problems without further ado. As he
put it, the discreteness of the Bohr orbits indicates that initial conditions cannot
be chosen freely. Then he asked, Can one nevertheless implement these quantum
constraints in a (causal) theory based on partial differential equations? His
answer: 'Quite certainly: we must only "overdetermine" the field variables by
[appropriate] equations.' Next he stated his program, based on three require-
ments: (1) general covariance, (2) the desired equations should at least be in accor-
dance with the gravitational and the Maxwell theory, and (3) the desired system
of equations which overdetermines the fields should have static, spherically sym-
metric solutions which describe the electron and proton. If this overdetermination
can be achieved, then 'we may hope that these equations co-determine the mechan-
ical behavior of the singular points (electrons) in such a way that the initial con-
ditions of the field and the singular points are also subject to restrictive conditions.'
He went on to discuss a tentative example and concluded, 'To me, the main point
of this communication is the idea of overdetermination.'
By 1923 Einstein had already been brooding about these ideas for a number of
years. In 1920 he had written to Born, 'I do not seem able to give tangible form
to my pet idea [meine Lieblingsidee], which is to understand the structure of the
quanta by redundancy in determination, using differential equations,' [E21].This
is the earliest reference to his strategy that I am aware of. It would seem likely
that ideas of this kind began to stir in him soon after 1917, when he had not only
completed the general theory of relativity but had also discovered the lack of caus-
ality in spontaneous emission [El6]. The early response of others to these attempts
by Einstein was recorded by Born: 'In those days [early 1925], we all thought that
his objective. .. was attainable and also very important' [B2]. Einstein himself
felt that he had no choice. 'The road may be quite wrong, but it must be tried'
[E22].