Berlin, 5 January 1924

Struggling with an idea for understanding what quanta mean.

Einstein apologises for not writing for such a long time [his preceding letter to Besso was in December 1922]: 'But outward experience remains superficial, and science is the most important thing. The idea I am struggling with concerns the understanding of the reality of quanta and is as follows: over-determination of the laws through more differential equations than those for field variables. Thus the absence of arbitrariness in the initial conditions can be grasped, without abandoning field theory. This path may be completely false, but it must be attempted and is in any case logically possible. The movement-equation of material points (electrons) will be entirely abandoned; their mechanical behaviour will be determined by the field-laws ... The mathematics is enormously difficult, and the connection with the experiential unfortunately becomes more and more indirect'.

Referring to a difficulty in the education of Besso's young grandson, Einstein remarks 'In any case, reason is powerless in the face of instinct'. The political situation is depressing, and the 'Prussians' continue to have the upper hand. Einstein refers bitterly to his satisfaction at extricating himself from 'the League of Nations racket', which he condemns as 'a waste of time and energy'. In a postscript he expresses delight at the character and scholarly attainments of his son Hans Albert: 'He is a real man, an excellent sailor, direct and trustworthy'.