Princeton, 15 April 1950

On the challenges of deep thought as an approach to God.

'One thing I have learnt in my long life: it is devilishly hard to approach closer to "Him" if one refuses to stick to the superficial'. Einstein finds it hard to respond to Besso's questions in a recent letter: 'The reason is that no consequential field theory has provided a real definition of the field. It is true that as a consequence one falls into a quixotic situation, in that one has no guarantee that it will ever be possible to know whether the theory is "true". A priori there exists no bridge to the empirical'. Einstein goes into further detail on the inherent difficulties in developing a unified field theory along his lines of reflection, noting that the complexity of the approach has provoked scepticism amongst his contemporaries: he considers however that they will come round to his way of thinking: 'Very slowly they will see that one does not approach the fundamentals of things with a semi-empirical method ... The question of "causality" is not really central, but rather the question of real existence and the question of whether there are any kind of rigorously valid (not statistical) laws for theoretically represented reality'. Einstein has recently successfully solved a mathematical problem which removes a significant formal critique of his theory – he sets out the equations.