Princeton, 30 November 1949

'I have defended the good Lord against the insinuation that he plays a continual game of dice'.

There is a new book out about Einstein in a series on 'contemporary philosophers' (Albert Einstein: Philosopher-Scientist, ed. P.A. Schilpp, 1949): 'In it I have defended the good Lord against the insinuation that he plays a continual game of dice [Darin habe ich den lieben Gott gegen die Zumutung beständigen Würfelns verteidigt]'. Einstein has at last understood what Besso means by his reflections on symmetry: something which does not work for a tetrahedron works well for a cube (he provides a small diagram). As for Einstein's own reflections: 'If I write something to you, you can show it to whomever you like. I have long risen above keeping secrets. And I am not like a parson, who is unhappy if he hasn't "converted" others to his stuff'. He goes on to discuss his work on differential equations, which cannot be compared with a railway network consisting only of intersections (or 'points'), but are rather 'nice strict equations of definition, actually even stricter than pure gravitational equations, indeed overdefined'. He has a new theory for the unified field – for which he provides the equations: but proving it runs up against 'completely insurmountable mathematical difficulties. In its foundation there is no room for the notion of probability', something which is likely to provoke considerable scepticism from Einstein's contemporaries.

Einstein's statement in his 1949 article that 'God does not play dice' – that is, that the foundations of physics cannot be random – is one of his most famous.