Princeton, 24 July 1949

'It is a happy fate to be fascinated by work right up to one's last gasp': on quantum theory, gravitational field equations and the happiness of work.

Einstein remains firmly opposed to the statistical theory of quanta, whose defenders such as Wolfgang Pauli he considers to be 'illogical', in that Pauli criticises Einstein's approach for being incomplete, and 'immediately after say that the function ψ is a statistical representation of the entirety of a system. Yet that is just another form of the statement: the description of the particular (individual) system is incomplete!'. Einstein has published his thoughts in a number of papers, so that 'At least posterity will know what I thought of it'.

As for his current work, he has at last found 'the natural generalisation of the equations of the gravitational field, from which I am expecting that it will become a usable theory of the complete field'. The mathematical challenges involved are apparently insuperable, and 'the augurs are agreed that current mathematics cannot accomplish it. But I have not given up the struggle, but toil away at it day and night'. This leads Einstein on to a reflection on the happiness of having such a project to work on: 'It is a happy fate to be fascinated by work right up to one's last gasp. Otherwise one would suffer too much from the stupidity and madness of mankind, especially as it expresses itself in politics'.

The letter opens with one of Einstein's characteristically graceful apologies for being such a dilatory correspondent, joking that he has accustomed himself to his bad conscience, like so many criminals. He discusses the positions he has publicly taken on subjects of human interest: 'I think that it all just gets worse if people who still have personal convictions remain silent'. Besso's ideas about nature's preference for symmetrical envelopes may well be right – he should discuss it with a theoretician of quanta.