Berlin, 12 December 1919

'Fretting' over the question of the finite universe, and memories of the birth of his 'finest thoughts' at the Swiss Patent Office.

Einstein had lost touch with Besso since the latter's move back to Zurich, and is delighted that a letter gives his new address: 'It interested me enormously that you want to go back to the Patent Office, that worldly monastery where I hatched my finest thoughts and where we lived through such pleasant times together. Since then our boys have grown up and we are old lads'. There is to be a conference in Basel to support the foundation of the Hebrew University in Jerusalem, although Einstein is not sure he will attend in person, even if he is willing to lend his name which 'since the English solar eclipse expeditions has been been in high renown', and perhaps will serve to persuade fellow Jews to lend support.

Scientifically, things are quiet – 'My life is too unsettled' – although he is working on an amusing technical project with Walther Nernst (probably a cooling system for a refrigerator, which they later patented). He is interested in a theory of Hermann Weyl, which may have a bearing on the question of whether or not the universe is finite: 'In Weyl's theory it is gradually being revealed that there are no static solutions with non-zero electrostatic potentials ... The question whether the cosmological solution holds true will perhaps yet be verifiable through fixed star astronomy. I am still fretting away about that'.

Einstein's mother is coming to live out her last months with him in Germany (she was mortally ill with cancer). He is also hoping to move Mileva and the boys to Germany, because of the prohibitive exchange rates. He has heard that his sister Maja is having marital difficulties (her husband Paul Winteler was the brother of Besso's wife, Anna), and rather brutally suggests that they should divorce sooner rather than later – 'Just don't wait too long (as I did)' – and adding with a touch of provocative humour that mixed marriages ('die Mischehen') never work – 'Anna says: oho!' (Einstein and his sister had both married non-Jews – but then, so had Besso).