Geneva, 28 July 1925

The equations for a new mixed unified field theory: 'a splendid possibility which could well correspond with reality'.

Einstein had hoped to see Besso in Bern, but his children are impatient to see him, and he must also see Mileva and his friend Marcel Grossmann, who is ill. 'I would have liked to have presented you in person with the egg which I have laid recently, but now I shall do it in writing'. He then presents the equations for a mixed unified theory, noting that if one stipulates that the two elements are symmetrical, one reaches the old gravitational law for empty space. 'If you drop the hypothesis of symmetry, you obtain as a first approximation the laws of gravitation and Maxwell's field laws for empty space, in which the asymmetrical parts [of the tensor] represent the electromagnetic field. This is a splendid possibility which could well correspond with reality. The question is now whether this field theory is incompatible with the existence of atoms and quanta ... If only the mathematics of special problems were easier! But there are ghosts everywhere'. A postcode notes that the pencilled letter was written during 'a boring sitting of the League of Nations'.