UNIFIED FIELD THEORY 343an equation akin to an Einstein equation with a cosmological constant. Then from
Eqs. 17.47 and 17.48 we derive rather than postulate a metric.
It is all rather bizarre, a Ricci tensor which is the sum of a metric and an
electromagnetic field tensor. In 1923 Weyl declared the theory not fit for discus-
sion ('undiskutierbar') [W5], and Pauli wrote to Eddington, 'In contrast to you
and Einstein, I consider the invention of the mathematicians that one can found a
geometry on an affine connection without a [primary] line element as for the pres-
ent of no significance for physics' [P6].
Einstein's own initial reaction was that Eddington had created a beautiful
framework without content [E40]. Nevertheless, he began to examine what could
be made of these ideas and finally decided that 'I must absolutely publish since
Eddington's idea must be thought through to the end' [E41]. That was what he
wrote to Weyl. Three days later, he wrote to him again about unified field theo-
ries: 'Above stands the marble smile of implacable Nature which has endowed us
more with longing than with intellectual capacity' [E42].* Thus, romantically,
began Einstein's adventures with general connections, adventures that were to
continue until his final hours.
Einstein set himself the task of answering a question not fully treated by
Eddington: what are the field equations for the forty fundamental FjJ, that take
the place of the ten field equations for the g^ in general relativity? The best equa-
tions he could find were of the form
*'... Dariiber steht das marmorne Lacheln der unerbittlichen Natur, die uns mehr Sehnsucht als
Geist verliehen hat.'(17.49)
where F*J, is the rhs of Eq. 17.21 and where the i had to be interpreted as the
sources of the electromagnetic field. Then he ran into an odd obstacle: it was
impossible to derive source-free Maxwell equations! In addition, there was the old
lament: 'The theory ... brings us no enlightenment on the structure of electrons'
[E38], there were no singularity-free solutions.
In 1925 Einstein referred to these two objections at the conclusion to an appen-
dix for the German edition of Eddington's book on relativity. 'Unfortunately, for
me the result of this consideration consists in the impression that the Weyl-
Eddington [theories] are unable to bring progress in physical knowledge' [E43].
1924-5. Three papers on the Bose-Einstein gas, Einstein's last major innova-
tive contribution to physics (see Chapter 23).- Einstein's first homemade unified field theory, also the first example of a
publicly expressed unwarranted optimism for a particular version of a unified
theory followed by a rapid rejection of the idea. 'After incessant search during the
last two years, I now believe I have found the true solution,' he wrote in the open-
ing paragraph of this short paper [E44].
Both the connection and a primary fundamental tensor s^ are nonsymmetric