THE EINSTEIN-GROSSMANN COLLABORATION 223Einstein did not at once perceive the apparent restrictions on general covariance
as a flaw. He felt that the problem had been solved. Early in 1913 he wrote to
Ehrenfest. 'The gravitation affair has been clarified to my full satisfaction
(namely, the circumstance that the equations of the gravitational field are covar-
iant only for linear transformations). One can specifically prove that generally
covariant equations which completely determine the [gravitational] field from the
matter tensor cannot exist at all. What can be more beautiful than that this nec-
essary specialization follows from the conservation laws?' (his italics) [E34].
This concludes a sketch of the arguments by which Einstein and Grossmann
arrived at a hybrid theory in which some basic elements of the ultimate theory are
already in evidence. I shall omit as of less interest the calculations which led them
to explicit expressions for 6^ and T^ in Eq. 12.34 that satisfy the conservation
laws. The effort had been immense. Apologizing to Ehrenfest for a long silence,
Einstein wrote in May 1913, 'My excuse lies in the literally superhuman efforts
I have devoted to the gravitational problem. I now have the inner conviction that
I have come upon what is correct and also that a murmur of indignation will go
through the rows of colleagues when the paper appears, which will be the case in
a few weeks' [E35].
I have now come to the end of the more complex and adventurous part of Ein-
stein's road to the general theory of relativity. It began in 1907 with the equiva-
lence principle, then there were the years of silence, then came the Prague papers
about the c field, and finally the collaboration with Grossmann. In 1913 the theory
was, of course, far from its logical completion. But the remaining story of Ein-
stein's contributions is much more straightforward. It consists mainly of the rec-
ognitions that general covariance can be implemented, that the Ricci tensor is the
clue to the right gravitational equations, and that there are the three classical suc-
cesses of the theory. All this will be discussed in later chapters.
12e. The Aftermath
In 1905 Einstein had dedicated his doctoral thesis to Grossmann. In 1955 he ded-
icated his last published autobiographical sketch [E32] to the same old friend, long
since deceased. The brief remainder of this chapter is devoted to the tale of Ein-
stein and Grossmann from the times following their epochal collaboration until
shortly before Einstein's death.the desired result.