FIELD THEORIES OF GRAVITATION: THE FIRST FIFTY YEARS 235deratum stressed by Einstein. 'In the context [of a theory of gravitation], the Eot-
vos experiment plays a role similar to that of the Michelson experiment for uni-
form motion.' When Mie asked afterward why Einstein had not mentioned his,
Mie's, work, Einstein replied that he would discuss only theories which, unlike
Mie's, satisfy the equivalence principle.* The bulk of Einstein's report was of
course devoted to his recent work with Grossmann. It added little to what has
already been described here. At Vienna, Mie was Einstein's principal antagonist.
Shortly after this meeting, Mie wrote a further critique on Einstein's theory [M4],
to which Einstein replied by giving arguments that were in part incorrect: once
again he stressed the inevitability of the invariance of the gravitational equations
for linear transformations only [El 3].
In summary, prior to 1912 no attempt to construct a field theory of gravitation
had led anywhere. Toward the end of 1913 the situation was thoroughly con-
fused. Nordstrom's was the only consistent theory of gravitation. Most physicists
were ready to accept special relativity. A few were willing to concede the funda-
mental role of the equivalence principle, but others thought that an exaggeration.
There is no evidence that anyone shared Einstein's views concerning the limita-
tions imposed by gravitation on special relativity, nor that anyone was ready to
follow his program for a tensor theory of gravitation. Only Lorentz had given him
some encouragement. 'I am happy that you receive our investigation [E.-
Grossmann] with favor,' Einstein wrote in the same letter in which he had
expressed his own doubts about the status of his theory [E3].
Despite these reservations, Einstein was in a combative mood. Commenting on
the criticisms by Abraham and Mie, he wrote, 'I enjoy it that this affair is at least
taken up with the requisite animation. I enjoy the controversies. Figaro mood:
"Will der Herr Graf ein Tanzlein wagen? Er soil's nur sagen! Ich spiel ihm auf"
[E14].** He felt sure that the four-dimensional pseudo-Euclidean description
needed revision. 'I enjoy it that colleagues occupy themselves at all with the theory,
although for the time being with the purpose of killing it. ... On the face of it,
Nordstrom's theory ... is much more plausible. But it, too, is built on the a priori
Euclidean four-dimensional space, the belief in which amounts, I feel, to some-
thing like a superstition' [E15]. In March 1914, he expressed himself as follows
about his own efforts. 'Nature shows us only the tail of the lion. But I do not
doubt that the lion belongs to it even though he cannot at once reveal himself
because of his enormous size' [E16].f
*In Mie's theory [M3], the ratio of gravitational and inertial mass depends on physical parameters
such as velocity and temperature. Also, there is neither a red shift nor a bending of light. I do not
discuss this complicated theory here (it contains two scalar fields) because it does not contain con-
ceptually interesting points of view.
"Would the Count like to dare a little dance? Let him but say so! I'll play him a tune.
fSee Chapter 14 for comments by Einstein in 1914 on the Nordstrom theory and [E17] for his
reminiscences on scalar theories.