SUBTLE IS THE LORD 117am not sure when I first heard of the Michelson experiment. I was not conscious
that it had influenced me directly during the seven years that relativity had been
my life. I guess I just took it for granted that it was true." However, Einstein said
that in the years 1905-1909, he thought a great deal about Michelson's result, in
his discussion with Lorentz and others in his thinking about general relativity. He
then realized (so he told me) that he had also been conscious of Michelson's result
before 1905 partly through his reading of the papers of Lorentz and more because
he had simply assumed this result of Michelson to be true' [S6].
c) December 1952, letter by Einstein to Shankland. 'The influence of the crucial
Michelson-Morley experiment upon my own efforts has been rather indirect. I
learned of it through H. A. Lorentz's decisive investigation of the electrodynamics
of moving bodies (1895) with which I was acquainted before developing the spe-
cial theory of relativity. Lorentz's basic assumption of an ether at rest seemed to
me not convincing in itself and also for the reason that it was leading to an inter-
pretation of the Michelson-Morley experiment which seemed to me artificial'
[S7].
What do we learn from these three statements?
First, that memory is fallible. (Einstein was not well in the years 1950-2 and
already knew that he did not have much longer to live.) There is an evident incon-
sistency between Einstein's words of February 1950 and his two later statements.
It seems sensible to attach more value to the later comments, made upon further
reflection, and therefore to conclude that Einstein did know of Michelson and
Morley before 1905. One also infers that oral history is a profession which should
be pursued with care and caution.
Second, there is Einstein's opinion that aberration and the Fizeau experiment
were enough for him. This is the most crucial statement Einstein ever made on
the origins of the special theory of relativity. It shows that the principal argument
which ultimately led him to the special theory was not so much the need to resolve
the conflict between the Michelson-Morley result and the version of aether theory
prevalent in the late nineteenth century but rather, independent of the Michelson-
Morley experiment, the rejection of this nineteenth century edifice as inherently
unconvincing and artificial.
In order to appreciate how radically Einstein departed from the ancestral views
on these issues, it is necessary to compare his position with the 'decisive investi-
gation' published by Lorentz in 1895 [L4]. In Section 64 of that paper, we find
the following statement, italicized by its author: 'According to our theory the
motion of the earth will never have any first-order [in v/c] influence whatever on
experiments with terrestrial light sources.' By Einstein's own account, he knew
this 1895 memoir in which Lorentz discussed, among other things, both the aber-
ration of light and the Fizeau experiment. Let us briefly recall what was at stake.
Because of the velocity v of the earth, a star which would be at the zenith if the
earth were at rest is actually seen under an angle a with the vertical, where