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NOTES ON THE ORIGIN OF THE GENERAL THEORY OF, RELATIVITY 285
. tion of masses and changes with it, the geometric structure of
this space is also dependent on physical factors. Thus, according
to this theory space is-exactly as Riemann guessed-no
longer absolute; its structure depends on physical infiuences.
(Physical) geometry is no longer an isolated self-contained science
like the geometry of Euclid.
The problem of gravitation was thus reduced to a mathematical
problem: it was required to find the simplest fundamental
equations which are covariant with respect to arbitrary coordinate
transformation. This was a well-defined problem that
could at least be solved.
I will not speak here of the experimental confinnation of this
theory, but explain at once why the theory could not rest permanently
satisfied with this success. Gravitation had indeed been
deduced from the structure of space, but besides the gravitational
field there is also the electromagnetic field. This had, to
begin with, to be introduced into the theory as an entity independent
of gravitation. Terms which took account of the
existence of the electromagnetic field had to be added to the
fundamental field equations. But the idea that there exist two
structures of space independent of each other, the metric-gravitational
and the electromagnetic, was intolerable to the theoretical
spirit. We are prompted to the belief that both·sorts of field
must correspond to a unified structure of space.
NOTES ON THE ORIGIN OF THE GENERAL
THEORY OF RELATIVITY
Mein Weltbild, Amsterdam: Querida Verlag, 1934.
I gladly accede to the request that I should say something
about the history of my own scientific work. Not that I have
an exaggerated notion of the importance of my own efforts, but
to write the history of other men's work demands a degree of
absorption in other people's ideas which is much more in the
line of the trained historian; to tllrow light on one's own earlier
thinking appears incomparably easier. Here one has an immense
advantage over everybody else, and one ought not to
leave the opportunity unused out of modesty.