2 0 6 D O C U M E N T 2 0 8 S O U N D R E C O R D I N G
208. Sound Recording for the Prussian State Library
[Berlin, 6] February
Ever since my youth, all my scientific strivings have been directed at penetrating
deeper into the foundations of physics; philosophical aspects and requirements in
a narrower sense had only a secondary influence on me. I give you here a brief re-
port about this striving and its results up to now. I am omitting everything that has
occupied me only occasionally or somewhat coincidentally.
My first problem lay in the apparent incongruity between the laws of the propa-
gation of light, in particular, Lorentz’s
and the equivalence of all inertial
systems according to experience. After seven years of pondering in vain (1898–
1905), the solution suddenly came to me with the thought that our concepts and
laws about space and time may claim validity only insofar as they stand in clear re-
lation to experiences, and that experience could very well lead to our modifying
these concepts and laws. Through a revision of the concept of simultaneity and the
form of rigid bodies I thus arrived at the special theory of relativity, whose four-
dimensional mathematical formulation, however, was only found three years later
In the attempt to incorporate the law of gravitation into special relativity, the
conviction was impressed upon me at the end of 1907 that the spatial state of a grav-
itational field was identical with the state of a space free of the gravitational field,
if the latter is only referred to an accelerated system of coordinates (in the sense of
This insight, briefly denoted as the principle of equiva-
lence, in connection with the natural tendency to generalize the principle of relativ-
ity, led me to the general theory of relativity, the consistent foundation of which
could only be laid at the end of
The main difficulty resided in the failure
of Euclidean geometry and in the difficulty of still ascribing clear meaning to the
laws of physics without it as a
The other great problem that I have been grappling with since about 1900 is the
theory of radiation and quanta. Inspired by Wien’s and Planck’s researches, I rec-
ognized that mechanics and electrodynamics stood in unresolvable contradiction to
observational facts, and contributed toward creating that complex of ideas known
under the name of quantum theory which has been developed to great fruitfulness
especially by
I shall probably devote the rest of my life to the fundamental
clarification of this problem, slight though the prospects of reaching this goal may
A. Einstein.
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