7 4 D O C . 7 5 N O B E L L E C T U R E
75. “Fundamental Ideas and Problems of the Theory of
Relativity”
[Einstein 1923q]
Completed 8 July 1923
Published 11 July 1923
In: Les Prix Nobel en 1921–1922. Stockholm: Norstedt & Fils, 1923.
Lecture delivered to the Assembly of Nordic Naturalists in Gothenburg on
11 July
1923[1]
If we consider that portion of relativity theory perceptible today in a certain
sense as part and parcel of secure science, we discern two aspects playing a leading
role in this theory. The entire development revolves around the question:
Do physically distinguished states of motion exist in nature? (The physical prob-
lem of relativity.) Furthermore, does the following epistemological postulate prove
to be fundamental:
Concepts and distinctions are permissible only insofar as they can be assigned
uniquely to observable factual findings (reality postulate of concepts and
distinctions).[2]
These two aspects become clear when we apply them to a specific case, e.g., to
classical mechanics. At first, we see that at every point occupied by matter there is
a preferred state of motion, namely, the motion of the matter at the observed point.
Our problem, however, only starts with the question of whether there are physically
preferred states of motion with respect to extended regions. From the standpoint of
classical mechanics, this must be affirmed; the states of motion physically distin-
guished from the standpoint of mechanics are the states of motion of inertial
frames.
This statement, just as the foundations of mechanics as they generally tended to
be described prior to the theory of relativity, does not come close to satisfying the
above-mentioned “reality postulate.” Motion can only be thought of as relative mo-
tion between bodies. In mechanics, when one speaks of motion per se, one means
the motion relative to the system of coordinates. This interpretation does not com-
ply with the reality postulate, though, when the coordinate system is regarded as
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