7 2 D O C . 1 3 D I A L O G U E A B O U T R E L A T I V I T Y T H E O R Y
thought he could attribute that idea to me. But all stars in the universe can be
thought of as taking part in the generation of the gravitational field, because they
are, during the acceleration phases of the coordinate system accelerated rela-
tive to the latter and, thus, can induce a gravitational field just as well as accelerat-
edly moving electric charges induce an electric field. Approximate integration of
the gravitational equations has indeed shown that such inductive effects actually
must occur with acceleratedly moving masses. From these considerations it is
clear that a complete clarification of the questions raised by you can only be
obtained if one forms a picture of the geometric-mechanical constitution of the
universe as a whole that is compatible with the theory. This I have tried last year
and have found—as it seems to me—a completely satisfying model; but going
into it would lead too far.
Krit.: After your last explanations it seems indeed that the clock paradox is
not suited to deduce internal contradictions in the theory of relativity. In fact, it
now does not seem improbable to me that the theory may have no internal contra-
dictions; but this is not sufficient to take the theory into serious consideration. I
just cannot see why it should be necessary to take upon oneself, for the sake of
one’s intellectual predilection—I mean the idea of relativity—such horrible com-
plications and mathematical difficulties. In your last answer you yourself showed
clearly enough that they are not minor. Will it, for example, occur to someone to
make use of the possibility offered by the theory of relativity to relate the move-
ment of the celestial bodies of our solar system to a geocentric system of coordi-
nates, a system which, of all things, takes part in the rotational movement of the
earth? Could such a coordinate system really be considered “at rest” and equiva-
lent to others, when relative to it the fixed stars race around the earth at horrendous
velocities? Would this idea not run counter to all common sense, and to the postu-
late of the economy of thinking? I cannot refrain from repeating some strong
words which Lenard recently uttered on this subject. After he discussed special
relativity, where he characterized the “moving” coordinate system by a railroad
train in motion, he said: “Now, let the imagined railroad train make a clearly non-
uniform motion. When then, due to inertial effects, everything in the train goes to
pieces while outside nothing is damaged, then—I believe—no common sense can
escape the conclusion that it was the very train and not the environment which
changed its motion with a jolt. Now, the generalized principle of relativity
demands, in its simple elementary sense, to admit even in this case that it might
possibly have been the environment which suffered a change in velocity, and the
whole disaster in the train was only a consequence of the jolt of the outside world,
transmitted through the “gravitational effect” of the outside world upon the inte-
rior of the train. For the obvious question why the church steeple next to the train
K′,
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