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 7 5
sense of the word. The general theory of relativity does not know of a distin-
guished state of motion in a distinct point, either, which possibly could be inter-
preted as the velocity of some ether. But, while in the special theory of relativity a
portion of space without matter and devoid of an electromagnetic field is truly
empty (i.e., not characterized by any physical quantities), it is quite different in
general relativity. There, empty space in the previous sense has physical qualities,
mathematically characterized by the components of the potential of gravitation
that determine the metrical behavior of that portion of space as well as its gravita-
tional field. This situation can very well be interpreted by speaking of an ether
whose state varies from point to point. However, one has to be careful not to
attribute to this “ether” any matterlike properties (e.g., a distinct velocity at each
point).
Translator’s Notes
{1} In the left column, the misprint from the German equivalent of “ remains at rest”
has been corrected here to “ remains at rest.”
{2} The preceding quote in its entirety is taken verbatim from P. Lenard’s “Über Rela-
tivitätsprinzip, Äther—Gravitation.” It has been reprinted unchanged in several later
editions (e.g., 3rd ed., Leipzig, 1921, by S. Hirzel Verlag).
U2
U1