D O C . 4 9 R E S P O N S E T O R E I C H E N B Ä C H E R 3 7 1
Published in Die Naturwissenschaften 8 (1920): 1010–1011. Dated 20 November 1920, published 17
December 1920. A manuscript has been preserved (Harvey Plotnick, Chicago). [83 687]. Significant
variations from and emendations in the manuscript are noted.
[1]Ernst Reichenbächer (1881–1944) was a high school teacher in Wilhelmshaven. His Reichen-
bächer 1920 attempted to dissociate a covariant theory of gravitation from Einstein’s generalized
principle of relativity with arguments similar to those given in Mie 1917a, 1917b, 1917c. Reichen-
bächer assumed that the principle of relativity should imply that a rotating coordinate system cannot
be distinguished empirically from a nonrotating one without reference to distant masses. He claimed
that this is in fact possible and that it is necessary to distinguish true gravitational forces from ficti-
tious forces such as the Coriolis force. Reichenbächer argued from this and the fact that it is not gen-
erally possible to eliminate a gravitational field in a finite region of space-time by a coordinate
transformation that the principle of relativity has to be abandoned.
He proposed a new epistemological justification for a covariant formulation of natural laws: al-
though there is an objective state of acceleration against the ether, this state could be known only if
we knew the distribution of all masses in the universe. The covariant formulation is appropriate since
we can formulate in it the laws of nature without having determined this objective state of accelera-
tion. Reichenbächer claims that the ether should be understood as Minkowski’s space-time manifold
with deformations caused by the presence of masses. (In Reichenbächer 1917, he had introduced a
model of an elastically deformable ether.)
[2]The superiority of a theory with fewer independent assumptions is discussed in Schlick 1917,
pp. 62–63.
[3]Einstein calls both general relativity and thermodynamics “theories of principle” in Einstein
1919f (Doc. 26) and argues that they have the advantage of logical completeness and of having secure
foundations.
[4]In the manuscript, “geboten” is deleted and replaced by “gerechtfertigt.”
[5]In the manuscript, “verschweigt” is deleted and replaced by “vergißt.”
[6]Friedrich Kottler (1886–1965) was Privatdozent in mathematical physics at the University of
Vienna. For Einstein's response to the criticism of the equivalence principle in Kottler 1916, see Ein-
stein 1916p (Vol. 6, Doc. 40).
[7]The manuscript has “Schwerebeschleunigung” instead of “Schwerbeschleunigung.”
[8]For Einstein’s disagreement with Willem de Sitter about this question, see Vol. 8, the editorial
note, “The Einstein-De Sitter-Weyl-Klein Debate,” pp. 351–357. Einstein’s position is laid out in Ein-
stein 1917b (Vol. 8, Doc. 43) as a justification for the introduction of the cosmological constant.
[9]In Einstein 1921c (Doc. 52), pp. 12–13, Einstein proposes a way of measuring the cosmological
constant and thus answering whether the masses in the universe completely determine the metric
field.
[10]The manuscript has “Weltkörper auf die beiden betrachteten durch” instead of “Weltkörper,
außer den beiden betrachteten, durch.”
[11]The passage in Reichenbächer 1917 that Einstein is referring to is summarized in the second
paragraph of note 1.
[12]Before “Wenn,” the manuscript has the deleted passage “Von dieser Stelle aus begreife ich
nicht, wozu er die ganze Abhandlung geschrieben hat. Denn er steht damit auf dem Boden der allge-
meinen Relativitätstheorie.”