236
DOCUMENT 179 JANUARY
1916
[1]See
Doc. 158.
[2]Because
of
the
frequent closing
of
the
border between
Germany
and
Switzerland
(see
Doc.
170).
[3]Wedding
plans were
traceable
to
Elsa
Einstein’s
parents,
Rudolf
and
Fanny
Einstein
(see
Doc.
152).
[4]The
projected
book
appeared as
Einstein
1917a
(Vol.
6,
Doc.
42).
[5]
An
example
of
a
misleading
popularization
was
provided by
Max Weinstein in the
pages
of
the
Berliner
Tageblatt
at
the
end
of
the
following
month
(see
Doc.
204).
[6]In
1908,
Einstein had
criticized
Hermann
Minkowski’s four-dimensional
approach
to
special
relativity as
placing
“rather
great
demands”
(“ziemlich
grosse
Anforderungen”) on
the
reader, though
two
years
later
his
appreciation
of
the mathematical
formalism
had
grown (see
Jakob Laub
to
Einstein, 18
May
1908
[Vol.
5,
Doc.
101], note 12),
and in his 1912 manuscript
on
the
special theory
of
relativity
(Vol. 4,
Doc.
1),
he
incorporated
it.
[7]Beginning
in the
summer
of
1913,
Einstein
and
Besso had collaborated
on a
calculation
of
the
perihelion
shift
of
Mercury
in the framework
of
the “Entwurf”
theory.
See Doc.
153,
note
4,
for
more
details.
[8]See
Docs. 162 and 168 for similar remarks
made
by
Einstein the
preceding
month.
[9]In
their
joint
work
on
the
perihelion
shift,
Einstein
and Besso had also
calculated
the effect
of
the sun’s rotation
on
the
perihelion
motion
of
Mercury (see
Vol. 4,
Doc.
14,
especially
[pp.
18-22],
[p.
32],
and
[pp.
34-35]).
Besso had
subsequently
added calculations
dealing
with the effect
of
the
rotation
of
the
sun
and
of
Jupiter on
the motion
of
the nodes
of
Mercury,
Venus,
and Mars
(see
Vol.
4,
Doc.
14,
[pp.
45-50]
and
[pp.
41-42]).
[10]See
Doc.
43,
note
2,
and Doc.
173,
note
3,
for
more on
the role
of
the “hole
argument”
in the
development
of
general relativity.
[11]This argument
was
first formulated
in Doc.
173.
[12]The
papers are
Einstein
1915f
and 1915g (Vol. 6,
Docs.
21
and
22);
Tis the
trace
of
the
energy-
momentum tensor
of
matter. See Doc.
139,
note
2,
for
more on
the
postulate.
[13]See
Einstein 1915i
(Vol. 6,
Doc.
25),
where
the
condition T
=
0 is abandoned.
[14]The
condition T
=
0 would have
suggested
that matter is
electromagnetic
in nature
(see
Ein-
stein
1915g [Vol.
6,
Doc.
22]).
See Einstein 1909b
(Vol. 2,
Doc.
56),
sec. 10,
for
the dimensional
con-
sideration
to
which
Einstein
alludes;
see
also
Einstein
to H. A.
Lorentz,
30
March
1909 and 23
May
1909
(Vol.
5,
Docs. 146 and
163),
and H. A.
Lorentz
to
Einstein,
6
May
1909
(Vol. 5,
Doc.
153),
for
a
discussion
of
this
point.
[15]Major
German
military successes
in the fall
of
1915 in the East had
dimmed
the
prospects
for
peace.
179. To
Paul Ehrenfest
[Berlin,]
3.1.
16
Lieber Ehrenfest!
Meine Anworten
zu
Deinen
Bemerkungen
bedürfen noch
einer
Ergänzung.[1]
Es
wäre nämlich
denkbar,
dass Deine
vier
Relationen
(IV)
den
Feldgleichungen
wi-
dersprächen,
d.
h.
nicht
mit Ihnen
vereinbar
wären. Deshalb ist
es
doch
von
Inter-
esse zu
sehen,
dass Deine vier
Gleichungen
identisch erfüllt sind. Dies sieht
man
im
Anschluss
an
meine
Entwicklungen
in den Arbeiten wie
folgt
am
leichtesten
ein.
(Beim
Zitieren ist
die Arbeit
"Zur
allg.
Rel. Theorie“ mit
A,
die Arb.
"Die
Feldgl.
d.
Gravitation“ mit
B
bezeichnet.[2]
Wenn
man
statt
(7)B
die
Gleichung[3]