716 DOCUMENT 504 APRIL 1918
H.
Weyl
hat durch mich eine
höchst
interessante Arbeit
der
hiesigen
Akademie
einreichen
lassen,
in welcher
er
Gravitation und
Elektromagnetismus
mit einem
einheitlichen
geometrischen Begriffssystem
zu
begreifen
sucht.[11]
Mathematisch
ist die
Sache wundervoll. Aber
physikalisch
scheint sie mir nicht
acceptabel.[12]
Ich
bin
neugierig,
was
Sie dazu
sagen
werden.
Mit herzlichen Grüssen bin ich Ihr
ganz ergebener
A.
Einstein.
ALSX
(GyGöU,
Cod. Ms. D. Hilbert
92b). [13 108].
There
are perforations
for
a
loose-leaf
binder
at
the left
margin
of
the document.
[1]Dated
by
the reference
to
Einstein’s attendance
at
a
session
of
the Prussian
Academy.
[2]Confined
to
his bed since the end
of
1917,
Einstein had first attended
a
session
of
the Prussian
Academy
the
previous
week
(see
the
minutes
of
the
plenary
session,
4
April
1918,
GyBAW,
II-V,
Vol.
94).
[3]The
Vahlbruch Prize
of
11,000
marks had
been awarded
to
Einstein
at
the end
of
March
by
the
philosophical
faculty
of
the
University
of
Gottingen.
See Doc. 492,
in
which Einstein
also
thanks
Felix Klein.
[4]Planck’s Wolfskehl lectures
on
quantum theory
in
mid-May
(see
Doc.
540).
[5]Paul
Ehrenfest
had characterized his
reasons
for
declining
Hilbert’s invitation to the Wolfskehl
lectures in
Gottingen as
external and internal
(see
Doc.
494).
[6]Willem
Hendrik
Keesom (1876-1956)
was
Professor of
Physics at
the
Veterinary
School of
Utrecht.
[7]See
Docs.
480, 487,
and 492.
[8]Objections
to
Einstein's
usage
of
the pseudo-tensor
tva
to
represent gravitational energy-
momentum
were
voiced in Lorentz
1916d,
Levi-Civita 1917b
(see
Doc.
368,
note 6,
for
discussion),
Klein, F.
1917
(see
also Doc.
487),
Nordstrom 1918b
(see
Doc.
382,
note
26,
for
discussion),
Schrödinger 1918a,
and Kottier 1918
(see
also Doc.
495).
Rudolf
Forster had also written
to
Einstein
that he
thought
that
gravitational energy-momentum
should be
represented by a generally
covariant
tensor
(see
Doc.
485). Shortly
afterwards,
it
was
shown that
it
is
possible
for Einstein’s
pseudo-tensor
to
be
non-zero
in Minkowski
space-time
(see
Bauer
1918).
Einstein
responded
to
some
of
this criti-
cism in Einstein 1918a
(Vol.
7, Doc.
1)
and Einstein 1918b
(Vol. 7,
Doc.
2),
and defended his
position
more systematically
in Einstein
1918g
(Vol. 7,
Doc.
9),
submitted in
May
1918.
[9]In
the
equation
above,
expressing
the
vanishing
of
the covariant
divergence
of
the
energy-
momentum tensor
for
matter,
the
multiplication sign
should be
a
plus sign.
For
an
energy-momentum
conservation law
of
the
form
3m(£mv
+
tmv)
=
0,
one
needs the
pseudo-tensor
tvo
(see
Einstein
1916o
[Vol.
6,
Doc.
41]
and Einstein
1918g
[Vol.
7,
Doc.
9]).
[10]This argument
is also
given
in Einstein
1918g (Vol.
7,
Doc.
9),
p.
449.
[11]See
Doc.
472,
note 3,
for
a
brief
characterization
of
this
theory, presented
in
Weyl
1918b.
[12]See
Docs. 507 and 512 for Einstein’s fundamental
objection.
504. From Wilhelm Schweydar
Targsorul
vechi
[Romania]
den
14.
April
1918
Lieber
Herr
Kollege!
Über
Ihren freundlichen
Brief
vom
6.
IV habe ich mich sehr
gefreut;
hier in der
mir fremden
Umgebung[1]
bin ich
für
eine Freude
ganz
besonders dankbar. Ich
dan–