lii
INTRODUCTION
TO
VOLUME
8
V-g
=
1, the
gravitational
field
of
a
point
mass
has
no energy.
Nordstrom had
to
derive this
result in
two different
ways
before
Einstein
accepted
it
(Docs.
382 and
393).
Nordstrom also
discovered that the
expression
for
tuv
given
in Einstein
1916g
(Vol. 6,
Doc.
32)
is
incompatible
with the
expression given
in Einstein 1916o
(Vol.
6,
Doc.
41).
This is
probably
what
alerted
Einstein to
a
serious
error
in
the
former
paper.
A
corrected
version
was published
as
Einstein 1918a
(Vol.
7,
Doc.
1).
In this
paper,
the
spurious gravitational waves are
eliminated
by showing
that
the metric
field
describing
them
is
simply
that
of
a
Minkowski
space-time
in
a
peculiar
coor-
dinate
system.
Einstein
apparently
neglected to
send the
corrected
version
of
the
paper to Mie, because,
later
in 1918,
Mie-whose
attempts
to convince Einstein
of
the need
of
privileged
coordinate
systems
had fallen
on
deaf
ears-confronted
Einstein with the
passage
in the
original
paper
proclaiming
the
privileged
nature
of
coordinates
satisfying
V-g
= 1
(Doc. 532).
IX
The
primacy
of
physical
over
mathematical
considerations
that
we
encounter,
for
instance,
in Einstein’s search for
gravitational
field
equations
and
in
his staunch
defense
of
his
gravitational energy-momentum pseudo-tensor
is also
very
much in
evidence in his
response to
early attempts
to find
a
unified
theory
of
gravitation
and
electromagnetism.
Einstein felt the
need for
such unification
(see, e.g.,
Docs.
400
and
565),
but his
role
at
this
stage was
restricted
to that
of
a
critic
of
the theories
proposed
by
others. He
quickly disposed
of
the
idea
suggested
to
him in
correspon-
dence in late 1917
by
Rudolf
Förster
to
construct
a
unified
theory on
the basis
of
a
nonsymmetric
metric
tensor,
with the
symmetric
and the
asymmetric parts repre-
senting
the
gravitational
and the
electromagnetic
fields,
respectively. Drawing
on
the
analogy
between
gravitational
and
electromagnetic waves
used in Einstein
1918a
(Vol.
7,
Doc.
1),
Einstein
pointed
out that
one
cannot
just
add
an electromag-
netic
field
to
a gravitational
potential (Doc. 439).
A few months
later,
Weyl
announced that
he had
found
a
unified
theory
based
on a generalization
of
Riemannian
geometry.[42]
The discussion
of
this
theory
dom-
inated the
correspondence
between
Einstein
and
Weyl
in
1918.[43]
Einstein imme-
diately objected
to
Weyl’s theory on
physical
grounds
and
never
wavered in his
conviction
that
the
theory
could not be
reconciled
with such basic
empirical
facts
as
the existence
of
sharp spectral
lines
(Doc. 512). Weyl quickly grew weary
of
the
reassurances
of
Einstein’s admiration
for
the mathematical
ingenuity
of
the
theory
that
accompanied
his harsh criticism
of
its
physical underpinnings, or
rather its lack
thereof. Einstein’s
admiration, however,
appears
to
have been
genuine,
as was
his
embarrassment when
Nernst,
after
learning
of
Einstein’s
reservations, objected
to
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