DOCS.
161,
162
DECEMBER
1915
159
161. To Arnold Sommerfeld
[Berlin,]
9
December
1915
Dear
Sommerfeld,
Here
you
have
both
manuscripts back,
which
I
have looked
through
with
interest.[1] Planck
is
also
working
on a
similar
problem
as
you (quantization
of
the
phase space
of molecular
systems).[2]
He is
also
laboring on
spectral
ques-
tions. General
relativity is
unlikely
to be able to assist
you,
because it
practically
coincides
with the
more
restricted
theory
of
relativity
for these
problems.[3]
From
what
I
know of Hilbert’s
theory,
it makes
use
of
an
approach
for
electrodynamic
events
that-apart
from the
treatment of
the
gravitational
field-is
closely
con-
nected to
Mie’s.[4]
Such
a
specialized approach
is
not in accordance with
the
point
of
view
of
general relativity.
The
latter
actually only
delivers
the
law
for
the
grav-
itational
field,
and
quite unambiguously
so
when
general
covariance
is
required.
You
will
see
this in the
papers
I sent out to
you
this
morning.[5] (Be sure
to have
a
look at
them;
it
is
the
most valuable
finding
I
have made in
my
life).
Conversely,
any
other
theory
that
corresponds
with
relativity
in
the
more
restricted
sense can
be taken
over
in
the
general theory
of relativity
through simple
transformation,
without the latter
delivering any
new
criteria. Thus
you
see
that
I
cannot
help
you
in
the
least.
The
result of
the
perihelion
motion of
Mercury
gives me
great satisfaction.[6]
How
helpful
to
us
here
is
astronomy’s
pedantic
accuracy,
which
I often used to
ridicule
secretly!
Do not let
yourself
be dissuaded from
looking
at
the
papers
more
closely by
the
fact that
as
you
read it the final
stage
in
the
battle
over
the
field
equations
is
being fought
out before
your
eyes!
Best
regards,
yours,
Einstein.
Tell
your
colleague Seeliger
that
he has
a
frightful temper.
I
relished it
recently
in
a
reply
that
he directed
to
the astronomer
Freundlich.[7]
162. To
Michele
Besso
[Berlin,
10
December
1915]
Dear
Michele,
Many
thanks
for
the
letter.[1] I
am
coming
to
Switzerland
now
after
all,
be-
cause
my
wife
has assured
me
by
letter
that
my
Albert
is
eager
to be with
me.[2]