DOC.
319
MARCH
1917 311
319. To Felix Klein
[Berlin,]
26
March
1917
Esteemed
Colleague,
Many
thanks
for
your
papers
and
your friendly
card.[1]
It
is
really astonishing
that
such different
points
of
departure
as
mathematics
and
physics
give
occasion
to
establishing
the
same
thought
structures in
the
end.
I
have
already
read
with
pleasure
the
marked
places
in
your papers;
the
other
will
follow.
As
I
have
never
done non-Euclidean
geometry,
the
more
obvious
elliptic
geometry
had
escaped
me
when
I
was
writing my
last
paper.[2]
Mr.
Freundlich has
already
made
me
aware
of
this
point.[3]
My
observations
are
just
altered
thus,
that
the
space
is
half
as
large;
the
relation between
R
(radius
of
curvature)
and
p (mean density
of
matter) is
retained.
The
new
version of
the
theory means, formally,
a
complication
of
the
foun-
dations
and
will probably
be looked
upon by
almost all
our
colleagues
as an
interesting, though
mischievous and
superfluous
stunt, particularly
since
it
is
un-
likely
that
empirical
support will
be
obtainable
in
the
foreseeable future.
But
I
see
the
matter
as a
necessary addition,
without
which
neither inertia
nor
the
geometry
are
truly
relative.
But
someone
who does
not
find it
disturbing
when
the
existence
of
a
guv-field
can
result from
the
theory
without
field-producing
matter and
when
a single mass (imagined as being
alone in
the
universe) can
have
inertia, cannot
be convinced
of
the
new
step’s
necessity.[4]
I
am
very
much
looking
forward to
seeing Debye
in
the
next
few
days
and
ask
you please
to
inform
me
when
you
are
coming
to Berlin
again
so
that
I
can
visit
you.
It
would
certainly
be desirable
if
between
Göttingen
and
Leyden
there
were
an
exchange
of
papers addressing
the
area
of
general relativity.
In
that
way,
much
intellectual
effort would be
spared.
For
ex.,
a
precise
treatment of
the
point
problem,
as
Hilbert
provides
in his
last
article,[5]
already
exists in
the dissertation
by
the Dutchman
Droste.[6]
Furthermore,
Lorentz has worked
on
many
things.[7]
With
kind
regards, yours truly,
A.
Einstein.
Document
description:
“Einstein
to
Klein.
To
Messrs.
Baade
and
Fréedericksz for
your
o[bliging]
perusal
and
return
on
Saturday.
K[lein].”