362
DOC. 484 NOVEMBER
1913
484. To
Paul Ehrenfest
[Zurich,
second
half
of
November
1913][1]
Dear
Ehrenfest,
Forgive
me
my ugly
silence.
First of
all, accept my
thanks for
your
congratulations
on
my
Berlinerization.[2]
I accepted
this
odd sinecure because
giving
lectures
gets
on
my
nerves
in such
an
odd
way
&
there
I
do
not
have to
lecture
on
anything.
And
now
to
business.
As
things
stand
now
with
my
appointment,
I
am
not
entitled
to
an
assistant.[3]
But
since I love to work in
collaboration
with others, I will
request
an
assistant. If
I
am
given
one,
I
will
gladly
take either of the
two
gentlemen;
whether Droste
or Fokker,[4]
I
don't
know.
Fokker
is
very
much
to
my liking,
and he
is quite
capable.[5]
One
sees
in
him,
most
of
all,
Lorentz's
excellent
training.
You
assure me
that the
same
is true
of Droste.
So I
don't
know
whom I should
prefer. But,
as
you
see,
the
thing
can
wait,
since it
is not
yet
sure
whether the
position
in
question
is
going
to
materialize.
With
Fokker
I have
already
discovered
something
that
is
as
interesting
as
it
is
curious,
namely
that
mechanics, electrodynamics-applied
to
the
rotating
dipole-and
Jeans's radiation
law
are
not
compatible
with
each
other; rather,
the
quasi-monochro-
matic
Planck oscillator
occupies
a
special
position here.[6]
The calculation that
we
employed
is
absolutely
flawless. This
conflicts with H. A.
Lorentz's
general result.[7] I
wonder
if
we might
not
yet
find
a
handle
for
the
modification
of
the
theory
with
the
help
of
our
methods.
The
questions regarding
the
gravitation
theory
that
were
still
unsettled
in
the
summer
have in
the
meantime been
clarified.[8]
An
unambiguous
determination of the
g^v
from
the
T^v
is
only possible
if
special
coordinate
systems
are
chosen
(can
be
rigorously
proved).[9]
Momentum-energy
conservation
permits
only
linear substitutions. This makes
the
theory completely
satisfactory.[10]
Only one
point
has
not
been
clarified:
Are there
straight
lines that
are
purely temporal (or purely spatial)
along
their entire
extension?
What the
answer
is, yes
or
no,
must follow from
the
equations
for
gravitation.
Unfortunately,
answering
this
question is
difficult from
a
mathematical
point
of
view.
But if
the
answer
turns
out
satisfactorily,
then the
theory
will be
perfectly
secure
from
a
logical
point
of
view.
With best
regards
to
you,
your
wife,
and the
little
ones,
also from
my family,
your
A.
Einstein