DOC.
311
MARCH
1917 301
311. To Willem de Sitter
[Berlin,
before 12 March
1917][1]
Dear
Colleague,
I
am
terribly
sorry
that
you
have
health
complaints
and
are
confined to
bed.[2]
I
hope you
will
soon recover.
There
is
something
amiss with
me too,[3]
but
at
least
I
am
allowed to
go
about
my
normal business.
Furthermore,
it
is
bad
that
they
have chosen
M.
instead
of K.
for
Potsdam,
in
spite
of
the
Academy’s
recommendation![4] All
who
mean
well
in
the
matter
are unhappy
about
it.
It
is
unclear
what
forces
are
to
blame in this. There
is
talk
of
von Seeliger.[5]
Now to
our
problem!
From the
standpoint of
astronomy,
of
course,
I
have
erected
but
a
lofty
castle
in
the
air.[6]
For
me, though,
it
was a
burning question
whether the
relativity concept
can
be
followed
through
to
the
finish
or
whether
it
leads to contradictions.
I
am
satisfied
now
that
I
was
able
to
think the
idea
through
to
completion
without
encountering
contradictions.
Now
I
am
no longer
plagued
with the
problem,
while
previously
it
gave
me
no
peace.
Whether
the
model I formed
for
myself
corresponds
to
reality is
another
question,
about
which
we
shall
probably
never
gain
information. On
the
value
of
R,
I contemplated
the
following.[7]
Astronomers have found
the
spatial
density
of
matter from star counts
up
to
the
nth
size class,
fairly independent
of
the
class
to
which
the
count
extends,
at
about
10-22g/cm3.
From
this,
approximately
R
=
107
light-years
results,
whereas
we
only
see as
far
as
104 light-years.
One
thing
seems
strange
to
me,
though.
Stars
close
to
our
antipodal
point
should be
emitting
a
lot of
light
to
us.[8]
It
is
doubtful, however,
that
they
could
appear
point-shaped,
since
the
light
velocity
varies
irregularly.
If such
a
thing
were
visible in
the
heavens,
it
would be noticeable
through
its
negative
parallax.[9]
We
should
at
least
keep
an
eye
out
whether
any
objects
with
a negative
parallax
exist
in
the
sky.
But
now,
enough
of
this,
or
else
you
will
laugh
at
me.
Of
course,
the
question
of the three-dimensional
composition
of the world
only
makes
sense
when
a
static
(approximated)
conception
is
possible
(independence
of all functions of
a
suitably
chosen
x4).
There
is
no
violation of
the
relativity
postulate.
Our
problem
can
be
illustrated
with
a
nice
analogy.
I
compare
the
space
to
a
cloth
floating (at
rest)
in
the
air,
a
certain
part of
which
we can
observe.
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