468
DOC.
460
FEBRUARY
1918
p
means
the
density
of
the stellar
matter
(conceived
as
evenly distributed)
in
the
world,
compared
to
the
density
of
liquid
water.
(2)nR,
the
length
in
natural
measure
of
the
geodesically
measured circumfer-
ence
of
the
world[4]
(i.e.,
measured with
the
cm
scale
(= 15
531.-
wavel[ength]
of
the
Cd
line))
That this
is
the
meaning
of
p
and R
according
to
my papers
is
easily
drawn from
my
considerations. The
crux
of
the
matter is
that
R
must not
be conceived
as
a
“coordinate
length”
but
as a
length
in
“natural
measure,”
and
thus
is
defined,
just
as p,
independently
of
the
coordinate
choice.-[5]
What
divides
us
most of
all is ultimately
the
circumstance
that
you
do
not
take the
standpoint I
call relativistic:
the
behavior
(continuation
of the
tempo[ral]
course
of
states)
of
every single physical body
is
such
that
it
is
uniquely
deter-
mined
by
its
own
state and
by
those of all
the other
bodies
(this
statement
must,
of
course,
be
interpreted
without
instantaneous action
at
a
distance). Only
the
observable
objects of
our
physical
world
are
to
be
understood
here
as
“natural
bodies.” The
varying
behaviors of
S1
and
S2
(in my pamphlet)[6]
must be
ex-
plained
in
that the
state of motion
of
the
remaining
world of bodies relative to
S1
is
different from
the
one
relative to
S2.
Any
other
interpretation is
not relativistic.
(Mach
has
already recognized
this
very
clearly.)
Now,
if
you
do not share
this
relativistic
point of
view,
then I
do
not
un-
derstand
in the least
why you
assign any significance
to
the
general
covariance
requirement.[7]
Either the
hypothesis
that
in
physics only
relative motions exist
is
taken
seriously,
i.e.,
that
only
relative motion
appears
as
efficacious in laws of
nature,
or
absolute
space
is
introduced
as an
independent
element in
the
causal
construction;
a
compromise point
of
view
between
these
two
does
not
exist.
In
justification
of
the
“Cosmological
Considerations,”
the
following:[8]
What
happens
at
infinity
is
all
the
same
to
me as
well. Nevertheless, I must
know
whether
what
I interpret
as
the
relativity
principle can
be
thought through
with-
out
encountering
contradictions.[9] For
this,
it
is
necessary
that the
gravitational
field
be
determined
entirely by
matter[10]
which, however,
is not true
for
the
quasi-Euclidean
world. The
latter rather
has
the
following
properties:
1)
The
mean
density (in
natural
measure)
of
matter
inside
a
spherical
surface
must
go
to
zero
with
the
spherical
surface’s radius.
(That
is,
the
world
is
essentially empty
and
has
a center.)
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