484 DOC.
470
FEBRUARY
1918
470. To
Gustav
Mie
[Berlin,]
22 February
1918
Dear
Colleague,
First
of
all,
to
what
I
called
the
“relativistic stance” in
my
last
letter.[1] I
maintain
that this
requires
the
following
interpretation
regarding
inertia. If L
is
the actual
path
of
a
certain
freely moving body
and L'
is
one
deviating
from it
with identical
initial
conditions,
the relativistic
point
of
view
requires
that the
actually
described
path
L be
preferred
over
the,
from
the
logical
point
of
view,
equally possible
paths
L',
on
the
basis of
a
real
cause,
which has
the
preference
of L
over
L'
as a
consequence. According
to
the theorem
you
recapitulated,
nothing
but the
(relative) positions
and states of motion of all
the
remaining
bodies
present
in
the
world
can
act
as
such
a
real
cause.
These
must
determine
entirely
and
uniquely
the inertial
behavior of
our mass.
Mathematically
this
means:
the
guv’s
must
be
determined
completely by
the
Tuv's-up to
the
4
arbitrary
functions,
of
course,
which
corre-
spond
to
the
free
choice
of
coordinates.[2]
This
requirement
is
not satisfied
by
Newton’s
theory,
but
also
just
as
little
by
mine
as
long
as
the world
is
conceived
as
quasi-Euclidean.
For
then the
guv's
are
predominantly fixed
by
nonrelativistic
boundary
conditions at
infinity.
Then
no
real
cause
exists for the
preference
of path L
over
certain other
L''s
(rectilinear
ones
against
non-Galilean
rigid
coordinate
bodies).
It
is
in
this
sense
that
I
said
that
Newton’s theory violates
the
causality requirement;
but
Schlick
is
right
when
he finds
fault with this
form of
expression.[3]
I
agree fully
with the
quote
from
Schlick[4]
but
not
with
the
use
you
make of it.
I
do not
deny
that the
description
of
the
world
proves
simpler
when
a
reference
system
is
introduced relative to which
the Earth
rotates in
a
specific
way.
But
I
do
contest
that the
corresponding
preference
of
one
coordinate
system
has essential
significance.
You
say,
in
one case
the
guv's
must be
assigned
particular properties
not
determined
by
the
matter
and
that,
on
the other
hand,
this
was
not
the
case
for
a
“natural
coordinate
choice.” If
you were
right
in
this, though,
I
would
regard
my standpoint, indeed, my
whole
theory altogether,
as
untenable.
But
let
us see
how
this
holds
up.
When
we
consider
the
solar
system or, perhaps,
the
Milky
Way,
in
any
case,
only
a
part
of
the
universe,
then the
differential laws
are
the
same
in
both