62 DOC.
47
JANUARY
1915
analysis.
If
I
require
that
a
coordinate
system
(p, q)
on
the
plane
be
selected in
such
a
way
that
ds2
=
dp2
+
dq2,
I therefore
assume
that then
the surface
can
be unfolded
on
to
a
[Euclidean]
plane.
Were
I
only
to
demand, however,
that the
coordinates be chosen in such
a
way
that
ds2
=
A(p,
q)dp2
+
B(p,
q)dq2,
i.e.,
that the
coordinates be
orthogonal,
then
I
am
assuming nothing
about the
nature
of the
surface;
this
can
be
obtained
on
any
surface.
You
say
that
regarding
coriolis and
centrifugal
forces
as
“real” field
compo-
nents is
unsatisfactory
because
we
cannot
attribute
any physical
cause
to
their
occurrence.
I would like to
respond
to this with
the
supposition
that
we never can
see
the
stars.
According
to
my
understanding,
these
force fields
are
determined
exclusively by
the
boundary
conditions and
the
field
equations,
if
the
influence
of
the
masses
belonging
to
the
system
under
study
can
be
disregarded
here.
It
is
admittedly
awkward
that the
boundary
conditions
must
be
picked
out suitably
instead
of
being
able
to
assume
that
all
boundary
conditions vanish
into
infinity.
But
are
you
so
sure
that
you
will
manage
with such
simple
boundary
conditions
in
you
view of the world?
Furthermore,
it
must
be considered that,
according
to
my view,
the
multifariousness
of
permissible
coordinate
systems
is
immense,
thus
also
the
multifariousness
of the attached
boundary conditions;
therefore,
if
these
boundary
conditions
appear
artificial in
the
individual
case,
this
does not
lie
in
the substance of
the
theory
but in the fact that
although justified,
the coordinate
system
is not suitably
chosen for
the
description
of
the
case
under
examination.
As
you know,
circumstances
are
similar
even
in normal mechanics. Let
the
world
to
be described
be
the
solar
system,
for
inst.;
then
it
is
clearly
useful
always
to
place
the
origin
of
the
coordinates
at
its
center
of
gravity,
but the
equations
are
obviously
also
valid
for
coordinate
systems
relative
to
which
this
center of
gravity
is
moving uniformly
and
in
a
straight
line. Here
also,
the
choice of
coordinates
is
prescribed
not
by
the
laws
of
nature
but
only
by
the
need for
the
simplest
possible description
of
the
case
at
hand.
Now
once
again
to
the
question
of whether
an
unrelativistic
physics
violates
the
postulate
of sufficient
cause.
You say
sufficient
cause (for preferring
K
over
K',
etc.)
can
be found in
that both
systems
move
in different
ways
relative to
the
ether. I
understand
“cause”
in
this
connection
as an
observable
fact
which
distinguishes
K
from
K'
not
as a
merely conceptual
characteristic.
I
ask
you please
to make allowances for
my
statements contained in
Kultur
der
Gegenwart.”[9]
Although
I
had
3
years
of time to
compose
it,
I
had
completely
forgotten
and
was
reminded of
my
commitment
by
Warburg
one
week
before
the
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