654
DOC.
626
SEPTEMBER
1918
626. To Hermann
Weyl
Berlin, 27 September
1918
Dear
Colleague,
I
was
just
busy
with
your
new paper[1]
when
your
letter
arrived.[2]
It
is
a
pleasure beyond
words for
me
to
read
your scrupulously
thought-out
things.
The
division
into the three
theoretical
themes
is
very
effective
and
clear.[3]
However,
the
point
of
sacrificing congruency
while
keeping similarity
does not
seem
to work
so
naturally
for
me.[4]
You
know,
of
course,
how I conceive
the relation
to
reality;
nothing
has
changed
in this
regard.[5]
I know how much easier
it
is
to convince
people
than
to find
truths,
especially
for
someone
who
is
such
an
incredible master
of
exposition
as
you
are.
But
ultimately,
far be
it
from
me
to be
presumptuous;
I
can
be mistaken
here,
as
I
have been countless times before. In
a
couple
of
years
it
will
be obvious whose
eyes saw more
clearly.
And
I
know
precisely
that the
only
goal
either
of
us
has
is to
see
the truth.
From
what
you
wrote
me,
I
was
very impressed by
the
fact
that the statics
comes
out
right,
and this
with
a
A
still at
one’s
disposal,
also
that
an
energy
equation,
EdIki/dxk
=
0,
results.[6]
This does indeed
mean more
to
me
than the
results
I already
knew
about
previously.
I
am
looking
forward
to
the
opportu-
nity
of
studying
this
more
closely.
The
expression
Rguvdxudxv
for
the
measured
length[7]
is,
in
my opinion,
by no means
acceptable, however,
when
the
curvature
invariant
is
taken
for
R,
because R
is
very dependent
on
the
mass
density.
A
very
small
change
in the
measurement
path
would have
a
very
pronounced
influence
on
the
integral
of
the
square
root
of this
quantity.[8]
Furthermore, although
it
is
correct
that
you
did
not
assert
anywhere
that
your geodesic
line
was
the
path
of
an uncharged
point-mass,[9]
nonetheless
this
does
appear necessary
to
me
without
extra
proof.
For
the
only
type
of world line
preferred
in
reality must
surely
cor-
respond
to
the
world line
preferred by
the
theory;
I at
least
cannot
think
of
any
other
arrangement.
If
this
is
so,
however,
we
encounter
a
contradiction with
your
theory
with the
energy principle,
in
the
following
manner.
The
vector potential
p1p2p3
would act
as
a
moving
force
upon
a
static
point;
a
permanent magnet
generates
closed lines
dx1
:
dx2
:
dx3
=
p1
:
p2
:
p3.[10]
Of
course,
I
know
very
well
that the
state of
the
theory,
as
I
have
set
it
up,
is
not
a
satisfactory
one, disregarding
the
fact
that
matter remains
unexplained.
The unrelated
juxtapositioning
of
the
gravitation
terms, electromagnetic
terms,
and
A-terms
is
undeniably a
product of
resignation.
I
share
your
firm conviction
that this must and
will
be otherwise.
I just
do
not
believe
that the
route
you
have embarked
on
is
the
right one,
as
finely
thought-out
as
it
is.
In
the
end,
the
answer
must include
that the
action densities do
not
have
to
be stuck
together
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