12 DOC.
5
APRIL
1914
5.
To
Joseph
Petzoldt
[Berlin,]
16[14]
April 1914[1]
Highly
esteemed
Colleague,[2]
I
read
your
comments
on
relativity
theory
in
the
Zeitschr. für
posit.
Philoso-
phie
with much
pleasure.[3]
From
it
I
see
with astonishment
that
you
are
closer
to
me
in
your
understanding
of
the
subject,
as
well
as
with
regard to
the
sources
from which
you
draw
your
scientific
convictions,
than
my
true
colleagues
in
the
field, even as
far
as
they
are
unconditional
supporters
of
relativity
theory.[4]
Af-
ter
great
exertion I have
now
succeeded in
establishing proof
that the
gravitation
equations
formed
last
year
have
a very high degree
of covariance with acceleration
transformations.[5]
Seen from the
physical
standpoint,
rotation
and acceleration
prove
to
be
entirely
relative;[6]
there
is
no
distinction
between
a
“real” gravita-
tional
field
and
an
“apparent”
gravitational field
produced through
the
accelera-
tion of
the
reference
system.
In
both
fields
the
same
field
equations
of
gravitation
apply.-
The
only
point
in
regard
to
which
I
do
not
agree
with
your
representations
is
the
matter of
the
moving
clock
(38).[7]
Relativity theory
allows
the strict
con-
clusion
that
a
clock U'
moving uniformly
and in
a
straight
line relative to
the
“justified”
reference
system
K travels
slower
(seen
from
K)
than
identically
con-
structed
clocks
U
at rest in
K
with which
we measure
the time
in
K.
We
know
nothing though
about
how
U'
proceeds
relative
to
K
while
U' is
in accelerated
motion.
But the
traveling speed
of U' relative
to
K
can
only
be influenced
finitely
by
a
finite acceleration.
Thus,
if
we
allow U'
to
describe
a
closed
path
relative
to
K in such
a way
that U''s
acceleration times
disappear
against
U''s
times while
moving
in
a
straight
line
(all
seen
relative
to K),
we can
then
disregard
the
influ-
ence
of acceleration
times
on
the
angles
traveled
by
the
hands
of
clock U'.
Then
we
must
conclude that
the
hands of
U'
advance
slower
while
traveling along a
closed
polygon[al path]
than
the hands of
an
identically designed
clock
that
was
constantly at
rest relative to
K.
On closer consideration of
this
case, doubtlessly
you
also
will
have to
come
to this result.
I would be
very pleased
if
we were
to
see
each
other
one
day
soon so
that
we
can
discuss
this
question
of
common
interest
to
us
both.
With
regards, your colleague
Einstein
Kais. Wilh.
Inst.
of
Phys. Chemistry.
Dahlem.