354
DOC.
18
DISCUSSION OF DOC.
17
detail.
The ether
was
of real
value
for the
intuitive
representation
of
optical processes
only
as
long
as one
actually
reduced these
processes,
with all
their
peculiarities,
to
mechanical
processes.
After the
concept
of
fields
of
lines
of
force
had been
put
into
the
foreground,
the ether
hypothesis
has
come
in fact to
play only a
fictitious
role.
[3]
Fritz Müller:
If there
are
two
synchronous
clocks at
point A,
and
one
of them
is
moved with
a given
velocity
from this
point
to
point
B,
then,
according
to
the
reasoning
of
the
speaker,
this
second
clock will
run slower,
if
only by a tiny
fraction.
What
happens
now
if this clock returns
by
a
polygonal
or
circular
path
to
point
A?
According
to
the
reasoning
given
in
the
lecture,
at
the
moment
of
its meeting
with
the other
clock at
point
A,
the second
clock will not
be
running
in
synchrony again.
How
can
this be
possible,
since, on
the other
hand,
Prof.
Einstein
says
that
a
rod of
a
specific
length
L
in
a system
at rest, which
he
holds in his hand, will
become shorter
by
a
definite
amount when it
is
set
in motion? But
as soon as
the rod
is
brought
to
halt
by
a
sudden
jerk,
its
length
is
once
again
=
L,
i.e.,
the rod
is
no longer
deformed. If
this
latter
argument
holds
good
for
length, i.e.,
for
a
specific
dimension,
and
if what
the mathematician
Minkowski
asserted,
which
was
termed
acceptable
by
Prof. Einstein,
is correct,
namely,
that
we
can
speak
of
a
4-dimensional
geometry,
so
that
we can compare length
with
time,
then
how
do
things
stand
with
the
clock? Must it not
then,
exactly
like
the
rod,
run synchronously
again
from the
moment it
is brought
to rest at
point
A?
This
reasoning
would suit
me
better,
whereas
I
cannot
grasp
the other
one.
Prof.
Einstein:
It
is not
the
clock's
indication of
time
that
is
to be
likened
to
the
rod,
but
its rate.
After
having
completed
its
motion and
returned,
the rod
has
the
same
length.
In the
same
way,
the
clock has
again
the
same
rate.
We
can designate
the rod
as
the carrier of the
space
differential,
and the
clock
as
the carrier of the
time
differential.
It
is
impossible
to
assume
that,
after
having
traveled
along a polygonal
path
and
returned
to
point
A,
the
clock
will
again
be
running
synchronously
with
the
clock
that
has
been
at rest at
point
A.
The
clock
runs
slower if it
is
in
uniform
motion,
but
if it
undergoes a
change
in
direction
as a
result of
a
jolt,
then the
theory
of
relativity
does not
tell
us
what
happens.
The sudden
change
of direction
might
produce a
sudden
change
in
the
position
of the hands of the
clock.
However,
the
longer
the
clock
is
moving
rectilinearly
and
uniformly
with
a given
speed
of
forward motion,
i.e.,
the
larger
the
dimensions of the
polygon,
the smaller
must be
the
effect
of
such
a
hypothetical
sudden
change.
[4]
Prof.
Prasil:
In
his famous
essay, "Space
and
Time,"
Minkowski wrote
about the
nature
of
dilation,
that the
latter
is
a
concomitant circumstance of the
state
of
motion.
[5]
He makes it
absolutely independent
of
any physical
influence.
Lorentz,
on
the other