DOC.
18
DISCUSSION OF DOC.
17 357
arbitrary
and
expedient
but
not
necessary?
If
we are
forced
to
give
up
the
ether,
then
we
must
consider
light as
a
substance
that
possesses
the
velocity
of
light.
As for
several
remarks that
we
heard
here,
I would like to
point
out
that the
analogy
between the
coordinates of
space
and
of time
is
only a
mathematical
one,
obtained
by way
of
definition.
For
a
mathematician,
things can
emerge
that
defy physical
representation.
Thus,
for
example,
/-1
occurs
in this
formula.
Prof.
Einstein:
If
we
had electrostatic
forces
instead of
gravitation,
what would be
the
result? Would
you
find
a velocity
of
propagation?
You
would
only
find
that
things go
infinitely
fast
because the
question
has
been
wrongly put.
The
thing
has
been calculated
as
if the
particles
had been hurled
out
from the
from
the
center
of
gravitation.
It
is
very
possible,
and it
is
even
to
be
expected,
that
gravitation propagates
with
the
velocity
of
light.
If there
existed
a
universal
velocity which,
like
the
velocity
of
light, were so
constituted
with
respect
to
a single system
that
a
stimulus would
propagate
with
a
universal
velocity
independent
of
the
velocity
of
the
emitting
body,
the
theory
of
relativity
would
be
impossible.
If
gravitation
were
to propagate
with
a (universal)
superluminal
velocity,
this would suffice to
bring
down
the
principle
of
relativity
once
and
for
all.
If
it
propagated
infinitely fast,
this would
provide
us
with
a means
to
determine
the
absolute
time.
The
comparison
of
light
with
other
"stuff"
is
not
permissible.
At
small
velocities,
material
stuff in
the usual
sense
of the word
moves according
to
Newton's
equations
of
motion.
This is
not
the
case
with
light;
the
parallel
is
therefore
not
permissible.
The
principle
of
relativity
is
a
principle
that
narrows
the
possibilities;
it
is
not
a
model,
just
as
the
second law
of
thermodynamics
is
not
a
model.
Dr. Lämmel:
The
question is
whether the
principle
is inevitable
and
necessary
or
merely
expedient.
Dr. Einstein:
The
principle is
logically
not
necessary:
it would be
necessary
only
if
it
would
be made
such
by
experience.
But it
is
made
only
probable
by
experience.
Prof.
Meissner:
The
discussion has shown what is
the
first
thing
to
be done. All
physical
concepts
will have to
be
revised,
they will
have to
be
reformulated, indeed,
in
such
a
way as
to
bring
out
any
invariance
with
respect
to
the transformation of the
relativity
principle
that
may
be
present.
Klein has in fact
already pointed
out in
a
lecture
that
one
must extract from
each
concept
that
which
can
be
maintained
unchanged
when
one
applies
the remarkable transformation of
space
and
time.
Only
then
will
one
have
extracted
epistemologically
one
of
the main results. Even if the whole
theory
of
relativity
were
to
prove untenable,
this would
represent
an
extraordinary
advance.
[12]
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