236
COMMENT ON
EHRENFEST'S
NOTE
Doc.
44
ON
THE NOTE
OF
MR. PAUL
EHRENFEST: "THE
TRANSLATORY MOTION
OF
DEFORMABLE ELECTRONS
AND
THE AREA LAW"
by
A.
Einstein
[Annalen
der
Physik 23 (1907):
206-208]
[1]
The
article
referred
to
above
contains
the
following
remarks:
"In
the
formulation
in which
Mr.
Einstein
published
it, Lorentzian
[2]
relativistic
electrodynamics
is
rather generally viewed
as a
complete system.
Accordingly,
it
must
also
be
able
to
provide purely
deductively
to
[3]
the
question
posed
by
transferring
Abraham's
problem
from
the rigid electron
to
the
deformable
one:
Granted
that there exists
a
deformable
electron that
[4]
has
some
nonspherical and
nonellipsoidal form
when
at
rest.
According
to
Mr.
Einstein,
this electron
undergoes
the
well-known
Lorentz
contraction
during
uniform
translation.
Well
then,
is it
possible
for this electron
to
undergo
[5]
force-free uniform translation in
every
direction,
or
is
it
not?"
Concerning
this
I have
the
1.
The
principle of
relativity,
or,
more
exactly,
the
principle of
relativity
together
with the
principle of
the
constancy
of velocity of
light,
is
not to be
conceived
as a
"complete
system,"
in
fact,
not
as a
system
at
all,
but
merely
as a
heuristic
principle
which, when
considered
by
itself,
contains
only statements
and
light signals.
It
is
only
by
requiring
relations
between
otherwise
seemingly
unrelated
laws
that
[6]
the
theory
of
relativity
provides
statements.
For
example,
the
theory
of the
motion of
electrons arises in the follow-
ing
way.
One
postulates
the
Maxwell equations
for
vacuum
for
a
system
of
space-time
coordinates.
By
applying
the space-time
transformation derived
by
means
of the
system
of
relativity,
one
finds the transformation
equations
for
the electric
and
magnetic
forces.
Using
the
latter,
and applying
the
space–
time transformation
once
again,
one
arrives
at
the
law
for the acceleration
of
an
electron
moving
at
arbitrary
speed
from
the
law
for the
acceleration of
the
[7]
slowly
moving
electron
(which
is
assumed
or
obtained
from
experience).
Thus,
we are
not
dealing
here
at
all with
a
"system"
in
which
the individual
laws
are
implicitly
contained
and
from which they
can
be found
by
deduction alone,
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