616 DOC.
594
AUGUST
1918
594. To
Friedrich
Adler
[Ahrenshoop,]
4 August 1918
Dear
Adler,
Yesterday your
manuscript
arrived.[1]
I have
already
studied the
first
chapter
and
am
thus
informed
about
all the
essentials.[2]
The basic
physical assumptions
are:[3]
a) no
Lorentz deformation
of
moving rigid bodies,
b) no
influence of motion
on
the
running
rate
of
the
clocks.
Thus the
geometrical
and kinematic elements
are entirely given, quite
apart
from
the mathematical
expression
in coordinates.
The
assumptions
(a)
and
(b)
are,
in
principle, directly verifiable,
but
not in
practice. (a)
leads
immediately
to Abraham’s
theory of
motion of
an
electron,
however,
which
is
refuted
empirically
as
soon
as
the
nonexistence of
the
deforma-
tion
of
moving
bodies
is
applied
also to
the
electron.[4]
It
must
be
considered, furthermore,
that
(a)
leads
straight
away
to
a
contra-
diction
with the
outcome
of
the
Michelson
experiment,
if
it
is assumed
that
the
law of
the
constancy
of
the
velocity
of
light
in
a
vacuum,
which
you
are
not
likely
to
question,
is
valid relative to
the
preferred
reference
system
K.
I
find
that
a
theory
can
be taken
seriously
from
the
physical
standpoint
only
when it does
justice to
the
following
observational results:
1)
Fizeau’s
experiment.
2)
Motion of electrons in
an
electromagn.
field.
3)
Aberration
law.
4)
Michelson’s
experiment.
For it
was
these
facts which
compelled
the
formulation
of
the
special
theory
of
relativity.
You have made
no
attempt
to
address these
fundamental
facts,
however.-
I
come now
to
the
formal
aspect. Basically,
on
making
arbitrary assumptions
about the
behavior of
measuring
rods and
clocks,
one can use
arbitrary
transfor-
mation
equations
without
coming
into conflict with
the
logic
or
with
experience.
If,
however,
as
corresponds
with
your
assumptions
about the behavior
of
the
measuring
rods and
clocks,
it
is
assumed
that
rigid
bodies
at rest
relative to
one
another
follow
Euclidean
geometry regarding
the
positioning
laws
[Lagerungsge-
setze],
and that static
clocks,
relative to
one
another,
run
equally quickly,
then
it
is certainly appropriate
(although logically
absolutely
not
necessary)
to
choose
the coordinates in such
a way
that
for all
legitimate
systems
the
following
is
valid: