144
DOC. 29 ERNST MACH
reach this conclusion unless there
are
other bodies
A, B, C,
...
relative to which
we
judge
the motion
of
the
body
K.
We do in fact know
a
relation
of
the
body
K toward
A, B,
C.
...
If
we now
suddenly
want to
ignore
A, B, C,
...
and instead talk about
the behavior
of
the
body
K
in absolute
space,
we are
liable
to
make
a
double
error.
First,
we
cannot know how
K
would behave in the absence of
A, B, C,
...;
but then
we
would also have
no means
to judge
the behavior of the
body
K
in order
to test
our
statement-which,
consequently,
has
no
meaning
in natural science."
"The
movement
of
a body
K
can always
and
only
be
judged
relative
to
other
bodies
A, B, C,
....
As
there is
always
a
sufficient number of bodies
available,
which
are
either
relatively
fixed
against
each other
or only slowly changing
in their
relative
positions, we are
not
dependent
upon
a specific
one
and
can occasionally
ignore
one or
the other. In this
manner,
the
opinion
arises that these bodies
are
completely
irrelevant."
"Newton's
experiment
with the
rotating
water
container teaches
us
that the
relative rotation of
water
toward the walls of the vessel do
not
stir
up
noticeable
centrifugal
forces,
but that
they
are
rather caused
by
the relative rotation toward the
mass
of the earth and the other
heavenly
bodies.
Nobody
can
tell the result of the
experiment
if the walls
of
the vessel
would become thicker and
more
massive
until,
finally,
they
reach
several miles in
thickness.
. .
."
These
quotations
show that Mach
clearly recognized
the weak
points
of
classical
[4]
mechanics,
and thus
came
close
to
demand
a
general theory
of
relativity-and
this
almost half
a
century
ago!
It is
not
improbable
that Mach would have hit
on
relativity
theory
when in his
time-when
he
was
in fresh and
youthful
spirit-physicists
would
have been stirred
by
the
question
of
the
meaning
of the
constancy
of the
speed
of
light.
In the absence
of
this
stimulation,
which flows from Maxwell-Lorentzian
electrodynamics, even
Mach's critical
urge
did not suffice to raise
a
feeling
for the
[5]
need
of
a
definition of
simultaneity
for
spatially
distant
events.
The
contemplations on
Newton's
experiment
with the
pail
demonstrate how close
his mind
was
to
the demands of
relativity
in
a
wider
sense
(relativity
of accelera-
tions).
Admittedly,
the vivid consciousness
was
missing
that the
equivalence
of
inertial and
gravitational
mass
elicits
a postulate
of
relativity
in
a
wider
sense,
because
we are
not
in
a position
to decide
by experiments
if the
falling
of
a body
relative
to
a
coordinate
system
is caused
by
the
presence
of
a
gravitational
field
or
by
a
state
of
acceleration of the coordinate
system.
[p.
104]
in
his intellectual
development,
Mach
was
not
a
philosopher
who chose natural
science
as
an object
of
speculation,
but rather
an
ardent researcher of nature with
many
interests who
obviously
found
pleasure
in
researching
detailed
questions
off the
[6]
trodden
path
of
general
interest.
Testimony
to this
are
the almost uncountable
individual
investigations
from the fields
of
physics
and
empirical psychology
which