DOC.
1
PRINCIPLE OF RELATIVITY
5
"relativity theory."
As
an
aid for the theoretical deduction of the laws of
nature,
this
theory
has
already proven
itself. Its
significance
lies in the fact that it
provides
conditions which
every general
law of
nature
must
satisfy,
for the
theory
teaches that
phenomena
in nature
are
such that the laws do not
depend upon
the
state
of motion
of the observer onto whom the
phenomena
are spatially
and
temporally
related.
Of
the
major
results of the
theory
of
relativity
two
should be mentioned
here,
because
they
are
also of interest
to
the
layman.
First: the
hypothesis
of
the existence
of
a
space-filling
medium for
light propagation,
the so-called
light-ether,
has
to
be
abandoned.
Light appears according
to
this
theory no longer
as a
state of motion of
an
unknown
carrier,
but
rather
as a physical
structure with
a
physical
existence of
its
own.
Second: the
theory
establishes that the inertia of
a
body
is
not
an absolutely
unchangeable
constant,
but rather that
it
grows
with the
energy
content.
The
important
conservation theorems
of
mass
and
of
energy
melt into
a
single
theorem:
the
energy
of
a
body
also determines its
mass.
Is the
theory
of
relativity,
sketched
above,
basically
complete-or is
it
only
a
first
step
in
a
continuing development?
On this
question physicists
who
value the
theory
of
relativity
still hold
differing opinions. Nevertheless,
weighty arguments speak
for
the second alternative. We have stated above that the laws
of
nature
are
the
same
for
a
"uniformly moving"
observer
as
they
are
for
one
"at rest." This
means
it is
impossible
for
an
observer
to
find criteria that would allow him
to
decide if he is at
rest
or
in
a
state
of
uniform motion. "At rest"
and
"in uniform
motion"
are
physically
equivalent.
This raises the
question
of
whether the
principle
of
relativity
is limited
to
uniform motion. Could the laws of
nature
not be such that
they
are
the
same
for
two observers
who
are
in nonuniform
motion relative to
each
other?
In
recent
years
it has turned
out
that such
an
extension
of
relativity theory
can
be carried
out,
and
that it leads
to
a
general theory
of
gravitation
which contains the Newtonian
theory
as a
first
approximation. According
to
this
theory, light rays
suffer
a
curvature in
a
gravitational
field;
though minute,
it is
just
within the
range
of
astronomical
measurement.
The future
will
teach
us
whether
this
generalized relativity theory,
which from
an
epistemological aspect
is
very satisfying,
conforms
to
reality.