DOC. 27
ON THE THEORY OF
GRAVITATION
291
Doc. 27
On
the
Theory
of Gravitation
by
A. Einstein
[Naturforschende Gesellschaft
in
Zürich.
Vierteljahrsschrift
59.
Part
2, Sitzungsberichte
(1914):
IV-VI]
[1]
Once
physicists recognized
the
superiority
of Maxwell's
theory
of
electromagnetic
phenomena
over
the earlier
action-at-a-distance
theories,
the conviction also
began
to
take hold that Newton's law of
gravitation represents only a
first
step
in the
understanding
of
gravitational phenomena.
One
can
hardly
dismiss the view that
we
have advanced
as
little in the
theory
of
gravitation
as
had
18th-century physicists
in
the
theory
of
electricity
when
they
knew
only
Coulomb's
law.
This realization
imposes
on us
the task of
completing
the
theory
of
gravitation
in such
a
way
that it also
encompasses
the
rapidly changing processes
and the
spatial–
temporal propagation
of
gravitational
effects. The
completion
of this task seemed
hopeless
at
first because of the arbitrariness
resulting
from the multitude of
possibilities.
However,
having
learned from the
theory
of
relativity
that time
enters
the laws
of
nature in
essentially
the
same
way
as
the
spatial
coordinates,
we
have
come
closer
to
the solution of the indicated
problem.
The theoretical
route
of march
is
almost
completely given
to
us
if
we assume
the
general
validity
of
a
fundamental
empirical law, namely
the
law of the
agreement
of the inertial and the
gravitational
mass
of
a
body.
Since the time of
Galileo,
we
know that the acceleration
of
falling
bodies is
independent
of the material of which
they are
made,
which
law
can
be
expressed as
follows: The
same
characteristic
constant
of
a
body
that determines
its
inertia also
determines
its
gravitational
action. This law
acquires
an even more
fundamental
significance by
the fact
that,
according
to the
theory
of
relativity,
there exists
a
general relationship
between the inertial
mass
and the
energy
of
a
body.
The
energy,
inertia,
and
gravity
of
a
body
are
thus reduced
to
one
another. The
equality
that exists
between inertia
and
gravitation
was
experimentally
demonstrated
by
Eötvös with such
accuracy
about 20
years ago
that relative deviations of the
gravitational
and the
inertial constant from each other of
the order of
magnitude
of 10-7
must
be ruled
out.
[2]
We have succeeded
in
establishing
two
theories that
satisfy
the above-indicated
demands,
that of Nordström and that
of
Einstein-Grossmann. The first of
these
theories
[3]
is
simpler
and
more
natural from the
point
of view of
the
original theory
of
relativity;
that
is to
say,
it adheres
to
the latter's fundamental
assumption
that
spatial-temporal
reference
systems
can
be chosen such that
light propagates everywhere
in the
vacuum
with the
same
velocity
c
(principle
of the
constancy
of the
velocity
of
light).