198
DOC.
17
PROBLEM
OF
GRAVITATION
Doc.
17
On the Present State of the Problem of Gravitation
by
A.
Einstein
[Physikalische Zeitschrift
14
(1913):
1249-1262]
[1]
§1.
General Remarks
on
the Formulation
of the
Problem
The first
area
of
physical phenomena
where
a
successful theoretical elucidation
was
achieved
was
that of the
general
attraction of
masses.
The laws of inertia and of the
motions of celestial bodies
were
reduced
by
Newton to
a simple
law of motion
of
the
mass
point
and
to
a
law
of
interaction
of
two
gravitating mass points.
These laws
have
proved
to
hold
so
exactly that,
from
an
empirical standpoint,
there is
no
decisive
reason
for
doubting
their
strict
validity. If,
nevertheless,
scarcely
a
physicist might
be
found
today
who believes in the strict
validity
of
these
laws,
then this is
to
be
attributed
to
the
transforming
influence
of
the
development
of
our
knowledge
of
electromagnetic
processes during
the last few decades.
For before
Maxwell,
electromagnetic processes
were
traced back
to
elementary
laws that
were
fashioned
as
closely
as
possible
on
the
pattern
of
Newton's force
law.
According
to these
laws,
electrical
masses,
magnetic masses,
current
elements, etc.,
are
supposed
to exert
on
each other
actions-at-a-distance that
require
no
time for their
propagation through space.
Then Hertz
showed
25 years
ago by
means
of
his
brilliant
experimental
investigation
of
the
propagation
of electrical force that electrical effects
[2]
require
time for their
propagation.
In
this
way
he
helped
in the
victory
of
Maxwell's
theory,
which
replaced
the unmediated
action-at-a-distance
by partial
differential
equations.
After the
untenability
of the
theory
of action-at-a-distance had thus been
demonstrated in the
area
of
electrodynamics,
confidence in the
correctness
of
Newton's action-at-a-distance
theory
of
gravitation was
also
shaken. The conviction
had
to force itself
through
that Newton's law of
gravitation
does
not
embrace
gravitational phenomena
in their
totality any more
than Coulomb's law of electrostat-
ics and
magnetostatics
embraces the
totality
of
electromagnetic phenomena.
The fact
that Newton's law
previously
sufficed for
calculating
the motions of the
celestial
bodies is
to
be attributed
to
the fact that the velocities and accelerations of those
motions
are
small. In
fact,
it
is
easy
to demonstrate that celestial bodies whose
motions
were
determined
by
electrical forces
stemming
from electrical
charges
situated
on
the celestial bodies would
not unveil Maxwell's laws
of
electrodynamics
to
us
if the velocities and accelerations of those celestial bodies
were
of the
same
order of
magnitude
as
in the motions
of
the celestial bodies with which
we are
familiar. One
would be able
to
describe those motions with
great accuracy
on
the
[3]