358
DOC.
71
PRINCETON LECTURES
(115)
in which
[125]
THE GENERAL THEORY
=
V
-g
g^g’^,
3’^V-sp-jf-dxu/-
If
we
introduce the
energy
tensor
of the
electromagnetic
field into
the
right-hand
side of
(96),
we
obtain
(115),
for
the
special
case
~3*‘=0,
as a
consequence
of
(96) by
taking
the
divergence.
This
inclusion of the
theory
of
electricity
in
the
scheme of the
general
theory
of
relativity
has
been
considered
arbitrary
and
unsatisfactory
by many
theoreticians. Nor
can we
in this
way
understand the
equilibrium
of the
electricity
which
constitutes
the ele-
mentary
electrically
charged
particles. A theory
in
which
the
gravitational
field
and
the
electromagnetic
field do
not
enter
as
logically
distinct
structures
would be
much
pref-
[126]
erable. H.
Weyl,
and
recently
Th.
Kaluza,
have
put
for-
ward
ingenious
ideas
along
this
direction;
but
concerning
them, I
am
convinced that
they
do
not bring
us nearer
to
the
true
solution of the fundamental
problem.
I
shall
not
go
into
this
further,
but
shall
give a
brief
discussion
of
the so-called
cosmological
problem,
for
without
this,
the
considerations
regarding
the
general theory
of
relativity
[127]
would,
in
a
certain
sense,
remain
unsatisfactory.
Our
previous
considerations, based
upon
the field
equa-
tions
(96),
had
for
a
foundation the
conception
that
space
on
the whole
is
Galilean-Euclidean,
and that
this
character
is
disturbed
only by
masses
embedded
in it.
This
con-
ception
was
certainly justified
as
long
as we were
dealing
with
spaces
of
the order
of
magnitude
of those
that
astron-
omy
has
mostly
to
do
with.
But
whether
portions
of
the
[98]
=
ff~'
ôx~