DOC.
28
NORDSTRÖM'S THEORY OF GRAVITATION 299
formal
considerations, i.e.,
without
recourse
to
additional
physical hypotheses.
It
seems
to
us
therefore that this
theory
deserves
to
be
preferred
over
all
of
the other
gravitation
theories that adhere
to
this
principle.
From
a
physical standpoint
this
is
all the
more
the
case
since this
theory strictly
satisfies
the law of the
equivalence
of
inertial and
gravitational
mass.
Let
us
note
that it
is
only
the
application
of
the invariant
theory
of the absolute
differential calculus that
can give us a
clear
insight
into the formal
content
of
Nordström's
theory. Furthermore,
this method enables
us
to
describe the influence
that the
gravitational
field
is
expected
to
have
on
arbitrary physical processes
according
to
Nordström's
theory
without
recourse
to
new
hypotheses.
Also,
the
relation
of
Nordström's
theory
to
the
Einstein-Grossmann
theory comes
to
fore with
full
clarity.
Finally,
the
role that the Riemann-Christoffel differential
tensor
plays
in the
present investigation suggests
that this
tensor
may
also
open
the
way
for
a
derivation
of the
Einstein-Grossmann
gravitation equations
that
is
independent
of
physical
assumptions.
The
proof
of
the existence
or
nonexistence of such
a
connection would
represent
an
important
theoretical advance.4
(Received
on
19
February
1914)
[15]
4The
argument
in
support
of
the nonexistence
of
such
a
connection,
presented
in
§4,
p.
36
of
"Entwurfs einer
verallgemeinerten
Relativitätstheorie"
["Outline
of
a
Generalized
Theory
of
Relativity"],
did not withstand closer
scrutiny.