Equation (13) is the center of a constellation
consisting of the following three results:
The main result is the recognition of the fact that a Klein-Gordon
charge has a property which displays the Poincare invariance of
Minkowski spacetime *without involving its specific mass*. This
property is the set of expectation values given by
Eq.(13). The presence of gravitation is expressed
by distortions of this mass-independent vector field. This property is
a quantum mechanical extension of the principle familiar from
classical mechanics, and it is dictated by the Braginski-Dicke-Eotvos
experiment, that the set of particle trajectories serve as the carrier
of the imprints of gravitation.

The second result is the fact that Eq.(13) are (twice) the
expectation values of the ``spin'' component operators

13 |

Their commutation relations

are those of the symmetry group

The third result is as obvious as it is noteworthy: The
components of the vector field coincide with the ``Planckian power''
and the ``r.m.s. thermal fluctuation'' spectra, in spite of the fact
that we have not made any thermodynamic assumptions. In fact, we are
considering only the quantum mechanics of a single charge,
*or* the Klein-Gordon dynamics of a classical wave field. That
these two spectra also arise within the framework of a strictly
classical field theory, has already been observed in
[14].
We would
like to extend this observation by pointing out that in the absence of
gravitation these two spectra express the invariance of spacetime
under translations and Lorentz trasformations (requirement 3.,
Poincare invariance)