  We have recently proposed a new action principle for combining Einstein
equations and the Dirac equation for a point mass. We used a length scale
$L_{CS}$, dubbed the Compton-Schwarzschild length, to which the Compton
wavelength and Schwarzschild radius are small mass and large mass
approximations, respectively. Here we write down the field equations which
follow from this action. We argue that the large mass limit yields Einstein
equations, provided we assume wave function collapse and localisation for large
masses. The small mass limit yields the Dirac equation. We explain why the
Kerr-Newman black hole has the same gyromagnetic ratio as the Dirac electron,
both being twice the classical value. The small mass limit also provides
compelling reasons for introducing torsion, which is sourced by the spin
density of the Dirac field. There is thus a symmetry between torsion and
gravity: torsion couples to quantum objects through Planck's constant $\hbar$
(but not $G$) and is important in the microscopic limit. Whereas gravity
couples to classical matter, as usual, through Newton's gravitational constant
$G$ (but not $\hbar$), and is important in the macroscopic limit. We construct
the Einstein-Cartan-Dirac equations which include the length $L_{CS}$. We find
a potentially significant change in the coupling constant of the torsion driven
cubic non-linear self-interaction term in the Dirac-Hehl-Datta equation. We
speculate on the possibility that gravity is not a fundamental interaction, but
emerges as a consequence of wave function collapse, and that the gravitational
constant maybe expressible in terms of Planck's constant and the parameters of
dynamical collapse models.
