Recent works have proved that semi-classical theories of gravity needed not
be fundamentally inconsistent, at least in the Newtonian regime. Using the
machinery of continuous measurement theory and feedback, it was shown that one
could construct well behaved models of hybrid quantum-classical dynamics at the
price of an imposed (non unique) decoherence structure. We introduce a
principle of least decoherence (PLD) which allows to naturally single out a
unique model from all the available options; up to some unspecified short
distance regularization scale. Interestingly, the resulting model is found to
coincide with the old --erstwhile only heuristically motivated-- proposal of
Penrose and one of us for gravity-related spontaneous decoherence and collapse.
Finally, this letter suggests that it is in the submillimeter behavior of
gravity that new phenomena might be found.Comment: 5
