  Runaway solutions can be avoided in fourth order gravity by a doubling of the
matter operator algebra with a symmetry constraint with respect to the exchange
of observable and hidden degrees of freedom together with the change in sign of
the ghost and the dilaton fields. The theory is classically equivalent to
Einstein gravity, while its non-unitary Newtonian limit is shown to lead to a
sharp transition, around $10^{11}$ proton masses, from the wavelike properties
of microscopic particles to the classical behavior of macroscopic bodies, as
well as to a trans-Planckian regularization of collapse singularities. A
unified reading of ordinary and black hole entropy emerges as entanglement
entropy with hidden degrees of freedom. The emergent picture gives a
substantial agreement with B-H entropy and Hawking temperature.
