  We provide general arguments regarding the connection between low-energy
theories (gravity and quantum field theory) and a hypothetical fundamental
theory of quantum gravity, under the assumptions of (i) validity of the
holographic bound and (ii) preservation of unitary evolution at the level of
the fundamental theory. In particular, the appeal to the holographic bound
imposed on generic physical systems by the Bekenstein-Hawking entropy implies
that both classical geometry and quantum fields propagating on it should be
regarded as phenomena emergent from the dynamics of the fundamental theory. The
reshuffling of the fundamental degrees of freedom during the unitary evolution
then leads to an entanglement between geometry and quantum fields. The
consequences of such scenario are considered in the context of black hole
evaporation and the related information-loss issue: we provide a simplistic toy
model in which an average loss of information is obtained as a consequence of
the geometry-field entanglement.
