  Since the main open problem of contemporary physics is to find a unified
description of the four interactions, we present a possible scenario which,
till now only at the classical level, is able to englobe experiments ranging
from experimental space gravitation to atomic and particle physics. After a
reformulation of special relativistic physics in a form taking into account the
non-dynamical chrono-geometrical structure of Minkowski space-time
(parametrized Minkowski theories and rest-frame instant form) and in particular
the conventionality of simultaneity (re-phrased as a gauge freedom), a model of
canonical metric and tetrad gravity is proposed in a class of space-times where
the deparametrization to Minkowski space-time is possible. In them it is
possible to give a post-Minkowskian background-independent description of the
gravitational field and of matter. The study of the dynamical
chrono-geometrical structure of these space-times allows to face
interpretational problems like the physical identification of point-events (the
Hole Argument), the distinction between inertial (gauge) and tidal (Dirac
observables) effects, the dynamical nature of simultaneity in general
relativity and to find background-independent gravitational waves. These
developments are possible at the Hamiltonian level due to a systematic use of
Dirac-Bergmann theory of constraints. Finally there is a proposal for a new
coordinate- and background-independent quantization scheme for gravity.
