  We discuss how, in a Universe restricted to the causal region connected to
the observer, General Relativity implies the quantum nature of physical
phenomena and directly leads to a string theory scenario, whose dynamics is
ruled by a functional that weights all configurations according to their
entropy. The most favoured configurations are those of minimal entropy. Along
this class of vacua a four-dimensional space-time is automatically selected;
when, at large volume, a description of space-time in terms of classical
geometry can be recovered, the entropy-weighted sum reduces to the ordinary
Feynman's path integral. What arises is a highly predictive scenario,
phenomenologically compatible with the experimental observations and
measurements, in which everything is determined in terms of the fundamental
constants and the age of the Universe, with no room for freely-adjustable
parameters. We discuss how this leads to the known spectrum of particles and
interactions. Besides the computation of masses and couplings, CKM matrix
elements, cosmological constant, expansion parameters of the Universe etc...,
all resulting, within the degree of the approximation we used, in agreement
with the experimental observations, we also discuss how this scenario passes
the tests provided by cosmology and the constraints imposed by the physics of
the primordial Universe.
