  We aim at gathering information from gravitational interaction in the
Universe, at energies where quantum gravity is required. In such a setup a
dynamical membrane world in a space-time with scalar bulk matter described by
domain walls, as well as a dynamical membrane world in empty Anti de Sitter
space-time are analysed.
  We later investigate the possibility of having shortcuts for gravitons
leaving the membrane and returning subsequently. In comparison with photons
following a geodesic inside the brane, we verify that shortcuts exist. For late
time universes they are small, but for some primordial universes they can be
quite effective.
  In the case of matter branes, we argue that at times just before
nucleosynthesis the effect is sufficiently large to provide corrections to the
inflationary scenario, especially as concerning the horizon problem and the
Cosmological Background Radiation.
