Description
Early time cosmology should include quantum gravity
effects, that are largely unknown up to now. There have
been many proposal to treat it through string theory,
leading to new inflationary mechanisms or even alternatives
based on brane models, but the actual quantum part of
such descriptions is not really emphasized. Using a Wheeler-
de Witt minisuperspace approach, we have found that the
singularity occurring at the origin of the Universe could
easily be removed and replaced by a bouncing phase: quantum
effects would then imply the currently expanding phase to
have been preceded by a contracting one. But from the strict
point of view of quantum mechanics, the previous statement
is hardly meaningful, since in particular the scale factor should
now be seen as an operator whose actual value should be
experimentally determined by an external observer ... an
obviously impossible constraint for a closed system like the
Universe itself! Using an ontological view however, we could
give a meaning to the background evolution and also describe
the perturbations in a completely quantum way; this leads to
a consistent description of the time development of primordial
cosmology and provides an alternative scenario to the usual
inflation paradigm that can be tested observationally.