  The beautiful scenario of pre-big-bang cosmology is appealling not only
because it is more or less derived from string theory, but also because it
separates clearly the problem of the initial conditions for the universe from
that of high curvatures. Recently, the pre-big-bang program was subject to
attack from on the grounds that pre-big-bang cosmology does not solve the
horizon and flatness problems in a ``natural'' way, as customary exponential
``new'' inflation does. In particular, it appears that an arbitrarily small
deviation from perfect flatness in the initial state can not be accommodated.
For this analysis, matter in the universe before the big bang was assumed to be
radiation. We perform a similar analysis to theirs, but using the equation of
state for ``string matter'' $\rho=-3p$ which seems more appropriate to the
physical situation and, also, is motivated by the scale factor duality (in the
flat case) with respect to our expanding, radiation dominated, universe. For an
open universe we find, exactly, the same time-dependence of the scale factor as
in the Milne universe, recently found to represent the universal attractor at
$t=-\infty $ of all pre big bang cosmologies. We conclude that our radiation
dominated universe comes from a flat rather than a curved region.
