  The issue of a self-consistent solution of Maxwell-Einstein equations
achieves a very simple form when all quantum effects are neglected but a weak
vacuum polarization due to an external magnetic field is taken into account.
  From a semi-classical point of view this means to deal with an appropriate
limit of the one-loop effective Lagrangian for electrodynamics. When the
corresponding stress-energy tensor is considered as a source of the
gravitational field a surprisingly bouncing behavior is obtained. The present
toy model leads to important new features which should have taken place in the
early universe.
