  We investigate solutions that are dynamically evolving between asymptotically
de Sitter and asymptotically anti-de Sitter regions in the context of Einstein
gravity coupled to general matter fields in d dimensions. We demonstrate the
existence of a no go theorem whenever the matter content of the theory is
'reasonable', i.e. such that the weak energy condition is satisfied. We show
that there exist solutions for which the energy conditions are violated in a
finite region of the spacetime. We speculate on the holographic interpretation
of these gravitational backgrounds by combining ideas from the AdS/CFT and the
dS/CFT dualities.
