Universality of decoherence

We consider environment induced decoherence of quantum superpositions to mi xtures in the limit in which that process is much faster than any competing one generated by the Hamiltonian H-sys of the isolated system. While the g olden rule then does not apply we can discard H-sys. By allowing for coupli ngs to different reservoirs, we reveal decoherence as a universal short-tim e phenomenon independent of the character of the system as well as the bath and of the basis the superimposed states are taken from. We discuss conseq uences for the classical behavior of the macroworld and quantum measurement : For decoherence of superpositions of macroscopically distinct states H-sy s is always negligible.