DECOHERENCE, EINSELECTION AND THE EXISTENTIAL INTERPRETATION (THE ROUGH GUIDE)

The roles of decoherence and environment-induced superselection in the emergence of the classical fi-om the quantum substrate are described. The stability of correlations between the einselected quantum pointer states and the environment allows them to exist almost as objectively as classical states were once thought to exist: there are ways of fin ding out what is the pointer state of the system which uses redundancy of its correlations with the environment, and which leave einselected states essentially unperturbed. This relatively objective existence o f certain quantum states facilitates operational definition of probabi lities in the quantum setting. Moreover, once there are states that 'e xist' and can be 'found out', a 'collapse' in the traditional sense is no longer necessary-in effect, it has already happened. The role of t he preferred states in the processing and storage of information is em phasized. The existential interpretation based on the relatively objec tive existence of stable correlations between the einselected states o f observers' memory and in the outside universe is formulated and disc ussed.