Abstract

It is explained why quantum mechanics applies principally to single systems and not to ensembles. A thorough analysis of thought-experiments shows clearly that irreversibility is connected with the storing of information rather than with the act of measurement. In order to avoid paradoxes one has to admit that the wave function does not represent the state of the system in itself, but information acquired in consequence of a complete measurement. The meaning of the time-energy uncertainty relation for stable systems is discussed