 Contrary to standard quantum mechanics, the GRW theory allows to locate precisely the ‘split’ between micro and macro, reversible and irreversible, quantum and classical. This is another way of saying that GRW solved the measurement problem. The transition between the two types of ‘regimes’ is governed by the number of particles, which are localized by the collapse process. A consequence of this is that GRW makes predictions, which are different from standard quantum mechanical predictions. We will come back on this important issue.