A general argument against the universal validity of the superposition principle

We reconsider a well-known problem of quantum theory, i.e. the so-called me asurement (or macro-objectification) problem, and we rederive the fact that it gives rise to serious problems of interpretation. The novelty of our ap proach derives from the fact that the relevant conclusion is obtained in a completely general way, in particular, without resorting to any of the assu mptions of ideality which are usually done for the measurement process. The generality and unescapability of our assumptions (we take into account pos sible malfunctionings of the apparatus, its unavoidable entanglement with t he environmment, its high but not absolute reliability, its fundamentally u ncontrollable features) allow to draw the conclusion that the very possibil ity of performing measurements on a microsystem combined with the assumed g eneral validity of the linear nature of quantum evolution leads to a fundam ental contradiction. (C) 2000 Elsevier Science B.V. All rights reserved.