A new concept of the truth in quantum mechanics and the individual superposition principle Jiří Souček Charles University in Prague, Faculty of Philosophy Ke Kříži 8, Prague 5, 158 00, Czech Republic jiri.soucek@ff.cuni.cz Abstract. Using a new concept of the truth in quantum mechanics we show that the individual superposition principle is scientifically unfounded. 1. Introduction. It may happen that two different theories are empirically indistinguishable. In quantum mechanics (QM) this has happened. The old example is the Bohmian mechanics which is theoretically different from QM but empirically equivalent to QM. A recent example of this type is the modified QM introduced in [1] which is theoretically different from QM but which gives the same empirical predictions as QM (this is proved in [1]). Such a situation where there exist two different theories which are empirically indistinguishable is rather special and this is the topic of the paper. It is not possible to discriminate among empirically indistinguishable theories. This implies that the concept of the truth must be in such situations redefined. The true statement in QM is a statement which is true in any theory which is empirically equivalent to QM. The undecidable statement in QM is a statement which is true only in some theories empirically equivalent to QM (but not in all such theories). Then we shall show that the superposition principle in QM can have two forms: the collective superposition principle and the individual superposition principle. We shall show that the individual superposition principle is undecidable in QM. This implies that the individual superposition principle is scientifically unfounded. 1 1 The collective superposition principle is a trivial consequence of axioms of QM.