Abstract

Bargmann’s superselection rule, which forbids the existence of superpositions of states with different mass and, therefore, implies the impossibility of describing unstable particles in non-relativistic quantum mechanics, arises as a consequence of demanding Galilean covariance of Schrödinger’s equation. However, the usual Galilean transformations inadequately describe the symmetries of non-relativistic quantum mechanics since they can produce phases in the wavefunction which are relativistic time contraction remnants and therefore, cannot be physically interpreted within the theory. In this paper we review the incompatibility between Bargmann’s rule and Lorentz transformations in the low-velocities limit, we analyze its classical origin and we show that the Extended Galilei group characterizes better the symmetries of the theory. Furthermore, we claim that a proper description of non-relativistic quantum mechanics requires a modification of the notion of spacetime in the corresponding limit, which is noticeable only for quantum particles