 A very natural question, which all scientists who are concerned about the meaning and the value of science have to face, is whether one can develop a coherent worldview that can accommodate our knowledge of natural phenomena as it is embodied in our best theories. Such a program meets serious difficulties with quantum mechanics, essentially because of two formal aspects of the theory according to its standard formulation, which are common to all of its versions, from the original nonrelativistic formulations of the 1920s, to current quantum field theories: the linear nature of the state space and of the evolution equation; in other words: the validity of the superposition principle and the related phenomenon of entanglement, which, in Schrödinger’s words: 