The Schroedinger equation is a mathematical model of the atom, in the simplest case also of light. It is a wave function what means that it can reflect the fact that a quantum of light, or atom, or electron is capable "to go two different ways" simultaneously, what is proved exactly by experiments today. The problem is what it physically means: On principle, bodies in mechanics or atomic entities cannot divide theirselves and nevertheless beeing a whole; but photons, electrons and atoms are indeed capable to perform this act without any doubt. This kind of behavior seems complete crazy for a mechanic - and this is the great dilemma of modern physics. But if one takes a nonprejudiced view on the experiments one is forced to the only one possible conclusion that atoms, electrons, and photons at the double slit perform a non-mechanical, holistic division process - only compareable with branching and cell division processes in biology!