Superselection rules claim that some superpositions are physically impossible. But why are they so? Consider an example from another thread: But why such a superposition makes no sense physically? Clearly, if such a state has been produced from a charge eigenstate, then such a superposition would violate charge conservation. Indeed, charge is conserved in the Standard Model of elementary particles. But still, it is not difficult to write down a field theory action in which charge is not conserved, and in which such superpositions can be created from a charge eigenstate. Moreover, I don't see why such a superposition could not be an INITIAL physical state even in the Standard Model. I believe the only true reason why certain superpositions never occur in nature is the fact that they are not stable under decoherence. Decoherence picks out some bases in the Hilbert space as "preferred" ones, while others, such as Schrodinger cat states, are not seen because (due to decoherence) they live too short to be observed. But I am open also for different opinions and facts I am not aware of, so please share them here.