I've just seen yet another reason to issue the reminder that, whatever a quantum superposition is, we shouldn't really be saying that the system is "in two states at once."
This is the realization that lead Giancarlo Wick to formulate his superselection rules. You can add two eigenstates of the electric charge observable with different eigenvalues. But you can't measure any observable that distinguishes the result from an incoherent superposition.
-
-
So if you want to affirm that every state formed by adding two other states is a coherent superposition, you must posit that every self-adjoint operator is observable. But this last assertion is known to be false (for, e.g., the electric charge observable.) So care is required.
Thanks. Twitter will use this to make your timeline better. UndoUndo
-
Loading seems to be taking a while.
Twitter may be over capacity or experiencing a momentary hiccup. Try again or visit Twitter Status for more information.