Indeterminacy

No simultaneous sharp values can be attributed to a set of two incompatible observables. A simultaneous observation of two observables Ô1 and Ô2 is represented by their product Ô1Ô2 which is not necessarily an observable:

the product of 2 hermitian operators (observables) is an hermitian operator (observable) if and only if the commutator is zero i.e. for incompatible observables no simultaneous sharp values can be determined.

From an epistemological point of view one could speak about quantum uncertainty (Heisenberg), as from an ontological point of view this is called quantum complementarity (Bohr).

Hereby, remember:
- an observable is (represented by) a hermitian operator.
- two incompatible observables have a nonzero commutator.