[itex][L_x,L_y]=i \hbar L_z \neq 0[/itex]. In fact it seems we can know only the modulus squared of the angular momentum and one component, at a same time. However if I take an electron say in the fundamental state in the hydrogen atom, L=0. Since the modulus squared is equal to 0, it means that all components are worth 0 or I'm missing something? Wouldn't that mean that we can know "the 3 components of the angular momentum without any uncertainty when it's worth 0"? Where does the Heisenberg's uncertainty principle applies here?