Ch 6.7 For any two observables $\hat{A}$ and $\hat{B}$: $\sigma_A \sigma_B \geq \frac{1}{2}|\langle[\hat{A}, \hat{B}]\rangle|$. For position and momentum: $\sigma_x\sigma_p \geq \hbar/2$. This is not a statement about measurement disturbance -- it is a fundamental property of the quantum state itsel