# X's expectation value in quantum physics

1. Dec 11, 2004

### Palindrom

When I'm in a dimension higher than 1, do I need to integrate over all space (V) or only the x axis?

2. Dec 11, 2004

### dextercioby

Let's consider a QM system whose states are described by the wavefunction
$\psi (x,y,z)$.You wish to calculate the expectation value for $\hat{x}$.That is nothing but the number.

$$<\hat{x}> =\int\int\int_{R^{3}} \psi^{*}(x,y,z) x \psi (x,y,z)$$

I hope your wave function is normalized/normalizable.Else,you might encounter some problems with the integration above.

Daniel.