Thanks, StatMechGuy, I agree on the point you talked about, there is a 'position' that simply is the parameter for the position dependent operator function \phi(x). But what I asked about is the position OPERATOR whose eigenstate is |x>, that's the operator in the expression...
I'm reading some QFT and have been puzzled by the following question:
What's the physical meaning of the position OPERATOR X_\mu in QFT? whose position does it measure?:confused: Thanks for any help.