Is it true that all expectation values must be real? So if I get an imaginary value, does it mean I made a mistake? Or it doesn't matter and I can just take the absolute value of the expectation? The momentum operator has an 'i' in it. But after doing, Psi*[P]Psi, I have an expression with 'i' which means I am left with an imaginary expectation value? What should I do?