# Zwiebach page 194

1. Oct 20, 2007

### ehrenfest

1. The problem statement, all variables and given/known data
I am confused about Quick Calculation 11.3. What does he mean "by viewing x_0^I as the explicitly time-dependent Heisenberg operator defined by (11.38)"?

Specifically, what does "viewing" mean?

2. Relevant equations

3. The attempt at a solution

2. Oct 20, 2007

### Jimmy Snyder

This one is not clear to me either. However, what I did was assume that $x_0^I$ does have explicit time dependence by rewriting equation (11.38) on page 193 as

$$x_0^I(\tau) = x^I(\tau) - \frac{p^I}{m^2}\tau$$

and then showing that the derivative w.r.t. $\tau$ is zero. It's not hard enough to justify a QC though.