Give a more rigorous proof that Eqs. (9.22) and (9.23) imply that a free particle initially at rest in the TT gauge remains at rest.
Eq. (9.22):
If a particle is initially at rest, the initial value of its acceleration is
(dU"/dt) = -r^2 = -n(h0,t + h0,t - h0,t).
Eq. (9.23):