Re-derive the result shown in class, that the minimum
uncertainty 
in the position of a particle at time t
grows as
Verify explicitly that this result holds exactly in the
case of the wave packet in problem 2.4 (problem 4 of PS # 2) if we
define 
as the variance in the expected position of
detection of particles, defined according to
(We take 
here because it is 
which
in 8.03 gives us the intensity or brightness.)