A series of experiments is performed on identically prepared electrons
(mass 
) moving in free space. Two groups of
measurements are performed. In the first group of measurements, the
position of the particles along the 
direction are measured at
time t=0; a histogram of the resulting positions is provided in
Figure 4a. In the second group, the
experimentalist first waits a time t=80 s, and then
measures the positions of the electrons; the results of this group of
measurements appear in Figure 4b.
According to the HUP, these results are 
Figure 4: Experiments on a wave packet. a) Results when the experiments
are performed at time t=0. b) Results when the experiments are
performed at t=80 s.