  It is noted that the duration of a fast radio burst (FRB), about $10^{-3}$ s,
is a smaller fraction of the time delay between multiple images of a source
gravitationally lensed by a galaxy or galaxy cluster than the human lifetime is
to the age of the universe. Thus repeating, strongly lensed FRBs may offer an
unprecedented opportunity for observing cosmological evolution in "real time".
The possibility is discussed of observing cosmic expansion, transverse proper
motion, mass accretion and perhaps growth of density perturbations, as a
function of redshift.
