Take the 2-minute tour ×  It seems like this experiment is
possible:    1. Fire a photon, and start a timer   2. The photon
travels through the slit(s)   3. The photon strikes a plate --
the timer is stopped.  Based on where on the plate the photon
struck, the time it took, and the speed of light, it seems
possible to deduce through which slit the photon passed.  Or,
would the times correspond with a direct line from the source to
destination?  share|improve this question This question becomes
more interesting if you diffract the clock itself through the
slits. Only identical clocks interfere, so whenever there is a
measure of time difference along the two paths, they do not
interfere. –  Ron Maimon Jan 9 '12 at 15:13 add comment  2
Answers  up vote 4 down vote accepted  It is possible. But it
doesn't change anything about the "we can't know through which
slit it went and still get an interference pattern" issue.
(Surprise!)  In order to do this you need photons that can be
timed very precisely, i.e. $\Delta