  When both slits of the double slit experiment are open, closing one
paradoxically increases the detection rate at some points on the detection
screen. Feynman famously warned that temptation to "understand" such a puzzling
feature only draws us into blind alleys. Nevertheless, we gain insight into
this feature by drawing an analogy between the double slit experiment and a
time reversed fire alarm. Much as closing the slit increases probability of a
future detection, ruling out fire drill scenarios, having heard the fire alarm,
increases probability of a past fire (using Bayesian inference). Classically,
Bayesian inference is associated with computing probabilities of past events.
We therefore identify this feature of the double slit experiment with a time
reversed thermodynamic arrow. We believe that much of the enigma of quantum
mechanics is simply due to some variation of time's arrow. In further support
of this, we employ a plausible formulation of the thermodynamic arrow to derive
an uncertainty in classical mechanics that is reminiscent of quantum
uncertainty.
