  The momentum of a photon may reveal the answer to the "which way" problem of
Young's double slit experiments. A photon passing through the boundary between
two media, in which a photon travels at different velocities, undergoes a
momentum change according to the law of conservation of momentum. The momentum
of the photon is transferred locally to the medium, and the boundary between
the media receives stress, which determines the photon trajectory. An
experiment is performed using a crystal plate that can transform the stress to
electric charge. We are able to detect the electric charge after the detection
of the photon on the screen, and control the sensitivity of photon detection.
By means of this proposed experiment it is determined whether or not an attempt
to detect the "which way" of photon travel destroys the interference patterns.
