  I propose an experiment that may be performed, with present low temperature
and cryogenic technology, to reveal Wheeler's quantum foam. It involves
coupling an optical photon's momentum to the center of mass motion of a
macroscopic transparent block with parameters such that the latter is displaced
in space by approximately a Planck length. I argue that such displacement is
sensitive to quantum foam and will react back on the photon's probability of
transiting the block. This might allow determination of the precise scale at
which quantum fluctuations of space-time become large, and so differentiate
between the brane-world and the traditional scenarios of spacetime.
