Title: Is a tabletop search for Planck scale signals feasible?
Abstract: Quantum gravity theory is untested experimentally. Could it be tested with tabletop experiments? While the common feeling is pessimistic, a detailed inquiry shows it possible to sidestep the onerous requirement of localization of a probe on the Planck length scale. I suggest a tabletop experiment which, given state-of-the-art ultrahigh vacuum and cryogenic technology, could already be sensitive enough to detect Planck scale signals. The experiment combines a single photon's degree of freedom with that of a macroscopic probe to test Wheeler's conception of ``quantum foam,'' the assertion that on length scales of the Planck order, spacetime is no longer a smooth manifold. The scheme makes few assumptions beyond energy and momentum conservations, and is not based on a specific quantum gravity scheme.