Gravity-wave interferometers as quantum-gravity detectors

Nearly all theoretical approaches to the unification of quantum mechanics and gravity predict 1, 2, 3, 4 that, at very short distance scales, the classical picture of space-time breaks down, with space-time becoming somewhat ‘fuzzy’ (or ‘foamy’). The properties of this fuzziness and the length scale that characterizes itsonset are potentially a means for determining which (if any) of the existing models of quantum gravity is correct. But it is generally believed 5 that these quantum space-time effects are too small to be probed by technologies currently available. Here Iargue that modern gravity-wave interferometers are sensitive enough to test certain space-time fuzziness models, because quantum space-time effects should provide an additional source of noise in the interferometers that can be tightly constrained experimentally. The noise levels recently achieved in one interferometer 6 are sufficient to rule out values of the length scale that characterizes one of the space-time fuzziness models down to the Planck length (∼10 −35 m) and beyond, while the sensitivity required to test another model should be achievable with interferometers now under construction.