TESTS OF QUANTUM-GRAVITY FROM OBSERVATIONS OF GAMMA-RAY BURSTS

The recent confirmation that at least some gamma-ray bursts originate at cosmological distances(1-4) suggests that the radiation from them c ould be used to probe some of the fundamental laws of physics. Here we show that gamma-ray bursts will be sensitive to an energy dispersion predicted by some approaches to quantum gravity. Many of the bursts ha ve structure on relatively rapid timescales(5), which means that in pr inciple it is possible to look for energy-dependent dispersion of the radiation, manifested in the arrival times of the photons, if several different energy bands are observed simultaneously. A simple estimate indicates that, because of their high energies and distant origin, obs ervations of these bursts should be sensitive to a dispersion scale th at is comparable to the Planck energy scale (similar to 10(19)GeV), wh ich is sufficient to test theories of quantum gravity. Such observatio ns are already possible using existing gamma-ray burst detectors.