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Astronomical observations of distant quasars may be important to test modelsfor quantum gravity, which posit Planck-scale spatial uncertainties ('spacetimefoam') that would produce phase fluctuations in the wavefront of radiationemitted by a source, which may accumulate over large path lengths. We showexplicitly how wavefront distortions cause the image intensity to decay to thepoint where distant objects become undetectable if the accumulated path-lengthfluctuations become comparable to the wavelength of the radiation. We alsoreassess previous efforts in this area. We use X-ray and gamma-ray observationsto rule out several models of spacetime foam, including the interestingrandom-walk and holographic models.

New constraints on quantum foam models from X-ray and gamma-ray observations of distant quasars