eldavojohn writes: Seven billion light years away seven billion years ago, a gamma-ray burst occurred. The observation of four Fermi-detected gamma-ray bursts (GRBs) has led physicists to speculate that space-time is indeed smooth (a prepublication PDF can be found here). Three such photons were observed to arrive very close together and the observers believe that these are from the same burst which means that there was nothing diffracting their paths from the gamma-ray burst to Earth. This observation doesn't prove that space-time is infinitesimally smooth like Einstein predicted but does give a nod that it is for a range of parameters. Before we can totally discount the theory that space-time is comprised of Planck-scale pixels, we must now establish that the proposed pixels don't disrupt the photons in ways independent of their wavelengths. For example, this observation did not disprove the possibility that the pixels exert a subtler "quadratic" influence over the photons nor could it determine the presence of birefringence — an effect that depends on the polarization of the light particles.