stuff about gammaray flare observations (dispersion?) http://arxiv.org/abs/0708.2889 Probing Quantum Gravity using Photons from a Mkn 501 Flare Observed by MAGIC J. Albert, et al., for the MAGIC Collaboration, John Ellis, N.E. Mavromatos, D.V. Nanopoulos, A.S. Sakharov, E.K.G. Sarkisyan 5 pages, 3 figures, submitted to Phys. Rev. Lett (Submitted on 21 Aug 2007) "We use the timing of photons observed by the MAGIC gamma-ray telescope during a flare of the active galaxy Markarian 501 to probe a vacuum refractive index ~ 1-(E/M_QGn)^n, n = 1,2, that might be induced by quantum gravity. The peaking of the flare is found to maximize for quantum-gravity mass scales M_QG1 ~ 0.4x10^18 GeV or M_QG2 ~ 0.6x10^11 GeV, and we establish lower limits M_QG1 > 0.26x10^18 GeV or M_QG2 > 0.39x10^11 GeV at the 95% C.L. Monte Carlo studies confirm the MAGIC sensitivity to propagation effects at these levels. Thermal plasma effects in the source are negligible, but we cannot exclude the importance of some other source effect." website for the "magic" collaboration http://magic.mppmu.mpg.de/ recent news http://magic.mppmu.mpg.de/physics/recent/index.htm exerpt: "We cannot exclude the possibility that the delay we find, which is significant beyond the 95% C.L., may be due to some energy-dependent effect at the source." As far as I know there was NOT a firm prediction to expect planckscale dispersion based on any of the main nonstring QG models. Smolin and others have published several papers showing how a very slight dispersion effect MIGHT show up (due to QG) in the course of a very long time while a pulse travels distances on the order of a billion lightyears. Smolin has argued for a small but observable energydependence of the speed of light. But I don't know of any QG paper where there is a clear firm prediction. Also I don't know if this "MAGIC" collaboration actually did observe a real dispersion. If someone has more clear perception of this, please help get it straight. This particular gammaray flare that they observed had traveled for an estimated 0.46 billion years by the time it reached us. That would be a long enough time for some faster photons to get out ahead of some slower photons----as Smolin and others have proposed---so that the receiver could pick up two spikes. this kind of dispersion, if it exists, is too slight to be observed in light traveling on ordinary timescales----it is only a four minute delay after a half-billion year travel. quite possibly, as they say in the paper, the observed delay could have been caused by some effect AT THE SOURCE. so conventional physics might apply and one would not actually be seeing a dispersion effect associated with the spatial medium.