HERE IS A WEBPAGE ABOUT HOW IACT WORKS http://magic.mppmu.mpg.de/introduction/iact.html this page helps to survey gammaray astronomy and put IACT in broader context. http://magic.mppmu.mpg.de/introduction/index.html Observing high energy gammarays which have traveled cosmological distances-----on the order of a billion lightyears----affords possible tests of quantum gravity For several years Lee Smolin has been predicting (seemingly every chance he could get) that the orbital gammaray telescope GLAST would see evidence of energydependent speed of light GLAST is scheduled for launch 5 February 2008, barring delays. It will detect gamma up to 0.3 TeV. http://en.wikipedia.org/wiki/GLAST Energydependence of the speed light travels is intimately bound up with Spinfoam LQG, and also may be generic to a variety of quantum gravity models. But the dependence (if it exists at all) is expected to be so slight that it would only show up in gamma photons that had traveled on the order of a billion years----allowing the higher energy ones to be delayed by a few seconds or minutes. So far no one has been able to prove rigorously that any of the leading QG models REQUIRE energydependent speed of light (the closest so far is the work of Laurent Freidel who proved it for 3D in 2005) but it keeps coming up. It would be a big stimulus to several QG approaches if energydependence were observed. ================ THE ODD THING IS THAT EXACTLY THIS seems to have been observed at a GROUNDBASE telescope on the island of La Palma in the Canaries. If the result is confirmed it will have a major impact on quantum gravity and cosmology. This is the MAGIC telescope and it is is of IACT type (imaging air cherenkov telescope). It it images gammaray-induced showers up to several TeV and is able to determine the direction from which the source photon came and the photon energy. 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) there is a kind of convergence happening between new gammaray astronomy (new gammaray instruments ground and orbit) and quantum gravity and its application to quantum cosmology and ordinary cosmology. The MAGIC telescope---17 meters diameter----is currently the world's largest telescope. It is built specifically to do IACT gammaray astronomy. It is funded by the same countries that fund the MAGIC group of some 120 astronomers----mainly Germany, Spain, Italy but also some minor participation by Switzerland, Finnland. In German, the word Jagd means "hunt" and is pronounced the same as IACT.