Hints of a breakdown in the theory of relativity?

Over at the Scientific American blog, George Musser posts of an odd observation:

The MAGIC gamma-ray telescope team has just released an eye-popping preprint (following up earlier work) describing a search for an observational hint of quantum gravity. What they’ve seen is that higher-energy gamma rays from an extragalactic flare arrive later than lower-energy ones. Is this because they travel through space a little bit slower, contrary to one of the postulates underlying Einstein’s special theory of relativity — namely, that radiation travels through the vacuum at the same speed no matter what?

The team studied two gamma-ray flares in mid-2005 from the black hole at the heart of the galaxy Markarian 501. They compared gammas in two energy ranges, from 1.2 to 10 tera-electron-volts (TeV) and from 0.25 to 0.6 TeV. The first group arrived on Earth four minutes later than the second. One team member, physicist John Ellis of CERN, says: “The significance of the time lag is above 95%, and the magnitude of the effect is beyond the sensitivity of previous experiments.”

Either the high-energy gammas were released later (because of how they were generated) or they propagated more slowly. The team ruled out the most obvious conventional effect, but will have to do more to prove that new physics is at work — this is one of those “extraordinary claims require extraordinary evidence” situations. But if the high-energy gammas really did lose the cosmic race, we’re talking Big Discovery. It could be a way to constrain string theory, loop quantum gravity, and other bleeding-edge theories.