This preview of a proprietary New Scientist article gives an interesting hint about something that may be important.
The idea as I understand it is that very high energy gamma rays may travel more slowly than lower energy ones due to the non-linear paths they take through the quantum foam (or some other such explanation).
Up till now, this has never been observed, but MAGIC looks at a *very* high range in the energy spectrum. A flare was observed in Markarian 501, and the super-high energy photons arrived four minutes late.
Does anyone have a link to an arXiv paper on this, or MAGIC press release?
If this is true, this is strong evidence for some flavor of String theory to be on the right track.