From the Universe Today:
“The speed of light is the speed of light, and that’s that. Right? Well, maybe not. Try and figure this out. Astronomers studying radiation coming from a distant galaxy found that the high energy gamma rays arrived a few minutes after the lower-energy photons, even though they were emitted at the same time. If true, this result would overturn Einstein’s theory of relativity, which says that all photons should move at the speed of light.
Uh oh Einstein.”
Read the rest: High Energy Gamma Rays Go Slower Than the Speed of Light?