exploder writes "String theory is notorious for its lack of testable predictions. But if the MAGIC gamma-ray telescope team's interpretation is correct, then a delay in the arrival of higher-energy gamma rays could point to a breakdown of relativity theory. A type of 'quantum lensing effect' is postulated to cause the delay, which is approximately four minutes over a half-billion year journey." Ars's writeup
is a little more fleshed-out than the Scientific American blog posting.