# Neutrinos might not have been faster than light after all.

Well, special relativity may explain why this happened. The clocks used to measure the time of flight may not have been synchronised properly, giving rise to a relativistic effect where the clocks on the GPS unit saw that the source and the detector positions were changing. This makes the journey appear shorter by 32 nanoseconds. Since this occurs at both ends, the total time missing is 64 nanoseconds – and CERN measured the discrepancy in time to be about 60 nanoseconds.

The irony is that the only experiment to have measured a particle travelling faster than light with a six-sigma* rating since Einstein proposed special relativity, which should contradict the theory, may actually reconfirm special relativity.

*In statistics, sigma is the symbol for the standard deviation. An experimental result that is rated six-sigma falls about six standard deviations away from the expected value, and hence it is highly unlikely to be a random effect. For the sake of comparison, for the Higgs boson’s existence to be confirmed, the results would have to be at least five standard deviations away from the expected mean value. Wikipedia has a diagram to explain the sigmas.

**UPDATE 19/10/2011**: A cautionary note from an atomic clock physicist.