One of the more interesting physics stories in the news recently concerns an experiment that purports to have measured neutrinos moving faster than the speed of light. A team of researchers sent a beam of neutrinos 700 km through the mountains from CERN in Switzerland, where the neutrinos were created, to a neutrino detector in Italy. The time of flight was 2.4 milliseconds, and the neutrinos arrived at the detector 60 nanoseconds earlier than they would have if they’d traveled at the speed of light. That’s a difference of a few parts in 10^5. People are pretty good at measuring small time intervals. This group used GPS satellites and atomic clocks to do the timing, and the accuracy in their time measurement was 1 nanosecond.
This result raises lots of questions! Like: is it right? I don’t know, but they’ve done it twice – in two slightly differently ways – and got the same result both times. Nonetheless, experiments like this are hard – neutrinos are pesky little things, and anyone who’s taken Physics 1052 knows that measuring time at two different places can be tricky when things are moving close to the speed of light. These folks have probably got the relativity right, but the possibility of some sort of systematic error in their measurements remains. Other experiments will have to be done to confirm – or refute – this result.
There’s one important data point that suggests that neutrinos are in fact well-behaved and do not travel faster than c. The neutrinos emitted by Supernova 1987A (which was discovered by a Canadian astronomy grad student) arrived at earth about three hours before the visible light from the supernova. In this case, the time difference is understood: It’s due to the fact that the refractive index of interstellar space is marginally greater than 1. If the speed of the neutrinos was as high as implied by the new CERN results, then the neutrinos from SN 1987A would have arrived here in 1983, four years before the light was detected in 1987.
If the new experiments are right, though, then perhaps “everything you know is wrong.” Or almost everything, anyway. That would be pretty exciting (lots of jobs for physicists, maybe), but distressing at the same time! Relativity has proven to be a pretty good theory so far, though, and I would be slow to abandon it.
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