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expert reaction to observations from the ICARUS group seeming to show neutrinos can’t travel faster than light after all

Results from another group of scientists within the Gran Sasso team, ICARUS, suggested that the putatively light-speed-beating neutrinos hadn’t lost energy en route, thus casting further doubt on the OPERA result. Their data were published in October but picked up by the press on 20th November.


Professor Jim Al-Khalili, of the Physics Department at the University of Surrey, said:

“The basic story is that there are two research groups, working in a sense in competition with each other, both at Gran Sasso Lab. OPERA measures the time of neutrino travel and hence their speed, whereas ICARUS – who also detect the same neutrino beam – measure the spread in energy of the arriving neutrinos. They found that the neutrinos don’t lose energy on their route. The problem of course is that they should do, IF they were travelling faster than light. This is the equivalent of the sonic boom when something goes faster than sound.

“Usually we see this effect when particles go faster than light through transparent media like water, when light is considerably slowed down. It’s called Cerenkov radiation. So these neutrinos should have been spraying out particles like electrons and photons in a similar way if they were going superluminal – and in the process would be losing energy. But they seemed to have kept the energy they started from, which rules out faster-than-light travel.

“The other evidence against OPERA is that neutrinos from supernova explosions of distant stars also do not arrive on earth ahead of the light. So if OPERA had been correct we’d have to explain why the neutrinos from stars do not travel faster than light through space.”

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