Faster Than Light Neutrinos

On September 23rd, a representative of the Opera collaboration came to CERN to give a talk entitled Measurement of the neutrino velocity with the OPERA detector in the CNGS beam. The speaker described the controversial finding that neutrinos sent through the Earth's crust 730km from CERN to the Gran Sasso laboratory south of Rome arrived some 60 nanoseconds too early. That's 60 billionths of a second. Not a lot, but still very significant! The Opera collaboration has been looking hard for any problems in their experiment for months now. Not finding any, they decided to bring the results in a public setting for further scrutiny. If true, this could completely change our understanding of some of the most fundamental theories of physics. And no, this doesn't mean relativity is wrong, simply that we can't hold c (the speed of light) as a maximum speed any longer. But this is a core assumption in many ideas that would need to be reconciled.

The speaker in front of a full house

The important figure is relative difference of the neutrino velocity with respect to the speed of light. The experiment finds (v-c)/c = (2.48±0.28(stat.)±0.30(sys.))*10^-5 . Also important is the statistical significance of the experiment, which at 6sigma means that there is only a 1 in 506,797,346 chance that the finding is due to a statistical fluctuation! Other experiments from SuperNova 1987A put limits on (v-c)/c of less than 10^-9 ! However, this was on a vastly different neutrino energy, further complicating the question.

It was so crowded people were sitting on the steps and standing in the back! You can just see K and I in the lower right corner, sitting on the floor.

So it is very unlikely that the measurement is due to a freak statistical fluctuation. The speaker gave a very good presentation, thoroughly explaining the quantification of each complication and how it was handled. The experiment looks to have been performed very thoroughly, and there were no gaping holes in the experimental setup. What remains to be seen is whether the collaboration has thought of ALL the systematic errors, and addressed them correctly. This was the focus of the questions after the talk, posed by many of the greatest minds in our field. The experiment is very complicated, especially with its very sensitive geodesy/gps and timing needs. Possible complications such as the rotation of the earth, tidal and seasonal influences, and complicated timing coincidence issues were raised. The speaker had an answer at every turn.

But I am avoiding the real question: Is it true? Do I, and the greater physics community, believe the result?

Its a hard question to answer. The experiment looks to have been done thoroughly and intelligently. At the same time, it is a very complicated experiment and there are a nearly infinite number of things that could go wrong. Not to mention the possibility that there is some obtuse systematic error that has not been considered.

If this result is true, the ramifications are huge, and far-reaching. This makes people reticent to embrace the results to quickly. The reality is that no one will take this result completely seriously unless there is an independent verification, which will take some time.

The looks on our faces, ranging from disbelief to confusion, say it all.

In the end, I can't speak for the community at large. For my part, I think it would be very exciting if it is true, but think that most likely the result comes from some small but significant complication that is not fully understood. I can say that most people I have spoken too feel the same way.

Hopefully I am wrong!