Faster-than-light neutrinos? Not so fast…

XKCD's take on public understanding of science

The Telegraph’s Tom Chivers might be a little premature with his “I told you so“, but the reality is that theoretical physicist Jim “I will eat my boxer shorts on live TV” Al-Khalili can probably put the ketchup down.

As the historically “somewhat excited” BBC report, “Faster-than-light neutrinos could be down to bad wiring“.  Needless to say, the situation is a little bit more complicated than the BBC headline suggests…

As the Guardian report notes

Late on Wednesday night, scientists at the Opera (Oscillation Project with Emulsion-tRacking Apparatus) collaboration in Gran Sasso, who carried out the initial experiments, released a statement outlining two potential errors in their hardware. “If confirmed, one would increase the size of the measured effect, the other would diminish it,” said the statement, which was published on the Cern website.

One of the possible errors lies with a faulty optical fibre connection in the mechanism used to time the arrival of the neutrinos at Gran Sasso. In order to make their measurements, scientists need to tag the exact moment the neutrinos are created in Cern and also the exact time the particles arrive at the Opera detector.

“They use a GPS synchronisation system and, for that to work, you need to have some antennas that can see the satellites and then you need to run cables from those antennas underground, hundreds or thousands of metres long, and work out correctly what the lengths of the cables are,” said Dr Ryan Nichol, who works on a similar experiment called the Main Injector Neutrino Oscillation Search (Minos) at Fermilab near Chicago.

The Opera scientists suspect that a connection in this optical fibre might have been broken or come loose during their experiments last year. “If this is the case, it could have led to an underestimate of the time of flight of the neutrinos,” said the Opera statement.

The second potential source of error could be a problem with the GPS system itself, which meant it produced incorrect time stamps at the Opera experiment. “They have one clock that’s timing events in the detector and then they have a GPS clock that’s somewhere else and tells them what the real time is,” said Nichol. “They have to transfer information between those clocks. [Opera] seem to suggest that one of those clocks was misbehaving in a way.”

This error, if confirmed, would imply an even more startling result than the one announced in September: that the neutrinos were travelling even faster than suspected and that the sixty billionths of a second anomaly was an understatement.

And the Guardian has a new quote from Prof Al-Khalili

Prof Al-Khalili said the Opera scientists were showing great integrity in announcing potential faults in their measurements. “But I suspect, now more than ever, that both Einstein’s theory and my boxer shorts are safe.”

The scientists will not know which of their suspected errors is the culprit (if it is either) until they carry out more experiments, which are planned for May.

Until then, as Matt Strassler points out in his updated post

Note also that just because they know there is an important problem with an optical wire doesn’t mean they know yet that it is the problem that caused the effect that they measured.   (You personally may suspect that it is, but there’s no way for you to know it if they don’t.) For all they say, and for all we know, there might be yet another issue, one that they haven’t yet identified, that’s the main cause of the 60 nanosecond shift.  

So don’t get me wrong; I’ve thought this experiment was almost certainly wrong from the beginning, and so did the vast majority of my colleagues.  As I’ve emphasized many times on this site, most experiments with a radical result turn out to be wrong, and this one was particularly implausible.  From my point of view, the whole story since September has mainly been a question of finding the cause.  But the cause has not yet been confirmed; it may have been found, or it may not yet have been found.  

That said, almost anyone would agree the experiment result is now on life-support, because any meaningful reduction in the original statistical significance (from an optimistic 6 standard deviations) basically takes most remaining credibility out of what was a highly implausible claim to start with.

But I suspect XKCD are already collecting their winnings…

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