I’ve been following this story of “faster than light neutrinos” since the news first came out in late September:
CERN says a neutrino beam fired from a particle accelerator near Geneva to a lab 454 miles (730 kilometers) away in Italy traveled 60 nanoseconds faster than the speed of light. Scientists calculated the margin of error at just 10 nanoseconds, making the difference statistically significant.
To date, there have been more than 80 papers published trying to explain the 60-nanosecond discrepancy. But according to one physicist, Ronald van Elburg at the University of Groningen, the scientists at CERN neglected to consider nuances of the time mechanism. In particular, in order to synchronize the two locations (they are more than 700km apart, after all), the team used GPS satellites, which each broadcast an accurate time signal from orbit some 20,000km overhead. But herein lies the problem, according to van Elburg:
So what is the satellites’ motion with respect to the OPERA experiment? These probes orbit from West to East in a plane inclined at 55 degrees to the equator. Significantly, that’s roughly in line with the neutrino flight path. Their relative motion is then easy to calculate.
So from the point of view of a clock on board a GPS satellite, the positions of the neutrino source and detector are changing. “From the perspective of the clock, the detector is moving towards the source and consequently the distance travelled by the particles as observed from the clock is shorter,” says van Elburg.
By this he means shorter than the distance measured in the reference frame on the ground.
The OPERA team overlooks this because it thinks of the clocks as on the ground not in orbit.
How big is this effect? Van Elburg calculates that it should cause the neutrinos to arrive 32 nanoseconds early. But this must be doubled because the same error occurs at each end of the experiment. So the total correction is 64 nanoseconds, almost exactly what the OPERA team observes.
Here is the full paper (PDF). And the conclusion:
We showed that in the OPERA experiment the baseline time-of-flight is incorrectly identified with the Lorentz transformation corrected time-of-flight as measured from a clock in a nonstationary orbit and in fact exceeds it by at maximum 64 ns. The calculation presented contain some simplifying assumptions, a full treatment should take into account the varying angle between the GPS satellite’s velocity vector and the CERN-Gran Sasso baseline. We expect that such a full treatment will find somewhat lower value for the average correction. This is because the velocity of the GPS satellite is most of the time not fully aligned with the CERN-Gran Sasso baseline. In addition full analysis should be able to predict the correlation between the GPS satellite position(s) and the observed time-of-flight.
We know from special relativity that time is reference frame specific. This paper shows that Coordinated Universal Time (UTC) happens to be less universal than the name suggests, and that we have to take in to account where our clocks are located. Finally, making all calculations from the correct reference frame might also lead to further improvement of the accuracy of GPS systems as the errors reported here for the time-of-flight amount to a ±18 m difference in location.
I am skeptical. This is rudimentary physics, and I can’t believe that the OPERA scientists would have neglected to consider such a triviality. I’ll be paying attention to how this story unfolds…