Faster than light

Some scientists created neutrinos at CERN in Geneva, and then measured how long it took them to reach a detector called OPERA, located in Italy. When they did the math, it looked like the neutrinos actually got there by traveling a hair faster than the speed of light! 60 nanoseconds faster, to be accurate.

Was relativity doomed? Nope. In fact, relativity may very well be what saves the day here.

First, most scientists were skeptical. Even the people running the experiment were skeptical, and were basically asking everyone else for help. They figured they might have made a mistake as well, and couldn’t figure out what had happened. Most everyone zeroed in on the timing of the experiment, which has to be extremely accurate. The entire flight time of a neutrino from Switzerland to Italy is only about 2.4 milliseconds, and the measurement accuracy needs to be to only a few nanoseconds...The scientists used a very sophisticated GPS setup to determine the timing, so that has been the focus of a lot of scrutiny as well. And a new paper just posted on the Physics Preprint Archive may have the answer… and it uses relativity.

The timing was measured using a GPS satellite orbiting the Earth, and moving relative to CERN and OPERA. That means the distance traveled by the neutrinos would be less as measured by the GPS sat as it would be from the ground, and therefore wouldn’t take as long to cover it. Doing the detailed math, van Elburg calculates how much faster the neutrinos would be expected to arrive accounting for the satellite’s motion, and he gets… 64 nanoseconds. That’s almost exactly the discrepancy measured by the original experimenters.

New high-precision tests carried out by the OPERA collaboration in Italy broadly confirm its claim, made in September, to have detected neutrinos travelling at faster than the speed of light. The collaboration today submitted its results to a journal, but some members continue to insist that further checks are needed before the result can be considered sound.

The collaboration has also checked its original statistical analysis, but today's decision to submit the results to a journal was not unanimous. "About four people" among the group of around 15 who did not sign the preprint have signed the journal submission, according to a source within the collaboration, while "four new people" have decided not to sign. That leaves the number of dissenters at about 15...

The question of whether or not OPERA really has seen faster-than-light neutrinos will probably be settled only once the results of other experiments are in.

Let me be clear: this new result does not confirm FTL neutrinos! What it did was essentially eliminate one possible source of error. A big one still remains. Most people, including me, think that the way they timed the experiment may be the source of the problem.

Another new twist in the science of scofflaw neutrinos: A second Italian physics group now says they are not moving faster than light after all. So the foundations of modern physics appear safe for now — but this debate will likely not be settled for some time.

But on Saturday, the ICARUS experiment, another experiment at Gran Sasso, said OPERA did not properly account for the neutrinos’ energy on arrival. If the ghostly particles were actually moving faster than light, they should have lost most of their energy, radiating decay products like photons and electron pairs. But they didn’t, and instead the ICARUS team found an energy spectrum that corresponds with neutrinos traveling at light speed.