“We tried to find all possible explanations for this,” said report author Antonio Ereditato of the Opera collaboration.
The OPERA particle detector may have spotted neutrinos traveling faster than light, which would bring down the curtain on special relativity as an exact theory.
Credit: OPERA collaboration
“We wanted to find a mistake – trivial mistakes, more complicated mistakes, or nasty effects – and we didn’t,” he told BBC News.
“When you don’t find anything, then you say ‘Well, now I’m forced to go out and ask the community to scrutinise this.'”
The data come from a 1300-metric-ton particle detector named Oscillation Project with Emulsion-tRacking Apparatus (OPERA). Lurking in Italy’s subterranean Gran Sasso National Laboratory, OPERA detects neutrinos that are fired through the earth from the European particle physics laboratory, CERN, near Geneva, Switzerland. As the particles hardly interact at all with other matter, they stream right through the ground, with only a very few striking the material in the detector and making a noticeable shower of particles.
Over 3 years, OPERA researchers timed the roughly 16,000 neutrinos that started at CERN and registered a hit in the detector. They found that, on average, the neutrinos made the 730-kilometer, 2.43-millisecond trip roughly 60 nanoseconds faster than expected if they were traveling at light speed. “It’s a straightforward time-of-flight measurement,” says Antonio Ereditato, a physicist at the University of Bern and spokesperson for the 160-member OPERA collaboration. “We measure the distance and we measure the time, and we take the ratio to get the velocity, just as you learned to do in high school.” Ereditato says the uncertainty in the measurement is 10 nanoseconds.
Dr Ereditato and his colleagues have been carrying out an experiment for the last three years that seems to suggest neutrinos have gone faster than light.
In the course of doing the experiments, the researchers noticed that the particles showed up a few billionths of a second sooner than light would over the same distance.
The team measured the travel times of neutrino bunches some 15,000 times, and have reached a level of statistical significance that in scientific circles would count as a formal discovery.
But the group understands that what are known as “systematic errors” could easily make an erroneous result look like a breaking of the ultimate speed limit, and that has motivated them to publish their measurements.
“My dream would be that another, independent experiment finds the same thing – then I would be relieved,” Dr Ereditato said.
But for now, he explained, “we are not claiming things, we want just to be helped by the community in understanding our crazy result – because it is crazy”.
“And of course the consequences can be very serious.”
The group will present their results tomorrow at CERN, and a preprint of their results will be posted on the physics website ArXiv.org.
At least one other experiment has seen a similar effect before, albeit with a much lower confidence level. In 2007, the Main Injector Neutrino Oscillation Search (MINOS) experiment in Minnesota saw neutrinos from the particle-physics facility Fermilab in Illinois arriving slightly ahead of schedule. At the time, the MINOS team downplayed the result, in part because there was too much uncertainty in the detector’s exact position to be sure of its significance, says Jenny Thomas, a spokeswoman for the experiment. Thomas says that MINOS was already planning more accurate follow-up experiments before the latest OPERA result. “I’m hoping that we could get that going and make a measurement in a year or two,” she says.
If MINOS were to confirm OPERA’s find, the consequences would be enormous. “If you give up the speed of light, then the construction of special relativity falls down,” says Antonino Zichichi, a theoretical physicist and emeritus professor at the University of Bologna, Italy. Zichichi speculates that the ‘superluminal’ neutrinos detected by OPERA could be slipping through extra dimensions in space, as predicted by theories such as string theory.
Ellis, however, remains sceptical. Many experiments have looked for particles travelling faster than light speed in the past and have come up empty-handed, he says