Not so fast: Second experiment refutes faster-than-light particles

March 16, 2012

Anyone who bet against Einstein better get out their wallet.

That’s because those supposedly faster-than-light particles that shook up the world of physics last September are now looking a lot slower.

A second experiment deep in an Italian mountain timed these subatomic particles, called neutrinos, traveling at precisely the speed of light and no faster, a team from the experiment, called ICARUS, announced Friday.

“For us, the timing is perfectly in line with the speed of light,” said Carlo Rubbia, a Nobel Prize-winning physicist and spokesman for the ICARUS experiment, in a telephone interview.

The new results pile on to revelations last month that a loose cable may have compromised the original experiment, called OPERA.

Although not the final word, the new results are “the greatest of hammer blows” against the faster-than-light findings, said Matt Strassler, a theoretical physicist at Rutgers University in New Jersey.

That’s because both OPERA and ICARUS operate in the same mountain in Italy, and timed the same neutrinos, which were generated at the giant CERN laboratory on the French-Swiss border some 450 miles north.

That makes the new ICARUS results, which were published online Thursday, “a clear, direct refutation of the OPERA measurement,” said Strassler.

The ICARUS results arrived during a test run of the CERN neutrinos in early November. The OPERA team also measured those neutrinos, and, as in its previous result, saw them flying faster than light.

“We have two experiments with different results,” said Rubbia. “We cannot be both right. One of us is wrong.”

Which experiment is correct?

“I know who is right,” Rubbia said, chuckling. “We are right.”

On Feb. 23, the OPERA group said that a crucial fiber-optic timing cable had a loose connection, possibly leading to an overestimate of the neutrinos’ speed.

Together, the new results and the loose cable all but restore the universe’s ultimate speed limit — the speed of light — set by Albert Einstein’s special theory of relativity in 1905.

For more than a century, this speed limit — 186,282 miles per second — has held up.

But in September, the large international team of OPERA physicists reported seeing neutrinos arriving at their experiment from CERN about 60 nanoseconds faster than light.

Despite dissent from some team members, the OPERA scientists announced their results in a scientific paper and a symposium Sept. 23. The announcement generated a wave of global publicity, but also strong skepticism from other scientists. “It’d be a very unlikely result, a very, very surprising result,” Harvard physicist Lisa Randall said at the time.

“No really decent theoretical physicist took this seriously from the very start,” said Nima Arkani-Hamed, a noted theoretical physicist at the Institute for Advanced Study in Princeton, N.J. — Einstein’s last academic home. “I certainly did not.”

The reason: Hundreds of experiments have probed the speed of light, and none have seen anything — even ghostly neutrinos — moving faster. And wild theories that propose faster-than-light particles rest on “very shaky foundations,” Arkani-Hamed said.

Final word should arrive in May, after CERN shoots more neutrinos at the OPERA and ICARUS detectors.

Antonio Ereditato, a member of the OPERA team and the head of the Albert Einstein Center for Fundamental Physics in Bern, Switzerland, said he welcomed the latest results.

“These results are in line with our recent findings about the possible misfunctioning of some of the components of our experimental setup,” he told the Associated Press on Friday.

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