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Speed of light picture: the tunnel of a neutrino-emitting experiment at CERN.

Workers help build the neutrino-beam facility used at CERN to shoot particles to Italy in a 2005 picture.

Photograph courtesy Maximilien Brice, CERN

Ker Than

for National Geographic News

Published September 23, 2011

Neutrinos—ghostly subatomic particles—may have been observed traveling faster than the speed of light, scientists announced this week.

If confirmed, the astonishing claim would upend a cardinal rule of physics established by Albert Einstein nearly a century ago.

"Most theorists believe that nothing can travel faster than the speed of light. So if this is true, it would rock the foundations of physics," said Stephen Parke, head of the theoretical physics department at the U.S. government-run Fermilab near Chicago, Illinois.

(Related: "Proton Smaller Than Thought—May Rewrite Laws of Physics.")

The existence of faster-than-light particles would also wreak havoc on scientific theories of cause and effect.

"If things travel faster than the speed of light, A can cause B, [but] B can also cause A," Parke said.

"If that happens, the concept of causality becomes ambiguous, and that would cause a great deal of trouble."

Don't Bet on Breaking Light Speed

Members of the Oscillation Project with Emulsion-tRacking Apparatus, or OPERA, at the European Center for Nuclear Research (CERN) described the unusual neutrino detection in a paper published this week on the research website arXiv.org.

The team shot neutrinos out of a particle accelerator near Geneva, Switzerland, and measured how long it took the particles to travel to a neutrino detector in Gran Sasso, Italy, 450 miles (724 kilometers) away.

(See pictures of a neutrino detector 1.5 miles [2.4 kilometers] under Antarctic ice.)

Neutrinos are subatomic particles that have almost no mass and can zip through entire planets as if they are not there.

Being nearly massless, neutrinos should travel at nearly the speed of light, which is approximately 186,000 miles (299,338 kilometers) a second.

To the astonishment of the OPERA team, the particles appear to have reached their destination about 60 nanoseconds faster than expected.

A nanosecond may not sound like much, but "the effect is quite large," said Fermilab's Parke, who was not part of the CERN team.

The extra speed would mean that, over a distance of 621 miles (1,000 kilometers), neutrinos travel about 66 feet (20 meters) farther than light travels in the same amount of time.

The results would be "revolutionary" if true, Parke said, but he added that he highly doubts the findings will hold up under closer scrutiny.

"If I was a betting man, I would bet against it," he said. "Your first response is it can't possibly be true, that they must have made a mistake."

Neutrino Speed an Instrument Error?

Parke is not alone in his skepticism. Many physicists have speculated that the OPERA results are due to a measurement or instrument error.

It would not be the first time such an error occurred, said Louis Strigari, an astrophysicist at Stanford University also not on the CERN team.

"There have been several instances where, through no fault of the experimenters, the equipment was not understood as well as it needed to be," Strigari said.

"It just so happens that you learn more as you get more data and you understand the machinery a little better."

Even the OPERA team is cautious about its results and is welcoming other researchers to repeat the neutrino experiment.

"We want just to be helped by the community in understanding our crazy result—because it is crazy," Antonio Ereditato, coordinator of the OPERA collaboration, told the BBC.

Supernova Neutrinos Not So Speedy

Dave Goldberg, an astrophysicist at Philadelphia's Drexel University, said that if faster-than-light neutrinos did exist, they would likely have been observed in nature before now.

For example, in 1987 detectors on Earth identified neutrinos and photons—light particles—from an exploding star. Both types of particles reached our planet at almost exactly the same instance.

(Related: "Supernova Caught Starting to Explode for First Time.")

According to Goldberg's calculations, if neutrinos travel faster than light by the amount the OPERA team claims, then neutrinos from that supernova should have been detected in 1984—three years before the photons.

"It's possible, but unlikely," Goldberg said, that detectors active on Earth at the time would have missed such an obvious spike in cosmic neutrinos.

Goldberg concedes that supernova neutrinos are less energetic—and would thus be traveling slower—than the neutrinos from CERN's particle accelerator.

However, "assuming Einstein was correct, both types [of neutrinos] would be moving at something like 99.999999999 percent the speed of light," Goldberg said in an email.

"In other words, from a measurement point of view, they'd be going at essentially identical speeds."

(Also see "Einstein Theories Confirmed by NASA Gravity Probe.")

Relativity Still Very Close to Right

Even if the OPERA results are confirmed by other scientists, they wouldn't totally invalidate Einstein's theories of general and special relativity, Stanford University's Strigari stressed. Those theories still explain a remarkable range of observed phenomena in the universe.

"I think it's long been understood that the theories we have today aren't the full answers," Strigari said.

"If this observation holds up, then it's probably a good piece of evidence that the theories we currently have need to be reworked."

Drexel University's Goldberg agreed that physicists won't be discarding Einstein's theories anytime soon.

"Even if relativity turned out to be wrong," he said, "it's clearly very, very close to being right."

Also see "Einstein's Relativity Affects Aging on Earth (Slightly)" >>

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