Speedy Particles Put Einstein to the Test

By GAUTAM NAIK

An experiment purporting to show that subatomic particles can travel faster than light has scientists' heads spinning. If confirmed, it would undermine key pillars of modern physics.

At a presentation in Switzerland, scientists said Friday they had recorded ghostlike particles, known as neutrinos, traveling a tiny bit faster than light—an apparent breach of the cosmic speed limit set down by Albert Einstein more than a century ago.

The result could turn out to be an embarrassing miscalculation by scientists—or portend a leap into a science fiction territory where particles theoretically travel backward in time. While a confirmation of the finding wouldn't mean anything has changed about the universe, scientists' understanding of how it works would be thrown into disarray.

"It would be the biggest physics discovery in a century because we'd have to completely revise everything from subatomic physics to what we know about how the universe evolved," said Neil Turok, director of the Perimeter Institute for Theoretical Physics in Ontario, Canada.

Like many physicists mulling the development, Dr. Turok was skeptical. He said neutrinos reaching the Earth from a supernova explosion have been observed to be traveling at the speed of light, which doesn't agree with the latest finding. Other scientists questioned the setup of the experiment and whether statistical errors might have affected the conclusion.

There also were questions about whether the researchers properly accounted for small glitches that could have had an unwanted effect—such as the rotation of the Earth, or the location of the moon and its role in altering the shape of the Earth's crust when the experiment was being conducted.

Even the scientists who conducted the neutrino experiment were wary about questioning one of Einstein's most powerful legacies. They spent six months verifying and reverifying the data, and called on physicists the world over to confirm—or refute—their finding through independent experiments.

"It's an anomaly, a discrepancy," said Dario Autiero, who was involved in the experiment, at a meeting held Friday at the European Organization for Nuclear Research, or CERN. But, if true, "it could have a potentially great impact" on science.

Neutrinos are particles with almost no mass and no charge, and they can pass through ordinary matter unaffected. At any given moment, billions harmlessly stream through a person's body.

In the experiment known as the Oscillation Project with Emulsion-Tracking Apparatus, neutrinos were measured as traveling slightly faster than light on a 450-mile trip from CERN near Geneva to the Gran Sasso underground lab in central Italy. The particles moved at a velocity just above the speed of light. That result was based on more than 15,000 neutrino events measured at the Italian lab, CERN said.

"This result comes as a complete surprise," said Antonio Ereditato of the University of Bern, a spokesman for the experiment. "After many months of studies and cross checks we have not found any instrumental effect that could explain the result of the measurement."

However, he added, "the potential impact on science is too large to draw immediate conclusions or attempt physics interpretations."

Einstein's theory of relativity incorporates his crucial idea that the speed of light—about 186,000 miles a second—is a barrier that can't realistically be breached. In the famous equation E=mc² that equates mass with the energy contained within it, for example, the "c" represents the speed of light. If particles go faster than light, things become troublesome.

Under such a scenario, an observer in a rocket ship traveling near the speed of light who was watching the Gran Sasso experiment taking place, "would detect the neutrino before it was emitted—they'd see it going backwards in time," said Dr. Turok.

The light-speed notion is also partly the basis for Einstein's theory of gravity. That, in turn, is the starting point for existing theories about how the universe evolved.

More practically, the speed of light calculation has been incorporated into billions of measurements done at particle accelerators in the quest to understand how the basic constituents of matter behave. If some particles can indeed outrun light, most of those calculations would need to be redone.

A few years ago, a similar neutrino experiment done at Fermilab in Illinois also showed that the particles could travel faster than light. Unlike the latest finding, that data were "below the threshold of precision needed for making a scientific claim," said Robert Plunkett, a particle physicist at Fermilab.

Dr. Plunkett and his colleagues now plan to go back to their data, refine it, and see if they come to any different conclusions about the speed of neutrino travel. They also plan to do a more ambitious experiment—essentially to check the Swiss-Italian result—though those findings won't be available for two or three years.