A surprising threat to Einstein’s theory

Physicists at the CERN laboratory in Geneva have clocked subatomic particles moving faster than the speed of light.

Could a fundamental principle of physics be wrong? That tantalizing question has been roiling the scientific community since physicists at the CERN laboratory in Geneva said last week they had clocked subatomic particles called neutrinos moving faster than the speed of light. Albert Einstein’s special theory of relativity, which established the foundation of modern physics in 1905, holds that nothing in the cosmos can outrun light, which travels at 186,282 miles per second. If neutrinos can move faster than that, they could, in theory, arrive at a destination before they had even left, opening the prospect of time travel. That idea is so shocking that most physicists can’t believe the results are correct. “If it’s true, then it’s truly extraordinary,” John Ellis, a theoretical physicist at CERN, tells Nature.com.

Even the CERN team is skeptical. “We wanted to find a mistake” in the study that would leave Einstein’s theory intact, but “we didn’t,” says lead researcher Antonio Ereditato. He and his colleagues did not set out to test relativity; they only wanted to learn more about neutrinos—ghostly particles that can travel straight through most types of matter. But when they shot the neutrinos from Geneva through the Earth to a lab beneath Italy’s Gran Sasso mountain, about 454 miles away, the particles consistently arrived about 60 nanoseconds faster than a beam of light could have. CERN’s tests were exhaustive: Over three years, the researchers tallied the speed of some 16,000 neutrinos, then spent six months searching their calculations and measurements for errors.

That precision has many scientists wondering if “there’s the chance” the finding actually is “a doorway into something fundamental and deep we don’t know about nature,” says Matthew Strassler, a theoretical physicist at Rutgers University. Perhaps no cosmic speed limit exists, or maybe neutrinos travel through an undiscovered fifth dimension—separate from the three dimensions of space and the one of time that we know about. Physicists at Fermilab, the Department of Energy facility in Illinois, will spend the next six months trying to overturn CERN’s results. But what if they can’t? “All the great revolutions in science,” Strassler says, “start with an unexpected discrepancy that wouldn’t go away.”

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