A malfunctioning cable may have been responsible for the claim that some particles may be able to travel faster than light speed, a potentially embarrassing outcome for physicists who had publicized the findings with great fanfare just a few month ago.
In September, scientists at the European Organization for Nuclear Research, or CERN, said that ghostlike particles called neutrinos zapped from a lab in Geneva to one in Italy had seemingly made the trip in about 60 nanoseconds less than light speed—a finding that garnered headlines around the world. It also induced much head-shaking among skeptical scientists who said they were convinced that the result was an error.
It turns out the only ghost may have been in the machine after all. CERN says it had identified two possible effects that could have affected the experiment: one relates to an oscillator used to provide time stamps for estimating particle speeds, and a possible glitch in a fiber-optic cable.
"If this is the case, it could have led to an underestimate of the time of flight of the neutrinos," CERN said in a one-paragraph "update" posted on its website. It plans new measurements in May.
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. That result was based on more than 15,000 neutrino events measured.
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 weird. For example, it suggests that particles can theoretically travel backward in time. Not only is such an outcome contrary to nature's laws as currently understood, it would require a drastic rewriting of modern particle physics.
The light-speed notion is partly the basis for Einstein's theory of gravity, which, in turn, is the starting point for existing theories about how the universe evolved.
The speed of light calculation has also 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 zoom around faster than light, most of those calculations would have to be redone.
After the September announcement, some scientists were skeptical because of earlier measurements that showed neutrinos reaching the Earth from a supernova explosion and traveling at exactly the speed of light—which contradicted the CERN finding. Others had wondered whether the setup of the experiment or statistical errors could have affected the conclusion.
Write to Gautam Naik at gautam.naik@wsj.com
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