In an experiment, neutrinos sent through the ground from Cern toward another laboratory more than 450 miles away seemed to arrive there a tiny fraction of a second earlier than the speed of light, long considered the universe's ultimate speed limit, the BBC reported Thursday.
The experimenters, who say their results will be posted online for other scientists to examine, are being cautious about their findings.
"We tried to find all possible explanations for this," report author Antonio Ereditato said.
"We wanted to find a mistake -- trivial mistakes, more complicated mistakes, or nasty effects -- and we didn't."
Much of modern physics theory, based largely on Albert Einstein's special theory of relativity, is grounded on the idea that nothing can exceed the speed of light.
Ereditato and his colleagues, carrying out neutrino experiments for the last three years, have found the particles apparently showed up a few billionths of a second sooner than light would over the same distance.
The experiment has been repeated about 15,000 times, with results reaching a level of statistical significance that in scientific circles would count as a formal discovery, some researchers say.
But Ereditato remains cautious.
"We are not claiming things, we want just to be helped by the community in understanding our crazy result -- because it is crazy," he said.