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.