causality19 Nov 2004
Physicists in Switzerland have confirmed that information cannot be transmitted faster than the speed of light. Nicolas Gisin and colleagues at the University of Geneva have shown that the “group velocity” of a laser pulse in an optical fibre can travel faster than the speed of light but that the “signal velocity” - the speed at which information travels - cannot (N Brunner et al. 2004 Phys. Rev. Lett. 93 203902).