Wait, so Bill And Ted's Bogus Journey is suddenly implausible? A group of Hong Kong University of Science and Technology physicists say they've proven that time travel is physically impossible, reports Discovery News. They demonstrated that a single photon obeys Einstein's theory that nothing can travel faster than the speed of light, meaning nothing can move through time.
Time travel seemed like a possibility a decade ago when researchers found faster-than-light propagation of optical pulses in certain mediums, but it was later dismissed as a visual trick. Until the Hong Kong study, nobody had proved Einstein's photon speed theory correct. "Einstein claimed that the speed of light was the traffic law of the universe or in simple language, nothing can travel faster than light," said the university website. "The study, which showed that single photons also obey the speed limit, confirms Einstein's causality; that is, an effect cannot occur before its cause." (Read more time travel stories.)