First the Chinese banned time travel stories from TV and the movies. Now comes the news, as reported in the Discovery News article Time Travel Impossible, Say Scientists, that Chinese scientists have proved that time travel is physically impossible.
Professor Du Shengwang of the Hong Kong University of Science and Technology and his team proved this by measuring a single photon and demonstrating that it could not travel faster than the speed of light. As they said, "The study, which showed that single photons also obey the speed limit c, confirms Einstein's causality; that is, an effect cannot occur before its cause."
Er... OK... I'll admit that I actually don't know what the heck that is supposed to mean, but I'll take their word on it.
Besides, I have a much simpler proof that time travel is impossible. Having carefully observed the record of numerous historical events, I've noticed that they have not turned into temporal tourist traps. Let's face it, if time travel were possible the soldiers landing on Normandy during the D-Day invasion would have been met with hawkers selling "I went to WWII and all I got was this lousey t-shirt" and other such tacky merchandise. Ergo, time travel doesn't happen so it must be impossible. Tautology aside -- QED.