By proving a single photon can't travel faster than light, scientists say they have proven time travel is impossible. THE GIST Hong Kong physicists say they have proven a single photon cannot travel faster than the speed of light. This demonstrates that time travel is impossible, they say. Hong Kong physicists say they have proved that a single photon obeys Einstein's theory that nothing can travel faster than the speed of light — demonstrating that outside science fiction, time travel is impossible. The Hong Kong University of Science and Technology research team led by Du Shengwang said they had...