In "A Breif History of Time" Stephen Hawkins states that time travel isn't impossible. If you can travel in time, you can go faster than light -- in the sense that temporal relations (such as "faster") lose their absolute meaning. If I need to go 100 lightyears (and can travel at c), I'll transport myself back 100 years and hit start. To a by stander, I'd have gone there in zero time.