When Carl Sagan the legendary astrophysicist was asked if he believed in the possibility of travelling back in time he answered "If we could travel into the past it s mind boggling what would be possible. For one thing history would become an experimental science which it certainly isn't today. The possible insights into our own past and nature and origins would be dazzling. For another we would be facing the deep paradoxes of interfering with the scheme of causality that has led to our own time and ourselves. I have no idea whether it s possible but it s certainly worth exploring."