As for time travelling, i can only say that human still has a long way to fully understand the nature. Even now we have several theories explain phenomenon that we observed, including time dilation, space-time deformation and other effects using theory in physics developed, those theory sometimes still cannot explain quite some phenomenon(even the quantum mechanics and Theory of relativity still have some part contradict to each other, there is still no theory that can unify all the fundamental force in one formula). So, until we get more understanding on the nature, we have the opportunity for time travelling. However, one got to keep in mind that according to Gödel's incompleteness theorems, no matter how complete a theory is, there will still be some case the theory not valid. So, a theory always need to be refined from time to time.

This post has been edited by VA1701wb: Sep 12 2009, 09:54 AM