There are many theories out there, and this only targets one of them. For example, the multiple universes theory states that we live in multiple realities of sp

There are many theories out there, and this only targets one of them. For example, the multiple universes theory states that we live in multiple realities of spacetime, all of which are isolated. So time travel could be as easy as finding a way to transport oneself between spacetime realities. Also, time travel here seems to be defined as "traveling back in time." The twin paradox still holds: http://en.wikipedia.org/wiki/Twin_paradox http://en.wikipedia.org/wiki/Twin_paradox