Cumulative concept of time, 10
You can travel to the future since your future-self contains your present-self:
you travel to the future as long as you, somehow, do not change your present-self.
However, you cannot travel to the past, because by definition, your past-self does not contain your present-self:
your present-self is neither part of the past, nor part of your past-self.
2011.08.21 Sunday (c) All rights reserved by ACHK