The shape of time

We all have the same question about what is time, could it be reversed? When I was a child, I love to see the movie "Back to the future", it says they go back to the past and try to come back to the future. It is always in my mind about "time travel". Could we find a way to travel forward or backward along time axis? Before think about that kind of question, we need to understand what is time firstly.
It is a qestionable issue and still an open discussion. If our physics describe the universe is somehow symmetric, then the physical symmetry should lead to time symmetry. Why there is only time axis propagates to one direction only without considering any possibility of "backward"? It is because there is no backward causation in humman intuition. But it is too anthropocentric to explain our nature phenomena. Maybe it's time to release our mind to widen the vision of the way we think about our universe. It is a great thing and a very important thing in my life, to pursue such an anwser for the most mystery in nature. This vedio is nice but not clear enough to explain the physics behind the time issue. I think it was made by some university students, if so, he will become a good science film producer one day.
Share it to all my friends, who love physics, animals and Earth.

http://tw.youtube.com/watch?v=y53hh-LAbLk&feature=related