A fascinating and easy to understand video explaining the arrow of time as it is ultimately linked to entropy.
From the TED Talks site of this video:
In Part 1 of his lecture at the University of Sydney, cosmologist Sean Carroll gives an entertaining and thought-provoking talk about the nature of time, the origin of entropy, and how what happened before the Big Bang might be responsible for the arrow of time we observe today. (Don't miss Part 2 of this talk!)
About Sean Carroll
A physicist, cosmologist and gifted science communicator, Sean Carroll is asking himself -- and asking us to consider -- questions that get at the fundamental nature of the universe. Full bio and more links