Carroll explains that in space there is no direction and no arrow of time. Small particles in simple systems move into larger collections of particles in complex systems. Left to it's own devices, the universe gets messier, just like your bedroom.
He said, "You never have to go into your apartment and mess it up because things have been busy organizing themselves."
According to Carroll, disorder is measured by entropy. Points of lower entropy and change are seen as the past, while moments of higher entropy are seen as the future. The past was lower in entropy because the early universe was very orderly. The past has no possible alterations. It happened; it is static. The future has more than one possible arrangement, so it is not static.
Carroll went on to say that understanding the arrow of time requires one to try to understand before the Big Bang. He believes that the big bang is like a fluctuation of a universe that comes to a point and a little bit pinches off, creating a new baby universe that will also expand and cool.
"You and I are the pretty little patterns that emerge as the house of cards fall."
Carroll's book From Eternity to Here: The Quest for the Ultimate Theory of Time discusses his theories, but not everyone agrees. He shared a letter from a ten year old boy that said, "I don't know if you exist, but I do. I do not agree with your article. I do not want the world to disappear from under my nose but if you do, I can't say I will be sorry. Signed, a ten year old boy that knows more than others. P.s. Some people have too much time."
More information about Carrol is available on his website. I highly recommend checking him out.