There's an interesting article on the PhysOrg science news site about a possible solution to the "arrow of time" problem.
The "arrow of time" problem (it's sometimes called a paradox, but it isn't, really) is as follows: the laws of nature aren't time-dependent. They work just as well in reverse as forward. When something falls, it releases energy. Put energy in, and you raise it up. The energy in the system remains constant. And yet we never see things spontaneously rise up into the air as the surroundings become slightly cooler. There's no law that says they can't, we just don't observe it. Over time the amount of entropy (disorganized, unusable energy) in the universe increases, it never spontaneously reverses itself.