Watch this: Arrow of Time
Why is time directional? We experience time heading away from the past and toward the future. Dr. Sean Carroll, a cosmologist at the California Institute of Technology made an appearance on Sixty Symbols, a physics web series, to talk about the directionality of time. He makes an analogy with the directionality of space. Imagine an astronaut floating out in space — the astronaut doesn't experience up or down. All the directions are the same. Now, here on earth, we distinguish up and down because of the presence of the giant rock beneath our feet. Carroll says that the Big Bang is analogous to earth, giving a direction to time. Give it watch to learn more about the thermodynamic roots of this cosmological problem.