The Big Bang
Here is an awesome site about it:
Here is something I enjoyed:
Q: If the second law of thermodynamics establishes that Entropy (measure of disorder) always increases… why, from the chaotic state of post-Big Bang, this universe --more complex and organized-- was built?
A: Well, the entropy of that (theoretical) tiny embyo universe was actually very low. You see, entropy, or order, is partly defined by how confined (or defined) in space everything is. It's like if you swept up all the dust in your room and confined it to a small dustpan. You would have decreased the entropy of the dust. But the second law of Thermodynamics would still apply, because you would have dissipated so much energy (in heat and noise, etc) in doing the job.
As the Universe expands, the matter in it becomes more and more spread out, so, overall, its entropy is increasing. Stephen Hawking has discussed the consequences of the possibility of us being in a collapsing universe. In this situation, entropy ought to decrease with time. But since we seem to measure the direction of the arrow of time by Entropy anyway, presumably time would be running backwards, and so we would not know !!! Intriguing ideas.