We live in a world governed by chance. Events tumble one after the other like pebbles washed down a stream. Some are small, such as the random puff of wind that spreads a dandelions seeds. Some are big, such as the Big Bang, which got our universe started. Most are in between, such as the movement of continents or the collapse of a civilization. Big and small, important and insignificant, event tumbles on top of event. Eventually you get history.