One of the most obvious facts about the universe is that the past is different from the future. We can turn an egg into an omelet, but can't turn an omelet into an egg. Physicists have codified this difference into the Second Law of Thermodynamics: the entropy of a closed system always increases with time. But why? The ultimate explanation is to be found in cosmology: special conditions in the early universe are responsible for the arrow of time. This talk will be about the nature of time, the origin of entropy, and how what happened before the Big Bang may be responsible for the arrow of time we observe today.