From the Cosmos to the Kitchen

One of the most obvious facts about the universe is that the past is different from the future.  The world around us is full of irreversible processes:  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.  In the 19th century, Ludwig Boltzmann explained why entropy tends to increase, but only under the assumption that it starts out small to begin with.  The initially low entropy can only be explained by cosmology:  why was the early universe in such a special state?  We don't know the answer, but modern theories lead us to think about the multiverse and what happened before the Big Bang.