International Year of Astronomy: Public Lecture Series

The Origin of the Universe and the Arrow of Time

Sean Carroll

Caltech

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. But why? The ultimate explanation is to be found in cosmology: special conditions in the early universe are responsible for the arrow of time. I will talk 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.