Ask Ethan: What was the entropy of the Universe at the Big Bang? (Synopsis) [Starts With A Bang]

“Entropy shakes its angry fist at you for being clever enough to organize the world.” -Brandon Sanderson

The universe was born hot, dense, expanding, full of matter, antimatter and radiation… and in a low-entropy state. If entropy is a measure of disorder, though, that sure does sound like an awfully high-entropy state, not a low-entropy one. So why, when we talk about the Universe, do we say that the early Universe had such low entropy?

The answer has much more to do with a comparison to the entropy of the Universe today, as well as in the far future. Today, the entropy is some quadrillion (or 10^15) times larger than it was around 13.8 billion years ago. And if we extrapolate into the very far future, it will be another 100 quintillion (10^20) times bigger than it is today. But what’s responsible for the difference?

It isn’t stars, galaxies, gravitational clustering or any of the other major changes you probably imagine. Find out the answer on this week’s Ask Ethan!

(And sorry, no Comments of the Week tomorrow; come back next week for a double dose, and I’ll see you for more science here on Monday!)