Rewinding the Universe to the Beginning of Time

Dive into the Friedmann equations

You are probably familiar with the fact that our universe is expanding, and that it used to be a very hot and dense some 13.8 billion years ago in what we generally call the Big Bang. You may also have heard that this expansion appears to be accelerating due to a mysterious repulsive force that we call dark energy. In this post I recapitulate what we know about these and show you quantitatively how this expansion really looks like.