Our universe has a long and complicated history. And scientists are still trying to understand it all.

The general picture says the universe was born 13.8 billion years ago, in the Big Bang. For the first tiny fraction of a second, the universe expanded at many times the speed of light – an epoch known as cosmic inflation. When inflation ended, the expansion slowed dramatically. But a lot happened over the following few minutes.

During the first second, the basic forces of nature took shape: gravity, electromagnetism, and the forces that bind matter together. These forces made it possible to forge protons and neutrons.

By about three minutes, the universe had expanded and cooled enough for these particles to stick together. They formed the nuclei of the first elements – mainly hydrogen and helium.

The universe was still extremely hot and dense. And it was “foggy,” so we can’t see anything from that era. By about 380,000 years, though, the fog began to clear. Electrons latched on to the nuclei to form complete atoms. That process left a faint “afterglow” that we see across the entire universe.

There are lots of questions about the details of this picture. And some scientists aren’t convinced about the overall outline – they have different views about the age of the universe, whether inflation ever happened, and more.

There’s a little more agreement about what came next, and we’ll talk about that tomorrow.

Script by Damond Benningfield