10-10 to 10-3 second

This fraction of the first second is known as the Particle Era. And it’s full of exciting changes.

You probably have a photograph of yourself as a small child in which you start to see features that truly look like you. Maybe it’s a freckle that’s formed on your cheek or the shape of your face. For the cosmos, this transitional time — from the Electroweak Era to the Particle Era — is like that. When it’s over, some of the basic building blocks of atoms will finally have formed.

For instance, quarks will have become stable enough to combine to form elementary particles. However, matter and antimatter are equally abundant. This means that as soon as a particle forms, it almost immediately gets annihilated by its antimatter opposite. Nothing lasts for more than an instant. But by the end of this Particle Era, the universe had cooled enough to enable the next phase to start, one that moves us toward normal matter.