The first protons and neutrons
A millionth of a second in, free quarks are captured for good inside the particles they still occupy.
- When
- Known to
- ± 20 million years
- Era
- Primordial
Until about 10⁻⁵ seconds the universe is a quark–gluon plasma: quarks and gluons move freely because it is too hot for the strong force to hold them together. As it cools past roughly 10¹² kelvin they become permanently confined into protons and neutrons. No free quark has been observed since, and every atomic nucleus that exists is assembled from particles made in this moment.