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How did the particles that compose the universe evolve?

All of the species of elementary particles in the standard model co-existed in the earliest moments following the Big Bang. As the universe expanded and cooled in the first few seconds, many particle species decayed or bound together to form composite particles. Free neutrons are composite particles composed of quarks and gluons that decay with a ten minute half-life. Most neutrons have been bound in nuclei with protons since the end of Big Bang Nucleosynthesis.

quark epoch: one picosecond < t < ten microseconds

hadron epoch: t < one second

lepton epoch: t < ten seconds

photon epoch: t < 370,000 years

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