In physical cosmology

Physical cosmology

Physical cosmology, as a branch of astronomy, is the study of the largest-scale structures and dynamics of the universe and is concerned with fundamental questions about its formation and evolution. For most of human history, it was a branch of metaphysics and religion...

 the quark epoch was the period in the evolution of the early universe when the fundamental interaction

Fundamental interaction

In particle physics, fundamental interactions are the ways that elementary particles interact with one another...

s of gravitation

Gravitation

Gravitation, or gravity, is a natural phenomenon by which physical bodies attract with a force proportional to their mass. Gravitation is most familiar as the agent that gives weight to objects with mass and causes them to fall to the ground when dropped...

, electromagnetism

Electromagnetism

Electromagnetism is one of the four fundamental interactions in nature. The other three are the strong interaction, the weak interaction and gravitation...

, the strong interaction

Strong interaction

In particle physics, the strong interaction is one of the four fundamental interactions of nature, the others being electromagnetism, the weak interaction and gravitation. As with the other fundamental interactions, it is a non-contact force...

 and the weak interaction

Weak interaction

Weak interaction , is one of the four fundamental forces of nature, alongside the strong nuclear force, electromagnetism, and gravity. It is responsible for the radioactive decay of subatomic particles and initiates the process known as hydrogen fusion in stars...

 had taken their present forms, but the temperature of the universe was still too high to allow quark

Quark

A quark is an elementary particle and a fundamental constituent of matter. Quarks combine to form composite particles called hadrons, the most stable of which are protons and neutrons, the components of atomic nuclei. Due to a phenomenon known as color confinement, quarks are never directly...

s to bind together to form hadron

Hadron

In particle physics, a hadron is a composite particle made of quarks held together by the strong force...

s. The quark epoch began approximately 10⁻¹² seconds after the Big Bang

Big Bang

The Big Bang theory is the prevailing cosmological model that explains the early development of the Universe. According to the Big Bang theory, the Universe was once in an extremely hot and dense state which expanded rapidly. This rapid expansion caused the young Universe to cool and resulted in...

, when the preceding electroweak epoch

Electroweak epoch

In physical cosmology the electroweak epoch was the period in the evolution of the early universe when the temperature of the universe was high enough to merge electromagnetism and the weak interaction into a single electroweak interaction . The electroweak epoch began when the strong force...

 ended as the electroweak interaction

Electroweak interaction

In particle physics, the electroweak interaction is the unified description of two of the four known fundamental interactions of nature: electromagnetism and the weak interaction. Although these two forces appear very different at everyday low energies, the theory models them as two different...

 separated into the weak interaction and electromagnetism. During the quark epoch the universe was filled with a dense, hot quark-gluon plasma

Quark-gluon plasma

A quark–gluon plasma or quark soup is a phase of quantum chromodynamics which exists at extremely high temperature and/or density. This phase consists of asymptotically free quarks and gluons, which are several of the basic building blocks of matter...

, containing quarks, leptons and their antiparticles. Collisions between particles were too energetic to allow quarks to combine into meson

Meson

In particle physics, mesons are subatomic particles composed of one quark and one antiquark, bound together by the strong interaction. Because mesons are composed of sub-particles, they have a physical size, with a radius roughly one femtometer: 10−15 m, which is about the size of a proton...

s or baryon

Baryon

A baryon is a composite particle made up of three quarks . Baryons and mesons belong to the hadron family, which are the quark-based particles...

s. The quark epoch ended when the universe was about 10⁻⁶ seconds old, when the average energy of particle interactions had fallen below the binding energy

Binding energy

Binding energy is the mechanical energy required to disassemble a whole into separate parts. A bound system typically has a lower potential energy than its constituent parts; this is what keeps the system together—often this means that energy is released upon the creation of a bound state...

 of hadrons. The following period, when quarks became confined within hadrons, is known as the hadron epoch

Hadron epoch

In physical cosmology, the hadron epoch was the period in the evolution of the early universe during which the mass of the Universe was dominated by hadrons. It started approximately 10−6 seconds after the Big Bang, when the temperature of the universe had fallen sufficiently to allow the quarks...

.