physical cosmology Physical cosmology is a branch of cosmology concerned with the study of cosmological models. A cosmological model, or simply cosmology, provides a description of the largest-scale structures and dynamics of the universe and allows study of fu ...

, the hadron era is a range of time in an obsolete model of the very early universe. It was said to have begun at a time of 10⁻⁴⁴ seconds, or at 10⁻⁸ seconds, and ended at 10⁻⁴ seconds. The temperature was high enough to allow the formation of hadron/anti-hadron pairs, which kept matter and anti-matter in

thermal equilibrium Two physical systems are in thermal equilibrium if there is no net flow of thermal energy between them when they are connected by a path permeable to heat. Thermal equilibrium obeys the zeroth law of thermodynamics. A system is said to be in t ...

. After the discovery of quarks and

gluons A gluon ( ) is a type of massless elementary particle that mediates the strong interaction between quarks, acting as the exchange particle for the interaction. Gluons are massless vector bosons, thereby having a spin of 1. Through the s ...

in the 1970s the model based on hadrons no longer made sense. However, hadron-antihadron pairs were only abundant for a brief time between about 5×10⁻⁵ seconds, the time of the QCD phase transition, and about 7×10⁻⁵ seconds, when the temperature of the universe dropped below the

pion In particle physics, a pion (, ) or pi meson, denoted with the Greek alphabet, Greek letter pi (letter), pi (), is any of three subatomic particles: , , and . Each pion consists of a quark and an antiquark and is therefore a meson. Pions are the ...

mass. Before the QCD phase transition, during the quark epoch, the universe was hot enough that quarks did not combine to form hadrons. At temperatures below the pion mass, most of the hadrons and anti-hadrons were eliminated in

annihilation In particle physics, annihilation is the process that occurs when a subatomic particle collides with its respective antiparticle to produce other particles, such as an electron colliding with a positron to produce two photons. The total energy a ...

reactions, leaving the Universe dominated by photons, neutrinos and electron-positron pairs. This subsequent period is referred to as the lepton era.

Constituents

Combining particle physics models with the standard

Lambda-CDM model The Lambda-CDM, Lambda cold dark matter, or ΛCDM model is a mathematical model of the Big Bang theory with three major components: # a cosmological constant, denoted by lambda (Λ), associated with dark energy; # the postulated cold dark mat ...

of cosmological expansion, suggests when expansion cooled the universe to a transition temperature around 150MeV hadron formation was favored. From this time until neutrino decoupling,

antimatter In modern physics, antimatter is defined as matter composed of the antiparticles (or "partners") of the corresponding subatomic particle, particles in "ordinary" matter, and can be thought of as matter with reversed charge and parity, or go ...

is an important constiutent of the universe.

References

Physical cosmology Big Bang {{physical-cosmology-stub

Constituents

See also

References