The Stages of the Formation of the Universe

The  Universe started through the big bang process. But the Big Bang itself doesn’t actually have stages, as a fact of discussion. However, physicists and astronomers who study the development of the cosmos over time, distinguish a number of different periods or epochs in the early history of the universe, some of which mere picoseconds long:

• The Planck epoch : (t < 10E−43 seconds)The Planck scale is the scale beyond which current physical theories do not have predictive value. The Planck epoch is the time during which physics is assumed to have been dominated by quantum effects of gravity.
• The Grand unification epoch : (t < 10E−36 s) The three forces of the Standard Model are unified (assuming that nature is described by a Grand unification theory).
• The Inflationary or Electroweak epoch : (t < 10E−32 s)Cosmic inflation expands space by a factor of the order of 10E26 over a time of the order of 10E−33 to 10E−32 seconds. The universe is supercooled from about 10E27 down to 10E22 kelvin. The Strong interaction becomes distinct from the Electroweak interaction.
• The Quark epoch : (10E−12 s < t < 10E−6 s) The forces of the Standard Model have separated, but energies are too high for quarks to coalesce into hadrons, instead forming a quark-gluon plasma. These are the highest energies directly observable in experiment in the Large Hadron Collider.
• The Hadron epoch : (10E−6 s < t < 1 s) Quarks are bound into hadrons. A slight matter-antimatter-asymmetry from the earlier phases (baryon asymmetry) results in an elimination of anti-hadrons.
• Neutrino decoupling : (t ~ 1 s) Neutrinos cease interacting with baryonic matter. The spherical volume of space which will become the Observable universe is approximately 10 light-years in radius at this time.
• The Lepton epoch, 1 s < t < 10 s: Leptons and anti-leptons remain in thermal equilibrium.
• Big Bang nucleosynthesis : (10 s < t < 103 s) Protons and neutrons are bound into primordial atomic nuclei, hydrogen and helium-4. Small amounts of deuterium, helium-3, and lithium-7 are also synthesized. At the end of this epoch, the spherical volume of space which will become the observable universe is about 300 light-years in radius, baryonic matter density is on the order of 4 grams per m3 (about 0.3% of sea level air density) – however, most of energy at this time is in electromagnetic radiation.
• The Photon epoch : (10 s ~ 1.2E13 s, 380,000 year) The universe consists of a plasma of nuclei, electrons and photons; temperatures remain too high for the binding of electrons to nuclei.
• Recombination : (t ~ 380,000 y) Electrons and atomic nuclei first become bound to form neutral atoms. Photons are no longer in thermal equilibrium with matter and the Universe first becomes transparent. Recombination lasts for about 100.000 year, during which Universe is becoming more and more transparent to photons. The photons of the cosmic microwave background radiation originate at this time. The spherical volume of space which will become the observable universe is 42 million light-years in radius at this time. The baryonic matter density at this time is about 500 million hydrogen and helium atoms per m3, approximately a billion times higher than today. This density corresponds to pressure on the order of 10E−17 atm.
• Dark Ages : (380 ka < t < 150 Ma, where, ka = kilo annum, or thousand years; Ma = mega annum, or million years): The time between recombination and the formation of the first stars. During this time, the only source of photons was hydrogen emitting radio waves at hydrogen line. Freely propagating CMB photons quickly (within about 3 million years) red-shifted to infrared, and Universe was devoid of visible light.
• Reionization : (150 Ma < t < 1 Ga) The most distant astronomical objects observable with telescopes date to this period; as of 2016, the most remote galaxy observed is GN-z11, at a redshift of 11.09. The earliest "modern" Population III stars are formed in this period.
• Galaxy formation and evolution : (1 Ga < t < 10 Ga) Galaxies coalesce into "proto-clusters" from about 1 Ga (z = 6) and into Galaxy clusters beginning at 3 Gy (z = 2.1), and into superclusters from about 5 Gy (z = 1.2), see list of galaxy groups and clusters, list of superclusters.