Diagram of the evolution of the (visible part) of the universe from the Big Bang (left), the CMB-reference afterglow, to the present.
1. The very early universe 2. The Dark Ages and large-scale structure emergence 3. The universe as it appears today. 4. The far future and ultimate fate.
Planck epoch: The Planck epoch is an era in traditional (non-inflationary) Big Bang cosmology immediately after the known universe began.
Grand unification epoch: As the universe expanded and cooled, it crossed transition temperatures at which forces separated from each other. As the universe cools, it becomes possible for the quantum fields that create the forces and particles around us to settle at lower energy levels and with higher levels of stability.
Electroweak epoch: The electroweak age began 10−36 seconds after the Big Bang. The universe’s temperature was low enough (1028 K) for the electronuclear force to begin to manifest as two separate interactions, the strong and the electroweak interactions.
Inflationary epoch and the rapid expansion of space: The metric defining distance within an area suddenly and very rapidly changed in scale. I am leaving the early universe at least 1078 times its previous size.
Supersymmetry breaking:Supersymmetry is a property of our universe, then it must be broken at an energy that is no lower than 1 TeV, the electroweak scale.
Electroweak symmetry breaking: As the universe’s temperature continued to fall below 159.5±1.5 GeV, electroweak symmetry breaking happened. So far as we know, it was the penultimate symmetry-breaking event in the formation of our universe, the final one being chiral symmetry-breaking in the quark sector.
Electroweak epoch and early thermalization: Sometime after inflation, the created particles went through thermalization, where mutual interactions lead to thermal equilibrium.
The quark epoch: The quark epoch began approximately 10−12 seconds after the Big Bang. This was the period in the evolution of the early universe immediately after electroweak symmetry breaking, when the fundamental interactions of gravitation, electromagnetism, the strong interaction, and the weak interaction had taken their present forms. However, the universe’s temperature was still too high to allow quarks to bind together to form hadrons.
Baryogenesis:Baryons are subatomic particles such as protons and neutrons that are composed of three quarks. It would be expected that both baryons and particles known as antibaryons would have formed in equal numbers.
Hadron epoch: The quark-gluon plasma that composes the universe cools until hadrons, including baryons such as protons and neutrons, can form. Initially, hadron/anti-hadron pairs could create, so matter, and antimatter was in thermal equilibrium.
Neutrino decoupling and cosmic neutrino background: At approximately 1 second after the Big Bang, neutrinos decouple and begin traveling freely through space. As neutrinos rarely interact with matter, these neutrinos still exist today, analogous to the much later cosmic microwave background emitted during recombination, around 370,000 years after the Big Bang.
Lepton epoch:Most hadrons and anti-hadrons annihilate each other at the end of the hadron epoch, leaving leptons (such as the electron, muons, and specific neutrinos) antileptons dominating the mass of the universe.
Photon epoch: After most leptons and antileptons are eradicated at the end of the lepton epoch, most of the mass energy in the universe is left in the form of photons. Much of the rest of its mass energy is in the form of neutrinos and other relativistic particles.
Nucleosynthesis of light elements: Between about 2 and 20 minutes after the Big Bang, the temperature and pressure of the universe allowed nuclear fusion to occur, giving rise to nuclei of a few light elements beyond hydrogen (Big Bang nucleosynthesis). About 25% of the protons and all of the Neutrons fuse to form deuterium, a hydrogen isotope, and most of the deuterium quickly combines to form helium-4. Atomic nuclei will easily unbind (break apart) above a specific temperature related to their binding energy. From about 2 minutes, the falling weather means that deuterium no longer unbinds and is stable. Starting from about 3 minutes, helium and other elements formed by the fusion of deuterium also no longer unbind and are durable.
Matter domination: Until now, the universe’s large-scale dynamics and behavior have been determined mainly by radiation—meaning those constituents that move relativistically (at or near the speed of light), such as photons and neutrinos. As the universe cools, from around 47,000 years, the universe’s large-scale behavior becomes dominated by matter instead. This occurs because matter exceeds both the energy density of radiation and the vacuum energy density. From this point on, and for several billion years to come, the presence of dark matter accelerates the formation of structure in our universe. In the early universe, dark matter gradually gathers in massive filaments under the effects of gravity, collapsing faster than ordinary (baryonic) matter because its collapse is not slowed by radiation pressure. There is overwhelming evidence that dark matter exists and dominates our universe. The presence of dark matter accelerates the formation of structure in our universe.
Recombination, photon decoupling, and the cosmic microwave background: About 370,000 years after the Big Bang, two related events occurred: the ending of recombination and photon decoupling. Before recombination, the baryonic matter in the universe was at a temperature where it formed a hot ionized plasma. Before recombination, the baryonic matter in the universe was at a temperature where it began a hot ionized plasma. Most photons in the universe interacted with electrons and protons and could not travel significant distances without interacting with ionized particles. As a result, the universe was opaque or “foggy.” Although there was light, it was not possible to see.
Dark Ages: After recombination and decoupling, the universe was transparent and had cooled enough to allow light to travel long distances, but there were no light-producing structures such as stars and galaxies. Stars and galaxies are formed when dense regions of gas form due to the action of gravity, and this takes a long time within a near-uniform density of gas and on the scale required, so it is estimated that stars did not exist for perhaps hundreds of millions of years after recombination. The first generation of stars, known as Population III stars, formed within a few hundred million years after the Big Bang. These stars were the first source of visible light in the universe after recombination. Since the start of the matter-dominated era, dark matter has gradually been gathering in colossal spread-out (diffuse) filaments under the effects of gravity.
Reionization: As the first stars, dwarf galaxies, and quasars gradually form, the intense radiation they emit reionizes much of the surrounding universe, splitting the neutral hydrogen atoms back into a plasma of free electrons and protons for the first time since recombination and decoupling. Reionization is evidenced from observations of quasars.
Galaxies, clusters, and superclusters: Matter continues to draw together under the influence of gravity to form galaxies. These Population III stars are also responsible for turning the few light elements in the Big Bang (hydrogen, helium, and small amounts of lithium) into many heavier elements.
Dark energy dominated era: From about 9.8 billion years of cosmic time, the universe’s large-scale behavior is believed to have gradually changed for the third time in its history. Its behavior was initially dominated by radiation (relativistic constituents such as photons and neutrinos) for the first 47,000 years. Since about 370,000 years of cosmic time, its behavior had been dominated by matter.
In cosmology, quintessence is a natural form of energy distinct from any ordinary matter or radiation or even “dark matter.” Its bulk properties – energy density, pressure, and so forth – lead to novel behavior and unusual astrophysical phenomena. Quintessence is a canonical scalar field introduced to explain the late-time cosmic acceleration. The cosmological dynamics of quintessence are reviewed, paying particular attention to the evolution of the dark energy equation of state.
