How the Universe began

[Petros Agapetos]

From our current understanding of how the Big Bang might have progressed, taking into account theories about inflation, Grand Unification, etc, we can put together an approximate timeline as follows:

Planck Epoch (or Planck Era), from zero to approximately 10^-43 seconds (1 Planck Time):

This is the closest that current physics can get to the absolute beginning of time, and very little can be known about this period. General relativity proposes a gravitational singularity before this time (although even that may break down due to quantum effects), and it is hypothesized that the four fundamental forces (electromagnetism, weak nuclear force, strong nuclear force and gravity) all have the same strength, and are possibly even unified into one fundamental force, held together by a perfect symmetry which some have likened to a sharpened pencil standing on its point (i.e. too symmetrical to last). At this point, the universe spans a region of only 10^-35 metres (1 Planck Length), and has a temperature of over 1032°C (the Planck Temperature).

Grand Unification Epoch, from 10^–43 seconds to 10^–36 seconds:

The force of gravity separates from the other fundamental forces (which remain unified), and the earliest elementary particles (and antiparticles) begin to be created.

Inflationary Epoch, from 10^–36 seconds to 10^–32 seconds:

Triggered by the separation of the strong nuclear force, the universe undergoes an extremely rapid exponential expansion, known as cosmic inflation. The linear dimensions of the early universe increases during this period of a tiny fraction of a second by a factor of at least 1026 to around 10 centimetres (about the size of a grapefruit). The elementary particles remaining from the Grand Unification Epoch (a hot, dense quark-gluon plasma, sometimes known as “quark soup”) become distributed very thinly across the universe.

Electroweak Epoch, from 10^–36 seconds to 10^–12 seconds:
As the strong nuclear force separates from the other two, particle interactions create large numbers of exotic particles, including W and Z bosons and Higgs bosons (the Higgs field slows particles down and confers mass on them, allowing a universe made entirely out of radiation to support things that have mass).

Quark Epoch, from 10^–12 seconds to 10^–6 seconds:

Quarks, electrons and neutrinos form in large numbers as the universe cools off to below 10 quadrillion degrees, and the four fundamental forces assume their present forms. Quarks and antiquarks annihilate each other upon contact, but, in a process known as baryogenesis, a surplus of quarks (about one for every billion pairs) survives, which will ultimately combine to form matter.

Hadron Epoch, from 10^–6 seconds to 1 second: The temperature of the universe cools to about a trillion degrees, cool enough to allow quarks to combine to form hadrons (like protons and neutrons). Electrons colliding with protons in the extreme conditions of the Hadron Epoch fuse to form neutrons and give off massless neutrinos, which continue to travel freely through space today, at or near to the speed of light. Some neutrons and neutrinos re-combine into new proton-electron pairs. The only rules governing all this apparently random combining and re-combining are that the overall charge and energy (including mass-energy) be conserved.

Lepton Epoch, from 1 second to 3 minutes:
After the majority (but not all) of hadrons and antihadrons annihilate each other at the end of the Hadron Epoch, leptons (such as electrons) and antileptons (such as positrons) dominate the mass of the universe. As electrons and positrons collide and annihilate each other, energy in the form of photons is freed up, and colliding photons in turn create more electron-positron pairs.

Nucleosynthesis, from 3 minutes to 20 minutes:
The temperature of the universe falls to the point (about a billion degrees) where atomic nuclei can begin to form as protons and neutrons combine through nuclear fusion to form the nuclei of the simple elements of hydrogen, helium and lithium. After about 20 minutes, the temperature and density of the universe has fallen to the point where nuclear fusion cannot continue.

Photon Epoch (or Radiation Domination), from 3 minutes to 240,000 years:
During this long period of gradual cooling, the universe is filled with plasma, a hot, opaque soup of atomic nuclei and electrons. After most of the leptons and antileptons had annihilated each other at the end of the Lepton Epoch, the energy of the universe is dominated by photons, which continue to interact frequently with the charged protons, electrons and nuclei.

Recombination/Decoupling, from 240,000 to 300,000 years:
As the temperature of the universe falls to around 3,000 degrees (about the same heat as the surface of the Sun) and its density also continues to fall, ionized hydrogen and helium atoms capture electrons (known as “recombination”), thus neutralizing their electric charge. With the electrons now bound to atoms, the universe finally becomes transparent to light, making this the earliest epoch observable today. It also releases the photons in the universe which have up till this time been interacting with electrons and protons in an opaque photon-baryon fluid (known as “decoupling”), and these photons (the same ones we see in today’s cosmic background radiation) can now travel freely. By the end of this period, the universe consists of a fog of about 75% hydrogen and 25% helium, with just traces of lithium.

Dark Age (or Dark Era), from 300,000 to 150 million years:
The period after the formation of ther first atoms and before the first stars is sometimes referred to as the Dark Age. Although photons exist, the universe at this time is literally dark, with no stars having formed to give off light. With only very diffuse matter remaining, activity in the universe has tailed off dramatically, with very low energy levels and very large time scales. Little of note happens during this period, and the universe is dominated by mysterious “dark matter”.

Reionization, 150 million to 1 billion years:
The first quasars form from gravitational collapse, and the intense radiation they emit reionizes the surrounding universe, the second of two major phase changes of hydrogen gas in the universe (the first being the Recombination period). From this point on, most of the universe goes from being neutral back to being composed of ionized plasma.
The process of star formation - click for larger version

Star and Galaxy Formation, 300 - 500 million years onwards:
Gravity amplifies slight irregularities in the density of the primordial gas and pockets of gas become more and more dense, even as the universe continues to expand rapidly. These small, dense clouds of cosmic gas start to collapse under their own gravity, becoming hot enough to trigger nuclear fusion reactions between hydrogen atoms, creating the very first stars.

The first stars are short-lived supermassive stars, a hundred or so times the mass of our Sun, known as Population III (or “metal-free”) stars. Eventually Population II and then Population I stars also begin to form from the material from previous rounds of star-making. Larger stars burn out quickly and explode in massive supernova events, their ashes going to form subsequent generations of stars. Large volumes of matter collapse to form galaxies and gravitational attraction pulls galaxies towards each other to form groups, clusters and superclusters.

Solar System Formation, 8.5 - 9 billion years:

Our Sun is a late-generation star, incorporating the debris from many generations of earlier stars, and it and the Solar System around it form roughly 4.5 to 5 billion years ago (8.5 to 9 billion years after the Big Bang).
Today, 13.7 billion years: The expansion of the universe and recycling of star materials into new stars continues.

[Petros Agapetos]

The chronology of the universe describes the history and future of the universe according to Big Bang cosmology. The metric expansion of space is estimated to have begun 13.8 billion years ago.[1] The time since the Big Bang is also known as cosmic time. For the purposes of this summary, it is convenient to divide the chronology of the universe into four parts:

The very early universe, from the Planck epoch until the cosmic inflation, or the first picosecond of cosmic time; this period is the domain of active theoretical research, currently beyond the grasp of experiments in particle physics.

The early universe, from the Quark epoch to the Photon epoch, or the first 380,000 years of cosmic time, when the familiar forces and elementary particles have emerged but the universe remains in the state of a plasma, followed by the "Dark Ages", from 380,000 years to about 150 million years during which the universe was transparent but no large-scale structures had yet formed.

The period of large-scale structure formation, including stellar evolution, galaxy formation and evolution and the formation of galaxy clusters and superclusters, from about 150 million years to present, and prospectively until about 100 billion years of cosmic time; The thin disk of our galaxy began to form at about 5 billion years.[2] The solar system formed at about 4.6 billion years ago, with the earliest traces of life on Earth emerging by about 3.5 billion years ago.

The far future, after cessation of stellar formation, with various scenarios for the ultimate fate of the universe.

[Petros Agapetos]

Planck epoch
0 seconds: Planck Epoch begins: earliest meaningful time. The Big Bang occurs in which ordinary space and time develop out of a primeval state (possibly a virtual particle or false vacuum) described by a quantum theory of gravity or "Theory of Everything". All matter and energy of the entire visible universe is contained in an unimaginably hot, dense point (Gravitational singularity), a billionth the size of a nuclear particle. This state has been described as a particle desert. Other than a few scant details, conjecture dominates discussion about the earliest moments of the universe's history since no effective means of testing this far back in space-time is presently available. WIMPS (weakly interacting massive particles) or dark matter and dark energy may have appeared and been the catalyst for the expansion of the singularity. The infant universe cools as it begins expanding outward. It is almost completely smooth, with quantum variations beginning to cause slight variations in density.

Grand Unification Epoch
10⁻⁴³ seconds: Grand unification epoch begins: While still at an infinitesimal size, the universe cools down to 1032 kelvin. Gravity separates and begins operating on the universe—the remaining fundamental forces stabilize into the electronuclear force, also known as the Grand Unified Force or Grand Unified Theory (GUT), mediated by (the hypothetical) X and Y bosons which allow early matter at this stage to fluctuate between baryon and lepton states.

Electroweak epoch
10⁻³⁶ seconds: Electroweak epoch begins: The Universe cools down to 1028 kelvin. As a result, the Strong Nuclear Force becomes distinct from the Electroweak Force perhaps fuelling the inflation of the universe. A wide array of exotic elementary particles result from decay of X and Y bosons which include W and Z bosons and Higgs bosons.

10⁻³³ seconds: Space is subjected to inflation, expanding by a factor of the order of 1026 over a time of the order of 10⁻³³ to 10⁻³² seconds. The universe is supercooled from about 1027 down to 1022 kelvin.

10⁻³² seconds: Cosmic inflation ends. The familiar elementary particles now form as a soup of hot ionized gas called quark-gluon plasma; hypothetical components of Cold dark matter (such as axions) would also have formed at this time.

Quarks epoch
10⁻¹² seconds: Electroweak phase transition: the four fundamental interactions familiar from the modern universe now operate as distinct forces. The Weak nuclear force is now a short-range force as it separates from Electromagnetic force, so matter particles can acquire mass and interact with the Higgs Field. The temperature is still too high for quarks to coalesce into hadrons, and the quark-gluon plasma persists (Quark epoch). The universe cools to 1015 kelvin.

10⁻¹¹ seconds: Baryogenesis may have taken place with matter gaining the upper hand over anti-matter as baryon to antibaryon constituencies are established.

Hadron epoch
10⁻⁶ seconds: Hadron epoch begins: As the universe cools to about 1010 kelvin, a quark-hadron transition takes place in which quarks bind to form more complex particles—hadrons. This quark confinement includes the formation of protons and neutrons (nucleons), the building blocks of atomic nuclei.

Lepton Epoch
1 second: Lepton epoch begins: The universe cools to 109 kelvin. At this temperature, the hadrons and antihadrons annihilate each other, leaving behind leptons and antileptons - possible disappearance of antiquarks. Gravity governs the expansion of the universe: neutrinos decouple from matter creating a cosmic neutrino background.

[Petros Agapetos]

Photon epoch

ca. 10 seconds: Photon epoch begins: Most of the leptons and antileptons annihilate each other. As electrons and positrons annihilate, a small number of unmatched electrons are left over - disappearance of the positrons.

ca. 10 seconds: Universe dominated by photons of radiation - ordinary matter particles are coupled to light and radiation while dark matter particles start building non-linear structures as dark matter halos. Because charged electrons and protons hinder the emission of light, the universe becomes a super-hot glowing fog.

ca. 3 minutes: Primordial Nucleosynthesis: nuclear fusion begins as lithium and heavy hydrogen (deuterium) and helium nuclei form from protons and neutrons.

ca. 20 minutes: Nuclear fusion ceases: normal matter consists of 75% hydrogen and 25% helium - free electrons begin scattering light.

ca. 70,000 years: Matter domination in Universe: onset of gravitational collapse as the Jeans Length at which the smallest structure can form begins to fall.

Cosmic Dark Age

ca. 370,000 years (z=1,100): The "Dark Ages" is the period between decoupling, when the universe first becomes transparent, until the formation of the first stars. Recombination: electrons combine with nuclei to form atoms, mostly hydrogen and helium. Distributions of hydrogen and helium at this time remains constant as the electron-baryon plasma thins. The temperature falls to 3000 kelvin. Ordinary matter particles decouple from radiation. The photons present at the time of decoupling are the same photons that we see in the cosmic microwave background (CMB) radiation

ca. 400,000 years: Density waves begin imprinting characteristic polarization (waves) signals.

ca. 10 million years: With a trace of heavy elements in the Universe, the chemistry that later sparked life Abiogenesis begins operating.

ca. 10-17 million years:The "Dark Ages" span a period during which the temperature of cosmic background radiation cooled from some 4000 K down to about 60 K. The background temperature was between 373 K and 273 K, allowing the possibility of liquid water, during a period of about 7 million years, from about 10 to 17 million after the Big Bang (redshift 137–100). Loeb (2014) speculated that primitive life might in principle have appeared during this window, which he called "the Habitable Epoch of the Early Universe".

ca. 100 million years: Gravitational collapse: ordinary matter particles fall into the structures created by dark matter. Reionization begins: smaller (stars) and larger non-linear structures (quasars) begin to take shape - their ultraviolet light ionizes remaining neutral gas

200-300 million years: First stars begin to shine: Because many are Population III stars (some Population II stars are accounted for at this time) they are much bigger and hotter and their life-cycle is fairly short. Unlike later generations of stars, these stars are metal free. As reionization intensifies, photons of light scatter off free protons and electrons - Universe becomes opaque again

200 million years: HD 140283, the "Methuselah" Star, formed, the unconfirmed oldest star observed in the Universe. Because it is a Population II star, some suggestions have been raised that second generation star formation may have begun very early on.[6] The oldest-known star (confirmed) - SMSS J031300.36-670839.3, forms.

300 million years: First large-scale astronomical objects, protogalaxies and quasars may have begun forming. As Population III stars continue to burn, stellar nucleosynthesis operates - stars burn mainly by fusing hydrogen to produce more helium in what is referred to as the Main Sequence. Over time these stars are forced to fuse helium to produce carbon, oxygen, silicon and other heavy elements up to iron on the periodic table. These elements, when seeded into neighbouring gas clouds by supernova, will lead to the formation of more Population II stars (metal poor) and gas giants.

400 million years (z=11): GN-z11, the oldest-known galaxy, forms.


Renaissance

600 million years: Renaissance of the Universe—end of the Dark Ages as visible light begins dominating throughout. Possible formation of the Milky Way Galaxy: although age of the Methusaleh star suggests a much older date of origin, it is highly likely that HD 140283 may have come into our galaxy via a later galaxy merger. Oldest confirmed star in Milky Way Galaxy, HE 1523-0901. Extent of the Hubble Extreme Deep Field.

630 million years (z=8.2): GRB 090423, the oldest gamma ray burst recorded suggests that supernovas may have happened very early on in the evolution of the Universe[9]

670 million years: EGS-zs8-1, the most distant starburst or Lyman-break galaxy observed, forms. This suggests that galaxy interaction is taking place very early on in the history of the Universe as starburst galaxies are often associated with collisions and galaxy mergers.

700 million years: Galaxies form. Smaller galaxies begin merging to form larger ones. Galaxy classes may have also begun forming at this time including Blazars, Seyfert galaxies, radio galaxies, normal galaxies (elliptical, Spiral galaxies, barred spiral) and dwarf galaxies. UDFy-38135539, the first distant quasar to be observed from the reionization phase, forms. Dwarf galaxy z8 GND 5296 forms. Galaxy or possible proto-galaxy A1689-zD1 forms.

720 million years: Possible formation of globular clusters in Milky Way's Galactic halo. Formation of globular cluster, NGC 6723, in the Milky Way's galactic halo

750 million years: Galaxy IOK-1 a Lyman alpha emitter galaxy, forms. GN-108036 forms—galaxy is 5 times larger and 100 times more massive than the present day Milky Way illustrating the size attained by some galaxies very early on.


Galaxy epoch

Formation of hyper-luminous quasar SDSS J0100+2802, which harbors a black hole with mass of 12 billion solar masses one of the most massive black hole discovered so early in the universe. HE1327-2326, population II star, speculated to have formed from remnants of earlier Population III stars. Visual limit of the Hubble Deep Field. Reionization complete—the Universe becomes transparent again. Galaxy evolution continues as more modern looking galaxies form and develop. Because the Universe is still small in size, galaxy interactions become common place with larger and larger galaxies forming out of the galaxy merger process. Galaxies may have begun clustering creating the largest structures in the Universe so far - the first galaxy clusters and galaxy superclusters appear.

1.1 billion years (12.7 Gya): Age of the quasar CFHQS 1641+3755. Messier 4 Globular Cluster, first to have its individual stars resolved, forms in the halo of the Milky Way Galaxy. Among the clusters many stars, PSR B1620-26 b, a gas giant known as the "Genesis Planet" or "Methusaleh", orbiting a pulsar and a white dwarf, the oldest observed extrasolar planet in Universe, forms.

1.4 billion years (12.4 Gya): Age of Cayrel's Star, BPS C531082-0001, a neutron capture star, among the oldest Population II stars in Milky Way. Quasar RD1, first object observed to exceed redshift 5, forms.

1.8 billion years (12 Gya): Most energetic gamma ray burst lasting 23 minutes, GRB 080916C, recorded. Baby Boom Galaxy forms. Terzan 5 forms as a small dwarf galaxy on collision course with the Milky Way. Dwarf galaxy carrying the Methusaleh Star consumed by Milky Way - oldest-known star in the Universe becomes one of many population II stars of the Milky Way

2.0 billion years (11.8 Gya): SN 1000+0216, the oldest observed supernova occurs - possible pulsar formed. Globular Cluster Messier 15, known to have an intermediate black hole and the only globular cluster observed to include a planetary nebula, Pease 1, forms

2.02 billion years (11.78 Gya): Messier 62 forms - contains high number of variable stars (89) many of which are RR Lyrae stars.

2.2 billion years (11.6 Gya): Globular Cluster NGC 6752, third-brightest, forms in Milky Way

2.4 billion years (11.4 Gya): Quasar PKS 2000-330 forms.

2.41 billion years (11.39 Gya): Messier 10 globular cluster forms. Messier 3 forms: prototype for the Oosterhoff type I cluster, which is considered "metal-rich". That is, for a globular cluster, Messier 3 has a relatively high abundance of heavier elements.

2.5 billion years (11.3 Gya): Omega Centauri, largest globular cluster in the Milky Way forms

3.0 billion years (10.8 billion Gya): Formation of Gliese 581 planetary system: Gliese 581 c, the first observed ocean planet and Gliese 581 d, a super-earth planet, possibly the first observed habitable planets, form. Gliese 581 d has more potential for forming life since it is the first exoplanet of terrestrial mass proposed that orbits within the habitable zone of its parent star.

3.3 billion years (10.5 Gya): BX442, oldest grand design spiral galaxy observed, forms

3.8 billion years (10 Gya): NGC 2808 globular cluster forms: 3 generations of stars form within the first 200 million years. Mu Cephei, giant red star forms

4.0 billion years (9.8 Gya): Quasar 3C 9 forms. The Andromeda galaxy forms from a galactic merger - begins a collision course with the Milky Way. Barnard's Star, red dwarf star, may have formed. Beethoven Burst GRB 991216 recorded. Gliese 677 Cc, a planet in the habitable zone of its parent star, Gliese 667, forms

4.1 billion years (9.7 Gya): 16 Cygni Bb, the first gas giant observed in a single star orbit in a trinary star system, forms - orbiting moons considered to have habitable properties or at the least capable of supporting water

4.5 billion years (9.3 Gya): Fierce star formation in Andromeda making it into a luminous infra-red galaxy

5.0 billion years (8.8 Gya): Earliest Population I, or Sunlike stars: with heavy element saturation so high, planetary nebula appear in which rocky substances are solidified - these nurseries lead to the formation of rocky terrestrial planets, moons, asteroids, and icy comets

5.1 billion years (8.7 Gya): Galaxy collision: spiral arms of the Milky Way form leading to major period of star formation.

5.3 billion years (8.5 Gya): 55 Cancri B, a "hot Jupiter", first planet to be observed orbiting as part of a star system, forms. Kepler 11 planetary system, the flattest and most compact system yet discovered, forms - Kepler 11 c considered to be a giant ocean planet with hydrogen-helium atmosphere.

5.8 billion years (8 Gya): 51 Pegasi b also known as Bellerophon, forms - first planet discovered orbiting a main sequence star

5.9 billion years (7.9 Gya): HD 176051 planetary system, known as the first observed through astrometrics, forms

6.0 billion years (7.8 Gya): Many galaxies like NGC 4565 become relatively stable - ellipticals result from collisions of spirals with some like IC 1101 being extremely massive. Rigel or Beta Orionis, an alpha cygni variable, forms.

6.0 billion years (7.8 Gya): The Universe continues to organize into larger wider structures. The great walls, sheets and filaments consisting of galaxy clusters and superclusters and voids crystallize. How this crystallization takes place is still conjecture. Certainly, it is possible the formation of super-structures like the Hercules-Corona Borealis Great Wall may have happened much earlier, perhaps around the same time galaxies first started appearing. Either way the observable universe becomes more modern looking.

6.3 billion years (7.5 Gya, z=0.94): GRB 080319B, farthest gamma ray burst seen with the naked eye, recorded. Terzan 7, metal-rich globular cluster, forms in the Sagittarius Dwarf Elliptical Galaxy

6.5 billion years (7.3 Gya): HD 10180 planetary system forms (larger than both 55 Cancri and Kepler 11 systems)

6.9 billion years (6.9 Gya): Orange Giant, Arcturus, forms

7 billion years (6.8 Gya): North Star, Polaris, one of the significant navigable stars, forms

7.64 billion years (6.16 Gya): Mu Arae planetary system forms: of four planets orbiting a yellow star, Mu Arae c is among the first terrestrial planets to be observed from Earth


Acceleration

7.8 billion years (6.0 Gya, z=0.4): Acceleration: dark-energy dominated era begins, following the matter-dominated era in during which cosmic expansion was slowing down.

7.8 billion years (6 Gya): Formation of Earth's near twin, Kepler 452b orbiting its parent star Kepler 452

8.8 billion years (5 Gya): Messier 67 open star cluster forms: Three exoplanets confirmed orbiting stars in the cluster including a twin of our Sun

9.13 billion years (4.67 Gya): Proxima Centauri forms completing the Alpha Centauri binary system

[Petros Agapetos]

Formation of the solar system

9.2 billion years (4.6 Gya): Primal supernova, possibly triggers the formation of the Solar System.

9.231 billion years (4.568 Gya): Sun forms - Planetary nebula begins accretion of planets.

9.25 billion years (4.55 Gya): Solar System of Eight planets, four terrestrial (Mercury (planet), Venus, Earth, Mars) and four Jovian planets (Jupiter, Saturn, Uranus, Neptune) evolve around the Sun. Because of accretion many smaller planets form orbits around the proto-Sun some with conflicting orbits - Early Bombardment Phase begins. Pre-Noachian Era begins on Mars. Pre-Tolstojan Period begins on Mercury - Large planetoid strikes Mercury stripping it of outer envelope of original crust and mantle, leaving the planet's core exposed - Mercury's iron content notably high. Vega, fifth-brightest star in our galactic neighbourhood, forms. Many of the Galilean moons may have formed at this time including Europa and Titan which may presently be hospitable to some form of living organism.

9.254 billion years (4.545 Gya): Major collision with a planetoid establishes the Martian dichotomy on Mars - formation of North Polar Basin (Mars)

9.266 billion years (4.533 Gya): Formation of Earth-Moon system following giant impact by hypothetical planetoid Thea (planet). Moon's gravitational pull helps stabilize Earth's fluctuating axis of rotation. Pre-Nectarian Period begins on Moon

9.3 billion years (4.5 Gya): Sun becomes a main sequence yellow star: formation of the Oort Cloud and Kuiper Belt from which a stream of comets like Halley's Comet and Hale-Bopp begins passing through the Solar System, sometimes colliding with planets and the Sun

9.4 billion years (4.4 Gya): Formation of Kepler 438 b, one of the most Earth-like planets, from a protoplanetary nebula surrounding its parent star

9.5 billion years (4.3 Gya): Massive meteorite impact creates South Pole Aitken Basin on the Moon - a huge chain of mountains located on the lunar southern limb, sometimes called "Leibnitz mountains", form

9.6 billion years (4.2 Gya): Tharsis Bulge widespread area of vulcanism, becomes active on Mars - based on the intensity of volcanic activity on Earth, Tharsis magmas may have produced a 1.5-bar CO2 atmosphere and a global layer of water 120 m deep increasing greenhouse gas effect in climate and adding to Martian water table. Age of the oldest samples from the Lunar Maria

9.7 billion years (4.1 Gya): Resonance in Jupiter and Saturn's orbits moves Neptune out into the Kuiper belt causing a disruption among asteroids and comets there. As a result, Late Heavy Bombardment batters the inner Solar System. Herschel Crater formed on Mimas (moon), a moon of Saturn. Meteorite impact creates the Hellas Planitia on Mars, the largest unambiguous structure on the planet. Anseris Mons an isolated massif (mountain) in the southern highlands of Mars, located at the northeastern edge of Hellas Planitia is uplifted in the wake of the meteorite impact

9.8 billion years (4 Gya): HD 209458 b, first planet detected through its transit, forms. Messier 85, lenticular galaxy, disrupted by galaxy interaction: complex outer structure of shells and ripples results. Andromeda and Triangulum galaxies experience close encounter - high levels of star formation in Andromeda while Triangulum's outer disc is distorted

9.861 billion years (3.938 Gya): Major period of impacts on the Moon: Mare Imbrium forms

9.88 billion years (3.92 Gya): Nectaris Basin forms from large impact event: ejecta from Nectaris forms upper part of densely cratered Lunar Highlands - Nectarian Era begins on the Moon.

9.9 billion years (3.9 Gya): Tolstoj (crater) forms on Mercury. Caloris Basin forms on Mercury leading to creation of "Weird Terraine" - seismic activity triggers volcanic activity globally on Mercury. Rembrandt (crater) formed on Mercury. Caloris Period begins on Mercury. Argyre Planitia forms from asteroid impac t on Mars: surrounded by rugged massifs which form concentric and radial patterns around basin - several mountain ranges including Charitum and Nereidum Montes are uplifted in its wake

9.95 billion years (3.85 Gya): Beginning of Late Imbrium Period on Moon. Earliest appearance of Procellarum KREEP Mg suite materials

9.96 billion years (3.84 Gya): Formation of Orientale Basin from asteroid impact on Lunar surface - collision causes ripples in crust, resulting in three concentric circular features known as Montes Rook and Montes Cordillera

10 billion years (3.8 Gya): In the wake of Late Heavy Bombardment impacts on the Moon, large molten mare depressions dominate lunar surface - major period of Lunar vulcanism begins (to 3 Gyr)

10.2 billion years (3.6 Gya): Alba Mons forms on Mars, largest volcano in terms of area

10.4 billion years (3.5 Gya): Earliest fossil traces of life on Earth (stromatolites)

10.6 billion years (3.2 Gya): Amazonian Period begins on Mars: Martian climate thins to its present density: groundwater stored in upper crust (megaregolith) begins to freeze, forming thick cryosphere overlying deeper zone of liquid water - dry ices composed of frozen carbon dioxide form Eratosthenian period begins on the Moon: main geologic force on the Moon becomes impact cratering

10.8 billion years (3 Gya): Beethoven Basin forms on Mercury - unlike many basins of similar size on the Moon, Beethoven is not multi ringed and ejecta buries crater rim and is barely visible

11.2 billion years (2.5 Gya): Proterozoic begins

11.6 billion years (2.2 Gya): Last great tectonic period in Martian geologic history: Valles Marineris, largest canyon complex in the Solar System, forms - although some suggestions of thermokarst activity or even water erosion, it is suggested Valles Marineris is rift fault

11.8 billion years (2 Gya): Star formation in Andromdea Galaxy slows. Formation of Hoag's Object from a galaxy collision. Olympus Mons largest volcano in the Solar System forms

12.1 billion years (1.7 Gya): Sagittarius Dwarf Elliptical Galaxy captured into an orbit around Milky Way Galaxy

12.7 billion years (1.1 Gya): Copernican Period begins on Moon: defined by impact craters that possess bright optically immature ray systems

12.8 billion years (1 Gya): Kuiperian Era (1 Gyr - ) begins on Mercury: modern Mercury, desolate cold planet influenced by space erosion and solar wind extremes. Interactions between Andromeda and its companion galaxies Messier 32 and Messier 110. Galaxy collision with Messier 82 forms its spiral patterned disc: galaxy interactions between NGC 3077 and Messier 81

13 billion years (800 Mya): Copernicus (lunar crater) forms from impact on Lunar surface in the area of Oceanus Procellarum - has terrace inner wall and 30 km wide, sloping rampart that descends nearly a kilometer to the surrounding mare

13.0-13.4 billion years (0.8-0.4 Gya): Epsilon Eridani, third-closest star to the Sun forms - From its planetary nebula Epsilon Eridani b (gas giant) forms

13.175 billion years (625 Mya): formation of Hyades star cluster: consists of a roughly spherical group of hundreds of stars sharing same age, place of origin, chemical content and motion through space

13.2 billion years (600 Mya): Collision of spiral galaxies leads to creation of Antenna Galaxies. Whirlpool Galaxy collides with NGC 5195 forming present connected galaxy system. HD 189733 b forms around parent star HD 189733: first planet to reveal climate, organic constituencies, even colour (blue) of its atmosphere

13.3 billion years (540 Mya) Cambrian explosion, first terrestrial animals.

13.5-13.6 billion years (200-300 Mya): Sirius, the brightest star in the Earth's sky, forms.

13.733 billion years (66 Mya): first mammals.

13.787 billion years (12 Mya): Antares forms.

13.791 billion years (7.6 Mya): Betelgeuse forms.

13.795 billion years (4.4 Mya): Fomalhaut b, first directly imaged exoplanet, forms

13.799 billion years: Present day.

[Petros Agapetos]

[Petros Agapetos]

Planck epoch; time <10⁻⁴³ s, Temp >1032 K
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.

Grand unification epoch; time <10⁻³⁶ s. The three forces of the Standard Model are unified.

Inflationary epoch, Electroweak epoch; time <10⁻³² s, Temp = 1028 K–1022 K
Cosmic inflation expands space by a factor of the order of 1026 over a time of the order of 10−33 to 10−32 seconds. The universe is supercooled from about 1027 down to 1022 kelvins.[3] The Strong Nuclear Force becomes distinct from the Electroweak Force.

Quark epoch; time >10⁻¹² s, Temp = 1012 K
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.

Hadron epoch; time = 10⁻⁶s to 1s; Temp = 1010 K–109 K
Quarks are bound into hadrons. A slight matter-antimatter-asymmetry from the earlier phases (baryon asymmetry) results in an elimination of anti-hadrons.

Lepton epoch time = 1 s–10 s 109 K Leptons and anti-leptons remain in thermal equilibrium; Neutrino decoupling

Photon epoch 10 s–1013s; <380 ka 109 K–103 K The universe consists of a plasma of nuclei, electrons and photons; temperatures remain too high for the binding of electrons to nuclei.

Big Bang nucleosynthesis 10 s–103 s
1011 K–109 K Protons and neutrons are bound into primordial atomic nuclei.

Matter-dominated era; time = 47 ka–10 Ga 104 K–4 K During this time, the energy density of matter dominates both radiation density and dark energy, resulting in a decelerated metric expansion of space.

Recombination time = 380 ka Temp = 1100 -4000 K
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. The photons of the cosmic microwave background radiation originate at this time.

Dark Ages time = 380 ka–150 Ma ; Temp = 4000 K–60 K
The time between recombination and the formation of the first stars. During this time, the only radiation emitted was the hydrogen line. The chemistry of life may have begun shortly after the Big Bang, 13.8 billion years ago, during a "habitable epoch" when the Universe was only 10-17 million years old.

Stelliferous Era 150 Ma–100 Ga Temp = 60 K–0.03 K
The time between the first formation of Population III stars until the cessation of star formation, leaving all stars in the form of degenerate remnants.

Reionization 150 Ma–1 Ga 20–6 60 K–19 K
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–10 Ga 6–0.4 19 K–4 K
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.

Dark-energy-dominated era >10 Ga
Matter density falls below dark energy density (vacuum energy), and expansion of space begins to accelerate. This time happens to correspond roughly to the time of the formation of the Solar System and the evolutionary history of life.

Present time 13.8 Ga 0 Temp = 2.7 K

Far future >100 Ga; Temp <0.1 K
The Stelliferous Era will end as stars eventually die and fewer are born to replace them, leading to a darkening universe. Various theories suggest a number of subsequent possibilities. Assuming proton decay, matter may eventually evaporate into a Dark Era (heat death). Alternatively the universe may collapse in a Big Crunch. Alternative suggestions include a false vacuum catastrophe or a Big Rip as possible ends to the universe.

[Petros Agapetos]

The Big Bang theory is the prevailing cosmological theory describing the origin and evolution of our universe. Religious acceptance of the concept varies between religions and denominations.

"The Big Bang, which today we hold to be the origin of the world, does not contradict the intervention of the divine creator but, rather, requires it."
— Pope Francis, head of the Catholic church

"... some theologians, at least, should be sufficiently well-versed in the sciences to make authentic and creative use of the resources that the best-established theories may offer them. Such an expertise would prevent them from making uncritical and overhasty use for apologetic purposes of such recent theories as that of the “Big Bang” in cosmology."
— John Paul II

[Petros Agapetos]

The Big Bang theory states that around 13.7 billion years ago the universe was condensed into an incredibly small, hot, dense "ball" of space and time. Some have speculated that it emerged from an infinitely dense and small object known as a singularity but most scientists prefer other hypotheses.

Physical cosmology
The name "Big Bang" is somewhat of a misnomer, since the universe did not expand in a conventional sense and didn't explode or produce sound as we normally understand it. The first fraction of a second saw significant changes in the way forces, matter and energy existed and was very unlike the universe as we currently observe it. The universe expanded very rapidly by a process called "inflation". As the expansion continued, the universe cooled, eventually reaching a point at which long lived particles of matter could "freeze out" of a mixture of mass and energy which was previously in continual flux and collide with each other to form the first simple atoms. Over billions of years, these particles combined to form "clouds" of matter which further condensed, because of gravitational attraction, into stars and planets. Atoms progressively formed "heavier" elements in stars through the process of nuclear fusion.

The history of the universe can be described in some detail back to the instant approximately 10^-43 seconds after the big bang. What precisely occurred in the first 10^-43 seconds (the Planck epoch) is current unknown with many competing theories, due to interactions between the theories of gravitation and quantum mechanics.

[Dick]