The Big Bang theory is the prevailing cosmological model for the universe from the earliest known periods through its subsequent large-scale evolution. The model describes how the universe expanded from a very high-density and high-temperature state, and offers a comprehensive explanation for a broad range of phenomena, including the abundance of light elements, the cosmic microwave background (CMB), large scale structure and Hubble’s law. If the known laws of physics are extrapolated to the highest density regime, the result is a singularity which is typically associated with the Big Bang. Physicists are undecided whether this means the universe began from a singularity, or that current knowledge is insufficient to describe the universe at that time. Detailed measurements of the expansion rate of the universe place the Big Bang at around 13.8 billion years ago, which is thus considered the age of the universe. After the initial expansion, the universe cooled sufficiently to allow the formation of subatomic particles, and later simple atoms. Giant clouds of these primordial elements later coalesced through gravity in halos of dark matter, eventually forming the stars and galaxies visible today.
1° Planck epoch <10−43 seconds
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.
2° 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.
3° 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.
4° 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.
5°
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.
6°
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.
7° Photon epoch (Matter era )
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.
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.
3 minutes: Primordial nucleosynthesis: nuclear fusion begins as lithium and heavy hydrogen (deuterium) and helium nuclei form from protons and neutrons.
20 minutes: Nuclear fusion ceases: normal matter consists of 75% hydrogen and 25% helium – free electrons begin scattering light.
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.
8° Cosmic Dark Age
370,000 years
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 microwavebackground (CMB) radiation.
10 million years: With a trace of heavy elements in the Universe, the chemistry that later sparked life begins operating.
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.
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.
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.
7.8 billion years: Acceleration: dark-energy dominated era begins, following the matter-dominated era in during which cosmic expansion was slowing down
Formation of the solar system
9.2 billion years: Primal supernova, possibly triggers the formation of the Solar System.
9.2318 billion years: Sun forms – Planetary nebula begins accretion of planets.
9.23283 billion years: Four Jovian planets (Jupiter, Saturn, Uranus, Neptune ) evolve around the sun.
9.257 billion years: Solar System of Eight planets, four terrestrial (Mercury (planet), Venus, Earth, Mars) evolve around the sun.
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