Chronology of the universe

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Diagram of Evolution of the universe from the Big Bang (left) - to the present.
External Timeline A graphical timeline is available at
Graphical timeline of the Big Bang

This chronology of the universe describes the history and future of the universe according to Big Bang cosmology, the prevailing scientific model of how the universe developed over time from the Planck epoch, using the cosmological time parameter of comoving coordinates. The instant in which the universe is thought to have begun rapidly expanding from a singularity is known as the Big Bang. As of 2013, this expansion is estimated to have begun 13.798 ± 0.037 billion years ago.[1] It is convenient to divide the evolution of the universe so far into three phases.



History of the Universe - gravitational waves are hypothesized to arise from cosmic inflation, a faster-than-light expansion just after the Big Bang (17 March 2014).[2][3][4]

In the second phase, this quark–gluon plasma universe then cooled further, the current fundamental forces we know take their present forms through further symmetry breaking – notably the breaking of electroweak symmetry – and the full range of complex and composite particles we see around us today became possible, leading to a gravitationally dominated universe, the first neutral atoms (~ 80% hydrogen), and the cosmic microwave background radiation we can detect today. Modern high energy particle physics theories are satisfactory at these energy levels, and so physicists believe they have a good understanding of this and subsequent development of the fundamental universe around us. Because of these changes, space had also become largely transparent to light and other electromagnetic energy, rather than "foggy", by the end of this phase.

The third phase started after a short dark age with a universe whose fundamental particles and forces were as we know them, and witnessed the emergence of large scale stable structures, such as the earliest stars, quasars, galaxies, clusters of galaxies and superclusters, and the development of these to create the kind of universe we see today. Some researchers call the development of all this physical structure over billions of years "cosmic evolution". Other, more interdisciplinary, researchers refer to "cosmic evolution" as the entire scenario of growing complexity from big bang to humankind, thereby incorporating biology and culture into a grand unified view of all complex systems in the universe to date.[5]

Beyond the present day, scientists anticipate that the Earth will cease to be able to support life in about a billion years, and will be drawn into the Sun in about 5 billion years. On a far longer timescale, 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. If particles such as protons are unstable then eventually matter may evaporate into low level energy in a kind of entropy related heat death. Alternatively the universe may collapse in a big crunch, although current data shows the rate of expansion is still increasing. If this is correct then it may end in a "big freeze" as matter and energy become very thinly spread and cool down. Alternative suggestions include a false vacuum catastrophe or a Big Rip as possible ends to the universe.

Very early universe[edit]

All ideas concerning the very early universe (cosmogony) are speculative. No accelerator experiments have yet probed energies of sufficient magnitude to provide any experimental insight into the behavior of matter at the energy levels that prevailed during this period. Proposed scenarios differ radically. Some examples are the Hartle–Hawking initial state, string landscape, brane inflation, string gas cosmology, and the ekpyrotic universe. Some of these are mutually compatible, while others are not.

Planck epoch[edit]

0 to 10–43 second after the Big Bang
Main article: Planck epoch



Grand unification epoch[edit]

Between 10–43 second and 10–36 second after the Big Bang[6]


Electroweak epoch[edit]

Between 10–36 second (or the end of inflation) and 10–32 second after the Big Bang[6]
Main article: Electroweak epoch

According to traditional big bang cosmology, the Electroweak epoch began 10−36 second after the Big Bang, when the temperature of the universe was low enough (1028 K) to separate the strong force from the electroweak force (the name for the unified forces of electromagnetism and the weak interaction). In inflationary cosmology, the electroweak epoch ends when the inflationary epoch begins, at roughly 10−32 second.

Inflationary epoch[edit]

Unknown duration, ending 10–32(?) second after the Big Bang
Main article: Inflationary epoch




On March 17, 2014, astrophysicists of the BICEP2 collaboration announced the detection of inflationary gravitational waves in the B-mode power spectrum, which if confirmed, would provide clear experimental evidence for the theory of inflation.[2][3][4][7][8][9] However, on June 19, 2014, lowered confidence in confirming the cosmic inflation findings was reported.[8][10][11]


Main article: Baryogenesis


Early universe[edit]

Cosmic History


Supersymmetry breaking (speculative)[edit]


Electroweak symmetry breaking and the quark epoch[edit]

Between 10–12 second and 10–6 second after the Big Bang




Hadron epoch[edit]

Between 10–6 second and 1 second after the Big Bang
Main article: Hadron epoch


Lepton epoch[edit]

Between 1 second and 10 seconds after the Big Bang
Main article: Lepton epoch


Photon epoch[edit]

Between 10 seconds and 380,000 years after the Big Bang
Main article: Photon epoch



Between 3 minutes and 20 minutes after the Big Bang[13]


Matter domination[edit]

70,000 years after the Big Bang




ca. 377,000 years after the Big Bang
9 year WMAP data (2012) shows the cosmic microwave background radiation variations throughout the Universe from our perspective, though the actual variations are much smoother than the diagram suggests.[14][15]


The photons present at the time of decoupling are the same photons that we see in the cosmic microwave background (CMB) radiation, after being greatly cooled by the expansion of the Universe. Around the same time, existing pressure waves within the electron-baryon plasma — known as baryon acoustic oscillations — became embedded in the distribution of matter as it condensed, giving rise to a very slight preference in distribution of large scale objects. Therefore the cosmic microwave background is a picture of the universe at the end of this epoch including the tiny fluctuations generated during inflation (see diagram), and the spread of objects such as galaxies in the universe is an indication of the scale and size of the universe as it developed over time.[18]

Habitable epoch[edit]

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.[19][20][21]

Dark Ages[edit]

See also: Hydrogen line


Structure formation[edit]

Another Hubble image shows an infant galaxy forming nearby, which means this happened very recently on the cosmological timescale. This shows that new galaxy formation in the Universe is still occurring.



150 million to 1 billion years after the Big Bang


Formation of stars[edit]

See also: Star formation


Formation of galaxies[edit]


Johannes Schedler's project has identified a quasar CFHQS 1641+3755 at 12.7 billion light-years away,[24] when the Universe was just 7% of its present age.

On July 11, 2007, using the 10-metre Keck II telescope on Mauna Kea, Richard Ellis of the California Institute of Technology at Pasadena and his team found six star forming galaxies about 13.2 billion light years away and therefore created when the universe was only 500 million years old.[25] Only about 10 of these extremely early objects are currently known.[26] More recent observations have shown these ages to be shorter than previously indicated. The most distant galaxy observed as of October 2013 has been reported to be 13.1 billion light years away.[27]

The Hubble Ultra Deep Field shows a number of small galaxies merging to form larger ones, at 13 billion light years, when the Universe was only 5% its current age.[28] This age estimate is now believed to be slightly shorter (see Reference quoted at the end of the previous paragraph).


Formation of groups, clusters and superclusters[edit]


Formation of the Solar System[edit]

9 billion years after the Big Bang



13.8 billion years after the Big Bang

The Big Bang is estimated to have occurred about 13.8 billion years ago.[30] Since the expansion of the universe appears to be accelerating, its large-scale structure is likely to be the largest structure that will ever form in the universe. The present accelerated expansion prevents any more inflationary structures entering the horizon and prevents new gravitationally bound structures from forming.

Ultimate fate of the universe[edit]

As with interpretations of what happened in the very early universe, advances in fundamental physics are required before it will be possible to know the ultimate fate of the universe with any certainty. Below are some of the main possibilities.

Fate of the Solar System: 1 to 5 billion years[edit]

Relative size of our Sun as it is now (inset) compared to its estimated future size as a red giant

Over a timescale of a billion years or more, the Earth and Solar System are unstable. Earth's existing biosphere is expected to vanish in about a billion years, as the Sun's heat production gradually increases to the point that liquid water and life are unlikely;[31] the Earth's magnetic fields, axial tilt and atmosphere are subject to long term change; and the Solar System itself is chaotic over million- and billion-year timescales;[32] Eventually in around 5.4 billion years from now, the core of the Sun will become hot enough to trigger hydrogen fusion in its surrounding shell.[31] This will cause the outer layers of the star to expand greatly, and the star will enter a phase of its life in which it is called a red giant.[33][34] Within 7.5 billion years, the Sun will have expanded to a radius of 1.2 AU—256 times its current size, and studies announced in 2008 show that due to tidal interaction between Sun and Earth, Earth would actually fall back into a lower orbit, and get engulfed and incorporated inside the Sun before the Sun reaches its largest size, despite the Sun losing about 38% of its mass.[35] The Sun itself will continue to exist for many billions of years, passing through a number of phases, and eventually ending up as a long-lived white dwarf. Eventually, after billions more years, the Sun will finally cease to shine altogether, becoming a black dwarf.[36]

Big Rip: ≥20 billion years from now[edit]

See also: Big Rip

This scenario is possible only if the energy density of dark energy actually increases without limit over time.[citation needed] Such dark energy is called phantom energy and is unlike any known kind of energy. In this case, the expansion rate of the universe will increase without limit. Gravitationally bound systems, such as clusters of galaxies, galaxies, and ultimately the Solar System will be torn apart. Eventually the expansion will be so rapid as to overcome the electromagnetic forces holding molecules and atoms together. Finally even atomic nuclei will be torn apart and the universe as we know it will end in an unusual kind of gravitational singularity. At the time of this singularity, the expansion rate of the universe will reach infinity, so that any and all forces (no matter how strong) that hold composite objects together (no matter how closely) will be overcome by this expansion, literally tearing everything apart.

Big Crunch: ≥102 billion years from now[edit]

See also: Big Crunch

If the energy density of dark energy were negative or the universe were closed, then it would be possible that the expansion of the universe would reverse and the universe would contract towards a hot, dense state. This is a required element of oscillatory universe scenarios, such as the cyclic model, although a Big Crunch does not necessarily imply an oscillatory Universe. Current observations suggest that this model of the universe is unlikely to be correct, and the expansion will continue or even accelerate.

Big Freeze: ≥105 billion years from now[edit]

This scenario is generally considered to be the most likely,[citation needed] as it occurs if the universe continues expanding as it has been. Over a time scale on the order of 1014 years or less, existing stars burn out, stars cease to be created, and the universe goes dark.[37], §IID. Over a much longer time scale in the eras following this, the galaxy evaporates as the stellar remnants comprising it escape into space, and black holes evaporate via Hawking radiation.[37], §III, §IVG. In some grand unified theories, proton decay after at least 1034 years will convert the remaining interstellar gas and stellar remnants into leptons (such as positrons and electrons) and photons. Some positrons and electrons will then recombine into photons.[37], §IV, §VF. In this case, the universe has reached a high-entropy state consisting of a bath of particles and low-energy radiation. It is not known however whether it eventually achieves thermodynamic equilibrium.[37], §VIB, VID.

Heat Death: 101000 years from now[edit]

The heat death is a possible final state of the universe, estimated at after 101000 years, in which it has "run down" to a state of no thermodynamic free energy to sustain motion or life. In physical terms, it has reached maximum entropy (because of this, the term "entropy" has often been confused with Heat Death, to the point of entropy being labelled as the "force killing the universe"). The hypothesis of a universal heat death stems from the 1850s ideas of William Thomson (Lord Kelvin)[38] who extrapolated the theory of heat views of mechanical energy loss in nature, as embodied in the first two laws of thermodynamics, to universal operation.

Vacuum metastability event[edit]

See also: False vacuum

If our universe is in a very long-lived false vacuum, it is possible that a small region of the universe will tunnel into a lower energy state (see Bubble nucleation). If this happens, all structures within will be destroyed instantaneously and the region will expand at near light speed, bringing destruction without any forewarning.

See also[edit]


  5. ^ Chaisson, E., (2001). Cosmic Evolution: The Rise of Complexity in Nature, Harvard University Press, ISBN 0-674-00987-8; see also Cosmic Evolution
  8. ^ a b Ade, P.A.R. et al. (BICEP2 Collaboration) (June 19, 2014). "Detection of B-Mode Polarization at Degree Angular Scales by BICEP2" (PDF). Physical Review Letters 112: 241101. arXiv:1403.3985. Bibcode:2014PhRvL.112x1101A. doi:10.1103/PhysRevLett.112.241101. Retrieved June 20, 2014. 
  9. ^
  12. ^ The Timescale of Creation
  13. ^ Detailed timeline of Big Bang nucleosynthesis processes
  23. ^ Ferreting Out The First Stars;
  24. ^ APOD: 2007 September 6 - Time Tunnel
  25. ^ "New Scientist" 14 July 2007
  26. ^ HET Helps Astronomers Learn Secrets of One of Universe's Most Distant Objects
  27. ^ Scientists confirm most distant galaxy ever
  28. ^ APOD: 2004 March 9 – The Hubble Ultra Deep Field
  33. ^ Zeilik & Gregory 1998, p. 320–321.

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