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Universe

For other uses, see Universe (disambiguation).

Universe
The Hubble Ultra-Deep Field image shows some of the most remote galaxies visible to present technology (diagonal is ~1/10 apparent Moon diameter)[1]
Age (within ΛCDM model)13.787 ± 0.020 billion years[2]
DiameterUnknown.[3]
Observable universe: 8.8×1026 m (28.5 Gpc or 93 Gly)[4]
Mass (ordinary matter)At least 1053 kg[5]
Average density (with energy)9.9×10−27 kg/m3[6]
Average temperature2.72548 K
(−270.4 °C, −454.8 °F)[7]
Main contentsOrdinary (baryonic) matter (4.9%)
Dark matter (26.8%)
Dark energy (68.3%)[8]
ShapeFlat with 0.4% error margin[9]

The universe is all of space and time[a] and their contents.[10] It comprises all of existence, any fundamental interaction, physical process and physical constant, and therefore all forms of matter and energy, and the structures they form, from sub-atomic particles to entire galactic filaments. Since the early 20th century, the field of cosmology establishes that space and time emerged together at the Big Bang 13.787±0.020 billion years ago[11] and that the universe subsequently expanded. Today, the universe has expanded into an age and size that is only partially observable from Earth; while the spatial size of the entire universe is unknown, the smaller observable universe is approximately 93 billion light-years in diameter at present.[3]

Some of the earliest cosmological models of the universe were developed by ancient Greek and Indian philosophers and were geocentric, placing Earth at the center.[12][13] Over the centuries, more precise astronomical observations led Nicolaus Copernicus to develop the heliocentric model with the Sun at the center of the Solar System. In developing the law of universal gravitation, Isaac Newton built upon Copernicus's work as well as Johannes Kepler's laws of planetary motion and observations by Tycho Brahe.

Further observational improvements led to the realization that the Sun is one of a few hundred billion stars in the Milky Way, which is one of a few hundred billion galaxies in the observable universe. Many of the stars in a galaxy have planets. At the largest scale, galaxies are distributed uniformly and the same in all directions, meaning that the universe has neither an edge nor a center. At smaller scales, galaxies are distributed in clusters and superclusters which form immense filaments and voids in space, creating a vast foam-like structure.[14] Discoveries in the early 20th century have suggested that the universe had a beginning and has been expanding since then.[15]

According to the Big Bang theory, the energy and matter initially present have become less dense as the universe expanded. After an initial accelerated expansion called the inflationary epoch at around 10−32 seconds, and the separation of the four known fundamental forces, the universe gradually cooled and continued to expand, allowing the first subatomic particles and simple atoms to form. Giant clouds of hydrogen and helium were gradually drawn to the places where matter was most dense, forming the first galaxies, stars, and everything else seen today.

From studying the effects of gravity on both matter and light, it has been discovered that the universe contains much more matter than is accounted for by visible objects; stars, galaxies, nebulas and interstellar gas. This unseen matter is known as dark matter.[16] In the widely accepted ΛCDM cosmological model, dark matter accounts for about 25.8%±1.1% of the mass and energy in the universe while about 69.2%±1.2% is dark energy, a mysterious form of energy responsible for the acceleration of the expansion of the universe.[17] Ordinary ('baryonic') matter therefore composes only 4.84%±0.1% of the universe.[17] Stars, planets, and visible gas clouds only form about 6% of this ordinary matter.[18]

There are many competing hypotheses about the ultimate fate of the universe and about what, if anything, preceded the Big Bang, while other physicists and philosophers refuse to speculate, doubting that information about prior states will ever be accessible. Some physicists have suggested various multiverse hypotheses, in which the universe might be one among many.[3][19][20]

Part of a series on
Physical cosmology
Full-sky image derived from nine years' WMAP data
Early universe
Backgrounds
Expansion · Future
Components · Structure
Components
Structure
Experiments
Scientists
Subject history
  1. ^ "Hubble sees galaxies galore". spacetelescope.org. Archived from the original on May 4, 2017. Retrieved April 30, 2017.
  2. ^ Cite error: The named reference Planck 2015 was invoked but never defined (see the help page).
  3. ^ a b c Greene, Brian (2011). The Hidden Reality. Alfred A. Knopf.
  4. ^ Bars, Itzhak; Terning, John (2009). Extra Dimensions in Space and Time. Springer. pp. 27–. ISBN 978-0-387-77637-8. Retrieved May 1, 2011.
  5. ^ Davies, Paul (2006). The Goldilocks Enigma. First Mariner Books. pp. 43ff. ISBN 978-0-618-59226-5.
  6. ^ NASA/WMAP Science Team (January 24, 2014). "Universe 101: What is the Universe Made Of?". NASA. Archived from the original on March 10, 2008. Retrieved February 17, 2015.
  7. ^ Fixsen, D.J. (2009). "The Temperature of the Cosmic Microwave Background". The Astrophysical Journal. 707 (2): 916–920. arXiv:0911.1955. Bibcode:2009ApJ...707..916F. doi:10.1088/0004-637X/707/2/916. ISSN 0004-637X. S2CID 119217397.
  8. ^ Cite error: The named reference planck2013parameters was invoked but never defined (see the help page).
  9. ^ NASA/WMAP Science Team (January 24, 2014). "Universe 101: Will the Universe expand forever?". NASA. Archived from the original on March 9, 2008. Retrieved April 16, 2015.
  10. ^ Zeilik, Michael; Gregory, Stephen A. (1998). Introductory Astronomy & Astrophysics (4th ed.). Saunders College. ISBN 978-0-03-006228-5. The totality of all space and time; all that is, has been, and will be.
  11. ^ Planck Collaboration; Aghanim, N.; Akrami, Y.; Ashdown, M.; Aumont, J.; Baccigalupi, C.; Ballardini, M.; Banday, A. J.; Barreiro, R. B.; Bartolo, N.; Basak, S. (September 2020). "Planck 2018 results: VI. Cosmological parameters". Astronomy & Astrophysics. 641: A6. arXiv:1807.06209. Bibcode:2020A&A...641A...6P. doi:10.1051/0004-6361/201833910. ISSN 0004-6361. S2CID 119335614.
  12. ^ Dold-Samplonius, Yvonne (2002). From China to Paris: 2000 Years Transmission of Mathematical Ideas. Franz Steiner Verlag.
  13. ^ Glick, Thomas F.; Livesey, Steven; Wallis, Faith (2005). Medieval Science Technology and Medicine: An Encyclopedia. Routledge. ISBN 978-0-415-96930-7.
  14. ^ Carroll, Bradley W.; Ostlie, Dale A. (2013). An Introduction to Modern Astrophysics (International ed.). Pearson. pp. 1173–1174. ISBN 978-1-292-02293-2. Retrieved May 16, 2018.
  15. ^ Hawking, Stephen (1988). A Brief History of Time. Bantam. p. 43. ISBN 978-0-553-05340-1.
  16. ^ Redd, Nola. "What is Dark Matter?". Space.com. Archived from the original on February 1, 2018. Retrieved February 1, 2018.
  17. ^ a b "Planck 2015 results, table 9". Archived from the original on July 27, 2018. Retrieved May 16, 2018.
  18. ^ Persic, Massimo; Salucci, Paolo (September 1, 1992). "The baryon content of the Universe". Monthly Notices of the Royal Astronomical Society. 258 (1): 14P–18P. arXiv:astro-ph/0502178. Bibcode:1992MNRAS.258P..14P. doi:10.1093/mnras/258.1.14P. ISSN 0035-8711. S2CID 17945298.
  19. ^ Cite error: The named reference EllisKS032 was invoked but never defined (see the help page).
  20. ^ "'Multiverse' theory suggested by microwave background". BBC News. August 3, 2011. Archived from the original on February 14, 2023. Retrieved February 14, 2023.


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