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Observable universe

Observable universe
Visualization of the observable universe. The scale is such that the fine grains represent collections of large numbers of superclusters. The Virgo Supercluster—home of Milky Way—is marked at the center, but is too small to be seen.
Diameter8.8×1026 m or 880 Ym (28.5 Gpc or 93 Gly)[1]
Volume3.566×1080 m3[2]
Mass (ordinary matter)1.5×1053 kg[note 1]
Density (of total energy)9.9×10−27 kg/m3 (equivalent to 6 protons per cubic meter of space)[3]
Age13.787±0.020 billion years[4]
Average temperature2.72548±0.00057 K[5]
Contents

The observable universe is a ball-shaped region of the universe consisting of all matter that can be observed from Earth or its space-based telescopes and exploratory probes at the present time; the electromagnetic radiation from these objects has had time to reach the Solar System and Earth since the beginning of the cosmological expansion. Initially, it was estimated that there may be 2 trillion galaxies in the observable universe.[7][8] That number was reduced in 2021 to only several hundred billion based on data from New Horizons.[9][10][11] Assuming the universe is isotropic, the distance to the edge of the observable universe is roughly the same in every direction. That is, the observable universe is a spherical region centered on the observer. Every location in the universe has its own observable universe, which may or may not overlap with the one centered on Earth.

The word observable in this sense does not refer to the capability of modern technology to detect light or other information from an object, or whether there is anything to be detected. It refers to the physical limit created by the speed of light itself. No signal can travel faster than light. Hence there is a maximum distance, called the particle horizon, beyond which nothing can be detected, as the signals could not have reached us yet. Sometimes astrophysicists distinguish between the observable universe and the visible universe. The former includes signals since the end of the inflationary epoch, while the latter includes only signals emitted since recombination.[note 2]

According to calculations, the current comoving distance to particles from which the cosmic microwave background radiation (CMBR) was emitted, which represents the radius of the visible universe, is about 14.0 billion parsecs (about 45.7 billion light-years). The comoving distance to the edge of the observable universe is about 14.3 billion parsecs (about 46.6 billion light-years),[12] about 2% larger. The radius of the observable universe is therefore estimated to be about 46.5 billion light-years.[13][14] Using the critical density and the diameter of the observable universe, the total mass of ordinary matter in the universe can be calculated to be about 1.5×1053 kg.[15] In November 2018, astronomers reported that extragalactic background light (EBL) amounted to 4×1084 photons.[16][17]

As the universe's expansion is accelerating, all currently observable objects, outside the local supercluster, will eventually appear to freeze in time, while emitting progressively redder and fainter light. For instance, objects with the current redshift z from 5 to 10 will only be observable up to an age of 4–6 billion years. In addition, light emitted by objects currently situated beyond a certain comoving distance (currently about 19 billion parsecs) will never reach Earth.[18]

  1. ^ Itzhak Bars; John Terning (2009). Extra Dimensions in Space and Time. Springer. pp. 27–. ISBN 978-0387776378. Retrieved 2011-05-01.
  2. ^ "volume universe Wolfram|Alpha". www.wolframalpha.com.
  3. ^ "What is the Universe Made Of?". NASA. Retrieved June 1, 2022.
  4. ^ Planck Collaboration (2020). "Planck 2018 results. VI. Cosmological parameters". Astronomy & Astrophysics. 641. page A6 (see PDF page 15, Table 2: "Age/Gyr", last column). arXiv:1807.06209. Bibcode:2020A&A...641A...6P. doi:10.1051/0004-6361/201833910. S2CID 119335614.
  5. ^ Fixsen, D. J. (30 November 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. S2CID 119217397.
  6. ^ "Planck cosmic recipe".
  7. ^ Conselice, Christopher J.; et al. (2016). "The Evolution of Galaxy Number Density at z < 8 and Its Implications". The Astrophysical Journal. 830 (2): 83. arXiv:1607.03909v2. Bibcode:2016ApJ...830...83C. doi:10.3847/0004-637X/830/2/83. S2CID 17424588.
  8. ^ Fountain, Henry (17 October 2016). "Two Trillion Galaxies, at the Very Least". New York Times. Retrieved 17 October 2016.
  9. ^ Lauer, T. R.; Postman, M.; Spencer, J. R.; Weaver, H. A.; Stern, S. A.; Gladstone, G. R.; Binzel, R. P.; Britt, D. T.; Buie, M. W.; Buratti, B. J.; Cheng, A. F.; Grundy, W. M.; Horányi, M.; Kavelaars, J. J.; Linscott, I. R.; Lisse, C. M.; McKinnon, W. B.; McNutt, R. L.; Moore, J. M.; Núñez, J. I.; Olkin, C. B.; Parker, J. W.; Porter, S. B.; Reuter, D. C.; Robbins, S. J.; Schenk, P. M.; Showalter, M. R.; Singer, K. N.; Verbiscer, A. J.; Young, L. A. (2022). "Anomalous Flux in the Cosmic Optical Background Detected with New Horizons Observations". The Astrophysical Journal Letters. 927 (1): l8. arXiv:2202.04273. Bibcode:2022ApJ...927L...8L. doi:10.3847/2041-8213/ac573d.
  10. ^ Lauer, Todd (12 January 2021). "NOIRLab Scientist Finds the Universe to be Brighter than Expected". NOIRLab. Retrieved 12 January 2021.
  11. ^ Lauer, Tod R.; Postman, Marc; Weaver, Harold A.; Spencer, John R.; Stern, S. Alan; Buie, Marc W.; Durda, Daniel D.; Lisse, Carey M.; Poppe, A. R.; Binzel, Richard P.; Britt, Daniel T.; Buratti, Bonnie J.; Cheng, Andrew F.; Grundy, W. M.; Horányi, Mihaly; Kavelaars, J. J.; Linscott, Ivan R.; McKinnon, William B.; Moore, Jeffrey M.; Núñez, J. I.; Olkin, Catherine B.; Parker, Joel W.; Porter, Simon B.; Reuter, Dennis C.; Robbins, Stuart J.; Schenk, Paul; Showalter, Mark R.; Singer, Kelsi N.; Verbiscer, Anne J.; Young, Leslie A. (11 January 2021). "New Horizons Observations of the Cosmic Optical Background". The Astrophysical Journal. 906 (2): 77. arXiv:2011.03052. Bibcode:2021ApJ...906...77L. doi:10.3847/1538-4357/abc881. hdl:1721.1/133770. S2CID 226277978.
  12. ^ Gott III, J. Richard; Mario Jurić; David Schlegel; Fiona Hoyle; et al. (2005). "A Map of the Universe" (PDF). The Astrophysical Journal. 624 (2): 463–484. arXiv:astro-ph/0310571. Bibcode:2005ApJ...624..463G. doi:10.1086/428890. S2CID 9654355.
  13. ^ "Frequently Asked Questions in Cosmology". astro.ucla.edu. Retrieved 2023-09-15.
  14. ^ Lineweaver, Charles; Davis, Tamara M. (2005). "Misconceptions about the Big Bang". Scientific American. 292 (3): 36–45. Bibcode:2005SciAm.292c..36L. doi:10.1038/scientificamerican0305-36.
  15. ^ See the "Mass of ordinary matter" section in this article.
  16. ^ Overbye, Dennis (3 December 2018). "All the Light There Is to See? 4 x 1084 Photons". The New York Times. Retrieved 4 December 2018.
  17. ^ The Fermi-LAT Collaboration (30 November 2018). "A gamma-ray determination of the Universe's star formation history". Science. 362 (6418): 1031–1034. arXiv:1812.01031. Bibcode:2018Sci...362.1031F. doi:10.1126/science.aat8123. PMID 30498122.
  18. ^ Loeb, Abraham (2002). "Long-term future of extragalactic astronomy". Physical Review D. 65 (4): 047301. arXiv:astro-ph/0107568. Bibcode:2002PhRvD..65d7301L. doi:10.1103/PhysRevD.65.047301. S2CID 1791226.


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