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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. | |
| Diameter | 8.8×1026 m or 880 Ym (28.5 Gpc or 93 Gly)[1] |
|---|---|
| Circumference | 2.764×1027 m or 2.764 Rm (89.6 Gpc or 292.2 Gly) |
| Volume | 3.566×1080 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] |
| Age | 13.787±0.020 billion years[4] |
| Average temperature | 2.72548±0.00057 K[5] |
| Contents |
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The observable universe is a spherical region of the universe consisting of all matter that can be observed from Earth; the electromagnetic radiation from these objects has had time to reach the Solar System and Earth since the beginning of the cosmological expansion. 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),[7] about 2% larger. The radius of the observable universe is therefore estimated to be about 46.5 billion light-years.[8][9] 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.[10] In November 2018, astronomers reported that extragalactic background light (EBL) amounted to 4×1084 photons.[11][12]
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 gigaparsecs (62 Gly)) will never reach Earth.[13]
- ^ Itzhak Bars; John Terning (2009). Extra Dimensions in Space and Time. Springer. pp. 27–. ISBN 978-0387776378. Retrieved 2011-05-01.
- ^ "volume universe Wolfram|Alpha". www.wolframalpha.com.
- ^ "What is the Universe Made Of?". NASA. Retrieved June 1, 2022.
- ^ 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.
- ^ 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.
- ^ "Planck cosmic recipe".
- ^ 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.
- ^ "Frequently Asked Questions in Cosmology". astro.ucla.edu. Retrieved 2023-09-15.
- ^ 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.
- ^ See the "Mass of ordinary matter" section in this article.
- ^ Overbye, Dennis (3 December 2018). "All the Light There Is to See? 4 x 1084 Photons". The New York Times. Retrieved 4 December 2018.
- ^ 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.
- ^ 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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