Editing Observable universe (section)

{{Short description|All of space observable from the Earth at the present}}
{{Infobox
| bodystyle        = width:25em;
| title            = Observable universe
| image            = [[File:Observable Universe with Measurements 01.png|300px]]
| caption          = 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.
| label1           = Diameter
| data1            = {{val|8.8|e=26|u=m}} or 880 [[Yotta-|Ym]] {{nowrap|(28.5 [[parsec|Gpc]] or 93 [[light-year|Gly]])}}<ref>{{cite book|author1=Itzhak Bars|author2=John Terning|title=Extra Dimensions in Space and Time|url=https://books.google.com/books?id=fFSMatekilIC&pg=PA27|access-date=2011-05-01|year= 2009|publisher=Springer|isbn=978-0387776378|pages=27–}}</ref>
| label2           = Circumference
| data2            = {{val| 2.764|e=27|u=m}} or 2.764 [[Ronna-|Rm]] {{nowrap|(89.6 [[parsec|Gpc]] or 292.2 [[light-year|Gly]])}}
| label3           = Volume
| data3            = {{val|3.566|e=80|u=m3}}<ref>{{Cite web|url=https://www.wolframalpha.com/|title=volume universe Wolfram{{pipe}}Alpha|website=www.wolframalpha.com}}</ref>
| label4           = Mass (ordinary matter)
| data4            = {{val|1.5|e=53|u=kg}}<ref group=note>Multiply percentage of ordinary matter given by Planck below, with total energy density given by WMAP below</ref>
| label5           = Density (of total energy)
| data5            = {{val|9.9|e=-27|u=kg/m3}} (equivalent to 6 [[proton]]s per cubic meter of space)<ref>{{cite web |url=http://map.gsfc.nasa.gov/universe/uni_matter.html |title=What is the Universe Made Of? |publisher=NASA |access-date=June 1, 2022}}</ref>
| label6           = Age
| data6            = {{val|13.787|0.020|ul=billion}} years<ref name="Planck 2018">
 {{cite journal
 |author=Planck Collaboration
 |year=2020
 |title=Planck 2018 results. VI.&nbsp;Cosmological parameters
 |journal=Astronomy & Astrophysics
 |volume=641 |at=page&nbsp;A6 (see PDF page&nbsp;15, Table&nbsp;2: "Age/Gyr", last&nbsp;column)
 |doi=10.1051/0004-6361/201833910
 |arxiv=1807.06209 |bibcode=2020A&A...641A...6P
 |s2cid=119335614
 }}</ref>
| label7           = Average temperature
| data7            = {{val|2.72548|0.00057}} [[Kelvin|K]]<ref>
 {{Cite journal
 | last1 = Fixsen
 | first1 = D. J.
 | title = The Temperature of the Cosmic Microwave Background
 | journal = The Astrophysical Journal
 | volume = 707
 | issue = 2
 | pages = 916–920
 | date = 30 November 2009
 | doi = 10.1088/0004-637X/707/2/916
 | bibcode = 2009ApJ...707..916F
 | arxiv = 0911.1955
 | s2cid = 119217397
 }}</ref>
| label8           = Contents
| data8            = {{plainlist|
* [[Baryon#Baryonic matter|Ordinary (baryonic)]] [[matter]] (4.9%)
* [[Dark matter]] (26.8%)
* [[Dark energy]] (68.3%)<ref>{{Cite web | url=https://www.esa.int/spaceinimages/Images/2013/03/Planck_cosmic_recipe | title=Planck cosmic recipe}}</ref>}}
}}

The '''observable universe''' is a [[Ball (mathematics)|spherical]] region of the [[universe]] consisting of all [[matter]] that can be [[observation|observed]] from [[Earth]]; the [[electromagnetic radiation]] from these [[astronomical object|objects]] has had time to reach the [[Solar System]] and Earth since the beginning of the [[metric expansion of space|cosmological expansion]].  Assuming the universe is [[isotropy|isotropic]], the distance to the edge of the observable universe is [[equidistant|the same]] in every direction. That is, the observable universe is a [[sphere|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 the observer yet.

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 [[parsec]]s (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),<ref name="mapofuniverse">{{cite journal|last = Gott III|first = J. Richard|display-authors=4|author2=Mario Jurić |author3=David Schlegel |author4=Fiona Hoyle |author5=Michael Vogeley |author6=Max Tegmark |author7=Neta Bahcall |author8=Jon Brinkmann |title = A Map of the Universe|url=http://www.astro.princeton.edu/universe/ms.pdf|journal = The Astrophysical Journal|volume = 624|issue = 2|pages = 463–484|date = 2005|doi = 10.1086/428890|bibcode=2005ApJ...624..463G| arxiv=astro-ph/0310571|s2cid = 9654355}}</ref> about 2% larger. The [[radius]] of the observable universe is therefore estimated to be about 46.5 billion light-years.<ref>{{Cite web |title=Frequently Asked Questions in Cosmology |url=https://astro.ucla.edu/~wright/cosmology_faq.html |access-date=2023-09-15 |website=astro.ucla.edu}}</ref><ref name="ly93">{{cite journal |last1=Lineweaver |first1=Charles |last2=Davis |first2=Tamara M. |date=2005 |title=Misconceptions about the Big Bang |journal=Scientific American |volume=292 |issue=3 |pages=36–45 |bibcode=2005SciAm.292c..36L |doi=10.1038/scientificamerican0305-36}}</ref> Using the [[Friedmann equations|critical density]] and the diameter of the observable universe, the total mass of ordinary matter in the universe can be calculated to be about {{val|1.5|e=53|u=kg}}.<ref>See the "Mass of ordinary matter" section in this article.</ref> In November 2018, astronomers reported that [[extragalactic background light]] (EBL) amounted to {{val|4|e=84}} photons.<ref name="NYT-20181203">{{cite news |last=Overbye |first=Dennis |author-link=Dennis Overbye |title=All the Light There Is to See? 4 x 10<sup>84</sup> Photons |url=https://www.nytimes.com/2018/12/03/science/space-stars-photons-light.html |date=3 December 2018 |work=[[The New York Times]] |access-date=4 December 2018 }}</ref><ref name="SCI-20181130">{{cite journal |author=The Fermi-LAT Collaboration |title=A gamma-ray determination of the Universe's star formation history |date=30 November 2018 |journal=[[Science (journal)|Science]] |volume=362 |issue=6418 |pages=1031–1034 |doi=10.1126/science.aat8123 |pmid=30498122 |arxiv=1812.01031 |bibcode=2018Sci...362.1031F }}</ref>

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]] ''[[Redshift#Measurement, characterization, and interpretation|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 {{convert|19|Gpc|Gly}}) will never reach Earth.<ref name=Loeb2002>{{cite journal|doi=10.1103/PhysRevD.65.047301|title=Long-term future of extragalactic astronomy|journal=Physical Review D|volume=65|issue=4|pages=047301|year=2002|last1=Loeb|first1=Abraham|arxiv=astro-ph/0107568|bibcode=2002PhRvD..65d7301L|s2cid=1791226}}</ref>