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Revision as of 18:26, 10 April 2013 editWyattmj (talk | contribs)337 edits The Misplaced Pages article explains what the Copernican principle is. We know what it is. Alignment to the ecliptic is anti-copernican, period.← Previous edit Latest revision as of 18:29, 17 November 2024 edit undoPraemonitus (talk | contribs)Autopatrolled, Extended confirmed users65,509 edits →Origin and implications: Para. break for better reading 
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{{Short description|Principle that humans are not privileged observers of the universe}}
In ], the '''Copernican principle''', named after ], states that the Earth is not in a central, specially favored position.<ref>{{cite book | author = H. Bondi | authorlink = Hermann Bondi | title = Cosmology | publisher = Cambridge University Press | year = 1952 | pages = 13}}</ref> More recently, the principle has been generalized to the ] concept that humans are not privileged observers of the universe.<ref>{{cite book | author = J. A. Peacock | title = Cosmological Physics | publisher = Cambridge University Press | page = 66 | year = 1998}}.</ref> In this sense, it is equivalent to the ], with important implications for the ].
{{cosmology}}

{{unsolved|physics|Are cosmological observations made from Earth representative of observations from the average position in the universe?}}
⚫ Since the 1990s the term has been used (interchangeably with "the Copernicus method") for ]'s ]-based prediction of duration of ongoing events, a generalized version of the ].
]'s 1617–1621 '']'', showing the ] as belonging to just one of any number of similar stars]]

In ], the '''Copernican principle''' states that humans are not privileged observers of the ],<ref>{{cite book |last=Peacock |first=John A. |title=Cosmological Physics |url=https://archive.org/details/cosmologicalphys0000peac |url-access=registration |publisher=] |page= |year=1998 |isbn=978-0-521-42270-3}}</ref> that observations from the Earth are representative of observations from the average position in the universe. Named for ], it is a working assumption that arises from a modified cosmological extension of ] argument of a moving Earth.<ref>{{cite book |last=Bondi |first=Hermann |author-link=Hermann Bondi |title=Cosmology |publisher=Cambridge University Press |year=1952 |page=13}}</ref>
Recent observations such as "the axis of evil", a signal embedded in the anisotropy of the CMB which is aligned to the ecliptic and the equinoxes, challenge the Copernican Principle.


== Origin and implications == == Origin and implications ==
] emphasizes the importance of the Copernican principle: "It is evident that in the post-Copernican era of human history, no well-informed and rational person can imagine that the Earth occupies a unique position in the universe."<ref>{{cite book | author = ] | title = Cosmology| edition = 3rd | publisher = Clarendon Press, Oxford | pages = 62}}.</ref>


] named the principle after Copernicus in the mid-20th century, although the principle itself dates back to the 16th-17th century ] away from the ], which placed ] at the center of the ]. Copernicus demonstrated the motion of the planets can be explained without the assumption that Earth is centrally located and stationary. He argued that the ] of the planets is an illusion caused by Earth's movement around the ], which the ] placed at the centre of the Universe. Copernicus himself was mainly motivated by technical dissatisfaction with the earlier system and not by support for any mediocrity principle.<ref>{{cite book | author = ] | title = The Copernican Revolution | publisher = Harvard University Press}}.</ref> In fact, although the Copernican heliocentric model is often described as "demoting" Earth from its central role it had in the Ptolemaic geocentric model, neither Copernicus nor other 15th- and 16th-century scientists and philosophers viewed it as such.<ref>{{cite journal |doi= 10.1038/scientificamerican0301-24a |journal= Scientific American |year=2001 |volume=284 |issue=3 |pages=24 |title= Copernican Counterrevolution |author= ] |url=http://www.scientificamerican.com/article.cfm?id=in-brief-2001-03}}</ref><ref>{{cite journal |doi= 10.1511/2009.76.50 |journal= American Scientist |year=2009 |volume=97 |issue=1 |pages=50–57 |title= The Bones of Copernicus |author= Dennis Danielson |url=http://www.americanscientist.org/issues/feature/the-bones-of-copernicus}}</ref> ] named the principle after Copernicus in the mid-20th century, although the principle itself dates back to the 16th-17th century ] away from the ], which placed ] at the center of the ]. Copernicus proposed that the motion of the planets could be explained by reference to an assumption that the Sun is centrally located and stationary in contrast to the ]. He argued that the ] of the planets is an illusion caused by Earth's movement around the ], which the ] placed at the centre of the universe. Copernicus himself was mainly motivated by technical dissatisfaction with the earlier system and not by support for any ].<ref>{{cite book |last=Kuhn |first=Thomas S. |author-link=Thomas Kuhn |title=The Copernican Revolution: Planetary Astronomy in the Development of Western Thought |url=https://archive.org/details/copernicanrevolu0008kuhn |url-access=registration |publisher=] |year=1957 |isbn=978-0-674-17103-9 |bibcode=1957crpa.book.....K }}</ref>


Although the Copernican heliocentric model is often described as "demoting" Earth from its central role it had in the Ptolemaic geocentric model, it was successors to Copernicus, notably the 16th century ], who adopted this new perspective. The Earth's central position had been interpreted as being in the "lowest and filthiest parts". Instead, as Galileo said, the Earth is part of the "dance of the stars" rather than the "sump where the universe's filth and ephemera collect".<ref>{{cite journal |doi=10.1038/scientificamerican0301-24a |journal=Scientific American |year=2001 |volume=284 |issue=3 |page=24 |title=Copernican Counterrevolution |author-link=George Musser |last=Musser |first=George |url=http://www.scientificamerican.com/article.cfm?id=in-brief-2001-03 |bibcode=2001SciAm.284c..24M }}</ref><ref>{{cite journal |doi=10.1511/2009.76.50 |journal=American Scientist |year=2009 |volume=97 |issue=1 |pages=50–57 |title=The Bones of Copernicus |first=Dennis |last=Danielson}}</ref> In the late 20th Century, Carl Sagan asked, "Who are we? We find that we live on an insignificant planet of a humdrum star lost in a galaxy tucked away in some forgotten corner of a universe in which there are far more galaxies than people."<ref>Sagan, Carl, ''Cosmos'' (1980) p. 193</ref>
In cosmology, if one assumes the Copernican principle and observes that the universe appears ] from our vantage-point on Earth, then one can infer that the Universe is generally homogeneous (at any given time) and is also isotropic about any given point. These two conditions comprise the ].


While the Copernican principle is derived from the negation of past assumptions, such as ], ], or ] which state that humans are at the center of the universe, the Copernican principle is stronger than ''acentrism'', which merely states that humans are not at the center of the universe. The Copernican principle assumes acentrism and also states that human observers or observations from Earth are representative of observations from the average position in the universe. ] emphasizes the Copernican principle as the threshold test for modern thought, asserting that: "It is evident that in the post-Copernican era of human history, no well-informed and rational person can imagine that the Earth occupies a unique position in the universe."<ref name="RowanRobinson1996">{{cite book |last=Rowan-Robinson |first=Michael |author-link=Michael Rowan-Robinson |title=Cosmology |edition=3rd |publisher=] |pages=62–63 |year=1996 |isbn=978-0-19-851884-6}}</ref>
⚫ In practice, astronomers observe that the Universe has heterogeneous structures up to the scale of ]s, ] and ]s, but becomes more and more homogeneous and isotropic when observed on larger and larger scales, with little detectable structure on scales of more than about 200 million ]s. However, on scales comparable to the radius of the observable universe, we see systematic changes with distance from the Earth. For instance, galaxies contain more young stars and are less clustered, and ] appear more numerous. While this might suggest that the Earth is at the center of the Universe, the Copernican principle requires us to interpret it as evidence for the evolution of the Universe with time: this distant light has taken most of the age of the Universe to reach and shows us the Universe when it was young. The most distant light of all, ], is isotropic to at least one part in a thousand.


Modern mathematical cosmology is based on the assumption that the Cosmological principle is almost, but not exactly, true on the largest scales. The Copernican principle represents the irreducible philosophical assumption needed to justify this, when combined with the observations. Most modern cosmology is based on the assumption that the cosmological principle is almost, but not exactly, true on the largest scales. The Copernican principle represents the irreducible philosophical assumption needed to justify this, when combined with the observations. If one assumes the Copernican principle and observes that the universe appears ] or the same in all directions from the vantage point of Earth, then one can infer that the universe is generally ] or the same everywhere (at any given time) and is also isotropic about any given point. These two conditions make up the ].<ref name="RowanRobinson1996" />


In practice, astronomers observe that the universe has ] or non-uniform structures up to the scale of ]s, ] and ]s. In the current ], the predominant model of cosmology in the modern era, the universe is predicted to become more and more homogeneous and isotropic when observed on larger and larger scales, with little detectable structure on scales of more than about 260 million ]s.<ref name="Yadav">{{cite journal |last1=Yadav |first1=Jaswant |last2=Bagla |first2=J. S. |last3=Khandai |first3=Nishikanta |date=25 February 2010 |title=Fractal dimension as a measure of the scale of homogeneity |journal=Monthly Notices of the Royal Astronomical Society |volume=405 |issue=3 |pages=2009–2015 |arxiv=1001.0617 |bibcode=2010MNRAS.405.2009Y |doi=10.1111/j.1365-2966.2010.16612.x |doi-access=free |s2cid=118603499}}</ref> However, recent evidence from ]s,<ref name="Billings">{{cite web |author=Billings |first=Lee |date=April 15, 2020 |title=Do We Live in a Lopsided Universe? |url=https://www.scientificamerican.com/article/do-we-live-in-a-lopsided-universe1/ |access-date=March 24, 2022 |website=]}}</ref><ref name="Migkas et al">{{cite journal |url=https://www.aanda.org/articles/aa/full_html/2020/04/aa36602-19/aa36602-19.html |title=Probing cosmic isotropy with a new X-ray galaxy cluster sample through the LX-T scaling relation |author1=Migkas, K. |author2=Schellenberger, G. |author3=Reiprich, T. H. |author4=Pacaud, F. |author5=Ramos-Ceja, M. E. |author6=Lovisari, L. |journal=Astronomy & Astrophysics |volume=636 |issue=April 2020 |page=42 |doi=10.1051/0004-6361/201936602 |date=8 April 2020 |arxiv=2004.03305 |bibcode=2020A&A...636A..15M |s2cid=215238834 |access-date=24 March 2022}}</ref> ]s,<ref>{{cite journal |last1=Secrest |first1=Nathan J. |last2=von Hausegger |first2=Sebastian |last3=Rameez |first3=Mohamed |last4=Mohayaee |first4=Roya |last5=Sarkar |first5=Subir |last6=Colin |first6=Jacques |date=February 25, 2021 |title=A Test of the Cosmological Principle with Quasars |journal=The Astrophysical Journal Letters |volume=908 |issue=2 |pages=L51 |arxiv=2009.14826 |bibcode=2021ApJ...908L..51S |doi=10.3847/2041-8213/abdd40 |s2cid=222066749 |doi-access=free }}</ref> and ]e<ref>{{cite journal |last1=Javanmardi |first1=B. |last2=Porciani |first2=C. |last3=Kroupa |first3=P. |last4=Pflamm-Altenburg |first4=J. |date=August 27, 2015 |title=Probing the Isotropy of Cosmic Acceleration Traced By Type Ia Supernovae |url=https://iopscience.iop.org/article/10.1088/0004-637X/810/1/47 |journal=The Astrophysical Journal Letters |volume=810 |issue=1 |page=47 |arxiv=1507.07560 |bibcode=2015ApJ...810...47J |doi=10.1088/0004-637X/810/1/47 |s2cid=54958680 |access-date=March 24, 2022}}</ref> suggests that isotropy is violated on large scales. Furthermore, various large-scale structures have been discovered, such as the ], the ],<ref name=apj624_2_463>{{Cite journal |display-authors=1 |last1=Gott |first1=J. Richard III |last2=Jurić |first2=Mario |last3=Schlegel |first3=David |last4=Hoyle |first4=Fiona |last5=Vogeley |first5=Michael |last6=Tegmark |first6=Max |last7=Bahcall |first7=Neta |last8=Brinkmann |first8=Jon |title=A Map of the Universe |journal=The Astrophysical Journal |volume=624 |issue=2 |pages=463–484 |date=May 2005 |doi=10.1086/428890 |bibcode=2005ApJ...624..463G |arxiv=astro-ph/0310571 |s2cid=9654355}}</ref> ], the ], the ],<ref>{{cite arXiv |eprint=1311.1104 |last1=Horvath |first1=I. |title=The largest structure of the Universe, defined by Gamma-Ray Bursts |last2=Hakkila |first2=J. |last3=Bagoly |first3=Z. |year=2013|class=astro-ph.CO }}</ref> and ],<ref>{{Cite web |url=https://www.newscientist.com/article/2280076-line-of-galaxies-is-so-big-it-breaks-our-understanding-of-the-universe/ |title=Line of galaxies is so big it breaks our understanding of the universe}}</ref> all which indicate that homogeneity might be violated.
⚫ Bondi and ] used the Copernican principle to argue for the ] which maintains that the universe is also homogeneous in time, and is the basis for the ]. However, this strongly conflicts with the evidence for cosmological evolution mentioned earlier: the Universe has progressed from extremely different conditions at the ], and will continue to progress toward extremely different conditions, particularly under the rising influence of ], apparently toward the ] or ].


⚫ On scales comparable to the radius of the observable universe, we see systematic changes with distance from Earth. For instance, at greater distances, galaxies contain more young stars and are less clustered, and ] appear more numerous. If the Copernican principle is assumed, then it follows that this is evidence for the evolution of the universe with time: this distant light has taken most of the age of the universe to reach Earth and shows the universe when it was young. The most distant light of all, ], is isotropic to at least one part in a thousand.
== Confirmation or Demise? ==
The ] (CMB) radiation signature presents a direct large-scale view of universe that can be used to identify whether our position or movement has any particular significance.
There has been much publicity about analysis of results from the ] (WMAP) and ] that show both expected and unexpected ] in the CMB.<ref name=hanson>{{cite arXiv|eprint=1210.6008|version=v1|author1=Anthony Challinor|title=CMB anisotropy science: A review|class=astro-ph.CO|year=2012}}</ref>


⚫ Bondi and ] used the Copernican principle to argue for the ] which maintains that the universe is also homogeneous in time, and is the basis for the ].<ref name="BondiGold1948">{{cite journal |last=Bondi |first=H. |author2=Gold, T. |title=The Steady-State Theory of the Expanding Universe |journal=] |year=1948 |volume=108 |issue=3 |pages=252–270 |bibcode=1948MNRAS.108..252B |doi=10.1093/mnras/108.3.252 |doi-access=free}}</ref> However, this strongly conflicts with the evidence for cosmological evolution mentioned earlier: the universe has progressed from extremely different conditions at the ], and will continue to progress toward extremely different conditions, particularly under the rising influence of ], apparently toward the ] or ].
In particular, ] have been reported to be aligned with the ] which would be a clear violation of the Copernican Principle<ref name=mariano>{{cite doi|10.1103/PhysRevD.87.043511}}</ref>, as would any preferred direction in space. The alignment with the ecliptic has been dubbed the Axis of Evil<ref name=land>{{cite doi|10.1103/PhysRevLett.95.071301}}</ref> due to the dire implications for current models of the cosmos. Studies on WMAP and COBE data have claimed to have refuted the alignments as statistical anomalies<ref name=buckley>{{cite doi|10.1103/PhysRevD.87.023524}}</ref><ref name=zhang>{{cite doi|10.1103/PhysRevLett.107.041301}}</ref> or local phenomena<ref>{{cite doi|10.1088/1475-7516/2012/10/059}}</ref>, but the latest data from the 2013 Planck satellite strongly assert the preferred direction and related anisotropies are present at around a three sigma level, confirming WMAP and COBE findings.<ref>Planck 2013 Results. Isotropy and Statistics of the CMB. planck.caltech.edu/pub/2013results/Planck_2013_results_23.pdf </ref> These alternate explanations have been discussed and shown not reasonable solutions by Copi, ''et. al.'', who looked to Planck to resolve whether the preferred direction and alignmments are spurious.<ref>Large-angle anomalies in the CMB, http://arxiv.org/abs/1004.5602</ref><ref>The Uncorrelated Universe: Statistical Anisotropy and the Vanishing Angular
Correlation Function in WMAP Years 1-3 http://arxiv.org/abs/astro-ph/0605135</ref>As noted, Planck has confirmed the preferred direction and alignment.


⚫ Since the 1990s the term has been used (interchangeably with "the Copernicus method") for ]'s ]-based prediction of duration of ongoing events, a generalized version of the ].{{clarify|date=April 2017}}
== Ecliptic alignment of cosmic microwave background anisotropy ==


==Tests of the principle==
Results from ] (WMAP) appear to run counter to Copernican expectations. The motion of the solar system, and the orientation of the plane of the are aligned with features of the microwave sky, which on conventional thinking are caused by structure at the edge of the observable universe<ref>CERN Courier ""</ref><ref>{{cite journal | author = C. J. Copi, D. Huterer, D. J. Schwarz, G. D. Starkman | title = On the large-angle anomalies of the microwave sky | journal = Monthly Notices of the Royal Astronomical Society | volume = 367 | year = 2006 | pages = 79–102 | doi = 10.1111/j.1365-2966.2005.09980.x | arxiv=astro-ph/0508047 | bibcode=2006MNRAS.367...79C}}</ref>
The Copernican principle has never been proven, and in the most general sense cannot be proven, but it is implicit in many modern theories of physics. Cosmological models are often derived with reference to the ], slightly more general than the Copernican principle, and many tests of these models can be considered tests of the Copernican principle.<ref name=clarkson>{{Cite journal |last1=Clarkson |first1=C. |last2=Bassett |first2=B. |last3=Lu |first3=T. |title=A General Test of the Copernican Principle |doi=10.1103/PhysRevLett.101.011301 |journal=Physical Review Letters |volume=101 |issue=1 |page=011301 |year=2008 |pmid=18764099 |arxiv=0712.3457 |bibcode=2008PhRvL.101a1301C |s2cid=32735465 }}</ref>


===Historical===
] is quoted as follows in the referenced Edge.org article:<ref>""</ref>
Before the term Copernican principle was even coined, past assumptions, such as ], ], and ], which state that Earth, the Solar System, or the Milky Way respectively were located at the center of the universe, were shown to be false. The ] dethroned Earth to just one of many planets orbiting the Sun. ] was mentioned by Halley. ] found that the Solar System is moving through space within our disk-shaped ] galaxy. ] showed that the Milky Way galaxy is just one of many galaxies in the universe. Examination of the galaxy's position and motion in the universe led to the ] and the whole of modern ].


⚫ ===Modern tests===
{{quote|But when you look at map, you also see that the structure that is observed, is in fact, in a weird way, correlated with the plane of the earth around the sun. Is this Copernicus coming back to haunt us? That's crazy. We're looking out at the whole universe. There's no way there should be a correlation of structure with our motion of the earth around the sun — the plane of the earth around the sun — the ecliptic. That would say we are truly the center of the universe.}}
Recent and planned tests relevant to the cosmological and Copernican principles include:
* time drift of cosmological redshifts;<ref name=uzan>{{Cite journal |last1=Uzan |first1=J. P. |last2=Clarkson |first2=C. |last3=Ellis |first3=G. |title=Time Drift of Cosmological Redshifts as a Test of the Copernican Principle |doi=10.1103/PhysRevLett.100.191303 |journal=Physical Review Letters |volume=100 |issue=19 |page=191303 |year=2008 |pmid=18518435 |arxiv=0801.0068 |bibcode=2008PhRvL.100s1303U |s2cid=31455609}}</ref>
* modelling the local gravitational potential using reflection of ] (CMB) photons;<ref name=caldwell>{{Cite journal |last1=Caldwell |first1=R. |last2=Stebbins |first2=A. |doi=10.1103/PhysRevLett.100.191302 |title=A Test of the Copernican Principle |journal=Physical Review Letters |volume=100 |issue=19 |page=191302 |year=2008 |pmid=18518434 |arxiv=0711.3459 |bibcode=2008PhRvL.100s1302C |s2cid=5468549}}</ref>
* the ] dependence of the luminosity of ];<ref name=clifton>{{Cite journal |last1=Clifton |first1=T. |last2=Ferreira |first2=P. |last3=Land |first3=K. |title=Living in a Void: Testing the Copernican Principle with Distant Supernovae |doi=10.1103/PhysRevLett.101.131302 |journal=Physical Review Letters |volume=101 |issue=13 |year=2008 |pmid=18851434 |arxiv=0807.1443 |bibcode=2008PhRvL.101m1302C |page=131302 |s2cid=17421918}}</ref>
* the kinetic ] in relation to dark energy;<ref name=zhang>{{Cite journal |last1=Zhang |first1=P. |last2=Stebbins |first2=A. |doi=10.1098/rsta.2011.0294 |title=Confirmation of the Copernican principle through the anisotropic kinetic Sunyaev Zel'dovich effect |journal=Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences |volume=369 |issue=1957 |pages=5138–5145 |year=2011 |pmid=22084299 |bibcode=2011RSPTA.369.5138Z |doi-access=free }}</ref>
* ];<ref name=jia>{{Cite journal |last1=Jia |first1=J. |last2=Zhang |first2=H. |doi=10.1088/1475-7516/2008/12/002 |title=Can the Copernican principle be tested using the cosmic neutrino background? |journal=Journal of Cosmology and Astroparticle Physics |volume=2008 |issue=12 |page=002 |year=2008 |arxiv=0809.2597 |bibcode=2008JCAP...12..002J |s2cid=14320348}}</ref>
* the integrated ]<ref name=tomita>{{Cite journal |last1=Tomita |first1=K. |last2=Inoue |first2=K. |doi=10.1103/PhysRevD.79.103505 |title=Probing violation of the Copernican principle via the integrated Sachs–Wolfe effect |journal=Physical Review D |volume=79 |issue=10 |page=103505 |year=2009 |arxiv=0903.1541 |bibcode=2009PhRvD..79j3505T |s2cid=118478786}}</ref>
* testing the isotropy and homogeneity of the CMB;<ref name=bull>{{Cite journal |last1=Clifton |first1=T. |last2=Clarkson |first2=C. |last3=Bull |first3=P. |title=Isotropic Blackbody Cosmic Microwave Background Radiation as Evidence for a Homogeneous Universe |doi=10.1103/PhysRevLett.109.051303 |journal=Physical Review Letters |volume=109 |issue=5 |year=2012 |pmid=23006164 |arxiv=1111.3794 |bibcode=2012PhRvL.109e1303C |page=051303 |s2cid=119278505}}</ref><ref name=kim>{{Cite journal |last1=Kim |first1=J. |last2=Naselsky |first2=P. |doi=10.1088/0004-637X/739/2/79 |title=Lack of Angular Correlation and Odd-Parity Preference in Cosmic Microwave Background Data |journal=The Astrophysical Journal |volume=739 |issue=2 |page=79 |year=2011 |arxiv=1011.0377 |bibcode=2011ApJ...739...79K |s2cid=118580902}}</ref><ref name=copi>{{Cite journal |last1=Copi |first1=C. J. |last2=Huterer |first2=D. |last3=Schwarz |first3=D. J. |last4=Starkman |first4=G. D. |title=Large-Angle Anomalies in the CMB |doi=10.1155/2010/847541 |journal=Advances in Astronomy |volume=2010 |pages=1–17 |year=2010 |arxiv=1004.5602 |bibcode=2010AdAst2010E..92C |s2cid=13823900 |doi-access=free}}</ref><ref name=planck>{{cite journal |arxiv=1303.5083 |collaboration=Planck Collaboration |last=Ade |title=Planck 2013 results. XXIII. Isotropy and Statistics of the CMB |year=2013 |doi=10.1051/0004-6361/201321534 |volume=571 |journal=Astronomy & Astrophysics |page=A23 |bibcode=2014A&A...571A..23P |s2cid=13037411}}</ref><ref name="longo">{{cite arXiv |eprint=astro-ph/0703325 |last=Longo |first=Michael |title=Does the Universe Have a Handedness? |year=2007}}</ref>
* Some authors claim that the ] violates the cosmological principle and thus the Copernican principle.<ref name="Haslbauer">{{Cite journal |last1=Haslbauer |first1=M. |last2=Banik |first2=I. |last3=Kroupa |first3=P. |date=2020-12-21 |title=The KBC void and Hubble tension contradict LCDM on a Gpc scale – Milgromian dynamics as a possible solution |journal=Monthly Notices of the Royal Astronomical Society |volume=499 |issue=2 |pages=2845–2883 |arxiv=2009.11292 |bibcode=2020MNRAS.499.2845H |doi=10.1093/mnras/staa2348 |issn=0035-8711 |doi-access=free}}</ref> However, other authors claim that the KBC void is consistent with the ] and the Copernican principle.<ref>{{Cite journal |last1=Sahlén |first1=Martin |last2=Zubeldía |first2=Íñigo |last3=Silk |first3=Joseph |date=2016 |title=Cluster–Void Degeneracy Breaking: Dark Energy, Planck, and the Largest Cluster and Void |journal=The Astrophysical Journal Letters |volume=820 |issue=1 |pages=L7 |doi=10.3847/2041-8205/820/1/L7 |issn=2041-8205 |arxiv=1511.04075 |bibcode=2016ApJ...820L...7S |s2cid=119286482 |doi-access=free }}</ref>


==Physics without the principle==
{{quote|The new results are either telling us that all of science is wrong and we're the center of the universe, or maybe the data is simply incorrect, or maybe it's telling us there's something weird about the microwave background results and that maybe, maybe there's something wrong with our theories on the larger scales. And of course as a theorist I'm certainly hoping it's the latter, because I want theory to be wrong, not right, because if it's wrong there's still work left for the rest of us.}}
The standard model of cosmology, the ], assumes the Copernican principle and the more general ]. Some cosmologists and theoretical physicists have created models without the cosmological or Copernican principles to constrain the values of observational results, to address specific known issues in the Lambda-CDM model, and to propose tests to distinguish between current models and other possible models.


A prominent example in this context is ], to model the observed ] and ]. Instead of using the current accepted idea of ], this model proposes the universe is much more inhomogeneous than currently assumed, and instead, we are in an extremely large low-density void.<ref name=void>{{Cite journal | last1 = February | first1 = S. | last2 = Larena | first2 = J. | last3 = Smith | first3 = M. | last4 = Clarkson | first4 = C. | title = Rendering dark energy void | doi = 10.1111/j.1365-2966.2010.16627.x | journal = Monthly Notices of the Royal Astronomical Society | volume = 405 | issue = 4 | page = 2231 | year = 2010 | doi-access = free |arxiv = 0909.1479 |bibcode = 2010MNRAS.405.2231F | s2cid = 118518082 }}</ref> To match observations we would have to be very close to the centre of this void, immediately contradicting the Copernican principle.
It would be somewhat surprising if the WMAP alignments were a complete coincidence, but the anti-Copernican implications suggested by Krauss are far more surprising, now that they are confirmed to be true by Planck <ref> http://www.esa.int/Our_Activities/Space_Science/Planck/Planck_reveals_an_almost_perfect_Universe</ref>. Other possibilities that were considered are (i) that residual instrumental errors in WMAP cause the effect (ii) that unexpected microwave emission from within the solar system is contaminating the maps.<ref>Copi et al. ''op. cit.''</ref>Later studies by Copi, ''et. al.'', dismissed these explanations as not feasible.<ref>Large-angle anomalies in the CMB, http://arxiv.org/abs/1004.5602</ref><ref>The Uncorrelated Universe: Statistical Anisotropy and the Vanishing Angular
Correlation Function in WMAP Years 1-3 http://arxiv.org/abs/astro-ph/0605135</ref>


While the ] model in cosmology is sometimes said to derive from the Copernican principle in conjunction with redshift observations, the Big Bang model can still be assumed to be valid in absence of the Copernican principle, because the ], primordial gas clouds, and the ], ], and distribution of ] all provide evidence, independent of the Copernican principle, in favor of the Big Bang. However, the key tenets of the Big Bang model, such as the expansion of the universe, become assumptions themselves akin to the Copernican principle, rather than derived from the Copernican principle and observations.
⚫ ==Modern tests==
From the news article "New tests of the Copernican Principle proposed,"<ref>, </ref>
{{quote|Robert Caldwell from Dartmouth College and Albert Stebbins from Fermi National Laboratory in the US explain how the Cosmic Microwave Background (CMB) radiation spectrum — an all pervasive sea of microwave radiation originating just 380 000 years after the Big Bang — could be used to test whether the Copernican Principle stands.<ref>{{cite journal | author = Caldwell, R. R. and Stebbins, A. | title = A Test of the Copernican Principle | year = 2008 | journal=] | volume=100 | page=191302 | doi= 10.1103/PhysRevLett.100.191302 | pmid = 18518434 | issue = 19 | bibcode=2008PhRvL.100s1302C|arxiv = 0711.3459 }}</ref>}}
{{quote|In a separate paper, Jean-Philippe Uzan from the Pierre and Marie Curie University in France along with Chris Clarkson and George Ellis from the University of Cape Town in South Africa suggest another way to test the Copernican Principle.<ref>{{cite journal | author = Uzan, Jean-Philippe; Clarkson, Chris; and Ellis, George F. R. | title = Time Drift of Cosmological Redshifts as a Test of the Copernican Principle | year = 2008 | journal=] | volume=100 | page=191303 | doi= 10.1103/PhysRevLett.100.191303 | pmid = 18518435 | issue = 19 | bibcode=2008PhRvL.100s1303U|arxiv = 0801.0068 }}</ref> Their scheme involves measuring the red-shift of galaxies — the shift in wavelength of light to longer wavelengths due to a speedup — very precisely over time to see if there are changes. The team argues that this red-shift data can be combined with measurements of the distance of the galaxies to infer if the universe is spatially homogeneous — which is a tenet of the Copernican Principle.}}


== See also == == See also ==

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== References == == References ==
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{{Nicolaus Copernicus}}
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Latest revision as of 18:29, 17 November 2024

Principle that humans are not privileged observers of the universe
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Figure 'M' (for Latin Mundus) from Johannes Kepler's 1617–1621 Epitome Astronomiae Copernicanae, showing the Earth as belonging to just one of any number of similar stars

In physical cosmology, the Copernican principle states that humans are not privileged observers of the universe, that observations from the Earth are representative of observations from the average position in the universe. Named for Copernican heliocentrism, it is a working assumption that arises from a modified cosmological extension of Copernicus' argument of a moving Earth.

Origin and implications

Hermann Bondi named the principle after Copernicus in the mid-20th century, although the principle itself dates back to the 16th-17th century paradigm shift away from the Ptolemaic system, which placed Earth at the center of the universe. Copernicus proposed that the motion of the planets could be explained by reference to an assumption that the Sun is centrally located and stationary in contrast to the geocentrism. He argued that the apparent retrograde motion of the planets is an illusion caused by Earth's movement around the Sun, which the Copernican model placed at the centre of the universe. Copernicus himself was mainly motivated by technical dissatisfaction with the earlier system and not by support for any mediocrity principle.

Although the Copernican heliocentric model is often described as "demoting" Earth from its central role it had in the Ptolemaic geocentric model, it was successors to Copernicus, notably the 16th century Giordano Bruno, who adopted this new perspective. The Earth's central position had been interpreted as being in the "lowest and filthiest parts". Instead, as Galileo said, the Earth is part of the "dance of the stars" rather than the "sump where the universe's filth and ephemera collect". In the late 20th Century, Carl Sagan asked, "Who are we? We find that we live on an insignificant planet of a humdrum star lost in a galaxy tucked away in some forgotten corner of a universe in which there are far more galaxies than people."

While the Copernican principle is derived from the negation of past assumptions, such as geocentrism, heliocentrism, or galactocentrism which state that humans are at the center of the universe, the Copernican principle is stronger than acentrism, which merely states that humans are not at the center of the universe. The Copernican principle assumes acentrism and also states that human observers or observations from Earth are representative of observations from the average position in the universe. Michael Rowan-Robinson emphasizes the Copernican principle as the threshold test for modern thought, asserting that: "It is evident that in the post-Copernican era of human history, no well-informed and rational person can imagine that the Earth occupies a unique position in the universe."

Most modern cosmology is based on the assumption that the cosmological principle is almost, but not exactly, true on the largest scales. The Copernican principle represents the irreducible philosophical assumption needed to justify this, when combined with the observations. If one assumes the Copernican principle and observes that the universe appears isotropic or the same in all directions from the vantage point of Earth, then one can infer that the universe is generally homogeneous or the same everywhere (at any given time) and is also isotropic about any given point. These two conditions make up the cosmological principle.

In practice, astronomers observe that the universe has heterogeneous or non-uniform structures up to the scale of galactic superclusters, filaments and great voids. In the current Lambda-CDM model, the predominant model of cosmology in the modern era, the universe is predicted to become more and more homogeneous and isotropic when observed on larger and larger scales, with little detectable structure on scales of more than about 260 million parsecs. However, recent evidence from galaxy clusters, quasars, and type Ia supernovae suggests that isotropy is violated on large scales. Furthermore, various large-scale structures have been discovered, such as the Clowes–Campusano LQG, the Sloan Great Wall, U1.11, the Huge-LQG, the Hercules–Corona Borealis Great Wall, and the Giant Arc, all which indicate that homogeneity might be violated.

On scales comparable to the radius of the observable universe, we see systematic changes with distance from Earth. For instance, at greater distances, galaxies contain more young stars and are less clustered, and quasars appear more numerous. If the Copernican principle is assumed, then it follows that this is evidence for the evolution of the universe with time: this distant light has taken most of the age of the universe to reach Earth and shows the universe when it was young. The most distant light of all, cosmic microwave background radiation, is isotropic to at least one part in a thousand.

Bondi and Thomas Gold used the Copernican principle to argue for the perfect cosmological principle which maintains that the universe is also homogeneous in time, and is the basis for the steady-state cosmology. However, this strongly conflicts with the evidence for cosmological evolution mentioned earlier: the universe has progressed from extremely different conditions at the Big Bang, and will continue to progress toward extremely different conditions, particularly under the rising influence of dark energy, apparently toward the Big Freeze or Big Rip.

Since the 1990s the term has been used (interchangeably with "the Copernicus method") for J. Richard Gott's Bayesian-inference-based prediction of duration of ongoing events, a generalized version of the Doomsday argument.

Tests of the principle

The Copernican principle has never been proven, and in the most general sense cannot be proven, but it is implicit in many modern theories of physics. Cosmological models are often derived with reference to the cosmological principle, slightly more general than the Copernican principle, and many tests of these models can be considered tests of the Copernican principle.

Historical

Before the term Copernican principle was even coined, past assumptions, such as geocentrism, heliocentrism, and galactocentrism, which state that Earth, the Solar System, or the Milky Way respectively were located at the center of the universe, were shown to be false. The Copernican Revolution dethroned Earth to just one of many planets orbiting the Sun. Proper motion was mentioned by Halley. William Herschel found that the Solar System is moving through space within our disk-shaped Milky Way galaxy. Edwin Hubble showed that the Milky Way galaxy is just one of many galaxies in the universe. Examination of the galaxy's position and motion in the universe led to the Big Bang theory and the whole of modern cosmology.

Modern tests

Recent and planned tests relevant to the cosmological and Copernican principles include:

Physics without the principle

The standard model of cosmology, the Lambda-CDM model, assumes the Copernican principle and the more general cosmological principle. Some cosmologists and theoretical physicists have created models without the cosmological or Copernican principles to constrain the values of observational results, to address specific known issues in the Lambda-CDM model, and to propose tests to distinguish between current models and other possible models.

A prominent example in this context is inhomogeneous cosmology, to model the observed accelerating universe and cosmological constant. Instead of using the current accepted idea of dark energy, this model proposes the universe is much more inhomogeneous than currently assumed, and instead, we are in an extremely large low-density void. To match observations we would have to be very close to the centre of this void, immediately contradicting the Copernican principle.

While the Big Bang model in cosmology is sometimes said to derive from the Copernican principle in conjunction with redshift observations, the Big Bang model can still be assumed to be valid in absence of the Copernican principle, because the cosmic microwave background, primordial gas clouds, and the structure, evolution, and distribution of galaxies all provide evidence, independent of the Copernican principle, in favor of the Big Bang. However, the key tenets of the Big Bang model, such as the expansion of the universe, become assumptions themselves akin to the Copernican principle, rather than derived from the Copernican principle and observations.

See also

References

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