Editing Cosmological principle (section)

== Implications ==
Since the 1990s, observations assuming the cosmological principle have concluded that around 68% of the mass–energy density of the universe can be attributed to [[dark energy]], which led to the development of the [[Lambda-CDM model|ΛCDM model]].<ref name="Ellis 2009">{{cite journal|last=Ellis|first=G. F. R.|title=Dark energy and inhomogeneity|journal=Journal of Physics: Conference Series|volume=189|doi=10.1088/1742-6596/189/1/012011|year=2009|issue=1 |page=012011|bibcode=2009JPhCS.189a2011E |s2cid=250670331 |doi-access=free}}</ref><ref>{{cite journal |last1=Colin |first1=Jacques |last2=Mohayaee |first2=Roya |last3=Rameez |first3=Mohamed |last4=Sarkar |first4=Subir |date=20 November 2019 |title=Evidence for anisotropy of cosmic acceleration |url=https://www.aanda.org/articles/aa/full_html/2019/11/aa36373-19/aa36373-19.html |journal=Astronomy and Astrophysics |volume=631 |pages=L13 |arxiv=1808.04597 |bibcode=2019A&A...631L..13C |doi=10.1051/0004-6361/201936373 |s2cid=208175643 |access-date=25 March 2022}}</ref><ref>{{cite web |last1=Redd |first1=N. T. |title=What is Dark Energy? |url=https://www.space.com/20929-dark-energy.html |website=space.com |archive-url=https://archive.today/20160519162257/http://www.space.com/20929-dark-energy.html |archive-date=19 May 2016 |date=2013 |access-date=28 October 2018 }}</ref>

Observations show that more distant galaxies are closer together and have lower content of chemical elements heavier than lithium.{{Citation needed|date=December 2022}} Applying the cosmological principle, this suggests that heavier elements were not created in the Big Bang but were produced by [[nucleosynthesis]] in giant stars and expelled via a series of [[supernova]]e and new [[star formation]] from the supernova remnants, which means heavier elements would accumulate over time. Another observation is that the farthest galaxies (earlier time) are often more fragmentary, interacting and unusually shaped than local galaxies (recent time), suggesting evolution in galaxy structure as well.

A related implication of the cosmological principle is that the largest discrete structures in the universe should be in [[mechanical equilibrium]]. Homogeneity and isotropy of matter at the largest scales would suggest that the largest discrete structures are parts of a single indiscrete form, like the crumbs which make up the interior of a cake. At extreme cosmological distances, the property of mechanical equilibrium in surfaces lateral to the line of sight can be empirically tested; however, under the assumption of the cosmological principle, it cannot be detected parallel to the line of sight (see [[Timeline of cosmological epochs|timeline of the universe]]).

Cosmologists agree that in accordance with observations of distant galaxies, a universe must be non-static if it follows the cosmological principle. In 1923, [[Alexander Friedmann]] set out a variant of [[Albert Einstein]]'s equations of [[general relativity]] that describe the dynamics of a homogeneous isotropic universe.<ref name=Friedman>{{cite book |title=Die Welt als Raum und Zeit (The World as Space and Time) |series=[[Ostwalds Klassiker der exakten Wissenschaften]] |author=Alexander Friedmann |author-link=Alexander Friedmann |isbn=978-3-8171-3287-4  |year=1923|oclc=248202523 }}.</ref><ref name="Abramovitch">{{cite book |last1=Tropp |first1=Ėduard Abramovich |url=https://z-lib.io/book/15374362 |title=Alexander A. Friedmann: The Man who Made the Universe Expand |last2=Frenkel |first2=Viktor Ya. |last3=Chernin |first3=Artur Davidovich |publisher=[[Cambridge University Press]] |year=1993 |isbn=978-0-521-38470-4 |page=219}}</ref> Independently, [[Georges Lemaître]] derived in 1927 the equations of an expanding universe from the General Relativity equations.<ref name=Lemaitre1927>{{Cite journal | last=Lemaître | first=Georges | author-link=Georges Lemaître | title=Un univers homogène de masse constante et de rayon croissant rendant compte de la vitesse radiale des nébuleuses extra-galactiques | year=1927 | journal=Annales de la Société Scientifique de Bruxelles | volume=A47 | issue=5 | bibcode=1927ASSB...47...49L | pages=49–56 }} ''translated by [[A. S. Eddington]]'': {{Cite journal | last=Lemaître | first=Georges | author-link=Georges Lemaître | title=Expansion of the universe, A homogeneous universe of constant mass and increasing radius accounting for the radial velocity of extra-galactic nebulæ | year=1931 | journal=[[Monthly Notices of the Royal Astronomical Society]] | volume=91 | issue=5 | bibcode=1931MNRAS..91..483L | pages=483–490 | doi=10.1093/mnras/91.5.483| doi-access=free }}</ref> Thus, a non-static universe is also implied, independent of observations of distant galaxies, as a result of applying the cosmological principle to [[general relativity]].