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The '''Relativistic cosmology''' or, more precisely, the general-relativistic theory of [[cosmology]] started in 1922 with the remarkable work of A. Friedmann, who solved the Einstein's [[gravitational field equations]] and found that they allow for non-static cosmological solutions presenting an [[expanding universe]]. An extension of the A.Friedmann models was carried out by [[Georges-Henri Lemaître|G.Lemaître]], who considered universes with zero energy-momentum but with a non-zero [[cosmological constant]].<ref>{{cite web |title=Cosmological Relativity: A New Theory OF Cosmology|author=Silvia Behar and Moshe Carmeli (Department of Physics, Ben Gurion University )|publisher=Intrn. Journal Theor. Physics|year=2000|issue=39 (1375)|url=http://arxiv.org/pdf/astro-ph/0008352.pdf|accessdate=July 7, 2013}}</ref>
The '''Relativistic cosmology''' or, more precisely, the general-relativistic theory of [[cosmology]] started in 1922 with the remarkable work of A. Friedmann, who solved the Einstein's [[gravitational field equations]] and found that they allow for non-static cosmological solutions presenting an [[expanding universe]]. An extension of the A.Friedmann models was carried out by [[Georges-Henri Lemaître|G.Lemaître]], who considered universes with zero energy-momentum but with a non-zero [[cosmological constant]].<ref>{{cite web |title=Cosmological Relativity: A New Theory OF Cosmology|author=Silvia Behar and Moshe Carmeli (Department of Physics, Ben Gurion University )|publisher=Intrn. Journal Theor. Physics|year=2000|issue=39 (1375)|url=http://arxiv.org/pdf/astro-ph/0008352.pdf|accessdate=July 7, 2013}}</ref>
The standard big-bang cosmologies are relativistic and usually referred to as Friedmann-Lemaître cosmologies or FL cosmologies.<ref name="DismantlingBB">{{cite book|author=Alex Williams, John Hartnett|title=Dismantling the Big Bang|publisher=Master Books|location=Green Forest, AR, USA|year=2005|pages=290|isbn=978-0-89051-437-5|url=http://books.google.com/books?id=FR7basoxkSwC&printsec=frontcover&dq=hartnett+dismantling+the+big+bang&hl=en&sa=X&ei=JvNwT_6nJJOP4gTP6fG_Ag&sqi=2&ved=0CC4Q6AEwAA#v=onepage&q=hartnett%20dismantling%20the%20big%20bang&f=false|quote=}}</ref> In order to fit the FL theory to the data, unobservable [[dark matter|'dark' matter]] and [[dark energy|'dark' energy]] have been invented.<ref name="starlight">{{cite book| last = Hartnett| first = John| authorlink = | title = Starlight, Time and the New Physics| publisher = Creation Ministries International| series = | year = 2007| doi = | isbn = 978-0-949-906687|pages=41|quote='Dark Matter' -today's 'fudge' factor; Technical Appendices: App.1: The large scale structure of the universe does not need 'dark' matter or 'dark' energy; App.6: Light-travel-time problem solved}}</ref>
The standard big-bang cosmologies are relativistic and usually referred to as Friedmann-Lemaître cosmologies or FL cosmologies.<ref name="DismantlingBB">{{cite book|author=Alex Williams, John Hartnett|title=Dismantling the Big Bang|publisher=Master Books|location=Green Forest, AR, USA|year=2005|pages=290|isbn=978-0-89051-437-5|url=http://books.google.com/books?id=FR7basoxkSwC&printsec=frontcover&dq=hartnett+dismantling+the+big+bang&hl=en&sa=X&ei=JvNwT_6nJJOP4gTP6fG_Ag&sqi=2&ved=0CC4Q6AEwAA#v=onepage&q=hartnett%20dismantling%20the%20big%20bang&f=false|quote=}}</ref>
==Link to Einstein's theory of general relativity==
Relativistic cosmologies are offshoot of Einstein's [[General theory of relativity|theory of general relativity]]. From there, several contributing principles are adopted:
*The basic proposition that the geometry of space is determined by the content of space (Einstein's [[gravitational field equations]] invented to describe the structure of the cosmos).
*A sheer assumption that all observers, regardless of their location, should see the same general picture of the universe ([[Cosmological principle]]). This second principle seems plausible to relativistic cosmologists as it appeals strongly to their so called ''sense of proportion'' and helps them to avoid the [[horror of a unique position]].
*Another important aspect of such cosmologies is highly abstract concept of [[spatial curvature]] allowing relativistic theorists to make assumption of homogeneity thus to adopt [[Riemannian geometry]] which operates in curved space.
The kinds of universes that would be compatible with these relativistic principles and the a priori assumption of homogeneity have been determined by intricate mathematical reasoning.<ref>{{cite web |title=The Observational approach to Cosmology|author=Edwin Hubble|publisher=Oxford University Press|year=1937|url=http://ned.ipac.caltech.edu/level5/Sept04/Hubble/Hubble3_4.html|accessdate=July 10, 2013}}</ref> In order to fit these FL theories to the data, unobservable [[dark matter|'dark' matter]] and [[dark energy|'dark' energy]] have been invented.<ref name="starlight">{{cite book| last = Hartnett| first = John| authorlink = | title = Starlight, Time and the New Physics| publisher = Creation Ministries International| series = | year = 2007| doi = | isbn = 978-0-949-906687|pages=64|quote=}}</ref>
==References==
==References==