# Relativistic cosmology

The **Relativistic cosmology** or, more precisely, the general-relativistic theory of cosmology started in 1922 with the 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 G.Lemaître, who considered universes with zero energy-momentum but with a non-zero cosmological constant.^{[1]}
The standard big-bang cosmologies are relativistic and usually referred to as Friedmann-Lemaître cosmologies or FL cosmologies.^{[2]}

## Link to Einstein's theory of general relativity

Relativistic cosmologies are offshoot of Einstein's 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.^{[3]} In order to fit these FL theories to the data, unobservable 'dark' matter and 'dark' energy have been invented.^{[4]}

## References

- ↑ Silvia Behar and Moshe Carmeli (Department of Physics, Ben Gurion University ) (2000). Cosmological Relativity: A New Theory OF Cosmology. Intrn. Journal Theor. Physics. Retrieved on July 7, 2013.
- ↑
Alex Williams, John Hartnett (2005).
*Dismantling the Big Bang*. Green Forest, AR, USA: Master Books, 290. ISBN 978-0-89051-437-5. - ↑ Edwin Hubble (1937). The Observational approach to Cosmology. Oxford University Press. Retrieved on July 10, 2013.
- ↑
Hartnett, John (2007).
*Starlight, Time and the New Physics*. Creation Ministries International, 41, 64. ISBN 978-0-949-906687.