Quantizer said:Q1
What Einstein model currently describes a Homogeneous and Isotropic approximated Universe with Matter with positive Lambda, is it still Friedmann (FLRW) or have models moved on
Which Einstein model describes an Inhomogeneous and Anisotropic very early universe with primordial density fluctuations
Thanks for that Mordred, a few pages in and already intrigued by some of the astronomical exponentials being put forwardMordred said:Its still the FLRW metric or more specifically the LCDM model, [itex]\Lambda[/itex]CDM. Which also involves the Eintein field equations..
as far as the De-sitter universe usages you will probably be interested in this article.
De-Sitter musings
http://arxiv.org/abs/1205.3855
also a string theory model variant uses ADS.
ADS/CFT Anti-Desitter correspondance I'm not too familiar with how this model works yet to supply any details.
The DeSitter Universe is a mathematical solution to Einstein's equations of general relativity, which describes the expansion of the universe. It is a hypothetical universe that is homogeneous and isotropic, meaning it appears the same from any point in space and in any direction.
The DeSitter Universe differs from our own universe in that it has a constant positive cosmological constant, which drives the accelerated expansion of the universe. In our universe, the expansion is slowing down due to the gravitational pull of matter and dark energy.
The AntiDeSitter Universe is also a solution to Einstein's equations of general relativity, but it has a negative cosmological constant. This results in a universe that is contracting instead of expanding, and it is often used as a theoretical model for a Big Crunch scenario.
In string theory, the DeSitter and AntiDeSitter universes are important because they are spaces with constant curvature, which is a key feature for certain theories in string theory. These universes also have a special symmetry known as conformal symmetry, which is crucial in the holographic principle.
As these universes are purely theoretical constructs, we cannot observe or visit them in the traditional sense. However, some scientists believe that the DeSitter Universe may have existed during the early stages of our universe's inflationary period, and there are ongoing studies and experiments to better understand these universes and their implications for our own universe.