Friedmann universe

Friedmann universe

[′frēd·mən ′yü·nə‚vərs]
(astronomy)
A nonstatic, homogeneous, isotropic model of the universe that displays expansion or contraction and has nonzero matter density.
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Introducing therefore gravitational potential, the Friedmann universe has been transformed into the Milne universe of R = ct cosmology, where the inverse value of the Hubble constant [H.sup.-1] is exactly the age of the universe.
Moreover, in Mongan [12], the author examines a vacuum-dominated Friedmann universe asymptotic to a de Sitter space, with a cosmological event horizon that its area in Planck's units determines the maximum amount of information that will ever be available to any observer.
The holographic principle indicates a possible nonlocality mechanism in any vacuum-dominated Friedmann universe. To be more precise, a holographic nonlocal quantum mechanical description can be possible for a finite amount of information in a closed vacuum-dominated universe.
The "dark matter" and "dark energy" parameters introduced are required in order to fit the Friedmann universe expansion equation to the type 1a supernovae [19,22] and CMB data [14].
of California-Davis) show that the Einstein equations for a spherically symmetric spacetime in Standard Schwazschild Coordinates close to form a system of three ordinary differential equations for a family of self-similar expansion waves, and that embedded as a single point in this family is the critical (k = 0) Friedmann universe associated with the pure radiation phase of the Standard Model of Cosmology.
Given these definitions, we may ask if there is a possible reconstruction of Newton-Smith's argument that is a viable argument for the claim that there is some Universe U' containing both the Friedmann universe U and a spatio-temporal structure earlier than the singularity that is occupied by physical processes that cause the singularity.
But this Schwarzschild black hole singularity should not be included in our reference class, since this singularity is an endpoint o spacetime curves in the Friedmann universe U and therefore is not sufficiently similar to the big bang singularity to give us a sound argument from analogy.
Consider the following: in 1927, Lemaitre's theory [6] already predicted the linear reshift law in an expanding space of Friedmann's metric (a Friedmann universe).
Then he calculated the redshift, assuming that it is a result of the Doppler effect on the scattering objects of the expanding Friedmann universe.
In other words, the Doppler formula of classical physics is assumed to be the same in an expanding Friedmann universe. This is a very serious simplification, because it is obvious that the Doppler effect should have a formula, which follows from the space geometry (Friedmann's metric in this case);
Herein I shall go into the details of just one of the obtained solutions - that in an expanding Friedmann universe, - wherein I obtained the exponential cosmological redshift, thus giving a theoretical explanation to the accelerate expansion of the Universe registered recently by the astronomers.
The preceding examples help to illustrate the variety possible in Friedmann universes. A fundamental concern worth mentioning is that all the Friedmann models are based on the assumption that the universe has the same density at all places (homogeneity) and the same expansion rate in all directions (isotropy).