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Also known as the cosmic scale factor or sometimes the Robertson–Walker scale factor, [1] this is a key parameter of the Friedmann equations. In the early stages of the Big Bang, most of the energy was in the form of radiation, and that radiation was the dominant influence on the expansion of the universe. Later, with cooling from the ...
The Annual Review of Astronomy and Astrophysics is an annual peer-reviewed scientific journal published by Annual Reviews. The co-editors are Ewine van Dishoeck and Robert C. Kennicutt . [ 2 ] [ 3 ] The journal reviews scientific literature pertaining to local and distant celestial entities throughout the observable universe , as well as ...
Background radiation is largely homogeneous and isotropic. A slight detectable anisotropy is present which correlates to galaxy filaments and voids. [2] [3] The discovery (by chance in 1965) of the cosmic background radiation suggests that the early universe was dominated by a radiation field, a field of extremely high temperature and pressure. [4]
The intensity of the radiation corresponds to black-body radiation at 2.726 K because red-shifted black-body radiation is just like black-body radiation at a lower temperature. According to the Big Bang model, the radiation from the sky we measure today comes from a spherical surface called the surface of last scattering.
These equations specify the evolution of the scale factor the universe in terms of the pressure and density of a perfect fluid. The evolving density is composed of different kinds of energy and matter, each with its own role in affecting the scale factor. [4]: 7 For example, a model might include baryons, photons, neutrinos, and dark matter.
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The Astrophysical Journal (ApJ [1]) is a peer-reviewed scientific journal of astrophysics and astronomy, established in 1895 by American astronomers George Ellery Hale and James Edward Keeler. The journal discontinued its print edition and became an electronic-only journal in 2015.
Each of the components decreases with the expansion of the universe (increasing scale factor), except perhaps the dark energy term. It is the values of these cosmological parameters which physicists use to determine the acceleration of the universe. The acceleration equation describes the evolution of the scale factor with time