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The term Friedmann equation sometimes is used only for the first equation. [3] In these equations, R(t) is the cosmological scale factor , G N {\displaystyle G_{N}} is the Newtonian constant of gravitation , Λ is the cosmological constant with dimension length −2 , ρ is the energy density and p is the isotropic pressure.
This combination greatly simplifies the equations of general relativity into a form called the Friedmann equations. 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 ...
This article is a list of notable unsolved problems in astronomy. Problems may be theoretical or experimental. Problems may be theoretical or experimental. Theoretical problems result from inability of current theories to explain observed phenomena or experimental results.
The equation of state may be used in Friedmann–Lemaître–Robertson–Walker (FLRW) equations to describe the evolution of an isotropic universe filled with a perfect fluid. If a {\displaystyle a} is the scale factor then ρ ∝ a − 3 ( 1 + w ) . {\displaystyle \rho \propto a^{-3(1+w)}.}
The deceleration parameter in cosmology is a dimensionless measure of the cosmic acceleration of the expansion of space in a Friedmann–Lemaître–Robertson–Walker universe. It is defined by: q = d e f − a ¨ a a ˙ 2 {\displaystyle q\ {\stackrel {\mathrm {def} }{=}}\ -{\frac {{\ddot {a}}a}{{\dot {a}}^{2}}}} where a {\displaystyle a} is ...
In modern physical cosmology, the cosmological principle is the notion that the spatial distribution of matter in the universe is uniformly isotropic and homogeneous when viewed on a large enough scale, since the forces are expected to act equally throughout the universe on a large scale, and should, therefore, produce no observable inequalities in the large-scale structuring over the course ...
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.
Unaware of Friedmann's work, in 1927 Belgian astronomer Georges Lemaître independently formulated an evolving Universe. [4] In June 1925 Friedmann was given the job of the director of the Main Geophysical Observatory in Leningrad. In July 1925 he participated in a record-setting balloon flight, reaching the elevation of 7,400 m (24,300 ft). [5]