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Relationship between redshift and age of the universe, from z = 5...20 [7]. Experimental observations confirm expansion of universe according to Hubble's law.Since the universe is expanding, the equation for that expansion can be "run backwards" to its starting point.
The second equation states that both the energy density and the pressure cause the expansion rate of the universe ˙ to decrease, i.e., both cause a deceleration in the expansion of the universe. This is a consequence of gravitation , with pressure playing a similar role to that of energy (or mass) density, according to the principles of ...
The fraction of the total energy density of our (flat or almost flat) universe that is dark energy, , is estimated to be 0.669 ± 0.038 based on the 2018 Dark Energy Survey results using Type Ia supernovae [7] or 0.6847 ± 0.0073 based on the 2018 release of Planck satellite data, or more than 68.3% (2018 estimate) of the mass–energy density ...
The scale factor is dimensionless, with counted from the birth of the universe and set to the present age of the universe: 13.799 ± 0.021 Gyr [4] giving the current value of as () or . The evolution of the scale factor is a dynamical question, determined by the equations of general relativity , which are presented in the case of a locally ...
Following theoretical developments of the Friedmann equations by Alexander Friedmann and Georges Lemaître in the 1920s, and the discovery of the expanding universe by Edwin Hubble in 1929, it was immediately clear that tracing this expansion backwards in time predicts that the universe had almost zero size at a finite time in the past.
Age of the universe; ... Solving this equation for a 50 percent ionization fraction yields a recombination temperature of roughly 4000 ...
Using a Friedmann-Robertson-Walker model of the expansion of the universe, redshift can be related to the age of an observed object, the so-called cosmic time–redshift relation. Denote a density ratio as Ω 0: = ,
The Universe passes through the Big Crunch and emerges in a hot Big Bang phase. In this sense they are reminiscent of Richard Chace Tolman's oscillatory universe; in Tolman's model, however, the total age of the Universe is necessarily finite, while in these models this is not necessarily so. Whether the correct spectrum of density fluctuations ...