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The accelerated expansion of the universe is thought to have begun since the universe entered its dark-energy-dominated era roughly 5 billion years ago. [ 8 ] [ notes 1 ] Within the framework of general relativity , an accelerated expansion can be accounted for by a positive value of the cosmological constant Λ , equivalent to the presence of ...
A higher expansion rate would imply a smaller characteristic size of CMB fluctuations, and vice versa. The Planck collaboration measured the expansion rate this way and determined H 0 = 67.4 ± 0.5 (km/s)/Mpc. [24] There is a disagreement between this measurement and the supernova-based measurements, known as the Hubble tension.
The Big Bang is a physical theory that describes how the universe expanded from an initial state of high density and temperature. [1] The notion of an expanding universe was first scientifically originated by physicist Alexander Friedmann in 1922 with the mathematical derivation of the Friedmann equations.
In this form H 0 = 7%/Gyr, meaning that at the current rate of expansion it takes one billion years for an unbound structure to grow by 7%. Although widely attributed to Edwin Hubble, [6] [7] [8] the notion of the universe expanding at a calculable rate was first derived from general relativity equations in 1922 by Alexander Friedmann.
The universe is now an almost pure vacuum (possibly accompanied with the presence of a false vacuum). The expansion of the universe slowly causes itself to cool down to absolute zero. The universe now reaches an even lower energy state than the earlier one mentioned. [50] [51]
The rapid expansion immediately after the Big Bounce explains why the present Universe at largest scales appears spatially flat, homogeneous and isotropic. As the density of the Universe decreases, the effects of torsion weaken and the Universe smoothly enters the radiation-dominated era.
In physical cosmology, the Big Rip is a hypothetical cosmological model concerning the ultimate fate of the universe, in which the matter of the universe, from stars and galaxies to atoms and subatomic particles, and even spacetime itself, is progressively torn apart by the expansion of the universe at a certain time in the future, until distances between particles will infinitely increase.
The fusion of nuclei occurred between roughly 10 seconds to 20 minutes after the Big Bang; this corresponds to the temperature range when the universe was cool enough for deuterium to survive, but hot and dense enough for fusion reactions to occur at a significant rate. [1] It was widespread, encompassing the entire observable universe.