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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. [26] There is a disagreement between this measurement and the supernova-based measurements, known as the Hubble tension.
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 ...
The universe's expansion rate, a figure called the Hubble constant, is measured in kilometers per second per megaparsec, a distance equal to 3.26 million light-years.
In using Hubble's law to determine distances, only the velocity due to the expansion of the universe can be used. Since gravitationally interacting galaxies move relative to each other independent of the expansion of the universe, [43] these relative velocities, called peculiar velocities, need to be accounted for in the application of Hubble's ...
Comparing this distance to the redshift of the supernovae gives a measure of the rate at which the universe has been expanding at different points in history. Since the expansion rate evolves differently over time in cosmologies with different total densities, Ω 0 can be inferred from the supernovae data.
Recent observations conclude, from 7.5 billion years after the Big Bang, that the expansion rate of the universe has probably been increasing, commensurate with the Open Universe theory. [9] However, measurements made by the Wilkinson Microwave Anisotropy Probe suggest that the universe is either flat or very close to flat. [2]
This is an accepted version of this page This is the latest accepted revision, reviewed on 5 March 2025. Hypothesis about life in the universe For the concept of a fine-tuned Earth, see Rare Earth hypothesis. Part of a series on Physical cosmology Big Bang · Universe Age of the universe Chronology of the universe Early universe Inflation · Nucleosynthesis Backgrounds Gravitational wave (GWB ...
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 ...