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[13] [14] [15] Combining Slipher's velocities with Henrietta Swan Leavitt's intergalactic distance calculations and methodology allowed Hubble to better calculate an expansion rate for the universe. [16] Hubble's law is considered the first observational basis for the expansion of the universe, and is one of the pieces of evidence most often ...
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.
Here is the Hubble parameter, a measure of the rate at which the universe is expanding. ρ {\displaystyle \rho } is the total density of mass and energy in the universe, a {\displaystyle a} is the scale factor (essentially the 'size' of the universe), and k {\displaystyle k} is the curvature parameter — that is, a measure of how curved ...
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. [30] There is a disagreement between this measurement and the supernova-based measurements, known as the Hubble tension.
Evaluating the Hubble parameter at the present time yields Hubble's constant which is the proportionality constant of Hubble's law. Applied to a fluid with a given equation of state , the Friedmann equations yield the time evolution and geometry of the universe as a function of the fluid density.
Gravitational wave astronomy helps understand the early universe, test theories of gravity, and reveal the distribution of dark matter and dark energy. Particularly, it can help find the Hubble constant, which tells about the rate of accelerated expansion of the universe.
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 ...
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 Lambda-CDM concordance model describes the expansion of the universe from a very uniform, hot, dense primordial state to its present state over a ...