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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. [24] There is a disagreement between this measurement and the supernova-based measurements, known as the Hubble tension.
These gravitational waves can work as sort of standard sirens to measure the expansion rate of the universe. Abbot et al. 2017 measured the Hubble constant value to be approximately 70 kilometres per second per megaparsec. [22]
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. A light-year is the distance ...
Detailed measurements of the expansion rate of the universe place the Big Bang singularity at an estimated 13.787 ± 0.020 billion years ago, which is considered the age of the universe. [12] There remain aspects of the observed universe that are not yet adequately explained by the Big Bang models.
"The discrepancy between the observed expansion rate of the universe and the predictions of the standard model suggests that our understanding of the universe may be incomplete.
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]
From that point on, it was generally accepted that the universe started in a hot, dense state and has been expanding over time. The rate of expansion depends on the types of matter and energy present in the universe, and in particular, whether the total density is above or below the so-called critical density. [citation needed]
Since 2000, "early universe" techniques based on measurements of the cosmic microwave background have become available, and these agree on a value near 67.7 (km/s)/Mpc. [64] (This accounts for the change in the expansion rate since the early universe, so is comparable to the first number.)