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Using the values known in 2018 and Planck units for Ω Λ = 0.6889 ± 0.0056 and the Hubble constant H 0 = 67.66 ± 0.42 (km/s)/Mpc = (2.192 7664 ± 0.0136) × 10 −18 s −1, Λ has the value of = = = where is the Planck length. A positive vacuum energy density resulting from a cosmological constant implies a negative pressure, and vice versa.
The values of these six parameters are mostly not predicted by theory (though, ideally, they may be related by a future "Theory of Everything"), except that most versions of cosmic inflation predict the scalar spectral index should be slightly smaller than 1, consistent with the estimated value 0.96. The parameter values, and uncertainties, are ...
These problems are solved by cosmic inflation which has . Measuring the equation of state of dark energy is one of the largest efforts of observational cosmology . By accurately measuring w {\displaystyle w} , it is hoped that the cosmological constant could be distinguished from quintessence which has w ≠ − 1 {\displaystyle w\neq -1} .
In cosmology, the cosmological constant problem or vacuum catastrophe is the substantial disagreement between the observed values of vacuum energy density (the small value of the cosmological constant) and the much larger theoretical value of zero-point energy suggested by quantum field theory.
H 0 is Hubble's constant and corresponds to the value of H (often termed the Hubble parameter which is a value that is time dependent and which can be expressed in terms of the scale factor) in the Friedmann equations taken at the time of observation denoted by the subscript 0. This value is the same throughout the universe for a given comoving ...
The first Friedmann equation is often seen in terms of the present values of the density parameters, that is [6] =, +, +, +,. Here Ω 0,R is the radiation density today (when a = 1 ), Ω 0,M is the matter ( dark plus baryonic ) density today, Ω 0, k = 1 − Ω 0 is the "spatial curvature density" today, and Ω 0,Λ is the cosmological constant ...
The speed of light in IAU is the defined value c 0 = 299 792 458 m/s of the SI units. In terms of this speed, the old definition of the astronomical unit of length had the accepted value: [ 3 ] 1 au = c 0 τ A = ( 149 597 870 700 ± 3 ) m, where τ A is the transit time of light across the astronomical unit.
The constants listed here are known values of physical constants expressed in SI units; that is, physical quantities that are generally believed to be universal in nature and thus are independent of the unit system in which they are measured. Many of these are redundant, in the sense that they obey a known relationship with other physical ...