hubble parameter การใช้

• The Hubble parameter is not thought to be constant through time.
• Evaluating the Hubble parameter at the present time yields Hubble's constant which is the proportionality constant of Hubble's law.
• In this regime, the Hubble parameter is constant, and the universe grows by a factor e each Hubble time:
• The Hubble parameter at a given redshift is then H ( z ) = H _ 0 E ( z ).
• Apart from notations for the Hubble parameter, the matter density parameter and the vacuum energy parameter, there is no further explanation.
• In this case the temperature T is proportional to the Hubble parameter H, i . e . T \ propto H.
• Many inflationary models are approximately de Sitter space and can be modelled by giving the Hubble parameter a mild time dependence.
• The Friedmann equation relates the energy density of the universe to the Hubble parameter and shows that the Hubble radius is continually increasing.
• However, the Hubble parameter is not constant in various cosmological models so that the Hubble limit does not, in general, coincide with a cosmological event horizon.
• By defining the dimensionless Hubble parameter and the Hubble distance d _ H = c / H _ 0, the relation between the different distances becomes apparent.
• The value of the Hubble parameter changes over time, either increasing or decreasing depending on the value of the so-called deceleration parameter q, which is defined by
• The Hubble parameter can change over time if other parts of the equation are time dependent ( in particular the mass density, the vacuum energy, or the spatial curvature ).
• As an example, the article on the Lambda-CDM model quotes values for Hubble parameter " h " and the fraction of the present universe made up of baryons, " ? " b.
• :Coming up with an estimate of the age of the universe by simply assuming that the Hubble parameter has had about the same value during the life of the universe works surprisingly well.
• Because the Hubble parameter is decreasing with time, there can actually be cases where a galaxy that is receding from us faster than light does manage to emit a signal which reaches us eventually.
• Since this radius is difficult to determine observationally, it is often approximated as the radius within which the average density is greater, by a specified factor, than the Hubble parameter and G is the gravitational constant.
• The physical conditions from one moment to the next are stable : the rate of expansion, called the Hubble parameter, is nearly constant, and the scale factor of the Universe is proportional to " e Ht ".
• Surprisingly, the deceleration parameter was measured by two different groups to be less than zero ( actually, consistent with  " 1 ) which implied that today the Hubble parameter is converging to a constant value as time goes on.
• For example, he said, the Hubble parameter ( expressed on the plaque as H ( EQ ) 70km / s / Mpc ), is the expansion rate of the universe : 70 kilometers per second, over a distance of one megaparsec.
• Where H is the Hubble parameter, a is the scale factor, G is the gravitational constant, k is the normalised spatial curvature of the Universe and equal to  " 1, 0, or + 1, and \ Lambda is the cosmological constant.