Time of Hubble

In General relativity and Cosmology, the time of Hubble corresponds on a time scale characteristic of a Univers in expansion; in practice, the age of the universe can be expressed in units of the time of Hubble.

The time of Hubble T _H results from the Paramètre of Hubble (or Constante of Hubble) H by the simple formula

t_H = \ frac {1} {H}

If one expresses like habit the constant of Hubble in Kilomètre S by second and mégaparsec in the form

H = 100 \; H \; {\ rm km} \; {\ rm S} ^ {- 1} \; {\ rm Mpc} ^ {- 1}

where H is a number without dimension, now estimated at 0,7, then the time of Hubble is worth

t_H = 9,78 \ times 10^9 \; h^ {- 1} \;

years.

By taking the value of H =0,7, one obtains approximately 14 billion years.

The relation between the age of the universe and the time of Hubble depends on the cosmological Modèle considered. For example, in a scenario of the type Big Bang without Constant cosmological, the age of the observable universe is equal to 2/3 of the time of Hubble (see Équations of Friedmann). In the presence of cosmological constant, this figure increases. When the Paramètre of density of the cosmological constant reaches 0,7 (commonly allowed value for our universe), then the age of the universe reaches a time of Hubble. It is incidentally about an indirect evidence of the existence of a cosmological constant or black energy. Without those the age of the universe would be lower than that of certain stars of the Milky Way.

See too

Ray of Hubble

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