age of the Universe

(redirected from Age of universe)

age of the Universe

The observed expansion and evolution of the Universe suggest that it has a finite age, considered as the time since the Big Bang. The inverse Hubble constant, 1/H 0, gives a measure of the age if the rate of expansion has always been constant. Since gravitation tends to diminish the expansion rate, H 0 can only give an upper limit. Using the value of H 0 of 75 km s–1 Mpc–1 gives an upper limit of 13 billion (109) years.

In the standard cosmology (solutions of Einstein's field equations without a cosmological constant) with deceleration parameter q 0, the age is given as one of the three alternatives:

H 0 –1q 0 (2q 0 – 1)–3/2[cos–1(q 0 –1 – 1) – q 0 –1(2q 0 – 1)½]
2/3H 0 –1
H 0 –1q 0 (1 – 2q 0 )–3/2[q 0 –1(1 – 2q 0 )½ – cosh–1(q 0 –1 – 1)]

The choice depends on whether q 0 exceeds, equals, or is less than ½ (and > 0), i.e. on whether the Universe is closed, flat, or open, respectively. Ages of 12 and 15 × 109 years thus correspond to values of q 0 of ½ and 0.15, for H 0 equal to 55 km s–1 Mpc–1.

Lower limits to the age of the Universe, other than through measurements of H 0 and q 0, can be found from radiometric dating of the Earth and Galaxy and from studies of globular clusters. For example, the relative abundances of radioactive elements, such as uranium, and their decay products yield an estimate of the time since formation of that body of material e.g., the Earth. The results give an age for the Universe of 14–16 × 109 years. The age of a globular cluster may be estimated by comparison of the observed main-sequence turnoff point in the Hertzsprung–Russell diagram for the cluster with theoretical models. The oldest globular clusters in our Galaxy then work out to be 14–18 × 109 years old. Both of these ages should be less than the age of the Universe and in particular they must be less than H 0 –1. If the expansion of the Universe is now accelerating due to a cosmological constant, then the Universe will be slightly older than given by the above estimates.

Collins Dictionary of Astronomy © Market House Books Ltd, 2006
References in periodicals archive ?
Our encryption is so strong that if anyone tries to break it, it will take the age of universe to break one set.
As derived from c [varies] [t.sup.-1/2], with the age of universe [approximately equal to] 13.8 x [10.sup.9] yr the current rate of decrease in the speed of light becomes
Provided the approximately uniform rate of Hubble flow, the derived from G [varies] [R.sub.u] current rate of increase of G becomes a simple inverse of the age of universe. In fact, the Hubble time does not significantly differ from estimations of the age of universe derived from Friedman equation equipped with definite values of k and [LAMBDA].
9.4 Variation of Newton's constant and the age of universe
Assuming that increase of G extends the age of universe, the rate of G variation would be smaller than the here quoted value 7.25 x [10.sup.-11] [yr.sup.-1] thus better fitting observations.
* Age of universe: 13.799 +/- 0.038 billion years (note: that means we know the age of the universe to within 38 million years)
In other words, one breath is to one lifetime what one lifetime is to the age of universe.
z Age of universe Light travel time to Earth 1 5.9 billion years 7.7 billion years 2 3.3 billion years 10.3 billion years 4 1.6 billion years 12.1 billion years 6 950 million years 12.7 billion years 8 650 million years 13 billion years 10 480 million years 13.2 billion years SOURCE: NED WRIGHT'S COSMOLOGY CALCULATOR, WWW.ASTRO.UCLA.EDU/~WRIGHT/COSMOCALC.HTML