The Age of the Universe

Three different techniques are currently used to calculate the age of the Universe. [See also http://www.astro.ucla.edu/~wright/age.html.]

  1. Velocity-distance relationships measured from galaxies
  2. The Hubble constant, the value for the rate of expansion of the Universe can be used to estimate the time that has elapsed since the formation of the Universe at the Big Bang. This is estimated from the relationship 1/H0.
  3. Recent improved measurement of the parameters Hubble's constant, the mass density of the universe, and the cosmological constant, yield an age for the universe of 13.4 ± 1.6 billion years, which is a billion years younger than other recent age estimates.
  4. See: Lineweaver, CH, 1999. A Younger Age for the Universe, Science, 284, Number 5419, pp. 1503-1507.
  1. Radioactive dating methods and models of galactic evolution
  2. The ratio of the isotopes of the radioactive element Uranium when this heavy element was synthesised can be used to estimate the age of the Universe. Combining measurements of uranium isotope ratios with models of galactic evolution allows us to infer an age for the Universe of between 12 and 15 billion years.

Measurement of stellar age from uranium decay

Nature, 409, pp.691-692 (2001) © Macmillan Publishers Ltd.

R. CAYREL, V. HILL, T. C. BEERS, B. BARBUY, M. SPITE, F. SPITE, B. PLEZ, J. ANDERSEN, P. BONIFACIO, P. FRANÇOIS, P. MOLARO, B. NORDSTRÖM & F. PRIMAS

The ages of the oldest stars in the Galaxy indicate when star formation began, and provide a minimum age for the Universe. Radioactive dating of meteoritic material and stars relies on comparing the present abundance ratios of radioactive and stable nuclear species to the theoretically predicted ratios of their production. The radioisotope 232Th (half-life 14 Gyr) has been used to date Galactic stars, but it decays by only a factor of two over the lifetime of the Universe. 238U (half-life 4.5 Gyr) is in principle a more precise age indicator, but even its strongest spectral line, from singly ionized uranium at a wavelength of 385.957 nm, has previously not been detected in stars. Here we report a measurement of this line in the very metal-poor star CS31082-0018, a star which is strongly overabundant in its heavy elements. The derived uranium abundance, log(U/H) = -13.7 ± 0.14 ± 0.12 yields an age of 12.5 ± 3 Gyr, though this is still model dependent. The observation of this cosmochronometer gives the most direct age determination of the Galaxy. Also, with improved theoretical and laboratory data, it will provide a highly precise lower limit to the age of the Universe.

  1. Models of stellar evolution
  2. The luminosity of a star of a specified chemical composition is determined by the supply of hydrogen to its core. We can therefore infer the age of a star from its mass. The oldest stars calculated in this way are between 12 and 15 billion years old.

The three independent methods of dating all broadly agree, although the precision claimed for the first model is currently thought to be the best estimate for the age of the Universe.