A New Approach using WMAPIn February 2003, the WMAP project released an all-sky map of the radiation emitted before there were any stars. This cosmic microwave background radiation (CMB) is the remnant heat from the Big-Bang and was predicted already in 1946 by George Gamow and Robert Dicke. Since then, astronomers have tried to detect and interpret the CMB. The first detection of the CMB was found in 1965 by chance by Arno Penzias and Robert Woodrow Wilson using a radiometer built to detect astronomical radio signals. They found an excess in their measurements which was later interpreted as the CMB, a 2.725 kelvin thermal spectrum of black body radiation that fills the universe. In 1992, the satellite Cosmic Background Explorer (COBE) which was designed to map the CMB showed for the first time large scale fluctuations in the CMB. These fluctuations were interpreted as evidences of what later formed clusters of galaxies and voids. However, only WMAP had the resolution and sensitivity to detect tiny fluctuations and constrain the age of the universe with high precision. The WMAP team's results are based on the underlying model used to fit their data. This model assumes that 70% of the energy of the present universe is in the form of dark energy, 26% of the energy is in the form of cold (not thermalized) dark matter, and the remaining 4% of the energy is in the atoms and photons. According to their estimates the universe is 13.7 billion years old with an uncertainty of 200 million years. The WMAP value of Ho is 71 ± 4 km/s/Mpc which is in agreement with the HST key project.
Another approachAnother way of obtaining the age of the universe is by dating stars. Some of the oldest stars live inside globular clusters and their ages have been extensively estimated in the past decade. For a while, astronomers were puzzled by the fact that those stars seemed to be a few billion years older than the age of the universe estimated from the Hubble constant. Is there a problem with Ho or with the cluster's age? It turned out that age dating of globular clusters stars is very tricky and inaccurate distances to the clusters, as well caveats in stellar evolution, can solve the mystery. The age of clusters is proportional to one over the luminosity of the RR Lyra stars which are used to determine the distances to globular clusters. Therefore, accurate distances were needed and could only be obtained after the European Hipparcos satellite in the mid-90s. By using the new distance estimates, the age of the clusters fell from 15 billion years to 11.5 billion years with an uncertainty of about 1 billion year. These results agree with the age of the universe from both the Hubble constant and WMAP.
Publication Date: May 2006