Age of the universe

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In Big Bang models of physical cosmology, the age of the universe is the cosmological time back to the point when the scale factor of the universe extrapolates to zero. Using the latest models and the data from the Planck project, the age of the universe is 13.8 billion years. Astronomers have two different approaches to determine the age of the universe. One is based on a particle physics model of the early universe called Lambda-CDM, matched to measurements of features from very early in the history of the universe, like the cosmic microwave background. The other is based on the distance and relative velocity of a series or "ladder" of different kinds of stars, making it depend on local measurements late in the history of the universe. These two methods give slightly different values for the Hubble constant, which is then used in a formula to calculate the age. The range of the estimate is also within the range of the estimate for the oldest observed star in the universe.

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